Lightweight Mirror Research Articles

Robert H. Koch's Work on Lightweight Medium-Aperture Mirrors

After a visit by Peter Waddell from the University of Strathclyde, Glasgow, UK in 1991, Robert H. Koch launched a program at the University of Pennsylvania to build lightweight pneumatic membrane mirrors, initially for balloon flight observations where weight is at a premium. Mirror cells were fabricated from sizes 0.18 m to 1.77 m, and experiments conducted to characterize the mirror figure and stability. Most of the work stopped after Prof. Koch's retirement in 1996 until 2006 when the authors expressed an interest in building an array of medium-aperture portable telescopes. The program restarted in earnest at Gravic, Inc. in Malvern, PA in 2008 with Koch using his extensive observational astronomy experience to guide the fabrication of a fully operational 1.07 m membrane mirror telescope with an optical tube assembly weighing under 45 Kg. Residual wavefront aberrations remediation resulted in Koch and the authors investigating membrane tensioning techniques with different cell designs, active secondary wavefront correction, photometric algorithms for aberrated images, and the use of additional lightweight mirror substrates from the Alt-Az Initiative Group, such as foamed glass. The best result for the lightweight mirrors was a point spread function spot size of several arc seconds. A lightweight 1.6 m cast aluminum cell alt-az telescope was subsequently designed by Koch and the authors for prime focus use.

Path to meter class single crystal silicon (SCSi) space optics

Abstract With the global financial crisis affecting funding for space systems development, customers are calling for lower cost systems. Yet, at the same time, these lower cost systems must have increased thermal response to operational environments and load survivability. We submit that single crystal silicon (SCSi) meets both of these requirements. This paper will highlight some key SCSi material properties, discuss the opportunities that led to the development of McCarter processing methods, and present the latest steps in the manufacturing path of McCarter Mirrors using SCSi, GFB (glass frit bonding) and MSF (McCarter super finish), including the concept drawing of a one meter SCSi lightweight mirror, which together sets up the last step toward a lower cost, high performing one meter SCSi space optic.

快反系统中平面反射镜的轻量化设计

The lightweight structure of a mirror in the Fast-steering Mirror(FSM) System was designed.Due to the high specific stiffness and low thermal deformation rate,SiC was used as a raw material to prepare the mirror.The lightweight mirror with a notched structure was supported by three points on the back.Several lightweight structures were analyzed by finite element method.The results show that the rigid of mirror increases with the width of rib.When the rib is wide enough,the rigid of mirror increases slightly.The stress and deformation of mirror caused by gravity increases with mirror thickness.Structure parameters of 4 mm rid and 4 mm mirror thickness are confirmed considering current mechanical manufacture process.The lightweight rate of mirror is 55%.The RMS value of mirror measured by Zygo interferometer is less than λ/30,which is in agreement with that of the analysis.

宇宙望遠鏡用C/C複合材料軽量反射鏡の開発

宇宙望遠鏡用C/C複合材料軽量反射鏡の開発

Development of Silicon Carbide Substrates for Aerospace Applications

ABSTRACTPayload and high-tech are important characteristics when the goals are aerospace applications. The development of the technologies associated to these applications has interests that transcend national boundaries and are of strategic importance to the nations. Ultra lightweight mirrors, supports and structures for optical systems are important part of this subject. This paper reports the development of SiC substrates, obtained by pressing, to be applied on embedded precision reflective optics. Different SiC granulometries, having YAG as sintering additive, were processed by: ball milling, drying and deagglomeration, sift, uniaxial and isostatic pressing, and, finally, argon atmosphere sintering at 1900°C. Different porosities were obtained according to the amount of organic material added. Into one side of the samples pellets of organic material were introduced to generate voids to reduce the weight of samples as a whole. The substrates were grinding and polished, looking for a SiC surface having low porosity, as porosity is directly related to light scattering that should be avoided on optical surfaces. Laser surface treatments were applied (using or not SiC barbotine) as a method to improve the surface quality. The samples were characterized by optical and laser confocal microscopy, roughness measurements and mechanical tests. The results are very promissory for future applications.

Integrated modeling for design of lightweight, active mirrors

Lightweight, active, silicon carbide mirrors have the potential to enable larger primary aperture, space-based optical systems, hence improving the resolution and sensitivity of such systems. However, due to the lack of design heritage, the best mirror designs are not yet known. Therefore, an integrated model of the lightweight mirrors is created in order to explore the design space. The model determines the achievable radius of curvature change within wavefront error limits, the peak launch stress, and the mass of a mirror segment. However, designing a mirror to meet any of these individual objectives results in a system that performs poorly in terms of the other objectives. Therefore, a full trade space analysis is run to determine the portions of the design space that best balance the trade-offs between metrics. These results are used to determine designs that perform well with respect to specific missions and can be used for future mirror designs.

