Agile Satellite Attitude Control Method Based On Hybrid Actuators

Agile satellites have the capability of rapid attitude maneuvering,so they can perform a variety of space tasks,and have broad application prospects in both military and civilian areas.Basis for agile satellites to do rapid maneuvering is an attitude actuator system with a large torque output,typically using thrusters or Control Moment Gyros(CMG for short).Considering the problem of on-orbit service life and control accuracy,agile satellite design is more inclined to use CMG as the main attitude actuator,and the reaction flywheel with smaller torque output is used to improve the pointing accuracy and stability of attitude.In this paper,the agile satellite attitude control problem with the pyramid-type SGCMG and the reaction flywheel hybrid actuator is as follows:The simplified agile satellite attitude dynamics with hybrid actuator is established.The calculation method of the angular momentum envelope and corresponding gimbal angle of CMG system in a specific direction is studied.All the gimbal angles of zero angular momentum of the pyramid-type SGCMG is obtained analytically.It is demonstrated that the null-motion of CMG system can not complete all maneuverings between two gimbal angles of zero angular momentum;accordingly,a fast maneuver method using the flywheel-assisted CMG system to adjust the angular angle of the zero angular momentum gimbal angles is designed to avoid the one-direction torque output singularity of a CMG system.The feasibility of the method is verified by simulation.The energy index related to the angular velocity of CMG gimbals and angular acceleration of the flywheels is designed.The local optimal control torque distribution formula is obtained by the Lagrangian multiplier method.The null-motion of CMG system is directly added to the gimbal angular velocity command and the gradient of a new singularity index is used to drives the null-motion toward moving away from the singular state.The feasibility is verified by simulation.Gaussian pseudo-spectral method is used to optimize the fast maneuvering trajectory of the agile satellite equipped with pyramid-type SGCMG and flywheel.The system state and control quantities in optimization problem are re-selected,and path constraint of the singularity index not only makes final optimized CMG gimbal angular trajectory avoid singularity,but also reduces constraint of the traditional satellite fast trajectory planning on hybrid actuators torque output,which greatly improves the maneuvering speed.Finally,the relevant control law is designed,and the agile satellite's attitude reference trajectory and the CMG system's tracking of the frame angle reference trajectory are guaranteed.