Disturbance rejection based optimal control scheme for landing on a celestial object

This paper presents an optimal control solution for celestial object landing problem, involving θ-D control technique and disturbance rejection mechanism. Based on the polar coordinate system, the control objective is to drive the probe to reach the surface of celestial object with the desired line-of-sight angle and zero velocity. θ-D technique is applied in the absence of disturbances to deal with the nonlinear optimal control problem. Then, the disturbances are estimated in the fast-estimation framework with bounded estimation errors. An additional variable-structure term is added to the composite control protocol to ensure stability under the time-varying disturbances. Comparative simulation results of the proposed approach are presented at the end of this paper, demonstrating the effectiveness of the proposed control protocol.