STS-118/ISS-13A.1 MISSION ARCHIVE (FINAL)
Updated through: 08/21/07

By William Harwood
CBS News/Kennedy Space Center

The following copy originally was posted on the Current Mission space page at http://cbsnews.com/network/news/space/current.html.

Comments, suggestions and corrections welcome!

TABLE OF CONTENTS

08/21/07: Shuttle Endeavour glides to smooth Florida landing
08/21/07: Shuttle braking rockets fired
08/21/07: Astronauts set up for landing
08/20/07: Hale optimistic about near-term external tank fix while long-term upgrade is implemented
08/20/07: NASA will staff KSC and Edwards for Tuesday landing; weather update
08/20/07: Crew preps for entry
08/19/07: Endeavour undocks from space station; Hurricane Dean less threatening to mission control
08/19/07: Shuttle crew prepares for undocking
08/108/07: Shuttle-station hatches closed; undocking on tap Sunday, landing Tuesday
08/108/07: Astronauts marvel at Hurricane Dean; wrap up abbreviated spacewalk
08/108/07: Spacewalk begins
08/108/07: Crew gears up for hurricane-shortened spacewalk, early hatch closure
08/17/07: Kelly supports fly-as-is decision; NASA managers study hurricane options
08/17/07: Crew prepares for Saturday spacewalk; continues supply transfer work
08/16/07: Shannon says tests show Endeavour can safely land as is; repair spacewalk ruled out; decision virtually unanimous; dissent centered on possibility of post-landing repairs, not crew safety
08/16/07: ADVISORY - Tile repair spacewalk ruled out; Endeavour cleared for entry 'as is'
08/16/07: ADVISORY - MMT meeting pushed back to 4 p.m.
08/16/07: Morgan talks with students, reporters; says she's not worried about heat shield gouge
08/16/07: Astronauts await tile repair decision; controllers expect word by early afternoon
08/15/07: Spacewalk No. 4 moved from Friday to Saturday; no decision yet on tile repair
08/15/07: Mastracchio cuts spacewalk short after noting glove damage; Anderson completes final tasks
08/15/07: Communications upgrade done ahead of schedule
08/15/07: Spacewalk No. 3 begins
08/15/07: Astronauts gear up for third spacewalk
08/14/07: Shannon 'cautiously optimistic' shuttle can re-enter without repairs; Kelly downplays tile concern; Morgan says spaceflight worth the wait
08/14/07: Astronauts begin equipment storage platform installation; Morgan interviews, educational event on tap
08/13/07: Shannon says tile damage not considered a threat to astronauts; spacewalk repair, if needed, would be intended to minimize post-landing repairs
08/13/07: New gyro installed; spacewalk ends
08/13/07: Suspect gyro removed
08/13/07: Spacewalk begins to replace gyroscope
08/13/07: Astronauts gear up for critical spacewalk
08/12/07: Heat shield inspection carried out; Russian computer repair work continues; mission extended for additional station assembly work (UPDATED at 7 p.m. with Shannon briefing
08/12/07: Space station computer successfully restarted; shuttle team gears up for heat shield inspection
08/11/07: Additional data indicate foam, not ice, caused shuttle tile damage; engineering analysis indicates shuttle could safely land as is; but officials say inspection Sunday needed to resolve all question
08/11/07: Spacewalk ends; all objectives accomplished
08/11/07: Engineers troubleshoot space station computer problem
08/11/07: S5 truss segment bolted in place
08/11/07: Spacewalk begins
08/11/07: Astronauts prepare for spacewalk
08/10/07: Shuttle Endeavour docks with international space station; NASA studies possible ice-strike damage to shuttle's heat shield; focused inspection planned for Sunday
08/10/07: Final rendezvous sequence begins
08/10/07: Shuttle Endeavour closes in on space station
08/09/07: Morgan describes first impressions of space
08/09/07: Engineers say shuttle tank foam performed well; only three small bits of debris under study; oxygen tank sensor issue no threat to mission
08/09/07: Astronauts work through busy day in space
08/08/07: Shuttle Endeavour thunders into space; Griffin comments on astronaut medical probe
08/08/07: Astronauts strap in; shuttle hatch closed for launch
08/08/07: Shuttle fueling complete
08/08/07: Shuttle fueling begins
08/07/07: Countdown on track; weather improves to 80 percent 'go'
08/06/07: STS-118 mission preview
08/06/07: Countdown on track; weather forecast unchanged
08/05/07: Russian Progress supply ship docks with international space station
08/05/07: Valve replaced and retested; engineers ready to start countdown
08/03/07: Astronauts fly to Kennedy Space Center
08/03/07: Shuttle launch delayed one day
08/03/07: Educator-astronaut Morgan ready for long anticipated flight
08/01/07: Valve replacement ordered
07/31/07: Engineers troubleshoot shuttle cabin leak; Mars launch delayed 24 hours
07/27/07: NASA managers vow more detailed review of alleged astronaut alcohol abuse; fight surgeon concerns
07/26/07: Endeavour tentatively cleared for launch; NASA investigates sabotage of black box; astronaut health care report on tap Friday
07/10/07: Shuttle Endeavour moved to launch pad
07/08/07: Shuttle Endeavour readied for rollout
06/22/07: Atlantis glides to California landing

12:45 PM, 8/21/07, Update: Shuttle Endeavour glides to smooth Florida landing (UPDATED at 1:40 p.m. with video of tile damage; UPDATED at 2:15 p.m. with crew departure; Morgan not seen; UPDATED at 4:30 p.m. with Griffin news conference; Morgan woozy after landing; UPDATED at 5:45 with crew news conference)

Falling back to Earth, the shuttle Endeavour streaked across Central America and high above Cuba today before gliding up the length of the Florida peninsula to a sunny landing at the Kennedy Space Center to close out a dramatic two-week space station assembly mission. The ship's gouged heat shield appeared to come through re-entry in good shape with only slightly more damage than it started with, vindicating an earlier decision to forego a spacewalk repair job.

"Houston, Endeavour, wheels stopped," commander Scott Kelly radioed as the shuttle rolled to a halt on the centerline of runway 15.

"Roger wheels stopped, Endeavour," astronaut Chris Ferguson replied from mission control in Houston. "Congratulations, welcome home. You've given a new meaning to 'higher' education."

He was referring to teacher-turned-astronaut Barbara Morgan, strapped into a seat on the flight deck just behind the two pilots. Christa McAuliffe's backup in the original Teacher-in-Space program, Morgan waited 21 years to fulfill the legacy of the fallen Challenger astronauts. While she did not teach any lessons from space as McAuliffe once planned, she chatted with school kids during two modest educational events and plans a busy schedule of post-flight appearances to promote science and math education.

Touchdown at 12:32:16 p.m. wrapped up a 5.2-million-mile voyage spanning 12 days 17 hours 55 minutes and 34 second over 201 complete orbits since blastoff Aug. 8 from nearby launch complex 39A. Endeavour's flight now sets the stage for a complex sequence of missions to attach a new docking module to the station in October, followed by the European Space Agency's Columbus laboratory module in December and two flights early next year to attach Japanese modules.

Endeavour made its fiery return to Earth with a small-but-deep gouge in two heat shield tiles on the belly of the ship behind its right main landing gear door. The gouge was caused by a half-ounce piece of foam insulation that fell off an external tank propellant feedline bracket 58 seconds after launch.

NASA managers spent more than half of Endeavour's mission studying the gouge to determine whether it posed any re-entry threat to the shuttle or its crew. Late last week, based on super-computer analysis and tests of a mockup in a furnace that can simulate re-entry heating, NASA's Mission Management Team concluded the damage would have little or no impact and cleared the shuttle for return to Earth as is.

"We agree absolutely 100 percent with the decision to not repair the damage," Kelly said during an in-flight news conference. "We've had shuttles land with worse damage than this. We gave this a very thorough look and I am very, very comfortable and there will be no extra concern in my mind (during re-entry) due to this damage."

Based on close-up video from the runway, the heat of re-entry did no apparent damage to surrounding tiles. The extent of the damage appeared roughly the same, although a gash at the deepest part of the pit looked a bit larger. But there were no other obvious signs of damage and it clearly had no impact on landing.

"There's maybe slightly a little bit more erosion on the, kind of the forward edge, but not too dramatic," said Bill Gerstenmaier, associate administrator for space flight at NASA headquarters. "It didn't get extremely hot and (the underlying material) didn't char. But again, I caution you with this quick analysis we're doing here, the teams will pop these tiles off, we'll take a look to make sure there's no damage, there's nothing going on."

Kelly, pilot Charles Hobaugh, flight engineer Rick Mastracchio, Tracy Caldwell, Al Drew and Canadian astronaut Dave Williams doffed their heavy pressure suits and gathered on the runway for a brief inspection of the shuttle an hour or so after landing. Morgan, feeling a bit woozy as she readjusted to gravity, did not join her crewmates, staying inside NASA's astronaut transporter for post-landing medical checks. All seven astronauts plan to spend the night in Florida before flying back to the Johnson Space Center in Houston on Wednesday.

"The flight was absolutely wonderful," Morgan, 55, told reporters five hours after landing. "I'm really proud of our whole team and the team on the ground. ... it all worked out really, really well I thought. How did I do? It took me a little while at first to get used to microgravity, it took a couple of days, and the first day - and I think this was the biggest surprise of all - I felt I was upside down the entire first day. It wasn't a bad feeling, it was just an unusual feeling."

Asked how she felt after landing, Morgan said: "The room still spins a little bit, but that's OK."

"What I really want to do is take what this experience was and figure out how we can do a better job to help serve our students and our teachers in a way they want that will be more helpful to them," Morgan said. "And I would love to figure out how we can make more and more of these opportunities available for more and more of our teachers."

With Endeavour back on the ground, NASA managers and engineers will carry out a detailed inspection to precisely determine the extent of damage related to the foam strike while debating a half-dozen potential near-term fixes to prevent insulation from falling off the liquid oxygen feedline brackets during upcoming launches.

A bracket redesign already was in work, scheduled to debut on a tank four missions from now. The question facing NASA is what to do about the next three flights, currently scheduled for launchings Oct. 23, Dec. 6 and Feb. 14.

Shuttle Program Manager Wayne Hale said Monday it's too soon to say what impact work to recover from Endeavour's unexpected foam debris incident might have on the upcoming schedule. But Gerstenmaier said today that at this point, major delays do not appear to be in the cards.

"We're still pointed toward Oct. 23," Gerstenmaier said. "We have a meeting today going on to have a look at the tank to see if there's anything we want to do in terms of modifying the tank ... or we leave it the way it is and head for Oct. 23. But I think we're still clearly focused on the next mission and we're ready to move forward."

From the local processing perspective, "it really and truly depends on how long we need to do the analysis for the repair if it turns out to be necessary or not," said Launch Director Mike Leinbach. "We were going to mate the external tank (and boosters) yesterday for the next mission, so we're in kind of a holding pattern here. We've got several days to work with, so we're in no immediate danger of delaying the next mission at all, that's certainly not in the cards. We have some time in the schedule to make up as we go along. So it's going to depend on the results of the study, whether we need to do a fix or not, how long we take to do that fix and then what that would translate into for (processing)."

Hale said engineers are working on "five different options to improve the situation on the next tank. We will expect there will be some readjustment to our schedule as we work through those options. However, I believe that based on the discussions we've had, that our impacts to the next flight in terms of the actual launch date of Oct. 23 will be small, we think we have plenty of time to evaluate some changes and in fact implement them if we feel that they are well justified."

At NASA's traditional post-landing news conference, NASA Administrator Mike Griffin showed off spectacular post-undocking pictures of the international space station, calling the unfinished lab complex "one of the great accomplishments of mankind."

"We're building a space station here, one flight at a time, and while I appreciated the media's attention on the ding in the tile, actually the orbiter overall was really pretty clean," he said. "We had one kind of ugly ding and we paid appropriate attention to it. I would have liked to have seen some media attention on what a magnificent accomplishment we're undertaking here. I think we're doing pretty well with it."

Endeavour docked with the space station Aug. 10 and the next day, the astronauts installed a short spacer segment on the right end of the station's main solar power truss. Two days later, Mastracchio and Williams replaced a faulty stabilizing gyroscope on the station amid work to transfer 5,000 pounds of equipment and supplies to and from the lab complex. The astronauts used robot arms on the shuttle and space station to attach a 7,000-pound equipment storage platform to the solar array truss and staged a third spacewalk Aug. 15 to complete a variety of station assembly get-ahead tasks.

Endeavour is the first shuttle equipped with a new station-to-shuttle power transfer system that enabled the orbiter to plug into the space station's solar power grid. As a result, NASA managers extended the flight three days and added a fourth spacewalk. Originally scheduled for last Friday, the excursion was delayed one day while NASA managers debated whether to turn the excursion into a tile repair spacewalk.

In the end, a repair was deemed unnecessary and Williams and space station flight engineer Clay Anderson were cleared to carry out the originally planned EVA on Saturday. But the threat of Hurricane Dean raised the possibility flight controllers at the Johnson Space Center might have to evacuate. As a result, NASA managers shortened Saturday's spacewalk and moved undocking from Monday to Sunday to get Endeavour back on the ground today.

As it turned out, Dean never threatened the Texas coast but by that point NASA was committed and the crew returned to Earth today.

Flying backward over the Indian Ocean at a velocity of 5 miles per second, Kelly and Hobaugh fired Endeavour's twin braking rockets at 11:25 a.m. for three minutes and 33 seconds, slowing the ship by 246 mph and lowering the far side of its orbit into the atmosphere. A half-hour later, the shuttle fell into the discernible atmosphere at an altitude of 76 miles. At that point, Endeavour was 5,020 miles from touchdown.

The shuttle's ground track carried it high above Central America just west of the Panama Canal on a course carrying it across central Cuba and up the Florida peninsula to the Kennedy Space Center.

11:30 AM, 8/21/07, Update: Shuttle braking rockets fired; landing on tap at 12:32 p.m.

With good weather expected, shuttle commander Scott Kelly and pilot Charles Hobaugh fired Endeavour's twin braking rockets at 11:25 a.m. for three minutes and 33 seconds, slowing the ship by 246 mph and lowering the far side of its orbit into the atmosphere. A half-hour later, the shuttle will reach the discernible atmosphere at an altitude of 76 miles. At that point, Endeavour will be 5,020 miles from touchdown.

The shuttle's ground track will carry it high above Central America on a course across Cuba and up the Florida peninsula to the Kennedy Space Center.

Dropping below the speed of sound at an altitude of 48,000 feet above the landing site, Kelly will take over manual control and guide the shuttle through a sweeping 210-degree left turn to line up on runway 15. Touchdown is expected around 12:32:23 p.m.

6:00 AM, 8/21/07, Update: Astronauts set up for landing

The Endeavour astronauts are working through a busy re-entry day timeline this morning, preparing the shuttle for landing at the Kennedy Space Center to close out a two-week space station assembly mission. Forecasters are predicting generally favorable weather, but crosswinds could be close to NASA's 15-knot limit.

Commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, Rick Mastracchio, Dave Williams, Barbara Morgan and Al Drew were awakened at 4:36 a.m. by a recording of Simon and Garfunkle's "Homeward Bound" beamed up from mission control.

"Good morning, Endeavour," astronaut Shannon Lucid radioed from Houston. "And the music this morning was sent to all of you by all of your families in anticipation of a happy landing day."

"Well that's very nice of them to think of that, Shannon," Kelly replied. "Although it's been a short two weeks, we've accomplished a lot and we still look very much forward to coming home today. Thanks."

The deorbit timeline begins at 7:25 and barring a turn for the worse with the weather, the crew will activate internal cooling and close Endeavour's cargo bay doors at 8:45 a.m.

Fresh out of a lengthy overhaul, Endeavour is the first space shuttle fully equipped with three Global Positioning System satellite navigation receivers, an upgrade intended to improve the precision of the orbiter's computer-controlled descent to the landing site.

Flying backward over the Indian Ocean at a velocity of 5 miles per second, Kelly and Hobaugh plan to fire Endeavour's twin braking rockets at 11:25:12 a.m. for three minutes and 33 seconds, slowing the ship by 246 mph and lowering the far side of its orbit into the atmosphere. A half-hour later, the shuttle will reach the discernible atmosphere at an altitude of 76 miles. At that point, Endeavour will be 5,020 miles from touchdown.

Two of Endeavour's heat-shield tiles, located on the belly of the craft behind the right main landing gear door, were damaged 58 seconds after launch by a small piece of foam insulation that broke off a liquid oxygen feedline bracket on the shuttle's external tank. After a lengthy analysis, NASA managers decided the damage did not require any repairs and Endeavour was cleared for re-entry as is.

The shuttle's ground track will carry it high above Central America just west of the Panama Canal on a course carrying it across central Cuba and up the Florida peninsula to the Kennedy Space Center.

If the weather prohibits an on-time deorbit rocket firing, the astronauts will go around the world one more time and make a second attempt 90 minutes later, at 1:00:12 p.m., for a landing at 2:06:44 p.m.

Kelly and his crewmates also have three landing opportunities today at Edwards Air Force Base in California's Mojave Desert. But under NASA's standard entry day strategy, they only plan to attempt a return to Florida. If the weather blocks both of today's Kennedy opportunities, the astronauts will re-open the shuttle's payload bay doors, stay in orbit another day and try again Wednesday.

In that case, Edwards, which is already staffed, would be activated for use if necessary. The forecast for Edwards calls for acceptable weather today through Thursday.

Here is a timeline for today's two Kennedy landing opportunities (in EDT):

EDT...........EVENT

Rev. 201 Deorbit to KSC

07:25:12 AM...Begin deorbit timeline
07:40:12 AM...Radiator stow
07:50:12 AM...Mission specialists seat installation
07:56:12 AM...Computers set for deorbit prep
08:00:12 AM...Hydraulic system configured for entry
08:25:12 AM...Flash evaporator cooling system checkout
08:31:12 AM...Final payload deactivation
08:45:12 AM...Payload bay doors closed
08:55:12 AM...Mission control 'go' for transition to OPS-3 software
09:05:12 AM...OPS-3 entry software loaded
09:30:12 AM...Entry switchlist verification
09:40:12 AM...Deorbit burn update
09:45:12 AM...Crew entry review
10:00:12 AM...Commander/pilot don entry suits
10:17:12 AM...Inertial measurement unit alignment
10:25:12 AM...Mission specialists don entry suits
10:42:12 AM...Braking rocket steering check
10:45:12 AM...Hydraulic power unit (APU) prestart
10:52:12 AM...Toilet deactivation
11:00:12 AM...Payload bay vent doors closed for entry
11:05:12 AM...Mission control 'go' for deorbit burn
11:11:12 AM...Astronaut seat ingress complete
11:20:12 AM...Single APU start

11:25:12 AM...Deorbit ignition (dT: 3:33; dV: 246 mph)
11:28:45 AM...Deorbit burn complete (alt: 213 statute miles)

12:00:25 PM...Atmospheric entry (alt 76 miles; range: 5,020 miles)
12:05:24 PM...1st roll command to left
12:20:32 PM...1st left-to-right roll reversal
12:25:55 PM...Velocity less than mach 2.5 (alt: 83,000 feet)
12:28:03 PM...Velocity less than mach 1 (alt: 48,000 feet)
12:29:12 PM...Shuttle on the HAC (alt: 33,000 feet; 210-degree left turn)
12:32:23 PM...Landing on runway 15


Rev. 202 Deorbit to KSC

12:40:12 PM...Mission control 'go' for deorbit burn
12:55:12 PM...Single APU start

01:00:12 PM...Deorbit ignition (dT: 3:33; dV: 246 mph)
01:03:45 PM...Deorbit burn complete (alt: 213 miles)

01:34:47 PM...Atmospheric entry (alt: 76 miles; range to KSC: 5,095 miles)
01:39:47 PM...1st roll command to right
01:49:10 PM...1st right-to-left roll reversal
02:00:08 PM...Velocity less than mach 2.5 (alt: 83,000 feet)
02:02:12 PM...Velocity less than mach 1 (alt: 52,000 feet)
02:03:07 PM...Shuttle on the HAC (alt: 39,000 feet; 260-degree left turn)
02:06:44 PM...Landing on runway 15

10:15 PM, 8/20/07, Update: Hale optimistic about near-term external tank fix while long-term upgrade is implemented; NASA focuses on Florida landing for shuttle Endeavour

NASA managers today formally cleared the shuttle Endeavour for re-entry and landing Tuesday, weather permitting, to close out an action-packed space station assembly flight. Program managers say a small-but-deep gouge in the shuttle's heat shield poses no threat to Endeavour or its crew. But the jury is still out on what sort of near-term fix might be needed to keep shuttles flying until the external tank problem that caused the damage can be eliminated.

"We will expect there will be some readjustment to our schedule as we work through those options," said Program Manager Wayne Hale. "However, I believe that based on the discussions we've had, that our impacts to the next flight, in terms of the actual launch date of Oct. 23, will be small."

With Hurricane Dean no longer threatening mission control in Houston, NASA is no longer under pressure to bring Endeavour down Tuesday, one way or the other, in Florida or backup landing sites in California or New Mexico. Instead, the astronauts will only attempt to land at the Kennedy Space Center and if the local weather doesn't cooperate, they will stay in orbit an additional day and try again Wednesday. NASA no longer plans to staff White Sands Space Harbor, N.M.. But if Endeavour doesn't make it home to Florida Tuesday, Edwards will be available for use as needed Wednesday.

Endeavour has enough on-board supplies to stay in orbit until Thursday, or even Friday in a worst-case scenario. But flight controllers are hopeful it won't come to that. Forecasters are predicting slightly out-of-limits crosswinds in Florida Tuesday, with just a slight chance of showers near the shuttle's runway. The forecast for Edwards calls for high headwinds, but conditions are expected to be within flight rule guidelines Tuesday through Thursday.

"We're proceeding with our nominal entry plans," Hale said. "Tomorrow, we will primarily look at the Kennedy Space Center and if weather conditions are not conducive to getting back to Florida with Endeavour, we most likely will wave off and attempt Kennedy on a subsequent day."

Commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, Rick Mastracchio, Dave Williams, educator-astronaut Barbara Morgan and Al Drew have two opportunities on successive orbits to land at Kennedy. The first opportunity calls for the shuttle's braking rockets to fire on orbit 201 at 11:25 a.m., setting up a touchdown on runway 15 at 12:32 p.m. The second deorbit opportunity comes at 1 p.m., for a landing at 2:06 p.m.

The gouge in Endeavour's belly was discovered after launch Aug. 8. Two heat-shield tiles were damaged when a chunk of foam debris, possibly including ice, slammed into the orbiter 58 seconds after liftoff. The impact gouged out an irregular pit crossing the boundary between two tiles, measuring roughly two inches by three inches across and nearly penetrating the full 1.12-inch thickness of the tile. A small, 1-inch by 0.2-inch gash at the bottom of the pit exposed an underlying support pad just above the shuttle's aluminum skin.

The shuttle Columbia was destroyed Feb. 1, 2003, when it re-entered the atmosphere with a gaping 4- to 6-inch hole in the leading edge of its left wing. The wing melted from the inside out, the shuttle broke apart above Texas and all seven crew members were killed. NASA managers do not view Endeavour's gouge as a Columbia-class problem. Mission Management Team Chairman John Shannon said the issue was simply whether re-entry heating might cause damage to the shuttle's aluminum skin in the immediate area that would require time-consuming post-landing repairs.

Testing and computer models predict the underlying aluminum skin of the shuttle's right wing will never get hotter than 350 degrees Fahrenheit, NASA's safety limit. At worst, Shannon said, a few downstream tiles could be damaged, along with the two that were gouged out by the impact during launch.

In the end, after nearly a week of around-the-clock testing and analysis, the Mission Management Team cleared Endeavour for re-entry as is, deciding that a spacewalk repair was not necessary and posed more risk to the shuttle than the gouge itself.

The damage was caused by three-hundredths of a pound of foam that fell away from a liquid oxygen feedline support bracket. In an unlucky break, the foam struck an aft strut that helps hold the shuttle to the external tank. Most of the debris survived that impact intact and ricocheted into the shuttle. NASA already was designing a fix for the brackets, but the upgrade will not be ready until the fourth flight from now.

Hale said today engineers are evaluating five near-term modifications to the feed line brackets, adding he is optimistic the next shuttle flight, scheduled for launch Oct. 23, can stay roughly on schedule. It will be more difficult to keep the flight after that on track, a high-priority mission to launch a European research module. Currently scheduled for launch Dec. 6, the launch window closes about one week later.

Today, Hale provided a snapshot of where the foam issue stands, how it might play out and why the debate over Endeavour's heat shield gouge is very different from the limited analysis that preceded Columbia's ill-fated re-entry.

But Hale would not predict where the foam will fit in NASA's probabilistic risk matrix and how that might play into the agency's planning for the next shuttle flight. Here are Hale's opening remarks at a news briefing Monday:

"When I was sitting in (entry flight director) Steve Stich's chair as entry flight director for 28 shuttle landings, we never knew what the condition of the entry heat shield was," Hale said. "It was always assumed to be good, we did no inspections, we did no analysis, we just trusted that it was a good thing and we would be safe to enter. Now, we're smarter. And over the past four or five years we have put together a great plan to inspect and make sure the heat shield is in good shape and if there are any concerns, we have put together the equipment, the procedures, the planning and the entire process to evaluate whether or not the heat shield is safe for re-entry and if it's not, to provide the capability to repair.

"However, repairs are in and of themselves somethings hazardous to execute. So like so many things in our business, it becomes a risk trade. At the final analysis, having allowed over 200 engineers and specialists in the areas of thermal protection systems, aerothermal heating, to work hundreds of hours, including 4,000-plus hours of super computer simulation (time) using well-anchored, test-validated models, a series of extremely accurate and extensive tests in the re-entry simulators both here at Johnson and at other facilities around the NASA team, and having been peer reviewed by specialists in supersonic flight, hypersonic thermal environments and so forth, we can say with a high degree of confidence that Endeavour is safe to come home without needing a repair.

"That does not mean that we're entirely happy with the situation and in fact, I had a discussion this morning with the team about what our future steps are to make sure that the next flight and those following it are safe to fly. Again, this was a problem that originally came from debris coming off the external tank. After Columbia, we had a long discussion about how we could best eliminate the hazards of debris coming off the external tank and it becomes very obvious in a very short order as you look at the system, it's an inherent design situation with the space shuttle that we will never be able to completely eliminate the potential of debris coming of the external tank, or some of the other elements of the launch vehicle stack. And so there will never be a launch where we have zero risk.

"We will continue to improve as we go forward. What we did, however, do for return to flight and are continuing to do to day, is to take a hard look at those areas where debris may be shed to try to categorize them in order of their risk factor, in other words, which are the most serious risks, and to methodically whittle away and reduce those risks by eliminating hazards one at a time. As you know, we got quite a lot of risk reduction and hazard improvement with the first return to flight, STS-114. We spent another period of time where we wanted to make another significant improvement and we whittled that risk down significantly more by the time we flew the second return to flight (mission), STS-121. We knew we were not finished at that point and in fact, set out on future redesigns. And we have a number of improvements that are coming forward on a tank that we will fly about four flights from now.

"We have three flights, however, with tanks that have not been modified. And in particular, one of the areas on that external tank that we have already got a design in work for is off these liquid oxygen feedline brackets that was the cause of the incident on Endeavour's launch. So we know that four flights from now we have a good fix that will eliminate that hazard. The discussions I've been having with the team in the last few days are what will we do with the next three tanks, and the next three flights, until we get that final design into the fleet to, again, mitigate and reduce the hazard.

"Today we had about a two hour telecon with the tank designers and the folks that are working on five different options to improve the situation on the next tank. We will expect there will be some readjustment to our schedule as we work through those options. However, I believe that based on the discussions we've had, that our impacts to the next flight in terms of the actual launch date of Oct. 23 will be small, we think we have plenty of time to evaluate some changes and in fact implement them if we feel that they are well justified.

"We are also looking at the further implications to the next flight because as we take time to prepare this tank it does impact the schedule on the subsequent flight and we would really like to hold that flight to the December launch window if we can do it safely. And I think that's the clue. As we look to the manifest ahead of us, we can expect there will be challenges, whether they're from hurricanes or from equipment that is causing us a problem on board the shuttle. However, we do have an amount of time ahead of us, a skilled work force and a umber of options that will allow us to fly the manifest as it's been laid out and complete the international space station with a significant margin of time before the date that the president and the congress have directed us to retire the space shuttle vehicle."

Going into Endeavour's flight, Hale said engineers viewed the risk posed by foam falling off oxygen feedline brackets as "rather low."

"In the analysis, it was assumed that if the aerodynamics carried this foam down to the attach bracket of the external tank and struck it, that the foam would come apart and that would be the end of the hazard. And in fact what we saw on the video ... we saw this piece of foam strike this strut which is angled at a 30- to 45-degree angle to the flight path and ricochet off and hit the bottom of the orbiter, it's clear as day.

"We didn't think that could happen before. So we would have told you that was a non-credible, non-possible thing to happen. Therefore, no risk, at least in a rebound case. Clearly, we're smarter now than we were a couple of weeks ago and we're looking very hard at those particular locations and those particular aerodynamic paths that might lead this foam or foam and ice combination to hit the strut and bounce off and strike the underside of the orbiter. So we have a more sophisticated risk analysis in work. That's why I think the risk is probably higher than we had characterized before."

But Hale said he does not believe the problem represents a "probable-catastrophic" threat to the shuttle, a level of risk that is not generally considered acceptable for flight.

"It is currently not categorized as probable-catastrophic," Hale said. "It is my belief that it will not be classified as probable-catastrophic. The risk assessment people, however, are off doing their work and we do not have the final numbers back from that. And we will be informed by that analysis when it comes in. So, it's under review."

11:15 AM, 8/20/07, Update: NASA will staff KSC and Edwards for Tuesday landing; weather update

The 11 a.m. forecast from the National Hurricane Center continues to show Hurricane Dean on a track that will take it into central Mexico late Wednesday. Assuming no major changes that would threaten mission control in Houston, NASA will attempt to bring the shuttle Endeavour back to Florida on Tuesday. But depending on the forecast for Wednesday, entry flight director Steve Stich could opt to divert the crew to Edwards Air Force Base, Calif., if the KSC weather doesn't cooperate.

"Hurricane Dean is kind of trending away, so we don't think that's going to be a factor," astronaut Chris Ferguson radioed the crew from mission control around 10:35 a.m. "We're still keeping our options open, however.

"For landing weather at the Cape tomorrow," he continued, "the weather is forecast to be pretty good. They're calling few (clouds) at 3,000 and few at 25,000. They are still, however, carrying a slight chance of rain showers and as we look at the radar here this morning, they seem to be sporadically building along the coast. So I'm sure that'll be a bit of a touch-and-go situation. But so far, it's looking pretty good.

"Probably the biggest issue right now might be the crosswinds," Ferguson said. "Right now, they're calling for, it looks like, one zero (100 degrees) at 10 (knots), peak to 18."

That translates into a crosswind component of nearly 14 knots. NASA's end-of-mission - EOM - flight rules forbid daylight landings in crosswinds higher than 15 knots.

"So for that reason, we will still continue to bring Edwards up most likely for tomorrow only because in addition to the winds at KSC, the end-of-mission plus one winds (Wednesday) at Edwards are forecast to grow and the winds at KSC will remain high for EOM plus one. So in a nutshell, weather's looking good at both KSC and at Edwards. Crosswinds may be an issue and for that reason, we'll have two sites most likely available for tomorrow."

A detailed re-entry timeline for Tuesday, Wednesday and Thursday, along with an updated weather forecast, will be posted here after today's mission status briefing.

6:30 AM, 8/20/07, Update: Crew preps for entry

The Endeavour astronauts are preparing the shuttle for landing Tuesday, packing up equipment, testing the ship's re-entry systems and enjoying a final few hours of off-duty time this afternoon.

Canadian astronaut Dave Williams, commander Scott Kelly and Barbara Morgan plan to participate in a Canadian Space Agency VIP/education event at 11:46 a.m., the final such event of the mission.

The astronauts were awakened for their final full day in space at 4:37 a.m. by a recording of "Flying" by the Long John Baldry Trio, a Canadian group, beamed up from mission control.

"Good morning, Endeavour, and a special good morning to Dave today, astronaut Shannon Lucid called from Houston.

"And Houston, Endeavour, good morning," Williams replied. "That's a great song to hear for a day before we come back to land."

Today's mission status briefing with entry flight director Steve Stich is planned for 2:30 p.m. and a final Mission Management Team update is scheduled for 4 p.m. Among the topics will be the results of Sunday's final heat shield inspection.

Here is an updated timeline of events (include revision Q of the NASA television schedule; in EDT and mission elapsed time):

EDT........DD...HH...MM...EVENT

Monday, 08/20/07

04:37 AM...11...10...00...Crew wakeup
07:42 AM...11...13...05...Cabin stow begins
07:52 AM...11...13...15...Flight control system checkout (began early)
09:12 AM...11...14...35...Maneuvering thruster hot fire test
09:27 AM...11...14...50...Deorbit review
11:47 AM...11...17...10...Canadian Space Agency VIP/educational event
12:57 PM...11...18...20...PILOT landing simulator practice
01:07 PM...11...18...30...Spacehab entry preps
01:52 PM...11...19...15...Crew meal
02:30 PM...11...19...54...Mission status briefing on NTV
03:12 PM...11...20...35...Crew off duty
04:00 PM...11...21...24...Post-MMT briefing on NASA TV
05:27 PM...11...22...50...Ergometer stow
05:53 PM...11...23...16...Orbit adjust rocket firing
05:57 PM...11...23...20...KU-band antenna stow
08:37 PM...12...02...00...Crew sleep begins

Tuesday, 08/21/07

04:37 AM...12...10...00...Crew wakeup
06:32 AM...12...11...55...Group B computer powerup
06:47 AM...12...12...10...Inertial measurement unit alignment
07:27 AM...12...12...50...Deorbit timeline begins
11:25 AM...12...16...48...Deorbit ignition (dT: 3:33; dV: 246 mph)
12:01 PM...12...17...24...Entry interface (alt: 400,000 feet)
12:05 PM...12...17...28...First left roll command
12:21 PM...12...17...44...Left-to-right roll reversal
12:26 PM...12...17...49...Mach 2.5
12:28 PM...12...17...51...Mach 1
12:30 PM...12...17...53...Shuttle banks to line up on runway 15
12:32 PM...12...17...55...Landing

The 5 a.m. forecast from the National Hurricane Center continues to show Hurricane Dean on a track that will take it into central Mexico late Wednesday. Assuming no major changes that would threaten mission control in Houston, NASA likely will attempt to bring Endeavour back to Florida on Tuesday and, if the weather at the Kennedy Space Center doesn't cooperate, extend the mission a day and try again on Wednesday.

The Sunday evening forecast from the Spaceflight Meteorology Group at the Johnson Space Center called for good weather at Kennedy on Tuesday, with scattered clouds at 3,000 and 10,000 feet and winds out of 110 degrees at 10 knots with gusts to 17. That translates into a maximum crosswind of about 11 knots, well below NASA's safety limit.

A detailed re-entry timeline for Tuesday, Wednesday and Thursday, along with an updated weather forecast, will be posted here after today's mission status briefing.

4:50 PM, 8/19/07, Update: Endeavour undocks from space station; Hurricane Dean less threatening to mission control; White Sands out of landing strategy

The Endeavour astronauts undocked from the international space station today and carried out a final inspection of the shuttle's carbon composite nose cap and wing leading edge panels to make sure the ship is ready for re-entry and landing Tuesday to close out a dramatic station assembly mission.

"Undocking, in a word, really was flawless, it was completely by the book, absolutely picture perfect," said lead flight director Matt Abbott. "Looking ahead to tomorrow, the crew wakes up at 3:30 a.m. (Central Time). It'll be pretty much a standard end-of-mission-minus-one day, with reaction control system hotfire checks and the flight control system checkout activities and cabin stowage. Tuesday is now our planned landing day.

Forecasters are predicting generally good weather at the Kennedy Space Center and at NASA's favored backup landing site, Edwards Air Force Base, Calif.

"KSC weather permitting in Florida, the plan is to go into KSC on Tuesday and of course, we do have some extension days beyond that, weather permitting here in Houston as we continue to watch the track of Hurricane Dean."

NASA originally planned for Endeavour's crew to undock Monday and land Wednesday. But a fourth and final spacewalk was cut short Saturday and the crew was ordered to undock and land a day early because of the possibility Hurricane Dean could force flight controllers to evacuate the Johnson Space Center in Houston. While NASA has contingency plans in place to control a shuttle flight from Kennedy, engineers would not enjoy the normal staffing levels and computer processing power. Moving landing up one day, NASA hoped to ensure normal mission control operations for at least one landing opportunity.

Because of the possibility of an evacuation later in the week, mission managers decided over the weekend to staff all three shuttle landing sites Tuesday - Kennedy, Edwards and White Sands Space Harbor, N.M. If JSC was threatened, the plan was to bring Endeavour down at one of those sites.

But Hurricane Dean is now tracking well south of Houston, an evacuation is not imminent and with good weather expected in Florida and California's Mojave Desert, mission managers today dropped White Sands from their landing plan.

"The latest track from the National Hurricane Center is favorable for the Johnson Space Center," said John Shannon, chairman of NASA's Mission Management Team. "It looks like it'll be passing by Jamaica today and heading for the Yucatan Peninsula and then into central Mexico. There is still uncertainty with a storm like this, but right now it's looking pretty good from our standpoint. The Johnson Space Center will be open for normal operations tomorrow. ... We will meet again tomorrow but the threat is certainly somewhat less than it was the last two days."

As a result, he said, "we're not going to execute any of those (contingency) plans right now. We're just going to wait. There's not going to be a change to the flight control team manning, we're not going to be sending people out to Florida right now, we're going to stand by a little bit.

"We'll come in tomorrow and we'll talk about the hurricane, we'll talk about the weather at the landing sites," Shannon said. "I think for Monday, we would probably leave all of our support for Edwards and for the Kennedy Space Center in place and then on Tuesday, we'd be one day smarter on where the hurricane is really going. It's possible Tuesday morning we would end up not exercising an Edwards option if the Kennedy Space Center was not go and end up going around to Wednesday to try and get into the cape."

NASA landing charts and data: http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts118/landing.html Here are updated deorbit and landing times for Tuesday, Wednesday and Thursday at the Kennedy Space Center and Edwards Air Force Base (in EDT):

ORBIT.SITE..DEORBIT....LANDING

Tuesday, 08/21/07

201...KSC...11:25 AM...12:32 PM
202...KSC...01:00 PM...02:06 PM
203...EDW...02:30 PM...03:37 PM
204...EDW...04:06 PM...05:11 PM
205...EDW...05:43 PM...06:48 PM

Wednesday, 08/22/07

217...KSC...11:52 AM...12:54 PM
218...KSC...01:27 PM...02:29 PM
219...EDW...02:57 PM...03:59 PM
220...EDW...04:33 PM...05:35 PM

Thursday, 08/23/07

232...KSC...10:40 AM...11:42 AM
233...KSC...12:15 PM...01:17 PM
234...EDW...01:45 PM...02:47 PM
235...EDW...03:20 PM...04:22 PM
236...EDW...04:57 PM...05:58 PM

"We've got two more days to go in the mission, so it's not over yet," Abbott said. "We've got to stay focused, but we're looking forward to a safe and successful couple of days and then an entry and landing on Tuesday."

Endeavour undocked from the international space station today at 7:56 a.m. as the two spacecraft sailed 210 miles above the south Pacific Ocean.

"Physical separation, Houston," one of the shuttle astronauts radioed as powerful springs pushed the two spacecraft apart.

As the shuttle slowly pulled away directly in front of the lab complex, station commander Fyodor Yurchikhin radioed: "Endeavour, from ISS. Endeavour departure." Following naval tradition, he then rang the ship's bell in the Destiny laboratory module.

"Thanks for everything, Scott and the Endeavour crew," station flight engineer Clay Anderson said to shuttle commander Scott Kelly. "Godspeed, I was proud to be a part of STS-118."

"And Endeavour, have a good landing," station flight engineer Oleg Kotov radioed.

"And to the ISS crew, we couldn't have gotten everything we accomplished without you guys," Kelly replied. "We look forward to seeing you back on planet Earth."

Endeavour pulled away to a distance of about 400 feet in front of the station before looping up and passing directly above it. From there, the shuttle fell behind and slowly left the immediate area.

With undocking complete, the major item on the crew's agenda today was a final heat shield inspection to make sure Endeavour's reinforced carbon carbon nose cap and wing leading edge panels have not suffered any damage from orbital debris or micrometeoroids since a similar inspection was carried out the day after launch.

No obvious damage was visible in downlinked television views of the survey, but it will take engineers a full day to assess the data and make a final determination.

"Just about every flight, we do see MMOD (micrometeoroid/orbital debris) damage on the wing leading edge and nose cap," Shannon said. "They're very small scrapes, very small pits in the silica carbide gray outer layer, but not down to the carbon. Matter of fact, I think on the last flight we had 17 small indications. Post flight, they go over it with high magnification and look for anything like that. That is just a function of flying in space. You have very small particles that can impact you. It would take a fairly significant one to affect us but it's not a zero probability, that's why we do the late inspection."

Impact sensors mounted directly behind Endeavour's leading edge panels have recorded 16 events corresponding to shocks ranging in strength from 0.5 to 2 Gs. Similar shocks have been recorded on previous post-Columbia shuttle flights. Engineers believe the events may be associated with thermal stress as the shuttle's structure responds to changes in temperature.

6:00 AM, 8/19/07, Update: Shuttle crew prepares for undocking

The Endeavour astronauts are preparing to undock from the international space station today after a busy, at times dramatic, nine days of orbital construction and supply transfer work. Hatches between the two spacecraft were closed Saturday and if all goes well, the shuttle will undock at 7:57 a.m.

