CFRP is a composite material composed of carbon fiber and resin. CFRP is commonly applied to the aerospace industry which requires lightweight and intensity. Thanks to superior formability of CFRP, we can form shape of Wolter-1 optics, which consists of paraboloid and hyperboloid, to a monolithic substrate. Since the surface roughness of CFRP substrate is a few microns, it is required to make the smooth surface for reflecting X-rays on the CFRP substrate. We have developed a new method of shaping the reflective surface by pasting thin sheet-glass with 50~100 μm thick onto the CFRP substrate. The surface roughness of the thin sheet-glass was measured to about 0.4 nm by Zygo. Our CFRP mirror is a candidate for backup mirrors in the FORCE mission, and are being developed for balloon-borne experiments planned in the near future. Current image quality of our CFRP mirror was measured to be about 60-120 arcsec by illuminating an X-ray pencil beam at the ISAS beam line. In order to achieve a high imaging quality less than 15 arcsec, we will improve the CFRP mirror surface using both the replica method, and an ultra-precision mold processed with a shape error of 0.1 µm or less. The mold will be completed in the summer of 2022. We report on the current status of the development of the CFRP mirrors.
The technology to manufacture main reflectors of satellite-mounted telescopes using CFRP (Carbon Fiber Reinforced Plastics) was studied. CFRP has high specific rigidity and zero thermal expansion which are required for space telescopes. However, the difficulty of high precision machining of CFRP and the fiber print-through appeared on the surface have prevented CFRP from achieving high accuracy and surface smoothness required for the mirrors. We studied the replica technology and process conditions in detail. The replica technology was improved not only to eliminate the fiber print-through on the CFRP surface, but also to achieve high shape accuracy of the mirrors. At the moment, shape accuracy of 0.6 μm and surface roughness of 3 nm were obtained. The area density of the CFRP mirrors was lighter than one-fifth of the conventional mirrors made of zero expansion glass which are machined for mass reduction. The lightweight and thermally stable CFRP mirrors are expected for reflectors of large aperture, and will improve the resolution of space telescopes.
K. Enya, M. Kobayashi, K. Ishibashi, S. Kobayashi, N. Namiki, H. Araki, S. Tazawa, H. Noda, S. Oshigami, S. Kashima, M. Utsunomiya, J. Kimura, K. Touhara, T. Yamawaki, S. Iwamura, N. Fujishiro, Y. Matsumoto, T. Iida, H. Nakagawa, H. Imai, O. Kirino, C. Hatakeyama, T. Yokozawa, Y. Sato, K. Kojima, N. Matsui, K. Tanimoto, M. Fujii, C. Althaus, S. Del Togno, J. Jänchen, B. Borgs, T. Behnke, H. G. Lötzke, R. Kallenbach, K. Lingenauber, H. Hussmann
The Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency to be launched in 2022 will provide an opportunity for a dedicated exploration of the Jovian system including its icy moons. The Ganymede Laser Altimeter (GALA) has been selected as one of the ten payloads of JUICE. GALA will enable unique studies of the topography and shape, tidal and rotational state, and geology of primarily Ganymede but also Europa and Callisto. The GALA project is an ongoing international collaboration led by Germany, together with Switzerland, Spain, and Japan. This paper presents the optical and mechanical design of the focal plane receiver, the Japanese part of GALA.
LiteBIRD is a candidate for JAXA’s strategic large mission to observe the cosmic microwave background (CMB) polarization over the full sky at large angular scales. It is planned to be launched in the 2020s with an H3 launch vehicle for three years of observations at a Sun-Earth Lagrangian point (L2). The concept design has been studied by researchers from Japan, U.S., Canada and Europe during the ISAS Phase-A1. Large scale measurements of the CMB B-mode polarization are known as the best probe to detect primordial gravitational waves. The goal of LiteBIRD is to measure the tensor-to-scalar ratio (r) with precision of r < 0:001. A 3-year full sky survey will be carried out with a low frequency (34 - 161 GHz) telescope (LFT) and a high frequency (89 - 448 GHz) telescope (HFT), which achieve a sensitivity of 2.5 μK-arcmin with an angular resolution 30 arcminutes around 100 GHz. The concept design of LiteBIRD system, payload module (PLM), cryo-structure, LFT and verification plan is described in this paper.
The Lite satellite for the studies of B-mode polarization and Inflation from the cosmic microwave background
(CMB) Radiation Detection (LiteBIRD) is a next generation CMB satellite dedicated to probing the inflationary
universe. It has two telescopes, Low Frequency Telescope (LFT) and High Frequency Telescope (HFT) to cover
wide observational bands from 34 GHz to 448 GHz. In this presentation, we report the optical design and
characterization of the LFT. We have used the CODE-V to obtain the LFT optical design based on a cross-
Dragonian telescope. It is an image-space telecentric system with an F number of 3.5 and 20 x 10 degrees2 field
of view. The main, near and far side lobes at far-field have been calculated by using a combination of HFSS and
GRASP 10. It is revealed that the LFT telescope has good main lobe properties to satisfy the requirements. On
the other hand, the side lobes are affected by the stray light that stems from the triple reflection and the direct
path from feed. In order to avoid the stray light, the way to block these paths is now under study.
