Space Mirror Research Articles

Micromechanical properties of reaction-bonded silicon carbide using atomic force microscopy and nanoindentation

Reaction-bonded silicon carbide (RB-SiC) ceramics have been produced using advanced technology for the production of space mirrors. Changing the volume content of SiC (from 78 to 93 %) in the ceramic's composition allows for improved the mechanical properties, which is achieved by a combination of the SiC and Si phases properties. In this work, a thorough study of the structure and micromechanical properties of individual SiC and Si phases for RB-SiC ceramics (with a SiC content of 78–93 vol%) was carried out at the micro- and nanolevel using atomic force microscopy and nanoindentation. The studies have shown the crack resistance limit each phase (an important factor for RB-SiC space mirrors) under mechanical loads, after which microcracks appear (sources of further degradation and destruction). The surface morphology, deformation area and crack propagation in each phase after exposure to mechanical load during indentation were studied using atomic force microscopy. Nanomechanical mapping of elastic modulus and microhardness on the surface, analysis of boundaries between phases (SiC and Si), assessment of mutual influence of phases and determination of micromechanical properties were carried out using the nanoindentation method. The fracture toughness KIC was determined using an improved indentation method with visualization of the deformation areas using atomic force microscopy. The highest values of microhardness H, elastic modulus E and fracture toughness KIC on the SiC and Si phases were obtained on a ceramic sample with 93 vol % SiC: for the SiC phase – E=486 GPa, H=35.6 GPa, KIC=5.03 MPa m1/2, for the Si phase – E=205 GPa, H=12.2 GPa, KIC=2.73 MPa m1/2. This study demonstrated the efficiency and possibility of using the atomic force microscopy and nanoindentation to determine the micromechanical properties of ceramics at the micro- and nanolevel.

Topology optimization of a double-sided space mirror based on additive manufacturing of SiC

Topology optimization of a double-sided space mirror based on additive manufacturing of SiC

Application and analysis of landscape recognition based on efficient net for natural scene

One significant assessing criteria of climate change is geometric evolution. The rate of evolution reveals the speed that environment worsens. Advanced space mirror monitors that and generates images timely. However, it might be difficult for human to deal with collected numerous image-related data. In previous research, convolutional neural network is regarded to have specific advantage in resolving image recognition tasks. Hence, a new type of convolutional neural network model is applied to identify different kinds of landscape. Virtually, this model is called Efficient Net which based on landscape recognition dataset with 5 classes of landscapes. The study also introduces the fine-tuning to further improve the performance of the model. To evaluate the model, the precision, recall, F1 score, accuracy and loss are adopted as assessing criteria. The results shows that the model predicts the target dataset to a great extent. However, it has been tested that the class of mountain might not be suitable for predicting because of vague criterion. That is helpful in real-condition geographical applications and environmental governance.

A new method for machining RB-SiC with high efficiency and quality: Laser assisted ultrasonic grinding

Reaction Bonded Silicon carbide (RB-SiC) ceramic is preferred material for space mirrors in aerospace field. However, the high hardness, brittleness and inhomogeneous structure bring great challenges for high quality and efficient machining. In this study, laser ablation assisted ultrasonic grinding (LAAUG) process was proposed. The high efficiency of laser ablation and high quality of ultrasonic grinding were effectively combined. Laser pre-ablation experiments were carried out firstly, and then thermal damage layer was removed through ultrasonic grinding. The results show that RB-SiC ceramics transform into relatively loose and homogeneous ablation products (SiO2 and recrystallized SiC) by laser irradiation. Moreover, it is accompanied by cracks development. Compared with conventional grinding, the maximum reduction of grinding force and surface roughness is 34 % and 13.8 %, respectively. Abrasive grain wear is significantly restrained and the percentage of plasticity removal is improved. This study indicates that LAAUG is feasible and efficient method for machining RB-SiC ceramics.

