Almost all of it is small enough. And orbiting junk is monitored really closely (so we can time rocket launches to avoid it), so when anything large enough to r

Almost all of it is small enough. And orbiting junk is monitored really closely (so we can time rocket launches to avoid it), so when anything large enough to reach the ground comes down (most prominently Mir: http://en.wikipedia.org/wiki/Deorbit_of_Mir http://en.wikipedia.org/wiki/Deorbit_of_Mir), people know in advance. Hey, there's even a schedule: http://www.aerospace.org/cords/reentry-predictions/upcoming-reentries/ http://www.aerospace.org/cords/reentry-predictions/upcoming-...