CHANG'E-3 contingency scheme and trajectory

This paper addresses contingency trajectories of CHANG'E-3 in the case of a failure of the lunar brake, which is crucial to the CHANG'E-3 mission, i.e., the first Chinese lunar soft-landing and rover mission. Considering the flight-time and control-energy requirements placed on the contingency trajectories, the paper proposes a direct return method and a low-energy return method and develops the corresponding contingency trajectories based on the CHANG'E-3 cislunar transfer trajectory. The direct return method was studied on return style, flight time, control energy, and influence of maneuver time on energy. The low-energy return method was investigated using the method of invariant manifold calculations for a Lissajous orbit, the method of direct libration-point orbit transfer and injection, and the control strategy used for a low-energy trajectory. The results demonstrate that the control energy for direct return trajectories can be reduced using a certain flight course. When a flight time of less than half of a month is desired, a trajectory from the north celestial pole should be selected as a lunar approach trajectory for CHANG'E-3. Otherwise, a trajectory from the south celestial pole should be selected. Furthermore, these two trajectories have approximately equal velocity increments if their flight-time difference is close to half of a month. In the case of the low-energy return method, methods using approximate manifold calculations for a Lissajous orbit and the direct transfer and injection to a libration-point orbit are proposed and shown to be useful. CHANG'E-3 would return via the Sun-Earth L2 libration point and would require four maneuvers during its flight. The low-energy return method offers remarkable energy savings of up to 267 m/s compared to the direct return method. The methodology not only provides a contingency control technique for CHANG'E-3 and for future lunar missions, but it also serves as a beneficial supplement to the present studies on lunar orbit injection contingencies and invariant manifold applications.