Astronauts Douglas Wheelock, below the antenna and astronaut Scott Parazynski, feet towards camera, work on stowing the broken antenna in the cargo bay of the Space Shuttle Discovery, 26 Oct 2007

Two spacewalking astronauts investigated a potential problem Sunday with one of the International Space Station's solar power arrays. They found what appear to be metal shavings in a joint that allows the array to rotate to follow the Sun.

The astronauts were asked to look at the joint because engineers had noticed unexpected power readings during the movement of the solar panels.

Astronaut Dan Tani collected some of the shavings. They will be returned to Earth aboard the space shuttle Discovery for analysis.

The primary purpose of Sunday's six-hour spacewalk was to begin the process of moving an 18-ton girder from one location on the space station to another.

The U.S. space agency NASA said they successfully unbolted the girder from its initial position.

During the mission's next spacewalk, scheduled for Tuesday, astronauts will reattach the girder at its new location.

Discovery's two-week construction mission is considered one of most difficult in the history of the U.S. space shuttle program.

Some information for this report was provided by AP.