Segmented mirrors are commonly used to construct large-aperture telescopes. We present a methodology for structural analysis and experimental results of an adjustment of a mm- to far-IR range (10 mm to 70 μm) segmented mirror panel to correct its deviation from an optimum paraboloid of rotation. The panel is made of high-modulus carbon fiber–reinforced plastic and has a shape of a 15-deg sector with a 1207 × 390 mm2 reflecting surface area. A system of mechanically operated adjusters for correcting large-scale surface deformations is described. We used our original method to correct fabrication errors and improved the surface shape accuracy from 23.8 to 4.5 μm (RMS values). The method is based on distance-to-target-surface minimization using vector influence functions and arbitrary movements. The results of the long-term panel shape stability monitoring and the effect of cooling the panel down to 77 K are also presented.
Millimetron Space Observatory is a 10-m aperture space telescope that will operate from millimeter to far-infrared wavelength range. To achieve an unprecedented sensitivity, the telescope with segmented primary mirror will be cooled down to a temperature less than 10K and the surface accuracy better than 10 μm will be provided. New materials and stateof- the-art technologies have been brought together to create the high precision and thermally stable primary mirror panels combining increased rigidity and low areal density (less than 9 kg/m2). Carbon fiber reinforced plastic was chosen as a material for the panels. It provides low coefficient of thermal expansion, high stiffness to weight ratio, and manufacturing flexibility. Nevertheless, it has significant drawbacks such as anisotropy, variation of mechanical properties of the ply, and microcracking that raise difficulties in achieving highly accurate and thermally stable design. The paper presents the design of the primary mirror panels and focuses on the most challenging steps of their development process. The main features of manufacturing based on replica technique and results of the numerical and experimental analyses are also discussed.
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