Fabrication of lightweight mirrors from low expansion glasses can be achieved using several techniques. Lightweighting can be obtained through fabrication of fusion-bonded cores, abrasive waterjetting (AWJ) technology and traditional fixed abrasive grinding. Lightweight cores can then be bonded to mirror plates using high temperature fusion, low temperature fusion, and frit bonding processes. Each mirror fabrication approach offers its own advantages and disadvantages in terms of lightweighting, cost and design flexibility. Each of these factors is discussed, along with Corning's proven size capability for each.

This paper addresses a NASA Marshall Space Flight Center development contract for Hextek Corporation to produce a 250 mm ultra-lightweight borosilicate mirror blank for cryogenic testing to 30°K. Published data has shown borosilicate glass to be a highly stable material at extremely cold temperatures, with a lower cte (coefficient of thermal expansion) then Zerodur, ULE or fused silica. Hextek would use the cost effective and rapid production Gas-Fusion technology to fabricate a 15 kg/m² substrate that would be figured and polished by NASA and tested cryogenically in the MSFC X-ray Calibration Facility. The expected payoff for NASA is the opportunity to prove out the performance for a substrate technology and mirror material that is capable of reducing cost, schedule and risk associated with the primary mirror in systems operating at cryogenic temperatures.

Fabrication of lightweight mirrors from low expansion glass can be achieved using various core and faceplate lightweighting techniques. Lightweighting can be achieved using abrasive waterjet (AWJ) cutting, CNC machining and a new approach that Corning is developing to produce lightweight cores based on Corning's patented extrusion process. The selection of which lightweighting technology to use is dependent on customer design considerations of the lightweight mirror. These lightweighting techniques are reviewed and discussed, along with advantages and disadvantages of each technique. Corning will also introduce and discuss its new extruded core lightweighting process.

Thermal requirements for the Jet Propulsion Laboratory (JPL) Technology Demonstration Mirror (TDM) to support the Terrestrial Planet Finder (TPF) Mission push the state-of-the-art for lightweight mirror design. A detailed evaluation by Brasher LP during the TPF TDM Mirror Study shows that Corning ULE glass is the best choice to meet these requirements. Even using ULE, careful selection of the grade and individual boule stacking are required to optimize the design and achieve the desired operational performance. The grade of ULE varies from premium to tooling and is determined by the distribution of Coefficient of Thermal Expansion (CTE) variation about a mean value, both radially and axially. The total range of CTE throughout the mirror must be carefully evaluated to determine operational performance. To support this evaluation, a specialized Finite Element Method (FEM) model generator was modified to assign CTE values to each element based upon its position within the boule and the specified mean CTE, radial and axial gradients for each run. The user can specify different CTE mean and radial gradients for front and back face sheets and for two levels of core to match the expected two boule stack for the TDM mirror blank. The program (model generator) can select random values for each of these inputs within the range of a given grade and generate a new model within minutes. This permits statistical studies of ranges as well as worst-case evaluations with ease. This paper describes the evolution of this type of modeler and some of the results obtained from recent studies of small variations in the CTE affecting mirror performance.

All materials undergo some degree of compaction or expansion when exposed to radiation. Multi-component materials are more susceptible to this effect than single-component materials (e.g., fused silica). Nonetheless, the much lower expansion characteristics of multi-component materials -- such as the ultra-low expansion glass-ceramic Zerodur -- preserves the attractiveness of such materials for applications that require superior dimensional stability. In this study, we present a reanalysis of experimental data describing the compaction effects of electron radiation on Zerodur. These data include high-dose, high dose-rate bulk density measurements as well as lower-dose, interferometrically-measured surface figure changes. We show that previous attempts to deduce linear compaction from figure changes are in error and in fact have precluded earlier attempts to predict radiation effects for an arbitrary optical geometry. By interpreting surface figure measurements in light of a more relevant physical model -- a simplified bimetal equation -- we are able for the first time to accurately predict expected deformation as a function of prescribed dose for both laboratory and space-based experiments. Moreover, we show that a real discrepancy exists between compaction estimates from bulk density experiments and those from surface figure measurements.

