Astronauts to Repair Solar Wing Motor in Wednesday Spacewalk

Astronauts aboard the International Space Station (ISS) are preparing for a Wednesday spacewalk to restore some of the power-generating ability of the orbiting laboratory?s expansive solar wings.

ISS Expedition 16 commander Peggy Whitson and flight engineer Dan Tani will replace a broken joint motor at the base of the station?s two starboard solar wings during a planned six-hour spacewalk.

The solar wing has been unable to track the sun continuously since early December, when the joint motor suffered a series of electrical shorts. Without the repair, the space station will have enough power to make it through at least the next shuttle mission - targeted for a Feb. 7 launch - but not much further said Kirk Shireman, NASA?s ISS deputy program manager.

If the Wednesday spacewalk is successful, the ISS will have power to last through the planned arrival of a massive Japanese laboratory in April and into the summer, he added.

The broken motor controls a beta gimbal joint that pivots one of the station's two starboard solar wings to face the sun. After the motor experienced electrical failures in December, Whitson and Tani made a spacewalk to inspect the joint and found no outward signs of damage. NASA hopes replacing the whole motor, a garbage-can sized device that weighs about 250 pounds (113 kilograms), with a backup will fix the problem.

For safety reasons, the astronauts can only work during eclipses, when the sun is blocked by the earth. If the sun was shining on the solar panels while Whitson and Tani were working on the joint, they would be at risk of shocks due to the high power levels surging through the arrays.

"We have to be very conscientious when we're opening connections that will expose us to that power," said Tani, adding that he and Whitson must also take special care since they will be working with latches that physically connect the solar wing to the ISS. ?That is probably the biggest danger of this [spacewalk].?

Once they begin working, the astronauts will have 33 minutes of complete shade at a time. If they can't replace the motor during one eclipse, they'll have to wait till the next one. The space station orbits the Earth about once every 90 minutes to make a single circuit above the planet?s day and night sides.

"They will be in a little bit of a timeline crunch when they're performing activities during the eclipse," said astronaut Thomas Marshburn, who has rehearsed the repair in a giant NASA swimming pool used for spacewalk training. "We found that it is very doable to get all this done."

The space station is currently afflicted by two unrelated power system glitches with its starboard solar arrays. In addition to the broken joint motor, known as a Bearing Motor Roll Ring Module, the orbital lab is also suffering from damage to a massive gear designed to rotate the station?s starboard solar arrays like a paddlewheel to track the sun.

Astronauts discovered metal grit from the gear?s attached metal ring during past spacewalks. Whitson and Tani will take another look at the 10-foot (3-meter) wide gear if they have extra time during Wednesday?s excursion, mission managers said.

Space station managers are still discussing when to repair the larger gear, called a Solar Alpha Rotary Joint, later this year, though any effort will likely require a series of spacewalks.

Wednesday?s excusion will mark the sixth career spacewalk for both Whitson and Tani, and the fifth for the station?s Expedition 16 crew.

"Any opportunity to go outside is a very special event," Whitson said. "The huge structure that we've built up there is just amazing to see. In its own way it's just as beautiful as looking at Earth."

NASA will broadcast the Expedition 16 crew's fifth spacewalk live on NASA TV beginning at 4:00 a.m. EST (0900 GMT) on Jan. 30. Click here for SPACE.com's live coverage and mission updates.

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