"A small piece of space junk drifted dangerously close to the International Space Station on Tuesday, prompting NASA to order the three astronauts to seek shelter in their attached capsule.

Mission Control gave the order after determining there was not enough time to steer the orbiting outpost away from the space junk.

The debris — about 6 inches — is from a Chinese satellite that was deliberately destroyed in 2007 as part of a weapons test. It was projected to pass within three miles of the space station, warranting a red threat level, NASA's highest.

Just last Friday, the space station had to move out of the way of an orbiting remnant from a two-satellite collision in 2009.

Debris is an increasingly serious problem in orbit, because of colliding and destroyed spacecraft. At 5 miles a second, damage can be severe, even from something several inches big. Decompression, in fact, is at the top of any spacefarers' danger list.

More than 12,500 pieces of debris are orbiting Earth — and those are the ones big enough to track.

Mission Control notified the crew of the latest threat Tuesday morning, a few hours after the risk was identified. The three crew members are Dmitry Kondratyev, the station's Russian commander, American Catherine Coleman and Italian Paolo Nespoli.

The orbit of the space junk is extremely erratic, and there's quite a bit of atmospheric drag on it, said NASA spokesman Josh Byerly. Experts monitored the debris into the early afternoon, to determine its exact path, and later told the crew that they might not have to close themselves off in the Soyuz spacecraft. The threat level, however, remained red..."

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