This PDF file contains the front matter associated with SPIE Proceedings Volume 11101, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

ECM received in May 2014 from OHB, Germany the contract for the design, fabrication, test and qualification of the Star Tracker Assembly Bracket for the next generation weather satellite (MTG - Meteosat Third Generation), developed by ESA and operated finally by EUMETSAT. In December 2018 ECM delivered the last two Flight models fully integrated and tested to OHB, Bremen. This project was for ECM a big challenge being for the first-time prime contractor of a small subsystem consisting of an assembly of metal components associated to our HB-Cesic® bracket structure. In this paper we will report about the successful manufacturing process of seven flight models including STM Model for qualification in a rather short time frame of less than 2 years after CDR. This paper is focused on the successful manufacturing and precision machining of these complex light-weighted HB-Cesic® structures with low tolerance requirements to demonstrate ECMs capability of fabricating such Star Tracker Assembly Bracket subsystems.

Silicon nitride is a ceramic material that has very interesting properties for space applications, especially for optical instruments and telescopes. Indeed, the objective for such structures is chiefly stability to ensure performance, associated with low mass and high stiffness to sustain launch loads. With its high strength and stiffness and low CTE, Silicon Nitride is therefore extremely well suited for stable Space structures. Thales Alenia Space has been using Silicon Nitride for more than a decade, and in that framework has evaluated the ability of the material to address those needs and requirements for complex designs such as tubes, brackets, brazed supports, beams and light-weighted plates. All these structures have been tested, qualified and are now flight proven. In order to improve knowledge and mastering of strength properties, a characterization campaign of the material is under way in a GSTP funded by CNES and driven by ESA. This paper describes the design of this test campaign, the choices for the sample types and dimensions, and prediction of the expected results. In addition to the mechanical strength testing, X-ray tomography has been implemented in order to detect flaws beforehand and to investigate the ability to predict failure from the extracted information. This will be especially useful since verification (in particular proof tests that are commonly used on ceramics for Space applications) is based on the relationship between strength and flaws. It is expected that by improving this knowledge a more straightforward verification process can be derived.

This paper presents four types of Continuous Fiber Ceramic Composites (CFCCs) manufactured using preceramic Polymer Infiltration and Pyrolysis (PIP) method for mechanical testing. Nicalon™ ceramic grade silicon carbide fiber was used as the reinforcements, and KiON CERASET® preceramic polymer was used as the matrix in this study. Further, the effects of nanoparticles, carbon nanotubes, and the combination of the two, as CFCC reinforcements, were evaluated and compared with their base CFCCs based on processing and flexural mechanical performance of Nicalon/KiON CERASET® CFCCs by PIP method. Nicalon™ ceramic fiber was used as the primary reinforcement and KiON CERASET® preceramic polymer was used as the matrix material for all four types of CFCCs in this work. KiON CERASET® preceramic polymer was mixed with nano-size fillers in the presence of a surfactant agent to give a good dispersion of the particles and was used as the Nanoresin. Yttrium oxide nanoparticles with an average size of about 25 nm were used as the inclusion with weight percentage of up to 15%. Carbon nanotubes were grown directly on the surface of Nicalon™ fabric via chemical vapor deposition process, and used as Nanoforest. Characterization analysis and distribution studies of the samples using scanning electron microscopy were conducted. Four-point bending test was also conducted to evaluate the flexural mechanical performance of the ceramic nanocomposites samples at room temperature. A combination of nanoparticle Nanoresin and carbon nanotube Nanoforest reinforced CFCCs, had the highest improvement among all the samples studied in this research. It was also found that the effects of Nanoforest was dominant over the effects of Nanoresin.

