Thermal design of the Solar-C (EUVST) telescope

The EUV High-Throughput Spectroscopic Telescope (EUVST) of Solar-C mission consists of only two imaging optical components; a 28-cm clear aperture off-axis parabolic primary mirror and a two-split ellipsoidal grating without a blocking filter for visible light before the primary mirror to achieve unprecedented high spatial and temporal resolution in EUV-UV imaging spectroscopic observations. For this reason, about 60 W of sunlight is absorbed by the multilayer coating on the mirror. We report a thermal design of telescope in which the temperature of the primary mirror bonding part and underlying tip-tilt and slit-scanning mechanisms is well lower than a glass transition temperature of adhesive (about 60°C) and thermal deformation of the primary mirror is small, although it is non-negligibly small.