NASA: No Danger In Endeavour Damage; Repair Job Said To Be Unneeded
Storm Forces Early Mission End; Landing At 12:32 P.M. ET Tomorrow
NASA officials decided that astronauts on Space Shuttle Endeavour can survive their impending reentry tomorrow without first having spacewalking crew members repair a gouged area in the protective thermal tiles on the bottom of their orbiter vehicle.
Reentry was to be Wednesday, but NASA hastened the return to Earth by a day because of fears that powerful Hurricane Dean, swirling in the Caribbean, might force Mission Control at Johnson Space Center in Houston to close before the shuttle could land at Kennedy Space Center (KSC).
The mission has been cut back from two weeks to 13 days, and landing now is set for a window that begins at 12:32 p.m. ET tomorrow. There also is a later 2:06 p.m. landing possibility at KSC, and still-later landing times at the alternative landing site at Edwards Air Force Base, Calif. However, no announcement has been made that weather is expected to obviate chances for the preferred Florida landing at KSC.
There is no danger that damage found in heat tiles covering Endeavour will cause a catastrophe during reentry if it isn’t repaired, a senior NASA official told the news media.
That damage occurred Aug. 8 when Endeavour launched on the STS-118 mission to the International Space Station (ISS) from KSC, and a piece of foam insulation, possibly coated with ice, broke free from the Endeavour external fuel tank.
This was precisely what NASA hoped to prevent when it redesigned the fuel tank and foam application over the past several years, improvements that all were incorporated on Endeavour.
The foam struck the bottom of Endeavour, gouging roughly all the way though the heat tile in an area about 3 by 2 inches, leaving little tile there to protect the structural elements of the shuttle orbiter vehicle and its crew of seven when they reenter the atmosphere and encounter blistering heat at 12,000 miles per hour.
A key concern here is that in 2003, Space Shuttle Columbia heat shielding was damaged by foam insulation during launch, punching an undetected hole in the leading edge of a wing. Later, when the mission concluded, Columbia attempted to return to Earth, but the searing super-hot gases of reentry rushed through the hole into the wing and heated structural components until they failed. The orbiter vehicle disintegrated, and the ship and crew were lost.
But the situation on Endeavour is markedly different, according to many NASA engineers.
First, the amount of reentry heat hitting the leading edge of an orbiter wing (Columbia) is higher than the heat toward the bottom rear of the orbiter vehicle (Endeavour).
Also, the scorching gases were hitting the Columbia wing-edge head-on, while reentry gases will be flowing over and past the damaged area on Endeavour.
And with Endeavour, the damage is known and assessed precisely, thanks to preventive procedures that were put in place in response to the Columbia disaster. With Columbia, the damage to the wing edge was unknown, merely suspected by some NASA staffers.
The decision not to repair the gouge in the Endeavour heat shielding came after days of lengthy meetings involving hundreds of personnel.
John Shannon, NASA deputy shuttle program director, laid out the exhaustive testing and review process that ended with a conclusion that Endeavour can safely return to Earth without repairs first being performed in space.
Asked whether there is zero chance that the orbiter vehicle and its crew of seven will be lost if repairs aren’t made and Endeavour then begins reentry, Shannon replied, “Yes.”
Assessing the gouged thermal-tile problem, Shannon said, “It does not constitute any risk to the crew.”
Therefore, he stated, it is “acceptable” to have the space shuttle negotiate reentry without first being repaired.
One crucial factor here, he said, is that tests performed on the ground with heat tiles that NASA damaged in a fashion similar to the gouge on Endeavour showed that the structure of the orbiter vehicle underneath the tiles wouldn’t suffer heating that could cause structural failure. “We understand that cavity,” he said, referring to the gouged area of the tile.
“We were above our factor of safety” by a wide margin, Shannon said.
Beneath the test thermal tile, “we had no heating problems underneath,” he explained.
