NASA: Satellite debris has hit Earth


This undated NASA image shows a conceptual image of the Upper Atmosphere Research Satellite, UARS. (HO/AFP/GETTY IMAGES)
September 24, 2011

A 12,500-pound decommissioned satellite that was lazily falling toward the Earth over the past two days finally came down around midnight Friday, NASA said early Saturday.

The Upper Atmosphere Research Satellite (UARS) fell back to Earth between 11:23 p.m. Friday and 1:09 a.m. Saturday, NASA said in an update on its website. The Joint Space Operations Center at Vandenberg Air Force Base in California said the satellite penetrated the atmosphere over the Pacific Ocean, the agency said. It is not yet known when exactly the satellite hit Earth, and whether it ended up in water or on land, NASA said.

The satellite took longer than expected to return to Earth after 20 years in space. Unpredictable, and completely out of control, the satellite was expected to shower 26 pieces of space junk across a 500-mile linear crash zone. Most of its parts are believed to be burned up.

At 10:30 p.m. Friday, NASA said the satellite’s reentry into the Earth’s atmosphere was expected between 11:45 p.m. Friday and 12:45 a.m. Saturday, and its path was over Canada, Africa and the Atlantic, Pacific and Indian oceans. The risk to public safety is very remote.

Small variations in reentry timing means vast differences as to where UARS would come down. The satellite, designed to help scientists understand climate change, circled the planet at a 57-degree inclination to the Equator, a path that took it every hour and a half from the frozen north to the frigid seas beyond the southern coast of Australia — and back again.

“It’s dancing all over the place. It looks like the trend is to go longer than we think,” said Bill Ailor, an engineer with the Aerospace Corp., who has been monitoring the satellite.

For two days, NASA had predicted that its satellite would arrive Friday afternoon or evening. But the satellite slowed down Thursday and Friday, showing no eagerness to leave space.

“There are random forces of nature acting on the satellite that we can neither control nor predict,” NASA spokeswoman Beth Dickey said Friday evening. “Very small changes have very large consequences over time, and in this case, the change has been in the orientation of the spacecraft.”

The difficulty in predicting the satellite’s behavior was demonstrated by changing predictions even over small periods of time. At 7:30 p.m. Friday, NASA put out an update saying the satellite was on track to come down between 11 p.m. Friday and 3 a.m. Saturday.

On Friday morning, the satellite was 100 miles up, NASA said. UARS was expected to heat up, partially melt and break into pieces, NASA said this week.

The biggest piece would weigh more than 300 pounds, which would pose a hazard if it fell on a populated area. But most of the planet is open ocean.

The Aerospace forecast Friday night, based on Air Force tracking data, showed that UARS would hit the atmosphere over the southern Indian Ocean at about 1 a.m. Eastern time.

That might mean that fiery fragments could be seen in Australia about 15 minutes later.

Joel Achenbach writes on science and politics for the Post's national desk and on the "Achenblog."
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