WASHINGTON - Astronauts aboard the
International Space Station (ISS) are gearing up for an extra spacewalk to
tackle solar array joint malfunctions outside their orbital laboratory.
Expedition
16 commander
Peggy Whitson and flight engineer Dan Tani will don their NASA spacesuits
on Tuesday to inspect the station's starboard solar array joint and potential
damage at the base of one of the segment's power-producing wings.
"I think
both Dan and I are looking forward to the [spacewalk] and getting going again,"
Whitson told reporters Thursday via a video link.
Whitson,
Tani and crewmate Yuri Malenchenko have enjoyed a relatively light work week after a
November packed with orbital
construction work and the delay of NASA's next shuttle flight earlier this
week.
During
Tuesday's spacewalk, they will focus all of their attention on the station's
starboard solar array truss segment, where they will conduct a comprehensive
inspection of a vital rotary joint contaminated
with metallic grit.
Tani first
discovered metal shavings inside the 10-foot (3-meter) wide gear, known as a
Solar Alpha Rotary Joint (SARJ) in a late October spacewalk. The gear is one of
two designed to rotate the station's outboard solar arrays like paddlewheels to
constantly track the sun.
Kirk
Shireman, NASA's deputy space station program manager, said Whitson and Tani
will peer under as many of the SARJ joint's 22 protective covers during their
inspection as time permits, use a mirror to seek debris inside the joint and
retrieve one of 12 trundle bearings that may be the source of the damage.
"The big,
key question for us is what caused the issue," Shireman said in an afternoon briefing,
adding that engineers are hesitant to switch to the starboard segment's sole
remaining backup SARJ ring until the source of the initial damage is found. "We
need to understand what is the root cause...so we're working very hard to get
that answer."
Whitson and
Tani will also examine a starboard beta gimbal joint that allows one of the segment's
two solar wing panels to pivot from side to side, on a different axis from the
SARJ, to continuously face the sun. Last weekend, the joint suffered what may
have been a micrometeorite hit that shorted out two power feeds and locked it in place, mission
managers said.
Some spare
parts for the system are onboard the station, and Tani is trained to repair the
vital gimbal joint, Shireman said. The new glitch has forced mission managers
to revisit the station's power margins for NASA's planned January launch of the
space shuttle Atlantis, he added.
"I hope
that we'll find out what it is based on the ground testing and our observations
in this [spacewalk], and we'll be able to go fix it without any additional
equipment," Shireman said.
Tuesday's
spacewalk will mark the 100th dedicated to space station construction and the
23rd of 2007, which will tie the all-time record for a single year set in 2002, NASA officials
have said.
"So far they've
all gone very, very well and we're pleased to get through 99 of them without
any major problems," Tani said.
Tani had
hoped to return to Earth before Christmas with the STS-122 crew of Atlantis
this month, but NASA postponed the mission to early January after faulty fuel
tank sensors thwarted
two launch attempts.
"As you
know, launches are very unpredictable," said Whitson, adding that she looks
forward to Atlantis' delivery of a new European lab in January and a planned
February shuttle mission to install part of Japan's Kibo lab at the ISS. "I'm
still optimistic [and] looking forward to getting a lot more work done in the
future."
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