月球测绘以及月球作为天然的深空探测中转基地，对地月系大尺度空间基准提出了迫切需求。目前以GNSS为代表的传统导航星座，其卫星高度决定了基准服务主要集中在GEO以内的近地空间，难以有效地波及40万千米的地月空间；此外，基于星间链路的GNSS星座自主定轨存在星座整体漂移问题。本课题拟着眼于由地-月-飞行器组成的限制性三体问题和平动点轨道在地月大空间基准建立中的独特作用和重要契机，开展非传统二体问题意义下的星座构型和定轨研究。构造地月系代表性平动点导航星座，利用周期轨道族在特定空间的分布单值性，建立基于平动点星座+GNSS星座的SST联合定轨理论和算法，解决GNSS星座的绝对定向，研究融合两类星座的地月空间（尤其是月球背面）用户的无缝导航和定位方法。GNSS和平动点星座的高度融合，具有嫦娥四号的月球背面和LL2平动点轨道探测任务应用背景，并对提升GNSS的应用层次具有重要的现实意义。

Lunar surveying and taking Moon served as a natural transfer base for deep space explorations demand a large-scale spatial reference covering cislunar space. Currently GNSS is the main PNT means for near-earth users with altitude below GEO, but is unfortunately limited by the orbital altitude of its constellation, and thus cannot serve users flying further up to moon. Meanwhile, the overall rotation of GNSS constellations is an inherited weakness if doing autonomous POD using inter-link data. We will study the construction and configuration of a novel constellation consisting of libration point orbits(LPOs) and the orbit determination theories in the earth-moon-spacecraft restricted three-body problem. We will construct some deputy LPO constellations around the lunar libration points, and exploit the mechanism of autonomous POD combined GNSS and LPO constellations based on the SST data. By utilizing the locally smooth one-parameter characteristics of a periodic orbit family, we will achieve the absolute spacial orientation for GNSS constellations. With the simultaneous observations from both types of navigation constellations, we will establish the seamless navigation and positioning theories and algorithms for user spacecraft in cislunar space and especially the landers and rovers on the far side areas of the moon. Based on the high-level fusion of GNSS and the LPO constellation, we expect to reach the goal of supporting for Change-4 and LL2 missions aiming to land on the far side of the moon. Meanwhile, the outcome of the project will significantly improve the GNSS applications and services.