Launch: 11:38 a.m. EST, 01/28/1986
End of Mission: 11:39:13 a.m. EST, 01/28/1986

Commander: Francis "Dick" Scobee
Pilot: Michael Smith
Mission Specialist: Elllison Onizuka
Mission Specialist: Judith Resnik
Mission Specialist: Ronald McNair
Payload Specialist: Gregory Jarvis
Payload Specialist: Christa McAuliffe

The Challenger astronauts, left to right: Ellison Onizuka, pilot Michael Smith, teacher Christa McAuliffe, commander Dick Scobee, satellite engineer Gregory Jarvis, Judith Resnik, Ronald McNair.

The shuttle Challenger, NASA's second manned orbiter, blasted off on its final mission at 11:38 a.m. EST on Jan. 28, 1986. The initial moments of the 25th shuttle flight appeared normal, but just over a minute into flight, Challenger exploded in a terrifying fireball. Here is part of one of the many stories the author wrote that day as Cape Canaveral bureau manager for United Press International (note: breaking news wire service stories are written "on the fly" in real time and readers familiar with Challenger's destruction will spot several inadvertent errors):

NASA says astronauts apparently dead

CAPE CANAVERAL, Fla. (UPI) – The space shuttle Challenger exploded shortly after blastoff today and hurtled into the Atlantic Ocean. The seven crew members, including teacher Christa McAuliffe, apparently were killed in the worst disaster in space history.

"It is a national tragedy," said Jesse Moore, director of the Johnson Space Center. "I regret that I have to report _ that searches _ did not reveal any evidence that the crew members are alive."

He said data from instruments, launch pad systems and other sources would be impounded for an investigation.

The explosion occurred while two powerful booster rockets were still attached to the shuttle. There was no way for the crew to escape the out-of-control spacecraft, which fell into the ocean 18 miles off the coast. Burning debris falling from the sky kept rescuers from reaching the scene immediately.

"We have a report that the vehicle has exploded," said NASA spokesman Steve Nesbitt. "We are now looking at all the contingency operations awaiting word from any recovery forces downrange."

On board the Challenger were commander Francis "Dick" Scobee, co-pilot Michael Smith, Judith Resnik, Ellison Onizuka, Ronald McNair, satellite engineer Gregory Jarvis and McAuliffe, the Concord, N.H. social studies teacher who was chosen from 11,000 candidates to be the first private citizen to fly on a shuttle.

Blow by: In this photo, black smoke can be seen billowing from an O-ring joint at the base of Challenger's right-side solid-fuel booster moments after ignition. The joint resealed itself but eventually reopened, triggering the shuttle's destruction 73 seconds after liftoff.

Unlike the shuttle Columbia during its first flights at the dawn of the shuttle era, Challenger was not equipped with ejection seats or other ways for the crew to get out of the spacecraft. McAuliffe's parents, Edward and Grace Corrigan, watching from the VIP site three miles from the launch pad, hugged each other and sobbed as the fireball erupted in the sky. Students at her school, assembled to watch their teacher's launch, watched in stunned silence.

Other students, friends and fellow teachers in Concord cheered the blastoff and then fell into stony silence as the disaster was brought home to them on television. Mark Letalien, a junior at the Concord high school, said "I didn't believe it happened. They made such a big thing about it. Everyone's watching her and she gets killed."

It was the 25th shuttle flight, the 10th for Challenger and the worst disaster in the nation's space program. It came exactly 19 years and a day from the only previous accident - aboard the first Apollo moon capsule on its launch pad Jan. 27, 1967. Astronauts Virgil "Gus" Grissom, Edward White and Roger Chaffee died in that fire.

NASA said Challenger's launch appeared entirely normal until one minute and 15 seconds after liftoff, when the shuttle had accelerated to a speed of 1,977 mph, three times the speed of sound. It was 4.9 miles up and 18 miles out over the ocean.

"Challenger, go at throttle up," mission control told the spacecraft 52 seconds after launch. Scobee's final words to mission control were: "Roger, go at throttle up." Television replays showed close-ups of the speeding ship suddenly enveloped in a ball of fire. Its engines continued firing, raising it out of the flames, but it was out of control.

Multiple contrails could be seen streaking through the sky as the $1.1 billion shuttle arced out over the Atlantic and debris fell into the sea.

In Washington, President Reagan was in an Oval Office meeting whe4n aides brought him the grim news. He rushed into a study in time to see a television replay of the explosion. His face was creased with horror and anxiety. The House of Representatives recessed in the face of the national tragedy.

Challenger's flight deck (left to right): Pilot Mike Smith, Ellison Onizuka, Judy Resnik,
commander Dick Scobee. (Credit: NASA)
Challenger's lower deck (left to right): Backup teacher-in-space candidate Barbara Morgan, Christa McAuliffe, Greg Jarvis, Ron McNair. (Credit: NASA)
Smoke billows out of the shuttle Challenger's right-side solid-fuel booster seconds after ignition as hot gas blows past O-ring seals in the joint between the lower two segments. The rupture initially sealed itself, but as the ascent proceeded it opened back up and quickly worsened as seen in the photos below. (Credit: NASA)
The space shuttle Challenger, subjected to extreme aerodynamic stresses after the failure of its external fuel tank, broke apart in the seconds after the initial conflagration. Debris from the orbiter can be seen above emerging from a cloud of burning propellant. (Credit: NASA)
The shuttle Challenger's left wing, aft engine compartment and crew cabin can be seen emerging from the initial fireball. (Credit: NASA)

A panel of outside experts led by former Secretary of State William Rogers concluded Challenger was destroyed by the rupture of an O-ring joint in the shuttle's right-side solid-fuel booster. The resulting "burn through" created a jet of flame that ultimately ate through Challenger's external tank, triggering its collapse 73 seconds after blastoff. Almost simultaneously, Challenger, traveling faster than sound, broke apart after being subjected to aerodynamic forces it was not designed to withstand. The ship's crew cabin broke away from the rest of the shuttle and crashed into the Atlantic Ocean at more than 200 mph.

The Rogers Commission report was delivered on June 6 to Camp David, Md., where President Reagan was spending the weekend. A formal presentation with the members of the commission was hgeld in the Rose Garden at the White House. The 256-page report was divided into nine chapters. The first two chapters presented a brief history of the shuttle program and past flights and detailed the events leading up to Challenger's launching on Jan. 28. The commission also presented a detailed timeline of the disaster before getting down to business in Chapter 4.

The Cause of the Accident

The Rogers Commission listed 16 findings on the primary cause of the accident before stating the following conclusion:

"The commission concluded that the cause of the Challenger accident was the failure of the pressure seal in the aft field joint of the right Solid Rocket Motor. The failure was due to a faulty design unacceptably sensitive to a number of factors. These factors were the effects of temperature, physical dimensions, the character of materials, the effects of reusability, processing and the reaction of the joint to dynamic loading."

A thorough analysis of all available evidence showed no abnormalities with the external fuel tank, Challenger and its three main engines or the shuttle's payload and records showed all the hardware used in flight 51-L met NASA specifications. Launch processing, from the initial stacking of the rocket boosters to work done at the launch pad was normal, but during assembly of the right-side booster, engineers ran into snags. One of the fuel segments that mated at the aft field joint was severely out of round and had to be forced into the proper shape with a high-power hydraulic tool. In addition, measurements showed that because of previous use, the two fuel segments in question had slightly larger diameters than normal but they still were within specifications.

Recall for a moment the construction of the joint. The upper rim of the bottom fuel segment, called a clevis, is an upward-facing U-shaped groove. The lower rim of the fuel segment above, called a tang, slides into the clevis and the resulting interlocking joint is bolted together with 177 high-strength steel pins. Running around the interior of the inner leg of the clevis are the two rubber O-ring seals. Because of the larger than normal joint diameters, at the moment of ignition, the tang and clevis had an average gap of .004 inches, which would have compressed the O-rings severely. Because the fuel segments were slightly out of round, the smallest gap was in the area where the rupture occurred during flight, although it is not known if the high compression on the O-ring was present at liftoff.

