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."
"Ok,
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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