2009 satellite collision
On 10 February 2009, the first satellite collision occurred in Earth orbit. It was the communications satellite Iridium 33 and Cosmos 2251 iridium systems or Strela. Both were operating in almost 800 kilometers altitude. The collision with the enormous relative velocity of 11.6 km / s arose over 100,000 fragments that are large enough to remain in orbit for decades and to cause serious damage in the event of a hit. 2201 large fragments of this space debris (radar border size 5 to 10 cm) are cataloged, 380 of them previously crashed due to air friction (as of January 2013). Multiple already flew to the International Space Station (ISS) evasive action if any of these parts had fallen to the level of the railway station and an impact could not be excluded.
This first satellite collision led the world community impressively demonstrated that without countermeasures - would contribute to the growth of satellite collisions dominant garbage problem in the near-Earth space - based on the exchange of more accurate orbital data. National, mostly military secrecy interests stand in the way.
Details
For 16:56:00 UTC a close encounter of the two satellites over North Siberia had been predicted: the service SOCRATES (Satellite Orbital Conjunction Reports Assessing Threatening Encounters in Space ) of the Center for Space Standards and Innovation ( CSSI ) and published since 2005 twice a day on the basis of freely accessible satellite orbital elements for possible collisions ( limit distance 5 km) from satellites with other satellites or parts of the cataloged space debris. These orbital elements describe the basis of the gravity field anomalies which tracks only approximate and become obsolete within a few rounds. In the final report before the collision, at 15:02 UTC, the roughly estimated minimum distance was on the flight path of 600 meters. The entry only rank 16 ranked among the approximately 1000 entries, which alone affected the Iridium system of 66 satellites that time in this report. An immediate concern did not exist at this location data.
At the predicted time, but surprisingly, broke off communication with Iridium 33. In accordance with physical models of Hochgeschwindigkeitsimpakten (NASA Standard Breakup Model, a Monte Carlo simulation) created two debris clouds, which largely followed the old orbits. This contradicts the everyday experience, after which both give huge distractions for elastic and inelastic collisions. Here, however, is the kinetic energy per unit mass is much higher than the chemical bond energy of matter, so for part of the satellite, which penetrate the elastic properties are insignificant. Rather, the strongly interacting mass elements merge into a plasma state within microseconds. As with detonation, the surrounding material is torn. The momentum transfer to larger, observable fragments is relatively low.
Within hours, the two debris clouds widened so that the radars of the Space Surveillance Network ( SSN ) could resolve individual objects in dozens. Some fragments, especially of the cosmos in 2251, had been pushed into significantly elliptical orbits in the altitude range 200-1700 km. The concern was not only the ISS, which then had an orbital altitude of 350 km, but in particular planned for the spring of 2009 service mission STS -125 to the Hubble Space Telescope ( HST) in 570 km height. The fragments individually pursued, one would be able to dodge, but it was expected a far larger number of small particles that are not observable with these radars, but nevertheless dangerous.
In order to assess the risk observations were made with two larger, more sensitive radars: the 70 - m antenna of the Goldstone Observatory and with the 37- m telescope of the Haystack Observatory. Both were because too cumbersome for tracking, operated with a fixed orientation with the Earth's rotation got the scan pivot the narrow antenna beams. In order to obtain representative results, we waited a few weeks, during which the particles spread out evenly along its path around the globe. The limiting magnitudes of the two telescopes were in these observations 2-3 and 10 mm respectively. The result of the tests: The increase in the number of particles with decreasing particle size fit to the physical models of high-speed collisions, and therefore was not as steep as the size distribution of the cataloged, larger fragments suggested and had feared.
Meanwhile, the operator of the Iridium system working to resolve the impact of the loss. Within 60 hours, the routing was changed, so that was no longer attempts to establish connections to / from the ground or between satellites over the missing satellites. Until 2 March of the same year, a circulation of products already in orbit spare satellite was maneuvered into the resulting gap.
Within 24 weeks of 1307 radar objects were cataloged, which apparently come from this event. In terms of the mass and size of the initial body this number appeared rather low. Apparently, most of the mass lies in two large fragments, the satellite wreckage. In fact, these wrecks, like other satellite at this level, visible from the ground. The light curve of the Iridium wrecks, occasionally with two light flashes per period, suggests that two of the three bottom- mounted antenna surfaces are still present.
From January 2013 until accepted into the catalog fragments - others were already identified - submitted in 1603 by Cosmos 2251 and Iridium 33 598 of them are due to air friction already 261 and 119 fragments (16 and 20% respectively ) crashed, mainly 2012. NASA orbital debris Program Office estimates that by the end of the current high solar activity (~ 2016) about 40 % and about 50 % of the fragments will have taken this path. The observed greater braking effect of the upper atmosphere on the fragments of Iridium 33 is due to the consistent lightweight construction of the satellite compared to the more robust Russian model.