Lateral Entry Guidance for Lunar Return Vehicles

A lateral entry guidance is designed based on azimuth error and crossrange error for a low L/D ratio lunar return vehicle. The conventional technique to determine the bank sign is according to the crossrange error, which might cause large crossrange deviation during Kepler phase if azimuth error at skip out point is large. This paper develops a combined lateral guidance logic to minish accumulate crossrange error caused by azimuth error during Kepler phase. The lateral logic decides the value of crossrange threshold by constantly predicting the crossrange at skip out point. The azimuth error at skip out point is regulated to a small value by only one bank reverse through online adjusting reversal threshold. The effect of earth rotation is compensated by moving the landing site to opposite direction. During the second entry, the lateral logical is designed based on the crossrange error to achieve precise lateral control. The lateral guidance logic is validated by numerical simulations. Monte Carlo simulations show that the proposed lateral guidance logic can deliver the vehicle to the desired landing site in the presence of large initial dispersions and disturbance.