Blended skip entry guidance for low-lifting lunar return vehicles

Abstract

A skip entry guidance algorithm blending numerical predictor-corrector and nominal trajectory tracking is presented for lunar return vehicles. The guidance is decoupled into longitudinal and lateral channels. A piecewise bank-vs-energy magnitude profile and a sign profile are adopted in the skip phase. A magnitude parameter is used to adjust the predicted downrange, and a pseudo-crossrange at the beginning of the final phase is selected as the lateral control variable. Prediction biases of both channels are nullified by a false position iteration algorithm. An on-line estimation and modeling method is introduced to compensate for aerodynamic and atmospheric uncertainties. A nominal trajectory for the final phase is generated based on actual reenter conditions, and the obtained nominal trajectory is tracked by a linear feedback law. A lateral corridor is used to manage the lateral state. The proposed guidance algorithm is assessed using three-degree-of-freedom Monte Carlo analyses, and the results show a satisfactory and robust performance under highly stressful dispersions.