This PDF file contains the front matter associated with SPIE Proceedings Volume 7018, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

For ground-based astronomy, more and more large telescopes are emerging all around the world. Similarly to space borne telescopes, for which the use of lightened optics has always been a baseline for purpose of mass reduction of payloads, same kinds of lightened/light mirrors are then now more and more intensively used also for ground-based instrumentation for astronomy, requiring larger and larger components. Through several examples of typical past realizations (class 0.5m-1m) for different astronomical projects requiring light or lightened mirrors for different reasons (optimisation of mass and stiffness, reduction of thermal inertia, increasing of dynamic performance for fast scanning purpose,....), the presentation will point out issues for lightening design, manufacturing and control of such parts, as well as brief overview of the corresponding existing "state of the art" for these technologies in SESO.

JSC LZOS is carrying out work on the manufacturing of the M1 primary hyperbolic Mirror with the 4100 mm diameter for the VISTA project (Visible and Infrared Survey Telescope for Astronomy). Vertex radius of Mirror is 8094 mm (F/0.98), conic constant -1.129792 and asphericity about 880 microns. The current situation of the work carried out is presented in the manuscript.

The very challenging goal of the Vlt-Sphere instrument, Exoplanet direct detection and characterisation, requires high contrast imaging and extreme adaptive optics.1 In order not to limit the overall imaging performances of the instrument, all the optics in the common path optical train need to be of the better quality over each range of spatial frequencies. Three Toric mirrors are placed in the common path to relay the beam to the deformable mirror and to the instruments. This paper details the Stress polishing principle developed at Laboratoire d'Astrophysique de Marseille (Lam) to get the better optical quality on the toric surfaces, using a spherical polishing with full size tools. The elasticity theory giving the optimisation of the blank geometry to be warped during the stress polishing process is detailed from analytical calculation to finite element analysis. The use of an angular thickness distribution allows us to reach the better optical quality of the deformation by canceling higher order terms. We also present the polishing results for the 366mm diameter Toric Mirror manufacturing.

The optical quality of the LLT unit of SUBARU NAOJ telescope was improved by new athermalized supports of the optics, in order to operate at the best performance at temperatures below 0°C. The ultimate wavefront correction of the whole LLT, that expands a laser beam from 40 mm to 500 mm, was made by Ion Beam Figuring on the small 40 mm LLT entrance window, in accordance to the WFE measured in operating conditions. The correction of small optics including high spatial frequencies, resulting by the LLT expanding ratio, was possible by a special technique of IBF process developed at the Astronomical Observatory of Brera (INAF-OAB), using a concentrator of the ion beam size, able to force the broader beam emitted from an ion source into a smaller spot having large removal rate.

During the last ten years, Astron has been a major contractor for the design and manufacturing of astronomical instruments for Space- and Earth based observatories, such as VISIR, MIDI, SPIFFI, X-Shooter and MIRI. The collaboration between optical- and mechanical designers at Astron led to new design philosophies and strategies. Driven by the need to reduce the weight of optically ultra-stiff structures, two promising techniques have been developed in the last years: ASTRON Extreme Lightweighting for mechanical structures and an improved Polishing Technique for Aluminum Mirrors. Using one single material for both optical components and mechanical structure simplifies the design of a cryogenic instrument significantly, it is very beneficial during instrument test and verification, and makes the instrument insensitive to temperature changes. Aluminum has been the main material used for cryogenic optical instruments, and optical aluminum mirrors are generally diamond turned. The application of a polishable hard top coating like nickel removes excess stray light caused by the groove pattern, but limits the degree of lightweighting of the mirrors due to the bi-metal effect. By directly polishing the aluminum mirror surface, the recent developments at Astron allow for using a non-exotic material for light weighted yet accurate optical mirrors, with a lower surface roughness (~1nm RMS), higher surface accuracy and reduced light scattering. This paper presents the techniques, obtained results and a global comparison with alternative lightweight mirror solutions.

Modern day telescopes for astronomy have very complex requirements. Both ground and space based telescopes are getting much larger placing significant productivity requirements on the manufacturing processes employed. Conventional manufacturing paradigms involving mechanical abrasion have limitations related primarily to the material removal mechanisms employed. Reactive Atom Plasma (RAP^TM) processing is a sub-aperture, non-contact, deterministic figuring technology performed at atmospheric pressures. The process has high material removal rates, and given the non-contact and atmospheric nature lends itself very well to scaling up for large aperture mirrors/segments. The process also benefits from its ability to simultaneously remove sub-surface damage (SSD) while imparting the desired figure to the surface. Developments are under way currently to scale the process up towards larger clear apertures while being able to figure in high spatial frequency features.

Next generation space telescopes, which are currently being developed in the US and Europe, require large-scale light-weight reflectors with high specific strength, high specific stiffness, low CTE, and high thermal conductivity. To meet budget constraints, they also require materials that produce surfaces suitable for polishing without expensive over-coatings. HB-Cesic - a European and Japanese trademark of ECM - is a Hybrid Carbon-Fiber Reinforced SiC composite developed jointly by ECM and MELCO to meet these challenges. The material's mechanical performance, such as stiffness, bending strength, and fracture toughness are significantly improved compared to the classic ECM Cesic material (type MF). Thermal expansion and thermal conductivity of HB-Cesic at cryogenic temperatures are now partly established; and excellent performance for large future space mirrors and structures are expected. This paper presents the design and manufacturing of an 800-mm mirror for space application, starting with the C/C raw material preparation to the finishing of the components, including the polishing of the mirror. The letters "HB" in HB-Cesic stand for "hybrid" to indicate that the C/C raw material is composed of a mixture of different types of chopped, short carbon-fibers.

"LZOS", JSC has completed the fabrication of M2 Primary mirror for VISTA Project (Visible and Infrared Survey Telescope for Astronomy). M2 Mirror has diameter 1241mm and hyperbolic figure surface. The Vertex Radius of the Mirror is 4018.81mm (F/0.96), the Conical constant is -5.548792, aspherical value is 306 μm. The Project works results are presented.

The first of the 8.4 m off-axis segments for the primary mirror of the Giant Magellan Telescope is being manufactured at the Steward Observatory Mirror Lab. In addition to the manufacture of the segment, this project includes the development of a complete facility to make and measure all seven segments. We have installed a new 28 m test tower and designed a set of measurements to guide the fabrication and qualify the finished segments. The first test, a laser-tracker measurement of the ground surface, is operational. The principal optical test is a full-aperture interferometric test with a null corrector that includes a 3.75 m spherical mirror, a smaller sphere, and a computer-generated hologram. We have also designed a scanning pentaprism test to validate the measurement of low-order aberrations. The first segment has been cast and generated, and is in the process of loose-abrasive grinding.

The Astronomical Observatory of Brera (INAF-OAB) is investigating a novel slumping technique for the manufacturing of stiff and lightweight optical segments. We propose a 2-steps technique: initially the procedure foresees to manufacture a mirror segment using the hot slumping technique. This step produces a thin and floppy Borofloat glass shell using the slumping of a glass sheet onto a ceramic mould that has a surface with a high optical quality. After this step, this curved shell is assembled and glued to a stiff substrate made in foamed and pre-shaped material. On the back of the substrate it is also glued a flat sheet of the same glass. This procedure combine the good optical performances achievable on optics produced by means of the hot slumping technique with the lightweight and stiffness of the foamed material and, finally, the good structural properties achievable in sandwich-like structures. This approach could be in principle used for the production of mirrors for a number of applications, from the primary segmented mirror for large telescopes to the mirrors for the future Cherenkov telescopes nowadays under development. This paper describes the process of production of a prototype optical segment and the status of the investigation.

