Abstract: The Chang′e-6 mission is the first lunar far-side sampling return mission in the world. The mission planning is an important assignment in the spacecraft system design. Mission planning problem is conventionally converted to the numerical constraints optimization problem in the traditional method. However, by using this method, the constraints could not be satisfied directly, and at the same time, the design variables dimension increased, the computing efficiency decreased, and the physical meaning was not apparent. A new mission planning approach using the mission geometry is proposed in this paper. According to the new approach, the periapsis constraints of the Earth-to-Moon and Moon-to-Earth transfer trajectories, the relative geometry constraints on sampling point and lunar orbit plane, and the geometry relationship of the Sun-Earth-Moon are fully considered. The new approach reduced the design variables dimension, improved the computing efficiency. In addition, it also has the advantage of intuitive spatial geometric interpretation, and the result can be verified easily. The new approach has been applied to mission planning and trajectory design in the Chang′e-5 and Chang′e-6 missions successfully, and will be adopted in the future lunar exploration mission.

Key words: Chang′e-6 mission, mission geometry, mission planning, retrograde orbit, lunar exploration