How are satellites prevented from crashing into each other?
Satellites stay on orbits that are very precise provided there are no external forces such as atmospheric drag to perturb them. The actual distances between most satellites are many hundreds of miles so there is no real danger of collision. However, there are now so many debris particles present in orbit that satellites, the Space Shuttle and the Space Station run an increasing risk of being hit by orbiting debris from past space missions and exploded satellites. It is these uncontrolled small particles that cannot be avoided. US Space Command can track objects the size of a walnut or a baseball in near Earth orbit, but cannot see ice droplets, flecks of paint or nuts and bolts. These travel at thousands of miles an hour and are lethal. The Hubble Space Telescope has been hit, as has a Space Shuttle, and at least two satellites have been disabled after a debris collision.