Lightweight Mirror Research Articles

Research on the position of the neutral surface of the space lightweight mirror with two-axis bipod flexible mount

Research on the position of the neutral surface of the space lightweight mirror with two-axis bipod flexible mount

Influence of Fabrication and Assembly Errors on the Root Mean Square Surface Distortion of a 2 m Lightweight Mirror and Its Correction

Influence of Fabrication and Assembly Errors on the Root Mean Square Surface Distortion of a 2 m Lightweight Mirror and Its Correction

Optimal design and analysis of a space lightweight mirror with a directionally oriented 2.5D-CVT structure

Reflective mirrors are the key imaging components of space-borne telescopes, which require a high lightweight ratio integrated with excellent optical properties. In this context, a novel, to our knowledge, 2.5D centroidal Voronoi tessellation (CVT) generation methodology is proposed for designing and optimizing a lightweight mirror structure. Firstly, the initial designs are obtained combining global sensitivity factor mapping and local distribution optimization. Then, the optimal model is selected through multi-objective optimization and decision making. Subsequently, the FEA (finite element analysis) results indicate that, under the same mass, the proposed design exhibits better optomechanical performance. Finally, in practical applications, the approach presented in this paper outperforms the traditional design for each technological requirement, including a 62% reduction in RMS and a higher lightweight ratio. This method offers a kind of novel design and optimization process for space-based optomechanical lightweight structures.

Precision finishing of nickel-phosphorus plated carbon fibre reinforced polymer

Carbon fibre reinforced polymer is a lightweight material having superior mechanical properties and thermal stability and a promising material for light-weight mirrors for space applications. In this work, the surface of carbon fibre reinforced polymer is electroless nickel-phosphorus plated. The morphologies of the substrate and as-plated surfaces are compared. The surface roughness of the plated surface showed a significant reduction after the plating process. The elemental composition and phase of the as-plated sample are studied. The plated carbon fibre reinforced polymer surface is polished using an elastic tool with a diamond abrasive pad having grit sizes of 45 and 9 μm. The topography and the morphology of the finished surface are analysed for understanding the material removal process. A minimum Ra of 48 nm is obtained on the plated surface after 28 min of polishing. At a finishing rate of 18.17 nm/min, a 91.4% drop in Ra is achieved in comparison to a plated surface.

Ultra-precision grinding of light-weighted SiC aspheric mirror

Based on the approximate 3D model of light-weighted SiC aspheric mirror, the deformation and stress at different positions along the radius caused by the grinding force on the mirror surface was analysed. Then the influence of processing parameters on grinding force was experimentally studied, and the prediction model of grinding force was established. Finally, the grinding experiment of light-weighted SiC aspheric mirror was carried out. The PV value of the aspheric surface form error was 4.15μm, and the Ra of surface roughness was about 28nm. The experimental results verified the feasibility of ultra-precision forming of lightweight SiC mirror by controlling grinding force based on process parameters.

The Application of a Topology Optimization Algorithm Based on the Kriging Surrogate Model in the Mirror Design and Optimization of an Aerial Camera.

In a Cassegrain optical system, the surface precision of the primary mirror is an important factor in the quality of the image. The design of a lightweight primary mirror with a high-quality optical surface is crucial. In this thesis, an integrated mirror light engine design optimization process is proposed for an aviation optoelectronic device. It is based on the Kriging surrogate model and nests the topology optimization algorithm, which constructs the mirror RMS value response surface and obtains the dominant relationship between mirror structure and surface accuracy. The optimal surface figure lightweight structure of the mirror is obtained by optimizing the surrogate model with an additive criterion and multi-objective optimization analysis. The root mean square value (RMS) of the corresponding primary mirror is 10.41 nm, which is better than 1/40 λ (λ = 632.8 nm). This meets the optical design specifications. The optimal primary mirror structure is analyzed by using the finite element method, which verifies the precision of the Kriging surrogate model. It has an error of 0.28%. The kinetic analysis of the primary mirror shows that the primary mirror does not yield to plastic deformation or even failure under a three-way 20 g acceleration load. This meets the environmental suitability requirements.

