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Parameters for mirror selection: trades between glass ceramics, glass, metals, ceramics and cordierites

A process to converge on selection of the most efficient spaceborne mirror substrate material is described. While parametric descriptors of structural efficiency and resilience to transient response have been used for this purpose over decades, significant parameter revisions are now possible with heightened precision of measuring characteristics that dominate thermal stability, principally coefficient of thermal expansion. An updated parametric diagram of materials will be presented for initial evaluation in the context of space environments and prescribed optical performance. Other important material factors that next enter the selection are heritage, mirror or size, homogeneity, isotropy, fracture mechanics, richness of design data and of course schedule and cost. SCHOTT has established ZERODUR® fabrication facilities to provide newest CNC generation of a full range of optical surface forms, and to enable advanced lightweighting up to 4 meters diameter.