A Practical Variable-Speed Control Moment Gyroscope Steering Law for Small Satellite Energy Storage and Attitude Control

Abstract

Recent practical work in developing combined energy storage and attitude control subsystems for small satellites has opened the door to more complex, demanding space missions. Laden with substantial benefits such as agile slewing, robust singularity avoidance, increased lifetime, mass savings, and favorable peak power density, these recently proposed systems use variable-speed control moment gyroscopes to store and drain energy while controlling satellite orientation. The full non-linear equations for simultaneous control of gimbal and wheel motors for this system were presented and theoretically unraveled in previous work, however that implementation assumed a single computer dictates the commands to these motors at each time step. The limitation of this method is that it is difficult to control the wheel and gimbal motors separately as required to immediately implement the flywheel motors in the passive electronics of an existing satellite energy storage subsystem. Such isolated control would impart disturbance torques on the system from torquing the wheel motors, but does not allow the simultaneous steering laws controllability of the wheels, an underlying assumption of these laws. To address this need, a novel gimbal steering law is derived to permit independent gimbal and wheel control of the actuators with continued singularity avoidance, a situation that allows direct incorporation of such a system into an existing small satellite energy storage subsystem. This law rejects the disturbance torques generated during independent wheel control. As it permits directly interfacing this small satellite combined energy storage and attitude control subsystem into a conventional satellite, this novel, composite gimbal steering law is more immediately practical than pre-existing simultaneous steering laws.