An enhanced analytical predictive corrector skip guidance for lunar return vehicles

Analytical predictive skip guidance law is suitable for on-line operation of the on-board computer due to its simplicity, but it has poor performance for the long target ranges. An enhanced guidance law is proposed to meet the requirement of long ranges. The main factors affecting the landing accuracy are analyzed. The tracking errors of altitude and velocity between calculated states and actual ones are minished by adjusting the control gain during the ascending phase. The desired velocity exiting the atmosphere is modified to compensate the undershoot range caused by drag during ballistic phase. The secondary entry makes use of numerical predictor-corrector guidance, and the step by step corrector is applied to solve convergence problem, thus avoiding the complicated reference trajectory design process. The numerical simulation indicates that the proposed algorithm is not sensitive to initial position error, mass error, aerodynamic error, atmospheric dispersion and so on. The landing point deviation is within 5km, so that the guidance law can be implemented onboard when the flight range is long, and offer more flexibility to a mission design team.