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 The spacewalks, the first of which is slated to begin at 7:10 a.m.
EST (1210 GMT) on Saturday, are needed to replace one of two cooling
pumps outside the $100 billion complex, which flies about 250 miles
above Earth.
U.S. spacewalks have been suspended since July after a spacesuit
helmet worn by Italian astronaut Luca Parmitano filled with water,
causing him to nearly drown.
The underlying cause of the leak remains under investigation but
engineers have learned enough to make modifications so the problem
will not happen again, NASA managers told reporters during a
conference call.
"I would be surprised if we have a problem with the suits," said
space station program manager Mike Suffredini.
As a contingency, the spacewalkers' helmets will be outfitted with
absorbent pads and home-made snorkels to funnel air from the body of
the water-cooled suits into an astronaut's mouth, if needed.
The snorkels, which were fabricated by the crew on Sunday, are made
from plastic water line vent tubes used in the spacesuits.
"This is your last resort," said Allison Bolinger, lead spacewalk
officer. "If water is encroaching your face, similar to what
happened to Luca, the crewmember can lean down and use this (the
snorkel) to breathe."
First-time spacewalker Michael Hopkins will wear Parmitano's
spacesuit, but it has been outfitted with a new fan pump separator,
a device that circulates water and air and removes moisture from
air.
The fan pump separator from Parmitano's suit was flown back to Earth
for analysis and engineers found tiny holes in the water-separator
portion of the device were clogged.
That allowed water to back up into the fan portion, get into a vent
loop and enter the helmet, said space station flight director Dina
Contella.
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Still unknown is how the water was contaminated.
"Unfortunately, it's a pretty complicated water chemistry problem,"
Contella said.
Suffredini said: "We believe the lines we're using today are clean.
We've put in new filters and we think the filter system works."
A new fan pump separator is among the cargo aboard Orbital Sciences
Corp's first supply ship to the station which had been slated to
launch this week. But it is being delayed until mid-January so NASA
can tackle the higher-priority work of getting the station's cooling
system back in operation.
One of two ammonia cooling systems shut down on December 11, forcing
astronauts to turn off unnecessary equipment and suspend some
science experiments.
The U.S. side of the station has a second cooling system, but it
cannot accommodate all the gear.
Hopkins will be joined by six-time spacewalker Rick Mastracchio for
three spacewalks to replace the faulty cooling system with a spare
that is in storage outside the station.
In addition to Saturday's 6.5-hour outing, spacewalks are planned
for Monday and Wednesday.
(Editing by Kevin Gray and Mohammad Zargham)
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