The Kessler collision cascade

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The mechanism, published by Donald Kessler and Burton Cour-Palais in the Journal of Geophysical Research in 1978, by which a debris population can become self-sustaining. Their argument was statistical rather than dramatic: as the number of objects in a given orbital band rises, the collision rate rises with roughly the square of that number, and each collision produces many fragments, each of which is itself a collider. Above a threshold density, fragment production from collisions exceeds fragment removal by atmospheric drag, and the population keeps growing even if nothing further is launched. The syndrome is often described as an event that would suddenly render orbit unusable; the paper describes something slower and more insidious — a band in which the background collision risk gradually rises until operating there requires more shielding, more manoeuvring propellant and more replacement spacecraft than the service is worth. The threshold is altitude-dependent, because atmospheric drag removes objects from 400 kilometres in years and from 1,000 kilometres in centuries. Not a place.

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