Formation Flying Strategies for Small Distributed SAR Satellites: A Trade-Off between Stability and Performance

Formation flying techniques have enabled advanced interferometric and radar imaging capabilities for Earth observation missions in low Earth orbit (LEO). At one end of the possible geometries lies the safe ellipse configuration, widely adopted for its intrinsic passive safety. However, the continuously varying baseline complicates SAR data processing and may degrade image quality. At the opposite end, the train-like formation features a constant along-track geometry that simplifies SAR imaging and processing, with the downside of perturbations induced along-track drift. Although these performance versus stability trade-offs are well documented for large formation flying missions, their implications for small satellite constellations and distributed SAR (DSAR) realizations remain unexplored. This paper compares safe ellipse and train-like DSAR formations through orbital dynamics simulations, assessing relative motion stability, passive safety, and formation-keeping requirements to identify optimal and cost-effective architectures for small-satellite DSAR missions.