Variable speed scissored pair dual gimbal Control Moment Gyro for nano-satellites

[摘要] ENGLISH ABSTRACT: The work presented in this thesis describes the development of an attitude controlactuator for use in CubeSats. This actuator uses novel Control Moment Gyro technologyto perform slew manoeuvres. The configuration consists of a symmetric pairof counter-rotating gyros mounted in scissoring dual gimbals. The outer gimbals aremechanically constrained using gears driven by a single stepper motor while the innergimbals are individually actuated using two additional stepper motors. Three-axiscontrol is achieved by changing the gimbal angles for roll and pitch manoeuvres andvarying the wheel speed for yaw rotations. Electronics were designed to control themomentum wheel motors and the gimbal angle actuators. A mathematical model wasderived from the mechanical design. The model was used in simulations where a slewmanoeuvre was performed in each axis individually in order to match the Hardware-inthe-Loop test conditions. The average power usage, for the three-axis implementation,during a slew manoeuvre was measured at 420 milli-Watt with maximum of 556 milli-Watt. The volume required for the actuator is only 10 cm x 5 cm x 5 cm and has amass of 260 g, making it suitable for CubeSat use.The attitude controllers tested include a Bang-Off-Bang and a Quaternion Feedbackcontroller. The controllers are typically combined for large slew manoeuvres: TheBang-Off-Bang controller is used first and at the required final attitude, the QuaternionFeedback controller is enabled to accurately track the reference angle. Hardwarein-the-Loop tests were done on a low-friction air bearing platform for ground basedattitude control demonstrations. Attitude knowledge was obtained from a MEMSinertial measurement unit and a laser pointer. Tests were repeated for various platformmoments of inertia in order to empirically determine the expected pointing accuracyof the system. Similar tests were also performed using a conventional reaction wheelconfiguration to compare the performance. A maximum torque of 0.52 mNm canbe achieved by this new actuator and a pointing accuracy of less than 0.2 degrees wasdemonstrated on the air bearing platform. Initial results show satisfactory performanceto justify further development of a flight actuator module.

[发布机构] Stellenbosch University