SCHOTT has developed a Low Temperature Bonding (LTB) technology for fabricating light weight Zerodur optics without the application of high temperature or pressure. The formation of mechanically stable, optically clear joints between two or more glass or glass ceramic parts can be achieved by simply sandwiching an inorganic, aqueous-based solution between chemically prepared surfaces followed by room temperature or slightly elevated temperature curing regimen. This new technology offers a host of advantages over current technologies including room temperature processing, lower production costs and reduced delivery times as well as broad design flexibility. The LTB technology was used in this study to fabricate a 285 mm light-weight plano-plano closed back mirror in an attempt to qualify the bonded assemblies made by this technology for space application. The mirrors were assembled by bonding Zerodur faceplates onto a Zerodur core structure, fabricated via abrasive water jet cutting, to produce a light weighted optic with an aerial density of 24.5 kg/m². In addition, smaller unit cell structures were also fabricated in a similar fashion for prototype testing. Both the large mirror and the smaller unit cell structures will be measured for surface figure stability before and after thermal cycling and for bonded mechanical strength.

The use and manufacturing of AlBeMet 162 material as an optical substrate for head mirrors, night vision systems and fire control optics is discussed. The paper discusses the validation AlBeMet 162's thermal stability over the military environmental temperature range of -40F to +140F. The paper will discuss the manufacturing processing to yield dimensional stable optics in AlBeMet material. It will also discuss the results of interferometric testing on 150 mm diameter flats produced by 3 separate optical fabrication companies. Demonstrating the ability of the process and material to produce optical mirrors over temperature with thermal distortions of less than 0.25 wavelengths P-V. The paper will show interfermetrically that AlBeMet and nickel have an excellent coefficient of thermal expansion match over the temperature range of interest, so that there is no bi-metallic issue or distortion due to the electroless nickel. The paper will also discuss the continuing characterization program with the initial results from testing a light weighted substrates with a spherical surface.

Ultimate tensile strength, yield strength, and elongation were obtained for the aluminum-beryllium alloy, AlBeMet162 (38%Al-62%Be), at cryogenic [(-195.5°C (-320°F) and (-252.8°C) (-423°F)] temperatures, and for an optical grade beryllium, O-30H (99%Be), at -252.8°C. AlBeMet162 material was purchased to the requirements of SAE-AMS7912, "Aluminum-Beryllium Alloy, Extrusions." O-30H material was purchased to the requirements of Brush Wellman Inc. specification O-30H Optical Grade Beryllium. The ultimate tensile and yield strengths for extruded AlBeMet162 material increased with decreasing temperature, and the percent elongation decreased with decreasing temperature. Design properties for the ultimate tensile strength, yield strength, and percent elongation for extruded AlBeMet162 were generated. It was not possible to distinguish a difference in the room and cryogenic ultimate strength for the hot isostatically pressed (HIP'ed) O-30H material. The O30H elongation decreased with decreasing temperature.

Beryllium aluminum material can present significant advantages for optical support structures. A very likely advantage of beryllium aluminum compared to aluminum or titanium for such structures is its higher specific stiffness. However, beryllium aluminum material is significantly more expensive than most competing materials. The cost problem with beryllium aluminum is exacerbated if structural fabrication methods that result in near net shape parts are not used. Near net shape methods result in the least amount of material “thrown away” in the fabrication process. Casting is a primary example of near net shape manufacturing that is appropriate for certain optical support structures. Casting aluminum, and other materials as well, is common. Casting of beryllium aluminum is very difficult, however, and has not had significant success. Diffusion bonding -- a different approach for achieving near net shape beryllium aluminum optical support structures, was pursued and accomplished. Diffusion bonding is a term used to describe the joining of solid metal pieces under high temperature and pressure, but without melting. Three different optical support structures were designed and built of beryllium aluminum using diffusion bonding. Relatively small solid beryllium aluminum pieces were arranged together and then joined under hot isostatic pressure conditions. The resulting relatively large diffusion bonded part was then machined to achieve the final product. Significant cost savings as compared to machining the part from a solid block were realized. Difficulties achieving diffusion bonds in complex joints were experienced and addressed.