In the last years, the technology of SiC mirrors took an increasingly significant part in the field of space telescopes. Sagem is involved in the JWST program to manufacture and test the optical components of the NIRSpec instrument. The instrument is made of 3 TMAs and 4 plane mirrors made of SiC. Sagem is in charge of the CVD cladding, the polishing, the coating of the mirrors and the integration and testing of the TMAs. The qualification of the process has been performed through the manufacturing and testing of the qualification model of the FOR TMA. This TMA has shown very good performances both at ambient and during the cryo test. The polishing process has been improved for the manufacturing of the flight model. This improvement has been driven by the BRDF performance of the mirror. This parameter has been deeply analysed and a model has been built to predict the performance of the mirrors. The existing Dittman model have been analysed and found to be optimistic.

A new ultra precision large optics grinding machine, BoX^® has been developed at Cranfield University. BoX^® is located at the UK's Ultra Precision Surfaces laboratory at the OpTIC Technium. This machine offers a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. This paper presents an analysis of subsurface damage assessments of optical ground materials produced using diamond resin bonded grinding wheels. The specific materials used, Zerodur^® and ULE^® are currently under study for making extremely large telescope (ELT) segmented mirrors such as in the E-ELT project. The grinding experiments have been conducted on the BoX^® grinding machine using wheels with grits sizes of 76 μm, 46 μm and 25 μm. Grinding process data was collected using a Kistler dynamometer platform. The highest material removal rate (187.5 mm³/s) used ensures that a 1 metre diameter optic can be ground in less than 10 hours. The surface roughness and surface profile were measured using a Form Talysurf. The subsurface damage was revealed using a sub aperture polishing process in combination with an etching technique. These results are compared with the targeted form accuracy of 1 μm p-v over a 1 metre part, surface roughness of 50-150 nm RMS and subsurface damage in the range of 2-5 μm. This process stage was validated on a 400 mm ULE^® blank and a 1 metre hexagonal Zerodur^® part.

The Large Synoptic Survey Telescope uses a unique optomechanical design that places the primary and tertiary mirrors on a single glass substrate. The honeycomb sandwich mirror blank was formed in March 2008 by spin-casting. The surface is currently a paraboloid with a 9.9 m focal length matching the primary. The deeper curve of the tertiary mirror will be produced when the surfaces are generated. Both mirrors will be lapped and polished using stressed laps and other tools on an 8.4 m polishing machine. The highly aspheric primary mirror will be measured through a refractive null lens, and a computer-generated hologram will be used to validate the null lens. The tertiary mirror will be measured through a diffractive null corrector, also validated with a separate hologram. The holograms for the two tests provide alignment references that will be used to make the axes of the two surfaces coincide.

A Configurable Slit Unit (CSU) has been developed for the Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE) instrument to be installed on the Keck 1 Telescope on Mauna Kea, Hawaii. MOSFIRE will provide NIR multi-object spectroscopy over a field of view of 6.1' x 6.1'. The reconfigurable mask allows the formation of 46 optical slits in a 267 x 267 mm² field of view. The mechanism is an evolution of a former prototype designed by CSEM and qualified for the European Space Agency (ESA) as a candidate for the slit mask on NIRSpec for the James Webb Space Telescope (JWST). The CSU is designed to simultaneously displace masking bars across the field-of-view (FOV) to mask unwanted light. A set of 46 bar pairs are used to form the MOSFIRE focal plane mask. The sides of the bars are convoluted so that light is prevented from passing between adjacent bars. The slit length is fixed (5.1 mm) but the width is variable down to 200 μm with a slit positioning accuracy of ± 18 μm. A two-bar prototype mechanism was designed, manufactured and cryogenically tested to validate the modifications from the JWST prototype. The working principle of the mechanism is based on an improved "inch-worm" stepping motion of 92 masking bars forming the optical mask. Original voice coil actuators are used to drive the various clutches. The design makes significant use of flexure structures.

An image slicer breadboard has been designed, manufactured and tested for MUSE (Multi Unit Spectroscopic Explorer) instrument, a second generation integral field spectrograph developed for the European Southern Observatory (ESO) for the VLT. MUSE is operating in the visible and near IR wavelength range (0.465-0.93 μm) and is composed of 24 identical Integral Field Units; each one incorporates an advanced image slicer associated with a classical spectrograph. This paper describes the original optical design, the manufacturing, component test results (shape, roughness, reflectivity, microscopic visualization) and overall system performance (image quality, alignment) of the image slicer breadboard. This one is a combination of two mirror arrays of 48 elements each. It is made of Zerodur and uses a new polishing approach where all individual optical components are polished together by classical method. This image slicer constitutes the first one which has the largest number of active slices (48) associated with strict tolerances in term of positioning. The main results of the tests on this image slicer breadboard will then be presented. Most of them are compliant with requirements. This demonstrates that the manufacturing process is mature and gives good confidence for serial production applied to MUSE instrument.

The Configurable Slit Unit (CSU) for EMIR shall enable the possibility to generate a multi-slit configuration, a long slit, or an imaging aperture at the entrance focal plane of the GTC-EMIR instrument. The CSU is therefore a cryogenic reconfigurable slit mechanism. It contains 110 sliding bars which can be positioned within the 340x340mm wide aperture of EMIR's instrument field of view. Based on the results which haven been obtained in the previously performed demonstration programme, the current developments have focused on the optimization of the performance and up scaling of the construction. Major progress and improvement have been made on the position measurement of the slits, as a result of conceptual improvements in the measurement system but also as a result of fundamental hardware changes. Furthermore an improvement of the thermal household of the instrument will contribute to the position stability performance. Main development advances on several aspects of the instrument design are presented. This work is performed under contract of the Instituto de Astrofisica de Canarias as part of the development of the EMIR instrument to be installed at the GTC telescope.

The use of monolithic glass to produce large, rigid segmented members for lightweight space-based mirror systems appears to have reached its limits due to the long production lead times, high processing costs, and launch load/weight requirements. New material solutions and processes are required to meet the US Air Force's optical needs for directed energy, reconnaissance/surveillance, and communications. Mirror structural substrates made out of advanced materials (metal, ceramic, and polymer), composites, foams, and microsphere arrays should allow for CTE and modulus tailorability, low-density, and high values in strength, stiffness, thermal conductivity and toughness. Conventional mechanical polishing to visual specifications for figure and surface finish roughness requirements will be difficult, due to the multi-phase complexities of these new systems. Advances in surface removal technologies as well as replication processes will be required to produce the required optical finishes with reduced schedule and cost. In this paper selected material and process solutions being considered will be discussed.

The paper will describe the new technologies utilizing aluminum beryllium (AlBeMet®) for optical systems. Focusing on advances in gimbal / structures through the use of electron beam welding. The paper will also discuss the characterization of material as an optical substrate, at room temperature and at cryogenic temperatures.

