Florida ? NASA asked its orbiting astronauts Monday to take a closer look at the gears that control the international space station’s solar wings to try to find out what’s grinding inside and causing steel chips to clog the system.

The impromptu work – “exploratory surgery” as the station’s program manager calls it – will keep shuttle Discovery in orbit an extra day.

During a spacewalk already planned for today, astronaut Scott Parazynski will inspect a good rotary joint that turns the space station’s left set of solar wings toward the sun. NASA wants to see what a perfectly running unit looks like to compare it to the one that is acting up on the opposite side.

On Sunday, spacewalker Daniel Tani found black dust that resembled metal shavings inside the motorized joint that controls the right set of solar wings. He said Monday that it was instantly apparent to him something was wrong.

At least some of the shavings are steel and could be from the bearings inside the joint, said Mike Suffredini, NASA’s space station program manager.