As expected, NASA today set a new, more realistic target date for launch of the next shuttle mission - between Sept. 12 and Oct. 10, 2004 - and announced a new flight that will be inserted into the launch manifest to complete tasks originally planned for the first mission.

Given post-accident requirements that sharply restrict when a shuttle can actually take off, however - launch and external tank separation in daylight and thermal constraints at the international space station - the shuttle's return to flight easily could slip into 2005 when all is said and done.

Those requirements currently translate into 26 days of launch opportunities between Sept. 16 and Oct. 11, 2004; Nov. 19-21, 2004; and Jan. 17 through 19, 2005. The next available launch window opens in March 2005.

Current estimates show photo documentation of external tank separation in daylight will not be possible until Sept. 16. But NASA managers say those estimates might change and so they added a bit of cushion to the front end of the target launch window.

Bill Readdy, NASA's associate administrator for space flight, stressed the new launch window, like the original March/April target window, remains a target only and that it may change again as planners get a better idea of how much work remains to be done.

Mission STS-114, currently assigned to the shuttle Atlantis, will include a robot arm extension and sensors to look for damage to the ship's heat-shield tiles and leading edge panels; a spacewalk to test tile and leading edge repair techniques; another spacewalk to install a new gyroscope on the space station; and supply and equipment transfers to and from the lab complex.

"We're going to be very much driven by the milestones and by the content we have to accomplish here in terms of the testing of the robotic arm, survey techniques, tile repair, modifications to the external tank, all the testing that's required," Readdy said in an evening teleconference with reporters. "So It comes down to being able to satisfactorily accomplish all of those.

"I can't tell you whether or not we're going to have more content creep in over time, whether we're going to come up on some technical hurdles. I can almost guarantee that this is going to be a long, uphill climb back to return to flight. But I also would tell you that we're getting an awful lot smarter about this and we're going to come back stronger and safer as a result."

To accommodate the tile/leading edge inspections and the repair demonstration spacewalk, NASA decided to split the original STS-114 mission into two separate flights. The new mission, known as STS-121, currently is assigned to the shuttle Discovery. It is targeted for launch Nov. 15. Again, that's a few days in advance of when a daylight tank separation because available.

Making the September launch date for the first post-Columbia mission will not be easy. Long poles include development of the robot arm extension boom and the sensors needed for in-orbit tile and leading edge inspections and development of viable techniques for repairing leading edge damage. A wild card is the impact of work to remove Atlantis' carbon composite nose cap for an extensive corrosion inspection.

But shuttle program manager Bill Parsons said it's too soon to predict how all of that might play out. As for the shuttle's sharply restricted launch windows, "I think we have some opportunities, some small opportunities in November and possibly January and some other places."

"But you know, again, we're still refining those requirements, we're still refining exactly what we need to do to meet the lit launch requirement," he said. "But I think there are some opportunities in November (2004) for us to go launch."

In perhaps the most convincing demonstration yet that NASA truly "gets it," the new chairman of the agency's mission management team today outlined major changes to improve communications among engineers and managers, to ensure dissenting views are heard and to correct the cultural shortcomings blamed in part for the Columbia disaster.

"Any arrogance I may have had went out the window on Feb. 1," said Wayne Hale, a widely respected ascent-entry flight director who brings clear credibility to the mission management team. "In my personal life, before February I thought we had it pretty much knocked. ... I would have told you we understood what we were doing and we had mature processes and good hardware. And I think all of those assumptions have been shattered."

As chairman of the revamped mission management team, Hale will oversee the conduct of all phases of flight, from the pre-launch review needed to clear a shuttle for launch to the in-flight management of its mission.

At a news conference, Hale unveiled an ambitious plan to resolve shortcomings found by the Columbia Accident Investigation Board as well as issues identified by NASA personnel in the wake of the accident. New members will be added to the MMT, outside experts will be brought in to coach the managers on decision making skills and regular mission simulations will be held to test those skills in make-believe emergencies.

Hale is even looking into what shape table to use in the MMT conference room.

"Now you laugh," he said to chuckling reporters, "but when you talk about culture and how people subconsciously deal with hierarchy and where they fit within an organization and whether they feel comfortable in bringing things up, things like the shape of the table matter.

"Being trained as an engineer, I'm wishing I'd taken more sociology classes in college. I'm learning a lot, I think we're all learning a lot in this arena and we're committed to opening lines of communication and making sure people get their dissenting opinions and minority opinions on the table so we can consider them."

Some agency veterans have criticized the new MMT plan, saying the additional voices and opinions will make it more difficult to make a final decision. But Hale disagrees.

"I am convinced that we not only should, but must, come to an understanding of why it's OK to proceed in the face of a minority opinion," he said. "My basic model is consensus. We will bring the person from the organization that's got the concern and we should be able to demonstrate in a technical, analytical, engineering sense why it's safe to proceed or we shouldn't proceed. I don't know any other way to do that.

"I will tell you I get resistance from some of the NASA alumni league who operated at a different time and a different culture who think this is not the right thing to do, who think we'll never fly again if we go down this road too far. So there is that element of folks out there. But I think we need to go down the road as far as we can to make sure that we fly safely. Because just going to fly, there's been a lot of noise in the system about launch schedules and launch dates and we've gotta go do this to make the launch schedule, you know. We have to make sure when we get ready to fly we have done everything we can to make sure it's safe."

The Columbia Accident Investigation Board was sharply critical of MMT operations during Columbia's ill-fated mission. Contrary to NASA's own rules, the MMT, under chairman Linda Ham, did not meet every day and did not seriously debate the results of a hurried analysis that mistakenly concluded Columbia was not seriously damaged by a foam debris strike during launch. Despite an almost complete lack of hard data about the possible threat posed by the strike, the MMT quashed efforts by lower-level engineers to obtain spy satellite imagery that might have revealed the extent of the damage.

Hale today vowed to learn from the mistakes of the past. And he left little doubt he believes the management culture at NASA needs to change.

"I have to say, STS-107, the Columbia flight, has been a significant emotional event in my life and I think in the life of everyone in the agency, certainly in the shuttle part of the agency," he said. "We had many of our assumptions and concerns shattered on Feb. 1.

"Those of us who lived through the events of this past spring have had our lives change in ways that are going to affect our decisions and our thought processes for years to come. We have come over the course of several months of introspection and analysis to a new understanding. In particular, the first thing we have to get out on the table is we were not good enough. We did not do what is necessary to keep the Columbia crew safe. And that is something we have to live with as a legacy that will compel us to do the right thing for future shuttle flights and for future human exploration of space."

While final details remain to be resolved, Hale said the new MMT will include:

• Seats for the directors of engineering at the Johnson Space Center in Houston and the Marshall Space Flight Center in Huntsville, Ala.;
• A seat for the director of propulsion technology at Marshall;
• Seats for the head of safety and mission assurance at NASA headquarters and for the newly formed NASA engineering safety center at the Langley Research Center in Hampton, Va.;
• A single manager (Hale) for pre-launch and in-flight operations;
• A re-emphasized rigor with permanent pre-defined agenda items covering all phases of damage assessment to make sure any possible sign of trouble is known to senior management and discussed as widely as possible;
• A dedicated group of engineers to identify possible anomalies across all disciplines;
• Participation by senior managers, not designated alternates;
• Daily meetings

An internal review of the new MMT plan will be complete by Oct. 2. By the middle of the month, all MMT members will attend a class defining the precise roles and responsibilities of panel members. By the first week in November, the MMT will participate in a so-called "warm-up" simulation, the first in a series of regularly scheduled simulations to test MMT decision-making skills.

By the first week in December, Hale hopes to stage a three-day simulation involving the shuttle and the international space station program. Another major simulation including NASA's international space station partners is planned for January with monthly management sims scheduled after that through return to flight.

Long term, outside safety and management experts will be brought in on a regular basis as part of a continuing education program. Bringing in outsiders has never been NASA's strong suit and many at JSC resented the appearance of sociologist Diane Vaughn, an expert on the decision to launch the shuttle Challenger, at a Columbia Accident Investigation Board Hearing. She now is among the experts being sought by NASA.

"I didn't know who Dr. Vaughn was when she appeared at the CAIB hearing," Hale said. "I came away a little unimpressed with it but I said I ought to go get her book and look at what she's got to say. I sat down and read ("The Challenger Launch Decision") and when I got done with it, I said wow, there is a lot of good stuff here that I never thought about. And there is valuable place for us to learn some things.

"And since then, I think I've added a number of books to my bookshelf that are decision-making related that I'm thinking about a lot more these days. And we're going to have a number of these folks come and talk to us."

NASA must develop the capability to repair damaged heat shield tiles in orbit, as well as cracks or breaches in the reinforced carbon carbon panels making up the shuttle's wing leading edges, before space shuttles return to flight, the Columbia Accident Investigation Board says.

In the board's final report, released earlier today, the CAIB made 29 recommendations, 15 of which are to be implemented before the next shuttle flight. Because of the way the report marked those recommendations, using boldface red type "RTF" tags, one five-paragraph recommendation was misinterpreted by some readers who initially thought RCC repair capability was not a requirement for return to flight.

At a news conference and later in an interview with CBS News, board chairman Harold Gehman left no doubt: NASA must be able to repair damage to both tiles and RCC panels before the next shuttle takes off.

"Recommendation 6.4.1 contains four provisions, all of which are return to flight," he said.

That is a significant requirement. While NASA is expected to have a working tile repair technique in hand within a few months, developing a reliable RCC fix is a much greater challenge because of the nature of the material and the extreme 3,000-degree temperatures it is exposed to during re-entry. Some observers believe that requirement alone will push the next shuttle flight into the summer 2004 timeframe if not later.

"We think that's probably the long pole in the tent," Gehman said in an interview. An innovative technique used by Thiokol to repair carbon composite rocket nozzles shows promise and other techniques are under study as well. But repairing breaches in RCC panels is, at present, a long way from reality.

In any case, here is the recommendation in question:

"For missions to the international space station, develop a practicable capability to inspect and effect emergency repairs to the widest possible range of damage to the Thermal Protection System, including both tile and Reinforced Carbon-Carbon, taking advantage of the additional capabilities available when near to or docked at the International Space Station.

"For non-Station missions, develop a comprehensive autonomous (independent of Station) inspection and repair capability to cover the widest possible range of damage scenarios.

"Accomplish an on-orbit Thermal Protection System inspection, using appropriate assets and capabilities, early in all missions.

"The ultimate objective should be a fully autonomous capability for all missions to address the possibility that an International Space Station mission fails to achieve the correct orbit, fails to dock successfully, or is damaged during or after undocking. [RTF]"

Editor's Note: The Columbia Accident Investigation Board, on page 77 of its final report, provided new insights into how the shuttle broke apart and the fate of the orbiter's crew. For the record, here are those observations.

At the Board's request, NASA formed a Crew Survivability Working Group within two weeks of the accident to better understand the cause of crew death and the breakup of the crew module. This group made the following observations.

Medical and Life Sciences
The Working Group found no irregularities in its extensive review of all applicable medical records and crew health data. The Armed Forces Institute of Pathology and the Federal Bureau of Investigation conducted forensic analyses on the remains of the crew of Columbia after they were recovered. It was determined that the acceleration levels the crew module experienced prior to its catastrophic failure were not lethal. The death of the crew members was due to blunt trauma and hypoxia. The exact time of death sometime after 9:00:19 a.m. Eastern Standard Time cannot be determined because of the lack of direct physical or recorded evidence.

Failure of the Crew Module
The forensic evaluation of all recovered crew module/forward fuselage components did not show any evidence of over-pressurization or explosion. This conclusion is supported by both the lack of forensic evidence and a credible source for either sort of event. The failure of the crew module resulted from the thermal degradation of structural properties, which resulted in a rapid catastrophic sequential structural breakdown rather than an instantaneous "explosive" failure.

Separation of the crew module/forward fuselage assembly from the rest of the Orbiter likely occurred immediately in front of the payload bay (between Xo576 and Xo582 bulkheads). Subsequent breakup of the assembly was a result of ballistic heating and dynamic loading. Evaluations of fractures on both primary and secondary structure elements suggest that structural failures occurred at high temperatures and in some cases at high strain rates. An extensive trajectory reconstruction established the most likely breakup sequence, shown below (see chart on page 77 of the CAIB report).

The load and heat rate calculations are shown for the crew module along its reconstructed trajectory. The band superimposed on the trajectory (starting about 9:00:58 a.m. EST) represents the window where all the evaluated debris originated. It appears that the destruction of the crew module took place over a period of 24 seconds beginning at an altitude of approximately 140,000 feet and ending at 105,000 feet. These figures are consistent with the results of independent thermal re-entry and aerodynamic models. The debris footprint proved consistent with the results of these trajectory analyses and models. Approximately 40 to 50 percent, by weight, of the crew module was recovered.

The Working Group's results significantly add to the knowledge gained from the loss of Challenger in 1986. Such knowledge is critical to efforts to improve crew survivability when designing new vehicles and identifying feasible improvements to the existing Orbiters.

Crew Worn Equipment
Videos of the crew during re-entry that have been made public demonstrate that prescribed procedures for use of equipment such as full-pressure suits, gloves, and helmets were not strictly followed. This is confirmed by the Working Group's conclusions that three crew members were not wearing gloves, and one was not wearing a helmet. However, under these circumstances, this did not affect their chances of survival.

NASA will use the Columbia Accident Investigation Board's final report as a blueprint for correcting the problems that led to the Feb. 1 shuttle disaster and returning the shuttle safely to flight, Administrator Sean O'Keefe said today.

"We have accepted the findings and will comply with the recommendations to the best of our ability," O'Keefe said in a statement. "The board has provided NASA with an important road map as we determine when we will be 'fit to fly' again.

"Due to the comprehensive, timely and open public communication displayed by the Board throughout the investigative process, we already have begun to take action on the earlier issued recommendations, and we intend to comply with the full range of recommendations released today."

Harold Gehman, chairman of the Columbia Accident Investigation Board, told CBS News this afternoon NASA has little choice. In the panel's view, he said, NASA cannot safely operate the space shuttle program without major changes in its management system.

"I think there's a little bit of denial that NASA, at least in the shuttle program, that NASA has modified its organizational structure over the years into one that no longer contains the attributes that they built their reputations on," Gehman said. "There may be some people who deny that, but the board is absolutely convinced, we think there's no room for any doubt whatsoever, the management system they have right now is not capable of safely operating the shuttle over the long term. That's the bottom line."

¾Gehman also said Congress and the White House must share blame for the Columbia disaster with NASA. Asked what he might tell President Bush about NASA and the agency's second in-flight tragedy, Gehman said he would point out that "NASA is a great organization that he and the country can have a lot of pride in. And that they are operating under and unrealistic set of rules and guidelines."

"Exploring space on a fixed cost basis is not realistic," the retired admiral said. "Launching shuttles on a calendar basis instead of an event-driven basis is not realistic. Demanding that you save money and run this thing in an efficient and effective way and that you get graded on schedule and things like that is not realistic. That the whole nation and Congress and the White House has an unrealistic view of how we do space exploration."

In addition, the board's report "clearly specifies that there is responsibility at both ends of Pennsylvania Avenue for this that are shared with NASA," Gehman said. "Now in some cases, NASA over markets what they can do. They promise more than they can deliver and they promise they can deliver it at a price that is less than it's really going to cost. But in some cases, it is demanded of them, in order to get a program approved, that they agree to unrealistic schedules and unrealistic price tags. So there's blame at both ends here."

The CAIB report focuses heavily on decisions made NASA's mission management team, the panel of senior agency leaders that oversaw the day-to-day conduct of Columbia's mission. The MMT, chaired by former flight director Linda Ham, shut down efforts to obtain spy satellite photography of Columbia's damaged wing and failed to challenge a hurried analysis that concluded the shuttle was in no danger of a catastrophic failure.

Gehman told CBS News the space agency's management system is so dysfunctional it hardly mattered who was in charge.

"We believe very, very strongly that you could substitute almost anybody in those positions and operate under the guidelines and rules and precedents that were being used in NASA and they would make the same errors," he said.

"Let me give you a specific case in point. Much has been made of the fact that the MMT didn't meet every day. NASA regulations require that they meet every day. So I had my board go back and see what were the meetings scheduled for the previous two shuttle missions? Guess what? They met every third day.

"So Linda Ham was doing her job according to the standards and precedents that were set by the establishment," he continued. "Even though the rules say you have to meet every day, you don't really have to. So that's an organizational flaw and she was performing her duties in that respect in accordance with the standards and precedents that had been previously established by her predecessors. And her predecessor's bosses had let that go on.

"So we feel very, very strongly that just moving the people around won't fix that problem. Unfortunately, we live in a town here in Washington, DC, in which they frequently demand someone pay. But we on the board were not influenced by that" and the board did not assign personal blame for any real or perceived errors in judgment.

Could a more experienced or proactive program manager or MMT chairman have made a different in Columbia's case?

"We feel there's some part of this, maybe even a lot of these problems, could have been mitigated by a stronger, a more suspicious, nervous kind of a person," Gehman said of the MMT and its chairman. "But our conclusion, our very, very strong conclusion is even if you had really brilliant people, really spectacular people, if you had the very, very best person you could get, that it would be a low probability bet that you could count on them to overcome the flaws in the organization. That is a low probability course of action."

Asked if NASA was "in denial" about serious management flaws and defects, Gehman said "in a lot of cases, they will deny that they have a basic organizational flaw which is dangerous. I think they'll deny that, some of them. Others will applaud it. It kind of depends on where you sit."

The CAIB's criticism of NASA drew an unusual response from Stephen Feldman, president of The Astronauts Memorial Foundation.

"One of the great risks of the Columbia tragedy and the subsequent report and commentary is that outstanding scientists and engineers may feel so criticized and unappreciated that they will leave NASA and the space program for higher paying and often less stressful jobs in the private sector," he said in a statement. "The outstanding safety record that NASA has compiled over the years shouldn't be forgotten because of one terrible accident on February 1, 2003." But O'Keefe's promise to full implement the CAIB recommendations drew praise from the National Space Society, a nonprofit advocacy group founded by German rocket scientist Wernher von Braun.

"The National Space Society urges NASA to embrace the recommendations of the CAIB and work diligently to fundamentally reform its decision-making processes and safety organizations so that we can safely return the Space Shuttle fleet to service," said Executive Director Brian Chase. "However, in order for NASA to fully implement the CAIB recommendations and continue the exploration of space, the agency will need appropriate funding to accomplish those tasks.

"The White House and the U.S. Congress must accept their share of responsibility for the future of our nation's space exploration efforts and provide the necessary leadership.

"Perhaps most importantly, NASA and our nation's leaders need to take this opportunity to foster development of new space transportation systems and renew a long-term commitment to human space exploration."

The Columbia Accident Investigation Board released its long-awaited report today, blaming the Feb. 1 disaster on bureaucratic inertia, slipshod internal communications and ineffective management at the top levels of NASA. The scathing, pessimistic tone of the report left little doubt the Board believes the so-called "NASA culture" is deeply flawed and in need of major modifications to prevent a repeat of the Columbia disaster in the years ahead.

"Based on NASA's history of ignoring external recommendations, or making improvements that atrophy with time, the Board has no confidence that the space shuttle can be safely operated for more than a few years based solely on renewed post-accident vigilance," the report states.

Unless NASA takes strong action to change its management culture to enhance safety margins in shuttle operations, "we have no confidence that other 'corrective actions' will improve the safety of shuttle operations. The changes we recommend will be difficult to accomplish - and they will be internally resisted."

For an agency with such a proud tradition - sending 12 men to the surface of the moon, establishing a permanent presence in low Earth orbit, exploring the solar system with unmanned robots and launching scientific sentinels to probe the depths of space and time - the criticism levied by the accident board likely will seem extreme in its harshness.

But the accident investigation board members and their investigators clearly believe the sharp tone is appropriate, in their view essential to ensuring that wide-ranging corrective actions are actually implemented. The board's investigation found that "management decisions made during Columbia's final flight reflect missed opportunities, blocked or ineffective communications channels, flawed analysis and ineffective leadership."

In the end, the report concludes, NASA managers never really understood the lessons of the 1986 Challenger disaster and "echoes of Challenger" abound in the miscues that led to Columbia's destruction.

"Connecting the parts of NASA's organizational system and drawing the parallels with Challenger demonstrate three things," the board found. "First, despite all the post-Challenger changes at NASA and the agency's notable achievements since, the causes of the institutional failure responsible for Challenger have not been fixed.

"Second, the Board strongly believes that if these persistent, systemic flaws are not resolved, the scene is set for another accident. Therefore, the recommendations for change are not only for fixing the shuttle's technical system, but also for fixing each part of the organizational system that produced Columbia's failure.

"Third, the Board's focus on the context in which decision making occurred does not mean that individuals are not responsible and accountable. To the contrary, individuals always must assume responsibility for their actions. What it does mean is that NASA's problems cannot be solved simply by retirements, resignations, or transferring personnel."

The 13-member Columbia Accident Investigation Board, under the leadership of retired Adm. Harold Gehman, spent seven months investigating the Feb. 1 Columbia disaster, reviewing more than 30,000 documents, conducting more than 200 formal interviews and collecting testimony from expert witnesses. The board also oversaw debris recovery efforts in Texas and Louisiana that involved more than 25,000 searchers. The investigation is expected to cost $19.8 million when all is said and done.

The board's 248-page report was released at 10 a.m. at the National Transportation and Safety Board in Washington. Reporters were allowed to review the report ahead of time, surrendering cell phones and wireless laptop network cards before entering a closed off "reading room" at 6 a.m. Gehman and other members of the panel plan to discuss the report during an 11 a.m. news conference. This status report will be updated as soon as possible thereafter.

In the meantime, key lawmakers vowed to take the board's recommendations to heart.

"The people of NASA have accomplished great things," Dana Rohrabacher, D-Calif., chairman of a key House space committee, told CBS News Monday. "They've put a man on the moon within a very short period of time, the people of NASA have been a source of great pride ... for the people of the United States.

"But for far too long, they've been resting on their laurels and bathing in past glories, nostalgic about the glory days," he continued. "It's time to look to the future and it's time to recapture a tough, hard-working body of people who have new challenges and are not just looking at the past but looking to the future. And that means Congress and the president have got to act on the Gehman report."

It should be noted, however, that NASA cannot develop new manned spacecraft or significantly change the general thrust of the nation's space program without approval and funding from Congress and the White House. The Bush administration has been virtually silent when it comes to the nation's manned space program and Congress has not endorsed any major changes beyond controlling the budget of the international space station.

President Bush has not yet weighed in on the report or its implications for NASA and the international space station project. He said last week he wanted a chance to review the report before commenting.

The report focuses on two broad themes: The direct cause of the disaster - falling external fuel tank foam insulation that blasted a deadly hole in the leading edge of Columbia's left wing 82 seconds after liftoff - and the management system that failed to recognize frequent foam shedding as a potentially lethal defect before Columbia even took off.

The report also focuses on how NASA's mission management team, a panel of senior agency managers responsible for the day-to-day conduct of Columbia's mission, failed to recognize the severity of the foam strike that actually occurred, virtually eliminating any chance to save the shuttle's crew, either by attempting repairs in orbit or launching a rescue mission.

The report makes 29 recommendations, 15 of which must be implemented before shuttle flights resume. Five of those were released earlier, requiring NASA to eliminate foam shedding to the maximum extent possible; to obtain better imagery from the ground and in orbit to identify any problems with the shuttle's thermal protection system; and development of tools and procedures to repair any such damage in space.

The more difficult recommendations address management changes and the establishment of an independent Technical Engineering Authority to verify launch readiness, oversee and coordinate requests for waivers and to "decide what is and is not an anomalous event." The TEA "should have no connection to or responsibility for schedule and program cost." In addition, NASA's Office of Safety and Mission Assurance should have direct authority over all shuttle safety programs and be independently funded.

"It is the Board's opinion that good leadership can direct a culture to adapt to new realities," the panel wrote. "NASA's culture must change, and the Board intends (its) recommendations to be steps toward effecting this change."

Columbia, carrying a crew of seven and scores of scientific experiments, blasted off from the Kennedy Space Center in Florida on Jan. 16. Strapped in on Columbia's upper flight deck were commander Rick Husband, making his second flight; rookie pilot William "Willie" McCool; flight engineer Kalpana Chawla, making her second flight; and rookie astronaut-flight surgeon Laurel Clark. Seated below on the shuttle's middeck were payload commander Michael Anderson, making his second flight; and two more rookies, physician-astronaut David Brown and Ilan Ramon, the first Israeli space flier.

At 81.7 seconds after liftoff from pad 39A, a suitcase-size chunk of foam broke away from the ship's external fuel tank and slammed into the left wing. The shuttle was racing skyward at more than twice the speed of sound at the time - 1,650 mph - and engineers later calculated the foam hit the left wing at some 530 mph.

The foam strike was not seen until the day after launch when engineers began reviewing tracking camera footage as they do after every launching. A film camera in Cocoa Beach that could have photographed the impact on the underside of the left wing was out of focus. A video camera at the same site was properly focused, but it lacked the resolution, or clarity, to show exactly where the foam hit or whether it caused any damage. A third camera at a different site showed the foam disappearing under the left wing and emerging as a cloud of debris after striking the underside. Again, the exact impact point could not be seen.

Stunned engineers immediately began analyzing the available film and video and ultimately determined the foam had struck heat shield tiles on the underside of the wing, perhaps near the left main landing gear door. No one ever seriously considered a direct heat on the reinforced carbon carbon panels making up the wing leading edge because no trace of foam debris was ever seen crossing the top of the wing. As the board ultimately concluded, however, the foam did, in fact, strike the leading edge on the lower side of RCC panel No. 8.

In hindsight, it's difficult to understand why the possibility of a leading edge impact didn't receive more attention. The board concluded that was due at least in part to the influential role of Calvin Schomburg, a senior engineer at the Johnson Space Center with expertise in the shuttle's heat-shield tiles.

"Shuttle program managers regarded Schomburg as an expert on the thermal protection system," the board wrote. "However, the board notes that Schomburg as not an expert on reinforced carbon carbon (RCC), which initial debris analysis indicated the foam may have struck. Because neither Schomburg nor shuttle management rigorously differentiated between tiles and RCC panels, the bounds of Schomburg's expertise were never properly qualified or questioned."

In any case, a team of Boeing engineers at the Johnson Space Center, under direction of NASA's mission management team, ultimately concluded the foam strike did not pose a safety of flight issue. Their analysis, using a computer program called CRATER, predicted areas of localized, possibly severe damage to the underside of the left wing, but no catastrophic breach. The concern, rather, was that any damage likely would require extensive repairs before Columbia could fly again.

While the damage assessment was getting under way, at least three different attempts were made to obtain spy satellite photography of the impact site to resolve the matter one way or the other. But in a series of communications miscues, the efforts ultimately were quashed by the MMT, under the direction of former flight director Linda Ham.

Ham says she was never able to find out who wanted such photographs and, without a formal requirement, had no reason to proceed. As for the debris assessment, Ham and other members of the MMT never challenged the hurried analysis or questioned the conclusion Columbia could safely return to Earth as is.

Many mid-level engineers said later they had serious misgivings about the debris assessment and heavy email traffic indicated fairly widespread concern about potentially serious problems if the foam strike had compromised Columbia's left main landing gear. Yet those concerns never percolated up the Ham, Dittemore or other members of the mission management team.

Ham and Dittemore both have said they were always open for questions or comments from lower-level engineers and that everyone on the team was encouraged, even duty bound, to bring any serious concerns to the attention of senior management.

But the CAIB disagreed.

"Communication did not flow effectively up to or down from program managers," the board wrote. "After the accident, program managers stated privately and publicly that if engineers had a safety concern, they were obligated to communicate their concerns to management. Managers did not seem to understand that as leaders they had a corresponding and perhaps greater obligation to create viable routes for the engineering community to express their views and receive information. This barrier to communications not only blocked the flow of information to managers but it also prevented the downstream flow of information from managers to engineers, leaving Debris Assessment Team members no basis for understanding the reasoning behind Mission Management Team decisions."

As for not hearing any dissent, the board wrote, "managers' claims that they didn't hear the engineers' concerns were due in part to their not asking or listening."

"Management decisions made during Columbia's final flight reflect missed opportunities, blocked or ineffective communications channels, flawed analysis and ineffective leadership," the board wrote. "Perhaps most striking is the fact that management - including Shuttle Program, Mission Management Team, Mission Evaluation Room (personnel) and flight director and mission control - displayed no interest in understanding a problem and its implications.

"Because managers failed to avail themselves of the wide range of expertise and opinion necessary to achieve the best answer to the debris strike question - 'Was this a safety-of-flight concern?' - some space shuttle program managers failed to fulfill the implicit contract to do whatever is possible to ensure the safety of the crew. In fact, their management techniques unknowingly imposed barriers that kept at bay both engineering concerns and dissenting views and ultimately helped create 'blind spots' that prevented them from seeing the danger the foam strike posed."

Shuttle program manager Dittemore and members of the mission management team "had, over the course of the space shuttle program, gradually become inured to external tank foam losses and on a fundamental level did not believe foam striking the vehicle posed a critical threat to the orbiter," the board wrote.

In the end, many NASA managers say privately, it was a moot point. Once the foam breached the leading edge of Columbia's left wing, the crew was doomed. The astronauts had no way to repair the breach - no robot arm and no tile repair equipment - and there was no realistic chance another shuttle could be readied in time for a rescue mission.

Maybe so. But NASA's flawed management system never gave the agency a chance to prove it still had the "right stuff."

It is that institutional system, or "culture," at NASA that must be changed, the board believes, to prevent another accident.

"An organization system failure calls for corrective measures that address all relevant levels of the organization, but the Board's investigation shows that for all its cutting-edge technologies, 'diving-catch' rescues and imaginative plans for the technology and the future of space exploration, NASA has shown very little understanding of the inner workings of its own organization," the report states.

"NASA's bureaucratic structure kept important information from reaching engineers and managers alike. The same NASA whose engineers showed initiative and a solid working knowledge of how to get things done fast had a managerial culture with an allegiance to bureaucracy and cost-efficiency that squelched the engineers' efforts.

"When it came to managers' own actions, however, a different set of rules prevailed. The Board found that Mission Management Team decision-making operated outside the rules even as it held its engineers to a stifling protocol. Management was not able to recognize that in unprecedented conditions, when lives are on the line, flexibility and democratic process should take priority over bureaucratic response."

The addition of a time-consuming tile inspection on the next shuttle flight, a spacewalk to test new tile repair equipment and techniques and lack of a third space station crew member to assist in equipment transfer work is forcing NASA managers to consider major changes to reduce the crew's workload.

While a variety of options is under study, it does not appear likely the STS-114 shuttle crew, commanded by Eileen Collins, will be able to accomplish its original objectives, including transfer of a fresh three-person crew and all associated equipment and supplies to the space station. NASA managers are considering the possibility of off-loading the crew transfer to a later flight, either to an additional shuttle mission or, possibly, to a Russian Soyuz flight later next year, and adding non-station crew members to the STS-114 mission to assist with logistics and equipment transfer work.

In addition, some of the mission's scientific objectives may be deferred as well because of weight limitations resulting from the expected addition of tile repair equipment and a long robot arm extension boom needed for post-launch inspection of the shuttle's thermal protection system.

Crew transfer issues depend in large part on when Atlantis can be ready for flight. A new two-person station crew is scheduled for launch aboard a Soyuz ferry craft in mid October. They will return to Earth next spring aboard Atlantis or, if the shuttle is not ready in time, aboard a Soyuz.

Most insiders, including several sources who discussed the issues last week, believe NASA will be hard pressed to get Atlantis off the ground before next summer. In that case, the October station crew likely would be replaced by two fliers launching aboard a Soyuz next April. Whether Atlantis then would take another crew up later that summer, or whether the April station crew would remain aloft until a fresh Soyuz crew arrives in Oct. 2004 - carrying either two or three station fliers - is part of the current debate about Atlantis' mission.

Any option off-loading crew rotation to the Soyuz, obviously, would require Russian concurrence. The Russians have not yet booked, or sold, a Soyuz seat for the October 2004 mission and that flight could, in theory, carry up a fresh three-person station crew. But that remains to be seen.

In the meantime, NASA managers are assessing a variety of options to alleviate the STS-114 crew timeline shortfall. The additional weight of a robot arm tile inspection camera boom, the tile repair demonstration kit and other items mean Atlantis cannot carry the originally planned complement of scientific equipment, the research gear needed to make the shuttle flight a space station "utilization" mission as originally envisioned.

"There is growing impetus, within both the shuttle and the station programs, to request (NASA) headquarters add a shuttle flight, a logistics flight, that would offload the strain of return-to-flight tasks from 114," said one NASA official familiar with the discussions.

Before Columbia's destruction Feb. 1, NASA was readying Atlantis for launch around March 1 to carry a fresh three-man crew to the space station along with supplies and research equipment stowed in a pressurized module known as an MPLM.

In addition, STS-114 features three spacewalks by astronaut Stephen Robinson and Japanese astronaut Soichi Noguchi. The objectives are to install a new control moment gyroscope, or CMG; to mount an external stowage platform, or ESP, on the outside of the station for use during upcoming solar array reconfigurations; and to mount TV camera gear and other equipment on the station's exterior.

In the wake of the Columbia tragedy, the station's three-man crew was replaced with two fliers, Yuri Malenchenko and Ed Lu. Because of limitations on fresh water, NASA and the Russian space agency will continue to staff the station with two-person crews until shuttle flights resume, leaving the STS-114 crew with a shortage of manpower in orbit to unloaded the pressurized logistics module.

The Columbia Accident Investigation Board, which will release its final report Tuesday, already has released five preliminary recommendations, including one requiring NASA to carry out extensive on-orbit tile inspections and another requiring development of an in-flight tile repair capability.

Since then, engineers have developed a lengthy tile inspection procedure expected to be carried out on the second day of the mission, in which cameras mounted on a long boom will be maneuvered about the orbiter by the shuttle's robot arm to look for signs of damage. The procedure will involve two astronauts and take up to seven hours or more to complete, throwing a wrench of sorts into normal flight-day two equipment check-out activity.

Areas of the shuttle that cannot be seen by the camera boom will be inspected by the station crew during Atlantis' final approach when Collins performs a pitch maneuver to expose the underside of the orbiter to view from the station above. She already is practicing the maneuver in flight simulators at the Johnson Space Center in Houston.

Once docked, the MPLM will have to be unloaded with one less station astronaut than usual. NASA managers are evaluating a variety of options to lighten the load, in some cases literally, by deferring some transfer items to later missions.

Agency officials hope to carry out at least two spacewalks. The CMG replacement and the tile repair demonstration. The ESP installation also is a top priority because it includes equipment that will be needed by an upcoming assembly crew. Whether it can be accommodated during Atlantis' mission is not yet clear.

The tile repair kit will be located at the back of the shuttle's cargo bay and feature a panel of deliberately damaged heat shield tiles. The spacewalkers will attempt to repair the tiles using materials and procedures currently in the development stage.

The work does not yet include any sort of repair demonstration for reinforced carbon carbon panels making up the orbiter's wing leading edges. While promising procedures are under study, it's not yet clear whether any repair techniques can be developed in time for a flight next spring.

NASA planners hope to refine the requirements of STS-114 in the next few weeks.

The co-chairman of a panel charged with assessing how well NASA meets the intent of recommendations from the Columbia Accident Investigation Board said today he's not sure the agency will have time to implement critical management changes before shuttle flights resume next year.

Richard Covey, a senior executive with Boeing who flew as pilot of the first post-Challenger mission, also said he was disappointed the safety-conscious management system implemented in the wake of the 1986 Challenger disaster broke down in Columbia's case.

"I wasn't surprised we had an accident," he told reporters after the panel's first public meeting. "Spaceflight is risky, those of us who have flown in space know there's risk and entry has always been (phase of flight) the crews have known was highly risky. So the fact that an accident happened on entry was not necessarily a surprise.

"Now, shocking? Yeah. Disappointing, particularly what I have learned of the process that maybe allowed the situation to develop where we had the accident. That was disappointing to me. It has similarities to the Challenger accident, but not perfectly."

Asked to be more specific, Covey said "the decision-making process, both pre flight and during flight, probably has some similarities to the decision-making process in the Challenger accident. If you look at the way that the known shedding of foam off the external tank was handled, you can go back and say well, all right, we knew we had some issues with the O-rings (in the flawed boosters used by) Challenger. They may not have been the same specific barriers to good decision making that occurred there, but the decision process was flawed, probably in both of those cases similarly."

Columbia was destroyed during re-entry Feb. 1 by a breach in the leading edge of the ship's left wing. The breach most likely was caused by a piece of foam insulation that fell off the shuttle's external tank during launch and struck the leading edge. The external tank project had a history of foam shedding, as Covey said, but it was not considered a safety-of-flight issue and it was not a constraint to launch. Likewise, NASA engineers knew about booster O-ring joint problems but did not ground the fleet before Challenger's final flight.

The Columbia Accident Investigation Board plans to release its report Aug. 26. To remove any doubt about NASA's willingness to follow those recommendations, NASA chartered an independent panel chaired by Covey and former Apollo astronaut Thomas Stafford to assess the agency's response to the CAIB's recommendations. The Return to Flight Task Group plans to submit its final report one month before the next shuttle flight, whenever that might be. NASA hopes to launch the shuttle Atlantis on mission STS-114 as early as March 11.

"The intent of our charter is to establish an independent assessment of NASA's responses to the Columbia Accident Investigation Board's recommendations," Covey said. "We also are asked to observe other safety and operational issues that may be pertinent relative to return to flight. It is not a broad charter, it is relatively narrow and focused. Our intent it to make sure we live up to the intent and the letter of our charter."

The task group includes numerous former NASA managers, including James Adamson, a former astronaut and aerospace executive who now runs his own consulting firm. He said the key element of the panel's charter is whether or not NASA meets the intent of the CAIB's recommendations.

"Our job, on the surface, may sound simple, but we're going to check and see if they've done that," he said. "It's not a simple yes or no question. I think everybody knows there's more than one way to skin a cat and we're going to try to look, to drill down into NASA's response to make sure they've met the intent of the recommendation."

One of the CAIB's five already released recommendations calls for improved imagery during ascent to make sure unwanted events like foam shedding do not go unnoticed. Adamson said that recommendation "is really intended to make sure that we don't re-enter with a hole in the vehicle without knowing it."

"The real intent of that is that NASA's got to take some action to be sure we don't do that again," he said. "And there are lots of ways to do that, some of them include imagery. But we're going to look at how you do that and what they're doing in response and we're going to make our assessment based on the intent."

The CAIB's final report is expected to be critical of NASA's management system and operational culture. Covey would not speculate on what the recommendations might involve, but he cautioned reporters not to expect too much too soon.

"We have already begun to try to scope the way we will address managerial, organizational type of recommendations when they come out of the CAIB," he said. "Because they may not be expected to be implemented before return to flight, then that puts us in a situation where we have to say well, what can we assess in the time period that we're chartered to do assessments? So our approach may be to look at plans, strategies or approaches that may be in place prior to the first flight and do an assessment. But it would not be a complete assessment because the real implementation may take longer."

Covey said he agreed with CAIB members who have said the shuttle should be viewed as an experimental spacecraft and not an operational vehicle.

"It goes back to my background as a test pilot and my understanding of those issues that really are important to make a vehicle operational," Covey said. "We've never been there with the space shuttle program and won't be through its life. So if indeed proper focus is the result of thinking in terms of it being experimental, I can support that. I like that."

But experimental vehicles, by their nature, face extreme risk and Covey said another failure will always be possible.

"Clearly with a fleet of three (remaining) orbiters and the demands of the space station program on our orbiter fleet ... then a safe return to fight and an ability to sustain safe flight without the loss of an orbiter is extremely important and there's no doubt about that," Covey said. "I think everybody's very sensitive to that.

"At the same time, we have to also recognize that the same demands of having safe flight and maintaining our orbiter fleet in order to support space station says we need to fly again. So there's a balance there. We'll never be absolutely sure we won't lose another orbiter. We can't do that and we should not have that expectation. We should be able, however, to find a way to make sure the things we know and the things we can learn about between now and the next flight and all those other flights" are properly implemented.

NASA will respond to the Columbia Accident Investigation Board's recommendations "almost to the letter," a senior agency official said today. But Frederick Gregory, NASA's deputy administrator, downplayed widely publicized criticism of NASA's management culture, saying "it would be difficult for me to define to you what the 'NASA culture' is."

Gregory, William Readdy, NASA's associate administrator for space flight, and Bryan O'Connor, associate administrator for safety and mission assurance - all former shuttle commanders - met with reporters at the Kennedy Space Center today after meeting with members of an independent board charged with assessing NASA's implementation of the accident board's recommendations.

Gregory was repeatedly asked about what NASA plans to do to correct problems with its management philosophy, the so called "NASA culture" that permeates agency operations. One reporter opined many believe it may prove easier to fix the shuttle's technical shortcomings than it will be to correct any major flaws in the agency's mindset before flights resume next year.

But Gregory chose not to answer the reporter's question about what NASA might be planning to address the culture issue in the weeks and months ahead.

"That's an interesting observation," he replied. "We have the five technical recommendations (already released by the CAIB), the report itself won't come out until the end of the month and perhaps some of those things you mentioned might be mentioned. But at this point, we have not received any comments officially from the accident investigation board, justifying or backing up your statements."

This reporter then asked Gregory to respond to the spirit of the first question in light of the virtual certainty the board will find fault with NASA's management procedures. Again, Gregory declined to provide any specifics.

"What we are looking at are not only are the technical issues, what we would look at is any process that might need to be modified or changed as we transition from an ops activity, an operations activity, into a return-to-flight activity," he said. "I think you will see there will be some changes, process changes, that will occur. But at this point only as we move from the operations of the standard activities that we're doing into this return to flight time."

Yet another reporter came at the question from another angle and Gregory replied that he believed most of the criticism of NASA's operating culture originated with a single CAIB member and that the board's findings would not be known until the panel's report is released Aug. 26.

"It would be difficult for me to define to you what the 'NASA culture' is," Gregory said. "As I sit here, and I have three astronauts here, I suspect if you tried to determine what the culture of the three of us is, you would find there are three different cultures here. So that's why I have said, I have to wait and see what, if anything, is being written (by the CAIB) about culture before I can respond to your question."

Readdy was somewhat more forthcoming.

"The comment that it's a 'culture thing' maybe does apply in some small area," he said. "I see a gentleman there who is wearing and Apollo shirt today. We were over in the Saturn 5 display area earlier today. There is a culture there, too, that after the Apollo 204 fire (in 1967) got us back to the moon and focused on mission. So there are different aspects of a culture.

"The real challenge will be for us to identify those things that are very positive about our culture and reinforce those and whatever the CAIB may say in terms of the negative aspects of the culture, to identify those very specifically and fix them."

How NASA plans to accomplish that before next spring was left unsaid.

NASA's current target date for the first post-Columbia mission is March 11, the opening of a window that extends through April 6. The launch window is based on a requirement to launch the next mission in daylight and to make sure its external fuel tank separates with enough lighting to ensure a good photographic assessment of its condition.

Columbia, of course, was destroyed by a breach in the ship's left wing leading edge that investigators believe was caused by a chunk of foam insulation that fell off the external tank during launch.

Most agency insiders believe the March time frame is overly optimistic and that a launching next summer is a more realistic expectation. Readdy said today the shuttle team needs a date to march toward from the standpoint of processing hardware, but he stressed that the next mission will not be launched until all parties agree it is safe to do so.

"We understand that one, we don't have the Columbia Accident Investigation Board final report in front of us so there will likely be adjustments there," he said. "Two, we also understand that perhaps March may be success oriented. But we need to have something to get the team all marching in step on and it appears the window, I think, from March 11 to April 6, honored all the constraints that we know thus far: Daylight launch, daylight external tank separation so we can do assessments there, the beta angle cutouts (for temperature control at the space station).

"Is March ambitious? Probably. But that's how you arrive at what the other, not-so-long poles are, the other things that may be potentially in the critical path and identify those so you can go off and solve them."

Gregory emphasized NASA's drive to launch would be driven by accomplishing milestones and not by any desire to meet a specific date.

""We're committed to return to flight but we are committed to doing so safely as we can," he said. "The point I want to make here is we are milestone-oriented focused, not schedule focused. If you see schedules that have a scheduled launch on it, it's only so our folks can work toward a launch date. But it does not necessarily represent the actual date that we will return to flight with the shuttle."

Earlier today, Gregory, Readdy and O'Connor met with members of the independent board charged with assessing NASA's implementation of CAIB recommendations. The panel is chaired by Apollo astronaut Thomas Stafford and shuttle veteran Richard Covey.

"Our commitment is to independently assess NASA's response and implementation of the findings and recommendations of the CAIB," Gregory said. "As you probably know, there will be no attempt whatsoever to argue or defend a recommendation from the CAIB. We will respond to each of the findings and recommendations and in fact ... we will go further than that. The Stafford-Covey task group will assess our response to the findings and recommendations and will have an opportunity, if they find some areas that they observe that have not been picked up, to make a recommendation to us."

As for when the next shuttle might get off the ground, "we will not fly until we are ready to, we have responded to the CAIB, we've had an assurance from the task group that we are headed down the right road, that we have not deviated, that we have not missed anything. Obviously, we will remain vigilant to any congressional discussions or inquiries."

Said O'Connor: "We're going to return to safe space flight by setting the bar higher than it was before."

The news conference ended with a question about whether NASA will implement every CAIB recommendation before the resumption of shuttle flights.

"I think we will be responding almost to the letter to the recommendations of the board," Gregory said. "Now again, the board has not published the report yet and I may have to back off a little bit. But what we will do is the right thing, my assumption is that we would follow to the letter the recommendations and that's why we have the Stafford-Covey task team there independently assessing our response to the board. They will tell us if we have gone down the wrong path or not."

In an emotion-charged meeting with reporters, Linda Ham, chairman of NASA's mission management team and a lightning rod for criticism of decisions made - or not made - during the shuttle Columbia's ill-fated voyage, spoke publicly for the first time today, defending NASA's management practices but agreeing major changes are needed.

Contrary to some earlier media reports, Ham said she never received any formal requests to obtain spy satellite imagery of Columbia to determine the severity of the foam strike and the issue was not discussed during any of the mission management team meetings held during Columbia's flight.

She said she accepted the results of a hurried Boeing-led analysis, carried out at the request of NASA, that concluded the foam strike was not a safety-of-flight issue. She insisted any lower-level engineers or managers who might have disagreed were free, even encouraged, to voice those concerns directly to her. But no one stepped forward and Ham had no reason to question the engineering analysis.

