This
story was updated at 3:00 p.m. EST.
Two
spacewalking astronauts took a close look at a pair of balky solar array joints
outside the International Space Station (ISS) Tuesday to help engineers on
Earth draw up repair plans.
Expedition
16 commander
Peggy Whitson and flight engineer Dan Tani found widespread contamination
inside a massive gear that rotates both of the station's starboard solar
arrays, but no sign of damage to a joint at the base of one of those solar
wings, during nearly seven hours of orbital work.
"Hopefully
we got a good amount of data for the folks on the ground," said Tani, who led
the spacewalk, after the reentering station's Quest airlock.
Whitson and
Tani began Tuesday's spacewalk at 4:50 a.m. EST (0950 GMT), marking the fourth
for their Expedition 16 mission. The excursion was initially scheduled as an
extra spacewalk during NASA's STS-122
mission aboard the shuttle Atlantis, but the flight's planned December
launch was thwarted twice by faulty fuel tank sensors.
As the
Expedition 16 crew worked in orbit high above Earth, engineers at NASA's Kennedy Space Center in Florida fueled Atlantis' external tank to test the erratic sensors.
Shuttle workers hoped to recreate, and then isolate, persistent glitches with
the fuel gauge-like sensors in order to proceed with Atlantis' rescheduled
Jan. 10 launch.
Fact-finding
inspection
Whitson and Tani focused
most of their spacewalk on a massive gear designed to rotate the station's
starboard solar arrays like a paddlewheel to keep its power-generating wings
continuously facing the sun.
Engineers will use the
astronauts' findings as a reference for any plans to repair the joint's
bearings, motors and metal race ring. Solving the station's solar array joint
woes is vital to allow the outpost to support the addition of a large
Japanese-built laboratory and other modules, mission managers have said.
"We didn't find anything
that stood out," said NASA's space station program manager Mike Suffredini
after the spacewalk. "It would be really nice if something stood out and said, 'Hey,
I'm the cause of your problem,' and we didn't get that. But we do know more
about the condition of the ring."
Tani first discovered
metal grit inside the joint, known as a Solar Alpha Rotary Joint (SARJ),
during a late October spacewalk after flight controllers noticed odd vibrations
and power spikes in the mechanism's telemetry. A second inspection by
spacewalkers last month confirmed the contamination, which Tani and Whitson
found to be widely distributed around the 10-foot (3-meter) wide joint during
today's excursion.
"You can
see the motion of the gear because the debris is kind of walking across the
housing," said Tani, adding that magnetized metal shavings appeared to walk
end-over-end on one of the SARJ motors. "It's hilarious...it's animated, like
they're alive. They're like ants."
The
spacewalkers retrieved a suspect set of bearings, one of 12 on the joint, which
may be responsible for the contamination. They also used orange Kapton tape to
take samples of the metal grit and clean the SARJ gear's damaged metal race
ring.
"I am getting almost all of
the debris off," Whitson said. "It seems less splotchy."
Using a mirror, Tani and
Whitson looked inside the SARJ gear to find that two sides of its three-sided
race ring were untouched by damage, boosting hopes that engineers can find a
way to continue using the joint in short spurts while continuing to study the
glitch.
"If we can figure out to
live with this, maybe roll on it for awhile when we have to...it gives us more
time to figure out root cause and figure out what the real issue is,"
Suffredini said. By taking that extra time, engineers could determine whether a
major switch to a backup race ring, which could potentially take up to four
spacewalks and be performed during a fall 2008 space station mission, will be
required, he added.
Tuesday's
spacewalk marked the 100th
outside the ISS and the 23rd this year alone, tying the all-time record for
excursions in a single year. The spacewalk was the fifth career outing for both
Tani and Whitson, who set a new world record during the outing for the most
spacewalking time for a female astronaut.
"Congratulations, there is
no pressure now because you are the queen of EVA," Mission Control told
Whitson, using NASA's abbreviation for extravehicular activities.
"It's just being in the
right place at the right time," replied Whitson, who is the space station's
first female commander and beat NASA astronaut Sunita Williams' benchmark
of 29 hours and 17 minutes to nab the title.
Hunting
for damage
In addition
to their SARJ joint inspection, the spacewalkers also surveyed cables and other
hardware for a beta gimbal joint that swivels one of the station's starboard
solar wings on a different axis from the SARJ. The joint suffered triple
electrical failures on Dec. 8, prompting concerns on Earth of a possible
micrometeorite strike.
"Everything
I can see is nominal," Tani said. "There is no damage, no frays that I can
see."
Despite her
bulky NASA spacesuit, Whitson squeezed herself inside the station's
backbone-like truss to reach the gimbal joint's power cables. Mission
controllers warned her that it would be a tight fit, prompting a laugh from the
spacewalker.
"Does this
[spacesuit] make me look fat," she joked.
Space
station managers said they are now confident that the gimbal joint's glitch
lies in its motor box. A spare for the unit is aboard the ISS and Tani is
trained to replace the motor.
Whitson
ended Tuesday's spacewalk with 32 hours and 36 minutes of spacewalking time
under her belt across five career excursions. Tani, meanwhile, ended with 32
hours and one minute as he concluded his fifth career spacewalk.
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