High-fidelity Earth observations for measuring geophysical parameters have become indispensable for areas such as climate science and resource management. In recent years, this industry has driven a shift toward formations of small and cost-effective satellites rather than single large platforms. These distributed systems enable simultaneous, multi-point measurements across wide areas, improving temporal coverage and resilience. Global Navigation Satellite System Reflectometry (GNSS-R) exploits navigation signals reflected from the Earth surface to retrieve geophysical parameters, and provides a low-cost and resilient approach for Earth observation, but is constrained by coarse spatial resolution, typically above 10 km. This study investigates a novel concept to overcome this limitation by employing a synchronized CubeSat formation that synthesizes a large aperture through beamforming, enabling sub-kilometer resolution. A comprehensive framework is developed to analyze the relationship between formation geometry, beamforming performance, and station-keeping requirements under orbital perturbations. The methodology combines Clohessy-Wiltshire-based relative motion modeling, perturbation analysis including Earth oblateness, and beamforming simulations to evaluate spatial resolution and sidelobe performance. A multivariable optimization explores trade-offs between resolution, ground-illumination stability, and formation complexity. The results indicate that spiral formations provide favorable performance, with a configuration of 29 satellites achieving near-optimal resolution while minimizing formation size. However, perturbations such as J₂ induce drift that degrades resolution beyond 1 km after a few orbits, highlighting the need for efficient formation-keeping strategies. Given the constraints of CubeSats, including limited volume, mass and power, propellant-less control methods, such as differential drag or solar radiation pressure, emerge as promising solutions for enabling long-duration, scalable missions within CubeSat constraints. These findings demonstrate the feasibility of distributed GNSS-R missions with significantly improved spatial resolution and lay the foundation for future work on control strategies and end-to-end mission design, enabling new applications in fine-scale Earth observation.
Du et al. (Fri,) studied this question.