Because the crew has had only a few hours of off-duty time since the mission began, flight controllers designed a straight-forward fly away, eliminating a slow loop around the station for photo documentation to give the astronauts a few more hours off at the end of the day. The second of two rocket firings at 8:54 a.m. will complete the undocking and separation procedure.

Along with beginning the process of packing up for landing Tuesday, the astronauts plan to carry out a final inspection of the shuttle's nose cap and wing leading edge panels, which experience the most extreme heating during re-entry. A similar inspection was carried out Aug. 9, the day after launch, to look for signs of ascent impact damage. This time around, the astronauts are looking for any signs of damage from space debris or micrometeoroids that might have occurred since the initial inspection.

The late inspection is scheduled to begin around 10:15 a.m. A laser scanner and high-resolution camera on the end of a 50-foot-long boom attached to the shuttle's robot arm will be slowly moved back and forth along the right wing leading edge panels, the carbon composite nose cap and then the left wing. The work should be finished by around 2:30 p.m.

Impact sensors mounted directly behind the leading edge panels have recorded 16 events corresponding to shocks ranging in strength from 0.5 to 2 Gs. Similar shocks have been recorded on previous post-Columbia shuttle flights, but no obvious signs of actual impacts were detected during late inspection. Engineers believe the events may be associated with thermal stress as the shuttle's structure responds to changes in temperature.

"The magnitudes seen on STS-118 have been very similar to previous missions although there has been a 50 percent increase in the number of indications compared to previous flights," NASA's Mission Management Team told the astronauts in a note uplinked Saturday as part of the crew's daily execute package. "This may be attributed to the fact that improvements have been made to the system to provide data simultaneously for both wings for longer periods of time and at colder temperatures. For example, the monitoring time during STS-118 before docking is twice as much as STS-117 and about three times that of STS-116.

"Most of the indications, a majority of which occurred on the port wing, were clustered early in the mission prior to and after docking. A few of the wing leading edge indications on previous flights have been correlated to minor impacts found on the wing leading edge panels during post-landing inspections. Many of the other WLE (wing leading edge) sensor indications from previous flights have not been correlated with anything including thruster firings, other mission events, thermal day/night cycles, etc. Many theories exist as to what has caused an increased number of wing leading edge indications on STS-118 including MMOD and the Perseid meteor activity. However, no definitive correlations were found between the Perseids and the increased indications since half of the indications occurred during Earth blockage. Only a single indication occurred during the Perseids peak with both wings being continuously monitored. Obviously, the MMOD (micrometeoroid/orbital debris) concern is the primary reason for executing the late inspection."

Here is an updated timeline of today's activity in space (in EDT and mission elapsed time; note: NASA rounds down to the nearest minute; this page rounds up or down as required):

EDT........DD...HH...MM...EVENT

08/19/07
04:37 AM...10...10...00...STS crew wakeup
06:17 AM...10...11...40...Group B computer power up
06:33 AM...10...11...56...Sunrise
07:01 AM...10...12...24...Noon
07:12 AM...10...12...35...Undocking timeline begins
07:28 AM...10...12...51...Sunset
07:57 AM...10...13...20...Undocking
07:57 AM...10...13...20...Initial orbiter separation (+10 seconds)
07:58 AM...10...13...21...Space station holds current attitude
08:01 AM...10...13...24...Range: 50 feet; reselect -X jets
08:02 AM...10...13...25...Range: 75 feet; low-Z jets
08:05 AM...10...13...28...Sunrise
08:26 AM...10...13...49...Range: 400 feet
08:26 AM...10...13...49...Separation burn No. 1
08:32 AM...10...13...55...Range: 600 feet
08:32 AM...10...13...55...Noon
08:54 AM...10...14...17...Separation burn No. 2
09:00 AM...10...14...23...Sunset
09:02 AM...10...14...25...ISS: Shuttle docking port depressurization
09:07 AM...10...14...30...Group B computer power down
09:07 AM...10...14...30...Post-undocking laptop computer reconfiguration
09:07 AM...10...14...30...Supply transfer cleanup
09:27 AM...10...14...50...Shuttle arm (SRMS) unberths inspection boom
10:17 AM...10...15...40...Starboard wing survey
10:52 AM...10...16...15...Spacesuit install in airlock
11:02 AM...10...16...25...EVA tool stow
11:57 AM...10...17...20...Nose cap survey
12:57 PM...10...18...20...Port wing survey
01:27 PM...10...18...50...ISS: Shuttle docking port leak check
02:42 PM...10...20...05...Inspection boom berthing
03:17 PM...10...20...40...SRMS power down
03:27 PM...10...20...50...Laser data downlink
03:32 PM...10...20...55...Crew meal
04:32 PM...10...21...55...Crew off duty
08:37 PM...11...02...00...STS crew sleep begins

The Mission Management Team continues to monitor the progress of Hurricane Dean. Concern about Dean's track and the possibility mission control at the Johnson Space Center might have to be evacuated prompted NASA to move undocking up one day and bring Endeavour back to Earth Tuesday - one day early - to ensure a Houston-controlled re-entry.

On Sunday, the MMT decided that if Hurricane Dean threatened the Johnson Space Center, Endeavour would land Tuesday at one of NASA's three shuttle landing facilities - the Kennedy Space Center in Florida, Edwards Air Force Base, Calif., or White Sands Space Harbor, N.M. If the storm did not pose a threat, the astronauts would attempt to land at Kennedy on Tuesday and, if conditions there were not acceptable, remain in orbit another day and try again on Wednesday. The shuttle has enough on-board supplies to remain in orbit until Friday if worse comes to worse.

Over the past few days, Hurricane Dean's predicted path has been creeping south and today's 5 a.m. forecast from the National Hurricane Center showed Dean crossing the heart of the Yucatan Peninsula early Tuesday before hitting the central Mexican coast late Wednesday or early Thursday. The cone of uncertainty has moved well away from Houston.

If the storm stays on that track, NASA likely will execute its normal entry strategy, focusing solely on a Florida landing Tuesday and, barring that, a landing at Kennedy or Edwards on Wednesday. The early forecast for Tuesday at Kennedy calls for general favorable conditions with a slight chance of showers in the area. Touchdown is targeted for 12:32 p.m.

6:19 PM, 8/18/07, Update: Shuttle-station hatches closed; undocking on tap Sunday, landing Tuesday

The Endeavour astronauts staged a final, abbreviated spacewalk today and closed hatches between the shuttle and the international space station to set the stage for undocking early Sunday and landing Tuesday - a day early because of concern about Hurricane Dean - to close out a dramatic station assembly mission.

NASA's Mission Management Team met today and after evaluating the hurricane's predicted track and speed, decided that if the storm threatens to force an evacuation of the Johnson Space Center in Houston, flight controllers in Texas will stay long enough to oversee a Tuesday landing in Florida or, if bad weather develops at Kennedy, at Edwards Air Force Base, Calf., or White Sands Space Harbor, N.M.

If the hurricane does not threaten Johnson, the astronauts will still attempt a landing at Kennedy on Tuesday but in that case, if bad weather crops up in Florida, they will stay in orbit another day and try again on Wednesday. The shuttle has enough on-board supplies to stay in orbit until Friday, but the last day is always held in reserve in case of last-minute technical problems. Cain said NASA hopes to have the shuttle on the ground by Thursday at the latest.

"End of mission day is now Tuesday," said LeRoy Cain, chairman of NASA's Mission Management Team for launch and landing. "Tuesday is our first landing day. So we have now changed our plan so that instead of end-of-mission being on Wednesday, end-of-mission is on Tuesday. The only thing to think about that might be different is whether or not the storm might be threatening us when we get to the late-Monday, early-Tuesday timeframe. Essentially, if the storm is indeed threatening (the Johnson Space Center) area, we will have all three landing sites called up Tuesday and we will land somewhere on Tuesday. And that'll be the going-in plan."

Canadian astronaut Dave Williams and Expedition 15 flight engineer Clay Anderson staged a five-hour and two-minute spacewalk today to finish up a few final space station assembly tasks. As soon as they were back aboard, the combined crews rushed to finish last-minute equipment transfer work and then gathered in the Destiny laboratory module for a final farewell just after 5 p.m.

"Unfortunately, time has only one meaning here, it comes very fast," said Expedition 15 commander Fyodor Yurchikhin. "We had some problems but (we did very well), very good job. Thank you very much for everybody. We will be here just a little more than two months. Come back again!"

"We got a lot accomplished," shuttle commander Scott Kelly agreed. "We couldn't have done all that stuff without you guys, we really appreciate your help and it's great being part of one big team between the shuttle crew and the station crew. Thanks."

The two crews then shared hugs and handshakes before the Endeavour astronauts floated back aboard the space shuttle. Hatches between the two spacecraft were closed around 5:10 p.m. If all goes well, Endeavour will undock at 7:57 a.m. Sunday. Here is an updated timeline of key events (in EDT and mission elapsed time):

EDT........DD...HH...MM...EVENT

08/19/07
04:37 AM...10...10...00...Shuttle crew wakeup
06:33 AM...10...11...56...Sunrise
06:37 AM...10...12...00...Group B computer power up
07:01 AM...10...12...24...Noon
07:12 AM...10...12...35...Undocking timeline begins
07:28 AM...10...12...51...Sunset
07:57 AM...10...13...20...UNDOCKING
07:57 AM...10...13...20...Initial orbiter separation (+10 seconds)
07:58 AM...10...13...21...ISS holds current attitude
08:01 AM...10...13...24...Range: 50 feet
08:02 AM...10...13...25...Range: 75 feet
08:05 AM...10...13...28...Sunrise
08:26 AM...10...13...49...Range: 400 feet
08:26 AM...10...13...49...Separation burn No. 1
08:32 AM...10...13...55...Range: 600 feet
08:32 AM...10...13...55...Noon
08:54 AM...10...14...17...Separation burn No. 2
09:00 AM...10...14...23...Sunset
09:02 AM...10...14...25...ISS: Station docking port depressurization
09:07 AM...10...14...30...Group B computer power down
09:07 AM...10...14...30...Post-undocking laptop reconfiguration
09:07 AM...10...14...30...Supply transfer cleanup
09:32 AM...10...14...55...Shuttle arm (SRMS) unberths heat shield inspection boom (OBSS)
10:22 AM...10...15...45...OBSS starboard wing survey
10:52 AM...10...16...15...Spacesuit install in airlock
11:07 AM...10...16...30...EVA tool stow
12:02 PM...10...17...25...OBSS nose cap survey
01:02 PM...10...18...25...OBSS port wing survey
01:27 PM...10...18...50...ISS: docking port leak check
02:47 PM...10...20...10...OBSS berthing
03:22 PM...10...20...45...SRMS power down
03:37 PM...10...21...00...Crew meal
03:42 PM...10...21...05...Laser data downlink
04:37 PM...10...22...00...Crew off duty
08:37 PM...11...02...00...Shuttle crew sleep begins

The astronauts originally planned to carry out a full-duration spacewalk today and finish up equipment and supply transfers to and from the lab complex Sunday. Hatches between Endeavour and the station were scheduled to be closed Sunday night to set the stage for undocking Monday. A now-routine post-Columbia final heat shield inspection was on tap Monday afternoon and the crew planned to pack up and test the shuttle's re-entry systems Tuesday. Touchdown at the Kennedy Space Center was targeted for around 12:52 p.m. Wednesday.

But Hurricane Dean has thrown a wrench into those plans because NASA may be forced to evacuate the Johnson Space Center early next week. If so, and if landing remained targeted for Wednesday, the agency would have to set up an emergency mission control center at the Kennedy Space Center. While controlling a shuttle from Kennedy is part of a long-established contingency plan, NASA would have to rely on a much smaller team and give up some of its ability to monitor the orbiter's myriad systems. By moving landing up a day, NASA likely could ensure a normal JSC-controlled re-entry.

"If by the time we show up in the late-Monday, early-Tuesday timeframe the storm is not threatening the area and looks like it is not going to be a threat, then the entry team will execute the normal deorbit-and-entry mission planning, which is typically on the first end-of-mission day we will try to land at Kennedy Space Center in Florida and if we're not able to - and again, if the storm is not threatening us (in Houston) - in all likelihood we would elect to go around and make a landing attempt on Wednesday."

The forecast for Tuesday calls for generally good weather in Florida with only a chance of showers in the area.

"It's really dependent on what the storm does," Cain said. "We are prepared to land on Tuesday if the storm is threatening us, we've set ourselves up to be able to do that. We will still attempt to land on Tuesday even if the storm is not threatening us. However, if we are not able to land at Kennedy Space Center on Tuesday and the storm is not threatening us then we will be in our normal landing operations and we would go around and show up on Wednesday and try to land at Kennedy."

Williams and Anderson accomplished three primary objectives during today's spacewalk. They installed clamps on the station's main solar array truss that will be used next year to temporarily hold a shuttle heat shield inspection boom; Anderson retrieved two space exposure experiments while Williams adjusted an antenna gimbal lock assembly. After that, the spacewalkers worked together to install a wireless instrumentation antenna on the Destiny laboratory module. Deferred to a future spacewalk was work to tie down debris shields on Destiny and the multi-hatch Unity connecting module.

As they worked to install the wireless antenna, the space station sailed 214 miles above Hurricane Dean.

"Oh, wow!" one of the astronauts - presumably Williams - exclaimed as he caught sight of the huge storm. "Oooo man, can't miss that!" "Holy smoke," Anderson said. Television views from the station showed the hurricane in its entirety, sporting a tight, well-defined eye at the heart of of the storm.

"That's impressive," Williams said.

"Can you see the eye?"

"Oh yeah," Williams said. "Definitely."

"Oh yeah, that's wild," Anderson said. "All right, Dave, I'm going to put another tether on there before I hand it to you."

"Copy that," Williams said as the two spacewalkers continued work to install a wireless instrumentation antenna. "Man, that's impressive."

"Very," Anderson agreed, adding: "They're only impressive when they're not coming to you."

"That's true."

The spacewalk began at 9:17 a.m. and ended at 2:19 p.m. for a duration of five hours and two minutes. Williams, Anderson and shuttle astronaut Rick Mastracchio logged a total of 23 hours and 15 minutes of spacewalk time across four outings during Endeavour's mission. This was the 92nd spacewalk since station construction began in 1998 and the 15th so far this year. Total station assembly EVA time now stands at 567 hours and 59 minutes.

2:25 PM, 8/18/07, Update: Astronauts marvel at Hurricane Dean; wrap up abbreviated spacewalk

Canadian astronaut Dave Williams and space station flight engineer Clay Anderson staged an abbreviated fourth and final spacewalk today, pausing for a moment to take in a spectacular bird's eye view of Hurricane Dean, the storm that prompted NASA managers to make preparations for an earlier-than-planned undocking and landing.

Concerned about the possibility of an evacuation that could force NASA to move mission control from Houston to more limited facilities at the Kennedy Space Center in Florida, NASA managers told the astronauts to shave two hours off today's spacewalk as part of a plan to preserve the option of undocking early Sunday and landing Tuesday, a day ahead of schedule.

By shortening today's spacewalk, the astronauts can make final equipment transfers and close the hatches between Endeavour and the space station around 5 p.m., setting the stage for undocking Sunday. NASA's Mission Management Team planned to review the forecast during an afternoon meeting and make a decision about how to proceed after hatch closure.

As they worked to install the wireless antenna, the space station sailed 214 miles above Hurricane Dean.

"That's impressive," Williams said.

"Can you see the eye?"

"Oh yeah," Williams said. "Definitely."

"Oh yeah, that's wild," Anderson said. "All right, Dave, I'm going to put another tether on there before I hand it to you."

"Copy that," Williams said as the two spacewalkers continued work to install a wireless instrumentation antenna. "Man, that's impressive."

"Very," Anderson agreed, adding: "They're only impressive when they're not coming to you."

"That's true."

Williams, Mastracchio, Endeavour commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, Al Drew and educator-astronaut Barbara Morgan plan to say goodbye to their space station colleagues - Expedition 15 commander Fyodor Yurchikhin, Oleg Kotov and Anderson - during a brief farewell ceremony in the Destiny laboratory module around 4:46 p.m. Hatches between the two spacecraft are expected to be closed about 15 minutes later. Today's mission status briefing is scheduled to begin at roughly the same time and this status report will be updated as soon as possible thereafter.

9:18 AM, 8/18/07, Update: Spacewalk begins

Floating in the space station's Quest airlock module, Canadian astronaut Dave Williams and flight engineer Clay Anderson switched their spacesuits to internal battery power at 9:17 a.m. to officially kick off an abbreviated four-and-a-half-hour spacewalk, the fourth and final excursion planned for the shuttle Endeavour's mission. The spacewalk began about 45 minutes ahead of schedule.

The first item on the agenda today is installation of clamps on the station's main solar array truss that will be used next year to temporarily hold a shuttle heat shield inspection boom. Anderson then plans to retrieve two space exposure experiments while Williams adjusts an antenna gimbal lock assembly. After that, the spacewalkers will work together to install a wireless instrumentation antenna, the last planned task for today's EVA.

6:58 AM, 8/18/07, Update: Crew gears up for hurricane-shortened spacewalk, early hatch closure

Canadian astronaut Dave Williams and space station flight engineer Clay Anderson are preparing for a shortened spacewalk today while their crewmates complete final equipment transfers to and from the station to clear the way for hatch closure later this afternoon. Concerned about the threat of Hurricane Dean, NASA managers have ordered the early hatch closure to protect the option of undocking Sunday and landing Tuesday, a day ahead of schedule, to get the shuttle back on the ground before mission control in Houston might have to be evacuated.

"Good Morning Endeavour! Thanks for the great day yesterday!" flight controllers said in a message uplinked to the crew early today. "You are an awesome crew! We are looking forward to the EVA today. As you were briefed last night, the EVA will be shortened so that hatch closure can take place this evening. You will undock tomorrow morning. Landing is being planned for Tuesday. This is all because of the potential threat to JSC posed by hurricane Dean. Thanks for your flexibility!"

Mission control commentator Rob Navias, however, said early today no final decisions have been made to undock Sunday and depending on updates to Hurricane Dean's projected track, mission managers presumably could change their minds. But barring a major change, the hatches will be closed around 5 p.m. today.

Today's spacewalk will be the 92nd since station construction began in 1998, the 15th so far this year and the fourth for Endeavour's mission. It will be the third for both Williams and Anderson. Going into today's EVA, 72 men and women had logged 562 days and 57 minutes of spacewalk time building and maintaining the international lab complex.

Items on today's agenda include installation of mounting brackets on the station's solar array truss to temporarily hold a shuttle heat shield inspection boom next year; retrieval of two space exposure experiment packages; get-ahead preparation of antenna gimbal locks; and installation of a wireless instrumentation antenna.

Anderson and Williams originally planned to carry out a six-and-a-half-hour spacewalk, but the revised flight plan shaved two hours off the excursion. Tasks that will be deferred to a future shuttle flight or to a station crew include work to tie down debris shields on the Destiny and Unity modules and a few other low-priority get-ahead tasks.

Here is the replanned timeline for today's activity (in EDT and mission elapsed time):

EDT........DD...HH...MM...EVENT

08/18/07
05:07 AM...09...10...30...STS/ISS crew wakeup
05:47 AM...09...11...10...EVA-4: Airlock repressurized to 14.7 psi
06:07 AM...09...11...30...EVA-4: Hygiene break
06:27 AM...09...11...50...EVA-4: Airlock depressurized to 10.2 psi
06:57 AM...09...12...20...EVA-4: Campout EVA preparations
08:27 AM...09...13...50...EVA-4: Spacesuit purge
08:42 AM...09...14...05...EVA-4: Spacesuit pre-breathe
08:57 AM...09...14...20...Logistics transfers resume
09:32 AM...09...14...55...EVA-4: Airlock depressurization
10:07 AM...09...15...30...EVA-4: Airlock egress and setup
10:22 AM...09...15...45...EVA-4: Orbiter inspection boom S1 mounting brackets installed
11:07 AM...09...16...30...Oxygen system tear-down
11:22 AM...09...16...45...EVA-4: EV3: S-band antenna sub-assembly gimbal locks
11:22 AM...09...16...45...EVA-4: EV3: MISSE space exposure experiment retrieval
12:07 PM...09...17...30...EVA-4: Wireless instrumentation system antenna installation
01:47 PM...09...19...10...EVA-4: Payload bay cleanup
02:12 PM...09...19...35...EVA-4: Airlock ingress
02:32 PM...09...19...55...EVA-4: Airlock repressurization
02:47 PM...09...20...10...Post-EVA spacesuit servicing
03:02 PM...09...20...25...MISSE disassembly
03:22 PM...09...20...45...MISSE transfer to shuttle
03:47 PM...09...21...10...Spacesuit transfer to shuttle
03:57 PM...09...21...20...Transfer tagup
04:47 PM...09...22...10...Farewell ceremony
05:02 PM...09...22...25...Hatches closed
05:27 PM...09...22...50...Rendezvous tools checkout
05:27 PM...09...22...50...Leak checks
08:07 PM...10...01...30...ISS crew sleep begins
08:37 PM...10...02...00...STS crew sleep begins

NASA's Mission Management Team will meet later today to evaluate Dean's progress and make a decision on when to undock. If the decision is to press ahead for a Tuesday landing, undocking would be targeted for 7:57 a.m. Sunday, setting up a landing back at the Kennedy Space Center around 12:29 p.m. Tuesday.

But to land Tuesday, the Endeavour astronauts will have to finish equipment transfers today, during and immediately after the spacewalk, and close hatches between the two spacecraft this evening. The crew then could undock Sunday and have the normal two days to carry out a final heat shield inspection, test the ship's re-entry systems and pack up for landing.

"After the crew went to sleep, we spent a lot of time replanning Saturday and Sunday's timelines," said overnight flight director Heather Rarick. "To land on Tuesday, that means we'd have to undock on Sunday, which means we'd have to close the hatch on Saturday night. So we developed a plan for that. Most of the morning stays the same for that timeline. We will go out and do the EVA, we are going to shorten it if we need to so that we can get the crew back inside and be able to transfer the spacesuits and tools back to the shuttle and then close the hatch in the evening."

Endeavour carried some 5,000 pounds of equipment and supplies for the station. Another 4,000 pounds of hardware and no-longer-needed equipment were to be brought back to Earth on the shuttle. Rarick said the crew was ahead of schedule on transfer activity and most of the resupply work will be finished before hatch closure.

"There are a couple of things that we need to do late, so we've been holding off on them intentionally," she said. "One of the items is a cycle ergometer (exercise bike), we've brought a new one onto space station to replace the current one. But before we can send the old one home, we need to install it and check it out. So we have that on the timeline early (today)."

During today's spacewalk, Anderson plans to retrieve two space exposure experiment packages that will be moved into the shuttle for return to Earth.

"Other items we need to pack late is we have some experiments in the space freezer on space station and we need to put those in cooler bags so they can be brought home and kept at the proper temperature and we want to do that as late as possible in the flight," Rarick said. "So we have that timelined for late in the afternoon, just before the hatch gets closed."

In the crew's daily execute package of notes and flight plan changes uplinked from mission control, NASA's Mission Management Team gave the crew a big-picture overview of hurricane preparations.

"Hurricane Dean Preparations: The MMT received a briefing on the latest Hurricane Dean National Hurricane Center forecast track from the Spaceflight Meteorology Group. The projected track places the eye of a Category 4 storm in the Gulf of Mexico on Wednesday, FD15. Uncertainties in the forecast may change this prediction by +/- 6 hours. A low pressure system is forecasted to track west across the Gulf of Mexico from Florida to Louisiana. This low pressure system may influence the hurricane to take a more northerly ground track. Additionally, a more northerly track could lead to additional strengthening since the storm could miss the Yucatan peninsula entirely.

"JSC Senior Management will be meeting daily to assess the hurricane and will be making decisions appropriately. If the track of the hurricane holds to the forecast, it is expected that JSC will be closed on Monday, FD13, allowing non-mission support personnel to care for their families. All disciplines reporting to the MMT are preparing a list of mandatory support personnel that could support the remainder of the mission from JSC. The flight control team is making preparations to staff accordingly to support mission operations through landing."

8:44 PM, 8/17/07, Update: Kelly supports fly-as-is decision; NASA managers study hurricane options (UPDATED at 8:07 p.m. with MMT decision to protect option of landing Tuesday; UPDATED at 8:46 p.m. with 'big picture' words to crew about possible Tuesday landing)

NASA's Mission Management Team, after resolving concerns about damage to the shuttle Endeavour's heat shield, shifted gears today and began discussing the possibility of bringing the astronauts back to Earth on Tuesday, a day early, because of concern Hurricane Dean could threaten a shutdown of mission control at the Johnson Space Center in Houston.

"The current forecast for the storm would have the eye of Dean in the center of the Gulf area sometime on Wednesday," said LeRoy Cain, co-chairman of NASA's Mission Management Team. "If you back up from there to look at evacuation plans, not only for Johnson Space Center but for surrounding areas here, our history from previous hurricanes and storms tells us we really have to start letting our personnel go and take care of themselves and their families in the Sunday kind of time frame, if not sooner.

"And so, we began to look at this and determined we would really like to protect an option to be able to end the mission on Tuesday," he said. "From an institutional standpoint, the center will have to make a decision sometime in the mid-Sunday to mid-Monday time frame as to whether or not to close the center, and if so, when will they close? For a storm that's headed for the Houston area, in all likelihood the center would look at closing sometime on the second half of Monday-to-certainly-by-Tuesday timeframe. ... So we factored all that in and determined we would really like to protect an option to land on Tuesday."

The Endeavour astronauts plan to carry out a fourth and final space station assembly spacewalk Saturday and finish up equipment and supply transfers to and from the lab complex Sunday. Hatches between Endeavour and the station are scheduled to be closed Sunday night to set the stage for undocking Monday. A now-routine post-Columbia final heat shield inspection will be carried out Monday afternoon and the crew will pack up and test the shuttle's re-entry systems Tuesday. Touchdown at the Kennedy Space Center is targeted for around 12:52 p.m. Wednesday.

But plans are being put in place to close hatches between Endeavour and the space station Saturday night to permit an undocking Sunday and landing Tuesday depending on Dean's eventual track. Astronaut Shane Kimbrough called the crew from mission control late Friday to explain the discussion.

"Endeavour and station on the big loop with big picture words," he radioed from Houston. "Due to Hurricane Dean and its potential impact to the Gulf Coast, we're working towards a plan that would land us a day early. The way we're going to get there is to give up some transfer activities tomorrow and possibly shorten EVA-4. That will allow us to close the hatches tomorrow night and then we'll undock on Sunday and land on Tuesday. We're working the timeline really hard down here as you might imagine, we'll have a detailed plan for you in the morning."

Mission control commentator Kyle Herring said no final decisions about landing Tuesday had been made, but there are "a number of items that protect for that option and those were relayed up to the crew, which basically focuses on the duration of the ... spacewalk tomorrow by Dave Williams and Clay Anderson."

The problem for NASA is the pace of Hurricane Dean, the time needed to complete normal mission work and when decisions would have to be made in advance of Dean's arrival in the Gulf of Mexico. The concern, in part, is the risk associated with controlling a flight from a backup mission control center in Florida with fewer engineers, and less computer processing power, to monitor the shuttle's myriad systems.

"There are two parts to the emergency mission control center activation," said shuttle flight director Matt Abbott. "One is you take a team of controllers and send them to KSC and have them set up and be there on standby and ready to take over if that becomes necessary. So that can be done as a precaution, just like we can do the same thing with the backup control center advisory team activities on the station side.

"But ... we have a lot more limited insight into the vehicle systems, or at least less people to monitor that insight into the vehicle systems. We do have the capability to keep things going and to get the vehicle on the ground safely, but again, when you look at the effort and the number of people we have involved in a mission and a landing here and then you skinny that down to a couple of dozen people, there is obviously an element of additional risk because you're not able to do all the things you used to be able to do here in Houston. So that's really it in a nutshell."

While controlling a shuttle from Kennedy is part of a long-established contingency plan, "the systems and facilities down there are set up to get vehicles launched and off the pad and the activities we do here (in Houston) are a little bit different," Abbott said. By moving landing up a day, NASA likely could ensure a normal JSC-controlled re-entry.

But to land Tuesday, if it came to that, the Endeavour astronauts would have to finish equipment transfers Saturday, during and immediately after the spacewalk, and close hatches between the two spacecraft Saturday night. The crew then could undock Sunday and have the normal two days to carry out a final heat shield inspection, test the ship's re-entry systems and pack up for landing.

Cain said senior managers planned to meet late Friday to prioritize the activities planned for Saturday's spacewalk. Because most of the work is made up of relatively low-priority "get-ahead" tasks that could be deferred with no major impact on station assembly, mission managers may opt to shorten the spacewalk to make it easier for the crew to complete the tasks required before the hatches would be closed.

At the same time, NASA managers are putting lists of key personnel together and determining what would be necessary to activate all three shuttle landing sites - the Kennedy Space Center, Edwards Air Force Base, Calif., and White Sands Space Harbor, N.M. - on Tuesday.

Space station controllers also are reviewing contingency plans for moving key flight personnel to a backup site in Texas. If Hurricane Dean shuts down the Johnson Space Center, the flight control team could route commands through Russian ground stations as required.

"It's really too early to say exactly how this is all going to play out," said Abbott. "We've got options that we're looking at, we're trying to lay all those out so we know exactly what our capabilities are and what we have available to us."

For the record, the shuttle has enough on-board supplies to remain in orbit until next Friday with two days beyond that held in reserve as always to handle major systems problems or bad weather.

Earlier today, the astronauts held their traditional in-flight news conference and shuttle commander Scott Kelly fielded a variety of questions about the health of the shuttle's heat shield and his comfort level with a management decision to forego a spacewalk repair job.

"We agree absolutely 100 percent with the decision to not repair the damage," Kelly said during an in-flight news conference. "There was a lot of engineering rigor put into making this decision, it took some time but that was because there was a lot of testing going on, arc jet testing in particular that took some time to get done. ... With the damage that we have, the maximum temperature (the shuttle's aluminum skin) will see is 340 degrees. The failing point of aluminum, I think, is somewhere over 1,000 degrees. So even though a repair could potentially provide a little bit more margin, there is certainly more risk in doing the repair than we're willing to take. We were certainly concerned that if we did the repair we could potentially cause more damage to the underside of the orbiter. Since a repair was not really warranted based on the data and the testing, the shuttle crew and the station crew, actually, agreed with the decision not to do the repair."

He said work to resolve the issue "was a very, very rigorous process" and "I for one am happy it took as long as it did."

"They delayed our fourth EVA a day to give themselves more time so they wouldn't be pressed by the schedule," he said. "If it had turned out the MMT decided we needed to do a repair, we could have done it tomorrow. ... So I think it was absolutely the right decision to forego the repair and I think they took the appropriate amount of time to come to that conclusion. I would have been a little bit more nervous if they had just looked at the data we provided in the focused inspection (last Sunday) and say you know, either we had to repair it or we didn't. This is a very complicated process and it takes time to complete. We are absolutely behind the MMT, we think they made absolutely the right decision."

Asked if he thought entry might be a bit more tense for the crew because of known damage to the heat shield, Kelly said "I personally do not. We've had shuttles land with worse damage than this. We gave this a very thorough look and I am very, very comfortable and there will be no extra concern in my mind due to this damage."

Added pilot Charles Hobaugh: "I totally agree with Scott. I don't think there's anything really to concern us. John Young (commander of the first shuttle mission) used to always sit in our Monday morning meetings and talk about all the tiles that fell off of STS-1 and how they made it back fine. So I don't think it's really an issue and I think it was a great decision."

10:24 AM, 8/17/07, Update: Crew prepares for Saturday spacewalk; continues supply transfer work

The Endeavour astronauts are working through a busy day in space today, trying to trace a subtle communications wiring problem, transferring supplies and equipment to and from the international space station and preparing for a fourth and final spacewalk Saturday. The astronauts plan to participate in a traditional in-flight news conference at 1:34 p.m. Today's mission status briefing is scheduled for 3 p.m.

Here is an updated timeline of today's activities, based on the crew's flight plan and revision N of the NASA television schedule (in EDT and mission elapsed time):

EDT........DD...HH...MM...EVENT

05:07 AM...08...10...30...STS/ISS crew wakeup
08:12 AM...08...13...35...EVA-4 tool preparation
08:27 AM...08...13...50...Logistics transfers resume
11:02 AM...08...16...25...DAIU communications troubleshooting
01:12 PM...08...18...35...Crew photo
01:34 PM...08...18...58...Joint crew news conference
02:12 PM...08...19...35...Joint crew meal
03:00 PM...08...20...24...Mission status briefing on NASA TV
03:12 PM...08...20...35...Logistics transfers resume
03:12 PM...08...20...35...Spacehab debris shields checked
03:32 PM...08...20...55...DAIU wrapup
04:07 PM...08...21...30...Spacesuit swap
04:37 PM...08...22...00...Equipment airlock prepared
05:22 PM...08...22...45...Logistics transfer tagup
05:37 PM...08...23...00...EVA-4: Procedures review
07:32 PM...09...00...55...EVA-4: Nitrogen purge mask pre-breathe and tool config
08:17 PM...09...01...40...EVA-4: 10.2 psi airlock depressurization
08:37 PM...09...02...00...ISS crew sleep begins
09:07 PM...09...02...30...STS crew sleep begins

Saturday's spacewalk by Canadian astronaut Dave Williams and station crew member Clay Anderson is devoted to a variety of get-ahead tasks that will help pave the way for future space station assembly missions. The excursion originally was planned for today, but it was delayed 24 hours to give flight controllers time to assess whether a heat shield repair job was needed to fill in two damaged tiles on the belly of the shuttle.

Late Thursday, mission managers decided test data and analysis proved Endeavour could safely return to Earth as is. A tile repair spacewalk was ruled out and the astronauts were told to press ahead with the station assembly EVA instead.

The damage assessment brought back memories of an internal debate after the shuttle Columbia's launching in 2003. In that case, a relatively limited study was carried out to determine the possible damage caused by a large piece of foam debris that hit the underside of the shuttle's left wing during launch. NASA's Mission Management Team accepted a hurried analysis by a small group of engineers and concluded Columbia could safely re-enter as is even though the actual impact site could not be seen in launch imagery.

The analysis was deeply flawed. Equally troubling in hindsight, the Mission Management Team did not hear, or take seriously, concerns from lower-level engineers who were not satisfied with the review. As it turned out, what NASA managers believed was relatively minor damage to heat-shield tiles was, in fact, a 4- to 6-inch hole in the leading edge of Columbia's left wing. Sixteen minutes from touchdown, the left wing failed, the spacecraft broke apart and all seven crew members were killed.

Memories of Columbia still linger and the MMT decision not to mount a repair spacewalk to fix the damage to Endeavour's heat shield made some outside observers uncomfortable. But Shannon said he was "100 percent" confident the team made the right decision.

Unlike the Columbia case, NASA now has the ability to photograph virtually every square inch of the shuttle's heat shield, high-resolution cameras to zoom in on damage sites and an on-board laser scanner to measure its extent in three dimensions. Sophisticated computer modeling software has been developed to help engineers accurately predict the effects of re-entry heating. And NASA has tried to set up a management system that encourages debate, peer review and minority reports.

All of those systems were in play during the analysis of Endeavour's heat shield, Shannon said. Mockups of the damage site were subjected to re-entry heating in a high-tech furnace at the Johnson Space Center. Computational fluid dynamics was brought to bear to model heating and its effects under a variety of conditions and that work was peer reviewed to ensure accuracy. When all was said and done, engineers unanimously concluded the damage did not pose any sort of catastrophic threat to the crew and all but one engineering organization voted to clear Endeavour for entry as is. The lone dissenting vote was cast by an engineering group at the Johnson Space Center that believed a repair might add a bit of additional margin.

"If we had a condition that I thought was a threat to crew safety I would go execute this EVA and feel pretty good about it," Shannon said. "Since that is not the case, since we had independent analyses to show this is not expected to be even a turn-around issue to the vehicle, there's no way I could justify sending the crew out on that EVA just because, just to go do something. And so it became, I think, a very simple decision once we got that analysis done."

The rigor of that analysis and the widespread multi-center approach to studying - and verifying - results, Shannon said, reflects a "night and day" difference between the way NASA approaches in-flight problems today versus four years ago. That doesn't mean mistakes can't be made. But Shannon clearly believes NASA has the safeguards in place to minimize the likelihood of a fatal error.

"Because we have expended the resources and spent the time to develop the tools, not just the hardware tools but the analytical tools, to be able to understand exactly what the condition of the thermal protection system is," he said. "You saw on this flight several things, one is all of the new capabilities that we have added since Columbia, from the ground cameras to the in-flight cameras to the in-flight radar system that's looking specifically for debris, we used every one of those. From the rendezvous pitch maneuver we do close to the station, we got that data. We did the leading edge scans with the (heat shield inspection) boom. And then we had the discussions on the analytical tool capability, our ability to analyze this high energy environment. And we have repair capabilities.

"The more important thing to me is the seriousness and thoroughness with which the entire community analyzed this particular case," Shannon said. "This is not different from the (displaced) OMS pod (insulation) blanket we had on the last flight. We do not clear anything until we have the data to clear it and we take things extremely seriously and we bring to bear the resources of the entire agency, even expertise outside of the agency when we can bring it in. We had computational fluid dynamics at Ames (Research Center). It was backed up at Langley Research Center. We have had expertise at Johnson, at Kennedy at Marshall (space centers), at all the NASA centers.

"It's a little bit of a double edged sword, right? Because I would have liked to come in early on and say guys, let's not blow this out of proportion, it doesn't look like a loss-of-crew-and-vehicle kind of case, let's not get too excited about this. But we really can't do that because we didn't know at that point.

"You have to go do the analysis to know," he said. "And I think that is the key, as I am 100 percent comfortable that the work that has been done has accurately characterized it and we will have a very successful re-entry. I am also 100 percent confident that if we had gotten a different answer and found out that this was something that was going to endanger the lives of the crew that we have the capability on board to go and repair it and then have a successful entry. So we're setting ourselves up really well both ways."

11:21 PM, 8/16/07, Update: Shannon says tests show Endeavour can safely land as is; repair spacewalk ruled out; decision virtually unanimous; dissent centered on possibility of post-landing repairs, not crew safety

NASA's Mission Management Team today ruled out an unprecedented heat shield repair spacewalk and cleared the shuttle Endeavour for re-entry and landing next week "as is" based on computer modeling and tests in a high-temperature furnace that show a small gouge in the ship's belly will not cause serious damage during the fiery plunge to Earth.

Assuming concern about a small tear in a spacesuit glove can be resolved, the MMT cleared the astronauts to press ahead instead with a fourth and final space station assembly spacewalk Saturday that will focus on a variety of relatively low-priority "get ahead" tasks to help pave the way for upcoming missions. If all goes well, Endeavour will undock from the station Monday and glide to a landing at the Kennedy Space Center in Florida around 12:52 p.m. Wednesday to close out an extended two-week mission.

"The MMT made two significant decisions tonight," Shannon said. "The first was a unanimous recommendation that the damage we saw after reviewing all the engineering tests and analysis was not a threat to crew safety, this was not something that the astronauts are in danger about. We had thought that for several days, but we were waiting for the final analysis to be complete.

"We did all the things that we said we were going to do over the last few days. We had engineering analyses, we had computational fluid dynamics of the cavity from both Ames Research Center and the Langley Research Center, they were both in agreement. We did the thermal analysis and that continued to show good margins and we also did two arc jet tests where we put a re-entry heating profile on the damage sites.

"We went through all of that data and it was unanimous that we were not in a loss of crew/vehicle case," Shannon said. "The discussion then centered on whether we should use as is and return Endeavour in its current condition or if the uncertainties in the analysis could potentially cause some underlying tile damage or structural damage that we would have to deal with at the Kennedy Space Center. So we had that debate. And it was not unanimous, but it was pretty overwhelming to go with the use-as-is condition, in other words not to do the tile repair."

Commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, flight engineer Rick Mastracchio, Canadian flier Dafydd Williams, Al Drew and educator-astronaut Barbara Morgan were informed of the decision at 9 p.m. as they were preparing for sleep.

"Just wanted to pass along the MMT just broke out of their meeting," astronaut Shane Kimbrough radioed from mission control. "The MMT has made a decision to fly the TPS (thermal protection system) as is, no EVA repairs will be required. MMT is still looking at the cut glove issue and any future EVAs on the flight will be per the nominal content. So just wanted to wish you a good night, another great day in space and looking forward to tomorrow."

"Please pass along our thanks for all the hard work," Kelly replied.

Two heat-shield tiles on the shuttle's belly were damaged when a chunk of foam debris, possibly including ice, slammed into the orbiter 58 seconds after launch last Wednesday. The impact gouged out an irregular pit crossing the boundary between two tiles, measuring roughly two inches by three inches across and nearly penetrating the full 1.12-inch thickness of the tile. A small, 1-inch by 0.2-inch gash at the bottom of the pit exposed an underlying support pad just above the shuttle's aluminum skin.

The shuttle Columbia was destroyed Feb. 1, 2003, when it re-entered the atmosphere with a gaping 4- to 6-inch hole in the leading edge of its left wing. The wing melted from the inside out, the shuttle broke apart above Texas and all seven crew members were killed. NASA managers have said all week that they do not view Endeavour's gouge as a Columbia-class problem. Shannon said the issue was simply whether re-entry heating might cause damage to the shuttle's aluminum skin in the immediate area that would require time-consuming post-landing repairs.

Playing it safe, Shannon earlier asked a team of astronauts, engineers, flight controllers and managers to study repair options to determine the best approach if the heat shield had to be fixed. To protect their options, a station assembly spacewalk planned for Friday - what was to have been the crew's fourth and final EVA - was delayed 24 hours to Saturday.

