March 21, 2008

Astronauts to Scan Shuttle Heat Shield at Station

HOUSTON - Astronauts aboard NASA's
shuttle Endeavour will scan their spacecraft's vital heat shield for dings
again Friday, even though the orbiter is still docked at 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.

"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."

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

"The Japanese module was built long
before the requirement to have the [boom] existed, so there's a clearance
problem in the payload bay," Mike Moses, lead shuttle flight director for
Endeavour's flight, has said.

Similar clearance problems existed
to 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.

Moses has said today's survey, which
is scheduled to begin at 4:03 p.m. EDT (2003 GMT), will take twice as long to
scan Endeavour's starboard wing because the station's Columbus lab is in the

"Pretty much, it's going to take us
the whole day to complete those scans and downlink the video and data," Moses

The shuttle boom also won't 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 16-day mission to deliver a new crewmember, Japanese
module and giant,
Canadian-built robot
to the ISS. The astronauts are slated to undock from
the station late March 24 and land on March 26.

NASA is broadcasting Endeavour's
STS-123 mission live on NASA TV. Click
for's shuttle mission coverage and NASA TV feed.