Six astronauts at the International Space Station took refuge in escape pods Saturday as a chunk of space debris whizzed by them.

The U.S. space agency NASA said this is the third time in a dozen years of space station operations that a crew has had to seek shelter because of orbiting space junk and prepare — if necessary — to rocket back to Earth.

The Russian space agency said a discarded piece of the Russian rocket Cosmos 2251, launched in 1993, passed within 23 kilometers of the space station.

At that distance, NASA said the astronauts were not at risk, but said it evacuated them as a precaution, in case the debris were to hit. The escape capsules are the Soyuz spacecraft the astronauts use to return to Earth, both routinely or in an emergency.

After the debris passed safely, the astronauts returned to their normal duties. Three Russians, two Americans and a Dutchman are aboard the space station.

Meanwhile, an unmanned rocket blasted off from French Guiana late Friday. The European Space Agency craft is carrying supplies for the International Space Station.