"It goes without saying we were all trying to do the right thing," she said. "All along, we were basing our decisions on the best information that we had at the time. Nobody wanted to do any harm to anyone. Obviously, nobody wants to hurt the crew. These people are our friends, they're our neighbors, we run with them, work out in the gym with them, you know my husband is an astronaut. I don't believe anyone is at fault for this."

But Ham, a 21-year NASA veteran, former flight director and one of the highest ranking women in the high-pressure world of human space flight operations, was removed from her post as manager of shuttle integration and chairman of the mission management team earlier this summer. She currently is in a sort of management limbo at the Johnson Space Center, where some insiders believe she is being made a scapegoat for decisions that were unanimously supported by the entire MMT.

"She did the best she could do given the information she had," said one official who asked not to be named. "She talked to people she trusted, she listened to the analysis. She doesn't deserve to be crucified for this. But she will be. She already has been. She made mistakes, but we all did."

Meeting with 10 reporters today, including the writer of this report, Ham endured occasionally pointed questions about her role in Columbia's flight, calmly fielding most with technical savvy and occasional glances at type-written notes. But when asked about criticism directed at her personally, she finally lost her composure.

"We were really doing the best we could," she said. "Our goal is to launch and of course keep the crew safe, that's the number one goal, and also bring the orbiter back safely and accomplish the mission. That's our job, our number one job. I think we all take some personal responsibility for this and I certainly feel accountable for the MMT. So it's been very difficult through this.

"I know the important thing to do right now is get the program back on (its) feet, get back to flight and get back to flight more safely than ever. My husband being an astronaut and having two kids, we've all gone through this together..."

She suddenly stopped, eyes filling with tears, and could not continue. Flight director LeRoy Cain, the man in charge of mission control during Columbia's re-entry Feb. 1, handed her a handkerchief while mission operations representative Phil Engelauf answered another question. The briefing continued. But the emotional torment on Ham's face was unmistakable. Whatever one might believe about her role in the management of Columbia's mission, there can be little doubt the disaster is never far from her mind.

"It's unconscionable to me that people can attribute to the members of the MMT or the flight control team or the rest of the folks during these missions anything other than the best of intentions," said Engelauf, himself a veteran shuttle flight director. "These are people of good conscience doing everything in their power to get the right answers. This is what we do for a living. LeRoy sits at that console and his job, and my job when I'm there, is to keep the crew safe and get them home in one piece. That is everything we do here and when we come to work that's all we're focused on.

"So in the end, yes, we lost the crew and we lost the vehicle and we can't escape that and nobody feels worse about that than every one of us who has their hands on these missions every day," Engelauf said. "But it is not because of lack of good intent or lack of effort on anybody's part. If the system fell down, we'll fix the system. But it's really difficult to me to attribute blame to any individual personalities or people. We can find mistakes in analyses and we can find places where we weren't good enough. But it's not because of malice or ill intent."

One of the enduring questions of the post-launch MMT agenda has been disposition of requests for satellite imagery of Columbia to better characterize the extent of any damage to the ship's left wing. At least two such efforts were initiated, but Ham said today the issue was never brought up to the MMT.

"That's interesting question," she said. "We have read (news) reports that the mission management team had declined a request for outside assistance and if you read through the transcripts, you'll note that the mission management team never addressed a request for outside assistance because it never came up in any of the meetings. It never came up to me personally.

"I did hear about a possible request for imagery via a phone call. When I did hear about that possible request, I began to research who was asking. What I wanted to do was find out who that person was and what exactly they wanted to look at so we could get the proper people from the ops team together with this group of people, sit down and make sure that when we made the request we really knew what we were trying to get out of it.

"So I went to our contractor, United Space Alliance, to see if they were making a request, I went to the space shuttle vehicle engineering office and I also went to the mission evaluation room where all the engineering work is done, thinking if anyone knows they will know if there's a such a request out there. I couldn't find any request so we did not pursue that."

She said she had "absolutely no reluctance to ask for outside assistance."

"We certainly would have done that if we could have gotten the right information together and the right people together and done that," she said. "Several weeks after the accident, I did find out who was asking and these folks that were asking were actually in the MMT and never brought it up. They were in the MER (mission evaluation room) meetings before the MMT and never brought it up. So for some reason, they didn't feel comfortable bringing it up in the MMT. Certainly, you would think they would have done that at those other meetings or in the hall or at any time. But it never, ever came up."

As most readers know by now, Columbia's left wing was struck by a falling piece of foam insulation that broke away from the ship's external fuel tank 81 seconds after blastoff Jan. 16. Two flights earlier, another large piece of foam had broken away from the same area of the tank and struck one of the shuttle Atlantis' solid-fuel boosters.

The Columbia debris strike was seen during analysis of launch film the day after liftoff. But the actual site of the impact was not visible and the extent of any resulting damage was unknown. A team of NASA-led contractor engineers began studying possible damage scenarios using a computer program designed to predict damage to the shuttle's heat-shield tiles. Ham said today she was content to give the team time to work before making any hasty decisions.

In the end, the engineers concluded the foam strike might lead to severe localized heat damage during re-entry but it did not pose a catastrophic "safety of flight" threat.

"We were trying to give the technical community sufficient time to do an in-depth analysis," Ham said. "They did do their analysis, they did use the Crater (program) and the other tools they had available to them, I do trust that the Mission Evaluation Room, with their mission experts, would bring forward the results of that and they did come forward on that Friday, the 24th, and said they did not believe there was a safety of flight issue and that there would be no burn through and that at most we would have a potential turn around issue, some work on the orbiter that we'd have to do post flight. I did trust that their analysis and the work they had done was correct."

No one in the MMT objected to the report. But after Columbia's catastrophic re-entry, some engineers let it be known then had deep concerns about the analysis. Ham said she never heard any such concerns. Engelauf and Cain agreed.

"We foster a culture here that very much encourages folks to talk, to communicate, the lines of communications are always open," Cain said. "That's the culture we very much encourage and foster around here. And the reason we do that, as you heard Linda mention earlier ... is because we have the safety of the crew the success of the missions at the forefront of our mind every single day we come to work.

"So in order for us to do our jobs effectively, it is crucial that we have open and clear lines of communications. It is absolutely critical and it is, frankly, expected of every single person in every organization, from the engineer all the way up to the management of the programs. Certainly for human spaceflight endeavors, that's the culture we foster. And I believe it's alive and healthy today."

Ham said lower-level engineers and managers have formal and informal avenues to approach senior management with technical concerns.

"For some reason, we didn't get it either way, which I think is also of interest," she said. "You know, whatever happened somewhere, we probably need to figure that out and see if there is a way we can improve that. But I'd also agree we have wide-open communications, our doors are always open and we're more than willing to hear what people have to say. That's the only way we can operate, that's the only way we're going to hear about these kinds of things and the only way we can continue to fly safely. So we really do need these people to feel comfortable and come forward with their issues."

Said Engelauf: "In the final analysis, every night when I go to bed, (I know) we lost STS-107, we lost the crew, we lost the vehicle. Clearly, that is not the way it is supposed to happen and that is not what we do here. So no matter how you do the arithmetic, we're getting a wrong answer and we have to fix that. We all know that. We're going to have to wait until we get some recommendations from people who look at this from a different perspective. It's very difficult to pinpoint the details. It may be something that just isn't obvious to us. I certainly don't want to leap to the easy answers and fix something that isn't' causing the problem."

Engelauf also addressed another issue that keeps popping up in the disaster investigation: The agency's long history of foam shedding and how senior managers slowly grew to accept what sociologist Diane Vaughan calls the "normalization of deviance."

"We've had incidences of foam coming off the tank throughout the history of the program and the same management processes that I think got us comfortable that that was not really a safety of flight issue have been allowed to continue, rightly or wrongly," Engelauf said. "I don't think you can point to individuals today and say that person got comfortable with it, because we've sort of inherited this from the time when Linda and I were back as front room flight controllers and there was a completely different set of people managing the program.

"But I think the intent is that our processes try to cover these sorts of things, we try to put all the checks and balances in place and we try to do all the analyses and in this particular case, I don't think the problem was that we didn't do the analysis or didn't take notice of the foam. I think we got the wrong answer on the analyses.

Cain said "at least part of the answer has to be that fundamentally, we are dealing with an incredibly complex system. It's the most complicated machine that humans have ever built. And over time, we are going to make some human errors. And that's got to be at least part of the answer. We do everything in our power, every single day in this business, to manage the systems to minimize that. And over time, with this complex of a system and the risky environment of space, that has to be at least part of the answer."

Finally, Ham, Engelauf and Cain agreed that NASA would have done everything possible to mount a rescue mission if the team had realized Columbia faced a catastrophic defect. While it is doubtful any such scenario would have succeeded, all three said NASA certainly would have made the attempt.

"Had we known that there was a catastrophic situation on orbit, we certainly would have done everything we could have, including is there anything we can do for the tile repair, we certainly would have pursued rescue. There's no doubt," Ham said.

Added Cain: "If we had known that we had a problem while we were on orbit, I certainly agree, we would have left literally no stone unturned. As to whether it would have made a difference, I think it's an impossible question to answer."

Editor's Note...
The mission management team transcripts posted by NASA today included little or no punctuation. Punctuation, based on context and content, has been added to the excerpts below to make the passages more readable.

Transcripts of meetings by senior NASA managers during the shuttle Columbia's ill-fated flight show mission management team chairman Linda Ham and other top officials, despite a dearth of technical data, simply did not believe falling insulation from the ship's external fuel tank could cause a catastrophic breach in the ship's left wing.

The transcripts, posted on a NASA web site today, include extensive discussions of relatively minor temperature control problems with Columbia's Spacehab research module and debate about the shuttle's slightly over-limit landing weight. But there is surprisingly little discussion about the foam strike investigators now believed doomed the ship 81 seconds after blastoff Jan. 16.

Instead, the management team unanimously accepted, with only a smattering of questions from Ham, the results of a hurried analysis that concluded the worst threat Columbia faced was possibly severe, but localized, tile damage that might require repairs between flights.

Ham has declined all interview requests since the shuttle tragedy and has not participated in any news briefings to this point. With the benefit of 20-20 hindsight, she has been criticized by some observers for not recognizing the severity of the foam strike and its potential for causing catastrophic damage. As chairman of the MMT, she also has been blamed for quashing efforts to obtain spy satellite photography of the shuttle to better characterize any potential damage.

But the widely reported, unsuccessful efforts to obtain spy satellite imagery were not discussed at the MMT meetings, the transcripts show, and in any case, sources say, those efforts primarily were derailed by lower level managers before reaching the MMT chairman.

Ham remains in the shuttle program office at the Johnson Space Center, but earlier this summer she was removed from her post as program integration manager and replaced by flight director John Shannon. Wayne Hale, a former flight director who now serves as deputy program manager under William Parsons, is expected to assume Ham's role in future MMT meetings.

As for Ham's role chairing the MMT meetings during Columbia's flight, the transcripts show no particularly unusual comments on her part or any obviously questionable decisions. But surprisingly, the foam strike was never a top-of-the-agenda item and it was discussed only sparingly, in summary format, and with no debate even though the strike was the most significant such impact ever observed.

When it was discussed, the team focused almost totally on possible damage to the heat shield tiles on the underside of Columbia's left wing and all but dismissed the possibility the foam strike could have damaged the reinforced carbon carbon - RCC - panels making up the wing leading edge. This was a particularly striking turn of events considering there was little or test data on how the carbon composite leading edge panels might respond to a strike by a large piece of foam and there was uncertainty about exactly where the foam had hit the wing.

During the third MMT meeting of Columbia's mission, held on Jan. 24, Don McCormack, representing NASA's mission evaluation room support team, told Ham engineers had started an assessment of potential tile damage using a program called "Crater."

While the analysis was not yet complete, McCormack said, "obviously thereÕs potential for significant tile damage here, but they do not indicate, the thermal analysis does not indicate that there is a potential for a burn through. There could be localized heating damage. Obviously, there is a lot of uncertainty in all this in terms of the size of the debris and where it hit and angle of incidence and, uh, its difficult..."

"No burn-through means no catastrophic damage and localized heating damage would mean a tile replacement?" Ham asked.

"It would mean possible impact to turnaround repairs and that sort of thing, but we do not see any kind of safety of flight issue here, yet, in anything that weÕve looked at."

"No safety of flight and no issue for this mission, nothing that weÕre going to do different, there may be a turn around (issue)?"

"Right, right, It could potentially hit the RCC and we donÕt indicate, other than possible coating damage or something, we donÕt see any issue if it hit the RCC. Although ... we could have some significant tile damage, we donÕt see a safety of flight issue."

Ham asked him to elaborate - "what do you mean by that?" - and McCormack said the foam could have scooped out a fairly large area of tile on the underside of the left wing. Even so, Calvin Schomburg, a tile expert, reassured the MMT that no burn throughs were expected and the foam strike did not represent a safety of flight issue.

In the process of discussing potential tile damage, Ham and her colleagues never revisited the RCC issue even though there was little or no data presented about how the carbon composite panels would respond to a significant impact. And the impact seen during Columbia's launching was the most significant on record.

After complaints that MMT participants listening in by phone could not hear, Ham repeated that Schomburg, who had no expertise in RCC systems, "does not believe that there is any burn throughs, so no safety of flight kind of issue. It's more of a turn around issue similar to what we have had on other flights. ThatÕs it? All right, any questions on that?"

There were no questions. And with that, any lingering concern about the health of the RCC panels was dismissed.

The foam in question broke away from the left-side "bipod ramp" area of the external tank where two large struts attach the nose of the shuttle to the top of the tank. To keep ice from forming on the struts and falling onto the shuttle, foam insulation is sprayed on the tank and then sculpted by hand to form two aerodynamic ramps, or slopes, at the base of each strut making up the bipod.

Eight-one seconds after Columbia blasted off from the Kennedy Space Center, a 1.67-pound chunk of foam from the left bipod ramp area broke free and slammed into the ship's wing at more than 500 mph. Engineers now believe it hit the leading edge on the lower side of RCC panel No. 8, punching a hole in the panel or causing enough damage to result in breach of some sort.

Recent tests at the Southwest Research Institute in San Antonio, Texas, clearly demonstrated such a breach was possible.

While the details are not known with certainty, engineers believe Columbia re-entered Earth's atmosphere Feb. 1 with a hole of some sort in the left wing leading edge. Sixteen minutes after falling into the discernible atmosphere, Columbia's flight computers lost control of the orbiter and the shuttle broke apart. Commander Rick Husband and his six crewmates were killed.

The foam strike was not discovered until engineers examined launch film the day after liftoff. The first of five mission management team meetings carried out during Columbia's flight was held earlier that day but there was no mention of the foam strike. Three days later, however, during the next MMT meeting on Jan. 21, McCormack briefed Ham and the rest of the team on the issue.

"As everyone knows, we took the hit ... somewhere on the left wing leading edge and the photo/TV guys are completed, I think, pretty much their work, although I know IÕm sure theyÕre still reviewing their stuff and they have given us, you know, approximate size for the debris and approximate area for where it came from and approximately where it hit. So we are, you know, talking about doing some sort of "parametric" type analyses and also, weÕre talking about looking at what you can do in event we really have some damage there. But..."

Ham interrupted, recalling shuttle mission STS-112 the previous October when a large piece of bipod foam fell off and struck one of the shuttle Atlantis' booster rockets. She said engineers should gather data collected in the wake of that launching, and after an earlier mission in which foam had caused damage, "and make sure that, you know, I hope we had good flight rationale then."

"Yeah, weÕll look at that," McCormack said. "You mention 87, you know we saw some fairly significant damage area between RCC panels 8 and 9 and main landing gear door down at the bottom on STS-87. We did some analyses prior to the STS-89 so, uh..."

He was not referring to actual RCC damage, rather to tile damage between the landing gear door and the leading edge just behind panels 8 and 9.

In any case, Ham interrupted again, saying "And really, I donÕt think there is much we can do, so you know itÕs not really a factor during the flight because there isnÕt much we can do about it. But what IÕm really interested in is making sure our flight rationale two flights ago was good. Maybe this is foam from a different area, IÕm not sure..."

Ham was saying, in effect, there was nothing the crew could do about tile damage in orbit. But she wanted engineers to go back and re-visit the rationale for continuing shuttle flights with a known foam shedding problem to make sure the reasoning was valid.

Toward the end of the Jan. 21 meeting, Lambert Austin, representing the shuttle integration team, made one slightly alarming observation, saying the strike that occurred later in the ascent, when the shuttle was moving faster, than what had occurred during the STS-112 launching.

"And higher machs (velocity) is going to be worse," Ham observed.

"Yes, but that, you know the debris impact locations will be different so thatÕs one of the reasons we have ... basically, like you said, give a little bit of parametric set of data to the orbiter (project) so they can decide what the worse-case scenario might be."

"OK," Ham replied.

At the next MMT meeting, on Jan. 24, McCormack reported that engineers believed there was no safety of flight issue based on the initial Crater results. Phil Engelauf, representing the mission operations directorate, told Ham flight directors had informed the crew about the foam strike and sent up a 16-second video clip "just so they are armed if they get any questions in the press conferences or that sort of thing. We made it very clear to them, no concerns."

Then, during the meeting after that - on Jan. 27 - McCormack provided an update, saying engineers still believed there was no safety of flight issue even if the foam had hit a sensitive area around the left main landing gear door.

"We looked at an area about the size of 30 inches by 7 inches, and, of course, you know, sloped, cratered out area, and our results there were similar to what we got elsewhere and that is, although local degradation of the door structure is likely if we were to have sustained a hit there, there is no predicted burn-through and no safety of flight issue."

"A turn-around issue?" Ham asked.

"Yeah, possibly."

"If it were hit there..."

"If it were hit there, itÕs a critical area there on the door, but also the Integration guys had indicated that they thought it was a low probability location but it was still one that we went off and looked at," McCormack said.

"OK," Ham replied.

"So, that completes the thermal analysis from the debris hit and with that, thatÕs all IÕve got."

The foam strike was mentioned a final time during the final MMT meeting on Jan. 30, two days before Columbia's re-entry. Ham wanted to make sure any film shot by Columbia's astronauts showing the external tank and, possibly, the area where the foam broke free, would be quickly extracted from the shuttle and returned to Houston for analysis. The foam issue would have to be addressed before the shuttle Atlantis could be cleared for launch on the next shuttle mission in March.

The astronauts aboard the shuttle Columbia, strapped into a reinforced module built to withstand extreme forces, likely survived a minute or more beyond the commander's final transmission, sources say. Engineers believe the crew died when the module, buffeted by increasingly extreme aerodynamic forces, finally broke open as it plunged steeply into the thickening atmosphere above Texas.

NASA managers and engineers have been reluctant to discuss the presumed fate of Columbia's crew out of deference to family members and because of the inherently morbid nature of such speculation. Speaking privately, NASA sources told CBS News last week the crew almost certainly survived the shuttle's initial breakup, but they spoke on background only and asked that details not be repeated. The New York Times, quoting sources with the Columbia Accident Investigation Board, reported a virtually identical scenario late Tuesday, putting the issue in the public spotlight.

Columbia was destroyed during re-entry Feb. 1 after superheated air burned its way into the ship's left wing through a deadly breach in the wing's carbon composite leading edge panels. The first sign of anything amiss was recorded on board the shuttle at 8:48:39 a.m., just four-and-a-half minutes after Columbia fell into the discernible atmosphere 400,000 feet above the Pacific Ocean northwest of Hawaii.

For the next 10 minutes, the shuttle's flight computers held the shuttle on course despite ever-worsening damage to the left wing. But finally, as the hot air burned its way into the left main landing gear wheel well, Columbia's computers displayed a tire pressure fault message on a cockpit display. The message was generated at 8:58:40 a.m. Commander Rick Husband called mission control at the Johnson Space Center in Houston seconds later, beginning "And, uh, Hou(ston)..." But his transmission was cut off.

A half minute or so later, astronaut Charles Hobaugh in mission control replied, "And Columbia, Houston, we see your tire pressure messages and we did not copy your last."

Moments later, Husband replied, "Roger, uh, buh..." and again, was cut off. He might have been saying "both" or "before," possibly referring to the tire pressure fault messages. He sounded calm, but the signal was cut off, engineers believe, by the orbiter's orientation: Radio transmissions from antennas atop the crew module were blocked by Columbia's tail fin.

In any case, nothing more was heard from the crew. At 8:59:32 a.m., all data from the shuttle suddenly stopped flowing to mission control. An on-board data recorder, however, continued operating, allowing engineers to reconstruct the shuttle's final moments after the recorder later was recovered.

A final two-second burst of downlinked telemetry was captured on the ground beginning at 9:00:02.66 a.m. At that point, the shuttle's left wing, or a large portion of it, was gone and Columbia's left orbital maneuvering system rocket pod showed signs of severe damage. The orbiter was in an "uncommanded orientation," rapidly yawing to one side. The shuttle's aft engine compartment, fuselage, right wing and crew cabin, however, were essentially intact. All three electricity producing fuel cells were operating and the life support system appeared to be functioning normally, although the ship's cooling system had shut down.

By that point, the astronauts clearly knew Columbia had suffered a catastrophic failure. But there was nothing they could do. A bit of telemetry toward the end suggested one of the pilots might have briefly moved his joystick hand controller beyond its neutral, or "detent," position. But Harold Gehman, chairman of the Columbia Accident Investigation Board, implied last week that likely was an inadvertent "stick bump" and not an attempt to take over control.

The final bit of downlinked telemetry from the shuttle timed out at 9:00:04.826 a.m. For the next 13 seconds, the shuttle's data recorder continued to function, drawing power from the fuel cells mounted beneath the floor of the payload bay. Finally, around 9:00:18 a.m., the recorder suddenly stopped as the fuselage broke apart and the electrical system failed.

The reinforced crew module, sources told CBS News, likely survived the breakup intact, much like Challenger's did when that shuttle broke up during launch in 1986. Up until the moment Columbia's fuselage failed, data from the recovered recorder indicates the crew module did not experience any fatal accelerations. How long the astronauts might have survived as the crew module plunged earthward will never be known. Sadly, they almost certainly had time to understand their fate.

The Columbia Accident Investigation Board today released a definitive scenario detailing the doomed shuttle's countdown, launch and re-entry, a scenario that merges all available telemetry from the orbiter, recorded data, debris analysis and complex computer simulations. The result is the most complete picture yet showing how a foam strike during launch punched a catastrophic hole in the shuttle's left wing that led to the ship's destruction during re-entry Feb. 1.

Board member Scott Hubbard also presented additional data from a dramatic test last Monday that lends additional credence to the updated scenario. In the test, a chunk of external tank foam insulation was fired at a wing leading edge mockup at the Southwest Research Institute in San Antonio under conditions that simulated the actual foam strike known to have occurred 82 seconds after Columbia's launching Jan. 1.

Along with blasting a 16-by-17-inch-wide hole in reinforced carbon carbon panel No. 8 - the same carbon composite panel believed to have been struck during Columbia's liftoff - the impact also broke an internal lug fitting and caused severe cracks in the surrounding material.

Hubbard said two large fragments of RCC material were blown into the breach by the impact. Dramatic high-speed camera footage shot inside a cavity behind the leading edge panels showed the fragments blowing inward with extraordinary violence. Hubbard said a similar fragment, having a surface area of 90 square inches or more, is perhaps the best explanation for a mysterious object detected by ground radar systems the day after launch that was seen slowly separating from the shuttle. The idea is a large fragment could have lodged in the breach during launch and then floated free after a day of maneuvering in orbit.

On top of that, cracking similar to that seen around the breach in the wing mockup likely led to debris shedding during re-entry. Amateur shuttle watchers on the ground filmed what appeared to be flaming debris falling away from the descending orbiter well west of Texas. Finally, the broken lug fitting observed after Monday's test would have provided a way for a so-called T-seal between RCC panels 8 and 9 to rock open and closed during entry, providing just the sort of intermittent heating needed to explain heat damage that, until now, had defied explanation.

"The board felt this testing was very, very important because it will help us, it will determine how strong a word we use to equate the foam strike, which we know happened, to the creation of some kind of damage that was pre-existing prior to the entry," CAIB chairman Harold Gehman said Friday. "This allows us now to use a word, which we haven't agreed to yet, but use a word that expresses high confidence, a very high degree of confidence that we have indeed found the cause here."

Board member James Hallock said the actual breach probably was in the six- to 10-inch-wide range. A larger hole would have let so much heat into the wing during the initial stages of re-entry that Columbia probably would not have survived all the way to Texas.

But figuring out the mechanical failure mode is only part of the CAIB's goal. The board's final report, now expected around Aug. 26, will focus just as strongly on management issues and shortcomings.

"We started off with kind of a hierarchy of factors," said Gehman. "We had the direct, mechanical thing and then below that, we had contributing factors. We've now decided that these things are equal. That's why we're being so cautious and so careful about the management sections and the safety sections and all those kinds of things. Because the way the report is going to characterize these things is we have what we're now calling the physical, or mechanical failure, and then we have the systemic failures and we're now giving them equal weight. It would be premature to go much further than that because we're writing that section."

But Gehman made it quite clear the board views the space shuttle as an experimental spacecraft as opposed to an operational vehicle. He has said that before, but today he gave a bit more background on how the board views the shuttle system.

"In the case of an operational vehicle, like a commercial airliner or something like that, the events that you use the vehicle for - takeoff and landing and transporting people and then also the turnaround in between flights - if it's an operational vehicle, you expect each one of these events will be nearly identical and repeatable," he said. "And therefore, it's easy and it's logical and it's prudent to contract that out because you essentially want repeatability, you want the thing to happen exactly the same way each time and you expect the same results each time.

"If, on the other hand, it's a developmental vehicle, your expectation is it will not be the same every time. You are always on the lookout for little, tiny little differences, your suspicious of little tiny little differences and also you demand extraordinarily accurate and intrusive instrumentation so you can detect little variances in how the thing operates.

"And you also don't have an expectation that when the thing lands that you can turn it around and get it back in the air again quickly," he said. "There is no expectation that you can do that and there's no expectation you can do that economically. To me, those are the big differences. I cannot emphasize too strongly how much the board is impressed with how deeply and how broadly the differences translate themselves into practical applications. ... We consider it to be truly significant."

Asked if NASA had to be able to repair RCC holes 16 inches across in order to resume shuttle flights, Gehman said "they have to be able to repair holes in RCC caused by debris."

"If they can't stop the debris, they've got to be able to fix the hole," he said. "If they can stop the debris to where it's tiny little pieces of debris and it causes tiny little holes, then they can have a tiny little hole fixer."

Columbia, of course, was struck with the largest piece of foam debris on record, a 1.8-pound suitcase-sized chunk that broke away from the so-called bi-pod ramp area where one of two large struts attaches the nose of the shuttle to the external fuel tank. NASA engineers now plan to launch future shuttles without any such foam insulation, using heaters instead to prevent ice buildups before launch.

"No shuttle is going to fly with a bi-pod ramp again, so you're not going to see this happen again, I don't think," Gehman said. "And I mentioned this before in press conferences and it's in our interim recommendations, that we view this as a system. NASA has to cut down on the amount of debris that comes off, they have to toughen the orbiter, they have to be able to inspect and repair the orbiter and then they've also got to give the crew a better chance to survive. All four of these contribute to safer operations and no any one of them, in my view, is a fix."

Whether NASA can address all such factors before next summer is an open question. Most insiders still believe NASA will have a hard time launching the next mission before the middle of next summer at the earliest, but agency leaders continue to hold out hope for a return to flight next spring.

While Gehman said he still believes NASA can make the necessary fixes in time for a flight six to nine months from now, he also said "the board is convinced that coming and going into orbit remains an enormously dangerous task."

"And even if you had the world's best engineers and world's best managers working on this thing, there's still a high degree of risk in what we're doing here. It's still not flying in a commercial airliner, it's not like taking a drive in your car. It's dangerous. It's very dangerous, and it will remain that way.

"So under that rubric, you could say that even if we had the best managers and best engineers in the world, you're in a business where something can still cause you to have a tragedy like this.

"On the other hand, when looking into this particular accident, we think we have found some issues, some practices, some managerial, budgetary kinds of things, which we believe could be done better even if we had not had this accident. I mean, if they had (formed) this panel to look at NASA for five months, seven days a week like we have, I suspect we would come up with probably the same set of recommendations even if the Columbia had not been lost."

While the mechanical cause of the accident seems clear, the CAIB report will not be 100 percent conclusive. Engineers simply cannot rule out a space debris impact of some sort or even impact by debris from a possibly faulty "bolt catcher" in the booster-external tank separation system.

As for management issues, Gehman declined to comment other than to toss out a few hints.

"We are not consciously saving up things for the report," he said. "But there are some parts of the report that really we have not said a whole lot about. ... The board is still wrestling with some of the words and some of the findings. That part is not very mature yet. ... And also, you haven't seen all of this written down on one piece of paper yet.

"We've talked about a thing here and a thing there, we've talked about inspections this and quality assurance that and testing of this and these things. But when you see it all written down, the tone may be something we haven't come across yet. ... There may be some news value in the tone of the report."

That might rank as one of the greater understatements of the investigation, which Gehman said likely will cost $15 million to $20 million when all is said and done.

"If you agree with me that we have not perfected, we have not learned everything we need to know yet about routinely going into space and coming back out of space, then even if you have a situation where you have a tragedy like this, your obligation to learn as much as you possibly can," Gehman said.

"And the fact that we've allowed cameras and range instrumentation and on-board instrumentation and all kinds of things like that to kind of gracefully atrophy over the years leads me to bring this issue up that there are some signs that it's been considered a routine operation or an operational vehicle rather than a test vehicle."

In a dramatic test that drew startled gasps from onlookers, engineers fired a chunk of foam insulation at a mockup of a shuttle wing leading edge today, blowing a gaping 16-inch-wide hole in the carbon composite structure and putting to rest any lingering doubts a launch-day foam strike was responsible for the Columbia disaster.

"We believe we have found the smoking gun, we believe we've established that the foam block that fell off the external tank (during Columbia's launching) was, in fact, the most probable cause, the direct cause of the Columbia accident," said Scott Hubbard, a member of the Columbia Accident Investigation Board. "I've now got a direct connection between foam shedding creating a hole that's the same order of magnitude as what must have been there when Columbia came home on Feb. 1."

Eighty one seconds after liftoff Jan. 16, a 1.67-pound chunk of foam insulation broke away from the shuttle's external fuel tank and slammed into the left wing at more than 500 mph. Enhanced video from the one camera that viewed the impact point indicated the foam struck the leading edge at or very near the lower side of reinforced carbon carbon panel No. 8, one of 22 such panels making up the leading edge of the left wing.

But the grainy video, unable to resolve anything smaller than two square feet, provided no direct evidence of actual damage. While most engineers believed the foam strike must have contributed to the breach that ultimately caused Columbia's destruction, they had no proof.

In the wake of the mishap, the Columbia Accident Investigation Board, working with NASA, decided to conduct a complex series of tests to find out whether impacts by low-density foam could, in fact, cause the kind of damage needed to bring down the shuttle. A full-scale mockup of the shuttle's wing leading edge system was built and shipped to the Southwest Research Institute in San Antonio, Texas, where a nitrogen gas cannon was available to simulate the launch-day foam strike.

Initial tests showed foam impacts could cause damage, but the results were not clear cut. Then again, the initial tests involved impacts at RCC panel No. 6, located closer to the shuttle's fuselage. RCC 6 is not as large as panel 8 and does not feature the same complex curvature. For today's test, a foam bullet was fired at the lower side of RCC panel 8, one taken from another shuttle and one with 27 previous flights to its credit.

This time around, the cannon barrel was "clocked," or tilted, 30 degrees to more accurately duplicate the predicted impact energy. The aim point was adjusted to strike the underside of RCC 8 closer to a seal between panels 8 and 9. And this time around, the results were dramatically different.

"There is a huge hole in panel 8!" one observer marveled moments after the test. "It's gone, I mean the foam didn't make it to the back (containment) curtain. You talk about an impact! Unbelievable. If you wanted a smoking gun, you've got it."

Speaking to reporters after the test, Hubbard said high-speed video showed an initial rip that "tears all the way across the panel and produces the hole. The hole is very ragged, about 16 inches by 16 inches, or about 256 square inches. There are a number of pieces that are inside the wing leading edge as well as pieces that fell outside."

One of the enduring mysteries of the investigation has been radar data indicating a piece of debris of some sort separated from Columbia the day after launch. In today's test, the foam essentially blew into the leading edge, pushing large pieces of RCC inside. Based on the size of the breach and the size of the fragments inside the leading edge cavity directly behind the RCC panels, Hubbard said the "flight day 2 object" likely was a large section of RCC 8 that worked its way free in the weightlessness of orbit.

The object seen by radar drifting away from Columbia could "very likely be part of the carbon panel itself," he said.

The foam was fired at the wing mockup at roughly 775 feet per second, or about 530 mph, at an impact angle of 22 degrees. That's higher than the impact angle during Columbia's launch. But by adjusting the impact angle, engineers were able to account for rotational energy imparted by the tumbling foam. Hubbard said the impact imparted about a ton of force to the RCC panel. All of the test parameters, taken together, represented an "average" set of conditions. The actual impact could have been somewhat worse or somewhat less violent. But the hole that was blown in RCC 8 leaves little doubt the foam strike caused the breach responsible for Columbia's destruction.

"I was surprised, I was very surprised," Hubbard said. "As a physicist conducting a test, I feel gratified that after months of work we were able to demonstrate this connection between the foam and the damage. But I know it was a source of tragedy, so that makes me feel very sad. This whole six months, we've constantly been reminded by pictures of the seven lost astronauts what this all means."

The CAIB already has released a preliminary recommendation calling for NASA to obtain spy-satellite imagery of shuttles in flight to look for possible signs of damage. The board also has recommended NASA develop techniques for repairing thermal protection system damage in orbit. Hubbard said today's test shows more data also is needed to understand how carbon composite materials age and react to impacts.

"We need to have better imagery, the shuttle program should have the capability for on-orbit inspection and repair," he said. "We need to realize this is a vehicle that needs to be looked at very carefully each flight. Aircraft, even experimental aircraft, often go through thousands of flights before they're determined to be operational. This vehicle has only 113 flights."

He said engineers are "working to try to determine whether you can do on-orbit repairs of the reinforced carbon. It is the highest temperature area of the orbiter, so finding materials that will patch that are very difficult. I don't know, personally, any way you can patch a hole this big. But that doesn't mean some expert (can't figure something out).

"The RCC has proven to be a very tough material. I think the first step is understanding RCC panels much better and understanding what kind of damage thresholds there are. Where is the dividing point? That database doesn't exist and I think that's one of the first things the shuttle program is going to have to work on."

The commander of the shuttle Columbia was informed about the foam strike most believe led to the ship's destruction in a casual email from mission control a full week after liftoff. Even though NASA's internal analysis of the foam incident was not yet complete, the email dismissed any concern about the strike as "not even worth mentioning" and said the only reason it was being brought up was to make sure the astronauts were not surprised by a question from reporters during upcoming interviews.

As it turned out, no reporters ever asked about the foam strike. But the wording of the email gave commander Rick Husband and pilot William "Willie" McCool no reason to question the conclusion that Columbia was in no danger. And indeed, the commander replied in a light-hearted manner, even making a small play on words and ending an email with a "smiley" - :) - face.

The email exchange was posted on a NASA website today. The full text follows (PAO: public affairs office; MCC/POCC: mission control center/payload operations control center; FD: flight day; chine: area of wing near the fuselage):

Rick and Willie,

You guys are doing a fantastic job staying on the timeline and accomplishing great science. Keep up the good work and let us know if there is anything that we can do better from an MCC/POCC standpoint.

There is one item that I would like to make you aware of for the upcoming PAO event on Blue FD 10 and for future PAO events later in the mission. This item is not even worth mentioning other than wanting to make sure that you are not surprised by it in a question from a reporter.

During ascent at approximately 80 seconds, photo analysis shows that some debris from the area of the -Y ET Bipod Attach Point came loose and subsequently impacted the orbiter left wing, in the area of transition from Chine to Main Wing, creating a shower of smaller particles. The impact appears to be totally on the lower surface and no particles are seen to traverse over the upper surface of the wing. Experts have reviewed the high speed photography and there is no concern for RCC or tile damage. We have seen this same phenomenon on several other flights and there is absolutely no concern for entry.

That is all for now. It's a pleasure working with you every day.

Husband replied to flight director Steve Stich the following day - Jan. 24 - saying "Thanks a million Steve!"

"And thanks for the great work on your part AND for the great poems!" Husband emailed. "I saw the word Chine below and thought it was "China". I guess it's believeable (sic) that you might meet someone from China by the name of Main Wing :)." Mission control uplinked a video of the foam strike Jan. 25 and Husband replied the next day, saying only "thanks for the super work! We appreciate it."

In hindsight, the emails are disturbing because of the remarkably casual manner in which the foam strike, the worst in shuttle history, was dismissed. Other emails that were released after Columbia's Feb. 1 destruction showed mid-level engineers were concerned about potentially severe re-entry damage all the way until the day before landing.

The Columbia Accident Investigation Board now believes the foam strike is the most probable cause of the Columbia disaster.

Eighty-one seconds after Columbia's launching, a suitcase-size chunk of foam insulation broke away from the shuttle's external fuel tank and slammed into the leading edge of the ship's left wing.

The foam strike was discovered during routine post-launch video analysis on Jan. 17. Mission managers promptly ordered an engineering assessment to determine whether or not Columbia's heat-shield tiles had been damaged enough to compromise safety during re-entry. An analysis carried out by Boeing concluded that while possibly severe heat damage to the underlying skin might require post-landing repairs, the impact did not pose a "safety of flight" issue.

The analysis indicated any impact on the reinforced carbon carbon leading edge panels would do little more than mar the coating. As it turned out, the analysis was deeply flawed. The engineers extrapolated from an earlier tile-impact study involving much smaller pieces of debris and had virtually no data at all regarding how such strikes might affect RCC panels. Post-accident analyses, impact tests using a nitrogen gas cannon, enhanced launch video and sensor data all indicated the 1.67-pound chunk of foam, which hit the leading edge at more than 500 mph, caused a breach that allowed super-heated air to burn its way inside during Columbia's re-entry Feb. 1. The wing ultimately failed and Columbia was destroyed.

But NASA's mission management team accepted the results of the Boeing analysis, quashed efforts to obtain spy satellite photography that might have resolved the issue one way or the other and informed the crew about the impact only in passing.

But according to a just-released transcript of internal mission control communications loops, the foam strike, or a debris impact of some sort, clearly was on the minds of flight controllers when the first signs of trouble developed during Columbia's return to Earth. Mechanical systems officer Jeffrey Kling - MMACS - was the man who first informed flight director Leroy Cain about unusual telemetry from Columbia's left wing. Kling, in turn, was backed up by other mechanical systems, or MECH, engineers, including Ken Smith and David Lechner, in a nearby support room.

"What in the world?" one of the MECH engineers wondered when the first sensor data dropped off line.

"This is not funny," Kling replied. "On the left side."

"On the left side," MECH agreed.

Seconds later, at 08:54:24 a.m., Kling informed Cain.

"FLIGHT, MMACS."

"Go ahead, MMACS."

"FYI, I've just lost four separate temperature transducers on the left side of the vehicle, hydraulic return temperatures. Two of them on system one and one in each of systems two and three. To the left outboard and left inboard elevon."

Columbia was passing over the California-Nevada state line at 22.5 times the speed of sound at an altitude of 227,400 feet. Seconds later, observers on the ground noticed a bright flash in the shuttle's plasma trail followed by the sixth known incident of debris falling away from the orbiter.

Kling's discussion with Cain has been posted previously, but the internal dialogue between Kling and the MECH officers sheds a chilling new light on the events of Feb. 1.

"OK, is there anything common to them? DSC (discrete signal conditioner) or MDM (multiplexer-demultiplexer) or anything?" Cain wondered. "I mean, you're telling me you lost them all at exactly the same time?"

"No, not exactly," Kling replied. "They were within probably four or five seconds of each other."

"OK, where are those, where is that instrumentation located?"

"All four of them are located in the aft part of the left wing, right in front of the elevons, elevon actuators. And there is no commonality."

"No commonality."

Kling then spoke to his support room, saying "OK. Keep an eye on the left side. Everything else... looks like the rest of the temperatures are good."

"Yep," MECH replied.

After answering another question from Cain about the systems involved, Kling continued his discussion with the MECH officers, struggling to figure out what might be going on. He apparently was thinking back to the foam strike on the left wing.

"Those are really spread too far apart to be pickin' up... like debris damage or anything to both of em', unless they cut a big swath... have to be two hits," Kling speculated.

"And MMACS, FLIGHT," Cain called.

"FLIGHT, MMACS," replied Kling.

"All other indications for your hydraulic system indications are good?"

"They're all good," Kling said. "We've got good quantities all the way across."

"And the other temps are normal?"

"The other temps are normal, yes sir."

"And when you say you lost these, are you saying that they went..."

"All four of them are off-scale-low," Kling replied.

"... to zero or off-scale-low?" Cain continued.

"Staggered, too," said MECH.

"And they were all staggered, they were, like I said, within several seconds of each other," Kling relayed to Cain.

"OK," the flight director said.

It was 8:58 a.m. Kling then resumed the conversation with MECH. "All the rest of the telemetry as we can see is still looking good."

"Yeah."

"Great," Kling said.

But not for long. At 8:58:48 a.m., Husband called down from Columbia, saying "And, uh, Hou(ston)," but his transmission was cut off. Seconds later, at 8:59:15 a.m., Kling called Cain with more alarming news.

"FLIGHT, MMACS."

"Go."

"We just lost tire pressure on the left outboard and left inboard, both tires."

Husband presumably was calling down to note the main landing gear tire pressure readings. Astronaut Charles Hobaugh, listening in on the flight control audio loop, promptly radioed Columbia to confirm the ground had, in fact, seen the tire data. "And Columbia, Houston, we see your tire pressure messages and we did not..."

"Is it instrumentation, MMACS? Gotta be..." Cain said.

"...copy your last."

"FLIGHT, MMACS. Those are also off, off-scale low," Kling said. Then, speaking again to MECH, he added "I am not believing this."

"No," said MECH.

Seconds later, Columbia broke apart above central Texas.

As expected, the Columbia Accident Investigation Board today released an interim recommendation requiring NASA to develop a capability to inspect the shuttle's heat shield system in orbit and to repair any significant damage that might be found.

The recommendation is the third issued by the CAIB in advance of its final report, expected around July 23, to give NASA as much time as possible to respond and to minimize the downtime before shuttle flights can resume. Two other preliminary recommendations were released April 17. One requires NASA to develop tools for evaluating the strength and integrity of heat-shield tiles and leading edge panels and the other requires NASA to obtain routine on-orbit imagery of the shuttle to look for signs of damage.

A detailed status report covering NASA's ongoing work to develop an on-orbit tile repair capability was posted on this page June 20. Here is the text of today's interim recommendation from the CAIB:

Recommendation Three:

• Before return to flight, for missions to the International Space Station (ISS,) develop a practicable capability to inspect and effect emergency repairs to the widest possible range of damage to the Thermal Protection System (TPS,) including both tile and Reinforced Carbon Carbon (RCC,) taking advantage of the additional capabilities available while in proximity to and docked at the ISS.

• Before return to flight, for non-station missions, develop a comprehensive autonomous (independent of station) inspection and repair capability to cover the widest practicable range of damage scenarios.

• An on-orbit TPS inspection should be accomplished early on all missions, using appropriate assets and capabilities.

• The ultimate objective should be a fully autonomous capability for all missions, to address the possibility that an ISS mission does not achieve the necessary orbit, fails to dock successfully, or suffers damage during or after undocking.

Facts:

• At present there is no certified on-orbit or on-station capability to inspect the orbiter TPS for damage, or to effect repairs.

• Past efforts, some predating STS-1, have not resulted in an operational capacity.

• Changes in imaging and inspection capabilities, materials technology, and the access provided by the ISS have greatly improved the prospects for deploying this capability.

Finding:

An inspection of the TPS, accomplished as soon as possible after achieving orbit/rendezvous, coupled with repair capability, would result in improved safety.

Background:

The Board is convinced of the necessity of taking all practicable steps to Òde-coupleÓ foam insulation shedding from loss of crew and vehicle, including: 1) design improvements to prevent foam shedding; 2) toughening the TPS; 3) improved TPS inspection and repair capability.

An inspection and repair capability is fundamental to improving the ability of the orbiter to experience TPS damage without catastrophic consequences.

This effort does not reduce the urgency or importance of aggressively reducing all sources of potential damage to the orbiter. Only by reducing the likelihood of damage to the orbiter, as well as developing the ability to detect and repair damage, can the maximum safety improvement be realized.

During the STS-107 flight and investigation, the lack of repair capability was cited repeatedly, and may have been a factor in decisions made during the STS-107 mission, including the decision not to seek images which might have assisted in the assessment of damage resulting from the foam strike on ascent.

A member of the Columbia Accident Investigation Board said today, for the first time, that a foam strike during the shuttle's launching is the "most probable cause" of the disaster. He also said analysis of recovered debris indicates a large portion of the ship's left wing broke off in the shuttle's final seconds at the point where the catastrophic breach occurred.

"This is probably the first time you've ever heard me say it's highly probable that the foam is the cause of the accident," said Roger Tetrault. "It's probably the first time you've heard members of the board say it with that kind of strength. We think, when you look at the analysis of all the things that are pointing to the same area in terms of the hole versus where the foam hit, that that's a fairly compelling story."

Columbia's left wing leading edge was struck by a suitcase-size chunk of foam insulation that broke off the shuttle's external fuel tank 81 seconds after liftoff Jan. 16. The foam hit the underside of the leading edge at a velocity of 500 mph or so. Investigators have long believed the foam strike played a role in the disaster, but Tetrault's comments today were the first by a board member to elevate the impact to the level of "most probable cause."

In other developments today, NASA released nearly 10 hours of videotape and still photography shot by Columbia's crew that was recovered in the ship's wreckage over the past several weeks and months. The photography provides no fresh insights into the cause of the disaster, but it no doubt provides sad comfort to family members, giving them one more glimpse of their loved ones as they cheerfully worked through their final days in orbit.

If nothing else, the video put a fresh human face on the disaster and the high stakes involved in the CAIB's efforts to make sure its final report properly addresses the "root cause" of the mishap as well as contributing factors. CAIB chairman Harold Gehman provided an impromptu preview of what that final report will include and said none of the recommendations would, by themselves, prevent NASA from resuming shuttle flights within nine months.

"I don't speculate on the date of return to flight," he told reporters at a news conference. "I would say that having read every word of the draft report and having gone over what might be possible recommendations, I don't see any recommendations which are so difficult to accomplish that they shouldn't be able to return to flight in six to nine months. Other than that, I wouldn't put any numbers on it."

