The technology to manufacture main reflectors of satellite-mounted telescopes using CFRP (Carbon Fiber Reinforced Plastics) was studied. CFRP has high specific rigidity and zero thermal expansion which are required for space telescopes. However, the difficulty of high precision machining of CFRP and the fiber print-through appeared on the surface have prevented CFRP from achieving high accuracy and surface smoothness required for the mirrors. We studied the replica technology and process conditions in detail. The replica technology was improved not only to eliminate the fiber print-through on the CFRP surface, but also to achieve high shape accuracy of the mirrors. At the moment, shape accuracy of 0.6 μm and surface roughness of 3 nm were obtained. The area density of the CFRP mirrors was lighter than one-fifth of the conventional mirrors made of zero expansion glass which are machined for mass reduction. The lightweight and thermally stable CFRP mirrors are expected for reflectors of large aperture, and will improve the resolution of space telescopes.
Near-net dome shaped ZnS window for the infrared region has been investigated using the Spark Plasma Sintering (SPS) technique. A dome with a large diameter of around 140mm and a height of more than 70mm has been successfully developed. The anti-reflection coated dome has optical transmittance of more than 94% and Knoop hardness above 220. We have found that in addition to the use of SPS technique, the refinement of the commercially used ZnS powder and its purification prior to sintering of the ZnS window was effective in enhancing the sintering time and improving the optical and mechanical properties of the window.
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