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What is Space Junk?

 , updated on May 17, 2016
Space junk is a term for man-made debris that is in orbit around the Earth that is mostly composed of defunct satellites and spent rocket stages. It is a hazard to satellites and manned space missions as there are over 170 million small pieces of space junk that can travel up to 17,500 mph.
Large pieces of space junk that can survive reentry into the atmosphere can also be a threat to people on the ground and aircraft. In 2007, airborne debris from a Russian spy satellite came within approximately 8 kilometers of an Airbus A340 carrying 270 passengers over the Pacific Ocean between Santiago and Auckland. The pilot reported seeing the debris and hearing a sonic boom.
Space junk can also represent an environmental hazard as their have been around 40 nuclear reactors put into Earth orbit. For example, in 1978 a Russian satellite containing a nuclear reactor known as Kosmos 954 disintegrated over northern Canada spreading radioactive debris over a wide area.


About one satellite a year is rendered inoperable by a collision with space junk. Satellite and other spacecraft are routinely hit by small particles that causes an effect similar to sandblasting that increases wear on susceptible equipment such as solar panels.
Manned space missions have encountered damage from impacts with space debris with damage such as chipped windows and lost tiles becoming commonplace by the 1980s. Space junk is considered a significant threat to both manned space missions and satellites.
Space Junk Estimates
Less 1 cm170 million (2013, ESA)
Bigger than a marble 500,000 (2013, NASA)
Bigger than a softball20,000 (2013, NASA)
Heavier than 100 kg (220 lbs)1,500 (2002, NASA)


Space junk eventually slows and reenters the Earth's atmosphere but this process can take thousands of years. Many countries, including the United States, require that decommissioned satellites be moved into a graveyard orbit that has no current commercial use.
A number of technologies for cleaning up space junk have been proposed including robotic clean up satellites that slow objects out of orbit using methods such as laser beams.
It is possible to design satellites to deorbit themselves at end of life using techniques such as deploying a solar sail. At the moment, there is little commercial incentive for companies to design robust and safe end-of-life procedures for satellites.
Overview: Space Junk
DefinitionMan-made debris in orbit around the Earth.
Also Known AsOrbital debris
Related ConceptsKessler Syndrome
Space Environment
Graveyard Orbit


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