Next generation space telescopes, which are currently being developed in the US and Europe, require large-scale lightweight
reflectors with high specific strength, high specific stiffness, low CTE, and high thermal conductivity. To meet
budget constraints, they also require materials that produce surfaces suitable for polishing without expensive overcoatings.
HB-Cesic® - a European and Japanese trademark of ECM - is a Hybrid Carbon-Fiber Reinforced SiC composite
developed jointly by ECM and MELCO to meet these challenges. The material's mechanical performance, such as
stiffness, bending strength, and fracture toughness are significantly improved compared to the classic ECM Cesic®
material (type MF). Thermal expansion and thermal conductivity of HB-Cesic® at cryogenic temperatures are now
partly established; and excellent performance for large future space mirrors and structures are expected.
This paper will present the whole manufacturing process of such a space mirror starting from the raw material
preparation until the polishing of the optic including cryo testing .
The letters "HB" in HB-Cesic® stand for "hybrid" to indicate that the C/C raw material is composed of a mixture of
different types of chopped, short carbon-fibers.
During the past several years, ECM carried out a large trade-off project with the objective of comparing CTEmeasurements
of samples of our Cesic® MF ceramic material performed by laboratories in Europe, USA, and Japan.
Our focus was on CTE measurements in the cryo-environment down to less than 20 K.
From past experience, we realized that we needed to pay particular attention to making the samples sufficiently large to
obtain realistic measurement results that relate to actual applications, especially for temperatures below that of LN2.
Thus, we made the samples as large as allowed by the size limitations of the test equipment at the different laboratories,
namely, from 15 mm to 250 mm in length.
The scatter in the test data obtained by the different laboratories was so large that the results were unreliable and not very
useful, which we interpreted to be principally due to the large length range of the samples.
Based on these results, we selected Mitsubishi Electric Corporation (MELCO), Japan, for follow-up cryo-measurements
because they were able to test 250-mm long samples down to < 10 K. More recently MELCO enlarged their cryo-test
equipment to sample sizes as large as 500 mm and with the rather high measurement accuracy of 0.1 ppm/K.
In this paper we present the CTE measurement data obtained by the different laboratories and describe the new cryo-test
facility at MELCO.
Next generation space telescopes, which are currently being developed in the US and Europe, require large-scale light-weight
reflectors with high specific strength, high specific stiffness, low CTE, and high thermal conductivity. To meet
budget constraints, they also require materials that produce surfaces suitable for polishing without expensive over-coatings.
HB-Cesic - a European and Japanese trademark of ECM - is a Hybrid Carbon-Fiber Reinforced SiC composite
developed jointly by ECM and MELCO to meet these challenges. The material's mechanical performance, such as
stiffness, bending strength, and fracture toughness are significantly improved compared to the classic ECM Cesic
material (type MF). Thermal expansion and thermal conductivity of HB-Cesic at cryogenic temperatures are now partly
established; and excellent performance for large future space mirrors and structures are expected.
This paper presents the design and manufacturing of an 800-mm mirror for space application, starting with the C/C raw
material preparation to the finishing of the components, including the polishing of the mirror.
The letters "HB" in HB-Cesic stand for "hybrid" to indicate that the C/C raw material is composed of a mixture of
different types of chopped, short carbon-fibers.
There is a growing demand in recent years for lightweight structures in aircraft systems from the viewpoints of energy
and cost savings. The authors have continued development of the Highly Reliable Advanced Grid Structure (HRAGS)
for aircraft structure. HRAGS is provided with health monitoring functions that make use of Fiber Bragg Grating (FBG)
sensors in advanced grid structures. To apply HRAGS technology to aircraft structures, a full-scale demonstrator
visualizing the actual aircraft structure needs to be built and evaluated so that the effectiveness of the technology can be
validated. So the authors selected the wing tip as the candidate structural member and proceeded to design and build a
demonstrator. A box-structure was adopted as the structure for the wing-tip demonstrator, and HRAGS panels were used
as the skin panels on the upper and lower surfaces of the structure. The demonstrator was designed using about 600 FBG
sensors using a panel size of 1 x 2 m. By using the demonstrator, damage detection functions of HRAGS system were
verified analytically. The results of the design and evaluation of the demonstrator are reported here.