But Shannon said late Thursday that a final round of tests agreed with computational fluid dynamics modeling and an independent review of the work turned up no major surprises. The MMT then voted and cleared Endeavour's crew for a standard station assembly spacewalk Saturday and an "as is" landing next week.

But the vote was not unanimous. While representatives of more than 30 organizations voted to proceed with landing as is, Johnson Space Center engineering argued it would be "prudent" to carry out a repair even though the data indicated Endeavour could safely return in its damaged state.

"It was almost unanimous to use as is," Shannon said. "The one dissenting organization was the Johnson Space Center engineering group, who took a look at the potential benefits of doing a repair and said that they could not see a reason why that would cause additional damage to the orbiter and thought that that was something we should think about as a program."

But Shannon said sister organizations at the Marshall Space Flight Center and the Kennedy Space Center, along with the astronaut office at Johnson "all of the safety organizations I have on my panels, they were all in agreement that the use-as-is was the appropriate way to go."

"Some of the rationale that was summed up by the team members that I think was fairly consistent across the management team was that we have a cavity in the tile that has been analyzed through computational fluid dynamics, through thermal analysis, through two different arc jet tests and we understand that cavity, it does not constitute a risk to the crew, it is not expected to cause any damage to the vehicle structure itself and it is fairly well understood.

"On the other hand, we could potentially do this spacewalk and add some (STA-54 repair) material to the bottom of this cavity ... then we would have a new cavity that we had not analyzed. That was a fairly simple decision, is you have something you know you can live with, why would you take the risk of doing the EVA to change that cavity into what could potentially be an even better situation but also could potentially be a worse situation?"

The MMT decision ended a week of high drama on the high frontier, with engineers working around the clock to assess the threat posed by the dinged tiles and, in parallel, develop repair plans in case they were needed. The astronauts received frequent updates as they pressed through a busy timeline that included three spacewalks to attach a solar array truss segment; replace a stabilizing gyroscope; and prepare a solar array for relocation later this year.

During the third spacewalk Wednesday, Mastracchio noticed a small tear in the Vectran material used in his left glove and flight controllers ordered him back to the space station's airlock as a precaution. This was the second spacewalk in three shuttle missions that has resulted in glove damage and engineers suspect something on the station has an unexpected sharp edge.

Before Saturday's spacewalk can proceed, spacewalk experts at the Johnson Space Center hope to confirm the problem with Mastracchio's glove was not part of a more generic problem that could affect Williams or Anderson. They also are reviewing helmet cam video from Mastracchio in a bid to identify what might have caused the damage.

Here is a revised timeline for Saturday's spacewalk (in EDT and elapsed time):

EDT........HH...MM...EVENT

10:06 AM...00...00...Airlock egress
10:26 AM...00...20...Orbiter boom sensor system (OBSS) boom stand installation
11:26 AM...01...20...Williams: Z1 S-band antenna sub-assembly gimbal locks
11:26 AM...01...20...Anderson: MISSE space exposure experiment package retrieval
12:11 PM...02...05...Wireless instrumentation antenna installation
01:51 PM...03...45...Destiny module debris shield cleanup
02:06 PM...04...00...Unity module debris shield cleanup
03:21 PM...05...15...Other get ahead tasks
03:51 PM...05...45...Cleanup
04:21 PM...06...15...Airlock ingress
04:36 PM...06...30...Airlock repressurization

On Wednesday, Shannon made it clear he viewed a heat shield repair spacewalk as risky and said that such a repair could only be justified if it was necessary to prevent serious damage during re-entry.

The repair plan called for a 50-foot-long extension called the orbiter boom sensor system, or OBSS, to be attached to the end of the shuttle's 50-foot-long robot arm. Mastracchio planned to ride on the end of the boom, his feet anchored in a work platform, while Williams provided assistance as a free floater, tethered to the boom.

Working from Endeavour's aft flight deck, Caldwell was to have moved the astronauts down under the shuttle and back to the damage site, located a few feet aft of the right main landing gear door. The repair planned called for Mastracchio first to dab a black paint-like material known as emittance wash into the gouge, using a simple device that works like a liquid shoe polish applicator.

After the walls of the gouge were coated with emittance wash, he was to use a different type applicator, one that works like a grease gun, to squeeze out and mix a thick, putty like material known as STA-54. Like epoxy, STA-54 mixes as it exits the applicator and it can be difficult to work with. But Mastracchio helped develop some of the necessary procedures and engineers were confident he could successfully fill in a portion of the gouge.

But on Wednesday, Shannon pointed out three areas of concern about the repair spacewalk, saying "none of these are real show stoppers but you kind of have to add them up in your mind."

First, he said, working under the shuttle on the end of a 100-foot boom with poor television coverage in proximity with a critical system has never been attempted before. "That was not a show stopper, but it was something to think about," he said.

Second, astronauts have never applied STA-54 in the vacuum of space and third, no one knows if the applicator will work properly or if the spacewalkers might have problems getting the thick material into the gash. "It takes a little bit of practice to get it in exactly the right spot."

Late Thursday, Shannon said he would not hesitate to order a spacewalk repair if the data showed repairs were needed to ensure a safe landing. In this case, he said, they simply didn't.

"We believe we're going to have to go replace a couple of tiles that got damaged," he said. "And that is within the normal turnaround flow of a vehicle."

Asked if there was zero chance of a catastrophic loss of vehicle and crew due to the heat shield gouge, Shannon said simply: "Yes."

9:00 PM, 8/16/07, Update: ADVISORY - Mission Management Team adjourns; tile repair spacewalk ruled out; Endeavour cleared for entry 'as is'

After a five-hour meeting to assess the health of the shuttle Endeavour's heat shield, NASA's Mission Management Team has ruled out a heat shield repair spacewalk Saturday and cleared the crew for re-entry as is. The astronauts now will focus on a final space station assembly spacewalk Saturday to complete the major goals of their mission. MMT Chairman John Shannon is scheduled to brief reporters at 9:30 p.m. This status report will be updated as soon as possible thereafter.

12:31 PM, 8/16/07, Update: ADVISORY - MMT meeting pushed back to 4 p.m.; tile repair decision expected late today

NASA's Mission Management Team will meet at 4 p.m. EDT today, two hours later than originally planned, to give engineers more time to complete a complex analysis of what impact, if any, a gouge in the shuttle Endeavour's heat shield might have during re-entry. As a result, a decision on whether to order a repair spacewalk Saturday - or a normal space station assembly EVA - is not expected until late in the day.

"We're expecting a fairly long afternoon's worth of meetings and our mission status briefing that is currently scheduled at (6 p.m. EDT) could easily be pushed back into the early evening hours," said mission control commentator Rob Navias.

Updates will be posted here as warranted.

11:10 AM, 8/16/07, Update: Morgan talks with students, reporters; says she's not worried about heat shield gouge

The Endeavour astronauts are content to follow the guidance of mission control when it comes to a divot in the shuttle's heat shield. Teacher-turned-astronaut Barbara Morgan said today "we have a lot of faith in the program and we'll do what the engineers decide is the best thing for us to do. We have all confidence we're going to be able to do the right thing."

Joining Morgan for round-robin media interviews, Al Drew told Reuters he viewed the now-famous gouge as "more of a divot on the belly of the ship rather than a hole" and said if the decision is made to bring Endeavour down as is, he's confident the orbiter will make a safe re-entry.

"We've been talking to the engineers who have been analyzing this far more than we have in space and they seem to feel that the biggest danger is more to just being able to reuse Endeavour once it's back on the ground," he said. "They seem to be confident, and I trust their confidence, that we can get home safely even with the divot that we have in the belly."

NASA's Mission Management Team is expected to make a decision this afternoon on whether to order a repair spacewalk Saturday or whether to bring Endeavour down as is. This status report will be updated as soon as the decision is announced.

Despite the heat shield problem, the memory of the 1986 Challenger disaster and the 2003 loss of the shuttle Columbia, Morgan said she would give NASA's manned orbiter an A plus.

"This work is incredibly challenging," she said, floating with Drew in the international space station's Destiny laboratory module. Given the sheer complexity of the project, "I think the shuttle program is an A plus. You know, once we don't have the shuttle any more I think it's going to be something that we all look back on with great nostalgia and we're really, really going to miss it. ISS (international space station) is a fantastic vehicle, it's a stepping stone to the future and I quite frankly can't wait until we get back to the moon for the long haul and then onto Mars."

Earlier today, Morgan and Drew fielded questions from students at a Challenger Center for Space Science Education in Alexandria, Va., the second of three educational events planned for Endeavour's mission. Today's session held special significance for Morgan because the event was hosted by June Scobee Rodgers, founding chairman of the Challenger centers and widow of Challenger commander Dick Scobee. Morgan was Christa McAuliffe's backup in the original Teacher in Space program and trained with the Challenger astronauts.

"Congratulations to the entire Endeavour crew," Rodgers radioed. "Thank you for the downlink to the Challenger Center. Barb, we've been standing by, waiting for your signal from space for 21 years!"

Morgan said later that "hearing June's voice anytime is a real pleasure. It made me so happy to know the Challenger Center was there, that we had a chance to speak with the kids this morning, that June was there leading the charge as always. It's in our hearts and it's wonderful."

Morgan and Drew demonstrated how astronauts live in weightlessness, showing how soap and shampoo are used, displaying an astronaut sleeping bag and inadvertently releasing a large blob of water in the Destiny laboratory module. Veteran space aficionados cringed, but the release had no apparent impact.

In one of the more interesting exchanges, a student asked if the astronauts could see constellations in space from their lofty perch above Earth's atmosphere.

"You know, initially when we first came up here, both the space shuttle and the space station were both very lit up, almost like a small city, and it made it tough to see anything," Drew said. "Actually, I had an easier time seeing stars in Houston. Last night, we turned out all the lights on both the shuttle and the station, looked out the window and it as a glorious sight out there. You could see the entire Milky Way, you could see the dust clouds of the Milky Way, I think Barb even saw a shooting star beneath us last night. We saw thunder storms over the world, it was pretty fabulous, you could make out all the constellations in the sky."

"It was interesting," Morgan said, "it started out in the orbit we were in, we were at night time and we were looking out at the night sky and all the things Al just described we could see. We were traveling over Africa at the time, but looking out at the night sky. And then as we got to the Indian Ocean, it was black, black, black and that's where we saw all the thunderstorms. And I don't think any of us had ever seen anything quite that bright, those flashes of light.

"And then off in the distance, in another, say, 20 minutes or so, a thin blue line started appearing. And that blue line got thicker and thicker, it started to get a little blurred and all these different colors of blue were in that line and we realized we were looking at the horizon with the sunrise coming and we could see layers of cloud in that horizon. Within just a few minutes, our faces were totally lit up and the space station was shimmering, the solar arrays were just like the orange filaments in your toaster, they were just shimmering, bright, bright, bright gold. It was a beautiful sight."

Later, Drew, a veteran military helicopter pilot making his first space flight, described what it's like to blast off aboard a shuttle for Idaho Public Television:

"There was no doubt when the solid rocket boosters lit, it was just like being inside of a washing machine that was in a bad spin cycle. There was a pretty good shake going up the whole way, just a tremendous amount of sheer fun. We knew we were heading off the planet! There was a big thump when the solid rocket boosters left the orbiter and then it was a much smoother ride from there on up but the Gs started picking up. It felt like there was something heavy standing on my chest. ... It took effort to breathe the whole time. In fact, I kind of felt myself wheezing for the last few minutes as we were going through three Gs. And then suddenly we went from 3 Gs to nothing, I felt my body just slam against the shoulder straps of the seat, it was almost like we recoiled off the back of the seat and we were weightless. I want to find another quarter to put back in there and go for another ride!"

7:50 AM, 8/16/07, Update: Astronauts await tile repair decision; controllers expect word by early afternoon

The Endeavour astronauts are awake and working through a revised flight plan today, awaiting word from NASA's Mission Management Team on whether the space shuttle's gouged heat shield can stand up to the rigors of re-entry as is or whether an unprecedented tile repair spacewalk will be needed Saturday. During a morning "big picture" update for commander Scott Kelly, astronaut Chris Ferguson in mission control said a decision was expected by noon or shortly thereafter.

"Understand the decision might be made today at noon and we won't actually pull any of the (tile repair) hardware out until then. Is that still something the guys are anticipating?" Kelly asked.

"Yeah, Scott, we have every reason to believe that a decision is going to be made by noon and that's why the flight plan for today was put together the way that it was," Ferguson replied. "The idea is to not have you drag anything out unless you need to have it out so you don't have to put it away. But you know, I mean the MMT working the way that sometimes these things work, it may get delayed. And if it does, we're going to have to stick to the flight plan and pull some of the equipment out. But, hopefully, by lunch we will have some words for you."

"OK. If that was to happen and they were to call the repair off, we were discussing the possibility of doing EVA-4 tomorrow," Scott said, referring to the crew's originally planned fourth and final station assembly spacewalk. "Is that something you guys are looking at?"

"Yeah Scott, I think we're going to kind of stick to the plan we have right now and that is, still plan for the EVA on flight day 11 (Saturday)," Ferguson said. "What that would mean, however, if they do call it off we'd make the latter part of the day after lunch off-duty for everyone."

The astronauts were awakened, appropriately enough, with a recording of "Times Like These" by the Foo Fighters. Flight controllers are preparing revised timelines to cover both possibilities for Saturday's spacewalk - tile repair activity by Rick Mastracchio and Dave Williams or the normal space station EVA by Williams and astronaut Clay Anderson.

Either way, the astronauts were asked today to expedite close-up photos of the spacesuit gloves used in a station assembly EVA Wednesday. Mastracchio had to end his participation in the excursion early when he noted a small tear in the Vectran outer layer of the material on his left thumb. The additional photos are required before Saturday's spacewalk, whatever its content might be, to confirm some sort of generic defect is not present.

At 8:06 a.m. today, teacher-turned-astronaut Barbara Morgan and Al Drew will participate in the second educational event of Endeavour's mission, chatting with students and officials at the Challenger Center in Alexandria, Va. The Challenger Centers for Space Science Education were created in the wake of the 1986 shuttle disaster by the crew's families. The founding chairman is June Scobee Rogers, widow of Challenger commander Dick Scobee, who will host today's event.

Along with the educational event, Morgan and other crew members also will participate in round-robin media interviews starting at 10:16 a.m.

If a heat shield repair spacewalk is ordered, Mastracchio and Williams will begin breaking out the required tools and equipment this afternoon. If the repair is deemed unnecessary, the astronauts will take a few additional hours off to relax.

In a morning message uplinked to the crew, flight controllers said "the short story on damage assessment is that the Arc Jet tests are thus-far supporting the CFD analysis and indicate that a repair may not be necessary. An additional arc jet test was conducted last night and these results along with the peer review of the CFD analysis and QA of the model will be the final determining factor.

"We have tried to leave as much flexibility in today�s Flight Plan as possible by deferring the actual retrieval of the repair tools until after lunch. The idea, of course, is to avoid gathering items we will only have to re-stow if the repair is not required. We�re hoping for a lunch-time decision, but in the event it is delayed we will have to begin opening bags."

An updated flight plan will be posted here after mission managers decide on a course of action. In the meantime, here is the flight plan for today as it now stands (in EDT and mission elapsed time; NOTE: NASA rounds all times down to the nearest minute. This page rounds up or down as required):

EDT........DD...HH...MM...EVENT

05:37 AM...07...11...00...STS/ISS crew wakeup
08:06 AM...07...13...30...Educational event with Barbara Morgan
08:17 AM...07...13...40...EVA-4 training and review
10:16 AM...07...15...40...News media interviews with Morgan
10:37 AM...07...16...00...Logistics transfer operations
11:17 AM...07...16...40...EVA-4 tagup with mission control
12:02 PM...07...17...25...Crew meals
01:02 PM...07...18...25...Crew off-duty time
03:37 PM...07...21...00...EVA tools gathered and unpacked
05:37 PM...07...23...00...STA-54 and emittance wash preparation for EVA-4
05:52 PM...07...23...15...Logistics transfer tagup
08:37 PM...08...02...00...ISS crew sleep begins
09:07 PM...08...02...30...STS crew sleep begins

At the Johnson Space Center, engineers are wrapping up analyses of the heat shield gouge and comparing sophisticated computer modeling results with final test runs in a high-temperature furnace to make sure the computer predictions match up with the actual re-entry environment.

Computational fluid dynamics calculations indicate the aluminum skin below the gouge in two tiles on the belly of the shuttle will not exceed NASA's conservative 350-degree design limit. The computer calculations indicated the skin temperature would only rise some 40 degrees above normal and stay below the limit. A mockup of the damage using tiles deliberately carved out to mimic the damage on Endeavour were put in the arc jet facility and subjected to the sort of 2,200-degree wind the shuttle will experience during peak heating. Again, the temperature of the aluminum skin under the tiles did not climb above 350 degrees.

The final tests carried out overnight involved a tile mockup with more idealized damage, a carved pit with the sort of straight lines and angles used in the computational fluid dynamics model. The idea is to make sure the computer models are accurate and do not include any incorrect assumptions. As an additional safety check, the analyses is being independently peer reviewed.

"The primary point of debate (Wednesday) was did we need to run the simplified model in the arc jet facility?" said John Shannon, chairman of the Mission Management Team. "Because a lot of folks thought that we had two fairly independent analyses, one was the thermal analysis done on computer, one is the arc jet that said you don't have a problem here. But just to tie the two together and make sure we didn't make some significant error in either of those, we're going to run this simplified model in the arc jet. That was the primary point of discussion. People thought we had enough data, some people wanted to go get some more data. So we're going to go get some more data."

Two heat-shield tiles on the shuttle's belly were damaged when a chunk of foam debris, possibly including ice, slammed into the orbiter 58 seconds after launch last Wednesday. The impact gouged out an irregular pit in the tile measuring roughly two inches by three inches across and nearly penetrating the full 1.12-inch thickness of the tile. A small, 1-inch by 0.2-inch gash at the bottom of the pit exposes an underlying support pad just above the shuttle's aluminum skin.

The shuttle Columbia was destroyed in 2003 when it re-entered the atmosphere with a gaping 4- to 6-inch hole in the leading edge of its left wing. NASA managers, and even commander Scott Kelly, say they do not view Endeavour's gouge as a Columbia-class problem. Shannon said the issue is whether re-entry heating might cause damage to the shuttle's aluminum skin in the immediate area that would require time-consuming post-landing repairs.

But Shannon made it clear he viewed the risk of a spacewalk repair as significant and that such a repair could only be justified if it was necessary to prevent serious damage during re-entry. And based on the testing and analysis through Wednesday, that did not appear to be the case. But, as Shannon cautioned, the analyses is not complete and any major surprise or disagreement between the computer models and the arc jet facility could change that assessment.

11:00 PM, 8/15/07, Update: Spacewalk No. 4 moved from Friday to Saturday; no decision yet on tile repair (UPDATED at 10:30 p.m. with mission status briefing; Shannon leaning toward 'fly as is,' but awaits final test data before making decision on heat shield repair

As expected, the Endeavour astronauts will delay their fourth spacewalk, from Friday to Saturday, to protect against the possibility of an unprecedented heat shield repair. Mission Management Team Chairman John Shannon said late today a decision one way or the other will be made Thursday, after a final round of tests in a high-temperature furnace to verify computer models accurately reflect the re-entry environment Endeavour will face when it returns to Earth. Barring an unexpected surprise, Shannon said he remains "cautiously optimistic" a repair spacewalk will not be needed. And he made it clear the risks associated with a repair spacewalk are high enough to rule out attempting a fix if it is not absolutely necessary. "We're pondering for 24 hours, but my personal feeling was that the data at the 80 to 90 percent level was that we could (return to Earth) as is and that the EVA carries sufficient risk to it that we would not just go do it (to add) additional margin," he said.

Two heat-shield tiles on the shuttle's belly were damaged when a chunk of foam debris, possibly including ice, slammed into the orbiter 58 seconds after launch last Wednesday. The impact gouged out an irregular pit in the tile measuring roughly two inches by three inches across and nearly penetrating the full 1.12-inch thickness of the tile. A small, 1-inch by 0.2-inch gash at the bottom of the pit exposes an underlying support pad just above the shuttle's aluminum skin.

The shuttle Columbia was destroyed in 2003 when it re-entered the atmosphere with a gaping 4- to 6-inch hole in the leading edge of its left wing. NASA managers, and even commander Scott Kelly, say they do not view Endeavour's gouge as a Columbia-class problem. Shannon says the issue is whether re-entry heating might cause damage to the shuttle's aluminum skin in the immediate area that would require time-consuming post-landing repairs.

Complex computational fluid dynamics modeling indicates the skin under the gouge would only get about 40 degrees hotter than normal during an "as is" re-entry and never exceed a 350-degree safety threshold. Overnight, engineers subjected a precise model of the damage, using tiles similar to, and gouged out, like those on Endeavour, to re-entry temperatures and flow fields in an arc jet facility at the Johnson Space Center in Houston.

The hellish wind in the furnace caused the aft face of the gouge to lengthen, creating a sort of groove in the tile behind the original pit. But Shannon said the groove did not bore into the denser lower layers of the tile and "we did not violate any temperature constraints on the underside of that aluminum sheet."

As a final test, engineers will roast another set of tile samples to the arc jet facility overnight. These tiles feature more idealized damage with straight lines and precise angles in a bid to duplicate the results from the computational fluid dynamics models. If the more idealized test matches up with the computer models, engineers will have high confidence the predictions of a safe "as is" re-entry are valid.

"The primary point of debate (today) was did we need to run the simplified model in the arc jet facility?" Shannon said. "Because a lot of folks thought that we had two fairly independent analyses, one was the thermal analysis done on computer, one is the arc jet that said you don't have a problem here. But just to tie the two together and make sure we didn't make some significant error in either of those, we're going to run this simplified model in the arc jet. That was the primary point of discussion. People thought we had enough data, some people wanted to go get some more data. So we're going to go get some more data."

But Shannon made it clear he views the risk of a spacewalk repair as significant and that such a repair could only be justified if it was necessary to prevent serious damage during re-entry. And based on the testing to date, that does not appear to be the case.

"The way I would summarize it is, if we were in a critical situation I think we could pull it off, I think we would have the rationale to put all those different things together and come off with a very successful EVA," he said. "But you have to recognize there is some additional risk in doing that task.

"The other side of the equation is on the thermal assessment side. We have almost finished the thermal analysis. I told you yesterday, if you remember, we did computational fluid dynamics to understand the flow within that cavity. That was done out at Ames Research Center and Langley Research Center is backing us up and doing an independent review of that computational fluid dynamics. And that work is still ongoing, it was not completed yet, we expect to have that tomorrow morning. And we're still performing a peer review where someone goes in who's totally independent, who checks all the math, who checks all the physics to make sure we did everything exactly right. That is 90 percent done, but it was not completely done.

"But the analysis that we have shows there would be no damage at all to the underlying structure, which was very good news to us, and we would not violate any of our certification temperature, we would not even reduce our 1.4 factor of safety. So that was all good news, but it was not a 100 percent story. It was more like an 85 percent story."

The risk associated with any spacewalk was made clear today when astronaut Rick Mastracchio had to cut short a space station assembly spacewalk after observing a small tear in the outer Vectran covering of his left spacesuit glove. A spare set of gloves is available if needed and uncertainty about what caused the tear would not stand in the way of a high-priority repair spacewalk.

If a heat shield repair is ordered, it will be carried out by Mastracchio and Canadian astronaut Dave Williams. Mastracchio, anchored to the end of a 50-foot-boom attached to the shuttle's own 50-foot-long robot arm, would be maneuvered to the damage site under the shuttle. Williams would be tethered to the boom to provide assistance as needed.

The repair plan would have Mastracchio dab on a black paint-like material known as emittance wash and then use a grease gun-like device to inject a thick heat-resistant material called STA-54 into the gouge.

Shannon pointed out three areas of concern about a repair spacewalk, saying "none of these are real show stoppers but you kind of have to add them up in your mind."

Second, astronauts have never used STA-54 in the vacuum of space and third, no one knows if the applicator would work properly or if the spacewalkers might have problems applying the thick putty like material. "It takes a little bit of practice to get it in exactly the right spot." Shannon said engineers today had a long discussion "about could we make the situation worse?"

"In my mind, I thought tomorrow would be a better day to make a decision," he said. "I think most of the data is in place for us to make a decision, but I wanted the team to go off and think about it overnight and at tomorrow's MMT we'll have all of the final assessment complete and the team will have thought about the different data for 24 hours and we'll discuss it some more and decide what the appropriate option is."

Late today, mission control told the astronauts a fourth spacewalk, originally planned for Friday, would be delayed to Saturday. That will give flight controllers time to refine their plans if the MMT does, in fact, decide a tile repair is needed. In that case, the repair work would be carried out Saturday and a fifth spacewalk could be added Monday to complete the delayed station work. That scenario likely would result in a two-day mission extension and a landing back at the Kennedy Space Center on Aug. 24.

If the tile repair is not needed, the astronauts would simply carry out the previously planned space station assembly spacewalk on Saturday and land as currently scheduled on Aug. 22. One wild card in the planning is the status of work to figure out what caused the tear in Mastracchio's glove today. While uncertainty likely would not prevent a repair spacewalk, it's not clear what sort of rationale might be needed to clear the way for a lower-priority station EVA.

"I'd like to give you some big picture words of what our plan forward is," astronaut Shannon Walker called from mission control to kick off a daily planning conference. "All the decisions have not been made yet, the MMT is actually still meeting as we speak, but one thing that has been decided is that EVA-4 will be on Saturday."

"Copy Shannon. And I hope everybody here is ready for this EVA, too, whatever it is," station commander Fyodor Yurchikhin replied.

"Yes, exactly. We do not know what the EVA will be," Walker said. "Obviously, it will either be TPS (thermal protection system) repair or the regular EVA-4. So what we have done is plan your day tomorrow as if it's going to be TPS repair, but stressing that no decision has been made either way."

"We copy," an astronaut said.

"OK, that being said, the plan is on board but don't go off and memorize it tonight because we're still working on it down here and it is not in synch with form 24 at all," Walker said. "But at the moment, you will see TPS-related activities on it."

Shuttle commander Scott Kelly then asked, "any word when the MMT's going to adjourn? Are they supposed to make a decision today on repair, or not repair?"

"Scott, we are hoping they are going to adjourn within the next hour or so, but actually we do not expect a decision today on whether or not we're going to repair or not repair," Walker replied.

"OK, thank you."

"At the moment, they don't have all the data they would like to make their decision," she continued.

"And no indication of which way they're leaning?" Kelly asked.

"Unfortunately, we have no idea which way the wind is blowing at the moment."

3:17 PM, 8/15/07, Update: Mastracchio cuts spacewalk short after noting glove damage; Anderson completes final tasks (UPDATED at 4:20 p.m. with official duration; hole in left glove sted right)

Making a routine inspection of his spacesuit gloves, a recently implemented safety procedure because of damage found after a December shuttle flight, astronaut Rick Mastracchio spotted a small hole in one of the outer layers of his left glove, prompting mission control to order him back to the space station's airlock as a precaution.

Mission control commentator Kyle Herring said Mastracchio was not in any danger and that his suit was not leaking. But the flight rules require a return to the airlock if any penetration is seen.

As it turned out, Mastracchio and fellow spacewalker Clay Anderson were in the final stages of a planned six-and-a-half-hour spacewalk, running well ahead of schedule. Despite the early termination of Mastracchio's excursion, the astronauts accomplished all of their major objectives and the only task left undone was the retrieval of two space exposure experiments. They will be collected during a future spacewalk.

The suit problem cropped up around 3 p.m. when Mastracchio was asked to check his gloves. The periodic checks are a now standard part of every NASA spacewalk after damage was seen during a December shuttle mission.

"Before we get too far, let's get a glove check on you," spacewalk coordinator Tracy Caldwell radioed from Endeavour's flight deck.

"OK. My left glove looks clean and unchanged in terms of RTV damage," Mastracchio said, referring to the outermost layer of the glove. "A lot of the (garble) I picked up is kind of gone. The right glove... ah, there might be a little more RTV missing between the thumb and forefinger but the Vectran looks... a little bit of RTV, just a small dot of RTV missing on the middle finger. A very small piece."

"OK, TC, I'm at the transponder, I'm just trying to figure out how I'm going to attack this," Anderson chimed in, pressing ahead with his own work.

"You take your time, Clay," Caldwell replied. "There might been a little bit of RTV damage on my right thumb," Mastracchio continued. "Just kind of looks like a, I don't know, like a scratch, a couple of missing threads maybe, I don't know."

A few moments later, looking at his left glove again, Mastracchio reported "I do have a little bit of a hole in the Vectran."

Vectran is a widely used, manufactured fiber noted for its strength, flexibility and tolerance to extreme temperatures. Vectran is the second of five layers of material making up an astronaut's spacesuit glove.

Examining his glove, Mastracchio said "I can actually see shiny metal fibers underneath it, I see the surface under the Vectran, in other words."

A few moments later, after examining the glove via television, astronaut Shannon Walker in mission control told Mastracchio to head back to the Quest airlock module.

"Tracy, we need Clay to stand by," Walker said. "And because we do have a hole in the Vectran, we're going to have to terminate Rick's activity today. So we need him to head back to the airlock and do the terminate procedure in the checklist."

"OK," Mastracchio replied, sounding disappointed. Later, back in the airlock, Caldwell asked how he was doing.

"I'm fine," Mastracchio replied. "Looking out the hatch. Wishing I was out there."

Anderson, meanwhile, completed the transponder retrieval and then joined Mastracchio in the Quest module.

The spacewalk, the third of four planned for Endeavour's mission, began at 10:37 a.m. Riding on the station's robot arm, Mastracchio removed an S-band antenna assembly from the P6 solar array truss atop the central Unity module and moved it down to its permanent location on the P1 segment of the lab's main solar array truss. Anderson installed a new transponder and signal processor as part of an S-band communications system upgrade.

Flight controllers at the Johnson Space Center in Houston then verified the electrical connections and activated heaters, saying the equipment appeared to be operating normally.

The astronauts then moved two equipment carts from the port, or left, side of the robot arm's mobile transporter, to the right side. The transporter and the so-called CETA carts move like a train along tracks on the front face of the solar array truss. The carts had to be moved to the right side of the transporter to permit the robot arm to reach the left-most worksite in October when a visiting shuttle crew plans to move the stowed P6 solar array segment to the left end of the power truss.

Mastracchio and Anderson were wrapping up that work when the glove problem was reported. After joining Mastracchio in the airlock, Anderson shut the hatch and commander Scott Kelly began airlock re-pressurization at 4:05 p.m. for an official duration of five hours and 28 minutes.

This was the 91st spacewalk devoted to station assembly and maintenance since construction began in 1998, the 14th so far this year, the third for Mastracchio and the second for Anderson. Seventy two men and women representing the United States, Russia, Canada, Japan, Germany, France and Sweden have now logged 562 hours and 57 minutes building and maintaining the international lab complex. The Endeavour crew's total through three spacewalk is 18 hours and 13 minutes.

12:30 PM, 8/15/07, Update: Communications upgrade done ahead of schedule

Running an hour ahead of schedule, astronauts Clay Anderson and Rick Mastracchio are wrapping up work to upgrade the space station's S-band communications system. Mastracchio, riding on the station's robot arm, removed an S-band antenna assembly from the P6 solar array truss and moved it down to its permanent location on the P1 truss segment. Anderson, meanwhile, installed a new transponder and signal processor as part of an S-band communications system upgrade.

Flight controllers at the Johnson Space Center in Houston then verified the electrical connections and activated heaters, saying the equipment appeared to be operating normally.

Anderson now is working to prepare two equipment carts for relocation from the port, or left, side of the robot arm's mobile transporter, to the right side. The transporter and the so-called CETA carts move like a train along tracks on the front face of the solar array truss. The carts must be moved to the right side of the transporter to permit the robot arm to reach the left-most worksite in October when a visiting shuttle crew plans to move the stowed P6 solar array segment to the left end of the power truss.

After the CETA cart relocation is complete, the spacewalkers will retrieve two space exposure experiment packages and a transponder on P6. All three items will be returned to Earth.

10:47 AM, 8/15/07, Update: Spacewalk No. 3 begins

Astronauts Rick Mastracchio and Clay Anderson switched their spacesuits to internal battery power at 10:37 a.m. to officially begin a planned six-and-a-half-hour spacewalk to upgrade the international space station's communications system and make final preparations for the relocation of a solar array truss in October. The spacewalk began about a half hour ahead of schedule.

9:00 AM, 8/15/07, Update: Astronauts gear up for third spacewalk

Shuttle flier Rick Mastracchio and station astronaut Clay Anderson are gearing up for a planned six-and-a-half-hour spacewalk today to upgrade the international space station's S-band communications system and make final preparations for the relocation of a stowed solar array during the next shuttle assembly mission in October.

At the Johnson Space Center in Houston, meanwhile, engineers are continuing tests to determine whether a small gouge in Endeavour's heat shield needs to be repaired before re-entry. The testing is not expected to be complete until late today and NASA's Mission Management Team may opt to defer a decision one way or the other until Thursday.

Today's spacewalk, the third of the Endeavour mission, the 14th so far this year and the 91st since station assembly began in 1998, is scheduled to get underway at 11:01 a.m. when the astronauts, floating in the station's Quest airlock module, switch their spacesuits to internal battery power. This will be Mastracchio's third spacewalk and Anderson's second. Preparations have gone smoothly and as of 9 a.m., the spacewalkers were running about 25 minutes ahead of schedule.

The first item on the agenda is to move the S-band antenna sub-assembly, or SASA, from the P6, or port 6, solar array truss segment down to the P1 segment. P6, located at the top of the Z1 truss extending up from the central Unity module, provided the station's power during initial assembly. The station's power now is provided by solar arrays on each end of a long truss that runs at right angles to the station's pressurized modules. In October, astronauts will use the station's robot arm to move P6 from its perch atop Z1 to its permanent location on the far left end of the solar array truss. Its stowed arrays then will be re-extended.

In preparation for that move, shuttle astronauts stowed the P6 solar panels during assembly flights in December and June. During the Endeavour crew's first spacewalk last Saturday, a large ammonia cooling radiator was folded and locked in place.

Today, Mastracchio and Anderson, assisted by shuttle pilot Charles Hobaugh, operating the station's robot arm, will move the SASA antenna gear from P6 to the P1 truss segment. They then plan to install a new S-band transponder and signal processor that will improve voice communications to and from the station.

With that work complete, the spacewalkers and Hobaugh will move two crew and equipment translation aid - CETA - carts from one side of the station arm's mobile transporter to the other. The CETA carts are coupled to the transporter, which moves along rails on the front face of the main solar array truss to position the robot arm at various work sites. The carts currently are on the port, or left, side of the transporter. They need to be on the opposite side so the transporter can reach the far left work site on the truss for the P6 relocation work planned for October.

Anderson then plans to retrieve a transponder from the P6 array while Mastracchio retrieves two space exposure experiment packages for return to Earth.

"We're going to move the SASA antenna off of P6," Mastracchio said in a NASA interview. "Again, P6 is going to eventually be moved from the zenith part of station to the port side. So, we have to kind of clean up P6. And part of it is to move this large antenna off of P6 and install it on P1. While I'm doing that, Clay Anderson ... will be installing two electronics boxes to support that antenna. That will give the space station its second set of antennas, I should say, communication antenna capability.

"The second part of that EVA is we've got two large CETA carts that run along the rail, the tracks on the truss. We'll be moving those CETA carts from the one side to the other side in preparation for a future mission. And then, there's some other clean-up work after that."

Here is a timeline of today's activity (in EDT and mission elapsed time):

DATE/EDT...DD...HH...MM...EVENT

08/15/07
06:07 AM...06...11...30...STS/ISS crew wakeup
06:47 AM...06...12...10...EVA-3: Airlock repress to 14.7 psi
07:07 AM...06...12...30...EVA-3: Hygiene break
07:27 AM...06...12...50...EVA-3: Airlock depress to 10.2 psi
07:57 AM...06...13...20...EVA-3; Campout EVA prep
09:27 AM...06...14...50...EVA-3: Spacesuit purge
09:42 AM...06...15...05...EVA-3: Spacesuit pre-breathe
10:32 AM...06...15...55...EVA-3: Airlock depressurization
11:07 AM...06...16...30...EVA-3: Airlock egress
11:07 AM...06...16...30...Station arm (SSRMS) maneuvers for SASA support
11:22 AM...06...16...45...EVA-3: Setup
11:42 AM...06...17...05...Russian segment computer work resumes
12:02 PM...06...17...25...EVA-3: EV1: P6 SASA relocation
12:02 PM...06...17...25...SSRMS SASA relocation
12:02 PM...06...17...25...EVA-3: EV3: P1 signal processor and transponder installation
12:37 PM...06...18...00...Spacehab debris shields inspection
01:32 PM...06...18...55...SSRMS maneuvers for CETA cart relocation
01:57 PM...06...19...20...EVA-3: CETA 1 moved to starboard side of transporter
02:42 PM...06...20...05...Crew meals begin
02:57 PM...06...20...20...EVA-3: CETA 2 moved to starboard side of transporter
03:57 PM...06...21...20...EVA-3: EV1: SASA gimbal locks prepared
03:57 PM...06...21...20...EVA-3: EV3: P6 transponder retrieval
04:27 PM...06...21...50...EVA-3: EV1: MISSE 3 and 4 removal
04:57 PM...06...22...20...EVA-3: Payload bay cleanup
05:12 PM...06...22...35...EVA-3: Airlock ingress
05:32 PM...06...22...55...EVA-3: Airlock repressurization
05:57 PM...06...23...20...MISSE-3 transfer to shuttle
06:17 PM...06...23...40...MISSE-4 transfer to shuttle
07:00 PM...07...00...24...Mission status briefing on NASA TV
07:12 PM...07...00...35...Logistics transfer tagup
09:07 PM...07...02...30...ISS crew sleep begins
09:37 PM...07...03...00...STS crew sleep begins
10:00 PM...07...03...24...Daily video highlights reel on NASA TV

8:40 PM, 8/14/07, Update: Shannon 'cautiously optimistic' shuttle can re-enter without repairs; Kelly downplays tile concern; Morgan says spaceflight worth the wait

Sophisticated computer analysis indicates the aluminum skin directly below a small gash in the shuttle Endeavour's heat shield will not exceed NASA's 350-degree safety limit during re-entry, a top NASA manager said late today, despite temperatures of up to 2,100 degrees just outside the gouge. If overnight tests in a high-temperature furnace show the computer models are accurate - and if independent analysts agree - NASA managers may decide there's no need for a spacewalk repair job.

"We've completed the initial thermal analysis," said John Shannon, chairman of NASA's Mission Management Team. "It is going through an independent quality check and that's to take people who were not involved in the process to look at the assumptions that were made, the math, to make sure everything was done correctly. We've also completed the computational fluid dynamics that tells you what the flow inside that small cavity would be. Ames Research Center did that work, it's currently being verified by the Langley Research Center.

"The results of that, we're cautiously optimistic that we can fly as is, that's what the results were today. However, that's without any of the arc jet testing that we've talked about. Last night, we ran a baseline case of non-damaged tiles in the arc jet facility and they got a baseline temperature measurement on the backside of the tiles. At 7 o'clock, in about 40 minutes, we're going to start the arc jet tests with the exact damage we have on orbit. That will play back into the analysis."

The computational fluid dynamics calculations indicate the temperature of the shuttle's aluminum skin under the tile gouge would not exceed 325 degrees Fahrenheit. Shannon said the 350-degree limit is conservative and intended primarily to ensure the glue-like material used to hold the tiles and their support pads in place does not break down.

"We should get roughly the same temperature measurements that were predicted by the analysis," he said. "If we do, we'll know we have a good analysis. That is approximately a 24-hour cycle. ... So I would think that by late tomorrow afternoon, maybe in the early evening, we will have all our quality checks done, we will have our verification of the computational fluid dynamics model and we'll have the arc jet data to say that that modeling was correct and then we can make a decision on whether we need to repair or not."

For his part, shuttle Commander Scott Kelly said today he would be comfortable flying Endeavour back to Earth "as is" if mission managers decide the gouge doesn't require repairs. But he would be equally at ease overseeing a repair spacewalk.

"I feel comfortable," Kelly told CBS News in a space-to-ground interview. "My understanding is this tile damage is not an issue of the safety of the crew, It's more an issue of the ability to reuse the orbiter and damaging the orbiter. So we still have analysis ongoing, we still might choose to repair it, but I'm not concerned with our safety."

A team of astronauts, flight controllers and engineers is studying repair options in case the ongoing computer modeling and arc jet tests indicate a repair is needed. If so, the preferred approach would be to defer a station spacewalk planned for Friday and instead stage a repair EVA on Saturday.

Astronaut Rick Mastracchio, anchored to the end of a 50-foot extension attached to Endeavour's 50-foot robot arm, would be maneuvered under the shuttle to reach the damaged tile just behind the ship's right-side main landing gear door. Canadian astronaut Dave Williams would assist, tethered to the orbiter boom sensor system extension.

Two repair options are on the table: application of emittance wash, a black paint-like material that would be dabbed into the gouge to improve the heat rejection capability of the damaged tiles and/or injection of a heat-resistant putty-like material called STA-54.

It's not yet clear who would operate the robot arm if a repair is ordered. Astronaut Tracy Caldwell and educator-astronaut Barbara Morgan have both operated the arm for other tasks and Kelly is qualified as well.

"Anytime you've got someone on the end of the arm, it's a tricky thing," Caldwell, celebrating her 38th birthday today, told CBS News. "So we need to be careful about all of the clearances. The shuttle attached to the space station is a really complex vehicle and we've got a lot of places we've got to look out for. But I would say the trickiest part is looking out for, coming underneath the orbiter. The payload bay doors on the port side where we have the shoulder of the shuttle arm based, just making sure we clear that, and the wing. And then just having really good coordination between those of us inside the cockpit operating the arm and our guys outside who may perhaps be on the end of it."

