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.

FMI: www.nasa.gov/station