Stability analysis of explorer in soft landing mode of engine shutdown at touchdown

The soft landing stability will be greatly reduced if the main engine of planetary explorer fails to shut down timely. In order to avoid this reduction, a new shutdown mode is introduced to serve as a remedy where engine is shut down at touchdown. The dynamic model of the explorer equiped with novel landing gear system was established, and the model of variable thrust rocket engine and attitude control thrusters were attached to it for the analysis of the remedy. The Monte Carlo simulation is used to analyze the soft landing stability of the explorer under three shutdown modes, which include the mode that main engine fails to be shut down, the mode of shutdown at touchdown mode and the mode of shutdown at touchdown with attitude controlling, considering the uncertainty of the landing site and the explorer state at touchdown. By adopting the descriptive sampling method and a termination criterion based on the relative error of the mean estimation, the efficiency of Monte Carlo simulation is improved on the premise of ensuring the accuracy. By comparing the landing reliability among three modes, the pad contact engine shutdown technique efficiently improves the landing stability by 11.6% after failure of main engine shutdown occurs, and the introduction of the attitude control system increases the reliability of successful landing by 9.7%.