Support design of the elliptical tertiary mirror of the 4-m JUST telescope (Invited Paper)

The 4-m Shanghai Jiaotong University Spectroscopic Telescope (JUST) is a segmented optical telescope to be sited at the Lenghu Observatory in Qinghai Province, China. The tertiary mirror of the telescope is an elliptical zerodur plano mirror of 1485x1025x160 mm3. A lightweighting scheme to is used to remove up to 60% of the mirror mass. A 12-point Whiffle-tree is used for axial support of the mirror and 4 sets of counter-weight for lateral support, with a central positioning mechanism. The reflecting shape of the mirror is down to 8 nm RMS under gravity in any working direction.