Cryogenic optical testing of sic mirrors for ASTRO-F and C/SiC composite mirrors for SPICA

Light-weight mirrors are developed for two Japanese infrared astronomical missions, ASTRO-F and SPICA. ASTRO-F is scheduled for launch in 2005, while the target year for launch of SPICA is 2010. The mirrors of the ASTRO-F telescope are made of a sandwich-type silicon carbide (SiC) material, comprising porous core and CVD coat of SiC on the surface. Cryogenic measurements of the ASTRO-F primary mirror and telescope assembly were performed extensively. As for the SPICA telescope, which has an aperture of 3.5-m diameter, carbon-fiber-reinforced SiC (C/SiC composite), as well as SiC, is one of the promising candidates for mirror material. C/SiC composite spherical test mirrors of 160-mm diameter has recently been manufactured and tested. This paper presents the experimental results of the cryogenic performance obtained for the sandwich-type SiC mirrors and the C/SiC composite mirrors.