Thermal design of interface region imaging spectrograph (IRIS) ULE primary mirror

This paper presents the overall thermal design of the Interface Region Imaging Spectrograph (IRIS) telescope with focused descriptions of the primary mirror thermal design, telescope active thermal control system, ULE® mirror substrate thermal properties, and the thermal math model supporting the thermal design. The challenge of the IRIS primary mirror thermal design was to manage the un-filtered solar flux that directly impinges on the optical substrate, while maintaining the mirror within a narrow range of temperatures throughout the mission life. This thermal problem is compounded by a change in the absorption properties of ULE over time, due to UV light.