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This paper presents a simple slit-mask-based sensing scheme that can be applied to a robust piston error sensor for segmented optical systems, even in space. Utilizing crossed fringes generated from multiple double-slit pairs, the sensor simultaneously detects multiple points in a segmented optical system in one shot. The experiments tested six pistons of a single-ring segmented mirror. The results showed measurement stability better than 15 nm in the range of 0–5 µm and absolute accuracy of λ / 20 . The theoretical perspective of applicability for larger piston measurement and N-ring segmented systems is also discussed, with simulation results for a two-ring system presented.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2020-11-12, 資料番号: PA2110033000

Moisture absorption and desorption by a matrix resin, and the resulting deformation, exert a critical adverse effect on the shape stability of carbon fiber reinforced plastic (CFRP) space structure...

Dimpling in the composite face sheets of honeycomb sandwich structures due to mismatch in the thermal expansion coefficients of the constituent materials was studied with emphasis on its monitoring and prediction. Strain distributions along optical fibers embedded in the face sheet were monitored during manufacturing. Dimple formation and in-plane strain distributions in the face sheets were studied using finite element analysis, and an analytical model based on the beam theory was constructed to predict the dimple depths from the strain data. A system using twin optical fiber sensors was proposed to accurately measure the dimpling-induced strains. The usability and performance of the system was evaluated using small scale specimens and finally on a more realistic large-scale specimen. The system could measure the strain changes due to dimpling of the face sheets and provided decent prediction of the dimple depth distribution along the sandwich panels.

In geostationary Earth observation satellite system with high-resolution optical system under conceptual study phase developed by Japan Aerospace Exploration Agency (JAXA), one of its main products for users is a video with one fps captured by the telescope and the optical sensor; however, there have been few examples of satellite video with high-rate fps, especially in geostationary satellite. A satellite video has instability of the video sequences caused by an undesired disturbance of the satellite. In this study, we propose the video stabilization method corresponding to various satellite imagery characteristics, using feature point matching and bundle adjustment with eliminating outliers by using RANdom SAmple Consensus (RANSAC). Moreover, we adopt a polynomial approximation to smooth global motions of all video frames. We demonstrate the video stabilization using the experimental video captured by the helicopter. Moreover, the performance test result shows that the proposed method can stabilize the satellite video less than one pixel accuracy. In addition, we discuss various issues specific to a satellite imagery, for example, moving cloud.

This paper presents the results of a conceptual study of an Earth observation system. The new system represents a technical breakthrough in larger telescope aperture, which is necessary to improve spatial resolution. The system makes it possible to improve temporal resolution while maintaining a practical spatial resolution. The observation system was designed to have a latency of 30 minutes from the observation request until data delivery. The mission study emphasized the system's need to immediately assess the situation when a natural disaster occurs and thus reduce human suffering. Due to the required spatial resolution, the optical system needed to have a 3.6 m aperture. A synthetic aperture optical sensor with a segmented primary mirror was investigated and adopted. The segmented-mirror optical system was the most technically challenging and was investigated using a full-scale one-segment prototype to evaluate the feasibility and identify technical risks. This paper presents the tentative design of the sensor and satellite system and reports on the technical demonstration and the proposed geostationary observation system.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2019-08-05, 資料番号: PA2010019000

Wavefront compensation techniques that do not require wavefront sensors are demanded in the on-orbit telescopes on Earth observation satellites. This is especially true for segmented or sparse aperture telescopes that could realize unprecedented high angular resolution. A promising wavefront sensorless approach is the stochastic parallel gradient descent (SPGD) algorithm. The wavefront correction by the SPGD optimization relies only on the intensity data in the acquired image. However, many previous observation targets are point light sources, not the extended ground scenes generally acquired by Earth observation satellites. This paper derives an efficient wavefront control method for imaging systems for the fast SPGD optimization. Wavefront compensation has been demonstrated by experiment on extended objects in single aperture optics, in which a microelectrome- chanical system deformable mirror controls the wavefront. Subsequent numerical simulations are reported for multi-aperture imaging systems. The paper also discuses a method to reduce the computational cost of SPGD optimization.

