HOUSTON -- Two astronauts took the plunge today during a training
exercise for one of three critical spacewalks to repair the International Space
Station (ISS) and test new techniques for fixing heat-resistant tiles during NASA's first shuttle launch since the Columbia
accident.
NASA
astronaut Stephen Robinson and Soichi Noguchi, of the
Japanese Aerospace Exploration Agency (JAXA), spent more than five hours
underwater at the Neutral Buoyancy Center near Johnson Space Center here rehearsing the spacewalk.
Today's
test run - the goal of which was to replace a broken gyroscope with a fresh
unit - went smoothly, but Discovery astronauts said more training is still
needed before Noguchi and Robinson will be ready to
test two methods to repair damaged shuttle tiles and cracks in the thermal
protection panels made of reinforced carbon carbon.
"Most of the EVA you saw today is practicing
and rehearsing stuff we've done before," said STS-114 pilot James Kelly, who
participated in today's rehearsal from the spacewalk control room. "On our EVA
1 and 3, we still have some things that are unknown, mostly things to do with tile
repair and RCC repair."
Training for repairs
It was
damage to the space shuttle Columbia's
RCC panels along a wing leading edge - sustained during launch when a chunk of
foam broke of the orbiter's external tank - that allowed hot gases to enter the
wing and destroy the spacecraft during reentry on Feb. 1, 2003. Since the
accident, researchers and engineers have been working to develop in-space
methods to detect and repair such damage should it be necessary.
Veteran
astronaut Eileen Collins, commander of the STS-114 mission, told reporters that
while she is fully confident that Discovery's spaceflight will be the safest
ever to fly, she does not believe that the tile and RCC repair techniques are
mature enough to rely on should the flight require putting them in practice.
"Until we
actually fly them in space and test them will [the repair techniques] really be
certified," Collins said.
During the
STS-114 spaceflight, Noguchi and Robinson are slated to test the a black,
putty-like substance that can be slathered onto cracks in RCC panels, as well
as another technique called Emmitance Wash
Application, where a gray substance is dabbed onto damaged tiles to shore up
their heat protection qualities.
But
Robinson agreed with his flight commander that those initial tests should not
be pressed into action if repairs prove necessary aboard Discovery.
"We don't
want to have the first test be with us inside," he said.
Other
untested methods of tile and RCC repair may be on hand during Discovery's
mission, but will not be tested by the spacewalking duo, NASA officials said.
A smooth, wet rehearsal
For today's
spacewalk rehearsal - one of many for Noguchi and Robinson - the two astronauts
donned training versions of U.S. spacesuits and entered the mock-space
environment of NASA's Neutral Buoyancy Laboratory - a vast pool containing large
models of the ISS and shuttle payload bay - at about 9:55 a.m. EST (1455 GMT).
Five hours
and 20 minutes later, they emerged after a long day of faux-spacewalking.
"Thanks for
the great work guys," Noguchi told EVA controllers near the end of the rehearsal.
The
spacewalk is set to be the second of a trio of extravehicular activities (EVAs) for Robinson and Noguchi during the STS-114 mission aboard
the Discovery orbiter, NASA's first shuttle flight since the 2003 loss of Columbia and its
During the
spacewalk rehearsal, Noguchi and Robinson practiced replacing a device called a
control moment gyroscope (CMG) used by the ISS to maintain its position in
space. The space station relies on four such gyroscopes for orientation, with
two serving as spares. One of the devices - the one Noguchi and Robinson expect
to replace - failed in 2002.
While the
STS-114 spacewalkers had run through the gyroscope repair before, today's
rehearsal was the first time they staged their EVA from Discovery's airlock,
rather than the space station airlock as originally planned.
"We've
basically been learning more and more," Robinson said. "It helps to have more
things in our bag of tricks."
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