Numerical and Experimental Analysis of Light-Weighted Primary Mirror for Cassegrain Telescope

This article reports an approach of light-weighted mirror design and analysis to increase the weight reduction ratio and improve optical performance based on the finite element method and opto-mechanical analysis. The approach is to represent mirror surface deformation derived from finite element analysis (FEA) by Zernike polynomials, such that the impact of deformation on optical system performance can be evaluated by the optical design and analysis program. The experimental modal analysis was also performed to validate the FEA results. The numerical result shows that the light-weighted primary mirror of Cassegrain telescope is obtained by this approach and predicted deformation fulfills the requirements of optical design.

真空反应烧结大尺寸碳化硅反射镜

The optical grade silicon carbide(SiC) ceramic was prepared by reaction sintering from SiC blank,which made by gel-casting method in vacuum furnace. The testing results showed that the structure of RB-SiC was full density,and the mechanical properties of RB-SiC were excellent. The line shrinkage was lower than 0.23%,and the ground surface roughness(RMS) could be better than 3 nm. So the RB-SiC ceramic was fine material for the space-borne large scale light-weight mirror.

30 cm 급 반사경 경량화 최적 설계

Optimization of a 30 cm lightweight mirror was proposed with the best optical performance under various loads of gravity and thermal loads with proper boundary conditions. A pattern for a lightweight mirror was generated based on the best optical performance combined with ease of manufacturing for proper design parameters of physical properties of face sheet, back sheet, rib, and web. Evaluation of the optical performances of a telescope mirror was obtained by using the finite element analysis program, NX I-DEAS. Surface errors, individual aberration terms, such as piston, tilts, focus and other aberrations were calculated by using Zernike polynomials. The proposed telescope mirror meets well the opto-mechanical design consideration of RMS surface error less than 16 nm.

An Investigation to Compare the Numerical Model Between Shell and Solid for Honeycomb Light-Weighted Mirror

This article reports an accurate analysis approach of finite element modeling and optical modeling. It has been used for design and analysis of many opto-mechanical systems such as large telescopes and laser systems. The approach is to represent mirror surface deformation derived from finite element analysis (FEA) by Zernike polynomials, such that the impact of deformation on optical system performance can be evaluated by optical design and analysis program. The methodology of shell-based and solid-based finite element modeling and the comparison of their results have been described in this paper. The result shows that the deformation of the light-weighted mirror designed by this approach fulfills the requirements of optical design. The simulation results of shell based FE model are in good agreement with those of solid based FE model.

Wavefront correction of optical beam for large space mirrors using robust control techniques

For an imaging spacecraft to provide higher resolution imaging capability, the satellite will require larger mirrors. Because of the weight and launch constraints for space-based optics systems, the mirrors will have to be segmented and light-weight, resulting in increased flexibility and lower structural frequencies. Consequently, achieving surface accuracy requirements for high resolution imaging with these large aperture light-weight mirrors become a challenging task. This paper investigates the use of adaptive optics for wavefront sensing and surface control of large segmented mirrors. An H ∞ robust control technique is considered for the control of the adaptive optics system with the reduced number of inputs and outputs using singular value decomposition and Zernike polynomials. The robust controller design with the reduced model is validated with a computer simulation for a full plant in the presence of disturbances.

Cryogenic optical testing of an 800mm lightweight C/SiC composite mirror mounted on a C/SiC optical bench

We tested the optical performance at cryogenic temperatures of an 800 mm diameter lightweight mirror, consisting of carbon-fiber reinforced silicon carbide and with a mass of 11.2 kg. The ceramic composite of the mirror was HB-Cesic, developed by ECM, Germany, and Mitsubishi Electric Corporation, Japan. The test was carried out while the mirror was mounted, via Invar stress relief supports, on a lightweight optical bench also made of HB-Cesic. During the test, both the mirror and the optical bench were cooled to 18 K in a liquid-helium chamber. The test consisted of measuring the mirror's change of surface figure with an interferometer installed outside the cryo-chamber. The cryogenic deformation of the mirror was 110 nm RMS with no significant residual deformation after cooling, which is very promising for the applicability of the HB-Cesic composite to large lightweight cryogenic space optics.

Large aperture telescope for advanced lidar system

The final optical design for a space-borne light detection and ranging (lidar) mission is presented, in response to the European Space Agency "Advanced lidar concepts" proposal for use of a differential absorption lidar system to measure water vapor distribution in atmosphere at 935.5 nm. The telescope adopts a double afocal concept (i.e., four reflections with two mirrors) using a lightweight and large aperture primary mirror. It is derived from a feasibility study that compares several different optical configurations, taking into account parameters such as cost, dimensions, complexity, and technological feasibility. The final telescope optical design is described in detail, highlighting a trade-off with other solutions and its optical tolerances.

