A description of the CMG and its application to space vehicle control.

Requirements for high pointing accuracies during long missions of large spacecraft make the use of momentum exchange devices in control systems attractive for the following reasons : 1) continuous control, 2) recoverable energy source, 3) efficient control of cyclic disturbances, and 4) ease of propellant management. Of the momentum exchange devices, control moment gyros (CMC's) have the following advantages over reaction wheels for large spacecraft: better efficiency, larger output moments, better bandwidth and dynamic range, and greater range of linearity. In this paper, particular emphasis is placed on development and implementation of CMC control laws for the Apollo Telescope Mount control system. The kinematic equations of motion for the CMC's are combined with their servo characteristics to describe their rigid-body dynamics.