## 2 Constellation Station Maintenance Analysis  
At present, the low-orbit large-scale constellation orbit-control strategy still faces many challenges, mainly in the following aspects [6]. 1. The maintenance degree of the constellation configuration is more complicated. Compared with MEO constellations, LEO constellations have larger numbers of satellites and larger scales, and the orbital elements of satellites in different orbital planes are quite different, so the initial deployment degrees of LEO constellations are more complicated. For example, currently, the number of satellites in orbit of the Starlink system exceeds several thousand, according to the publicly available website www.space-track.org (accessed on 22 October 2024). These satellites are deployed on multiple orbital planes in a process that roughly follows a complex orbital maneuver (or docking orbit) from the initial orbit to the operational orbit. Due to the differences in orbital elements, such as the initial orbital altitude, right ascension, and phase difference of satellites with the same and different orbital planes, the constellation initialization control strategy should be designed from the top overall level. The maintenance of the constellation configuration should be comprehensively considered from the existing satellite-Earth measurement and control. As a result, the initialization of the constellation deployment and the maintenance of the constellation configuration are more complicated. 2. The main perturbative effects and drift rules of the constellation are not assimilated. Compared with MEO constellations, due to the differences in the main perturbation forces, the orbital drift characteristics of the low-orbit constellations are different. For example, an initial deviation of the semi-major axis of an LEO satellite on the order of 100 m causes a phase difference of nearly 36\({}^{\circ}\) over the course of a year, while an MEO satellite's phase difference is only 1.5\({}^{\circ}\). Due to the relatively low orbital altitude of the satellite, the atmospheric drag is greatly affected, and the orbital altitude of the satellite decreases continuously with the atmospheric drag. The orbital deviations of the initial orbital elements of the satellite and the capture error of the ground measurement and control system cause the cumulative drift of the phase angle, resulting in the continuous divergence of the overall geometry of the constellation. Therefore, satellite orbit deviations and perturbation forces are important factors affecting the constellation coverage characteristics and mission realization. To compensate for the satellite orbital altitude attenuation caused by atmospheric drag, the control laws, control methods, and control strategy analysis of the satellite relative phase angle in the same orbital plane and the right ascension of different orbital planes are also different. 3. Constellation orbit-control mode and orbit-control technology are more integrated. The control and maintenance technologies and the control methods of medium- and high-orbit constellations mainly include perturbation compensation methods based on the average orbit root number and the constellation-configuration numerical differential correction method based on the instantaneous root number. Compared with MEO constellations, large-scale low-orbit constellations have large numbers of satellites, low orbital altitudes, and large cumulative influences of initial deviations and capture error perturbations. Therefore, the stable and safe operation requirements of large-scale low-orbit constellations are more stringent, and constellation geometry maintenance tasks occur more frequently. There are still many theoretical problems to be studied and many engineering application problems to be solved if the existing orbit-control and orbit-maintenance technology, control methods, and control modes of medium- and high-orbit constellations or small low-orbit satellite constellations are extended to large-scale low-orbit satellite constellations.