Singularity Avoidance Using Null Motion and Variable-Speed Control Moment Gyros

Abstract

A variable speed control moment gyroscope (VSCMG) null motion steering law is introduced that continuously attempts to minimize the condition number of the control in uence matrix. By doing so, the gimbal angles are rearranged to less singular conŽ gurations without exerting a torque onto the spacecraft. By allowing the reaction wheel speeds to be variable in this steering law, more general reconŽ gurations are possible than what are possible with conventionalCMG. No a priori calculations of preferred sets of gimbal angles are necessary with this method. Numerical studies show that superimposing this VSCMG null motion on the VSCMG steering law can result in a drastic reduction in the required reaction wheel power consumption when operating near CMG singular gimbal conŽ gurations.The reaction wheel torque required by this VSCMG steering law is typically very small and achievable with existing CMG hardware.