The most common subject of spacecraft collision avoidance research and development is for human-made satellites in geocentric orbits.
Orbital speed around large bodies (like the Earth) is fast, resulting in significant kinetic energy being involved in on-orbit collisions.
The 2009 satellite collision entirely obliterated both spacecraft and resulted in the creation of an estimated 1,000 new pieces of space debris larger than 10 cm (4 in) and many smaller ones.
Most protective measures ensure that satellites and other artificial objects only remain in their operational orbits for as long as they are functional and controllable.
Objects launched onto suborbital trajectories such as sounding rocket payloads and ballistic missile warheads do not achieve orbital velocities and fall back to earth at the end of the flight, so they do not require any intentional care on the part of the operator to ensure reentry and disposal.
Most modern designs include sufficient fuel margins for de-orbit burns after injecting payload into orbit.
SpaceX's Falcon 9 is a launch vehicle designed to minimize the effect of its upper stage on space debris.
It reenters within minutes of launch, either intentionally using fuel reserved for stage recovery to land for reuse or is left to continue on its ballistic trajectory and disintegrate upon reentry into the atmosphere.
For Low Earth orbits, the second stage uses remaining fuel to perform a de-orbit burn and disintegrate in the atmosphere.
The United States Department of Defense Space Surveillance Network maintains a catalog of all known orbiting objects approximately equal to a softball in size or larger.
NASA conducts orbital projections and assesses collision risk for known objects larger than 4 inches (10 cm).
NASA policy for crewed spacecraft, which all have onboard propulsion, like the Space Shuttle and the International Space Station (agreed upon by all international partners) requires planning for avoidance maneuvers if the probability of collision is[4] As of August 2020, the ISS has conducted 27 collision avoidance maneuvers since its initial launch in 1999 and is trending upwards with time.
[3] The population of debris in this size range is significant and difficult to track accurately with current methods, meriting further research.
Most human-launched satellites without onboard propulsion are small CubeSats which rely on alternative devices for orientation control.
CubeSats are often launched into Low Earth orbit, where the atmosphere still provides a small amount of aerodynamic drag.
If only one of the objects is an operational satellite, it would be the sole contributor to an avoidance maneuver, significantly cutting into or entirely using up remaining fuel reserves.
Collision avoidance maneuvers require significant planning and execution time, which can be an issue if the risk isn't predicted sufficiently in advance.
A launch window is said to have a COLA blackout period during intervals when the vehicle cannot lift off to ensure its trajectory does not take it too close to another object already in space.