The new astronomical instruments require high-performance structures. Technological innovation and new materials are needed for a structure such as the ALMA radio-telescope in order to guarantee the specifications. The use of Carbon Fibre is highly important. The choice of CFRP helps to control the stiffness of the structure and the thermal behavior of the pieces, but a deep qualification of the material and process is fundamental. Technologies like hand lay-up vacuum bag, compression moulding, and filament winding, identify the ideal solutions for big objects, like Main Reflector Structure, Receiver Cabin, Quadripod Legs and small subassemblies like adjusters system etc.

The new generation of survey telescopes and future giant observatories such as E-ELT or TMT do not only require very fast or very large mirrors, but also high sophisticated instruments with the need of large optical materials in outstanding quality. The huge variety of modern optical materials from SCHOTT covers almost all areas of specification needs of optical designers. Even if many interesting optical materials are restricted in size and/or quality, there is a variety of optical materials that can be produced in large sizes, with excellent optical homogeneity, and a low level of stress birefringence. Some actual examples are high homogeneous N-BK7 blanks with a diameter of up to 1000 mm, CaF2 blanks as large as 300 mm which are useable for IR applications, Fused Silica (LITHOSIL^®) with dimensions up to 700 mm which are used for visible applications, and other optical glasses like FK5, LLF1 and F2 in large formats. In this presentation the latest inspection results of large optical materials will be presented, showing the advances in production and measurement technology.

With an increasing number of applications mirrors and support structures made of the zero expansion glass ceramic material ZERODUR® has to endure high mechanical loads, e.g. rocket launches or controlled deformations for optical image correction. Like for other glassy materials, the strength of glass ceramics is dominated by its surface condition. Test specimens have been ground with fine grain tools (e.g. D64 diamond grains) and / or subsequently etched. The strength data basis for the design of highly stressed structures has been extended and new information has been derived for the extrapolation to low failure probabilities.

Designing highly mechanically loaded structures made of the zero expansion glass ceramic material ZERODUR® means to analyze the stress for the whole loaded surface, considering changes of the stress state occurring over the total lifetime. Strength data are obtained from specimens with small size and relatively short loading duration, making them not directly applicable to the much larger areas that occur in practical cases. This publication gives guidelines for calculating a fracture probability for mirrors and structures on the basis of existing strength data.

The NIRSpec OA (optical assembly) design largely relies on SiC components. The properties of the SiC material and very tight stability budgets required a dedicated development process. Starting from validation of design principles by breadboard testing, this paper describes the development process up to the SM test of the NIRSpec optical assembly. From breadboard testing the design of the mounting interface was established. The test programme also included gluing processes, torque free mounting of mirrors and verification of stability of friction joints. The basic design rules for the mirrors to cope with distortion of mirror surfaces due to bi-metallic bending effects and flatness deficiencies were derived. A modular design using 3 TMAs (Three Mirror Anastigmats) was followed for the OA. From the overall design, budget allocations and design loads for the TMAs were determined. The detailed design process was then driven by distortion budget allocations derived from optical analysis. Due to stringent stability requirements and high mechanical loads, most elements needed several design iterations to meet the budget allocations. Finally, distortions and displacements of the optical elements under the predictable in-orbit conditions were calculated and used in the optical model. The effects can be partially compensated by adjustment. The budget allocation was then revised to account for non-predictable effects only. An extensive test programme on all level is applied. Proof testing is done on parts level; only for some structural parts the load introduction was too complex to allow full coverage. For those, proof test coverage was completed on TMA level. Structural qualification is done on TMA and OA level. Material properties of the SiC and associated design implications led to an extremely low structural damping. The strong responses found in sinusoidal vibration testing required high effort for test item monitoring, data evaluation and shaker control.

The Thirty Meter Telescope (TMT) project, a partnership between ACURA, Caltech, and the University of California, is currently developing a 30-meter diameter optical telescope. The primary mirror will be composed of 492 low expansion glass segments. Each segment is hexagonal, nominally measuring 1.44m across the corners. Because the TMT primary mirror is curved (i.e. not flat) and segmented with uniform 2.5mm nominal gaps, the resulting hexagonal segment outlines cannot all be identical. All segmentation approaches studied result in some combination of shape and size variations. These variations range from fractions of a millimeter to several millimeters. Segmentation schemes for the TMT primary mirror are described in some detail. Various segmentation approaches are considered, with the goal being to minimize various measures of shape variation between segments, thereby reducing overall design complexity and cost. Two radial scaling formulations are evaluated for their effectiveness at achieving these goals. Optimal tuning of these formulations and detailed statistics of the resulting segment shapes are provided. Finally, we present the rationale used for selecting the preferred segmentation approach for TMT.

The Cornell Caltech Atacama Telescope (CCAT) is a 25 m diameter telescope that will operate at wavelengths as short as 200 microns. CCAT will have active surface control to correct for gravitational and thermal distortions in the reflector support structure. The accuracy and stability of the reflector panels are critical to meeting the 10 micron HWFE (half wave front error) for the whole system. A system analysis based upon a versatile generic panel design has been developed and applied to numerous possible panel configurations. The error analysis includes the manufacturing errors plus the distortions from gravity, wind and thermal environment. The system performance as a function of panel size and construction material is presented. A compound panel approach is also described in which the reflecting surface is provided by tiles mounted on thermally stable and stiff sub-frames. This approach separates the function of providing an accurate reflecting surface from the requirement for a stable structure that is attached to the reflector support structure on three computer controlled actuators. The analysis indicates that there are several compound panel configurations that will easily meet the stringent CCAT requirements.

L-3 Communications, SSG-Tinsley reports the optical performance demonstrated with an EUV quality aspheric mirror. The off axis ellipsoidal reflector demonstrates a surface figure of < 3 nm RMS and a surface finish which ranges from 3 - 7 Angstroms RMS depending on the spatial period of interest. Interferometric data is provided along with surface roughness results obtained with phase measuring microscopy. The capability to produce high quality SiC aspheric optics, combined with the inherent thermal stability associated with SiC, enables a number of advanced mission concepts, including next generation solar observing.

The development of lightweight glass mirrors manufactured via cold-slumping technique for Imaging Atmospheric Cherenkov Telescope is presented. The mirror elements have a sandwich-like structure where the reflecting and backing facets are composed by glass sheets with an interposed honeycomb aluminum core. The reflecting coating is deposited in high vacuum by means of physical vapor deposition and consists of aluminum with an additional protective layer of SiO₂. The mirror fabrication and environmental qualification by accelerated ageing, thermal cycling and coating adhesion are presented together with the optical performances measured as angular resolution and reflectivity obtained on spherical, 1 squared meter mirror prototypes.

