Regenerative Power-Optimal Reaction Wheel Attitude Control

Abstract

This paper develops an analytical instantaneous power-optimal attitude control for a spacecraft using an integrated reaction wheel–flywheel system allowing for energy storage and return. The control is formulated in a general manner to use an arbitrarily large number of reaction wheels. It is applicable to systems with redundant wheels spanning three-dimensional space, which are controlled by a general attitude control law. The instantaneous power usage is minimized by modifying the wheel control torques using the wheel torque null motion. In this study, reducing the wheel speed results in negative power usage with perfect energy recuperation. Applying the maximum available wheel torque constraints, the null torque solution space is reduced to a hyperdimensional vector geometry problem, and the power-optimal wheel control torques are uniquely determined. The control modifications are applied to both attitude regulation and tracking control laws, demonstrating its performance for a variety of initial spacecraft states. Not only does the new control maximize the energy extraction from the reaction wheels, it also maintains the smallest flywheel spin rates, which helps reduce the maneuver-wide power usage.