It was a record 36 degrees when Challenger took off and infrared measurements taken at the launch pad showed the temperature around the circumference of the aft field joint was in the neighborhood of 28 degrees in the area where the rupture occurred, the coldest spot on the booster. To understand the significance of the temperature factor, consider again the operation of the rocket motor at ignition when internal pressure shoots from zero to nearly 1,000 pounds per square inch. This tremendous force pushes outward and causes the joints to bulge slightly, a phenomenon known as joint rotation. During the ignition transient, the tang and clevis typically separate as much as .017 and .029 inches where the primary and secondary O-rings are located. The gap opening reaches maximum about 600 milliseconds after ignition when the motor reaches full pressure. To keep the joint sealed as the tang-clevis separation increases during ignition, the O-rings must seat properly and the commission said cold O-rings take longer to reach the proper position.

"At the cold launch temperature experienced, the O-ring would be very slow in returning to its normal rounded shape. It would not follow the opening of the tang-to-clevis gap. It would remain in its compressed position in the O-ring channel and not provide a space between itself and the upstream channel wall. Thus, it is probable the O-ring would not be pressure actuated to seal the gap in time to preclude joint failure due to blow-by and erosion from hot combustion gases," the report said.

Further, the commission found that experimental evidence showed other factors, such as humidity and the performance of the heat-shielding putty in the joint "can delay pressure application to the joint by 500 milliseconds or more." Records showed that in each shuttle launch in temperature below 61 degrees, one or more booster O-rings showed signs of erosion or the effects of heat. Complicating the picture, there was the possibility of ice in the suspect joint because Challenger had been exposed to seven inches of rainfall during its month on the launch pad prior to blastoff. Research showed ice could have prevented proper sealing by the secondary O-ring.

Launch pad cameras showed puffs of black smoke shooting from the region of the aft field joint beginning about the same time the motor reached full pressure. The commission said two overall failure scenarios were possible: a small leak could have developed at ignition that slowly grew to the point that flame erupted through the joint as photographs indicated some 58 seconds after blastoff. More likely, however, the gap between the burned O-rings and the clevis probably was sealed up by "deposition of a fragile buildup of aluminum oxide and other combustion debris. The resealed section of the joint could have been disturbed by thrust vectoring (steering), space shuttle motion and flight loads induced by changing winds aloft." NASA revealed after the accident that wind shear was higher for Challenger's mission than for any previous shuttle flight.

That the shuttle booster joints were faulty and overly dependent on a variety of factors was clear. The commission's findings on the secondary causes of the disaster were more subtle but just as damning to the space agency.

The Contributing Cause of the Accident

"The decision to launch the Challenger was flawed," the Rogers Commission said. "Those who made that decision were unaware of the recent history of problems concerning the O-rings and the joint and were unaware of the initial written recommendation of the contractor advising against the launch at temperatures below 53 degrees Fahrenheit and the continuing opposition of the engineers at Thiokol after the management reversed its position. They did not have a clear understanding of Rockwell's concern that it was not safe to launch because of ice on the pad. If the decision makers had known all of the facts, it is highly unlikely that they would have decided to launch 51-L on January 28, 1986."

Before shuttles are cleared for flight, a formal "flight readiness review" is held by top NASA managers to discuss any open items that might affect a launch. Previous flights are reviewed to make sure any problems had been addressed before commiting the next shuttle for launch. Mulloy testified NASA management was well aware of the O-ring issue and cited the flight readiness review record as proof. He was correct in that during several preceding flight readiness reviews, the O-ring problem was mentioned. But it was only mentioned in the context that it was an acceptable risk and that the boosters had plenty of margin. It was not mentioned at all during the 51-L readiness review.

"It is disturbing to the commission that contrary to the testimony of the solid rocket booster project manager, the seriousness of concern was not conveyed in Flight Readiness Review to Level 1 and the 51-L readiness review was silent."

Keel said later the real turning point in the commission investigation came on Feb. 10 during a closed hearing in Washington. It was there the commission learned of the launch-eve debate over clearing Challenger for launch. Boisjoly would later recall the events of Jan. 27 in this manner:

Boisjoly: "I felt personally that management was under a lot of pressure to launch and that they made a very tough decision, but I didn't agree with it. One of my colleagues that was in the meeting summed it up best. This was a meeting where the determination was to launch and it was up to us to prove beyond a shadow of a doubt that it was not safe to do so. This is in total reverse to what the position usually is in a preflight conversation or a flight readiness review. It is usually exactly opposite that."

Commission member Arthur B.C. Walker: "Do you know the source of the pressure on management that you alluded to?"

Boisjoly: "Well, the comments made over the [teleconference network] is what I felt, I can't speak for them, but I felt it, I felt the tone of the meeting exactly as I summed up, that we were being put in a position to prove that we should not launch rather then being put in the position and prove that we had enough data for launch. And I felt that very real."

The Rogers Commission concluded that a "well structured" management system with the emphasis on flight safety would have elevated the booster O-ring issue to the status it deserved and that NASA's decision-making process was clearly faulty. One can only wonder how many other launch-eve debates occurred during the previous 24 missions that were never mentioned because the flight turned out to be a success.

"Had these matters been clearly stated and emphasized in the flight readiness process in terms reflecting the views of most of the Thiokol engineers and at least some of the Marshall engineers, it seems likely that the launch of 51-L might not have occurred when it did," the commission said.

The commission also determined that the waiving of launch constraints based on previous success came at the expense of flight safety because the waivers did not necessarily reach top-level management for a decision. Finally, the commission charged engineers at the Marshall Space Flight Center where the booster program was managed had a "propensity" for keeping knowledge of potentially serious problems away from other field centers in a bid to address them internally.

An Accident Rooted in History

"The Space Shuttle's Solid Rocket Booster problem began with the faulty design of its joint and increased as both NASA and contractor management first failed to recognize it as a problem, then failed to fix it and finally treated it as an acceptable flight risk," the Rogers Commission said.

Morton Thiokol won the contract to build shuttle boosters in 1973. Of the four competitors, Thiokol ranked at the bottom for design and development but came in first in the management category. NASA later said Thiokol was selected because "cost advantages were substantial and consistent throughout all areas evaluated." The result was an $800 million cost-plus-award-fee contract.

Morton Thiokol hoped to keep costs down by borrowing heavily from the design of the Titan 3 solid rocket motors. Both systems, for example, used tang and clevis joints but the shuttle design had major differences as well. Unlike in the Titan, which relied on a single O-ring seal, two rubber O-rings were employed in the shuttle booster and both faced heavy pressure loads at launch. The way the seals worked in the shuttle boosters was elegant in its simplicity. Before fuel joints were to be mated, an asbestos-filled putty would be used to fill in the gap between the two propellant faces of the fuel segments. The putty, then, would serve as a barrier to prevent hot gas from reaching the O-ring seals. But the putty was plastic so when the rocket was ignited, internal pressure would force the putty to flow toward the outside of the joint. In doing so, air between the putty and the O-ring would become pressurized, forcing the O-ring to "extrude" into the minute gap between the clevis and tang. In this manner, the joint would be sealed and even if the primary O-ring failed to operate, the secondary seal would fill in the gap, so to speak. To make sure the O-rings were, in fact, able to seal the joints prior to ignition, Thiokol included a "leak test port" in each booster joint. Once assembled, the space between the two O-rings could be pressurized with 50 psi air. If the pressure stayed steady, engineers would know the joint was airtight and that no path from the propellant to the primary O-ring existed for hot gas or flame.

So much for theory. When testing began, results were not what Thiokol engineers expected.

The design of the joint had led engineers to believe that once pressurized, the gap between the tang and clevis actually would decrease slightly, thereby improving the sealing action of the O-rings. To test the booster's structural integrity, Thiokol conducted "hydroburst" tests in 1977. In these tests, water was pumped inside a booster case and pressurized to 1.5 times actual operating pressure. Careful measurements were made and to their surprise, engineers realized that the tang and clevis joint actually bulged outward, widening the gap between the joint members. While Thiokol tended to downplay the significance of the finding at the time, engineers at Marshall were dismayed by the results. John Q. Miller, a chief booster engineer at the Alabama rocket center, wrote a memo on Jan. 9, 1978, to his superiors, saying, "We see no valid reason for not designing to accepted standards" and that improvements were mandatory "to prevent hot gas leaks and resulting catastrophic failure." This memo and another along the same lines actually were authored by Leon Ray, a Marshall engineer, with Miller's agreement. Other memos followed but the Rogers Commission said Thiokol officials never received copies. In any case, the Thiokol booster design passed its Phase 1 certification review in March 1979. Meanwhile, ground test firings confirmed the clevis-tang gap opening. An independent oversight committee also said pressurization through the leak test port pushed the primary O-ring the wrong way so that when the motor was ignited, the compression from burning propellant had to push the O-ring over its groove in order for it to extrude into the clevis-tang gap. Still, NASA engineers at Marshall concluded "safety factors to be adequate for the current design" and that the secondary O-ring would serve as a redundant backup throughout flight.

