A knowledge base for the stuff in orbit.

What is Space Debris?

Space debris (noun) | ‘spās də-’brē | plural space debris

“Any man-made object in orbit about the Earth which no longer serves a useful purpose” - NASA

Also known as orbital debris or colloquially “space junk,” these objects can be pieces of spacecraft, decommissioned satellites, rocket upper stages, lost astronaut equipment, and other materials as small as flecks of paint. Before large-scale human activity in space, orbital debris broadly referred to miscellaneous pieces of asteroids, comets, and other celestial bodies in the solar system. This definition changed when NASA opened their Orbital Debris Program Office in 1979.



1991 Upper Atmosphere Research Satellite. Credit: NASA

1991 Upper Atmosphere Research Satellite. Credit: NASA


Dead satellites and testing from anti-satellite weapons (ASAT) are the most common, and concerning, forms of debris. Non-operational satellites are dead weights that cannot avoid collisions, and ASAT tests are known to create thousands of pieces of debris. Propulsion leaks can also freeze in space, creating small crystals of fast-moving debris.

Photo of Saturn V third stage taken from the Apollo 8 spacecraft. Credit: NASA

Photo of Saturn V third stage taken from the Apollo 8 spacecraft. Credit: NASA


Spent rocket boosters and upper stages are often left in orbit which increases risk of debris collisions. NASA requires upper stage passivation - using up all remaining fuel - by U.S. launch providers to decreases the risk of explosions in orbit, but other space actors like Russia and China do not.

Astronaut Peggy Whitson looses a blanket while on a space walk. Credit: NASA

Astronaut Peggy Whitson looses a blanket while on a space walk. Credit: NASA


Although not as threatening, debris can also appear in the form of lost astronaut equipment, trash dumped from human-occupied spacecraft, and other paraphernalia. Some companies today are proposing services that would allow people to send their own personal items to space, creating some concern that those would multiply the amount of debris.

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Debris in Orbit

More than 29,000 human-made objects, larger than 10 cm, are orbiting the Earth, but only 6% are operational (Maury, ArianeGroup). Most artificial debris lie in three key orbits: low Earth orbit (LEO), geostationary orbit (GEO), and a higher orbit often called the graveyard orbit. The amount of debris, as well as how long debris remains, can depend on the orbit and altitude.

Credit: ESA

Credit: ESA

low earth orbit (100-2,000 km above earth’s equator)

LEO is the most dangerous orbit for debris. Most satellites and human space activity happens in LEO, and the US Strategic Command is tracking more than 8,500 pieces of debris there. Objects in LEO have different orbital planes and inclinations, making the field quite chaotic. LEO satellites can orbit the Earth up to 15 times per day, increasing the likelihood of high-velocity collisions.

A key issue is that the International Space Station (ISS), where humans live and work in space, also lies in LEO. It is not just billions of dollars worth of hardware at risk, but human lives.

Credit: ESA

Credit: ESA

geostationary orbit (35,786 km above Earth’s equator)

GEO (also abbreviated as GSO) mostly consists of large communications and weather satellites that are allocated specific orbital “slots” to avoid radio frequency interference. There are far fewer satellites in GEO, all deliberately placed far apart, meaning there is far less debris.

Credit: ESA

Credit: ESA

Graveyard orbits (>36,000 km above earth’s equator)

Graveyard orbits are higher orbits where mostly large communications and weather satellites are decommissioned to avoid collisions with operational spacecraft and other pieces of debris. Satellites are placed in graveyard orbits when there is not enough fuel to slow down the spacecraft and bring it to a lower altitude where it can decay. A common graveyard is the supersynchronous orbit above GEO. The International Telecommunication Union (ITU) requires proof that satellites in GEO can be moved into a graveyard orbit 350 km higher at the end of its life. These dead satellites will remain virtually undisturbed, with little change of altitude, for at least 50 years.

Kessler Syndrome

In 1978, NASA scientists Donald Kessler outlined a scenario in which the density of debris in orbit becomes so high, that it causes a collision cascade of compound debris. Two objects collide creating smaller pieces of debris, which collide with more debris, and then again creates new debris in an unending cycle that could render space exploration near impossible for decades.

The Kessler Syndrome applies mostly to low Earth orbit (LEO) where the unevenness of the Earth’s magnetic field means collisions can come from any direction at high velocity up to 16 km/sec head-on, twice the orbital speed. Resulting debris could then cross other orbits in LEO and start the cascade.

Credit: TU Braunschweig/AP

Credit: TU Braunschweig/AP

Fun Fact

Google search “space debris,” and this is one of the first images you will find.

This computer-generated representation of debris in low Earth orbit is one of the most commonly used images used to visualize just how much debris is circulating Earth. Within 2,000 km of Earth’s surface, approximately 95% of objects represented here are defunct satellites.

But it can be slightly misleading. The dots of orbital debris here are scaled according to image size of the graphic for visibility, not scaled to Earth. If you were to take an actual picture of Earth from the same vantage point, you would likely only be able to see the International Space Station. Space debris is a significant problem and can put certain missions at risk, but there is still far more space in LEO than many people think. [EXACT NUMBER?] Two pieces of debris can be as close [COMPARISON TO TWO PLACES ON EARTH?]

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How it Escalated



NASA opens the Orbital Debris Program Office based out of Johnson Space Center in Houston, Texas focused on the modeling, measurement, protection, and mitigation of orbital debris.


China successfully tests an anti-satellite missile system (ASAT) on their own Fengyun-1C weather satellite. Considered the first serious break up in orbit, U.S. Space Surveillance Network is still tracking more than 35,000 fragments Fengyun-1C larger than 1 cm in low Earth orbit (LEO). NASA’s Terra spacecraft maneuvers to avoid impact from the debris.


The Iridium 33 communications satellite collides with Russia’s non-operational Kosmos 2251 satellite, the first accidental collision between two spacecraft. The U.S. Space Surveillance Network catalogues over 2,000 debris fragments.

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The International Space Station executes a collision avoidance maneuver as a precaution against approaching debris from the 2009 Iridium-Kosmos collision. According to procedure, any collision chance over 1/10,000 is cause for a collision avoidance maneuver.


ESA loses contact with Envisat, an Earth observation satellite in polar orbit, and declares the mission dead two years early. It is expected to remain in orbit 150 years before falling back to Earth. It is now considered one of the most dangerous pieces of debris currently in orbit passing two other objects within 200 meters every year. Impact with either of these objects could set off a dangerous debris cascade.


NASA attaches the Space Debris Sensor to the outside of the International Space Station on a 2-3 year mission to monitor debris between 5 and 0.5 mm in diameter.


A European coalition of 9 institutions launches the RemoveDEBRIS platform to the International Space Station and begins demonstrating new orbital debris removal techniques never before tested in orbit.