# Design of Mega-Constellations for Global Uniform Coverage with Inter-Satellite Links
###### Abstract  
Constellation configuration design is a prerequisite and critical step in the construction of a mega-constellation system in low Earth orbit. However, the huge number of satellites and the intricate changes in relative positions among them make the configuration design the most challenging part. In this paper, we propose a configuration design scheme for mega-constellations considering collision-avoidance constraints with the objective of uniform global coverage. In this design scheme, the constellation is made up of multiple Walker constellations with the same orbital altitude and different orbital inclination. Moreover, the analytical expression for the minimum distance between any two satellites in the same orbital altitude is derived, and the constellation internal collision-avoidance constraint is established accordingly. Finally, a permanent inter-satellite link design scheme without dynamic reconstruction is presented based on the mega-constellation configuration. Simulation results show that the mega-constellation design scheme introduced in this paper can achieve relatively uniform global coverage (its N Asset Coverage ranges from 18 to 25). The mixed Walker constellation is capable of providing a greater number of N Asset Coverage for most of the world than the Walker constellation of the same satellite order of magnitude. In addition, the inter-satellite link scheme designed in this paper can ensure continuous and stable communication between any satellite nodes. mega-constellations; collision avoidance; uniform global coverage; inter-satellite link; Walker constellation; sub-satellite point +
Footnote †: journal: Aerospace  
0000-0002-4400-0000]Y. Xie  
is the optimization design method [5], which applies intelligent optimization algorithms to find the configuration that makes the constellation performance optimal. The representative geometric analytical method is the Walker constellation, proposed by [PERSON] [6]. It can be accommodated to global coverage requirements. The properties of any satellite in the Walker constellation are the same. Afterward, various constellation configurations were derived based on the Walker constellation. Researchers such as [PERSON] [7], [PERSON] [8], and [PERSON] [9] contributed fruitful research results intending to use the minimum number of satellites to achieve global coverage. [PERSON] [10] is concerned with the analysis of the coverage of latitudinal zones. The flower constellations (FCs) defined by [PERSON] [11] are similar to the Walker constellations. The FCs are suitable for the Earth observation missions due to their repeat ground track. Based on FCs theory, scholars later expanded the design possibilities and proposed constellation configurations such as 2D [12], 3D [13], and 4D [14] Lattice FCs, and then the Necklace FCs [15] and 2D [16] and 3D [17] Necklace FCs were developed. [PERSON] [18] presented a detailed simulation analysis for the application of 2D Necklace FCs to Earth observation missions. [PERSON] [19] presented a systematic method for designing continuous global coverage Walker and Street-of-Coverage constellations by taking seven critical constellation properties as design criteria. The authors of [20] proposed a semi-analytical method in designing constellations to deal with a sequence of Earth revisit missions. The intelligent optimization design methods have significant strengths when the number of satellites is small or for regional coverage tasks. [PERSON] [21] solved the design of navigation constellations using the Multi-Objective Particle Swarm Optimization algorithm. [PERSON] [22] designed a hybrid constellation using a genetic algorithm on an LEO-based navigation augmentation system. [PERSON] [23] proposed a novel optimization method, the hybrid-resampling particle swarm optimization (HRPSO) algorithm, which improved the computational efficiency of constellation design. The above research mainly focused on the design of traditional constellations with fewer than 100 satellites.