Image: Spacewalker
NASA TV
With his back to the video camera, Japanese astronaut Akihiko Hoshide works on equpment during a spacewalk at the International Space Station on Wednesday.
By
updated 9/5/2012 7:23:09 PM ET 2012-09-05T23:23:09

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 onto their mission after the stuck space station bolt prevented the astronauts from properly installing the power unit — called a main bus switching unit, or MBSU — on the outpost's backbone-like truss on Aug. 30.

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 had been unable to relay power from two of the eight solar arrays on the massive orbiting complex.

"Looks like you guys just fixed the station," astronaut Jack Fischer radioed from Mission Control at NASA's Johnson Space Center in Houston. "It's been like living on the set of 'Apollo 13' the past few days. NASA does impossible pretty darn well, so congratulations to the whole team."

At the beginning of the spacewalk, Williams and Hoshide removed the 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 are designed to secure it in place on the space station's truss.

The spacewalkers undid the bolts, 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. "Small metal shavings — smaller than last time we saw in the housing." [Photos: Spacewalkers Fix Space Station Power Unit]

Improvised tools
The spacewalkers used improvised cleaning tools and a pressurized can of nitrogen gas to clean out the metal shavings from the bolt receptacles. Hoshide said he saw "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 Johnson Space Center to devise ways to fix the stuck bolt, NASA spokesman Josh Byerly said in 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 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," Fischer replied.

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.

Try, try again
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. Last week's outing 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.

Things went much more smoothly on Wednesday. After securing the MBSU, the spacewalkers went on to remove a faulty camera from the station's Canadarm 2 robotic arm and replaced it with a new one. Then they returned to the Quest airlock and ended the spacewalk at 1:34 p.m. ET.

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Wednesday's outing was clocked at 6 hours and 28 minutes, and marked a record-setting excursion for Williams. Roughly two hours into the spacewalk, Williams 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.

The spacewalk was the sixth for Williams and the second 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+.

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Video: Women’s spacewalk record broken

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