104 宇宙望遠鏡光学系用SiC材料の製造品質評価(セラミックス/セラミックス基複合材料(1),ものづくりにおける基礎研究と先端技術の融合)

As a key technology in future earth observation and astronomical missions, a large-scale lightweight mirror constructed of silicon carbide-based material has been studied at JAXA. Silicon carbide was selected as the most promising candidate due to excellent characteristics of high specific stiffness and low CTE. One of the most important technical issues for large-scale ceramic components is quality stability (viz. differing in material property depending on part and processing) that might influence thermal and/or structural reliability due to unforeseen deformation and breakage. In this study, a propositional approach for the quality assurance technique of a practical flight mirror was examined, in which coupon samples extracted from various parts of the surrounding area of a newly manufactured φ800mm mirror were put to evaluation for estimating basic physical characteristics and homogeneity.

Ultra light-weight and high-resolution X-ray mirrors using DRIE and X-ray LIGA techniques for space X-ray telescopes

We are developing novel ultra light-weight and high-resolution X-ray micro pore optics for space X-ray telescopes. In our method, curvilinear micro pore structures are firstly fabricated by silicon deep reactive ion etching (DRIE) or X-ray LIGA processes. Secondly, side walls of the micro structures are smoothed by magnetic field assisted finishing and/or hydrogen annealing techniques for high reflectivity mirrors. Thirdly, to focus parallel X-ray lights from astronomical objects, these structures are elastically or plastically bent into a spherical shape. Fourthly, the bent structures are stacked to form a multi-stage X-ray telescope. In this paper, we report on fabrication and X-ray reflection tests of silicon and nickel X-ray mirrors using the DRIE and LIGA processes, respectively. For the first time, X-ray reflections were confirmed on both of the mirrors. Estimated rms roughnesses were 5 nm and 3 nm for the silicon and nickel mirrors, respectively.

Prototype Design and Evaluation of Lightweight Mirror and Wavelength Selective Filter for Space Solar Power Systems

The large scale SSPS (Space Solar Power System) needs large reflection mirrors for sunlight concentration. To use film mirror in space, the mirror must have lightweight structures and resistive to harsh space environment. The wavelength selective filter to avoid heat is a dielectric multilayer film which has FGM structure. In this article, we will report the development of a lightweight wavelength selective mirror and wavelength selection on the solar light excitation laser.

Shaped silicon wafers obtained by hot plastic deformation: performance evaluation for future astronomical x-ray telescopes

In order to develop lightweight and high angular resolution x-ray mirrors, we have investigated hot plastic deformation of 4 in. silicon (111) wafers. A sample wafer was deformed using hemispherical dies with a curvature radius of 1000 mm. The measured radius of the deformed wafer was 1030 mm, suggesting that further conditioning is indispensable for better shaping. For the first time to our knowledge, x-ray reflection on a deformed wafer was detected at Al K(alpha) 1.49 keV. An estimated surface roughness of <1 nm from the x-ray reflection profile was comparable to that of a bare silicon wafer without deformation. Hence, no significant degradation of the microroughness was seen.

Optical Performance of Metal Plated Contoured Back Lightweight Mirrors

Optical Performance of Metal Plated Contoured Back Lightweight Mirrors

Development of light-weight spherical mirrors for RICH detectors

Glass-coated beryllium and carbon-fiber light-weight spherical mirrors, with radii of curvature of ∼ 2700 mm , have been successfully developed and tested as part of the LHCb RICH experimental programme. The low mass mirror is necessary to minimize the amount of material within the LHCb spectrometer acceptance, with a requirement of less than 2% of a radiation length. Both technologies are suitable for light-weight mirror applications. The R&D and characterization of the mirrors are reported.

Adhesion Analysis of Electroless Ni Coating on SiCp/Al Composite Mirror Substrate

SiC p /Al composite, which has light mass, high thermal conductivity and strength, enhanced specific modulus, compatible coefficient of thermal expansion (CTE), and sufficiently high wear resistance, is considered as a promising material for the space lightweight mirror. In order to improve the polishing properties of the material, electroless Ni plating on SiC p /Al composite surface was carried out. The adhesion of the coating and substrate was also studied by experiments and molecular simulations. The morphologies of the coated layers were inspected by means of scanning electron microscope (SEM). The experimental results demonstrate that the coating is uniform and compact. The assessments of coatings adhesion were made using scratch test, and the critical load L c is more than 100 N. Molecular dynamics (MD) was used to simulate the interactions of the coating and composite, and the calculated interaction energy is 108.4 kJ·mol −1 .