Old Nasa research spacecraft crashes to earth

The biggest spacecraft to fall uncontrolled in 32 years, a six-tonne satellite, has fallen to earth, Nasa said.

The satellite clung to space overnight, apparently flipping position in its ever-lower orbit and stalling its plunge.

The old research spacecraft was targeted to crash through the atmosphere sthis weekend, putting Canada, Africa and Australia in the potential crosshairs, although most of the satellite was set to burn up during re-entry.

The United States wasn’t entirely out of the woods; 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.

McDowell said the satellite’s delayed demise demonstrates how unreliable predictions can be.

That said, “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 35-foot, bus-size satellite to freefall more quickly. But late 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.

“The risk to public safety is very remote,” Nasa said in a statement.

The Upper Atmosphere Research Satellite, or UARS, is 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.

Russia’s 135-ton Mir space station slammed through the atmosphere in 2001, but it was a controlled dive into the Pacific.

Some 26 pieces of the UARS satellite – representing 1,200 pounds of heavy metal - are expected to rain down somewhere. The biggest surviving chunk should be no more than 300 pounds.

Earthlings 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 somewhere 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.

“Keep in mind that we have bits of debris re-entering the atmosphere every single day,” Nasa orbital debris scientist Mark Matney said.

In any case, finders definitely aren’t keepers.

Any surviving wreckage belongs to Nasa, and it is 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 keep hands off and call police.

The satellite was launched in 1991 from space shuttle Discovery to study the atmosphere and the ozone layer. At the time, the rules weren’t as firm for safe satellite disposal; now a spacecraft must be built to burn up upon re-entry or have a motor to propel it into a much higher, long-term orbit.