A spacewalking astronaut on Sunday found metal shavings inside a joint that is needed to turn a set of solar power panels.
The 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. It has been experiencing electrical current spikes in the past 1½ months.
NASA officials have limited the joint's motion to prevent the debris from causing permanent damage. But that also limits the system's ability to generate power for the station.
The glitch raises the stakes for the Discovery crew's ongoing attempt to move the giant solar array truss from one part of the orbiting complex to another.
Failing to install the girder or to unfurl its enormous folded solar wings could cause problems for the planned December installation of the European Space Agency's science laboratory, named Columbus. The lab is supposed to latch onto the new Harmony module that Discovery delivered last week.
Mike Suffredini, NASA's space station program manager, said it's too soon to know whether the joint trouble will affect future flights.
"We have lots of time to work through this problem. It's not an immediate issue," Suffredini said on Sunday afternoon.
On Monday, the astronauts were using two robotic arms to move the girder into place for its scheduled installation during a spacewalk the following day.
Tuesday's spacewalk schedule also includes time for an inspection of the joint for the left solar wings. That joint is working fine. Spacewalker Scott Parazynski has been asked to take pictures and samples like those gathered Sunday at the other joint so NASA can compare the findings.
The astronauts have spare parts for the joint with them in orbit, including extra bearings.
But space station flight director Heather Rarick said late Sunday that the astronauts probably won't have time to do repairs while Discovery is docked to the orbital lab. Even more inspections may be added to the two other planned spacewalks, and the three station crewmembers could troubleshoot later.
Discovery is set to undock from the station on Sunday and land on Nov. 6. Mission managers have determined the ship's thermal shielding is in good shape for re-entry.
Monday's schedule also includes some off-duty time for the astronauts. The day started well for astronaut and Boston native Stephanie Wilson, who heard from Mission Control that the Red Sox had swept the World Series.
"That's great news!" Wilson said. "Go Sox! Woooo!"