SiC ultralight mirror for large space telescope and for extremely huge ground-based telescope II

摘要

SiC (silicon carbide) lightweight mirrors are used for a large number of space telescopes, and SiC is also candidate as hopeful material for segmented mirrors of the next generation ground based telescopes from 30 to 100 m in diameter. However, an SiC mirror is difficult to shape because the material is very hard and brittle. We are developing an SiC mirror by means of the ELID (ELectrolytic In-process Dressing) grinding method, a grinding machine with rotary table of 800 mm in diameter and precision of 10 nm in control resolution, and computational simulations. The ELID grinding method is versatile for fabrications of very hard materials. In this study, we introduce test fabrications of SiC mirrors with 360 mm in diameter and equilateral triangle rib structures in the rear face. We developed a support tool with air actuator and oil pressure clamp for suppression of the mirror deformation for manufacturing of the thin mirror.