Preliminary structure design and analysis of the Chinese Future Giant Telescope

The Chinese Future Giant Telescope (CFGT) has an aperture of 30 m with primary f-ratio of 1.2. Its primary mirror is segmented with 1020 annular submirrors arranged in 17 concentric annuluses. Each segment has average length and width both of 0.8 m. Apart from a conventional Cassegrain focus, four Nasmyth foci on two double-deck platforms on both sides are fundamental in CFGT. Still, there is a Coude focus provided for joining interferometric array. The comparatively small secondary mirror is 2.74 m in diameter, which will serve active corrections. Following optical system requirement, the preliminary structural configuration of CFGT is considered and presented in this paper, including related design schemes of driving systems, bearing systems and mirror support systems. Special consideration on overcoming dead gravitational and random thermal distortion has been taken into the support structure design of both primary and secondary mirrors. In order to evaluate the structural performance of the design, finite element analyses are performed for assemblies and full model of the CFGT.