HOUSTON -- Astronauts aboard NASA's shuttle Endeavour will prepare for a possible spacewalk repair of their orbiter's dinged heat shield, even as NASA deferred a decision on whether the fix will be required, mission managers said late Wednesday.
Shuttle officials delayed a planned Friday spacewalk for Endeavour's STS-118 crew by 24 hours to perform a few final tests, and will decide Thursday whether leave a small gouge in the heat-resistant tiles on the orbiter's underbelly as is or stage a risky spacewalk repair.
"I am cautiously optimistic that repair will not be needed," Shannon maintained in a briefing here at NASA's Johnson Space Center.
A piece of foam insulation popped free from Endeavour's external fuel tank about one minute after NASA's Aug. 8 launch, then bounced off a metal strut to bite into the heat-resistant tiles just aft of the shuttle's right landing gear door. The resulting 3 1/2-inch (nine-centimeter) long gash etched through one tile to expose a thin strip of felt coating Endeavour's aluminum skin.
NASA has kept a close watch on fuel tank debris and shuttle heat shield integrity since the fatal 2003 Columbia accident. But Endeavour's ding, mission managers said, is not deemed a safety risk for its STS-118 crew.
"This is not a catastrophic case," Shannon stressed of the tile damage on Endeavour. "This is a turnaround discussion.
Endeavour is slated to fly in February to haul the first of Japan's three-part laboratory to the International Space Station (ISS), where it is currently docked. Any extensive repairs after the shuttles planned landing next week could lengthen that turnaround time and crimp NASA's already tight schedule to complete ISS construction before the shuttle fleet's September 2010 retirement date.
But staging an untried spacewalk repair, which would put two astronauts at the top of Endeavour's 100-foot (30-meter) robotic arm and inspection boom, perched close to the shuttle's fragile tiles, carries its own risks that must be weighed against the merits of the fix itself, Shannon said.
NASA astronaut Shannon Walker radioed Endeavour's seven-astronaut crew from Mission Control to pass on news of the spacewalk delay and the possible repair to their shuttle's thermal protection system (TPS). ISS mission managers said they hoped the now-Saturday spacewalk won't include any tile repair tasks, but want Endeavour's crew to be ready just in case.
"Unfortunately, we have no idea which way the wind is blowing at the moment," NASA astronaut Shannon Walker told the joint crews of Endeavour and the ISS late Wednesday from Mission Control. "Plan your day tomorrow as if it's going to be a TPS repair, but stressing that no decision has been made either way."
thank you," shuttle commander Scott Kelly replied.
NASA's initial computer modeling and subsequent mockup tests to recreate the searing heat of reentry found that the small gouge on Endeavour's underbelly, which sits just aft of the orbiter's right landing gear doors, will not exceed NASA's safety margins for a safe Earth return. It might cause additional tile damage, but none that would be a threat to the orbiter or its crew, Shannon 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," he added.
Meanwhile, delaying the next STS-118 spacewalk to Saturday will also give NASA engineers time to root out the source of a small hole in the outer layers of Endeavour astronaut Rick Mastracchio's left spacesuit glove. The damage forced mission managers to cut short a Wednesday spacewalk, and they hope to understand its implications before the next spacewalk outside the ISS.
"I think we'll get there," Steve Doering, NASA's spacewalk office manager, said Wednesday. "We're going to be looking at some of the data tomorrow."
NASA is broadcasting Endeavour's STS-118 mission live on NASA TV. Click here for mission updates and SPACE.com's NASA TV feed.
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