Distributed On-Demand Routing for VLEO Constellations with 3-Terminal Inter-Satellite Links

This paper investigates routing strategies for Very Low Earth Orbit (VLEO) satellite constellations constrained by a three-terminal (3T) inter-satellite architecture, which is gaining interest as currently adopted by major operators (e.g., Starlink). In the 3T configuration, two terminals enable alongtrack communication, while a third hemispherical terminal can dynamically connect to either the left or right cross-plane neighbor, but not both simultaneously. This contrasts with the traditional four-terminal (4T) architecture, where four directional terminals enable full inter-plane links. The 3T constraint reduces crossplane connectivity, impacting path diversity, reachability, and latency. To address these challenges, we develop InterleavedScenario MinHopCount (IS-MHC) and DisCo3T, modified versions of the state-of-the-art routing algorithms Minimum Hop Count (MinHopCount) and Distributed On-Demand Routing for MegaConstellations (DisCoRoute) for the 3T case. Our new model accurately captures the limitations of 3T connectivity and reduces hop count in this scenario. We conduct a comprehensive evaluation of DisCo3T in terms of latency, hop count, and computational complexity, including a comparative analysis with the original 4T implementation. Results show that the topological constraints of the 3T configuration cause an average hop count increase of $\mathbf{2 1. 7 \%}$ compared to the 4T baseline; however, DisCo3T retains the processing efficiency of the original 4 T algorithm.