A Search-Based Approach to Steering Single Gimballed CMGs

Single gimballed Control Moment Gyroscopes (SGCMGs) are proposed as torque actuators that can effectively answer the attitude control requirements of future spacecraft. The kinematic properties of SGCMGs are reviewed, existing steering laws are summarized, and the structure of singular surfaces are examined for a 4-CMG pyramid-mounted array. A guided depth-first search that manages null motion about torque-producing trajectories calculated with a singularity-robust (SR) inverse is proposed as a practical feedforward steering law that can globally avoid (or minimize the impact of) singular states in minimally-redundant SGCMG systems. Cost and heuristic functions are defined to guide the search procedure in improving CMG trajectories. On-orbit implementation of the steering law is proposed as an extension to momentum management algorithms. A series of simulation examples are presented, illustrating the search performance for a 4-CMG pyramid-mounted array. Sensitivities of feedforward gimbal trajectories are examined in the presence of unmodelled disturbances, and techniques are proposed for avoiding excessive divergence. A "users manual" appendix describes the interactive Macintosh software package written to define, search over, and investigate SGCMG trajectories. The Charles Stark Draper Laboratory, Inc. Cambridge, MA. 02139