KEYWORDS: Space operations, Cryogenics, Radiative energy transfer, Space telescopes, Telescopes, Solar radiation, Cryocoolers, Satellites, Optical properties
The conceptual thermal design of the payload module (PLM) of LiteBIRD utilizing radiative cooling is studied. The thermal environment and structure design of the PLM strongly depend on the precession angle α of the spacecraft. In this study, the geometrical models of the PLM that consist of the sunshield, three layers of Vgrooves, and 5 K shield were designed in the cases of α = 45° , 30° , and 5° . The mission instruments of LiteBIRD are cooled down below 5 K. Therefore, heat transfers down to the 5 K cryogenic part were estimated in each case of α. The radiative heat transfers were calculated by using geometrical models of the PLM. The conductive heat transfers and the active cooling with cryocoolers were considered. We also studied the case that the inner surface of the V-groove is coated by a high-emissivity material.
We present our design and development of a polarization modulator unit (PMU) for LiteBIRD space mission. LiteBIRD is a next generation cosmic microwave background (CMB) polarization satellite to measure the primordial B-mode. The science goal of LiteBIRD is to measure the tensor-to-scalar ratio with the sensitivity of δr < 10-3. The baseline design of LiteBIRD is to employ the PMU based on a continuous rotating half-wave plate (HWP) at a telescope aperture with a diameter of 400 mm. It is an essential for LiteBIRD to achieve the science goal because it significantly reduces detector noise and systematic uncertainties. The LiteBIRD PMU consists of a multi-layered sapphire as a broadband achromatic HWP and a mechanism to continuously rotate it at 88 rpm. The whole system is maintained at below 10K to minimize the thermal emission from the HWP. In this paper, we discuss the current development status of the broadband achromatic HWP and the cryogenic rotation mechanism.
Very lightweight mirror will be required in the near future for both astronomical and earth science/observation missions. Silicon carbide is becoming one of the major materials applied especially to large and/or light space-borne optics, such as Herschel, GAIA, and SPICA. On the other hand, the technology of highly accurate optical measurement of large telescopes, especially in visible wavelength or cryogenic circumstances is also indispensable to realize such space-borne telescopes and hence the successful missions.
We have manufactured a very lightweight Φ=800mm mirror made of carbon reinforced silicon carbide composite that can be used to evaluate the homogeneity of the mirror substrate and to master and establish the ground testing method and techniques by assembling it as the primary mirror into an optical system. All other parts of the optics model are also made of the same material as the primary mirror.
The composite material was assumed to be homogeneous from the mechanical tests of samples cut out from the various areas of the 800mm mirror green-body and the cryogenic optical measurement of the mirror surface deformation of a 160mm sample mirror that is also made from the same green-body as the 800mm mirror.
The circumstance and condition of the optical testing facility has been confirmed to be capable for the highly precise optical measurements of large optical systems of horizontal light axis configuration. Stitching measurement method and the algorithm for analysis of the measurement is also under study.
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.
LiteBIRD is a next generation satellite aiming for the detection of the Cosmic Microwave Background (CMB) B-mode polarization imprinted by the primordial gravitational waves generated in the era of the inflationary universe. The science goal of LiteBIRD is to measure the tensor-to-scaler ratio r with a precision of δr < 10-3♦, offering us a crucial test of the major large-single-field slow-roll inflation models. LiteBIRD is planned to conduct an all sky survey at the sun-earth second Lagrange point (L2) with an angular resolution of about 0.5 degrees to cover the multipole moment range of 2 ≤ ℓ ≤ 200. We use focal plane detector arrays consisting of 2276 superconducting detectors to measure the frequency range from 40 to 400 GHz with the sensitivity of
3.2 μK·arcmin. including the ongoing studies.
We fabricated x-ray mirrors from carbon-fiber-reinforced plastic with a tightly nested design for x-ray satellites, using a replication method for the surfaces. We studied the effects of print-through on the mirror surface as a function of curing temperature. With room temperature curing, the root-mean-square value of the surface error was 0.8 nm. The reflectivity was measured using 8-keV x-rays, and the roughness was calculated as 0.5 nm by model fitting—comparable to that of the ASTRO-H/HXT mirror. We verified the long-term stability of the mirror surface over 6 months. We fabricated Wolter type-I quadrant-shell mirrors with a diameter of 200 mm and performed x-ray measurements at BL20B2 in the SPring-8 synchrotron radiation facility. We obtained reflection images of the mirrors using a 20-keV x-ray spot beam with a slit size of 10×1 mm in the radial and circumferential directions, respectively. The averaged half-power diameter (HPD) of the images in one mirror was 1.2 arc min in the circumferential center of the mirror and 3.0 arc min at the edge. In the spot images with a smaller slit size of 10×0.2 mm, we achieved an HPD of 0.38 arc min in the best case.
