Thermo-mechanical sizing and stress-induced birefringence analysis for the MezzoCielo assembly

MezzoCielo telescope aims to be a revolutionary optical instrument, designed to exhibit a field of view of around 104 square degrees. As such, it will be able to carry out whole-sky patrolling, which could be exploited, for instance, to track space debris or localize transient phenomena. From an optical stand-point, the telescope is a monocentric lens, composed by an outer glass shell enclosing an inner cavity filled with optical fluid (having proper refractive index for light convergence). From a mechanical point of view, instead, given the limitations related to manufacture large glass elements having high performance, the adoption of a segmented structure, presenting, for example, a platonic solid-like shape, is required. In this paper, the main aspects concerning the sizing of such frame (chosen to be a dodecahedral one) and the thermo-mechanical analysis of the lenses support system assembly, both analytical and numerical, will be presented. In particular, it will be shown how the lenses will be able to operate with little temperature difference across their volume independently from the surrounding conditions and the way in which the telescope can withstand external low temperatures without manifesting high thermal stresses, while maintaining, at the same time, constant focal length. Subsequently, a birefringence investigation, carried out to select the more appropriate lens shape, will be described. From our analysis, pentagonal-shape lenses turn out to be the most suitable ones for the MezzoCielo application.