# Summary of Lunar Constellation Navigation and Orbit Determination Technology
## 4 Constellation Navigation and Orbit Determination Technology
### Inter-Satellite Measurement Autonomous Navigation Method  
The orbital information of the current global navigation satellite system is mainly measured on the ground, and then the satellite ephemeris is updated via ground stations. In order to prevent ground stations from being destroyed during war, the United States first proposed the concept of autonomous navigation of navigation constellations, which uses the mutual ranging between navigation satellites in the navigation constellation. The American scholars [PERSON] and [PERSON] designed an autonomous orbit determination scheme [70] and used 21 satellites for simulation demonstration. The results show that the system can operate autonomously for 180 days using UHF inter-satellite ranging based on the predicted ephemeris GPS constellation, and URE is better than 7.33 m. The Galileo system and the GLONASS system also have inter-satellite ranging autonomous navigation functions [71]. All Beidou-3 satellites are equipped with Ka-band inter-satellite link payloads to achieve autonomous orbit determination and satellite-ground joint orbit determination [72; 73]. The inter-satellite link of Beidou-3 not only includes the construction of links between MEO satellites, but also includes the construction of links between GEO and MEO, IGSO and MEO and other links among satellites on different orbits, greatly improving the system's survivability and service performance [74; 75]. [PERSON] used the Starlink constellation to investigate the self-induced collision risk caused by malfunctioning satellites [76]. Research shows that because the Earth's gravity plays an absolutely dominant role in the orbital position of the Earth satellite, and the Earth's gravitational field itself has strong rotational symmetry, Earth satellites can only determine the size and shape of the satellite's orbit using only inter-satellite ranging observations. For relative pointing, the absolute position of the satellite in inertial space cannot be determined. There is an unobservable problem of the overall rotation and translation of the constellation, so it is impossible to determine the long-term autonomous orbit of the constellation. Regarding the constellation rotation problem, [PERSON] analyzed the impact of constellation rotation on orbit determination accuracy [77]. [PERSON] proposed a method of constraining the right ascension of the ascending node of the orbit to solve the rank deficiency problem [78]. [PERSON] conducted simulation demonstration for the method of constraining the orientation parameters of the satellite orbital plane [79], and [PERSON] studied the situation with anchoring stations. Based on the centralized autonomous orbit determination of four test satellites, the radial overlap arc accuracy of IGSO satellites is better than 15 cm, and that of MEO satellites is better than 10 m [80]. [PERSON] studied the joint orbit determination method based on anchoring stations [81]. [PERSON] et al. studied the impact of EOP forecast errors on autonomous orbit determination results [82]. [PERSON] et al. studied the algorithm and simulation results of autonomous orbit determination of navigation satellites [83]. [PERSON] studied the simulation algorithm of satellite-ground joint orbit determination [84], and [PERSON] studied the weighting problem of joint orbit determination [85]. [PERSON] studied the distributed autonomous orbit determination filter algorithm [86]. [PERSON] studied the impact of prior information error on autonomous orbit determination [87]. [PERSON] et al. studied the rotation error analysis and control of navigation satellite autonomous orbit determination constellations [88]. [PERSON] studied the equipment time delay estimation method in joint orbit determination of navigation satellite inter-satellite/satellite-ground link [89]. [PERSON] studied the time synchronization method of autonomous navigation [90].