The Midcourse Space Experiment (MSX) satellite is a DoD sponsored spacecraft currently under development that will collect phenomenology in a variety of wavebands. MSX is required to perform on-orbit closed loop tracking of various objects of interest including not only dedicated targets but also targets of opportunity and atmospheric phenomena such as stars, auroral surges, and cloud structures. The onboard tracking system consists of, in part, (a) redundant tracking processors that determine, from sensor data, the trajectory of the object(s) and the desired attitude and rate to maintain observation, and (b) several tracking sensors, in particular, a suite of ultraviolet, visible, and spectrographic imagers and image processor incorporated into one instrument (called UVISI). This instrument is capable of isolating potential targets from various and possibly cluttered backgrounds and of providing both scientific and tracking data. We discuss the image processing algorithms implemented in the UVISI instrument image processor subsystem onboard MSX. We discuss details of the MSX tracking processor (TP) algorithms that provide either open-loop pointing or closed- loop tracking. Included are discussions of TP's star removal algorithm via frame-to-frame data association that renders the probable target based on inertial motion.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.