NASA May Try Shuttle Repair
Monday, August 1, 2005
HOUSTON, July 31 -- NASA hopes to decide Monday whether to order an unrehearsed spacewalk to make the first exterior "repair" of the space shuttle in orbit. An astronaut would try to eliminate a potential reentry hazard by removing two protruding bits of heat shielding on the belly of the shuttle Discovery.
Wayne Hale, the shuttle's deputy project manager, said he thought such a spacewalk would be a relatively "easy thing," but "we are not making light" of a problem that NASA officials earlier had appeared to dismiss.
"The risk here of going underneath the vehicle is, we hope, relatively remote," Hale said during a Johnson Space Center news conference Sunday. "But it is surely something you have to think about. That is part of the calculation."
Even if planners ultimately determine a repair is not needed, the potential danger from the two "gap fillers" offered another cause for alarm for a shuttle fleet already grounded because Discovery's external fuel tank shed large pieces of foam insulation during launch last Tuesday.
A similar, but larger, piece of foam damaged space shuttle Columbia's heat shielding during launch, causing the orbiter to disintegrate on reentry Feb. 1, 2003. NASA spent the next 2 1/2 years designing a new tank. Discovery's launch was supposed to herald its successful debut.
Hale said he expects to hear Monday from aerodynamics experts studying how much effect the protruding gap fillers could have in increasing the heat from atmospheric turbulence during reentry. "I expect we'll have some decisions for you," he said.
The analysis "may very well show" that the fabric does not pose a reentry problem, he added. In that case, NASA shuttle directors would tell commander Eileen Collins and her six fellow crew members simply to come home to Kennedy Space Center in Florida as planned on Aug. 8.
The shuttle crew, along with space station commander Sergei Krikalev and flight engineer John Phillips, spent a quiet Sunday transferring equipment and supplies, and preparing for a second planned spacewalk Monday to replace a broken gyroscope on the station. Hale said if a spacewalk were ordered for the gap fillers, it would most likely be an added task for the final scheduled spacewalk, on Wednesday.
Protruding gap fillers have nothing to do with debris damage. They are the space shuttle equivalent of shims -- thin pieces of treated fabric or ceramic inserted between thermal tiles that have separated beyond design tolerances.
Not all the tiles in the quilt-like pattern on the shuttle's underside need gap fillers, but there are thousands of them on every orbiter. They have been used since the dawn of the program nearly 25 years ago to "caulk" openings in the shielding that protects the orbiter during reentry.
Steve Poulos, NASA's orbiter project office manager, said engineers preparing for Discovery's flight were "fully aware" of the tendency of the gap fillers to come loose, probably due to the expansion and contraction of the heat shield during launch.
He said Discovery is stocked with the necessary tools -- including pliers, scissors and a hacksaw-like implement -- for removing an offending gap filler by slicing it off. Both Discovery spacewalkers, Soichi Noguchi and Steve Robinson, have used the tools during training.