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"  Iridium Satellite (Photograph by ideonexus via Flickr. Some rights reserved.)) Two satellites collided with each other nearly 500 miles over northern Siberia. One was a 12-foot-long, 1200-pound U.S. telecommunications satellite owned by Iridium Satellite company in Maryland, serving as part of a 66-satellite network. The other was a Russian military satellite called Kosmos-2251, which hasn&amp;#039;t been operational in a decade. It weighed more than a ton and, like many other Russian satellites, was powered by a nuclear reactor. The collision on Tuesday created 500 to 600 new pieces of debris.   This is the first known major satellite crash, but no one has yet said for sure why the collision occurred. One hypothesis is that because the Russian satellite was no longer operational, its steering mechanism was deactivated. Russian leaders have yet to comment on that. Iridium announced that its satellite was working fine before the crash. Experts say predicting crashes through the noise of the debris in orbit is always tricky, and Reuters reported today that scientists trying to prevent this collision were additionally confounded because it happened near the debris of the weather satellite that China destroyed with a missile in 2007.   Space officials from both Russia and the U.S. say there should be minimal danger to the International Space Station from this new cloud of debris. The ISS orbits at an elevation of about 220 miles, more than 250 miles lower than the collision. Still, scientists are tracking the wreckage, and are ready to move the ISS to avoid danger from wayward debris. While most of the small debris could burn up in the atmosphere, some of it could still pose a threat to other satellites. NASA&amp;#039;s chief orbital scientist, Nicholas Johnson, said that the launch of the space shuttle Discovery, which is bound for the ISS, is still planned for some time after Feb. 22, and Russia just launched a Soyuz rocket that will dock with the station tomorrow. The Kosmos-2251 carried a nuclear reactor, like many Russian satellites, but most experts agree that there is a minuscule risk that the small amount of nuclear material would survive entry into our atmosphere.   NASA and military studies in the coming days will tell us more about how the crash happened and just how much havoc its debris could create. Though thousands of pieces of space junk are now orbiting the Earth, space in orbit is expansive, and this kind of accident, with proper surveillance of satellites in space, should continue to be rare. Still, there is no space-traffic controller, which is why countries are trying to nail down the rules and laws of space operations before a crash happens again.\u2014Andrew Moseman       "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/space/satellites/a4190/4303472/>