Lightweight Design and Evaluation of Square Reflector

In order to reduce the weight of optical elements in space remote sensors while increasing their stiffness, this paper takes an off-axis system secondary mirror as an example to design a square mirror with a size of 500 mm × 500 mm. The mirror adopts ultra-low expansion glass as the raw material. The paper proposed a lightweight form of gradual reinforcement and conducted the mirror assembly simulation analysis. The analysis results show that the weight of the lightweight mirror is 13.6 kg, and the surface density can reach 54.4 kg/m2. Under the circumstances of 1 g gravity and the temperature change of 15 °C~25 °C, the surface shape accuracy of the mirror assembly can reach 1/90λ (λ = 632.8 nm). Through the final testing, the first-order intrinsic frequency of the reflex mirror components is 167.8 Hz. The gap between the test results and the theoretical simulation results is less than 3%, which proves that the mirror assembly in the lightweight form of gradual reinforcement fully meets the index requirements and can provide a theoretical reference for the assembly of a mirror of similar size and type.

Verification of deformation of thin mirror by polishing pressure using additive manufacturing

In this study, magic and deformable mirrors were fabricated using an additive manufacturing (AM) process. This was to confirm the magic mirror effect caused by the grinding pressure of the mirrors produced by the AM-based manufacturing process. For verification, eight magic mirrors were fabricated under different conditions. The results showed that the magic mirror effect occurred on two mirrors with a diameter of 10 mm and wall thicknesses of 0.1 and 0.2 mm. AM is easy to machine thin-wall; therefore, a pneumatically deformable mirror was fabricated. The shape-control performance through air pressure fluctuations was confirmed. In this study, magic mirrors and deformable mirrors have been successfully fabricated using additive manufacturing technology. The method proposed in this study enabled the efficient production of lightweight and thin mirrors.

Material removal characteristics and particle motions in abrasive water jet quantitative machining.

Abrasive water jet quantitative machining (AWJQM) is a method that enables the production of lightweight mirrors. Investigating material removal characteristics and particle motions in AWJQM is necessary to understand its erosion mechanism and improve its processability. A material removal model based on computational fluid dynamics was established in this study by integrating the transition condition of the brittle-ductile mechanism and the single-particle erosion model. Quantitative machining experiments were carried out to verify the material removal model, and experimental data were consistent with the simulation results. Further simulation experiments were carried out to explore the particle distribution under different working pressures or slurry viscosities. Results showed that operating parameters affect the workpiece surface profile by changing the flow field distribution and particle behavior.

Design and optimization of the tripod flexure for a 2m lightweight mirror for space application.

In order to ensure optimal optical performance, primary mirror assembly must be impervious to environmental influences. These environmental influences include gravity, assembly error, and thermal change, under which external loads are imposed on the mirror. The external loads degrade the mirror surface accuracy and cause misalignment between mirrors. In this paper, a tripod flexure with a flexible hinge is designed to alleviate the influence of the external load on the surface accuracy of a 2m primary mirror. This structure can effectively release the rotational freedom, provide a certain translational flexibility, and yield high axial stiffness. The axial stiffness is used to increase the frequency of the primary mirror assembly. According to the fast optimization model, the derivation of close form compliance equations is developed to characterize the flexibility, and parameter optimization is done to achieve the maximum performance. Then a finite element analysis and test are used to verify the final design. The results show that the index requirements of the 2m primary mirror have been met.

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.

Equivalent Modeling and Verification of a High-Steepness and Lightweight Elliptical Aluminum Mirror

In order to realize the compact layout of aerospace payloads, the design and manufacture of high-steepness lightweight aluminum alloy mirrors is a key technology to be explored. For high-steepness mirrors, the traditional method is to establish the initial thickness that satisfies the bending stiffness through finite element optimization iteration, which cannot achieve fast modeling and performance estimation. In this paper, firstly, the equivalent modeling method of the mirror with high steepness is proposed to achieve the equivalent of the elliptic mirror with a diameter of 410 × 310 mm and F# less than 0.7. Based on the mathematical model, topology shape optimization was used to build a highly lightweight mirror structure that could be quickly assembled, and the equivalent area–mass density of the mirror is less than 34 kg/mm2. Next, the rationality of design feasibility was verified by simulation analysis. Finally, by using single point diamond turning combined with post polishing process, the high-precision manufacturing of conventional aluminum alloy mirror was realized. The results show that the mirror shape accuracy is 1/10 λ (λ = 632.8 nm), and the surface roughness Ra is 3.342 nm. This research provides strong theoretical support and application prospects for the low-cost and rapid manufacturing of high-steepness lightweight aluminum alloy mirrors.

