State-Dependent Riccati Equation Control for Motion Planning of Space Manipulator Carrying a Heavy Payload

In this paper, a nonlinear optimal control approach is proposed to plan the motion of a redundant free-floating space manipulator (FFSM) when carrying a heavy payload. Optimal joint trajectories are determined to track a desired end-effector path, for which limitations of the manipulator’s load-carrying capacity and tracking accuracy are simultaneously considered. In this method, FFSM is described as a nonlinear system using the dynamics equation. The integrated performance indicator is proposed as the cost function, which includes tracking error punishment of the endeffector, joint-torques optimization, total energy improvement and instability avoidance of the base. Then the statedependent Riccati equation (SDRE) is established and solved by Taylor series approximation method. The motion planning algorithm is presented, subject to multi-constraints. Simulations are performed for a 7-DOF space manipulator and the results are discussed to illustrate the effectiveness of the proposed approach.