Impacts of Control Moment Gyroscope Gear Slack on Spacecraft Pointing Performance

Testing spacecraft attitude control hardware and algorithms is difficult to perform in a lab setting and models are sometimes impractical or very challenging to create. Satellite simulators allow testing of integrated hardware and software in a laboratory setting. The Air Force Research Laboratory (AFRL) is developing a spacecraft simulator called the Resilient Bus Experimental Laboratory (REBEL) that utilizes Control Moment Gyroscopes (CMGs) developed by the Air Force Institute of Technology (AFIT). The REBEL CMG gimbal motors have triple junction planetary gear trains that have inherent gear slack. The objective of this research is to better understand the impacts of CMG gimbal gear slack on overall spacecraft attitude control performance. The specific application of this research is on REBEL, but is not constrained to spacecraft simulators. To show how gimbal gear slack impacts attitude control, a MATLAB model of REBEL was created. The simulation was run with three different values for gear slack. Moderate gear slack in CMG gimbals slightly affects maneuver durations for large maneuvers. For small maneuvers, moderate gear slack has little to no effect on maneuver duration.