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Collision Avoidance for Satellite Orbits and Low Thrust Transitions
Assmann, Kaja
Thomas Wagner
This thesis presents a capacious collision avoidance method named COLA. The method has been designed to predict collisions for Earth orbiting spacecraft (S/C) with other space-born objects. The COLA method is able to detect the point of time and the probability of collisions for objects flying on all kinds of Earth orbits, including high impulse and low thrust transfers. To guarantee an effective solution of all tasks in the process of the collision prediction, the COLA method uses a modular design and is composed of several components : A filtering device, the close approach determination, the collision detection and the collision probability calculation. The filtering includes a series of three filters which reduce the great number of possible collision objects by eliminating the impossible ones. Two geometrical filters and a time depending filter were implemented, deduced from filtering methods developed by Vallado and Hoots. The close approach algorithm determines the point of time and the minimum distances between two objects on different orbits. Therefore, two algorithms are evaluated: A method developed by Alfano/Negron, which determines close approach cases from the distance of objects, and a method developed by Coppola/ Woodburn, which uses the distance of ellipsoids. The COLA method includes a modified version of the Alfano/Negron method. To decide, whether a collision is likely to occur, two collision detection methods are presented: A method developed by Wang/Choi/Chan/Kim/Wang via the detection of ellipsoidal intersection and a method developed within this thesis which compares the minimum distance and the maximum positional error of the objects. The latter is included in the COLA method. Due to the error introduced by the orbit determination and propagation of the objects, their positions are given as a predicted position surrounded by an error ellipsoid, defined by positional covariances. For the calculation of the collision probability, four algorithms which use this error information, are explained and compared: The algorithms by Foster, Chan, Patera and Alfano. The COLA method uses the Alfano algorithm. All algorithms and modifications to existing algorithms are described in detail, including the adaptation of algorithms for low thrust transfers and other particularities. The adaptations enable the COLA method to serve as a capacious and all-encompassing collision detection method. A software implementing the COLA method in C++ code has been developed. It can be used with the Mission Design Tool (MDT) of the LSE Space Engineering & Operations AG (LSE). The COLA software has been verified using various test cases built from sample missions which were generated by the MDT. The results of the collision determination for all test cases are presented and discussed in detail.
Àrees temàtiques de la UPC::Física::Astronomia i astrofísica
Collisions (Astrophysics)
Satellite earth
Col·lisions (Astrofísica)
Satèl·lits Moviments orbitals
Universitat Politècnica de Catalunya;
Technishe Universität München

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