Many NASA insiders believe launch likely will be delayed well into next year, but senior agency officials continue to hold out hope for a flight by the end of the year. One major wild card in all such speculation is what actions Congress might take when it begins considering the CAIB report later this fall.

In any case, Gehman said a "goodly portion of the report, perhaps half, is going to deal with the issue of management and management techniques at NASA."

"We will not tell NASA how to organize, we will not draw a wiring diagram for them," he said. "But we will tell them what we believe are the characteristics of what we believe to be essentially a flight development program that would help ensure safe operations. We won't tell them how to do it, but we will tell them what needs to be done."

By including the phrase "flight development program," Gehman was serving notice that the board views shuttle operations as more of a series of on-going test flights than as any sort of routine, operational program. He said the CAIB report will force NASA to address the issue of foam shedding, debris impacts and on-orbit inspection and repair of possible post-launch damage.

"I believe the report is going to suggest that you have to take action in each of four areas," he said. "First, you have to take action to either minimize or prevent as best you can foam loss and certainly you have to prevent the egregious foam loss, the big pieces.

"But we're also going to suggest you have to toughen the orbiter's ability to take debris hits because the orbiter is going to continue to take debris hits. It was designed not to, but that's now proven to be not the case. So you have to increase the orbiter's ability to take hits.

"You also - number 3 - you also have to improve your ability to recover from a hit," Gehman said. "That means you have to be able to inspect the orbiter after it's launched and if you find something wrong, you have to be able to make emergency, temporary, one-mission repairs in case the first two steps don't accomplish it."

The fourth item on his list was crew escape. While the board will not make any specific recommendations in that area, Gehman said "we're going to comment on how we got to the present status. But whether or not improvements need to be made, we're leaving that to NASA."

An interim recommendation that will require NASA to develop an in-flight ability to repair damage to heat shield tiles and reinforced carbon carbon leading edge panels is nearing completion. Its release has been held up while the board struggles to fine-tune the wording. "We're trying to state what we want to happen, not how to do it," Gehman said.

A detailed overview of NASA's efforts to develop just such a tile repair capability is available in the June 20 CBS News status report posted below.

Tetrault provided a fresh look at Columbia's final moments today, outlining how the shuttle's left wing broke apart in the ship's final seconds. He reviewed earlier evidence pointing toward a breach at or near reinforced carbon carbon panel No. 8, the largest of 22 such panels that make up the left wing's leading edge. The panel is located at the point where the wing's sweep angle changes and as such features a complex, curved shape.

Tetrault briefly reviewed recorded sensor data and the timing of sensor failures as a plume of super-heated air burned its way through wire bundles inside the left wing, both of which indicate a breach at or near RCC 8.

He reminded reporters that very little debris has been recovered from the area of RCC panels 8 through 10. No attachment fittings, known as spanner beams and spar fittings, have been found. No portions of the lower halves of the RCC panels themselves have been recovered. So-called knife-edge erosion, indicative of extreme heating, is present in the few fragments of RCC 8 and 9 that have been found, suggesting the breach occurred at or near the lower half of panel 8.

"The fact that there's such a significant amount of missing material from this particular area is very telling and it certainly in my mind points to a problem between panels 8 to 10," Tetrault said. "And it also points to the fact that we are likely to have burned up much of this material, particularly in the spanner beams and spar fittings from these areas."

He showed a map pinpointing where every piece of recovered wing debris had been found. Interestingly, the tiles found farthest to the west, indicating they fell away early in the shuttle's breakup, were located directly behind RCC panels 8 and 9.

"What that indicates is there was probably a breach somewhere in the 8 to 9 area, the hot gas flowed into that breach, it heated up the inside of that wing, the RTV (adhesive) which holds the tiles to the outside skin of the wing heated up and basically lost its adhesion capability at approximately 400 degrees Fahrenheit and fell off to the west," Tetrault said.

"One of the other important parts are in this area, we have a number of tiles which have a light brown deposit on them. And we've taken some preliminary chemical analysis of that light brown deposit. And what we find out from that preliminary analysis is that deposit is high in iron and it's also high in nickel.

"You may recall the spanner beams which hold the RCC, which appear to be missing, are, in fact, high in nickel," he said. "And the spar fittings, which hold the panels to the spar itself, are stainless steel, so they would be high in iron. What you can surmise from that, in fact, is the hole was somewhere in the 8 and 9 area and as the airflow was flowing in, some of this molten material from the spar fittings and from the spanner beams was in fact being deposited on the lower side of the wing. And that's what we're seeing when we do the chemical analysis."

He reminded reporters that so-called "knife-edge" erosion patterns were found on what few pieces of RCC 8 and 9 material that were recovered, indicating the flow of extreme heat from 8 toward 9. He said unusual slag deposits found on the interior surface of fragments from the upper half of RCC 8 showed high concentrations of nickel, "again indicating one of the first things to melt inside the wing leading edge after the breach occurred were the spanner beams."

The spherical slag deposits indicate molten material was splattered back on the inner surface of the panel from a breach on the lower side of RCC 8.

Showing a plot of recovered wing debris, Tetrault said debris from RCC panels 8 through 22 were found farther west than any other fragments from the left wing leading edge. Next came fragments of RCC 1 through 7, then debris from the shuttle's vertical stabilizer and finally, wreckage from the right wing.

"What this suggests is that at breakup, what we first saw was the left wing or a portion of the left wing left the aircraft, fell to the ground, followed by the tail, followed by the right wing," Tetrault said. "What's really important in all of this, when you look at the left wing it's a very long (debris) stream.

"What we believe happened is somewhere in this area a portion of the left wing came off," he said. "A portion of the left wing continued to ride with the aircraft downstream and that would have contained panels 1 through 7. And at some point later on, panels 1 through 7 began to come off the aircraft, we believe it probably ablated (melted) as much as fell off, that the pieces were just open to the airstream.

Interestingly, fragments of panel 8 were found in widely separated areas.

"That begins to indicate to us that, in fact, the breach, not only the breach but also the wing, broke apart at panel number 8 region," Tetrault said. "Otherwise, you wouldn't have those pieces strewn over that lengthy piece of territory. So those are the indicators that we have from the debris.

"I think when you look at it you could probably conclude from the debris alone that the most likely breach that we had in the wing occurred at panel No. 8 or in the vicinity of panel number 8. ... I would also include the T-seals on either side of it. So we feel fairly certain on where the breach was."

As for exactly how the left wing came apart, Tetrault said investigators don't yet known whether "half the wing that came off at area 8 or just the leading edge of half the wing."

"I think the prevailing theory right now is it was more than likely the leading edge of wing (that came off) and heavy spars held for some period later. But if you lost the leading edge, you would lose the RCC panels from 8 through 22."

Looking at all the data and how they fit together, Tetrault said, "they certainly are pointing us to the area of RCC panel 8 as being an indicator of where the breach occurred in the wing. Not only that, but as you well know we have the photographic analysis and evidence that indicates the foam struck on panels 6 through 9. And when you put all of those pieces of Swiss cheese together, it's a pretty compelling story that, in fact, the foam is the most probable cause of the shuttle accident."

Gehman said the full board has yet to decide on what terminology will be used in the panel's final report. But a final round of tests at the Southwest Research Institute in San Antonio, Texas, could go a long way toward determining how strongly the board links the foam strike to Columbia's destruction.

Using a powerful nitrogen gas cannon, researchers have been firing foam debris at a wing leading edge mockup to determine whether a strike like the one observed during Columbia's launching could actually break one of the carbon composite panels or an associated T-seal. A test shot at RCC panel No. 6, taken from the shuttle Discovery, resulted in multiple cracks and showed the impact forces were transmitted to adjacent panels and T-seals. Just as important as showing cracks were possible, the impacts showed the leading edge components responded to the impact as an integrated system.

But panel 6 is smaller than 8 and does not have the same complex curvature. As a result, CAIB member Scott Hubbard has decided to shoot at RCC panel 8 from the shuttle Atlantis. Adjacent panels and mounting hardware also will be flight articles.

"The thing that I'm trying to do with these tests, and I think the board is looking at this information as a piece of that most probable cause, is to connect that dot, from foam to breach," Hubbard said today. "So that's where I stand. I think the panel 6 tests that we did showed that we've got a plausible failure scenario, we created a substantial crack, five inches long, but we haven't created yet a breach that is like what has been described by the debris.

"Maybe I'm one step behind Roger in coming to a conclusion, but as Admiral Gehman said, that's part of our discussion here."

Gehman said the board will have to decide "what words we want to use when we describe the degree of certainty we use to say the foam caused damage to the leading edge of the left wing. Do we want to say we 'think' it did, we're 'sure' it did, it 'might have,' we think 'most likely' it did, the board is 'confident that?' I have 13 different opinions on that and at some time I'm going to have to lock everybody in a room and come out with one set of words."

Shuttle engineers believe the tools and techniques needed for spacewalking repair crews to access and patch areas of potentially catastrophic damage to an orbiter's heat-shield tiles will be in place by the end of the year.

Major challenges include development of reliable techniques for inspecting a shuttle for damage, gaining access to all possible damage sites and perfecting the tools and materials needed to actually patch over cracked, eroded or missing tiles. But so far, engineers have not identified any show-stoppers, sources say, at least for shuttle missions bound for the international space station where access is less of an issue.

But techniques for repairing damage to a shuttle's wing leading edge panels pose a much more difficult challenge and likely will take longer to develop. A breach in the leading edge of the shuttle Columbia's left wing led to the ship's destruction during re-entry Feb. 1, allowing a plume of super-heated air to burn its way into the wing's interior.

NASA has studied in-flight tile repair options in the past and is drawing on that background now to develop a workable repair technique for future flights. But no previous efforts were undertaken for the shuttle's carbon composite nose cap and wing leading edge panels, which are made of different material, feature complex curved surfaces and experience the most extreme temperatures during re-entry.

The panels play a critical role in the creation of a so-called boundary layer as the shuttle plows through the region of maximum heating. The boundary layer provides a natural insulating effect, limiting entry temperatures to "just" 3,000 degrees or so. Any repair option would have to not just plug a breach but also ensure the smooth airflow needed to set up an insulating boundary layer.

Analysis of a dozen or so possible RCC repair options and materials is underway, sources say, but testing is in its early stages and a final solution is far from clear.

Even in the case of tile repair options, engineers have not yet settled on what sort of caulk-like patch material is best suited for repairing broad areas of tile damage. Issues include the viscosity of the material, which astronauts must be able to apply and then spread or mold to some degree, and the time needed for any such material to cure, or "set up." Engineers currently are testing a silicon-based compound similar to one developed in the late 1970s as part of a tile repair technique that was never implemented.

Tests also will be required to ensure any such material can stand-up to worst-case re-entry temperatures and conditions.

The Columbia Accident Investigation Board is expected to recommend that NASA develop capabilities for on-orbit repair of tile and reinforced carbon carbon (RCC) leading edge panels. The board's final report is expected around the end of July. But NASA is not waiting for the final report or even any interim recommendations to begin developing a repair capability. A "tiger team" under the leadership of space station flight director Paul Hill at the Johnson Space Center in Houston has been in place for months.

A request for an interview with Hill was turned down by Michael Kostelnik, deputy associate administrator for the shuttle and space station programs at NASA headquarters, on the grounds that any such discussion is "pre-decisional" and that no final decisions have been made. The real issue, however, appears to be a general reluctance on NASA's part to publicly address any topic the CAIB might discuss in its final report or any interim recommendations that might be released between now and then.

Even so, a broad outline of NASA's on-orbit repair strategy has emerged in recent weeks that focuses on four general areas:

• Defining the critical damage size, i.e., the damage threshold that would trigger some sort of spacewalk inspection and/or repair attempt
  
• Techniques for inspecting a shuttle for damage
  
• The materials and tools needed to repair damage
  
• The spacewalk access required to implement any such repairs
  

For the purposes of this discussion, it is assumed any inspections and repairs would be staged at the international space station. Only one non-station flight is currently on the books - a mission to service the Hubble Space Telescope - and it's not yet clear how inspections or repairs could be carried out in the absence of the space station's robot arm, multiple EVA anchor points and numerous external cameras. The Hubble flight, however, is several launchings down the road and engineers will have more time to develop viable "stand alone" repair techniques.

In the near term, shuttle missions to the space station will be launched in daylight to give engineers a better chance of spotting debris impacts that might damage an orbiter's thermal protection system (TPS). In addition, mission managers likely will require external fuel tank separation in daylight as well, to improve the odds of spotting any areas of foam shedding in orbit. Given those two requirements alone, and the orbital mechanics required to rendezvous with the space station, the number of possible launch days in a given month will be sharply reduced.

In any case, the TPS damage threshold is believed to be roughly a quarter of an inch for an RCC wing leading edge panel, a half-inch or so for the RCC nose cap and 1 inch around critical seals in the thermal protection system. It's not known what powerful spy satellites might be able to detect, but approaching shuttles will perform a pirouette 400 to 600 feet below the station to give lab crews a chance to photograph the orbiter's underside.

Tests indicate pre- and post-docking photography, by the crew and by cameras on the shuttle's robot arm and the mobile Canadarm2 spacecrane attached to the space station, should provide the coverage needed to spot any significant damage. But determining the depth of any tile damage - a critical factor - might not be possible without a spacewalk inspection or the development of some sort of laser scanner.

The materials and tools need to carry out a TPS repair in orbit are based on an existing "cure-in-place" ablator compound that would be applied by a spacewalking astronaut using a sort of high-tech caulk gun. Tests are planned later this summer during flights aboard a NASA aircraft that provides brief periods of weightlessness. Sources say other tests are planned to determine vacuum cure times and temperature limits.

Different materials and application techniques are being developed for RCC damage but details are not yet available.

The most significant challenge, perhaps, is figuring out how to anchor a spacewalker in the weightlessness of orbit to apply the patch material and, depending on the situation, smooth it out or shape it.

One possibility under consideration is using the shuttle's robot arm to lock onto a grapple fixture on the space station and then, after docking latches are released, to properly position the orbiter. Spacewalkers then would ride the station's robot arm to the actual repair site.

An engineering analysis indicates the shuttle's robot arm is strong enough to move the 120-ton space shuttle, but a telescoping boom of some sort may be needed to extend the reach of the Canadarm2 to all possible damage sites. A similar boom is being considered for use by the shuttle arm during non-station missions.

Engineers initially considered the possibility of astronauts using small jetpacks, known as SAFERs, to reach possible damage sites for repair work, but that no longer appears feasible. The backpacks could, however, be used under certain conditions for initial inspections to determine the severity of any damage.

NASA is considering five options for redesigning the so-called "bi-pod" ramp on the shuttle's external fuel tank, the area where a chunk of foam insulation broke away during Columbia's launch, hit the left wing and possibly caused a catastrophic breach. The currently favored option calls for eliminating the use of foam in the area in favor of an exposed fitting equipped with heaters to prevent pre-launch ice buildups.

Senior NASA and contractor managers and engineers met Tuesday and today in Michoud, La., where Lockheed Martin Space Systems Co. builds the external tanks, to review the bi-pod redesign options in preparation for making a final selection in the next few weeks. While most observers believe NASA will not be able to resume shuttle flights until well into 2004 at the earliest, senior agency managers say they believe launchings could resume as early as mid-to-late December. In any case, engineers plan to have the bi-pod fix in place as soon as possible, eliminating what many believe was the initiating event in the Columbia disaster.

"Clearly, there's been a lot of focus on the foam, the bi-pod foam in particular, and our redesign efforts have been ongoing in that particular activity for a couple of months already," Michael Kostelnik, NASA's deputy associate administrator for shuttle and space station, told reporters today. "We will solve the shedding problem of foam in that particular area and our technical plan for that allows us a return to flight window in December."

The external fuel tank forms the structural backbone of the shuttle "stack" for the climb to space. Solid-fuel boosters are attached on each side with massive explosive bolts while the shuttle is attached by fittings under its nose and engine compartment. The aft end of the shuttle is attached with massive fittings where 17-inch propellant lines from the external tank feed into the ship's aft engine compartment. The nose is attached by a so-called bi-pod, two cylindrical struts that meet at a single attachment plate just behind the nose landing gear doors. The struts attach to a pair of fittings on the external tank, forming a triangular bi-pod assembly.

At launch, the tank is loaded with a half-million gallons of supercold liquid oxygen and liquid hydrogen rocket fuel. From the beginning, the bi-pod strut attachment fittings have been buried in hand-sprayed foam insulation to prevent ice from forming around the aluminum fittings. Any such ice likely would break away when subjected to the vibration of launch, posing an impact hazard to the underside of the shuttle. The foam covering the bi-pod fittings is hand carved to form an aerodynamically benign ramp allowing the smooth flow of air over the protrusions.

As it turns out, the bi-pod ramp prevented ice buildups but created another impact hazard: The foam itself.

A suitcase-size chunk of foam from Columbia's left bi-pod ramp area pulled free during launch Jan. 16 and struck the left wing's leading edge at some 500 mph. The foam strike presumably caused the breach that led to the ship's destruction during re-entry Feb. 1. Another large piece of foam broke away from the same area during an October shuttle flight and hit a booster. All told, investigators have identified at least six missions, and possibly seven, in which large pieces of foam debris fell off the bi-pod ramps of the external tanks.

It is not yet clear what causes the foam to break away. Many engineers believe some form of "cryopumping" may be involved, in which trapped air in the foam liquifies after the tank is chilled during fueling. In this scenario, heating during ascent causes the trapped liquid to warm and expand, weakening the foam in that area. But recent tests by the Columbia Accident Investigation Board indicate cryopumping alone is not the answer and that some combination of factors may be responsible.

In any case, there is little doubt the CAIB's final report, expected in late July, will include a recommendation to redesign the bi-pod attachment system to preclude foam shedding in the future. In the meantime, NASA is pressing ahead with work to do just that.

Of the five options currently on the table, the favored solution, known as option 2a, is one in which the aerodynamically shaped foam ramp is eliminated entirely in favor of an exposed fitting equipped with one or more heaters to eliminate the possibility of pre-launch ice buildups. Aluminum end covers and caps would be replaced with tougher Inconel covers. Other changes include the addition of wiring for the heaters and additional electrical power from ground-support equipment prior to liftoff.

Other options include:

• Option 1: Reduced volume ramp with a minimum 50 percent reduction in the amount of foam required; aluminum end covers replaced by super lightweight ablator material; new heater elements and wiring.

• Option 2: Partially exposed fitting with an 80 percent reduction in foam ramp volume; Inconel end covers and caps; new heater and wiring.

• Option 3: Inconel fairing over the entire bi-pod fitting, eliminating need for a foam ramp. Strip heaters would be attached to the interior of the welded fairing. This option was an early favorite.

• Option 3A: Small Inconel fairing, equipped with strip heaters, that covers the central shaft of the bi-pod fitting. No ramp foam is required.

Agency managers, with input from the Columbia Accident Investigation Board, hope to settle on a redesign option in the next few weeks.

Accident investigators have stumbled on a potentially catastrophic shortcoming in the explosive bolt attachment system used to latch a space shuttle's boosters to its external fuel tank. While there is no evidence Columbia was struck by falling debris from a faulty "bolt catcher" during its launching Jan. 16, corrective actions almost certainly will be required before shuttle flights resume.

Members of the Columbia Accident Investigation Board said today a foam strike during launch remains the most plausible explanation for the breach in the shuttle's left wing leading edge that ultimately doomed the orbiter and its crew during re-entry Feb. 1. One of the more intriguing aspects of the failure scenario is the rapidity with which a plume of super-heated air managed to eat its way inside during the first moments of Columbia's descent into the discernible atmosphere.

The accident board today released dramatic video of a test using an 8,000-degree arc jet that vividly illustrates just how fast a small breach can deteriorate into a gaping hole. Engineers fired the jet of super-heated air at a circular one-inch-wide hole in a strip of aluminum representing a wing spar, the metal structure directly behind the carbon composite panels making up the leading edge. Like a match flame burning through tissue paper from below, a one-inch hole in the plate grew to six inches across in just 20 seconds. The plume also burned through a thick wire bundle in less than one minute, in generally good agreement with the way the plume that burned into Columbia's wing quickly ate through sensor wiring once inside.

"It's really very impressive. You cannot imagine the destructive power of the gases that would flow in through that hole," said Douglas Osheroff, a Nobel laureate in low-temperature physics and a member of the accident board. "It's really pretty scary to see."

During a normal shuttle entry, the maximum temperatures experienced by the wing leading edges and the ship's carbon composite nose cap is 3,000 degrees. The temperature is moderated by the way air smoothly flows across the skin of the shuttle, setting up what is known as a boundary layer that acts as an insulator of sorts. But in a breach, no such protection exists and temperatures can soar much higher, "so hot that in fact the oxygen molecules are split into individual atoms," Osheroff said. "That makes them much more highly reactive."

"It was just very impressive to see how quickly that kind of an atmosphere, simulating as best they could the conditions on re-entry, would slice through aluminum in particular," he said. "It was just absolutely amazing."

Osheroff is the second Nobel prize winner to sit on a shuttle accident board. Richard Feynman served in that capacity for the 1986 Challenger disaster, performing a memorably simple experiment during an early hearing that showed how booster O-ring seals are affected by cold weather. He dipped a small O-ring into a glass of ice water, held it up and showed how it had stiffened, a characteristic that would have reduced a real O-ring's ability to work properly during cold weather. Challenger, of course, was destroyed by an O-ring seal failure during launch in cold weather.

Today, Osheroff discussed a modest experiment of his own, carried out in his kitchen with about $100 in equipment, that suggests NASA has never understood the mechanism responsible for external tank foam shedding. It also suggests, to borrow a phrase from Apple Computer, that Nobel prize winners "think different."

"I became rather rapidly interested in the properties of this foam," said Osheroff, a Mac user. "It's really fascinating stuff. It's highly anisotropic, that is to say it's mechanical properties depend upon which direction you squeeze it, for instance. So I decided to do some experiments on the foam."

Osheroff, with the help of a graduate student, had a metal plate machined to serve as a stand-in for the skin of the external tank. He then glued a cube of BX-250 to the plate, a sample of the same type of foam that came off Columbia's tank. A small hole in the plate allowed him to apply pressure at the interface between the foam and the metal.

"The idea was to try to understand, as I increased the pressure, how ultimately this resulted in some sort of a fault that propagated through to the surface," Osheroff said. "This is important because for many years, people at NASA assumed, in fact, that one of the main mechanisms for foam shedding from the external tank was that liquid nitrogen (from trapped air) would somehow condense in a void or something inside the foam near the metal surface. And as you started getting aero heating (during launch), this liquid nitrogen would warm up, pressure would build up and it would throw foam off of the external tank.

"What I found was that, in fact, the mechanism by which the liquid expands is not consistent in any way with ejection of foam from the surface. What it does, it tends to make a two dimensional, rather flat crack or fault, which propagates up to the surface and it meets the surface normal to the surface in almost every case. This has to do with anisotropic properties of the foam."

Translation: Expanding gas in a pocket, or void, near the ultra-cold skin of an external tank produces linear surface cracks in the foam, it doesn't blow out the overlying material. In addition, calculations show heating due to atmospheric friction would not have had time to turn any pockets of liquified air into a gas by 81 seconds into flight.P> "That's less than 30 seconds into aero heating," Osheroff said. "Is it possible for the heat to propagate through the foam and actually boil off the liquid nitrogen that might have condensed in that brief period of time? ... The thermal relaxation times are much too long for that."

"So the conclusion I have reached, and that independently the people at Marshall Space Flight Center have reached, is that the process by which foam is ejected is undoubtedly a very complex one involving more than just cryo condensation and ejection.

"I dare say, in fact, that these sorts of experiments which I have done, which were actually done in my kitchen at home for about a hundred dollars, are the sorts of things I think we need to see more of done. Specifically, experiments to try to understand the physical mechanisms (behind) why the foam behaves the way it does."

In a revelation that generated quite a bit of media interest, board member John Barry revealed investigators are looking into apparent problems with the system used to capture and restrain pieces of the exploding bolts used to hold a shuttle's boosters to its external tank during launch.

The boosters separate two minutes and five seconds or so into flight when explosive charges cut the massive 80-pound bolts in half. The upper half of a bolt is blown upward and captured in the dome of a fully enclosed "bolt catcher" assembly on the tank. The bottom half is captured by a bolt catcher on the booster.

The bolt catchers are designed to prevent any debris from a blown bolt from getting into the airstream and possibly impacting the shuttle.

"The problem we found was the original certification was done without the real flight hardware in 1979," Barry said. "The other thing we found out, this bolt that was used in STS-107 (Columbia) was done with a new vendor and the NDE, the non-destructive evaluation, wasn't done as well as it should have been.

"They did some bolt static tests that resulted in this dome fracturing at a lower pressure than was anticipated," he said. "In fact, it was below a 1.4 safety margin. So this dome is made of aluminum and covered with ablative. If that comes loose, with or without that half of the bolt in it, it still can cause some serious risk to the orbiter. So this is a possible return to flight issue that we're examining."

Complicating the picture, radar data from Columbia's launching shows unidentified debris separating from the shuttle 126 seconds into flight, right about the time of booster separation. Debris has been seen on radar during past missions, presumed chunks of ice, for example, and there is no evidence the debris seen during Columbia's flight involved the bolt catcher. Certainly there's no recorded data or telemetry from Columbia suggesting any kind of an impact 126 seconds into flight.

But engineers cannot rule out the possibility debris may have been released into the airstream.

"What we have here is a possibility that we have found another source of debris," said CAIB chairman Harold Gehman. "We don't have any evidence that it was a source of debris except the radar tracking of the Columbia indicated that at the time of SRB separation, 126 seconds, at a time when there's not supposed to be any debris, it noticed a piece of debris. We don't know what that was."

He said engineers are trying to determine if a bolt catcher failure could "create any debris which might fall back on the wing?"

"We're just at the front end of this and we're not ready to make any statements about how this affects the process. The question, then, is we have a potential piece of debris here now. Or in a future flight. But in this particular case, STS-107, it's a potential that we've got a piece of debris.

"Then we go back to the radar of the launch. ... And lo and behold, at 126 seconds after launch, at the time of SRB separation, something is seen on the radar which indicates that there's a piece of debris ejected from the separation. It could be the bolt catcher. We can't prove that. But in an effort to positively close out the fault tree - and you multiply this times a thousand - you can see why this investigation has taken five months. So here's one we can't close out."

But he and other board members downplayed the possibility that a 40-pound bolt fragment could have hit Columbia without being detected by the shuttle's myriad sensors. The real issue is fixing the problem before flights resume.

"There's no indication, in either the (recorded) OEX data that we know about or any of the telemetry, that something hit the wing past 120 seconds," Barry said.

"What we're trying to couch here is it's very important that we understand all potential debris. We're not changing our working scenario, it's still pretty evident foam came off and hit the wing. But we also have to take into consideration any other future debris elements that could be potentially catastrophic to the orbiter."

Engineers studying the effects of a foam impact test today that cracked a shuttle wing leading edge panel found a second crack late this afternoon. The initially observed crack, in reinforced carbon carbon panel No. 6, measured about three inches long. The second crack was found in a so-called T-seal between RCC panels 6 and 7. The dimensions of the second crack were not immediately available.

The 6:45 p.m. status report below has been updated to reflect the presence of the second crack.

The final report of the Columbia Accident Investigation Board will go far beyond identifying the most probable cause of the Feb. 1 shuttle disaster. According to a draft outline of the 10-chapter report, the board will provide a contextual history of the shuttle program, a review of the engineering tradeoffs and budget issues that resulted in the shuttle's current design and operation as well as a critical evaluation of the NASA management practices.

A source close to the investigation said today the draft outline, currently in revision 6, is a "work in progress" and that additional revisions are expected. But in its current form, the outline provides the following breakdown:

• Chapter 1: Evolution of the Space Shuttle Program. A comprehensive overview of the early history of the shuttle, design tradeoffs, the Challenger disaster and how NASA operated the shuttle system in the post-Challenger environment.
  

• Chapter 2: Columbia's Final Flight. An overview of pre-launch and launch preparations and events, a discussion of the mission objectives and a review of "notable pre-launch conditions" such as the causes of launch delays, the amount of time Columbia spent on the launch pad and security issues related to the presence of Israeli crew member Ilan Ramon. Chapter 2 also will discuss on-orbit events such as the separation of a mystery object on flight day 2, re-entry events including the shuttle's destruction, NASA's response to the crises, the establishment of the CAIB and debris recovery.
  

• Chapter 3: The Proximate Causes of the Accident Sequence. Beginning with a review of the proximate cause of the disaster - presumably a foam strike on the left wing's leading edge - Chapter 3 will review the CAIB's impact analysis, issues involving external tank foam application and in-flight shedding as well as a discussion of the performance of the shuttle's leading edge systems. The chapter also will deal with the re-entry sequence, walking through a detailed timeline based on telemetry, recorded data and debris analysis that leads to a most probable failure scenario.
  

• Chapter 4: Beyond the Proximate Cause. As board chairman Harold Gehman has repeatedly promised, the final report will go far beyond identifying the most probable cause of the accident. In Chapter 4, the board will lay out NASA's organization policy and budget factors, including the influence of Congress, the White House and past NASA administrators "on the ability of the space shuttle team to manage the shuttle program," the source said. The analysis will include a review of the Challenger disaster and policy changes in the aftermath, an overview of NASA's efforts over the years to privatize the program or at least turn over segments of it to private industry and an evaluation of NASA's safety and mission assurance program. Other issues include the effects of moving shuttle program management from the Johnson Space Center back to NASA headquarters in Washington.
  

• Chapter 5: Factors that Contributed to the Loss. This chapter focuses on a discussion of contributing factors, everything from vulnerability in the original shuttle design to eroding safety margins and what sociologist Diane Vaughan calls the "normalization of deviance," the slow acceptance of problems, like foam shedding, as normal events after repeated flights with no major difficulties. The chapter will deal with the "signals that were coming from the orbiter and what actions NASA took to detect those signals," the source said. This chapter also will focus on the performance of NASA's mission management team and will outline the results of a study on whether the wing damage could have been repaired in orbit or whether NASA could have mounted a rescue mission of some sort.
  

• Chapter 6: The Accident's Underlying Causes. An evaluation of NASA's organizational culture and performance. This chapter will review literature outlining how other high reliability organizations - like off-shore oil rigs, aircraft carrier flight decks, nuclear submarines and reactors - deal with safety and look at how NASA's safety organization works.
  

• Chapter 7: A Look Ahead. The implications of the accident on the future of the shuttle program and U.S. space policy in general. The chapter includes sections on the conditions necessary for a return to flight. The board won't designate "what kind of bolt needs to be used or that sort of thing," the source said, rather it will focus on goals and safety issues in general. The source said it will identify issues that need to be resolved, like the effects of shuttle aging, operational costs and long-term upgrades or modifications that might be required.
  

• Chapter 8: Other Significant Observations. Issues not directly related to the accident, but potential problems that need to be addressed. Lapses in flight controller certification, for example, fall into this category.
  

• Chapter 9: Findings and Recommendations. The draft outline does not yet include any actual recommendations beyond those already announced by the CAIB. But the final report will include a requirement for a detailed follow up to make sure the recommendations are implemented. NASA has already set up an independent panel under former astronaut Thomas Stafford to do just that.
  

• Chapter 10: The CAIB Investigation. The final chapter will provide documentation on how the board was established, expanded and operated.

"The board is looking at this as a pretty thorough look at what happened, and not just the immediate technical issues," the source said. "Nothing in the report is secret. (The outline) is a pre-decisional document and it's not the final version. (But) I think the report is consistent with the admiral's public statements."

The report will be released in late July in Washington, in book form and on CD-ROM. The CD will include a variety of graphic presentations and video clips to support the board's conclusions.

In a potentially significant breakthrough, engineers fired a 1.7-pound chunk of foam insulation at shuttle wing mockup today, visibly cracking a leading edge panel in a test that strongly supports the widely held hypothesis that a foam strike during Columbia's launch doomed the orbiter and its crew.

With a throng of reporters, engineers and a member of the Columbia Accident Investigation Board looking on, a powerful nitrogen gas cannon at the Southwest Research Institute in San Antonio, Texas, fired the box-shaped foam "bullet" at a mockup of a shuttle wing leading edge at a blistering 523.7 mph (768 feet per second). The foam hit a reinforced carbon carbon - RCC - panel taken from the shuttle Discovery. The foam instantly disintegrated in a shower of debris reminiscent of the powdery debris that fell away from Columbia.

From a viewing site 50 yards away, no cracks or other obvious signs of damage were evident. But a close-up inspection revealed a three-inch long crack in the panel through an interior rib. The crack penetrated the panel and high-speed cameras mounted inside the leading edge cavity showed foam fragments blasting into the interior. The force of the impact jammed the inboard side of the panel up against a T-seal between RCC panel 6 and a Fiberglass panel in the inboard No. 5 position and widened the gap between the outboard side of RCC 6 and the T-seal between panel 6 and 7.

Late this afternoon, engineers discovered a second crack in the T-seal itself, near the location of the RCC crack. no dimensions were immediately available.

While today's test doesn't prove the foam lost during Columbia's launch was the initiating event of the disaster, it's the best evidence yet a foam strike could have been, in fact, the root cause.

"This is the first evidence that we've had that a piece of foam that approximates what was observed in the accident can, in fact, crack and damage a piece of flight reinforced carbon panel," said CAIB member Scott Hubbard.

But Hubbard would not speculate on whether damage similar to what was seen today could have led to Columbia's destruction.

"The obvious question one asks is what does this mean in terms of the thermal and structural characteristics and at this point, it's simply too early to draw a conclusion," he said. We've got a couple of the world's experts in RCC and structures over here and they're scratching their heads and trying to figure out what this might mean. As you saw, the response of this is quite different than the response of the Fiberglass."

He was referring to a test last week in which foam was fired at a Fiberglass leading edge panel taken from the prototype shuttle Enterprise. In that test, the impact caused visible shock waves to ripple across the structure, pushing the outboard T-seal out of place and leaving a large gap between the seal and the edge of the target panel.

"Given that the response of the Fiberglass was so dramatic, I think many of us felt there was going to be something perhaps equally dramatic (today)," Hubbard said. "But as I've said, this is why you do the experiment. Drama, of course, wasn't the point of the test, although reporters made friendly wagers on its outcome. As Hubbard pointed out later, the Fiberglass shot, while dramatic, did not cause any cracks or other major damage.

"We didn't show any damage at all on the Fiberglass," Hubbard said. "We had a lot of movement and a lot of high stresses, but here we demonstrated for the first time that foam at the speed of the accident can actually break RCC.

"To me, that's a step forward, maybe a significant step forward in our knowledge."

Eighty one point seven seconds after the shuttle Columbia's liftoff Jan. 16, a suitcase-size piece of foam insulation broke away from the ship's external tank. Columbia was traveling at better than twice the speed of sound at the time - 1,568 mph - and the foam underwent a sharp deceleration when it fell into the airstream. Even so, engineers believe it slammed into the lower side of the left wing's leading edge at some 775 feet per second, or 528 mph while tumbling at 18 revolutions per second.

Columbia was destroyed during re-entry by a breach in the lead edge of its left wing. Analysis of sensor data and evaluation of recovered debris indicates the breach occurred on the lower side of reinforced carbon carbon panel No. 8, one of 22 U-shaped heat-resistant panels making up the leading edge of the wing.

Detailed analysis of launch day footage indicates the external tank foam hit at or very near RCC panel 8. But in the absence of any hard data, investigators have been unable to make a direct connection between the foam strike and the failure.

To find out if foam is at least capable of causing enough leading edge damage to result in a catastrophic breach, the Columbia Accident Investigation Board and NASA, working with the Southwest Research Institute, decided to fire foam bullets at a leading edge mockup in an attempt to duplicate the failure mode. While such tests cannot prove the hypothesis, they can at least show whether it is possible and thus help confirm or rule out various scenarios.

The nitrogen cannon normally is used to fire gel-filled "chicken simulators" at aircraft components to study the effects of bird strikes. For the shuttle tests, a heavily instrumented leading edge mockup was built at the Johnson Space Center and shipped to San Antonio. The mockup includes RCC panels 5 through 10 as well as the T-seals between each panel that effectively lock them in place.

The tests were designed before engineers pinpointed the general location of the breach. As a result, RCC panels 6 and 9 were taken from Enterprise to "bracket" all possible breach locations. For today's test, the foam was fired at RCC panel 6. Upcoming tests will aim at panel 9, both a Fiberglass stand in and the real thing.

For today's experiment, all of the leading edge panels but one - RCC-6 - and all of the T-seals except the one between panels 6 and 7 were made of Fiberglass. Real T-seals and RCC panels, valued at some $800,000 each, are considered too valuable to be risked in any but the most significant of tests. Only one complete "ship set" of spare RCC panels is available, along with the panels already in use by the shuttle's Discovery, Atlantis and Endeavour.

As a result, the first test last week involved firing foam at a Fiberglass panel in the No. 6 position. At least four such firings were planned, but the first test provided dramatic results: The foam lifted and permanently deformed the T-seal between panels 6 and 7, leaving a visible quarter inch gap in the leading edge. Stain gauges measured impact forces up to seven times higher than predicted by computer analysis.

"What we saw was a system response," Hubbard said in a teleconference Wednesday. "We expected to observe an impact and measure that on panel 6, of course. What we found was that we had ... created a response that involved at least three of the panels, maybe more. It was clear the force went from panel 6 to the T-seal to panel 7 and even some measurements in panel 8. So in the accident, then, we have to think of not just the impact point but also the response of the entire wing leading edge."

Worried additional test firings could damage RCC support hardware and make it more difficult to ensure accurate results, Hubbard decided to forego any additional Fiberglass firings and to press ahead with the real RCC panel. To make the test as accurate as possible, a panel was taken from Discovery that has flown in space 30 times, making it comparable to the panels on Columbia's wings.

The foam fired last week and today measured 22.5 by 5.5 by 11.5 inches and weighed 1.67 pounds. The mass, impact angle and velocity were chosen to duplicate the actual impact conditions that occurred during Columbia's launching. Because the nitrogen cannon could not impart the kind of rotational energy seen in the real foam strike, the impact angle was increased, from the actual 15 degrees to 20 degrees, to achieve the same level of kinetic energy.

An initial attempt to fire the cannon failed when an electrical component malfunctioned. Engineers fixed the problem and successfully fired the gun at 3:19 p.m. The blast could be felt by reporters, who were clustered behind a rope watching the test through binoculars.

Speaking to reporters later, Hubbard said "the first significant finding is that we cracked a rib on the structure. Let me emphasize this is the first finding. We will do a complete set of evaluations on this panel, including some specialized non-destructive evaluation, perhaps later today or tomorrow, and we'll be looking at the sensor readings."

The crack, while relatively small, "is not anything you would fly with," Hubbard said. "This would be a piece of hardware that would be rejected. Whether or not this was sufficient to cause structural damage to the whole leading edge or whether it represents a thermal problem is yet to be determined."

Over the next week or so, engineers will prepare the gun to shoot at RCC panel 9.

"We have about a week break here while we reposition the gun and we'll be taking shots at first Fiberglass panel nine and then a shot against the RCC panel nine as well," Hubbard said. "Between then and now we're going to closely evaluate (RCC panel 6), we're going to look at the internal structure and integrity, we're going to look at the sensor readings and see where the forces were and we'll be thinking very carefully about where we want the aim point on panel 9 to be. Nobody has ever characterized this material in this way to see where the point of maximum flexure or maximum strength is."

Stormy weather in Texas forced the Columbia Accident Investigation Board to delay a critical test designed to find out whether foam debris could have caused the kind of wing leading edge damage that doomed the shuttle and its crew during re-entry.

The test, a potentially critical milestone in the ongoing shuttle investigation, had been planned for this afternoon at the Southwest Research Institute in San Antonio. But heavy rains grounded CAIB investigators in Houston and delayed work to prepare a wing leading edge mockup for the test. As a result, the test was delayed to Friday, between noon and 5 p.m., weather permitting.

"I know everybody there is disappointed, we're disappointed as well," said CAIB member Scott Hubbard, who is overseeing the test. "But in the interest of doing a really correct test and doing it in the manner in which we'd been planning to do, we felt this was the best decision."

Hubbard, other members of the CAIB and key NASA personnel were grounded in Houston by heavy rains. Hubbard spoke to reporters gathered at the Southwest Research Institute by telephone.

"This is like a launch delay," he said. "We had several other things I wanted to do at the test site, particularly I wanted to personally discuss and inspect a few features of the test plan. We don't have a signed test plan yet and just like in a space launch where there are go/no-go criteria, one of our go/no-go criteria is a signed test plan and I needed to put my personal eyes on a few areas and discuss them with the crew there to be sure we are all ready to go.

"This is a complex test with hundreds of sensors and a lot of other features, so seeing we were unable to get there and we had another delay at both ends it seemed like the right thing to do to not rush it and to be sure we had everything exactly correct."

Columbia was destroyed during re-entry Feb. 1 by a breach in the leading edge of its left wing. Sixteen days earlier, a piece of foam insulation broke off the shuttle's external tank during launch and hit the left wing at or very near the point where the breach occurred. While many observers believe the foam strike was the "root cause" of the breach, there is no actual data to prove that one way or the other.

To find out if external tank foam is even capable of causing that kind of damage, engineers at the Southwest Research Institute have rigged a nitrogen gas cannon to fire a similar-size chunk of foam at a mockup of a shuttle wing, duplicating the conditions known to exist during Columbia's launching. The cannon, normally used to fire gel-filled "chicken simulators" at aircraft components to simulate bird strikes, will fire the foam at 530 mph while a bank of high-speed cameras and hundreds of sensors record the results.

See the June 4 status report below for additional details.

Computer analysis and the results of a dramatic test last week indicate a critical experiment on tap Thursday may help investigators determine, to the satisfaction of most, that a foam strike during the shuttle Columbia's launching was the initiating event that led to the ship's destruction. While the root cause will never be known with 100 percent certainty, engineers believe Thursday's experiment could go a long way toward eliminating any lingering doubt about what damaged the leading edge of the shuttle's left wing, creating the breach that ultimately doomed the ship and its crew.

"From my perspective, and I'm not speaking for the board now, I think it moves us a lot closer toward a very likely initiating event," said Scott Hubbard, a member of the Columbia Accident Investigation Board overseeing the tests. "I think it establishes foam can break (wing leading edge panels) in a realistic environment and for my own sake, I think it moves us a significant step toward establishing that is an initiating event. There could have been other initiating events, but I think this moves us a lot closer to saying the foam can do this kind of damage."

Columbia was destroyed Feb. 1 by a breach in the leading edge of the ship's left wing that allowed super-heated air to burn its way into the interior. At issue is what caused the breach in the first place. During launch Jan. 16, a large piece of foam insulation broke off Columbia's external fuel tank and slammed into the underside of the left wing's leading edge at some 530 mph. A NASA analysis during the mission concluded the foam might damage heat-shield tiles, but that it wouldn't cause any safety of flight concerns. The analysis all but dismissed any possibility of significant leading edge damage.

Since the accident, engineers have been trying to pin down exactly what sort of damage might actually have been caused such an impact. They have refined their initial estimates of the mass of the foam, based on enhanced photography and computer analysis, and they now believe it struck the leading edge, while rapidly rotating, at an angle of 15 degrees.

During the test last week at the Southwest Research Institute in San Antonio, Texas, a 1.7-pound piece of external fuel tank foam insulation was fired at a mockup of a shuttle wing leading edge by a nitrogen gas canon. The foam, traveling at some 531 mph, stuck a Fiberglass leading edge panel, taken from the prototype shuttle Enterprise, at an angle of 20 degrees. The higher angle was chosen to account for rotational energy in the actual impact that cannot be simulated. The Fiberglass panel, mounted in position No. 6, served as a stand in for the reinforced carbon carbon panels actually used on the space shuttle.

Fiberglass is 2.5 times tougher than RCC carbon composite material and engineers were surprised by the results. The impact lifted and deformed a so-called T-seal between panels 6 and 7 while generating up to seven times the force computer models had predicted. Nothing broke and there was no direct gas path into the interior of the structure, but the higher-than-expected impact force caught investigators off guard.

"I was standing there and I heard all these assertions about well, this only weighs a pound and a half and (the leading edge) is tough stuff," Hubbard said today. "When the gun fires, there's a blast wave that comes out and you can feel it and then I saw the streak and clearly, something happened. I thought to myself, this is more than I had expected. ... I thought oh my God, this is something! This isn't just a light bounce.

"People's intuitive sense of physics is sometimes way off. You don't feel this can do anything. But you fire this at 500 mph and there you saw it, I really did think oh my God, this is really an impact, this is a significant effect. Then when we actually looked at it and saw things spread apart and all that, that's when it really came home to me what one-half MV squared really means."

He was referring to the formula for computing kinetic energy. While the mass of the foam is low, the velocity is very high and that is the term in the equation that is squared. The impact force delivered by the foam is roughly equivalent to catching a basketball moving at 500 mph.

Hubbard and his team originally planned four foam shots at Fiberglass panel No. 6 before shooting at a real RCC panel taken from the shuttle Discovery that is similar in age to the panels making up Columbia's leading edge. But given the higher-than-expected forces observed during last week's test, engineers have decided to forego any additional shots at panel 6 to make sure they don't inadvertently damage any critical support hardware. Instead, they plan to shoot at Discovery's RCC panel Thursday.

"Because the observed effects, the fact that the peak loads were higher than expected in panel 7, the fact that we deformed permanently the T-seal, the fact that the loads in panel 6 were in some cases a factor of seven higher than anticipated, all led us to believe we probably had learned as much as we needed to and that we should proceed to the RCC," Hubbard said.

Thursday's test will use an identical piece of foam as the one fired last week. The foam will hit at the same velocity and impact angle. Computer models, adjusted with a correction factor to account for the different strengths of Fiberglass and RCC carbon composite material, indicate Thursday's impact will deliver more than enough energy to break the RCC panel.

"Those predictions would say that we have by maybe 70 percent more force than we need to break the RCC," Hubbard said. "Now, whether it actually turns out that way or not, that's why we do the experiment. But the analysts are saying it looks like it'll break it."

If it does, or if it causes any remotely significant damage, investigators will have solid evidence the launch day foam strike could have been the root cause of the Columbia disaster. Not absolute proof, but solid evidence.

Engineers for the first time today fired a large chunk of foam insulation at a Fiberglass wing leading edge panel, knocking a so-called T-seal out of place and leaving a long gap between two panels. Such a gap on a real shuttle wing leading edge would provide an entry point for deadly super-heated gas during the descent from orbit. Today's test results, assuming no problems are found, mark the first concrete evidence supporting the widely held theory that a foam impact during the shuttle Columbia's launch doomed the orbiter and its seven-person crew by creating a breach in the left wing's leading edge.

