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U.S. space shuttle astronauts took their second
spacewalk in three days Monday, acting as orbiting mechanics at the
International Space Station. They made repairs to the outpost's cooling
system and its railroad flatcar.
The spacewalk by shuttle Discovery astronauts Mike Fossum
and Piers Sellers lacked the theater of their Saturday venture, when they
bounced and twisted at the end of a 30-meter long pole like circus
high-wire performers to test its stability as a platform to make shuttle
repairs in orbit.
For this outing, they continued more mundane
maintenance they began Saturday on the space station's rail car, which
rolls back and forth to position the outpost's mechanical arm and heavy
equipment during construction. They replaced a backup cable that delivers
power, video, and data to the car. It had been inadvertently severed
by a cable cutter in
December.
Shuttle pilot Mark Kelly, who supervised the spacewalk from inside,
spoke to Fossum as the astronauts prepared to replace the reel from which
the cable unwinds as the railcar moves.
Kelly: "You look pretty comfortable out there, Mike.
Fossum: "Well, I'm working up a sweat."
Sellers found the working conditions on this task a
bit cramped .
"This is a tricky place to work," said Piers Sellers.
The two astronauts also replaced a spare external pump on the station's
cooling system.
Sellers and Fossum have one more spacewalk on
Wednesday. They will test techniques to inspect and repair the reinforced
carbon panels on the front edges of the shuttle wings while in orbit. That
was the part of the shuttle Columbia punctured by a piece of hard insulating foam
that rushed
down from the external fuel tank during its 2003 launch, dooming it to a
fiery disintegration during its re-entry into the atmosphere.
Discovery's flight has tested changes the U.S. space agency, NASA, has
made to the fuel tank to minimize the amount of threatening foam it sheds
at launch. Ground controllers have used new in-flight inspection cameras
and sensors installed since the Columbia accident to look over the
orbiter's fragile heat shield. They have found no launch or any other
damage that would prevent Discovery's safe return, so they have cleared it
for re-entry.
Shuttle official Phil Engelauf says the successful Discovery mission so
far and the refurbishment of the space station's railcar prepare the way
for the resumption of station assembly, which has been stopped since
Columbia's demise.
"We have a huge amount of work coming ahead and the success of this
mission is a good indicator that we are heading toward another launch in
the August time frame unless anything new comes up," said Phil Engelauf.
"The assembly sequences is set to proceed fast and furious here. We're
only six or seven weeks out from the next mission."
In the meantime, Discovery is due back on Earth next Monday to end a
13-day mission that has delivered cargo and a third crew member to the
space station, German astronaut Thomas Reiter.
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