satellite collision

In an unprecedented space collision, a commercial Iridium communications satellite and a defunct Russian satellite ran into each other Tuesday above northern Siberia, creating a cloud of wreckage, officials said today. The international space station does not appear to be threatened by the debris, they said, but it's not yet clear whether it poses a risk to any other military or civilian satellites.

The collision, which took place on Tuesday in low-earth orbit, involved a spacecraft of privately owned Iridium Satellite LLC and a "non-operational" Russian communications satellite, said Air Force Lieutenant Colonel Les Kodlick of the U.S. Strategic Command.

"We believe it's the first time that two satellites have collided in orbit,It's a very important orbit for a lot of satellites," he said.

The command's Joint Space Operations Center was tracking 500 to 600 new bits of debris, some as small as 10 centimeters (3.9 inches) across, in addition to the 18,000 or so other man-made objects it has catalogued in space, Kodlick said.

"They collided at an altitude of 790 kilometers (491 miles) over northern Siberia Tuesday about noon Washington time," said Nicholas Johnson, NASA's chief scientist for orbital debris at the Johnson Space Center in Houston. "The U.S. space surveillance network detected a large number of debris from both objects."

Air Force Brig. Gen. Michael Carey, deputy director of global operations with U.S. Strategic Command, the agency responsible for space surveillance, said initial radar tracking detected some 600 pieces of debris. He identified the Russian spacecraft as Cosmos 2251, a communications relay station launched in June 1993, and said the satellite is believed to have been non-operational for the past 10 years or so.

Iridium Satellite LLC operates a constellation of some 66 satellites, along with orbital spares, to support satellite telephone operations around the world. The spacecraft, which weigh about 1,485 pounds when fully fueled, are in orbits tilted 86.4 degrees to the equator at an altitude of about 485 miles. Ninety-five Iridium satellites were launched between 1997 and 2002 and several have failed over the years.

The International Space Station flies at a lower altitude and is the command's No. 1 priority in attempting to prevent collisions, Kodlick said.