This paper applies non-reciprocal phase error analysis approach to the fiber optic gyroscope coil made of multi-core fiber and fan-in/fan-out devices to estimate the thermal sensitivity analytically for the first time. In the case of MCF symmetric coils, the relationship between the coil parameters, which can take advantage of MC-FOG in terms of sensitivity to temperature change, is quantitatively clarified in comparison with SMF symmetric coils. In addition, the non-reciprocal phase error of the FIFO element under temperature disturbance is quantitatively clarified. The design policy of the coils proposed from these results is also discussed. And method for connecting cores that minimizes the phase error is proposed. As analytical results, besides lowering the manufacturing cost of the coil due to the shorter fiber length, the multi-core fiber coil was found to further reduce the phase error sensitivity compared to a single-mode coil of equivalent length.

The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is to be launched into orbit around the second Lagrangian point (L2) in the Sun-Earth system. Taking advantage of the thermal environment in L2, a 2.5m-class large IR telescope is cooled below 8K in combination with effective radiant cooling and a mechanical cooling system. SPICA adopts a cryogen-free system to prevent the mission operation lifetime being limited by the amount of cryogen as a refrigerant. Currently, the mechanical cooler system with the feasible solution giving a proper margin is proposed. As a baseline design, 4K / 1K-class Joule-Thomson coolers are used to cool the telescope and thermal interface for Focal Plane Instruments (FPIs). Additionally, two sets of double stage stirling coolers (2STs) are used to cool the telescope shield. In this design, nominal operation of FPIs can be kept when one mechanical cooler is in failure. In this paper, current baseline configuration of the mechanical cooler system and current status of mechanical coolers developments which need to satisfy the specific requirements of SPICA cryogenic system are presented.

A demand for responsive, high-resolution Earth observations is emerging for mitigating the human suffering and damage that follow large-scale disasters. One of the most promising advances is a sophisticated optical imager with a large, 3.6-m satellite-mounted telescope in geostationary orbit. The imager of the proposed space telescope has a segmented mirror and offers a ground sampling distance of better than 10 m and a latency of shorter than 30 minutes. For the imager to realize diffraction-limited performance, deformable mirrors are planned to be installed at the exit pupil of the telescope system. One candidate for the deformable mirrors in segmented telescope is based on a micro-electromechanical system (MEMS) that offers a small actuator pitch, fine step resolution, and excellent hysteretic motion response. This paper presents the wavefront correction of aberrations with a high and low spatial frequency using MEMS deformable mirror on an optical testbed. The expected image quality is also evaluated through numerical simulation.

We present an overview of the cryogenic system of the next-generation infrared observatory mission SPICA. One of the most critical requirements for the SPICA mission is to cool the whole science equipment, including the 2.5 m telescope, to below 8 K to reduce the thermal background and enable unprecedented sensitivity in the mid- and far-infrared region. Another requirement is to cool focal plane instruments to achieve superior sensitivity. We adopt the combination of effective radiative cooling and mechanical cryocoolers to accomplish the thermal requirements for SPICA. The radiative cooling system, which consists of a series of radiative shields, is designed to accommodate the telescope in the vertical configuration. We present thermal model analysis results that comply with the requirements to cool the telescope and focal plane instruments.

Low expansion glass materials have been widely applied to space optics due to their extremely low thermal expansion properties and outstanding mirror polishing characteristics. Meanwhile, the authors have focused on cordierite ceramics as promising candidate materials for space optics because they have higher specific stiffness than the conventional low expansion glass materials, having extremly low coefficient of thermal expansion. In the previous study, we evaluated the material properties of cordierite ceramics and established the key technology for manufacturing lightweight structures and polishing precise mirror surfaces. However, a reliable strength evaluation on a large number of specimens with various surface conditions was insufficient. Because measurement of breakage stress is often susceptible to the method of evaluation, strength characteristics of the brittle material need to be evaluated using many specimens of different surface conditions and the same test standard and methodology. In this research, ring-on-ring test, an ISO standard (ISO EN 1288- 5), was selected as the strength test standard for brittle materials. The Weibull distribution was used as the extreme value distribution for the breakage analysis. The strength distribution of two cordierite ceramics (NEXCERA™ CD107 and CO720) with various surface conditions generated in grinding, polishing, and sintering processes were evaluated and compared with a low thermal expansion glass-ceramic (ZERODUR®). These results showed the cordierite ceramics tend to have higher strength and Weibull parameter than the glass-ceramic under some surface conditions. This paper describes the effect of the surface condition of cordierite ceramics on bending strength.

