The most notable collision involving a satellite was in 1993, when the large communications satellite Olympus-1 became caught up in a severe meteor shower. Spinning out of control, the satellite used up all its fuel in an effort to read just its trajectory and was rendered useless. Collisions are rare and many satellites now have tracking systems in place to shift their course when potential collisions are imminent. The biggest danger for satellites, however, is not from large asteroids, but from the millions of tiny leftover pieces of defunct satellites. At less than one centimetre (0.4 inches) in diameter they are far too small for us to track, and can travel at speeds of 35,400 kilometres (22,000 miles) per hour – so fast that even a fleck of paint could cause devastation to a satellite.
Answered by Rik Sargent