Abstract
We study a lightweight x-ray mirror with a carbon fiber reinforced plastic (CFRP) substrate for next-generation x-ray satellites. For tightly nested x-ray mirrors, such as those on the Suzaku and ASTRO-H telescopes, CFRP is the suitable substrate material because it has a higher strength-to-weight ratio and forming flexibility than those of metals. In flat CFRP substrate fabrication, the surface waviness has a root mean square (RMS) of ∼1 μm in the best products. The RMS approximately reaches a value consistent with the RMS of the mold used for the forming. We study the effect of moisture absorption using accelerated aging tests in three environments. The diffusivity of the CFRP substrate at 60°C and at relative humidity of 100% is ∼9.7×10−4 mm2·h−1, and the acceleration rate to the laboratory environment was 180 times higher. We also develop co-curing functional sheets with low water-vapor transmissivity on the CFRP substrate. Co-curing the sheets successfully reduced the moisture absorption rate by 440 times compared to the un-co-cured substrate. Details of the CFRP substrate fabrication and moisture absorption tests are also reported.
Highlights
The design of x-ray telescopes is roughly classified into two types based on the mirror configuration, focusing on high spatial resolution and large effective area
We have developed carbon fiber reinforced plastic (CFRP) x-ray mirror fabrication for a telescope with a tightly nested design
We report the current status of CFRP substrates for x-ray mirrors as well as the results of accelerated moisture absorption tests and our attempt to reduce the speed of moisture absorption by co-curing thin sheets with low water-vapor
Summary
The design of x-ray telescopes is roughly classified into two types based on the mirror configuration, focusing on high spatial resolution and large effective area. Mirrors with large effective areas are formed by nested thin substrates made of aluminum foil and are mounted on Japanese x-ray observatories, such as ASCA,[4] Suzaku,[5] and ASTRO-H.6,7 These telescopes have higher collecting area to weight ratios than other x-ray telescope designs, but the angular resolution of the telescopes is limited to ∼1 arc min. The coating was tested for the mirror body of a ground-based telescope and for reduced moisture absorption.[13] We study the effect of the swelling using accelerated tests on the CFRP substrate in high temperatures and humid air, and we apply the coating to the thin substrate using a functional sheet with a low water-vapor transmissivity. The replication process and the results of the x-ray measurement for the CFRP mirror will be reported in a second publication of detailed studies on the CFRP mirror
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