Passive cooling system of the PRISMA hyper-spectral camera in LEO

PRISMA (PRecursore IperSpettrale della Missione Applicativa) is an ASI (Agenzia Spaziale Italiana) mission aiming at in-orbit imaging capabilities from LEO (Low Earth Orbit): the payload is designed for the acquisition of Earth hyper-spectral and panchromatic images and will be ready to fly in 2017. The Thermal Control System (TCS) of the payload is conceived to be passive, and one of the key element needs to be cooled at cryogenic temperature of 180 K. Passive cooling system guarantees solid thermal control performance and design robustness. The LEO environment is very demanding for such a passive cooling; for this reason the detailed design has been focused on three aspects: the passive cooler design- including its shielding and multiple reflections, the heat transport device selection and testing an ethane heat pipe, the heat leak control by means of intermediate cooling stages. The thermal design has been numerically analysed, verified against modelling parameters uncertainties and its fundamental elements have been tested.