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.