Fabrication of large-size SiC mirror with precision aspheric profile for artificial satellite

This paper presents an on-machine surface profile measurement system for a large mirror to be used on artificial satellites. The measurement system is constructed by mounting a long-stroke length gauge on a commercial rotary grinder for fabrications of mirror profiles. Mounting the length gauge on slides of the rotary grinder enables evaluations of the mirror profiles, which results would be used to compensate profile errors of the mirrors. In the developed system, both positioning errors and tilt misalignments of the length gauge would induce significant measurement errors. In this study, a quantitative alignment method and a compensation method are therefore developed to reduce the measurement errors related to both the positioning errors and tilt misalignments of the length gauge. In addition, a measurement uncertainty of the developed system has been systematically investigated to confirm its feasibility on the mirror profile measurements. The measured results were finally fed back to the mirror profile fabrication so that the profile error could be reduced to less than 5 μm. Mirror profiles measured on machine before and after compensation machining are also reported.