In high-energy astrophysics, X-ray telescopes play a key role as a primary source of information. However, the weight of the satellite-based telescope mirrors limits their size and thus their light collecting power. The research project "precision bending of thin glass" aims to develop lightweight and precise alternatives for X-ray mirrors based on thin glass segments. Glass has many material-specific advantages, and glass samples with thicknesses < 0.5 mm and an extremely low micro-roughness are commercially available. They can be shaped by a thermal treatment during which the shape of an underlying mould is transferred to the glass in a process called glass slumping. The project's core is the investigation of heat-resistant porous ceramic materials for the production of moulds and the development of appropriate high-precision machining processes. The project aims for the manufacturing of an exemplary mould, which allows the slumping of mirror segments for an X-ray optics with shaping supported using vacuum pumping from the mould side. The necessary dimensional accuracy of < 1 μm / 100 mm on the mould and on the glass should be finally demonstrated. The requirements to an open-pored and chemically inactive ceramics, which is dimensionally stable under the thermal process, are demanding, so the range of suitable materials is narrow. Our primary choice for the mould material is a carbon-fiber reinforced silicon carbide (HB-Cesic®). HB-Cesic® is well known for its thermal and mechanical stability and has already been used for glass slumping. The following Fig. 1 shows a fully polished mould out of dense HB-Cesic®.

Mirrors with excellent mechanical, thermal and optical properties are suitable for a broad spectrum of modern optical application. A growing number of multi- and hyperspectral imaging devices such as telescopes and spectrometers are based on all-reflective metal optics. Optics with higher mechanical or dynamic loads are often made of ceramics; at higher thermal loads, they are made of glass-ceramics. The DLR Earth Sensing Imaging Spectrometer (DESIS) is a space-based hyperspectral instrument developed by German Aerospace Center (DLR). The optical system of the spectrometer was designed, fabricated and pre-aligned by the Fraunhofer Institute of Applied Optics and Precision Engineering (IOF). The instrument was realized as an all-reflective system using metal-based mirrors using a modular, so-called snap-together approach. Parts of the system are flat mirrors for the pointing unit of the instrument. Two flat mirrors based on a metallic substrate material (Al 42Si) and one flat mirror based on a ceramic (HB Cesic®) were realized. The cost-efficient manufacturing technology of metal mirrors has an important advantage over glass, glass-ceramic and ceramic mirrors. For the pointing mirror, a more rigid and stiff material like HB-Cesic® was used. Different and tailored process chains were applied for both kinds of mirrors. The paper summarizes the fabrication of optical mirrors by i) grinding and polishing of ceramic matrix composite substrates; and ii) diamond machining combined with post-polishing techniques, like magnetorheological finishing (MRF) and chemical mechanical polishing (CMP) for metallic substrates. The process chains are described including testing setup and results with regard to different materials and manufacturing technologies. The mirrors show an excellent quality regarding flatness (lower 15 nm rms) and roughness (lower 1 nm rms, WLI magnification 50x).

The processes of Additive Manufacturing (AM) are nowadays mostly used for mechanical and fluid components and have already made the transition from Rapid Prototyping (RP) to Rapid Manufacturing (RM). In the electronic industry however, mostly additive printing technologies are used to a large extent. This paper reveals a new process for the additive production of copper-ceramic composites using Selective Laser Melting (SLM). With this process, 3D metallizations can be produced on Al₂O₃ and spinel-like compounds, as known from Direct Copper Bonded (DBC) technology, can be formed by means of thermal post-treatments. Moreover, high adhesive strengths of up to 44 N/mm², determined with shear testing, can be reached. The technology of melting copper or copper based powder on ceramic substrates can be used for example for power electronic applications for high current capabilities due to the possibility of manufacturing thick 3D metallizations without the occurrence of warpages as known from the DBC technology. In this study, extensive parameter analysis have been conducted with respect to laser power, laser velocity, hatching distance as well as focus shifting. On the other hand, the substrate temperature during the printing process was varied and post thermal treatments were applied in order to fully densify the metallization as well as form reaction layers between the ceramic-metal interface.

Due to the high toughness of SiC material, in general, the polishing time of a SiC mirror has been challenging to determine by optician. In the optical shop, optician normally enters input parameters into a polishing machine prior to polish out the mirror surface. The target surface removal rate, specified by an optician, are highly depending on polishing schedule. A very tight polishing schedule commonly thrusts adventurous larger target quantities on the optician. However, the target numbers should be determined by the reliability of relationships between the machine input parameter and output removal rate. In this paper, we introduce an initial model which can reliably suggest machine input parameters for polishing head. These parameters can control polishing processes to achieve the target TIF (Tool Influence Function) depth which is an unit polishing removal quantity on the SiC mirror optical surfaces.

