On February 10, 2009, an inactive Russian communications satellite, designated Cosmos 2251, collided with an active commercial communications satellite operated by U.S.-based Iridium Satellite LLC. The incident occurred approximately 800 kilometers above Siberia. This collision produced almost 2,000 pieces of debris, measuring at least ten centimeters in diameter, and many thousands more smaller pieces. Much of this debris will remain in orbit for decades or longer, posing a collision risk to other objects in Low Earth Orbit (LEO). This was the first-ever collision between two satellites in orbit.
Iridium 33 was a 689-kilogram LM700 series satellite operated by U.S.-based Iridium Satellite LLC. It was launched along with six other Iridium satellites aboard a Russian Proton launch vehicle on September 14, 1997 from Baikonur, Kazakhstan. The satellite, which was manufactured by Motorola and Lockheed Martin, represented one of a 66-member constellation orbiting at an altitude of 780 kilometers distributed across six orbital planes (about 10 satellites per plane along a “string of pearls” configuration). These satellites provide L-band mobile telephone and communications services to users on the ground.
The 900-kilogram Cosmos 2251 was a Strela 2M military store-and-forward communications platform launched on June 16, 1993 from Plesetsk, Russia aboard a Kosmos 3M launch vehicle. Typically, Strela 2 series satellites have a service life of five years, and thus Cosmos 2251 was not functional at the time it collided with Iridium 33. Strela 2M uses the same KAUR-1 satellite bus as that of the Strela 1 series, pictured at right. Strela-2M satellites were launched one at a time into orbits of 800 kilometers altitude in three orbital planes inclined 74 degrees to the equator, each unit spaced 120 degrees apart. The satellites are built by Reshetnev and operated by the Russian Ministry of Defense.
The Collision and Resulting Debris
Iridium 33 and Cosmos 2251 collided at almost right angles to each other, and at a relative speed of nearly 10 km/s. Although the exact geometry of the collision and point of contact on each satellite is unknown, video taken of the Iridium 33 after the collision indicated that at least two of the antennas at the bottom of the spacecraft were intact, suggesting that the Iridium was struck on the top, and much of the satellite was left intact.
NASA projections indicate that less than 50% of the generated debris is still in orbit.
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