Earth imaging satellites in geostationary orbit (GEO) are proving to be of great public utility such as disaster prevention and damage mitigation by providing satellite images. JAXA has been conducting research and development of an optical space telescope that allows ground observations with a ground sampling distance less than 10 meters at nadir from GEO. These optical systems must have stable thermo-optical properties even in long-term operation. The authors have been evaluating the resistance of candidate materials to the space environment as part of their investigation into suitable materials for optical system mirrors. Cordierite ceramics have become promising candidate materials in addition to glass materials since their excellent physical properties, such as a high Young’s modulus, low bulk density, high thermal conductivity, and a low coefficient of thermal expansion (CTE). Cordierite ceramics have not been used for space optics, so how their optical properties change in a space environment needs to be evaluated. Cordierite ceramics have not been used for space optics, so how their optical properties change in a space environment needs to be evaluated. The thermooptical properties of mirrors may be degraded by prolonged exposure to the unique conditions in space, such as ultraviolet light, radiation, and atomic oxygen. The authors evaluated the changes in thermo-optical properties due to these environments for three candidate materials. Changes in optical parameters will be used to design optical system. It was confirmed that samples with the SiO2 protective coating showed no significant changes in their resistance to radiation and ultraviolet light, even after irradiation equivalent to twenty years of exposure to the space environment. The thermo-optical properties of silver coated samples without SiO2 protective coatings showed a significant degradation under atomic oxygen, which will be present in low-orbit applications. This is due to the surface formation of silver oxide.

In space cryogenic missions, the thermophysical properties of materials must be studied and measured to establish a highly reliable cooling chain. An Al-alloy is a primary material in cryogenic thermal structural designs and is particularly used for providing high thermal conductance of thermal shields and thermal straps. We measured low-temperature properties (the thermal conductivity and the electrical resistivity) of several Al-alloys and found that A6063 had a lower thermal conductivity than that reported previously. We also found that the Al-alloy ST-60, which has equivalent thermal conductivity as pure aluminum, has higher thermal conductivity than A6061 and A6063, and the material is a good candidate for the space cryogenic design at the temperature range between 4K and 300K. These results are critical for the thermal study of upcoming next-generation space astronomy missions, such as LiteBIRD, SPICA and ATHENA.

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.

As part of leading research for future space missions, we have been conducting a feasibility study on an optical imager system assumed to be mounted on a geostationary satellite for instantaneous Earth observation as needed. The target for ground sampling resolution was less than 10 m from geostationary orbit, and the primary mirror was set to a diameter of 3.5 m based on our previous conceptual study. Moreover, the primary mirror was conceptually designed with cuttingedge technologies such as segmented mirror technology for scalability to larger sizes in the future. The main technical challenges in achieving such a large optical system entailed reducing the primary mirror weight and minimizing dimensional changes in the space environment. Optical material selection was a particularly key consideration in defining the optical system performance. Therefore, a trade-off study was conducted on the selection of materials for the segmented primary mirror. The thermal deformation behaviors of certain low thermal expansion materials as mirror substrates were analytically compared under the assumed unsteady and inhomogeneous thermal conditions in geostationary orbit, in consideration of the deterioration induced by radiation.

