An Experimental Comparison of CMG Steering Control Laws

Control moment gyros (CMGs) are spacecraft attitude control actuators which act as torque amplifiers. They are thus suitable for attitude hold and reorientation of large spacecraft or for slew maneuvering. They provide the necessary torques via gimballing a spinning flywheel. A major problem encountered with the use of CMGs in practice is the possibility of singularities for certain combinations of gimbal angles. In such singular gimbal angle configurations the CMG cluster cannot generate torques along a certain direction. Several singularity avoidance and escape steering logics have been reported in the literature to solve the CMG singularity problem. In this paper, we experimentally compare three of the most common CMG steering logics using a realistic spacecraft simulator. We compare the relative merits of these steering laws with respect to their singularity avoidance capabilities and their efficiency in generating the commanded control torques. An adaptive feedback stabilizing control law is also used in conjunction with each CMG steering law to account for the gravity disturbance torque.