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Abstract

Space-based interferometry has gained prominence in recent years, largely because higher spatial resolutions of celestial observations can be achieved with multi-telescope formations compared to those achieved with a fixed-aperture, single telescope. IRASSI is a space interferometer composed of five spacecraft, whose aim is to observe particular chemical and physical processes in cold regions of space, such as dust clouds and stellar disks, in the far-infrared frequencies. Ultimately, the goal is to study the genesis of planets, star formation and evolution processes in these cold regions and to understand how prebiotic conditions in Earth-like planets are created. IRASSI will orbit the second Lagrange point, L₂, of Sun-Earth/Moon system. The operating principle of IRASSI is based on free-drifting baselines, which dynamically change during the observations and measure therefore the incoming wavefront of a celestial target at different locations in space. This process relies on very accurate measurements of the baselines - at micrometer level - rather than on precise control of the formation. Naturally, a free-flying formation comes with a set of challenges, namely identifying a nominal formation geometry, that is, a suitable dispersion of the telescopes in three-dimensional space. In addition, understanding how this free-drifting geometry is expected to change is crucial, particularly if this may affect the operation of the telescope instruments and thus the quality of the final synthesized images. The present paper describes therefore the major requirements for establishing a desired formation geometry and proposes a preliminary nominal formation for the observations. The relative dynamics of the free-drifting spacecraft are modeled and evaluated. Final considerations regarding formation control are presented and the paper concludes with a summary of the work and outlook for the future.