Precision pointing control of agile spacecraft using single gimbal control moment gyroscopes

Abstract

Agile spacecraft control requires high torque on demand, with low power and emitted disturbance, to maintain the attitude control, manage the spacecraft momentum, and provide structural disturbance rejection. These demands almost exclusively call for control moment gyroscopes to produce the actuation torque. Single gimbal control moment gyroscopes have been shown to have significant advantages over double gimbal control moment gyroscopes in this role. The advantage of torque amplification translates to power, cost, weight, and performance improvements over double gimbal control moment gyroscopes. However, the use of either type in agile spacecraft gives rise to problems in their implementation; 1) disturbances manifested in the gyroscope gimbal actuators are multiplied and transmitted to the spacecraft, and 2) the presence of singularities prevents utilization of the gyroscope array to its maximum potential. Linear and nonlinear external disturbances have been shown to be easily eliminated utilizing disturbance rejection filters. In addition, non-linear disturbances caused by the control moment gyroscopes that are feed-forward in nature have been shown to be mitigated using the same approach; however, nonlinear disturbances in the feedback loop are more pervasive in nature and are often more difficult to reject. This paper explores rejection of nonlinear disturbances and includes a discussion of control moment gyroscopes array configuration based on singularity and momentum considerations.