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 The spacewalk, which was broadcast live on NASA Television, was
the first for NASA since July when the spacesuit helmet worn by
Italian astronaut Luca Parmitano began filling with water, a
situation that could have caused him to drown.
No such leaks were detected in Saturday's spacewalk, the first of
two or possibly three that will be needed to complete the cooling
system repair.
The operation was prompted by the December 11 shutdown of one of the
station's two U.S. ammonia cooling systems, which forced the crew to
turn off non-essential equipment and shut down dozens of science
experiments.
While the six-member crew is not in danger, the remaining cooling
system cannot support the three laboratories and other modules on
the U.S. side of the $100 billion station, a project of 15 nations.
The Russian side of the station has a separate cooling system.
Engineers at the Johnson Space Center in Houston tried devising ways
to bypass a suspected faulty pump valve, but with time running
short, managers decided to have astronauts replace the pump, located
outside the station, with a spare.
The work, which began shortly after 7 a.m. EST, went smoothly, with
station flight engineers Rick Mastracchio and Mike Hopkins finishing
up an hour earlier than expected.
They were able to not only disconnect the old pump, but also remove
it from its pallet on the station's exterior truss, a task slated
for a second spacewalk originally planned for Monday and later
delayed until Tuesday, NASA said late on Saturday.
A third spacewalk, if needed, presumably also would slip one day,
from Wednesday to Thursday.
NASA said an extra day was needed to prepare a backup spacesuit for
Mastracchio to use.
"During repressurization of the station's airlock following the
spacewalk, a spacesuit configuration issue put the suit Mastracchio
was wearing in question for the next excursion," NASA said in a
statement.
The issue is not related to the water leak that was seen during the
July spacewalk, NASA said.
"Both Mastracchio and Hopkins reported dry conditions repeatedly
throughout (Saturday's) activities," the statement said.
Mastracchio, a veteran of six previous spacewalks, and Hopkins, a
rookie, wore spacesuits that were modified to protect them from
another possible water leak. The problem in July was traced to
contamination in piece of equipment called a fan pump separator that
circulates water and air in the spacesuit and removes moisture from
air.
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How the water-separator portion of the device became clogged remains
under investigation.
Hopkins wore Parmitano's spacesuit, but it had been outfitted with a
new fan pump separator. In addition, both Hopkins and Mastracchio
rigged their helmets with homemade snorkels, fabricated out of
pieces of plastic tubing and Velcro, which they could have used for
breathing in case of another water leak. The helmets also included
water-absorbent pads.
FAILED PUMP
During Saturday's spacewalk, Mastracchio and Hopkins disconnected
electrical and fluid lines and removed the 780-pound (354-kg),
5-foot (1.5-metre) wide cooling system pump.
The failed pump, which was then anchored in a temporary storage
site, will remain on the station for possible future repair and
reuse.
It was installed in 2010 during an unexpectedly difficult series of
spacewalks by astronauts Doug Wheelock and Tracy Caldwell Dyson.
"What makes this pump very difficult (to work on) are (the) fluid
disconnects because they are so large and they are pressurized and
they contain liquid ammonia, so that's a hazard for us if it were to
come in contact with us or our suits," Caldwell Dyson said in an
interview with a NASA TV mission commentator.
Maintaining focus also can be a challenge, she added.
"When you're on one of those pallets, you really have that sensation
that you are sticking out on the edge of a skyscraper. Especially
when you look down, you see your feet and then you see the Earth
going 17,500 mph beneath you, it really does get your attention,"
she said.
Mastracchio and Hopkins encountered no major problems during
Saturday's outing.
"These guys really went out there and were so efficient," Caldwell
Dyson said. "It may be more difficult to remove the pump because you
don't know exactly what to expect," she added.
(Reporting by Irene Klotz; editing by Vicki Allen and Sandra Maler)
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