Constrained predictor-corrector guidance via bank saturation avoidance for low L/D entry vehicles

The predictor-corrector guidance method, when utilized for a low lift-to-drag (L/D) entry flight with strict path constraints and high dispersions, is likely to encounter control saturation of the bank angle. This study analyzes the saturation problem through a transfer coefficient, and presents a saturation avoidance strategy. The transfer coefficient describes the impact of the current modification on the whole bank profile. To avoid the saturation, a novel bank profile is designed based on an exponential decaying function which has lower transfer coefficient, and a predictor-based modification strategy is utilized to adaptively update the bank angle limit. The saturation avoidance strategy, consisting of the novel bank profile and the adaptive bank limit, is verified on the Crew Exploration Vehicle. Results demonstrate that the novel bank profile performs much better than the constant and linear bank profiles on the saturation avoidance, and the adaptive limit can improve the guidance precision while satisfying the path constraints.