Attitude Determination Using a Single Star Sensor and a Star Density Table

Abstract

An alternative approach to attitude determination using a star sensor is presented. Whereas conventional star trackers require star vector observations through an identification of star constellations and a tracking of the identified stars, the proposed method takes multiple vector observations of virtual lines of sight instead of stars. A virtual line of sight is the pointing direction of a small portion of a star sensor's field of view and the vector to this line of sight is measured by searching celestial positions having the same theoretical star densities with the measurements, defined as the number of detected stars in the field of view. The suggested approach is based on the fact that the distribution of stars in the sky is not homogeneous. A stepwise search method to determine the pointing directions of multiple lines of sight that give the vector observation sequences is proposed, and a simple least-squares solution is applied for the attitude determination using these vector sequences. The proposed method allows not only a stabilized spacecraft but also a rotational one to take measurements; in the latter case the vector observations of stars are usually difficult owing to the sensor's motion.