Introduction Various hydrogen sensitive gasochromic materials, such as V2O5 [1], MoO3 [2], and Y-Mg [3], have been reported. Among them, Catalyst-loaded WO3 film has been intensively studied to apply to smart windows or optic hydrogen sensors. Although there are many fabrication methods of WO3, sol-gel method [4, 5] is relatively cost-effective, does not need a large-scale apparatus, can be operated easily, and makes it possible to fabricate metal oxide film on complex shape surface. However, the gasochromic performance and its long-term stability sensitively depends on fabrication conditions. In this study, the effect of calcination temperature on crystalline structure, chemical state and hydrogen response of Pt-loaded WO3 (Pt/WO3) fabricated by sol-gel method were evaluated. Then, degradation behaviors were tested under various conditions. Principle In the presence of hydrogen, Pt/WO3 is reduced into tungsten bronze through reactions (1) and (2). Hydrogen molecules dissociate on the surface of catalyst into hydrogen adatoms even at room temperature. Consequently, they react with WO3 through spill-over mechanism. In the recovery process, tungsten bronze is oxidized into initial WO3 by oxygen gas in air following reaction (3). With exposure to hydrogen gas, it is well known that WO3 turns into dark blue color. In this study, transmission loss is focused as a tool for evaluating the hydrogen sensing properties of tested materials. Method WO3 precursor solution was prepared by ion-exchange method. This solution was added to the Pt containing solution which was composed of H2PtCl6, ethanol, and surfactant to make molar ratio of Pt:W about 1:5. After mixing, Pt/WO3 precursor solution was spin-coated onto the quartz glass substrates at 500 rpm for 300 seconds. The film was dried for over 1 hour. Then, the films were calcined for 1 hour in air. Calcination temperature was set in the range from 250°C to 500°C. X-ray diffraction measurements of the hydrogen sensing films were performed with CuKα radiation. The accelerating voltage and current were 40 kV and 45 mA, respectively. Fig. 1 represents the experimental set-up of transmitted light intensity measurement. The fabricated Pt/WO3 film was set into a homemade gas chamber. The one end of fiber cable was coupled with 1.3 µm LED light source. The light transmitting through the film was monitored by the optical power meter. 4 vol.% H2 gas balanced with N2 gas was used as test gas in order to evaluate hydrogen sensitivity of the film. Air as recovery gas was fed into the chamber by using an air compressor. Results and Conclusions The results of XRD measurement of Pt/WO3 films calcined at various temperature are shown in Fig. 2. The broad peak around 21° appears in all results comes from the quartz glass substrate. A sharp peak appeared at 24.0° in the film calcined at 500°C. This peak indicates formation of crystalline WO3. This peak became smaller for film calcined at 400°C and disappeared below 350°C. It indicates that crystal structure of WO3 films calcined below 350°C were amorphous. On the other hand, any peak related to Pt did not appeared. It is surmised that Pt exists in the form of microcrystalline and is well dispersed in the WO3 film. Fig. 3 represents the optical transmittance changes of the fabricated Pt/WO3 films calcined at various temperature with exposure to hydrogen containing gas. The transmitted light intensity sensitively responded to hydrogen gas and immediately reached steady states. The recovery reaction by air readily proceeded. Although the sensitivity increased with increasing calcination temperature, the response speed became slower. It would be closely related to amount of Pt° formed as a result of decomposition reaction of H2PtCl6. In order to evaluate long-term stability of Pt/WO3 film in severe condition, the effect of sodium addition to Pt/WO3 film was tested. In this experiment, Pt/WO3 coated substrate covered with small NaCl salt particles was calcined at 500°C in air at 500°C for 1 hours. Fig. 4 represents the result of hydrogen sensing test of Na-doped Pt/WO3 film. No variation in optical transmittance was observed. XPS studies suggested that catalyst-poisoning compounds generated and therefore gasochromic property of the film was considerably degraded. References [1] Y.K. Ho, C.C. Chang, D.H. Wei, C.L. Dong, C.L. Chen, J.L. Chen, W.L. Jang, C.C. Hsu, T.S. Chan, Krishna Kumar, and M.K. Wu, Characterization of gasochromic vanadium oxides films by X-ray absorption spectroscopy, Thin Solid Films 544 (2013) 461-465. [2] Shankara S. Kalanur, Il-Han Yoo, and Hyungtak Seo, Pd on MoO3 nanoplates as small-polaron-resonant eye-readable gasochromic and electrical hydrogen sensor, Sensors and Actuators B: Chemical 247 (2017) 357-365. [3] Tsveta Radeva, Peter Ngene, Martin Slamen, Ruud Westerwaal, Herman Schreuders, and Bernard Dam, Highly sensitive and selective visual hydrogen detectors based on YxMg1-x thin films, Sensors and Actuators B: Chemical 203 (2014) 745-751. [4] Abdelhamid Boudiba, Chao Zhang, Polona Umek, Carla Bittencourt, Rony Snyders, Marie-Georges Olivier, and Marc Debliquy, Sensitive and rapid hydrogen sensors based on Pd-WO3 thick films with different morphologies, International Journal of Hydrogen Energy 38 (2013) 2565-2577. [5] N. Matsuyama, S. Okazaki, H. Nakagawa, H. Sone, and K. Fukuda, Response kinetics of a fiber-optic gas sensor using Pt/WO3 thin film to hydrogen, Thin Solid Films 517 (2009) 4650-4653. Figure 1

