Optimal Attitude Control of Agile Spacecraft Using Combined Reaction Wheel and Control Moment Gyroscope Arrays
Abstract
This dissertation explores the benefits of combined control moment gyroscope (CMG) and reaction wheel array (RWA) actuation for agile spacecraft. Agile spacecraft are capable of slewing to multiple targets in minimum time. CMGs provide the largest torque capability of current momentum exchange actuation devices but also introduce singularity events in operation. RWAs produce less torque capability than CMGs but can achieve greater pointing accuracy. In this research, a combined RWA and CMG (RWCMG) system is evaluated using analytical simulations and hardware experiments. A closed-loop control scheme is developed which takes advantage of the strengths of each actuator set.The CMGs perform slews for a representative target field. Borrowing from variable-speed CMG theory, a system of switching between CMG and RWA actuation allows the RWA to assume control of the spacecraft when desired pointing tolerance is met for a given target. During collection, the CMG gimbals may travel along null motion trajectories towardpreferred angles to prepare for the next slew. Preferred gimbal angles are pre-computed off-line using optimization techniques or set based on look-up tables. Logic is developed to ensure CMG gimbal angles travel the shortest path to the preferred values. The proportional-integral-derivative, quaternion feedback, and nonlinear Lyapunov-based controllers are assessed for the RWCMG system. Extended and unscented Kalman filter techniques are explored for improved accuracy in analytical simulation. Results of RWCMG hardware experiments show improvements in slew capability, pointing accuracy, and singularity avoidance compared to traditional CMG-only systems.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2015
- Accession Number
- AD1003574
Entities
People
- Cole C. Doupe
Organizations
- Air Force Institute of Technology