三十米望远镜三镜底支撑的优化设计

Optimization Design of TMT Tertiary Mirror Axial Support

三十米望远镜(TMT)是一台Ritchey-Chrétien(R-C)式的30m口径光学红外望远镜,其三镜为椭圆形平面镜,口径为3.594m×2.568m,重量达到1.8t,三镜系统需要把来自次镜的光折转到望远镜两侧耐氏平台上的一系列科学仪器上,具有跟踪和快速定向功能。三镜支撑系统必须保证镜面面形优于λ/5(波长λ=632.5nm)或者均方根(RMS)斜度小于1μrad。支撑系统包括底支撑系统和侧支撑系统,底支撑系统采用18点Whiffletree结构,通过优化分析,面形RMS值达到118.5nm。针对三镜在支撑结构作用下的面形不能满足设计要求的特点,提出了采用力矩进行校正的方法,使镜面面形满足了设计要求。

Thirty Meter Telescope （TMT） is a 30 m Ritchey-Chretien optical-infrared telescope. It tertiary mirror （TMT M3） is an elliptical flat mirror with the aperture of 3. 594 mX 2. 668 m and weight of 1.8 t. The M3 system reflects the light coming from the secondary mirror system （M2S） to the science instruments that are located on the Nasmyth platforms, and the M3 System must rotate and tilt as the telescope tilts about the elevation axis and tracks astronomical objects across the sky. The M3 support system should support the M3 mirror so that the mirror surface figure will be less than A/5 （wavelength A = 632.5 nm） or root-mean-square （RMS） slope will be less than 1 μrad. The M3 support system includes axial support system and lateral support system. The axial support system uses 18- point whiffletree structure, and after optimization the RMS mirror surface figure achieves 118. 5 nm. When the tertiary mirror surface figure error cannot meet the requirement with the support structure, correct moment is used to corrective the surface figure error.