Under the Saturday repair scenario, the astronauts would inspect the damage site again on Sunday, using a laser scanner and high-resolution camera on the end of the orbiter boom sensor system arm extension, and then stage an additional spacewalk Monday to make up space station assembly tasks deferred from Friday. That spacewalk, if approved, would be carried out by Williams and space station astronaut Clay Anderson.

NASA managers are enjoying an unfamiliar luxury during Endeavour's flight - more time than usual to assess their options. Endeavour's mission is the first to include use of a new station-to-shuttle power transfer system, or SSPTS, which lets the orbiter tap into the station's solar power grid. That, in turn, helps conserve the hydrogen and oxygen used by the shuttle's electricity producing fuel cells.

Based on the successful operation of the SSPTS, mission managers on Sunday extended Endeavour's mission by three days, from 11 to 14 days, and added the fourth spacewalk Friday. As of late Monday, engineers were predicting the shuttle would have enough power to remain docked to the space station an additional three days beyond that, if necessary, while still holding two days in reserve for landing-day weather issues or other problems.

Adding a fifth spacewalk to the mission likely would require a two-day mission extension, pushing Endeavour's landing from Aug. 22 to Aug. 24. But that is just one possible repair scenario and mission managers have not yet made any final decisions one way or the other.

The tile damage in question was caused by a piece of foam insulation, possibly mixed with ice, that broke away from a propellant feedline bracket on the side of Endeavour's external tank 58 seconds after blastoff Wednesday. Shannon said today analysts believe the debris originally measured 4 inches by 3.8 inches by 1.8 inches and weighed just 0.336 ounces.

The debris hit an aft strut at a relative velocity of about 205 mph. Surprisingly, the debris bounced off the strut and a large piece hit the belly of the orbiter at a relative velocity of about 150 mph. Engineers were surprised by the ricochet, believing a chunk of foam or ice would break up into numerous small pieces rather than bounce off a strut as the debris in question actually did.

In any case, the debris gouged out an irregular cone-like pit that tapers to a gash measuring 1-inch long and 0.2 inches wide at the base of the 1.12-inch thick tile. Laser scans of the gouge were used to fabricate precise three-dimensional mockups using tiles identical to those on Endeavour. Engineers are running complex computational fluid dynamics calculations to model the flow of re-entry heat inside the damage zone. Those models will be verified by subjecting the deliberately damaged tiles to an arc jet furnace capable of duplicating re-entry heating and flow fields.

If the tests show the underlying aluminum skin of the shuttle will not be damaged by re-entry heating, mission managers could opt to forego any repair work and bring Endeavour home on Aug. 22 as is. If the test results are ambiguous, or if they indicate a higher likelihood of damage, a repair spacewalk will be ordered.

"Through the preliminary thermal assessment, which was based on the computational fluid dynamics, we did not exceed the structural temperature constraints of the underlying aluminum," Shannon said today. "And of course, we have to go through the quality assurance checks and the independent verifications but if that holds, it'll be real good news to us."

He said the computer models were conservative and assumed, once the temperature in the cavity reached 1,600 degrees, that an underlying layer of material that provides some insulation was suddenly gone.

"They just completely took it away, and we still did not reach the limit on the underlying aluminum structure," he said.

Interestingly, Shannon said a review of past foam loss from external feedline support brackets indicates more instances of debris in the wake of the Columbia accident than before. One of NASA's post-Columbia improvements was to add an hour of "hold" time to the shuttle's countdown, after the external tank is loaded with supercold rocket fuel, for a thorough launch pad inspection.

It is possible, Shannon said, that the additional hold time contributes to the formation of additional ice. It is believed that ice near the feedline brackets plays a role in the liberation of foam insulation. In any case, Shannon said engineers and managers will discuss possible additional inspections and analysis before the shuttle Discovery is attached to its fuel tank early next month in preparation for launch in late October.

Speaking to reporters today, Morgan said the ride to orbit was thrilling and added that it took several days to fully adapt to life in space. Named as backup to Christa McAuliffe in the original Teacher in Space program, Morgan waited 21 years for a chance to ride the shuttle and continue McAuliffe's legacy.

"It's remarkable," she said of launch last Wednesday, "it's a lot noisier than I expected and it actually did not shake as much as I'd expected the shaking to be. But you feel the thrust and it keeps going and going and going. Towards the very end, before MECO, before main engine cutoff, it gets a little bit difficult to breathe. And then as soon as those main engines cut off, you pretty much pitch forward and if you unstrap, of course, you're floating free. But you can definitely feel that floating feeling right away."

After "three or four days on orbit, the floating is fantastic," she said, "it's something you get used to and have a lot of fun with. At first, it's a little disconcerting. That very first day on orbit, the entire day I felt like I was upside down the whole time."

Morgan has downplayed her role as the first teacher in space and instead has focused on the astronaut part of her title, overseeing the transfer of supplies and equipment from the shuttle to the station and operating the robot arm today to help install a 7,000-pound storage platform on the lab complex.

"Teachers and astronauts really do the same thing, it's all about doing work, it's about exploring, it's about experimenting, it's about discovering and sharing it," she told CBS News "And that's what we're here to do."

Later in the day, Morgan fielded questions from kids at a Discovery Center in Boise, Idaho, her home state, the first of three modest educational events planned for Endeavour's mission. Joined by Williams, Anderson and Al Drew, Morgan took delight in demonstrating the effects of weightlessness, turning somersaults, slurping balls of liquid from a drink bag and demonstrating exercise techniques by picking up Drew and Williams with one hand each.

Surprisingly, Morgan handed the microphone to her crewmates more often than not and the event resembled a typical astronaut question-and-answer exercise more than an educational event. But the kids clearly enjoyed the demonstrations, frequently laughing and applauding the astronauts' antics.

9:45 AM, 8/14/07, Update: Astronauts begin equipment storage platform installation; Morgan interviews, educational event on tap

The Endeavour astronauts are working to robotically install a 7,000-pound equipment storage platform on the international space station today, a complex procedure requiring tight choreography between the shuttle and station robot arms.

Educator-astronaut Barbara Morgan, assisted by Tracy Caldwell, used Endeavour's 50-foot-long robot arm to lock onto a grapple fixture on External Storage Platform No. 3 around 9:13 a.m. She began slowly pulling the platform from its perch in the orbiter's cargo bay a half hour later. Shuttle pilot Charles Hobaugh, operating the station's arm from a work station inside the Destiny laboratory module, was standing by to latch onto ESP-3 for the actual installation on the left side of the station's solar power truss.

"This is the first ESP (equipment storage platform) that is being installed only by robotics," said station flight director Heather Rarick. "Station-wide, this is the first major element that's been brought up and installed this way. So it's a new moment for us here in using the robotic arms. And of course, it will take both robotic arms to do this.

"It is a challenge because there is the choreography of handing the piece of equipment from one arm to the next and then getting it into the correct location, the attach system on the truss where it needs to live permanently. There are also heaters and electrical power ... for equipment that is located on this platform. This platform holds spare equipment for us so that in the future we don't have to rely on another vehicle reaching the space station to make any repairs."

This afternoon, Morgan and Caldwell, who is celebrating her 38th birthday in space today, will participate in a series of media interviews starting around 2 p.m. This will be teacher-turned-astronaut Morgan's first opportunity to answer questions from reporters about her experiences in space since Endeavour's launching last Wednesday. Later today, around 5:09 p.m., Morgan plans to participate in the first of three educational events planned for the mission.

Here is an updated timeline of today's activity in space (in EDT and mission elapsed time):

EDT............DD...HH...MM...EVENT

08/14/07
Tue 06:37 AM...05...12...00...STS/ISS crew wakeup
Tue 08:17 AM...05...13...40...Shuttle arm (SRMS) grapples ESP-3
Tue 08:22 AM...05...13...45...BOK-3 Russian computer replace/testing
Tue 08:32 AM...05...13...55...SRMS ESP-3 unberthing
Tue 09:02 AM...05...14...25...SRMS ESP-3 handoff
Tue 09:42 AM...05...15...05...Station arm (SSRMS) ESP-3 grapple
Tue 09:57 AM...05...15...20...SRMS ungrapples ESP-3
Tue 09:57 AM...05...15...20...EVA-3: Tools configured
Tue 10:12 AM...05...15...35...SSRMS maneuvers ESP-3 to install position
Tue 11:12 AM...05...16...35...ESP-3 installation
Tue 11:57 AM...05...17...20...SSRMS ungrapples ESP-3
Tue 11:57 AM...05...17...20...Spacesuit swap
Tue 12:12 PM...05...17...35...SSRMS WS4 configured for translation
Tue 12:27 PM...05...17...50...Equipment lock preps
Tue 12:32 PM...05...17...55...Crew meals begin
Tue 01:57 PM...05...19...20...EVA-3: Tools configured
Tue 02:01 PM...05...19...25...U.S. network interviews with Morgan, Caldwell
Tue 03:22 PM...05...20...45...OBSS OSE EVA-4 prep
Tue 04:22 PM...05...21...45...Lab window pane replacement
Tue 05:09 PM...05...22...33...PAO educational event
Tue 05:30 PM...05...22...54...Mission status briefing on NASA TV
Tue 06:22 PM...05...23...45...EVA-3: Procedures review
Tue 08:32 PM...06...01...55...EVA-3: Mask pre-breathe
Tue 09:17 PM...06...02...40...EVA-3: Airlock depress to 10.2 psi
Tue 09:37 PM...06...03...00...ISS crew sleep begins
Tue 10:07 PM...06...03...30...STS crew sleep begins
Tue 11:00 PM...06...04...24...Daily video highlights reel on NASA TV

At the Johnson Space Center in Houston, meanwhile, engineers are pressing ahead with testing and contingency planning to deal with a small gouge in the shuttle's heat shield tiles. A decision on whether to order a spacewalk repair is expected later this week, after a series of tests to assess what sort of damage, if any, the shuttle's fuselage might experience during re-entry.

John Shannon, chairman of NASA's Mission Management Team, said Monday the damage is not believed to pose a catastrophic threat to the shuttle or its crew and if some other emergency forced a speedy return to Earth, Endeavour could safely land as is.

"We're not talking about catastrophic damage," Shannon said. "But if I have to pull off five or six tiles (after landing) and put a doubler on some structure, replace a rib or anything like that, that's going to increase my turnaround time between (flights) and I'd like to avoid that if possible, if I have an EVA that I think is easy to execute. Now all of that assumes we come back and show that we would have localized heating that could cause some damage underneath and we haven't done that yet."

The testing will determine whether a spacewalk is needed.

"If you ask me whether I think it will or not, I'd probably lean toward it's not going to be absolutely required to do," he said. "The initial simplified cavity model that they ran today passed with no structural damage, no reduction of structural margins at all. But again, it's a simplified model. Since the flow is a little tricky, we want to make sure that we get it exactly right and we'll run that, make sure we understand it and if we don't have to do anything, well we had good practice in pulling together these procedures. And if we do have to do it, I feel fully confident we could execute that with a minimal impact to the mission."

To protect against the possibility of a spacewalk, a team of engineers and astronauts is assessing various repair options. The astronauts are trained for three different types of repair, ranging from the application of a black paint-like material and/or the injection of a thick putty-like insulator to a large carbon composite panel that could be screwed into surrounding tiles to form a thermal barrier. Late Monday, engineers ruled out the latter option because of the small size of the gouge and the complexity of the panel installation procedure.

The Endeavour astronauts plan to carry out space station assembly spacewalks Wednesday and Friday. The Friday EVA involves relatively low-priority get-ahead work and mission managers could opt to substitute a tile repair spacewalk instead. Another option would be to extend Endeavour's mission an additional few days and stage a fifth spacewalk. But no final decisions will be made until testing is complete.

For additional background, the NASA Technical Reports server includes an analysis of the risks associated with a heat shield repair spacewalk that was prepared by Science Applications International Corp. in May:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070020343_2007018370.pdf Revision K of NASA's STS-118 television schedule is posted on the CBS News STS-118 Quick-Look page, along with an updating flight plan and spacewalk statistics.

8:40 PM, 8/13/07, Update: Shannon says tile damage not considered a threat to astronauts; spacewalk repair, if needed, would be intended to minimize post-landing repairs

The foam-damaged heat-shield tiles on the belly of the shuttle Endeavour do not represent a Columbia-class threat of catastrophic failure during re-entry, the chairman of NASA's Mission Management Team told reporters today. John Shannon said the issue is more a matter of whether post-landing repairs might be needed that could delay Endeavour's next flight or whether it might make more sense to stage a relatively simple spacewalk repair job to give the shuttle additional margin during re-entry.

Asked a second time about the threat represented by the tile damage, Shannon said "this is not a catastrophic loss-of-orbiter case at all. This is a case where you want to do the prudent thing for the vehicle."

The damage was caused by a softball-size piece of insulation, possibly mixed with ice, that broke away from a propellant feedline bracket on the side of Endeavour's external tank 58 seconds after blastoff Wednesday. The debris hit an aft strut at a relative velocity of 205 mph. Surprisingly, the debris bounced off the strut and a large piece hit the belly of the orbiter at a relative velocity of about 150 mph. Shannon said engineers were surprised by the ricochet, believing a chunk of foam or ice would break up into numerous small pieces rather than bounce off a strut as the debris in question actually did.

Regardless of the underlying physics, the debris gouged out an irregular cone-like pit that tapers to a gash measuring 1-inch long and 0.2 inches wide at the base of the 1.12-inch thick tile. The small gash reveals so-called filler bar material, a strip of heat-resistant material that underlies the boundary between adjacent tiles. That was good news, Shannon said, because no bare aluminum is visible.

Another bit of good news was the location of the gouge. As luck would have it, the pit is directly under the intersection of two internal ribs on the other side of the shuttle's aluminum outer skin. The structural components would help dissipate any heat that managed to soak into the skin under the gash.

Laser scans of the gouge were used to fabricate precise three-dimensional maps of the damage as well as precise three-dimensional mockups using tiles identical to those on Endeavour. Shannon said engineers are running complex computational fluid dynamics calculations to model the flow of re-entry heat inside the damage zone. Those models will be verified by subjecting the deliberately damaged tiles to an arc jet furnace capable of duplicating re-entry heating and flow fields.

"That takes time, and I was not comfortable, as the MMT chairman, in waiting for the final answer from that team before we got started on any type of repair options," Shannon said. "So we kicked off a Team 4, which is a standing team of operators, spacewalk experts, crew members, engineering team members, they are standing by on every flight to work any problems like this and they're meeting right now to go discuss different types of repair options.

"We have the emittance wash, which is the black, it's almost like paint or shoe polish that keeps heat from building up in a cavity. We have the gun that squirts the caulk-like material that's very heat resistant into a cavity. And we have the overlay, which is a 15-by-24 (inch) sheet of silica carbide that you auger in, they almost look like drywall screws but they're better, and you auger that in to cover up any kind of a damage area.

"That team is meeting, they're going to look at different options," Shannon said. "Pretty much everybody at this point, even without doing the analysis, is very comfortable that if we just come in and we fill up this little area right here, that will provide us with some additional margin. The analysis is still in work to say whether that margin is even required or not."

Regardless of which repair option might be selected, Shannon said, "we could execute it if required and we have the team working really hard to understand whether it will be required."

A decision one way or the other is expected by late Tuesday or Wednesday.

Based on foam loss seen during the first post-Columbia mission, the external tank brackets in question are in the process of being redesigned. The new design will not be ready until three missions from now. But based on the experience with Endeavour, engineers have reviewed other missions and Shannon said they now believe they might have spotted losses during two other flights. But he said the foam in question is small and it's not at all clear it represents the sort of problem that could ground the fleet.

"To me, it's quite a bit of a stretch on the bracket to say wow, you had this, how do you keep flying? Well, this is kind of a pain to have to go and run all these assessments, it's kind of a pain if I have to get somebody under the vehicle to put a little squirt of goo (in a gouge). But to put this in a little bit of perspective, it's not very big. But it's something, I don't want to impact the turnaround of the vehicle. So I'm going to go and address it. If I had to go do half an EVA of repair on every flight from now until 12 flights from now, we'd go do that. We're set up to understand exactly what's on the vehicle and we have the repair capability. But we'd like not to do that, we'd like to devote the entire mission to just doing the ISS assembly or the ISS logistics. But we have it, we're going to go address it."

If a spacewalk repair is required, it will be carried out by Rick Mastracchio and Dave WIlliams. Williams and station astronaut Clay Anderson already are scheduled for spacewalks Wednesday and Friday. If a repair is ordered, it likely would take the place of the Friday excursion, which includes a variety of relatively low-priority tasks. To reach the damage site, the astronauts would ride on a 50-foot-long boom attached to the shuttle's robot arm.

Mastracchio and Williams "completed a standard flow of tile repair classes and their last class was literally about three or four weeks before flight," said spacewalk officer Paul Boehm. "We are actually very fortunate in this situation that Rick has actually performed some of these things in a vacuum (chamber) to see how the material reacts in that. So Rick and Dave would be our two candidates for doing that particular type of EVA."

As for the risk involved in working under the space shuttle, Boehm said "one of the concerns we have, obviously, is they're wearing a 300-pound EMU (spacesuit) with about 150 pounds of tools on them. ... Obviously, any of those things dinging into the tile underneath potentially could damage the tile. So we take extra care to make sure all our safety tethers and tools and everything are safely away from the orbiter when we go in for those type of repairs."

06:30 PM, 8/13/07, Update: New gyro installed; spacewalk ends

Astronauts Rick Mastracchio and Dave Williams successfully replaced an ailing control moment gyroscope on the international space station today to accomplish the primary goal of their second spacewalk. The spacewalk began at 11:32 a.m. and ended at 6 p.m. for a duration of six hours and 28 minutes. This was the 90th spacewalk devoted to station assembly and maintenance since construction began in 1998 and the 13th so far this year. Seventy two men and women from the United States, Russia, Canada, Japan, Germany, France and Sweden have now logged 557 hours and 29 minutes of EVA time building and maintaining the lab complex.

The space station uses four control moment gyroscopes, or CMGs, to control the lab's orientation without burning hard-to-replace rocket fuel. One of them, CMG No. 3, acted up last year and was taken off line on Oct. 10, 2006. The unit installed today will restore full redundancy to the critical orientation system.

The replacement CMG rode into space mounted on a 600-pound pallet in the shuttle's cargo bay. Mastracchio and Williams first removed the suspect CMG-3 from its place in the Z1 truss atop the station's central Unity module and temporarily mounted it on a handrail fitting. Then they moved down to the shuttle's cargo bay - Williams on the end of the station's robot arm - and removed the new CMG and a carrier platform.

Williams, still on the robot arm, manually carried the hardware up to External Stowage Platform No. 2 near the Quest airlock. The new CMG then was removed from its carrier plate and installed in Z1. CMG-3 was mounted on the ESP-2 carrier plate where it will remain until it is returned to Earth later this year.

The new CMG will not be fully spun up to 6,600 rpm until later this week. But initial electrical checks showed it was properly wired into the lab's electrical system.

"How's the ride, Dave, and the stability of that big boy?" one of the astronauts inside the space station asked Williams at one point.

"Great. It's got a lot of mass," Williams said, manually holding the 600-pound gyro and a 600-pound mounting plate.

"This is NOT a jettison mission, OK?" the other astronaut joked.

Later, referring to the old gyro, station astronaut Clay Anderson quipped: "If you have time, you might want to whip out a piece of gray tape and a Sharpie and stick it on the CMG and write 'suspect, return to ground.'"

Mastracchio had a brief scare around 4 p.m. when a faulty carbon dioxide sensor indicated an apparent CO2 buildup in his spacesuit.

"Our assessment right now would be to clock it..." someone was saying.

"Break, break, break...

"...counterclockwise..."

"Break! Break!" someone yelled urgently.

"CO2 sensor bad. CO2 high," Mastracchio radioed.

"Stand by," someone said.

"48.3 millimeters. I guess the CO2 sensor went bad, I'm hoping. It says 'open purge valve,' but I'm not going to do that."

"Stop arm motion. Stop arm motion," someone said.

"How you feeling, Rick?" astronaut Tracy Caldwell asked from inside the shuttle.

"I feel fine."

Flight controllers monitoring telemetry from the suit told the astronauts Mastracchio's spacesuit was in good shape and the two astronauts were cleared to continue the spacewalk.

1:09 PM, 8/13/07, Update: Suspect gyro removed

Astronaut Rick Mastracchio and Canadian flier Dave Williams have removed a faulty 600-pound gyroscope from its mount in the Z1 truss of the international space station. The gyro has been temporarily mounted on a hand-rail fitting while the astronauts turn their attention to retrieving a replacement gyroscope from the shuttle Endeavour's cargo bay.

Williams, anchored to the end of the station's robot arm, was carried to the shuttle's payload bay to pickup the replacement, mounted on a cargo carrier that on Tuesday will be mounted on the station to hold spare parts and equipment. Mastracchio was on hand to help unbolt the new gyro, still attached to a mounting plate, and hand it to Williams.

Shuttle pilot Charles "Scorch" Hobaugh, operating the station arm, then will move Williams and the new CMG back up to a hardware storage platform near the Quest airlock module. The mounting plate will be bolted to the storage platform and then the new CMG will be removed and installed in the Z1 truss. The old CMG will be bolted to the mounting plate on External Storage Platform No. 2 and stored until it can be returned to Earth in December.

Today's work is going smoothly and the astronauts are about 15 minutes ahead of schedule.

"Hey Scorch, the motion of the arm is incredibly smooth," Williams radioed as he was being moved down to the cargo bay.

"It's because I ain't doing it," Hobaugh joked, referring to the arm's computer control.

"I thought you were driving real well there."

"Man, I could have taken credit for that," Hobaugh said.

"This is the most amazing ride I've ever had," Williams marveled.

"There's work on the other end," Hobaugh reminded him.

"Yeah, I can see it coming up."

11:35 AM, 8/13/07, Update: Spacewalk begins to replace gyroscope

Astronauts Rick Mastracchio and Dave Williams switched their spacesuits to internal battery power at 11:32 a.m. today to officially kick off a planned six-and-a-half-hour spacewalk to replace one of the international space station's four stabilizing gyroscopes. The space station uses four 600-pound control moment gyroscopes, or CMGs, to control the lab's orientation without burning hard-to-replace rocket fuel. One of them, CMG No. 3, acted up last year and was taken off line on Oct. 10, 2006. The refurbished unit being installed today will restore full redundancy to the critical orientation system.

The replacement CMG rode into space mounted on a 600-pound pallet in the shuttle's cargo bay. Mastracchio and Williams first will remove the suspect CMG-3 from its place in the Z1 truss atop the station's central Unity module and temporarily mount it on a handrail fitting. Then they'll move down to the shuttle's cargo bay, remove the new CMG and a carrier platform and move them up to External Stowage Platform No. 2 near the Quest airlock. The new CMG then will be removed from its carrier plate and installed in Z1. CMG-3 will be mounted on the ESP-2 carrier plate and returned to Earth later this year.

6:20 AM, 8/13/07, Update: Astronauts gear up for critical spacewalk

Amid ongoing work in Houston to assess the potential impact of heat shield tile damage, the Endeavour astronauts are gearing up for a planned six-and-a-half-hour spacewalk today to replace one of the international space station's stabilizing gyroscopes, one of four needed to maintain the lab's orientation, or attitude, in orbit.

Astronauts Rick Mastracchio and Dave Williams spent the night in the station's Quest airlock module to purge nitrogen from their bloodstreams in preparation for their second spacewalk in three days. The excursion will be the 90th devoted to station assembly and maintenance since construction began in 1998 and the 13th so far this year. Going into today's spacewalk, 72 men and women from the United States, Russia, Canada, Japan, Germany, France and Sweden had logged 551 hours and one minute of EVA time building and maintaining the lab complex.

The Endeavour astronauts staged the first of four planned outings on Saturday. A third spacewalk, with Mastracchio and station astronaut Clay Anderson, is on tap Wednesday and the fourth, with Anderson and Williams, is planned for Friday.

The space station uses four massive control moment gyroscopes, or CMGs, to control the lab's orientation without burning hard-to-replace rocket fuel. One of them, CMG No. 3, acted up last year and was taken off line on Oct. 10, 2006. The refurbished unit being installed during Endeavour's mission will restore full redundancy to the critical orientation system.

The replacement CMG rode into space mounted on a pallet in the shuttle's cargo bay. Mastracchio and Williams first will remove the suspect CMG-3 from its place in the Z1 truss atop the station's central Unity module and temporarily mount it on a handrail fitting. Then they'll move down to the shuttle's cargo bay, remove the new CMG and a carrier platform and move them up to External Stowage Platform No. 2 near the Quest airlock. The new CMG then will be removed from its carrier and installed in Z1. CMG-3 will be mounted on the ESP-2 carrier and returned to Earth later this year.

"Our second spacewalk, I think, is almost going to be as exciting as the first," Williams said in a NASA interview. "Our job is to replace one of the gyros that we use to stabilize the position of the space station. There are four gyros that we currently have on board the space station. The gyro essentially is a spinning disk that conserves momentum. It's used to stabilize the station. One of them isn't functioning properly, so we have to replace it.

"To do that, Rick and I will go up to the Z1 area, take out the old gyro that's not working properly, temporarily stow it, then Rick is going to go down to the payload bay of the space shuttle, I'm going to get onto the robotic arm and I will go down to the payload bay of the space shuttle on the robotic arm. We're going to remove the new CMG, the new gyro, from the payload bay of the shuttle. It weighs 1,200 pounds. I'm going to be holding on to it on each side, with my heels turned outward holding me in place in the foot restraint on the end of the robotic arm.

"And then we're going to come back up to the stowage platform, ESP-2, right by the airlock, install the stowage assembly for the new gyro, then take the new gyro off, bring it back to the work site where we had the old gyro, swap the two and bring the old one back to the stowage platform. A lot of choreography there. It gets kind of confusing about which is going where and things. So we've worked very hard on the choreography."

Here is an updated timeline of today's activity (in EDT and mission elapsed time):

DATE/EDT.......HH...MM...SS...EVENT

08/13/07
05:00 AM...04...10...24...Flight director update on NASA TV
06:37 AM...04...12...00...STS/ISS crew wakeup
07:17 AM...04...12...40...EVA-2: Airlock repress to 14.7 psi
07:30 AM...04...12...54...Video file on NASA TV
07:37 AM...04...13...00...EVA-2: Hygiene break
08:07 AM...04...13...30...EVA-2: Airlock depress to 10.2 psi
08:27 AM...04...13...50...EVA-2: Campout EVA prep
09:37 AM...04...15...00...Logistics transfers resume
09:57 AM...04...15...20...EVA-2: Spacesuit purge
10:12 AM...04...15...35...EVA-2: Spacesuit pre-breathe
11:02 AM...04...16...25...EVA-2: Crew lock depressurization
11:31 AM...04...16...55...EVA-2: Spacesuits to battery power; EVA-2 begins
11:37 AM...04...17...00...EVA-2: Airlock egress
11:52 AM...04...17...15...EVA-2: Tethers/tools set up
12:22 PM...04...17...45...EVA-2: Remove failed control moment gyro
12:52 PM...04...18...15...EVA-2: Transfer new CMG to ESP-2
01:37 PM...04...19...00...Crew meals begin
02:22 PM...04...19...45...EVA-2: Remove new CMG from ESP-2
03:12 PM...04...20...35...EVA-2: Install new CMG on Z1 truss
04:07 PM...04...21...30...EVA-2: Install failed CMG on ESP-2
05:17 PM...04...22...40...EVA-2: Payload bay cleanup
05:42 PM...04...23...05...EVA-2: Airlock ingress
06:02 PM...04...23...25...EVA-2: Airlock repressurization
06:17 PM...04...23...40...Spacesuit servicing
06:22 PM...04...23...45...Station arm (SSRMS) walk off lab to PDGF-2
07:30 PM...05...00...54...Mission status briefing on NASA TV
07:37 PM...05...01...00...Transfer tagup
09:37 PM...05...03...00...ISS crew sleep begins
10:07 PM...05...03...30...STS crew sleep begins

Back at the Johnson Space Center in Houston, engineers assessing data collected Sunday on the depth and extent of a gouge in the shuttle's heat shield tile planned to subject a mockup to the extreme heat of re-entry in a furnace that can mimic the sort of environment Endeavour will experience during its return to Earth.

During launch Wednesday, a softball-size piece of foam insulation broke away from a propellant feedline support bracket, hit a strut near the base of the shuttle's external tank and broke apart. One piece then ricocheted off the strut and hit the belly of the shuttle, gouging a deep pit in two heat shield tiles. The tiles are only about 1.12 inches thick in that area and the inspection Sunday revealed the impact blasted out a pit that almost reached the aluminum skin of the orbiter in a small 1-inch by .2-inch area.

Based on pictures snapped by the space station's crew during Endeavour's final approach Friday, mission managers had already decided the shuttle could safely re-enter as is if some other emergency forced a speedy return to Earth. The close-up pictures taken Sunday did not change that judgment and John Shannon, chairman of NASA's Mission Management Team, said the orbiter's heat shield was healthy enough to handle re-entry as is if another emergency of some sort forced a speedy return to Earth.

That means engineers do not believe the gouged tile is a Columbia-class problem.

"I did poll the team and it was still unanimous that there was no change in the thought process," Shannon said. "If we were in a significant emergency case we would feel comfortable deorbiting this vehicle. However, not being in an emergency case, we're going to proceed very methodically, understand exactly what we have and go get the vehicle in the best configuration we can for re-entry."

Data from a laser scanner used to map out the damage site Sunday was expected to provide the three-dimensional data needed to carve an exact duplicate of the damage site using tiles identical to those on Endeavour. How that mockup fares in NASA's arc jet facility will play a major role in deciding whether to order an emergency spacewalk repair job or whether Endeavour can safely return to Earth as is. A decision is expected by Tuesday.

NASA managers have plenty of time to mount a repair effort if one is needed. On Monday, the Mission Management Team extended Endeavour's mission by three days based on the near-flawless performance of a new station-to-shuttle power transfer system that lets Endeavour tap into the station's solar power grid. Drawing up to 6 kilowatts from the station, the shuttle's on-board supplies of liquid oxygen and hydrogen, which are combined to produce electricity in the orbiter's fuel cells, will last longer, permitting the mission extension.

Under the extended mission scenario, four spacewalks are planned. The final excursion, however, is devoted primarily to get-ahead activities that are not considered critical to the next station assembly mission. If NASA managers decide to order a tile repair, it likely would be carried out Friday, during the slot originally booked for the mission's fourth and final spacewalk.

Endeavour's crew is trained and equipped to make three different types of heat shield repairs.

A spacewalking astronaut anchored to the same boom used to inspect the tiles Sunday could apply a black, paint-like "emittance wash" to the exposed silica fibers of the damaged tiles to improve their ability to reject heat. The astronauts also could fill the gouge with a putty like material known as STA-54. They even have carbon composite panels that can be screwed into the tile to cover large areas of damage.

While it's too soon to say whether a repair might be needed, "I have a lot of confidence based on the testing we've done that if a repair is required, that we can go execute it," Shannon said Sunday. "As to which way we'll go, we'll see through the analysis over the next 24 to 48 hours."

Even before Sunday's inspection, engineers assumed a deep pit for purposes of worst-case modeling of re-entry heat loads. As luck would have it, the damage site is right above an internal rib in the right wing called a stringer. Even if the tile was gouged out all the way to its base, Shannon said Saturday, any unusual heat during re-entry that made it to the underlying aluminum skin would spread out in the structure and not result in a localized hot spot. In addition, there is no wiring or any other systems on the interior of the right wing in that area.

Shannon said Sunday the actual damage closely mirrored the presumed worst-case scenario.

"Surprisingly, it's almost exactly what we thought we had after the 2D images where you potentially have a very small piece of the filler bar material showing," he said. "We have some flight history and now that we know exactly what we have, we'll go and make sure we understand the differences between flight history and what we have here today and we will test the exact condition. I can't stress enough how incredibly valuable the laser data is and the optical data is. Now I have the opportunity to go model exactly what I have and put it in an arc jet (furnace), put it through a re-entry environment. That's really valuable.

"This is something we would rather not deal with, but we have really prepared for exactly this case," Shannon said. "So I feel very comfortable that whatever is required we con go do and do successfully."

A larger question is how NASA will handle what apparently is an ongoing problem with the external fuel tank: foam shedding from the feedline support brackets. NASA and tank builder Lockheed Martin already were implementing a design change, but it won't be ready for flight until next year. The next three missions will rely on tanks similar to Endeavour's and NASA managers now face the prospect of trying to develop a flight rationale or implementing some sort of a fix in the near term.

The next shuttle launch is scheduled for Oct. 23, followed by a high-profile Dec. 6 flight to attach a European lab module to the station.

07:00 PM, 8/12/07, Update: Heat shield inspection carried out; Russian computer repair work continues; mission extended for additional station assembly work (UPDATED at 7 p.m. with Shannon briefing

A "focused inspection" of the shuttle Endeavour's heat shield today, prompted by concern over foam impact damage spotted earlier in the mission, revealed a deep gouge that nearly penetrates two adjacent tiles on the orbiter's belly. The damage was not apparent in realtime imagery downlinked from the shuttle, but higher resolution photos seen later in the day clearly showed a deep, scooped-out pit in the heat shield.

Based on pictures snapped by the space station's crew during Endeavour's final approach Friday, mission managers had already decided the shuttle could safely re-enter as is if some other emergency forced a speedy return to Earth. The close-up pictures today did not change that judgment and John Shannon, chairman of NASA's Mission Management Team, said the orbiter's heat shield was healthy enough to handle re-entry as is if another emergency of some sort forced a speedy return to Earth.

Engineers believe a softball-size chunk of foam insulation broke away from a bracket supporting a 17-inch-wide liquid oxygen feel line attached to the outside of the shuttle Endeavour's external tank during launch Wednesday. An instant later, the foam slammed into a support strut that helps hold the back end of the shuttle to the tank. The debris broke into several pieces and one ricocheted off the strut and directly into the belly of the shuttle, gouging a pit measuring 3.48 by 2.31 inches across.

But photos taken before today did not reveal how deep the pit might be - a key factor in determining the tile's ability to withstand the heat of re-entry - and so mission managers ordered today's focused inspection to find out.

Astronaut Tracy Caldwell, assisted by teacher-turned-astronaut Barbara Morgan and commander Scott Kelly, used Endeavour's robot arm and a 50-foot-long instrument boom to inspect five damage sites with a laser scanner and a high-resolution camera. During realtime downlink of black-and-white television camera views, the damage looked relatively minor. But high-resolution pictures seen later told a different story.

"As you can see ... it's a fairly deep gouge," Shannon said. "If you remember, the tile itself is 1.2 inches thick and the gouge goes pretty much through the entire thickness of the tile and there's a small area of the what we call filler bar, which is the material that is on the edge of the tile that the tile is mounted to that is showing. We think that that filler bar area is about .2 inches by about 1 inch. And then it impacts the second tile and just kind of took a scoop out of that part of the tile. So this is the data we were looking for.

"Not only did we get really good imagery, we got a good laser scan of it as well. And the process is we'll make a point cloud map of exactly what that damage is. And we'll do two things with that map. The first is we'll be able to model it and run our thermal analysis models to understand what the actual heating impact during re-entry would be for damage of this type. The second is a test method. We have already made up 2-foot by 2-foot sections of tile that are about that thickness and we'll take that cloud map and actually mimic the exact same damage on those test articles. And we'll put them in the arc jet facility here at Johnson Space Center and simulate re-entry conditions.

"That will be able to ground the analysis models with actual test data," Shannon said. "So we feel very comfortable with that. I expect we'll have the thermal analysis to discuss tomorrow at the Mission Management Team and the arc jet facility run will either be tomorrow or on Tuesday."

The arc jet facility can produce the 2,000-degree temperatures the shuttle's belly experiences during re-entry. Using stereo lithography based on the laser scan data, engineers will fashion an exact duplicate of the damage, put it in the furnace and see what happens. They also can test repair procedures to help determine the best course of action. Until then, Shannon said, it was premature to talk about possible repair scenarios or even if the damage needs fixing in the first place.

But Endeavour's crew is trained and equipped to make three different types of heat shield repairs. A spacewalking astronaut anchored to the same boom used to inspect the tiles today could apply a black, paint-like "emittance wash" to the exposed silica fibers of the damaged tiles to improve their ability to reject heat. The astronauts also could fill the gouge with a putty like material known as STA-54. They even have carbon composite panels that can be screwed into the tile to cover large areas of damage.

While it's too soon to say whether a repair might be needed, "I have a lot of confidence based on the testing we've done that if a repair is required, that we can go execute it," Shannon said. "As to which way we'll go, we'll see through the analysis over the next 24 to 48 hours."

Even before today's inspection, engineers assumed a deep pit for purposes of worst-case modeling of re-entry heat loads. As luck would have it, the damage site is right above an internal rib in the right wing called a stringer. Even if the tile was gouged out all the way to its base, Shannon said Saturday, any unusual heat during re-entry that made it to the underlying aluminum skin would spread out in the structure and not result in a localized hot spot. In addition, there is no wiring or any other systems on the interior of the right wing in that area.

Today, Shannon said the actual damage closely mirrored the presumed worst-case scenario.

The shuttle Columbia burned up during re-entry on Feb. 1, 2003, because of a gaping hole in the leading edge of its left wing. The hole was the result of a briefcase-size piece of foam insulation that hit the wing during launch 16 days earlier.

The foam responsible for Columbia's demise is no longer used on the external tank and NASA has implemented a variety of other changes to minimize foam shedding across the board. Ongoing problems with the feedline brackets in question have led NASA to implement a design change that will make its debut three flights from now. Given the problem with Endeavour's heat shield, mission managers could be forced to re-think the rationale for flying the current design in the interim.

"We're all of about 24 hours into the realization that this is something that has happened on several flights," Shannon said. "It's an anomaly, we've got to go either develop flight rationale or develop a fix."

The next shuttle flight is scheduled for launch Oct. 23. NASA hopes to close out the year with launch of a European Space Agency research module on Dec. 6.

"We don't rely on luck," Shannon said. "But we do know that it is possible to have foam loss, it is possible to have ice, it is possible to have other debris events and what we do is we run a probabilistic risk assessment. We don't say it is zero risk, we say the risk is some number. And as we fly more, as we understand more, as we understand how the material properties work we're able to better refine those probabilistic risk assessments. It's not zero. The risk is not zero and we have known that from day one.

"So what we'll do is, we'll go look at the flight history, now that we understand the mechanism better, we'll go look at the debris transport analysis, we'll look at the potential impact tolerance of the vehicle, both the tile and the RCC (reinforced carbon carbon) and wing leading edge thermal seals and all the critical areas we have on the vehicle and we'll do a probabilistic risk assessment. And if it turns out that is not acceptable to us, we will go and do a redesign before we fly again. That is just the process that we follow."

While today's inspection work was going on, space station commander Fyodor Yurchikhin and flight engineer Oleg Kotov were busy replacing cables attached to a computer processing unit known by the English version of a Russian acronym, BOK-3. In the wake of widespread Russian computer failures in June, engineers discovered quite a bit of corrosion on cables leading to the BOK-3 unit, located near an air conditioner in the Zvezda command module.

Opening access panels today, Yurchikhin reported finding a fair amount of condensation and water in the area. The BOK-3 unit itself will be removed Tuesday and replaced with a freshly delivered spare on Wednesday.

Astronauts Rick Mastracchio and Canadian flier Dave Williams, meanwhile, spent part of the day preparing the tools they will use during a second spacewalk Monday to replace one of the station's four stabilizing control moment gyroscopes. The excursion is scheduled to begin around 11:30 a.m. Monday.

Along with looking at the tile damage photos, the Mission Management Team also reviewed the performance of a new station-to-shuttle power transfer system, or SSPTS, that is allowing the orbiter to plug into the station's solar power grid.

Going into the mission, flight planners said if the SSPTS operated as expected, they would recommend extending Endeavour's mission by three days and adding a fourth spacewalk. The SSPTS has been operating flawlessly, delivering some 6 kilowatts of power to the shuttle and allowing the astronauts to reduce the consumption of liquid oxygen and hydrogen used by the ship's fuel cells. As a result, the MMT today approved the mission extension, setting the stage for station assembly spacewalks Monday, Wednesday and Friday.

Under the new flight plan, Endeavour will remain docked to the lab complex until Aug. 20 and return to Earth two days later. A revised flight plan will be posted here as soon as possible.

7:30- AM, 8/12/07, Update: Space station computer successfully restarted; shuttle team gears up for heat shield inspection

Amid planning for an afternoon inspection to assess the extent of shuttle heat shield damage, space station controllers successfully restarted a command-and-control computer that locked up Saturday because of an apparent software glitch.

"Last night we did power cycle it and reconfigured all the computers so they are in a good state for today's operations and everything's back to nominal," said station flight director Heather Rarick. "The main focus (today), especially for the shuttle team, will be to perform the focused inspection of the bottom of the shuttle to review some potential tile damage and see what the extent of that is."

Space station commander Fyodor Yurchikhin and flight engineer Oleg Kotov, meanwhile, plan to continue preparations for replacing critical computer cabling and a command processor known by its Russian acronym BOK-3 on Tuesday. Corroded cables connectors at the BOK-3 unit may have played a role in crippling Russian computer crashes during the last shuttle visit in June. The computers have been running normally since Yurchikhin and Kotov installed jumpers to bypass suspect secondary power supply surge protectors and those jumpers will remain in place during the BOK-3 replacement work later in the week.