Fundamental study on optical performance of low-melting-point metal mirrors for space telescopes

The installation of telescopes with larger primary mirrors in outer space is required for the study of the early universe. However, the shipping, assembling and maintenance of the primary mirror are technical challenges. The primary mirror made of low-melting-point metal (LMPM) enables to simplify these procedures. The rotating liquid metal surface is shaped into a parabola and solidified on the site. The technological feasibility depends on the dynamic transformation of the parabolic LMPM mirror and its optical reflectance. The dynamic transformation of LMPM mirror was clarified by means of experiments with liquid gallium (Ga) which has a melting point of 302.91 K. The parabolic shape of solid Ga mirror was produced by the axial rotation and the solidification. The parabolic shape agreed with the theoretical curve obtained by a physical model. The reflectance spectra on the surface of various LMPMs solidified (i.e., Ga, lead (Pb), tin (Sn), bismuth (Bi), lead-bismuth eutectic (Pb-Bi) and Wood’s metal (Bi-Pb-Sn-Cd)) were measured. The reflectance of Ga solidified was approximately 70 % and was not degraded in the near-infrared wavelength due to the favorable optical characteristics. The reflectance both for p-polarized and s-polarized light of Ga solidified was measured by the spectrophotometer with the polarizer at the angle of incidence of 30°, 45°, 60° and 75°. The trend of measured reflectance agreed with theoretical prediction.

Всероссийский студенческий конкурс «Инновационные разработки»

The Department of Engineering Graphics of the RTU MIREA, has been holding the All-Russian Student Competition "Innovative Developments" as part of the All-Russian Student Olympiad in Descriptive Geometry, Engineering and Computer Graphics since 2008. This competition is a stage in the concept of a methodological system for the development of the student's intellectual abilities.
 The article describes the original system for evaluating works at the competition, the principle of forming the jury, the principles for selecting works for the competition. The goals of the competition were announced, namely: approbation and presentation of new ideas, including in the field of graphic disciplines; development of modern information technologies by students; development of cooperation between teams of university departments and production teams. The criteria for comparing past competitions with each other are described, the methodology for assessing the success of the competition, the success of competitions is analyzed by year.
 From 2008 to 2022 inclusive representatives of 24 universities presented 96 works for the competition. The article gives the titles, authors and scientific supervisors of the best projects - winners and prize-winners of competitions who scored 200 or more points, ranked by the points scored for the places taken by the students - participants in the competitions. The geography of participating universities is analyzed, universities are ranked by total achievements. There is a positive trend in the number of works submitted to the competition.
 It is noted that some works became the first step in serious scientific research, for example, “Spatial fractals” by L.A. Zhikharev, later became the topic of his dissertation, “Reflections from curvilinear mirrors in space and on a plane” by O.S. Suntsov are currently one of the registered areas of research at the department.

A demisability analysis based on materials properties for space telescope mirrors

The increasing menace of space debris, stimulated by the current explosion of the small satellite commercial sector, urges the implementation of effective strategies for debris mitigation. Among these, substituting critical materials with more demisable ones represents an appropriate action to reduce the survivability of the component. Yet, improvements in demisability are often associated to performance penalties. In this contribution, the important topic of design for demise in the framework of material selection for optical elements has been addressed. In accordance with the typical mechanical and thermal stability requirements applied to optical systems, relevant figures of merit for the selection of optical materials have been identified. These have been exploited to optimize the design, aiming for the concurrent minimization of mass and heat required for the ablation of the component. The analysis has been applied to the most common materials currently used to fabricate space mirrors, which constitute one of the fundamental components in optical instrumentation. The proposed approach represents a valuable asset for implementing effective and innovative solutions for the sustainable use of space, aiming to concurrently reduce the casualty risk while avoiding performance penalties.

