SP-Search: A new algorithm for star pattern recognition
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The new Spherical-Polygon (SP) Search approach, to identify stars observed by wide Field-Of-View (FOV) star tracker, which does not require initial guess of the spacecraft attitude and which does not use magnitude information, is presented. The principal idea of the proposed method is based on ,he fact that any star direction can always be expressed as a linear combination of two non-parallel star directions (star pair basis) together with their vector cross-product. The star identification problem is, therefore, transformed into the simpler problem of finding which stars, within a large star catalog, are admissible with a given direction. This is straightforwardly solved by approximating a cone with a spherical polygon and using the K-vector technique applied to all of the three components of the given direction. Numerical and analytical studies are used to evaluate the main characteristics of the proposed method and to show how the could be improved (increasing the CCD precision and the star pair basis angular displacement). This new method to identify observed stars can be used within any general star pattern recognition technique based on stars triangles, especially for the multiple-FOVs star sensors (DIGISTAR II and III sensors) because they observe stars in orthogonal directions. Numerical plots validate this method, which is particularly suitable for the lost in space general case, by showing its very good probability of success (95% in average) to identify stars.
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