On Sept. 15, 1980, the solid rocket booster joints were classified as criticality 1R, meaning the system was redundant because of the secondary O-ring. Even so, the wording of the critical items list left much room for doubt: "Redundancy of the secondary field joint seal cannot be verified after motor case pressure reaches approximately 40 percent of maximum expected operating pressure." The joint was classified as criticality 1R until December 1982 when it was changed to criticality 1. Two events prompted the change: the switch to a non-asbestos insulating putty - the original manufacturer had discontinued production - and the results of tests in May 1982 that finally convinced Marshall management that the secondary O-ring would not function after motor pressurization. Criticality 1 systems are defined as those in which a single failure results in loss of mission, vehicle and crew. Even though the classification was changed, NASA engineers and their counterparts at Morton Thiokol still considered the joint redundant through the ignition transient. The Rogers Commission found this to be a fatal flaw in judgment.

Criticality 1 systems must receive a formal "waiver" to allow flight. On March 28, 1983, Michael Weeks, associate administrator for space flight (technical) signed the document that allowed continued shuttle missions despite the joint concerns.

"We felt at the time, all of the people in the program I think felt that this solid rocket motor in particular ... was probably one of the least worrisome things we had in the program," Weeks said.

Then came the flight of mission 41-B, the 10th shuttle mission, launched Feb. 3, 1984. Prior to that time, only two flights had experienced O-ring damage: the second shuttle mission and the sixth. In both cases, only a single joint was involved. But after 41-B, inspectors found damage to a field joint and a nozzle joint. Marshall engineers were concerned about the unexpected damage, but a problem assessment report concluded: "This is not a constraint to future launches." For the next shuttle flight, 41-C, NASA managers were advised launch should be approved but that there was a possibility of some O-ring erosion. Meanwhile, to make absolutely sure the O-rings were seated properly prior to launch, the leak test pressure was increased to 100 psi and later to 200 psi, even though Marshall engineers realized that increased the possibility of creating blow holes through the insulating putty. Such blow holes, in turn, could provide paths for hot gas to reach the O-rings. In any case, the statistics are simple: of the first nine shuttle flights, when joints were tested with 50 psi or 100 psi pressure, only one field joint problem was noticed. With the 200 psi tests, more than 50 percent of the shuttle missions exhibited some field joint O-ring erosion.

So even though research was underway to improve the joint design, shuttles continued flying. On Jan. 24, 1985, Discovery took off on the first classified military shuttle mission, flight 51-C. The temperature at launch time was a record 53 degrees and O-ring erosion was noted in both boosters after recovery. Damage was extensive: both booster nozzle primary O-rings showed signs of blow by during ignition and both the primary and secondary seals in the right booster's center segment field joint were affected by heat. Thiokol engineers would later say temperature apparently increased the chances for O-ring damage or erosion by reducing resiliency. Concern mounted after the flight of mission 51-B in April 1985 when engineers discovered a nozzle primary O-ring had been damaged and failed to seat at all and that the secondary seal also was eroded. This was serious and more studies were ordered. Mulloy then instituted a launch constraint, meaning a waiver was required before every succeeding mission. Mulloy signed such waivers six flights in a row before Challenger took off for the last time.

On Aug. 19, 1985, NASA managers in Washington were briefed on the O-ring issue and the next day, Morton Thiokol established an O-ring task force because "the result of a leak at any of the joints would be catastrophic." But company engineers told the commission the task force ran into red tape and a lack of cooperation.

"The genesis of the Challenger accident - the failure of the joint of the right solid rocket motor - began with decisions made in the design of the joint and in the failure by both Thiokol and NASA's solid rocket booster project office to understand and respond to facts obtained during testing," the Rogers Commission concluded.

The panel said NASA's testing program was inadequate, that engineers never had a good understanding of the mechanics of joint sealing and that the material presented to NASA management in August 1985 "was sufficiently detailed to require corrective action prior to the next flight."

Pressures on the System

"With the 1982 completion of the orbital test flight series, NASA began a planned acceleration of the Space Shuttle launch schedule," the Rogers Commission said. "One early plan contemplated an eventual rate of a mission a week, but realism forced several downward revisions. In 1985, NASA published a projection calling for an annual rate of 24 flights by 1990. Long before the Challenger accident, however, it was becoming obvious that even the modified goal of two flights a month was overambitious."

When the shuttle program was conceived, it was hailed as the answer to the high cost of space flight. By building a reusable space vehicle, the United States would be able to lower the cost of placing a payload into orbit while at the same time, increase its operational capability on the high frontier. The nation's space policy then focused on the shuttle as the premier launcher in the American inventory and expendable rockets were phased out. Once shuttle flights began, NASA quickly fell under pressure to meet a heavy schedule of satellite launches for commercial, military and scientific endeavors. And as the flight rate increased, the space agency's resources became stretched to the limit. Indeed, the Rogers Commission said evidence indicated even if the 51-L disaster had been avoided, NASA would have been unable to meet the 16-launch schedule planned for 1986.

But NASA's can-do attitude refused to let the agency admit its own limitations as it struggled along against increasingly significant odds and diminishing resources. The Rogers Commission found that astronaut training time was being cut back, that frequent and late payload changes disrupted flight planning and that a lack of spare parts was beginning to manifest itself in flight impacts at the time of the Challenger accident.

The Rogers Commission concluded:

1. "The capabilities of the system were stretched to the limit to support the flight rate in winter 1985/1986," the commission wrote. "Projections into the spring and summer of 1986 showed a clear trend; the system, as it existed, would have been unable to deliver crew training software for scheduled flights by the designated dates. The result would have been an unacceptable compression of the time available for the crews to accomplish their required training.

2. "Spare parts are in short supply. The shuttle program made a conscious decision to postpone spare parts procurements in favor of budget items of perceived higher priority. Lack of spare parts would likely have limited flight operations in 1986.

3. "Stated manifesting policies [rules governing payload assignments] are not enforced. Numerous late manifest changes (after the cargo integration review) have been made to both major payloads and minor payloads throughout the shuttle program.

4. "The scheduled flight rate did not accurately reflect the capabilities and resources.

5. "Training simulators may be the limiting factor on the flight rate; the two current simulators cannot train crews for more than 12-15 flights per year.

6. "When flights come in rapid succession, current requirements do not ensure that critical anomalies occurring during one flight are identified and addressed appropriately before the next flight."

Other Safety Considerations

The Rogers Commission also identified a number of safety considerations to be addressed by NASA before the resumption of shuttle flights. The realization that Challenger's crew had no survivable abort options during solid rocket flight prompted the commission to recommend a re-evaluation of all possible abort schemes and escape options.

Two types of shuttle aborts were possible at the time of the Challenger accident: the four intact aborts, in which the shuttle crew attempts an emergency landing on a runway, and contingency aborts, in which the shuttle is not able to make it to a runway and instead "ditches" in the ocean. But the commission said tests at NASA's Langely Research Center showed an impact in the ocean probably would cause major structural damage to the orbiter's crew cabin. In addition, "payloads in the cargo bay are not designed to withstand decelerations as high as those expected and would very possibly break free and travel forward into the crew cabin." Not a pleasant prospect.

"My feeling is so strong that the orbiter will not survive a ditching, and that includes land, water or any unprepared surface," astronaut Weitz told the commission. "I think if we put the crew in a position where they're going to be asked to do a contingency abort, then they need some means to get out of the vehicle before it contacts earth."

If there was a clear "winner" in the Rogers Commission report is was the astronauts. Nearly every concern raised by Young and his colleagues was addressed and NASA managers privately grumbled that with the re-emergence of "astronaut power," the agency would become so conservative it would be next to impossible to get a shuttle off the ground.


