The UARS (Upper Atmosphere Research Satellite) is a satellite which was launched by the Discovery space shuttle in 1991 to study the ozone layer. It was decommissioned by NASA in 2005. It is about 35ft long – the size of a bus – and weighs six tonnes.
After being decommissioned it was inevitable that the satellite would drop out of orbit at some point. On Sept 7 NASA announced that it would fall to Earth in weeks.
NASA’s guess is as good as yours. It could come down anywhere between 57 degrees north and 57 degrees south of the equator, which leaves out the poles but covers most of the populated world. The space agency’s latest estimate is that it will arrive on Earth on Friday evening, and they have reassured US citizens that “the satellite will not be passing over North America during that time period.” It could still land almsot anywhere in Europe, Africa and Asia. NASA says there is no way to know where it will fall. Because the satellite travels thousands of miles in a matter of minutes, even minutes before re-entry, it will be impossible to pinpoint an exact location, Mark Matney of NASA’s Orbital Debris team said Wednesday.
Much of the satellite will burn up in the atmosphere, but experts estimate that 26 pieces – the largest weighing 300lb, the same as a large refrigerator – will be scattered over an area of up to 500 miles.
NASA has identified 26 pieces, ranging from tens of pounds to a few hundred pounds, that could make it.
Because water covers about 70 percent of the Earth’s surface, NASA believes most, if not all the debris that survives will land in an ocean or sea. And even if pieces strike dry land, there’s very little risk any will hit people.
Why there is so much uncertainty?
The satellite’s unorthodox shape means it is tumbling to Earth in an unpredictable spiral rather than plunging down like an arrow. Factors like the warmth of the air and the amount of drag make it impossible to tell exactly how it will come down. Also, space debris can bounce – meaning that when it hits our atmosphere it could skim across it like a stone on a lake before re-entering.
Has this happened before?
It has indeed. The last satellite to crash down to Earth was the Skylab in 1979, which was 15 times heavier than the UARS. It landed in Western Australia but the US kindly footed the clean-up bill.
No one has ever been hurt by space junk falling to Earth, but it is worth keeping an eye out if only for the potential for a spectacular light show. Sputnik’s return to Earth in 1958 was a fantastic affair, leaving a trail of bright sparks as it raced from New York to the Amazon in ten minutes.