As spacecraft begin to utilize higher performance flight computers, more processing is being performed on-orbit. This paper discusses four tpics that support on-orbit star processing using multi-star star trackers. The first topic addresses the considerations for creating an application specific star catalog and presents a newly developed, computational and memory efficient star catalog storage technique named the Sperical Rectangles Method. The Spherical Rectangles Method is used to extract a subset of stars from a very large (5000 or more stars) star catalog. This subset of stars is used as the candidate set of stars to support star identification and directed search commanding. The second topic examines star identification techniques and discusses their applicability to multi-star star trackers. Each of the star identification techniques discussed has advantages and disadvantages depending upon the star tracker operational mode and tracking status. No single technique is optimal for all scenarios, so a combination of the techniques is used, depending upon tracking status, to ensure a higher probability of successful star identification. The third topic is a comparison of directed search commanding of the star tracker versus full field acquisition. Also, a directed search technique is presented that determines which stars in the star tracker field of view should be tracked to support a more accurate attitude determination solution. In this technique, consideration is given to star brightness, star separation, and computational efficiency. The fourth topic identifies several measurement errors such as data latency, velocity aberration, and parallax that should be compensated for depending upon attitude knowledge requirements.