It is estimated that there are about a half a million pieces of space junk orbiting the Earth. This junk includes " spent rocket stages, old satellites, and fragments from disintegration, erosion, and collisions." Space launches have to pass though this layer of junk. Some of the junk is orbiting in the same orbits of satellites and poses a threat of collision. Most of the space junk consists of small particles that are less than one centimeter in size. About three hundred thousand particles are between one and five centimeters in size. There are amost twenty thousand particles bigger than five centimeters that are currently being tracked.
The damage caused to satellites by the smallest particles consists on erosive weathering like being sandblasted. Bigger pieces of junk can cause serious damage. There is a density of space junk called the Kessler syndrome beyond which interaction of pieces of space junk produce more particles than natural processes remove which would result in a run-away chain reaction. If this happens, human access to space could be severely limited. A number of companies have designed systems to remove space junk from orbit.
The European Space Agency has proposed the e.DeOrbit mission in 2014. This particular mission would find pieces of space junk between five hundred and six hundred miles up that are in a polar orbit. There have been proposals for a variety of "capture mechanisms" including nets, harpoons, robotic arms and robotic tentacles.
A Swiss Space Systems demonstration spacecraft called the CleanSpace One is slated for launch in 2018 from the back of a modified Airbus A300 jumbo jet. Upon launch, the CleanSpace One would rendezvous with a decommissioned SwissCube nanosatellite and then move the satellite out of orbit.
The Japanese Aerospace Exploration Agency has designed an electrodynamic tether. When attached to a satellite, the tether would interact with the Earth's magnetic field to impose a drag on the satellite, bringing it lower into the Earth's atmosphere where it will burn up. The system is supposed to be tested in 2015.
Texas A&M University has proposed the Sling-Sat Space Sweeper which would rendezvous with a piece of space junk and sling it toward the Earth to burn up in the atmosphere. Gaining momentum lost from the captured junk, the SSS would sail off to find another piece to remove from orbit.
The United Kingdom has a proposal for using the drag of a solar sail to slow a satellite and drop it from orbit. It was supposed to be tested in 2011 but the design was not finished. Work continues on the project using experience from a nanosatellite that launched in February of 2013.
Raytheon BBN Technologies in the U.S. has suggested a method for junk elimination they call Space Debris Elimination. This system would use bursts of air in the upper atmosphere to decelerate pieces of space junk in low Earth orbit. The bursts could be delivered by high altitude balloon or high altitude planes.
Star Technologies and Research, Inc. proposes a solar powered system called the ElectroDynamic Debris Eliminator that would consist of a string of nanosatellites connected by a electrically conducting metallic tape that could be up to two miles long. It would knock space debris down as it passes through the Earth's magnetic field and generates voltage. They claim it can clear all large pieces of space junk in low-Earth orbit in twelve years.
Whatever system or combinations of systems are chosen and implemented to clear orbiting space junk, this is a project that should be carried out as soon as possible to avoid the Kessler syndrome.
