Strategies of primary mirror segment fabrication for CFGT

摘要

An extremely large telescope named Chinese Future Giant Telescope (CFGT) has been presented. The primary mirror of CFGT is a 30-meter diameter hyperboloid with a focal ratio F/1.2 and it consists of over one thousand of sector-shaped segments with the size about 1.1-meter in diagonal. Based on the optical design concept and the experience of existing large segmented primary mirror, we explore the segment fabrication and testing issues in this paper. The relationship between external contour, the size and the asphericity of sub-mirror is studied. Two potential segment fabrication approaches for mass-production-scale are discussed. One is the optical replication. The other is stressed-mirror polishing. Both of two processes are tightly combined with several key techniques and devices, the ion-beam figuring, large annular polisher, and the stressed lap. Some preliminary concepts for testing of 1-meter class convex/concave off-axis aspheric surface are discussed.