Mirror-Descent Inverse Kinematics with Box-constrained Joint Space⋆

To control humanoid robots, the reference pose of end effector(s) is planned in task space, then mapped into the reference joints by IK. By viewing that problem as approximate quadratic programming (QP), recent QP solvers can be applied to solve it precisely, but iterative numerical IK solvers based on Jacobian are still in high demand due to their low computational cost. However, the conventional Jacobian-based IK usually clamps the obtained joints during iteration according to the constraints in practice, causing numerical instability due to non-smoothed objective function. To alleviate the clamping problem, this study explicitly considers the joint constraints, especially the box constraints in this paper, inside the new IK solver. Specifically, instead of clamping, a mirror descent (MD) method with box-constrained real joint space and no-constrained mirror space is integrated with the Jacobian-based IK, so-called MD-IK. In addition, to escape local optima nearly on the boundaries of constraints, a heuristic technique, called ϵ-clamping, is implemented as margin in software level. Finally, to increase convergence speed, the acceleration method for MD is integrated assuming continuity of solutions at each time. As a result, the accelerated MD-IK achieved more stable and enough fast tracking performance compared to the conventional IK solvers. The low computational cost of the proposed method mitigated the time delay until the solution is obtained in real-time humanoid gait control, achieving a more stable gait.

Magnetorheological Finishing of Chemically Treated Electroless Nickel Plating

Electroless nickel plating with a nanofinished surface is used in space mirrors, automobile parts, aircraft components, optical instruments, and electronic equipment. Finishing of these components using conventional finishing techniques is limited due to size, shape, material, and process constraints. This work reports the nanofinishing of electroless nickel-plated surfaces using a magnetorheological finishing process where the surfaces are pre-treated with chemicals. The chemicals used in this work are hydrogen peroxide (H2O2) and hydrofluoric acid (HF). The effect of exposure time and concentration on the microhardness and roughness is studied to understand the surface chemistry after chemical treatment. The hydrogen peroxide forms a passivated layer, and it helps in easy material removal. Hydrofluoric acid improves surface quality and also helps in the removal of contaminants. The finished surface is characterized to understand the effect of chemical treatment on the finishing rate and surface topography. Normal and tangential forces are mainly affected by the hardness and surface condition after the chemical treatment. The best combination of parameters (chemical treatment with 1% HF for 30 min) was obtained and finishing was carried out to obtain a nanofinished surface with its areal surface roughness (Sa) reduced to 10 nm.

A Review of Lightweight Design for Space Mirror Core Structure: Tradition and Future

With the continuous improvement of the imaging quality requirement of the space optical system, the large-aperture mirror becomes the research focus. However, the increase of the aperture will increase the whole weight which results in high launch cost and degrades the mirror surface figure accuracy. Therefore, the lightweight design method of the mirror structure is of great importance. In recent years, many space telescope system schemes have demonstrated the progress of the structural lightweight design of mirrors, such as Spitzer, SOFIA, JWST, etc. This article reviews the main content and innovations of the research on the structural designs of mirrors including conventional machining designs and topology optimization structures. Meanwhile, some emerging designs (e.g., lattices and Voronoi structures) considering additive manufacturing (AM) are also introduced. Several key elements of different structural design approaches for lightweight mirrors are discussed and compared, such as material, lightweight ratio, design methods, surface figure, etc. Finally, future challenges, trends, and prospects of lightweight design for mirrors are discussed. This article provides a reference for further related research and engineering applications.

Fabrication of high-strength Si/SiC composites with low shrinkage rates via vat photopolymerization technology and liquid silicon infiltration

Vat photopolymerization (VPP) technology has shown great application potential in the manufacture of high-precision complex silicon carbide (SiC) based ceramic components. However, in comparison with the conventional fabrication technologies, the SiC ceramics produced by VPP technology have insufficient strengths or relatively larger shrinkage rates to meet the requirements of practical applications. Herein, we develop a novel bimodal SiC material recipe for VPP technology and prepare Si/SiC composites by the consequent liquid silicon infiltration (LSI) method. The addition of fine SiC particles improves the material’s mechanical properties significantly. The final products possess low shrinkage rates (3.52 ± 0.26% in the x-direction, 3.73 ± 0.39% in the y-direction, and 4.69 ± 0.35% in the z-direction) as well as high flexural strength (363.23 ± 14.21 MPa) and low open porosity of 0.097%. The material compositions and fabrication strategies proposed in this work demonstrate an efficient way for the additive manufacturing of high-precision complex Si/SiC ceramic parts (e.g. lightweight space mirrors and structural ceramic parts). • A novel material recipe is developed for vat photopolymerization-fabricated Si/SiC composites. • The final Si/SiC composites have high strength (>350 MPa) and low shrinkage rates (< 5%). • A large-size reflective mirror ( Ф 172 mm) is manufactured in this study.