Experimental study of diamond turned quilt formation in metal foams and using simulated pores

Sandwich structures used to lightweight telescope mirrors result in subsurface pore or cell-induced surface deformation (called quilting), in the unsupported sub-surface regions, during diamond turning of the optical surface. An alternative to sandwich structure is metal foams made by the melt route which have a monolithic porous-nonporous interface naturally formed by a gravitationally induced drainage effect. This work compares effect of naturally formed pores on quilt formation in A357 and Al 6061 metal foams, while also studying the influence of pore size and cutting speed on the quilting effect using simulated controlled diameter single-pore samples made of Al 6061. Results show that the quilt height observed in Al 6061 foam is more than that of A357 foam. Quilting with a height of 0.89 µm appeared on the diamond turned surface of A357 metal foam corresponding to a subsurface pore of diameter 3.87 mm when the thickness of the nonporous region reaches 140 µm. In Al 6061 foam, the quilt with a 0.97 µm peak is observed at 100 µm thickness corresponding to a 2.25 mm pore. The measured quilt heights of metal foams are normalized by their corresponding pore radius, and the effect of material strength on quilt formation is reported. Simulated pore studies in Al6061 show that both pore size and cutting speed significantly influence quilt formation, indicating that optimizing cutting conditions can reduce quilt formation effects. This study facilitates effective adoption of monolithic metal foams for lightweight mirrors.

Optomechanical Performances of Advanced Lightweight Mirrors Based on Additive Manufacturing.

Additive manufacturing (AM)—layer-by-layer printing—completely changes the conventional manufacturing method. The design freedom for mirrors is increased without the limits of the manufacturing process. Advanced lightweight mirrors (ALM), new-type mirrors designed using the generative method and lattice technologies, have emerged as the times require. Contrasting with conventional lightweight mirrors (CLM), the performances of ALM are drastically improved. This paper took the Voronoi mirrors as an ALM case study and introduced a design flow. In addition, a conventional honeycomb mirror was designed using the analytical method as the control. The optomechanical performances of the two were further compared through finite element analysis (FEA). Finally, ALM’s optomechanical performances outperformed CLM’s, including the area density, structural stiffness, surface stability, and quilting deflection.

Design and Fabrication of Extremely Lightweight Truss-Structured Metal Mirrors.

Three-dimensional printing, also called additive manufacturing (AM), offers a new vision for optical components in terms of weight reduction and strength improvement. A truss, which is a triangulated system of members that are structured and connected in such a way that they mainly bear axial force, is commonly used in steel structures to improve stiffness and reduce weight. Combining these two technologies, an extremely lightweight truss-structured mirror was proposed. First, the finite element analyses (FEA) on surface shape deviation and modal properties were carried out. Results showed that the mirrors had sufficient stiffness and a high weight reduction of up to 85%. In order to verify their performance, the truss-structured mirror blanks were fabricated with AM technology. After that, both the preprocessing and the postprocessing of the mirrors were carried out. The results show that without NiP coating, a surface shape deviation of 0.353λ (PV) and 0.028 λ (RMS) (λ = 632.8 nm) with a roughness of Ra 2.8 nm, could be achieved. Therefore, the truss-structured mirrors in this study have the characteristics of being extremely lightweight and having improved stiffness as well as strong temperature stability.

A Weighted Current Summation Based Mixed Signal DRAM-PIM Architecture for Deep Neural Network Inference

Processing-in-Memory (PIM) is an emerging approach to bridge the memory-computation gap. One of the major challenges of PIM architectures in the scope of Deep Neural Network (DNN) inference is the implementation of area-intensive Multiply-Accumulate (MAC) units in memory technologies, especially for DRAM-based PIMs. The DRAM architecture restricts the integration of DNN computation units near the area optimized commodity DRAM Sub-Array (SA) or Primary Sense Amplifier (PSA) region, where the data parallelism is maximum and the data movement cost is minimum. In this paper, we present a novel DRAM-based PIM architecture that is based on bit-decomposed MAC operation and Weighted Current Summation (WCS) technique to implement the MAC unit with minimal additional circuitry in the PSA region by leveraging on mixed-signal design. The architecture presents a two-stage design that employs light-weight current mirror based analog units near the SAs in the PSA region, whereas all the other substantial logic is integrated near the bank peripheral region. Hence, our architecture attains a balance between the data parallelism, data movement energy and area optimization. For an 8-bit CNN inference, our novel 8Gb DRAM PIM device achieves a peak performance of 142.8GOPS while consuming a power of 756.76mW, which results in an energy efficiency of 188.8GOPS/W. The area overhead of such an 8Gb device for a 2ynm DRAM technology is 12.63% in comparison to a commodity 8Gb DRAM device.

