Orbital collision risk

February 10, 2009, 789 kilometers above Siberia: Iridium 33, in service, strikes the defunct Cosmos 2251 at about 11.7 kilometers per second, and both spacecraft break up into debris. Orbital collision risk is the risk that an operating satellite strikes another object in orbit, whether an active satellite, a defunct spacecraft or debris, at a relative speed high enough to destroy both. Unlike an internal failure, this peril depends directly on the density of objects in a given orbit and on the quality of conjunction tracking, which has to flag a close approach early enough to allow an avoidance maneuver. As active satellites and debris multiply, operators with propulsion maneuver more and more often, while non-maneuverable satellites remain fully exposed. A collision leaves a debris cloud that often persists for years and degrades the orbital environment for every operator at the same altitude, well beyond the two parties directly involved. For insurers, orbital collision combines a classic total physical loss peril with a liability risk toward the owner of the struck object, plus an accumulation risk through the secondary debris it generates.