Kyocera Fine Cordierite (CO720) is a highly promising material for optical mirrors and structural components for space applications due to its excellent properties such as high rigidity, low thermal expansion, and high thermal conductivity. It has already demonstrated its performance in space applications and is begin considered for adoption in many future projects. However, detailed material property data of Fine Cordierite in the space environment has not been made publicly available. Therefore, despite its excellent characteristics, there is a prevailing hesitation to adopt it actively in ongoing or planned projects. In order to address this issue, we have prepared Fine Cordierite test samples and conducted ground tests that simulated the prominent effects of radiation (γ-ray) and atomic oxygen exposure in the space environment and compiled the results into a database. This database includes mechanical properties (bending strength, Young's modulus, and bulk density), thermal properties (coefficient thermal expansion and thermal conductivity), and optical properties (surface accuracy) before and after applying radiation and atomic oxygen exposure. In the presentation, we will discuss the availability and practicability of Fine Cordierite in the space environment, comparing the inspection results of low thermal expansion glass and glass-ceramic conducted at the same time.
Although segmented mirror technology is essential for realizing large telescope, it has potential problems, which should be solved, on the difficulties for aligning independently-supported mirrors and the leakage of thermal radiation from the mirror gaps. To overcome them, we proposed Alignment-Free Gapless Segmented Mirror (AFGSM). AFGSM is an assembled mirror consisting of several mirrors that are mechanically connected to each other with metal bolts. With the tightly fixed mirrors and no gap between mirrors, both the alignment work and the thermal radiation can be reduced. Nakahori et al. (2018) fabricated a 300mm flat AFGSM with 6 ribbed fan-shaped pieces[7]. It uses cordierite CO720, developed by Kyocera. Cordierite is thought to be an alternative choice for developing segmented mirror because it has not only a low coefficient of thermal expansion (0 ± 0.02 ppm/K) but also various advantages on a very small aged deterioration in dimension, a high Young's modulus, and a high thermal conductivity compared to classical low expansion glasses such as ULE or Zerodur[1-6]. The first trial of AFGSM by Nakahori et al., however, could not pass environmental tests: the large surface deformation around the central hole (~ 7.12 um (PV)) and the misalignment between segmented mirrors (~ 0.5um) were occurred after a thermal cycle test and a vibration test[6]. Therefore, we newly proposed an improved AFGSM that has intentionally-produced gaps (< 0.3 mm) to prevent the surface deformation due to the thermal stress generated by the variation of the ambient temperature or the stress release among segmented mirrors by the vibration. The thermal radiation from the small gaps are negligible compared to that of classical segmented mirrors. In this paper, we present the design of improved AFGSM and report results of the optical performances before and after environmental tests.
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