A Systems Approach to Star Trackers

A signal processing analysis of star trackers for navigation and guidance was conducted as a part of the Star Tracker Aerospace Reference Study. The signal processing analysis is based on the similarity between communication system theory and the several types of star trackers. The navigation system and star tracker parameters are the trade-off items that permit operation within the bounds set by the star field and transmission path. A tracker parameter analysis is an aid in formulating criteria for selecting a tracker and judging performance. This paper is primarily concerned with the internal parameters of star tracker design; specifically, what methods are available to the designer to meet navigation, guidance, and star ephemeris requirements. Equations describing the modulation process are developed and compared to communication practices. To aid in the comparison of the various types of trackers, a representative set of parameters has been developed. The comparison is done on a graphical basis where the primary trade-offs are effective optical area, information bandwidth and angular accuracy. The expected range of background radiance, star distribution and effective irradiance are described in summary form. Sources of additional information are listed in a bibliography.