Every space-borne optical system has a unique set of requirements and challenges. In the end, all need to achieve a delicate balance of performance, cost, and schedule to be successful. Principal to achieving this goal is the correct selection of the mirror materials from among a variety of common options: glass, aluminum, beryllium, and silicon carbide. Many engineering disciplines -- optical, mechanical, thermal, and materials -- are required to design an optical system. The intent of this paper is to describe the strengths and limitations of each mirror material from the perspective of an optical systems engineer, who must balance all disciplines in order to select the best material combination for a specific application. Several topics are discussed, including: (1) Mechanical and thermal figures of merit; (2) stability and design considerations (K/α, ΔL/L, and cryogenic test data); (3) fabrication issues: schedules, relative costs, achievable figures, and finishes; and (4) stray light rejection and achievable BRDF's. Data is presented from many recent projects in support of these topics.

A photo patterned fabrication process for manufacture of passive polymer composite waveguide structures and devices is presented. The process takes advantage of compatibility between certain polymer/high vapor pressure monomer blends and their refractive index differences to directly photo define passive waveguide structures. With suitable catalysts, monomers present in the composite blend are polymerized in exposed areas, while allowed to evaporate in unexposed areas during a brief post exposure bake. Areas thus produced will have a different composition (i.e. refractive index) in exposed vs. unexposed areas and different thickness due to reactant loss. Composite blends consisting of polysulfone/epoxy or acrylic/epoxy have excellent compatibility for providing photo defined waveguide core regions in either the unexposed areas or exposed areas of processed thin films. Optical loss measurement comparisons for bulk polymer samples and composite thin films to the photo patterned waveguides indicate loss in the patterned waveguides are similar to the polymer intrinsic loss. Additionally, by taking advantage of the process providing control over refractive index and surface topography, other photonic components such as micro lenses can be fabricated.

Silicone lens materials, baselined for space power applications, were exposed to various components of a Geosynchronous Earth Orbit (GEO) radiation environment to determine the suitability of the material for long-term missions. Sample materials were exposed to electrons, protons, Near Ultraviolet (NUV), and Vacuum Ultraviolet (VUV) radiation. The samples were exposed to individual and to various combinations of these space environmental components. The electron and proton exposure levels were determined from radiation measurements performed in GEO. NUV and VUV radiation exposures were based on solar emissions at zero air mass (AM0). Lens material degradation was determined by the change in optical spectral transmission of the silicone materials. A reduction in the transmittance of the material will reduce the power generating potential of solar cells. The spectral transmission was measured at Marshall Space Flight Center (MSFC), after exposure to space environmental elements including electrons, protons, VUV and NUV. Entech, Inc. conducted performance tests on samples exposed to short duration proton and electron radiation. Results of these tests will be discussed. Minor degradation was witnessed on samples exposed to NUV and VUV light. The largest transmission spectral degradation occurred in the wavelength range below the quantum efficiency of space qualified solar cells. Transmission degradation in the wavelength range of maximum solar cell quantum efficiency was small.

A unique ultra-light solar concentrator has recently been developed for space power applications. The concentrator comprises a flexible, 140-micron-thick, line-focus Fresnel lens, made in a continuous process from space-qualified transparent silicone rubber material. For deployment and support in space, end arches are used to tension the lens material in a lengthwise fashion, forming a cylindrical stressed membrane structure. The resultant lens provides high optical efficiency, outstanding tolerance for real-world errors and aberrations, and excellent focusing performance. The stretched lens is used to collect and focus sunlight at 8X concentration onto high-efficiency multi-junction photovoltaic cells, which directly convert the incident solar energy to electricity. The Stretched Lens Array (SLA) has been measured at over 27% net solar-to-electric conversion efficiency for space sunlight, and over 30% net solar-to-electric conversion efficiency for terrestrial sunlight. More importantly, the SLA provides over 180 W/kg specific power at a greatly reduced cost compared to conventional planar photovoltaic arrays in space. The cost savings are due to the use of 85% less of the expensive solar cell material per unit of power produced. SLA is a direct descendent of the award-winning SCARLET array which performed flawlessly on the NASA/JPL Deep Space 1 spacecraft from 1998-2001.