Cavity-based single photon emission possesses a very high potential for future quantum networks and quantum communication systems. Fabry-Perot cavities especially, are a good candidate for these applications, thanks to a circular mode profile emission and low-lasing threshold. These properties are related to the small volume of the active region and the use of highly reflective Distributed Bragg mirrors (DBRs). The reflectance of the DBRs is related to the finesse of the cavity. In order to assure a strong coupling in the cavity, a high finesse is required and therefore a reflectivity value as high as 99.9999%. Achieving such a difficult goal faces many technical challenges and limiting parameters such as optical losses (scatter and absorption) and other limitations related to thin film coating technologies. The control of the mirror fabrication and losses will be addressed in this paper.

Reducing the reflection of silicon surface is an effective way to enhance its optical absorption performance in optical and optoelectronic devices. In this paper, the influence mechanism of heat accumulation effect existing in the material substrate on the multi-scale porosity properties of surface structure during femtosecond laser irradiation is investigated. Micro-nano structures will lose their multi-scale porous properties at high-repetition-rate laser irradiation due to excessive agglomeration, nucleation or melting. By rapidly cooling the material substrate, the porosity of surface micro-nano structure are optimized, and the antireflection performance of the material surface is improved obviously. Our study opens a novel and convenient route for preparation of broadband antireflective black silicon surfaces for various applications.

The wide field survey telescope (WFST for short) is a new generation survey telescope located in Lenghuzhen, Qinghai Province in China, and has outstanding performance in sky survey. However, the feature demands a rigid flatness 20μm PV of the prime focus plane of the prime focus camera. The CCD290-99 flatness 15μm PV and -100°C working condition pose challenges to the CCD splicing. In order to verify the CCD mosaicing technology for WFST’s prime focus camera before the sensor arriving, we use the CCD 303-88 in our lab to set up the verification platform. In this article, we mainly introduce the recent research status of the platform.

Ground- and space-based optical observations of space objects rely on knowledge concerning how spacecraft materials interact with light. One common surface material for many currently active spacecraft is Kapton-HN® polyimide. Changes in optical signature for polymeric materials can occur due to surface degradation, leading to altered reflectivity, or due to radiation induced chemical modification, leading to an alteration of a material’s absorption/transmission properties. The optical fingerprints of commonly used materials change continuously under exposure to high energy electrons, a primary damaging species in geostationary Earth orbit (GEO). Laboratory observations show that these changes in a material’s optical signature are wavelength dependent and to some degree transient. This work investigates the changes in the optical reflection behavior of a variety of aerospace materials before and after electron irradiation. The results of this investigation will find use in the space debris remediation community for characterization of high area to mass ratio (HAMR) objects and other larger space debris.

Of interest to Jet Propulsion Laboratory and multiple NASA cost centers are laser communications telescopes (LCTs) with 30 to 100 cm clear aperture, wavefront error (WFE) less than 62 nm, cumulative WFE and transmission loss not to exceed 3-dB in the far field, advanced thermal and stray light design for operation while sun-pointing (3-degrees from the edge of the sun); -20° C to 50° C operational range (wider range preferred), and areal density <65kg/m². Telescope dimensional stability, low scatter, extreme lightweighting, and precision structures are a common theme across the NASA 2017 Physics of the Cosmos (PCOS) and Cosmic Origins (COR) Program Annual Technology Reports. Multiple Priority Tier 1-4 technology gaps can be found, and the higher priorities require a solution in time for the next Decadal Survey. A common solution of interest that has been cited is silicon carbide and 3D printing or additive manufacturing. RoboSiC™ technologies provide both. Under NASA SBIR I Contract #80NSSC18P1995 the Goodman Technologies (GT) team performed feasibility demonstrations of 3D printed and additively manufactured off-axis RoboSiC™ mirror substrates and coarse and fine threaded RoboSiC™ bolts. RoboSiC-S provides the degree of passive athermality required for the LCT optical pathlength and wavefront error stability, concomitant with low areal density mirrors (7.75-10 kg/m²) and structures (4-5 kg/m²), and a theoretical first unit cost for an LCT with a fast steering mirror is $1.5M, a factor of 3-4 less than current LCTs. Team GT will further explore a preliminary Gregorian LCT on NASA SBIR II Contract #80NSSC19C0138.

