PASSIVE DISTRIBUTED RADAR BASED ON FORMATION FLYING FOR EARTH OBSERVATION: A PRELIMINARY STUDY

This paper explores the feasibility of a passive distributed radar, realized through a formation of compact satellite receivers flying in Low Earth Orbit. The cluster is conceived as a rapid-re-configurable system, able to capture the backscattered echoes of existing space-borne SAR satellites moving on higher orbits. This feature allows the component antennas to change their arrangement in order to perform different multi-static applications. The paper analyzes the relative dynamics of the space systems involved, with the receivers imagined as a single deputy-satellite at a completely different altitude from the chief-transmitter. This assumption increases the number of potential illuminators, but makes multi-static acquisitions achievable only at given times, when the along-track separation between the spacecrafts is below a threshold. Furthermore, the difference in altitude implies different perturbing effects on the satellite trajectories, with the cluster being affected by the aerodynamic drag to a greater extent. Two different solutions are investigated, with the receiver “co-rotating” or “counter-rotating” with the transmitter. The relative motion is described using reduced order analytical models. They are derived assuming small differences between the orbital elements and allow to well approximate the relative dynamics in the neighbourhood of the "conjunction".