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WASHINGTON — Iridium Satellite LLC confirmed today that one of its satellites was destroyed Feb. 10 in an unprecedented collision with a spent Russian satellite and that the incident could result in limited disruptions of service.

According to an e-mail alert issued by NASA today, Russia’s Cosmos 2251 satellite slammed into the Iridium craft at 11:55 a.m. Eastern Standard Time over Siberia at an altitude of 790 kilometers. The incident was observed by the U.S. Defense Department’s Space Surveillance Network, which later was tracking two large clouds of debris.

“This is the first time we’ve ever had two intact spacecraft accidentally run into each other,” said Nicholas Johnson, chief scientist of NASA’s Orbital Debris Program Office at the Johnson Space Center in Houston. “It was a bad day for both of them.”

The collision appears to be the worst space debris event since China intentionally destroyed one of its aging weather satellites during a 2007 anti-satellite test, Johnson said. That 2007 event has since left about 2,500 pieces of debris in Earth orbit, but more time is needed to pin down the extent of the Feb. 10 satellite collision, he added.

“We’re tracking more than 500 pieces of debris which pose an additional risk to satellites,” said U.S. Navy Lt. Charlie Drey, a spokesman for the U.S. Strategic Command which oversees the U.S. Space Surveillance Network.

In a prepared statement, the Bethesda, Md.-based Iridium characterized the incident as a “very low probability event” and said it was taking immediate action to minimize any loss of service. Iridium, which operates a constellation of 66 low Earth orbiting satellites providing mobile voice and data communications globally, said its system remains healthy and that it would implement a ?network solution? by Friday.

“Within the next 30 days, Iridium expects to move one of its in-orbit spare satellites into the network constellation to permanently replace the lost satellite,” the statement said.

The 560-kilogram Iridium 33 satellite involved in the collision was launched in 1997; the 900-kilogram Russian satellite was launched in 1993 and presumed nonoperational. It did not have a maneuvering system, NASA said.

Iridium’s spacecraft circle the Earth along a near-polar orbit once every 100 minutes and fly at a speed of about 27,088 kilometers per hour, the company states on its website.

An unprecedented crash

Johnson said outdated spacecraft, rocket stages and other components break apart in space every year, but there have only been three relatively minor collisions between such objects in the last 20 years. Never before have two intact satellites crashed into one another by accident, he added.

The debris created in the Feb. 10 collision is being tracked to assess its risk of damaging other satellites and the International Space Station, which is currently home to two American astronauts and one Russian cosmonaut.

The space station flies at an altitude of about 354 kilometers, well below the impact point between the Russian and U.S. satellites 790 kilometers up. Johnson said that only a very minor portion of debris from the two clouds is expected to descend across the space station?s orbital path.

“We believe that the increased risk above the normal every day background risk is very, very small,” Johnson said

NASA’s orbital debris experts are also assessing the threat to other spacecraft. The agency’s Earth Observing System satellites, which orbit at 705 kilometers, “are of highest interest for immediate consideration,” NASA said in its e-mail alert, a copy of which was forwarded to Space News.

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Drey said that the first hint of the collision came when Iridium officials contacted a U.S. Strategic Command support office to report that they had lost contact with one of their satellites.

“Shortly after, our space surveillance center reported that they had observed multiple new objects in low orbit,” Drey said. The U.S. Space Surveillance Network continuously tracks more than 18,000 separate man-made objects and debris at any given time, he added.

The Feb. 10 collision is the latest in a series of satellite woes in recent weeks.

Last month, the nascent Eutelsat W2M telecommunications satellite failed in orbit just five weeks after it launched into space. Another communications satellite, ASTRA 5A owned by SES Luxemburg, also failed and was adrift in orbit. The loss forced its operators to warn the owners of neighboring satellites to be prepared for the remote possibility of having to maneuver their spacecraft to avoid a collision with Astra 5A.

NASA’s Orbital Debris Program Office also released an update last month on Russia’s Soviet-era satellite Cosmos 1818 stating that the spacecraft appeared to spew a cloud of debris on July 4, 2008, that may be the result of leaking reactor coolant from a debris strike or fragmentation.

SPACE.com Senior Editor Tariq Malik contributed to this story from New York City.

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