Solar Geoengineering Modeling and Applications for Mitigating Global Warming: Assessing Key Parameters and the Urban Heat Island Influence

In this paper, solar geoengineering modeling is presented with a goal to simplify reverse forcing assessments and the capability to apply it to a wide variety of applications. Results find improvements on sun-shade space mirror and desert surface treatment estimates, stratosphere sun-dimming methods, and the Urban Heat Islands (UHIs) influence. A heat amplification parameter is added to the model allowing it to be applied to UHI estimates. UHI amplification effects are due to the large solar area of buildings, reduction of wind cooling, solar canyons, and so forth. The UHI reverse forcing requirements are assessed with amplification estimates of 3.1 and 5.2, yielding 7.6% to 12.7% of gross global warming could be due to the urbanization effect, respectively. The gross warming 7.6% estimate, accurately compares to the author's prior study, and the 12.7% represents very recent results by other authors from new measurement methods. Key issues are pointed out that without including a heat amplification estimate and other modeling parameters, the UHI intensity, that likely dominates the urbanization warming effect could be severely underestimated, yielding urbanization estimates possibly as low as 2.4%. It is important to identify possible reasons where underestimates may occur from a modeling perspective to help understand controversies that may be occurring. The new model helps to clarify such parameters, allows for a significant reduction in complexity and calibration, and is shown to be helpful for numerous solar geoengineering applications including the serious need to reduce the UHI effect worldwide. Solar geoengineering solutions will require a lot of creativity, in addition to modeling, suggestions are provided for drought relief ideas and Paris Accord goals required for any successful urban solar geoengineering coordinated effort.

Analysis and elimination of adhesive bonding force of flexible supported space mirror

Analysis and elimination of adhesive bonding force of flexible supported space mirror

Research and Experimental Verification on Topology-Optimization Design Method of Space Mirror Based on Additive-Manufacturing Technology

As one of the most-critical components in space optical cameras, the performance of space mirrors directly affects the imaging quality of space optical cameras, and the lightweight form of mirror blanks is a key factor affecting the structural quality and the surface-shape accuracy of mirrors. For the design requirements of lightweight and high surface-shape accuracy with space mirrors, this study proposes a design and manufacturing method that integrates topology-optimization with additive-manufacturing technology. This article firstly introduced the basic process and key technologies of space-mirror design and analyzed the superiority of combining a topology-optimized configuration design and additive-manufacturing technology; secondly, the topology-optimized design method of a back-open-structure mirror was used to complete the scheme design of a Φ260 mm aperture mirror; finally, the laser selective-melting manufacturing technology was used to complete the Φ260 mm aperture mirror blank. The mirror and its support structure were assembled and tested in a modal mode; the resonant frequencies of the mirror assembly were all over 600 Hz; and the deviation from the analytical results was within 2%. The optical surface of the mirror was turned by the single-point diamond-turning (SPDT) technique. The accuracy of the optical surface was checked by a Zygo interferometer. The RMS accuracy of the mirror surface was 0.041λ (λ is the wavelength; λ = 632 nm). In the test of the influence of gravity on the surface-shape accuracy, the mirror was turned over, which was equivalent to twice the gravity, and the RMS of the mirror surface-shape accuracy was 0.043λ, which met the requirement. The verification results show that the mirror designed and fabricated by the additive-manufacturing-based mirror-topology-optimization method can be prepared by the existing process, and the machinability and mechanical properties can meet the requirements, which provides an effective development method for improving the structural design and optimizing the manufacturing of space reflectors.

Fast Optimization Design of the Flexure for a Space Mirror Based on Mesh Deformation

According to the requirements of high force-thermal stability and high performance of a space telescope, a space mirror assembly must not be influenced by environmental factors. In this study, a space mirror assembly under load conditions, such as gravity, thermal, and assembly error, is considered. After the mirror is optimized, the surface shape error is reduced by 22%, and the mass is increased by 0.113 kg. In order to improve the efficiency of integration optimization, we present a fast optimization method using mesh deformation to be applied to the flexure. The size parameters of flexure and axial mount position are obtained by optimization. With our method, the single optimization time reduces from 10 min to 40 s, which can improve the efficiency of multi-objective optimization. The mirror assembly is fabricated and assembled based on optimization results. Finite element analysis (FEA) and test results for the space mirror assembly confirm the validity and feasibility of the fast optimization method, and we believe that the flexure based on fast optimization meets the requirements of a space mirror assembly for space applications.

