5 September 2017 Trade-off studies on LiteBIRD reflectors
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Abstract
The LiteBIRD satellite aims at detecting a signature imprinted on the cosmic microwave background (CMB) by the primordial gravitational wave predicted in inflation, which is an exponentially expanding era before the hot big bang. The extraction of such weak spiral polarization patterns requires the precise subtraction of our Galaxy’s foreground emission such as the synchrotron and the dust emission. In order to separate them from the CMB by using their spectral shape differences, LiteBIRD covers a wide range of observing frequencies. The main telescope, Low Frequency Telescope (LFT), covers the CMB peak frequencies as well as the synchrotron emission. Based on the required sizes of optical elements in the LFT, an order of one meter, the telescope will consist of reflectors rather than lenses since the latter is limited in size availabilities of the corresponding materials. The image quality analysis provides the requirements of reflector surface shape errors within 30um rms. The requirement on surface roughness of 2μm rms is determined from the reflectance requirement. Based on these requirements, we have carried out tradeoff studies on materials used for reflectors and their support structures. One possibility is to athermalize with aluminum, with the expected thermal contract of 0.4% from room temperature to 4-10 K. Another possibility is CFRP with cyanate resin, which is lighter and has negligibly small thermal contraction. For the reflector surface shape measurements including in low temperature, photogrammetry is a strong candidate with suitable accuracy and dynamic range of measurements.
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Hajime Sugai, Hajime Sugai, Tomotake Matsumura, Tomotake Matsumura, Junichi Suzuki, Junichi Suzuki, Muneyoshi Maki, Muneyoshi Maki, Mitsugu Hosumi, Mitsugu Hosumi, Masashi Hazumi, Masashi Hazumi, Nobuhiko Katayama, Nobuhiko Katayama, Shin Utsunomiya, Shin Utsunomiya, Shingo Kashima, Shingo Kashima, Yuki Sakurai, Yuki Sakurai, Hiroaki Imada, Hiroaki Imada, Hirokazu Ishino, Hirokazu Ishino, Takenori Fujii, Takenori Fujii, "Trade-off studies on LiteBIRD reflectors", Proc. SPIE 10372, Material Technologies and Applications to Optics, Structures, Components, and Sub-Systems III, 103720I (5 September 2017); doi: 10.1117/12.2273765; https://doi.org/10.1117/12.2273765
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