"Investigators are always a little cautious and there were no raised eyebrows, but it certainly is an interesting initial result," said a spokesman for the Columbia Accident Investigation Board.

The tests are being conducted at the Southwest Research Institute in San Antonio, Texas, using a nitrogen gas canon capable of firing large pieces of foam insulation at velocities of more than 500 mph. Earlier test runs focused on firing foam chunks at panels of heat-shield tiles like those on the belly of the shuttle. Today's test was the first using a large mockup of a wing leading edge.

The goal was to collect engineering data to ensure the validity of future tests. Investigators eventually plan to fire foam at an actual shuttle reinforced carbon carbon panel taken from the shuttle Discovery that has a flight history similar to panels that were aboard Columbia.

For today's test, a 1.67-pound chunk of foam with a volume of 1,200 cubic inches was fired at a Fiberglass panel in RCC position No. 6. The foam was fired at a velocity of 779 feet per second, or 531 mph, striking the Fiberglass panel at an angle of 20 degrees. The actual angle of impact in the Columbia foam strike is believed to have been less than that.

The leading edge panels are attached to the wing spar with so-called T-seals. Each edge of an RCC panel fits into a T-seal that is bolted to the front of the spar. The result is an alternating pattern of RCC panel, T-seal, RCC panel, T-seal and so on.

In today's test, the the foam strike caused the T-seal between RCC panels 6 and 7 to lift and pull away toward the outboard panel 7, the CAIB spokesman said, leaving an opening approximately 22 inches long. The width of the resulting gap varied from the thickness of a dime to more than a quarter inch.

A suitcase-size chunk of foam insulation broke away from Columbia's external fuel tank 81 seconds after launch, slamming into the left wing around RCC panels 7 and 8 at more than 500 mph. Engineers have long suspected the impact caused damage that left the shuttle with an open breach when the crew began re-entry Feb. 1. Today's test is the first to provide concrete evidence such an impact could actually displace a T-seal.

But the CAIB spokesman pointed out that Fiberglass is 2.5 times more resilient to impacts than the carbon composite material making up a real RCC panel. And the angle of impact was different, imparting more energy than a lower angle-of-incidence impact. How those variables are balanced in upcoming tests aiming at an actual RCC panel will go a long way toward determining whether or not a foam strike could have doomed Columbia.

Interestingly, the day after launch a piece of debris drifted away from Columbia that was detected by Air Force radar systems. Subsequent tests show the debris could have been a T-seal or, perhaps, a large section of an RCC panel. It is possible, some investigators believe, that the foam strike weakened a T-seal or cracked an RCC panel and that a piece of the damaged component finally broke free the day after launch. The Southwest Research Institute tests may provide the hard data needed to support, if not prove, that theory or some variation. Computer modeling software developed and refined in the wake of the Columbia accident predicted damage similear to what was observed after today's test. Engineers plan to begin shooting foam at an actual RCC panel around June 10. More information on today's test will be provided as it becomes available.

The chairman of the Columbia Accident Investigation Board said today he has no plans to require NASA to recertify shuttle systems before flights resume or to mount a test flight of some sort to validate recommended design changes or to collect more data.

But Harold Gehman said recertification is being assessed as a potentially useful long-range project in light of NASA's stated goal of flying its remaining three orbiters for another 15 years or more.

"The board is considering but has not yet ruled on whether or not a recertification or a requalification of either part or all of the STS system should be necessary for another 20 years of flight," he said during the board's final Houston news conference.

"My own personal opinion is that would not be a return to flight issue. The recertification or requalification issue is related to the announced intention of NASA to fly these things for another 20 years. It's not our charter to address that issue, but we may comment upon it."

Asked if the board might recommend a shuttle test flight before resumption of space station assembly missions, Gehman said "it's a matter under consideration." But after the news conference, when asked to clarify his thoughts on the need for a test flight, the retired admiral said he did not think the board would make any such recommendation.

The board hopes to have its final report finished before the end of July, when Congress adjourns for its summer recess. But that is strictly a target and "we'd rather get it right than get it in a hurry," Gehman said. While the board is still developing and refining its conclusions, Gehman gave reporters a hint of what to expect when the printing presses finally start rolling.

"I can tell you it is going to be a very, very thick report and that it will be in narrative form, that is, it's going to start off 'once upon a time,' you know, at the beginning and it's going to be a multi-layered report," he said.

"That is, you'll be able to have a beginning where it has a very high level cursory discussion of something and then you just keep going and it gets down to the next layer and you keep going and it gets down to a very, very detailed engineering layer. And I also know you're going to kind of have to read the report to pull the recommendations out. It's not going to be a comic book kind of a report."

To the relief of reporters ultimately faced with the challenge of digesting the report on deadline, Gehman said later a list of all the panel's recommendations will be available in an appendix. He said three professional writers have been hired to combine and edit reports from individual board members to give the final document a consistent "layered narrative" style.

"We're going to try and make it easy to read in the sense that each chapter will be kind of a stand-alone chapter," he said. "You're not going to have to be flipping back and forth to appendixes and things like that to find things. Whatever charts and graphs and pictures we refer to will be right there in the text. But it'll be a thick report. It'll be voluminous."

And it won't necessarily blame Columbia's destruction on the impact of foam debris on the ship's left wing 82 seconds after liftoff. While the foam clearly hit the left wing's leading edge at or near where investigators believe a breach occurred during re-entry, it might not be possible to prove a direct connection.

"We may or may not be able to state with unequivocal, complete certainty that the foam strike, which obviously did happen, knocked a hole in the leading edge of the orbiter," Gehman said. "There's no question the foam hit the orbiter, but we may not be able to prove it actually caused some kind of a breach or not. Therefore, because we're working so hard on determining exactly what caused this shuttle not to return safely to Earth and (because) we're looking at so many engineering and physical and mechanical processes, chemical processes, that took place, it has caused us to look broader, much more broadly at the material condition and the operation of the shuttle program."

He said the final report will probe NASA's shuttle operation "probably more broadly than any review in the past. This probably is a blessing in disguise, particularly if you're thinking about operating the shuttle for another 20 years."

"Therefore our findings and our recommendations are going to be based on this very, very broad review and not based on a single, solitary initiating event like the foam hitting the orbiter," he said. "We're not going to rule it out, I mean the foam hitting the orbiter may have caused a breach and that may have been what allowed the heat to get into the wing. But since we can't prove that, and we can't disprove, for example, orbital debris or micrometeorite (impacts), we're left with the position of having the report stand on its own weight.

"And all of these other things that we're looking into, like safety and management and risk assessment and work force issues and the stature of the (safety and mission assurance) organization, all these other things are going to have to stand on their own. Our conclusions and findings will have to stand on the merits of our work and we cannot refer back to the foam hitting the orbiter as proof of everything.

While the board may end up concluding the foam strike was the most likely initiating event, "we can't prove it," Gehman said. "We have to allow for the possibility that something else initiated this event and our report will have to take that into account."

One reporter, using a murder mystery analogy, said enough circumstantial evidence was available for most people to indict the foam. But Gehman disagreed.

"We do indeed have witnesses that saw someone shoot a gun," he said. "But the problem is we don't have a hole. We have a patient who died but we don't know why he died. There's where the analogy breaks down. ... If I had a picture of a hole or if we came back and somebody found a piece of RCC (reinforced carbon carbon) on the ground some place that had a (hole in it), I might change my mind. But as you well know, in this area where we're projecting the breach occurred, we have no RCC. It's all burned away."

Management issues will be a major focus of the final report and the perception that agency managers somehow lost sight of the post-Challenger emphasis on proving it's safe to launch a shuttle rather than proving it's not.

"A considerable part of our report is going to be addressing this underlying and hard-to-pin-down attitude or climate," Gehman said. "Some people have characterized it as a change in posture from one in which you had to prove that it was safe to fly to one in which you had to prove it was unsafe to fly," Gehman said. "In other words, the people who had doubts about anything were essentially outside the circle and had to work their way in rather than the doubters being inside the circle.

"Of course, there are a lot of reasons for this, this is not criminal activity or anything. You have 112 successful flights, you've got to assume you're doing something right. You've got thousands and thousands of dedicated people being very careful about what they do, catching many, many flaws before you launch. So they've got lots and lots of successes to prove they're doing a lot of things right. But there are a number of underlying issues we're going to attempt to address in this report. And we want to be sure that we've got them addressed in a responsible way."

Along those lines, the board will look into what other outside panels determined about the foam threat in years past because "NASA is being reviewed by somebody all the time. Well, what do all these other panels say about this? ... We are actually conducting a review of the literature to see where all these other wise people were on the subject of foam and whether or not if we had been called in before the space shuttle Columbia took off, whether or not we would have raised alarm bells about this foam business ourselves.

"In hindsight, it's really easy to find these flaws," Gehman said. "So if these flaws are out there laying around and everybody should have seen them, OK, well tell me what the next one is if you're so smart. Tell me the next one. If we as a board can't answer that question, we are very slow to sling spears at other people who also failed to answer that question."

But he said "if there's a flaw in the system or a better way to do that, we are going to document that and be very straight-forward in pointing that out."

The CAIB is in the process of wrapping up its operations in Houston before relocating in Washington. Gehman said the board's "hot lines" for public comments and suggestions will be taken down at the end of the month. Since Feb. 1, the board has received 3,150 unsolicited public comments, half of them "what I would call serious inputs," Gehman said.

"A goodly number of them were just letters which said 'I know where a piece of debris is' or something like that. But about half of them were serious analytical suggestions."

He said 778 of the 3,150 unsolicited comments and observations were actually checked out by board investigators.

"About 25 percent of the inputs we got were serious, were valuable, were things we actually followed up on to see if they were actually right or not," he said. "I consider that to be a pretty successful enterprise."

If NASA managers had realized early on that Columbia had suffered a catastrophic breach in its left wing during launch - either by obtaining satellite imagery or, more likely, by having the astronauts stage an inspection spacewalk - they might have had time to mount a repair spacewalk or even an emergency rescue mission with the shuttle Atlantis, the chairman of the Columbia Accident Investigation Board said today.

But both scenarios, while emotionally dramatic, had virtually no chance of being executed in reality because of two assumptions the CAIB made that restricted the NASA study to technical feasibility alone. The first assumption was that NASA managers had conclusive proof of a catastrophic breach by the third or fourth day of Columbia's mission. They had no such evidence. The second assumption was that agency managers would commit another orbiter to flight without knowing whether it might fall victim to the same problem. Given NASA's past history, that's extremely unlikely.

"This whole question that we asked, and NASA's whole response, is based on a set of assumptions ... which set conditions which were not present in January of 2003," CAIB Chairman Harold Gehman told reporters today in a teleconference. "In other words, we set a scenario here that was not the scenario of the Columbia. Nobody told us on day 4 that we had a hole in the leading edge of the left wing. So these are two different sets of conditions."

But the bottom line, he said, "is that it's all feasible. There are no show stoppers. But it all turns out to be extraordinarily (difficult)."

Investigators believe Columbia re-entered the atmosphere Feb. 1 with a sizeable breach in the leading edge of its left wing, a breach presumably related to the impact of external tank foam insulation that broke away and hit the orbiter 82 seconds after liftoff Jan. 16.

Engineers first saw the foam strike the day after launch while reviewing long-range tracking camera footage. NASA managers ordered an engineering analysis to determine the severity of the problem and ultimately concluded the impact had not caused any catastrophic damage. Initial requests for spy satellite imagery to examine the impact site in detail were halted.

The day of the accident, shuttle program manager Ronald Dittemore said shuttle managers didn't ask for imagery because past experience indicated it would not have helped all that much and because there was nothing the crew could have done even if a major problem had been spotted.

"Recall a year or two ago, we lost the drag chute door (from a shuttle)," Dittemore said. "Right at liftoff, it fell off. And we actually tried to take some pictures of the back end of the vehicle to see what was really there so that we can understand our thermal heating in that case, and those pictures that we received were not very useful to us. So that was part of our background.

"Combine that - our feeling that we didn't believe the pictures would be very useful to us - with the fact that there was not much, there was zero that we could do about it, and in this case, we elected not even to take the pictures.

"We believed that our technical analysis was sufficient. We couldn't do anything about it anyway. We were in the best possible position, and so we elected not to take any pictures from any other sources, and that's the way it played out."

Gehman said today the CAIB commissioned the repair/rescue mission study in part because board members were disturbed by repeated comments from NASA and contractor engineers and managers that nothing could have been done to save Columbia's crew even if they had known about the breach.

"To us, the area that we thought becomes more problematic when you deal with a question like this is the implications of the decisions made regarding the photography and the foam strike analysis and whether or not you should get on-orbit photography changes from being kind of a bureaucratic, administrative, fumbling, bumbling, to a much more serious life and death kind of a decision process," he said.

"Because it turns out a lot of people were saying, well it doesn't make any difference if you take photography or not because there's nothing we can do, it doesn't make any difference if the foam strike analysis was good, bad or indifferent because there was nothing that you could have done anyway.

"Now, those kinds of benign administrative decisions which were taken now look more ominous because now it looks like maybe there was something you could do. That's the area we were concerned about."

Ever since the shuttle's loss, reporters, politicians and the public have wondered whether anything could have been done to save Columbia and its seven astronauts if NASA had realized the severity of the problem. An internal NASA study concluded the astronauts would not have been able to survive entry on board Columbia, even if they managed to dump 15 tons of equipment overboard to minimize entry heating.

But in a subsequent study commissioned by the CAIB and discussed today for the first time by Gehman, agency engineers concluded the crew might have been able to patch the breach during an emergency spacewalk. Whether the makeshift patch would have protected the wing long enough for Columbia to make it through the region of peak heating is unknown. A better option, although only marginally so, would have been to rush the shuttle Atlantis to the launch pad for an emergency rescue mission.

Columbia had enough food, water and power to remain in orbit more than a month. The limiting consumable was lithium hydroxide, a chemical used to scrub carbon dioxide form the shuttle's air supply. Normally, NASA does not allow the partial pressure of CO2 to rise above 2 percent. But by relaxing those restrictions and accepting levels of up to 3.5 percent or so, the shuttle's air supply would have supported the crew for 30 days, until the evening of Feb. 15.

To make it that long, the crew would have had to power down the orbiter and do everything possible to minimize physical activity and their consumption of oxygen. Staging more than one spacewalk likely would have eliminated the Atlantis rescue option because of air lost overboard when the airlock was cycled.

But the spacewalk repair option is interesting if for no other reason than NASA managers initially ruled out any chance for an on-orbit fix.

"They inventoried everything that was on board the Columbia," Gehman said. "There are two EVA suits. They devised a successful way to get out to the area of the damage without further damage to the TPS (thermal protection system). They devised a way that they thought they could work out there and they ... came up with a patch that they would jam stuff in the hole."

After plugging the breach, the spacewalkers would position a plastic water bag over the opening.

"Then, after a day or two of maneuvering the orbiter so that section of the wing was in the shade all the time, the water would freeze solid and then that holds the stuff in place," Gehman said. "They would then put something over the top of the hole, some Teflon tape or something like that, and then they would attempt to re-enter.

"No studies have been done on the thermal characteristics of this patch," he said. "Whether it would hold for 30 seconds, 60 seconds, 90 seconds or three minutes we have no clue. Those studies will be done, but we've got no clue, we can't put a number, a probability, that this patch would have worked. It kind of comes under the category of 'at least we would have done something.'"

The Atlantis rescue scenario is a bit more believable, but only just. At the time of Columbia's launching, Atlantis was being prepared for a flight to the international space station in March. It's tank and boosters were mated in early January and Atlantis was scheduled to be moved from its hangar to the Vehicle Assembly Building Jan. 29 for attachment and subsequent roll out to the pad.

Assuming an inspection spacewalk by flight day 5 - Jan. 20 - and a decision that day to begin around-the-clock processing of Atlantis, the NASA study concluded the shuttle could, in theory, be ready for a launch by Feb. 10 or 11. That corresponds to flight day 26/27 for Columbia's crew. The launch schedule assumes the elimination of non-essential countdown "holds," the elimination of non-essential pre-launch tests and simulations, no mechanical problems or processing snags and good weather.

"The study indicates if you have five or six 'ifs' that line up and you get an affirmative answer to each of the five or six 'ifs,' the launch of the second shuttle and the rescue was conceivable," Gehman said. "It isn't easy, it's not even highly likely. But it is conceivable.

"By the six ifs, I'm saying if you could have reduced the processing time satisfactorily and if you could go through the launch countdown and prelaunch preparations without a mechanical problem and if the weather was suitable and if the rendezvous was successful and the two orbiters could maintain station on each other and if the multitude of EVAs worked all right, you could have done this. It is possible."

Atlantis would carry four veteran astronauts and would launch at night, rendezvousing with Columbia within 24 hours. The shuttle's flight computers would use a software "load" developed for the March shuttle mission, patched to take into account altitude changes and other factors relating to an immediate rendezvous.

Columbia would be oriented with its payload bay facing Earth and its tail in the direction of travel. Atlantis would approach from below in a manner similar to past linkups with the Russian Mir space station. Picturing Columbia moving upside down and tail first to the left, Atlantis would approach from directly below with its left wing facing the direction of travel and its open payload bay facing Columbia. The long axis of Atlantis would thus be turned 90 degrees with respect to the long axis of Columbia.

Once on station at a distance of 50 to 60 feet, spacewalkers from Atlantis would carry two spacesuits and additional lithium hydroxide to Columbia, staying in contact with safety tethers at all times. The final two astronauts to leave Columbia would configure cockpit switches and on-board software to permit flight controllers to remotely deorbit Columbia.

"Columbia would be lost," Gehman said. "There was no way to recover Columbia. The last two astronauts who left the Columbia would flip certain switches in certain positions so Columbia could be deorbited on command from Houston. And then the Columbia would be lost, ditched in the ocean."

All 11 astronauts - four of them sitting on the floor of Atlantis's lower deck - then would return to Earth. "Based on the verbal report the board got, it indicated the launch of the Atlantis was the less risky and the more probable (of the two options studied)," Gehman said. "The on-orbit repair was very, very unknown as to whether or not it would have worked or not. But obviously, it's inconceivable that we would have done nothing if we had known."

He said the decision to launch a rescue mission ultimately would have depended "solely on how good the knowledge of the damage to the orbiter was."

"In other words, if somebody came and said we've got a little tiny hole in the leading edge and we think the orbiter can re enter safely but it might not, then probably the decision to launch another orbiter would be very hard to come by," he said. "If on the other hand an inspection said 'holy mackerel, we've got a great big hole and the orbiter is doomed, the crew has no chance whatsoever,' then the probability they would have launched a rescue mission probably would have gone up."

He summed up the rescue scenario by saying "it's technically possible, very, very risky and a whole bunch of ifs have to line up. ... But I have no idea if it would have been successful or not."

Based on chemical analysis of slag found on the back side of a wing leading edge fragment, investigators now believe the breach that destroyed the shuttle Columbia occurred at or very near the lower inboard corner of reinforced carbon carbon panel No. 8, very close to where a so-called T-seal was mounted between RCC panels 7 and 8.

But a member of the Columbia Accident Investigation Board said today it's unlikely Columbia began its Feb. 1 re-entry with a large hole in RCC panel No. 8. It's more likely the disaster began with a smaller breach, possibly a gap caused by a missing T-seal, or part of the T-seal between RCC panels 7 and 8.

"If it is, for example, a T-seal, you're talking about a narrow slit which eventually is going to have to start growing in size," said James Hallock, one of the CAIB members trying to pin down the exact failure scenario. "And how does it grow? Maybe it grows by having the bottom part of panel 8 break off and that's when you're now talking about a large amount of this hot gas getting in there and things happening rather quickly after that.

"With this very small hole, things would slowly transpire and take place over a period of time. And the timing is very critical. The comment we constantly keep saying to each other is gee, this craft made it (all the way) to eastern Texas. If we had an eight-inch hole (in RCC panel 8) out over the Pacific, I'm not sure we're going to make it to Texas.

"So we have to have something that has to evolve with time," he said. "So that's the part where I'm saying, I don't think we had a big eight-inch hole there initially, I think we had something that then grew with time."

The day after Columbia's launch, military radars detected an object separating from the space shuttle. More than two dozen shuttle components have now been tested at Wright Patterson Air Force Base to compare their radar "signatures" with the flight day two mystery object. Only two components match: Part of a T-seal with support hardware attached and a large section of an RCC panel.

While the bottom half of RCC panel 8 is missing, portions of the upper section of the U-shaped panel have been recovered. Investigators have found small globules of slag-like material on the inner surface of the recovered fragments. Those globules apparently were blown there by a plume of super-heated air rushing into a breach, melting insulation and support hardware and splattering molten material back onto the inner surface of the panel.

"By taking X-rays of this thing, they've been able to find a lot of very small globular shapes, spherical shapes," Hallock said. "And when they analyze them, they all turn out to be inconel (or a related material). Why is that important? These globular shapes we're finding only behind Number 8, which is quite interesting. We're looking at doing both a chemical analysis as well as trying to understand the pattern of the deposition of all this slag. It's very interesting.

"If you look at just the chemical analysis and just the slag itself, particularly behind panel 8, it's very much talking about perhaps a breach right down in the lower part of panel 8, right near 7. Why do I say that? When you look at the layers of all the material, the molten layers that have formed, the slag itself, the lowest layer of this thing contains inconel. Now inconel is stuff that comes from the spanner beam, and foil insulation and the fittings.

"So it's beginning to tell us that indeed, when this so-called breach happened, that it was the fittings that were hit," Hallock said. "The reason we're saying it's more toward (panel 7) is that over on (the outboard) side we have a lot of other mounting hardware and it's all stainless steel and we did not find any stainless steel in the slag in behind panel No. 8. So that's sort of telling us a little bit about direction."

Inconel melts at about 3,200 degrees Fahrenheit.

"When you look at all of that, particularly around panel 8, it really does line up very nicely with a breach in the lower left hand corner of it," Hallock said. "The part of it that we're still trying to decide is that THE event or is that something that came along later? Because it's fairly clear from what we've seen, the bottom pieces of all these RCC panels in this neighborhood all came off. So was this before or after the initial event?

"For the most part, I'd say maybe 90 percent of us think that probably was the place where it came in but I can't really put it down as saying absolutely it is at this point. I hope to, but I don't know if I'll get to that stage or not."

CAIB Chairman Harold Gehman said the board plans to begin relocating in the Washington, DC, area beginning the week of June 2 and to hold a public hearing there on June 12. In the near term, investigators are gearing up to begin critical tests with a mockup of Columbia's left wing leading edge in an attempt to find out whether the impact of external tank foam insulation could have broken a T-seal or cracked an RCC panel during Columbia's launching.

A suitcase-size piece of debris broke away from Columbia's external tank 81 seconds after liftoff Jan. 16 and slammed into the left wing leading edge at more than 500 mph. Hallock said today an accelerometer on board the shuttle actually detected the impact. But investigators have not yet been able to prove whether the foam strike caused the breach that doomed the shuttle during re-entry.

"The issue that's the hard part in all of this thing is the cause and effect," Hallock said. "There's no question I can prove foam hit the shuttle and I think we can prove it hit underneath the left wing. ... Not only do we have a lot of movies that show that, we even have an accelerometer that was bouncing around, like plus or minus 1 G, and then suddenly went to 2 Gs at precisely the same time it looks like it hit. That I can do.

"Now, did it do damage? That is the hard part. How do you show whether it did damage then or not? If you didn't, and I don't know this, then where do I turn? So all of these things play together in a very complex type of thing. Right now, what we're trying to do, because we're looking at the calendar ... we're going to have to make some calls here."

The leading edge simulator was shipped to the Southwest Research Institute in San Antonio, Texas, Monday. A Fiberglass panel substitutes for RCC panel No. 5 while RCC-6, taken from the shuttle Discovery, has flown 30 times and is considered a close match to the panels in place aboard Columbia. Using a nitrogen gas canon, SRI engineers plan to fire foam debris at the Fiberglass panel starting May 28 to collect critical engineering data.

If all goes well, foam will be fired at the flight article - RCC panel 6 - starting June 7. Whether the foam impacts actually break anything remains to be seen. But Gehman said in the end, it doesn't matter.

"The board's report is not going to be scenario dependent," he said today. "By that I mean, unlike the Rogers report on the Challenger, in which they had a specific event with a specific cause that was directly related to the accident and then they went right at how to fix that, we are conducting a much broader review of NASA here.

"Not only are we going to address the foam shedding issue, but we're going to address a dozen other issues that we're concerned about. We're going to tell them to fix the foam shedding, absolutely. But we're actually looking more broadly than that. Maybe the fact that we can't prove that the foam actually broke a hole in the orbiter, it may actually be a good thing in the long run because it really is causing us to look much, much broader at contributing factors in this accident, down to and including climate and atmosphere and leadership and management and safety programs and things like that which I believe will give a much, much deeper and broader report in the end.

"So it may be the fact we don't have a cause and effect that hits us in the head like a 2-by-4 may actually be a blessing in disguise. Obviously, we find that the process of rationalizing away the impact of foam hitting the orbiter over a period of all these years is not one that we're going to be able to live with."

Gehman said it "doesn't bother me in the least" if the CAIB fails to define a root cause of the Columbia disaster. And he pointed out the current best-fit scenario could quickly change.

"You heard Jim Hallock just now talking about T-seals and lower halves of RCC panels," he said. "I would point out that the entire lower half of RCC panel No. 9 is missing. One of the reasons we're not talking about the slag on RCC panel No. 9 is because there isn't any RCC panel No. 9. Suppose tomorrow we wake up and farmer Brown finds all of panel No. (9) out on his field? Well, there goes that theory. We can't write a report that's that scenario dependent because somebody will find the offending piece.

"On the other hand, I do believe we can do NASA and the shuttle program a world of good if we take a very broad and complex view of this and go after multiple causes and multiple flaws and shore them all up. I'm quite confident with that approach. It's harder and it may be a little bit of a challenge for us o write the report in ways people understand the point we're trying to make here. But I believe it actually (will be) a better report."

Gehman said the board hopes to have its final report finished before Congress takes its summer recess in August.

The Columbia Accident Investigation Board today released the clearest video yet showing a tumbling piece of foam insulation slamming into the shuttle's left wing during launch Jan. 16. Investigators say the enhanced video, along with ongoing mathematical modeling, indicates the foam struck the wing at some 529 mph, imparting up to a ton of force across an area of the leading edge measuring roughly six by 12 inches.

Investigators believe the foam impact likely cracked or breached one of the reinforced carbon carbon panels making up the leading edge of the left wing or damaged a so-called T-seal between two adjacent panels. Whatever the exact mechanism, investigators believe Columbia began its re-entry Feb. 1 with a breach at or near RCC panel 8 or perhaps near the T-seal between panels 8 and 9. Super-heated air burned its way into the wing through this presumed breach, leading to the shuttle's eventual destruction.

CAIB and NASA investigators are gearing up for a crucial series of tests at the Southwest Research Institute in San Antonio, Texas, early next month to help pin down whether the foam impact was, in fact, a "root cause" of the disaster.

Five initial test runs already have been carried out shooting foam "bullets" at heat shield tiles on a landing gear door taken from the prototype shuttle Enterprise. The tests were set up early on in the investigation, before engineers knew the impact had actually occurred at the leading edge.

In a teleconference with reporters today, CAIB member Scott Hubbard said only minimal tile damage resulted from the initial impact tests using foam bullets, weighing between 1.2 and 2.5 pounds, impacting at angles between 5 and 13 degrees. But the tests have helped verify the predictions of two computer models and confirm the actual impact happened at or very near the leading edge.

Early next month, engineers will begin firing foam at a high-fidelity mockup of a shuttle leading edge, complete with RCC panels taken from the shuttle Discovery that have flown more than two dozen times. The leading edge simulator will be heavily instrumented with more than 100 channels of data charting the stresses and strains imparted by the impacts.

The foam will be fired from a 30-foot-long nitrogen-gas canon with a rectangular bore measuring 5.5 inches by 11.5 inches. Foam bullets similar in size to the actual debris that hit Columbia will be fired at the simulator at velocities of up to 775 feet per second, or 528.5 mph. Six high-speed cameras, some capable of recording 7,000 frames per second, will photograph the impacts in exquisite ultra slow-motion detail, permitting precise determination of impact velocities and angles.

"All the experts looking at all the data have begun to home in on a sweet spot," Hubbard said of work to determine the size of the foam debris that struck Columbia. "The current best guess, and this may change a little bit over the next week or so, is an impact projectile of about 1,240 cubic inches traveling at about 775 feet per second."

One wild card is the contribution of the foam's rotational velocity. Up until now, engineers have calculated the force imparted by the impact based on the foam's straight-line velocity. But Hubbard said the debris was tumbling wildly and that regardless of the direction of the tumble, the rotational velocity must be factored in.

"A major element has been to include the rotational velocity," he said. "This is something that had personally been gnawing at me in looking at the video, of how this piece was rotating. It seemed to me to be a source of additional energy. ... Some preliminary calculations show that we may need to either adjust the velocity or the angle to compensate for this."

Some outside observers worried the initial test results, showing only minimal damage to the landing gear door tiles, might indicate the foam would have little effect on the RCC panels, leaving NASA without a clear-cut root cause for the disaster.

But Hubbard said today there is little or no data on how RCC panels respond to impacts. And unlike the tiles, which are supported across their full length and width, RCC panels are only supported at their edges, by the T-seal. The central, unsupported area is just a third of an inch thick.

"The difficulty is in modeling this curved surface," he said of the U-shaped RCC panels. "There was some initial ... analysis that was done on an impact of a piece of foam of the 2-pound variety traveling at 700 feet per second against a flat plate (of carbon composite material). What that seems to indicate - and I really underscore 'seems' - is that it should break the panel.

"But I don't want to go any further than that because that's a flat panel and not a curved surface. As we've learned from doing this first set of tests, getting the tumbling, the angle and all of that just right is a tricky business. So I don't think at this point we know exactly what we might find. That's why we're doing the tests."

The impact angle chosen for the tests is especially critical. That angle is measured relative to the flat bottom of the wing, not relative to the tangent of the curve at the point of impact as common sense might dictate. Relative to the belly of the orbiter, impact angles for debris striking the lower side of the leading edge RCC panels could range from 10 to 20 degrees or so.

Velocity also is critical. As every high school physics student learns, an object's kinetic energy is one half its mass multiplied by the square of its velocity. While the mass is low in this case, the velocity is high and that is the term being squared.

"Very light things, when you accelerate them to very high velocities, carry an enormous amount of force and the types of forces we're dealing with here, with the foam size and velocities we're talking about, even at these relatively shallow angles, are something close to a ton of total force, upwards of 2,000 pounds of total force delivered in relatively small area of about 5 or 6 inches by a foot," Hubbard said.

Trying to extrapolate the results of the initial tile impacts to the RCC panels is not possible because "it's a little bit apples and oranges," Hubbard said. While engineers understand how tiles respond to impacts, no such database exists for carbon composites.

"The tiles have a certain crush force that we now understand fairly well based on all the earlier tests," Hubbard said. "We don't have that same level of information yet for aged RCC. One case (tile), you have a glass-like material that is very sensitive to the angle of the impact and that angle, I feel almost certain, has something to do with how the edge of the foam digs into it. If the leading edge were at 20 degrees or so and made out of tiles, I think we would see a substantial amount of damage. The fact is, that angle that we saw, the angle that exists on the bottom of the orbiter, is only 5 or 10 degrees. That's one story.

"A completely different story is the RCC panel, which is only supported on the ends and is maybe a third of an inch thick or so and has quite different material properties. It will probably show some angular dependence. The smallest angle of intersection that we've measured is about 10 degrees and it goes up to well over 20 degrees.

"At that range of angles, you transfer a lot of force and that amount of force could be, we think, enough to break it. But we won't know for sure until we do the tests."

Investigators have not yet decided exactly where they will aim their foam bullets at the high-fidelity leading edge simulator. Because each strike will affect the simulator in some fashion, causing an unknown amount of damage, only a limited number of firings will be possible.

The current schedule calls for shooting at panels 5 through 7 beginning the week of June 2. Panels 8 through 10 will be hit starting the week of June 23rd.

"At this point I'm fairly well convinced we're going to hit panel 6 pretty much in the middle of the panel," Hubbard said. "I'm looking at two or three options for the panel 8-9 tests. One is down at the bottom of the panel. The other though is ... the T-seal area (between panels 8 and 9). And I haven't made, nor have we agreed with NASA yet, exactly the best place to put that impact and that's one of the things we're going to be looking at in the next two weeks or so."

NASA today named William Parsons, director of the agency's Stennis Space Center, as the new manager of the space shuttle program, replacing Ronald Dittemore who announced his retirement late last month. Parsons, who began his NASA career at the Kennedy Space Center in 1990, will take over from Dittemore sometime this summer, after an on-the-job training transition period.

"This is not a job that just anybody could do and this is not a time for other than the very best candidate," said Michael Kostelnik, deputy associate administrator for shuttle and space station. "We were fortunate all these things came together.

"We looked far and wide, both within NASA and exterior to NASA, looked at a lot of great candidates with a lot of great skills. We were concerned with leadership, we were concerned with management acumen, we were concerned with professional characteristics and obviously wanted somebody experienced in the program."

Parsons is widely respected by agency insiders, bringing a wide range of experience to a difficult job, a man "who's spent time at a variety of (NASA facilities) and has learned what works and doesn't work," said one senior manager. "Personally, I believe he brings a level of leadership not often found."

Parsons began his space career readying military cargos for launch on the space shuttle and ultimately joined NASA's shuttle workforce at the Kennedy Space Center, integrating payloads for launch and eventually serving as a flow director in charge of the shuttle Discovery's ground processing.

He then moved to the Stennis Space Center where he ran space shuttle main engine testing before moving on to the Johnson Space Center in Houston, serving as manager of center operations and then as deputy center director. A native of Mississippi, he returned to Stennis in 2001 and was named center director in 2002.

The job of center director is one of the highest management positions in NASA. In some respects, one could look at Parsons' decision to take over management of the shuttle program as a step down, even though the shuttle program has a much larger budget and a much larger workforce.

"I don't look at things that way," Parsons said today. "I'm proud to be a member of this agency, I'm proud to be able to serve this agency, I look forward to being asked to do this and I look forward to being given this challenge and to have an opportunity to help this program get back to flying."

Said Kostelnik: "Looking both exterior to NASA and interior to NASA, we could not have found a better qualified candidate. A natural leader, trained in leadership early on in his Marine Corps days, a very astute manager, technical degrees and solid technical experience in these programs. ... He has great people skills, he is well respected in our industry."

Parsons said he plans to work closely with Dittemore over the next two months or so to learn the intricacies of an inherently complex program before taking over later this summer.

"I think I can learn some good things from Ron," Parsons said. "I think Ron has been an outstanding program manager. ... I think his approach to running the shuttle program has been very solid, I think he has good processes in place, I think we'll use those processes to maximize the efficiencies and effectiveness of what we do from this point forward.

"I think Ron also showed us a strong character when we had our tragedy. I hope I don't have to deal with a situation like that, but I think I learned a lot from Ron on how he approached that event."

Asked what he considered his greatest challenge, Parsons said "to take the findings of the Columbia Accident Investigation Board and work with the entire community to then lay out a plan on how we're going to return to flight."

"It's probably not the easiest time to come in and take over the shuttle program," he said. "But then again, I look forward to the challenge, I think I have a great team in place right now that will help work through those issues and as we get the findings from the board, then we'll start working hard on trying to do the right things so we can get back to flying safely."

He took issue with comments by Rep. Joe Barton, R-Texas, who said Thursday the space shuttle "is an unsafe system and it is technically impossible to make it safe enough, in my opinion."

"I find it troublesome, maybe, that there are thoughts like that out there," Parsons said today. "But we have to work our way through that. I think we can fly this shuttle safely and so we look forward to doing that in the future."

Even so, he took the job with "quite a bit of trepidation. I mean, this is a big challenge for me and I had to think my way through it. But again, the shuttle program is extremely important to this agency and to have the opportunity to work with the contractors and the program folks to get this shuttle flying again so we can complete the international space station is something I look forward to."

Dittemore, a former flight controller, flight director and chief of shuttle engineering, was named shuttle program manager in 1999. He won widespread respect in the aftermath of the Feb. 1 Columbia disaster for holding daily news briefings to keep the public informed about the progress of NASA's ongoing investigation.

In late April, Dittemore told reporters he had made plans to retire before Columbia's launch and that he initially put those plans on hold following Columbia's loss. But he said it was important for NASA to select a replacement as soon as possible, before return-to-flight activities mature, so the new program manager can have time to absorb the intricacies of the job.

Kostelnik agreed today, saying Parsons will need to work closely with Dittemore in the weeks ahead to get up to speed on shuttle operations from the perspective of program manager.

"The shuttle is an incredibly complex piece of machinery," Kostelnik said. "It has an annual budget of about $3.5 billion or so, there are not only operational issues there are acquisition aspects, it'a a very complex management job and it does take some time to have a transition.

"Bill's a great leader and a solid manager, but has not been involved intimately with some of the moving parts of the shuttle and this will give them a reasonable time to do a graceful transition."

Parsons graduated from the University of Mississippi with a bachelor's degree in engineering. He also holds a master's degree in engineering management from the University of Central Florida. No specific date has been set for his replacement of Dittemore.

Reliable sources say NASA plans to name a new space shuttle program manager Friday to replace Ronald Dittemore, the widely-respected man in charge during the Columbia disaster who announced his retirement late last month. The identity of Dittemore's replacement is not yet known and a NASA headquarters spokesman reached at home late Wednesday said he had no knowledge of any such announcement. But sources said a successor has, in fact, been selected and that an announcement is planned for Friday in Washington.

In other developments, researchers have begun initial test runs firing external fuel tank foam insulation at a shuttle landing gear door in a bid to calibrate damage prediction software and to assess how much damage high-speed impacts might actually do to a shuttle's heat-shield tiles. Engineers ultimately plan to fire foam debris at a mockup of the shuttle's wing leading edge system, the location of the breach that doomed Columbia.

In the initial runs, firing foam from a nitrogen gas canon at the Southwest Research Institute in San Antonio, Texas, only minor damage was observed in the landing gear door tiles, sources said.

Columbia's left wing was struck by falling external tank insulation 82 seconds after launch Jan. 16. Investigators suspect the impact damaged the leading edge of the wing in some fashion, directly causing, or at least contributing to, the creation of a breach that destroyed the ship during re-entry on Feb. 1.

The Columbia Accident Investigation Board is overseeing a complex series of tests at the Southwest Research Institute that will culminate early next month with firings aimed at a highly-instrumented mockup of a wing leading edge.

In three of four initial runs this past week, tiles on a landing gear door taken from the prototype shuttle Enterprise withstood foam impacts at angles of 5 degrees with little or no damage, sources said. The foam samples were not as large as the piece of debris that hit Columbia, but engineers can achieve the desired results by properly varying mass and velocity to achieve the range of kinetic energy imparted in the actual launch impact.

The fourth run in the series, in which the canon fired a foam sample at an 8-degree impact angle and a slightly higher-than-planned velocity, caused visible but relatively minor gouging. The foam that hit Columbia's wing was moving between 416 and 573 mph, engineers believe.

CAIB members have stressed that the landing gear door target was selected early on, before engineers knew the breach occurred in the leading edge, and that these results are not directly applicable to the board's current failure scenario. The real test will come next month, when investigators begin firing foam at the leading edge mockup.

Dittemore, a former flight controller, flight director and chief of shuttle engineering, was named shuttle program manager in 1999. He won widespread respect in the aftermath of the Feb. 1 Columbia disaster for holding daily news briefings to keep the public informed about the progress of NASA's ongoing investigation.

CBS News reported Dittemore's plans to retire April 19. The following week, he told reporters he had made plans to retire before Columbia's launch and that he initially put those plans on hold following Columbia's loss. But he said it was important for NASA to select a replacement as soon as possible, before return-to-flight activities mature, so the new program manager can have time to absorb the intricacies of the job.

"It would be very important to have new leadership in place, to have that foundation established," he said. "And as you move forward over the coming months, building on that foundation from a new leader perspective, you're going to be that much more prepared, both from a leadership point of view and a team responding to that leadership, to move right into return to flight and then, picking up the flight rate again.

"I believe personally this transition time frame would be extremely beneficial to allow this new leader time to prepare, the time to respond to recommendations, the time to implement recommendations, to have a strong foundation, to have a strong springboard to jump forward into the coming years."

For the first time, the Columbia Accident Investigation Board has endorsed a detailed failure scenario developed by NASA and contractor engineers that traces the shuttle's destruction to a breach in the ship's left wing at or near leading edge panels 8 and 9. That scenario, first reported by CBS News on April 20, assumes Columbia began its ill-fated Feb. 1 descent to Earth with a breach in the leading edge and that hot gas ate its way into the interior of the wing less than eight minutes after the orbiter fell into the discernible atmosphere 76 miles above the Pacific Ocean.

How large the initial breach might have been is not yet known. But the day after Columbia's launching, military radars tracked an object separating from the orbiter. Investigators believe the "flight day 2 mystery object" left an opening of some sort that provided a direct path for hot air to enter a cavity behind the U-shaped reinforced carbon carbon panels making up the leading edge of the left wing. More than two dozen shuttle components have been tested to find the best match with the radar data and today, experts testified before the CAIB that only two candidates are still on the table (a third has yet to be tested).

One is a large section of an RCC panel measuring up to 120 square inches. The other is a T-seal, one of 22 such fasteners used to lock the RCC panels together. Under the scenario developed by NASA and the CAIB, the mystery object could be either the T-seal between RCC panels 8 and 9 or a large section of the lower portions of the RCC panels themselves.

"From all the testing and analysis we've done, we feel RCC T-seals as a class cannot be excluded and RCC, what we call acreage, or pieces of the panel, cannot be excluded," said Steve Rickman, chief of the thermal design branch at the Johnson Space Center. "But there is another point to be made there, that the panel acreage itself would have to be on the order of 0.33 inches thick for it to have the correct ballistics. ... It turns out that on the lower panel acreage in the panel 8-to-9 region you do have RCC panel acreage that is of this thickness."

The loss of a T-seal would have left a slot-like gap between panels 8 and 9 just a few inches across as opposed to the much larger hole represented by the loss of a section of RCC panel measuring between 90 and 120 square inches. Engineers currently are trying to determine how big the actual breach must have been to permit the entrance of enough heat to explain the timing of sensor readings and dozens of subsequent sensor failures.

"My understanding is that NASA is, in fact, doing specific analyses for those different shapes, sort of two-dimensional analysis," said board member Sheila Widnall. "My understanding is the hole sizes they've been using to date are quite a bit smaller than the RCC panel that was suggested in the Wright Patterson radar tests. So I think more analysis is clearly required."

Board chairman Harold Gehman said "this is one of the key areas we're going to continue to focus on."

"The way I like to describe it is that the breach that was there at the time of entry has to be big enough to cause the heat scenario that we saw but it also has to be small enough to permit the orbiter to get all the way to Texas. Keeping in mind that we've got some bounds in there and we've got a very, very rich timeline, I believe we've got a good chance of achieving the analysis it's going to take to be more specific about this. We're talking about weeks of work here. It's just plain hard work."

But it is critical work and it will play a major role in how NASA and CAIB investigators design upcoming tests at the Southwest Research Institute in San Antonia, Texas, to fire external tank foam insulation into leading edge components in a bid to simulate what went wrong in the first place.

As is well known by now, just 82 seconds after liftoff Jan. 16, a large piece of foam broke away from Columbia's external fuel tank. The debris originated at or near the left bipod ramp, an aerodynamically shaped area of foam just in front of a strut that helps hold the nose of the shuttle to the tank. At least three distinct pieces can be seen falling away from the bipod area in enhanced footage from ground cameras. But only one - the largest - actually hit the left wing. Experts testified today the large piece measured 24 inches by 15 inches with an uncertainty of 3 inches. The thickness of the debris has not been determined but it is believed to be relatively thin. The impact velocity was somewhere between 610 feet per second and 840 feet per second, or between 416 mph and 573 mph.

The debris hit the left wing in a "footprint" centered on the lower side of RCC panels 6 through 9. It's possible the impact damaged the T-seal between panels 8 and 9 - or cracked one of the RCC panels - and that the damaged component finally shook free the day after launch, leaving an opening into the cavity behind the leading edge. Investigators have not yet come up with a credible mechanism to explain how the damaged component was able to remain in place for a full day and then separated on flight day two.

But for their part, Gehman said the board has deliberately excluded the foam impact as a direct cause of the disaster in its working hypothesis of what went wrong.

"We were careful not to say the foam knocked a hole in the leading edge of the orbiter because we can't prove it," he said. "Now that's not to say we don't believe that's what happened, but we were careful here to base our working scenario on agreed facts and right now, we aren't willing to make that kind of a statement."

Whatever caused the breach in the leading edge, the pathway for hot air was large enough to trigger a remarkably rapid series of events. The shuttle entered the atmosphere at 8:44:09 a.m. Less than eight minutes later, at 8:52:05 a.m., the shuttle began responding to unusual aerodynamic forces. At some point between that moment and 8:52:16 a.m. - 11 seconds later - the hot air had burned its way through the wing spar and into the wing's interior. One minute later, by 8:53:10 a.m., 120 sensors had dropped off line as the super-heated air burned through wiring inside the wing just behind the spar.

That data was recorded on board and not transmitted to the ground. The first realtime indication of a possible problem in the left wing came at just about that same moment - 8:53:10 a.m. - showing up on a computer display monitored by the mechanical systems officer in mission control. By that point, the wing was in severe distress and complete failure was just seven minutes away.

The upcoming tests at the Southwest Research Institute, scheduled to begin in early June, "will demonstrate to us whether or not we have a plausible scenario," Gehman said. "But it doesn't seem to me that it will prove anything one way or the other."

Gehman said the board hopes to begin writing its report later this month. No more hearings are currently scheduled for Houston but the board plans to relocate in Washington next month and one or more hearings may be held there to flesh out questions about NASA's management and operating philosophy. Gehman said it will not matter in the long run whether investigators ever conclusively link the foam impact with the leading edge breach.

"We can make fairly good case of what we think the return-to-flight criteria should be with or without any positive knowledge or positive proof that the foam caused the accident," he said. "Because we're going to make return-to-flight recommendations that are designed to enhance the safety of the orbiter in every way we find that it needs to be enhanced.