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.
Small-JASMINE program (Japan Astrometry Satellite Mission for INfrared Exploration) is one of applicants for JAXA (Japan Aerospace Exploration Agency) space science missions launched by Epsilon Launch Vehicles, and now being reviewed in the Science Committee of ISAS (Institute of Space and Astronautical Science), JAXA. Telescope of 300 mm aperture diameter will focus to the central region of the Milky Way Galactic. The target of Small-JASMINE is to obtain reliable measurements of extremely small stellar motions with the highest accuracy of 10 μ arcseconds and to provide precise distances and velocities of multitudes of stars up to 30,000 light years. Preliminary Structure design of Small- JASMINE has been done and indicates to satisfy all of requirements from the mission requirement, the system requirement, Epsilon Launch conditions and interfaces of the small science satellite standard bus. High margin of weight for the mission allows using all super invar structure that may reduce unforeseen thermal distortion risk especially caused by connection of different materials. Thermal stability of the telescope is a key issue and should be verified in a real model at early stage of the development.
We studies lightweight X-ray mirror with Carbon Fiber Reinforced Plastic (CFRP) substrate for next generation X-ray satellites.
CFRP is suitable material as substrate for thin-foil highly nested X-ray mirrors like telescope of Suzaku, ASTRO-H since it has properties of higher strength-to-weight ratio and flexibility of forming than that of metals.
In the current year we made flat panels for basic research and full/partial shell substrates by quasi-isotropic laminate with 8 ply prepregs, and performed reflector replication based on technique for the HXT mirror.
CFRP (Caron fiber reinforced plastics) have superior properties of high specific elasticity and low thermal expansion for satellite telescope structures. However, difficulties to achieve required surface accuracy and to ensure stability in orbit have discouraged CFRP application as main mirrors. We have developed ultra-light weight and high precision CFRP mirrors of sandwich structures composed of CFRP skins and CFRP cores using a replica technique. Shape accuracy of the demonstrated mirrors of 150 mm in diameter was 0.8 μm RMS (Root Mean Square) and surface roughness was 5 nm RMS as fabricated. Further optimization of fabrication process conditions to improve surface accuracy was studied using flat sandwich panels. Then surface accuracy of the flat CFRP sandwich panels of 150 mm square was improved to flatness of 0.2 μm RMS with surface roughness of 6 nm RMS. The surface accuracy vs. size of trial models indicated high possibility of fabrication of over 1m size mirrors with surface accuracy of 1μm. Feasibility of CFRP mirrors for low temperature applications was examined for JASMINE project as an example. Stability of surface accuracy of CFRP mirrors against temperature and moisture was discussed.
Ultra-lightweight and high-accuracy CFRP (carbon fiber reinforced plastics) mirrors for space telescopes were fabricated
and their feasibility for low temperature applications was demonstrated. The CFRP mirrors were composed of sandwich
panels with CFRP skins and CFRP honeycomb cores. Surface was deposited with epoxy thin layers by using a replica
technique. The surface accuracy of the demonstrate mirrors of 150 mm in diameter was 0.8 μm RMS and the surface
smoothness was improved to 5 nm RMS. Surface accuracy degradation was 0.6μm RMS (root mean square) from
ambient temperature to liquid nitrogen. Surface asperity was classified with respect of their wave intervals and
measurement areas. Surface accuracy and dimensional stability were strictly affected by raw materials and
manufacturing conditions. Surface accuracy was measured at each process on the way of mirror forming. Manufacturing
conditions to depress asperity were discussed.
Ultra-lightweight and high-accuracy CFRP (carbon fiber reinforced plastics) mirrors for space telescopes were fabricated
to demonstrate their feasibility for light wavelength applications. The CTE (coefficient of thermal expansion) of the all-
CFRP sandwich panels was tailored to be smaller than 1×10-7/K. The surface accuracy of mirrors of 150 mm in diameter
was 1.8 um RMS as fabricated and the surface smoothness was improved to 20 nm RMS by using a replica technique.
Moisture expansion was considered the largest in un-predictable surface preciseness errors. The moisture expansion
affected not only homologous shape change but also out-of-plane distortion especially in unsymmetrical compositions.
Dimensional stability due to the moisture expansion was compared with a structural mathematical model.
CFRP (Carbon Fiber Reinforced Plastics) is the ideal material for space based mirror due to its low thermal expansion,
and high specific modulus. To expand the use of CFRP, we investigated the long-term stability of CFRP under humid
environment. CFRP mirror was made as precise as possible by using special class of material and adopting particular
design techniques. Dimensional stability of CFRP mirror was evaluated by nano-scale measurement. The factors which
cause out-of-plane deformation of the mirror is discussed.
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