Mode-Scheduling Steering Law of VSCMGs for Multi-Target Pointing and Agile Maneuver of a Spacecraft

This study proposes a method of selecting a set of gimbal angles in the final state and applies the method to the mode-scheduling steering law of variable-speed control moment gyros intended for multi-target pointing manoeuvres in the threeaxis attitude control of a spacecraft. The proposed method selects reference final gimbal angles, considering the condition numbers of the Jacobian matrix of the reaction wheel mode in the final state of a single manoeuvre and that of the constant-speed control moment gyro mode at the start of the upcoming manoeuvre to keep away from the singularities. To improve the reachability of reference final gimbal angles, the nearest set of gimbal angles among nominated sets according to the Euclidean norm is selected as the reference final set at the middle of the single manoeuvre, and then realised by adopting gimbal angle feedback steering logic using null motion. In addition, the manoeuvre profile is designed such that the second half of the single manoeuvre is more gradual and takes longer than the first. Numerical simulation confirms the validity of the proposed method in consecutive manoeuvres. Keywords—Variable-Speed Control Moment Gyros; Attitude Control; Singularity; Steering Law; Spacecraft