The U.S. Air Force currently tracks about 13,400 objects in space, of which only between 6 and 7 percent are active satellites. The rest is debris.
Not all space debris can be located and tracked with current capabilities. The Air Force’s Space Surveillance Network – the best in the world – can see objects down to 10 centimeters (the size of a baseball) in diameter in LEO, where the Space Shuttle, the International Space Station (ISS), most Earth imaging satellites, and satellites providing mobile communications reside); and down to about 1 meter in diameter in Geosynchronous Orbit (GEO, where most of the world’s communications and broadcast satellites reside).
There are more than 100,000 pieces of smaller, untrackable debris, down to the size of a marble (1 centimeter in diameter) in orbit; and possibly trillions of pieces smaller yet. Scientists estimate that there is about 4 million pounds of space junk in LEO alone.
Even tiny pieces of debris can damage or destroy satellites, the Space Shuttle, the ISS, or penetrate astronaut suits. Debris in LEO travel at 10 times the speed of a rifle bullet; a marble-sized bit of junk would slam into a satellite with the energy equal to a 1-ton safe hitting the ground if dropped from a five-story building. Indeed, a tiny paint fleck put a pit in the window of the Challenger Space Shuttle during Sally Ride’s historic first mission.
The amount of space junk is increasing by about 5 percent per year; meaning that by the end of the century a satellite in GEO will have a 40 percent chance of being struck during its operational life-time.
NASA has found that of the 20 problems most likely to cause the loss of a Space Shuttle, 11 involve debris.
NASA data shows a current risk of a “catastrophic” debris strike to the Shuttle of 1 in 200. By comparison, the lifetime risk of a U.S. citizen dying in a car accident is about 1 in 100; the risk of dying in an attack with a firearm, about 1 in 325; the risk of dying in a fire, about 1 in 1,116.
While debris in LEO eventually de-orbits and most burns up in the Earth’s atmosphere (unfortunately, sometimes very large pieces of debris actually hit the Earth intact), debris in GEO remains on orbit, and thus a threat to spacecraft there, forever.
The 1985 test of an ASAT missile fired from a U.S. F-15 fighter at a U.S. Air Force satellite named Solwind resulted in more than 250 pieces of space debris that took 17 years to clear out of LEO. One piece of that debris came within a mile of the ISS.
Most space-faring nations have incorporated into national legislation and regulations requirements for space operators designed to limit debris creation. NASA and the Federal Communications Commission have been leaders in this arena, with the United States currently setting the highest bar in the battle against space junk. Indeed, as noted above, the U.N. Committee on the Peaceful Uses of Outer Space is now working on development of an international code of conduct in hopes of slowing the creation of space debris
