Logic-based gimbal compensator for the double-gimbal scissored-pair control moment gyroscope using magnetic torquers

Abstract

Control Moment Gyroscopes (CMGs) are effective torque-producing actuators for satellite missions requiring agile maneuvering and accurate pointing. CMGs can develop relatively large torques compared to other momentum storage actuators like reaction wheels; however, using CMGs for three-axis attitude control is complicated by inherent mechanical singularities associated with CMGs. The singularity effect is worsened by common disturbances, such as aerodynamic or magnetic torques, which influence the CMG momentum state. A recent CMG design known as the Double-Gimbal Scissor-Pair CMG (DGSPCMG) has shown promise for use in small satellites because it has manageable singular conditions and has the potential to achieve three axis control using only two flywheels. This paper proposes a novel extension of the DGSPCMG control law and supplements it with a classical sliding-mode attitude controller to allow for the DGSPCMG momentum to be managed such that the gimbals may be restored to desirable positions by way of magnetic torques. The proposed solution achieves agile maneuvering by differentiating when singularity escape is possible through a steering control law and when magnetic torques are necessary for gimbal compensation in the DGSPCMG. The effectiveness of the control scheme is demonstrated by numerical simulations in MATLAB which subject the design to a detailed space environment. For the simulation conditions used in this research, the results indicate that the proposed control scheme would be an effective solution for attitude control of small satellites using a DGSPCMG in Low-Earth Orbit.