A pair of spacewalking
astronauts will work on the oldest U.S. solar arrays of the International Space
Station on Saturday, taking care to safeguard themselves against the remote
chance of electric shocks near the orbital power plant.
NASA
astronauts Steven Swanson and Joseph Acaba plan to float outside the space
station at about 12:43 p.m. EDT (1643 GMT) to work near the batteries for a pair
of 8-year-old solar wings on the outpost's port-most edge. The chore is one of several
to prime the station for future construction and comes one day after Discovery
shuttle astronauts unfurled a
pair of new solar arrays on the outpost's starboard side, completing its
backbone-like main truss.
But before the
spacewalkers exit the station today, they will carefully wrap some of the metal
connecting rings on their spacesuits with insulating tape to protect against any
slight electrical shocks near their portside worksite, which can be prone to
arcing from the surrounding plasma environment.
"With the
suits as designed, we believe we have sufficient protection," space station
flight engineer Kwatsi Alibaruho told reporters late Friday."We've just applied
some additional factor of safety to drive the probability of a problem absolutely
as low as we could."
Alibaruho
said the risk an astronaut receiving even a mild electric shock is extremely
remote, and the voltage and currents involved are very small. But NASA rules
call for an immediate end to any spacewalk if any shock – no matter how small -
should one occur, he added.
Spacewalking
astronauts rely on their spacesuits functioning properly, including onboard electronics,
while working outside a spacecraft.
Busy
spacewalk on tap
Today's
spacewalk is the second of three for Discovery's
13-day mission, but has been revamped after launch delays prompted NASA cut
a planned fourth excursion in order to complete the shuttle flight before the
arrival of a Russian Soyuz spacecraft ferrying a new station crew next week.
The
spacewalk will be the fourth for Swanson and the first for Acaba, a former
schoolteacher who is making his first spaceflight. It will send them to various
locations across the space station's metallic backbone, a massive truss that is
longer than a football field.
"They're
ready to go," Discovery skipper Lee Archambault told Mission Control late
Friday. "We're very much looking forward to another day on orbit."
Swanson and
Acaba will loosen bolts on the portside solar wing batteries so future spacewalkers
can replace them later this year. They also plan to prepare the station to
receive two future cargo carriers, take infrared photographs of a damaged
radiator and install a new navigation antenna to help Japan's first unmanned
cargo ship - the H-2 Transfer Vehicle - dock at the orbiting lab later this
year.
While the
spacewalkers work outside the station, astronauts inside are expected to begin
testing repairs to part of the outpost's urine
recycling system. The device, a distillation assembly, is part of a larger
system to recycle condensation, astronaut urine and sweat back into pure water
for drinking, food preparation, bathing and other uses. It has been broken
since December.
Astronaut
Sandra Magnus removed the broken
distillation gear on Friday and plans to test its replacement in a dry run
later today. If successful, the urine recycler will then be used to purify a
batch of water late in Discovery's mission so new samples can be returned to
Earth.
"We have a considerable
about of urine in storage containers," Alibaruho said, adding that the urine is
usually discarded aboard disposable Russian cargo ships. "We'll take some of
that ...and attempt to process into clean water."
NASA wants
to revive the space urine recycler in order to restore the station's full recycling
system and certify that the water it produces is fit for astronaut consumption.
Recycling
water aboard the station is key to plans to boost the outpost's crew size up to
six people later this year. It would allow an extra 15,000 pounds (6,803 kg) of
cargo and other supplies, weight that was previously reserved for water
deliveries, to be launched to the station, NASA has said.
Discovery
and its shuttle astronaut crew launched toward the station on Sunday and are
due to land on March 28.
SPACE.com
is providing continuous coverage of STS-119 with reporter Clara Moskowitz and
senior editor Tariq Malik in New York. Click here for mission
updates, live spacewalk coverage and SPACE.com's live NASA TV video feed. Live spacewalk coverage begins at 11:45 a.m. EDT (1545 GMT).
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