Satellite's fall to Earth slows

24 Sep 2011

A six-ton Nasa satellite on a collision course with Earth is clinging to space, apparently flipping position in its ever-lower orbit and stalling its death plunge.

The old research spacecraft was on target to crash through the atmosphere during Friday night or early on Saturday, putting Canada and Africa in the potential crosshairs, although most of the satellite should burn up during re-entry. The United States was not entirely out of the woods as the possible strike zone skirted Washington state.

“It just doesn’t want to come down,” said Jonathan McDowell of the Harvard-Smithsonian Centre for Astrophysics.

Mr McDowell said the satellite’s delayed demise demonstrates how unreliable predictions can be. That said, he explained that “the best guess is that it will still splash in the ocean, just because there’s more ocean out there”.

Until Friday, increased solar activity was causing the atmosphere to expand and the 10-metre, bus-size satellite to fall more quickly. But late on Friday morning, Nasa said the sun was no longer the major factor in the rate of descent and that the satellite’s position, shape or both had changed by the time it slipped down to a 100-mile orbit.

“In the last 24 hours, something has happened to the spacecraft,” said Nasa orbital debris scientist Mark Matney.

On Friday night, Nasa said it expected the satellite to come crashing down while passing over the Atlantic, Pacific and Indian oceans, as well as Canada, Africa and Australia.

The Upper Atmosphere Research Satellite, or UARS, will be the biggest Nasa spacecraft to crash back to Earth, uncontrolled, since the post-Apollo 75-ton Skylab space station and the more than 10-ton Pegasus 2 satellite, both in 1979.

People can take comfort in the fact that no-one has ever been hurt by falling space junk – to anyone’s knowledge – and there has been no serious property damage. Nasa put the chances that somebody on Earth would get hurt at one in 3,200. But any one person’s odds of being struck were estimated at one in 22 trillion, given there are seven billion people on the planet.

Any surviving wreckage belongs to Nasa, and it will be against the law to keep or sell even the smallest piece. There are no toxic chemicals on board, but sharp edges could be dangerous, so the space agency is warning the public to call police if they find any.

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