Optimal reorientation of a free-floating space robot subject to initial state uncertainties

Abstract

This paper focuses on the dynamics and optimal reorientation of a free-floating space robot system in the presence of initial state uncertainties. A control strategy combining optimal motion planning and feedback control is presented based on the dynamic model of the system. In the design of the optimal motion planning, Legendre pseudospectral method (LPM) is used to transform the optimal reorientation problem into a nonlinear programming problem. Then, sequential quadratic programming algorithm is employed to solve the nonlinear programming problem and off-line generate the optimal reference trajectory of the system. In the design of feedback control, the state equation is linearized around the reference trajectory obtained by LPM. The tracking control problem is converted into a two-point boundary value problem based on Pontryagin’s maximum principle. Then LPM is used to discretize the two-point boundary value problem and transform it into a set of linear algebraic equations. This process does not require any integration calculations and has good performance in real time. Numerical simulations indicate that the control strategy is effective with good robustness.