With all of the communication, military, and scientific satellites orbiting the earth, how much traffic do the space shuttle astronauts have to worry about?
That's a good question. One of the duties of the US Space Command is to track all of those satellites, bits of junk, even lost screwdrivers (!) which are in orbit. During a shuttle mission, that information is forwarded to NASA. So far, NASA has had to change trajectories only two or three times since the program began, and in neither of those cases was there any real threat of collision. You have to remember that space is BIG, and a collision between two objects, even very nearby orbits, is extremely small.
The worst collision the shuttle has yet encountered was with a paint fleck some ten years ago or so which was too small to be tracked by Space Command. It nearly shattered the windshield. So although the probabilities are small, it is a concern.
Update 2016: Space junk no longer poses a threat to the space shuttles as they are no longer flown.
This page was last updated on February 10, 2016