Robust spacecraft rendezvous using a variable speed control moment gyro and thruster

Robust, co-ordinate free, thrust-vector tracking controls are designed for a single Variable Speed Control Moment Gyro (VSCMG). The proposed controls, based on an adaptive active disturbance rejection control and higher-order sliding mode control are presented and compared. These controls guarantee the closed-loop pointing error converges to and remain within a bounded region of the zero error even in the presence of the variable inertia induced by the VSCMG, thruster off-set and uncertain disturbance torques. Secondly, the pointing control law is developed to address the problem of spacecraft rendezvous using only a single thruster and a single VSCMG. Here a pointing guidance law is developed that weights the desired thrust of the rendezvous using a scaling function of the pointing error. This guidance law is shown to significantly improve the performance of the rendezvous maneuver with respect to a guidance law that does not utilize the scaling function. Simulations of a rendezvous maneuver with a 12 U CubeSat are undertaken to demonstrate the applicability of the developed control laws.