The Kessler syndrome (Also called the Kessler effect, collisional cascading or ablation cascade), proposed by the NASA scientist, Donald J. Kessler in 1978 was a scenario in which the density of objects in low Earth orbit (LEO) was high enough that collisions between objects could cause a cascade—each collision generating space debris which increased the likelihood of further collisions. One implication was that the distribution of debris in orbit could render space exploration and even the use of satellites, unfeasible for many generations.
Gravity featured a Kessler syndrome catastrophe as the event which set the plot in motion after the Russians shot a presumed defunct spy satellite down which resulted in a cloud of debris moving at 20,000 to 50,000 miles per hour.
Every satellite, space probe and manned mission had the potential to create space debris. A cascading Kessler syndrome became more likely as satellites in orbit increased in number and old satellites became inoperative. The most commonly used orbits for both manned and unmanned space vehicles are low Earth orbits which covered an altitude range low enough for residual air drag to be sufficient to help keep the zone clear. Collisions that occurred in this altitude range are also less of an issue because the directions into which the fragments flew and/or their lower specific energy often resulted in orbits intersecting with Earth or having perigee below this altitude. Orbital decay was much slower at altitudes where atmospheric drag was insignificant. Slight atmospheric drag, lunar perturbation and solar wind drag could gradually bring debris down to lower altitudes where the fragments finally re-entered, but this process could take millennia at very high altitudes.
Image made from models used to track debris in Earth orbit. The Kessler syndrome was especially insidious because of the "domino effect" and "feedback runaway" wherein impacts between objects of sizable mass spalled the debris off from the force of collision. The shrapnel could hit the other objects, creating even more space debris: If a large enough collision or explosion are to occur such as between a space station and a defunct satellite or as the result of hostile actions in space, the resulting debris cascade could render low Earth orbit essentially impassable.
Avoidance and reduction
Designers of a new vehicle or satellite are frequently required to demonstrate that it could be safely disposed of at the end of it's life, for example by use of a controlled atmospheric re-entry system or a boost into a graveyard orbit. One technology proposed to help deal with fragments from 1 cm to 10 cm in size was the laser broom, a proposed multimegawatt land-based laser that could deorbit debris: The side of the debris hit by the laser would ablate and create a thrust that would change the eccentricity of the remains of the fragment until it would re-enter harmlessly.
The Envisat satellite was a large, inactive satellite with a mass of 8,211 kg (8.211 t) that drifted at 785 km (488 mi), an altitude where the debris environment was the greatest—2 catalogued objects could be expected to pass within about 200 meters of Envisat every year—and likely to increase. It could easily become a major debris contributor from a collision during the next 150 years that it would remain in orbit.
Fictional and dramatic representations
- An ablation cascade was a key plot point in Ken MacLeod's future history novel, The Sky Road.
- An offshoot of humanity used asteroid debris to "close the sky" in Peter F. Hamilton's stand-alone sci-fi novel, Fallen Dragon.
- The Japanese manga/anime, Planetes revolved around a team of space debris collectors based in the debris craft, Toy Box in the year, 2075. A Kessler syndrome scenario was referenced directly when a "Space Defense Front" terrorist group attempted to ram a satellite into a space station, thus cutting the world's economic powers off from space-borne resources.
- In the book, World War Z, the Chinese are revealed to have a small space station, believed to be unmanned. When the crew from the International Space Station boarded it after a brief radio message, they found out that the Chinese crew are both dead, one having killed the other and the entire station was a bomb, set up to explode and cause a cascade effect denying all nations the use of space.
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