Two
astronauts will head outside the International Space Station Wednesday to
begin the delicate task of replacing old batteries at the very edge of the
orbital outpost.
Spacewalkers
Dave Wolf and Chris Cassidy will replace four of six old solar array batteries
on the station's on the port side during the tricky
maintenance call, which is slated to begin at about 10:58 a.m. EDT (1458
GMT) and last more than six hours. It is the third of five spacewalks for
astronauts while the shuttle Endeavour is linked to the station.
"We've
always wrestled with how to do this battery change out," Wolf told SPACE.com
before flight. "We've been wringing our hands for upwards of seven years on
this task."
A tricky
chore
While it
seems straightforward, the batteries are the oldest ones on
the space station, which uses solar arrays to generate power. They are
attached to the station's Port-6 (P6) solar wing - the first ever launched to
the outpost - and have been in space since 2000.
Simply
reaching the work site is challenging since it sits at the end of the port side
on the station's backbone-like main truss. The space station's metallic
backbone is as long as an American football field and serves as
the foundation for its four sets of solar arrays. Wolf and Cassidy will be
working hundreds of feet away from the station's core, with no quick way back.
"I think
it's the farthest you could get from the airlock hatch...since the airlock's on
the starboard side," Cassidy said in a NASA interview.
All six of
the new batteries to be installed are attached to cargo pallet that is
currently perched at the tip of the station's 57-foot (17-meter) Canadarm2
robotic arm. Astronauts moved the arm into position on Tuesday and will stretch
it out to its full length today, with the battery carrier extended toward
today's portside worksite.
Moving the individual
batteries has its own challenges. Wolf and Cassidy will have to shuffle the old
and new batteries between their work site and the carrier on the robotic arm.
Each battery weighs 367 pounds (166 kg) and is the size of a refrigerator.
"It's a
long, complicated choreography to change all these batteries," Wolf told
reporters before flight. "They're heavy, delicate, so there's a lot of chance
for error...it just all has to go right."
Other
tasks on tap
Wolf is a veteran
NASA astronaut making his seventh career spacewalk with today's excursion.
He also serves the spacewalk branch chief in NASA's astronaut office.
Cassidy, a
U.S. Navy SEAL, will be making his first spacewalk during the orbital work and
is making his first spaceflight on Endeavour's construction flight to the space
station. He became the 500th person to reach space when Endeavour launched
toward the station last week.
In addition
to their battery swap work, Wolf and Cassidy also plan to prepare a trio of new
experiments for installation on the station's
Japanese porch. They are also expected to finish adding insulation to power
lines that allow visiting shuttle like Endeavour to tap into the station's
power grid.
The last
two of the six old batteries being replaced at the station will be swapped out
during a Friday spacewalk - the fourth for Endeavour's seven-astronaut crew,
mission managers said.
The
astronauts are currently in the middle of a 16-day mission to deliver the
station's new experiment porch and a new crewmember. They are slated to return
home July 31.
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