Kessler syndrome

The Kessler Syndrome, also known as collisional cascading, is a scenario, proposed by NASA scientist Donald J. Kessler in a 1978 publication, where the volume of space debris in low Earth orbit is so high that objects in orbit are frequently struck by debris, creating even more debris and a greater risk of further impacts.^[1] The implication of this scenario is that the escalating amount of debris in orbit could eventually render space exploration, and even the use of satellites, infeasible for many generations.^[1]

The term Ablation cascade has been used to describe a single explosion or crash in space, the debris from which start a chain reaction of further explosions eventually destroying all other satellites thereby creating Kessler Syndrome. The term was first used in the 1999 fiction novel The Sky Road.

Debris generation and destruction

Every satellite, space probe and manned mission has the potential to create space debris. As the number of satellites in orbit grows and old satellites become obsolete, the risk of a cascading Kessler Syndrome becomes greater.

Fortunately, at the most commonly used Low Earth Orbits residual air drag helps keep the zones clear. Collisions that occur under this altitude are also less of an issue, since the energy lost in the collision results in fragment orbits having perigee below this altitude.

At altitudes above the levels where atmospheric drag is significant, the time required for orbital decay is much longer. Slight atmospheric drag, lunar perturbation, and solar wind drag can gradually bring debris down to lower altitudes where fragments finally re-enter, but at very high altitudes this can take millennia.

Seriousness

The Kessler Syndrome is especially insidious because of the "domino effect" and "feedback runaway". Any impact between two objects of sizable mass spalls off shrapnel debris from the force of collision. Each piece of shrapnel now has the potential to cause further damage, creating even more space debris. With a large enough collision or explosion (such as one between a space station and a defunct satellite, or the result of a war in space), the amount of cascading debris could be enough to render low Earth orbit essentially impassable.^[2][3]

Avoidance and reduction

To minimize the chances of damage to other vehicles, designers of a new vehicle or satellite are frequently required to demonstrate that it can be safely disposed of at the end of its life, for example by use of a controlled atmospheric reentry system or a boost into a graveyard orbit^[4].

One technology for the bigger fragments that can be tracked is the laser broom, a multimegawatt land-based laser that could be used to target fragments. When the laser light hits a fragment, one side of the fragment would ablate, creating a thrust that would change the eccentricity of the remains of the fragment until it would re-enter harmlessly.^[5]

Kessler Syndrome in fiction

Generation of space debris to the point where space travel is impacted has been a subject of several works of science fiction, including various movies and novels.

• In the anime series Cowboy Bebop, an accident in space has caused debris to cloud space around Earth. Entering and leaving the atmosphere is dangerous, and falling debris makes living on the Earth's surface risky.^[6]
• Kessler Syndrome was explicitly mentioned by name in the manga/anime series Planetes, where efforts to remediate the problem serve as a running backdrop for the series.^[7]
• An ablation cascade is part of the background to Ken Macleod's 1999 novel The Sky Road.^[8]
• In the 2008 Disney movie WALL-E, Earth orbit is depicted as completely clogged with satellite debris.^[9]
• The UFO episode Conflict features a campaign to clear excess space debris in earth orbit.^[10]

See also

• Space debris
• Laser broom
• 2007 Chinese anti-satellite missile test
• 2009 satellite collision

Further reading

An article in the July, 2009 issue of Popular Mechanics by Glenn Harlan Reynolds discusses the Kessler Syndrome in regards to the February, 2009 satellite collision and how international law may need to address the problem to help prevent future incidents.^[11]

References

External links

• Don Kessler's Web Page
• APOD - Satellites Collide in Low Earth Orbit
• Mathematical Modeling of debris flux
• New York Times: Orbiting Junk, Once a Nuisance, Is Now a Threat
• Wired: Houston we have a trash problem
• Debris Spews Into Space After Satellites Collide
• aggregated public information research on space debris, graveyard orbits etc