The Rogers Commission made nine recommendations to conclude its investigation of the worst disaster in space history.

1. A complete redesign of the solid rocket booster segment joints was required with the emphasis on gaining a complete understanding of the mechanics of seal operation; the joints should be as structurally stiff as the walls of the rockets and thus less susceptible to rotation; and NASA should consider vertical test firings to ensure duplication of the loads experienced during a shuttle launch. In addition, the panel recommended that NASA ask the National Research Council to set up an independent review committee to oversee the redesign of the booster joints.

2. NASA's shuttle program management system should be reviewed and restructured, with the program manger given more direct control over operations, and NASA should "encourage the transition of qualified astronauts into agency management positions" to utilize their flight experience and to ensure proper attention is paid to flight safety. In addition, the commission said NASA should establish a shuttle safety advisory panel.

3. The commission recommended a complete review of all criticality 1, 1R, 2 and 2R systems before resumption of shuttle flights.

4. NASA was told to set up an office of Safety, Reliability and Quality Control under an associate administrator reporting to the administrator of the space agency. This office would operate autonomously and have oversight responsibilities for all NASA programs.

5. Communications should be improved to make sure critical information about shuttle systems makes it from the lowest level engineer to the top managers in the program. "The commission found that Marshall Space Flight Center project managers, because of a tendency at Marshall to management isolation, failed to provide full and timely information bearing on the safety of flight 51-L to other vital elements of shuttle program management," the panel said. Astronauts should participate in flight readiness reviews, which should be recorded, and new policies should be developed to "govern the imposition and removal of shuttle launch constraints."

6. NASA should take action to improve safety during shuttle landings by improving the shuttle's brakes, tires and steering system and terminating missions at Edwards Air Force Base, Calif., until weather forecasting improvements are made at the Kennedy Space Center.

7. "The commission recommends that NASA make all efforts to provide a crew escape system for use during controlled gliding flight." In addition, NASA was told to "make every effort" to develop software modifications that would allow an intact landing even in the event of multiple engine failures early in flight.

8. Pressure to maintain an overly ambitious flight rate played a role in the Challenger disaster and the Rogers Commission recommended development of new expendable rockets to augment the shuttle fleet.

9. "Installation, test and maintenance procedures must be especially rigorous for space shuttle items designated criticality 1. NASA should establish a system of analyzing and reporting performance trends in such items." In addition, the commission told NASA to end its practice of cannibalizing parts from one orbiter to keep another flying and instead to restore a healthy spare parts program despite the cost.

❏ ❏ ❏

Along with redesigning the O-ring booster joints, the agency reviewed the status of the overall shuttle program and ordered hundreds of modifications and improvements to beef up the safety of the shuttle itself. The shuttle "critical items list," which ranks systems and components according to the results of a failure, underwent a thorough review with far-reaching results. Criticality 1 components are those in which a failure leads to loss of vehicle and crew while criticality 1R systems are those in which a redundant backup is in place. Before the Challenger disaster, NASA listed 617 criticality 1 and 787 criticality 1R systems, a total of 1,404. As a result of the post-Challenger review, 1,514 criticality 1 systems were identified along with 2,113 criticality 1R components, a total of 3,627.

The numbers increased because NASA took a much harder look at the shuttle and its systems in the wake of Challenger and while at first glance they would appear to imply the shuttle is more dangerous than before, in reality they mean NASA simply has a better, more realistic understanding of the ship.

In the shuttle itself, more than 210 changes were ordered for first flight along with about 30 to widen safety margins in the powerful hydrogen-fueled main engines by improving welds and reducing bearing wear and turbine blade cracks, a source of concern in the past. Among the shuttle modifications were landing gear brake improvements and a redesign of the 17-inch valves in the main engine propellant feed lines to prevent premature closure and inadvertent engine shutdown.

Other major changes include installation of ribs to strengthen the structure of the shuttle's airframe, an automatic cutoff system to prevent maneuvering rocket problems and modifications to improve the ability of the nose section of the shuttle to withstand the tremendous heat of atmospheric re-entry. About 100 changes were made in the computer programs that actually fly the shuttle to take into account the performance of modified hardware and to improve safety margins.

NASA re-emphasized safety in mission design, implementing stricter weather criteria, new launch commit criteria and a revamped management structure that gave the final responsibility for clearing a shuttle for launch to an astronaut.

Shuttle flights resumed Sept. 29, 1988, and NASA launched 87 successful flights in a row before Columbia returned to Earth on Feb. 1, 2003.

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The Fate of Challenger's Crew

"NASA is unable to determine positively the cause of death of the Challenger astronauts but has established that it is possible, but not certain, that loss of consciousness did occur in the seconds following the orbiter breakup." NASA Press Release

"We have now turned our full efforts to the future, but will never forget our seven friends who gave their lives to America's space frontier." - Rear Adm. Richard Truly, Associate Administrator for Space Flight

The Rogers Commission did not discuss the fate of the crew or provide much detail about the crew cabin wreckage. Indeed, all references to "contact 67," the crash site of the crew compartment, were deleted from the official record, including charts that mapped various debris areas. This was done, perhaps, to preclude the possibility that anyone could find out the latitude and longitude of the cabin wreck site for diving and personal salvage. But ultimately, it was simply an extension of NASA's policy of no comment when it came to the astronauts. After all, hundreds of reporters knew the exact coordinates by eavesdropping on Navy radio. In any case, while the astronauts were not discussed in the commission report, the crew module was.

Analysis of crew cabin wreckage indicates the shuttle's windows may have survived the explosion. It is thus possible the crew did not experience high altitude decompression. If so, some or all of the astronauts may have been alive and conscious all the way to impact in the Atlantic some 18 miles northeast of the launch pad. The cabin hit the water at better than 200 mph on Scobee's side. The metal posts of the two forward flight deck seats, for example, were bent sharply to the right by force of impact when the cabin disintegrated.

"The internal crew module components recovered were crushed and distorted, but showed no evidence of heat or fire," the commission report said. "A general consistency among the components was a shear deformation from the top of the components toward the +Y (to the right) direction from a force acting from the left. Components crushed or sheared in the above manner included avionics boxes from all three avionics bays, crew lockers, instrument panels and the seat frames from the commander and the pilot. The more extensive and heavier crush damage appeared on components nearer the upper left side of the crew module. The magnitude and direction of the crush damage indicates that the module was in a nose down and steep left bank attitude when it hit the water.

"The fact that pieces of forward fuselage upper shell were recovered with the crew module indicates that the upper shell remained attached to the crew module until water impact. Pieces of upper forward fuselage shell recovered or found with the crew module included cockpit window frames, the ingress/egress hatch, structure around the hatch frame and pieces of the left and right sides. The window glass from all of the windows, including the hatch window, was fractured with only fragments of glass remaining in the frames."

Several large objects were tracked by radar after the shuttle disintegrated. One such object, classified as "Object D," hit the water 207 seconds after launch about 18 nautical miles east of launch pad 39B. This apparently was the crew cabin. "It left no trail and had a bright white appearance (black and white recording) until about T+175 seconds," an appendix to the Rogers Commission report said. "The image then showed flashes of both white and black until T+187 seconds, after which time it was consistently black. The physical extent of the object was estimated from the TV recording to be about 5 meters." This description is consistent with a slowly spinning crew module, which had black heat-shield tiles on its bottom with white tiles on its side and top.

The largest piece of crew cabin wreckage recovered was a huge chunk of the aft bulkhead containing the airlock hatch that led into the payload bay and one of the two flight deck windows that looked out over the cargo hold. The bulkhead wreckage measured 12 feet by 17 feet.

