The 2009 satellite collision was the first accidental hypervelocity collision between two intact artificial satellites in Earth orbit.[1] The collision occurred at 16:56 UTC on February 10, 2009, at 789 kilometres (490 mi)[2] above the Taymyr Peninsula in Siberia, when Iridium 33 and Kosmos-2251 collided.[3][4][5] The satellites collided at a speed of 11.7 kilometres per second (7.3 mi/s), or approximately 42,120 kilometres per hour (26,170 mph)[6][7], faster than escape velocity on Earth.
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The collision destroyed both Iridium 33 (owned by Iridium Communications Inc.) and Kosmos 2251 (owned by the Russian Space Forces). While the Iridium satellite was operational at the time of the collision, the Russian satellite had been out of service since at least 1995 and was no longer actively controlled.[8][9] Kosmos-2251 was launched on June 16, 1993, and went out of service two years later, in 1995, according to Gen. Yakushin.[10] U.S. space agency NASA reported that a large amount of debris was produced by the collision. By July 2011, the U.S. Space Surveillance Network had cataloged over 2000 large debris.[11] NASA determined the risk to the International Space Station, which orbits about 430 kilometres (270 mi) below the collision course, is low,[12][13] as was any threat to the shuttle launch (STS-119) then planned for late February 2009.[13] However, Chinese scientists have said that the debris does pose a threat to Chinese satellites in Sun-synchronous orbits.[14]
As of December 2011, many pieces of debris are in a steady decay towards Earth, expected to burn up in the atmosphere within one or two years.
Several smaller collisions had occurred previously, often during rendezvous attempts or the intentional destruction of a satellite, including the DART satellite colliding with MUBLCOM,[15] and three collisions involving the manned Mir space station, during docking attempts by Progress M-24, Progress M-34, and Soyuz TM-17.[16] In 1996, the Cerise satellite collided with space debris.[17] There have been eight known high-speed collisions in all, most of which were only noticed well after the fact.[18]
Kosmos-2251 was a 950-kilogram (2,094 lb) Strela communications satellite.[13] It was launched on a Kosmos-3M carrier rocket on June 16, 1993.[4] It had been deactivated prior to the collision, and remained in orbit as space debris. Iridium 33, a 560-kilogram (1,235 lb) satellite that was part of the Iridium satellite constellation of 66 communications satellites,[4] was launched on September 14, 1997 atop a Proton rocket.
Nicholas L. Johnson, NASA's chief scientist for orbital debris, estimated that the satellite collision created approximately 1,000 pieces of debris larger than 10 centimeters (4 inches), in addition to many smaller ones.[19]
A number of reports of heavenly phenomena in Texas, Kentucky, and Italy were attributed to debris from the explosion. However, the National Aeronautics and Space Administration and the United States Strategic Command, which tracks satellites and orbital debris, did not announce any reentries of debris at the time.[20]
Further, some reports of the phenomena include details that rule out the collision as a cause, as, for instance, no piece of debris from the satellites would have been large enough to shake houses in Kentucky, so these phenomena can probably be attributed to a meteoroid shower on that date.[20]
On February 13, witnesses in Kentucky began hearing sonic booms.[21] The National Weather Service issued an information statement alerting residents of "explosions and or earthquakes" due to the falling satellite debris.[22] Similar reports from as far west as New Mexico were all attributed to falling debris from the collided satellites by "The Raw Story".[23] The Federal Aviation Administration also released a notice warning pilots of the re-entering debris.[24]
A bolide ("fireball") over Texas on February 15 was mistaken for reentering debris.[25]The United States Strategic Command, which tracks satellites and orbital debris, reported that the booms and flashes of light in the sky were unrelated to the satellite collision.[26]
Events where two satellites approach within several kilometers of each other occur numerous times each day. Sorting through the large number of potential collisions to identify those that are high risk presents a challenge. Precise, up-to-date information regarding current satellite positions is difficult to obtain. Calculations made by CelesTrak had expected these two satellites to miss by 584 meters.[27]
Planning an avoidance maneuver with due consideration of the risk, the fuel consumption required for the maneuver, and affects the satellite's normal functioning can also be challenging. John Campbell of Iridium spoke at a June 2007 forum discussing these tradeoffs and the difficulty of handling all the notifications they were getting regarding close approaches, which numbered 400 per week (for approaches within 5 km) for the entire Iridium constellation. He estimated the risk of collision per conjunction as one in 50 million.[18]
This collision and numerous near-misses have renewed calls for mandatory disposal of defunct satellites (typically by deorbiting them), but no such international law exists as of yet.[28]