The main focus today, however, is an up-close inspection of heat shield tile damage spotted after Endeavour's launch on Wednesday. John Shannon, chairman of NASA's Mission Management Team, told reporters late Saturday engineers believe the damage in question was caused by a chunk of foam insulation that popped off a propellant line support bracket on the shuttle's external fuel tank 58 seconds after liftoff. The debris slammed into an aft strut that helps hold the shuttle's back end to the tank and shattered into multiple fragments. One of those ricocheted off the strut and into the shuttle's belly, hitting between the right main landing gear door and an aft door covering the ship's liquid oxygen feedline inlet.

The damage, visible in photographs taken by the station crew during Endeavour's approach on Friday, measures 3.48 by 2.31 inches. The tiles in that area are about 1.12 inches thick. The photos do not show how deep the gouge might be and the depth of the damage is critical for the thermal analysis of its impact during re-entry.

As luck would have it, the damage site is right above an internal rib in the right wing called a stringer. Even if the tile was gouged out all the way to its base, Shannon said, any unusual heat during re-entry that made it to the underlying aluminum skin would spread out in the structure and not result in a localized hot spot. Engineers concluded that in an emergency, Endeavour could safely return to Earth as is.

But the crew's flight plan has always included time for a so-called focused inspection on the day between the first two spacewalks of the mission. When engineers spotted the tile damage, mission managers immediately told the flight control team to carry out the inspection today, as protectively planned, to fully assess the impact. While engineers do not appear overly concerned, Shannon emphasized they do not yet know how deep the gouge is, a critical part of the thermal analysis.

Starting the day with a bit of humor, the Endeavour astronauts were awakened at 7:06 a.m. by a recording of Shania Twain's "Up" played by mission control in Houston. The song began:

It's 'bout as bad as it could be
Seems everybody's buggin' me
Like nothing wants to go my way -
Yeah, it just ain't been my day
Nothin's comin' easily

The chorus concludes "There's no way but up from here."

"Good morning Endeavour, and a special good morning to you today, Dave," called astronaut Shannon Lucid from Houston.

"Good morning from the Spacehab," Canadian flier Dave Williams replied. "Really enjoyed the wakeup music this morning."

"Well, we aim to please."

The astronauts will first attach a 50-foot extension to the shuttle's robot arm, called the orbiter boom sensor system. The OBSS features a high-resolution camera and a laser scanner that will help engineers map out the damage in three dimensions.

Because of clearance issues when the shuttle is docked at the space station, the OBSS must be picked up from its perch in the orbiter's cargo bay by the space station's robot arm, operated by pilot Charles Hobaugh. He will pick up the OBSS around 9:50 a.m. and hand it off to Caldwell shortly after 11 a.m. Assisted by teacher-turned-astronaut Barbara Morgan, Caldwell plans to begin the actual inspection work a few minutes past noon.

"The shuttle arm cannot reach over and grab the end of the orbiter boom sensor system, the OBSS," Shannon said Saturday. "So there's a grapple fixture about a third of the way down. We will use the station arm to pick it up with that grapple fixture and then hand it off to the shuttle arm. We'll go underneath the vehicle, do all of our laser work, it will take about three hours, about two hours underneath the belly of the vehicle, it'll come back up and then the reverse will happen. We'll hand it back to the SSRMS (station arm), the SSRMS will put it down into the holder in the shuttle payload bay."

Here is an updated timeline of today's activity (in EDT and mission elapsed time):

EDT........DD...HH...MM...EVENT

08/12/07
07:07 AM...03...12...30...STS/ISS crew wakeup
09:22 AM...03...14...45...ISS: Russian BOK-3 computer repair work (5 hours)
09:37 AM...03...15...00...Shuttle arm (SRMS) moves to OBSS pre-grapple position
09:47 AM...03...15...10...Station arm (SSRMS) grapples/unberths OBSS
10:32 AM...03...15...55...SSRMS moves OBSS to handoff position
11:12 AM...03...16...35...SRMS grapples OBSS
11:22 AM...03...16...45...SSRMS ungrapples OBSS
11:32 AM...03...16...55...Spacewalk tools configured
12:07 PM...03...17...30...Heat shield inspection begins
12:07 PM...03...17...30...Logistics transfer operations
12:42 PM...03...18...05...Spacesuit battery charging
02:37 PM...03...20...00...Shuttle crew meals begin
03:37 PM...03...21...00...SSRMS grapples OBSS
03:37 PM...03...21...00...Equipment airlock preps for Monday spacewalk
04:07 PM...03...21...30...SRMS ungrapples OBSS
04:07 PM...03...21...30...SAFER emergency jetpack checkout
04:22 PM...03...21...45...SSRMS berths OBSS
04:52 PM...03...22...15...Spacewalk tools configured
05:00 PM...03...22...24...Mission status briefing on NASA TV
05:07 PM...03...22...30...SSRMS releases OBSS
05:27 PM...03...22...50...Educational experiment transfer and video
06:32 PM...03...23...55...Logistics transfer tagup
06:47 PM...04...00...10...Spacewalk procedures review
07:47 PM...04...01...10...Station arm walk off to lab
09:02 PM...04...02...25...EVA-2: Mask pre-breathe
09:47 PM...04...03...10...EVA-2: Airlock depress to 10.2 psi
10:07 PM...04...03...30...ISS crew sleep begins
10:37 PM...04...04...00...STS crew sleep begins
12:00 AM...03...05...24...Daily video highlights reel on NASA TV

11:30 PM, 8/11/07, Update: Additional data indicate foam, not ice, caused shuttle tile damage; engineering analysis indicates shuttle could safely land as is; but officials say inspection Sunday needed to resolve all questions

Digital video from cameras mounted on the shuttle Endeavour's solid-fuel boosters shows debris that hit the underside of the orbiter during launch Wednesday was a chunk of foam, not ice, that first hit a support strut, broke apart and ricocheted into the ship's belly. A worst-case engineering analysis indicates the spacecraft could safely return to Earth "as is" if some other emergency forced a quick re-entry. But John Shannon, chairman of NASA's Mission Management Team, told reporters late Saturday that a focused inspection Sunday using a laser scanner and a high-resolution camera is needed to fully assess the extent of the damage and what, if any, impact it might have during re-entry.

In the same briefing, space station flight director Joel Montalbano said the unexpected shutdown of a command-and-control computer aboard the lab complex today apparently was caused by a software glitch and not a hardware failure. Responding to the shutdown, a backup computer immediately took over and a third machine switched from standby to backup as expected. Both of those computers are operating normally. Montalbano said experts are studying telemetry from the computer that locked up to find out what process or potential software conflict might have caused it to freeze. But he expects the problem to be resolved in fairly short order.

"We think once we ahead and get all the information, do all the data dumps of what happened, we'll power cycle this computer (turn it off and back on) and we expect it to be fully operational," Montalbano said.

Shannon said the Mission Management Team spent most of its time today discussing the heat shield impact that caught the team's attention after launch. The damage site is located on the bottom of the right wing near the shuttle's fuselage between the right main landing gear door and a smaller panel that covers the main liquid oxygen feedline inlet.

Looking at imagery from ground cameras, the engineering community initially thought the debris in question was ice. Being more dense than foam, ice could potentially cause more damage to the shuttle's fragile heat-shield tiles. But today, digital video from cameras mounted on Endeavour's twin solid-fuel booster rockets was recovered and the imagery showed the debris was, in fact, a baseball-size chunk of foam insulation from a propellant feedline bracket on the external fuel tank that broke away 58 seconds after launch. The foam then slammed into one of the struts that holds the back end of the shuttle to the external tank. It broke apart and a smaller piece bounced up into the belly of the shuttle.

Endeavour was roughly 6.5 miles up at that point and moving at a relative velocity of nearly 1,000 mph. Engineers do not yet have enough data to assess the mass of the initial debris.

Shannon said engineers are in the process of redesigning the bracket in question because of past incidents in which pre-launch ice formed, causing foam in that area to break away during launch.

Photos shot by the space station crew during Endeavour's approach to the lab complex Friday show a small area of damage measuring 3.48 by 2.31 inches where the debris in question struck. The tiles in that area are about 1.12 inches thick. The photos do not show how deep the gouge might be and the depth of the damage is critical for the thermal analysis of its impact during re-entry.

As luck would have it, the damage site is right above an internal rib in the right wing called a stringer. Even if the tile was gouged out all the way to its base, Shannon said, any unusual heat during re-entry that made it to the underlying aluminum skin would spread out in the structure and not result in a localized hot spot. In addition, there is no wiring or any other systems on the interior of the right wing in that area.

Shannon said engineers do not believe the tile in question was gouged out all the way to its base. But for a preliminary thermal analysis, that's what they assumed.

"We assumed if we had lost all of the tile down to the felt area (at its base), we modeled that, and because it was along that rib assembly, we didn't have loss of structural margin," Shannon said. "It was OK, basically is what you would say. That was our best judgment. We looked at the model and made our best judgment on what we thought the potential thermal impact would be. It looked like it was OK. Again, we don't exactly know what we have until we do the focused inspection.

"Based on the flight history we saw, based on this location and based on that thermal analysis, it was a unanimous consensus in the MIssion Management Team that if we had an emergency kind of case we'd be OK to deorbit with the vehicle as is. ... I think once we have the focused inspection tomorrow we'll know exactly what we're dealing with and those decisions will be much easier to make. But it was the engineering judgment of the team that if we were in an emergency we could come home as is."

Shannon said engineers collecting data on the incident know much more now than they did Thursday and Friday.

"We kind of have a chain of evidence here," he said. "We looked at the pre-launch photos and saw some ice buildup in that bracket, we have a history of cracking that foam from that ice buildup, the SRB (booster) photos show that foam loss from that bracket area and the flight path it took. We got a little unlucky that it hit the ET (external tank) attach strut, but that can happen. The ground cameras showed the puff where it hit, the radar showed the ice so maybe we got some ice liberation behind it. The (rendezvous) pitch maneuver showed us the damage site and now we're going to take the next step and do a focused inspection tomorrow. I expect we'll have a final resolution on Monday once we've run through the thermal analysis and understand what we have.

"There was some discussion about the depth (of the damage). I think the consensus was, in the MMT, that the flight history we have, the location of this (damage), all are very good signs this will not be something we will have to worry about. But again, we're going to just march through the procedures we had set up preflight and execute those and see where we come out on Monday."

He said "if we have even half the tile left we won't have any issues at all."

Asked if it was possible that Endeavour's crew might have to make repairs, Shannon said based on "the data that we pulled together today on exactly where the location was, what is under that location and the flight history data would say that that is much more doubtful than it was yesterday."

The focused inspection is scheduled to begin just after noon Sunday. Astronaut Tracy Caldwell, assisted by teacher-turned-astronaut Barbara Morgan, will use Endeavour's robot arm to position a laser scanner and high-resolution camera on the end of the 50-foot-long boom as close to the damage site as possible. The laser scanner will collect data allowing engineers to make a three-dimensional model of the damage site. Caldwell also will use the system to inspect a few other areas of interest. The entire procedure is expected to take about three hours.

Because of clearance issues when the shuttle is docked at the station, the space station's robot arm will be used to pull the 50-foot orbiter boom sensor system - OBSS - heat-shield inspection boom from its place in the shuttle's cargo bay and hand it off to Caldwell, operating the shuttle arm. Here is an updated timeline of Sunday's crew schedule (in EDT and mission elapsed time):

EDT........DD...HH...MM...EVENT

08/12/07
07:07 AM...03...12...30...STS/ISS crew wakeup
09:22 AM...03...14...45...ISS: Russian BOK-3 computer repair work (5 hours)
09:37 AM...03...15...00...Shuttle arm (SRMS) moves to OBSS pre-grapple position
09:47 AM...03...15...10...Station arm (SSRMS) grapples/unberths OBSS
10:32 AM...03...15...55...SSRMS moves OBSS to handoff position
11:12 AM...03...16...35...SRMS grapples OBSS
11:22 AM...03...16...45...SSRMS ungrapples OBSS
11:32 AM...03...16...55...EVA-2: Tools configured
12:07 PM...03...17...30...Heat shield inspection begins
12:07 PM...03...17...30...Logistics transfer operations
12:42 PM...03...18...05...Spacesuit battery charging
02:37 PM...03...20...00...Shuttle crew meals begin
03:37 PM...03...21...00...SSRMS grapples OBSS
03:37 PM...03...21...00...Equipment lock preps for EVA-2
04:07 PM...03...21...30...SRMS ungrapples OBSS
04:07 PM...03...21...30...SAFER backpack checkout
04:22 PM...03...21...45...SSRMS berths OBSS
04:52 PM...03...22...15...EVA-2: Tools configured
05:07 PM...03...22...30...SSRMS releases OBSS
05:27 PM...03...22...50...EPO educational experiment transfer and video
06:32 PM...03...23...55...Logistics transfer tagup
06:47 PM...04...00...10...EVA-2: Procedures review
07:47 PM...04...01...10...Station arm walk off to lab
09:02 PM...04...02...25...EVA-2: Mask pre-breathe
09:47 PM...04...03...10...EVA-2: Airlock depress to 10.2 psi
10:07 PM...04...03...30...ISS crew sleep begins
10:37 PM...04...04...00...STS crew sleep begins

6:20 PM, 8/11/07, Update: Spacewalk ends; all objectives accomplished

Astronaut Rick Mastracchio and Canadian flier Dave Williams floated back into the space station's Quest airlock, closed the hatch and began repressurizing the module at 6:45 p.m. to wrap up a successful six-hour 17-minute spacewalk. The astronauts accomplished all of their objectives, attaching a new solar array truss segment and latching down a folding radiator on another solar array segment to clear the way for relocation later this year.

This was the 89th spacewalk devoted to station assembly and maintenance since construction began in 1998 - the 12th so far this year - pushing cumulative station EVA time to 551 hours and one minute by 50 U.S. astronauts, 15 Russians, three Canadians and four fliers from Japan, Germany, France and Sweden. If all goes well, Mastracchio and Williams will stage a second spacewalk Monday; station astronaut Clay Anderson will join Mastracchio for a third EVA Wednesday; and Anderson and Williams will stage a fourth spacewalk Friday.

While today's spacewalk was underway, the primary command-and-control computer in the U.S. Destiny lab module unexpectedly shut down. There are three computers in the set and the backup immediately assumed the duties of the primary computer and a third machine that had been on standby was activated and configured for backup duty.

Mission control commentator Kyle Herring said late today engineers were still troubleshooting the problem, but the two operational computers remain healthy and in control of critical station functions.

"Just to update folks on the status of the station computers, there's no change to the earlier comments relative to the health of the command-and-control computers on the station," Herring said around 6:30 p.m. "At about (3:52 p.m.), the primary command-and-control computer shut down, the automatic sequence showed the backup basically taking over the primary computer's functions and then the third computer, which remains in standby, that computer was brought out of standby and took over as the backup and that configuration remains the same.

"There are three command-and-control computers located in the Destiny laboratory and the station flight control team, as time permits in and around the other activity ... will continue to look at why that computer went off line earlier this afternoon. But at this point, there are no issues with any of the systems on board the station."

4:05 PM, 8/11/07, Update: Engineers troubleshoot space station computer problem

A U.S. command-and-control computer, one of three in charge of critical functions on the international space station, unexpectedly shut down today at 3:52 p.m. A backup C&C computer immediately took over and a third computer that was in standby mode reconfigured itself to serve as a "hot backup" in case of additional problems.

"The backup computer immediately kicked in and took over the functions of the primary computer and also the third computer in line, which is essentially a computer that remains in standby, that computer transitioned into the backup mode," said mission control commentator Kyle Herring. "So two of the three command-and-control computers are working just fine and there's no implication for the spacewalk or the health of the station right now."

Space station engineers are studying telemetry to figure out what happened, "but again, the backup did exactly what it was supposed to do and it took over the command-and-control functions," Herring said.

The computers are located in the U.S. Destiny laboratory module. Known as command-and-control computers, or C&C MDMs, the machines oversee the operation of the station's stabilizing gyroscopes, its high-speed communications links with Earth, the station's robot arm and other critical systems.

Each computer uses an internal hard drive to store programs and system software. Only one computer is in control at any given moment with a second serving as a hot backup and the third in standby.

During shuttle mission STS-100 in April 2001, C&C-1 suddenly dropped off line because of a hard drive problem and C&C-2, which was the backup machine, switched to primary mode. It, too, experienced hard drive errors and flight controllers decided to call up C&C-3. That computer promptly failed.

After five days of troubleshooting, engineers concluded a hard drive problem with C&C-2 was a known issue and not an outright failure. The other two computers apparently were the victims of unlikely, near-simultaneous failures of two critical hard drives."

Last June, during shuttle mission STS-117, the Russian segment's three C&C computers, along with three guidance and navigation computers, crashed after the attachment of the S4 solar array truss. The computers were recovered after commander Fyodor Yurchikhin and Oleg Kotov bypassed suspect secondary power supply surge circuitry.

Coincidentally, today's U.S. computer glitch happened while Yurchikhin and Kotov were gearing up to begin a complex 28-hour repair job to replace corroded cables leading to a computer processing unit known as BOK-3 that may have played a role in the June failures.

Spacewalkers Rick Mastracchio and Dave Williams, meanwhile, are pressing ahead with their planned six-and-a-half-hour spacewalk. They have successfully attached the S5 solar array truss segment to the right side of the station's power truss and are wrapping up a few get-ahead tasks before moving up to the central Z1 truss to lock down a cooling radiator. As of 4 p.m., the spacewalk was running about 10 minutes ahead of schedule.

02:30 PM, 8/11/07, Update: S5 truss segment bolted in place

Running 45 minutes ahead of schedule, astronauts Rick Mastracchio and Dave Williams successfully bolted a 5,000-pound spacer segment to the right end of the international space station's solar power truss today to accomplish the primary objective of the crew's first spacewalk.

The boxy truss segment was moved into position by shuttle pilot Charles Hobaugh, operating the space station's robot arm. Guided by the spacewalkers, Hobaugh positioned the S5 truss segment so that coarse alignment pins slipped into the proper holes to line up the bolts necessary to lock it in place on the end of the S4 solar array truss segment. Mastracchio and Williams then drove the bolts home to complete the installation, just under two hours into the planned six-and-a-half-hour spacewalk.

With S5 in place, the astronauts will move a robot arm grapple fixture to keel of the segment and, if time permits, make cable connections between S5 and the S4 solar arrays that will carry power and data from S6 when the new outboard arrays are attached next year.

After final cleanup work, the spacewalkers will move to the top of the station's central Z1 truss to monitor the retraction of a cooling radiator and to lock it down. The radiator is on the P6 solar array segment, mounted atop Z1 to provide power during the initial stages of station assembly. The two P6 arrays were stowed during shuttle flights in December and June and if all goes well, the segment will be moved to the left end of the main power truss in October and the arrays re-extended.

"The view is incredible," WIlliams marveled at one point.

12:37 PM, 8/11/07, Update: Spacewalk begins

Astronauts Rick Mastracchio and Dave Williams, floating in the international space station's Quest airlock module, switched their suits to internal battery power at 12:28 p.m. to officially begin a planned six-and-a-half-hour spacewalk.

The primary goal of today's excursion is to bolt a 5,000-pound truss segment known as starboard 5, or S5, in place on the far right end of the station's main solar power truss. S5, which Mastracchio and Williams will bolt to the S4 solar panel segment today, will serve as a spacer segment between the S4 and S6 arrays when the latter are attached next year.

The station's solar arrays are designed to rotate to track the sun. Before today's work began, the S4 arrays were locked in place. After Mastracchio and Williams stow a grapple fixture and complete initial connections, the S4 arrays will begin rotating again and the spacewalkers will move on to other tasks.

This is the 89th spacewalk devoted to station assembly and maintenance since construction began in 1998. Going into today's EVA, 70 men and women representing the United States, Russia, Japan, Canada, Germany, France and Sweden had logged 544 hours and 44 minutes of station spacewalk time. This is the 12th station EVA so far this year, the first of up to four planned for the shuttle Endeavour's visit and the first for Mastracchio and Williams.

See the 7:45 a.m. status report for a detailed overview of today's spacewalk.

7:45 AM, 8/11/07, Update: Astronauts prepare for spacewalk

Amid ongoing work to assess the health of the shuttle Endeavour's heat shield, astronauts Rick Mastracchio and Dave Williams are gearing up for a six-and-a-half-hour spacewalk today to attach a 5,000 pound spacer segment to the space station's main solar array truss. The two astronauts spent the night in the station's Quest airlock module at a pressure of 10.2 pounds per square inch, part of a normal "camp out" procedure to help acclimate their bodies for working in NASA's 5-psi spacesuits.

Before the spacewalk begins, the right-side S4 solar array wings, which normally rotate to track the sun, will be stopped and locked in place in preparation for the attachment of the S5 segment. S5 fits on the end of S4, serving as a spacer to provide the clearance needed by a final set of solar arrays - S6 - that will be attached next year.

"S5 is a very small piece of the space station truss segments," Mastracchio said in a NASA interview. "S4 has a large set of solar arrays on it; S6 will have another large set of solar arrays. In between S4 and S6 is obviously S5. It�s a very small piece. It�s basically an interface or an adaptor so that you could attach S6 to the first set of solar arrays."

The shuttle astronauts were awakened today at 7:39 a.m. by a recording of John Mayer's "Gravity" beamed up from mission control in Houston.

"Good morning, Endeavour," called astronaut Shannon Lucid from Houston. "And a special good morning today to you, Scorch."

"Thanks, Shannon," replied shuttle pilot Charles "Scorch" Hobaugh. "Why'd you turn the music off so quick? I'd like to thank my family for that nice selection of a song. Seems kind of appropriate and we're excited to get off to a great day with our EVA team, getting outside."

Mastracchio and Williams plan to begin their first spacewalk just after 12:30 p.m. when they switch their spacesuits to battery power a few minutes before floating out of the airlock hatch.

"It's going to be a really exciting spacewalk for us," Williams said in a NASA interview. "We're both highly trained spacewalkers, and we've both been to space, but neither one of us has actually done a spacewalk before. So, you can imagine opening the hatch of the airlock, sticking your head out, looking down at the Earth below you, traveling 25 times the speed of sound, reaching out and, handrail by handrail, moving out to the extreme limit on the starboard side of the space station.

"Once we get out there, we'll be looking out into free space as the robotic arm comes around with S5, brings it towards us, and we attach S5, driving a number of bolts with an electric power drill and doing a number of electrical connections and things. Then, once we get S5 in place, the grapple fixture that the robotic arm used to move S5 has to be moved (to permit S4 to rotate). So, we will go out right on the end of S5, the structure we just attached to the station, and we're going to grab on to this grapple fixture. I'm going to be standing in a foot restraint and Rick is going to push me around the corner of S5 and I'm going to hand off the grapple fixture to Rick.

"When I get out of that foot restraint, I no longer have handrails beside me to grab on to," Williams said. "So, I will use a tether attached to the foot restraint, reach down, pull myself out, and float freely in space tethered to this foot restraint, and pull myself back towards the space station. You can imagine what that's going to be like. We're really looking forward to it."

Here is an updated timeline of today's activity, based on the crew's revised flight day four timeline and revision D of the NASA television schedule (in EDT and mission elapsed time):

EDT............DD...HH...MM...EVENT

08/11/07
07:37 AM...02...13...00...STS/ISS crew wakeup
08:17 AM...02...13...40...EVA-1: 14.7 psi repress
08:37 AM...02...14...00...EVA-1: Hygiene break
09:02 AM...02...14...25...EVA-1: Crew lock depress to 10.2 psi
09:27 AM...02...14...50...EVA-1: Campout EVA preps
10:27 AM...02...15...50...Logistics transfers resume
10:57 AM...02...16...20...EVA-1: Spacesuit purge
10:57 AM...02...16...20...Station-to-shuttle power transfer system shut down for EVA-1
11:12 AM...02...16...35...EVA-1: Spacesuit prebreathe
12:02 PM...02...17...25...EVA-1: Crew lock depressurization
12:07 PM...02...17...30...Station arm (SSRMS) to pre-install position
12:37 PM...02...18...00...EVA-1: Airlock egress
12:52 PM...02...18...15...SSRMS support
12:52 PM...02...18...15...EVA-1: Sortie setup
01:22 PM...02...18...45...EVA-1: S4/S5 launch lock removal
01:37 PM...02...19...00...ISS: BOK-3 computer unit repair review
01:57 PM...02...19...20...SVA-1: S5 truss installation
03:07 PM...02...20...30...SSRMS ungrapples S5
03:27 PM...02...20...50...EVA-1: PVR grapple fixture relocation
03:37 PM...02...21...00...ISS: BOK-3 study
04:07 PM...02...21...30...ISS: BOK-3 preparation for repair
04:27 PM...02...21...50...EVA-1: Get ahead tasks
04:42 PM...02...22...05...EVA-1: S5 cleanup
05:17 PM...02...22...40...EVA-1: P6 forward radiator retraction
06:27 PM...02...23...50...EVA-1: Payload bay cleanup
06:42 PM...03...00...05...EVA-1: Airlock ingress
07:02 PM...03...00...25...EVA-1: Airlock repressurization
07:17 PM...03...00...40...Spacesuit servicing
08:30 PM...03...01...54...Mission status briefing on NTV
08:32 PM...03...01...55...Transfer tagup
08:52 PM...03...02...15...SSPTS re-activated
10:37 PM...03...04...00...ISS crew sleep begins
11:07 PM...03...04...30...STS crew sleep begins

08/12/07
12:00 AM...03...05...54...Daily video highlights reel on NTV
05:30 AM...03...10...54...Flight director update on NTV
07:06 AM...03...12...30...Crew wakeup

After S5 is attached, Williams and Mastracchio will move to Z1 truss, make their way up to the P6 solar array segment, monitor the retraction of a cooling radiator and then lock it in place for the move later this fall to the left end of the power truss.

"After we�re done with the S5 work, we�ll go up to P6, which is the solar array pointing zenith on the space station, and we will retract the forward radiator and cinch it down and stow it and get it ready to be moved, because P6 is going to be moved from the zenith to the port side of the space station on a future mission," Mastracchio said. "So by us retracting that radiator, it gets it ready, it�s one step closer to being ready for a move."

While the spacewalk is in progress, station Commander Fyodor Yurchikhin and flight engineer Oleg Kotov plan to begin a long, complex repair job to replace a critical component in the Russian computer system. The unit is mounted near an air conditioner in the Zvezda command module and engineers believe corrosion found on cables leading to and from the box, known as BOK-3, may have played a role in widespread computer failures during a June shuttle visit.

The new hardware was delivered to the station Aug. 5 aboard an unmanned Russian Progress supply ship. It will take the station crew four days to complete the computer overhaul and test the wiring.

NASA planners, meanwhile, are making plans for a focused inspection of the shuttle's heat shield Sunday to gather additional data on a tile that was damaged during launch, possibly by the impact of a chunk of ice. The inspection is expected to begin just after noon and an updated flight plan will be posted here as soon as it becomes available.

Flight controllers say the shuttle's new station-to-shuttle power transfer system, or SSPTS, continues to work normally, delivering some 6.5 kilowatts of electricity to the orbiter from the space station's solar power grid. The system is designed to let the shuttle reduce its use of hydrogen and oxygen for its fuel cells to remain docked at the station longer than otherwise possible.

Because power to SSPTS comes in part from the S4 solar arrays, which must be locked in place for today's spacewalk, the power transfer system will be deactivated just before 11 a.m. and restarted about a half hour after the spacewalk ends. Assuming the system continues to work normally, mission managers are expected to extend Endeavour's mission by three days and add a fourth spacewalk.

07:00 PM, 8/10/07, Update: Shuttle Endeavour docks with international space station; NASA studies possible ice-strike damage to shuttle's heat shield; focused inspection planned for Sunday

The shuttle Endeavour, deftly piloted by commander Scott Kelly, glided to a gentle docking with the international space station today after a spectacular trans-Atlantic somersault to give the lab crew a chance to inspect the orbiter's heat-shield tiles. While analysis of high-resolution digital images will take several days to complete, engineers spotted a small gouge in the heat shield tile behind the right landing gear door that may have been caused by a chunk of ice that hit the orbiter 58 seconds after launch.

John Shannon, chairman of NASA's Mission Management Team, said the astronauts will take a close-up look at the gouge Sunday, using a 50-foot-long extension to the shuttle's robot arm that is equipped with a powerful camera and a laser scanner to precisely measure the depth and extent of the damage.

In a close-up photo snapped from the station during the pitch-around maneuver today, the damage site looked relatively minor and not as extensive as past incidents of tile damage discovered after landings that caused no problems during re-entry. But in the post-Columbia era, NASA managers take no chances when it comes to heat shield damage and Shannon would not predict how the assessment might turn out.

"We have a rich flight history of tile damage, some of which is more significant looking than what we have right here," Shannon said. "But instead of guessing, we'll go and get the right characterization of exactly what the damage is and then run the thermal models and then we'll know. In the past, we didn't even know we had damage and we flew back home (safely). So what I would tell you is, we're going to do all the work required to understand it and if something is required, we'll go do that. I would not even venture to guess what the probability is we would have to go repair this."

The now-standard post-Columbia rendezvous pitch maneuver, or RPM, began at 12:56 p.m. with Endeavour about 600 feet below the station as the two craft passed just off the northeast coast of Brazil. The slow-motion back flip ended about 10 minutes later above northwest Africa. Flying from the shuttle's aft flight deck, Kelly then guided Endeavour through a slow pitch up to a point about 300 feet directly in front of the station before driving in for a precision docking at 2:02 p.m.

"Capture confirmed, Endeavour has pulled into port at the international space station," said mission control commentator Rob Navias.

A few seconds later, Expedition 15 commander Fyodor Yurchikhin rang the ship's bell mounted in the Destiny laboratory module and formally announced Endeavour's arrival.

"Endeavour arrive to ISS station," he said in English. "Welcome on board."

It took the astronauts about two hours to firmly lock the two spacecraft together, carry out leak checks and open hatches leading into the Destiny laboratory where Yurchikhin, Oleg Kotov and Clay Anderson were waiting to welcome Kelly, pilot Charles Hobaugh, Tracy Caldwell, flight engineer Rick Mastracchio, Canadian flier Dafydd Williams, Al Drew and educator-astronaut Barbara Morgan aboard.

Sporting broad smiles, the two crews hugged and shook hands amid laughter and popping camera flashes, enjoying a few moments of camaraderie before a mandatory safety briefing from Yurchikhin. Teacher-turned-astronaut Morgan, Christa McAuliffe's backup in the original Teacher in Space program, floated through the laboratory operating a movie camera for an educational video, grinning broadly and clearly enjoying herself.

A few minutes earlier, before the shuttle crew floated into the station, Caldwell unlimbered Endeavour's 50-foot-long robot arm and latched onto a 5,000-pound solar array truss segment in the shuttle's cargo bay. After the safety briefing, she moved back to the shuttle's flight deck and used the robot arm to carefully pull the boxy S5 truss from its perch in the cargo bay, starting shortly before 5 p.m.

A half hour later, Hobaugh, operating the space station's robot arm from a work station inside Destiny, locked onto the truss segment and Caldwell disengaged the shuttle arm. Hobaugh then maneuvered it to an overnight park position near the right side of the station's main solar power truss. If all goes well, the segment will be bolted to the far right end of the main truss Saturday during a spacewalk by Mastracchio and Williams. Both men plan to spend the night in the station's Quest airlock module at a reduced pressure of 10.2 pounds per square inch to help purge nitrogen from their blood in preparation for the spacewalk Saturday.

Late today, the astronauts activated a new shuttle-to-station power transfer system, or SSPTS, and Endeavour began drawing 6.5 kilowatts of electricity from the station's solar power grid. Using station electricity, the shuttle crew can reduce the consumption of hydrogen and oxygen by the ship's three electricity producing fuel cells. If the new system works as expected, NASA managers are expected to extend Endeavour's mission by three days and add a fourth spacewalk. A decision could come as early as Sunday.

Sunday, the crew's flight day five, is also the day the astronauts will carry out a focused inspection of the shuttle's heat shield to measure the extent of the gouge on the underside of the shuttle. During the climb to space Wednesday, a camera mounted on the shuttle's external tank spotted about nine small bits of foam debris falling away, including three that may have struck the orbiter. The debris in question was the second one, seen at about 58 seconds.

The best close-up picture from today's RPM shows an area of white in roughly the center of a 6-by-6-inch black tile midway between the shuttle's right side main landing gear door and the right-side door that covers a propellant feedline inlet. Shannon said the area of damage on the tile in question appears to measure less than three inches across.

On Thursday, ascent video showed a spray of whitish material streaming away from the shuttle's underside after the impact, presumably from a piece of foam that hit the belly of the orbiter. Today, based on analysis of radar data, engineers believe the debris may have been the remnant of a small chunk of ice.

"If you remember yesterday, I said we had one debris event where we saw a streak, or potentially a spray of some material from the underside of the vehicle, at 58 seconds," Shannon said. "That was tracked by radar and the ballistic coefficient, or how that particle was tracked, looked more like ice than foam. Yesterday, we were thinking it might be foam. Today, that radar data says it looked like ice and we're going to continue to go look at that. It perked up our ears a little bit because ice is much more dense, of course, than foam and it can do more damage to tile. ... So that was interesting."

Describing a close-up picture from today's rendezvous pitch maneuver, Shannon said it as difficult to assess the extent of the damage "because it's just not a great picture and there's a little bit of shading on here. We think potentially the black streak in the middle of that white hole is just a shadow. But you can almost see some color where that tile comes up against some other tile. Potentially, that color is the material on the edge of the tile at the very base of the aluminum structure, It's called filler bar material. We don't know that for a fact, but it's certainly got our attention and we're looking at it."

Columbia was brought down during re-entry Feb. 1, 2003, by a gaping hole in one of the left wing's leading edge panels caused by the impact of a briefcase-size piece of foam debris during launch. Among NASA's post-Columbia upgrades are heat shield repair techniques that could be used by spacewalkers to fix relatively minor pits and dings. The options range from application of a black "emittance wash" paint-like material to restore lost heat rejection capability, to a thick goo-like material known as STA-54 that can fill in large voids. A third option is to screw on a carbon composite overlay, depending on the extent of the damage.

The Endeavour astronauts are trained for all such repair techniques but Shannon said any such talk is premature until all the data are in.

"What does this mean? I don't know at this point," he said. "On flight day five (Sunday), we had preplanned a time in the timeline when we could do a focused inspection and we will do that on this spot. ... They will take the orbiter boom sensor system with the laser on it, they wlll put it underneath the vehicle and get a very high fidelity model of exactly what the dmaage is. It's too hard to tell from a two-dimensional picture with different shading to tell if this gouge is deep or it's not deep.

"So we'll put the laser on it and we'll get an exact size of it, we'll get a cloud model of exactly what the gouge looks like. And then we have extremely accurate thermal models to say given this particular gouge what would that mean for re-entry. And that's the work that's going to go on."

11:15 AM, 8/10/07, Update: Final rendezvous sequence begins

Trailing the international space station by about 9.2 miles, shuttle commander Scott Kelly and pilot Charles Hobaugh fired Endeavour's left-side orbital maneuvering system rocket for nine seconds today at 11:15 a.m., changing the orbiter's velocity by less than 5 mph to begin the terminal phase of today's rendezvous and docking with the lab complex.

The so-called "TI" rocket firing, and subsequent small adjustments, should bring Endeavour to a point directly below the outpost by around 12:45 p.m. If all goes well, Kelly will guide the shuttle to a docking at the front end of the station around 1:54 p.m. See the 9:30 a.m. status report for a detailed timeline.

9:30 AM, 8/10/07, Update: Shuttle Endeavour closes in on space station

The shuttle Endeavour is closing in on the international space station this morning, on track for a docking around 1:54 p.m. The terminal phase of the rendezvous begins at 11:16 a.m. when commander Scott Kelly and pilot Charles "Scorch" Hobaugh fire the shuttle's maneuvering rockets to begin moving in from a point about 9.2 miles behind the space station.

A few minutes before 1 p.m. - about an hour before docking - the shuttle will move into position some 600 feet directly below the space station. At that point, Kelly will guide the orbiter through a slow 360-degree back flip, exposing the shuttle's belly and critical heat-shield tiles to the crew aboard the station.

Expedition 15 commander Fyodor Yurchikhin, flight engineer Oleg Kotov and Clay Anderson will film the maneuver using video and digital still cameras equipped with 400 mm and 800 mm lenses to capture high-resolution images of Endeavour's heat shield.

It will take about 10 minutes to complete the rendezvous pitch maneuver. After that, Kelly plans to guide Endeavour in an arc up to a point about 300 feet directly in front of the space station with the shuttle's nose pointed toward deep space and its open payload bay facing the front end of the lab complex. From there, Kelly will carefully guide Endeavour in to a docking at pressurize mating adapter No. 2 on the front end of the Destiny laboratory module.

"The rendezvous will be pretty much a standard rendezvous as you've seen before," said shuttle flight director Matt Abbott. "We'll approach from behind and below the station. When we come to a point about 600 feet below the station on what we call the R-bar, we'll do the R-bar pitch maneuver, sometimes called the rendezvous pitch maneuver, which is the 360-degree back flip that allows the space station crew Fyodor and Oleg to take photographs of the underside of the vehicle. So we'll get some high resolution photographs of the tiles and all the thermal protection system to be able to analyze that on the ground and make sure it's all in good shape.

"After the RPM is complete, Scott and Scorch will transition the vehicle up to what we call the V-bar, the velocity vector, which is out in front of the direction the space station is traveling. And then Scott will begin a slow and methodical manual approach into docking on PMA-2. There's a little pause at 30 feet, which allows the crew the ability to fly out any angular errors, which we may or may not need to do, and then we go in and dock."

As with the past several station assembly missions, docking is merely one more step in a busy day of work. While part of the crew carries out leak checks and works to open hatches between the two spacecraft, astronaut Tracy Caldwell plans to use the shuttle's robot arm to pull a 5,000-pound solar array truss segment known as S5 from Endeavour's cargo bay.

After hatches are opened and the station crew welcomes their shuttle colleagues aboard, Hobaugh will use the station's robot arm to latch onto S5. He then will move the truss segment to an overnight park position near the right side of the station's solar array truss where it will remain until installation Saturday.

"After docking, we have about two hours of hatch operations, leak checks, configuration of the shuttle to kind of get ready for the docked mission," said station flight director Joel Montalbano. "While we're doing the hatch checks and getting the EVA suits ready and getting everything ready for docked operations, we'll go ahead and grapple the S5. We'll have a short safety briefing, a meet and greet, and then it's down to work pretty quickly.

"We have a rule that we only move one of the robotic arms at a time and so, prior to (Caldwell) moving the S5 out of the payload bay, Scorch will have positioned the station arm to be ready for handoff. Tracy will go ahead and take the payload to Scorch and again, we're using different camera views on board the shuttle assets and station assets on both robotics teams to make sure they have good views. What will happen is Scorch will go ahead and grab the S5 payload. The shuttle arm will back off and we'll stay in that position overnight."

The S5 truss segment will be attached Saturday during a spacewalk by astronauts Rick Mastracchio and Dave Williams. Both astronauts will spend the night in the station's Quest airlock module at a reduced pressure of 10.2 pounds per square inch to help purge their bodies of nitrogen. The low-pressure airlock "camp out" is needed to help prevent the bends after working in NASA's 5-psi spacesuits.

Here is an updated timeline of critical events, based on the crew's rendezvous timeline, revision D of the NASA television schedule and the crew's flight plan (in EDT and mission elapsed time; NOTE: NASA rounds down to the nearest minute while this page rounds up or down as required):

EDT........DD...HH...MM...EVENT

08/10/07

07:37 AM...01...13...00...STS/ISS crew wakeup
08:30 AM...01...13...54...NASA video file on NTV
08:42 AM...01...14...05...Group B computer powerup
08:57 AM...01...14...20...Begin rendezvous timeline
09:45 AM...01...15...08...NC-4 rendezvous rocket firing
10:47 AM...01...16...10...Spacehab prepped for docking
11:16 AM...01...16...39...TI rendezvous burn; Range: 9.2 miles
11:27 AM...01...16...50...Spacesuit removal
11:52 AM...01...17...15...Sunset
12:00 PM...01...17...23...U.S. solar arrays feathered
12:14 PM...01...17...37...Range: 10,000 feet
12:23 PM...01...17...46...Range: 5,000 feet
12:24 PM...01...17...47...Sunrise
12:29 PM...01...17...52...Range: 3,000 feet
12:33 PM...01...17...56...MC-4 rendezvous rocket firing
12:37 PM...01...18...00...Approach timeline begins
12:37 PM...01...18...00...Range: 1,500 feet
12:38 PM...01...18...01...Rendezvous pitch maneuver (RPM) start window open
12:42 PM...01...18...05...Range: 1,000 feet
12:45 PM...01...18...08...KU antenna to low power
12:46 PM...01...18...09...Shuttle directly below ISS
12:51 PM...01...18...14...Range: 600 feet
12:53 PM...01...18...16...Start rendezvous pitch maneuver
12:54 PM...01...18...17...Noon
01:01 PM...01...18...24...End rendezvous pitch maneuver
01:01 PM...01...18...24...RPM full photo window close
01:03 PM...01...18...26...Initiate pitch up maneuver
01:09 PM...01...18...32...RPM start window close
01:15 PM...01...18...38...Shuttle directly in front of station; range: 310 feet
01:16 PM...01...18...39...Range: 300 feet
01:20 PM...01...18...43...Range: 250 feet
01:23 PM...01...18...46...Sunset
01:24 PM...01...18...47...Range: 200 feet
01:27 PM...01...18...50...Range: 170 feet
01:28 PM...01...18...51...Range: 150 feet
01:32 PM...01...18...55...Range: 100 feet
01:35 PM...01...18...58...Range: 75 feet
01:40 PM...01...19...03...Range: 50 feet
01:43 PM...01...19...06...Range: 30 feet; start station keeping
01:48 PM...01...19...11...End station keeping; push to dock
01:52 PM...01...19...15...Range: 10 feet

01:54 PM...01...19...17...DOCKING

01:56 PM...01...19...19...Sunrise
02:17 PM...01...19...40...Leak checks
02:17 PM...01...19...40...Post-rendezvous laptop reconfig
02:47 PM...01...20...10...Airlock prepped for ingress
02:57 PM...01...20...20...Group B computer powerdown
03:17 PM...01...20...40...Shuttle arm (SRMS) grapples S5
03:22 PM...01...20...45...Hatch opening
03:32 PM...01...20...55...Spacehab post-docking reconfig
03:32 PM...01...20...55...SRMS unberths S5
04:02 PM...01...21...25...Welcome aboard!
04:07 PM...01...21...30...Safety briefing
04:32 PM...01...21...55...Station arm (SSRMS) moves to pre-grapple position
04:52 PM...01...22...15...SRMS maneuvers
05:22 PM...01...22...45...SSRMS grapples S5
05:30 PM...01...22...54...Mission status briefing on NASA TV
05:37 PM...01...23...00...SRMS ungrapples S5
05:37 PM...01...23...00...Equipment lock prep
06:07 PM...01...23...30...REBA checkout
06:22 PM...01...23...45...EVA tools transferred to ISS
06:37 PM...02...00...00...Station-to-shuttle power transfer system activated
06:42 PM...02...00...05...EVA-1: Tools prepped
07:22 PM...02...00...45...EVA-1: Procedures review
10:02 PM...02...03...25...EVA-1: Mask pre-breathe
10:47 PM...02...04...10...EVA-1: Airlock depress to 10.2 psi
11:07 PM...02...04...30...ISS crew sleep begins
11:37 PM...02...05...00...STS crew sleep begin
08:07 AM...02...13...30...STS/ISS crew wakeup

10:50 PM, 8/9/07, Update: Morgan describes first impressions of space

In her first downlink from space, teacher-turned-astronaut Barbara Morgan took a few moments late Thursday to describe her initial impressions of space, saying she felt upside down during her first day in orbit despite her best efforts to stay oriented.