"Just fixing the foam alone won't do it. So I'm not the least bit concerned that our inability to make a positive statement with proof that the foam knocked a hole in the leading edge of the orbiter in any way slows us up or in any way restricts what we need to do in order to come up with a criteria for return to flight. Most of our work on return-to-flight issues has to do with the fact that the safety margins have been changed over the years and we're going to try to restore those safety margins back to at least as far as we're comfortable with."

Lest there be any doubt Gehman is serious about addressing a wide-range of issues in the board's final report, he stressed again today that "we're looking at this program and these shuttles in a very, very broad way. We have to, because we don't have a single point failure like the O-rings (that caused the Challenger disaster). And therefore we're going to come up with a broad range of recommendations, which taken together, we believe, will make the program safer. The fact that we don't have a single causal event doesn't bother me in the least. ... It may not be quite so easy to explain, but practice wise and function wise, it doesn't bother me in the least."

He also said the board plans to address the overall risk of flying the shuttle to stimulate public debate.

"The board is going to attempt to characterize the true risk in our own words," Gehman said. "Whether or not we put a number on that, the board hasn't decided. But we are going to attempt to describe for our constituents - the Congress, the administration, the astronauts and the people of the United States - what the risk is in this enterprise. It's not zero, it's not anywhere near zero.

"I don't know that the board would be interested in putting a number on it. ... Whether or not we pass judgment on any number that NASA uses remains to be seen. But we will attempt to characterize the risk in our own terms and if it differs from NASA's, so be it. But that will be one of our goals, to restate the risks in terms that there can be a good public policy debate on whether or not we should be doing this or not."

Readers are encouraged to review the April 20 CBS News status report below for details about NASA's failure scenario. Here is the text of a CAIB news release today summarizing the board's conclusions to date:

Columbia Accident Investigation Board Releases Working Scenario

Houston, Texas Ğ The Columbia Accident Investigation Board (CAIB) today released their working scenario.

After three months of intense investigation including thorough reviews of hardware forensic analysis, orbiter telemetry, Modular Auxiliary Data System (MADS) recorder measurements, general public still and video photography, hypersonic wind tunnel testing, and aerodynamic and thermal analysis, the Columbia Accident Investigation Board, with the assistance of the NASA Accident Investigation Team (NAIT), has reached the following preliminary conclusions.

Launch:
Approximately 81 seconds after a 10:39 EST launch on January 16, 2003, post launch photographic analysis determined that foam from the External Tank (ET) left bipod ramp area impacted Columbia in the vicinity of the lower left wing RCC panels 5-9.

Orbit:
While Columbia was on orbit for 16 days, there was no indication of damage based on orbiter telemetry, crew downlinked video, still photography or crew reports.

An Air Force Space Command post flight evaluation of radar tracking data indicated an object in the vicinity of the orbiter on flight day two, remained on orbit for approximately two and a half days, then reentered the atmosphere. Radar testing and ballistics analysis of various thermal protection system items and thermal blankets, along with careful inspection of downlinked orbiter payload bay video, has been used in an attempt to identify that object. Testing and analysis to date have eliminated from consideration all but a piece of an RCC T-seal or RCC panel with a rib. However, there is no conclusive evidence that either of these items was the object that departed the orbiter.

Entry:
The de-orbit burn and entry targeting were accomplished using well-established Mission Control Center procedures. There were no problems identified with this process.

On the morning of February 1, Columbia entered with unknown damage to an RCC panel or T-seal in the left wing RCC panel 5-9 area. Hardware forensic analysis and a review of MADS temperature and strain measurements on the left wing leading edge structure point to the RCC panel 8/9 area as the most likely area of damage. The forensic evidence indicated the RCC panel 8/9 area was subjected to extreme entry heating over a long period of time, leading to RCC rib erosion, severely slumped carrier panel tiles, and substantial metallic slag deposition on the RCC panels nearest the damaged area.

MADS data indicated the RCC cavity temperature and the temperature behind the wing leading edge spar began to rise at approximately 8:49:00 EST. This indicates that hot gas flowed into the RCC cavity between entry interface 8:44:09 EST and 8:49:00 EST. Three minutes later, at 8:52:00 EST, temperature and strain measurements indicated that hot gas penetrated the internal part of the wing via a breach in the wing leading edge spar. Immediately, the hot gas inside the wing began to heat wire bundles containing real-time telemetry and MADS data. A MADS upper left wing pressure measurement was the first to fail at approximately 8:52:16 EST. Over the next four minutes, 164 other measurements fail, with the last failure at approximately 8:56:24 EST. Most measurements failed very quickly, within the first two minutes of the breach.

ColumbiaÕs flight control system began to sense increased drag on the left wing due to the damage at 8:52:05 EST. The vehicle easily compensated for the initial aerodynamic disturbance. A significant change in the vehicle aerodynamics was observed at 8:54:20 EST, indicating a change in the damage to the left wing. At the same time several very bright debris events were seen in ground-based videos.

Soon after the hot gas entered the left wing multiple debris events were captured on video by observers on the ground. These video images begin at 8:53:46 EST (20 seconds after California coastal crossing) and end with ColumbiaÕs final break-up. The exact source of the debris may never be fully understood. However, upper wing skin and Thermal Protection System (TPS) parts are possible candidates. Damage to the internal aluminum wing structure was most probable during this timeframe as well. These debris events appeared to affect orbiter communication. There were 13 unexplained communication dropouts in this timeframe.

By 8:56:16 EST hot gas had penetrated the wheel well wall as indicated by an off-nominal rise in hydraulic line temperatures. Another significant change in ColumbiaÕs aerodynamics occurred at 8:58:09 EST, accompanied by several more debris events. The vehicle responded to this event with a sharp change in its aileron trim. Additionally, by 8:58:56 EST all left main gear tire pressure and temperature measurements were lost, indicating a rapid progression of damage inside the wheel well. A continual progression of left wing damage caused another abrupt change in the vehicleÕs aerodynamics at 8:59:29 EST. Columbia attempted to compensate by firing all four right yaw jets. By 8:59:32 EST the Mission Control Center had lost all telemetry data. MADS recorder data was lost at 9:00:14 EST. Based on video imagery, main vehicle aerodynamic break-up occurred at 9:00:23 EST.

Analysis and Testing Underway to Support the Working Scenario:
Although there is an abundance of existing evidence supporting the Working Scenario described above, the CAIB and NAIT have the following analyses and testing underway to refine the details of the scenario:

1. Completion of RCC and tile impact testing at Southwest Research Institute.

2. Aerothermal analyses to correlate off nominal heating trends in left fuselage sidewall and left Orbiter Maneuvering System (OMS) pod heating that were observed in the MADS data.

3. Instrumentation wire burn-through arc jet tests and thermal analyses to support the timing of observed instrumentation failures.

4. Instrumentation circuit analyses or testing to confirm the failure signatures observed in the data.

5. Hypersonic wind tunnel testing and aerodynamic analyses to explain aerodynamic roll and yaw moments observed in flight data.

6. Thermal analysis of RCC panel 9 clevis and spar temperature sensor responses to support or refute flight data.

7. Gas flow and heat transfer calculations internal to the wing to support the MADS sensor readings in and around the wheel well.

8. Arc jet testing and/or analysis of previous arc jet testing to determine feasibility of RCC erosion observed in several key pieces of RCC panel 8/9 debris.

9. Continued forensic testing and analysis of significant recovered debris.

10. ET dissection and cryopumping tests.

The CAIB has not reached any final conclusions and has not determined the cause of the loss of the shuttle and crew. The board's final report will be issued later this summer.

"By building a working hypothesis, it really enables us to focus the testing, it enables us to much more narrowly direct the analysis, it really produces a very synergistic effect on different disciplines," Gehman said.

"The real value of this is that it tells us what to do now and where to go next," he said. "The foam impact testing is very important to us, we have to continue the very, very hard work on the aerothermal analyses to correlate some of these events that we have really good data on but yet we can't quite fully understand everything that's happening, like how long does it take to burn through Kapton wiring, how long does it take to create a knife edge (burn pattern) in a piece of RCC that's a third of an inch thick, how long does it take to burn through aluminum skin and those kinds of things."

As NASA and independent investigators close in on the root cause of the Columbia disaster, one question lingers in the minds of many armchair analysts: What, if anything, could have been done to save the crew if engineers had known early on that the orbiter had a non-survivable breach in the leading edge of its left wing?

The answer, according to a detailed NASA analysis obtained by CBS News, is that Columbia was doomed from the moment the wing was damaged, most likely during ascent, and that nothing could have been done to reduce the stress of re-entry enough to save the ship and its seven astronauts.

Not that NASA wouldn't have tried. But given the severity of the leading edge breach investigators now know was present at the start of Columbia's descent, there simply were no Apollo 13-class engineering rabbits to pull out of the hat.

"I have wracked my brains over this," LeRoy Cain, the entry flight director for mission STS-107, said in an interview. "There just was no way we were getting that vehicle back. If we'd gone and taken some pictures and done whatever else anybody could think of, it wouldn't have changed the outcome for Columbia."

NASA's oldest space shuttle was launched Jan. 16 on a planned 16-day science mission. Eighty one seconds after liftoff, a large piece of foam insulation broke away from the ship's external fuel tank and hit the left wing's leading edge at some 450 mph.

While an independent investigation into the disaster is not yet complete, many engineers believe the foam impact, possibly in combination with other factors, damaged one of the wing's reinforced carbon carbon composite panels, providing a path for super-heated air to enter the wing during re-entry Feb. 1.

In the wake of the resulting catastrophe, Cain was charged with carrying out an "entry options" review to determine what might have been possible to reduce re-entry temperature extremes, or loads. The study will be presented to shuttle program management next week.

As it turned out, the only viable options involved lowering the shuttle's orbit before beginning the descent and drastically reducing the ship's weight by as much as 15 tons.

Diverting Columbia to the international space station was never an option because the two spacecraft were in different orbital planes and the shuttle did not carry nearly enough fuel to make such a rendezvous. Cain's review did not address the possibility of launching an emergency shuttle rescue mission. But engineers say they do not believe it would have been possible to get the next shuttle in the launch sequence - Atlantis - into orbit before Columbia's crew ran out of carbon dioxide-scrubbing lithium hydroxide.

That said, three options were evaluated in Cain's review but the best results were achieved in the third, most extreme scenario, one that assumed the astronauts dumped everything possible overboard to reduce the shuttle's weight to an absolute minimum while keeping barely enough fuel and other supplies on board to ensure a survivable landing.

It is not a scenario flight controllers would ever actually implement in its entirety. It is fraught with extreme risk and major unknowns, risks that might well outweigh the threat posed by a damaged thermal protection system. But the goal of the entry options review was to assess what might be possible, in theory, regardless of likely operational constraints.

Scenario 3 assumed the astronauts, staging at least two emergency spacewalks, could dump 31,321 pounds of equipment and supplies overboard, including Columbia's pressurized Spacehab research module (18,071 pounds), a pallet of experiments in the cargo bay known as Freestar (4,428 pounds) and unneeded crew equipment (4,663 pounds). Another 4,159 pounds of consumables - propellants, hydrogen, oxygen, water, hydraulic power system fuel - also would have to be dumped or used up.

The scenario requires numerous flight rule violations and would leave the shuttle at "absolute minimums in critical systems" with no deorbit waveoff opportunities and only a minimal ability to cope with additional failures. But it did reduce the maximum temperatures associated with re-entry.

"When we messed around enough with the weight, we started to see some reductions, getting some thermal relief in a generic sense, which makes sense," Cain said. "If we bring the altitude down before we deorbit, we're reducing the energy, if we get a bunch of weight off then we're reducing the energy. All that weight translates into energy dissipation we have to do during entry.

"So we did that. And really, what we did here is we tried to bound the problem and that's important to understand. We did it not because we said this is realistically things we can go do, this is throwing everything in the kitty, pulling out all the stops, doing things we really wouldn't really be able to accomplish all of and adding it all up and seeing what it does for you."

The study examined heating at three representative points on the orbiter leading edge and under belly. In an important caveat, all the scenarios assumed there was no damage to the shuttle's thermal protection system (TPS) because there are no computer models capable of accurately predicting how even minor damage might affect heating.

"One of the major, significant caveats to the whole thing is we did this for a nominal TPS," Cain said. "If I have exposed structure, then even getting rid of 32,000 pounds isn't going to save the day for me. It's just not, whether it's exposed structure on the lower surface or its on the wing leading edge.

"We don't know what we had (on STS-107), but we had somewhere from some amount of damage to exposed structure. We don't have a model to put in some amount of damage and then understand the resulting thermal protection."

That said, the scenario 3 results show:

• A 7 percent reduction in the wing leading edge maximum temperature near reinforced carbon carbon panel No. 9;

• A 24 percent reduction in heat load and a 34 percent reduction in heat rate for tiles just in front of the main landing gear doors;

• A 29 percent reduction in heat load and a 56 percent reduction in heat rate for tiles aft of the main landing gear doors.

Heat rate is the maximum temperature a component might experience during entry while the heat load is a measure of the amount of time the heat is applied to the orbiter's structure. To see how this works, consider a shuttle making a shallower descent than normal. While that would reduce the maximum temperatures experienced by the orbiter, it would increase the peak load because heating would be stretched out over a longer period of time.

"The thermal tradeoff line that we have today is a balancing act of those two things for the various surfaces," Cain said. "It's a delicate balance and the shuttle TPS is so complex. It just boggles my mind. It's even more complex than I thought it was before STS-107, just in terms of the different kinds of TPS we have and everything."

In Columbia's case, of course, it was the leading edge that mattered. Cain said a 7 percent reduction in leading edge temperature would not have been enough to prevent disaster. Even if the crew oriented the shuttle so that the belly of the craft was in shadow for more than two full days prior to entry, "cold soaking" the thermal protection system and lowering its temperature by 65 degrees, the outcome would have been the same.

"On STS-107, wing temps may have increased as much as 700 degrees in 400 seconds post EI (entry interface)," the entry options review stated. "A 65-degree decrease in EI wing temp would have resulted in (about a) 37-second delay in onset of same max temps and heat load."

Cain said the temperature improvement, however minor, possibly could be useful "if you had something that wasn't totally nominal in terms of TPS but it was maybe minor damage."

"Let's say on the wing leading edge you had a crack, you didn't have a breach yet but somehow you'd compromised the integrity of that part of the structure," he said. "Then that 6 or 7 percent, it might be significant for that case. I don't know enough to say today one way or the other. I do know that with respect to the 107 case it definitely wasn't significant."

During Columbia's flight, engineers concluded the foam impact during launch was not a "safety of flight" issue. As such, NASA managers did not request any spy satellite imagery to provide additional insight. Whether that was a good decision or not, the management team had no conclusive evidence that Columbia faced a serious threat.

But to have accomplished the extreme measures listed in scenario 3, planning would have had to begin almost immediately, meaning NASA managers would have needed convincing proof a safety of flight issue did, in fact, exist, within a day or two of launch.

"Excessive risks associated with any of the three options (scenario 1, 2 or 3 or any other combination) would require that significant and convincing data exist proving that the orbiter could not survive entry," the entry options review noted.

The scenarios all assumed "certified" re-entry profiles, meaning "our models match what we really see in flight," Cain said. "'Uncertified' means we don't know, we haven't done it for sure in flight, we haven't analyzed it and we haven't simulated it."

He said he could not imagine a real-world scenario that would lead the flight control team to order an uncertified entry requiring, for example, a higher- or lower-than-normal angle of attack to reduce heating on a specific area.

"There are certainly things that I can dream up where if you had some situation in flight that really put us in a bad situation, we're going to brainstorm and think of anything we can and at some point you've got to pick an option and go with it because you're running out of time," Cain said. "But for this case, I can't really imagine (that scenario)."

Ongoing analysis of recovered debris from the shuttle Columbia indicates the deadly breach in the ship's left wing may have been centered on a broken leading edge panel and not slightly outboard at a so-called "T-seal" as investigators were thinking last week, the Columbia Accident Investigation Board said today.

While a T-seal failure has not yet been ruled out, several lines of evidence now point to a failure at or very near the lower half of leading edge panel No. 8. That's where NASA investigators assumed the breach was located in their own failure scenario, which was briefed to the CAIB last week (see the April 20 status report below for complete details).

"I wouldn't say that T-seal No. 8 is totally out of the picture," said board member Roger Tetrault. "I've found that every time you think you have an answer ... something shows up that takes the wind out of your sails. But I'd say it was getting more probable that the breach is a little bit farther to the inboard side of the wing than where T-seal No. 8 is."

Columbia was destroyed Feb. 1 during re-entry when a breach in the leading edge of its left wing allowed a plume of super-heated air to eat its way inside, ultimately triggering a catastrophic structural failure. The damage is believed to have been caused, at least in part, by the impact of foam insulation that broke away from the shuttle's external fuel tank 81 seconds after liftoff Jan. 16. The foam slammed into the leading edge of the left wing at more than 450 mph.

The leading edge is made up of 22 U-shaped reinforced carbon carbon panels that handle the aerodynamic loads and extreme temperatures of re-entry. The panels are held in place at each end by U-shaped T-seals bolted to the front spar of the wing.

The day after Columbia's launching, military radar systems detected an object moving away from the shuttle. That mystery object, first reported by CBS News, is now believed to have separated from the breach area. CAIB investigators said last week a T-seal, or a substantial piece of a T-seal, was consistent with the "radar signature" and area-to-mass ratio of the mystery object.

That is still true. But today, Tetrault said additional evidence raises questions about the T-seal hypothesis. First of all, there is now some uncertainty as to whether recovered T-seal fragments came from the inboard side of RCC panel 9 or from father outboard on the wing. More telling, perhaps, X-ray analysis of slag-like deposits found on the inner surface of fragments from RCC panel 8 are consistent with a breach in the lower part of that panel. NASA has recovered three pieces that once made up the upper section of RCC panel 8 but nothing from the lower half.

"What you see on the X-ray you do not see visually," Tetrault said. "What you begin to see (are) deposits of heavy metals in certain patterns that we don't see when we look at it visually. ... There are small nodules of metal which are being deposited in a very uniform pattern.

"If you stood behind the RCC panel and took a paint brush and sprayed it at the back of the RCC panel, you would get deposits that look very similar to this. They are very uniform and very straight up and down. It begins to indicate that we're not getting a lot of side flow from, say, a T-seal position or even a panel further back."

Translation: Assume a hole in the lower half of RCC panel 8 and visualize the shuttle oriented in a 40-degree nose-up entry attitude. Hot air would enter such a breach at an angle, impinge on and ultimately burn through insulation on the front of the spar and eventually through the spar itself. Molten droplets of metal would have been blown backwards as this process proceeded, onto the inside surface of the upper part of RCC panel 8. The slag pattern seen in the X-rays Tetrault referred to is not consistent with the sort of "side flow" one would expect if the breach was located at the outboard T-seal or farther out the leading edge.

When the plume finally burned its way into the wing's interior, it hit the upper surface of the outboard side of the left main landing gear wheel well and burned through cable bundles mounted there in a top-to-bottom sequence.

Based on analysis of the known locations of sensor wires just behind the spar; the timing of sensor failures as the plume burned through various wire bundles; the observed heat damage to recovered debris from RCC panel 8; and heat damage seen in debris from areas adjacent to panel 8, it now appears the breach may have, in fact, occurred on the lower side of panel 8 as NASA investigators assumed when they developed their own "best fit" failure scenario.

The plume "probably hit the (insulation) material before it hit the spar and that was the first deposits that were made to the back of the RCC panels," Tetrault said today. "With regard to the cutting of the wires along the wheel well, actually by moving a little bit father inboard, you actually close the distance between those wires that were cut along the spar versus the wires that were probably cut along the wheel well and that makes it even more possible this sequence works properly."

Starting next week, investigators using a nitrogen gas canon at the Southwest Research Institute in San Antonio, Texas, will begin firing large pieces of foam insulation at selected wing targets to determine what sorts of damage might result from high-speed impacts.

Foam will be fired first at large areas of heat-shield tiles representative of the surface of the underside of Columbia's left wing. By early June, investigators hope to begin firing foam at a test rig that will simulate the left wing leading edge system between RCC panels 6 through 9.

"The testing starts this week," said board chairman Harold Gehman. "But the testing is limited by the target, not by the bullets. We have plenty of foam. But when we decided to do foam testing 30 days ago, we were talking about (landing gear) wheel well breaches and so the first test rig that we built was a wheel well. That's what we're ready to shoot at. Now we're talking about the leading edge system and it'll take us a couple of weeks to build a representative of the leading edge."

To make the test as accurate as possible, high-flight-time leading edge panels from other shuttles, as well as pristine panels from the prototype shuttle Enterprise, will be mounted on the test rig using T-seals.

"We're building up a leading edge section that's going to be essentially from panel No. 6 to panel No. 9 so that we can shoot at anything we want," Gehman said. "By the time we get ready to actually shoot at it, we'll know more about what angles we cover. We may want to shoot it at an angle that covers two T-seals and one panel or two panels and one T-seal. And we may shoot a couple of times."

He said the tests are being designed to indicate "whether or not a foam strike of the size and the velocity we saw in this particular event has the capacity to damage the leading edge system with sufficient damage to cause a hole that would initiate this event."

"Even if we do create damage on the test article that is of sufficient magnitude to initiate this event, that doesn't prove it did it," Gehman said. "It just proves it could have done it. And oh by the way, we have oversimplified to some degree what we're talking about here. I can pound on this table with a sledge hammer and not do any damage to the table, but (I might still) break a leg. The same thing could be true of the leading edge system. We could hit the outside of the leading edge system and not do any damage to it, but we could break the support structure, break a bolt, break a pin, in which case we would have something flapping in the breeze that might come off later.

"So we're going to carefully instrument the inside of this target so that we can, through analysis, better characterize all the ways that it could fail, not just a fracture through the RCC."

The NASA Accident Investigation Team today presented results of the agency's on-going analysis of the Columbia disaster to the independent board charged with finding the root cause of the disaster. That presentation is believed to have included one or more possible "best-fit" scenarios based on telemetry, recorded data and debris recovered to date.

One such scenario, which assumes a breach in Columbia's left wing at or near leading edge panel No. 8, was outlined on this page last weekend. Major elements of that scenario presumably were briefed to the CAIB today. Ten members of the board were either present for the briefing or listening in via telecon. Between 30 and 40 NASA and contractor personnel participated.

But in a short news release, the board said "in order to finalize a primary working scenario, more work is required in four areas of analysis.

"Those four areas are: aerothermal analysis, foam impact testing, testing of flown reinforced carbon carbon panels, and metallurgical analysis from debris," the statement said. "The NAIT provided an overview of the latest data recorder information and the CAIB issued its guidance based on that data and board investigatorsÕ continuing analysis of the latest orbiter debris."

The release concluded that "the CAIB has not reached any final conclusions and has not determined the cause of the loss of the shuttle and crew."

A source close to the board said CAIB investigators were in "violent agreement" on the basics of the accident scenario, i.e., a breach in the left wing led to the disaster. But there is not yet agreement on the finer details of how the plume of super-heated air entering the breach propagated through the wing and ultimately led to its failure.

"It has to do with the level of detail of the (NASA) scenario," the source said. "At a very high level, there's a whole series of facts that I believe we're getting very good agreement on. When you go and penetrate down to detailed timelines, to detailed interpretations, that is where we need to do more work.

"And that's part of what's laid out (in the CAIB press release) in terms of aerothermal analysis, how did the heat that got into the left wing propagate and can you really demonstrate that this sensor going up here is consistent with that or did it come from a different direction? You have to get down to that next level or two of detail. They called it multiple scenarios, I'd say multiple interpretations of the facts."

In case there were any doubts, the chairman of the Columbia Accident Investigation Board said Wednesday that finding the root cause of the shuttle disaster is only part of the panel's charter and that lawmakers in Washington have made it clear they expect broad changes in NASA's organizational structure.

And that's exactly what they're going to get.

"You can see the depth and the details that we are exploring (in) these issues of risk, risk management," Harold Gehman told reporters after the board's fifth public hearing. "We're going to interview many, many more experts on this subject and we're going to approach this issue probably more broadly than the Challenger report did. But we're also going to approach it with great care because of the 'law of unintended consequences.' We are not experts in this area, but clearly this area can stand some scrutiny."

"I'm just probably a little bit dense," a reporter said, "but it finally sunk in to me today, listening to some of your questions, that the management system-slash-culture, and I'm not sure how you separate those two, really is going to come under your microscope and you really are going to change it, aren't you?"

"That's correct," Gehman replied. "This is a result of my direct liaison with all of the (congressional) oversight committees, both the chairmen and minority members, who want a broader report than just what happened. And that's what they're going to get."

In earlier testimony before the board, a sociologist who spent years researching the organizational flaws that led to the 1986 Challenger disaster said that she, like former astronaut and CAIB member Sally Ride, hears "echoes of Challenger" in the way NASA managers came to accept as normal serious problems in a critical system.

In the case of Challenger, that critical system involved the O-ring seals in the joints of the shuttle's solid-fuel boosters. Flame from the interior of the rocket was never supposed to reach the O-rings, but heat damage was seen so frequently it came to be accepted as a normal occurrence and not a "safety of flight" issue. Challenger was destroyed by an O-ring burn-through.

In the case of Columbia, the critical system was the shuttle's thermal protection system. Foam insulation on the external fuel tank is not supposed to come off in flight. Yet dozens of protective heat-shield tiles on the shuttle's belly are damaged in virtually every flight by bits of foam debris breaking away during ascent. A large foam impact is believed by many to have played a role in the Columbia disaster.

In testimony at an earlier hearing, external tank engineers told the board that a top level requirement calling for no foam shedding at all remains on the books and that project engineers were well aware that a large enough piece of foam debris could pose a catastrophic threat to the shuttle.

A large piece broke off during a flight in October, hitting one of the shuttle's boosters. But foam shedding was not considered a safety of flight issue and while the impact was discussed at a flight readiness review before the next launch, it was not discussed in any detail during Columbia's FRR.

Eighty-one seconds after Columbia took off on Jan. 16, a suitcase-size piece of foam broke off the tank. One second later, it slammed into the leading edge of the shuttle's left wing at 450 mph, disintegrating in a shower of debris. A hurried analysis during the mission concluded the wing might have been damaged, but not to any catastrophic extent. It was not, in other words, a safety of flight issue and requests for close-up satellite imagery to inspect the area were turned down.

"I want to start from the point of view of Sally Ride's now famous statement, (that) she hears echoes of Challenger in Columbia," Diane Vaughan, author of "The Challenger Launch Decision," told the Columbia Accident Investigation Board Wednesday. "The question is what do these echoes mean? When you have problems that persist over time in spite of the change in personnel, it means that something systematic is going on in the organizations where these people work.

"Challenger was not just an O-ring failure, but it was a failure of the organizational system," she said. "What the echoes mean is that the problems that existed at the time of Challenger have not been fixed, despite all the resources and all the insights the presidential commission found, that these problems have still remained.

"And so one of the things that we need to think about is when an organizational system creates problems, the (corrective) strategies to make, the changes have to, in fact, address the causes in the system. If you don't do that, then the problems repeat and I believe that's what happened with Columbia."

Vaughan, a professor at Boston College, described the process in which well-intentioned NASA managers came to accept O-ring damage - or external tank foam shedding - as normal an "incremental descent into poor judgment" based on the "normalization of deviance."

"This was (a) design from which there were predicted to be no problems with the O-rings, no damage," she said. "An anomaly occurred early in flights of the shuttle and they accepted that anomaly. And then they continued to have anomalies and accepted more and more. This was not just blind acceptance, but they analyzed them thoroughly and on the basis of their engineering analysis and their tests they concluded that it was not a threat to flight safety.

"It's important to understand that this history was the background on which they made decisions on the eve of launch and that was one more step in which they, again, gradually had expanded the bounds of acceptable risk."

So how did this normalization of deviance, this eventual acceptance of damage in a system that was not supposed to experience regular damage, become standard operating procedure?

"It's important to know they were making decisions against a backdrop where problems were expected," Vaughan said. "Because the shuttle was designed to be reusable, they knew it was going to come back from outer space with damage and so there was damage on every mission. Put simply, in an environment like that, to have a problem is itself normal.

"So what to us in hindsight seemed to be clear signals of danger that should have been heeded, that is, the number of flaws in O-ring erosion that had happened prior to Challenger, looked different to them. What we saw as signals of danger they saw as mixed signals.

"They would have a problem flight, it would be followed by a flight in which there was no problem. They would have weak signals, something that in retrospect seemed to us to be a flight stopper to them was interpreted differently at the time. For example, cold, which was a problem with the Challenger flight, was not a clear problem and not a clear cause on an earlier launch.

"Finally, what we saw as signals of danger came to be routine," Vaughan said. "In the year before Challenger, they were having O-ring erosion on seven out of nine flights. At this time, it became a routine signal, not a warning sign."

By implication, NASA's acceptance of foam shedding as a routine event resulted in a mindset that played a role in the agency's post-launch decision-making process. The Boeing analysis of the foam impact was accepted even though it was based on limited test data based on impacts by much smaller pieces of debris. The analysis concluded there was no safety of flight issue. Requests for satellite imagery were never made, officials have said, because there was no safety of flight issue.

"What was obvious with Challenger was that on the eve of the launch that the concerns of the engineers were not prioritized," Vaughan said. "It also seems to be the case in the requests for the imagery from Columbia that concerned engineers discovering the foam strike at this point described it as large, there was nothing in their experience like this. It was the size of a Coke cooler. This was unique.

They wanted better imagery, she said, to help determine how extensive the damage might be.

"But somebody up the hierarchy canceled the request," Vaughan said. "The request did not go through proper channels, which points to me the significance of rules and hierarchies over deference to technical expertise."

In both Challenger and Columbia, she said, "following the normal rules and procedures seemed to take precedence. And we know that, in fact, in conditions of uncertainty, people do follow habits and routines.

"However, under these circumstances, where you have something without precedent, it would seem that this would be a time not for hierarchical decision making, but for a more collective, collaborative, what does everybody think, let's open the floodgates and not pull on the usual people but especially, what are the concerns of our engineers?

"And also to let up on the idea that you have to have hard data. Engineering hunches and intuitions are not what you want to launch a mission with. But when you have a problem that occurs that's a crisis and you don't have adequate information ... engineering hunches and intuition ought to be enough to cause concerns."

Vaughan also cited external pressures on the system - policy directives from Washington, budget shortfalls and unrealistic expectations - as factors affecting the way decisions are made. But the focus of her testimony was lessons learned from Challenger and how NASA might develop a better way to track problems and to identify those that pose potential risks before those risks are manifested.

"When you're working in a situation where problems are expected, you have problems every day and people are busy with daily engineering decisions, it becomes very difficult to identify and stay in touch with the big picture," she said. "How do you identify the trend so that people are aware when they're gradually increasing the bounds of acceptable risk? It is certainly true based on what we know about organizations and accidents that this is a risky system. And what we know is the greater the complexity of the organization, the greater the possibility of failure."

In a series of questions, Gehman displayed a strong interest in figuring out how to improve the system without falling victim to what he called the "law of unintended consequences."

"I'm still trying to understand the principles here," he said to Vaughan. "It seems to me that in a very, very large, complex organization like NASA is, with a very, very risky mission, some decisions have to be taken at middle management levels. Not every decision and not every problem can be raised up to the top. And there must be a process by which the level 3 and level 4 (managers), the decisions are taken, minority views are listened to, competent engineers weigh these things and then they take a deep breath and say OK, we've heard you now we're going to move on. Then they report up that they've done their due diligence, you might say.

"I'm struggling to find a model, an organization model in my head, when you've got literally thousands and thousands of these decisions to make that you can keep bumping them up higher in the organization with the expectation that people up higher in the organization are better positioned to make engineering decisions than the engineers. You said yourself hindsight is perfect. We've got to be really careful about hindsight.

"I'm trying to figure out what principles to apply," Gehman repeated. "We as a board are certainly skittish about making organizational changes to a very complex organization for fear of invoking the law of unintended consequences. So I need to understand the principles, I'm trying to figure out a way I can apply your very useful analysis here and apply it to find a way to figure out what the principles are we ought to apply to this case. So the part I'm hung up on right now is how else can you resolve literally thousands of engineering issues except in a hierarchical manner in which some manager, he has 125 of these and he's sorted through them and he reports to his boss that his 125 are under control. I don't know how to do that."

Vaughan offered two observations.

"Somehow or other in the shuttle program there is a process by which when a design doesn't predict an anomaly it can be accepted," she said. "That seems to me to be a critical point, that if this is not supposed to be happening, why are we getting hundreds of debris hits if it wasn't supposed to happen at all?

"It's certainly true that in a program where technical problems are normal, you have to set priorities. But if there is no design flaw predicted, then having a problem should itself be a warning sign, not something that is taken for granted. The idea is to spot little mistakes so that they don't turn into big catastrophes, which means spotting them early on.

"Two things, both of them NASA may be very aware of, is that engineers' concerns need to be dealt with. I can understand the requirement for hard data. But what about the more intuitive kinds of arguments? People feel disempowered because they've got a hunch or intuition and let somebody else handle it because they feel like they're going to be chastised for arguing on the basis of what at NASA is considered subjective information and they're not going to speak up. So there need to be channels to assure that, even giving engineers special powers if that's what's necessary. The other is the idea of giving more clout to the safety people to surface problems."

In the end, she said, "What we find out from this comparison between Columbia and Challenger is that NASA as an organization did not learn from its previous mistakes and it did not properly address all the factors the presidential commission identified.

"They need to reach out and get more information and look at other models as well. Thinking about how you might restructure the post-launch decision making process so that what appears to have happened in Columbia doesn't happen again. How can that be made more efficient? Maybe it needs to look more like the pre-launch decision process. But is there any evidence that NASA has really played with alternative models? My point about organizational structure is as organizations grow and change, you have to change the structures. But don't do it without thinking about what the consequences might be on the ground."

For its part, NASA has expressed no interest in Vaughan's conclusions or expertise. In a particularly insightful - and funny - exchange, board member John Logsdon asked Vaughan if anyone at NASA had ever called her for organizational advice, pointing out that her book is required reading in the Navy's nuclear training program.

"The book did get quite a lot of publicity," she replied. "I heard from many organizations that were concerned with reducing risk and reducing errors and mistakes. The U.S. Forest Service called and I spoke to hot shots and smoke jumpers, I went to a conference the physicians held looking at errors in hospitals, I was called by people working in nuclear regulatory operations, (by) regular businesses where it wasn't risky in the sense that human lives were at cost. Everybody called. My high school boyfriend called. But NASA never called."

Shuttle program manager Ronald Dittemore, the straight-talking "voice of NASA" credited with boosting the agency's image in the immediate aftermath of the Columbia disaster, will leave NASA after an independent accident investigation board completes its work, he told reporters today.

In an interview following a teleconference in Washington, Dittemore told CBS News he was not at all concerned about anyone getting the impression he had been sacked in the wake of the disaster.

"I made this personal decision some time ago in the fall," he said by telephone, waiting for a flight back to Houston. "Of course the timing was terrible right after (Columbia). So I just delayed it and (now) feel the timing is right. No, I'm not worried about the perceptions. It's one of those things where you make a personal decision and you feel that it's right and you just go with it."

The Orlando Sentinel and CBS News reported Saturday that Dittemore had planned to retire and take a job in private industry after the successful completion of Columbia's mission and that he stayed on in the wake of the disaster to oversee return-to-flight activities and to support the Columbia Accident Investigation Board.

Varous sources, however, said Dittemore planned to take a job with a particular shuttle contractor. But he told CBS News today that "I've made no agreements with anybody on any particular opportunities."

"Those opportunities in my opinion are wide open for me to discuss and think about and to entertain and whether it's in the human spaceflight business or some other business, I think they're all going to be something I'll look at. But at this stage, that's not my first priority and I'll work on that as time is available."

As a senior NASA manager, Dittemore would need a waiver from agency Administrator Sean O'Keefe before taking any job in which he would be representing a shuttle contractor in any future negotiations with the government. Without such a waiver - and they are rare - senior managers must wait a year before taking on such jobs.

During a teleconference from NASA headquarters earlier today, Dittemore said he began discussing his retirement with senior management last year and that now, as the accident probe begins transitioning from investigation to recommendations for corrective actions, was a good time to make his own personal transition.

"When you first come into a job like this, program manager for space shuttle, you recognize you have a tremendous opportunity," he said. "You get to work with some of the most capable and creative people ever gathered together in one place for one common cause. But you also recognize you cannot do it forever.

"Last summer, my wife and I and our family discussed the possibilities for the future and felt ... it was time for us to consider other opportunities. That's when the dialogue began with (senior management) about the possibilities and potential of leaving early in the spring of 2003.

"As the events unfolded in February, certainly all personal plans had to take a back seat," Dittemore said. "As the last two months have unfolded and now I see we're starting to move into a different realm of our investigation ... it seemed to me it was appropriate to talk with (management) again and pick this time to make a transition in leadership."

Dittemore, a former flight controller, flight director and chief of shuttle engineering, was named shuttle program manager in 1999. He said today it is important to begin the process of searching for his replacement now, before return-to-flight activities mature, so the new program manager can have time to absorb the intricacies of the job.

"It would be very important to have new leadership in place, to have that foundation established," he said. "And as you move forward over the coming months, building on that foundation from a new leader perspective, you're going to be that much more prepared, both from a leadership point of view and a team responding to that leadership, to move right into return to flight and then, picking up the flight rate again.

"I believe personally this transition time frame would be extremely beneficial to allow this new leader time to prepare, the time to respond to recommendations, the time to implement recommendations, to have a strong foundation, to have a strong springboard to jump forward into the coming years."

Michael Kostelnik, who oversees the shuttle and station programs for Bill Readdy, NASA's associate administrator for spaceflight, said he and Dittemore first discussed the program manager's departure last fall. And then the Columbia tragedy occurrred.

"Ron put aside his plans and his thoughts for pursuing opportunities because there clearly was a tough job to be done and I think you all were as much as anybody a beneficiary of his expertise because early on, when there were a lot of questions, Ron Dittemore was the voice of the program for the things that were happening, trying to put in context what we had experienced," Kostelnik said.

"I think most of you will agree that Ron during that time period did an outstanding job relaying some very complex, very technical thoughts in a way the media could deal with. And I think a lot of the credit NASA received early on for being open and being forthcoming with as much information as we had at the time, a lot of that we owe to Ron. In his role as the program manager, he did an outstanding job.

He said it will be difficult to find a suitable replacement for Dittemore because "it takes a certain kind of individual to step up to the challenge, not only a big program management job but one that has human life on the line."

"It's not very often we ask people in this country to do this," Kostelnik said. "It is a unique role and although we're sad to see Ron choose to go at this time, we know it's the right kind of thing for him if his chooses to do that. We wish him well as he pursues other opportunities downstream. We're all grateful for his 26 years of service."

Dittemore would not discuss the ongoing accident investigation, saying he did not want to comment on any potential findings before the Columbia Accident Investigation Board releases its final report this summer.

He did say NASA would need to do a better job tracking potentially dangerous trends across all the components of the vehicle to spot and recognize the potential severity of problems like foam insulation falling from the external fuel tank during launch. Foam shedding was a well-known known problem in the program and a foam impact on Columbia's left wing 82 seconds after launch probably played a role in the disaster. But foam shedding was never considered a "safety of flight" issue.

"Tracking trends is in the eye of the beholder and it's a difficult job," Dittemore said. "We have six or seven hardware elements in different locations. They have different databases of anomalies that may have happened either in manufacturing, or production or even in processing. We link those databases together today, but perhaps that linkage is not as optimized as it could be. And we're going to have to take a look at that, to do a better job of trending."

During shuttle mission STS-112 late last year, a large piece of foam insulation broke free and struck one of the shuttle's boosters. In the wake of the Columbia accident - and with the benefit of hindsight - many observers have questioned the wisdom of continuing to launch missions without first correcting the foam shedding problem.

Dittemore today defended the agency's response, saying every senior manager in the program was briefed on the matter.

"As a result of the foam strike on STS-112, there were actions that were given to the appropriate individuals and elements to discuss that strike, to understand its impact," he said. "There were actions to discuss that both at our change board within the program and at the level one flight readiness review. So that scenario and repercussions of that scenario were briefed across the program and to senior agency management in the flight readiness review and it was a healthy discussion.

"And so I consider that an appropriate response to an event," he said. "Now whether or not we nailed everything down and pounded it flat, I think hindsight might call that into question. But at the time, we followed our processes and we investigated it as thoroughly as we thought we should at the time and we'll develop lessons learned from that activity."

Dittemore also was asked about decisions made during Columbia's mission not to request spy satellite imagery of the shuttle to look for signs of damaged after engineers realized a large piece of foam insulation had struck the shuttle's left wing. Dittemore declined to comment.

"The thing to concentrate on is that over the last two months we have learned a lot about our system, about capabilities," he said. "And I believe we will find some lessons learned out of all these activities that we can correct. ... So my focus is not on what coulda, shoulda happened or what I might have said, my focus is on what (are the) lessons learned and how are we going to implement corrections and how are we going to be better in the future?"

As for his personal plans, Dittemore said he hopes to end up in aerospace when he moves into the private sector.

"The last thing on my priority list is my personal opportunities," he said. "I have invested most of my professional career in the human spaceflight business. I feel passionately about it, I think it's the right thing for us as a nation to do, I think it offers many side benefits to our society. And I think it's our destiny to do these types of things. I would hope that as I consider opportunities that those opportunities would remain in human space flight. That's where I feel emotionally attached."

Dittemore joined NASA in 1977 as a shuttle propulsion systems engineer, became a flight controller and ultimately a shuttle flight director. In 1992, he was named deputy assistant director of the space station program before transitioning to shuttle program management the following year.

In 1995, Dittemore became manager of space shuttle integration and served as chairman of NASA's mission management team, which oversees the day-to-day conduct of a shuttle mission. He was serving as manager of the shuttle engineering office when he was named to replace Tommy Holloway as overall manager of the shuttle program in 1999.

Investigators probing the Columbia disaster are developing an increasingly detailed scenario that explains the sequence of events that led to Columbia's destruction, a scenario that matches up with telemetry and recorded data as well as the damage seen in recovered debris. Only two out of 10 initial scenarios are still being actively developed by NASA investigators, officials say, but one of them, which assumes a breach in the left wing at or near leading edge panel No. 8, has emerged as the leading contender.

This scenario, No. 2 on the original list of 10 being assessed by agency managers and engineers, matches the telemetry downlinked from the shuttle before its breakup as well as data recorded on board by Columbia's payload experiment support recorder, or OEX, which was recovered near Hemphill, Texas, March 19. It also explains unusual communications dropouts and unexplained flashes seen in the wake of the shuttle as it descended across the southwest United States.

The scenario matches up well with the known point of impact where foam debris from Columbia's external fuel tank slammed into the left wing at 450 mph just 82 seconds after liftoff. In fact, OEX data from thermocouple V07T9895, located on the left wing spar just aft of reinforced carbon carbon panel No. 9, shows a slight temperature increase after the strike that may be indicative - this is not yet confirmed - of leading edge damage.

OEX data recorded during re-entry also is consistent with the severe heat damage seen in recovered debris, which strongly suggests a breach at or very near the underside of RCC panel 8, one of 22 such carbon composite panels making up the leading edge of the left wing.

The U-shaped panels, held in place by so-called T-seals that are bolted to the front face of the wing spar with inconel fittings, are designed to protect the wing from 3,000-degree re-entry temperatures and to handle aerodynamic loads as the shuttle falls into the thickening atmosphere.

"Independent teams examining the recovered debris are finding that the most likely location of (the) initial breach into the vehicle was into the left hand wing RCC panel 8/9 area," according to a summary of the scenario. Scott Hubbard, a member of the Columbia Accident Investigation Board, said much the same thing during a news conference last Tuesday.

The only other scenario still under active consideration by NASA engineers involves a breach in RCC panels closer to the shuttle's fuselage. But it does not fit the facts as closely as scenario No. 2.

NASA's development of failure scenarios is in support of the Columbia Accident Investigation Board, which is responsible for determining the root cause of the disaster. All such scenarios must be confirmed by the accident board and readers are cautioned that the scenario presented below is preliminary and subject to change. That said, here is how scenario No. 2 currently plays out.

Columbia fell into the discernible atmosphere 400,000 feet above the Pacific Ocean northwest of Hawaii - entry interface, or EI - at 8:44:09 a.m. on Feb. 1. Scenario No. 2 assumes the shuttle began its descent with significant damage to the underside of RCC panel No. 8. The scenario assumes spar insulation behind the RCC panels was directly exposed to re-entry heating.

During a news conference Tuesday, members of the Columbia Accident Investigation Board said investigators were focusing on the possibility a lost "T-seal" between RCC panels 8 and 9 might have left a gap an inch wide or greater between the adjacent panels, providing a direct path into the leading edge.

What caused the damage has not yet been pinned down, although most investigators believe it likely was caused by a piece of foam insulation that broke off Columbia's external fuel tank 81 seconds after liftoff and slammed into the left wing's leading edge one second later at some 450 mph. That impact may have cracked or penetrated an RCC panel or damaged a T-seal enough to result in failure.

The day after launch, military radars detected debris floating away from Columbia after a routine maneuver. The debris has not yet been identified, but radar tests are underway at Wright Patterson Air Force Base to determine whether a T-seal or a piece of an RCC panel could explain the sightings.

Regardless of the exact location of the breach - RCC panel 8 or an adjacent T-seal - it did not take long for hot gas to penetrate Columbia's left wing during re-entry. At 8:48:39 a.m., 270 seconds after entry interface, a strain gauge (V12G9921) in the leading edge near RCC panel 9 first showed an unusual increase.

"Thermal stresses build due to the breach in the wing and hot gas impingement on the spar," the scenario reads. "Pressure also starts to build in the RCC wing cavity adding to the load on the spar. The damaged wing causes a change in the load path that increases the wing spar strain. All these loads combine and put an off nominal strain on the spar."

Twenty seconds later, at 8:48:59 a.m., heat entering the RCC cavity through the presumed breach in panel 8 is first registered by a temperature sensor on a fitting between RCC panels 9 and 10 (V09T9910). Almost simultaneously, insulation on the forward face of the spar was compromised, allowing super-heated air to begin eroding the spar structure itself.

As the leading edge heating continued, temperature sensors on Columbia's left-side orbital maneuvering system rocket pod began sensing cooler temperatures than usual. This trend began developing at 8:49:49 a.m., or 340 seconds after entry interface. Computational fluid dynamics calculations indicate this was due to leading edge RCC panel damage affecting the flow of air over the wing.

At 8:50:00 a.m., the first in a series of brief communications drop outs were observed. Engineers now believe these interruptions were caused by the release of molten metals from the eroding wing spar and spar insulators into the hot air surrounding the space shuttle. The effect was similar to that of "chaff" released from military aircraft to foil weapons sensors.

