A closed loop system reduces pointing errors in one or more spacecraft instruments. Associated with each instrument is a electronics package (3) for commanding motion in that instrument and a pointing control system (5) for imparting motion in that instrument in response to a command (4) from the commanding package (3). Spacecraft motion compensation logic (25) compensates for instrument pointing errors caused by instrument-motion-induced spacecraft motion. Any finite number of instruments can be so compensated, by providing each pointing control system (5) and each commanding package (3), for the instruments desired to be compensated, with a link to the spacecraft motion compensation logic (25). The spacecraft motion compensation logic (25) is an electronic manifestation of the algebraic negative of a model of the dynamics of motion of the spacecraft. An example of a suitable model, and computer-simulated results, are presented