We report on the production and implementation of 100 square panels 1 m x 1 m, based on the innovative approach of cold slumping of thin glass sheets. The more than 100 segments will cover around one half of the 240 m-square reflecting surface of the MAGIC II, a clone of the atmospheric Cherenkov telescope MAGIC I (with a single-dish 17 m diameter mirror) which is already operating since late 2003 at La Palma. The MAGIC II telescope will be completed by the end of 2008 and will operate in stereoscopic mode with MAGIC I. While the central part of the of the reflector is composed of by diamond milled Aluminum of 1m² area panels (following a design similar to that already used for MAGIC I), the outer coronas will be made of sandwiched glass segments. The glass panel production foresees the following steps: a) a thin glass sheet (1-2mm) is elastically deformed so as to retain the shape imparted by a master with convex profile - the radius of curvature is large, the sheet can be pressed against the master using vacuum suction -; b) on the deformed glass sheet a honeycomb structure that provides the needed rigidity is glued ; c) then a second glass sheet is glued on the top in order to obtain a sandwich; d) after on the concave side a reflecting coating (Aluminum) and a thin protective coating (Quartz) are deposited. The typical weight of each panel is about 12 kg and its resolution is better than 1 mrad at a level of diameter that contains the 90% of the energy reflected by the mirror; the areal cost of glass panels is ~2 k per 1m². The technology based on cold slumping is a good candidate for the production of the primary mirrors of the telescopes forming the Cherenkov Telescope Array (CTA), the future large TeV observatory currently being studied in Europe. Details on the realization of MAGIC II new mirrors based on cold slumping glass will be presented.

The European Southern Observatory (ESO) has started technology development for their next generation optical telescope. Due to its ultra large collecting area, The European Extremely Large Telescope (E-ELT) will require a paradigm shift in telescope design to keep the overall program cost at an acceptable level. The E-ELT will feature a 42 meter segmented primary mirror and will make extensive use of active and adaptive optics. Each primary mirror segment will be supported by three actuators that control piston and tilt. TNO has developed a low cost nanopositioning actuator (PACT) for the primary mirror segments. The actuators will be tested by IAC and ESO, with support from TNO, under operational conditions in a Wind Evaluation Breadboard (WEB) at the Roque de Los Muchachos observatory in La Palma.

This paper presents refinements to the design of the TMT primary mirror segment passive-support system that are effective in reducing gravity print-through and thermal distortion effects. First, a novel analytical method is presented for tuning the axial and lateral support systems in a manner that results in improved optical performance when subject to varying gravity fields. The method utilizes counterweights attached to the whiffletrees to cancel astigmatic and comatic errors normally resulting when the lateral support system resists transverse loads induced by gravity. Secondly, several central diaphragm designs are presented and analyzed to assess lateral-gravity and thermal distortion performance: 1) a simple flat diaphragm, 2) a stress-relieving diaphragm having a slotted outer rim and a circumferential convolution near the outside diameter, and 3) a flat diaphragm having a slotted outer rim. The latter design is chosen based on results from analytical studies which show it to have better overall optical performance in the presence of gravity and thermal environments.

In this paper we address two interrelated issues important to primary mirror segments for extremely large telescopes - edge-control, and the detailed topography over the segment surface. Both affect the intensity and distribution of stray light and infrared emissivity. CNC polishing processes typically deploy spiral or raster tool-paths, tending to leave repetitive features. We compare and contrast two novel families of pseudo-random tool-paths for Precessions CNC polishing. We then show how CNC control of the three-dimensional tool-path can optimize edge-profiles. Finally, we demonstrate fluid-jet polishing used to clean up residual edge defects.

Construction of the Southern African Large Telescope (SALT) was largely completed by the end of 2005 and since then it has been in intensive commissioning. This has now almost been completed except for the telescope's image quality which shows optical aberrations, chiefly a focus gradient across the focal plane, along with astigmatism and other less significant aberrations. This paper describes the optical systems engineering investigation that has been conducted since early 2006 to diagnose the problem. A rigorous approach has been followed which has entailed breaking down the system into the major sub-systems and subjecting them to testing on an individual basis. Significant progress has been achieved with many components of the optical system shown to be operating correctly. The fault has been isolated to a major optical sub-system. We present the results obtained so far, and discuss what remains to be done.

The Giant Magellan Telescope achieves 25 meter aperture and modest length using an f/0.7 primary mirror made from 8.4 meter diameter segments. The systems that will be used for measuring the aspheric optical surfaces of these mirrors are in the final phase of development. This paper discusses the overall metrology plan and shows details for the development of the principal test system - a system that uses mirrors and holograms to provide a null interferometric test of the surface. This system provides a full aperture interferometric measurement of the off-axis segments by compensating the 14.5 mm aspheric departure with a tilted 3.8-m diameter powered mirror, a 77 cm tilted mirror, and a computer generated hologram. The interferometric measurements are corroborated with a scanning slope measurement from a scanning pentaprism system and a direct measurement system based on a laser tracker.

Determination of the shape of very thin x-ray mirrors employed in spaced-based telescopes continues to be challenging. The mirrors' shapes are not readily deduced to the required accuracy because the mount induced distortions are often larger than the uncertainty tolerable for the mission metrology. In addition to static deformations, dynamic and thermal considerations are exacerbated for this class of mirrors. We report on the performance of one temporary mounting scheme for the thin glass mirrors for the Constellation-X mission and prospects for deducing their undistorted shapes.

Optical testing of large mirrors for space telescopes can be challenging and complex. Demanding optical requirements necessitate both precise mirror figure and accurate prediction of zero gravity shape. Mass and packaging constraints require mirrors to be lightweighted and optically fast. Reliability and low mass imply simple mounting schemes, with basic kinematic mounts preferable to active figure control or whiffle trees. Ground testing should introduce as little uncertainty as possible, ideally employing flight mounts without offloaders. Testing mirrors with their optical axes horizontal can result in less distortion than in the vertical orientation, though distortion will increase with mirror speed. Finite element modeling and optimization tools help specify selective reinforcement of the mirror structure to minimize wavefront errors in a one gravity test, while staying within mass budgets and meeting other requirements. While low distortions are necessary, an important additional criterion is that designs are tolerant to imperfect positioning of the mounts relative to the neutral surface of the mirror substrate. In this paper, we explore selective reinforcement of a 2-meter class, f/1.25 primary mirror for the proposed SNAP space telescope. We specify designs optimized for various mount radial locations both with and without backup mount locations. Reinforced designs are predicted to have surface distortions in the horizontal beam test low enough to perform optical testing on the ground, on flight mounts, and without offloaders. Importantly, the required accuracy of mount locations is on the order of millimeters rather than tenths of millimeters.

Flat mirrors as large as 4 meters in diameter can be manufactured to high accuracy, limited by the surface metrology. We present metrology systems that are specifically optimized for measuring very large flats to high accuracy. A large aperture vibration insensitive Fizeau interferometer combined with stitching software provides high resolution surface measurements. Low order shape errors can be measured using scanning slope measurements from precision inclinometers or an autocollimator with scanning pentaprism.

Telescopes with very large diameter or with wide fields require convex secondary mirrors that may be many meters in diameter. The optical surfaces for these mirrors can be manufactured to the accuracy limited by the surface metrology. We have developed metrology systems that are specifically optimized for measuring very large convex aspheric surfaces. Large aperture vibration insensitive sub-aperture Fizeau interferometer combined with stitching software give high resolution surface measurements. The global shape is corroborated with a coordinate measuring machine based on the swing arm profilometer.

Telescopes use primary mirrors with spherical shape to reduce the cost of the mirror fabrication and to allow the mirror to operate at fixed elevation. These advantages become significant as the size of the telescope grows. However, the disadvantage of the spherical primary is a large amount of spherical aberration which needs to be corrected. We present an analysis of alignment issues for four-mirror spherical aberration correctors for spherical primary mirror telescopes. The sensitivities of image quality across the field (in terms of spot size) to mirror misalignments are found. These sensitivities are useful in choosing the tolerances for the mechanical assembly holding the corrector. A singular value decomposition of the sensitivity matrix shows the combination of element motions that result in orthogonal aberration modes. Studying these combinations of modes and misalignments can lead to a conceptual understanding of the system, which aids in the initial and operational alignment of the spherical aberration corrector.