At 8:50:09 a.m., the disrupted airflow over the leading edge of the left wing resulted in a cooling trend on the left side of Columbia's fuselage. Ten seconds later, at 8:50:19 a.m., increasing damage to the leading edge caused a thermocouple on the lower side of the wing near RCC panel 9 to begin sensing an off-nominal increase.

The inside surface of the left wing spar then began showing an unusual temperature rise (sensor V09T9895) at 8:51:14 a.m. This reading, following the RCC interface temperature increase noted at 8:48:59 a.m., confirms hot gas penetrated the cavity behind the RCC panels before entering the interior of the wing itself.

At 8:52:05 a.m., telemetry from the shuttle showed the start of an unusual yawing motion pulling the nose of the orbiter to the left. This was due to the growing damage to the leading edge affecting the aerodynamic behavior of the spacecraft. Computational fluid dynamics confirms this unbalanced force would continue to increase as the damage worsened.

Just four seconds later, at 8:52:09 a.m., the plume of super heated air in the RCC cavity finally burned through the wing spar itself, allowing hot gas to flow into the wing's interior. The plume of hot air impinged on the main landing gear wheel well box, about halfway down its outboard side, and began burning through cable bundles, cutting off data from scores of left wing sensors.

Based on the order of the cable bundle burn throughs, it is possible the hot gas plume impacted the upper skin of the wing and then was deflected along the skin to the wire bundles running along the upper part of the wheel well box. The top two cable bundles were damaged first, followed 30 seconds later by a third bundle lower down the side of the wheel well.

Analysis of the timing of the cable burn throughs appears to confirm the general location of where the burn throughs are believed to have occured and they are consistent with a breach at RCC panels 8/9.

The hot gas quickly spread throughout the interior of the unpressurized wing, triggering a sharp rise in the temperature being recorded by sensor V09T9895 - the same interior sensor that first detected higher spar temperatures a minute earlier - at 8:52:10 a.m. Seven seconds later, hot gas in the wing was first registered by a brake line sensor in the left main landing gear wheel well.

"As heat enters wing, thermal stresses are created and structural failures start to occur," reads a scenario entry for 8:52:19 a.m. "Hot gas continues to flow into wing, with pressure and temperatures building in the wheel well cavity." At 8:52:41 a.m., a second wheel well temperature sensor begins indicating an unusual increase.

In the meantime, the leading edge continued to deteriorate, affecting the flow of air over the wing. At 8:53:29 a.m., OEX data indicated the left fuselage began heating up as a vortex of disturbed air began moving forward along the side of the orbiter. The movement of this shock wave occurred at the same time as a sudden increase in yaw motion, which appears to confirm increasing leading edge damage.

It was at roughly this point, beginning at 8:53:44 a.m., that observers along Columbia's ground track began noticing debris falling away from the shuttle. At 8:54:20 a.m., the shuttle's "roll moment" changed sign, going from negative to positive. One explanation is an unexplained increase in lift on the left wing, presumably due to increasing structural damage. Another explanation, however, is damage to the upper surface of the wing.

"Hot gas continues to progress down the RCC and may burn through top of wing shedding skin and creating a hole," the scenario reads. "Damage pushes shock wave/vortex onto vertical tail leading to large increase in rolling moment."

Ground controllers at the Johnson space Center in Houston did not notice anything unusual until 8:54:24 a.m. when mechanical systems officer Jeff Kling informed flight director Leroy Cain "I've just lost four separate temperature transducers on the left side of the vehicle, hydraulic return temperatures. Two of them on system one and one in each of systems two and three."

Nine seconds later, at 8:54:33 a.m., a bright flash was noted by ground observers. This is now believed to be the result of maneuvering jet firings and interactions with debris falling away from the shuttle.

Then, at 8:56:16 a.m., the super-heated air entering the wing from the breach in the leading edge finally burned through the outboard wall of the left landing gear wheel well, triggering dramatic temperature increases in sensors located inside the wheel well. The plume is believed to have impinged directly on the left main landing gear strut. One such strut has been recovered and while engineers have not yet determined whether it was from the right or left landing gear, it shows severe melting consistent with a direct plume impingement.

Forty-four seconds after the wheel well was breached - at 8:57:00 a.m. - the plume burned through the forward inboard corner of the main landing gear door, providing an exit path for the hot gas in the wing. As a point of reference, the famous Kirtland Air Force Base telephoto view of Columbia, a photograph showing obvious signs of distress at the leading edge, was taken at 8:57:14 a.m.

At 8:58:03 a.m., a sharp aileron trim change was noted, an indication large pieces of the wing's overheated skin were blowing off and falling away. At the same time, the wheel well continued to heat up. All tire pressure and temperature data were lost during a 20-second period beginning at 8:58:38 a.m.

Ten seconds later, commander Rick Husband radioed, "And, uh, Hou(ston)..." The transmission was garbled. Thirty seconds later, Kling told Cain "We just lost tire pressure on the left outboard and left inboard, both tires."

"And Columbia, Houston, we see your tire pressure messages and we did not copy your last," astronaut Charles Hobaugh called form mission control.

"Roger, uh, buh..." Husband replied at 8:59:32 a.m., interrupted again by a comm drop out. It was the final transmission from the crew.

"The aerodynamic forces and the aero heating become more intense leading to further structural degradation of the vehicle," the scenario concludes. Columbia ultimately became aerodynamically unstable and broke up around 9:00:21 a.m.

Evidence supporting scenario No. 2 includes:

• Heavy slag-like deposits on the interior of RCC panel 8 fragments. The slag presumably is the result of molten aluminum spraying away from the point where hot gas impinged the wing spar.
• Severe heat damage on a tile carrier panel located between the lower edge of RCC panel 9 and the heat shield tiles permanently bonded to the lower side of the wing; erosion and slumping of the heat-resistant tiles indicate prolonged exposure to extreme temperatures.
• Severe heat damage to a tile carrier panel located just behind the upper edge of RCC panel 8.
• "Knife-edge" erosion of pieces from RCC panels 8 and 9; RCC erosion requires temperatures in excess of 3,000 degrees Fahrenheit; the knife-edge pattern, only seen on debris from panels 8 and 9, is indicative of such extreme heating.
• Recovery of an upper wing tile farther west than any other confirmed shuttle debris; the tile, originally mounted on the upper surface behind RCC panel 9, presumably fell off earlier than others because of the disturbed airflow and heating caused by the breach.

"Data is emerging that shows very significant and unusual damage at the interface between (RCC) panels 8 and 9," Hubbard said Tuesday. "For example, the splattered metal on panel 8 is much heavier than elsewhere and there is erosion of the reinforced carbon carbon elements, the ribs, what's called the lug where the attachment occurs.

"What we see is something that's not seen thus far anywhere else on the wing leading edge or indeed in the orbiter debris, which is pieces of a very tough material, this reinforced carbon carbon, eroded to knife edges. Where a normal piece is a half an inch (thick), it's been eroded to about the thickness of a dime. This kind of heating event indicates long duration, very extreme heating.

"We don't know quite what to make of this yet, other than what I said, a very severe heating event in the intersection between panels 8 and 9," Hubbard said. "The carrier panel, that is, the piece of material that goes between the reinforced carbon carbon and all the tiles on the bottom of the orbiter, that carrier panel also shows severe heating. It's slumped, like you overheated Styrofoam. That's another indication of some very severe heating events."

Shuttle program manager Ronald Dittemore, the clean-cut, straight-talking engineer whose daily briefings in the wake of the Columbia disaster won widespread respect, plans to leave NASA in the near future, sources say, presumably to take a job in private industry. Calls to Dittemore's home Friday evening and Saturday were not successful and NASA officials were not immediately available for comment.

Reliable NASA and contractor sources, however, said Dittemore made plans to leave the space agency before Columbia's ill-fated mission and that he had planned to step down once the flight was complete. Those plans changed in the wake of the Feb. 1 disaster and he remained on the job to help coordinate NASA's investigation of the tragedy.

Dittemore's daily briefings lasted just a week before the independent Columbia Accident Investigation Board took over the public conduct of the accident probe. But Dittemore's willingness to share initial flight data and to answer questions in a public forum was in stark contrast to NASA's no-comment response to the 1986 Challenger disaster 17 years earlier. While some NASA insiders privately groused about Dittemore's openness, many more praised his performance, crediting him with convincing skeptics that NASA had the right stuff to deal with the disaster.

"Let me say it is with some relief that I welcome (the accident board) here," Dittemore said Feb. 6, in his final news briefing. "We need their expertise, we need their independent look at what we have been doing and we will work closely with (board chairman Harold Gehman) and his board.

"These five days have been exhausting to the team. They have been difficult emotionally and physically. But we're going to carry on and we're going to continue our determination to find the root cause and do so as quickly and reasonably as we can."

As a senior NASA manager, Dittemore would need a waiver from agency Administrator Sean O'Keefe before taking any job in which he would be representing a shuttle contractor in any future negotiations with the government. Without such a waiver - and they are rare - senior managers must wait a year before taking on such jobs.

The specifics in this case are not yet known, but the loss of Dittemore's firm hand at the helm of the shuttle program will be keenly felt.

"He did a good job, Ron is a solid manager," said one senior aerospace manager. "One of his traits was he was not unwilling to make hard decisions. He made decisions that weren't always popular, but they were the right thing to do."

Dittemore joined NASA in 1977 as a shuttle propulsion systems engineer, became a flight controller and ultimately a shuttle flight director. In 1992, he was named deputy assistant director of the space station program before transitioning to shuttle program management the following year.

In 1995, Dittemore became manager of space shuttle integration and served as chairman of NASA's mission management team, which oversees the day-to-day conduct of a shuttle mission. He was serving as manager of the shuttle engineering office when he was named to replace Tommy Holloway as overall manager of the shuttle program in 1999.

"The space shuttle is more reliable, more capable and more efficient today than ever before," Dittemore said in a statement when he took on the program management job. "At the same time, with assembly of the station, the shuttle has a bigger job ahead of it than ever before. As we do that job, above all, my goal is to fly the shuttle safely and continue the tradition of excellence that has been instilled in this program.

"The shuttle has a lot of life ahead with the capability to continue to fly for decades to come, and we plan to continue to make it as safe and efficient as possible as we build the station and prepare for the future."

As expected, the Columbia Accident Investigation Board today released its first two interim recommendations to NASA, calling for routine spy satellite imagery of shuttles in orbit and detailed pre-flight inspections of the protective panels on the leading edges of the shuttle's wings. A breach in a reinforced carbon carbon (RCC) panel on Columbia's left wing is believed to have triggered the shuttle's breakup during re-entry Feb. 1.

An agreement to make classified on-orbit imagery a routine requirement during shuttle flights is already in work by NASA and the National Imagery and Mapping Agency, or NIMA. But what might be required to implement the board's other recommendation - extensive pre-flight tests of the shuttle's leading edge panels - and how long such tests might take to complete is not yet clear.

"This recommendation was issued because of the board's finding that current inspection techniques are not adequate to assess structural integrity of RCC, supporting structure, and attaching hardware," the board said.

During Columbia's launching Jan. 16, a chunk of external tank foam insulation broke off 81 seconds after liftoff and slammed into the left wing leading edge, at 450 mph, one second later. NASA managers decided not to request satellite imagery of the shuttle's wing after concluding the orbiter could safely land as is. That decision has faced criticism and second guessing in the aftermath of the disaster and the accident investigation board has concluded such imagery should be routine for future flights.

"Prior to return to flight, NASA should modify its Memorandum of Agreement with National Imagery and Mapping Agency (NIMA) to make on-orbit imaging for each Shuttle flight a standard requirement," the board stated today.

The interim recommendation included three supporting facts: A) The U.S. government has the capability to image the shuttle on orbit; B) a Memorandum of Agreement exists between NASA and NIMA regarding on-orbit imaging of the shuttle; and C) "during the flight of STS-107, there were no on-orbit images taken of sufficient resolution to assess the orbiter's condition."

But the board's primary recommendation was for NASA to implement non-destructive evaluation, or NDE, to determine the heath of the RCC leading edge panels before shuttles are cleared for launch.

"Prior to return to flight, NASA should develop and implement a comprehensive inspection plan to determine the structural integrity of all Reinforce Carbon-Carbon (RCC) system components," the board wrote. "This inspection plan should take advantage of advanced non-destructive inspection technology."

The board noted that the RCC panels are a non-redundant, "crit 1" system, meaning a failure results in the loss of the vehicle and its crew. During initial manufacturing, the carbon-carbon composite is tested at various stages in the assembly process "by physical tap, ultrasonic, radiographic, eddy current, weight gain, and visual tests."

"In addition, a flat plate control panel made in parallel with the production piece is destructively tested at various points in the production process," the board wrote. The projected lifetime of the panels assumes the material and its support hardware are free of any internal defects.

Going into Columbia's mission, "visual external inspections and tactile checks" were the only tests required to assure the RCC panels were safe to fly unless visually obvious problems results in replacement.

But in the wake of the Columbia disaster, "non-destructive testing of some post-flight RCC components has shown indications of RCC material defects not previously identified by visual inspection methods currently employed," the board wrote, recommending the implementation of routine NDE of the leading edge.

A major question mark, however, is what technology is needed to implement such tests and inspections and how long it might take to thoroughly examine the 44 RCC panels on each orbiter. And the board did not specifically state whether such inspections are required before return to flight or before every flight.

Ongoing analysis of sensor data and recovered debris indicate the deadly breach in the shuttle Columbia's left wing was located slightly outboard of the best previous guess, possibly at or near the intersection of leading edge panels 8 and 9, investigators said today. Recovered debris from that area shows damage consistent with extreme, prolonged heating and matches up well with telemetry and recorded data showing unusual temperature increases in the early phases of the shuttle's catastrophic re-entry.

The Columbia Accident Investigation Board also revealed today that investigators are now focusing on a so-called T-seal, part of the leading edge system, as a possible candidate to explain a mystery object seen floating away from the shuttle on the second day of its mission. Board members initially believed the object might have been a carrier panel that somehow shook loose following impact by a piece of foam debris during launch.

But testing at Wright Patterson Air Force Base to determine the radar signature of various potential debris candidates does not match up with a carrier panel. In addition, search crews have now recovered fragments from all of the carrier panels originally located behind leading edge panels 5 through 10. Engineers now plan to test a variety of components, including a T-seal, a large fragment of a reinforced carbon carbon - RCC - leading edge panel and other leading edge components to find a better match with the radar data.

"Given that we have found pieces of all of the carrier panels in this region, it's looking less likely that was a drift away object, although it could have been an impact zone," said board member Scott Hubbard.

He said ongoing analysis of launch video shows a large piece of external tank foam insulation struck Columbia's wing between RCC panels 7 through 9. Recovered fragments of these RCC panels show slag-like deposits on their inner surfaces, presumably the result of a plume of super-heated air melting underlying components and splashing molten material on nearby components.

"Data is emerging that shows very significant and unusual damage at the interface between (RCC) panels 8 and 9," Hubbard said. "For example, the splattered metal on panel 8 is much heavier than elsewhere and there is erosion of the reinforced carbon carbon elements, the ribs, what's called the lug where the attachment occurs.

"What we see is something that's not seen thus far anywhere else on the wing leading edge or indeed in the orbiter debris, which is pieces of a very tough material, this reinforced carbon carbon, eroded to knife edges. Where a normal piece is a half an inch (thick), it's been eroded to about the thickness of a dime. This kind of heating event indicates long duration, very extreme heating.

"We don't know quite what to make of this yet, other than what I said, a very severe heating event in the intersection between panels 8 and 9," Hubbard said. "The carrier panel, that is, the piece of material that goes between the reinforced carbon carbon and all the tiles on the bottom of the orbiter, that carrier panel also shows severe heating. It's slumped, like you overheated Styrofoam. That's another indication of some very severe heating events."

Temperature data from the OEX recorder recovered March 19 shows severe heating in the cavity just behind RCC panel 9 and "we have the debris speaking to us and saying something severe happened in the interface between panels 8 and 9," Hubbard said. Even so, he emphasized other explanations might be possible and "this story of exactly what happened and where it happened, while we're closing in on it, is going to continue to evolve."

In the meantime, engineers are gearing up for a critical series of tests at Southwest Research Institute in San Antonio to validate or disprove the leading suspicion about what caused the disaster: The impact of foam debris 82 seconds after liftoff.

Using a nitrogen gas canon, engineers plan to begin firing foam at representative heat-shield tiles by the end of the month. By mid May, a leading edge mock-up, including RCC panels 6 through 10, will be ready for impact tests. Panels from the prototype shuttle Enterprise will be used on the mockup, along with flight panels from the shuttle Discovery that closely match Columbia's panels in terms of age and flight experience.

The idea is to fire foam closely matching the debris from Columbia's external tank at leading edge components at some 500 mph to determine what sort of damage might result. Of special interest are the T-seals bolted to the front of the wing spar that form the interlocking framework holding the RCC panels in place. The T-seals, in turn, are held in place by two bolts at each end and it's possible to lose or break a T-seal without breaking an adjacent RCC panel.

"The space between panels 8 and 9 happens to line up with where the T-seal is," Hubbard said. "So that has become a suspicious region. And in the preliminary planning for the impact tests, we're putting strong consideration on hitting not the middle of a panel, but that intersection where the T-seal is and seeing what happens, what kind of damage would be caused."

Board chairman Harold Gehman said a lost T-seal would leave a slot-like gap between adjacent RCC panels. That gap could be an inch or more in width, providing a direct path into the leading edge. If a T-seal was damaged during launch and somehow separated from Columbia on the second day of the mission, the left wing would have been vulnerable to hot gas intrusion during re-entry on Feb. 1. Engineers now are running complex calculations to determine if a slot-like initial breach can explain the entry data and observed debris damage.

"The jury is still out on how much of a breach you would have to have in order to create the effects you see, in particular the understanding or the feeling, from the visual data that we may not be dealing with a round hole, but instead something that created a long narrow slit," Hubbard said. "So the thermal dynamics people have gone back to the drawing board to figure out what a long, narrow slit would do as distinguished from a hole."

The search for Columbia's wreckage is now drawing to a close. Underwater searches are virtually complete, grid searches on land have covered 78 percent of the primary debris field and aircraft searches are 80 percent complete. More than 70,000 pieces of shuttle debris have been recovered, representing about 78,000 pounds or roughly 36 percent of Columbia's dry weight. In early May, NASA plans to shut down its Disaster Field Office in Lufkin, Texas, and to consolidate remaining recovery efforts at a Columbia Recovery Office at the Johnson Space Center in Houston. In addition, four Incident Command Posts managed by the U.S. and Texas Forest Services will be closed by the end of the month.

Shuttle program manager Ronald Dittemore, in the first issue of a new internal newsletter aimed at keeping the shuttle workforce informed about the progress of the Columbia investigation, said "we have turned the corner" and "we have reason to be optimistic." He also said Linda Ham, manager of NASA's mission management team during Columbia's flight, will represent the shuttle program office in return-to-flight planning.

"I recently received a letter in the mail expressing support for the human space flight program and reaffirming their belief in our team that we would "find it, fix it and fly," Dittemore wrote in a section titled "Program Manager's Comments." "I wholeheartedly agree with this simple statement. It summarizes our efforts and our unceasing dedication to return to flight.

"We have made great progress since February 1st. I believe we have turned the corner and are beginning to see the light at the end of the tunnel. Fault trees are beginning to be closed. Special testing is being planned and completed. Important clues that will lead to the root cause are being identified and assessed.

"We have reason to be optimistic. Our teams are continuing to work very hard and have been fortunate in recovering important elements of Columbia that will help us determine the root cause of the accident. A special return to flight planning team, led by Col. Jim Halsell, has been established and we are embarking on the path that will lead us back to flight. Ms. Linda Ham will represent the Space Shuttle Program on this planning team."

The newsletter, dated April 4, also said the Columbia Accident Investigation Board has indicated "their belief that major activities will wrap up in 6-8 weeks. CAIB findings and recommendations will be identified to NASA as soon as the findings are agreed upon by the CAIB."

In addition, the newsletter said the leading candidate for replacement of foam insulation in front of the struts holding the nose of the orbiter to the external fuel tank is "a simple metal cover that could be installed at KSC on the delivered tanks. A final down select for the design will be completed prior to the end of April."

Foam debris falling from the so-called bipod strut area hit Columbia's left wing during launch.

Harold Gehman, chairman of the Columbia Accident Investigation Board, said today two interim recommendations will be released late this week or early next and that the panel likely will write its final report in June. Gehman also said "privileged," or confidential testimony from senior shuttle managers, engineers and technicians, will never be made public, either in a public hearing or in final report transcripts.

"If a witness under privilege tells us that a board meeting was a sham and people weren't free to speak up or something like that, then we will corroborate that, which will see the light of day," Gehman said in a brief interview following a news conference. "But as far as the public hearings are concerned, the public hearings are essentially board meetings in public. That's what we do all day long. We interview, we talk to people like that and it's simply an opportunity for the public to see how we work and go along with us. I mean, you're learning at the same time we're learning. It's not a press event, it's not a news event, it's just an opportunity to do some of our business in public. And that's the intent of it."

The CAIB is interviewing senior shuttle managers and engineers under conditions of confidentiality. By granting such privileged status, the board guarantees witnesses their testimony will never been made public and that criticisms of systems, procedures or other individuals will not be traceable. The idea is to encourage a more open, more honest dialogue with board members and investigators.

Under this policy, the public will never hear directly from Linda Ham, for example, chairman of NASA's mission management team during Columbia's flight, or any other managers responsible for deciding what to do about the foam impact during launch that is now believed to have played a major role in the disaster.

Asked if conducting such interviews in secret might represent a disservice to the public, Gehman said "we consider this to be a strength, not a weakness."

"We are going to be able to get at the intricacies of that process in a way that you could never, the Rogers Commission (that investigated the Challenger disaster) could never, for example, get," Gehman said. "By granting people privilege, we're going to find things out that they wouldn't say in public. And so we believe we'll actually be able to go deep and get a richer and more fundamental understanding of these processes than you can in public.

"Now in order for it to get into our report, we're going to have to corroborate what they say. Just because somebody's mad at his boss or somebody doesn't listen to his opinion, he can say that in privilege. That doesn't mean it's going to make it into our report."

Gehman said the board is finalizing two interim recommendations, one formally asking NASA to routinely obtain in-flight imagery of shuttles to look for signs of damage - already in work by NASA - and the other aimed at implementation of non-destructive evaluation or testing - NDE - to check the health of various systems like the panels making up the leading edge of the shuttle's wing. Gehman said those interim recommendations are undergoing final technical review and could be released as early as Friday.

As for the board's future activities, Gehman said "I think the months of April and May, I suspect we're still going to be receiving data."

"But I suspect in May, the rate of receiving things is going to start to taper off," he said. "We're still interviewing witnesses, still picking up debris, we've got the OEX (data) recorder, which hasn't been analyzed yet. So we're clearly going to be on the receiving end through at least the rest of April.

"I think around May it's going to shift to where we're going to start doing more deliberations and more output-oriented things, issuing more interim recommendations and then start to shrink the staff down. In June, the board's going to have to roll its sleeves up and start writing."

Asked if the final recommendations might include any directives to redesign or strengthen the leading edge systems, Gehman said "I can't give you any sense of that at all." But he said the CAIB is "very concerned about the characterization of an aging vehicle."

One such age-related issue is the health of the carbon composite leading edge panels that protect the shuttle's wings from the fierce heat of re-entry. At present, engineers do little more than visually inspect the panels between flights for signs of damage that might need repair. They do not subject the panels to more sophisticated types of NDE that might reveal hidden problems.

"If NASA doesn't know the condition of its vehicles, we would be leery of recommending that they fly," Gehman said. "Some of these things might be pretty simple, you know, a CAT scan of the leading edge, you can do it in place, you don't have to remove it, if it passes you're good to go. But there are other areas, too.

"I'll tell you one of the things that's really hanging out in my mind is, I find it to be an intellectual weakness to take the O-ring story and the foam story and keep beating NASA over the head with it unless you could point to exhibit C, D and E."

He was referring to the O-ring seal failure that doomed Challenger in 1986 and the foam debris impact to Columbia's left wing during launch that is believed to have led to the wing's failure during re-entry. In both cases, NASA continued to launch shuttles even though engineers knew the systems in question - booster O-ring seals and external tank foam insulation - were not operating properly. But Gehman said two such instances do not necessarily make a trend.

"What are the other three things that are continuously sending you signals? I'd like to find what those other three things are," he said. "I'd like to find some more things that are kind of strange looking, kind of funny looking and NASA says we're going to live with them. ... I find it to be not very intellectually honest to just beat (NASA) about the hindsight thing. I'd like to find other funny looking numbers they've also decided to live with and then be able to make a judgment about that."

Editor's Note...
The following status report recaps highlights from two days of hearings before the Columbia Accident Investigation Board. A separate status report will be filed later covering a CAIB news conference Tuesday.

The shedding of foam insulation from space shuttle external tanks was never considered a safety-of-flight issue, experts told the Columbia Accident Investigation Board this week. But tank engineers have worried for more than 20 years about potentially catastrophic impacts and a top level program requirement held that any shedding of large, potentially dangerous pieces of debris was forbidden.

Even so, despite years of work to eliminate foam shedding, the fleetwide average for foam impact damage resulting in tile blemishes more than one-inch across runs about 30 per mission. So instead of meeting the still existing design goal of no shedding, shuttle program managers somehow came to accept a certain level of impact-related tile damage as a normal occurrence.

In hindsight, the reasoning that allowed NASA to continue launching space shuttles even after a large piece of foam debris broke away from the shuttle Atlantis last October is even more difficult to understand given the critical nature of the shuttle's fragile heat-shield tiles and other insulation. The thermal protection system, or TPS, is one of three systems that have no backup and are not considered fail safe.

"The shuttle was designed with the philosophy that you should not have a system in which you suffer a failure and you lose your vehicle or your crew," said James Halsell, a senior shuttle commander and former launch integration manager at the Kennedy Space Center. "It needs to be fail safe. Furthermore, there was a high operational desire to be fail operational, that is, suffer a failure and still complete the mission.

"The basic requirements are the vehicle and all of its subsystems will be fail safe. From the very beginning, there were three systems which it was acknowledged we could not achieve that desired goal. The thermal protection system was one, it was recognized as being criticality 1, that is, if it doesn't work you're going to lose the vehicle and/or the crew. And we don't have a backup system to it."

Columbia's left wing was struck by a large piece of external tank foam debris 82 seconds after launch Jan. 16. The debris broke away from an aerodynamic ramp in front of the left bipod attachment strut, one of two struts that hold the nose of the orbiter to the tank. The impact is believed to have damaged the wing's leading edge enough to permit a catastrophic plume of super-heated air to burn its way into the wing during re-entry Feb. 1, triggering the shuttle's destruction.

Investigators now believe the fatal breach occurred just outboard of leading edge panel No. 6 - the panel in the center of the foam debris impact "footprint" - somewhere at or near panels 7 through 9. Ongoing wind tunnel testing shows unusual temperature increases seen on Columbia's aft left rocket pod can be explained, for example, by a breach at or near panel 9. Whether the breach occurred because of damaged leading edge panel or because of damage to a so-called carrier panel is not yet clear.

In any case, during a flight by Atlantis late last year - mission STS-112 - a large piece of foam broke away from the bipod ramp area and hit one of the shuttle's solid-fuel boosters. That impact did not cause any major damage, but NASA managers ordered engineers to explore redesign options to minimize or eliminate such bipod ramp foam shedding. But they did not declare the shedding an "in-flight anomaly," or IFA, with a constraint to flight. In other words, the shuttle program could continue flying while the redesign was implemented.

The reasoning behind that decision was that foam shedding did not represent a "safety of flight" concern. It was viewed as a maintenance issue only, i.e., the impact could cause re-entry heating damage requiring tile repairs after a flight that could delay processing for a shuttle's next mission.

How that conclusion might have evolved into a mindset is the subject of intense scrutiny by the Columbia Accident Investigation Board. For board member Sally Ride, the first American woman in space and a member of the presidential commission that investigated the 1986 Challenger disaster, the nature of that evolution is of more than passing interest.

"We're actually trying to understand that," she said Tuesday at a post-hearing news conference. "There is the guiding principle that nothing should hit the orbiter. And it's written in the documentation. The other thing that's written in the documentation is that the TPS (thermal protection system) is criticality 1. That's on the one side and on the other side is that through the history of the hundred flights or so, there's been debris impacting the orbiter on virtually every flight.

"I can tell you, tile damage was a very big concern in the early stages of the shuttle program, a huge concern," she said. "Everyone was worried about the main engines on ascent and the tile on re-entry. Those were the two leading issues in the early days of the program. The early flights came back with some tile damage, but in almost every case it was a turn-around issue.

"As time went on, people, I think. got used to tile damage from debris off the external tank, got used to repairing that between flights, got used to thinking of it as a turnaround issue and I think we saw that in the way that problems were handled after STS-87, STS-112 and during 107. And that is just the sort of thing that we're trying to get at.

"Of course, during the Rogers Commission, one of the things that came out early on was that the (solid-fuel booster) O-rings (blamed for the mishap) were not a problem for the first time on that flight, on 51L (Challenger). They'd been a problem on not just one, not just two, not just three, but several shuttle flights before the Challenger accident. It was almost the case that if you, you know, the famous discussion of Richard Feynman, that you survived it the first time so suddenly it becomes more normal. And it happened enough and now it's a normal occurrence. I think that we're trying to understand whether that same thinking crept in with the foam off the tank."

Richard Blomberg, president of Dunlap and Associates Inc. and former chairman of NASA's independent Aeropace Safety and Advisory Panel, said in the end, the Columbia disaster will be blamed on human error or oversight. But he said NASA could not be faulted for not trying as hard as humanly possible to prevent such oversights from happening.

"I'm a human factors person and I'm the first one to tell you humans are perhaps the mosty fallable part of any system," he told the CAIB. "We design the systems, we operate the systems, we make the decisions to go. So somewhere in whatever you're going to find for Columbia, humans failed. But the question I would want asked is did we fail through malice, did we fail through neglect or did we fail through ignorance? If we failed through ignorance, let's learn from it, let's increase our vigilence and make the system better and keep that closed loop going. That's all we can do with any vehicle.

"I am sure that whatever caused the accident escaped a process at some point," he added. "It had to have, because it flew. So at some point in the process, somebody missed it and it may have been my panel. We may have been staring it in the face and missed it. But it wasn't for lack of trying, I'm convinced, on the part of all concerned because as I said in my opening remarks, I just have never seen a system more safety conscious and people more dedicated to safety. That's not a hundred percent assurance, it just says their heart is in the right place."

For their part, tank experts have known foam shedding was a potentially serious problem for years. And they have been aware all along that the tank isn't supposed to shed any foam in the first place. But they, like everyone else, grew to accept the reality of foam impacts as an unavoidable aspect of flight.

"The program level requirement is that we shall release no debris that is harmful to the orbiter," said Lee Foster, a senior engineer at the Marshall Space Flight Center with extensive experience in external tank issues. "So it's a very subjective thing and while we have been working hand and glove with the system over the years, you know, we've worked with them on debris teams and all that, again, everything was judged as a maintenance item and not a safety of flight issue. I'm not going to say that was right or wrong in the past, but that's the way it happened."

In a hearing Monday, Air Force Maj. Gen. Kenneth Hess asked Foster and Scott Sparks, a senior tank engineer at Marshall, "did you ever think that it was possible to pop a big enough piece of foam of this external tank to severely damage the shuttle itself?"

"The answer is yes," Foster said. "We have large areas where we have closeout materials that we know are hard to spray. So yeah, we are always worried there's going to be a big piece that comes out that would throw us over that maintenance item line."

Said Sparks: "I agree with Lee, we watch (ascent) very closely. Because we know that material could come off and cause some damage. We understand that's a potential and we understand it does require a lot of focus on that material to make it not do that."

So why, in the wake of mission STS-112, didn't NASA managers view the bipod ramp foam shedding as a safety of flight issue?

"It looks to me like something hitting the thermal protection system or damaging the thermal protection system, it's a crit 1 system and therefore damaging, anything that hits the TPS ought to be an IFA, looks to me like," said CAIB chairman Harold Gehman. ""How in the world ... does the system determine there's no safety of flight issue?"

Halsell, who until recently oversaw launch processing and provided the final "go" for flight for the agency's mission management team, said engineers and managers believed the STS-107 foam shedding event was a random occurrence and not evidence of a generic problem.

"The nature of the rationale that was presented in that forum was that the external tank (project) had gone back, even at that point in time, before they had responded to the follow on action, and they had vigorously tried to understand did we do something different with the tank where we had this problem as compared to all the other tanks that had flown successfully?

"And what came out of that was they felt comfortable there was no generic new issue that they could identify ... that they had no generic issue that indicted follow on future tanks that we were going to go fly. ... There was no elevated level of concern that anything liberated from that location would have impacted the orbiter. And what all this added up to was the conclusion that we had not moved up and to the right on the risk matrix with respect to the previously accepted hazard."

Sparks and Foster testified that despite more than two decades of work to eliminate foam shedding, the shuttle's external tank continues to release enough debris during every ascent to cause an average of 30 or so "hits" on the shuttle's belly that cause blemishes larger than one inch across. In at least five cases, foam broke away from the bipod ramp area.

The majority of these shedding events occur in the intertank region of the external fuel tank, the section that separates the ET's liquid oxygen and hydrogen tanks. The intertank features ribbed structural members, or stringers, and other components used to attach the solid-fuel boosters and the bipod assembly struts that hold the nose of the orbiter in place.

The ribbing, bolts in the flange area where the top of the hydrogen tank connects to the intertank, the bipod components and other components must be insulated by hand with sprayed-on foam. How that foam is applied and how it bonds with the complex geometry of the underlying structure is believed to play a role in debris shedding. Air inside voids in the foam, for example, can liquefy once the tank is loaded with supercold propellants. During launch, such liquid air can warm up and explosively evaporate, blowing off pieces of insulation.

"You've got a foam that has to be applied over a certain type of underlying structure and making that so that it is free from shedding seems to be, over the last 20 years, a tough thing to do," observed board member Scott Hubbard.

"Yes sir. And generally, you've really got to go back to the beginning as far as the design of the tank," said Sparks. "I'm not so sure the TPS (thermal protection system) processors were in the same room when they designed the tank.

"Because it was designed structurally to be optimized. It's not designed for the TPS to be processed on there. If you were to redesign completely a tank, you would make the exterior a bit smoother, you know, you'd have those people in the same room."

In the meantime, despite ongoing work to eliminate shedding, the current impact average evolved into a baseline of sorts that is accepted as a routine occurance.

"This is a very impressive list of all the things that have been done over the past 22 years to address the shedding of external tank debris," Hubbard said. "Nevertheless ... the line is pretty much a flat line there, whether it's 10 or 15 or 20 or whatever. So do you see any way to drive that line down to zero or near zero?"

"We're always trying to improve the product," Sparks said. "But we don't want to change the product unless we're justifiably sure that's going to improve the product. ... There have been several improvements that I think the program has been proactive in pursuing. But indeed, there's still a level (of debris) and generally they're coming from those closeouts in that intertank region that seem to be problematic. So we try to improve our processing to the extent possible but thus far, it's staying in that (average) range."

Hubbard followed up, saying "I guess if I had a problem that in over 20 years, the average stayed essentially constant, it seems to me that that might argue something about the basic chemistry, or basic properties of the thing you're dealing with, the foam itself. Do you see the foam as being difficult to control in a very precise manner?"

"No, I don't, Mr. Hubbard," Sparks replied. "Really, what I'm seeing ... is that it's an issue of trying to process that material the best you can. If I had to take a guesstimate as far as the location where we're shedding the most debris, it would be in that hydrogen-intertank-flange area. That's just a hard area to close out, there's a lot of bolts there and when you're spraying that material a lot of potential for shadowing of that foam and possibly having some voids behind that. We've always attributed that to the reason why we're losing some of that material from that area."

As for STS-112, Sparks said "the position was that it was a random occurrence of faulty processing and that nothing had changed in this system to indicate that was a systemic issue as far as processing or material, they had gone and done their homework as far as that goes."

In earlier testimony, Halsell strongly defended NASA's post-Challenger management practices, saying problems are thoroughly discussed before each flight and that engineers are encouraged to weigh in with contrary opinions or to challenge assumptions.

"I know that after Challenger it was recognized that these processes were not as disciplined and rigorous as they should be and what I hope to tell you today, what I hope comes out, is that following the Challenger disaster we went back and did rigorously enforce that discipline," he said. "And the degree to which we fell short in the Columbia accident, that's why we're here today and that's what we want to find out."

Halsell defended NASA's waiver process, whereby components can be cleared for flight even if they don't meet specifications. A study was conducted in 2000, he said, to find out "how many are out there, are they all still valid, how often do we review this situation so that we're not guilty of unknowingly accumulating waivers, to what degree are we confident that we have good rationale for retaining waivers in place? And what we found out from that review is that we do have a good process in place. There's an annual review of the waivers to make sure it's still appropriate, it's still applicable, it's still necessary."

Halsell also defended NASA's flight readiness approval process. Board member Steven Wallace pointed out that by the time a mission's flight readiness review is held a few weeks before launch, most major issues already have been addressed by lower-level engineers and managers.

"This is sort of a recurring message, the work is kind of done before these meetings," Wallace said. "I'm curious, is it fair to say these meetings then don't get scheduled until the work is done, or is it unusual that things get stopped at these meetings because you know, does the meeting become sort of a sign off formality?"

Halsell said when he first moved into management, "I perceived some of the same flavor that you're talking about, that is, the important work was being done and being done exceptionally well, so well in fact that when we got to some of these milestone reviews, it appeared to me that all of the hard issues had been discussed, all of the hard decisions and tradeoffs had been made. So I questioned the value to our senior management of these level of reviews.

"But after being in the job for a longer period of time and having discussed the situation with a number of my project managers, they had a different point of view. They didn't disagree with the fact that the way we do business is such that most of these problems - not always - but most of them had been flattened out by the time of the formal review.

But it's because of the presence of these formal reviews and the fact that you know that senior NASA management, the people you answer to and the people who are ultimately responsible for the safety of the upcoming mission, because you know they're going to be there to hear that story, it drives all that outstanding work that happens before. So from the point of view of the projects and elements, they did not want to change or consider any dramatic changes to the form or to the agenda of any of these reviews because from their perspective, they were driving the kind of reaction within the system that was healthy and needed."

Halsell also went to great lengths to defend the analysis following the foam impact during the launch of Atlantis on mission STS-112.

"It's well known that we did liberate a piece of foam on STS-112," he said. "The process by which we went through understanding what had happened, how that related to our previously accepted hazards ... and what was the appropriate course of action from that point on, all followed the processes we had in place to try to ensure the right decision and right tradeoffs and risks got made.

"For example, the in flight anomaly situation for STS-112, that did come to a program requirements change board, it was decided there that an in-flight anomaly designation was not required for this particular item because the previously accepted and documented hazards, and if I remember correctly there were two integrated hazards which were violated, or which were called into question by this particular instance, two of them dealing with the external tank liberating foam and creating a hazard to some other vehicle component, there was nothing about that particular instance which invalidated the rationale for the previously accepted risk.

"In other words, we didn't move up into the right on the risk matrix according to what we knew at that point in time," Halsell said. "So the action that was levied at that program requirements change board was to the external tank project, to go back and fully understand what had happened, why it had happened and what we were going to do to keep it from happening in the future. Also another action was levied to bring that item forward at the flight readiness review to make sure it was discussed fully prior to STS-113. So using that as my example, I would say that that's an example of how the process worked properly and the item was brought forward to the flight readiness review and it was discussed at some considerable length there."

Asked who had the ultimate responsibility for accepting or rejecting such analyses, Halsell said "the short answer is that it's the space shuttle program manager's job to organize the appropriate response to any and all issues when it comes to making the final determination if we can recommend to the associate administrator that we're ready to go fly safely. So if Ron Dittemore was sitting here in front of me, he would say it's my in box because he's the one who controls the resources and the application of those resources."

Revision I of the CBS News-compiled STS-107 integrated entry timeline has been posted. This revision includes initial OEX recorder data - OEX start time, seven data points (from four sensors), PCM/FDM data stop times - and a few other relatively minor updates. As always, suggestions, corrections and comments are appreciated.

The radar signature of an object floating away from the shuttle Columbia on the second day of its mission matches up well with a wing leading edge carrier panel, members of the Columbia Accident Investigation Board revealed today. The tile-covered carrier panels form a smooth surface between the edges of U-shaped reinforced carbon carbon - RCC - panels making up the wing leading edge and heat-shield tiles permanently bonded to the wing's lower surface. If Columbia began its ill-fated re-entry with a missing carrier panel, enough heat could have entered the left wing to trigger the catastrophic chain of events that led to the shuttle's destruction.

But board member Roger Tetrault said other explanations are possible and that it's still not certain a carrier panel is what was separating from the orbiter on flight day two. Asked if one could conclude a missing carrier panel was the root cause of the disaster based on all the data to date, Tetrault said "your logic could lead to someone's death."

Even though photo analysis shows foam debris from Columbia's external fuel tank hit Columbia's left wing leading edge around RCC panel 6 - and that it could have hit the carrier panel immediately behind RCC panel 6 or an adjacent panel - that doesn't mean the breach that doomed Columbia began at that location.

At least not until engineers rule out other scenarios that are still on the table.

"You can't rule out all of these (other scenarios) and make this leap of faith that something you know happened between (RCC) panels 6 and 12 actually happened in this particular area," Tetrault said. "You just can't make that leap of faith."

But he agreed that the loss of a single carrier panel almost certainly would have allowed enough heat to enter the wing behind the leading edge to trigger the temperature increases seen early on. And "early on" is clearly the operative expression when it coms to Columbia's catastrophic descent.

Ongoing analysis of data recovered from a salvaged telemetry recorder shows the onset of heating in Columbia's left wing began 270 seconds after the shuttle entered the discernible atmosphere. That's three minutes and 26 seconds earlier than the previously known first indication of anything unusual - an unexpected yawing motion - and three minutes and 38 seconds before the previous first indication of elevated temperatures in a brake line in the left main landing gear wheel well.

As it turns out, that earlier brake line reading, a 1.5-degree Fahrenheit increase detected at 8:52:17 a.m., may have been normal. Tetrault said NASA investigators have identified at least 13 previous shuttle flights with so-called 1.5-degree "bit flips" in the first eight minutes and 20 seconds after atmospheric entry, or EI+500 seconds. In 11 of those missions, bit flips occurred earlier than the one seen aboard Columbia.

"We are finding brake line temperature D (sensor), which established the first sensor previously, is probably not off nominal at the time that's on the timeline," Tetrault said. "It's probably later than that. That's an important point because sensor D goes off first and it is in the aft of the wheel well and it is high in the wheel well, which tends to indicate heat is coming from the aft part of the wheel well moving forward.

"If you really look at it, it is much more likely that the heat is coming from the forward side of the wheel well going aft," he said. "Temperature D is probably nominal for a much longer period of time."

In any case, more than a hundred engineers working over the weekend have managed to extract key data from the recovered payload experiments recorder, or OEX recorder, that was found by search crews near Hemphill, Texas, on March 19. Tetrault briefed reporters today on the performance of four specific sensors in the left wing.

Columbia fell into the discernible atmosphere - entry interface, or EI - 400,000 feet above the Pacific Ocean northwest of Hawaii at 8:44:09 a.m. Sensor G9921, a strain gauge located in the interior of the shuttle's left wing roughly in line with RCC panel 9, began to show signs of unusual stress at 8:48:39 a.m., or EI+270 seconds. That was 206 seconds earlier than the first signs of unusual yaw moments at EI+476 seconds.

Twenty seconds after sensor G9921 went "off nominal," a temperature sensor mounted on a support brace on the outboard side of RCC panel 9 began sensing unusual temperatures. This sensor was located under insulation in a cavity behind the U-shaped RCC panels just in front of the wing spar. It began sensing high heat at 8:48:59 a.m. and then failed at 8:52:19 a.m., after reading 50 degrees, presumably because the hot air rushing into the wing cut through its wiring.

The next sensor to show unusual readings was located on the front side of Columbia's left orbital maneuvering system rocket pod. At 8:49:53 a.m., sensor 9220 started seeing unusually low temperatures. Nine minutes later, the sensor showed a rapid increase in heating, climbing as high as 1,200 degrees Fahrenheit. The normal reading is 600 degrees.

"First, we think there is a change in the mass flow, which moves the mass flow probably below the OMS pod, and then there is something else that happens that brings the temperature rapidly up, which may be burning or burning aluminum or a number of other effects we have to go look at," Tetrault said.

At 8:51:14 a.m., or EI+425 seconds, sensor 9895, located directly behind RCC panel 9 on the inner side of the wing spar, began recording an unusual temperature rise. One minute and 35 seconds later, the sensor failed after reaching 450 degrees.

Analysis of the OEX data is continuing and the investigation board plans to wrap that information into NASA's existing re-entry timeline, which currently stands at revision 15.

The OEX tape contains two types of data. One set ends at 9:00:13.4 a.m. and the other stops at 9:00:19.4 a.m. The latter is 15 seconds beyond the point where telemetry that was downlinked in realtime came to a sudden stop on Feb. 1. During a final two-second burst of downlinked telemetry, the shuttle was seen to be yawing rapidly to one side. Main vehicle breakup, based on video analysis, began around 9:00:21 a.m.

The OEX data likely will help engineers pinpoint how Columbia began breaking apart and what major components tore off first. In addition, the OEX data will shed light on what was going on during a 25-second dropout in the downlinked telemetry that occurred between 8:59:37 a.m. and 9:00:02 a.m.

At the front end of the timeline, the OEX data "will show us that when we start looking at where the electrical lines were cut - a lot of them cut 540 seconds after EI - that it will begin to help us to localize where in the front edge the problem is," Tetrault said. "Up until now, if I took collectively all the data we had, I could in my mind locate this event somewhere between RCC panel no. 5 and no. 12. I think this will help shrink that down to some much narrower (focus).

"When you begin to put that where the photos have shown where the foam hit, I think you can start making some assessments of what are the probabilities of that being an initiating event, if you will. I wouldn't say necessarily the cause, but there may be an initiating event that leads to a whole series of other things that winds up at the accident."

One possible initiating event is the loss of a carrier panel on flight day two. NASA sent 29 leading edge components and tiles to Wright Patterson Air Force Base for testing to match up their radar signatures with the debris seen leaving Columbia. As of today, a carrier panel is the only item that has not been ruled out.