One of the key technologies for next generation space telescopes requiring large-scale reflectors are light-weight
materials having high specific strength, high specific stiffness, low coefficient of thermal expansion and high coefficient
of thermal conductivity. Several candidates, such as fused silica, beryllium, silicon carbide and carbon fiber reinforced
composites, have been evaluated.
An example of the latter material is a Hybrid Carbon-Fiber Reinforced SiC composite or HB-Cesic - a trademark of
ECM - which has been developed by ECM and MELCO to meet the stringent space telescope requirements. Mechanical
performance, such as stiffness, bending strength and fracture toughness, were significantly improved using HB-Cesic
compared to our classic Cesic material. Thermal expansion and thermal conductivity of HB-Cesic at cryogenic
temperatures are now partly established and excellent performance for large future space mirrors and structures are
expected. In this paper we will report on the current status of development of HB-Cesic and describe the first successful
applications made with this new improved material.
There is a growing demand for lightweight structures in aircraft systems for energy and cost savings. The authors have
therefore continued development of the Highly Reliable Advanced Grid Structure (HRAGS) with the aim of application
of the same to aircraft. HRAGS is provided with health monitoring functions that make use of Fiber Bragg Grating
(FBG) sensors in advanced grid structures, which have been the focus of attention in recent years as lightweight
structures. It is a new lightweight structural concept that enables lighter weight to be obtained while maintaining high
reliability.
This report describes the tests and evaluation of the Proto System conducted to verify experimentally the concept of the
highly reliable advanced grid structure. The Proto System consists of a skin panel embedded with 29 FBG sensors and a
wavelength detection system. The artificial damage to the skin panel of the specimen was successfully detected by
comparing the strain distributions before and after the introduction of the damage measured by FBG sensors. Next, the
application of HRAGS to the wing tip was studied. The results of the studies above are reported here.
In this research, the authors target on the construction of structural health monitoring system of Advanced Grid Structure (AGS) made of Carbon fiber reinforced plastic (CFRP). AGS has often been applied to aerospace structures because of the following advantages: (1) Since ribs carry only axial forces, the weakness in the transverse direction of the CFRP unidirectional laminates is negligible. (2) AGS has damage tolerance because the fracture of a rib hardly affects other ribs, namely AGS is a fail-safe structure. In this research, in order to detect existence and regions of rib fractures in AGS, we embedded multiplexed fiber Bragg grating (FBG) sensors into AGS in rib longitudinal directions for measurement of strains. Monitoring of the change in rib longitudinal strains is the most effective SHM system for AGS. In order to confirm our proposal, we carried out following discussions. First, we analytically revealed that the change in rib longitudinal strains was the most sensitive signal for damage detection because of AGS's structural redundancy. Then, we introduced a statistical outlier analysis technique into the SHM system for damage recognition. Finally, we established AGS with the SHM system and verified experimentally. The result of the test showed that damage existence and regions in AGS could be detected with the proposed SHM system.
There is a growing demand for lightweight structures in aircraft systems for realizing energy and cost savings. The authors are developing a new lightweight grid structure for aircraft applications equipped with a health monitoring system utilizing fiber Bragg grating (FBG) sensors. The grid structure has a very simple path for stress, which is easily detected by FBG sensors embedded in the ribs. In this research, the difference in the strain distributions before and after damage to the grid structure was evaluated analytically, and a damage detection method was established. The correspondence between damage detection ability and damage tolerance design strength was clarified. Furthermore, the damage tolerance design method was established based on the evaluation of residual strength corresponding to the detected damage level of rib. Next, the prototype of a highly reliable grid structure embedded with FBG sensors was manufactured, and the damage detection ability was experimentally verified. The panel size of the specimen was 525 x 550 mm and 29 FBG sensors were embedded at the center of the panel. Load was applied on the grid panel, and the strain distribution was measured by the multipoint FBG sensors. The artificial damage introduced in one rib of the specimen and the position of the damage, were successfully detected by comparing the strain distributions before and after the introduction of the damage.
