Materials for Large Space Optics

Abstract

Materials are compared on the basis of their ability to minimize static, thermal and dynamic load induced deflections at the center of a large spherical mirror segment or panel. The analysis considers a 0,5m diameter mirror in two environmerits expected in space applications: (A) low incident radiation and low operating temperature (150°K) and (B) high incident radiation, moderate operating temperature (350°K). Although the analysis permits examination of various geometrical and loading parameters, the chief objective has been to compare twelve promising mirror construction materials, including composites, glasses, ceramics and alloys. Fused silica and carbon/graphite are prime candidates for type A and B environmerits, respectively. The ranking of the materials is sensitive to local variations in thermal expansion coefficients, possible actuator compensation for thickness changes and/or improvemerits in properties perpendicular to the mirror plane. Additional considerations in the choice of mirror materials are also discussed.