There is a significant amount of research devoted to developing materials and processes for spaceborne mirrors. Carbon fiber mirrors and advanced ceramic mirrors such as SiC are being developed. These materials provide excellent stiffness to weight ratios and thermal stability. The principal problem with using these lightweight materials for mirrors is the difficulty of polishing the surface to achieve the required optical quality finish. Carbon fiber mirrors also suffer from fiber print through and ceramic mirrors are difficult and costly to polish due to the material hardness and porosity. SRS has been developing processes for depositing a very thin, optical-quality membrane layer of space-qualified polymer onto the surface of a mirror still in a rough-polished state to eliminate the need for expensive and time consuming final surface finishing of lightweight mirrors. By flow casting a polymer onto the surface, remaining peaks and valleys are filled in resulting in an extremely smooth surface. Initial research has shown that the membrane mirror surface can have a significantly better surface finish than the casting substrate, thus eliminating the need for costly final polishing.

The Air Force, as well as many other organizations, has considerable interest in developing deployable space-based parabolic membranes. One of the key factors for the success and user acceptance of this technology is 'performance' of the deployed optical membrane. Performance hinges critically on the precision of obtaining a near-net shape parabolic membrane. In a net shape optics concept, these parabolic membranes are maintained by stresses developed due to optical coatings. Continuum-based predictive models of coating requirements must be translated into a prescription for the coating process, which is an atomistic-based activity. In this paper we present some preliminary results of experiments performed to validate the coatings applied to polymer membranes in order to match numerical predictions. Bulge tests were performed to determine the coating stress of a thin film membrane. The bulge tests related the deflection of a pressurized thin film to the film's mechanical proprties (incuding coating stress). A finite element model was created using ABAQUS for comparison with the bulge test data. Vibration tests were also performed to determine the coating stress, since natural frequencies give an estimate of the intrinsic coating properties. An ABAQUS model provided the first few natural frequencies for comparison against the experimental results. In a net shape optics concept, these parabolic membranes are maintained by stresses developed due to optical coatings. Continuum-based predictive models of coating requirements must be translated into a prescription for the coating process, which is an atomistic-based activity. In this paper we present some preliminary results of experiments performed to validate the coatings applied to polymer membranes in order to match numerical predictions. Bulge tests were performed to determine the coating stress of a thin film membrane. The bulge tests related the deflection of a pressurized thin film to the film's mechanical properties (including coating stress). A finite element model was created using ABAQUS for comparison with the bulge test data. Vibration tests were also performed to determine the coating stress, since natural frequencies give an estimate of the intrinsic coating properties. An ABAQUS model provided the first few natural frequencies for comparison against the experimental results.

A novel shape memory composite material for the fabrication of thin, lightweight deployable mirrors is presented. The material has been evaluated for shape memory performance and dimensional stability. In addition, preliminary efforts have been directed toward the fabrication of lab-scale, replica mirrors. The concept combines a shape memory composite substrate with an electroplated metal reflective surface to provide a thin mirror with the ability to be deformed for packaging with good shape-recovery on deployment and reasonable post-deployed compliance that facilitates active shape control. The shape memory composite substrates are composed of Elastic Memory Composite (EMC) materials with appropriate reinforcements (i.e. fibers, particulates, or nanoreinforcements). The reflective surfaces are composed primarily of electroplated nickel with a variety of surface preparations to promote good adhesion to the composite substrate and provide optical-quality reflectance. Thin (i.e. less than 508 μm or 20 mils), EMC-composite mirrors have been prepared with adhered, electroplated nickel metal surfaces, which are less than 25.4 μm (i.e. 1 mil) thick. A single method of fabrication has been examined; electroplated thin metal deposition on a mandrel followed by subsequent adhesion to an EMC laminate. Investigative results of material fabrication, packaging and deployment testing, and preliminary optical-performance testing are presented.

The James Webb Space Telescope (JWST) will be a 6-meter diameter segmented reflector that will be launched at room temperature and passively cooled to about 40 Kelvin at the L2 point. Because of the large thermal load, understanding the thermophysical properties of the mirror, secondary optics, and supporting structure materials is crucial to the design of an instrument that will provide diffraction limited performance at 2 microns. Once deployed, JWST will perform continuous science without wave front re-calibrations for durations ranging from one day to a month. Hence understanding of how small temperature fluctuations will impact the nanometric stability of the optical system through thermal expansion is required. As a result, the JWST materials testing team has designed and built a novel cryogenic dilatometer capable of coefficient of thermal expansion (CTE) measurements of ULE accurate to ~ 1.6 and 0.1 ppb/K for a nominal CTE = 30 ppb/K and 20 and 280 K thermal loads, respectively. The dilatometer will be used to measure the CTE of samples from JWST primary mirror prototypes, local CTE variations from multiple locations on a prototype mirror, CTE variations from batch to batch of the same material, and thermal and mechanical creep measurements from room temperature down to 30 K.