Point-to-point laser metrology systems can be used to stabilize large structures at the nanometer levels required for precision optical systems. Existing sensors are large and intrusive, however, with optical heads that consist of several optical elements and require multiple optical fiber connections. The use of point-to-point laser metrology has therefore been limited to applications where only a few gauges are needed and there is sufficient space to accommodate them. Range-Gated Metrology is a signal processing technique that preserves nanometer-level or better performance while enabling: (1) a greatly simplified optical head - a single fiber optic collimator - that can be made very compact, and (2) a single optical fiber connection that is readily multiplexed. This combination of features means that it will be straightforward and cost-effective to embed tens or hundreds of compact metrology gauges to stabilize a large structure. In this paper we describe the concept behind Range-Gated Metrology, demonstrate the performance in a laboratory environment, and give examples of how such a sensor system might be deployed.

The controls by optical mean of coatings deposited on optical components are generally made with flat witnesses. But when the components are spherical or aspherical, like lenses or mirrors, the spectral response can vary because of the nonuniformity of thickness that is really linked to the deposition process. For large radius of curvature, control can be achieved even with classical spectrophotometers. However, control becomes more and more difficult when the radius of curvature decreases or when the optical device has a complex shape such as slicers for example. So to perform this kind of measurement, special devices are needed. The CEA Ripault has designed a new facility of measurements of spectral reflection. This reflectometer can be used to measure optical coating with a very high accuracy on steeply curved parts. The aim of this paper is to enhance the limits of this device by studying measurement uncertainty and giving some examples of measurement. One of our most relevant measurements is the study of an aspheric condenser having a 38 mm focal length. Furthermore, the obtained reflectivity on an angle iron will be achieved and commented. Soon, WINLIGHT SYSTEM Company will manufacture this device.

Weather effects on foldable domes, as used at the DOT and GREGOR, are investigated, in particular the correlation between the wind field and the stresses caused to both metal framework and tent clothing. Camera systems measure contactless the displacement of several dome points. The stresses follow from the measured deformation pattern. The cameras placed near the dome floor do not disturb telescope operations. In the set-ups of DOT and GREGOR, these cameras are up to 8 meters away from the measured points and must be able to detect displacements of less than 0.1 mm. The cameras have a FireWire (IEEE1394) interface to eliminate the need for frame grabbers. Each camera captures 15 images of 640 × 480 pixels per second. All data is processed on-site in real-time. In order to get the best estimate for the displacement within the constraints of available processing power, all image processing is done in Fourier-space, with all convolution operations being pre-computed once. A sub-pixel estimate of the peak of the correlation function is made. This enables to process the images of four cameras using only one commodity PC with a dual-core processor, and achieve an effective sensitivity of up to 0.01 mm. The deformation measurements are well correlated to the simultaneous wind measurements. The results are of high interest to upscaling the dome design (ELTs and solar telescopes).

In this paper we identify and attempt to quantify all effects of Atmospheric Dispersion (AD) which might affect the performance of a European ELT. For each effect, we examine the implications and possible methods of correction. We produce "demonstration-of-possibility" ADC designs for the proposed 42-m ("E-ELT"). The rotational (RADC) and linear ADC (LADC) optical designs are compared at the Nasmyth focus and at the intermediate focal plane.

The crucial component of an Adaptive Optics unit is the actuation system of the deformable mirror. One possible implementation comprehends a linear force motor and a capacitive sensor providing the feedback measure signal. Due to the extreme accuracy required by the optics, a proper design of the actuator is essential in order to fulfill the specifications. In the device, mechanics, electrostatics, electromagnetism and thermal effects are mutually related, and they have to be properly considered in the design phase. This paper analyzes such a multiphysics behavior of the actuation system, providing an inter-disciplinary approach able to define the optimized device: a capacitive sensor measuring the displacements at the nanometer accuracy and a closed loop linear motor delivering the requested force with the lowest possible power dissipation, in order to minimize the degrading of the optical waves propagation.

Small deformable mirrors (DMs) produced using microelectromechanical systems (MEMS) techniques have been used in thermally stable, bench-top laboratory environments. With advances in MEMS DM technology, a variety of field applications are becoming more common, such as the Gemini Planet Imager's (GPI) adaptive optics system. Instruments at the Gemini Observatory operate in conditions where fluctuating ambient temperature, varying gravity orientations and humidity and dust can have a significant affect on DM performance. As such, it is crucial that the mechanical design of the MEMS DM be tailored to the environment. GPI's approach has been to mount the MEMS DM using high performance optical mounting techniques rather than a typical laboratory set-up. This paper discusses the design of the opto-mechanical mounting scheme for a 4096 actuator MEMS DM, developed by Boston Micromachines Corporation for use in the GPI adaptive optics system. Flexures have been incorporated into the DM mount to reduce deformations on the optical surface due to thermal fluctuations. These flexures have also been sized to maintain alignment under varying gravity vector orientations. Finally, a system for environmentally sealing the mirror has been designed to prevent degradation due to humidity effects. A plan for testing the mechanical mount to ensure that it meets GPI's performance and environmental requirements is also presented.

The effects of atmospheric dispersion are well known in astrometry and astronomical spectroscopy. To reduce these effects, glass prisms are used. Two different prisms, coupled together, give better corrections. However glass dispersion curves do not match very well the dispersion of the atmosphere and secondary spectrum of the order of 50-100 milliarcseconds (mas) or more will be present. I propose a method to find solutions with residuals less than few parts of 10 milliarcsecond and I show some results.

At the MMT Observatory, the adaptive secondary system is producing well corrected images using natural guide stars. Shortly after the system came online, however, it was found that vibrations in the telescope structure were limiting the Strehl of the corrected image. The worst of these vibrations are at 19 Hz, which puts them just outside of the system correction bandwidth. The laser guide star system at the MMT is also impacted by a different vibration mode at 14 Hz that affects the pointing of the laser beacon on the sky. To correct these errors, accelerometers were installed on the secondary mirror to measure its motion. The measured motion was then used to generate a feed-forward correction term which has already been proven in on-sky testing to work for the LGS case. The NGS case is more difficult and attempts to correct image motion have failed due to excessive feedback.

FAST, five-hundred-meter aperture spherical radio telescope will be the largest radio telescope in the world which has been established science and research items recently. One of the innovative engineering concepts is the active main reflector which corrects spherical aberration on the ground to achieve full polarization and a wide band without involving a complex feed system. Besides the reflector simulation, it is very important to study the supporting structure for the reflecting surface. As the cable-net structure has been adopted, the in-depth study of back-structure is very important which is connected between cable-net and panel. In this paper, structure forms and parameters are studied in detail due to catch the costs and technical requirements. Throughout analysis, parameters are compared and modified. Meanwhile, Comparing experiments has carried out on some sample frames. The stiffness experiments with different load situations are going to confirm the feasibility of certain back-structure. Some conclusions is obtained, which can avail in further study.