"With 3,100-plus observations of Columbia by the DOD, we've got a lot of radar cross section feedback," said board member Maj. Gen. John Barry. "There have been 29 various materials examined at Wright Patterson Air Force Base and we've concluded that right now, that only the carrier panel remains a viable candidate for the day two object. ... We think with the (attachment hardware) and the carrier panel, it gives us one of the best candidates we've had so far after reviewing all the testing. But we still have some more testing to do."

The carrier panels are mounted in place by bolts at each end. The bolts run through the heat-shield tiles on their outer surface and the bolt holes are filled with ceramic plugs. The bolt holes are relative weak spots and tests are planned to determine what sort of damage might have been caused by an impact on one of those tiles during launch.

Tetrault said video of Columbia's launch and the subsequent foam impact had been enhanced by the National Imagery and Mapping Agency, or NIMA, and that investigators now believe the shuttle was stuck just once, by a piece of foam measuring 24 inches by 15 inches by 5 inches, with an uncertainty of a few inches in any dimension. The debris, thought to have weighed about two pounds, slammed into the left wing at 640 feet per second, or 436 mph.

The foam hit the left wing in a two-foot-wide footprint centered on the lower surface of RCC panel 6. The footprint includes parts of two carrier panels.

Tests are on tap at the Southwest Research Institute in San Antonio, Texas, to fire foam debris into leading edge panels, carrier panels and other hardware to determine damage scenarios. Those tests originally were scheduled to begin early next week, but they will be delayed a week or so to give engineers more time to develop procedures incorporating foam samples closer to the size the new NIMA analysis indicates.

On another front, Barry said engineers have cut into the insulating foam of an external tank similar to Columbia's and found numerous voids where the material is bonded to the tank structure. The area in question is the so-called bipod ramp, an aerodynamic slope in the insulation that protects struts holding the nose of the shuttle to the tank from aerodynamic stress.

Engineers looking under the foam in the bipod ramp area of tank 120 found 14 voids, or open spaces, under bipod ramp foam on the right side of the tank and 18 on the left. Such voids are potential trouble spots because extreme low temperatures in the tank during launch can cause air to liquefy in the voids and then explosively evaporate during ascent, blowing foam off in the process. That mechanism is one possible explanation for the foam that came off during Columbia's launch.

To double-check their findings to date, engineers plan to cut into the foam of a tank that is virtually identical to Columbia's - tank 94 - to find out if similar voids are present.

On yet another front, investigators are looking into the formation of pinhole defects in the RCC panels themselves. Barry said today any given RCC panel has between 20 and 40 such age-related pinholes. Any such defects greater than 0.04 inches across are repaired or refurbished. Virtually all of Columbia's leading edge panels had experienced such repairs or refurbishment and investigators are looking into how that process is carried out.

As it turns out, the pinholes may be caused by material from launch pad primer that causes oxidation on the RCC panels. But that remains to be seen.

Finally, Tetrault said the OEX data showed no clear evidence any kind of response from the foam impact on the left wing. But sources familiar with the OEX analysis say a pressure sensor located on the lower surface of the wing, roughly in line with RCC panel 9, shows a small "spike" at 84 seconds that could be the result of post-impact cloud of foam debris sweeping past the detector. No other sensors detected anything unusual.

NASA late Monday posted nearly 30 megabytes of internal email traffic and attachments regarding the potential threat of foam debris striking the shuttle Columbia's left wing; concerns about corrosion that could interfere with proper operation of the ship's body flap during entry; and discussions regarding Columbia's heavier-than-usual landing weight. NASA also posted charts and data used to clear Columbia for flight during a formal flight readiness review before launch.

The sheer volume of the posted material precludes a quick analysis, but a cursory review turned up no significant departures from the tone and general context of concern found in emails released by NASA last month. Quite a few engineers were seriously concerned about the potential threat posed by the debris impact, saying it was the most significant such impact to date and one that was well outside NASA's previous experience. But most ultimately deferred to an analysis carried out by Boeing that concluded whatever damage might be present was a turnaround/repair issue and not a "safety of flight" concern.

One draft memo posted separately, however, did show a previously unseen level of concern about senior management's decision not to request spy satellite photography of Columbia's left wing to better characterize the potential damage. The memo was in draft form and never sent via email to 14 listed recipients. Instead, according to a hand-written note, the contents of the memo - drafted around Jan. 22, six days after Columbia's launch - were discussed verbally with an unknown number of engineers and managers.

"In my humble technical opinion, this is the wrong (and bordering on irresponsible) answer from the SSP [Editor's note: space shuttle program] and Orbiter not to request additional imaging help from any outside source," wrote Rodney Rocha, a chief engineer in the structural engineering division at the Johnson Space Center.

"I must emphasize (again) that severe enough damage (3 or 4 multiple tiles knocked out down to the densification layer) combined with the heating and resulting damage to the underlying structure at the most critical location (viz, MLG Door/wheels/tires/hydraulics or the X1191 spar cap) could present potentially grave hazards. The engineering team will admit it might not achieve definitive high confidence answers even with additional images, but, without action to request help (to) clarify the damage visually, we will guarantee it will not.

"Can we talk to Frank Benz before Friday's MMT [Editor's note: mission management team]? Remember the NASA safety posters everywhere around site stating 'if it's not safe, say so?' Yes, it's that serious."

A more detailed review of the newly posted emails and supporting documents will be posted here later this week as warranted.

Ongoing analysis of a "treasure trove" of data from a recorder recovered in the wreckage of the shuttle Columbia shows a deadly plume of super-heated air first began eating its way into the ship's left wing just five minutes after the orbiter fell into the discernible atmosphere. The sudden temperature increase, in a cavity behind the U-shaped panels making up the leading edge of the left wing, came a full three minutes earlier than previous telemetry indicated the start of unusual heating.

Entry interface occurred at 8:44:09 a.m. and a sensor mounted on a brace behind leading edge panel No. 9 began responding to a very sharp temperature increase at 8:49:09 a.m., nearly two minutes before the shuttle entered the region of maximum heating (this is earlier than officials reported Sunday evening based on quick-look data analysis of the OEX data). In any case, exactly three minutes after that initial temperature rise, the sensor failed and dropped off line after detecting a temperature of 450 degrees Fahrenheit. Eight seconds later, at 8:52:17 a.m., a sensor mounted on a brake line in the left main landing gear wheel well recorded the start of an unusual temperature rise.

Harold Gehman, chairman of the Columbia Accident Investigation Board, said today the timing of these events suggests Columbia began its re-entry with a fatal flaw that allowed hot gas to first enter the cavity behind the leading edge panels and then to burn its way into the interior of the wing. The hot gas presumably entered the wheel well through a vent on its forward face, triggering the brake line temperature increase.

A few seconds later, beginning at 8:52:49 a.m., a sensor mounted on the forward interior edge of the wing, just behind the failed sensor in the leading edge cavity, began registering a rapid increase as hot gas shot through the interior. Seven seconds after that, data from sensors mounted toward the back of the wing began dropping off line as the plume burned its way through a wire bundle routed around the outside of the landing gear wheel well.

"Now interestingly enough, the first temperature rise we see inside the wheel well occurs at 52:17," Gehman said. "Just about the time the sensor outside the wing spar fails, the temperature inside the wing spar starts to go up. So this is interesting to us."

The sensor mounted on the inner surface of the wing spar roughly behind leading edge panel No. 9 "starts to rise 520 seconds after EI, which is something like eight minutes and 40 seconds, which would make it something like 52:49," Gehman said. "The temperature sensor inside the wing starts to rise almost coincidentally with the time the temperature sensor outside the spar goes off line, which leads you to believe there was a whole lot of heat outside the spar which finally ate its way into the wing.

"Remembering the melting temperature of aluminum is something like 900 degrees, it got really hot outside the spar, ate its way through and the temperature sensor outside the spar goes off line," he said. "It probably got destroyed."

Enhanced video of Columbia's launching shows a suitcase-size piece of foam debris from the shuttle's external fuel tank pulled away and slammed into the left wing about 82 seconds after liftoff. The two-foot-wide impact footprint is centered on reinforced carbon carbon - RCC - leading edge panel No. 6. The impact could have affected two adjacent RCC panels as well as protective tiles atop so-called "carrier panels" marking the interface between the lower edge of the RCC panels and permanent heat-shield tiles on the lower surface of the wing.

Gehman said the temperature data recovered from Columbia's orbiter payload experiments recorder, or OEX recorder, does not rule out or confirm an initial breach at or near RCC panel 6. He said engineers will be making calculations over the next few days to determine what sort of breach would be required near RCC 6 to produce a temperature increase like the one seen on the sensor behind RCC 9. At the shuttle's extreme altitude, the dynamic pressure was low and there was not much air to transmit heat. Whether the aluminum structure of the wing spar could have conducted that much heat, or whether a breach occurred outboard of RCC 6, is not yet known.

But it now seems all but certain Columbia began its entry with a fatal flaw already in place, an entry point for the super-heated air that ultimately led to its destruction.

"At the altitude and the speed the orbiter was going at the time the new temperature rise was seen, the aerodynamic pressures are extraordinarily low," Gehman said. "So you could conclude the orbiter began it's entry with a pre-existing fault. In other words, it wasn't air pressure that knocked this thing off, it wasn't some kind of a weakness in which some part of the orbiter was ripped off when it entered the atmosphere, this looks to us like it probably had a pre-existing condition."

But Gehman urged reporters not to jump to any conclusions about the possible location of the initial breach.

"Where the temperature sensor is does not suggest where the breach is," he said. "We are still pulling all the data together to attempt to indicate where the breach is. But this certainly leads us away from things like tile and landing gear doors and things like that."

The OEX recorder is capable of recording data from some 721 sensors scattered across the shuttle. About 150 sensors were not operational during Columbia's entry because of past problems or wiring issues. Gehman said engineers hope to recover data from about 570 sensors when all is said and done.

"It's a treasure trove of data," Gehman said.

Along with showing when the first signs of heating occurred in the left wing, the OEX data shows unusual heating effects on the left orbital maneuvering system rocket pod just to the left of the shuttle's vertical stabilizer.

"Temperature sensors on the skin of the orbiter high up in the vicinity of the OMS pod, the maneuvering engine covers high up on the port side, they start to do all kinds of strange things," Gehman said. "Some of them go up, some are going down. Some go down and then rise later. Some rise and then cool off. We don't know what to make of that except the heating pattern and the flow pattern over the top of the left wing, which then spreads over the side of the fuselage, is obviously disturbed in some way."

Prior to the discovery of the OEX recorder, realtime telemetry from the shuttle showed an initial loss of contact at 8:59:32 a.m. Thirty seconds later, a final two-second burst of telemetry was received that showed Columbia was in the process of yawing out of control to the left. Gehman said today the OEX recorder ran for an additional eight seconds. That data has not yet been recovered, but it should shed additional light on how much of the ship was still intact at that point and when final breakup began.

At the other end of the scale, investigators are working to extract data about the forces acting on Columbia during launch. Gehman said engineers are especially interested in seeing what sorts of forces were acting on the orbiter around the time the external tank debris hit the left wing. Columbia encountered high wind shear during launch, prompting more extreme booster steering movements than normal. Whether those forces contibuted to stresses that, when aggravated by the debris strike, could have led to an RCC failure or a carrier panel problem is not yet known. But Gehman said OEX data from ascent will be factored into upcoming tests in which foam will be fired at leading edge components to determine what sort of damage they might have suffered.

Gehman said engineers will add the OEX data to NASA's current entry timeline (revision 15) and issue updates as warranted. Whenever those updates are made available, they will be added to the CBS News integrated timeline, currently in revision H.

A data recorder recovered in the wreckage of the shuttle Columbia shows hot gas entered the leading edge of the spacecraft's left wing within 16 seconds of the point when the orbiter entered the region of maximum aerodynamic heating during re-entry Feb. 1. Temperature sensors located behind two leading edge panels, both just outboard of the point where engineers believe a deadly breach occurred, showed a sudden rapid spike, or increase, before the sensors failed and dropped off line. The readings, which occurred a minute and eight seconds earlier than previous signs of trouble - suggest Columbia almost certainly began its descent with a pre-existing problem and that it might have suddenly worsened as the ship plunged back into the atmosphere.

"They go way up and then they go to zero," said a representative of the Columbia Accident Investigation Board. Along with showing unusual heating effects earlier than previous telemetry that was downlinked in realtime, "I think what it also indicates is the mechanism of failure was already in place."

Columbia was destroyed by a breach in the ship's left wing. Up until now, NASA engineers relied on telemetry that was downlinked from the orbiter in realtime to reconstruct what might have gone wrong. That data indicated the shuttle began responding to unusual aerodynamic forces around 8:52 a.m., more than a minute after the orbiter entered the region of maximum heating at 8:50:53 a.m. The downlinked telemetry shows the first signs of unusual heating occurred at 08:52:17 a.m. when a brake line in the left main landing gear wheel well began showing an unusual rise.

From that point on, a series of sensors failed as a plume of super heated air burned its way into the left wing, eating through sensor cables and causing temperatures to climb throughout the wheel well. The presumed entry point of the plume - at or near the underside of leading edge panel No. 6 - is believed to have worsened as entry proceeded, causing increasing aerodynamic drag. The shuttle eventually yawed out of control and broke up over Texas about 20 seconds after 9 a.m.

But re-entry readings from hundreds of other temperature, vibration and pressure sensors were stored on a data recorder and not downlinked to the ground. The recorder was recovered by search crews March 19 and after work to clean and stabilized the tape, engineers began work this weekend to examine what data might be present.

The board representative said the tape holds valid data and shows unusual heating in the left wing, behind leading edge panels 9 and 10. One of those sensors is located on the front surface of the wing spar, underneath insulation, while the other is behind it, on the other side of the spar.

The sudden temperature spikes, which began at 8:51:09 a.m. - 16 seconds after the shuttle entered the region of maximum heating off the coast of California - would be consistent with the entry of hot air through a pre-existing breach in the leading edge. The hot air would have shot down a cavity in the U-shaped leading edge panels, trigging the observed temperature spikes in the two outboard sensors, before working its way into the wing's interior.

The timing of how the leading edge sensors responded to the increased temperature is unclear. One of them failed and went off line 20 seconds or so after its counterpart. But they showed sharp temperature increases that were clearly above what the sensors would detect during a normal entry, the board's representative said.

While it is too soon to draw any concrete conclusions, the OEX recorder promises to provide a gold mine of new aerodynamic and thermal data to engineers trying to re-construct the devastating chain of events that led to Columbia's destruction.

"The board is very, very happy that the data could be retrieved," the board representative said. "They're anxious to see what more we can learn about how the heating was moving along the left wing."

Engineers plan to meet Monday to discuss the status of the OEX data reconstruction. Over the next several days, they will begin the process of weaving the new information into NASA's entry timeline. They also plan to continue work to recover OEX data recorded during Columbia's ascent to determine if any readings might be indicative of external tank foam striking the left wing 82 seconds or so after liftoff.

A preliminary look at the ascent data shows a potentially interesting signature, but officials say it may well be the result of a wiring defect. Additional analysis should resolve the matter one way or the other in the days ahead.

The National Imagery and Mapping Agency, one of the government organizations that sets targets for spy satellites, has agreed to routinely inspect space shuttles in orbit for signs of possible damage.

In a March 25 letter to NIMA Director James Clapper, NASA Administrator Sean O'Keefe wrote that he appreciated NIMA's "willingness to add our requirements to your routine operations."

"Thank you very much for the briefing that you and your staff presented to us at NASA on March 13, 2003," O'Keefe wrote. "We appreciate your offer of close cooperation regarding the use of NIMA assets relative to future space shuttle operations.

"As agreed during that session, we deeply appreciate your intention to make available the products of NIMA assets on a routine basis, without specific tasking from NASA. This will be very helpful as we continually assess the condition of the shuttle during on-orbit operations. Significantly, your willingness to employ NIMA assets during targets of opportunity without specific tasking will be another useful source of information to help us assess the potential for on-orbit anomalies."

The issue of shuttle imagery was discussed in the days following Columbia's launch because of concern about possible damage to the ship's left wing following impact by foam debris during launch. But senior NASA managers ultimately decided not to request any spy satellite or ground-based imagery of the spacecraft based on an analysis that concluded the shuttle was not in any danger.

That decision has been the subject of second-guessing and criticism in the wake of the disaster. In the days after the mishap, shuttle program manager Ronald Dittemore said no request for satellite imagery was made because the resolution of the imagery, based on past NASA experience, would not be high enough to reveal damage to individual tiles and because the damage assessment, carried out by Boeing, had concluded Columbia could land safely.

During Columbia's mission, however, Wayne Hale, a senior flight director now serving as launch integration manager at the Kennedy Space Center, made inquiries about the possibility of Air Force help inspecting Columbia. Those initial efforts later were terminated by senior management.

As it turned out, NASA didn't even have to ask for help. An unidentified agency - presumably NIMA - offered to inspect Columbia if NASA made a request for emergency assistance. But William Readdy, associate administrator for spaceflight, declined to make such a request because NASA engineers did not believe the imagery would help all that much and because "there was no safety of flight issue. For those reasons," Readdy wrote in a letter to the Columbia Accident Investigation Board, "there was no rationale for requesting emergency or high priority support."

Prior to today, this page included every CBS News shuttle status report filed since Feb. 1, the day the shuttle Columbia was destroyed. Even though these status reports are essentially unformatted text files and as such, fairly compact, the sheer volume of copy - more than 50,000 words - has made the Current Mission page increasingly slow to download for readers with dial-up modems.

As a result, all previous status reports have now been added to the CBS News STS-107 Mission Archive. In a departure from past practice, however, the archive now ranks status reports in reverse order, with the latest copy at the top of the file and the oldest at the bottom. Consistent with past practice, status reports will remain posted on the Current Mission page for a day or so before being transferred into the Mission Archive.

Editor's Note...
Due to other commitments, I was unable to immediately file the following update on the status of Columbia's OEX recorder. I apologize for the inconvenience.

Time-code information at the end of a tape in a recovered data recorder designed to store critical flight information shows the device apparently operated until 9:00:18 a.m. on Feb. 1, stopping less than 10 seconds before the shuttle Columbia's fuselage broke apart during re-entry.

Assuming the entire tape proves to hold valid data, engineers attempting to reconstruct Columbia's final minutes stand to gain crucial insights into the aerodynamic forces acting on the spacecraft as it plunged back into the atmosphere. Investigators may even be able to pinpoint the location of a breach in Columbia's left wing by using data from dozens of OEX temperature sensors - including two in close proximity to the presumed breach location - to plot the path of a deadly plume of super-heated air as it burned its way into the wing's interior.

The OEX recorder can hold about two hours of data on a one-inch-wide 28-track tape that is recorded at 15 inches per second. The recorder only operates during launch and re-entry. For launch, the recorder is activated 15 minutes before liftoff and shut down six minutes after main engine cutoff. Total runtime is about 15 minutes. For entry, it begins running 10 minutes prior to the moment the shuttle falls into the discernible atmosphere at an altitude of 400,000 feet - entry interface - and continues through landing. For Columbia's entry, that translates into a start time of around 8:34 a.m. on Feb. 1. Landing originally was scheduled for 9:16 a.m., but the recorder failed in the final seconds before vehicle breakup, which began around 9:00:21 a.m.

Engineers believe 721 sensors feeding the OEX recorder were operational during Columbia's mission. Here is a breakdown of the number of sensors providing specific types of data:

• Main engine vibration data: 29 FDM (frequency division multiplexer data)
• Thermal aerodynamic pressure: 182 PCM (pulse code modulation data)
• Thermal aerodynamic temperature: 38 PCM
• Thermal protection system temperature: 15 PCM
• Structural loads: 24 FDM
• Wing box stress and strain: 246 PCM
• Elevon stress and strain: 52 PCM
• Vertical tail fin stress and strain: 38 PCM and 6 FDM
• Rudder and speed brake strains: 12 FDM
• Mid fuselage loads: 40 PCM and 9 FDM
• Fuselage aft head shield and tail cone: 18 FDM
• Timing data: 2 FDM
  
  
• TOTAL: 721

Engineers plan to examine the OEX data in exhaustive detail to map out the flow of hot air through the left wing and to gain a more precise knowledge about how the craft was being buffeted by disturbed airflow over the damaged wing and how the shuttle's flight control system responded to keep the ship on course.

They also plan to examine the launch phase to look for any evidence - elevon flutter, strain gauge readings, etc. - that might indicate the force imparted by external tank foam debris that slammed into the left wing leading edge around 82 seconds after liftoff. That debris impact may have caused the initial damage that led to Columbia's destruction during re-entry. OEX data, in theory, could give engineers a more precise idea about the actual force imparted to the shuttle.

But the foam impact occurred when the shuttle was still experiencing high aerodynamic pressure and the impact likely was "drowned out" (low signal-to-noise ratio) by the strength of normal readings during this phase of flight. But engineers nonetheless are going to look for an impact signature.

Engineers hope to begin analyzing data this weekend from a recovered tape recorder that stored readings from some 721 sensors throughout the shuttle Columbia during its final 45 minutes of flight. Analysts hope the data will help them precisely map out the flow of hot gas through the doomed ship's left wing to confirm and refine - or possibly modify - current theories about where the initial breach occurred and how the deadly plume then worked its way through the interior of the wing.

The orbiter payload experiments, or OEX, recorder was found during a grid search March 19 near Hemphill, Texas. The device was remarkably intact with one edge buried about three inches in soft soil. Over the weekend, engineers with Imation Corp. in Minnesota cleaned and stabilized the 1-inch-wide, 28-track tape and sent it on to the Kennedy Space Center for duplication. Engineers at the Johnson Space Center in Houston hope to begin analyzing whatever data was recorded this weekend.

"In a perfect world, we will have 721 measurements, sensor outputs," said Scott Hubbard, a member of the Columbia Accident Investigation Board. "This covers the wings, the fuselage and the vertical tail surfaces. Of particular interest are going to be 182 pressure measurements, 53 temperature measurements and 447 loads, dynamics and stress measurements.

"Among these will include a series of measurements - if we get all the data back - on the left wing: strains, stresses and strains, temperature and pressures.

"Now we have to note, this has been through a very severe environment," he cautioned. "We don't know if the tape has been demagnetized, we don't know yet the quality of the data in there."

But if the tape is, in fact, readable, "this would be a gold mine of information that could lead us to a much, much better understanding of what happened throughout the vehicle and particularly on the left wing."

During a news conference following a public hearing by the CAIB, Hubbard said additional study of enhanced photography of foam debris slamming into Columbia's left wing shows the material hit the underside of the ship's leading edge in a roughly two-square-foot region centered on a specific panel of protective carbon composite material just forward of the left main landing gear wheel well.

Ongoing analysis of recovered debris, meanwhile, shows the concentration of metallic slag splattered on the inner surface of the leading edge panels increases as one approaches the region where the foam impact occurred.

The two independent lines of evidence are consistent with a breach at or near reinforced carbon carbon - RCC - panel No. 6, or an adjacent closeout panel, that allowed a deadly plume of superheated air to burn its way into the wing, triggering a catastrophic chain of events that led to Columbia's destruction 200,000 feet above Texas.

At today's hearing, two CAIB investigators revealed yet another piece of evidence that supports a burn through near the suspected foam impact point at RCC-6: A partially melted RCC support strut from just behind RCC panel 11, located outboard of RCC-6, that shows hot gas in a cavity enclosed by the wing's RCC panels was moving outboard, as one would expect from a breach located closer inboard to the fuselage.

"There's actually an open space inside the leading edge," said Gregory Kovacs, a professor at Stanford University. "So it's possible if there was a breach, something could have flowed down that open space and then eroded the components in there. So on that score, I think we are thinking about flows down there, where they're concentrated maybe closer to the breach. That's the kind of thinking we're going through."

As it turns out, two temperature sensors monitored by the OEX recorder were mounted underneath insulation on the wing spar behind RCC panels 9 and 10. If a breach really did occur inboard of there, near RCC-6, for example, those sensors may have recorded the initial intrusion of hot gas before it ate its way into the interior of the wing.

"It's expected that if this was a normal mission, (the OEX recorder) would have about 30 minutes of data from ascent and in a nominal mission, an hour of entry data," Hubbard said.

But Columbia's re-entry ended 45 minutes after it began. In addition, the wiring from many sensors in the left wing was routed around the left main landing gear wheel well. Many of those wires may have been severed by the super-heated plume that ultimately burned its way into the wheel well. Even so, that would not affect data from other sensors expected to shed light on the thermal environment and the aerodynamic forces acting on the ship in its final moments.

To put all of that in perspective, here is a brief recap of what investigators believe may have happened to Columbia. Readers are cautioned that details almost certainly will change and the timing of some events is uncertain. The board has not yet presented any theory as a "leading candidate" and some of what follows is an interpretation of what the CAIB has revealed to date:

• A large piece of foam insulation weighing about one pound and measuring three inches thick, 12 inches wide and 24 inches long pulled away from the external tank bipod ramp area 81 seconds after launch. The bipod ramp is just that, an aerodynamic ramp of shaped foam just in front of one of the two struts that held Columbia's nose to the tank.
  
  
• The foam, moving at roughly 500 mph in the slipstream between the orbiter and tank, hit the lower side of the left wing leading edge in a two-foot-wide footprint centered on RCC panel 6. It may have damaged parts of RCC panels 5, 6 and 7 or, more likely some believe, one or two so-called carrier panels that form a flush surface between the RCC panels and heat-shield tiles permanently bonded to the lower surface of the wing.
  
  
• The day after launch, military radars tracked an object leaving the space shuttle. It is not yet known what that object might have been, but sources close to NASA's investigation believe it may have been part of an RCC panel or one of the carrier panels in question. Tests to determine precise radar signatures of various types of possible debris are not yet complete.
  
  
• During re-entry, hot gas breached the leading edge from the presumed foam impact damage site. The gas presumably first moved through the cavity behind the RCC panels, damaging various support structures, before entering the wing itself. At about this same time - before any realtime sensors detected anything unusual - the shuttle's flight control system began responding to unusual aerodynamic forces. Whatever was wrong with the front of the wing presumably was disrupting the airflow over the wing's upper and lower surfaces enough to prompt a response from Columbia's digital autopilot.
  
  
• The plume began melting leading edge support components and the forward wing spar, splattering molten metal back across the inner surface of the RCC panels. The timing of such splattering is uncertain, but the slag can be seen on recovered debris, concentrated near the region of the presumed breach.
  
  
• At the same time, pieces of the leading edge, support structure or adjacent tiles began falling off. Some components may have fallen into the worsening breach. "If you think about the static pressure loads, certainly at the beginning, there's a lot of force," said Kovacs. "So if a piece is sort of flapping around and it's on the underside, if you think about the (40-degree) angle of attack, it's easy to believe a piece could be folded and broken off and end up wedged inside there. It would be driven back as things are melting and if it's RCC (material), it may well survive that and end up stuck there."
  
  
• A brake line temperature sensor in the left main landing gear wheel well recorded a slight but unusual increase as hot gas swirling into the wing entered the wheel well through a vent on its forward face.
  
  
• The breach worsened as Columbia's descent continued until a plume of super-heated air impacting the side or forward face of the wheel well burned through wiring from sensors located toward the rear of the wing. Lost data from those sensors were among the first indications in mission control that anything was amiss.
  
  
• The plume eventually burned through the outboard wall of the wheel well, or perhaps through its forward face depending on the actual breach location, dramatically raising temperatures in the well. A titanium pin used to mount the left landing gear door to the outboard side of the wheel well is partially melted, indicated it was subjected to temperatures as high as 3,400 degrees. Other debris from an area just inboard of the forward corner of the door shows signs of hot gas outflow. Engineers believe the plume of hot gas entering the wheel well likely exited around the corners of the heat-softened landing gear door.
  
  
• Columbia's flight control system struggled to keep the shuttle on course, counteracting increasing aerodynamic drag by adjusting the ship's roll trim and, when that wasn't enough, firing four right-side yaw thrusters. Eventually even that was not enough, and the spacecraft yawed out of control, breaking up at Mach 18.
  
  

The OEX data could prove crucial to confirming and refining the above scenario or, possibly, sending investigators down another path.

"We have focused a lot of our attention on the left wing and particularly the left wing leading edge," Hubbard said. "If the sensors that are there were active and working and got recorded, that information would be extremely valuable. If for some reason those sensors dropped out, the orientation of the vehicle, from some of the other sensors that also help us determine the attitude of the vehicle, might give us a better sense of what was going on."

Starting around April 6, engineers at the Southwest Research Institute in San Antonio, Texas, plan to being firing large pieces of foam insulation at RCC panels and carrier panels at various angles of incidence to determine what sort of damage might have occurred during launch. The foam will be fired from a nitrogen gas canon at impact velocities of around 500 mph.

An RCC panel and upper and lower carrier panels taken from the prototype shuttle Enterprise will be heavily instrumented to determine impact stresses. An RCC panel taken from the shuttle Discovery, which has flown 30 times and closely matches the original-equipment panels that were on Columbia for its 28th flight, also will be subjected to foam impact for a more realistic assessment of what might have happened to Columbia. In addition, foam will be fired at so-called acreage tile, that is, normal heat-shield tiles located in the presumed foam debris footprint just behind the lower carrier panels.

In the meantime, NASA and CAIB investigators are continuing detailed chemical and metallurgical analysis of recovered debris to decipher complex damage patterns in hopes of pinning down the breach location and plume propagation path.

Mark Tanner, an expert in failure and forensic analysis with Mechanical and Materials Engineering, said "what we're trying to do is get an idea from the flow patterns, the splatter patterns and the deposits, where was the breach, where was the origin this whole thing started from. Or origins."

Complicating the picture is the ever present problem of determining when the observed damage occurred.

"A key question when we're looking at these pieces is with the damage we see, was it caused by something that happened on ascent, on descent, breakup or ground impact," Kovacs asked. "A lot of these pieces, you look at them and there's pine needles embedded in them. So clearly that did not happen in space and we're taking great care to understand the relationships of those issues."

All in all, he said, "there's a lot of jigsaw puzzling going on out there. It is like putting together a multi-thousand piece 3D jigsaw puzzle on a 2D surface."

So far, some 54,000 pounds of shuttle wreckage have been recovered, or about 24 percent of Columbia's 223,000-pound dry weight. That total represents 45,762 different parts or pieces of debris, of which just 1,406 have been laid out on a grid mapping the shuttle's lower surface. Dozens of RCC fragments have been found, but most have not yet been precisely identified as to their original location. Almost nothing from the RCC panel 6 location has been recovered, but sections of adjacent panels, along with RCC support hardware, are under analysis.

Engineers believe between 35 percent and 50 percent of the shuttle actually made it to the ground. The rest presumably burned up in the atmosphere following breakup, including virtually all of the aluminum skin structure of the wings.

"A lot of the parts have come through an aluminum molten rain cloud if you will, where they have aluminum splatter over much of the debris," NASA test director Steve Altemus said of the wreckage recovered to date. "We see that molten aluminum on almost everything we have back. It may also speak to why we don't have upper wing surface on the left wing in that that's very thin aluminum. So yes, we expect a great deal of the aluminum not to have made it to the ground."

Asked if anything unusual leaps out under casual inspection, Altemus said "what did strike me as odd, first of all, is the size of the pieces, how small they actually are, and also there's very little left wing lower surface structure and very little left wing upper surface structure. When you walk the grid, hat's what you notice, what is not present as opposed to what is there."

In any case, with spring blooming fast approaching, NASA expects to conclude its massive ground search in the next four to six weeks.

"As the spring comes on, the undergrowth begins to leaf out and the canopy begins to cover," said Michael Rudolphi, deputy director of NASA's Stennis Space Center. "Obviously, the first area you'll lose search capability will be from the helicopter. And then on the ground, as the brambles and the briars begin to leaf out, it's going to damage our ability to see and to identify any material on the ground.

"The forest service thinks we've got another four to six weeks before that becomes real serious," he said. "But ... it is already starting to green up. And It will impair our ability to find as much as we would like to find. There is a time element to do the thoroughness we would like to do. Obviously, we can keep walking around in the woods after it's greened up and we can keep looking, we just won't be as successful."

Shuttle debris fell in a 4- to 5-mile-wide footprint stretching some 250 miles across central Texas and western Louisiana. The debris field impacts some 169 counties in Texas and 39 in Louisiana. Of that total, 143 Texas counties have been searched, 10 counties are in the process of being searched and 26 remain to be searched. Thirty one Louisiana counties have been cleared with eight left to go.

While some 1,800 potential targets have been found on lake bottoms in the debris field using sonar, no major pieces of wreckage have yet been recovered by divers. And no debris has been found west of Texas.

Two flatbed truckloads of debris, each one carrying about 4,000 pounds of wreckage, arrive at the Kennedy Space Center each week. It is then examined, identified and bar coded and analyzed. A two-dimensional reconstruction of the shuttle's lower surface is being laid out on a grid in a 40,000-square-foot hangar near the shuttle landing facility.

Analysts are in the process of developing a computerized three-dimensional virtual reconstruction that will show recovered debris modeled on an imaginary orbiter much like aircraft wreckage is sometimes reassembled to aid visualization and to map out the actual locations of various pieces of debris.

"There are a couple of hundred small pieces of RCC panels," Tanner said. "This would be like putting together a solid gray puzzle. What complicates this is in some cases the fractures that would mate normally really well have been eroded away. So it is going to be a time consuming process of putting this together."

Just how long it might take is anyone's guess at this point.

"We're doing our very best. But this is the first time in human history anyone's had to analyze a hypersonic space re-entry disintegration of a craft," Kovacs said. "And so there's no one to ask how long will it take. And there's nothing out there on the floor I look at and go, well, it's going to be another month and we're out of here."

Even so, he said, "I'm very optimistic. I think we're going to be able to figure it out. We feel pretty confident."

An independent aerospace expert told the Columbia Accident Investigation Board today NASA managers somehow missed the obvious when it came to the potential threat of foam debris falling off the space shuttle's external fuel tank. Aloysius Casey, a retired Air Force lieutenant general with decades of experience managing intercontinental ballistic missile programs and heavy-lift launchers, implied that NASA managers allowed themselves to be lulled into a false sense of security by their own past successes.

"I'm not going to act like I'm some expert in this particular failure because I am not," he told the board during a hearing in Port Canaveral, Fla. "But I would make these observations: High-speed impacts of material on the shuttle wings are beyond the qualification envelope of the orbiter. ... Regardless of the specific sequence and the details of the failure events, it seems to me the remedy is to preclude debris from impacting critical systems during ascent or any time. I believe this was doubtless an original design requirement for the whole system, that you do not have debris impact some vehicle systems. However, I think this is a design requirement that was not achieved. Demonstrably not achieved."

Board chairman Harold Gehman could be seen nodding in agreement during Casey's opening comments.

The shuttle Columbia was destroyed Feb. 1 when a plume of superheated air burned its way into the ship's left wing, at or near the leading edge just in front of the left landing gear wheel well. The deadly breach disrupted the airflow around the orbiter during the hottest part of its re-entry and severely weakened the wing itself, setting up a catastrophic chain of events that ultimately led to the orbiter's breakup 200,000 feet above Texas.

What might have caused the breach remains under investigation, but a major suspect is impact damage from external tank foam that ripped away 81 seconds after launch and slammed into the left wing on the lower surface of the leading edge. High-speed tracking cameras show a suitcase-size piece of foam fell away from the left bipod ramp area, where the nose of the shuttle attaches to the tank.

The accident board has been looking into past flights in which foam debris fell away from the tank and examining the decision-making process that allowed the shuttle fleet to keep flying despite a known problem that was, in hindsight, clearly beyond the shuttle's design criteria.

Casey said the key issue is retaining built-in safety margins and not exceeding them. Shuttle systems are certified, based on testing and analysis, to be able to withstand a certain, specified level of stress that is above and beyond what the system might actually see in flight. But Casey said the shuttle's wings were not designed to be struck by 500 mph-foam and that the foam wasn't supposed to come off in the first place.

Shuttle program manager Ronald Dittemore has not hesitated to ground the fleet in the past to correct seemingly minor problems. But the foam shedding problem was never viewed as a safety of flight issue. CAIB members have made no secret of their concern that NASA was lulled into a sense of false security in this case and Casey seemed to agree.

"It's absolutely critical that we retain margins," Casey said. "A concerted effort needs to be made to operate within design margins, and again, I'm talking about margins that are verified and qual tested for each and every one of the subsystems. A series of successful flights does not verify margin. You may be skating on the very edge and you come up to that flight where either the environment or the hardware causes you to go negative.

"Special efforts should be made to preclude waivers or deviations in production and assembly or pre-flight checkout or any other kind of method that's used for accepting the things you've been talking about here today, that they do not, in fact, reduce the margin. And that's very difficult to decide, it requires expert system engineering judgment to look at that particular point, how we buy this thing off does not in fact reduce our margins.

"Aging and repeated use may also erode the margin unbeknownst to the operators of the system," he said. "I believe it is absolutely essential that comprehensive system engineering effort is made to not only know what the margins are, but to be sure that we protect them in all the ensuing operations."

Casey's comments clearly struck a chord with Gehman.

"Your comments are very helpful because in some of the readings we've all done as part of our review of some of these programs, that subject, of successful flights don't re-establish margins, has come back again and again," Gehman said.

He said successful flights prior to Challenger's destruction were no indication that flawed O-ring seals were safe to fly and "they should not be used to indicate everything is OK here."

"When you use the term 'qualify the system,' if you take the case of the ET for example, the external tank, we would agree in its present situation, the ET is an unqualified system because it's shedding foam continuously," Gehman said. "It wasn't designed to shed foam, we didn't design this thing to have the shuttle orbiter to be impacted by foam, therefore it's currently not qualified in the sense we're using in this room."

"Exactly. That's right," Casey said. "There's no way in my mind that you can say I'm operating within margin if I have an unknown mass impacting an aerodynamic surface."

Gehman then brought up Challenger again, at least obliquely, by questioning the very decision-making philosophy NASA uses to clear shuttles for flight, echoing discussions in hearings 17 years ago that were focused on Challenger and its O-rings.

"What we should do is we should change the operative question on the table here," he said. "The present question is that you've got to prove to me that something is unsafe before I'll change it. What we need to do is, we should require the system to prove it is safe, particularly if we have something that appears to be exhibiting anomalies. The impetus should be to prove it's safe, the burden shouldn't be on me to prove it's not safe. The burden should be on the system to prove it is safe."

"Yes I would agree with that," Casey said. "Obviously, we have to give a lot of credence to any indicators we get. But I am equally as worried about those things that, in fact, are so subtle you haven't seen them yet but in fact, the margin isn't there and you can lose it."

Of course, such a discussion benefits from 20-20 hindsight. Roy Bridges, director of the Kennedy Space Center and one of the managers who signs off on the certificate of flight readiness, or COFR, said he never had any idea the foam represented a safety of flight issue. "To be honest, I did not think the bipod foam coming off had caused any significant damage in the program to date," he told the board today. "I believe it came off about four times before that we know of. I personally looked at every shuttle that's come back during my tenure here and I've seen no significant damage from any of the foam coming off.

"It's certainly been a maintenance concern, it's a lot of work to go out and have to repair all of those things and we don't take that lightly," he said. "We want to get to the root cause of those things and get them fixed. I personally was not aware there was any safety of flight concern with the ramp foam coming off prior to this flight. Had I been aware of that, I certainly would have put my hand up at the FRR (flight readiness review) that we would stop flying. I think this is certainly a surprise to all of us."

In answer to a question by board member John Logsdon, a space policy analyst at George Washington University, Bridges said the launch team was not influenced by any undue pressure to continue space station assembly flights. Schedule pressure was cited as a contributing factor to the Challenger disaster.

"Certainly it was something that I was aware of, trying to make sure we did not lapse back into that mode," Bridges said. "I was an active astronaut before Challenger and I was watching the flight rate go up to one a month about the time I was flying and was aware of intense schedule pressure at that time frame. So I'd say I was pretty highly tuned to trying make sure we didn't fall back into that situation."

He agreed that NASA was driving to meet the space station's initial completion date, saying "we were on a roll and we would have liked to finish it in February of '04. It would have been a brilliant achievement if we could have done that.

"But we were not going to let things like (propellant line) cracks or any other items like that that popped up be, you might say, squashed in order to meet that schedule milestone," he said. "I never felt any concern that if we brought this up to (NASA spaceflight chief) Bill Readdy or the administrator, Sean O'Keefe, that they would do anything except applaud us for letting them know we had a serious problem, we need to take a time out to fix it."

Bridges is a commander of the Air Force Flight Test Center at Edwards Air Force Base, Calif. As such, he had broad experience dealing with test programs, the problems that routinely come up and the decision making needed to work through them.

Discussing problems during flight tests of F-15 fighter jets, Bridges provided a bit of insight into how he views such issues and what it takes to consider grounding a vehicle.

"Certainly, we're interested inn anything that falls off test aircraft and anything that could cause a problem," he said. "I will tell you that the desert floor around Edwards is littered with so-called F-15 tail feathers, little flaps around the engine nozzles, and other things like that that did not work out too well on aircraft but were not thought to cause damage.

"And while we really didn't like dropping things on the desert out there, in order to get the test program moving forward we did not ground the fleet every time we had some minor thing like that happen. So it really depends on what the potential for damage was. If it was a safety issue, certainly I would engage and recommend that we stop flying until we fixed it. If it's not a safety issue, we certainly tried to come up with some kind of fix."

The problem, of course, is being able to recognize a safety issue in the first place. And that's not always easy in a system as complex as the space shuttle.

"Our challenge is to receive those (warning) messages and do something about them," Gehman said later to Casey. "That's the tricky part. I agree with you completely, your presentation made some of those things crystal clear. I would say there really are two cases. There's one where you have the indicators and you have to act on them. And the other one is where in fact, you're losing your margin and you don't have indicators. And those are the really tough ones."

Casey concluded his presentation by arguing shuttle flights will remain relatively risky events regardless of any post-Columbia changes that are implemented and that as a result, NASA should consider limiting the shuttle's crew size to the bare minimum necessary to support a given mission. He also said NASA should not launch shuttles if a mission can be conducted using unmanned rockets and/or robotic systems.

After the hearing, Gehman said the board likely will not address the issue of shuttle crew size or how the vehicle is used.

"Our recommendations, our report, will attempt to quantify the costs and the risks and the benefits," he said. "It will be up to someone else to determine what you're going to charge and how we're going to pay for those things. I doubt we will specify a crew size."

Magnetic tape inside a data recorder recovered last week in Texas appears to be in remarkably good shape, despite the stresses it experienced during the shuttle Columbia's catastrophic breakup Feb. 1 and the recorder's long fall back to Earth. Engineers are increasingly optimistic about recovering potentially valuable data from the salvaged tape that could shed additional light on the aerodynamic forces and temperatures the shuttle experienced during its final minutes.

"They're taking a great deal of care with it," said Bradley Allen, a spokesman for Imation Corp., a Minnesota company that specializes in data storage and recovery. "My understanding is at least visually, it came in in fairly good condition considering what the device went through."

The so-called OEX recorder was located last week by search crews walking a grid near Hemphill, Texas. It was found slightly embedded in soft ground and while the case showed signs of damage, it appeared to be surprisingly intact.

The recorder was shipped to Imation Friday for initial inspection. Imation engineers opened the OEX recorder over the weekend and first removed unrecorded tape from the supply reel to gain experience handling the material. They then removed the recorded tape on the takeup reel and began cleaning it by hand.

The tape will be shipped to the Kennedy Space Center Tuesday, where it will be copied. Only then will engineers begin the process of playing back whatever data might be present.

Unlike the reel-to-reel recorders familiar to audiophiles, those with side-by-side takeup and supply reels, the OEX recorder features two large reels stacked on top of each other. The lower supply reel plays out tape when the machine is activated and after data is encoded, the tape is wound onto the upper takeup reel.

The OEX tape was broken between the supply and takeup reels, but engineers say the amount of tape seen on the takeup reel indicates the recorder began operating as planned roughly 15 minutes before Columbia's descent began.

Columbia was the only shuttle equipped with an OEX recorder. Columbia was NASA's first space shuttle and as such, it was more heavily instrumented than subsequent orbiters to provide essential test flight data.

While NASA already has telemetry from Columbia that was beamed back to Earth in realtime during the shuttle's descent, the OEX recorder was designed to store data from hundreds of other sensors, providing direct measurements of temperature, vibration, dynamic pressure and other forces during launch and re-entry.

Assuming the tape holds readable data, NASA investigators hope to gain potentially crucial new insights about Columbia's final minutes. At the very least, officials say, the OEX data should help investigators validate, or confirm, the realtime telemetry already in hand, which in some cases was garbled during transmission.

The OEX recorder carried 9,400 feet of 1-inch-wide 28-track magnetic tape. The device operates at 15 inches per second - 75 feet per minute - and can hold two hours worth of data. NASA officials say the recorder was activated 15 minutes before Columbia's re-entry began, or around 8 a.m. on Feb. 1. The recorder presumably ran until vehicle breakup a few seconds past 9 a.m.

But at least some of the tape near the point where it separated between the takeup and supply reels is too damaged for any data recovery. That lost data presumably covered the very final seconds of entry just prior to breakup.

NASA today announced a revamped management team to oversee the agency's internal investigation of the Columbia disaster in accordance with a request made late last month by the independent Columbia Accident Investigation Board.

The concern by the board was that senior NASA managers overseeing the disaster investigation - managers who played a role in clearing Columbia for launch and then managing its mission - would at some point face questioning by the CAIB about the decisions they made leading up to launch and during the conduct of the flight.

"It has become apparent that some of the chief managers of the investigation which NASA and this board share are also members of these boards that we're going to be looking at," Harold Gehman, CAIB chairman, said March 4. "We are then put into the place of having the investigators investigate themselves.

"That's not exactly true because NASA is not investigating management issues. Only we are investigating management issues," he said. "But ... I can't possibly have key investigatory managers also be the people whose performance we're looking at in other areas."

NASA today announced the formation of a new team - the NASA Accident Investigation Team, or NAIT - that will take over the role of the original Mishap Response Team that was formed immediately after Columbia's destruction Feb. 1. The MRT was chaired by Linda Ham, a former flight director who served as chairman of the agency's mission management team.

The MMT, a panel of senior shuttle managers formed in the wake of the 1986 Challenger disaster, was responsible for clearing Columbia for launch and for the top-level day-to-day decisions during the mission that defined the flight.

The MMT, for example, declined to request spy satellite imagery during Columbia's mission to inspect the shuttle's left wing for signs of damage after external tank debris fell off and hit the wing 81 seconds after blastoff. Instead, the MMT accepted a Boeing analysis indicating the shuttle could safely land despite potentially significant wing damage.

