Why do satellites fall to Earth?
A satellite that has exceeded its useful purpose has several different potential ﬁnal resting places. These depend on the amount of fuel still available on the satellite, and whether ground control is still able to manoeuvre it. One technique is to move the satellite slightly higher in its orbital band, into a ‘graveyard orbit’. This is an area where no other satellites are orbiting, and the dying satellite can be left to degrade over time. However, as it breaks up and potentially shifts in orbit, this could still prove dangerous to other satellites.
Some satellites are merely left in their current orbits, either by choice or through necessity if they are uncontrollable. Other satellites are purposely moved lower into the atmosphere, where they are left to burn up and hopefully disintegrate before reaching the Earth. While this is usually the case there have been some notable exceptions, including NASA’s Skylab station that failed to deteriorate completely in July 1979, spreading debris over western Australia. More recently, debris from NASA’s UARS satellite is scheduled to fall back to Earth at some point this evening, with a 1 in 3,200 chance of hitting a human.