Abstract: Ignition point determination (IPD) is an important part for lunar soft landing process, which is a complex iterative process dealing with orbit design, guidance law design, targeted sampling site determination, landing and lifting-off safety analysis, etc.. IPD may directly influence the final position of landing site and landing safety, and also indirectly influence the realization for lunar surface sampling. In view of the mission requirement of IPD for lunar soft landing, a IPD method by coupling control strategy based onorbit control for multiple times and optimal search on nominal flight track was proposed. Firstly, the principle and constraint condition of IPD were designed and summarized according to unmanned automatic lunar sampling and return mission. Then, the method of IPD for lunar soft landing mission was introduced in detail. Finally, the influence on IPD by major orbit control mission before powered descent ignition of lunar soft landing was analyzed. Meanwhile,the analysis on topographic features and the influence on landing and lifting-off safety of targeted landing region were implemented and then the ultimate ignition point was determined and verified according to the final in-orbit flight results. With in-orbit flight verification of Chang’e-5 mission, the IPD method based on successive approximation and optimization strategy (SAOS) proposed in this paper was effective for this mission and also available for soft-landing mission on celestial body in the coming future.

Key words: Chang’e-5 lunar probe, unmanned lunar sampling and return, target optimization, landing safety, ignition point determination for powered descent phase