Optimal Concurrent Control for Space Manipulators Rendezvous and Capturing Targets under Actuator Saturation

This article proposes a control method for space manipulators rendezvousing with and capturing a target, involving concurrent operation of an optimal and a coordinated controller. The optimal controller drives the whole system to rendezvous with the target, which saves onboard fuel and satisfies obstacle avoidance constraint and base spacecraft thrust limits. The optimal control problem is solved using calculus of variations method, with state inequality constraints transformed into extended dynamical subsystems and thrust limits formulated as saturation functions. The coordinated controller is designed based on the dynamic equations of the space manipulator on a noninertial frame attached to the system center of mass, which drives the end-effector to approach the target along a desired trajectory while making the base attitude follow a desired profile. It also generates proper reaction moments on base through manipulator motions to ensure controlling the base attitude when base attitude actuators reach their torque limits. The solution optimality of the optimal controller and the stability of the coordinated controller are demonstrated. Numerical simulations verify the performance of the proposed concurrent control method.