OPTICAL MIRRORS DESIGN USING TOPOLOGY OPTIMIZATION FOR ADDITIVE MANUFACTURING (ABSTRACT) Author : Nisrine Louh1 Co-authors : Malorie Villemaire1, Stéphanie Behar Lafenêtre1, Nicolas Rousselet2, Vincent Costes3 Contact : Nisrine Louh – nisrine.louh@thalesaleniaspace.com 1. Thales Alenia Space, 5 Allée des Gabians, 06150 Cannes, France 2. 3D Ceram, Limoges 3. CNES Themes – Mirrors, topology optimization, space structures, additive manufacturing For scientific satellite, the mirrors are always on the critical path of a project. The design and the sizing of the mirrors are constrained by the mechanical holding, the mass, the cost and the manufacturability. These criteria require numerous compromises and therefore, optical mirrors are designed as early as possible to anticipate the leanings, the manufacturing time and the risks during this manufacture. In this article, we will describe a new method developed to optimize the space optics taking into account the various specifications and using topology optimization. This development is settled in the perimeter of a CNES study named FAME in collaboration with 3DCERAM. The goal is to highlight the feasibility and interest to “print” a telescope mirror. Our objective is to define a way to reduce the weight, to avoid deformation of the optical surface and at the same time to keep a stiffness that allows the structure to withstand the vibration loads. Moreover, this new approach permits very innovative designs. First, the optimization is made on both the mass and the stiffness. Then, mechanical analyses are performed to verify that the design is viable on the mechanical environment of the mirror. Besides, we verify that the Wavefront Error and the optical performances are compliant with our needs and requirements. Thales Alenia Space is interested in studying and introducing additive manufacturing in its processes. The advantages and limits of this new technology to “print” complex designs are presented.

The purpose of NASA Small Business Innovation Research (SBIR) topic S2.02 Precision Deployable Optical Structures and Metrology is to develop enabling, cost effective component and subsystem technology for deploying large aperture telescopes. Referencing the 2017 Cosmic Origins (COR) Program Annual Technology Report (PATR), the COR Program Office recommended that the NASA Astrophysics Division at HQ solicit and fund the maturation of technologies to fill multiple Priority Tier 1-3 technology gaps. Future NASA astrophysics missions such as the New Worlds Technology Development Program (NWTDP) require telescopes with 10-30 m apertures, operating at temperatures from 4-300 K, in wavelengths from the visible to far-infrared. Besides the large optics, technologies such as coronagraphs, external occulters, and interferometers require concomitant advancements in opto-mechanical technologies, including ultra-stable materials with areal density form 1-10 kg/m² areal density, and capable of achieving a packaging efficiency of 3-10 deployed/stowed diameter. RoboSiC™ is a “Mission Agnostic” solution for affordable, passively athermal opto-mechanical structures (trusses, booms, hinges, bolts, actuators, strongbacks, whiffle trees, optical benches, etc.) required by the Habitable Exoplanet Explorer, Large UV/Optical/IR Surveyor, and Origins Space Telescope (HabEX, LUVOIR, OST) and gravity wave missions. Goodman Technologies (GT) 3D printed and additively manufactured (AM) nanoceramic composite provides low areal density (4-5 kg/m²), has no coefficient of moisture expansion (unlike M55J/954-6), and can be used to perform active precision adjustment. On NASA Phase I SBIR Contract # 80NSSC18P2058 GT produced a 3D/AM truss and created a plan to cryotest a 1.2-m Pathfinder Truss with nanoceramic hinges that can be later scaled to >2.4m and tested at NASA MSFC.

