Improved ZEM/ZEV feedback guidance for Mars powered descent phase

An improved zero-effort-miss (ZEM) and zero-effort-velocity (ZEV) optimal feedback guidance algorithm is proposed in this paper for Mars powered descent phase, which has taken into account the no-subsurface constraints when designing the guidance law. Detailed descriptions have been given to this algorithm. The main advantage of this optimal guidance law is that it can successfully avoid collision to the Martian surface, at the same time preserving high landing precision and fuel optimality. For future Mars landing mission, the thrust-limited engine is most likely to be used. We propose a simulation method to study and determine the optimal final time which can minimize the fuel usage while ensuring precision landing and no-subsurface constraints. Monte Carlos are run to test the robustness and reliability of the improved and original guidance algorithms which show the superiority of the improved guidance law in preventing collision to the surface over the original one.