A unique experimental facility has been designed to measure damping of materials at cryogenic temperatures. The test facility pays special attention to removing other sources of damping in the measurement by avoiding frictional interfaces, decoupling the test specimen from the support system, and by using a non-contacting measurement device. Damping data is obtained for materials (Al, GrEp, Be, Fused Quartz), strain amplitudes (<10^-6 ppm), frequencies (20 Hz-330Hz) and temperatures (20K - 293K) relevant to future precision optical space missions. The test data shows a significant decrease in viscous damping at cryogenic temperatures and can be as low as 10^-4%, but the amount of the damping decrease is a function of frequency and material. Contrary to the other materials whose damping monotonically decreased with temperature, damping of Fused Quartz increased substantially at cryo, after reaching a minimum at around 150°K. The damping is also shown to be insensitive to strain for low strain levels. At room temperatures, the test data correlates well to the analytical predictions of the Zener damping model. Discrepancies at cryogenic temperatures between the model predictions and the test data are observed.

Coefficient of thermal expansion is an integral part of the performance of optical systems, especially for those which operate at cryogenic temperatures. The measurement of the coefficient of relevant materials has been of continuous interest. Besides commercial measurement sources, development of one-of-a-kind tools has always been of interest due to local needs. This paper describes one such development at the University of Alabama in Huntsville (UAH). The approach involves two vertical rods (one sample and one reference) on a flat platform. A probe bar is held horizontally atop the two samples. A temperature change will generally cause rotation of the probe bar. A mirrored surface on one end of the probe bar is used to measure the rotation using the reflection of an incident laser beam upon it. The change of the reflected beam spot position is measured by a position-sensing detector. Using other known quantities, the change determines the coefficient of thermal expansion of the sample material as a function of temperature. A parallel measurement of the rotation of the sample support platform is also performed to account for any unwanted background effects. This system has been demonstrated in a cryogenic chamber at the NASA Marshall Space Flight Center X-ray Calibration Facility (XRCF). We present the system details, achievable sensitivity, and up-to-date experimental performance.

At 6-7 meters in diameter, the James Webb Space Telescope (JWST) will require structures that remain stable to levels that are on the order of 10 nanometers under dynamic and thermal loading while operating at cryogenic temperatures. Moreover, the JWST will be the first telescope in space that is deployed, resulting in an aperture that is not only segmented, but has hinge-lines and the associated joining systems or latches in it. In order to understand the behavior and reduce the risk associated with very large, deployed structures and the stability of the associated structure and latches, we developed and tested the largest cryogenic structure ever built and then characterized its stability. This paper presents a description of the design of the Development Optical Telescope Assembly (DOTA), the testing performed, and the results of the testing performed on it. We discuss the material selection and characterization processes, give a description of the test configurations, describe the metrology equipment and the validation process for it, provide the test results, and summarize the conclusions drawn from the results. The testing and associated results include characterization of the thermal stability of the large-scale structure, characterization of the micro-dynamic stability of the latching system, and measurements of the deployment capability of the mechanisms. We also describe how the DOTA design relates to the JWST design and how the test results relate to the JWST requirements.

The value of glass frit bonding to assemble silicon parts wa demonstrated by the successful evaluation of cryostability of a small multi-piece silicon mirror. This bonding technique has been extended to the assembly of a 44kg block of silicon, 113 x 400 x 400 mm. Such an assembly was considered to be a cost competitive alternative to the purchase of a custom sized silicon boule. Various types of evaluation provided the foundation upon which this accomplishment is based. Included were cryocycling of frit bonded plates, comparison of the strength of bonded silicon bend bars with that of silicon bend bars, and the fabrication and cryotest of a small concave frit bonded silicon mirror. Of the 16 bonded bars in two groups only 2 had failures in the bondline, 11 failed in the silicon, and origins could not be determined for 3 bars. The two groups of bonded silicon bars had average strengths that were 84% and 91% of the average strength of the plain silicon bars. In view of the relatively small number of bars in each group this is not surprising. The cryostability of the concave bonded silicon mirror was demonstrated by a figure error of less than 0.06 wave rms at 633 nm, cold to warm, compared to a specification of 0.1 wave rms, and 0.014 wave rms, warm to cold to warm, over an 80% clear aperture. These results are reviewed before interesting features of the large block are discussed. Finally, projections are made regarding possible future applications for this bonding process.

