German Satellite To Fall From Sky

BBC News reports that a German satellite is soon to fall from sky. According to the article: "The Roentgen Satellite (Rosat) is due to come back to Earth at some stage over the weekend - possibly Sunday. Just as for NASA's UARS satellite, which plunged into the atmosphere in September, no one can say precisely when and where Rosat will come in. What makes the redundant German craft's return interesting is that much more debris this time is likely to survive all the way to the Earth's surface. Experts calculate that perhaps as much as 1.6 tonnes of wreckage - more than half the spacecraft's launch mass - could ride out the destructive forces of re-entry and hit the planet."

Comments

Back of the envelope calculation

[JoshuaZ]

Relevant comic: http://www.askdreldritch.com/comic687.html. More substantially, there's now a twitter feed with regular updates http://twitter.com/#!/ROSAT_Reentry. The rate of descent is pretty fast. One thing to keep in mind is that although the chance of someone being hit by debris is around 1 in 3000 or so, the chance of a specific person being hit is much lower. It is extremely unlikely that two people will be hit so by a rough approximation, if someone is hit there is a 1 in 6 billion chance that it is you. So the chance is about 1/(3000 * 10^9)= 1 in 3 trillion. Even if one assumes a fairly high probability that when one person gets hit multiple people will get hit, the chance is still on the order of 1 in a trillion. That said, this sort of uncontrolled reentry is not ideal. But most satellites are either in higher orbits or are small enough such that everything will burn up when they reenter. Large satellites entering in an uncontrolled fashion is pretty rare.