High-Capacity Reaction-Wheel Attitude Control

A possible method of controlling the attitude of satellites and space vehicles makes use of a reaction-wheel control system based upon the conservation of angular momentum. Such reaction-wheel systems are currently under consideration for use in earth satellites. The development of high-capacity systems (i.e., systems which have the ability to develop large control torques and to store high values of angular momentum) can extend the applicability of reaction-wheel control to include deep-space missions. The problems encountered in the design of such systems are mainly those which arise from cross-coupling of torques among the principal axes and from component nonlinearities. A design for a 3-axis control system, in which control torques about each axis are derived solely from angular information measured about the same axis, is presented. The system is designed for maximum obtainable rates of several degrees per second. System stability and bounds on the magnitudes of the interaxial disturbances are investigated analytically from a linearized model. Nonlinear effects are investigated by means of digital computer simulation and an experimental model.