Conceptual design of giant steerable science mirror cell assembly for TMT

With the design requirements, we have developed the conceptual design of the GSSM with 18 points whiffletree structure as axial support and 12 points whiffletree structure as lateral support to make sure the mirror surface figure error with SlopeRMS less than 0.89 micro radian. Within the required volume, the mirror cell assembly could meet the lowest resonant frequency requirement with more than 22.5Hz. The interface between mirror cell assembly and cradle of positioner assembly has to meet the principle of kinematic so that the repeatability of installing could be less than 0.025mm in the nominal direction and less than 0.2mm in the long axial direction and short axial direction respectively. We have completed the conceptual design and met the design requirements with CAD model and FEA results. The conceptual design of the cell assembly will be presented in the paper.