Characterization and Modeling of a Control Moment Gyroscope
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
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The Air Force Research Laboratory AFRL is developing a spacecraft simulator that uses Control Moment Gyroscopes CMGs. Prior to the research herin, the Air Force Institute of Technology AFIT designed and built six laboratory-rated CMGs for use on the AFRL spacecraft simulator. The main contributions of this research are in the testing and modeling of a single CMG. Designing, building, and operating spacecraft simulators is time consuming and expensive, but less so than tests with on-orbit spacecraft. Reductions in cost and schedule can be realized by investing in modeling the spacecraft simulator and payload before testing. A model of the spacecraft simulator was created in previous research e orts, but was an ideal model it did not include dynamics based on real CMGs. The objective of this research is to characterize and model a single CMG to determine the effects the real CMGs performance will have on the performance of the AFRL spacecraft simulator. The gimbal motor utilizes a planetary gearbox, which has gear lash of 5 deg . Gear lash makes the existence of gravitational disturbance torques noticeable in the gimbal angular position measurements. An analytical model of the CMG gimbal was created in MATLAB. The model predicts the nonlinear dynamic behavior of the real CMG. A model of the spacecraft simulator was run through a sequence of pointing commands to generate gimbal angle commands which were then used to command the CMG to evaluate the systems performance under realistic conditions. Gear slack has a cumulative time delay effect on vehicle slew responses of approximately one second over five maneuvers. The results of the tests performed in this thesis can be used to predict performance of CMG and spacecraft simulator behavior.
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