In spaceflight, collision avoidance is the process of preventing a spacecraft from colliding with any other vehicle or object.
Collision avoidance is a concern during spaceflight launch windows. Typically, a Collision On Launch Assessment (COLA) needs to be performed and approved before launching a satellite. 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.
A collision avoidance manoeuvre or Debris Avoidance Manoeuvre (DAM) is a manoeuvre conducted by a spacecraft to avoid colliding with another object in orbit. One is most commonly used in order to avoid a piece of space junk.
Collision avoidance manoeuvres conducted by the International Space Station consist of a short burn by the main engines of a docked cargo spacecraft – usually a Progress spacecraft or Automated Transfer Vehicle – in order to raise or lower the orbit of the station by a few kilometres.
Another use of a collision avoidance manoeuvre is to abort an automated docking, and such a procedure is built into the software that controls the docking of Automated Transfer Vehicles to the ISS. This can be initiated by the crew aboard the space station, as an emergency override, in the event of a problem during the docking. This manoeuvre was demonstrated shortly after the launch of the first ATV, Jules Verne, and subsequently during demonstration approaches to the station which it conducted in late March 2008.