Monday, September 26, 2011

The Sky is Falling

Evidently, there was a satellite, the Upper Atmosphere Research Satellite (UARS), that was decommissioned and it is thought, to have reentered the atmosphere plummeting towards land sometime between Friday and Saturday. But alas, no one knows where it went. The risk assessment report produced by NASA and available on their website is interesting... and bizarre. Some fun factoids from the report:

-Tracking and Impact Prediction messages provide the best estimates of reentry time and location but have large uncertainties. Even at T –2 hours, the uncertainty of reentry time is on average +/-25 minutes for nearly circular orbits. This equates to +/-12,000 km on the Earth.

NASA conducted a detailed reentry risk assessment for UARS in 2002.
– Number of potentially hazardous objects expected to survive: 26
– Total mass of objects expected to survive: 532 kg (~242 tons, my info)
– Estimated human casualty risk (updated to 2011): ~ 1 in 3200

NASA, the USG, and some foreign space agencies now seek to limit human casualty risks from reentering space objects to less than 1 in 10,000.

In 2009, automobile fatalities was ~11 per 100,000 people. So, if my math is anywhere near right, then, in the US alone, one is 3 times more likely to get hit by a satellite plummeting towards Earth then to die in a car crash. Of course, that is for those limited occasions when a satellite is falling.

Now, couple this with the recent headlines of a space junk problem.

(9/28/11: My boyfriend brought to my attention that 1/3200 may not mean 1/3200 people. It may mean 1/3200 area units or satellite reentering events, etc. He may be right. I don't know. My assumption seems more intriguing though...)

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