Here is a chronology of the crew cabin recovery operation and the efforts to determine the fate of the astronauts:

Mid-March -- Four astronaut "personal egress air packs," called PEAPs, are recovered along with other cabin wreckage.
April 18 -- NASA announced the crew cabin recovery operation was complete and that identifiable remains of all seven astronauts were on shore undergoing analysis.
April 25 -- The Armed Forces Institute of Pathology notified NASA it had been unable to determine a cause of death from analysis of remains. Joseph Kerwin, director of life sciences at the Johnson Space Center, began an in-depth analysis of the wreckage in a search for the answer.
May 20 -- Johnson Space Center crew systems personnel began analysis of the four PEAPs, emergency air packs designed for use if a shuttle crew must attempt an emergency exit on the ground when dangerous vapors might be in the area.
May 21 -- Investigators found evidence some of the PEAPs had been activated.
June 4 -- Investigators determined PEAP activation was not caused by crew cabin impact in the ocean.
June 9 -- Smith's PEAP was identified by serial number.
June 25 -- The PEAPs were sent to th Army Depot in Corpus Christi, Texas, for further analysis.
June 27 -- Scobee's PEAP was identified by serial number; Army investigators determined that three of the four air packs had been activated.
July 18 -- Truly received Kerwin's preliminary report on the fate of the astronauts. On July 24, NASA began informing the astronauts' families about what the investigation had found.

Some of the first wreckage recovered included four flight computers and both the cabin's operational flight recorders, used to record data about various shuttle systems and also used for the cabin's intercom system. It was on this tape that NASA heard Smith say "Uh oh" an instant before the shuttle broke apart, showing that at least some of the astronauts had a brief moment of awareness before the explosion that would claim their lives. On July 28, six months to the day after the disaster, NASA staged a news conference in Washington to discuss the investigation. Kerwin said the cause and time of death remained unknown.

"The findings are inconclusive," he wrote in a letter to Truly. "The impact of the crew compartment with the ocean surface was so violent that evidence of damage occurring in the seconds which followed the explosion was masked. Our final conclusions are:

The cause of death of the Challenger astronauts cannot be positively determined;

The forces to which the crew were exposed during orbiter breakup were probably not sufficient to cause death or serious injury; and

The crew possibly, but not certainly, lost consciousness in the seconds following orbiter breakup due to in-flight loss of crew module pressure."

Accelerometers, instruments that measure the magnitude and direction of forces acting on the shuttle during flight, lost power when the nose section ripped away two tenths of a second after structural break up began. Independent analysis of all recovered data and wreckage concluded the nose pitched down as soon as it broke away and then slowed rapidly from aerodynamic forces. Calculations and analysis of launch photography indicate the acceleration forces the astronauts felt were between 12 and 20 times the force of gravity in a vertical direction, that is, as the cabin broke away, the astronauts were violently pushed down in their seats.

"These accelerations were quite brief," Kerwin wrote. "In two seconds, they were below four G's; in less than 10 seconds, the crew compartment was essentially in free fall. Medical analysis indicates that these accelerations are survivable, and that the probability of major injury to crew members is low."

When Challenger broke up, it was traveling at 1.9 times the speed of sound at an altitude of 48,000 feet. The crew module continued flying upward for some 25 seconds to an altitude of about 65,000 feet before beginning the long fall to the ocean. From breakup to impact took two minutes and 45 seconds. Impact velocity was 207 mph, subjecting the module to a braking force of approximately 200 times the force of gravity. Any astronaut still alive at that moment was killed instantly.

When the cabin ripped away from the fuselage, the crew's oxygen supplies were left behind in the payload bay, "except for a few seconds supply in the lines," Kerwin said. But each astronaut's airtight flight helmet also was connected to a PEAP that contained about six minutes of breathing air. Kerwin said because of the design of the activation switch, it was highly unlikely the PEAPs were turned on by impact. But unlike the oxygen system, the PEAPs did not provide pressurized air and if the cabin lost pressure, they would not have allowed the crew to remain conscious.

"It is possible, but not certain, that the crew lost consciousness due to an in-flight loss of crew module pressure," Kerwin wrote. "Data to support this is:

The accident happened at 48,000 feet and the crew cabin was at that altitude or higher for almost a minute. At that altitude, without an oxygen supply, loss of cabin pressure would have caused rapid loss of consciousness and it would not have been regained before water impact.

PEAP activation could have been an instinctive response to unexpected loss of cabin pressure.

If a leak developed in the crew compartment as a result of structural damage during or after breakup (even if the PEAPs had been activated), the breathing air available would not have prevented rapid loss of consciousness.

The crew seats and restraint harnesses showed patterns of failure which demonstrates that all the seats were in place and occupied at water impact with all harnesses locked. This would likely be the case had rapid loss of consciousness occurred, but it does not constitute proof."

Despite NASA's best efforts, engineers were never able to determine if cabin pressure was lost. Astronaut Crippen said later he was convinced it did, however, because had the cabin maintained pressure there would have been no need to activate the PEAPs. He said in his view, the astronauts made a "desperate" attempt to survive by activating the PEAPs when pressure was suddenly lost.

Of the four PEAPs recovered, the one that belonged to Scobee had not been activated. Of the other three, one was identified as Smith's and because of the location of the activation switch on the back of his seat, Truly said he believed Resnik or Onizuka turned the pilot's emergency air supply on in a heroic bid to save his life. The exact sequence of events will never be known.

❏ ❏ ❏

Timeline of Challenger's Final Flight

This timeline, assembled by William Harwood and Rob Navias when both worked for United Press International, was assembled from telemetry beamed down from the shuttle, recordings made of the mission control voice command circuits, the NASA-Select audio circuit and the intercom transcript (times given in seconds after launch at 11:38 a.m. EST, Jan. 28, 1986).

0.000 - Solid rocket ignition command is sent.

Resnik, intercom: "Aaall Riight!"

0.008 - First of eight 25-inch-long, 7-inch-wide exploding bolts fire, four at the base of each booster, freeing Challenger from launch pad.

0.250 - First continuous vertical motion is recorded.

0.678 - Film developed later shows the first evidence of abnormal black smoke appearing slightly above the suspect joint in Challenger's right-hand solid rocket booster.

0.836 - The black smoke appears darkest; jets in puffs of three per second, roughly matching harmonic characteristics of the shuttle vehicle at launch, characteristics directly related to the energy stored in the shuttle structure by the twang phenomenon and released as the spacecraft is freed from the launch stand.

0.890 - Ground launch sequencer computers begin post-liftoff "safing" of launch pad structures and equipment.

1.000 - Smith, intercom: "Here we go."

2.733 - Last positive evidence of smoke above the aft attach fitting that holds the rear of the right-side booster to the external fuel tank. The aft attach fitting is a little less than two feet above the fuel segment joint.

3.375 - Last positive visual indication of smoke swirling under the bottom of the external fuel tank.

Launch commentator Harris (continuing) "... Liftoff of the 25th space shuttle mission, and it has cleared the tower."

4.339 - The three liquid-fueled main engines throttle up from 90 percent thrust to 104 percent thrust as planned. The capability for 104-percent performance is the result of improvements made in main engine systems over the decade they were in development.

5.000 - Data processing systems (DPS) engineer Andrew Algate, mission control, Houston: "Liftoff confirmed."

Flight director Jay Greene, Houston: "Liftoff..."

5.000 - Loss of data from the shuttle at NASA's Merritt Island antenna complex for four data frames. Four more "data BIT synch dropouts" occur in the next one minute and six seconds. These are normal and are caused by flame and objects on the horizon that attenuate radio signals.

5.615 - The backup flight system computer aboard Challenger commands the S-band PM (phase modulated) and S-band FM radio systems to switch antennas to maintain communications during the upcoming roll maneuver.

5.674 - Internal pressure in the right-side booster is recorded as 11.8 pounds per square inch higher than normal.

7.724 - The shuttle clears the launch pad tower and begins a maneuver to roll over, putting the crew in a "heads down" position below the external tank.

8.000 - Scobee, air-to-ground: "Houston, Challenger. Roll program."

10.000 - Covey, mission control: "Roger roll, Challenger."

Flight dynamics officer (FIDO) Brian Perry, mission control: "Good roll, flight."

Greene: "Rog, good roll."

11.000 - Smith, intercom: "Go you mother."

12.000 - Another antenna switch is ordered to transfer data to the Ponce De Leon tracking station.

14.000 - Resnik, intercom: "LVLH." Resnik is reminding Scobee and Smith about proper cockpit switch configurations. "LVLH" is an acronym that stands for "local vertical, local horizontal."

15.000 - Resnik, intercom: "(Expletive) hot."

Scobee: "OK."

16.000 - Mission Control spokesman Nesbitt in Houston: "Good roll program confirmed. Challenger now heading downrange."

19.000 - Smith, intercom: "Looks like we've got a lot of wind here today."

Scobee: "Yeah."

