What goes up, must come down, especially if it happens to be a low earth orbit satellite. The NASA Upper Atmosphere Research Satellite (UARS) was launched from the Space Shuttle in 1991 and performed fabulous earth observation science for many years, but all good things must come to an end.
The US$750 million (€547 million) satellite, which is 35ft (10.7m) long, 15ft (4.6m) wide and weighs around six tons, is expected to re-enter the Earth’s atmosphere sometime between this Thursday, Friday or Saturday (22nd-24th September 2011). NASA does not know for certain when it will happen because it depends on the atmospheric drag and how UARS might start to disintegrate.
NASA also do not know where it could come down, as it could be anywhere between along its orbit track which lies between latitudes 57 degrees north and 57 degrees south (for example, from northern Canada to southern South America) and potentially anywhere where the almost 7 billion Earthlings live. As the satellite breaks up, the debris field could stretch over 800kms (5oo miles).
NASA estimates that 26 large satellite items could survive re-entry and 450kgs (992lbs) of debris could strike land or the ocean. All the lighter satellite parts, including insulation, wiring, aluminum panels and electronic boxes will disintegrate. Fuel tanks, titanium, high temperature steel, and beryllium parts could survive quite intact.
The chance of a person being hit is 1 in 3,200, which sounds quite likely but it probably assumes all the world population, when in reality the debris zone is much smaller than the entire planet and so the actual likelihood of being hit is 1 in a few trillion, according to some sources.
Since it is a US satellite, if it does hit you or your property, then the US government is liable to pay you compensation. If you do find any bits of it, you are advised not to pick it up (it still belongs to the Americans) and you definitely cannot sell it on eBay.
UARS monitored the ozone layer, at a time when the ozone hole over the Antarctic was of major environmental concern. Since then of course lots of other environmental concerns have arisen (as well as more ozone holes over the Arctic and Tibet) and many more low earth orbit satellites have been placed in orbit, so we should expect more to re-enter the atmosphere over the coming decades.
The UARS was decommissioned in 2005 after 14 years of good science, and NASA used up all its fuel to set it into a path to re-enter Earth’s atmosphere. If UARS is anywhere near you when it re-enters then you are likely to see a spectacular fiery display as it disintegrates.
The YouTube videos are a little ‘dry’, with a lot of science geeky stuff but they really do explain the value of UARS.
YouTube NASA UARS Part 1
YouTube NASA UARS Part 1
Trevor Williams is a University of Victoria Mechanical Engineering PhD candidate specializing in renewable energy, power grid modeling and plug-in hybrid electric vehicles. He has a bachelors in Aeronautical Engineering, a Masters in Management Science and over 23 years international experience in the space industry, having worked on Earth observation and telecommunications satellites. He is the author of the Eco-Geek blog.
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