Reaction wheels control allocation for reducing input command noise

Abstract

Reaction wheels are rotating device generating torque command continuously for precise attitude control. In case of satellite installed with more than three reaction wheels, the desired control command is defined by combination of reaction wheel torques obtained by control allocation processing. Control allocation method allocates command obtained by controller to each wheels. In real system, because attitude control command uses estimated parameter from attitude estimation (EKF), perturbation due to noise of sensors or system is added in the spacecraft control command. General allocation based on equality constraint problem transfers such noise components to each wheel, in every step. Satellite at steady-state also receives perturbed command, continuously. As a result, it has a bad influence upon performance and pointing stability of satellite. In this study, to reduce the noise of input command in the control allocation process, new approach is introduced. Instead of equality constraint problem, weighting function and dynamic allocation method applied to new allocation method. The new approach is applied to attitude transfer of spacecraft using quaternion feedback control. Simulation results illustrate that the suggested control allocation provides noise-reduced stable torque command to each re-action wheel, and improves the pointing stability at steady-state compared with pseudo-inverse.