Attitude Control Using Three Control Moment Gyros

Abstract

In the case of three-axis attitude control of spacecraft by control moment gyros (CMG), more than three CMGs are typically used for redundancy. Even when one CMG fails and the redundancy is lost, the attitude control must be maintained. In this paper, by focusing on attitude control with three CMGs, suitable steering laws are considered. In order to use the full angular momentum workspace of three CMGs, singularity problems occur. The problems occur more severely than four CMG case. Two steering laws for the four CMG pyramid configuration with one CMG failure are proposed; Inverse Kinematics Steering Logic (IKSL) and Forward And Backward Reaching Inverse Kinematics (FABRIK). The aim of each steering law is to provide gimbal rates from the calculation of gimbal angles by inverse kinematics of the CMGs. IKSL exactly solves the inverse kinematics of the system, whereas FABRIK uses a heuristic approach to finding an approximate solution of the inverse kinematics problem. Numerical simulations are performed to validate the effectiveness of the proposed steering laws as compared with the Singular Direction Avoidance (SDA) steering law.