-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...)