Performance Prediction of the TMT Tertiary Mirror Support System - art. no. 70184F

The Ritchcy-Chretien (RC) optical design of Thirty Meter Telescope (TMT) calls for a 3.1 in diameter secondary mirror (M2M) and an elliptical tertiary mirror (M3M) of 3.5m alone its major axis and 2.5m along its minor axis. The M3M thin, large, flat, solid elliptical mirror which directs the f/15 beam from the M2M to the multiple instruments oil both Nasmyth platforms. The MW will weigh approximately two metric tons and the mirror support system will maintain the mirror figure at different gravity orientations. A recent reduction of the field of view to 15 arc minutes allows a reduction in the size of the M3M, which in turn requires re-optimization of the mirror support system. The proposed MW optimized Support system consists of 60 tri-axial supports Mounted at the mirror back surface. These tri-axial Supports accommodate motions of M3M in three gravity directions. The print-though RMS surface errors of M3M are 10nm for axial gravity loadings and 1 nm for lateral gravity loadings. The M3 system (M3S) has an active optics (aO) capability to accommodate potential mechanical or thermal errors; its ability to correct low-order aberrations has been analyzed. A Structure function (SF) of the axial gravity Support print-through was calculated.