Processing of semiconductors, including machining, grinding, or polishing, involves thermomechanical deformation of a thin surface layer, thus coupling temperature and stress fields. Si, Ge, and other III-V semiconductors, exhibit complex constitutive laws coupling mechanical deformation with an evolving microstructure, typically dislocation density or coordination number. Irreversible shear flow and phase transitions are induced by combined stresses and temperatures. We discuss constitutive laws applicable to the machining of silicon.

Surface properties of single crystal silicon are of great interest to many people in research and development as well as in industry, particularly the semiconductor industry. In this paper we present and discuss the results of a series of nanoindentations as they relate to the elasticity and microhardness properties on the surface of a large single crystal silicon sphere. The sphere is 94 mm, it has a total roundness error of <213 nm P-V, and a super-polished surface <0.4 nm rms. The cubic structure of a silicon crystal displays different properties of hardness and elasticity in the different crystallographic planes. We present a study of the measurable differences in these mechanical properties as they relate to the <111> and the <100> directions. We show how these differences affect the overall shape of the sphere during the surface finishing process.

Cesic -- a trademark of ECM for carbon-fiber reinforced silicon carbide -- allows relatively quick and cheap manufacturing of components because the components can be shaped with conventional tools in a milling and/or drilling process of the greenbody material. Through a joining process and our new development of optical surfaces based on a slurry cladding technology, Cesic allows for a direct up-scaling of structures and optical surfaces to large-size applications and systems. The size of the structures and mirrors that can be manufactured is limited only by the scale of the available furnaces facilities, the largest of which currently is 2.4 m in diameter.

Flat surfaces of reaction bonded SiC and aspheric surfaces of Si clad reaction bonded SiC were polished to yield rms surface roughnesses less than 30Å. These surfaces were then overcoated with two formulations of a typical front surface protected silver film and their reflectances and roughnesses compared with highly polished fused silica flat surfaces that were silver coated at the same time. Surface roughness and BRDF measurements performed before and after coating with protected silver indicated no significant increase in surface roughness or measured scatter for either silver coating formulation and a barely detectable measured roughness difference between the two coating formulations.

In view of the NIRSpec-JWST program, a trade-off study is currently in progress under an ESA-ESTEC contract, to select design, blank materials, coatings and relevant technologies for high quality mirrors operating at cryogenic temperatures. The behavior of two prototype lightweight mirrors, made in cold- pressed-sintered SiC and in Carbon-SiC (Cesic) are compared by interferometric measurements at 20 K. The prototypes are spherical mirrors, but realized using optical manufacturing technologies suitable for highly demanding aspherics (i.e. computer controlled polishing, ion beam figuring), in the perspective of the foreseen NIRSpec-TMA(s) optics.

The SOPHI (Segmented Optics PHase Integration) Phase 1 project has demonstrated the original goals for the SOPHI breadboard to enable it to meet the challenge of the Phase II full 1 meter optical quality segmented mirror project: one of these goals is that the mirror segments can be phased without edge sensors and without referencing each other (no 2 π ambiguities). To do this, an optical metrology is utilized (the subject of a separate paper and reference 1). The stiffness and lightweight criteria are met by utilizing CSIC and Cesic ceramics.

A process for fabricating high quality light weight mirrors from single crystal silicon is described. The process uses conventional fabrication techniques in an unconventional sequence. It is capable of producing mirrors with 1/4th the mass of an equivalent solid quartz mirror. Each mirror is a monolithic structure of single crystal silicon. Mirrors with optical figures better than 1/10th wave peak-to-valley (@633 nm) have been demonstrated.

The optical and thermal design of the 1.5 m solar telescope GREGOR is presented. The three first main mirrors of GREGOR will be made from Cesic, a silicon carbide material. One major constraint of large solar telescopes is the thermal load of the structure and the mirrors. The mirrors are heated by the solar radiation and introduce potentially harmful mirror seeing. GREGOR will use an active mirror cooling system and an open telescope structure to reduce these negative effects. A thermal analysis shows that the equilibrium temperature of the Cesic Mirror without active cooling is 6° above ambient temperature. Additional cooling will reduce the temperature difference of the optical surface and ambient air to below 0.1° K. With tempered airflow (about 2.5 m³/s per square meter mirror surface) the temperature gradient on the surface of the face sheet is less than 0.1°K. The telescope will have an open structure and a complete retractable dome to support mirror and structure cooling by wind.

