ORLANDO, Fla. -- A small piece of debris from an old satellite hurtling toward the International Space Station sent a scare through NASA and the three astronauts aboard the station, but the debris ultimately sailed harmlessly by.
The debris, about 5 inches across, passed by the station at 4:21 p.m. EDT, missing the station by a little more than three miles, according to NASA calculations.
For much of the day, as NASA tracked the space junk, the three astronauts were advised to be ready to scramble into the Soyuz capsule that's attached to the station that could fly them back to Earth.
But the red-level alert was canceled around 3 p.m. EDT, when NASA became confident enough in the track of the debris.
The astronauts on the space station are American Catherine Coleman, Italian Paulo Nespoli, and Russian Commander Dmitry Kondratyev.
Despite the scare, the incident was considered fairly routine. NASA begins preparing for action any time a piece of space junk appears likely to pass close to the space station, which happens fairly regularly. Usually the alert is dropped as the debris gets close enough for NASA to project an exact path, and determines it's going to miss. The last time debris got close enough to force an evacuation was in 2009.
Nothing significant has ever struck the station, said NASA spokesman Josh Byerly.
Space debris moves at orbital speeds of about 18,000 mph. So an impact by a 5-inch chunk, Byerly said, "depending on where it hits, it could be severe. Something even the size of a grain of sand can punch a hole."
Orbital debris has become a growing problem for space travelers. The amount of space junk has been multiplying in recent years, as collisions between larger pieces create even more smaller ones.
But two recent events have added to the mess. In 2007, China destroyed one of its own probes with an anti-satellite missile in a show of military force, creating a huge cloud of debris. In fact, the piece that threatened the station today is from the Chinese FENGYUN 1C satellite destroyed in that weapons test.
Also, in February 2009, a Russian and an American communications satellite collided over Siberia. That crash created another round of new space junk. On Friday, the space station had to take evasive action to avoid debris from that event.
As of July 2009, more than 19,000 pieces of space debris larger than 10 centimeters were known to be circling the Earth, according to NASA researchers who track it. Another 500,000 pieces are between 1 cm and 10 cm. The tiniest pieces number in the millions.
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