Robotic Arm Ballet: Astronauts Move Massive Truss, Take Time Off

HOUSTON - Astronauts aboard NASA?s shuttle Discovery will take a few hours off Monday after some delicate robotic arm work to move a massive girder outside the International Space Station (ISS), while engineers on Earth study contamination in one of the orbital laboratory?s solar array-turning joints.

Working together with the station?s Expedition 16 crew, Discovery?s STS-120 astronauts were handing off the 17.5-ton Port 6 (P6) solar array truss segment between their two spacecraft?s robotic arms to position it for installation on the port edge of the orbital laboratory?s main truss during a Tuesday spacewalk.

Reattaching the port side girder and unfurling its two wing-like solar arrays successfully is even more vital after a spacewalker discovered what appeared to be metal shavings inside a 10-foot (three-meter) wide joint designed to rotate the space station?s starboard solar arrays like a paddlewheel to track the Sun.

ISS Expedition 16 commander Peggy Whitson tested samples of the shavings early Monday, finding them to be magnetic.

?It?s definitely ferrous,? Whitson told Mission Control.

Expedition 16 flight engineer Daniel Tani collected the samples from inside the station?s starboard Solar Alpha Rotary Joint (SARJ) during a Sunday spacewalk. Astronauts installed the joint at the ISS last June, but over the last 50 days it has exhibited slight current spikes and vibrations suggesting added friction as it rotated its solar arrays.

ISS flight controllers have parked the station?s starboard solar arrays in a fixed position that should generate adequate power while Discovery remains docked at the space station through Nov. 4. Mission managers also plan to send astronaut Scott Parazynski out to a similar solar array-turning joint on the space station?s port side, which has been working properly since its September 2006 installation, during Tuesday?s spacewalk.

Mike Suffredini, NASA?s ISS program manager, said that inspecting the port joint will give engineers a baseline against which they can measure the starboard joint?s contamination. If Tuesday?s P6 solar array relocation goes as planned and the starboard solar wing can be adjusted in optimum Sun-catching positions periodically, the station will be in a good power configuration to support the planned December arrival of the European Space Agency?s Columbus laboratory, he added.

But a definitive plan to either clean up the starboard joint contamination or conduct lengthy repairs using spare parts already in orbit will have to wait until after Discovery?s current STS-120 construction flight, which NASA has called its most ambitious to date. In addition to moving the seven-year-old P6 truss from its central mast-like perch atop the ISS to the station?s port side, Discovery?s crew has also swapped out one Expedition 16 crewmember and delivered the new connecting node Harmony to the orbital laboratory.

?For this mission, we don?t really think we?ll be able to have time to come up with a plan to do any serious troubleshooting,? ISS flight director Heather Rarick said late Sunday. ?We?ll probably do some more inspections though, so we are leaving some of our options open to get some more inspection time.?

Astronauts aboard Discovery and the ISS also watched early Monday as flight controllers on Earth commanded a pair of starboard radiators to unfold and join a third one already deployed from the station?s Starboard 1 (S1) truss. Shuttle commander Pamela Melroy, who helped install the S1 truss on a previous spaceflight, said the girder looked great ?with all its flags flying.?

NASA roused Discovery?s crew with the song ?One by One? performed by Wynton Marsalis and selected for Discovery astronaut Stephanie Wilson, the crew?s lead robotic arm operator.

?Space is certainly a special to be,? Wilson said. ?I'd like to thank my parents, Barbara and Gene, for that song. I love them very much and I couldn't do this mission, or anything that I've done in my life, without their love and their support.?

Wilson, a Boston native, received some welcome news from Mission Control when she learned her beloved Red Sox won the World Series Sunday night.

?Woooo!? she exclaimed. ?That?s great news!?

NASA is broadcasting Discovery's STS-120 mission operations live on NASA TV. Click here for mission updates and NASA TV from SPACE.com.

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