There are over 500,000 pieces of debris in Earth orbit placed there by humans. Fortunately, space is big and the probability of anything colliding with this junk is low – but it isn’t zero. This was illustrated in the near miss between NASA’s Fermi Gamma Ray Telescope and a derelict Soviet spy satellite that nearly collided with it last year. The NASA mission controllers had to maneuver the spacecraft out of the way or it would have been hit, and destroyed, by the collision in much the same way an American Iridium Satellite was destroyed by a defunct Soviet-era Cosmos satellite in 2009. That collision shattered both satellites and places thousands more pieces of debris into orbits that will last hundreds, if not thousands, of years. The relative speed between the satellites when they collided was about 26,000 miles per hour.
The first junk entered space at the dawn of the space age when we began launching our first rockets. Only recently have several countries agreed to try and stop the growth of space debris by limiting the amount of time a new satellite may remain in orbit after it completes its mission. This usually means the owner of the spacecraft has to make sure it either de-orbits and burns up in the atmosphere or is moved to a higher ‘parking orbit’ out of harm’s way. But not all countries have signed up and that’s a problem.
The amount of debris is still growing and the probability of more collisions happening grows with it. If we don’t do something, then there will come a day that there is so much junk up there that any new satellite will be hit shortly after it launches and we will lose the benefits of space entirely.