"Hey, it's great being up here," Morgan said, appearing in a brief "crew choice" video downlink with Endeavour commander Scott Kelly. "We've been working really hard, but it's a really good, fun kind of work, so we're really having a great time and we're very much looking forward to docking with the international space station tomorrow and joining in with our crewmates, Clay (Anderson), Oleg (Kotov) and Fyodor (Yurchikhin).

"One thing I wanted to tell you about was when you first get into orbit, it takes a little getting used to," she said. "And all of yesterday, even though I kept my head upright so it looked like a normal ceiling and a normal floor and normal walls, I felt like I was upside down the whole time.

"And the other surprise is, when you have something that you just set aside, even if it has Velcro on it, you set it aside and within 30 seconds it's gone again, no idea where it went to. So we've got a lot of fun challenges up here and we'll be playing some treasure hunts."

7:13 PM, 8/9/07, Update: Engineers say shuttle tank foam performed well; only three small bits of debris under study; oxygen tank sensor issue no threat to mission

Preliminary analysis of launch photography indicates about nine small bits of foam insulation came off the shuttle Endeavour's external fuel tank during the climb to space Wednesday. But only three are believed to have possibly struck the orbiter and there are no obvious signs of any impact damage, officials said today.

"Very quiet day at the Mission Management Team," said MMT Chairman John Shannon. "It looked like the launch was extremely successful yesterday. About all we did in the way of data assessment was, we looked at the external tank photography that's automatically taken at separation and we saw nothing significant. It looks like the tank has been very consistent over the last several flights and there was good performance out of it from a debris standpoint. We're not looking at anything significant at all."

The three incidents listed by Shannon occurred at 24, 58 and 173 seconds after launch. The first incident may have involved a bit of "purge barrier" used around a propellant feed line prior to launch that appeared to strike the rear of the shuttle's body flap. Similar debris events have been seen on past flights and no major damage was found.

The second piece of debris appeared to cause slight discoloration, or a spray, when it hit the shuttle's right wing, but Shannon said "it's really, really hard to see" and engineers do not believe it represents a serious problem. The third event happened well beyond the first 135 seconds of flight when the air is still thick enough to produce the kind of impact velocities that can cause damage.

Shannon said all three areas will be photographed in detail Friday - along with the rest of the shuttle's heat shield - during final approach to the international space station. In a now-routine post-Columbia maneuver, commander Scott Kelly will guide Endeavour through a slow 360-degree back flip just a few hundred feet below the lab complex so the station crew can photograph the heat shield with powerful digital cameras.

It will take several more days for analysts to review launch photography, radar data and wing leading edge sensor data recorded during launch and laser scans of the shuttle's nose cap and wing leading edge panels that were carried out by the astronauts today. Along with the rendezvous pitch maneuver photography expected Friday, engineers also must assess film from cameras mounted in the shuttle's twin solid-fuel boosters that will provide additional views of Endeavour's fuel tank. Shannon said film from the boosters should be in hand by late this weekend, after the spent boosters are towed back to port.

Along with giving engineers high-resolution views of the heat shield, the rendezvous pitch maneuver Friday also is expected to confirm two doors on the belly of the shuttle that cover propellant feedline inlets after external tank separation are properly closed for re-entry.

"We believe the ET doors are closed as expected," said shuttle flight director Matt Abbott. "We did see a few indications early on that things may have been, in terms of the mechanism, not completely seating. But that later cleared. We'll be looking at the photography taken during the r-bar pitch maneuver tomorrow, which will help make us very confident the doors are closed."

Abbott said engineers were continuing to develop plans to cope with the failure of a pressure sensor controller that has disabled the automatic system used to activate and deactivate heaters used by liquid oxygen tank No. 2 in the shuttle's fuel cell system. The shuttle uses three fuel cells that combine oxygen and hydrogen to produce electricity and, as a by product, water.

"In order to force the oxygen and hydrogen out of the tanks, we require heaters that cycle on and off," Abbott said. "As the heaters come on and build up pressure in the tank, it forces the oxygen ... out of the tanks. With the failure, we're going to have to use manual heater control, the automatic control is not functional on that tank, and that's going to mean a little bit of a change in some of our planning for the rest of the mission."

Engineers consider the issue an inconvenience and Abbott said he didn't expect any impact on the mission.

"It will probably develop into an every-other-day kind of thing," he said. "It will require some baby-sitting in terms of probably every 30 to 45 minutes early on to power the heaters on and power them back off. Later on in the mission, it will get to where the heaters need to be on for maybe four or five minutes and then off for an hour and a half or so. It'll vary as the oxygen is used up out of the tank. We don't really have any concerns about being able to do that, we have plenty of days where we've got the crew on the flight deck and they'll be able to handle that without any problem."

Abbott said the pressure control problem is the only glitch of any significance and that given Endeavour is making its first flight since December 2002, "the vehicle is very, very clean."

"It's really a testament to the fantastic job the folks at the Kennedy Space Center did over the past four-and-a-half years getting the vehicle ready to fly," he said.

10:00 AM, 8/9/07, Update: Astronauts work through busy day in space

The Endeavour astronauts are working through a busy first full day in space, completing setup of the ship's laptop computer network, checking out their spacesuits and carrying out an exhaustive inspection of the shuttle's nose cap and wing leading edge panels later this afternoon.

Early today, the shuttle was trailing the international space station by 1,242 miles, closing the gap at about 160 miles per 90-minute orbit. Two rendezvous rocket firings are planned today to fine tune Endeavour's ongoing rendezvous and if all goes well, commander Scott Kelly will guide the shuttle to a linkup with the lab complex around 1:54 p.m. Friday.

The astronauts were awakened during their sleep period earlier today when an alarm sounded because of apparent low pressure in one of the five liquid oxygen tanks in the shuttle's fuel cell system. Flight controllers initially thought the alarm was the result of an instrumentation problem, but they now suspect the pressure controller for oxygen tank No. 5 has failed.

By manually activating and deactivating tank heaters, the astronauts can control the pressure in the tank and the flow of oxygen to the fuel cell system. Engineers view the problem as an inconvenience at this point and barring additional trouble, it is not expected to have an impact on the mission.

The highlight of today's activity in space is a detailed inspection of the shuttle's nose cap and wing leading edge panels, the reinforced carbon composite panels that experience the most extreme heating during re-entry. The inspection is a now-standard part of every shuttle mission to look for signs of impact damage following launch.

Today's inspection will be carried out by Tracy Caldwell and Rick Mastracchio, with assistance from pilot Charles Hobaugh and Barbara Morgan. Using an instrumented 50-foot-long boom on the end of the shuttle's robot arm, the astronauts will make laser scans and take high-resolution pictures of the nose cap and and wing leading edge panels for analysis on the ground.

The inspection work will begin around 12:22 p.m. and take some five hours to complete.

Here is an updated timeline of today's activity in space (in EDT and mission elapsed time; note: NASA rounds down to the nearest minute; this page rounds up or down as required. As a result, times listed below may disagree slightly with NASA's television schedule):

08/09/07
08:37 AM...00...14...00...Crew wakeup
10:37 AM...00...16...00...Laptop computer setup (part 2)
10:39 AM...00...16...02...NC2 rendezvous rocket firing
11:22 AM...00...16...45...OBSS unberth
11:47 AM...00...17...10...Spacesuit checkout preps
12:22 PM...00...17...45...OBSS starboard wing survey
12:27 PM...00...17...50...Spacesuit checkout
02:17 PM...00...19...40...OBSS nose cap survey
02:47 PM...00...20...10...Ergometer setup
03:17 PM...00...20...40...OBSS port wing survey
03:17 PM...00...20...40...Logistics transfer preps
04:17 PM...00...21...40...Crew meals begin
05:32 PM...00...22...55...OBSS berthing
06:00 PM...00...23...24...Mission status briefing on NTV
06:17 PM...00...23...40...Centerline camera installation
06:17 PM...00...23...40...Spacesuit transfer preps
06:17 PM...00...23...40...OMS pod survey
06:47 PM...01...00...10...Orbiter docking system ring extension
06:47 PM...01...00...10...LDRI downlink
06:52 PM...01...00...15...Rendezvous tools checkout
07:52 PM...01...01...15...EVA tools transfer preps
08:57 PM...01...02...20...Morgan/Kelly downlink on NTV
10:00 PM...01...03...23...NC3 rendezvous rocket firing
11:37 PM...01...05...00...Crew sleep begins
12:00 AM...01...05...24...Flight Day 2 highlights on NTV

For readers interested in a look ahead, here is an updated rendezvous timeline for Friday's docking with the international space station (in EDT and mission elapsed time):

DATE/EDT...DD...HH...MM...EVENT

08/10/07
11:00 AM...01...16...23...ISS in attitude
11:16 AM...01...16...39...TI burn; range: 9.2 miles
11:52 AM...01...17...15...Sunset
12:00 PM...01...17...23...US arrays feathered
12:14 PM...01...17...37...Range: 10,000 feet
12:23 PM...01...17...46...Range: 5,000 feet
12:24 PM...01...17...47...Sunrise
12:29 PM...01...17...52...Range: 3,000 feet
12:33 PM...01...17...56...MC-4 rendezvous burn
12:37 PM...01...18...00...Range: 1,500 feet
12:38 PM...01...18...01...RPM start window open
12:42 PM...01...18...05...Range: 1,000 feet
12:45 PM...01...18...08...KU antenna to low power
12:46 PM...01...18...09...+R bar arrival directly below ISS
12:51 PM...01...18...14...Range: 600 feet
12:53 PM...01...18...16...Start pitch maneuver
12:54 PM...01...18...17...Noon
01:01 PM...01...18...24...End pitch maneuver
01:01 PM...01...18...24...RPM full photo window close
01:03 PM...01...18...26...Initiate pitch up maneuver
01:09 PM...01...18...32...RPM start window close
01:15 PM...01...18...38...+V bar arrival; range: 310 feet
01:16 PM...01...18...39...Range: 300 feet
01:20 PM...01...18...43...Range: 250 feet
01:23 PM...01...18...46...Sunset
01:24 PM...01...18...47...Range: 200 feet
01:27 PM...01...18...50...Range: 170 feet
01:28 PM...01...18...51...Range: 150 feet
01:32 PM...01...18...55...Range: 100 feet
01:35 PM...01...18...58...Range: 75 feet
01:40 PM...01...19...03...Range: 50 feet
01:43 PM...01...19...06...Range: 30 feet; start station keeping
01:48 PM...01...19...11...End station keeping; push to dock
01:52 PM...01...19...15...Range: 10 feet
01:54 PM...01...19...17...DOCKING
01:56 PM...01...19...19...Sunrise

7:08 PM, 8/8/07, Update: Shuttle Endeavour thunders into space (UPDATED at 9:15 p.m. with Griffin comments on astronaut medical probe)

The shuttle Endeavour, making its first flight since the 2003 Columbia disaster, blasted off today on a space station assembly mission carrying a crew of seven that includes teacher-turned-astronaut Barbara Morgan, Christa McAuliffe's backup in the original Teacher in Space program.

With its three hydrogen-fueled main engines roaring at full throttle, Endeavour's twin solid-fuel boosters flashed to life at 6:36:42 p.m. and the 4.5-million-pound spacecraft vaulted away from launch complex 39A at the Kennedy Space Center atop a churning cloud of fire and exhaust.

Climbing straight up into a hot, hazy Florida sky, Endeavour rolled about its vertical axis into a heads down position below the external tank and rocketed away to the northeast on a trajectory paralleling the East Coast.

One minute after launch, the shuttle had burned up half its weight in fuel and a minute and four seconds after that, at an altitude of 29 miles and a velocity of some 3,650 mph, Endeavour's solid-fuel boosters were jettisoned and the orbiter continued its climb to space on the power of its three main engines.

Endeavour completed its last mission in December 2002 - the flight before Columbia's ill-fated voyage - and despite years of down time to complete a thorough overhaul and to upgrade critical systems, NASA's newest shuttle - built to replace Challenger and named by school kids - sailed through a near-flawless countdown.

"The weather's great, Endeavour is ready to fly after four-and-a-half years so good luck, Godspeed and have some fun up there," Launch Director Mike Leinbach radioed the crew minutes before liftoff.

"Thanks, Mike," commander Scott Kelly replied. "This is a serious business we're in here. I'm proud of your team for getting Endeavour ready to go fly. I'm also proud of my crew and the rest of the astronaut office for their competence and professionalism for consistently making something that is incredibly difficult look easy. We'll see you in a couple of weeks and thanks for loaning us your space shuttle."

"Good, Scott, thanks a lot," Leinbach said. "Take good care of that great ship, Endeavour."

Kelly's comments followed a recent letter he wrote to the media, strongly defending the astronaut office in the wake of a NASA-chartered medical report that included anecdotal allegations of at least some instances of alcohol abuse in the past. NASA is currently carrying out an internal investigation to determine whether the alleged incidents actually occurred. So far, NASA Administrator Mike Griffin said today, investigators have not found any evidence supporting the allegations in the report.

"We are conducting a full-scale investigation, flight by flight, to determine whether it's even reasonable or possible that a crew under the influence of alcohol got on a space shuttle, or a Soyuz or third, on a T-38 (jet trainer)," he said. "We'll look at all that. Right now, we've gone back 10 years. And we can't even find where it would be a possibility that there was a crew under the influence on either a (Russian) Soyuz or a shuttle."

But Griffin stressed the probe is not yet complete. The allegations are "extremely serious," he said, and "I take it as my responsibility to find out."

Endeavour chalked up a picture-perfect climb to space with no obvious signs of external tank foam debris that might pose a threat to the ship's heat shield. Eight-and-a-half minutes after liftoff, at an altitude of 65 miles, the shuttle's three main engines shut down and the spacecraft slipped into its planned preliminary orbit, racing through space at some five miles - 88 football fields - per second. Kelly and pilot Charles Hobaugh fired the ship's orbital maneuvering system engines 37 minutes after launch to raise the low point of Endeavour's orbit and put the ship on course for a Friday linkup with the international space station.

Joining Kelly, Hobaugh and Morgan aboard Endeavour were Tracy Caldwell, flight engineer Rick Mastracchio, Canadian flier Dafydd Williams and Al Drew.

Morgan, who was selected as McAuliffe's backup on July 19, 1985, has waited 21 years to fulfill the legacy of the Teacher in Space, becoming a full-fledged NASA astronaut in 1998. She originally hoped to fly in late 2003, but the mission, originally planned for Columbia, was put on hold when that shuttle crashed during re-entry.

"I am going up doing the job of an astronaut, the work of an astronaut, but I'm going up with a teacher's eyes, ears, heart and mind," Morgan said in an interview. "And so I look very much forward to doing that with an open mind and being able to come back and ... translate that into how can we best provide wonderful opportunities for our colleagues and our students."

NASA managers were eager to get Endeavour back into orbit after a four-and-a-half-year hiatus. Now sporting state-of-the-art satellite navigation gear and converters to tap into the space station's solar power grid, Endeavour should be able to reduce the load on its own generators and stay docked at the lab complex longer than any previous flight.

"The return of Endeavour to flight status is personally an emotional milestone for me," said Program Manager Wayne Hale, who served as ascent/entry flight director during Endeavour's last mission in November 2002. "It's like a new space shuttle. It's been completely inspected from stem to stern for any defects in the wiring, any structural corrosion and it's come out clean. It's like driving a new car off the showroom floor."

Going into the mission, the flight is officially planned for 11 days and includes three spacewalks. But if the shuttle-to-station power transfer system works as expected, the flight will be extended three days and a fourth spacewalk will be added. Under either scenario, Endeavour is expected to dock with the space station Friday around 1:51 p.m. If the flight is not extended, the shuttle will undock on Aug. 17 and land two days later. In the extended mission scenario, Endeavour would undock Aug. 20 and land on Aug. 22.<

The goals of shuttle mission STS-118 include installation of a 5,000-pound solar array spacer segment; replacement of a critical stabilizing gyroscope; installation of a 7,000-pound external equipment storage platform; and delivery of fresh water and some 5,000 pounds of needed hardware and supplies.

While the shuttle astronauts are plowing through their busy schedule, the space station crew - Expedition 15 Commander Fyodor Yurchikhin, Oleg Kotov and Clay Anderson - will carry out a long, complex repair job to replace a critical component in the Russian computer system. The unit is mounted near an air conditioner in the Zvezda command module and engineers believe corrosion found on cables leading to and from the box may have played a role in widespread computer failures during a June shuttle visit.

The new hardware was delivered to the station Aug. 5 aboard an unmanned Russian Progress supply ship. It will take the station crew four days to complete the computer overhaul and test the wiring.

"It's got a little bit of everything," lead shuttle Flight Director Matt Abbott said of Endeavour's mission. "We've got some assembly operations with the S5 truss installation, some repair operations with the control moment gyroscope replacement, a lot of resupply - the Spacehab module has about 5,000 pounds of cargo going up in it and we'll bring back about 4,000 pounds of cargo. We've also got some external spares to be installed on the outside of the station, we've got some science going on, several middeck payloads and really a very, very busy timeline."

Endeavour's flight will clear the way for a dramatic shuttle mission in October to move a huge set of stowed solar arrays to the far left end of the station's main power truss and attach a multi-hatch node called Harmony. The new module, temporarily mounted on the left side of the central Unity compartment, will be moved to the front of the station after the shuttle departs, providing docking ports for European and Japanese research modules scheduled for launch in December and early next year.

"It's an awesome schedule," Griffin said in an interview Tuesday. "We think we know what to do. We've had some pretty awesome flights in the recent past on space station assembly and we expect the upcoming ones to surpass them. So I would say stay tuned.

"I have frequently characterized space station assembly as the greatest construction project human beings have ever attempted," he said. "And I believe when you take it all in, that that's true. There is and there will continue to be much debate on the scientific merits of the space station and I think there should be that debate, that's fine. We will find a way to utilize the space station to help benefit human exploration of the solar system. But leaving all of that aside, it is the most amazing construction project ever attempted by human beings."

On a more human level, Morgan's journey from an Idaho classroom to the space shuttle has generated widespread interest in Endeavour's mission.

Morgan was selected on July 19, 1985, to train as McAuliffe's backup in NASA's original Teacher in Space program. McAuliffe and seven crewmates died in the Jan. 28, 1986, Challenger disaster but Morgan never gave up her dream of carrying education to the final frontier.

"This mission is symbolic and I know that people will be thinking about not just Christa, but the Challenger crew and the Challenger mission. And that's a good thing. And I know they will be thinking about so many people over the years, the families, friends, colleagues and people the Challenger crew never ever even knew ... who for so many years have been working so hard at continuing on their work and their dreams."

As a full-fledged astronaut, Morgan will not teach any lessons from space as McAuliffe once planned. A few modest educational events are planned, but her focus will be on mission-critical work, operating the shuttle's robot arm and overseeing logistics transfer activity.

"I know people are going to think about Challenger, and they should," Morgan said. "And I want people to remember what great folks they were and that what happened with Challenger was wrong, but what the crew and NASA was trying to do was absolutely right. I'm grateful that we are continuing that."

5:01 PM, 8/8/07, Update: Astronauts strap in; shuttle hatch closed for launch

Wearing bright-orange pressure suits, commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, flight engineer Rick Mastracchio, Canadian flier Dafydd "Dave" Williams, Al Drew and educator-astronaut Barbara Morgan climbed into the orbiter and strapped in for liftoff today on a space station assembly mission.

Forecasters are now predicting a 90 percent chance of good weather for tonight's launch try and there are no technical problems of any significance at the pad. Liftoff remains targeted for 6:36:42 p.m. This status report will be updated after Endeavour takes off or as conditions warrant.

1:02 PM, 8/8/07, Update: Shuttle fueling complete

The shuttle Endeavour's external tank has been loaded with a half-million gallons of liquid oxygen and hydrogen rocket fuel. There are no technical problems of any significance and forecasters continue to predict good weather for this evening's launch.

Endeavour's crew - commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, flight engineer Rick Mastracchio, Canadian flier Dafydd Williams, Al Drew and educator-astronaut Barbara Morgan - were awakened shortly after 9 a.m. At a traditional launch-day photo op just before 12:30 p.m., the astronauts appeared relaxed and at ease in crew quarters.

After a final weather briefing, the astronauts will suit up and head for the launch pad around 2:45 p.m. Launch remains targeted for 6:36:42 p.m.

09:00 AM, 8/8/07, Update: Shuttle fueling begins

Working by remote control, engineers at the Kennedy Space Center began pumping a half-million gallons of supercold liquid oxygen and liquid hydrogen rocket fuel into the shuttle Endeavour's external tank early today, setting the stage for launch on a space station assembly mission at 6:36:42 p.m.

The three-hour-long fueling process began at 8:11 a.m. with transfer line chilldown and should be complete by around 11:15 a.m. Forecasters are continuing to predict an 80 percent chance of acceptable weather.

There are no technical problems of any significance at pad 39A and if all continues to go well, Endevour's crew - commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, Rick Mastracchio, Dave Williams, educator-astronaut Barbara Morgan and Al Drew - will begin strapping in around 3:15 p.m.

Liftoff is scheduled for 6:36:42 p.m., roughly the moment Earth's rotation carries the launch pad into the plane of the international space station's orbit. The launch window for a Friday linkup with the station closes at 6:41:42 p.m. But if problems develop, mission managers can extend the window an additional three minutes and 14 seconds, to 6:44:56 p.m., which would set up a Saturday docking.

A Friday docking is preferred, but Endeavour is equipped with a new station-to-shuttle power transfer system that would enable the crew to make up a lost day if necessary.

Here is a timeline of today's countdown activities, key ascent events and the crew's evening in orbit. All times in EDT (ascent velocities include a component of Earth's rotation):

EDT...........EVENT

..............COUNTDOWN

08:11 AM......Liquid oxygen, hydrogen transfer line chilldown
08:21 AM......Main propulsion system chill down
08:21 AM......LH2 slow fill
08:30 AM......NASA TV coverage begins
08:41 AM......Resume countdown (T-minus 6 hours)
08:51 AM......LO2 slow fill
08:56 AM......Hydrogen engine cutoff sensors go wet
08:59 AM......Astronaut wakeup
09:01 AM......LO2 fast fill
09:11 AM......LH2 fast fill
10:26 AM......LH2 topping
11:06 AM......LH2 replenish
11:11 AM......LO2 replenish

11:41 AM......Begin 3-hour built-in hold (T-minus 3 hours)
11:41 AM......Closeout crew to white room
11:41 AM......External tank in stable replenish mode
11:56 AM......Astronaut support personnel comm checks
12:26 PM......Pre-ingress switch reconfig
12:29 PM......Astronaut photo opportunity
02:06 PM......Final crew weather briefing
02:16 PM......Astronauts don pressure suits
02:41 PM......Resume countdown (T-minus 3 hours)

02:46 PM......Astronauts depart crew quarters
03:16 PM......Crew reaches launch pad; begins strapping in
04:06 PM......Astronaut communications checks
04:21 PM......Hatch closure
05:16 PM......White room closeout

05:21 PM......Begin 10-minute built-in hold (T-minus 20m)
05:31 PM......NASA test director countdown briefing
05:31 PM......Resume countdown (T-minus 20m)

05:32 PM......Backup flight computer to OPS 1 software
05:36 PM......KSC area clear to launch

05:42 PM......Begin final built-in hold (T-minus 9m)
06:12 PM......NASA test director launch status verification
06:27:42 PM...Resume countdown (T-minus 9m)

06:29:12 PM...Orbiter access arm retraction
06:31:42 PM...Launch window opens
06:31:42 PM...Hydraulic power system (APU) start
06:31:47 PM...Terminate liquid oxygen replenish
06:32:42 PM...Purge sequence 4 hydraulic test
06:32:42 PM...Inertial measurement units to launch mode
06:32:47 PM...Aerosurface movement check
06:33:12 PM...Main engine steering test
06:33:47 PM...Oxygen tank pressurization
06:34:07 PM...Fuel cells to internal reactants
06:34:12 PM...Clear caution-and-warning memory
06:34:42 PM...Crew closes visors
06:34:45 PM...Hydrogen tank pressurization
06:35:52 PM...Solid-fuel booster joint heater deactivation
06:36:11 PM...Shuttle computers take control of countdown
06:36:21 PM...Booster steering test
06:36:35 PM...Main engine start
06:36:42 PM...Booster ignition/launch

..............ASCENT EVENTS

06:36:53 PM...T+00:11...Start roll maneuver (927 mph)
06:37:00 PM...T+00:18...End roll maneuver (1,002 mph)
06:37:15 PM...T+00:33...Main engine throttle down (1,214 mph)
06:37:27 PM...T+00:45...Main engine throttle up (1,384 mph)
06:37:42 PM...T+01:00...Maximum aerodynamic pressure (1,616 mph)
06:38:46 PM...T+02:04...Booster separation (3,655 mph)
06:38:56 PM...T+02:14...Start OMS rocket assist (3,750 mph)
06:39:16 PM...T+02:34...Trans-Atlantic abort option available (3,955 mph)
06:40:35 PM...T+03:53...Negative return to KSC (5,591 mph)
06:41:45 PM...T+05:03...Abort to orbit option available (7,364 mph)
06:42:28 PM...T+05:46...Shuttle rolls heads up (9,001 mph)
06:42:56 PM...T+06:14...Press to MECO (10,024 mph)
06:44:03 PM...T+07:21...3G limiting (13,706 mph)
06:45:04 PM...T+08:22...Main engine cutoff (17,524 mph)

..............ON-ORBIT EVENTS

07:14:00 PM...OMS-2 orbit circularization rocket firing
09:07:00 PM...Spacehab activation
09:07:00 PM...Laptop computer network setup
09:32:00 PM...NC1 rendezvous rocket firing
10:07:00 PM...Shuttle robot arm (SRMS) powerup
10:12:00 PM...Group B computer powerdown
10:22:00 PM...SRMS checkout
10:27:00 PM...Wing leading edge sensor system setup
10:47:00 PM...External tank handheld photography
11:12:00 PM...Umbilical well camera downlink
11:12:00 PM...External tank video downlink
12:37:00 AM...Crew sleep begins
08:37:00 AM...Crew wakeup

10:15 AM, 8/7/07, Update: Countdown on track; weather improves to 80 percent 'go'

The shuttle Endeavour's countdown is ticking smoothly toward launch Wednesday, with no significant technical problems and with forecasters now predicting an 80 percent chance of good weather. This will Endeavour's first flight since the 2003 Columbia disaster and the second of four space station assembly missions planned this year.

"After five long years, Endeavour is poised once again on the launch pad and is ready for tomorrow's launch," said NASA Test Director Jeff Spaulding. "I'm pleased to report that all of our systems are in great shape, we're on schedule and this long overdue vehicle is ready to fly."

Shuttle weather officer Kathy Winters said forecasters are no longer worried about electrically active anvil clouds moving into the launch area. The only concern is a slight chance for showers. The forecast improved from 70 percent to 80 percent "go," with a 70 percent go forecast Thursday and 80 percent again on Friday.

"So overall, the weather's looking really good for this time of year here in Florida," Winters said. "We have a 20 percent chance of KSC weather prohibiting launch and two good TAL (trans-Atlantic landing) sites on the first two days."

Late Monday, engineers working by remote control loaded liquid hydrogen and oxygen to power the shuttle's three electricity producing fuel cells, enough to support four launch tries in five days. Early today, technicians began checking out the ship's three main engines and their control systems and conducting final inspections of Endeavour's external fuel tank.

This afternoon, the shuttle's communications system will be activated and checked out while engineers complete preparations for rotating a huge protective gantry away from the orbiter around 9 p.m. to set the stage for fueling early Wednesday.

"The countdown continues to go well and we're tracking no significant issues at the pad," Spaulding said. "Last night we got a lot of work done and we're on schedule."

A detailed countdown timeline is available on the CBS News STS-118 Quick-Look page, along with a launch windows chart, the crew's flight plan and NASA's television schedule (revision A).

ENDEAVOUR SET FOR LAUNCH ON
CRITICAL STATION ASSEMBLY MISSION

By WILLIAM HARWOOD
CBS News

Fresh out of a lengthy overhaul, the shuttle Endeavour is poised for blastoff Wednesday on a space station assembly mission, the orbiter's first flight since the 2003 Columbia disaster. The high-profile multi-spacewalk mission features Barbara Morgan, a 55-year-old elementary school teacher-turned-astronaut who has waited 21 years for a chance to fulfill Christa McAuliffe's legacy as the original Teacher in Space.

"I am going up doing the job of an astronaut, the work of an astronaut, but I'm going up with a teacher's eyes, ears, heart and mind," Morgan, McAuliffe's backup, said in an interview. "And so I look very much forward to doing that with an open mind and being able to come back and ... translate that into how can we best provide wonderful opportunities for our colleagues and our students."

NASA managers are especially eager to get Endeavour back into orbit after a four-and-a-half-year hiatus. Now sporting state-of-the-art satellite navigation gear and converters to tap into the space station's solar power grid, Endeavour should be able to reduce the load on its own generators and stay docked at the lab complex longer than any previous flight.

While the shuttle astronauts are plowing through their busy schedule, the space station crew - Expedition 16 Commander Fyodor Yurchikhin, Oleg Kotov and Clay Anderson - will carry out a long, complex repair job to replace a critical component in the Russian computer system. The unit is mounted near an air conditioner in the Zvezda command module and engineers believe corrosion found on cables leading to and from the box may have played a role in widespread computer failures during a June shuttle visit.

The new hardware was delivered to the station Aug. 5 aboard an unmanned Russian Progress supply ship. It will take the station crew four days to complete the computer overhaul and test the wiring.

"This flight really sets the stage for the remainder of the year for the ISS," said Kirk Shireman, deputy manager of the space station program at the Johnson Space Center in Houston. "In October, we're going to launch node 2, the Harmony module, which is the place where we'll berth all the international partner modules. In December, we're going to launch the first international partner module, the Columbus (laboratory, which) will be berthed to node 2. Early next year in February, we're going to launch the first piece of the Japanese research module Kibo. So we're looking forward, not only to this flight, but we're looking forward to the remainder of the year."

On a human level, at least, space station hardware, no matter how important, cannot compete with Morgan and the compelling drama of an elementary school teacher's journey from an Idaho classroom to the space shuttle.

Morgan was selected on July 19, 1985, to train as backup to Christa McAuliffe in NASA's original Teacher in Space program. McAuliffe and seven crewmates died in the Jan. 28, 1986, Challenger disaster but Morgan never gave up her dream of carrying education to the final frontier.

Now, more than two decades after Challenger and nine years after she was accepted as a full-fledged NASA astronaut, Morgan is finally ready to continue McAuliffe's legacy.

Joining Morgan aboard Endeavour will be commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, Rick Mastracchio, Canadian astronaut Dafyyd "Dave" Williams and Benjamin "Al" Drew. Kelly, Hobaugh, Mastracchio and Williams each have one previous flight to their credit. Caldwell, Morgan and Drew are rookies.

Liftoff from pad 39A at the Kennedy Space Center is targeted for 6:37 p.m. on Aug. 8, roughly the moment Earth's rotation carries the shuttle into the plane of the station's orbit.

The astronauts initially hoped to take off Aug. 7, but the flight was delayed one day because of time lost replacing a leaky positive pressure relief valve located behind the orbiter's toilet. Engineers replaced the valve with one borrowed from the shuttle Atlantis and a subsequent pressure check revealed no problems.

"We found a little tiny piece of debris in the sealing surface, which was causing that slight leak rate," said NASA Test Director Steve Payne. "Once we removed it and retested the valve, it was tight as can be. So there's nothing wrong systemically with any of the valves."

Morgan will ride into space strapped into the center seat on the shuttle's lower deck, the same seat position used by McAuliffe aboard Challenger.

"A lot of people, maybe from outside NASA, look at Barbara Morgan as the 'teacher-in-space' type of thing," Mastracchio said in an interview. "We don't look at Barb as a teacher, we look at Barb as another astronaut. She's a crew member on this mission. And she's got a lot of responsibilities on the mission and oh yeah, by the way, she's going to do some public affair events where she's going to do some question and answers with some students to help promote education.

"NASA's been promoting education since day one, this is just another step in maybe trying to reach into the classroom, trying to get kids interested in space, science, math, any way to motivate kids to learn. Barb is a very hard working person and she really believes in what she's doing. I think she'll do a really good job and we're happy to have her."

Said Kelly: "She's got an incredible amount of willpower, I think. She's been involved in this program for a long time, a lot longer than any of us on the crew. She's just kind of pressed ahead through a lot of adversity so you've got to really respect her for that."

Appropriately enough, Endeavour was built to replace Challenger and it was named by school kids in a nationwide competition. Fresh from its final orbiter maintenance and down period, or OMDP, Endeavour will fly seven more times before closing out the shuttle program with a final flight in July 2010. "This will be our 22nd shuttle flight to the international space station and we're really excited to have Endeavour ready to fly again," said Kim Doering, deputy shuttle program manager. "It's been almost five years since Endeavour last landed in December of 2002 and we've made good use of that time."

During the 1,665 days Endeavour spent in the Orbiter Processing Facility at the Kennedy Space Center, NASA and its contractors delivered 1,657,173 parts, replaced 2,045 heat-shield tiles and completed 13,156 checks to make sure the flight hardware met specifications.

In a first for the shuttle program, Endeavour's three main engines are equipped with new vibration sensors and control software to safely - and automatically - shut an engine down before a problem can trigger a catastrophic failure.

NASA also upgraded the solid-fuel booster self-destruct system to lower weight and reduce power consumption while improving reliability. An improved power system was added to the wing leading edge impact sensor system, a post-Columbia upgrade designed to record impact-related forces that might occur during launch or because of micrometeoroid strikes in orbit."

A major upgrade was installation of Global Positioning System satellite navigation system technology, replacing the orbiter's original Tactical Air Navigation - TACAN - system that used UHF radio signals from a transmitter at the landing site to determine distance and bearing information during return to Earth.

"GPS has been a long time coming," Hale said. "GPS on board the space shuttle is not like the little GPS's that you stick on the window of your car that tell you where to turn to get to the restaurant off the next exit on the interstate. This is completely integrated into the navigation system on board the space shuttle.

"We have taken the 1950s-era technology of TACANs, which have been used for a long time in aviation, they're obsolete and being phased out world wide, and we've replaced them with the new technology, global positioning satellite technology, and we've got a far superior system, far safer, far more accurate to fly our big glider back home with."

One of the most noticeable upgrades is the new station-to-shuttle power transfer system, or SSPTS. By tapping into the station's solar power grid, a visiting SSPTS-equipped shuttle can minimize the use of limited supplies of hydrogen and oxygen to power its own fuel cells and remain docked longer.

"It basically takes the power on the space station, which is 120 volts, steps it down to 28 volts for the shuttle to use, allows the shuttle to power down and actually stay on board the ISS," said Shireman.

"It's important for this flight, it's really important for continued assembly of the international space station. Because having an additional six to seven crew members on board ISS for a few extra days allows a tremendous amount of work in terms of assembly, in terms of preparing the ISS to maximize the use of these remaining shuttle flights. It's really important to us and we're very much looking forward to the successful activation of SSPTS."

Said Mastracchio: "It's a very simple concept. The space station has these large solar arrays, it's creating a lot of power. The shuttle has very limited power, because it runs on cryogenics, hydrogen, and oxygen, and we run out of those things after a certain number of days. So if we could utilize the solar arrays of the space station to power the space shuttle, the space shuttle can stay docked to the station a longer period of time. That's what the station-to-shuttle power transfer system is. We dock with the station. We then utilize their power to maintain our time on orbit, and we reduce the amount of cryogenics we need to stay docked to them. And that allows us to stay docked to the station two or three days longer. It's a simple concept, but it's a good idea."

Playing it safe, however, NASA is going into STS-118 with a flight plan that assumes SSPTS does not work properly. Based on fuel cell hydrogen and oxygen consumption alone, Endeavour's mission is baselined to last 11 days and include just three spacewalks.

SSPTS will be automatically plugged in when Endeavour docks with the space station. The system will be turned on later that day, allowing electricity to flow from the station into the shuttle. The system will be powered down the day after docking for a spacewalk to attach a short spacer segment to the right side of the station's main solar power truss. Because SSPTS draws its power from arrays on that side of the truss - and because the normally rotating panels must be locked in place for the truss work - SSPTS must be powered down.

But the system will be reactivated after the spacewalk and if it continues to work normally, NASA's Mission Management Team will extend the flight by three days and give the crew permission to press ahead with a fourth spacewalk.

"We intend to hook up the power transfer system shortly after docking to the space station," Shireman said. "And we'll take a couple of days to look at the performance of that, transferring power. And at a certain point in the mission, if the mission operations director and flight director feel that system is performing as expected, they'll come to the Mission Management Team with a recommendation that we extend the flight. So we're going to make sure we see everything we need to see up there and then we'll make that decision."

Assuming a launch on Aug. 8, Endeavour will dock with the space station around 1:53 p.m. on Aug. 10. Mastracchio and Williams would conduct spacewalks on Aug. 11 and 13 while Mastracchio and Anderson would perform spacewalk No. 3 on Aug. 15. Assuming the flight is extended, the fourth and final spacewalk, by Anderson and Williams, would follow on Aug. 17.

Under the extended mission scenario, Endeavour would undock from the lab complex around 8 a.m. on Aug. 20 and land back at the Kennedy Space Center around 12:49 p.m. on Aug. 22.

"STS-118 is going to be a really exciting mission," Williams said in a NASA interview. Along with installing the S5 solar array truss segment and delivering other needed supplies and equipment, "the third objective of the spaceflight, which is really exciting, is the first flight of the educator astronaut.

"Barbara Morgan will be flying with us as a mission specialist-educator astronaut, trying to captivate the imagination of the youth of America, looking at that next generation of space exploration, what we're going to need in terms of technology, to live and work on the surface of the moon or send humans to Mars."

A CRITICAL YEAR FOR STATION ASSEMBLY HEATS UP

In March 2004, President Bush ordered NASA to complete space station assembly and retire the shuttle by the end of fiscal 2010, freeing up money to support development of a new manned spacecraft to replace the shuttle. The new Orion crew capsule, expected to debut around 2015, will ferry astronauts to and from the station and eventually back to the moon as part of a long-range push to establish a permanent lunar base in the early 2020s.

NASA now views the space station as a test bed for technology development and to collect the medical data needed for future long-duration stays on the moon or voyages to Mars. Completing the station is equally or even more important to the European and Japanese space agencies, which have spent billions developing flight hardware and facilities only to suffer through repeated delays, most recently because of the 2003 Columbia disaster.

To pave the way for attachment of the international modules late this year and early next, NASA has been concentrating on building out the station's solar power truss to provide the necessary cooling and electrical power. Two of the main truss's four sets of solar arrays - starboard 4 and port 4 - are now in place, slowly turning like giant paddlewheels to stay face on to the sun.

A third set, port 6, was launched first, back in 2001 and attached to a short truss extending straight up from the Unity module. P6 provided the station's initial power and cooling while the main solar array truss was assembled. During shuttle flights last December and June, the P6 arrays were retracted and its cooling system disconnected. If all goes well, P6 will be moved to the far left end of the main truss during the next shuttle mission in October and re-extended. A final set of arrays - S6 - is scheduled for launch next year.

The international space station currently consists of six pressurized modules. At the back end of the outpost is the Russian Zvezda command module featuring two solar arrays and an aft docking port that can accommodate Progress supply ships, Soyuz crew ferry capsules and the European Space Agency's upcoming Automated Transfer Vehicle.

A combined airlock/docking module called Pirs is attached to a downward-facing port on Zvezda's front end. The module's forward port is attached to the Russian Zarya module, a supply and propulsion unit equipped with its own pair of solar arrays. Zarya's front end features a downward-facing docking port used by Progress and Soyuz spacecraft.