In recent years, JAXA has been conducting a technical survey for a geostationary Earth observation satellite using a 3.5 m diameter aperture with a segmented primary mirror. One of the problems associated with such a large optical observing satellite is a reduction in image quality due to thermal deformation of the optical elements and the metering structure. In this paper, we present our first conceptual structural design and thermal analysis of that design. We also propose a solar light incident avoidance maneuver for this satellite and show the validity of that maneuver.

A feasibility study was conducted for an optical imager system assumed to be mounted on a geostationary orbit satellite for Earth observation. The targeted spatial resolution was less than 10 meters for panchromatic mode at nadir observation conditions, and the observation area was assumed to 100 × 100 square kilometers. The optical system was designed based on a Korsch three mirror anastigmat; the primary mirror was 3.5 meters in diameter, and the focal length was approximately 45 meters. The worst wavefront error was estimated at less than 0.017 λrms in the field of view. As the next step, the primary mirror was segmented, and a trade-off study was conducted on two types of segmented mirror configurations. The optical performance of each configuration was compared in terms of PSF and MTF. Moreover, the deterioration of optical performance due to the misalignment and distortion of the segmented mirror was discussed and numerically estimated by using the Monte Carlo method. The sensitivity of the wavefront error was consequently estimated for the segmented mirror assembly.

We present an overview of the thermal and mechanical design of the Payload Module (PLM) of the next- generation infrared astronomy mission Space Infrared Telescope for Cosmology and Astrophysics (SPICA). The primary design goal of PLM is to cool the whole science assembly including a 2.5 m telescope and focal-plane instruments below 8 K. SPICA is thereby expected to have very low background conditions so that it can achieve unprecedented sensitivity in the mid- and far-infrared. PLM also provides the instruments with the 4.8 K and 1.8 K stages to cool their detectors. The SPICA cryogenic system combines passive, effective radiative cooling by multiple thermal shields and active cooling by a series of mechanical cryocoolers. The mechanical cryocoolers are required to provide 40 mW cooling power at 4.8 K and 10 mW at 1.8 K at End-of-Life (EoL). End-to-end performance of the SPICA cryocooler-chain from 300 K to 50 mK was demonstrated under the framework of the ESA CryoChain Core Technology Program (CC-CTP). In this paper, we focus on the recent progress of the thermal and mechanical design of SPICA PLM which is based on the SPICA mission proposal to ESA.

