This
story was updated 11:25 p.m. EDT.
HOUSTON -
Astronauts aboard NASA's shuttle Endeavour scanned their spacecraft's vital
heat shield for dings again Friday as they prepared for their fifth spacewalk
outside the International Space Station (ISS).
The late
heat shield inspection is a now standard task for astronauts to ensure their orbiter's
sensitive heat shield panels are free of damage from micrometeorites or other
orbital debris. But the laborious scan is typically performed after a shuttle
has undocked from the ISS and has room to move its laser sensor-tipped
inspection boom - a 50-foot (15-meter) extension of the shuttle's robotic arm.
"From what we
saw, there was no obvious report of anything funny," shuttle flight director
Mike Moses said late Friday. Engineers will spend the next 24 hours sifting
through the survey's detailed laser imagery and data to be sure Endeavour's
heat shield is pristine, Moses added.
NASA has
kept a close eye on the integrity of its shuttle heat shields since the 2003 Columbia accident, in
which wing damage led to the loss of the orbiter and its crew during landing.
Astronauts now inspect the shuttle for damage just after launch, photograph its
tile-covered belly before docking at the station, then survey the heat shield
again before reentry to be sure it is safe to land.
Mission
managers have already cleared Endeavour's heat shield of any concerns from its March
11 launch. But they also decided before liftoff to move up today's late
inspection of the heat resistant carbon-composite panels lining the shuttle's
wing edges and nose cap - which experience the hottest temperatures during
reentry - in order to leave Endeavour's inspection boom at the station for its
sister ship Discovery.
Set to
launch on May 25, Discovery will be hauling Japan's primary
Kibo laboratory module, a massive, tour bus-sized cylinder that leaves no
room in the cargo bay for its own starboard sill-mounted boom, mission managers
said. Endeavour's crew will stow their shuttle's inspection boom at a berth on
the space station's backbone-like main truss during a Saturday spacewalk, the
fifth of their record 16-day mission to the ISS.
"The
Japanese module was built long before the requirement to have the [boom]
existed, so there's a clearance problem in the payload bay," Moses has said.
Similar
clearance problems existed for Europe's Columbus lab delivered last month and
the Japanese
storage room installed by Endeavour's current STS-123 astronaut crew last
week. While engineers were able to remove some fixtures to make room for those
modules, they can't for Kibo's main segment because the laboratory is simply
too big.
Instead,
Endeavour commander Dominic Gorie, pilot Gregory H. Johnson and Japanese
astronaut Takao Doi will spend a few more hours conducting their late survey
than normal, and be extra careful that the shuttle's 100-foot (30-meter)
robotic arm-boom combo does not strike the space station's outer hull.
"We haven't
done a full what we call a late inspection while we're docked," said ISS flight
director Dana Weigel in a morning status briefing, adding that some station
structure is in the way. "It's really a geometry challenge."
Moses has
said today's survey, which began just after 4:00 p.m. EDT 2000 GMT), would take
twice as long to scan Endeavour's starboard wing because the need to work
around the station's European-built Columbus lab, which juts out above the
shuttle's docking port. The shuttle boom also could not get as close to the
heat shield as normal, so some regions on the bottom of the orbiter's starboard
wing will not be scanned as clearly as they would be in an undocked inspection,
he added.
But
Endeavour astronauts said that it was debris from their shuttle's launch that
would pose the greatest risk to the spacecraft. Losing some image resolution
and a day or two on the late inspection to aid a future shuttle flight was not
a major concern, they added.
"I'm very
confident in our inspection," Gorie said of today's survey before launch.
Gorie and his
crew are currently in the midst of a packed 12-day stay at the space station,
where they have delivered a new crewmember, Japanese module and giant,
Canadian-built robot to the ISS. The astronauts are slated to undock from
the station late Monday and land Wednesday evening.
NASA is
broadcasting Endeavour's STS-123 mission live on NASA TV. Click here for SPACE.com's
shuttle mission coverage and NASA TV feed.
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