Late last month, Gehman asked NASA Administrator Sean O'Keefe to remove senior shuttle managers who played a role in the conduct of Columbia's mission from duties supporting the ongoing accident investigation.

O'Keefe initially balked at making any immediate changes, but he later agreed to assign NASA personnel not directly involved in the conduct of shuttle missions to key teams supporting the board's investigation.

And so Randy Stone, a widely respected former flight director who now serves as deputy director of the Johnson Space center, will take over as chairman of the newly formed NASA Accident Investigation Team.

The new team will be made up of three subdivisions matching similar elements of the CAIB's structure. Stone, along with chairing the NAIT, will manage a subdivision focusing on flight operations, mission control, flight planning and crew training.

Frank Benz, director of engineering at the Johnson Space Center, will oversee engineering and technology issues, including debris analysis, imagery and fault tree analysis. He will replace Ralph Roe, director of the shuttle vehicle engineering office at JSC. Jim Kennedy, deputy director of the Kennedy Space Center, will manage a review of maintenance, program management and internal processes.

"The Mishap Response Team met for the first time within two hours of the Columbia accident, and its demanding work has been highly efficient, methodical and productive," Stone said in a statement. "They have done a tremendous job under extremely difficult circumstances. Now, many of the initial mishap response activities are nearing their close, and it is time for NASA's accident support structure to transition to an organization designed to provide long term investigation support."

The statement says that over the next four to six weeks, search teams hope to wrap up search and recovery efforts in east Texas.

"Most of the organized search effort should be completed around May 1, 2003, weather permitting," the statement said. "Other activities coming to a close include NASA's Emergency Operations Center, which assisted in fielding thousands of calls about the accident and received almost 7,000 images from sources external to NASA."

The NAIT will meet for the first time Monday.

Search crews walking a grid near Hemphills, Texas, have found the shuttle Columbia's orbiter experiments recorder, or OEX, a tape recorder that stored key data about the shuttle's performance during re-entry. The recorder was found essentially intact, according to a spokeswoman for the Columbia Accident Investigation Board, but the device may have suffered heat damage and in any case, the condition of the data tape inside is not yet known.

But if data on the tape can be recovered, NASA investigators could find a gold mine of information shedding more light on the aerodynamic forces acting on the spacecraft as its flight control system struggled to keep the doomed ship on course.

"We have no way of knowing whether the data's in a condition where it can be recovered or not," said Laura Brown, a spokeswoman for the CAIB. "They suspect there may be heat damage. We just don't know what condition it might be in."

The OEX recorder was found essentially intact on the ground. Seventeen years ago, divers recovered tapes from the submerged wreckage of the shuttle Challenger and managed to extract data despite extensive damage. Engineers are hopeful they can recover data from Columbia's recorders as well.

"They're taking it to JSC (Johnson Space Center) for analysis," Brown said. "They'll clean it and they're developing a testing plan for it. They want to be as careful as they can with it so they don't lose any data."

The recorder stores data on aerodynamic pressure, temperature, vibration and other variables. Only Columbia, NASA's original space shuttle, is equipped with an OEX recorder as part of a complex system used to collect data during the ship's initial test flights. The OEX recorder should not be confused with the shuttle's operational recorders, which store additional flight data as well as voice traffic from the crew's intercom. The OPS recorders have not yet been located.

Here is a bit of background on the OEX recorders from NASA's shuttle reference book:

The support system for the orbiter experiments was developed to record data obtained and to provide time correlation for the recorded data. The information obtained through the sensors of the OEX instruments must be recorded during the orbiter mission because there is no real-time or delayed downlink of OEX data. In addition, the analog data produced by certain instruments must be digitized for recording.

The support system for OEX comprises three subsystems: the OEX recorder, the system control module and the pulse code modulation system. The SCM is the primary interface between the OEX recorder and the experiment instruments and between the recorder and the orbiter systems. It transmits operating commands to the experiments. After such commands are transmitted, it controls the operation of the recorder to correspond to the experiment operation. The SCM is a microprocessor-based, solid-state control unit that provides a flexible means of commanding the OEX tape recorder and the OEX and modular auxiliary data system.

The PCM system accepts both digital and analog data from the experiments. It digitizes the analog data and molds it and the digital data received directly from the experiments into a single digital data stream that is recorded on the OEX recorder. The PCM also receives time information from the orbiter timing buffer and injects it into the digital data stream to provide the required time correlation for the OEX data.

The SCM selects any of 32 inputs and routes them to any of 28 recorder tracks or four-line driver outputs to the T-0 umbilical; executes real-time commands; controls experiments and data system components; and provides manual, semiautomatic and automatic control.

The recorder carries 9,400 feet of magnetic tape that permits up to two hours of recording time at a tape speed of 15 inches per second. After the return of the orbiter, the data tape is played back for recording on a ground system. The tape is not usually removed from the recorder.

Editor's Note...
Due to other commitments, I was unable to immediately file a status report covering the March 18 hearing by the Columbia Accident Investigation Board. My apologies for the delay.

As investigators increasingly focus on a breach at or just behind the leading edge of the shuttle Columbia's left wing as the root cause of the Feb. 1 disaster, engineers poring over telemetry from the doomed ship are zeroing in on exactly where the breach must have occurred - and how it must have propagated - to explain the orbiter's response to the resulting aerodynamic forces that ultimately ripped the ship apart.

Within 600 seconds of the shuttle's plunge back into the discernible atmosphere 400,000 feet above the Pacific Ocean, a deadly plume of super heated gas managed to work itself into the ship's left wing, burning through a thick bundle of wires carrying data from various wing sensors and then into the left main landing gear wheel well. Once inside the wheel well, the plume apparently burned its way through the heat-softened corners of the left landing gear door, spewing out in jets at right angles to the flow of hot air rushing across the belly of the ship.

During the second day of a hearing by the Columbia Accident Investigation Board, NASA specialists outlined a wide-ranging, multi-center effort using wind tunnels, computational fluid dynamics and other sophisticated tools to develop scenarios that best explain the telemetry from the stricken spacecraft.

While the work is far from complete, they are zeroing in on a breach at or very near the leading edge of the left wing. And they are beginning to rule out scenarios that received attention earlier in the investigation, including a breach at or near the left main landing gear door and the earlier-than-normal onset of turbulence and high heating that might have resulted from any inherent "roughness" in the surface of the left wing or from unusually high atmospheric density.

Instead, investigators are assuming a small breach near the leading edge of the left wing allowed hot gas to begin entering the structure 488 seconds after entry interface, the moment Columbia began encountering the discernible atmosphere. The breach probably was there before the shuttle dropped out of orbit, but for the purposes of developing credible scenarios, investigators are assuming it opened up 488 seconds past "EI" because that's when the first signs of a temperature increase inside the wing showed up in telemetry from the shuttle.

"We're looking at about the first 600 seconds of entry, what happened from entry interface to the point where we believe there's a breach in the wheel well and the temperatures start rising," Stephen Labbe, chief of NASA's applied aeroscience and computational fluid dynamics branch, told the CAIB. "So if we can get that solved, we feel we'll have made a significant contribution to the investigation."

Entry interface occurred at 8:44:09 a.m. on Feb. 1. At 8:52:05 a.m., telemetry shows Columbia's autopilot starting to adjust the shuttle's wing flaps, or elevons, to counteract subtle but unusual aerodynamic forces acting on the left wing. Twelve seconds later, a landing gear brake line temperature sensor registered a "one bit flip" change, indicating an increase of about 1.5 degrees. The sensor was located in the left main landing gear wheel well.

At 8:52:59 a.m., data from a temperature sensor at the back of the wing suddenly went "off-scale low," indicating a complete failure. Other sensors at the back of the wing soon followed suit. The wiring for those sensors was routed forward, along the left side of the landing gear wheel well and then across the well's forward face just a foot or so from the area of the left wing's leading edge where engineers believe the breach occurred.

At 8:54:10 a.m., temperatures began rising dramatically across the wheel well and 10 seconds after that, telemetry indicates an unusual trend acting to pull the shuttle's nose to the left somehow reversed, as if the left wing suddenly gained more lift.

Labbe painted an intriguing picture of how the data might fit together. The brake line temperature increase, he said, "suggests a breach, a first initial breach into the wing."

"There must have been ingestion of hot gas in order to create that change in the wheel well," he said. "The second one is a burn through of the wire bundle that holds all of those instruments so that whatever was being ingested had to be able to burn through that wire bundle. When we get to the wheel well breach, we see a significant rate of change. Instead of just drifting up, now we see a large increase in the rate of change and that corresponds to a change in the aerodynamic trend where (the shuttle's rolling moment) was drifting negative and now it's starting to go back positive."

In the shuttle coordinate system, yaw and roll are considered positive when the shuttle is moving to the right and negative when moving to the left. During normal re-entries, the shuttle's flight control system keeps both centered around zero. But in Columbia's case, both roll and yaw went negative very early on, indicating aerodynamic forces were acting to pull the ship's nose to the left while at the same time trying to roll the ship slightly in the same direction.

Around 8:53:46, the first known piece of debris fell away from Columbia as documented in amateur video shot during the shuttle's descent across California. At 8:54:07 a.m., the fifth such "debris shedding" event was noted. The unusual change in the shuttle's rolling moment - from negative to positive - occurred at 8:54:20 a.m., just 10 seconds after the onset of a rapid climb in wheel well temperature.

At 8:54:22 a.m., a sensor mounted on the sidewall of Columbia's fuselage, well above the left wing, recorded an unusual temperature rise. Eleven seconds after that, a bright flash was seen by ground observers, followed seconds later by what appears to be a relatively large piece of debris falling away, the sixth such event and one of the two most significant.

"Somewhere between debris 5 and 6 is when we see this event where the rolling moment was drifting negative, the change in rolling moment, and it changes direction and starts this positive trend," Labbe said. "And we think this is a very key point for us in trying to understand what happened. Something changed about the configuration, some damage, and since we know we were shedding debris, something significant happened there that changed the trend on rolling moment."

Board chairman Harold Gehman then asked what sort of change in the aerodynamics of the spacecraft could cause it to suddenly start rolling back to the right.

"You've asked the $64,000 question there, I believe, and that's what our work is going to be," Labbe replied. "What it suggests early on is that I was losing lift on the left wing. And then something changed to start creating lift on the left wing, or pushing up on the left wing. ... The damage is so significant, it's creating locally a very high pressure that's on the lower surface of the wing and starting to push up on the wing."

An opening on the underside of the wing could provide that sort of lift, but engineers believe the left main landing gear door remained in place until vehicle breakup or just before. But jets of hot air spewing out around the corners of the door probably could provide sufficient pressure to reverse the rolling moment.

"I think if you have a jet, if it's coming out with a strong enough rate that you create a jet or create enough flow out of there, it will set up a shock in front of that, which will create a high pressure, which would be on the lower surface, which would push up on the wing and probably create more lift," Labbe said.

It's also possible disturbed air flow caused by a worsening breach near the leading edge could have had the same result. John Bertin, a professor of aeronautics at the U.S. Air Force Academy, told the board the loss of two or three reinforced carbon carbon panels from the leading edge could create a shock zone of higher pressure.

"That could have caused the pressure to be higher and giving you an asymmetric force," he said.

NASA's integrated aerodynamics, aerothermodynamics and thermal analysis review is attempting to figure out, using wind tunnel tests, complex computational fluid dynamics and other tools just what sort of breach must have occurred to explain what happened to Columbia.

"So what kind of hole or damage can be created in from entry interface to 488 seconds that could produce that initial change in the instrumentation?" Labbe asked, referring to the initial brake line temperature rise. "Then we go on to the next step. Step B is we burn through that wire (bundle) in another 42 seconds. So if we pick a location and we have a burn through, can it then also burn through the wire 42 seconds later?

"Then we have the breach into the wheel well at 600 seconds where we see the rate of change and of course, that has to be consistent with the initial breach and the burning through the wire. So you can see how we're trying to piece all these together. And then finally, we see this change in the fuselage wall temperatures and whatever is producing that, is the damage consistent?"

Contact with Columbia was lost a few seconds after 9 a.m. when the vehicle, yawing sharply to the left, broke up high above Texas. Because of the shuttle's high altitude - more than 200,000 feet - the dynamic pressure acting on the shuttle was roughly equivalent to what one would feel at sea level in a 150 mph wind. One maneuvering thruster, or just a degree or so of aileron trim can keep the ship properly oriented.

Toward the end of Columbia's flight, however, the shuttle was experiencing some 160,000 foot pounds of force acting to the left.

"That requires all four (right-firing yaw) jets, three or four degrees of aileron, sideslip, everything the vehicle had to try to counteract that moment, it was using," he said.

"Hold your arm outside of a car, you can feel (the wind) trying to pull your arm back," he explained. "That's a moment of what you're feeling about your shoulder and you're talking maybe, you know, 10 pounds, 20 foot pounds of moment. Not very much at all. And we're talking about over a hundred thousand food pounds of moment."

Even with all the damage that must have occurred because of the initial, quickly worsening breach, "the flight control system still was commanding the vehicle to do exactly what it guidance was telling it to do," Labbe said. The unusual change in sign indicating a positive roll due to increase lift on the left wing was "almost like the damage has returned the vehicle back to its original flight characteristics," Labbe said. "But then, of course, we see a rapid increase and then essentially going off the cliff there at the end."

Damage patterns in recovered debris and ongoing analysis of telemetry indicates the initial breach probably occurred at or near RCC panels 6 and 9 on the left leading edge. Or just behind them. So-called carrier panels, covered with heat-shield tiles, are bolted in place just behind the RCC panels to provide a flush surface between the carbon-carbon composite material and the tiles permanently bonded to the wing's underside.

Some investigators believe it is likely a damaged carrier panel or a broken/missing tile on a carrier panel just behind the RCC panels in question could have provided the entry point for the plume of hot air that ultimately destroyed the left wing. The day after launch, ground radars detected an object separating from Columbia that was roughly the same size as a carrier panel.

Whether a carrier panel came off before or during entry, "it would be very easy to have damage occur and such that the RCC panels themselves would come off," said board member James Hallock. "They're only held on by, I believe, two bolts. Get this thing out, get some heat in there in the right place on those inconel bolts and they could come loose and that's what could be happening, all this stuff is starting to open up into a larger area."

Engineers are conducting wind tunnel tests and carrying out complex computational analyses to determine how such a breach might worsen.

"We're going to be looking at multiple panels in this thing and other panels missing and that's really where our future work is focused, is to first do a survey of the wing leading edge and then start looking at other damage scenarios that try to produce that," Labbe said. "And then eventually, get our higher fidelity CFD (computational fluid dynamics) analysis to get to the actual flight conditions."

One issue that remains to be resolved is whether the initial breach was present before re-entry began, which most observers believe, or whether it opened up during the descent, which Labbe's scenario suggests. In recent weeks, much has been made of NASA's decision not to request high-resolution spy satellite photography of Columbia in the days after launch to look for signs of damage.

Whether the breach was the result of some weakened component failing during descent or whether a visible defect was present prior to entry is significant.

"It bears on a lot of things because if the fault just manifests itself right here (during entry), even though aerodynamic pressures are practically nothing but maybe enough to remove something or cause something that was weakened (to fail), then all this stuff about on-orbit photography becomes irrelevant," Gehman said. "It's important to know whether or not the orbiter had a pre-existing condition, which then didn't manifest itself heat wise until you got enough heat."

Regardless of when it actually opened up, the presumed breach between RCC panels 6 and 9 was in a particularly bad area. As it turns out, RCC panel 9 is precisely where two hypersonic shock fronts interact during shuttle descents.

"For the shuttle, without damage, the sweep angle (of the wing) is such that the interaction effects are relatively benign," Bertin said. "So that while there's a shock-shock interaction, the highly swept leading edge prevents you from having strong interactions."

But if multiple RCC panels were missing, providing what amounts to an unswept wing leading edge, "you'd have strong interactions and very large heating going on," Bertin said.

A blurry photograph of Columbia taken by off-duty personnel at Kirtland Air Force Base in New Mexico shows the shuttle within a minute or so of its destruction. The photo has been enhanced now and it clearly shows signs of significant damage to the left leading edge area. Bertin believes the imagery is actually showing the high-density shock zone that formed just in front of the damaged area.

"So if you were missing, maybe not one panel but maybe two panels and maybe it's downstream from the initial problem that you had and stuff like that, then you've got a little like two teeth missing from the leading edge and you've got a little notch in there," he said. "Now the flow can go in that notch and create a shock pattern that in my mind kind of looks like what the Kirtland photograph might be telling you."

He said the initial breach might have started out small, but it would have quickly worsened.

"I'm assuming RCCs possibly were lost in time and a very early one, maybe one would be missing, maybe more," Bertin said. "But then because the under structure is exposed, that some additional damage occurred and other ones would have come off in some fashion. With just one missing, you could get the damage that maybe was observed eventually. But from seeing the Kirtland (photo), I'd think you'd have a pretty good piece missing."

Once the plume from the breach got into the wing, it quickly made its way into the left landing gear wheel well. The exact mechanism is not yet known but investigators have recovered debris from the landing gear door attachment system that indicates some areas in the well were subjected to temperatures high enough to melt titanium, nearly 3,000 degrees. Interestingly, sensors in other areas of the well did not record anything out of the ordinary.

"When this plume entered, it can bounce around," Hallock said. "This is a very rarified atmosphere still and so we could be having 3,000 degrees at one end, which is melting titanium, and at the other end we'll have a sensor that doesn't even know much is happening. You've got to have enough molecules in there, atoms in there, to be able to convey the temperature itself.

"Temperature is a quantity that depends on having something for it to register on," he explained. "You've seen in these reports where they say astronomers have found a place where the temperature is 10 million degrees and this is a place in space itself. Why? There's two or three molecules moving around with such energy that yes indeed, if you had a thing that those things could hit against, they would register a temperature that high.

"So don't think of it as being like heating up the air in this room. It's very different because there are so few molecules there that you can get a great gradation right across the entire area."

Gehman said the board was particularly interested in the sort of chemical reactions that can occur when aluminum is subjected to extreme temperatures.

"What we're leading to, of course, is a scenario in which a new path into the wheel well could be developed in seconds," he said. "We're trying to establish just how rapidly other kinds of processes can rearrange the inside of the wheel well and then match up with these temperatures. Right now, we're still in the exploratory stage of that."

In other developments, Gehman said the board is close to releasing "interim recommendations" to NASA. He would not discuss what those recommendations might require, but after the news conference he told reporters one of them will focus on how NASA and the operators of military imaging systems like spy satellites should work together in the future.

"The business of NASA and the various intelligence gathering agencies of United States getting their act together so at they don't talk past each other - we're talking about on-orbit photography and things like that - NASA doesn't need to wait, they can go ahead and get that sorted out right now," Gehman said. "I'm not going to comment on exactly what could be done, but one of the earliest recommendations we think is coming up for board consideration is guidance to NASA to get their act together."

He said NASA personnel were not at all up to date on the capabilities of modern military imaging assets and that no interface existed to bridge that gap. Agency managers decided early on not to request spy satellite imagery of Columbia's left wing because they did not believe the systems had enough resolution to see presumably small signs of damage on the leading edge or in the heat-shield tiles.

While Gehman did not discuss the capabilities of modern imaging systems, Ted Molczan, a respected satellite observer, has calculated that Columbia could have been imaged on multiple occasions by classified optical imaging satellites. Resolution would have varied from six to 16 centimeters, or 2.3 to about six inches.

"We think both sides of the house bear equal blame," Gehman said. "Improvements in on-orbit photography that have come along, nobody from that part of the house has come down here (to NASA), knocked on their door and said, you know, things have changed since we made this agreement. And NASA doesn't have the right people cleared to receive the data. ... They made decisions without having the right information. The point is, this is a system that broke."

Editor's Note...
Due to other commitments, I was unable to immediately file a status report covering the March 17 hearing by the Columbia Accident Investigation Board. My apologies for the delay.

A NASA flight director told the Columbia Accident Investigation Board Monday he was amazed the doomed spacecraft was able to continue flying in relatively normal fashion for nearly 10 minutes while shedding multiple pieces of flaming debris as a plume of superheated air burned its way into the stricken ship's left wing.

The shuttle's flight computers faced an impossible task. But in silent testimonial to the foresight and cleverness of their programmers, the computers methodically adjusted the positions of wing flaps, or elevons, to offset steadily increasing levels of aerodynamic drag acting to pull the ship's nose to one side.

At 8:52:05 a.m. on Feb. 1, one minute and 12 seconds after Columbia entered the region of peak heating off the coast of California, analysis of telemetry from the doomed craft shows the first indications of the computer system reacting to counteract an unusual yaw to one side by adjusting the shuttle's aileron trim. Fifty-six seconds later, the computers began counteracting an additional rolling motion, or moment.

The space shuttle is not equipped with ailerons like a typical airplane. Instead, each wing has two large flaps, or elevons, one inboard and one outboard, that can be positioned independently to produce the same effect as ailerons.

"The aileron is a theoretical difference between the elevon position on one side of the vehicle and the elevon position on the other side of the vehicle," said Robert "Doug" White, director of operational requirements for United Space Alliance, the shuttle prime contractor. "By adjusting the elevons ... you can create an aileron effect. So that aileron effect was keeping the vehicle flying the way we wanted it to. So as the forces began to change on the vehicle, the trim changed and we saw that in the data."

At 8:58:03 a.m., the telemetry shows a sharp increase in the movement of the shuttle's elevons to keep the ship pointed in the right direction.

"The vehicle was in control and was responding to commands up to that point and after that point something changed, apparently," White told the CAIB. "It still continued to be in control and still continued to respond to commands, but the rates and the amount of muscle it needed to continue flying the vehicle the way it should be flown was continuing to increase. Something definitely happened at that point, again we don't know what, but something definitely happened at that point to cause the flight control system to need more muscle and start having to fight harder to control the vehicle."

Board member Sheila Widnall, an aerodynamicist, observed: "That really coincides with a rather sharp increase in the rate of rise of dynamic pressure."

"Yes," said White, "it does."

What might have happened at that moment is not yet known. But Columbia was in distress almost from the moment it began experiencing the effects of atmospheric heating high above the Pacific Ocean approaching the California coast. Video shot by amateurs, several of them technically accomplished amateur astronomers, show multiple pieces of debris falling away from Columbia beginning at 8:53:44 a.m., roughly three minutes after entering the region of peak heating. It is likely debris was shed even earlier than that, out of view of the cameras.

Investigators believe a breach at or near the leading edge of the left wing allowed a jet of super-heated air to burn its way into the unpressurized structure. The latest thinking, NASA sources say, is that the plume entered the wing around the position of reinforced carbon carbon panel No. 6, one of 22 such protective carbon composite panels making up the leading edge of the wing. This region of the wing was hit by debris falling off the shuttle's external tank 81 seconds after liftoff. The RCC panel or its mounting hardware may have been damaged enough by the debris strike to cause a breach during entry. It's also possible damage to a carrier panel just behind the lower edge of the panel provided an entry point for hot air as Columbia descended.

NASA is having tests conducted at Wright Patterson Air Force Base in part to determine if debris seen floating away from Columbia the day after launch could have come from this area. While engineers are still working to pin down the exact breach location, the above scenario provides the best match yet with telemetry and the known aerodynamic forces acting on Columbia as it returned to Earth.

Once inside the wing, the plume of super-heated air appears to have burned through electrical cables routed along the outside of the left main landing gear wheel well just a foot or so behind the RCC panel, ultimately eating its way into the well itself where it triggered additional sensor failures and elevated temperatures. The plume may have jetted out of the wing through gaps near the corners of the heat-softened aluminum landing gear door.

Whatever the exact sequence of events, the left wing ultimately failed as the shuttle yawed out of control around 9 a.m.

Flight director Paul Hill, who has been coordinating NASA's efforts to integrate amateur video into the agency's second-by-second entry timeline, said imagery of Columbia's catastrophic plunge across the southwest holds no clues as to exactly what was falling away from Columbia or even how large the pieces, whatever they were, might have been. Only relative sizes can be inferred. "I am confident that many, if not all, of the things we label as 'debris shedding events' are, in fact, some object coming off of the orbiter," Hill said. "Can I tell you is it golf ball sized, or is it the size of this sheet of paper? I can't.

"It very well could be something as small as a marble in most of those videos and the ones we think are so significant and have gotten us so excited, those things could be golf ball sized. We really don't know. We know relative sizes, we know relative motions, but we don't know specifically what they are.

"But we are very confident, based on the way they behave after they separate from the orbiter, that they are, in fact, separate ballistic objects or objects that have mass in almost all cases. In the case of some of these flares, they could be something different like combustion products."

A major flaring event occurred around 8:54:33 a.m., just prior to the separation of an object known as debris 6. Other flares were observed later in the sequence.

"It is possible it is something that burned and came off the vehicle," Hill said of debris 6 and its associated flare. "It is what you would expect to see if we were to, say, vent a fluid or if we were to burn something and as we gave off combustion products - significant combustion products, not something on the order of, say, one of our reaction control jets - but if we were actually burning something substantial and as we put that out in the plasma wake, you would expect, because that would have relatively no mass, certainly when compared to an object, that those combustion products would immediately go essentially static compared to the orbiter or compared to what we consider normal ballistic behavior for an object that has significant mass.

"So it is reasonable to assume that something came off that was very light or that was some kind of combustion product, like potentially aluminum slag that also was burning as it came off the orbiter and then went stationary there in the wake and looked more persistent."

Of 16 documented debris shedding events, debris 6 and 14 were by far the brightest. Debris 14 was the brightest of all. "Debris 6 you can see persists, depending on the video you look at, for between 6 and 12 seconds," Hill said. "Debris 14 we see persist for four-and-a-half to seven-and-a-half seconds. But debris 14 also is much, much brighter than any other object, including debris 6. How do you interpret that? We're not sure.

"We do think that relative brightness is an indicator of something that's larger and more massive," he said. "We think the amount of time that individual flares or the light around the debris persists is also indicative of the larger ballistic numbers, which tells you you're dealing with something that's probably larger and heavier. But that's as much as we know."

While the video does not yet shed light on the nature of the debris, it clearly documents a surprising number of events. Hill said engineers "continue to be shocked that we had debris coming off the orbiter as we crossed the California coast."

"We clearly had an external breach in the vehicle and had hot gas somewhere in the left wing for that significant period of time and the vehicle flew perfectly, no indication of what was going on in flight control and virtually no indication of what was going on in telemetry on the ground, other than we saw a few temperature, pressure indications that didn't make sense to us," he said. "But aside from that, the vehicle flew like a champ until right up until the breakup. So that did surprise us."

But Hill said he was not surprised search teams combing eastern Texas for debris have not recovered more wreckage.

"Are we surprised that we only have 15 to 20 percent by weight of the orbiter? I don't think so," he said. "I would think when you first see the debris count and you see how many individual pieces of debris (have been recovered), our first reaction was one of surprise, how could we have gotten that much of the orbiter down from 200,000 feet intact?

"I think you've all seen at KSC, what they have is a whole lot of little tiny pieces of what used to be an orbiter. And if you go look at it laying on the ground there in the high bay at KSC, you don't have a spacecraft laying there, you've got a whole lot of nothing. And I think that fits in with what our conventional wisdom was prior to this."

At Monday's hearing, the second held by the Columbia Accident Investigation Board, an expert in re-entry breakups said the shuttle's destruction was in keeping with the mechanisms known to be at work during more mundane satellite entries.

"The heating is like, in a sense, cooking an onion," said William Ailor, director of the Aerospace Corp.'s Center for Orbital and Reentry Debris Studies. "You basically start from the outside and then as you heat the pieces up to a point where the materials will fail, that'll expose some new materials, they'll go through the same process and the object can be broken apart."

Interestingly, Columbia's breakup, in general, mirrored the way much smaller, fragile satellites and rocket stages break apart when falling through the atmosphere.

"Basically, a typical way for things to break up when they re-enter is they will come down through the atmosphere for a certain amount of time, they look absolutely fine, we've seen videos of these things where they just look like spacecraft coming down. All of the sudden, they come apart and when they come apart, they just disintegrate.

"That altitude typically is around 42 nautical miles plus or minus a few nautical miles," he said. "But that's a pretty good guess. Just as a rule of thumb, it seems like a critical point for spacecraft re-entry and breakup is around 42 miles."

Unlike re-entering satellites, Columbia had a thermal protection system and wings to provide some amount of lift. Even so, the orbiter only made it to an altitude of around 38 miles before suddenly, and catastrophically, breaking up.

Ailor said the recovery of debris shed early in Columbia's descent likely will prove critical to determining the root cause of the disaster.

"The orbiter was controlled for a good period of the time and if evidence is found that could have occurred during that period and it indicates a particular flow pattern or something like that, I think that could be very useful," Ailor said. "I think the early debris would be very critical to an analysis like that."

Such debris will be difficult to find. As of now, nearly seven weeks after the disaster, no wreckage has been found west of Texas. But Hill's team has been able to determine the probable trajectories of several pieces of debris that fell off early. Using that data, researchers have found ground radar traces matching at least four debris shedding events, three of them in the debris 6 "footprint." Investigators are just now beginning to look for radar traces in the presumed debris 14 footprint.

"We think the brighter objects are more massive, are more significant, potentially higher ballistic numbers," Hill reiterated. "Certainly the (brightening associated with) the individual pieces of debris persists longer. We expect that those objects are more massive, higher ballistic number, because we think that the reason they persist longer is they are moving faster so they stay lit, they have their own plasma wake longer than, say, some lighter things, say an individual tile comes off versus some other heavier object.

"But I'll also say we cannot just look at these videos and determine what is it that's coming off the vehicle. Are we losing a tile here, are we losing some section of ... thermal blanket that's on part of the external surface of the vehicle? We can't tell that. And until this day, with the good data we have on the ballistic analysis and the footprints, we still cannot say exactly what it is we see coming off. We are making some judgments on which of them are more significant or more massive than the others (such as) debris 6 and debris 14."

Said Ailor: "The work that's going on relative to finding the debris is really an important part and that really has to be emphasized. That's going to be a key to solving this puzzle, I believe."

Revision H of the CBS News-compiled STS-107 integrated entry timeline has been posted. This revision includes significant updates from NASA's latest STS-107 Master Timeline (rev. 15), including the location and start/stop times of video shot during Columbia's descent, unexpected S-band communications drop outs and other details about the shuttle's post loss-of-signal trajectory. As always, suggestions, corrections and comments are appreciated.

William Readdy, associate administrator for spaceflight and a former shuttle commander, told the Columbia Accident Investigation Board he did not consider asking for a spy satellite inspection of Columbia's left wing during the doomed ship's mission because the agency had already concluded the shuttle could land safely.

But in a letter to the CAIB, the Senate and House Intelligence committees and the NASA Inspector General, Readdy said he agreed that NASA could accept an offer from an unnamed government agency - presumably the National Imagery and Mapping Agency - to perform such an inspection on a "not-to-interfere basis."

But no such inspection was ever formally requested by NASA and no such remote inspection ever took place.

"If we had thought for a moment there was a problem, we would have asked," Readdy told reporters today in Washington.

During Columbia's launching Jan. 16, three pieces of debris broke away from the shuttle's external fuel tank about 81 seconds into flight. One piece, roughly the size of a suitcase, slammed into the underside leading edge area of the orbiter's left wing.

When the impact was discovered during routine post-launch analysis of ascent film and video, NASA managers ordered Boeing to carry out an analysis to determine what sort of damage such an impact might have caused. The Boeing team ultimately concluded the tank debris could have caused enough damage to the shuttle's fragile heat-shield tiles to produce localized, potentially severe damage. But the engineers concluded the potential damage did not pose a safety-of-flight concern and that Columbia could safely land.

NASA's mission management team, chaired by Linda Ham, a former ascent/entry flight director, accepted that analysis and the space agency never requested help from NIMA or other agencies operating the nation's most sophisticated imaging satellites and ground-based satellite-tracking telescopes.

That decision has been the subject of second-guessing and criticism in the wake of the disaster. In the days after the mishap, shuttle program manager Ronald Dittemore said no request for satellite imagery was made because the resolution of the imagery, based on past NASA experience, would not be high enough to reveal damage to individual tiles and because the Boeing analysis had concluded Columbia could land safely.

During Columbia's mission, however, Wayne Hale, a senior flight director now serving as launch integration manager at the Kennedy Space Center, made inquiries about the possibility of Air Force help inspecting Columbia. But those initial efforts were terminated by senior management.

"The SSP (space shuttle program) did not want any data and in fact there was never a formal MOD (mission operations directorate) request made from the FDOs (flight dynamics officers) or the Flight Director," Steve Stich, a flight director himself, wrote in an email to a colleague.

In a February interview, Hale declined comment on the matter, saying "I probably ought to wait until I tell the board my story. That's coming up."

Readdy's letter to the CAIB, obtained by CBS News today, shows more senior managers also discussed the issue.

"A NASA individual visited me in my office," Readdy's letter to the CAIB begins. "That person and another individual from another agency had been discussing the external tank debris issue during STS-107 ascent. He wanted to discuss an 'offer of support' from the other agency with respect to observing the space shuttle Columbia on orbit. He explained that NASA would have to request that support on an emergency or high priority basis.

"I explained that the ET debris and possible implications to the left wing thermal protection system had been analyzed and reported to the Mission Management Team and documented in MER (mission evaluation report) daily report FD (flight day) 12 dated 1/28/03 1245 GMT.

"My understanding was that the space shuttle program was well aware of those capabilities that could be provided by the other agency and it had concluded that the offer would not contribute to the analysis. I related that as well as the conclusion reached by the MMT that there was no 'safety of flight' issue, and for those reasons there was no rationale for requesting emergency or high priority support.

"He reiterated that the other agency desired to support on a 'not-to- interfere' basis. I acknowledged this information, told him again that this was not viewed as a 'safety of flight' issue, but told him to accept the offer of support on a 'not-to-interfere' basis."

Ted Molczan, a respected satellite observer, has calculated that Columbia could have been imaged on multiple occasions by classified optical imaging satellites. Resolution would have varied from six to 16 centimeters, or 2.3 to about six inches.

"As of this writing, the precise cause of the Columbia accident is unknown, so it is impossible to know whether or not high-resolution imagery would have been useful," Molczan writes on a web page devoted to the topic. "There may not have been any outwardly visible signs. Even if there was something portentous to be seen, the outcome might have been the same. At this point in the investigation, having clear imagery of the left wing probably would be valuable, but that is easy to say in hindsight."

In other developments, Readdy sent a letter Wednesday to Michael Kostelnik, deputy associate administrator for the space shuttle and the international space station programs, asking him to "begin to identify those critical actions now that we believe need to be completed before a safe return to flight can be assumed. We will adjust this preliminary planning as necessary as we receive recommendations from the CAlB."

"The Deputy Associate Administrator for International Space Station and Space Shuttle Programs will establish a formal "Return to Flight" team, and provide direction for the team to address these actions and other actions determined necessary to comply with the formal recommendations of the CAIB," Readdy wrote.

The team "will plan for a safe return to flight as soon as practicable. As a goal, the SSP shall plan for corrective actions and reviews which support a launch opportunity as early as the Fall of 2003. The team will work closely with the leadership of the International Space Station (ISS) program to ensure that return to flight plans support an optimal return to the tasks of ISS assembly and continued logistics support."

Readdy said the team should consider:

• A thorough review of key shuttle systems, including the insulation currently used on the external tank;
• Development of in-flight tile inspection and repair kits;
• A review of radar and photographic coverage policies for launch and entry;
• A review of failure modes and effects analyses, critical items lists, waivers and hazards; Operational concepts for on-orbit inspection and repair of TPS;
• How in-flight safety issues are resolved, "including the appropriate level of management visibility and decision in that process."

"I am asking you to initiate these Return to Flight activities as soon as possible, establish this team, and provide a preliminary action plan no later than 1 April 2003," Readdy concluded. "You will be responsible for providing the team charter and day-to-day direction."

Readdy plans to establish and chair a Spaceflight Leadership Council to oversee return-to-flight activities. Michael Greenfield, associate deputy administrator for technical programs, will co-chair the panel.

"Much needs to be done as we move forward to fly again," Readdy concluded. "I anticipate that our processes will be strengthened and that the safety of flight enhanced as we return to flight."

Readers should keep in mind that setting this Fall as a goal for return to flight is little more than motivational talk at this point. Until the CAIB completes its report and NASA assesses what corrective actions might be necessary, talk of launch dates seems more than a bit premature.

Investigators have recovered debris from the shuttle Columbia that appears to support the increasingly held belief that the doomed ship's left landing gear door remained in place as a plume of super-heated air entering through a breach near the leading edge of the left wing wreaked havoc inside the wheel well. The heat-weakened door may have deformed enough to permit jets of hot air to spew out around the corners as the wing literally burned up from the inside, its skin buckling and shedding tiles along the way.

On another front, examination of contrast-enhanced video shot during Columbia's Jan. 16 launching indicates the possibility foam debris from the ship's external tank may have struck at least two different areas on the orbiter's left side, one well in front of the left wing, according to sources close to the accident investigation.

Running a video clip on a laptop computer, one of the sources, who spoke on condition of anonymity, showed how a suitcase-size piece of debris falling away from the external tank slammed into the lower leading edge of Columbia's left wing. That much was already known. But playing the clip over and over again in a loop, he pointed out a subtle brightening as the debris fell past the left side of Columbia's fuselage near the extreme forward part of the wing known as the "chine" area.

"It tumbles and then I want to point out a subtlety to you," he said. "Watch the contrast against this black line (in the chine area) and you'll see what appears to be an apparent contact way up here. We're not sure if it actually contacts it or not. It may just be the light foam against the dark background. ... But you can see it against the dark."

(Editor's note: For readers with access to the time-stamped video, look for a subtle brightening in the black chine area at 15:40:21.847 GMT. The leading edge impact occurs at 15:40:21.882 GMT.)

One of the earliest signs of anything amiss aboard Columbia during re-entry was an unusual temperature increase in a water dump nozzle located on the left side of the fuselage just behind the crew cabin hatch. No one has yet been able to explain that telemetry, but the nozzle is located near the chine area in question.

Regardless of whether the chine area suffered an actual debris impact - the brightening may simply be the result of lighting effects as the debris tumbled toward the wing - the sources said investigators are increasingly convinced a major breach occurred at or near the site where that same piece of debris crashed into the bottom side of the leading edge of the shuttle's left wing near where it joins the fuselage. And they are increasingly convinced a plume of super-heated air entering the breach worked its way into the left main landing gear wheel well and that the landing gear door remained in place as the disaster unfolded.

Heat-damaged debris indicates the plume of rarified but extremely hot air shooting into the well heated the aluminum structure of the left landing gear door enough to cause it to deform slightly, possibly forming gaps at the corners that allowed jets of hot air to spew out.

The sources stressed that no conclusions have been drawn and that scenarios like the one outlined above may be incorrect. "Think of what kind of disaster we'd have if we jump to a conclusion that fits all the facts and come up with the answer and it's the wrong answer," one of the investigators said. "So we have to be prepared to really look at multiple answers and not jump to a conclusion."

But so far, a leading edge scenario, or one very much like it, provides the best fit with telemetry from the shuttle and damage patterns seen in recovered debris.

"This event started to evolve almost immediately after EI (entry interface), it's fairly clear that the mechanism of failure had to be in place before the re-entry," one of the sources said. "So we're looking for mechanisms which lead to a very rapid problem occurrence after Ei.

"There was a lot of concern about the (landing gear) door because as everybody knows, that's a very weak area. And the initial photographs appeared to indicate the foam may have hit the door area or adjacent to it. Where we're at now has been really moved. In my opinion, it is low probability that we're looking at a strike on the door or a door issue or acreage issue around it. That it's much more likely that we have a problem or a breach that occurred up in the RCC area or the carrier panels adjacent to that."

He was referring to the 22 reinforced carbon carbon composite panels making up the leading edge of the left wing and narrow, removable panels equipped with protective tiles on one side that form a flush interface between the RCC panels and heat-shield tiles permanently bonded to the underside of the wing. The carrier panels are bolted in place with screws that go through the tiles on each end making such tiles inherently weaker than those without such holes. The screws are covered by a ceramic plug.

Three pieces of debris appeared to separate from Columbia's external fuel tank 81 seconds after launch. In the contrast-enhanced video released Tuesday, a chunk measuring 25 by 15 inches can be seen slamming into the left leading edge around RCC panels 6, 7 and 8. This same piece may have glanced off the chine area as well. "It may be more complicated than we have assumed it to be because it's possible - not probable, but possible - that there may be multiple breaches," one of the sources said. "We know there were three pieces that came down, if three pieces come down you have to think in terms of there potentially having been multiple breaches. As we look at this, we may be seeing sprays coming from different directions, which will be confusing to us as we go through this."

Whether the known foam impact occurred directly on one of the RCC panels or a carrier panel or both is not yet known. But the sources interviewed for this story said relatively minor problems with either component likely would grow in the fierce heat of re-entry, quickly leading to a re-entry disaster like the one that claimed Columbia and its crew.

For example, if one of the so-called T-seals used to hold an RCC panels in place was damaged or missing, enough of a gap probably would exist to let super-heated air into the void behind the leading edge. Likewise, a missing carrier panel tile would leave an exposed surface susceptible to burn through. While the gas in this case is not ionized enough to meet the textbook definition of a plasma, it is more than hot enough to melt the wing's aluminum sub-structure.

"You've got a gas there that is at 10,000 degrees," one of the investigators said. "Because it's so rarified, the transfer of the heat from that creates a temperature in (the wing) of about 2,500, 2,800 degrees. The transfer mechanism in here is what they're struggling with. It's not strictly convection, it's not strictly radiation. You're dealing with a hundred thousand times lower pressure than you have on the surface."

The resulting plume may well have moved about as Columbia rolled through normal entry maneuvers and as the breach itself worsened, subjecting different areas to extreme heat.

"If you think of a fire hose that you're not holding and it's moving all around, we may find that's more what we're dealing with," one of the investigators said. "As it hits a hole that has different surfaces, the surfaces are going to be directing it in different directions. I think when (Columbia is) in the right bank, it may very well be forcing some of this air ... laterally down the spar and then when you go into the left bank, it actually moves up. It goes from one side to the other and you might find this thing changing over periods of time depending on the hole size as it eats away, what's in its way and those kind of things. So it may be much more complicated than just trying to point a finger and say it came in this hole and it went right through the wing here."

Despite those extreme temperatures and the mercurial nature of such a plume, investigators say it would be very difficult to trigger a disaster without having a fairly sizeable area of damage. Whatever happened to Columbia, it may have started out small and rapidly worsened.

"One RCC doesn't do it and a couple of tiles won't do it," one of the sources said. "So we have to look for things that may increase in size over periods of time. One of the things we're looking at is if one panel comes off, it's likely others will come off because you've got hot air ... melting pieces and you would have a cascading kind of event. People have talked about unzippering of tiles. We're talking about unzippering of RCCs."

Alternatively, a small but growing breach in the leading edge area could cause surrounding RCC panels to partially melt and collapse inward. So far, recovered RCC panel fragments and support hardware don't provide definitive clues as to which scenario may be more accurate.

But it now seems likely a plume of hot gas entered the wing just forward of the landing gear wheel well, burning through the forward skin of the wing, spraying aluminum slag back on the inner surfaces of nearby RCC panels and ultimately working its way into the main landing gear wheel well.

Damage found in recovered debris increasingly indicates the left landing gear door remained in place until the wing itself began breaking up late in Columbia's re-entry and that a plume of super-heated air entering the wing from the breach near the leading edge worked its way into the wheel well and then out through seals around the landing gear door.

Burn damage on recovered debris just inboard of the door indicates a plume of hot gas spewed out of the well's forward inboard corner in the direction of the shuttle's centerline. Recently recovered debris indicates the possibility of a similar jet from the outboard forward corner of the door."

"There is a similar one, but much smaller in nature, on the other side," one source said. "We have a piece on the outboard side that has a very small indication of the same effect. You can't have that effect if the door is gone. You have to have something that's holding the pressure in and allowing the vent hole to occur. Again, we're coming back to the theory that if the door is lost, the door is lost very, very late in the event.

"We also have another debris item," he added, "a door hook roller uplock. It's not the hook itself, it's the pin, uplock pin, the door latches to. And it appears to be eaten away on one corner, which may be a key to us for the direction of flow.

"We believe you're getting heat coming into the well, heat and air coming into the well, building up temperature on the inside and pressure on the inside. What's happening is then that temperature and pressure is allowing the aluminum corners to get a little bit soft and the pressure pushes up the corners a little bit and that's where the events are coming from. That also indicates, again, that the door is still on."

Adding credence to that picture, search crews in Texas have recovered numerous tiles that came off the door. Had a major breach occurred in the door area, investigators believe, fewer tiles would have been recovered. And in the initial video showing the debris impact, there are no obvious signs of tile damage. Admittedly, the resolution is low, but one would expect to see a lighter color on the belly of the orbiter if the black surface layer of many tiles was removed in an impact event. No obvious brightening, however, can be detected.

"No item would you rest a case on individually," the source said. "But when you put all these together, it appears to give you a story that we're really dealing with something which is farther up from the wheel well and all these things about the wheel well and tile fractures is probably not the story."

In the next few weeks, investigators at the Southwest Research Institute plan to begin a series of tests that could shed light on just what happened when the foam impact occurred. Pieces of foam insulation roughly the same size as the chunks seen falling away from Columbia's external tank will be fired into various wing components with a powerful "chicken gun" normally used to shoot debris into jet engines.

One RCC panel and support hardware taken from the shuttle Discovery will serve as a target, as will two RCC panels removed from Enterprise, a non-space worthy shuttle prototype. In addition, foam will be fired at a landing gear door removed from Enterprise and "acreage" tile to determine the effects of impacts with broad areas of tile on the underside of the wing.

Unlike earlier tests carried out at Southwest Research Institute in 1999, the upcoming runs will use large pieces of foam and include impacts on tile edges and other areas. The tests will not be exhaustive, but "they will, I think, provide a piece of information that's going to be critical to determining what kind of damage you can do, what kind of damage you can't do."

"This isn't going to just be a piece of carbon carbon on plywood," he said. "They're actually taking the structure and instrumenting it with accelerometers and strain gauges to figure out how much of a lateral push it gets, how much compression it gets and then do the before and after."

Said the other source: "I don't see where foam is going to hit an RCC and break the (RCC). I can see more likely where it might break some of the support structure underneath it, a T-seal potentially, or shear a bolt or something. But inherently, this is a very weak area."

NASA managers meeting 90 minutes after the Columbia disaster Feb. 1 discussed a re-analysis of the potential damage caused by foam debris slamming into the shuttle's left wing during launch. But senior managers decided the public would be told, during an initial press co