Zerodur® is a well-known glass-ceramic used for optical components because of its unequalled dimensional stability under thermal environment. In particular it has been used since decades in Thales Alenia Space’s optical payloads for space telescopes, especially for mirrors. The drawback of Zerodur® is however its quite low strength, but the relatively small size of mirrors in the past had made it unnecessary to further investigate this aspect, although elementary tests have always shown higher failure strength. As performance of space telescopes is increasing, the size of mirrors increases accordingly, and an optimization of the design is necessary, mainly for mass saving. Therefore the question of the effective strength of Zerodur® has become a real issue. Thales Alenia Space has investigated the application of the Weibull law and associated size effects on Zerodur® in 2014, under CNES funding, through a thorough test campaign with a high number of samples (300) of various types. That test campaign demonstrated a strength in fast fracture higher than 40 MPa ([1], [2]) for the tested surface finish, thus allowing much more versatility in the designs than the previously accepted strength limit (10 MPa). Another concern had however been raised: glasses are known to be susceptible to sub-critical crack growth, i.e. slow propagation of cracks under loads below fracture toughness, thus reducing fast fracture strength capabilities (since failure is linked to sudden propagation of those cracks). Taking into account data from literature, no effect was expected on Zerodur® in the conditions of use for space applications, but the very high variability of data made those computations not reliable enough. A dedicated test campaign was therefore defined in order to assess this effect and its consequences in conditions as representative as possible of real conditions. In this paper we show the outcome of this test campaign: the effect of subcritical crack growth is confirmed to be negligible and the minimum strength of 40 MPa is confirmed. In time, Zerodur® strength seems to even increase but this phenomenon was not investigated in the study.

A material with a novel structure combines a material that is transmissive of radio waves, such as a widely used glass fiber-reinforced plastic (GFRP), with a radio wave shutter that can be controlled to reflect or transmit radio waves. When this new material is employed in a radome, the radome can be used as an active substitute for the reflector of a parabolic antenna. As a result, a parabolic antenna reflector is unnecessary; just a radome and a primary feed may operate as a parabolic antenna. This means radio waves can be emitted in any desired direction. Accordingly, structural components of a parabolic antenna, such as a main reflector and a supporting structure, can be omitted and the burden on a driving mechanism can be reduced. In the radio wave shutter, reverse voltages are applied to varactor diodes that are connected in series along equidistantly spaced parallel wires, switching the varactor reactances between short-circuit states and open-circuit states. In this manner, the radome is configured to be reflective in certain directions and to be transmissive in directions in which radio waves should be emitted. Because varactors are controlled by reverse biases, power consumption can be kept small. In addition, the bias directions of the varactors are alternated; consequently, the voltages of a whole set of varactors may be controlled with a voltage sufficient for control of a single varactor. Therefore, high voltage is not required even when a radio wave shutter with a large area is formed.

This paper describes superior candidate substrate material- aluminum nitride (AlN), for the cost-effective and high-performance requirements for aerospace mirrors. In fact, high specific stiffness and thermal stability are not only two major considerations to select ideal material but also machinability, dimensional stability, and cost. Silicon carbide shows the best figure of merits 12627, but it has extremely low remove rate and expensive raw material properties. Extremely low expansion ceramics such as Zerodur may be difficult to obtain in large quantities and its figure of merit is 1151. On the contrary, AlN has outstanding thermal conductivity (~170 W/m°C) and maintain high figure of merit 2222 without compromise. In our fabrication processes, the AlN substrate can be easily polished to 53±1nm Ra surface texture and 66.4±2nm RMS surface form. Its unique thermal stability, specific stiffness, and good figure of merits, associated with its easy machinability and low-cost raw materials, makes AlN an ideal selection for superior mirror substrate in the future space mirror optics.

From 2015, NSPO (National Space Organization) began to develop off-axis Korsch telescope system for next generation earth observation mission. The experimental Korsch telescope system is consist of five mirrors, including: (1) M1: 550mm diameter clear aperture concave primary mirror, (2) M2: Convex secondary mirror, (3) M3: Off-axis concave tertiary mirror with rectangular aperture, (4) FM1 & FM2: Two folding mirrors with rectangular aperture and flat surface. All the experimental mirrors are designed with lightweight structure and made of fused silica. Since early 2016, we collaborated with Taiwanese domestic company and manufactured all the mirrors for the experimental Korsch telescope. Moreover, we not only accomplished the assembly of M1 but also implemented the form error metrology technique to measure the surface error of M1 with high repeatability in 2017. Recently, in order to validate the structural and athermal design of opto-mechanical structures, several vibration tests and thermal experiments have been accomplished in 2018. The experimental data could not only help us to enhance the analysis accuracy of the finite element model but also benefit to our automated opto-mechanical design system. For next developed phase, the aspheric polishing and reflective coating will be achieved till 2021.