Collision risk for high inclination satellite constellations

We assess the collision hazard for a constellation of telecommunication satellites such as IRIDIUM, arising from the possible chance impact break-up of one of the satellites. The resulting swarm of fragments will orbit the Earth at about the same altitude as the surviving satellites, but will gradually spread due to orbital perturbations, so as to make possible impacts with satellites staying on orbital planes different from that of the parent satellite. We find that at intermediate fragment masses of the order of 1 kg, sufficient to trigger subsequent catastrophic impacts, the self-generated collision hazard for the constellation satellites exceeds the background level due to the overall debris population for several years. This is true, in particular, when differential precession of the orbits leads the fragments to encounter satellites revolving around the Earth in the opposite sense, resulting both in higher impact speeds and in enhanced collision probabilities. We estimate that there is about a 10% chance that a first-generation fragment will trigger subsequent disruptive collisions in the constellation within a decade.