Space debris

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Space debris or orbital debris, also called space junk, are any of the objects in orbit around Earth created by man that no longer serve any useful purpose. They consist of everything from entire spent rocket stages and defunct satellites to explosion fragments, paint flakes, dust and slag from solid rocket motors, coolant released by RORSAT nuclear powered satellites, and other small particles.

According to Edward Tufte's "Envisioning Information" , floating in space there is (or was) also a glove astronaut Ed White lost on the first American space-walk, a camera Michael Collins lost near the spacecraft Gemini 10, garbage bags, droplets of radioactive coolant from a Russian nuclear powered spaceship, a wrench and a toothbrush. Debris are most concentrated in low Earth orbit, though some extends out past geosynchronous orbit.

Space debris has become a growing concern in recent years, since collisions at orbital velocities can be highly damaging to functioning satellites and can also produce even more space debris in the process. Some spacecraft, like the International Space Station, are now armored to deal with this hazard. Also astronauts on EVA are vulnerable, see Extra-vehicular activity.

In order to mitigate the generation of additional space debris, a number of measures have been proposed: The passivation of spent upper stages by the release of residual fuels is aimed at decreasing the risk of on-orbit explosions that could generate thousands of additional debris objects. De-orbiting satellites at the end of their operational life would also be an effective mitigation measure. In orbital altitutes where it would not be economically feasible to de-orbit a satellite, like in the geostationary ring, they are brought to "graveyard orbits" where no operational satellites are present.

Proposals have been made for ways to "sweep" space debris back into Earth's atmosphere, including automated tugs, laser brooms to vaporize or nudge particles into rapidly-decaying orbits, or huge aerogel blobs to absorb impacting junk and eventually fall out of orbit with them trapped inside. However, currently most effort is being devoted to prevention of collisions by keeping track of larger debris, and prevention of more debris.

The United States Military is maintaining a catalogue currently containig about 10,000 objects. Observation data gathered by a number of ground based radars and telescopes as well as by a space based telescope is used. Nevertheless, the majority of debris objects remain unobserved. There is an approximate number of 330 million debris objects larger than 1 mm in orbit.

Clouds of very small particles are not as serious but cause erosive damage, like sandblasting.

See also Near-Earth object.