月面无人自主采样返回任务动力下降点确定及验证

动力下降点确定是实施月面软着陆的重要环节，是多系统间复杂迭代的过程，涉及轨道设计、制导律设计、着陆目标的采样区确定、着陆及起飞安全分析。其设计结果直接影响了最终着陆点的位置和着陆过程的着陆安全，也间接影响采样安全和采样工程目标的实现结果。针对嫦娥五号在实施月面软着陆前确定动力下降点的任务需求，提出了通过多次轨道控制与最优标称制导轨迹搜索联合控制策略的动力下降点确定方法。首先，根据月面无人自主采样返回任务设计总结了动力下降点确定原理和约束条件；然后，详细论述了月面无人自主采样返回任务软着陆过程动力下降点确定方法；最后，通过嫦娥五号在着陆前主要的几次轨控实施结果分析了其对动力下降点的影响，同时综合了着陆区地形分析及着陆、起飞安全性分析，对动力下降点进行确定并根据最终在轨飞行结果进行验证。验证结果表明，基于“逐次逼近寻优方法”的月面软着陆环节动力下降点的确定方法有效，可以为后续地外天体软着陆等任务提供参考和借鉴。

Ignition point determination for powered descent phase and in-orbit verification of lunar unmanned sampling and return misson

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.