Thermal design, analysis and testing of Solar Orbiter Stood-Off Radiator Assembly

Solar Orbiter is a solar-heliospheric ESA mission investigating how processes on the Sun drive the properties and phenomena of the heliosphere. To achieve this, Solar Orbiter will perform 22 orbits around the Sun, with perihelions up to 0.28 AU and 1.02 AU as maximum aphelions, carrying a payload of six remote sensing instruments and four in-situ instruments. Five of the six remote sensing instruments (EUI, METIS, PHI, SPICE, STIX) have very stringent temperature requirements and are therefore mounted on the internal side of the spacecraft (S/C). To maximize efficiency of the radiators of these instruments it is necessary to thermally decouple the radiators from the S/C’s interior and structure to a maximum extent. Therefore, they are attached to the external sides of the S/C via insulating iso-static mounts, forming the so-called Stood-Off Radiator Assembly (SORA). The instruments are thermally coupled to the radiators by flexible thermal links and rigid conduction bars. For an improved thermal efficiency of the radiators in some cases encapsulated annealed pyrolytic graphite (APG) is used. Heat pipes are also used for heat transportation to allow for the geometric distribution of the separate radiators in the limited available volume. The SORA radiators are white-coated except for one, which uses optical surface reflectors (OSRs). In addition to an extensive testing and characterization on component level a sub-system verification was performed via a Thermal Balance (TB) test on a subset of the SORA containing all relevant technologies (iso-static mounts, flexible thermal links, conduction bars, encapsulated APG, white coating, OSRs, heat pipes and multi-layer insulation). The paper provides details about the thermal design of the SORA, the component and TB test campaign as well as the correlation of the TB test thermal model yielding verified modelling parameters for flight predictions of the SORA.