A vast force of engineers and experts reviewed the matter, including test results, and most of them agreed that repairs were unnecessary, including staff at Marshall Space Flight Center, KSC, Mission Operations, the Flight Crew Office, and more. “They were all in agreement that use-as-is” would be “the way to go,” he said.
The only dissent, he said, came from an engineering group at Johnson Space Center, which would have preferred to see repairs executed, although not asserting that reentry without repairs would pose grave safety risks.
Also agreeing with the decision to brave reentry without first repairing the damage were members of the Endeavour STS-118 crew, who held a news conference in space, fielding questions from reporters on Earth.
Crew members are Navy Cdr. Scott J. Kelly as mission commander and Marine Corps Lt. Col. Charles O. Hobaugh as pilot. Veteran astronauts Richard A. Mastracchio and Dafydd (Dave) Williams of the Canadian Space Agency are mission specialists, as are first-time space fliers Barbara R. Morgan, Tracy E. Caldwell and Benjamin Alvin Drew.
Morgan has waited decades for her ride into the void of space.
A teacher, she was the backup astronaut to Christa McAuliffe for a mission on Space Shuttle Challenger. When Challenger launched on Jan. 28, 1986, a problem with O-rings in the solid rocket boosters led to an explosion shortly after liftoff that killed McAuliffe and the other crew members.
Why No Repairs
Even if tests and analysis indicate that Endeavour likely will be able to survive reentry without repair, why not make the repairs anyway, just to err on the side of safety?
Shannon indicated there are sound reasons for the no-repair decision.
First, the potential threat that the gouge might pose was examined and reexamined by an army of highly expert staffers, including an hours-long open conference/teleconference discussion with literally hundreds of engineers debating the issue.
As well, to make repairs, such as using paint and goo filler in the gouged dent, would change its shape from the shape of mimicked damage on tiles that were tested on the ground by NASA. Thus the repairs on Endeavour would introduce an element of uncertainty.
Too, any spacewalk to repair the damage would necessitate astronauts venturing around to the bottom of the shuttle, which faces away from the space station. That far journey itself would carry risk, and there also could be a risk of an astronaut inadvertently damaging tiles.
Other issues surrounding reentry and return of Endeavour tomorrow include a debris strike on an orbiter vehicle window in the cockpit, perhaps caused by foam or by space junk, and the storm problem.
KSC weather problems previously have delayed shuttle landings, and the last one, involving Space Shuttle Atlantis, had to be shifted from KSC to Edwards Air Force Base, Calif. That landing was followed by Atlantis taking a piggyback ride on a special Boeing 747 jumbo jet aircraft that carried it the final leg back to KSC, after weather problems in Florida abated.
Endeavour undocked from the space station yesterday, a day earlier than planned, in a hurried departure that followed closing of the hatches between the shuttle and ISS Saturday afternoon.
Routine inspections of the shuttle protective heat shields on its leading wing edges and nose cap were performed, using a sensor on a robotic arm.
Another part of the mission that was rushed and ended faster than scheduled was the fourth and final spacewalk in STS-118.
Astronauts Williams and Clay Anderson, who has spent months on the space station, had to move quickly to finish their work in the void of space.
Williams and Anderson shortened their spacewalk to 5 hours, 2 minutes, to allow the early hatch closing and departure.
They installed a stand for the shuttle’s robotic arm extension boom on the station’s truss structure, installed an External Wireless Instrumentation System antenna and retrieved two containers of the Materials ISS Experiment. They also had a chance to look down at the hurricane as it swirled in the Caribbean Sea.
The spacewalk began at 9:17 a.m. and concluded at 2:19 p.m., bumping up the total time for STS-118’s four spacewalks to 23 hours and 15 minutes. Saturday’s excursion was the 92nd spacewalk devoted to station assembly.
Among key goals achieved during the spacewalks were installation of the Starboard 5, or S5, truss on the steadily-growing space station construction job, and replacement of a faulty control moment gyroscope needed to keep the space station at the correct attitude, along with transport of tons of items and supplies to the space station, and the transport of tons of unneeded items from the station back to Earth.