19.859 - Challenger's three main engines receive commands to begin throttling down to 94 percent power, as planned.

21.124 - The roll maneuver is completed and Challenger is on the proper trajectory.

21.604 - Right hand SRB thrust decreases before shuttle reaches maximum dynamic pressure. This is accomplished by the burn down of ridges in the solid propellant of the forward fuel segment. Thrust is a function of surface area of propellant burning.

22.000 - Scobee, intercom: "It's a little hard to see out my window here."

22.204 - Left hand SRB thrust decreases as planned.

27.000 - Booster systems engineer (Booster) Jerry Borrer, mission control: "Throttle down to 94."

Greene: "Ninety four..."

28.000 - Smith, intercom: "There's 10,000 feet and Mach point five." The shuttle is 10,000 feet high traveling at half the speed of sound.

Nesbitt: "Engines beginning throttling down, now at 94 percent. Normal throttle (setting) for most of the flight is 104 percent. We'll throttle down to 65 percent shortly.

35.000 - Scobee, intercom: "Point nine."

35.379 - The three main engines begin throttling down to 65 percent thrust to reduce acceleration as aerodynamic pressure builds up.

36.990 - Telemetry data shows the shuttle's computer system responds properly to wind shear to adjust the ship's flight path.

40.000 - Smith, intercom: "There's Mach 1."

Scobee: "Going through 19,000."

43.000 - Scobee, intercom: "OK, we're throttling down."

45.000 - Nesbitt: "Engines are at 65 percent. Three engines running normally..."

45.217 - A flash is observed downstream of the shuttle's right wing.

48.118 - A second flash is seen trailing the right wing.

48.418 - A third unexplained flash is seen downstream of the shuttle's right-hand wing. 70 mm tracking camera closeup: brilliant orange ball of flame, apparently, emerges from under the right wing and quickly merges with the plume of the solid rocket boosters. This phenomenon, observed during analysis of tracking film after launch, has been seen on previous launches but has never been explained.

48.900 - Booster engineer (Borrer): "Three at 65."

Nesbitt: "... Three good fuel cells. Three good APUs (auxiliary power units)..."

Greene: Sixty-five, FIDO..."

FIDO (Perry): "T-del confirms throttles." Perry is referring to computer software monitoring the flight in realtime.

Greene: "...Thank you."

51.860 - Challenger's main engines receive commands from the onboard flight computers to begin throttling back up to 104 percent thrust as planned.

52.000 - Nesbitt: "Velocity 2,257 feet per second (1,539 mph), altitude 4.3 nautical miles, downrange distance 3 nautical miles..."

57.000 - Scobee, intercom: "Throttling up."

Smith: "Throttle up."

Scobee: "Roger."

58.788 - Tracking cameras show the first evidence of an abnormal plume on the right-hand solid rocket booster facing away from the shuttle. Scobee and Smith had no data on the performance of the solid rockets except for a software system that would have alerted them to malfunctions in the booster steering mechanism.

59.000 - Challenger passes through the region of maximum aerodynamic pressure, experiencing 720 pounds per square foot.

59.262 - A continuous "well defined intense plume" of exhaust is seen on the side of the suspect booster by tracking cameras. This is clear evidence of a burn through.

59.753 - First visual evidence of flame on the right-side booster. 70 mm tracking camera closeup: a flickering tongue of flame appears on side of booster away from shuttle and quickly becomes continuous.

60.000 - Smith, intercom: "Feel that mother go!"

Unknown, intercom: "Wooooo Hooooo!"

60.004 - Data radioed from Challenger shows the internal pressure in the right-side SRB begins dropping. This is because of the rapidly increasing hole in the failed joint.

60.238 - First evidence of flame from the rupture deflecting after impinging on the external fuel tank. This is a sign that the burn through has increased to the point where the jet of flame is deflected by the rush of air along the external tank.

60.248 - First evidence of the anomalous plume "attaching" to the fitting that couples the aft end of the right-side rocket to the base of the external fuel tank.

60.988 - The plume deflection is continuous. 70 mm tracking camera closeup: thick, well-defined plume of flame arcs away from right solid rocket booster.

61.724 - The shuttle rolls slightly in response to high winds aloft.

62.000 - Smith, intercom: "Thirty-five thousand, going through one point five."

62.084 - The steering mechanism of the left-hand booster suddenly moves on computer command as Challenger's flight control system compensates for wind shear. It is later noted that wind shear during Challenger's launch was more extreme than for any of the previous 24 shuttle missions, although still within design limits.

62.484 - Challenger's computers order the shuttle's right-hand "elevon," or wing flap, to move suddenly in response to wind.

63.924 - A pressure change is recorded in the right-hand outboard elevon, indicating movement.

63.964 - The shuttle's computers order a planned change in Challenger's pitch to ensure the proper angle of attack during this phase of the trajectory.

64.660 - The plume from the burn through changes shape suddenly, indicating a leak has started in the shuttle's liquid hydrogen tank to fuel the fire.

64.705 - A bright, sustained glow is photographed on the side of the external fuel tank.

64.937 - The main engine nozzles move through large arcs, trying to keep the shuttle on course as the flight computers attempt to compensate for the unbalanced thrust produced by the booster burn through. The shuttle stops the minute pitching. It is doubtful the crew was aware of the computers' efforts to keep the ship on course. At this point in the launch phase, the crew is experiencing normal extreme longitudinal vibrations and steadily increasing acceleration forces. Slight movement of the shuttle appears visible in NASA's closed-circuit television system but this could be an illusion.

65.000 - Scobee, intercom: "Reading four eighty six on mine." This is a routine airspeed indicator check.

Smith: "Yep, that's what I've got, too."

65.164 - First recorded evidence of Challenger experiencing transient motion.

65.524 - Data shows the left wing's outboard elevon moves suddenly.

66.000 - Booster (Borrer): "Throttle up, three at 104."

Greene: "Capcom (Covey), go at throttle up."

66.174 - Tracking cameras show a bright spot suddenly appears in the exhaust plume from the side of the right-side solid rocket motor and bright spots are detected on the side of the rocket facing the belly of the shuttle.

66.764 - The pressure in the shuttle's external liquid hydrogen tank begins to drop, indicating a massive leak. Smith had realtime readings of pressure in the liquid hydrogen tank, but it is doubtful he noticed anything unusual because of the rapidity of the failure. It made no difference, ultimately, because even if Challenger's pilots had suspected an SRB problem there was nothing they could have done about it. While the shuttle separates from its external fuel tank shortly before reaching orbit, it does so with no engines firing and in a benign aerodynamic environment. As Scobee and Smith well knew, separating from the tank while the SRBs were firing would drive the shuttle into the bottom of the fuel tank.

67.650 - The abnormal plumes on the bottom and top of the booster appear to merge into one. This means the flame has wrapped around the joint as the leak deteriorated.

67.684 - Telemetry indicates falling pressure in the 17-inch-wide liquid oxygen propellant lines feeding the three main engines.

68.000 - Nesbitt: "Engines are throttling up. Three engines now at 104 percent."

Covey: "Challenger, go at throttle up."

70.000 - Scobee calmly responds, air-to-ground: "Roger, go at throttle up."

72.204 - Data shows divergent up and down motions in nozzles of both solid rocket boosters.

72.284 - The two solid rocket boosters change position relative to each other, indicating the right-side booster apparently has pulled away from one of the two struts that connected its aft end to the external fuel tank. TV tracking camera: A large ball of orange fire appears higher on other side of main fuel tank, closer to Challenger's cabin, and grows rapidly.

72.478 - A "major high rate actuator command" is recorded from one of the boosters, indicating extreme nozzle motions.

72.497 - The nozzles of the three liquid-fueled main engines begin moving at high rates: five degrees per second.

72.525 - Data shows a sudden lateral acceleration to the right jolts the shuttle with a force of .227 times normal gravity. This is felt by the crew.

72.564 - Start of liquid hydrogen pressure decrease. Solid rocket boosters again demonstrate high nozzle motion rates.

72.624 - Challenger beams back what turns out to be its final navigation update.

72.964 - Main engine liquid oxygen propellant pressures begin falling sharply at turbopump inlets.

73.000 (approximate) - Smith, intercom: "Uh oh..." This is the last comment captured by the crew cabin intercom recorder. Smith may have been responding to indications on main engine performance or falling pressures in the external fuel tank.

