Astronauts
aboard the International Space Station (ISS) will step outside their spacecraft
early Tuesday to inspect a pair of critical joints serving the orbital lab's
starboard solar wings.
Station commander
Peggy Whitson and flight engineer Dan Tani are due to begin the fourth
spacewalk of their Expedition 16 mission no later than 6:00 a.m. EST (1100 GMT)
to take an in-depth look at a large gear contaminated by metallic grit and a
locked solar wing joint.
"What
we're providing is additional data," Whitson told reporters last week,
adding that engineers on Earth will use tomorrow's inspections to draw up possible
repair plans.
The two
joints, each on a different axis, are designed to rotate the station's
wing-like solar panels to continuously face the sun and maximize energy
production.
During a
late October spacewalk, Tani discovered
damage and metal shavings inside the station's starboard Solar Alpha Rotary
Joint (SARJ), a massive, 10-foot (3-meter) wide gear that turns the station's
outboard starboard solar arrays like a paddlewheel. Engineers will use
Tuesday's inspection to help decide whether the joint can be cleaned by
spacewalking astronauts or will require a complicated repair over multiple
spacewalks.
"We're
still in the throes of understanding what happened and how to move
forward," said Kirk Shireman, NASA's deputy ISS program manager, in a
mission briefing.
Another
joint, a Beta Gimbal Assembly used to pivot an individual solar wing from side
to side, was locked in place earlier this month after two
power feeds dropped out, possibly due to damage from a micrometeorite,
mission managers said.
"We'll
try and figure out what's going on there as well," Whitson said.
Tuesday's
spacewalk will mark the fourth for the Expedition 16 crew and the 100th
dedicated to space station construction. The astronauts were scheduled to begin
camping out inside the station's Quest airlock at 2:50 p.m. EST (1950 GMT) to prepare their bodies to work in the 100 percent oxygen environment of
their NASA-issue spacesuits.
An
orbital hunt
Whitson and
Tani will make a systematic inspection of the space station's starboard SARJ joint
in hopes of finding the source of damage to the mechanism's large metal ring.
They will
remove and peer under as many of the joint's 22 protective covers and retrieve
one of 12 bearings that will be returned to Earth for study.
"The
ground has data that suggests that maybe that's where the problem is,"
Whitson said of the bearing, known as Trundle Bearing 5. "But if we can
visibly tell that it is a different one, we'll bring in the one we think is a
troublemaker."
Whitson
said that, at face value, staging a series of spacewalks to repair the SARJ
joint by switching it to a backup ring appears simpler than a full-scale clean
up operation, but Tuesday's inspection will help engineers decide what future
steps to take.
Mission
managers initially scheduled the joint inspection as an extra excursion during
NASA's planned STS-122
shuttle mission to deliver the European-built Columbus laboratory to the
ISS earlier this month. But the spaceflight's delay to no
earlier than Jan. 10 allowed its addition to the Expedition 16 mission.
"We
were pretty set for this [spacewalk] in terms of tools and spacesuit
configuration," Tani said of the upcoming extravehicular activity (EVA).
"I don't think we're going to be losing any planned work for this
EVA."
NASA
will broadcast the Expedition 16 crew's fourth spacewalk live on NASA TV
beginning at 4:30 a.m. EST (0930 GMT). Click here for SPACE.com's live coverage and
mission updates.
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