Astronauts find debris in joint that aims solar gear

Spacewalking astronauts doing construction work outside the International Space Station on Sunday made a disturbing discovery: what appear to be metal shavings inside a joint needed to turn solar power panels.

The rotary joint, 10 feet in diameter, has experienced intermittent vibrations and power spikes for nearly two months. Space station managers were hoping that a thermal cover or bolt might be hanging up the mechanism. That would have been relatively easy to fix. Officials were disheartened when Daniel Tani radioed down that metal shavings were numerous.

“It’s quite clear that it’s metal-to-metal grating or something, and it’s widespread,” Tani said.

“Wow,” said his spacewalking partner, Scott Parazynski.

The shavings resembled small flakes and were clinging to the joint as if to a magnet, Tani said. “It looks like a dusty table that you’d want to dust at home,” he called down.

The astronaut used tape to dab up some of the shavings. The tape will be returned to Earth aboard Discovery next week for analysis. NASA is uncertain whether the flecks are actually metallic, possibly from the aluminum foil lining the thermal covers, or some other material.

This rotary joint, launched and installed just four months ago, controls the huge solar panel wings on the right side of the space station, to make sure they’re facing the sun. The joint for the left solar wings is working as intended.

The right rotary joint will remain in a parked position as much as possible until the problem is solved, said Michael T. Suffredini, NASA’s space station program manager. Flight controllers were trying to determine whether any more inspections or even repairs will be needed in the coming week, or whether they can continue to work around the problem following Discovery’s departure.

The astronauts have spare parts for the joint with them in orbit, including extra bearings.

It’s possible that the debris could cause permanent damage, Suffredini said. Another possibility is that the joint could stall in a position that would diminish solar power, which is why he wants to move it as little as possible for now.

It’s too soon to know whether the joint -- if it continues to malfunction -- will affect science operations aboard the European laboratory that is scheduled to fly to the space station in December, or the Japanese lab that will follow, Suffredini said.

The problem overshadowed the rest of the spacewalk, the second of five planned for Discovery’s construction mission.

The spacewalkers’ first job outside the hatch was to disconnect bolts and cables holding a 35-foot-long, 35,000-pound girder to the orbiting complex so that astronauts working inside could pull it away with the robot arm.

It was the first time the girder and its attached solar wings were moved since being installed seven years ago, and the job went well.

The girder will be reattached to another position on the space station Tuesday, and its solar wings unfurled to their full 240 feet across. NASA considers this one of the most difficult construction jobs ever attempted in orbit.

During their 6 1/2 hours outside, Tani and Parazynski also added handrails and other equipment to the outside of Harmony, the school-bus-size compartment that was delivered by Discovery and attached to the space station last week. They did not have enough time to finish installing a grappling hook to Harmony. They had to forgo some other work as well.

Another last-minute chore involved checking the railroadlike tracks for the space station’s robot arm to see whether any sharp edges might be protruding. Tani found dozens of micrometeorite dings on a handrail for the tracks, but he said that they did not look particularly sharp.

Spacewalking astronauts have cut their gloves twice on previous missions, and NASA wants to find out where that may be happening.

Mission managers, meanwhile, formally cleared Discovery for reentry on Nov. 6, saying its thermal shielding is in solid condition.