Collision Avoidance
The process of predicting and preventing close approaches between active spacecraft or between spacecraft and debris.
Explanation
Collision avoidance begins with conjunction screening — comparing ephemeris data for all tracked objects to identify close approaches within a threshold (typically 1 km in position and 1 km/s in relative velocity). When a conjunction is identified with a probability above a threshold (commonly 1 in 10,000), operators evaluate whether a maneuver is needed. If so, the spacecraft performs a collision avoidance maneuver (CAM) — typically a small delta-v burn days or hours before the predicted close approach to shift the trajectory. CAMs consume propellant, disrupt operations, and require ground team coordination. The growing number of active satellites and debris has made collision avoidance an almost routine operation for constellation operators. Automation is becoming essential — SpaceX's Starlink constellation performs thousands of autonomous CAMs each year. False positives are a concern; too many maneuvers waste propellant, while too few risk collisions.
Why It Matters
Collision avoidance is the last line of defense against orbital collisions. As the number of satellites grows, the frequency of conjunctions increases, making automated and reliable collision avoidance critical for space safety.
Concept Map
How Collision Avoidance connects to other glossary terms:
Frequently Asked Questions
How often do satellites perform collision avoidance maneuvers?
Large constellations execute hundreds to thousands of automated CAMs per year. Most individual satellites perform 0-2 per year depending on orbit.
Who decides which satellite maneuvers in a close approach?
There is no central authority. Operators coordinate manually or follow industry best practices. Automated systems negotiate maneuvers based on pre-agreed rules.
Sources
Last updated: July 1, 2026