DEVELOPMENT OF LARGE-APERTURE COOLED LIGHT-WIGHT MIRRORS FOR SATELLITE USE

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We have developed mirrors made of carbon-fiber reinforced plastic (hereafter CFRP) for cooled infrared telescope. The major goal of this research is to establish the method to make CFRP mirrors by replication and we have the following improvements and results.1. We have confirmed that CFRP that has the coefficient of thermal expansion less than 2ppm/K for K150K can be produced.We have also measured the thermal conductivity of CFRP at low temperatures.2. We have tried several methods for replication of CFRP flat mirrors and made CFRP mirrors with the surface roughness less than 10-20mm (rms). We have further improved the roughness by increasing the dispersion of fibers.3. We have also tried epoxy coating to improve the surface roughness and made mirrors with the surface roughness less than a few nm (rms). We have also confirmed the applicability of gold and aluminum coating.4. We have applied the above method to spherical mirrors and confirmed that similar surface qualities can be achieved, We have found that the back structure is needed to improve the surface figure. The thickness of the surface skin is also found to be critical to maintain good figures.5. Based on the above investigations we have established the basic replication method for CFRP mirrors and summarized future improvement possibilities.