One of the key technologies for next generation space telescope with a large-scale reflector is a material having high specific strength, high specific stiffness, low coefficient of thermal expansion and high coefficient of thermal conductivity. Several candidates such as fused silica, beryllium, silicon carbide and carbon fiber reinforced composites have been evaluated. Pitch-based carbon fiber reinforced SiC composites were developed for the SPICA space telescope mirror to comply with such requirements. Mechanical performance such as bending stiffness, bending strength and fracture toughness was significantly improved. Evaluation procedures of thermal expansion and thermal conductivity behavior at cryogenic temperatures (as low as 4.5K) were established and excellent performance for the SPICA mirror was demonstrated.
Grid structures are the structures made of the trusses consisting of simple ribs. Especially, the structure which uses carbon fiber reinforced plastic (CFRP) unidirectional composites as ribs is called advanced grid structures (AGS). Highly Reliable Advanced Grid Structure (HRAGS) is one of the AGS in which fiber Bragg grating (FBG) sensors are embedded in the longitudinal direction of the ribs in order to detect various damages that appear in the composite grid structures. In this research, the authors tried to identify the damage location in AGS from the structural strain distribution measured by FBG sensors embedded in all ribs. When some damages appear in the AGS, the structural strain distribution in the AGS changes accordingly. Considering the tendency of change, the damage location was identified. At first, FBG sensors were embedded into AGS and three point bending test was examined. The result showed that these embedded sensors could detect the strains applied to the corresponding ribs. Then, low velocity impact test was carried out, which revealed that only fiber breakage was appeared in the AGS. Moreover, three types of models for finite element analysis (FEA) were proposed and compared with the experimental result. According to the comparison, the authors selected beam element model (BEM) for damage-location identification in this research. Furthermore, strain distributions in the structure including damages were calculated with this model. The result proved that the identification of damage location could be realized.
The authors have been developing a new lightweight composite grid structure equipped with a health monitoring system utilizing FBG (Fiber Bragg Grating) sensors for aircraft applications. A grid structure, comprising multiple interconnected ribs in a truss-like arrangement, has a very simple path of stress, which is easily detected with FBG sensors embedded in the ribs.
In this study, manufacturing technology for embedding optical fibers into the grid structure was studied, in order to enable an embedded multi-point FBG sensor network. A total of 29 FBG sensors were embedded in a 525 x 550 mm test panel. A third test panel was also fabricated to evaluate effect of steering the optical fiber through the grid panel nodes. The strain data obtained from embedded FBG sensors were compared to ones from conventional strain gages in several loading conditions, which showed very good accordance. An appropriate arrangement of the grating wavelength of the embedded FBG sensors was also studied to show the feasibility a new lightweight composite grid structure with an excellent health monitoring system.
We report the surface structure and roughness of the mirrors made of carbon fiber reinforced silicon carbide (C/SiC) composite improved for the SPICA (Space Infrared telescope for Cosmology and Astrophysics) mission. The improved C/SiC is a candidate of material for the SPICA light weight mirrors because of its superior properties: high toughness, high stiffness, small thermal deformation, feasibility to make large single dish mirror, low cost, and short term for production. The surface of the bare C/SiC composite consists of carbon fiber, silicon carbide and silicon, each of which has different hardness, so it is difficult to polish this surface smoothly. Our improved polishing technique achieved the surface roughness of better than 20nm RMS for the C/SiC composite flat mirror, which satisfies the requirement of the SPICA mission. For curved bare surface of the C/SiC mirror, the roughness is larger than 30 nm and now under improving. The Change of Bidirectional reflectance distribution function (BRDF) of the bare C/SiC composite at cryogenic temperature was measured with 632.8nm lasar. No significant difference was found between the BRDFs at 95K and that at room temperature. In order to improve surface roughness further, we are planning to apply the SiSiC slurry coating on the surface of the improved C/SiC composite. This combination can realize the surface roughness well enough to be applied even for optical telescopes.