Cordierite ceramics offer several interesting advantages over traditional glass materials for ultra-lightweight and thermally-stable space optics. The authors have conducted a research and development activity to establish a technology for manufacturing lightweight cordierite mirrors for next-generation space telescopes. In this activity, a 0.7-m spherical cordierite mirror was manufactured as a mock-up. The mirror substrate was formed to a lightweight rib structure using a near net shape forming process. The rib pattern was designed assuming a hexagonalshaped mirror segment, and the original outer shape was circular for an easy polishing process before outline machining. The weight was 21.3 kg with the original circular shape, but will be reduced to 12.3 kg (at areal density of 38.5 kg/m 2 ) by processing it into the hexagonal outline. The surface figure accuracy was 154 nm RMS (root mean square). As the outer shape will then be processed to become hexagonal, there was no need to further improve the accuracy. The prototype of a 0.3-m aspherical cordierite mirror was also manufactured with more difficulty. This mirror was parabolic in shape, assuming the primary mirror of a Cassegrain telescope, and its substrate was further reduced in weight. Thus, a weight of 1.91 kg was achieved (at areal density of 24.6 kg/m 2 ), and the surface figure accuracy reached 35 nm RMS. As a result of these prototyping efforts, cordierite mirrors are expected to be applied in space optics that require extremely high observation performance, combined with large-size, ultra-lightweight, and high-precision features.

Indentation loading or low-velocity impacts on foam core sandwich structures can leave only barely visible damage on the face sheets while causing notable damage in the core due to the thin face sheets and relatively weak core. In practical applications, the measurement and damage detection can also be notably affected by environmental conditions and relaxation of the foam core. To detect the damages, a Rayleigh-scattering-based fiber optic strain monitoring system with high spatial resolution was applied to foam core sandwich structures. Damage detection ability of the system was therefore tested by indentation tests on sandwich beam and panel specimens while also considering the aforementioned effects. Finite element analysis verified by the measurements was used to provide a method to estimate the damaged core area from the measured strain data. Finally, the monitoring ability of the system was demonstrated by low-velocity impact tests on a large scale sandwich panel. The used system provided detailed strain data during and after indentation and impact tests. Due to the high resolution of the system, the damage location and size could be estimated from the obtained strain data even when barely visible dent remained on the face sheet, thus demonstrating the damage detection ability even at various environmental conditions and after relaxation of the foam core.

A highly sensitive hydrogen gas sensor based on a fiber Bragg grating (FBG) has been developed. Various potential hydrogen sensor materials were screened by assessing the catalytic activities of oxide-supported platinum particles prepared by a sol–gel method. It was determined that a Pt/SiO2 film was the most appropriate sensor material; exposure of this film to 4 vol% H2 in humid air for 30 s at room temperature produced a temperature change of 65 K. In addition, the Pt/SiO2 was able to respond to a concentration as low as 0.1 vol% H2 in dry air. Two types of sensor structures were fabricated and evaluated. The device incorporating a quartz glass substrate covered with the sensor film on one side was able to detect 0.4 vol% H2 in dry air at room temperature with a response time of approximately 25 min. The other device, in which the sensor film was immobilized on the periphery of the FBG section, exhibited rapid response to 0.6 vol% H2 within 20 s.

Thermal strain significantly affects stability of fiber optic gyroscope (FOG) performance. This study investigates thermal strain development in a lightweight carbon fiber-reinforced plastic (CFRP) FOG under thermal vacuum condition simulating space environment. First, we measure thermal strain distribution along an optical fiber in a CFRP FOG using a Brillouin-based high-spatial resolution system. The key strain profile is clarified and the strain development is simulated using finite element analysis (FEA) to understand the mechanism of the strain development. Several materials for FOG bobbins are then quantitatively compared using experimentally validated FEA from the aspect of the thermal strain and the weight to illustrate the clear advantage of CFRP. Finally, a hybrid concept combining low thermal conductivity polyacrylonitrile-based (PAN-based) CFRP and high stiffness pitch-based CFRP is proposed to minimize the thermal strain with minimal weight., 資料番号: PA1510042000

Optical mirrors for space telescopes, which require high precision and high thermal stability, have commonly been made of glass materials such as ultra low expansion glass (e.g. ULE®) or extremely low expansion glassceramic (e.g. ZERODUR® or CLEARCERAM®). These materials have been well-known for their reliability due to their long history of achievements in many space applications.

