Prof. Panagiotis Tsiotras
Spacecraft Adaptive Attitude And Power Tracking With Variable Speed Control Moment Gyroscopes
Recently, NASA has proposed the integration of the Attitude Controls System (ACS) and the Power Management and Distribution System (PMDS) into a single Integrated Power and Attitude Control System (IPACS) by eliminating chemical batteries on-board low-earth orbiting spacecraft. In lieu of chemical batteries, high-speed flywheels are to be used to store energy during sunlight and release this energy during the eclipse. Studies have shown a net gain of upto 40% mass savings using an IPACS architecture. In this work we develop control laws for an IPACS system for a satellite using variable speed single-gimbal control moment gyros (VSCMGs) . While 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. The gimbal rates of the VSCMGs are typically used to provide the reference-tracking torques, while the wheel accelerations are used for both attitude and power reference tracking. A model-based control and an indirect adaptive control for a spacecraft with uncertain inertia properties will be presented. The issue of singlularities will be briefly discussed. A control law for equalization of the wheel speeds will be proposed to evenly distribute the kinetic energy among the wheels, thus minimizing the possibility of wheel speed saturation and the occurrence of zero-speed singularities. An experimental facility at Dynamics and Control Systems Lab at Ga Tech designed to test these control laws will also be presented.