Design and Analysis of the Pentagonal segments for the CGST

Ring-segmented primary mirror is an important option for 8-meter Chinese Giant Solar Telescope (CGST). Conventional hexagonal segment are not suitable for ring segmentation, and petal segment has relatively weak interlocking property. According to the characteristics of ring primary mirror of CGST, a pentagon shaped segment is proposed, which combines the advantages of hexagonal segment and petal segment. Pentagonal segment have a good interlocking property, meanwhile, the primary mirror has a smooth profile and needs fewer types of segment surface shape. Segments arranging in a ring facilitates the adjustment of segments’ radial position relative to primary mirror, this kind of adjustment can compensate for the aberrations caused by conic constant error of segment surface, thereby reducing the requirements of segment fabrication precision.