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How NASA dodged a derelict Soviet spy satellite

In March 2012, NASA's Fermi space telescope could have collided with a Russian naval signals satellite, were it not for an untested maneuver.   

NASA | Fermi's Close Call with a Soviet Satellite
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Thanks to an emergency maneuver in March 2012, a NASA space telescope avoided a potentially nasty encounter with a Cold War relic.

More than a year later, NASA is now telling the story of how its Fermi Gamma-ray Space Telescope sidestepped a collision with a defunct Soviet spy satellite.

It all began on the evening of March 29, 2012, when Julie McEnery, the project scientist for the Fermi telescope, received an automatically generated email from NASA's Robotic Conjunction Assessment Risk Analysis team. Fermi was a week away from crossing paths with Cosmos 1805, a 3,100-lb. naval signals reconnaissance satellite launched by the USSR in 1986.

Cosmos was moving relative to Fermi at a speed of 27,000 miles per hour, fast enough to obliterate both spacecraft.

NASA actually predicted that the two craft would miss each other by 700 feet. But there was reason to be skeptical. After all, just two years earlier, a study found that another dead Russian satellite, Cosmos 2251, would pass within roughly 1,900 feet of an Iridium phone satellite. The prediction was slightly off, and both spacecraft became clouds of fast-moving orbital debris, in the first known collision of two intact satellites. 

"It's similar to forecasting rain at a specific time and place a week in advance," said Eric Stoneking, an engineer for Fermi at NASA's Goddard Space Flight Center in Greenbelt, Md., in a press release. "As the date approaches, uncertainties in the prediction decrease and the initial picture may change dramatically."


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