January 30, 2008

Spacewalkers Replacing Solar Wing Motor

Expedition 16 Commander Peggy Whitson and Flight Engineer Dan Tani are replacing a motor at the base of one of the International Space Station's solar wings during a spacewalk that began at 4:56 a.m. EST Wednesday.

Whitson is wearing the spacesuit with red stripes as the lead spacewalker, while Tani is wearing the spacesuit with broken stripes. The spacewalk, in U.S. suits, began from the station's Quest airlock.

Most of the spacewalk focuses on replacement of the motor, called the Bearing Motor Roll Ring Module (BMRRM). Called the 'broom," the motor drives the starboard solar wings as they tilt along their axis to follow the sun for optimal power generation as the station orbits the Earth.

Major activities of the BMRRM replacement take place during the night part of the orbit, when less voltage is generated by the solar wings than when they are exposed to the sun. The replacement BMRRM was retrieved from its stowage place in Pressurized Mating Adapter-3 early this month in preparation for the spacewalk.

The motor is part of the Beta Gimbal Assembly, which experienced electrical failures Dec. 8. The removal and replacement of the BMRRM is expected to take about four hours, including pauses during the daylight part of the orbit.

A second major task of the spacewalk is inspection of the starboard Solar Alpha Rotary Joint (SARJ). That device causes the starboard solar wings to rotate in a paddlewheel-like motion to keep the arrays pointed toward the sun.

Previous inspections revealed contamination and debris inside that joint.

Station Flight Engineer Yuri Malenchenko helped the crew with suiting up and is providing other support. Astronaut Tom Marshburn is the ground intravehicular officer. He is in the station flight control room in Houston's Mission Control Center, acting as spacewalk choreographer.

Once tasks have been completed and after cleanup the spacewalkers will re-enter the Quest airlock and close its hatch. The beginning of repressurization marks the official end of the spacewalk.


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