Improved numerical predictor-corrector guidance for lunar return capsule

To decrease the bank angle reversal frequency in the skip phase and suppress the aerodynamic load effectively in the final phase of the numerical predictor-corrector guidance for lunar return capsule, an improved guidance scheme is proposed by searching for the energy point of the only one bank reversal in the skip phase and compensating the guidance command with drag acceleration feedback in the final phase. Firstly, the secant method is used to search for the bank angle reversal energy point, so that the bank angle is just reversed once in the skip phase. Secondly, based on the exponential atmosphere assumption, the derivative of the drag acceleration is obtained, and a reference drag acceleration profile is determined according to the load constraint. Finally, the errors of the drag acceleration and its derivative between the reference profiles and the actual profiles are used to compensate the basic bank angle magnitude in the final phase to relieve the aerodynamic load. The testing results demonstrate that the proposed algorithm can reduce the bank angle reversal frequency in the skip phase and suppress the aerodynamic load effectively with strong robustness, which show that the problems have been successfully solved and the scheme can provide a reference for practical guidance system design.