73.010 - Last data is captured by the tracking and data relay satellite in orbit overhead, indicating structural breakup has begun in that area.

73.044 - Start of sharp decrease in liquid hydrogen pressure to the main engines.

73.045 - Another lateral acceleration, this one to the left, is felt by the crew. Lateral acceleration equals .254 time the force of gravity.

73.124 - Internal pressure in the right-side rocket booster is recorded as 19 pounds per square inch below that of its counterpart, indicating about 100,000 pounds less thrust. Tracking cameras detect evidence of a circumferential white pattern on the left side of the base of the external tank indicating a massive rupture near the SRB-tank attach ring. The is nothing less than the aft dome of the liquid hydrogen tank blowing out and backwards. The resulting forward acceleration blasts the tank up into the liquid oxygen tank in the tip of the external fuel tank.

73.137 - Vapors appear near the intertank section separating the hydrogen and oxygen sections accompanied by liquid hydrogen spillage from the aft dome of the external tank.

73.143 - All three main engines respond to loss of oxygen and hydrogen inlet pressure.

73.162 - Ground cameras show a sudden cloud of rocket fuel appearing along the side of the external tank. This indicates the nose of the right-hand booster may have pivoted into the intertank area, compounding the liquid oxygen rupture.

73.191 - A sudden brilliant flash is photographed between the shuttle and the external tank. TV tracking camera: Fireballs merge into bright yellow and red mass of flame that engulfs Challenger. A single crackling noise is heard on air-to-ground radio, originally thought to be the sound of the explosion transmitted through the crew's voice-activated microphones. Engineers later determine the sound is the result of ground transmitters searching the shuttle's frequency range for a signal.

73.211 - Telemetry data from the main engines exhibits interference for the next tenth of a second.

73.213 - An explosion occurs near the forward part of the tank where the solid rocket boosters attach.

73.282 - The explosion intensifies and begins consuming the external fuel tank. Television tracking camera: a ball of brilliant white erupts from the area beneath the shuttle's nose.

73.327 - The white flash in the intertank area greatly intensifies.

73.377 - Tank pressure for on board supplies of maneuvering rocket fuel begins to fluctuate.

73.383 - Data indicates the liquid-fueled main engines are approaching redline limits on their powerful fuel pumps.

73.482 - Channel A of main engine No. 2's control computer votes for engine shutdown because of high pressure fuel turbopump discharge temperature. Channel B records two strikes for shutdown.

73.503 - Main engine No. 3 begins shutdown because of high temperatures in its high pressure fuel pump. Last data captured by main engine No. 3's controller.

73.523 - Main engine No. 1 begins shutdown because of high temperatures in high pressure fuel pump.

73.543 - Last telemetry from main engine No. 1.

73.618 - The last valid telemetry from the shuttle is recorded as it breaks up: pressure fluctuations in a fuel tank in the left rocket pod at Challenger's rear and chamber pressure changes in auxiliary power unit No. 1's gas generator.

73.631 - End of last data frame.

74.130 - Last radio signal from orbiter.

74.587 - A bright flash is observed in the vicinity of the orbiter's nose. Television tracking camera closeup: The nose of the shuttle and the crew compartment suddenly engulfed in brilliant orange flame as rocket fuel in forward maneuvering jet supplies ignites.

"At that point in its trajectory, while traveling at a Mach number of 1.92 (twice the speed of sound) at an altitude of 46,000 feet, the Challenger was totally enveloped in the explosive burn,"

said the Rogers Commission report. "The Orbiter, under severe aerodynamic loads, broke into several large sections which emerged from the fireball. Separate sections that can be identified on film include the main engine/tail section with the engines still burning, one wing of the Orbiter, and the forward fuselage trailing a mass of umbilical lines pulled loose from the payload bay."

The nose section had ripped away from the payload bay cleanly, although a mass of electrical cables and umbilicals were torn from the cargo hold, fluttering behind the crew cabin as it shot through the thin air, still climbing. Challenger's fuselage was suddenly open like a tube with its top off. Still flying at twice the speed of sound, the resulting rush of air that filled the payload bay overpressurized the structure and it broke apart from the inside out, disintegrating in flight. Challenger's wings cartwheeled away on their own but the aft engine compartment held together, falling in one large piece toward the Atlantic Ocean, its engines on fire because of their sudden shutdown with more oxygen in the system than hydrogen. The TDRS satellite and its big IUS booster rocket were blown free of the cargo bay as was Spartan Halley. All this happened as the external tank gave up its load of fuel, which ignited in the atmosphere in what appeared to be an explosion. It was more of a sudden burning than an explosion. In any case, the two solid rockets emerged from the fireball of burning fuel and continued on, bereft of guidance from the shuttle's now-silent flight computers.

75.000 - Nesbitt (not realizing immediately there had been an explosion): "One minute 15 seconds. Velocity 2,900 feet per second (1,977 mph). Altitude 9 nautical miles. Downrange distance 7 nautical miles."

76.437 - The nose cap of the right hand solid rocket booster separates and its drogue parachute deploys. Tracking camera closeup: lone parachute seen emerging from plume of solid rocket booster.

79.000 - TV tracking camera, different view: White streamers of smoking debris blossom in all directions from cloud of smoke and flame marking the spot where Challenger had been. One large burning piece falls toward the ocean. Two solid rocket boosters emerge from the fireball and corkscrew through the sky on their own. Nesbitt's commentary stops.

89.000 - Greene in mission control utters the first words since the explosion 13 seconds ago: "FIDO, trajectories..."

FIDO (Perry): "Go ahead."

Greene: "Trajectory, FIDO."

FIDO: "Flight, FIDO, filters (radar) got discreting sources. We're go."

Ground control (GC) engineer N.R. Talbott, mission control: "Flight, GC, we've had negative contact, loss of downlink (of radio voice or data from Challenger)."

Greene: "OK, all operators, watch your data carefully."

FIDO: "Flight, FIDO, till we get stuff back he's on his cue card for abort modes."

Greene: "Procedures, any help?"

Unknown: "Negative, flight, no data."

110.250 - Range safety control officers send radio signals that detonate the self-destruct package on right-hand solid rocket.

110.252 - The left-hand booster self destructs. Tracking camera closeup: a thick cloud of black smoke suddenly engulfs rocket and brilliant but quick explosion ensues. Numerous fragments of the booster emerge from the fireball, including what appears to be a complete aft fuel segment, slowly tumbling.

(Editor's Note: The following times in minutes and seconds)

1:56 - Nesbitt: "Flight controllers here are looking very carefully at the situation. Obviously a major malfunction."

2:01 - Ground control officer: "Flight, GC, negative downlink."

Greene: "Copy."

2:08 - Nesbitt: "We have no downlink."

2:20 - TV tracking camera: falling bits of debris create white contrails arching through the blue sky. A larger object, trailing a thin cloud of vapor, plummets toward the ocean.

2:25 - FIDO: "Flight, FIDO."

Greene: "Go ahead."

FIDO: "RSO (range safety officer) reports vehicle exploded."

Greene (long pause): "Copy. FIDO, can we get any reports from recovery forces?"

FIDO: "Stand by."

2:45 - Greene: "GC, all operators, contingency procedures in effect."

2:50 - Nesbitt: "We have a report from the flight dynamics officer that the vehicle has exploded. The flight director confirms that. We are looking at checking with the recovery forces to see what can be done at this point."

3:03 - Greene: "FIDO, flight..."

FIDO: "Go ahead."

Greene: "LSO (Lockheed Safety Officer) and recovery forces, any contacts?"

3:09 - Nesbitt: "Contingency procedures are in effect..."

FIDO: "We're working with them, flight."

Greene: "OK."

3:22 - Nesbitt: "We will report more as we have information available. Again, to repeat, we have a report relayed through the flight dynamics officer that the vehicle has exploded. We are now looking at all the contingency operations and awaiting word from any recovery forces in the downrange field."

3:25 - TV tracking camera: The first pieces of debris can be seen splashing into the ocean.

3:53 - FIDO: "Flight, FIDO, for what it's worth, the filter shows 'em in the water."

Greene: "Copy."

