# Summary of Lunar Constellation Navigation and Orbit Determination Technology
## 1 Introduction
Combined with low-orbit constellations, joint high-, medium- and low-orbit fast and high-precision positioning has become the development direction of the next generation of intelligent location services. Astronomical navigation includes methods such as angle measurement, velocity measurement, and ranging. Combined with orbital dynamics, real-time satellite positioning can be achieved. However, it also faces the problem of limited accuracy and low maturity of high-precision navigation instruments. Therefore, the existing single-satellite orbit determination method for lunar probes cannot meet the needs of future large-scale lunar resource development. Future lunar exploration will be more complex and diversified, and using lunar constellation for exploration can effectively solve these problems. The lunar relay communication and navigation positioning systems will become a necessary part of the future lunar exploration infrastructure. Correspondingly, the lunar navigation and communication system architecture LunaNet [10], Project Moonlight [11; 12], the Lunar Pathfinder Mission [13], the new hybrid data relay satellite CommStar-1 [14] and other plans for supporting lunar probe relay communications were proposed. China has also proposed its own 'Queqiao comprehensive constellation for communications, navigation and remote sensing' [15], which is planned to be completed in three phases to provide relay communications, navigation, positioning and timing services for cislunar space transfer and lunar surface exploration activities. The lunar exploration constellation composed of Moon orbiters and relay satellites on the Earth-Moon balance point can achieve continuous coverage of specific areas of the lunar surface or even the entire lunar surface, and can provide necessary relay communication, navigation, positioning and other services for human beings to fully carry out lunar exploration in the future. Among them, the lunar orbit can achieve full lunar coverage and communicate with lunar targets at close range. Its orbital characteristics are similar to those of Earth satellites, so it is easy to apply. Compared to lunar orbit, the observation coverage on the libration point orbit is wider. Additionally, the L2 point of the Earth-Moon system keeps its position over the back of the Moon, so one satellite on libration points can provide a relentless lunar coverage equivalent to a lunar orbit constellation. The disadvantage is that the libration point is farther from the lunar surface compared to the circumlunar orbit, resulting in insufficient communication timeliness and navigation accuracy. The lunar space probe's demand for communications, navigation, surveying and other services has increased significantly. The construction of the communication and navigation remote sensing constellation will significantly improve the efficiency of lunar resource surveying, development and utilization while meeting the technical requirements of future exploration missions. In response to the demand for high-precision lunar navigation and orbit determination, this article first analyzes the principles of related technologies, research status, and key difficulties that need to be solved urgently. Finally, the future development trends are outlined, providing reference directions for the construction of future lunar navigation constellations.