Future large aperture telescope projects will require very lightweight mirrors that can be produced at significantly lower cost and faster production times than currently possible. Tailorable, low thermal expansion composite materials offer an attractive path to achieve these goals. Application of carbon/carbon composites is particularly attractive as these materials do not exhibit the moisture-absorption-related expansion problems observed in typical resin matrix composites. The National Astronomical Observatory of Japan and Mitsubishi Electric Corporation are collaborating to develop materials and surface finishing technologies to enable future carbon/carbon composite mirror applications. Material processing techniques for improved substrate surface finish have been developed. An innovative surface finish approach involving high precision machining of a metal layer applied to the mirror surface has also been developed. As a result, 150mm diameter C/C spherical mirror with honeycomb sandwich structure was successfully demonstrated.
One of the key technologies for next generation space telescope with a large-scale reflector is a material having high specific strength, high specific stiffness, low coefficient of thermal expansion and high coefficient of thermal conductivity. Several candidates such as fused silica, beryllium, silicon carbide and carbon fiber reinforced composites have been evaluated. Pitch-based carbon fiber reinforced SiC composites were developed for the SPICA space telescope mirror to comply with such requirements. Mechanical performance such as bending stiffness, bending strength and fracture toughness was significantly improved. Evaluation procedures of thermal expansion and thermal conductivity behavior at cryogenic temperatures (as low as 4.5K) were established and excellent performance for the SPICA mirror was demonstrated.
Building on our successful production of a world-class dimensionally stable composite optical bench structure for the SOLAR-B space telescope, Mitsubishi Electric is continuing to develop high performance lightweight composites for optical structures including mirrors. A key feature of composite materials is the ability to design the material to optimally meet the application requirements. Thus, various materials with individual characteristics are under development, each providing significant improvement over the state of the art.
Recent satellites, growing in size and electrical power capacity, require sophisticated technology in terms of thermal and structural design. On the other hand, reducing their lifecycle cost while maintaining their reliability remains a definite necessity. From this point of view, a health monitoring system, designed to monitor the thermal and structural condition of a satellite during all its life stages, is expected to be a very useful tool. The authors are developing a health monitoring system for satellites utilizing a FBG (fiber Bragg grating) sensor. This paper first reports on a newly developed optical fiber connector that is used to install FBG sensors in satellite structures. Then, the assessment of a FBG sensor system in a space environment simulated in a thermal vacuum chamber is described. Finally, the results of an experimental study are presented in which damage due to thermal stress, that is typical in satellite structure, is detected by investigating the reflection spectrum from the embedded FBG sensor.
Although there have been many researches concerning health monitoring system in the aerospace field, most of such researches relate to aircraft; there are only few that relate to satellite structures. This research first points out merit of the health monitoring system. The health monitoring system usually utilizes optical fiber sensor of which the diameter is 125 micrometer. However, such fiber sensors tend to be perceived as obstacles within the structure, which affects the soundness of the structure. This is especially the case in satellite structure, which utilizes especially thin composite laminates. In view of this problem, this study utilizes small diameter optical fiber, which is less likely to affect the soundness of the structure. The optical fiber is 40 micrometer in cladding diameter, and is embedded in the composite laminate structure. The structure and the optical fiber have been visually observed. Also, tensile test has been conducted on the structure. The result of the study indicates that the small diameter optical fiber can be embedded in the structure without affecting the soundness of the structure. The study further found that compressive destruction of a face sheet of a honeycomb sandwich panel having thin face sheets can be detected by utilizing this optical fiber.
This paper reports on the newly developed graphite-cyanate composite pipes for high-precision space optics such as the Solar-B optical telescope. Fundamental mechanical, thermal, and hygroscopic properties of unidirectional graphite- cyanate laminates were evaluated, first. The orientation of fibers in the pipe was designed to minimize longitudinal thermal deformation. Model pipes were fabricated based on the design, and have conducted a series of measurements to evaluate the thermal expansion behavior, the hygroscopic performance, the thermal conductivity, and the long-term stability. Excellent performance of the pipe was successfully verified and the material was found to be the most promising candidate for space optics structures.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.