Design and performance analysis of a satellite constellation for maritime communications

This thesis investigates the preliminary design and performance evaluation of a satellite constellation for the space segment architecture of the Very High Frequency Data Exchange System (VDES), with the objective of providing reliable maritime communications over the areas of interest. The study addresses constellation design as a coupled orbital and communication problem, considering constellation geometry, antenna configuration, link availability, and the non-uniform distribution of maritime traffic. A multi-layer simulation and optimization methodology is developed to efficiently explore the large design space. Maritime activity is represented through a reduced spherical mesh generated using an icosphere and a Voronoi partition, with the original density data remapped onto the spherical Earth and integrated over the corresponding regions. The final analysis considers 388 study points within the selected NAVAREAs. In parallel, the VDES uplink and downlink link budgets are evaluated and converted into binary availability masks, enabling efficient assessment of different antenna configurations and pointing directions. To reduce the computational cost of the analysis, a statistical performance evaluation method is introduced. Visibility events are extracted from a reduced propagation interval and representative spatial samples, then aggregated as a function of latitude to derive pooled distributions and statistical metrics. These results are applied to the target mesh and weighted according to the spatial distribution of maritime activity. The method is validated against higher-resolution simulations, showing that a propagation interval of approximately one orbital period and a temporal resolution of 15 s or less provide a suitable compromise between accuracy and computational cost. The constellation selection is formulated as a multi-objective design problem, combining a tree-based exploration of orbital parameters with a Genetic Algorithm for antenna optimization. The results indicate that two antennas per satellite provide a favourable compromise between communication performance and system complexity, with optimal pointing directions tending respectively towards 90◦ and 270◦. Among the best performing configurations, a recurring T/P/F = 24/6/3 architecture is identified. Based on the combined uplink and downlink assessment, the final design is a Walker Delta constellation with 24 satellites distributed over 6 orbital planes, at an altitude of approximately 600 km and an inclination of approximately 98◦. The selected architecture provides a balanced solution in terms of coverage, service continuity and system complexity. An extended simulation is finally performed to characterize its access, revisit time, and overlap performance. Overall, the work demonstrates the importance of jointly considering orbital geometry, communication constraints, antenna pointing and maritime traffic distribution in the preliminary design of VDES satellite constellations. The proposed statistical framework significantly reduces the computational burden while preserving the relevant performance trends, providing an efficient methodology for constellation analysis and optimization.