Hybrid constellation design using a genetic algorithm for a LEO-based navigation augmentation system

Abstract

A low earth orbit (LEO) constellation can support broadband Internet access and can also be a platform for navigation augmentation for global navigation satellite systems. LEO satellites have the potential to transmit very strong navigation signals; they also show rapid changes in spatial geometry as they come closer to earth and travel faster over stations than satellites in medium or high orbits do. Before the establishment of a LEO-based navigation augmentation system, constellation design is a critical task. Previous LEO constellations have usually employed single polar or near-polar orbits for global coverage, resulting in fewer visible satellites at low latitudes. We propose and optimize several hybrid LEO-augmented constellations using a genetic algorithm to realize globally even coverage. When there are 100 LEO satellites, the average numbers of visible satellites during a regression period are 5.49, 5.44 and 5.47, with standard deviations of 0.44, 0.18 and 0.28, for the optimized hybrid polar-orbit/Walker, orthogonal circular-orbit/Walker and Walker/Walker constellations, respectively. For the hybrid orthogonal circular-orbit/Walker constellation type, the necessary numbers of LEO satellites to realize globally even coverage with six visible satellites are 109, 172 and 221 for elevation mask angles of 7°, 15° and 20°, respectively. For coverages with four and five visible satellites with an elevation mask angle of 7°, the required numbers of satellites are 90 and 93, respectively. All proposed hybrid constellations can provide 100% global coverage availability with one to three visible satellites for broadband Internet access.