The paper reports a recently started project for a 2,5 meter diameter robotic telescope dedicated to astronomy and education for the University of Moscow's Sternberg Institute. As a prime contractor Sagem Defense Securite's REOSC department will take on the program design as well as the production of the optical components. The project includes the Alt-Az mount, the dome and its cooling and air stabilization system, the weather station, the high-resolution camera and realization, transport and installation on-site at the Kislovodsk solar station located in the Caucasus mountains as well as the initial training for the operators. The telescope will provide a wide field of view of 40 arcmin at the Cassegrain F/8 focus. An escapable and rotating tertiary mirror will allow to direct the light to the two Nasmyth foci and two student ports located at 90° from the Nasmyth foci. A 4k x 4k CCD camera cryogenically cooled to 140 K will be provided as a first light camera. All will be delivered by end 2009. Remotely controlled via the internet, the telescope will allow Russia to train doctors in astronomy, participate in international research projects and draw up the future specifications of a larger and more advanced telescope.

The increasing demand within the astronomy community for direct detection of extrasolar Jovian planets is driving the development of the next generation of ground-based, precision instruments like the Gemini Planet Imager (GPI). The precision and stability of the opto-mechanical components within GPI needed to achieve the required 10^-7 contrast will challenge the limits of design and material properties. This study examines the challenge of mounting small, high-precision mirrors (~1nm RMS WFE) for all gravity orientations, for 30°C temperature fluctuations and for vibration conditions typical of a cassegrain-mounted instrument on the Gemini telescopes. Various flexure-based mounting schemes, typically used for small optics (12 mm to 50 mm diameter), are considered in the context of the GPI opto-mechanical requirements. Through this study several candidate designs are selected for detailed investigation. The further design, analysis, and optimization of these candidate flexure designs are presented and evaluated against the relevant requirements. Special consideration and discussion is devoted to finite element analysis techniques and optimization procedures. Finally, the chosen flexure configuration is prescribed for the range of mirror sizes within GPI.

The Array for Microwave Background Anisotropy (AMiBA) is a radio interferometer for research in cosmology, currently operating 7 0.6m diameter antennas co-mounted on a 6m diameter platform driven by a hexapod mount. AMiBA is currently the largest hexapod telescope. We briefly summarize the hexapod operation with the current pointing error model. We then focus on the upcoming 13-element expansion with its potential difficulties and solutions. Photogrammetry measurements of the platform reveal deformations at a level which can affect the optical pointing and the receiver radio phase. In order to prepare for the 13-element upgrade, two optical telescopes are installed on the platform to correlate optical pointing tests. Being mounted on different locations, the residuals of the two sets of pointing errors show a characteristic phase and amplitude difference as a function of the platform deformation pattern. These results depend on the telescope's azimuth, elevation and polarization position. An analytical model for the deformation is derived in order to separate the local deformation induced error from the real hexapod pointing error. Similarly, we demonstrate that the deformation induced radio phase error can be reliably modeled and calibrated, which allows us to recover the ideal synthesized beam in amplitude and shape of up to 90% or more. The resulting array efficiency and its limits are discussed based on the derived errors.

The European ALMA antenna dish including Back-Up Structure, Panel Adjusters and Panels are designed and manufactured using high level technologies and innovative production processes. The On Site installation is performed thanks to high performances measurements and alignments processes, with short alignment duration. Special design features of the European ALMA antennas are described, Manufacturing mass production works are presented, Alignment methods defined.

Two prototypes of fully retractable enclosures with diameters of 7 and 9 m have been built for the high-resolution solar telescopes DOT (Dutch Open Telescope) and GREGOR, both located at the Canary Islands. These enclosures protect the instruments for bad weather and are fully open when the telescopes are in operation. The telescopes and enclosures also operate in hard wind. The prototypes are based on tensioned membrane between movable but stiff bows, which fold together to a ring when opened. The height of the ring is small. The prototypes already survived several storms, with often snow and ice, without any damage, including hurricane Delta with wind speeds up to 68 m/s. The enclosures can still be closed and opened with wind speeds of 20 m/s without any problems or restrictions. The DOT successfully demonstrated the open, wind-flushing concept for astronomical telescopes. It is now widely recognized that also large future telescopes benefit from wind-flushing and retractable enclosures. These telescopes require enclosures with diameters of 30 m until roughly 100 m, the largest sizes for the ELTs (Extreme Large Telescopes), which will be built in the near future. We discuss developments and required technology for the realization of these large sizes.

Operation of the Five-Hundred-Meter Aperture Spherical Telescope (FAST) requires accurate positioning and movement of the receiver platform on a spherical workspace with a radius of 160 m. Supported above the 500 m diameter main reflector it has to be positioned with an accuracy of several millimeters. To achieve this, the receiver is located in the receiver cabin that is suspended on six cables. The cables are attached to six towers located on the circumference of the main reflector and can be actuated via six capstans. In this paper a control concept for the cable-system is presented. Using a detailed mathematical model of the system the performance of the control and the sensitivity to wind and other disturbances is evaluated via simulation. The mechanics are modeled via FEM, the capstan-drives as lumped-mass elements including nonlinear effects like friction and backlash. The control scheme presented consists of position control loops for the capstans and numerically optimized PID-controllers for the positioning of the cabin platform.

SALT developed an automated CO₂ Mirror Cleaning System (MCS) for its 11 meter diameter segmented primary mirror. In this paper we report on the mechanical design of the system, the safety considerations taken into account given that the mechanism has to be lowered over the primary mirror for every cleaning cycle, the computerized control system and the CO₂ installation which feeds the cleaning wand with liquid CO₂. The paper also addresses the complexities experienced in providing high pressure liquid CO₂ for the effective operation of the cleaning wand as well as the safety precautions implemented to ensure the safety of staff members at all times. The performance results are also presented although the system is still being optimised in a trade off between cleaning efficiency, CO₂ consumption, the duration of a cleaning cycle and the cleaning frequency.

In the context of the NASA CNES FIREBALL balloon borne experiment, we present the design of a semi-kinematic mount to hold the 1 meter class mirrors of this mission. To maintain these large optics in a reasonable mass and price budgets we choose thin ULE mirrors with a thickness over diameter ratio of 1/16. Such thin mirrors require a multi support mount to reduce self weight deflection. Classical multi support mount used for ground based telescope would not survive the level of shock observed in a balloon experiment either at parachute opening or landing. To firmly maintain these mirrors in several points without noticeably deforming them we investigated the design of a two stages semi-kinematic mount composed of 24 monopods. We present the detailed design of this innovative mirror mount, the finite element modeling with the deduced optical wavefront deformation. During the FIREBALL integration and flight campaign in July 2007 at CSBF, we confirmed the validity of the mechanical concept by obtaining an image quality well within the required specifications. Variants of this approach are potentially applicable to large thin mirrors on ground-based observatories.

