NASA space officials predict that the decommissioned 5.9 tonne UARS (Upper Atmosphere Research Satellite) will re-enter the Earths atmosphere and plummet towards the surface within a day or two of Friday 23rd September 2011.
Essentially spiralling out of control, NASA has no control over the spacecraft and cannot tell exactly where it will land. They estimate that up to 26 parts of the spacecraft, one weighing 159 kilograms, will survive re-entry and hit either the Earths surface or land in one of the Oceans. However, according to the NASA the chances of a person being hit by a piece of the disintegrating satellite are small, only 1 in 3200.
The drop zone, the area where parts of the satellite could land is anywhere between 57 degrees North and 57 degrees South latitude – basically, most of the populated world. But since three quarters of Earth is covered with ocean, there is a high likelihood that the satellite will re-enter over the sea. If it does land on land, observers on the ground nearby will see a dazzling show of fireworks as UARS burns up in the Earth atmosphere.
The satellite was deployed from Space Shuttle Discovery mission STS-48 in 1991. Its primary mission was to study the Earth’s atmosphere and in particular the ozone layer. With a planned lifetime of only 3 years, the mission was a great success and after 14 years more than half the experiments were still working. More recently, on 26th October 2010 the International Space Station performed a manoeuvre operation to avoid any collision with debris from UARS.
**UPDATE: 24 Sep 2011 **
NASA officials have confirmed that UARS returned to Earth between 11:23 p.m. EDT Friday, Sept. 23 and 1:09 a.m. EDT Sept. 24. The Joint Space Operations Center at Vandenberg Air Force Base in California said the satellite penetrated the atmosphere over the Pacific Ocean. The precise re-entry time and location are not yet known with certainty.
**UPDATE: 29 Sep 2011 **
NASA stated on their website that: NASA's decommissioned Upper Atmosphere Research Satellite fell back to Earth at 12 a.m. EDT (0400 GMT), as Friday, Sept. 23, turned to Saturday, Sept. 24 on the United States east coast. The Joint Space Operations Center at Vandenberg Air Force Base in California has determined the satellite entered the atmosphere over the Pacific Ocean at 14.1 degrees south latitude and 189.8 degrees east longitude (170.2 west longitude). This location is over a broad, remote ocean area in the Southern Hemisphere, far from any major land mass. The debris field is located between 300 miles and 800 miles downrange, or generally northeast of the re-entry point. NASA is not aware of any possible debris sightings from this geographic area.