2009 satellite collision
On February 10, 2009, two communications satellites—the active commercial Iridium 33 and the derelict Russian military Kosmos 2251—accidentally collided at a speed of and an altitude of above the Taymyr Peninsula in Siberia. It was the first time a hypervelocity collision occurred between two satellites – until then, all accidental hypervelocity collisions had involved a satellite and a piece of space debris. Spacecraft. Kosmos 2251 was a Russian Strela military communications satellite owned by the Russian Space Forces. It was launched on a Russian Cosmos-3M carrier rocket on June 16, 1993. It had been deactivated  prior to the collision, and remained in orbit as space debris. Iridium33 was a US-built commercial satellite and was part of the Iridium constellation of 66 communications satellites owned by Iridium Communications. It was launched on September 14, 1997, atop a Russian Proton rocket. Collision. The collision occurred at 16:56 UTC and destroyed both the Iridium 33 and Kosmos-2251. The Iridium satellite was operational at the time of the collision. Kosmos-2251 had gone out of service in 1995. It had no propulsion system, and was no longer actively controlled. Fallout. U.S. space agency NASA initially estimated ten days after  the collision that the satellite space incident had created at least 1,000 pieces of debris larger than , in addition to many smaller ones. By July 2011, the U.S. Space Surveillance Network had catalogued over 2000 large debris fragments from the collision. NASA determined the risk to the International Space Station, which orbits about below the collision course, to be low, as was any threat to the shuttle launch (STS-119) then planned for late February 2009. However, Chinese scientists have said that the debris does pose a threat to Chinese satellites in Sun-synchronous orbits, and the ISS did have to  perform an avoidance maneuver due to collision debris in March 2011. By December 2011, many pieces of the debris were in an observable orbital decay towards Earth, and were expected to burn up in the atmosphere within one to two years. In 2016, "Space News" listed the collision as the second biggest fragmentation event in history, with Kosmos-2251 and Iridium 33 producing respectively 1,668 and 628 pieces of catalogued debris, of which 1,141 and 364 pieces of tracked debris remain in orbit as of January 2016. A small piece of Kosmos-2251 satellite debris safely passed by the International Space Station  at 2:38 a.m. EDT, Saturday, March 24, 2012, at a distance of approximately . As a precaution, ISS management had the six crew members on board the orbiting complex take refuge inside the two docked Soyuz rendezvous spacecraft until the debris had passed. A number of reports of phenomena in the US states of Texas, Kentucky, and New Mexico were attributed to debris from the collision in the days immediately following the first reports of the incident in 2009, although NASA and the United States Strategic Command, which tracks satellites and orbital debris, did not announce any reentries of debris at  the time and reported that these phenomena were unrelated to the collision. On February 13, 2009, witnesses in Kentucky heard sonic booms. The National Weather Service issued an information statement alerting residents of sonic booms due to the falling satellite debris. The Federal Aviation Administration also released a notice warning to pilots of the re-entering debris. Some reports include details that point to these phenomena being caused by a meteoroid shower. A very bright meteor over Texas on February 15, 2009, was mistaken for reentering debris by some witnesses. Cause. 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 . Planning an avoidance maneuver with due consideration of the risk, the fuel consumption required for the maneuver, and its effects on 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 ) for the entire Iridium constellation. He estimated the risk of collision per conjunction as one in 50million. This collision and numerous near-misses have renewed calls for mandatory disposal of defunct satellites (typically by deorbiting them, or at minimum, sending them to a graveyard orbit), but no such international law exists as of 2021. Nevertheless, some countries have adopted such a law domestically, such as France in December 2010. The United States Federal Communications Commission (FCC) requires all geostationary satellites launched after March 18, 2002  to commit to moving to a graveyard orbit at the end of their operational life.