The material characteristics of various optical materials that are known to possess a low thermal expansion property were studied for mechanically and thermally ultra-stable optical applications. In this comparative study on material selection, the key mechanical and thermal properties of four potential low thermal expansion ceramics and three conventional low thermal expansion glass were evaluated under exactly the same testing configurations. This paper describes the results of basic material testing and outlines a comparison of material properties between the potential ceramics and conventional glass. The material testing results showed that the elastic modulus and thermal conductivity of cordierite ceramics were one-and-a-half or more times higher than those of conventional low thermal expansion glass, while ensuring the thermal expansion coefficient roughly matching that of compared glass materials. It was therefore revealed that the cordierite ceramics had most favorable physical properties and could be advantageous alternative materials to the conventional low thermal expansion glass for ultra-lightweight and thermally-stable optical applications.

A fiber-optic hydrogen gas sensor based on a shift of Bragg wavelength induced by reaction heat and strain was developed. Platinum-supported tungsten trioxide (Pt/WO3) film which was utilized as hydrogen sensitive material was derived by sol-gel method. In this study, two types of the sensor structures were fabricated and evaluated. The sensor device where fiber Bragg grating (FBG) was fixed on the quartz glass substrate coated with the Pt/WO3 film using adhesive tape showed good sensitivity. It was found that both reduction of WO3 and oxidation of tungsten bronze were exothermic reaction. The heat generated by the oxidation process was considerably larger than that of reduction. The response behavior of the other type FBG sensing device directly coated with Pt/WO3 film was complicated. It was suggested that there seemed to be competitive response mechanisms related to generation of reaction heat and strain in reduction and oxidation process of sensing film.

We present the new design of the cryogenic system of the next-generation infrared astronomy mission SPICA under the new framework. The new design employs the V-groove design for radiators, making the best use of the Planck heritage. The new design is based on the ESA-JAXA CDF study (NG-CryoIRTel, CDF-152(A)) with a 2 m telescope, and we modified the CDF design to accommodate the 2.5 m telescope to meet the science requirements of SPICA. The basic design concept of the SPICA cryogenic system is to cool the Science Instrument Assembly (SIA, which is the combination of the telescope and focal-plane instruments) below 8K by the combination of the radiative cooling system and mechanical cryocoolers without any cryogen.

The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is a pre-project of JAXA in collaboration with ESA to be launched in the 2020s. The SPICA mission is to be launched into a halo orbit around the second Lagrangian point in the Sun-Earth system, which allows us to use effective radiant cooling in combination with a mechanical cooling system in order to cool a 2.5m-class large IR telescope below 8K. Recently, a new system design in particular thermal structure of the payload module has been studied by considering the technical feasibility of a cryogenic cooled telescope within current constraints of the mission in the CDF (Concurrent Design Facility) study of ESA/ESTEC. Then, the thermal design of the mechanical cooler system, for which the Japanese side is responsible, has been examined based on the CDF study and the feasible solution giving a proper margin has been obtained. As a baseline, 4K / 1K-class Joule-Thomson coolers are used to cool the telescope and thermal interface for Focal Plane Instruments (FPIs). Additionally, two sets of double stirling coolers (2STs) are used to cool the Telescope shield. In this design, nominal operation of FPIs can be kept when one mechanical cooler is in failure.

In response to the maturation of Fiber Optic Gyro technologies, FOGs are being used in various applications. Also in Japan, the demand for FOG is high, and is used in some space applications. In this paper, we introduce examples of Japanese products that apply to space-use. It also describes some efforts for high-grade navigation use in Japan.

This study establishes an innovative composite cure monitoring technique by utilizing a newly developed hybrid Brillouin–Rayleigh optical fiber sensing system. The new system can separately measure strain and temperature distribution with only one optical fiber. This study began by evaluating the measurement accuracy of the hybrid system in a composite application in a step-by-step manner. A single optical fiber was then embedded in a carbon–epoxy specimen, and thermal residual strain development and temperature change were measured during the cooling period of the curing process. The temperature and residual strain obtained by the hybrid Brillouin–Rayleigh system agreed well with the results measured by a conventional sensor set (i.e. fiber Bragg grating sensors and thermocouples). Furthermore, the system could identify a nonuniform thermal residual strain field induced by a nonuniform cure temperature. These results clearly demonstrated that the proposed technique is quite useful for cure monitoring of ...

