No Apparent Damage To Gimbal Assembly; Shavings Found In
Joint
Expedition 16 astronauts Dan Tani and Peggy Whitson found no
"smoking gun" for problems involving power generation onboard the
International Space Station. The two astronauts wrapped up a
6-hour, 56-minute spacewalk focused on solar array issues at 1146
EST Tuesday morning.
NASA states the spacewalkers looked for the cause of partial
loss of electrical power to one of the station's two Beta Gimbal
Assemblies (BGAs) for starboard solar wings. They also examined
damage to the starboard Solar Alpha Rotary Joint (SARJ) during the
spacewalk, the 100th associated with assembly and maintenance
onboard the ISS.
The SARJ enables the arrays to rotate to track the sun as the
station orbits Earth. The BGA lets the solar wings tilt along their
long axis to point more directly to the sun; the BGA's primary
power was lost December 8, after three circuit breakers tripped. A
backup power source still functions, but because of the loss of
redundancy, the device was latched with the wing in a position
suitable for docking of the shuttle Atlantis on STS-122.
Tani and Whitson found no apparent damage to BGA 1A during their
45-minute inspection. They disconnected two cables to facilitate
ground tests; the circuit remained closed, apparently clearing the
cables as suspects. Whitson reconnected them late in the
spacewalk.
Next the spacewalkers moved to the SARJ. Working together, they
removed two large drive lock assembly covers and inspected the race
rings and bearings beneath them. Then they removed and inspected
beneath most of the 22 covers.
That SARJ was locked after vibrations were noted and increased
power consumption was seen. Inspection findings Tuesday showed
various degrees of contamination under the individual covers.
Generally it was similar to what had been seen previously.
Tani and Whitson described what they saw, took photos and used
tape and a scraper to collect samples of debris in the SARJ. That
debris included metal shavings and "dusting" in the SARJ race ring,
which Tani compared to marching ants.
"It's hilarious," he reported, according to The Associated
Press. "It's like it's animated, like they're alive."
The starboard array continues to produce some power, NASA
reports, and no station operations have been affected. But managers
want to resolve the SARJ and BGA problems before launch of the
Japanese Kibo laboratory next year.
The spacewalk was the 100th for the construction and maintenance
of the station. During the spacewalk, Whitson set a new record for
cumulative spacewalk time by a woman.