Collision avoidance (spacecraft)

Spacecraft collision avoidance is the implementation and study of processes minimizing the chance of orbiting spacecraft inadvertently colliding with other orbiting objects. The most common subject of spacecraft collision avoidance research and development is for human-made satellites in geocentric orbits. The subject includes procedures designed to prevent the accumulation of space debris in orbit, analytical methods for predicting likely collisions, and avoidance procedures to maneuver offending spacecraft away from danger.

Orbital speed around large bodies (like the Earth) is fast, resulting in significant kinetic energy being involved in on-orbit collisions. For example, at the Low Earth orbital velocity of ~7.8 km/s, two perpendicularly colliding spacecraft would meet at ~12.2 km/s. Almost no known structurally solid materials can withstand such an energetic impact. Most of the satellite would be instantly vaporized by the collision and broken up into myriad pieces ejected at force in all directions. Because of this, any spacecraft colliding with another object in orbit is likely to be critically damaged or completely destroyed.

Necessity

A cascading series of collisions between orbiting satellites and other objects could take place if a critical mass of space debris is allowed to accumulate in Earth orbit, dubbed the Kessler syndrome. More collisions would make new smaller fragments which make more collisions and so forth.