On the Optimal Number of Relays for Nanosatellite Swarm Downlink under Ground Station Reconfiguration Overhead

Abstract

Advances in satellite miniaturization and launch cost reduction have enabled the deployment of increasingly large nanosatellite swarms in Low Earth Orbit. However, the ground infrastructure supporting these missions has not evolved at the same pace: many operators rely on a single ground station that can serve only one satellite at a time and must observe a non-negligible reconfiguration delay between consecutive contacts. This creates a critical bottleneck for missions requiring rapid offloading of large observation datasets within a few orbital passes. We introduce a simulation framework that evaluates two data offloading strategies, namely direct transmission and relay-based aggregation, as a function of the number of relay satellites k. Our analysis uncovers two competing effects governing system performance: insufficient relay count leaves ground station slots under-utilized due to incomplete Inter-Satellite Links aggregation, while excess relays incur unnecessary reconfiguration overhead, whose balance determines an optimal relay count k* that maximizes the completion ratio. We further show that k* decreases with crosslink capacity, and that the sensitivity to reconfiguration time rises sharply beyond k = W orbital passes. These results provide actionable guidance for mission designers choosing between investing in higher-rate crosslink hardware or faster ground station antenna systems.