Zarya's front end is bolted to a pressurized mating adapter that, in turn, is attached to NASA's Unity module, a multi-hatch node with six ports. Its starboard, or right-side port, connects to the U.S. Quest airlock module while its upper zenith port accommodates the Z1 truss and the now stowed P6 solar arrays.

Unity's downward facing port is used by cargo modules brought up by the shuttle and its port hatch is home to another pressurized mating adapter, PMA-3.

Unity's forward port is attached to the Destiny laboratory module. On the forward end of Destiny is another pressurized mating adapter, PMA-2, used as a docking port by visiting space shuttles. The lab module also is home to the station's Canadarm 2 robot arm, a marvel of engineering that is capable of moving, end-over-end like an inchworm, from work site to work site on the solar array truss.

On top of the lab module is the station's main solar array truss, which is mounted at right angles to the long axis formed by the pressurized modules.

The S0 truss segment sits in the middle atop the lab, flanked by the S1 (starboard 1) and P1 (port 1) truss elements. S1, S0 and P1 house four critical electrical equipment and the station's main ammonia cooling system, including huge articulating radiator panels.

Electricity from the solar arrays, known as "primary power," is routed to components in the S0 truss called main bus switching units, or MBSUs. The four MBSUs take that 160-volt primary power and route it to transformers known as DC-to-DC Converter Units, or DDCUs, which lower the voltage to a precisely controlled 124 volts DC. This so-called "secondary power" is then directed to the station's myriad electrical systems using numerous electro-mechanical switches known as remote power controllers.

The eight solar array wings on the completed space station, four on each side, will feed power through separate lines to the MBSUs. For redundancy, power from four SAWs will flow to a pair of major circuits - 1 and 4 - while power from the other four SAWs will be directed to a second pair of circuits - 2 and 3.

The cooling system features two independent ammonia loops - loop A and B - that include large ammonia reservoirs, pumps, cold plates and the plumbing required to route the coolant through the big radiators to dissipate heat.

The loop A and B pumps were powered up during Discovery's visit last December. Expedition 14 commander Michael Lopez-Alegria and Sunita Williams completed the cooling system activation during spacewalks early this year, repositioning large fluid jumpers to route ammonia from the permanent system in loops A and B to heat exchangers in the laboratory module. The interim cooling system then was disabled.

S1 and P1 each feature three sets of ammonia radiators but only one set of cooling panels on each segment is currently extended. Later this fall the Zarya module's two solar panels will be folded up to provide the clearance necessary for the eventual extension of the other S1 and P1 radiators.

During a shuttle flight last September, the P3 truss segment and P4 solar arrays were bolted to P1 (there is no P2 or S2). Then, during a flight by Atlantis in June, the corresponding S3 and S4 truss segments were bolted onto the right side of the solar power truss. P3 and S3 both feature massive dual-motor solar alpha rotary joints, or SARJs, which are designed to rotate the outboard solar arrays like giant paddle wheels to track the sun. The S4 and P4 arrays, identical to the now-stowed P6 panels, feature solar blankets that stretch 240 feet from tip to tip when fully extended.

In December, a short spacer truss, known as P5, was bolted to the outboard side of P4 to permit the eventual attachment of P6 later this fall. During Endeavour's upcoming flight, an identical spacer segment - S5 - will be bolted to S4 to permit the eventual attachment of the S6 solar arrays when they are launched next year.

During shuttle mission STS-120 in October, the flight that will carry the Harmony node into orbit, the P6 solar array now mounted atop the Z1 truss will be moved to the left end of the main solar power truss, bolted to P5 and redeployed.

Moving and redeploying P6 is "probably the sportiest robotic ops we're going to do for the whole assembly," said Paul Hill, deputy director of mission operations at the Johnson Space Center in Houston.

On that same flight, Harmony will be bolted to Unity's left-side hatch. PMA-3, currently bolted to the left port of Unity, will be moved to the module's downward facing port after Endeavour departs. After the October shuttle mission, station astronauts will use the lab's robot arm to remove PMA-2, the shuttle docking port, from Destiny's front end, attach it to Harmony and then move the two components back to the front of the lab module.

This is an especially critical point in the station's construction because space shuttles will be unable to dock at the outpost until PMA-2 and Harmony are in the proper location.

"After shuttle undocks, pulling off PMA-2 from the front of the lab, moving it over to the node and then re-installing the node on the front of the lab, that's huge," Hill said. "Because first, there's no shuttle there so there's only three crew members to get all that done with very limited views outside. And, from the time we pull the PMA off until the whole thing is complete, there's not a shuttle docking port. So that'll be sporty. But all the robotics necessary to do it are well within our experience base."

If all that goes well, including complex spacewalks to route power and cooling to Harmony, Atlantis will return to orbit on mission STS-122 in December to attach the Columbus research module to Harmony's right-side hatch and make the required electrical and cooling connections.

With Columbus in place, powered and cooled by the station's main solar array truss, NASA will turn its attention to launching two modules for the Japanese Space Agency. First up is a pressurized experiment module next February that will be temporarily mounted to the upper hatch on Harmony. The huge Kibo research module then will be launched next April and bolted to Harmony's left-side hatch. The experiment module then will be moved to an upward-facing port on Kibo.

Eight additional shuttle/station flights are required after that to carry up a final set of solar arrays - S6 - a cupola, a third and final node, supplies and spare parts. Station crew size will expand from three to six in 2009. Here is the current manifest (some dates TBD):

DATE........STS/ISS........Orbiter......MISSION

08/08/07...STS-118/13A.1...Endeavour....S5 spacer segment; supplies
10/23/07...STS-120/10A.....Discovery....Harmony connecting node;
........................................P6 relocation
12/06/07...STS-122/1E......Atlantis.....Columbus research module
02/14/08...STS-123/1JA.....Endeavour....Japanese experiment module;
........................................Canadian dextrous manipulator
04/24/08...STS-124/1J......Discovery....Japanese Kibo research module
08/07/08...STS-125.........Atlantis.....Hubble Space Telescope upgrade
........................................flight; final Atlantis mission
09/18/08...STS-126/ULF-2...Endeavour....Supplies/spares
11/06/08...STS-119/15A.....Discovery....S6 solar array truss segment
03/XX/09...STS-127/2JA.....Endeavour....Japanese exposed experiment
........................................facility
04/XX/09...STS-128/17A.....Discovery....Crew equipment (6-person
........................................capability)
08/XX/09...STS-129/ULF-3...Endeavour....Supplies/spares
10/XX/09...STS-130/19A.....Discovery....Supplies/spares
02/XX/10...STS-131/ULF-4...Endeavour....Contingency re-supply flight
04/XX/10...STS-132/20A.....Discovery....Node 3, cupola; final
........................................Discovery mission
07/XX/10...STS-133/ULF-5...Endeavour....Contingency re-supply flight;
........................................final shuttle mission

By the end of assembly, the international space station will mass nearly 1 million pounds and have the pressurized volume of two 747 jumbo jets. Its finished solar array truss will stretch the length of a football field and its eight huge solar array wings will generate, on average, some 75 kilowatts of power, enough to supply 55 average homes. Crew size will be bumped up to six astronauts and cosmonauts by early 2009 with Russian Soyuz spacecraft and NASA's new Orion capsules providing crew ferry and lifeboat capability after the shuttle is retired.

"The international space station originally was conceived as a world class research facility," station program manager Mike Suffredini said last year. "It will continue to provide that capability for research that you can do in space that can open our eyes to problems on the ground. Today, we have a number of plans to up the research capability, the research suite of hardware, during the assembly process such that we will be able to utilize it.

"However, what we look to ISS for as well is the exploration," he said. "We will use it to test systems that we plan to utilize on the moon and Mars, it's going to be really critical that we build highly reliable systems. The best place to test systems, particularly that have to operate in a zero-gravity environment, would be on the space station."

ENDEAVOUR'S CREW STEPS UP

Following standard post-Columbia procedure, NASA will monitor Endeavour's launching with scores of cameras, radars and other sensors to look for any signs of foam insulation falling from the ship's external tank that might threaten impact damage to the shuttle's fragile heat shield.

Based on the performance of the shuttle Atlantis' external tank during the most recent flight in June, NASA appears to have turned the corner in its work to minimize foam shedding in the wake of the Columbia disaster. Atlantis' tank was one of the most debris free to date and NASA managers are optimistic Endeavour's tank and subsequent models will perform well.

But that doesn't mean leaving anything to chance. As with all post-Columbia crews, the Endeavour astronauts will unlimber the shuttle's robot arm the day after launch, attach a 50-foot instrument boom and inspect the shuttle's critical reinforced carbon carbon nose cap and wing leading edge panels with a laser scanner and a high-resolution camera.

The shuttle's heat shield tiles will receive their closest scrutiny on flight day three during final approach to the space station. Passing 600 feet directly below the outpost, Kelly will guide Endeavour through a slow 360-degree back flip known as a rendezvous pitch maneuver, or RPM, exposing the ship's belly to powerful digital cameras wielded by the station crew.

With the RPM maneuver complete, Kelly will guide Endeavour to a point about 400 feet directly in front of the station. From there, with the orbiter's nose pointing toward deep space and its open payload bay toward the station, Kelly will guide the shuttle to a docking with pressurized mating adapter No. 2 on the forward end of the Destiny laboratory module.

"We'll come up from beneath the space station," Kelly explained in a NASA interview. "And inside of 1,000 feet, we'll do this rendezvous pitch maneuver where the shuttle flips around. And then once that's complete, we'll get the vehicle stabilized below the space station, close in a little bit further and then start a fly-around where I'll fly the shuttle 90 degrees to what's called the V-bar. It's really the velocity vector."

"So, I'm flying in front of the space station as we both kind of head around the same orbit and then close in from there. And basically you fly the vehicle manually using these camera views and out-the-window views until you get about two inches away, and then you push a button and the autopilot fires a series of firings to kind of complete the last part of the contact to make sure that you have the right contact parameters where you're actually connecting the two docking systems."

When the docking systems engage, the new station-to-shuttle power transfer system, or SSPTS, will automatically plug into the lab's solar power system. But the power converters in the orbiter will not be activated until later in the day. First up for the shuttle crew is a brief "meet and greet" with their station colleagues in the Destiny module and work to pull the S5 solar array spacer truss out of Endeavour's cargo bay.

Caldwell, operating the shuttle's robot arm, will begin that process about two hours after hatch opening, pulling the S5 truss out of the cargo bay and positioning it for handoff to the station arm. Hobaugh, operating the lab's Canadarm2, will then grapple the truss and move it to an overnight storage location.

Mastracchio and Williams, meanwhile, plan to get the station's Quest airlock module ready for their first spacewalk the next day to attach S5 to the S4 solar array segment on the right end of the lab's main power truss. Both astronauts will spend the night in the airlock at a reduced pressure of 10.2 pounds per square inch to help purge nitrogen from their bloodstreams and prevent the bends after working in their 5-psi spacesuits.

Before the spacewalk begins the following day, the S4 solar array's SARJ will be stopped and the array locked in place in preparation for the attachment of S5. Mastracchio and Williams plan to begin their first spacewalk around 1:07 p.m. on Aug. 11.

After S5 is attached, Williams and Mastracchio will move to the Z1 truss, make their way up to the P6 solar array segment, monitor the retraction of a cooling radiator and then lock it in place for the move later this fall to the left end of the power truss.

DATE/EDT.......HH...MM...SS...EVENT

08/11/07
Sat 12:07 AM...02...05...30...STS crew sleep begin
Sat 08:07 AM...02...13...30...STS/ISS crew wakeup
Sat 08:47 AM...02...14...10...EVA-1: 14.7 psi repress
Sat 09:07 AM...02...14...30...EVA-1: Hygiene break
Sat 09:32 AM...02...14...55...EVA-1: Crew lock depress to 10.2 psi
Sat 09:57 AM...02...15...20...EVA-1: Campout EVA preps
Sat 11:27 AM...02...16...50...EVA-1: Spacesuit purge
Sat 11:27 AM...02...16...50...SSPTS shut down for EVA-1
Sat 11:42 AM...02...17...05...EVA-1: Spacesuit prebreathe
Sat 12:32 PM...02...17...55...EVA-1: Crew lock depressurization
Sat 12:37 PM...02...18...00...SSRMS to pre-install position
Sat 01:07 PM...02...18...30...EVA-1: Airlock egress
Sat 01:22 PM...02...18...45...SSRMS support
Sat 01:22 PM...02...18...45...EVA-1: Sortie setup
Sat 01:52 PM...02...19...15...EVA-1: S4/S5 launch lock removal
Sat 02:27 PM...02...19...50...SVA-1: S5 installation
Sat 03:37 PM...02...21...00...SSRMS ungrapples S5
Sat 03:57 PM...02...21...20...EVA-1: PVR grapple fixture relocation
Sat 04:57 PM...02...22...20...EVA-1: Get ahead tasks
Sat 05:12 PM...02...22...35...EVA-1: S5 cleanup
Sat 05:47 PM...02...23...10...EVA-1: P6 forward radiator retraction
Sat 06:57 PM...03...00...20...EVA-1: Payload bay cleanup
Sat 07:12 PM...03...00...35...EVA-1: Airlock ingress
Sat 07:32 PM...03...00...55...EVA-1: Airlock repressurization
Sat 07:47 PM...03...01...10...Spacesuit servicing
Sat 09:02 PM...03...02...25...Transfer tagup
Sat 09:22 PM...03...02...45...SSPTS re-activated
Sat 11:07 PM...03...04...30...ISS crew sleep begins
Sat 11:37 PM...03...05...00...STS crew sleep begins

The day after EVA-1 - flight day five - the astronauts will focus on equipment and supply transfers and preparations for a second spacewalk the next day. If any problems are seen in launch imagery or the crew's orbiter boom sensor system - OBSS - inspections on flight day two, the crew will carry out a so-called "focused inspection" on flight day five to give engineers on the ground close-up high-resolution views of whatever the problem might be.

Once again, Mastracchio and Williams plan to camp out in the Quest airlock to purge nitrogen from their blood in preparation for EVA-2. The goal of the second excursion is to remove and replace one of the station's four control moment gyroscopes, or CMGs.

The station uses four massive CMGs to control the lab's orientation without burning hard-to-replace rocket fuel. One of them, CMG No. 3, acted up last year and was taken off line on Oct. 10, 2006. The refurbished unit being installed during Endeavour's mission will restore full redundancy to the critical orientation system. For readers interested in technical detail, here is a description from an earlier NASA press kit:

The motion control subsystem (MCS) hardware launched as part of the Z1 element includes the CMGs and the CMG assemblies.
The CMG assembly consists of four CMGs and a micrometeorite/orbital debris shield. The four CMGs, which will control the attitude of the ISS, have a spherical momentum storage capability of 14,000 ft-lb/sec, the scalar sum of the individual CMG wheel moments. The momentum stored in the CMG system at any given time equals the vector sum of the individual CMG momentum vectors.
To maintain the ISS in the desired attitude, the CMG system must cancel, or absorb, the momentum generated by the disturbance torques acting on the station. If the average disturbance torque is nonzero, the resulting CMG output torque is also nonzero, and momentum builds up in the CMG system. When the CMG system saturates, it is unable to generate the torque required to cancel the disturbance torque, which results in the loss of attitude control.
The CMG system saturates when momentum vectors have become parallel and only momentum vectors change. When this happens, control torques perpendicular to this parallel line are possible, and controllability about the parallel line is lost.
Russian segment thrusters are used to desaturate the CMGs.
An ISS CMG consists of a large flat wheel that rotates at a constant speed (6,600 rpm) and develops an angular momentum of 3,500 ft-lb/sec about its spin axis. This rotating wheel is mounted in a two-degree-of-freedom gimbal system that can point the spin axis (momentum vector) of the wheel in any direction.
At least two CMGs are needed to provide attitude control. The CMG generates an output reaction torque that is applied to the ISS by inertially changing the direction of its wheel momentum. The CMG's output torque has two components, one proportional to the rate of change of the CMG gimbals and a second proportional to the inertial body rate of the ISS as sensed at the CMG base. Because the momentum along the direction of the spin axis is fixed, the output torque is constrained to lie in the plane of the wheel. That is why one CMG cannot provide the three-axis torque needed to control the attitude of the ISS.
Each CMG has a thermostatically controlled survival heater to keep it within thermal limits before the CMGs are activated on Mission 5A. The heaters are rated at 120 watts and have an operating temperature range of -42 to -35 F.

The replacement CMG will ride into space mounted on a pallet in the shuttle's cargo bay. Mastracchio and Williams first will remove CMG-3 from its place in the Z1 truss and temporarily mount it on a handrail fitting. Then they'll move down to the shuttle cargo bay, remove the new CMG and a carrier platform and move them up to External Stowage Platform No. 2 near the Quest airlock. The new CMG then will be removed from its carrier and installed in Z1. CMG-3 will be mounted on the ESP-2 carrier and returned to Earth later this year.

"Our second spacewalk, I think, is almost going to be as exciting as the first," Williams said. "Our job is to replace one of the gyros that we use to stabilize the position of the space station. There are four gyros that we currently have on board the space station. The gyro essentially is a spinning disk that conserves momentum. It's used to stabilize the station. One of them isn't functioning properly, so we have to replace it.

DATE/EDT.......HH...MM...SS...EVENT

08/13/07
Mon 07:07 AM...04...12...30...STS/ISS crew wakeup
Mon 07:47 AM...04...13...10...EVA-2: Airlock repress to 14.7 psi
Mon 08:07 AM...04...13...30...EVA-2: Hygiene break
Mon 08:37 AM...04...14...00...EVA-2: Airlock depress to 10.2 psi
Mon 08:57 AM...04...14...20...EVA-2: Campout EVA prep
Mon 10:07 AM...04...15...30...Logistics transfers resume
Mon 10:27 AM...04...15...50...EVA-2: Spacesuit purge
Mon 11:32 AM...04...16...55...EVA-2: Crew lock depressurization
Mon 12:07 PM...04...17...30...EVA-2: Airlock egress
Mon 12:22 PM...04...17...45...EVA-2: Setup
Mon 12:52 PM...04...18...15...EVA-2: Remove, temp stow failed CMG
Mon 01:22 PM...04...18...45...EVA-2: Transfer new CMG to ESP-2
Mon 02:07 PM...04...19...30...Crew meals begin
Mon 02:52 PM...04...20...15...EVA-2: Remove new CMG from ESP-2
Mon 03:42 PM...04...21...05...EVA-2: Install new CMG on Z1
Mon 04:37 PM...04...22...00...EVA-2: Install failed CMG on ESP-2
Mon 05:47 PM...04...23...10...EVA-2: Payload bay cleanup
Mon 06:12 PM...04...23...35...EVA-2: Airlock ingress
Mon 06:32 PM...04...23...55...EVA-2: Airlock repressurization
Mon 06:47 PM...05...00...10...Spacesuit servicing
Mon 08:07 PM...05...01...30...Transfer tagup
Mon 10:07 PM...05...03...30...ISS crew sleep begins
Mon 10:37 PM...05...04...00...STS crew sleep begins

The day after EVA-2, Morgan will use the shuttle's robot arm to lift the 7,000-pound External Stowage Platform No. 3 from its perch inside Endeavour's cargo bay. She will hand the stowage platform to Hobaugh, operating the station arm, and he will move it to the P3 truss segment where it will be robotically attached. The installation procedure will take about 40 minutes from the time Hobaugh takes the handoff from Morgan.

That night, Mastracchio and station astronaut Clay Anderson will sleep in the Quest airlock module to prepare for spacewalk No. 3.

Anderson originally was scheduled to take off aboard Endeavour to replace long-duration station astronaut Sunita Williams. But after the shuttle Atlantis was delayed three months, from March to June, because of hail damage to the ship's external tank, NASA managers decided to launch Anderson aboard Atlantis and to bring Williams home in June as originally planned. Anderson's place in Endeavour's crew was given to Drew.

"Once those guys arrive, I'll pretty much do the same jobs with them that I was planning on doing had I launched with that crew, and that includes EVAs No. 3 and 4, one with Rick Mastracchio and one with Dave Williams, and then I'll also be helping Charlie Hobaugh when he manipulates the arm to install the S5 truss," Anderson said in an interview.

The goals of the third spacewalk are to upgrade the station's S-band communications system; to relocate two logistics carts attached to the mobile transporter on the front side of the main solar array truss; and to retrieve two experiment packages.

"We're going to move the SASA antenna off of P6," Mastracchio said in a NASA interview. "Again, P6 is going to eventually be moved from the zenith part of station to the port side. So, we have to kind of clean up P6. And part of it is to move this large antenna off of P6 and install it on P1. While I'm doing that, Clay Anderson, who will be living on space station when we get there, will be installing two electronics boxes to support that antenna. That will give the space station its second set of antennas, I should say, communication antenna capability.

DATE/EDT.......HH...MM...SS...EVENT

08/15/07
Wed 06:37 AM...06...12...00...STS/ISS crew wakeup
Wed 07:17 AM...06...12...40...EVA-3: Airlock repress to 14.7 psi
Wed 07:37 AM...06...13...00...EVA-3: Hygiene break
Wed 07:57 AM...06...13...20...EVA-3: Airlock depress to 10.2 psi
Wed 08:27 AM...06...13...50...EVA-3; Campout EVA prep
Wed 09:57 AM...06...15...20...EVA-3: Spacesuit purge
Wed 10:12 AM...06...15...35...EVA-3: Spacesuit pre-breathe
Wed 11:02 AM...06...16...25...EVA-3: Airlock depressurization
Wed 11:37 AM...06...17...00...EVA-3: Airlock egress
Wed 11:52 AM...06...17...15...EVA-3: Setup
Wed 12:32 PM...06...17...55...EVA-3: EV1: P6 SASA relocation
Wed 12:32 PM...06...17...55...EVA-3: EV3: P1 BSP and transponder installation
Wed 02:27 PM...06...19...50...EVA-3: CETA 1 move starboard
Wed 03:07 PM...06...20...30...Crew meals
Wed 03:27 PM...06...20...50...EVA-3: CETA 2 move starboard
Wed 04:27 PM...06...21...50...EVA-3: EV1: SASA gimbal locks
Wed 04:27 PM...06...21...50...EVA-3: EV3: P6 transponder retrieval
Wed 04:57 PM...06...22...20...EVA-3: EV1: MISSE 3 and 4 removal
Wed 05:07 PM...06...22...30...Spacehab debris shields
Wed 05:42 PM...06...23...05...EVA-3: Airlock ingress
Wed 06:02 PM...06...23...25...EVA-3: Airlock repressurization
Wed 06:12 PM...06...23...35...SRMS powerdown
Wed 06:27 PM...06...23...50...MISSE-3 transfer
Wed 06:47 PM...07...00...10...MISSE-4 transfer
Wed 07:42 PM...07...01...05...Transfer tagup
Wed 09:37 PM...07...03...00...ISS crew sleep begins
Wed 10:07 PM...07...03...30...STS crew sleep begins

Activities after EVA-3 - starting with flight day nine - will depend on which mission scenario NASA opts to implement. If the station-to-shuttle power transfer system works normally, the flight will be extended three days, the crew will concentrate on logistics transfer work on flight day nine and stage a fourth and final spacewalk on flight day 10. Under that scenario, the shuttle would undock from the station Aug. 20 and land back at the Kennedy Space Center around 12:50 p.m. on Aug. 22.

If the mission extension isn't possible for some reason, Kelly and company will wrap up their transfer work on flight day nine, enjoy a final joint meal and seal hatches between the shuttle and the space station in preparation for undocking on flight day 10. Under that scenario, Endeavour would undock on Aug. 17 and land around 2:10 p.m. on Aug. 19.

But NASA managers are optimistic the SSPTS will work normally, allowing the mission extension and the fourth spacewalk. The tasks planned for EVA-4 are not critical, but they will save time during upcoming assembly missions and NASA managers would like to get the work done now if possible.

Assuming the mission is extended, flight day nine will be devoted to logistics transfer work.

"We have about 110 hours of transfer activity scheduled for the mission, that includes the hardware in the Spacehab as well as the hardware in the middeck," said station flight director Joel Montalbano. "If we don't get a good jump on this during the flight day five, flight day nine is our big day.

"Why are we waiting until flight day nine? One of the things we try and do is during robotics operations you don't want people doing transfer operations. And the reason is, for robotics operations you're basically in the U.S. laboratory trying to do critical movements with the robotic arm and you don't want anybody running by you or floating by you with a bag and bumping your arm or anything. So we basically baseline no transfer activities during robotics."

For spacewalk No. 4, Anderson and Williams will spend a final night in the Quest airlock before venturing outside again on flight day 10 to install wireless instrumentation equipment on the station's solar array truss; to tie down micrometeoroid debris shields on the Destiny module; and to install clamps on the power truss that will permit a future crew to temporarily store a heat shield inspection boom on the station.

DATE/EDT.......HH...MM...SS...EVENT

08/17/07
Fri 05:37 AM...08...11...00...STS/ISS crew wakeup
Fri 06:17 AM...08...11...40...EVA-4: Airlock repress to 14.7 psi
Fri 06:37 AM...08...12...00...EVA-4: Hygiene break
Fri 06:57 AM...08...12...20...EVA-4: Airlock depress to 10.2 psi
Fri 07:27 AM...08...12...50...EVA-4: Campout EVA prep
Fri 08:37 AM...08...14...00...Logistics transfers resume
Fri 08:57 AM...08...14...20...EVA-4: Spacesuit purge
Fri 09:12 AM...08...14...35...EVA-4: Spacesuit pre-breathe
Fri 10:02 AM...08...15...25...EVA-4: Crew lock depress
Fri 10:37 AM...08...16...00...EVA-4: Airlock egress and setup
Fri 10:52 AM...08...16...15...EVA-4: OBSS OSE installation
Fri 12:22 PM...08...17...45...EVA-4: EV3: EWIS antenna installation
Fri 12:32 PM...08...17...55...EVA-4: EV1: EWIS antenna installation
Fri 02:02 PM...08...19...25...EVA-4: Lab debris shields (C2-3)
Fri 02:32 PM...08...19...55...EVA-4: Lab debris shields (C2-2)
Fri 03:02 PM...08...20...25...EVA-4: CP1 WETA antenna installation
Fri 04:17 PM...08...21...40...EVA-4: Payload bay cleanup
Fri 04:42 PM...08...22...05...EVA-4: Airlock ingress
Fri 05:02 PM...08...22...25...EVA-4: Airlock repressurization
Fri 05:17 PM...08...22...40...Post-EVA spacesuit servicing
Fri 06:07 PM...08...23...30...Transfer tagup
Fri 08:37 PM...09...02...00...ISS crew sleep begins
Fri 09:07 PM...09...02...30...STS crew sleep begins

The day after the fourth spacewalk, the astronauts will continue the logistics transfer work, transfer their spacesuits back to the shuttle and troubleshoot a station audio system problem. The next day, Aug. 19, the crew will enjoy a half day off before a final joint meal, a brief farewell ceremony and work to seal hatches between the station and the shuttle. Undocking is on tap the day after that with landing expected on Aug. 22.

"We will close the hatch between the station and the shuttle the night before we undock," Kelly said. "When we wake up the next morning, there are some things we need to do with the tunnel to get it ready to undock. And then we command the undocking and some springs will push off the shuttle at a specific rate. The pilot, Charlie Hobaugh, is actually doing the flying during the undocking.

"He'll back away to about 600 feet and then he will manually fly the shuttle - very similar to what we do during the docking when we go from underneath the space station to in front of it. But he'll fly the shuttle all the way around, probably a full lap (360 degrees). We do that to take photo documentation of the outside of the space station just to make sure that it's as we expect it to be."

After the fly around, the astronauts will use the shuttle's robot arm a final time to carry one a so-called late inspection to make sure no space junk or micrometeoroids hit the shuttle's critical nose cap or wing leading edge panels while Endeavour was in orbit.

"If we see something during those inspections that we don't like, there are several things we can do," Kelly said. "One is do nothing, if there is damage that's OK to land with. The other is we could potentially send our EVA crew members out to repair it. Or we could go back to the space station and dock and use that as a safe haven for the crew.

"After that day, we use the next day to get the shuttle back configured from kind of a spaceship to a re-entry vehicle. There's a lot of work to be done there. We check out the flight control system. We check out the reaction control system jets, make sure they're all working OK. And then the very next day we come back."

11:00 AM, 8/6/07, Update: Countdown on track; weather forecast unchanged

Engineers started the shuttle Endeavour's countdown Sunday evening and with good weather expected, officials said today that so far, there are no technical problems at pad 39A that would prevent an on-time liftoff Wednesday.

"At this point, we are on schedule and we are tracking no significant issues," said NASA Test Director Jeff Spaulding.

Shuttle weather officer Kathy Winters said she still expects a 70 percent chance of good weather at launch time Wednesday with the only concern being a chance for thunderstorms or electrically active anvil clouds to blow into the launch area. The forecast remains 70 percent "go" Thursday and improves to 80 percent Friday should launch be delayed.

Liftoff is targeted for 6:36:39 p.m. Wednesday, the middle of the shuttle's 10-minute launch window and roughly the moment Earth's rotation will carry the launch pad into the plane of the space station's orbit. If Endeavour takes off between 6:36:39 p.m. and 6:41:39 p.m., commander Scott Kelly will be able to catch up with the station for a docking on Friday, flight day three (NASA considers launch day flight day one).

But if some problem crops up Wednesday, mission managers can extend the launch window an additional three minutes and 10 seconds. A launch between the end of the flight-day-three window and 6:44:49 p.m. would result in a space station linkup on Saturday - flight day four.

NASA normally passes up FD-4 launch opportunities because the extra day required to complete the rendezvous is not available for the docked phase of the mission. But Endeavour, fresh out of a major overhaul and making its first flight since the 2003 Columbia disaster, is equipped with a new station-to-shuttle power transfer system that will allow the orbiter to plug into the lab's solar power grid.

As such, Endeavour's crew could get to the station a day late and still accomplish all of the mission objectives by utilizing station power to get an additional docked day.

This afternoon, engineers plan to clear the pad and remotely load liquid oxygen and hydrogen aboard the shuttle to power the ship's three electricity producing fuel cells. The goal is to get 11 days of liquid oxygen aboard and five days of liquid hydrogen, permitting four launch attempts in five days. If Endeavour is not off the ground by then, the launch team will stand down for 48 hours and reload the fuel cell system.

A detailed countdown timeline is posted on the CBS News STS-118 Quick-Look page, along with an updated launch windows chart, the NASA television schedule (rev. A) and a detailed flight plan (all also available in the SpaceCalc Data sidebar to the right). Updates will be posted as warranted.

03:00 PM, 8/5/07, Update: Russian Progress supply ship docks with international space station

An unmanned Russian Progress caro ship, loaded with computer replacement gear, propellant and other needed supplies, docked with the international space station today. The Progress 26 spacecraft, launched Aug. 2 from the Baikonur Cosmodrome in Kazakhstan, engaged the docking mechanism on the downward facing Pirs airlock module at 2:40 p.m. EDT.

The cargo ship is loaded with 5,111 pounds of wet and dry cargo, including 1,587 pounds of propellant; 107 pounds of oxygen; 463 pounds of water; and 2,954 pounds of dry cargo. The latter includes computer replacement gear that will be installed over a four-day period during the shuttle Endeavour's upcoming visit to attach a new solar array truss segment and other equipment.

During a shuttle visit in June, the three computers making up the Russian segment's guidance and navigation system, along with all three "lanes" making up the Russian command and control computer system, crashed because of apparent problems with secondary power supply surge protectors. The computers were coaxed back into operation after station commander Fyodor Yurchikhin and flight engineer Oleg Kotov installed jumper cables to bypass the suspect power supply circuitry.

A later inspection revealed widespread corrosion on computer cable connectors at a critical black box located near an air conditioner in the Zvezda command module. Russian engineers believe the corrosion played a role in the computer crashes.

"We're continuing to try to fully understand what caused this problem," Kirk Shireman, deputy manager of the space station program at the Johnson Space Center in Houston, said last month. "The debugging has looked at not only the computers, but looking at all the command string, if you will. The commands that come to these computers fall through a number of hardware devices along the way.

"We had some anomalous readings on some cables and also a box upstream of the computers called the BOK-3. If you look at the BOK-3 itself, it also looks like it has some corrosion on that box."

The box and cabling will be replaced by Yurchikhin and Kotov over a four-day period during the shuttle Endeavour's upcoming visit. All in all, some 28 hours of crew time will be needed to complete the repair job.

"We believe we can execute 118 (Endeavour's mission) in the current configuration with no limitation," Shireman said.

Engineers initially believed the computer problems might have been caused by subtle changes in the space station's electrical grid due to the attachment of a new set of solar arrays by the visiting shuttle astronauts.

"At this point in time, it's looking like that was not the cause," Shireman said. "But absolutely, we're very suspicious of coincidences so we're continuing to pursue it."

10:40 AM, 8/5/07, Update: Valve replaced and retested; engineers ready to start countdown

Engineers at the Kennedy Space Center are gearing up to start the shuttle Endeavour's countdown this evening at 8 p.m., setting the stage for launch on a space station assembly mission at 6:36:39 p.m. Wednesday. Forecasters are predicting a 70 percent chance of good weather Wednesday and Thursday, improving to 80 percent "go" on Friday.

"All our systems are in very good shape right now," said NASA Test Director Steve Payne. "Countdown work is on schedule and we have no issues to report. The team is ready, Endeavour's ready and we're looking forward to Wednesday's launch and a safe and successful mission."

Commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, Rick Mastracchio, Dave Williams, educator-astronaut Barbara Morgan and Al Drew flew to the Florida spaceport Friday.

They originally hoped to take off Tuesday evening, but last week NASA managers delayed the flight one day because of time lost replacing a valve in the shuttle's crew module. Located behind the orbiter's toilet, the positive pressure relief valve failed a pressure test and engineers opted to replace it with a valve borrowed from the shuttle Atlantis.

"We found a little tiny piece of debris in the sealing surface, which was causing that slight leak rate," Payne said today. "Once we removed it and retested the valve, it was tight as can be. So there's nothing wrong systemically with any of the valves.

"We did borrow one from OV-104, from Atlantis, and we put it in there and we just finished a leak check, I believe early this morning, and it's very, very tight. So we're good to go as far as valves and we're not concerned about anything system wide."

Shuttle weather officer Kathy Winters said she expects a 70 percent chance of good weather Wednesday, with the only concern being a chance of isolated showers and electrically active anvil clouds moving into the launch area. Two of NASA's three European emergency runways are forecast "go," as is Edwards Air Force Base in California's Mojave Desert.

The outlook is much the same Thursday, still 70 percent go with less chance of anvil clouds, and by Friday, Winters said drier air is expected, prompting an 80 percent go forecast.

"The weather looks good overall," Winters said.

Endeavour has enough on-board liquid hydrogen and oxygen for it's three electricity producing fuel cells to make four launch attempts in five days. If the shuttle isn't off the ground by then, the team would stand down for 48 hours to top off fuel cell supplies before making additional attempts.

A detailed countdown timeline is posted on the CBS News STS-118 Quick-Look page, along with NASA's television schedule (revision A), a launch windows chart and the latest version of the crew's flight plan (also available in SpaceCalc Data sidebar to the right).

Mission planners are prepared for two options - an 11-day three-spacewalk mission and a 14-day four-EVA flight - depending on how a new station-to-shuttle power transfer system works. The SSPTS was designed to let the shuttle plug into the station's solar power grid, reducing the load on the orbiter's fuel cells and extending the docked phase of the mission.

Until the SSPTS is plugged in and verified operational, however, Endeavour's mission is officially considered an 11-day flight. Because of last-minute planning and the one-day launch delay, the flight plan posted on the CBS News Quick-Look page is slightly out of synch. Revision A of the NASA TV schedule is up to date through the official 11-day scenario. Updates will be posted as warranted.

5:12 PM, 8/3/07, Update: Astronauts fly to Kennedy Space Center

The shuttle Endeavour's seven-member crew flew to the Kennedy Space Center today to prepare for launch next week on a space station assembly mission. Commander Scott Kelly said the astronauts agreed with the decision earlier today to delay launch 24 hours, from Tuesday to Wednesday, to get back on schedule after unexpected work to replace a suspect valve in the shuttle's crew cabin pressurization system.

"It's great to be in Florida for launch week," Kelly said at the shuttle runway. "I would like to congratulate all the orbiter teams here at the Kennedy Space Center for the really outstanding effort they gave trying to get Endeavour ready to go for a Tuesday launch. They had some real challenges with the weather, we understand the decision to delay until Wednesday and we agree with it completely."

Joining Kelly on the runway were pilot Charles Hobaugh, Tracy Caldwell, flight engineer Rick Mastracchio, Canadian flier Dave Williams, Al Drew and educator-astronaut Barbara Morgan, Christa McAuliffe's backup in the original Teacher in Space Program.

Engineers plan to begin Endeavour's countdown at 8 p.m. Sunday, setting up a launch attempt at 6:36:36 p.m. Wednesday. The goals of the flight include installation of a new space station solar array truss segment; replacement of a faulty control moment gyroscope; attachment of an external stowage platform; and the delivery of some 5,000 pounds of equipment and supplies.

"As you know there's a strong educational element to this mission," Williams said after arriving in Florida. "This flight is really not so much about teaching in space, but about creating learning opportunities for students here on the ground and there's no better person to do that than our own Barb Morgan."

"Thank you, it's great to be here," Morgan said, smiling broadly in the hot Florida sun. "We thank everybody and I especially thank my colleagues in education all across the country."

Al Drew took the microphone last, saying NASA first formed the STS-118 crew in 2002. Two astronauts - Lisa Nowak and Scott Parazynski - were assigned to other flights after the Feb. 1, 2003, Columbia disaster and Drew was added to the crew earlier this year to replace Clay Anderson, now aboard the international space station.

"We've had a crew first assigned to this mission back in late 2002," Drew said. "We've been putting the training together, the plans together, putting Endeavour together to go do this mission. In the words of the great philosopher-poet Larry the Cable Guy, it's time to get 'er done. Let's go have a fine countdown and a fine mission and we'll see you in a few weeks."

1:46 PM, 8/3/07, Update: Shuttle launch delayed one day

Launch of the shuttle Endeavour on a space station assembly mission has been delayed 24 hours, from Tuesday to Wednesday at 6:37 p.m., because of time needed to complete preparations after unscheduled work to fix a cabin leak, officials said today. Endeavour's crew still plans to fly to the Kennedy Space Center later today but the start of the shuttle's countdown, originally scheduled for 9 p.m. Saturday, will slip one day. Additional details will be posted as they become available and an update to the mission flight plan, countdown chart and other flight data files will be updated as soon as possible.

12:45 PM, 8/3/07, Update: Educator-astronaut Morgan ready for long anticipated flight

Twenty-one years after the shuttle Challenger crashed to Earth, the fallen astronauts, their mission and the management failures that cost them their lives have faded from public memory. Once eulogized by President Ronald Reagan, the crew's names now grace schools, bridges and other public works, quiet honors that symbolize the inevitable transition from front page news to somber history.

But for their families, friends and co-workers at NASA - and for now-grown students across the country who tuned in that day to watch New Hampshire high school teacher Christa McAuliffe blast off - Challenger remains a sad, still-vivid mixture of shock and disillusionment, a tragedy underscored by the sacrifice of seven men and women who rode to their deaths on national television.

Idaho school teacher Barbara Morgan was looking on that day, too, watching Challenger's ground-shaking launch up close and personal from the press site at the Kennedy Space Center just 4 miles from launch complex 39B. Morgan, a bright young teacher with an engaging smile and endless optimism, finished second out of 11,000 entrants in the competition to select NASA's first Teacher in Space. She trained with McAuliffe and the rest of the crew for six months and was wishing them well when Challenger lifted off at 11:38 a.m. EST on Jan. 28, 1986.

Seventy three seconds later, she watched with dawning horror as Challenger disintegrated in the cold, blue sky, killing seven�friends and co-workers in a brutally public way: commander Frances "Dick" Scobee, pilot�Michael Smith, Ellison Onizuka, Ronald McNair, Judith Resnik, civilian satellite engineer Gregory Jarvis and, of course, McAuliffe.

Most people in Morgan's position - a school teacher with no background in aviation or space flight - would have been content, if not eager, to walk away from NASA and back into the relative safety of the classroom.

But not Morgan. To her, McAuliffe's interrupted flight was a lesson untaught, a promise to students everywhere that adults had a moral obligation to fulfill. And there was never any doubt in her mind that if NASA ever offered a chance to step into McAuliffe's shoes, she would jump at the opportunity.

"We had school kids, not only all over the country but all over the world looking at adults and watching to see what adults do in a bad situation," Morgan told reporters last month. "And I felt it was really important to show them that adults do the right thing, that we're going to work hard to figure out what was wrong, work hard to figure out how to fix it and keep the future open ended. I've carried that with me ever since."

Morgan did, in fact, go back to teaching in the aftermath of Challenger. But she never gave up the dream, working with NASA to develop education initiatives, traveling across the country to talk with students and quietly lobbying agency leaders to fly in space. But NASA was reluctant to put another civilian aboard the space shuttle and few agency observers gave Morgan much chance of realizing her long-held goal.

That all changed in January 1998 when former NASA Administrator Daniel Goldin announced that Mercury 7 astronaut and retiring Sen. John Glenn had been offered a seat on a shuttle. That same day, in news release that was overshadowed by the Glenn announcement, NASA said that Morgan had been invited to join the astronaut corps.

In April 2002, Goldin's successor, Sean O'Keefe, announced a new category of "educator-astronaut," a classification that later evolved into "educator-mission specialist." Morgan was the first member of that group and on Dec. 12, 2002, she was assigned to mission STS-118, a space station assembly flight aboard shuttle Columbia. Launch, with a crew that originally included former astronaut Lisa Nowak, was scheduled for the fall of 2003.

