Towards Co-operative Space Domain Awareness (CoSDA): Space-based Sub-THz Inverse Synthetic Aperture Radar

The proliferation of mega-constellations in low Earth orbit (LEO) has led to an enormous increase in the number of satellites occupying this region of space. Currently, they number over ten thousand and are expected to grow by tens of thousands in the next decade. This has led to increased demand for fit-for purpose, high-fidelity on-orbit sensing systems for (i) accurate orbit determination, conjunction assessment and collision avoidance in an increasingly congested space environment, for enhanced Space Domain Awareness (SDA); (ii) supporting the autonomy of future space infrastructure including in-orbit servicing, assembly, and manufacturing. This paper discusses two strategies for on-orbit SDA provision– dedicated and co-operative– performed using space based sub-THz inverse synthetic aperture radar (ISAR) imaging, in monostatic and bistatic configurations. Initially, a dedicated observational platform for satellite constellation observations, with an ISAR capability separate from the constellation, is assessed. Then, a concept of co-operative space domain awareness (CoSDA) is presented, accompanied by the comprehensive analysis of density, dynamics, and rates of conjunctions in existing and projected future constellations. The feasibility of simultaneous monostatic, bistatic, and multistatic ISAR observations is discussed, with a use case considered in detail. Diverse ISAR images are simulated in the Graphical Electromagnetic ISAR Simulator for Sub-THz waves (GEIST). The simulation results are analysed to determine the advantages of simultaneous mono-, bi-, and multi-static sub-THz ISAR for characterisation of the imaged Resident Space Object (RSO).