Radiation resistance of physical properties of low CTE ceramics and glass in high-dose-rate environments

This study examines optical materials for use in a geostationary Earth observation satellite. Cordierite ceramics are promising materials for mirror substrates because they have excellent physical properties such as a high elastic modulus, low bulk density, high thermal conductivity, and low coefficient of thermal expansion (CTE). Since cordierite ceramics have not been used in a space equipment, the resistances of their physical and optical properties to space environments are unknown and must be evaluated. Long-term exposure to radiation in space may change physical properties of materials that could degrade telescope performance. Changes in a parameter can also be used to analyze the performance of these mirrors. Therefore, the authors tested two cordierite ceramics, and three traditional glasses for comparison. Irradiation used an electron beam of 10 MeV to apply a dose of about 7 MGy, which corresponds to a total cumulative dose received over 20 years by an observation satellite in a geostationary Earth orbit (GEO). The elastic modulus did not change significantly in any material, and the CTEs of the two glass materials at around room temperature increased significantly after irradiation. This CTE deterioration may have been induced by the excessively accelerated test conditions, so the dose-rate dependence of the deterioration was also evaluated by gamma ray irradiation. Although the dose rate under the gamma ray irradiation was the three orders of magnitude lower than that under electron beam irradiation, changes in the CTEs of the two glass materials were measured.