Strain and temperature measurement, especially in cryogenic environments, was studied using fiber Bragg grating (FBG) sensors for the purpose of the aerospace structural health monitoring. Although the relationship between the applied strain and the Bragg wavelength shift was the same as that at room temperature, the temperature-wavelength relationship became non-linear under cryogenic environment. In order to show the applicability of the sensor in aerospace applications, FBG strain and temperature sensors were embedded in a composite liquid hydrogen tank and measured in the cryogenic and pressurized environment. Encapsulated and small-size temperature sensors were used in this article and the temperature drift of the strain sensor was compensated by using the output of the temperature sensor. It was revealed throughout the experiment that the optical power loss could be critical in the case of existing large temperature difference. The practical solution for this issue was also discussed in this article.

FBG (Fiber Bragg Grating) sensors and optical fibers were embedded into CFRP dry preforms before resin impregnation in VaRTM (Vacuum-assisted Resin Transfer Molding). The embedding location was the interface between the skin and the stringer in a CFRP-stiffened panel. The reflection spectra of the FBG sensors monitored the strain and temperature changes during all the molding processes. The internal residual strains of the CFRP panel could be evaluated during both the curing time and the post-curing time. The temperature changes indicated the differences between the dry preform and the outside of the vacuum bagging. After the molding, four-point bending was applied to the panel for the verification of its structural integrity and the sensor capabilities. The optical fibers were then used for the newly-developed PPP-BOTDA (Pulse-PrePump Brillouin Optical Time Domain Analysis) system. The long-range distributed strain and temperature can be measured by this system, whose spatial resolution is 100 mm. The st...

Optical fibre sensors (OFSs) are promising as tools for damage and structural health monitoring (SHM) of aerospace composite structures. Hence, many researchers have conceived various kinds of OFSs. First, a brief summary of OFSs used for composites is presented. Then, the authors' studies on the small-diameter fibre Bragg grating (FBG) sensors for damage monitoring and SHM of composite structures are described. The authors and Hitachi Cable, Ltd have developed a small-diameter optical fibre and its FBG sensor for embedment inside a lamina of composite laminates without strength reduction. Then, some recent results in the current Structural Integrity Diagnosis and Evaluation of Advanced Composite Structures (ACS-SIDE) project are presented on optical fibre-based SHM for some feasible applications in aerospace composite structures.

Although demand for composite structures rapidly increase due to the advantages in weight, there are few effective assessment techniques to enable the quality control and guarantee the durability. In particular, an invisible microscopic damage detection technology is highly required because damages such as transverse cracks, debondings, or delaminations can lead to the critical failure of the structures. Among many non-destructive evaluation (NDE) methods for composite structures, fiber optic sensors are especially attractive due to the high sensitivity, the lightweight, and the small size. In the current trend of the structural health monitoring technology, fiber Bragg gratings (FBG) sensors are frequently used as strain or temperature sensors, and Brillouin scattering sensors are also often used for a long distance distributed measurement. The Brillouin distributed sensors can measure strain over a distance of 10km while a spatial resolution was limited to 1m. Some novel sensing method is proposed to improve the spatial resolution. The pulse-prepump Brillouin optical time domain analysis (PPP-BOTDA) is one of the latest distributed sensing applications with a cm-order high spatial resolution. The PPP-BOTDA commercial product has the spatial resolution of 10cm, and can measure the strain with a precision of ±25og. This precision, however, can be achieved by using conventional single-mode optical fibers. In our research, small-diameter optical fibers with a cladding diameter of 40om were embedded in the CFRP laminate to avoid the deterioration of the CFRP mechanical properties. Thus, in order to verify the performance of PPP-BOTDA, the distributed strain measurement was conducted with the small-diameter optical fibers embedded in the CFRP laminate.