On hand to get a look at her shuttle, Morgan was at the Kennedy Space Center on Feb. 1, 2003, making runway approaches in a NASA training jet with chief astronaut Kent Rominger while awaiting Columbia's descent from orbit to close out mission STS-107. STS-118 was Columbia's next flight.

But NASA's first space shuttle never made it home, breaking apart above Texas 16 minutes from touchdown. All seven astronauts were killed and Morgan, like so many others at NASA, was once again touched by tragedy. STS-118 was put on hold and Nowak and another crew member were assigned to other missions.

Now, 21 years after Challenger and four years after Columbia, Morgan is finally ready to blast off aboard the shuttle Endeavour, the orbiter that was built to replace Challenger and named by school kids. In a very real sense, Morgan's career has come full circle, a living thread that weaves together the memory of Challenger and Columbia, of lives and dreams lost, and the unfulfilled promise of the Teacher in Space.

"Christa was and is and always will be a great representative of the teaching profession," said Morgan, now 55. "And we are really, really proud of her. She was, is, and always will be our Teacher in Space. This mission is symbolic and I know that people will be thinking about not just Christa, but the Challenger crew and the Challenger mission. And that's a good thing. And I know they will be thinking about so many people over the years, the families, friends, colleagues and people the Challenger crew never ever even knew ... who for so many years have been working so hard at continuing on their work and their dreams."

Morgan readily accepts her place as "Christa McAuliffe's backup" and the seemingly unbreakable link to the Challenger disaster that she represents to her many younger co-workers. To her, the focus has always been on students and the opportunity an educator-astronaut would have to expand their horizons. Whatever purely personal goals and motivations she might have are left unsaid. Anything else, her silence seems to imply, would take away from McAuliffe's legacy and the cherished memory of her fallen comrades.

June Scobee Rogers appreciates that effort. Wife of Challenger commander Dick Scobee and a teacher herself, Rogers founded the Challenger Centers for Space Science Education in the wake of the 1986 disaster. She said it was typical of Morgan to deflect media attention from herself and to focus on the broader education program. But it's a bit of a lost cause, Rogers said, because "she's a rock star among teachers."

"I'm over the moon happy for Barbara," she said in an interview. "She is persistent, determined and she still has that youthful bubble and spark of enthusiasm that she had as a young woman when she first was training along side Christa McAuliffe. She is representing educators everywhere, showing that it's a truly honorable profession. She's (showing people that) persistence pays off and saying to kids, reach for the stars, keep plugging away at those dreams. What a message she's getting out to the general public in addition to teachers and kids."

Her astronaut status aside, "Barbara is still a teacher first," Rogers said. "Her heart is in that honorable profession. She may be trained as an astronaut but she is first and foremost a teacher who loves the classroom and that is still in her and will always be with her."

Morgan will ride into space strapped into the center seat on Endeavour's lower deck, the same seat position used by McAuliffe.

"I actually haven't thought about that!" she said at the launch pad last month. "But I've definitely thought about Christa and thought of the whole Challenger crew and that's something, those folks are with us in here (pointing at her heart) and they've been with us every single day of the training and all the way through.

"I know people are going to think about Challenger and they should. And I want people to remember what great folks they were and that what happened with Challenger was wrong, but what the crew and NASA was trying to do was absolutely right. I'm grateful that we are continuing that."

As for fulfilling McAuliffe's legacy, Morgan said "Christa and the Challenger crew's legacy is open ended. It will go on forever. Every teacher's legacy is open ended. And every crew's legacy is open ended. I hope this goes on past when you and I are long gone, and we've gone back to the moon and onto Mars and who knows where."

Classified as an educator-mission specialist, NASA managers and her fellow crew members view her as an astronaut first, with critical, mission-specific responsibilities. While she plans to participate in a few relatively modest educational events in space, she will not teach any lessons as McAuliffe once planned to do. Instead, she will operate Endeavour's robot arm and oversee the transfer of some 5,000 pounds of equipment and supplies to the space station.

"I think it's fantastic that Barbara is flying on this mission," said lead flight director Matt Abbott. "NASA's very committed to education and ... some of the experiments and the events Barbara will be participating in are directly furthering that cause. In my mind, Barbara is a full-up mission specialist astronaut, she's an integral part of the crew, she's doing a lot of robotics operations and she's very much in charge of a lot of our transfer operations.

"One of the things I look forward to the most is hearing her characterization of the flight experience from an educator perspective," he said. "I expect her to have some very interesting insights and comments and feelings about it once she gets back."

Said space station flight director Joel Montalbano: "To us, she's not an educator-astronaut, she's one of the full crew members. She's worked in the ISS control center with us and she understands our job extremely well and we're looking forward to Barbara's mission."

Crewmate Rick Mastracchio, a spacewalker and Endeavour's flight engineer, agreed, saying "a lot of people, maybe from outside NASA, look at Barbara Morgan as the teacher-in-space type of thing. We don't look at Barb as a teacher, we look at Barb as another astronaut."

"She's a crew member on this mission. And she's got a lot of responsibilities on the mission and oh yeah, by the way, she's going to do some public affairs events where she's going to do some question and answers with some students to help promote education. NASA's been promoting education since day one, this is just another step in maybe trying to reach into the classroom, trying to get kids interested in space, science, math, any way to motivate kids to learn. Barb is a very hard-working person and she really believes in what she's doing. I think she'll do a really good job and we're happy to have her."

For cynics who might not believe role models always live up to their billing, Endeavour astronaut Tracy Caldwell, who holds a Ph.D. in chemistry, is proof to the contrary. As a high school student, she decided to become an astronaut after reading about McAuliffe's preparations to fly aboard Challenger.

"I got real serious about it when I was 16 and had one more year left in high school before i went on to college," she said in an interview. "I knew I wanted to go to college, but I didn't know what I wanted to do. ... And it was right around that time that the nation was buzzing about NASA and it was all because of Christa McAuliffe and the Challenger mission.

"Of course, this was before the accident but it was the first time I realized that astronauts were more than test pilots," she said. "I associated with her so quickly because teachers impacted my life every day. I spent more time with teachers in my day than I did my own parents. So when I looked at Christa, I started to look at what is this astronaut thing? ... And as I looked more at what they were doing, I looked back at my list and I kind of made a connection."

Flying with an astronaut who could have been one of Christa McAuliffe's students illustrates the long road Morgan has followed from Idaho to the launch pad.

"It really does just seem like yesterday," she said last month. "I was reflecting on some things, one of the things that comes to mind right away with being on Endeavour is not only was it the replacement for Challenger, but it was named by school children all over this country.

"And so more than anything, it's such a joyful feeling and rewarding for everybody that's ever been involved in any of this. I know for Christa and me, we got to be here ... but there were teachers all over the country who were part of that program and still are today and who have been working extremely hard over the last 20 years to bring aerospace education, bring this stuff alive for kids and teachers in their communities and in their states.

"What I think pleases me most of all, is it's going on into the future, we've got three other teachers in the astronaut corps now, they're training for flights to come."

Born Nov. 28, 1951, in Fresno, Calif., Morgan earned a bachelor's degree in biology from Stanford University in 1973 and a teaching certificate from the College of Notre Dame in Belmont, Calif., in 1974. She is married to Clay Morgan and has two sons.

Morgan began teaching in 1974 on the Flathead Indian Reservation in Arlee, Mont. She then taught remedial reading and math at McCall-Donnelly Elementary School in McCall, Idaho, and spent a year teaching English and science to third grade students in Ecuador. She was back at McCall-Donnelly teaching second, third and fourth grades when she was selected as McAuliffe's backup on July 19, 1985.

After the Challenger disaster, Morgan returned to McCall-Donnelly Elementary School and continued working with NASA as "Teacher In Space Designee," giving talks and helping with curriculum design and development until 1998 when she was selected as an astronaut.

"She's got an incredible amount of willpower, I think," Endeavour commander Scott Kelly said in an interview. "She's been involved in this program for a long time, a lot longer than any of us on the crew. She's just kind of pressed ahead through a lot of adversity, so you've got to really respect her for that."

Given her close association with Challenger and Columbia, Morgan could be forgiven if she feels a bit nervous on launch day. But in an interview at the Johnson Space Center, she insisted she will not be scared.

"I will be alert on the launch pad," she said. "I won't be scared, but I will be alert. And that's a good thing."

Asked what she is looking forward to the most, Morgan said "actually doing the work. It's like teaching, the work is fun, it's interesting, it's challenging, it's rewarding and we've worked long and hard at it and that's what I look forward to, actually doing the work. I think that's going to be really rewarding."

"I am going up doing the job of an astronaut, the work of an astronaut, but I'm going up with a teacher's eyes, ears, heart and mind. And so I look very much forward to doing that with an open mind and being able to come back and take what it is I've learned and be able to translate that into how can we best provide wonderful opportunities for our colleagues and our students."

Rogers will help with that goal when she participates in an educational downlink with Morgan from a Challenger Center in Washington, DC.

"For the general public, Challenger was lost and the teacher in space mission was lost," Rogers said. "But for the Challenger legacy, for all those teachers out there who are watching and for all those students who are waiting, they are still waiting. They have never forgotten. Whereas the general public might have put it aside, teachers everywhere have not forgotten. So the rest of the nation is catching up with us."

6:47 PM, 8/1/07, Update: Valve replacement ordered

NASA managers today ordered engineers to replace a suspect positive pressure relief valve in the shuttle Endeavour's crew module to fix an apparent leak that showed up over the weekend during routine launch pad testing. While the schedule is tight, engineers expect to complete the work in time for Endeavour's launch Tuesday on a space station assembly mission.

"It's extremely tight," a NASA spokesman said late today. "On paper, yes, we can make it. But everything has to go right from this point forward."

The valve in question is one of two in the crew module that ensure the cabin air pressure stays within required limits. Engineers plan to replace the valve, located behind the shuttle's toilet on the lower deck of the split-level crew cabin, with one taken from the shuttle Atlantis. The work should be completed Thursday. Engineers then will have to carry out additional pressure tests to confirm the system is operating normally before Endeavour can be cleared for flight.

While the unplanned work poses a challenge to the shuttle launch team - there is no contingency time left in the schedule - engineers say Endeavour should be ready for blastoff on time at 7:02 p.m. Tuesday. Earlier concern about thermostats in one of the orbiter's hydraulic power units has been resolved and NASA plans to start Endeavour's countdown on time at 9 p.m. Saturday.

11:33 AM, 7/31/07, Update: Engineers troubleshoot apparent shuttle cabin leak; Mars launch delayed 24 hours

Engineers readying the shuttle Endeavour for the start of its countdown Saturday and launch next Tuesday on a space station assembly mission are wrestling with an apparent crew cabin leak that is proving difficult to isolate.

On Saturday, engineers carried out a standard crew module-airlock leak test and were surprised to note a pressure decay rate of 0.06 pounds per square inch in one hour. The allowable limit is 0.022 psi over four hours. After opening the crew cabin hatch and verifying the position of numerous valves, additional checks were carried out with similar results.

Troubleshooting continued Sunday and by Monday, engineers believed they had isolated the problem to a loose fitting in ground equipment. But tests Monday night to confirm that were not successful and engineers now suspect a real leak. Endeavour passed a similar leak test on May 15, before the shuttle was moved to the launch pad, and it's not clear what might have changed.

Endeavour is carrying a pressurized logistics module in its cargo bay that is connected to the shuttle's external airlock by a short tunnel. The airlock, in turn, is attached to the aft bulkhead of the crew module and there are multiple hatches, valves and seals where a leak could occur. Engineers suspect possible problems with a pressure relief valve located behind the back wall of the shuttle's toilet.

It's not yet clear what impact work to replace the valve, if required, might have on Endeavour's launch date. Such work would be invasive, however, and time is short.

The Endeavour astronauts - commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, Rick Mastracchio, Dave Williams, educator-astronaut Barbara Morgan and Al Drew - plan to fly to the Kennedy Space Center on Friday. The countdown is scheduled to begin at 9 p.m. Saturday for a launch at 7:02 p.m. Tuesday.

A wild card in the shuttle's ground processing flow is the planned launch of the Mars Phoenix lander atop a Delta 2 rocket from the Cape Canaveral Air Force Station. Liftoff had been targeted for 5:35:18 a.m. Friday, but the high-priority flight has slipped 24 hours, to 5:26:31 a.m. Saturday, because of anticipated bad weather later today.

Phoenix could launch as late as Sunday morning, at 5:17:23 a.m., and not impact NASA's plans to launch Endeavour on Tuesday. But bad weather or additional problems with the Mars mission could have an impact on the shuttle. The $414 million mission has a limited 22-day launch window that won't reopen for another two years. NASA managers have said Phoenix likely would be given additional launch tries, if necessary.

9:42 PM, 7/27/07, Update: NASA managers vow more detailed review of alleged astronaut alcohol abuse; fight surgeon concerns

NASA managers today vowed to carry out a detailed follow-up study to flesh out an agency-ordered review of astronaut health care issues that included anonymous allegations of alcohol abuse in the astronaut corps. The initial review was ordered in the wake of the Lisa Nowak affair earlier this year but it appeared to raise more questions than it answered. The review, released today, provided few details and relied mainly on anecdotal reports of alcohol abuse and the perceived reluctance of senior astronauts and NASA managers to heed concerns raised by flight surgeons and even other astronauts.

"Interviews with both flight surgeons and astronauts identified some episodes of heavy use of alcohol by astronauts in the immediate preflight period, which has led to flight safety concerns," the report said. "Alcohol is freely used in crew quarters. Two specific instances were described where astronauts had been so intoxicated prior to flight that flight surgeons and/or fellow astronauts raised concerns to local on-scene leadership regarding flight safety. However, the individuals were still permitted to fly."

That allegation touched off a firestorm of internal and external speculation because the report did not specify whether either of the two incidents in question involved the space shuttle, flights in T-38 jet trainers or U.S. astronauts launching aboard Russian Soyuz rockets. Today, Air Force Col. Richard Bachmann Jr., chairman of the NASA Astronaut Healthcare System Review Committee, attempted to clarify the issue.

"There were two incidents described to us in more detail as representative of a larger concern," he said. "One of those incidents involved both the shuttle and a T-38 during the course of the same incident. The second incident involved the Soyuz."

In the case of the shuttle, he said, a T-38 incident allegedly occurred after a shuttle launch was called off because of technical problems. But it was not clear whether the astronaut in question was believed to be intoxicated aboard the shuttle or later, after the crew left the area. Many agency insiders privately scoffed at the idea of a drunken astronaut getting aboard a shuttle given the numerous suit technicians, fellow astronauts and managers they come in contact with on launch day.

But Bachmann defended the report and said the details were not the focus.

"The two specific incidents of alcohol use that we put into the report were specifically chosen to illustrate a larger problem, to call attention to the larger issue, which is the role of the flight surgeon in protecting both the individual's health, flight safety and mission completion," he said. "And the fact that the flight surgeons and other astronauts who described their role in these incidents and in others which we did not obtain further details on, used these to say they felt concerned that their professional input seemed to be disregarded, at least at the local level, and they were demoralized by that disregard to the point that they felt like they would be less likely to report concerns ... in the future.

"The committee was not concerned in the details of these specific instances to the degree where we felt compelled to get names and dates and times. It was not a legal investigation, we did not take sworn testimony or depositions or make transcripts. We were performing a review, an overview to identify areas of concern back to NASA for them ... to conduct a much more extensive and rigorous anonymous survey in order to find out whether these isolated incidents are, in fact, isolated or whether they are pervasive."

Asked about the lack of detail in a report raising serious questions about astronaut behavior, Bachmann said "there is certainly no intent to impugn the entire astronaut corps."

"Our desire when these incidents were told to us by volunteer NASA personnel who accepted the opportunity to come and talk to us, we were compelled to raise those to NASA's attention," he said. "We don't have enough data to call it alcohol abuse. We have no way of knowing if these are the only two incidents that have ever occurred in the history of the astronaut corps or if they are the tip of a very large iceberg.

"We have no way of making any judgments on that. And that's why we recommended to NASA that they do a lot more evaluation and the only way you're going to get that kind of information is number one, leadership has to ask for it and support it and number two, the people you're asking for it from need to feel safe, that they can participate in this process without endangering their careers."

Former shuttle commander Rick Searfoss, veteran of three space missions, said the report was not consistent with his own experience in the astronaut corps.

"I can speak probably more directly to that than anyone because of my religion," he told CBS Radio. "As a Latter Day Saint, I do not drink at all and I am not going to compromise that for anything, I wouldn't compromise that even to go to fly in space. And I never felt like I had to the least little bit. ... I never once felt any bit of pressure to compromise that and I can't see where any of my colleagues would feel that pressure. This is just very flummoxing to me to see this thing, it's entirely inconsistent with what I saw in my nine years in the corps."

Searfoss said he was "extremely disappointed there weren't more specifics in this report."

"It just smacked to me of rumor mongering and at this point, I just kind of look at the whole thing as kind of like the Duke lacrosse case," he said. "Let's have some facts and specific missions and some names and get down to it. These are very, very serious allegations that are in my experience completely inconsistent with both the culture and things I personally observed supporting a whole bunch of launches from 1990 to 1998, and of course, my own three launches. I mean, this report is so inconsistent with anything I ever saw. I never saw that with any of the flight surgeons I worked with, that they would compromise their professional ethics and integrity that way."

But Bachmann said his review panel found the anonymous interviews credible enough to pass on to NASA management.

"Many of the cultural and structural issues identified in the report have existed for many years, pre-dating the current leadership team, are deeply ingrained and will take senior leadership action to (correct) them," he said. "Members of the medical and astronaut communities raised significant concerns regarding barriers to communication. They described instances where medical personnel or a fellow astronaut raised concerns about an astronaut's fitness for flight due to alcohol use in the immediate pre-flight period. And these concerns appeared to them to be disregarded or over ridden.

"The committee was concerned about this perception of disregard for human factors input and recommends that NASA conduct further evaluation using tools such as anonymous surveys to determine the extent of such perceptions and insure that human factors concerns are appropriately identified and dealt with."

Deputy NASA Administrator Shana Dale said NASA would do just that:

- NASA�s Medical Policy Board "will further assess the medical and behavioral findings and recommendations in the JSC internal review as well as the report of the external Review Committee," she said. "The board will provide advice on policy changes that will improve the NASA health care system, and will provide oversight of the implementation of those policies.

- NASA will consider developing a formal "astronaut code of conduct."

- NASA will evaluate the organizational structure of the astronaut office at the Johnson Space Center in Houston "with a renewed interest in establishing what are referred to as, 'enduring supervisor relationships,'" Dale said. "We plan to develop an anonymous survey to be completed by members of the astronaut corps and flight surgeons to initiate even more feedback on the findings and recommendations of the report in order to optimize supervisory relationships, health care delivery, and mission success."

- NASA will act "immediately on the more troubling aspects of the report, with respect to alcohol use and the anecdotal references to resistance of agency leadership to accepting advice or criticisms about the fitness and readiness of individuals for space flight. The report does not provide specific information about alcohol-related incidents and the Review Committee has left it to NASA to determine the scope of these alleged incidents."

Dale said NASA Administrator Mike Griffin has directed the agency's senior safety manager to carry out an internal safety review to determine the accuracy of the anecdotal references to alleged alcohol abuse and to recommend corrective actions if any such abuse can be documented.

"In the meantime, NASA�s existing T-38 aircraft alcohol use policy that historically has been applied to space flight has been explicitly extended as an interim policy to flight on any spacecraft," she said. "This interim policy limits alcohol use for 12 hours prior to flight and further states that astronauts will neither be under the influence nor the effects of alcohol at the time of launch. A comprehensive review of alcohol use policy prior to aircraft use or space flight is already underway."

5:30 PM, 7/26/07, Update: Endeavour tentatively cleared for launch; NASA investigates sabotage of black box; astronaut health care report on tap Friday

Wrapping up a two-day flight readiness review, NASA managers today tentatively cleared the shuttle Endeavour for blastoff Aug. 7 on a space station assembly flight featuring educator-astronaut Barbara Morgan. NASA's inspector general, meanwhile, is investigating the apparent sabotage of an electronic black box that is part of a wireless instrumentation system bound for the lab complex. NASA managers had no immediate comment on an Aviation Week & Space Technology magazine report citing an agency-ordered review of astronaut health care issues and alleged alcohol abuse.

Endeavour is scheduled for launch at 7:02 p.m. on Aug. 7. At the controls will be commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, Rick Mastracchio, Dave Williams, Al Drew and Morgan, NASA's first educator-astronaut and backup to Christa McAuliffe in the original Teacher in Space Program.

This will be Endeavour's first flight since late 2002 following an extensive maintenance and overhaul period in the wake of the 2003 Columbia disaster.

Endeavour has been equipped with Global Positioning System navigation gear and a new station-to-shuttle power transfer system that will allow the orbiter to use electricity generated by the station's solar arrays. If the system works as expected, the crew will be able to extend the mission by three days and remain docked to the lab complex longer than previously possible.

"It's like a new space shuttle," said Program Manager Wayne Hale. "It's been completely inspected from stem to stern for any defects in the wiring, any structural corrosion and it's come out clean. It's like driving a new car off the showroom floor. But even more than that, we made 194 modifications to improve safety on board Endeavour."

"It was a tremendous amount of work in the OPF," said Launch Director Mike Leinbach. "The processing (at the pad) is going really well. ... The launch countdown will pick up Saturday night, Aug. 4, shooting for an on-time launch on Aug. 7. On behalf of all the people who worked on Endeavour, both here and really across the country, it's a great feeling to have Endeavour back on the pad and looking forward to a great launch."

Bill Gerstenmaier, associate administrator for spaceflight at NASA headquarters in Washington, said engineers are expected to resolve a handful of outstanding technical issues between now and Aug. 7.

One of those open issues is work to repair an electronic component that apparently was deliberately sabotaged. Gerstenmaier said the company that supplied the component notified NASA of deliberate damage found in a qualification unit in the factory. A subsequent inspection of the flight hardware revealed similar intentional wire cuts. The component in question does not play a critical role on the station and it will be repaired in time for launch.

"There was some intentional damage done internal to a qual unit," Gerstenmaier said. "We then inspected the flight unit and determined that some wires were cut on the inside of that unit. This is currently being investigated by the inspector general's office. The subcontractor on the space station side will fix the hardware and we'll get ready to go fly it."

The computer component is part of a system used to collect data from sensors on the station's main solar array truss to better characterize the stresses and strains the structure experiences.

"The subcontractor told us about it as soon as they found it," Gerstenmaier said. "We went and checked the flight unit and it had the same kind of damage inside. We will fix it and go fly the unit. It's a device we use to take data off some sensors out on the truss."

Gerstenmaier declined to comment on media reports today about a NASA review of astronaut health care issues in the wake of the Lisa Nowak arrest earlier this year.

Aviation Week & Space Technology magazine reported today that the NASA-chartered review "has found that on at least two occasions astronauts were allowed to fly after flight surgeons and other astronauts warned they were so intoxicated that they posed a flight-safety risk."

"The panel also reported 'heavy use of alcohol' by astronauts before launch, within the standard 12-hour 'bottle to throttle' rule applied to NASA flight crew members."

The story did not say whether the two flight incidents in question involved the space shuttle, NASA jet trainers or U.S. astronauts launched aboard Russian Soyuz rockets from the Baikonur Cosmodrome in Kazakhstan. Several sources told CBS News the report does not include any names or other specific details and is generally anecdotal in nature.

Two sources said they believed one of the incidents in question may have involved a Soyuz launch and another a T-38 flight. Another source noted shuttle astronauts leave their quarters at the Kennedy Space Center and board the orbiter on live NASA television, wearing 70-pound pressure suits, and that he was not aware of any crew member ever showing obvious signs of intoxication on launch day.

But NASA officials had no official comment and speculation today about the nature of the two incidents remained just that - speculation.

At a news conference to discuss Endeavour's flight readiness review, Gerstenmaier said he could not discuss the details of the health care report before its planned release Friday. But he did say he was not aware of any past disciplinary actions related to alcohol abuse or any instance in which a shuttle flight was jeopardized by such behavior.

"Again, I don't know, you guys are going to keep asking me the same question a bunch of different ways," he said. "But the obvious answer is no, I've never had any instances of that. You know the astronauts and where we are. That's all I really want to say on that. But there's not been a disciplinary action or anything I've been involved with regarding this type of activity."

A NASA spokesman contacted by CBS News said the agency planned to hold a news conference Friday afternoon to discuss the medical review.

8:57 AM, 7/10/07, Update: Shuttle Endeavour moved to launch pad

Running late because of last-minute work and the threat of bad weather, the shuttle Endeavour, carried by a powerful crawler-transporter, began the 3.2-mile trip to launch pad 39A Tuesday evening at 8:10 p.m. Six hours and 50 minutes later, at 3 a.m. today, the shuttle and its mobile launch platform were parked atop the pad. Launch on a space station assembly mission is targeted for 7:02 p.m. Aug. 7.

Rollout originally was scheduled to begin at 12:01 a.m. Tuesday, but the move was held up by minor problems and the threat of afternoon thunderstorms. With rollout Tuesday evening, mission managers say at least one full day of contingency time is available to handle unexpected problems between now and launch.

Endeavour's crew - commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, flight engineer Rick Mastracchio, Canadian flier Dafydd "Dave" Williams, Benjamin "Al" Drew and educator-astronaut Barbara Morgan - plans to fly to the Kennedy Space Center next Monday for emergency procedures training and a dress rehearsal countdown July 19.

A two-day flight readiness review to assess the status of ground processing and to set an official launch date is scheduled for July 25 and 26. If all goes well, Kelly and his crewmates will fly back to Florida on Aug. 3 - the same day NASA hopes to launch the Phoenix Mars polar lander - for the start of Endeavour's countdown the evening of Aug. 4.

The goal of the 119th shuttle mission is to attach a short spacer segment to the international space station's main solar power truss; to replace one of four stabilizing gyroscopes; to attach an external equipment platform; and to deliver needed supplies and equipment.

The mission is baselined for 11 days with three spacewalks. But if a new power transfer system works, allowing the shuttle to tap into the space station's solar power grid, the flight will be extended to 14 days and a fourth spacewalk will be added.

11:36 AM, 7/8/07, Update: Shuttle Endeavour readied for rollout; flight plan updated

Engineers are readying the shuttle Endeavour for rollout to pad 39A early Tuesday and launch Aug. 7 on a space station assembly and resupply mission. The flight features NASA's first educator-astronaut, Barbara Morgan, who served as backup to Christa McAuliffe in the original Teacher-in-Space program. There are no major technical problems with the shuttle or the space station, but NASA managers could opt to delay Endeavour's launch a few days if the agency's next Mars probe - the Phoenix polar lander - runs into problems getting off its pad as planned on Aug. 3.

Either way, Morgan and her crewmates - commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, flight engineer Rick Mastracchio, Canadian flier Dafydd Williams and Benjamin "Al" Drew - plan to participate in media briefings next Wednesday at the Johnson Space Center in Houston before flying to Florida July 16 for final emergency procedures training and a dress-rehearsal countdown July 19.

STS-118 crew (left to right): Rick Mastracchio, Barbara Morgan, pilot Charles Hobaugh, commander Scott Kelly, Tracy Caldwell, Dafydd "Dave" Williams, Benjamin Alvin Drew

Aboard the international space station, meanwhile, astronaut Clay Anderson and Expedition 15 commander Fyodor Yurchikhin plan to stage a spacewalk July 23 to replace a failed electrical component needed to restore redundant power to the mobile transporter used to move the lab's robot arm from one work site to another.

In one of the more dramatic moments of the excursion, Anderson plans to jettison a no-longer-needed 1,400-pound ammonia tank that was part of the station's early power-and-cooling system. The spacewalkers also will clean the mating surfaces of the common berthing mechanism on the downward facing hatch of the Unity module. After Endeavour departs, a pressurized mating adapter currently mounted on Unity's left-side port will be moved to the downward facing hatch to make way for upcoming assembly work and engineers want to ensure a good seal.

"It won't be a problem," Anderson said of the ammonia tank in a pre-launch interview. "It's about 1,500 pounds, I believe. I tell everybody it's about the size of a refrigerator. (In training), I've been relatively consistent with being able to chuck it at around 40 centimeters per second (0.9 mph) and we really only need five centimeters a second. So I think I can send it on its way."

To clear the way for the spacewalk, Russian flight controllers plan to carry out a test reboost maneuver July 21 to make sure computers in the Russian segment are up to the task of controlling the lab's orientation and position.

During a shuttle mission last month to install a new set of solar arrays, secondary power supply switches, presumably detecting minor power quality changes in the station's electrical grid, triggered major problems, preventing critical guidance computers and command-and-control computers from rebooting. Yurchikhin and flight engineer Oleg Kotov eventually installed jumper cables to bypass the suspect switches and the computers powered back up normally.

The July 21 test will serve as another test of the hot-wired system's ability to control the station's attitude. A longer reboost maneuver is planned a few hours after the July 23 spacewalk to ensure plenty of clearance between the lab complex and the jettisoned ammonia tank. The reboost also will set up docking opportunities for a Progress supply ship as well as for Endeavour.

A Progress vehicle loaded with trash and no-longer-needed equipment is scheduled to undock from the Pirs airlock and docking module Aug. 1. The Progress 26 spacecraft, carrying replacement computer gear and other supplies, is scheduled to blast off from the Baikonur Cosmodrome in Kazakhstan at 1:33 p.m. EDT on Aug. 2. Docking is expected on Aug. 5, two days before Endeavour's launching on mission STS-118.

In the midst of space station activity and shuttle launch preparations, NASA is gearing up to launch the Mars Phoenix polar lander atop a Delta 2 rocket at 5:35 a.m. on Aug. 3, the day before Endeavour's countdown is scheduled to begin. This is a high-priority $414 million mission with a limited 22-day launch window that won't reopen for another two years. As such, shuttle managers could be asked to put Endeavour's countdown on hold if Phoenix runs into problems getting off the ground.

Concern, in part, about a possible conflict with Phoenix prompted NASA Administrator Mike Griffin to approve a decision to delay launch of NASA's Dawn asteroid exploration mission from this month to September after a series of problems pushed launch, also aboard a Delta 2 rocket, toward the end of its July launch window.

Endeavour, making its first flight since November 2002, is fresh out of a lengthy overhaul. It is equipped with a new station-to-shuttle power transfer system that will enable the orbiter to use electricity generated by the station's solar panels, easing the load on the shuttle's three fuel cells.

Going into the STS-118 mission, the approved flight plan calls for an 11-day mission with three spacewalks. But if the station-to-shuttle power transfer system works, Endeavour's mission will be extended three days and a fourth spacewalk will be added to the timeline. The SSPTS will be activated shortly after docking, but it will be shut down just before the first spacewalk on flight day 4 because the array it draws power from cannot track the sun during the assembly work. The power transfer system will be reactivated after the spacewalk. At some point after that, if there are no problems, the flight will be extended three days.

The primary goal of Endeavour's mission is to install a short spacer segment on the right end of the station's main solar power truss; to install a refurbished control moment gyroscope to replace one that has shown signs of impending failure; to attach an external equipment stowage platform; and to deliver needed supplies and equipment.

The flight will receive more public attention than most because of Morgan's presence as the first educator-astronaut, a designation approved by former Administrator Dan Goldin when he announced in 1998 that Morgan had been accepted as a full-time astronaut.

Morgan served as backup to high school social studies teacher Christa McAuliffe in the original Teacher in Space program and was looking on from the Kennedy Space Center press site on Jan. 28, 1986, when Challenger took off on its final mission. Morgan never gave up her dream of flying in space and on Aug. 7, she will strap into the center seat on Endeavour's lower deck - the same seat position used by McAuliffe aboard Challenger - to finally fulfill the legacy of the first teacher in space.

"Christa McAuliffe�s legacy is open-ended," Morgan said in a NASA interview. "Every teacher�s legacy is open-ended. I know people will be looking at this and remembering Challenger, and that�s a good thing. They will also be thinking about all the people - teachers and other people - who have been working really hard and will continue working really hard to carry on the work that Christa was doing. I�m happy about that."

Assuming an on-time liftoff, Endeavour will dock with the space station around 3:50 p.m. on Thursday, Aug. 9. SSPTS activation is targeted for 7:47 p.m. that evening, just after the S5 spacer segment is unberthed by the shuttle's robot arm and handed off to the station's arm.

The next day, around 2 p.m., Mastracchio and Williams plan to begin a busy spacewalk to bolt S5 onto the end of the main truss; to relocate a grapple fixture and, if time permits, to connect electrical cables between S5 and the S4 solar panel segment and to prepare S5 for the eventual attachment of a final set of solar arrays, known as S6. They also will monitor the retraction of a folding radiator on the P6 solar array segment to prepare it for relocation to the left end of the main truss later this year.

The S4 solar array will be locked in place for the S5 attachment and as such, unable to track the sun. Because of that, the SSPTS must be deactivated before the spacewalk begins. Once S5 is in place and S4 resumes its normal rotation to track the sun, the SSPTS will be reactivated. A decision to extend the mission is expected after engineers verify the system is working normally.

Mastracchio and Williams plan to venture outside again two days later, around 1:30 p.m. on Aug. 12, to install the new control moment gyroscope. The station uses four massive CMGs to control the lab's orientation without using hard-to-replace rocket fuel. One of them, CMG No. 3, acted up last year and was taken off line on Oct. 10, 2006. The refurbished unit being installed during Endeavour's mission will restore full redundancy to the critical orientation system.

The external stowage platform will be attached to the station's truss structure the day after the second spacewalk using the lab's robot arm. That will set the stage for the third spacewalk of the mission, this one by Mastracchio and Anderson, to upgrade the station's S-band communications; to relocate two logistics carts attached to the mobile transporter; and to retrieve two experiment packages.

Anderson originally was scheduled to take off aboard Endeavour to replace astronaut Sunita Williams. But after the shuttle Atlantis was delayed three months, from March to June, because of hail damage to the ship's external tank, NASA managers decided to launch Anderson aboard Atlantis and to bring Williams home in June as originally planned. Anderson's place in Endeavour's crew was given to Drew.

Assuming the SSPTS is working properly, mission managers are expected to extend Endeavour's flight to permit a fourth spacewalk by Anderson and Williams that would begin around noon on Aug. 16. The goals of the final excursion are to install supports that eventually will permit a shuttle heat shield sensor boom to be stored on the station; to install two wireless instrumentation antennas on the U.S. lab module; to retrieve a failed Global Positioning System satellite antenna; and to install a wireless video transceiver on the S3 truss segment.

Under the extended mission scenario, Endeavour would undock from the station around 10 a.m. on Aug. 19 and return to Earth around 1:13 p.m. on Aug. 21.

A detailed timeline covering highlights of the 11-day and 14-day mission options is posted on the CBS News STS-118 Quick-Look page. A detailed mission preview will be posted here as soon as possible after the upcoming briefings in Houston.

04:00 PM, 6/22/07, Update: Atlantis glides to California landing (UPDATED at 5:15 PM with indications repaired insulation blanket peeled back during entry; UPDATED at 5:45 p.m. with quotes from commander, pilot)

Running a day late because of blustery Florida weather, the space shuttle Atlantis dropped out of a sunny Mojave Desert sky and swooped to a smooth touchdown on runway 22 at Edwards Air Force Base, Calif., to close out an action-packed space station assembly mission.

Flying upside down and backward over the Indian Ocean half a world away, shuttle commander Rick Sturckow and pilot Lee Archambault fired Atlantis' twin braking rockets at 2:43:47 p.m. EDT for 2 minutes and 33 seconds, slowing the ship by about 200 mph - just enough to drop it into the atmosphere for an hourlong glide back to Earth.

The astronauts had hoped to return to Florida, but cloudy weather and rain showers prevented a landing Thursday. With a forecast for more of the same on tap today, entry Flight Director Norm Knight diverted the crew to Edwards one orbit after waving off the first of two opportunities to land at the Kennedy Space Center.

Approaching California from the southwest just off the Baja peninsula, Atlantis streaked above San Diego in a steep descent toward Edwards some 100 miles northeast of Los Angeles. Heralded by twin sonic booms, Sturckow took over manual control as the shuttle descended through 50,000 feet, guided the orbiter through a sweeping right overhead turn and then down to a picture-perfect touchdown on runway 22 at 3:49:38 p.m. EDT.

"Houston, Atlantis, wheels stopped," Sturckow radioed mission control when the shuttle rolled to a halt.

"Atlantis, Houston, copy wheels stopped. Welcome back, congratulations on a great mission," replied astronaut Dominic "Tony" Antonelli from the Johnson Space Center.

Flight surgeons were standing by to assist returning space station astronaut Sunita Williams, who made the trip back to Earth resting on her back in a recumbent seat bolted to the floor of the shuttle's lower deck. Launched to the station last December, Williams logged 195 days off the planet - a single-flight record for female astronauts.

"I can't wait to get back and feel the air on my face and the sea breeze," Williams told a reporter Wednesday. "I'm looking forward to hopefully going to the beach and taking a walk with my husband and my dog. That's the first thing. And secondly, I just can't wait for a good piece of pizza."

And a hair cut.

"I think I'm going to have a lot flatter hair when I get back," she laughed. "So I think I'm going to have to work on getting a hair cut as soon as I get back so it looks a little bit normal. I have been living like this with hair up and flying around for a little while, so it's going to be funny to see what it looks like when I get home."

She might get the haircut, but it might be a while before Williams feels up to a stroll on the beach. It typically takes returning space station astronauts a month or so to get their land legs back and up to a full year to completely recover from the bone and muscle loss associated with long stays in weightlessness.

Williams said earlier she had exercised as required throughout her stay aboard the station and she did not anticipate any major problems readapting to gravity.

Her shuttle crewmates - Sturckow, Archambault, flight engineer Steve Swanson, Pat Forrester, Danny Olivas and Jim Reilly - doffed their pressure suits and greeted NASA officials on the runway for a quick inspection of the orbiter. All seven astronauts plan to spend the night at Edwards before flying back to the Johnson Space Center on Saturday.

"It's great to be back here ... in California, it's just great to be back on planet Earth right now," Sturckow said from the runway. "We had just a wonderful mission. ... There were a lot of challenges on this mission and they were all surmounted, all the solutions worked well and we had a very successful flight."

Echoing the same sentiments, Archambault said "we're very proud that the mission is complete. We got the mission done, we brought the orbiter back in great shape and we're here safe and sound at Edwards. Just want to thank everybody, not only here at Edwards recovering us today, but also the folks back at KSC as well as JSC who helped make STS-117 a very successful mission. Thank you very much."

Mission duration was 13 days 20 hours 11 minutes and 34 seconds covering 219 complete orbits and 5.8 million miles since blastoff June 8.

Atlantis blasted off three months late because of hail damage to the ship's external fuel tank. The shuttle's primary payload was a 36,000-pound $367 million solar array truss segment, along with a fresh station crew member - Clay Anderson - to replace Williams.

The S3/S4 solar array truss was attached to the right side of the lab's main power truss the day after docking and hooked up during three spacewalks by Reilly, Olivas, Swanson and Forrester. The astronauts also completed the retraction of another set of arrays that must be repositioned later this year.

Because of concern about a peeled-back insulation blanket on the shuttle's left-side Orbital Maneuvering System rocket pod, NASA managers extended the shuttle flight two days and added a fourth spacewalk to give the crew time to make repairs and complete their other work. The repair job eventually was added to the third spacewalk and Olivas, anchored to the end of the shuttle's robot arm, pushed the blanket back down and used a surgical stapler and stainless steel pins to hold it in place.

Engineers will examine the rocket pod later to make sure it didn't suffer any heat damage during re-entry. In long-range television views from the runway, the blanket appeared intact. In later close-up views, it appeared the same corner might have pulled back up during entry. But there were no obvious signs of heat damage and surrounding tiles and blankets were not discolored.

Atlantis' mission was challenging enough without major space station problems but that's exactly what happened last week during installation of the S3/S4 solar array truss. At roughly the same time the new arrays were attached, the Russian command module's three guidance, navigation and control computers, known collectively as the terminal computer, along with three high-level command-and-control machines known as the central computer, failed to reboot after the guidance system crashed. After three days of around-the-clock troubleshooting, Russian engineers asked station commander Fyodor Yurchikhin and flight engineer Oleg Kotov to install jumper cables to bypass suspect secondary power supply switches.

The repair worked and after additional tests and checkout, two computers, or "lanes," in each system were brought back on line. The other two were kept off line in backup mode. But engineers still don't know what caused the so-called soft switches in the secondary power supplies to act up. The circuitry is designed to cut off power to the computers if the incoming electricity isn't stable to within fairly narrow parameters.

Some engineers suspected the new solar arrays caused some slight change in the station's power grid that affected the power supply switches. But during a test last Friday, the computers were isolated from the new arrays and they still failed to boot up. Yurchikhin and Kotov then bypassed the secondary power supply switches and all six computers ultimately were successfully activated.

On Thursday, the two off-line backup computers - lane No. 1 of the central computer and lane No. 2 in the terminal computer - were powered back up, verified to be healthy and then shut down so Yurchikhin and Kotov could remove the power supply bypass jumpers in a test to help engineers determine whether the cause of last week's problem was transitory or the result of some ongoing issue.

But the computers failed to boot up without the jumpers, indicating whatever caused the problem last week is still there, or at least the problem in the power supplies is still present. Russian mission managers plan to launch replacement computer gear aboard an unmanned Progress supply ship scheduled for takeoff July 22. But before they install any new gear, engineers would like to pin down the root cause of the earlier computer problems.

Next up for NASA is launch of the shuttle Endeavour around Aug. 7 to deliver a short spacer segment that will be attached to the S4 solar array permitting the eventual attachment of a new set of arrays - S6 - next year. The crew also will deliver an external equipment storage platform.

The Endeavour mission features educator-astronaut Barbara Morgan, backup to Challenger "teacher-in-space" Christa McAuliffe. Morgan is now a full-fledged astronaut making her first flight.