3:58 - Challenger's crew cabin smashes into the Atlantic Ocean at about 200 mph. The astronauts, still strapped in their seats, experience a braking force of 200 times normal gravity. The crew cabin disintegrates and settles to the bottom 100 feet below.

4:15 - Television tracking camera closeup shows ocean surface east of Patrick Air Force Station. A large cloud of ruddy brown smoke hangs over surface of water as objects splash on impact nearby. The cloud probably was caused by leaking hydrazine rocket fuel from wreckage that hit the water.

4:27 - Greene: "FIDO, flight. ... FIDO flight."

FIDO: "Go ahead."

Greene: "Did the RSO's have an impact point?"

FIDO: "Stand by."

5:03 - Nesbitt: "This is mission control, Houston. We have no additional word at this time."

5:05 - FIDO: "Flight, FIDO."

Greene: "Go ahead."

FIDO: "The vacuum IP (impact point) is 28.64 North, 80.28 West."

Greene: "How does that stack with the solid (rocket) recovery forces?" Greene is referring to the Liberty Star and the Freedom Star, two NASA ships on station in the Atlantic to recover Challenger's boosters after a normal launch.

FIDO: "We're still talking to them."

Greene: "OK."

5:24 - Nesbitt: "Reports from the flight dynamics officer indicate that the vehicle apparently exploded and that impact in the water (was) at a point approximately 28.64 degrees North, 80.28 degrees West."

5:36 - TV tracking camera: A dark, irregularly shaped piece of debris - thought to be one of Challenger's wings- cartwheels down from the sky and splashes into the Atlantic. It is the largest piece of Challenger seen on TV impacting in the ocean.

5:46 - Nesbitt: "We are awaiting verification as to the location of the recovery forces in the field to see what may be possible at this point and we will keep you advised as further information is available. This is mission control."

6:15 - NASA television switches from ocean views to the grandstand area at the press site. A large cloud of white smoke remains visible towering into the sky, twisted by winds aloft and slowly dissipating. Small, helical streamers mark contrails of the solid rocket boosters.

6:41 - Greene: "OK, everybody stay off the telephones, make sure you maintain all your data, start pulling it together."

7:17 - Greene: "Flight, FIDO..."

FIDO: "FIDO, flight, go ahead sir."

Greene: "Are the LSO's on the loop?"

FIDO: "We can get 'em."

Greene: "Get 'em up on the loop, please."

LSO: "Yes sir, this is the LSO."

Greene: "OK, are there any forces headed out that way?"

LSO: "Yes sir. DOD (Department of Defense) LSO reports that all ... forces have been scrambled and they are on their way."

Greene: "OK, do we have an ETA?"

LSO: "Negative, sir."

8:00 - Greene conducts a poll of his flight controllers to determine if any data indicates what may have gone wrong.

Greene: "Booster, flight."

Booster: "Flight, booster."

Greene: "Did you see anything?"

Booster: "Nothing, sir, I looked at all the turbine temps were perfect, right on the prediction. All the redlines were in good shape."

Greene: "RMU?"

RMU (Reiley): "We looked good, flight."

Greene: "ECOM? ECOM, flight."

ECOM (Electrical, environmental and communications systems engineer John Rector): "Flight, ECOM, we looked normal."

Greene: "DPS?"

DPS (Algate): "All our data's normal, flight."

Greene: "PROP?"

Propulsion systems (PROP) engineer A.J. Ceccacci: "Everything looked good, flight."

Greene: "GNC?"

GNC (Guidance, navigation and control engineer J.W. Bantle): "Flight, the roll maneuver looked fine, what we saw of it. We were on our way decreasing roll rate as we lost data."

Greene: "Copy."

8:03 - NASA select television shows launch pad 39-B with smoke still hanging over the mobile launch platform.

8:37 - NASA select television focuses on a small parachute seen slowly drifting down out to sea.

9:11 - FIDO: "That's, uh, probably a paramedic." Later it is determined that this is the nose cap to one of the solid rocket boosters swinging from its drogue parachute.

9:19 - Nesbitt: "This is mission control, Houston. We are coordinating with recovery forces in the field. Range safety equipment, recovery vehicles intended for the recovery of the SRBs in the general area."

9:36 - Greene: "LSO, flight. LSO, flight..."

Nesbitt: "Those parachutes believed to be paramedics going into that area..."

FIDO: "We're getting them, flight."

Nesbitt: "...To repeat, we had an apparently normal ascent with the data..."

LSO: "This is LSO on flight loop."

Greene: "Rog, are you getting any inputs?"

LSO: "Sir, we've got a Jolly 1 (helicopter) on route right now. We've got ships on the way and we've got a C-130 on the way out."

Greene: "Rog."

9:41 - Nesbitt: "...coming from all positions being normal up through approximately time of main engine throttle back up to 104 percent. At about approximately a minute or so into the flight, there was an apparent explosion. The flight dynamics officer reported that tracking reported that the vehicle had exploded and impact into the water in an area approximately located at 28.64 degrees North, 80.28 degrees West, recovery forces are proceeding to the area including ships and a C-130 aircraft. Flight controllers reviewing their data here in mission control. We will provide you with more information as it becomes available. This is mission control, Houston."

11:05 - NASA select television shows the interior of mission control at the Johnson Space Center in Houston. Covey and astronaut Frederick Gregory sit silently at the Capcom console, obviously stunned.

11:39 - LSO: "Flight, LSO."

Greene: "Go ahead."

LSO: "Uh, Jolly's have not been cleared in yet, there's still debris coming down."

Greene: "Copy. Who's controlling this operation, please?"

LSO: "S & R (search and recovery) forces out of Patrick (Air Force Base)."

Greene: "Rog. Do we have a coordination loop with those people?"

LSO: "We're working with the SOC on DDMS coord right now." He is referring to a radio network used by Defense Department personnel.

LSO: "Flight, LSO."

Greene: LSO..."

LSO: "Would you like us to try to get up on DDMS coord also?"

Greene: Yes. GC, flight."

GC: "Flight, GC."

Greene: "Take that loop into one of the playback loops please, internal to the building only."

GC: "I didn't copy what you said."

Greene: "DDMS coord, patch it into one of the playback loops internal to the building."

GC: "Copy."

12:37 - Greene: "GC, flight."

GC: "Flight, GC."

Greene: "Checkpoint status, have we taken one?"

GC: "Negative."

Greene: "Take one now."

GC: "Copy."

13:27 - GC: "All flight controllers, hold inputs, lock checkpoint in progress." This is a procedure to take a "snapshot" of all computer data recorded so far to ensure its recovery for documentation."

14:24 - Greene: LSO, flight."

LSO: "LSO here, sir."

Greene: "Any updates?"

LSO: "No sir. No sir, nothing to report."

15:06 - Greene: "Operators, contingency plan copies are coming to each console position. If you have an FCOH (flight control operations handbook) you can start on the checklist, page 27-4, that's page 27-4. Don't reconfigure your console, take hard copies of all your displays, make sure you protect any data source you have."

LSO: "Flight, LSO."

Greene: "LSO?"

LSO: "Looks like about 50 minutes, five zero minutes, before the helicopters are cleared in because of debris."

Greene: "Fifty minutes from what time, LSO?"

LSO: "OK, from the time of the explosion."

21:53 - Nesbitt: "This is mission control, Houston. Repeating the information that we have at this time. We had an apparently nominal liftoff this morning at 11:38 Eastern time. The ascent phase appeared normal through approximately the completion of the roll program and throttle down and engine throttle back to 104 percent. At that point, we had an apparent explosion. Subsequent to that, the tracking crews reported to the flight dynamics officer that the vehicle appeared to have exploded and that we had an impact in the water down range at a location approximately 28.64 degrees North, 80.28 degrees west. At the time, the data was lost with the vehicle. According to a poll by the flight director, Jay Greene, of the positions here in mission control, there were no anomalous indications, no indications of problems with engines or with the SRBs or with any of the other systems at that moment through the point at which we lost data. Again, this is preliminary information. It is all that we have at the moment and we will keep you advised as other information becomes available. We had, there are recovery forces in the general area. Others being deployed, including aircraft and ships. We saw what we believed to be paramedics parachuting into impact area and we have no additional word at this point. We will keep you advised as details become available to us. This is mission control, Houston."

Challenger's crew departs the Kennedy Space Center.