NASA Eyes Worrisome Debris in Space Station Joint
STS-120 shuttle commander Pamela Melroy displays a bag with metal shaving samples (attached to orange Kapton tape) collected from the station's starboard Solar Alpha Rotary Joint by astronaut Daniel Tani during an Oct. 28, 2007 spacewalk.
Credit: NASA TV.

HOUSTON - NASA engineers are studying the potentially serious contamination of a vital joint used to turn solar arrays aboard the International Space Station (ISS) after a spacewalking astronaut collected samples of the grit on Sunday.

U.S. astronaut Daniel Tani used orange tape to pick up what he described as metal shavings from the surface of the massive joint, which rotates the station?s starboard solar arrays like a paddlewheel to track the Sun. While mission managers are unsure if the bits are actually metal, one thing is certain: they shouldn?t be there at all.

?With this kind of contamination in the system, you don?t want to see it anywhere,? Mike Suffredini, NASA?s ISS program manager, told reporters after today?s spacewalk.

The material could force the joint to draw too much power and stall, or cause significant damage to its internal mechanism if left unchecked, he added.

Tani found the debris while inspecting the starboard Solar Alpha Rotary Joint (SARJ), a 10-foot (three-meter) wide gear that sits between two massive girders on the right side of the side of the station?s backbone-like main truss. The samples he collected will be returned to Earth aboard the shuttle Discovery once its STS-120 astronauts complete their construction mission.

?There?s quite a bit,? Tani said of the material adding that one of the joint?s gear teeth-bearing rings appeared to be discolored. ?I?d almost say that it looks like it?s been corroded in some way.?

Suffredini said that the ring?s appearance could be the normal state of its surface coating or the result of some material rubbing against it, such as metal or an aluminum foil-like Mylar attached to insulation just a half-inch (1.27-centimeters) above the device.

The starboard solar arrays are parked for the time being, and may be moved into a better Sun-facing position every few days while engineers decide whether to send spacewalkers back out to inspect afflicted joint while Discovery?s STS-120 crew remains at the ISS.

It is still too early to tell whether the joint?s contamination could affect plans to launch the European Space Agency?s Columbus laboratory to the ISS in December or deliver components of Japan?s Kibo laboratory next year, Suffredini said.

Any lengthy clean up or repairs, if required, could be deferred until sometime after the December launch of Columbus, he added.

?We?ve got lots of time to work this problem, it?s not an immediate issue,? Suffredini said.

Astronauts installed the space station?s starboard solar arrays and rotary joint during a June shuttle flight, but it only began experiencing slight current spikes and vibrations over the last 50 days. An engineer discovered the vibration almost by accident after noticing the view from an ISS video camera shake, station managers said.

A similar rotary joint on the port side of the station's main truss is performing as designed to rotate its own solar wings, NASA said.

Flight controllers hoped the glitch stemmed from a slight obstruction, such as bolt of thermal blanket, and sent Tani to investigate during a spacewalk primarily aimed at removing a separate solar array from atop the ISS and outfitting the station?s new Harmony node with handrails and other equipment.

?It?s gotten more attention than just your average anomaly has,? he said. ?Now everybody is probably kicked into a slightly higher gear.?

While ISS engineers study the joint contamination, Discovery's own mission managers hit a major flight milestone: they cleared the spacecraft's heat shield of any concern from its Oct. 23 launch.

"We have unequivocally cleared the thermal protection system of Discovery for entry," mission management team chair LeRoy Cain said Sunday.

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