Optimization design of an ultralight large-aperture space mirror.

The ultralight space mirror has long been a hot topic in the research field of space telescopes. In this paper, an ultralight mirror is designed by obtaining the structure and parameters of a mirror with an aperture of 2 m through experimental design and multiobjective integrated optimization. Specifically, the materials near the neutral surface were replaced with elliptical holes. The back of the mirror was supported at three points. Finite-element analysis shows that the mirror had a surface figure error of 10.4 nm under 1 g in the x direction (gravity direction), which is sufficiently high to be applied to visible light optical systems. Further, the eigenfrequencies of mirror components were obtained through finite-element analysis: 70 Hz in the x direction, 70 Hz in the y direction, and 90 Hz in the z direction. The results demonstrate the excellent dynamics performance of the designed mirror. Compared with test results, the relative error of eigenfrequencies was within 4%. Hence, our ultralight design outputs reliable optimization results and applies to the development of large-aperture ultralight space mirrors. Finally, the ultralight mirror was prepared from reaction-bonded silicon carbide. The mass and surface density of the prepared mirror were 105 kg and 34kg/m2, respectively. The mirror mass was 50% lighter than that of the mirrors designed by traditional lightweight methods.

Dynamic Analysis and Experiment of a Space Mirror Based on a Linear State Space Expression

Dynamic analysis of the optical–mechanical structure based on the linear state space expression is performed for a three-point flexural mount lightweight space mirror with a diameter of ϕ740 mm. Using linear structure dynamics and linear state space theories, the state space model of the mirror assembly is established based on modal information. The DC gain method is used to reduce modes and a frequency response analysis of the reduced modes is performed to obtain the frequency domain transfer function between the excitation input and response output points and determine the contribution of each mode to the total frequency response. The frequency response curve is plotted. A mechanical vibration test is performed to verify the accuracy and rationality of simulation analysis. The dynamic analysis method based on state space theory provides a new method of investigating optical and mechanical structures, which can help efficiently and accurately analyze the frequency response characteristics of complex linear systems.

Glass ceramic ZERODUR®: Even closer to zero thermal expansion: a review, part 2

Observational astronomy has sought better telescopes with higher resolution from its beginning. This needs ever-larger mirrors with stable, high-precision surfaces. The extremely low-expansion glass ceramic ZERODUR® has enabled such mirrors for more than 50 years with significant improvements in size and quality since then. We provide a survey of the progress achieved in the last 15 years. Equally important as the thermal expansion coefficient CTE is its homogeneity. The CTE variation in 4-m mirror blanks lies below 5 ppb / K in radial and axial directions on large and short scales. Improved measurement capabilities allow reduced bias, which in the past made variations look greater than they were. Isotropy and uniformity of ZERODUR are outstanding. A method for lifetime calculation increases reliability considerably with respect to mechanical loads. The production and metrology capability and capacity are greatly extended. Surface figure and texture of large blanks allow starting directly with polishing. Filigree structures with up to 90% weight reduction are well-suited for space mirrors. The progress with low thermal expansion and its measurement, the insensitivity of ZERODUR against ionizing radiation in space, and outstanding application examples are presented in the first part of our review.

A Non-uniform Lattice Structure Size Optimization Design Based on Space Mirror

A Non-uniform Lattice Structure Size Optimization Design Based on Space Mirror

Working efficiency analysis of space mirror antenna reflector made of composite materials

The study is devoted to the possibility of using composite materials, composite sandwich panels and composite mesh structures as constructions for space mirror antennas using at space satellites. The modelling of the thermal and stress-strain states of the structure, which are characteristic of radiation heat transfer in open space operating conditions, has been carried out. Based on the results obtained, a design with the best indicators of mass-dimensional stability under operating conditions was selected.