A pair of Endeavour
shuttle astronauts will venture outside the International Space Station (ISS) today
on the first of four scheduled spacewalks to clean up a clogged solar array
gear.
Spacewalkers
Heide Stefanyshyn-Piper and Steve Bowen are due to don their NASA-issue
spacesuits and float outside the station at about 1:45 p.m. EST (1845 GMT)
today to begin the complicated chore of de-griming and lubricating a
starboard-side gear that helps the space station continuously turn its solar
panels toward the sun.
"We're
going to going to be working on the starboard solar array system, trying to
make it come back to life," Bowen said in a televised interview Monday. "We've
got a little cleaning and greasing to do."
Today's
planned spacewalk is just the first of a four-part plan to clean the ailing
solar array gear, which has been jammed
by metal grit from grinding into itself for more than a year.
Stefanyshyn-Piper,
a veteran of two spacewalks, and first-time spaceflyer Bowen are taking the
first shift. They also plan to retrieve a station nitrogen tank for return to
Earth and perform other maintenance tasks, but all eyes will be on how their
gear cleaning goes.
"Certainly,
the first [spacewalk] of any mission you want to go well," space station flight
director Holly Ridings said Monday. "We have a lot of confidence that
tomorrow's going to go well."
Stefanyshyn-Piper
is leading Endeavour's spacewalking crew on the orbital clean-up job. For
today's planned 6 1/2-hour excursion, Donald Pettit and Sandra Magnus will
operate the station's robotic arm in an orbital assist.
NASA's
shuttle Endeavour launched
Friday night and docked two days later on a planned 15-day mission to the
space station. Besides the four spacewalks, the seven-astronaut shuttle crew is
also delivering a cargo pod full
of life support equipment to prepare the space station to double its crew
size up to six astronauts next year.
"For
the most part, during the early part of the mission, there's very little free
time," said Stefanyshyn-Piper said in a preflight interview.
Stefanyshyn-Piper
and her spacewalking crew will don some new NASA spacesuit gloves during their
excursions. The new space mitts are designed to be more durable and resistant
to potentially fatal cuts or slices from sharp edges on the station's exterior.
Space station
tune-up
The
astronauts will use grease and space wipes to clean the metal filings and grit
from the starboard solar array gear, where a previous spacewalker discovered the
damage in October 2007.
That
critical Solar Alpha Rotary Joint (SARJ) is a massive, 10-foot (3-meter) wide
gear that allows the station's starboard solar panel to turn like a
paddlewheel. Future enlarged crews will draw additional power from the space
station, and so the extravehicular activities (EVAs) are focused on getting the
solar array gear unstuck.
"The
lion's share of those EVAs will be devoted to repairing this large alpha joint
which was deemed to be in a state of disrepair because it was essentially
disintegrating," explained Endeavour commander Chris Ferguson in a
preflight interview.
"Parts
of the protective coating were coming off and we had to lock one of those
critical alpha joints," he added. "So it's hoped through the efforts
of our four EVAs that we could lubricate and change out some components to
enable those alpha joints to completely function normally again."
Astronauts
will remove 11 bearings in the joint and replace them with new ones over the
course of the four spacewalks, while also cleaning off troublesome debris. They
will also do preemptive cleaning on the portside solar array gear during the
fourth spacewalk, after taking care of the ailing starboard gear.
"We'll
replace some of the bearing assemblies, and then we'll bring them home so that
that will give more information for the engineers here on the ground to look at
and to try to come up with the, with the root cause," Stefanyshyn-Piper
noted.
The
spacewalkers have repurposed a space caulk gun initially developed as part of
NASA's shuttle heat shield repair plan to squeeze out gray Braycote vacuum grease
to lubricate the joint. A scraper similar to a putty knife can dislodge debris
that has become stuck on any surfaces. Wet wipes will help clear away metal
filings and grit, and special bags are available to catch the clouds of
filings.
Stefanyshyn-Piper
expressed hope that the four spacewalks would both fix the current problem and
help extend the life of the solar array gear.
"But
that's not a task that can be done in just a couple of hours so our work on the
SARJ is spread out over three EVAs," she added. "On EVA 1 we just
start it."
NASA is
providing live coverage of Endeavour's STS-126 mission on NASA TV. Click here for SPACE.com's
mission coverage and NASA TV feed.
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