The operational wind speed for the 1.5 m solar telescope GREGOR which will be erected in 2004 on the Spanish island of Tenerife is specified at 20 m/s. At this wind speed the seeing conditions at the telescope site are good for observations of the solar physics and the effects of internal seeing will be minimized by the wind blowing through the largely open telescope structure. The requirements for an absolute pointing accuracy of 1 arcsec rms and for a relative pointing error of 0.25 arcsec rms have to include the wind load influences. In this paper the numerical analyses of the structural response under static and dynamic wind loads and their impact on the telescope design are presented. For the analyses a response spectrum method using a finite element program system and a time history simulation including the servo system were utilized. For the analyses and simulations detailed finite element models of the telescope were used. The dynamic wind loads on the structure were calculated using a wind turbulence spectral density function and simulated wind speed time histories including site-specific wind characteristics. A pointing model taking into account the displacements of the telescope's mirrors with respect to the adjusted configuration was included in the investigations.

The mechanical division of EADS Astrium GmbH, Friedrichshafen Germany, the former Dornier Satellitensystem GmbH is currently engaged with the development, manufacturing and testing of three different advanced dimensionally stable composite and ceramic material structures for satellite borne optics: -CFRP Camera Structure -Planck Telescope Reflectors -NIRSpec Optical Bench Breadboard for James Web Space Telescope The paper gives an overview over the requirements and the main structural features how these requirements are met. Special production aspects and available test results are reported.

A fundamental limitation for using fiber reinforced polymer composites in fabrication of reflective mirror substrates for space telescopes is the fiber print through phenomenon. Because of fiber print through, the typical surface roughness of composite substrates is orders of magnitude higher than what's required for IR and visible optics. This paper presents and demonstrates a new approach to overcome this inherent problem with composites, thus allowing these materials to be considered for mirrors operating in the IR and possibly the visible range of the electromagnetic spectrum.

The Mars Orbiter Camera (MOC) narrow angle system is a 3.5 m focal length camera that has operated for the last five years as part of the Mars Global Surveyor (MGS) Mission. Folded into a total package (including electronics) of less than 1 m length and weighing just over 20 kg, MOC's Ritchey-Chretien optical design is extremely sensitive to primary-to-secondary despace. Because of this, providing proper focus over the range of operational conditions was the primary challenge of the MOC development effort. As initially proposed, the instrument used a graphite-epoxy metering structure to provide a completely athermal system. Given of the sensitivity of the design and large operational temperature range, this turned out not to be realizable. The first fallback from a completely athermal design was to model the response of the system over temperature, and set the detector so the system would be focus over the range of operational conditions. Prototype testing revealed this was also not a workable solution. Late in the development flow, the system was retrofitted with a set of heaters to control focus in flight by application of radial thermal gradients across the primary mirror. Despite the loss of the first copy of the MOC on Mars Observer in 1993, the MOC on MGS has been an outstanding success, returning over 140,000 images of Mars to date and making a number of new discoveries about the planet.

For many years, lightweighted sandwich-style mirror blanks made from Corning's Ultra-Low Expansion glass (ULE) have been used in space telescope systems that demand superior optical performance. Despite the superior performance of this technology, the historically high cost and long schedule to procure such a blank has limited their use to only the most elite missions. Future missions, such as JWST, will seek to dramatically reduce the historical cost/schedule paradigm for ULE blanks by capitalizing on economies-of-scale associated with a multi-segment design. However, for this blank technology to become accessible to a broader range of missions, fundamental changes in technical and business approaches are needed. Over the last four years, ATK COI has worked to develop the requisite technologies to produce ULE mirror blanks in-house, with an emphasis on reducing cost and schedule. Our focus has been in three areas: process development to enable reclamation of ULE glass residuals, glass fusion process qualification, and tooling cost reduction. The status of each of these areas is presented, and conclusions drawn about possible future costs of lightweight ULE mirror blanks.