CNES Operational Experiences in Collision Avoidance for LEO Satellites

CNES (French Space Agency) performs collision risks monitoring for the 15 LEO (Low Earth Orbit) satellites it controls. Most of the operational collision avoidance (CA) activities are gathered at OCC (Orbit Computation Centre) in the CNES Operations Sub-directorate. First this paper briefly presents the current CNES Collision Avoidance Process which includes OCC contingency operational procedure for collision risks management partially put to test with the recent IRIDIUM and COSMOS collision case. Then the key results since the beginning of the operational activities are introduced: number of alerts, number of avoidance maneuvers and the most often encountered debris. In order to give an idea of the variety of situations which needs to be handled some examples of real encountered cases are discussed: a typical close approach, a close approach between two controlled satellites and finally a close approach between an operational satellite with a non-operational one which is on almost the same orbit.