In the near future ELTs (Extreme Large Telescopes) will be built. Preferably these telescopes should operate without obstructions in the near surrounding to reach optimal seeing conditions and avoid large turbulences with wind-gust accelerations around large obstacles. This applies also to future large solar telescopes. At present two foldable dome prototypes have been built on the Canary Islands: the Dutch Open Telescope (DOT, La Palma) and the GREGOR Telescope (Tenerife), having a diameter of 7 and 9 meter, respectively. The domes are usually fully retracted during observations. The research consists of measurements on the two domes. New camera systems are developed and placed inside the domes for precise dome deformation measurements within 0.1 mm over the whole dome size. Simultaneously, a variety of wind-speed and -direction sensors measure the wind field around the dome. In addition, fast sensitive air-pressure sensors placed on the supporting bows measure the wind pressure. The aim is to predict accurately the expected forces and deformations on up-scaled, fully retractable domes to make their construction more economically. The dimensions of 7 and 9 meter are large enough for realistic on-site tests in gusty wind and will give much more information than wind tunnel experiments.

The Ritchey-Chretien (RC) design of the Thirty Meter Telescope (TMT) optics calls for a 3.1 m diameter Secondary Mirror (M2), which is a large meniscus convex hyperboloid. The M2 converts the beam reflected from the f/1 primary mirror into an f/15 beam for the science instruments. The M2 Mirror (M2M) has a mass of approximately two metric tons and the mirror support system will need to maintain the mirror figure at different gravity orientations. Recent changes in the telescope configuration to RC from Aplanatic Gregorian (AG) prescription and reduction of the fully-illuminated field of view to 15 arc minutes required a design change in the M2 mirror figure from a concave radius to a convex radius, with a significant reduction in diameter, which in turn requires re-optimization of the mirror support systems. The optical performance evaluations were made based on the optimized support systems resulting from the change from AG to RC. The M2 optimized support system consists of 60 axial supports, mounted at the mirror back surface, and 24 lateral supports mounted along the outer edge. The predicted print-though errors of the M2M supports are 10nm RMS surface for axial gravity and 2nm RMS surface for lateral gravity. This M2M support system has an active optics capability to accommodate potential mechanical or thermal errors; its performance to correct low-order aberrations has been analyzed. A structure function of the axial gravity support print-through was calculated.

Secondary mirrors and lenses in several planned ground-based telescopes have masses on the order of 5000 kg and require a positioning system that is repeatable to one-tenth the pixel size of the optical sensors, nominally 10 micrometers or less. Hexapods, or Stewart Platforms, are frequently integrated into the support structure as six degree of freedom parallel positioning and alignment systems. These systems are limited in resolution by friction in the 36 kinematic degrees of freedom (DOF) necessary for properly constrained motion of the platform. The 30 passive DOF, typically implemented with one 3-DOF and one 2-DOF joint on each hexapod leg, introduce unwanted friction and/or backlash into the positioning system. Backlash is generally unacceptable and elimination requires significant preloading of the joints, which in turn increases joint friction. This paper will: review various joint types including rolling element, plain bearing (sliding), and flexure; examine the backlash and friction tradeoffs involved in selecting joint type including unwanted deflections due to joint moments, static position resolution limitations, dynamic positioning settling time effects, self-locking mechanisms, and power dissipation; compare with experimental data and previously published results; present methods for modeling both static and dynamic effects of friction; and suggest recommendations for general positioning system design. Considerations for both equatorial and altitude-azimuth telescopes will be discussed, along with variation of effects due to telescope positioning. Analyses will be reinforced with friction and backlash measurements made on several physical joints.

The performance requirements for the next generation of ground-based instruments for optical and infrared astronomy on current telescopes and future ELTs are generating extreme requirements for stability, for instance to carry out precise radial velocity measurements, imaging and spectroscopy with high contrast, and diffraction-limited performance at a level of tens of milliarcsecond. As it is not always possible to make use of a gravity-invariant focal station, flexure must be accommodated while still minimising thermal loads for cryogenic instruments. Variable thermal loads are another source of dimensional changes. High stability will require the minimising of the effects of vibration sources, either from the telescope systems or mechanical coolers. All this must be done while maintaining mass budgets, an especial challenge for large, wide-field, multi-object spectrographs.

The detection and characterization of exo-solar planets, which are 25 to 30 magnitudes fainter than their (5th to 6th visual magnitude) central stars, requires large aperture telescopes that must be folded to fit within the payload fairings of existing launch vehicles, and then deployed after reaching orbit. Many other elements of the various terrestrial planet finding observatories which have been proposed also must be deployed on orbit, including sunshades, solar arrays, high gain antennas and the external occulters ("starshades") that we have been designing for a "New Worlds Observer" mission. In this paper we discuss the requirements, tolerances, design options and technology readiness levels for deployment technologies for TPF-Coronagraph, -Interferometer, and -Occulter missions and describe our strawman design concepts.

The James Webb Space Telescope (JWST) mission is a collaborative project between the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA) and is considered as the successor to the Hubble Space Telescope (HST). The European contribution consists in providing the Ariane 5 launcher and two out of the four instruments: a combined mid-infrared camera/spectrograph (MIRI) and a near infrared spectrograph (NIRSpec). This article will address the mechanical aspects of NIRSpec by providing an overview of the design drivers and the related solutions for the structure, the thermal design and the mechanisms so as to achieve the required stringent optical performances. The industrial set-up and the project development status will also be presented.

A novel cryogenic refocusing mechanism (RMA) has been designed by Galileo Avionica (GA) for the Near Infra-Red Spectrograph (NIRSpec), one of the instruments of the James Webb Space Telescope (JWST). The RMA shall correct possible in orbit focal length variations by a rigid translation of a set of two mirrors in a 6 mm range, with an accuracy of 50 microns and 15 microns step size. The RMA development has been driven by the operation at 30K temperature while being still fully functional at room temperature, by the need to incorporate two mirrors with demanding quality as part of the mechanism and by tight envelope constraints. This paper reports details of the RMA opto-mechanical design and analysis and about the dedicated optical set-up developed for its verification.

This paper reports some details about the optical technologies used for manufacturing the mirrors of the Refocusing Mechanism Assembly (RMA). The RMA is a novel cryogenic mechanism designed by Galileo Avionica for the Near Infrared Spectrograph (NIRSpec), one of the instruments of the James Webb Space Telescope (JWST). The RMA contains two flat mirrors in Zerodur coated with Protected Silver. Severe constraints for accommodation in the Nirspec imposed very lightweighted substrates to the RMA mirrors and required state of art technologies in order to achieve the specified quality and its maintenance at cryogenic temperatures.

The Grating and Filter Wheel Mechanisms of the JWST NIRSpec instrument allow for reconfiguration of the spectrograph in space in a number of NIR sub-bands and spectral resolutions. Challenging requirements need to be met simultaneously including high launch loads, the large temperature shift to cryo-space, high position repeatability and minimum deformation of the mounted optics. The design concept of the NIRSpec wheel mechanisms is based on the ISOPHOT Filter Wheels but with significant enhancements to support much larger optics. A well-balanced set of design parameters was to be found and a considerable effort was spent to adjust the hardware within narrow tolerances.

The Near-Infrared Spectrograph (NIRSPEC) on board the James Webb Space Telescope can be reconfigured in space for astronomical observation in a range of NIR sub-bands as well as spectral resolutions. Reconfiguration of the NIRSpec instrument will be achieved using a Filter Wheel Mechanism (FWA) which carries 7 transmission filters and one reflective mirror and a Grating Wheel Mechanism (GWA) which carries six gratings and one prism. The dispersive components on the grating wheel (GWA) cooperate with the edge transmission filters mounted on the filter wheel (FWA) which block the higher dispersion orders of the gratings. The paper gives an overview on the design of all optical elements, their key requirements and the employed manufacturing approach. Test results from breadboard and component level qualification phase are also given.

