Spacecraft Adaptive Attitude and Power Tracking with Variable Speed Control Moment Gyroscopes

Abstract

Control laws for an integrated powerlattitude control system (IPACS) for a satellite using variable-speed single-gimbal control moment gyroscopes (VSCMGs) are introduced. Whereas the wheel spin rates of the conventional CMGs are constant, the VSCMGs are allowed to have variable speeds. Therefore, VSCMGs have extra degrees of freedom and can be used to achieve additional objectives, such as energy storage, as well as attitude control. We use VSCMGs in conjunction with an IPACS system. The gimbal rates of the VSCMGs are used to provide the reference-tracking torques, whereas the wheel accelerations are used for both attitude and power reference tracking. The latter objective is achieved by storing or releasing the kinetic energy in the wheels. The control algorithms perform both the attitude and power tracking goals simultaneously. A model-based control and an indirect adaptive control for a spacecraft with uncertain inertia properties are developed. Moreover, control laws for equalization of the wheel speeds are also proposed. Wheel speed equalization distributes evenly the kinetic energy among the wheels, minimizing the possibility of wheel speed saturation and the occurrence of zero-speed singularities. Finally, a numerical example for a satellite in a low Earth, near-polar orbit is provided to test the proposed IPACS algorithm.