First satellite collision

The first hypervelocity collision between two satellites occurred on 10 February 2009, when the active commercial satellite Iridium 33 was struck by the derelict Russian military satellite Kosmos-2251. The collision occurred at a relative speed of 11,700 m/s (42,120 km/h; 26,172 mph) and scattered an estimated 10,000 pieces of debris in Low Earth Orbit.

The two satellites were both fairly large and intact before the collision, orbiting at 790 km (490 mi). The orbital planes of the two satellites intersected at a right angle over Siberia at 16:56 UTC. NASA sources speculated that the volume of debris implied a glancing blow, rather than a direct impact between the two satellites' centres of mass.

Kosmos-2251 was a Strela-2M communications satellite, designed to handle encrypted Russian military communications. It had a mass of 950 kg (2,094 lb) and measured roughly 17 m (55 ft) along its longest axis (most of which was a long stabilization boom). The satellite was launched in 1993 and deactivated in 1995. As it had no propulsion system that could be used for a de-orbit burn, the deactivated satellite was left in orbit after it was decommissioned.

Iridium 33 was a Lockheed Martin LM-700A communications satellite that formed part of the first-generation Iridium satellite constellation, which provides voice and data transmission for satellite phones and other communications equipment. It had a mass of around 560 kg (1,234 lb) and was about 5 m (16 ft 4 in) wide including its solar arrays.

Close approaches between satellites are a fairly routine occurrence, but it is possible to model the paths of each satellite years into the future, meaning that each potential collision has usually been predicted a long time in advance. Typically one (or both) satellites will perform what is called a Collision Avoidance Manoeuvre, boosting itself into a lower or higher orbit.

Prior to this event, there had only been three other hypervelocity collisions between two catalogued objects (satellites, spacecraft or debris large enough to be tracked by ground-based observers). All three were collisions between a large object and a small speck of debris.