Spacewalkers fix pesky power system

Two spacewalking astronauts successfully replaced a vital power unit on the International Space Station on Wednesday, defeating a stubborn bolt that originally delayed the fix with the help of some improvised tools made of spare parts and a toothbrush.

NASA astronaut Sunita Williams and Japanese spaceflier Akihiko Hoshide performed the spacewalk repair. The fix-it job in space was actually an extra spacewalk tacked on to their mission after the stuck space station bolt prevented the astronauts from properly installing the power unit on the outpost's backbone-like truss last week on Aug. 30.

During Wednesday's outing, Williams and Hoshide removed the power box ? called a main bus switching unit, or MBSU ? from where it had been temporarily tied down with a tether last week. The duo then spent several hours troubleshooting the unit and the two bolts that were designed to secure it in place on the space station's truss.

After undoing the bolts, the spacewalkers examined them for possible damage, and inspected the corresponding receptacles on the MBSU for debris that was suspected to be inside.

"I see metal shavings," Williams said as she looked at the MBSU. "Small metal shavings ? smaller than last time we saw in the housing." [Photos: Spacewalkers Troubleshoot Space Station Power Unit]

Improvised tools
The spacewalkers used improvised cleaning tools and a pressurized can of nitrogen gas to clean out the shavings from the bolt receptacles. Hoshide reported that there were "a lot of metal shavings coming out" as he maneuvered a wire cleaner around one of the bolt holders.

Williams and Hoshide then lubricated a spare bolt and manually threaded it into the place where the real bolt was eventually driven, in an effort to ensure that the receptacle was clear of any debris.

Following last week's failed attempt to install the replacement MBSU, mission managers, engineers and veteran spacewalkers worked around the clock at NASA's Johnson Space Center in Houston to devise ways to fix the stuck bolt, NASA spokesman Josh Byerly said during his live spacewalk commentary.

Part of their brainstorming included fashioning tools from existing supplies on the orbiting complex for Williams and Hoshide to use to remove debris from inside the bolt housings. One of the cleaning tools used today was made from a spare toothbrush.

The key turning point for the spacewalk came around the four-hour mark, when the astronauts were given the option to proceed with installing the MBSU or clean it off and bring the unit inside the station for more analysis. The two spacewalkers unanimously agreed to proceed.

"I think we can press," Hoshide said. "Get 'er done."

"Copy, get 'er done," astronaut Jack Fischer said from Mission Control.

When Hoshide reported that the troublesome bolt was finally locked into place, the flight managers in Mission Control erupted in applause. "That is a little slice of awesome pie," Fischer radioed to the crew.

What the MBSU does
The International Space Station has four 220-pound (100-kilogram) MBSUs that harness power from the outpost's solar arrays and distribute it throughout the orbiting complex. Without the use of one unit, the station is unable to relay power from two of the eight solar arrays on the massive orbiting complex.

Last week, Williams and Hoshide removed a faulty MBSU and tried to install the spare, but they were unable to drive in one of the bolts that secures the unit to the station's truss. After several unsuccessful attempts, the astronauts were forced to wrap up their marathon spacewalk.

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The Aug. 30 spacewalk lasted 8 hours and 17 minutes, making it the third longest spacewalk in history and the longest one ever performed by a space station crew.

In addition to installing the replacement MBSU, the spacewalkers' agenda included removing a faulty camera from the station's Canadarm 2 robotic arm and replacing it with a new one. If there is extra time after that, Williams and Hoshide may also install a micrometeoroid debris shield over part of an American module.

Williams set a spacewalking record during Wednesday's outing: Roughly two hours into the operation, she overtook Peggy Whitson, a veteran spaceflier and former chief of NASA's Astronaut Office, as the record holder for the most time spent working in the vacuum of space by a female astronaut, Byerly said.

This outing is the sixth spacewalk for Williams and the second spacewalk for Hoshide, who is only the third Japanese spaceflier to work outside in the vacuum of space.

The International Space Station is currently home to six astronauts: Williams and Joe Acaba of NASA, Hoshide of the Japan Aerospace Exploration Agency, and Russian cosmonauts Gennady Padalka, Yuri Malenchenko and Sergei Revin.

Follow Denise Chow on Twitter @denisechow or Space.com @Spacedotcom. We're also on Facebook and Google+. This report was supplemented by NBC News.

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Source: http://www.msnbc.msn.com/id/48906172/ns/technology_and_science-space/

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