Analysis of the consequences in low earth orbit of the collision between COSMOS 2251 and IRIDIUM 33

On 10 February 2009, Cosmos 2251 and Iridium 33 collided in orbit at an altitude of about 790 km. It was the first accidental catastrophic collision between two intact objects, leading to the formation of two sizable debris clouds in the orbital region already most affected by previous launch activity and breakups. Having no specific information on the physical characteristics of the fragments, the ballistic parameter, based on decay calibrations, was estimated for five random samples of the fragments, three for Cosmos 2251 and two for Iridium 33, and the statistical inference method was then applied to infer the properties of the whole populations. In particular, it was found that both clouds presented a significant fraction of cataloged fragments with very high area-to-mass ratios, hundreds or thousands of times greater than those of intact satellites, leading to the conclusion that the generation of such orbital debris might be more common than formerly supposed. In an attempt to assess the impact of the collision on the low Earth environment, the clouds of cataloged debris were propagated for 100 years, taking into account the relevant orbit perturbations and the debris ballistic coefficient distributions based on orbit decay calibrations. It was found that a substantial fraction of the fragments will remain in space for several decades and approximately one century will be needed to remove most of the wreckage from orbit. Concerning, finally, the four Italian satellites operational in low Earth orbit (AGILE and three COSMO-SkyMed), as of the end of June 2009, the collision probability with cataloged objects had been increased by less than 10%.