Manufacturing and testing SiC aspherical mirrors in space telescopes

ABSTRACT Reaction Bonded (RB) SiC mirrors due to their excellent specific stiffness and thermal properties have been widely used in space telescopes. However, polishing large SiC aspherical mirrors is difficult compared to other materials such as fused silica or Zerodu. In addition, surface roughness of the polished SiC mirrors is limited by the defects of the materials and needs to be improved by means of surface coating technique. This paper introduces the current progress of large SiC aspherical mirrors manufacturing and testing in CIOMP. In particular, the procedures of making large off-axis aspherical mirrors were discussed in detail. A proprietary computer controlled optical surfacing (CCOS) technique was utilized to grind and polish the mirrors and the computer aided null test was used to measure the surface figure. As results, a 600mm class off-axis SiC aspherical mirrors was demonstrated with figure error less than 13nm rms. Key words: SiC, off-axis aspherical mirrors, CCOS, null test.