In recent years, the space debris has gained a lot of interest as part of the space environment due to the increasing population of uncontrolled man-made objects orbiting the Earth, which is causing a significant risk of collision with the operating satellites. Currently, there are more than 600,000 objects larger than 1 cm in orbit (according to the ESA MASTER-2005 model) particularly concentrated in the most busy and interesting orbits for current and future missions; and after each collision or event a considerable amount of new debris appear in space.CRASS for Collision Risk Assessment and ODIN for Orbit Determination have been developed as part of the initiative for a future European Space Situational Awareness System to answer the concerns of satellite operators. These software packages initially used by the Space Debris Office at ESOC are also the basis for closeap, GMV's integrated solution for the analysis and mitigation of space collision situations. Implementation of the CRASS algorithms of Smart Sieve and revised and up to date SGP equations in the orbit propagation module have led to a more efficient assessment of the conjunctions, to predict the collisions and provide this as input for the computation of avoidance manoeuvres. The revised SGP models have improved the deficiencies of the previous implementations and have been integrated with NAPEOS (Navigation Package for Earth Orbiting Satellites) to improve the orbit determination, prediction and analysis capabilities.In this work the implementation of these algorithms in closeap, and the resulting capabilities for conjunction assessment, and collision probability prediction are described. Whereas the algorithms are normally described from a general point of view and also analyzed in this way, the interesting situations are those not covered by the generic approach. All software used in closeap is operational and fully validated; however, the nature of the collision risk assessment problem leaves always a certain level of uncertainty about whether all possible approach events have been detected. The work described by this paper focuses in the identification of those limiting scenarios and the ability of closeap to detect them and to provide adequate collision probability values that can be fuerther used operationally.
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