Angular rate determination using star sensors and novel algorithms based on geometrical investigations

In this paper, a geometrical investigation of the star sensor image is performed under dynamic conditions. It is shown that, when the spacecraft is rotating, the streaks left by the stars' signal onto the star sensor detector belong to portions of conic sections which features depend on the angles between the instantaneous rotation axis, the sensor line of sight and the stars direction. The geometrical properties discussed in the first part of the paper can be used to develop new numerical methods for the evaluation of the angular velocity. The chord method is a simple but effective approach to get a preliminary estimation of the spacecraft rate which needs at least two stars. The method is described and then is applied by using a high fidelity star sensor simulator. Results are presented and discussed, and future development are proposed.