According to NASA, more than 500,000 pieces of orbital debris as big as a marble or larger are tracked as they orbit the Earth. More than 20,000 of these are larger than a softball.
Space debris, junk, trash is the collection of defunct man-made objects in space like old satellites, spent rocket stages, and fragments from disintegration, erosion, and collisions. They all travel at speeds up to 17,500 mph, fast enough for a relatively small piece of orbital debris to damage a satellite or a spacecraft, which is a dramatic potential danger to all space vehicles, especially to those that are manned spacecrafts like the International Space Station.
The greatest risk to space missions comes from non-trackable debris, said Nicholas Johnson, NASA chief scientist for orbital debris. Claiming that space shuttle windows have been replaced because of damage caused by material that was analyzed and shown to be paint flecks. It's a wonder, with so much orbital debris, there have been only a few disastrous collisions.
In 1957 after the beginning of the space race (started by the launch of Sputnik),the North American Aerospace Defense Command (NORAD) started compiling a database of all known debris. The Department of Defense maintains a highly accurate satellite catalog on objects in Earth orbit that are larger than a softball. NASA and the DoD cooperate and share responsibilities for characterizing the satellite (including orbital debris) environment.