HOUSTON -- Astronautsaboard NASA's shuttle Endeavour will prepare for a possible spacewalk repair oftheir orbiter's dinged heat shield, even as NASA deferred a decision on whetherthe fix will be required, mission managers said late Wednesday.
Shuttleofficials delayed a planned Friday spacewalk for Endeavour's STS-118 crew by 24hours to perform a few final tests, and will decide Thursday whether leave asmall gougein the heat-resistant tiles on the orbiter's underbelly as is or stage a riskyspacewalk repair.
"I amcautiously optimistic that repair will not be needed," Shannon maintainedin a briefing here at NASA's Johnson Space Center.
A piece offoam insulation popped free from Endeavour's external fuel tank about oneminute after NASA'sAug. 8 launch, then bounced off a metal strut to bite into theheat-resistant tiles just aft of the shuttle's right landing gear door. Theresulting 3 1/2-inch (nine-centimeter) long gash etched through one tile toexpose a thin strip of felt coating Endeavour's aluminum skin.
NASA haskept a close watch on fuel tank debris and shuttle heat shield integrity sincethe fatal 2003 Columbiaaccident. But Endeavour's ding, mission managers said, is not deemed asafety risk for its STS-118 crew.
"Thisis not a catastrophic case," Shannon stressed of the tile damage onEndeavour. "This is a turnaround discussion.
Endeavouris slated to fly in February to haul the first of Japan's three-part laboratoryto the International Space Station (ISS), where it is currently docked. Anyextensive repairs after the shuttles planned landing next week could lengthenthat turnaround time and crimp NASA's already tight schedule to complete ISSconstruction before the shuttle fleet's September 2010 retirement date.
But stagingan untried spacewalk repair, which would put two astronauts at the top of Endeavour's100-foot (30-meter) robotic arm and inspection boom, perched close to theshuttle's fragile tiles, carries its own risks that must be weighed against themerits of the fix itself, Shannon said.
NASAastronaut Shannon Walker radioed Endeavour's seven-astronaut crew from MissionControl to pass on news of the spacewalk delay and the possible repair to theirshuttle's thermal protection system (TPS). ISS mission managers said they hopedthe now-Saturday spacewalk won't include any tile repair tasks, but wantEndeavour's crew to be ready just in case.
"Unfortunately,we have no idea which way the wind is blowing at the moment," NASA astronautShannon Walker told the joint crews of Endeavour and the ISS late Wednesdayfrom Mission Control. "Plan your day tomorrow as if it's going to be a TPSrepair, but stressing that no decision has been made either way."
"Ok,thank you," shuttle commander Scott Kelly replied.
NASA's initialcomputer modeling and subsequent mockup tests to recreate the searing heat ofreentry found that the small gouge on Endeavour's underbelly, which sits justaft of the orbiter's right landing gear doors, will not exceed NASA's safetymargins for a safe Earth return. It might cause additionaltile damage, but none that would be a threat to the orbiter or its crew,Shannon said.
"I thinkmost of the data is in place for us to make a decision but I wanted the team togo off and think about it overnight," he added.
Meanwhile,delaying the next STS-118 spacewalk to Saturday will also give NASA engineerstime to root out the source of a small hole in the outer layers of Endeavourastronaut Rick Mastracchio's left spacesuit glove. The damage forced missionmanagers to cutshort a Wednesday spacewalk, and they hope to understand its implicationsbefore the next spacewalk outside the ISS.
"Ithink we'll get there," Steve Doering, NASA's spacewalk office manager,said Wednesday. "We're going to be looking at some of the datatomorrow."
NASA is broadcastingEndeavour's STS-118 mission live on NASA TV. Click here for mission updates andSPACE.com's NASA TV feed.
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