Examination of the Blank Error on Mirror Accuracy of Lightweight SiC Mirror and a Compensation Method

Due to excellent characteristics of specific stiffness and thermal stability, silicon carbide-based (SiC) material is commonly selected to construct large-scale lightweight mirror. In general, the fabrication process of SiC mirror is similar to the casting process. The blank error of SiC mirror is 0~1 mm. Due to the high hardness of SiC, only the mirror surface and some positioning surface will be milled. The mirror surface accuracy will be degraded due to the fact that the blank error can cause significant changes in weight distribution. In this paper, Monte Carlo analysis is firstly performed to examine the blank error on gravity center, stiffness and mirror accuracy of a SiC mirror. It is found that according to the designed mount location, the amount of degradation is more than 2.5 nm of which the probability is 40.3%. It is known that the error of gravity center can be compensated by optimizing the axial mount location. Then inverse modeling and testing of gravity center for the SiC mirror is carried out in order to determine the optimal axial mount location. Based on the proposed method, the mirror degradation introduced by the blank error has been eliminated to the greatest extend.

The Effects of Radiation Pressure on Orbiting Mirrors with Non-Zero Eccentricity

The search for extraterrestrial life has been approached from many angles. For Korpela, et al, among others, the search comes in the form of analyzing stars’ light curves for hints of satellites around exoplanets. Such satellites could be in the form of large, thin, lightweight mirrors, possibly used to redirect sunlight from a star to the surface of a planet. The feasibility and fuel efficiency of such an undertaking would depend heavily on the effects of radiation pressure. My colleagues and I have simulated those satellites using REBOUND (Rein and Liu 2012), an N-body simulator, to understand the effect of radiation pressure on mirrors orbiting an exoplanet. We changed the types of stars, initial orbit orientations, eccentricities, and other variables. Each simulation ran to a pre-set 1000 orbits or until the mirror crashed into the planet or escaped orbit. A list of survival times and other data trends was compiled to identify potentially stable (or quasi-stable) orbits. Overall, it appeared that simulations with initial eccentricity close to zero (0.1, sometimes 0.3) were more like previously investigated initially circular simulations. There were extreme exceptions to this however; some of the initially eccentric simulations lasted for 1000 orbits, while the equivalent initially circular simulations crashed or escaped very early on. We also used the data output from the simulations to create plots like a mirror’s distance from the planet over time and a mirror’s eccentricity over time in order to find possible stability trends. We are still investigating potentially stable configurations.

Micro-stress bonding analysis of high precision and lightweight mirrors.

We propose analysis methods for mirror bonding. The functional relationship between the shrinkage of the adhesive layer and the shape accuracy of the mirror is established numerically. By designing the structural form of the optical mounting and setting an appropriate stiffness ratio between the mirror and bonding position of the optical mounting, the theoretical surface shape accuracy change can be determined. Accordingly, the mirror is bonded, and the surface shape accuracy of the mirror after bonding is found to be 0.020λ. This approach is useful in mirror design applications that require rapid preparation and accuracy control.

The simulation of thermal deformation on lightweight optics with thick coatings

Lightweight optics utilized in high-power laser system can dissipate heat better and reduce system weight. Dielectric films can be designed for laser pulse modulation, high reflect rate and wide bandwidth. However, the deformation caused by coating residual stress will be large due to the large thickness of dielectric films and low stiffness of lightweight mirror, which brings a large bending deformation with the temperature variation. The traditional surface compensation technology is double-sided coating, but it is not suitable for lightweight mirrors. In this study, we construct a finite shell-element model to estimate the surface shape error caused by dielectric film coating residual stress on a lightweight mirror for surface pre-processing. Thermal deformation and bimetal effect deformation are also simulated.