A new steering law of control moment gyroscopes (CMGs) is proposed to ensure extended life and to reduce the risk of failure. Because major failure mode of the CMG is the defective lubrication of the spin bearings resulting from being put on the excessive radial loads by radical motion of gimbals, the proposed method attempts to level gimbal angular displacements and to suppress radical motion of gimbals applying a relation between the gimbal angular displacement of each CMG and the initial condition of gimbal angles. A suitable set of initial gimbal angles is selected using a defined evaluation function in an offline preliminarily calculation. The evaluation function considers the average and variance of the gimbal angular displacement and the acceleration of the upcoming maneuver. The dynamics of a typical pyramid configuration of four single-gimbal CMGs was modeled and a numerical simulation was carried out to evaluate the performance of the proposed method. Numerical simulation confirmed that the proposed method levels the gimbal angular displacements of CMGs and suppresses radical motion of gimbals without degrading attitude control. The leveling of CMG loads was more effective in the case that the CMGs do not pass a singularity. In contrast, the suppression of radical motion of gimbals was more effective in the case the CMGs pass through the singularity. Moreover, the validity in the case of repetitive maneuvers was also verified by executing null motion at appropriate intervals.
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