The JWST Mid-Infrared Instrument (MIRI) is designed to meet the JWST science requirements for mid-IR capabilities and includes an Imager MIRIM provided by CEA (France). A double-prism assembly (DPA) allows MIRIM to perform low-resolution spectroscopy. The MIRIM DPA shall meet a number of challenging requirements in terms of optical and mechanical constraints, especially severe optical tolerances, limited envelope and very high vibration loads. The University of Cologne (Germany) and the Centre Spatial de Liege (Belgium) are responsible for design, manufacturing, integration, and testing of the prism assembly. A companion paper (Fischer et al. 2008) is presenting the science drivers and mechanical design of the DPA, while this paper is focusing on optical manufacturing and overall verification processes. The first part of this paper describes the manufacturing of Zinc-sulphide and Germanium prisms and techniques to ensure an accurate positioning of the prisms in their holder. (1) The delicate manufacturing of Ge and ZnS materials and (2) the severe specifications on the bearing and optical surfaces flatness and the tolerance on the prism optical angles make this process innovating. The specifications verification is carried out using mechanical and optical measurements; the implemented techniques are described in this paper. The second part concerns the qualification program of the double-prism assembly, including the prisms, the holder and the prisms anti-reflective coatings qualification. Both predictions and actual test results are shown.

The Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope, scheduled for launch in 2013, will provide a variety of observing modes such as broad/narrow-band imaging, coronagraphy and low/medium resolution spectroscopy. One filter wheel and two dichroic-grating wheel mechanisms allow to configure the instrument between the different observing modes and wavelength ranges. The main requirements for the three mechanisms with up to 18 positions on the wheel include: (1) reliable operation at T ~ 7 K, (2) optical precision, (3) low power dissipation, (4) high vibration capability, (5) functionality at 6 K < T < 300 K and (6) long lifetime (5-10 years). To meet these stringent requirement, a space-proven mechanism design based on the European ISO mission and consisting of a central bearing carrying the optical wheels, a central torque motor for wheel actuation, a ratchet system for precise and powerless positioning and a magnetoresistive position sensor has been selected. We present here the detailed design of the flight models and report results from the extensive component qualification.

The Photodetector Array Camera and Spectrometer (PACS), on board the Herschel Space Observatory, is designed for imaging and low and medium resolution spectroscopy in the wavelength region between 57 and 210 μm. This paper reports the design and the testing results of the grating cryogenic mechanism of the PACS spectrometer. The PACS diffraction grating is made from an aluminium substrate, mechanically ruled with a periodicity of 8.5 grooves per mm and gold coated for optimum reflectivity at PACS operating wavelengths. The grating mechanism is capable of accurate positioning (4") of the flat diffraction grating within a large angular throw (44°) in cryogenic environment (4.2 K). Technologies of actuators, position sensors, bearings, servo-control and cryogenic test set-up are presented. The grating mechanism was thoroughly tested, alone and when integrated in the PACS Focal Plane Unit (FPU). The tests were performed in cryogenic conditions, in a set-up fully representative of the flight conditions. Actual mechanical and optical performance obtained with the Flight Model (FM) is presented in detail. Quality of the angular positioning of the mechanism, spectral resolution and optical quality of the grating are analysed.

Based on its experience of space application instrument and its development of cryomechanism for astronomical ground based instrument VLT / VISIR, CEA Saclay is proposing a new concept of Space Cryomechanism. This design is based on VLT/VISIR cryo-mechanism design adapted to space requirements taking into account all the specification of space environment (vibrations at launch, cryogenic vacuum, materials, radiations, ...). The original concept of the design is based on the association of the key elements: a dog-clutch with Hirth teeth jaws coupled to a step-by-step space qualified cryo-motor, a bellows that allows for separation of indexing and rotating functions, and enlarged bearings design in "O" arrangement that increase robustness to vibration. The actuator has 360 steady positions that can be reached within les than a second with repeatability of 5 arcsec peak to peak. After a presentation of the details of the concept and of its benefits to robustness to space environment, the paper describes the thoroughly qualification program of the cryo-mechanism with respect to space requirements (cryo-cycling, indexing accuracy, power consumption, heat dissipation, motorisation margins, vibrations). This cryo-mechanism may be built in 3 different sizes for wheels up to 10 kg.

Cost estimation for space science missions is critically important in budgeting for successful missions. The process requires consideration of a number of parameters, where many of the values are only known to a limited accuracy. The results of cost estimation are not perfect, but must be calculated and compared with the estimates that the government uses for budgeting purposes. Uncertainties in the input parameters result from evolving requirements for missions that are typically the "first of a kind" with "state-of-the-art" instruments and new spacecraft and payload technologies that make it difficult to base estimates on the cost histories of previous missions. Even the cost of heritage avionics is uncertain due to parts obsolescence and the resulting redesign work. Through experience and use of industry best practices developed in participation with the Aerospace Industries Association (AIA), Northrop Grumman has developed a parametric modeling approach that can provide a reasonably accurate cost range and most probable cost for future space missions. During the initial mission phases, the approach uses mass- and powerbased cost estimating relationships (CER)'s developed with historical data from previous missions. In later mission phases, when the mission requirements are better defined, these estimates are updated with vendor's bids and "bottoms- up", "grass-roots" material and labor cost estimates based on detailed schedules and assigned tasks. In this paper we describe how we develop our CER's for parametric cost estimation and how they can be applied to estimate the costs for future space science missions like those presented to the Astronomy & Astrophysics Decadal Survey Study Committees.

For integral field spectroscopy R&D activities in progress at LAM, and particularly in relation with SNAP - SuperNova/Acceleration Probe - spectrograph, LAM has an on-going program to qualify Image Slicers for space instrumentation. In this context, an optomechanical concept of an image slicer supported by three bipods has been designed, realized and tested at the laboratory. This paper presents the mechanical design of the invar mount equipped with three bipods and supporting an assembly of 60 thin zerodur slices tied together thanks to optical contact. We document the design improvement made from last blades flexures prototype and we describe all the tests conducted on this new prototype: optical contact tests, vibration tests and thermal cycles. Thanks to a detailed FEM analysis on this three bipods concept, we correlate simulations with tests.

This paper describes the development of the detector motion stage for the instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch). The detector movement is necessary because the instrument SPHERE has exceptional requirements on the flatfield accuracy: In order not to limit planetary detections, the photon response of every pixel with respect to the detector's mean response must be known to an accuracy of 10^-4. As only 10^-3 can be reached by calibration procedures, detector dithering is essential to apply ~100 pixels at a single spatial detection area and time-average the result to reduce the residual flatfield noise. We will explain the design of the unit including the detector package and report on extensive cold and warm tests of individual actuators. The novel, patented NEXLINE^® drive actuator design combines long travel ranges (hundreds of millimeters) with high stiffness and high resolution (better than 0.1 nm). Coordinated motion of shear and longitudinal piezo elements is what allows NEXLINE^® to break away from the limitations of conventional nanopositioning actuators. Motion is possible in two different modes: a high resolution, high dynamics analogue mode, and a step mode with theoretically unlimited travel range. The drive can always be brought to a condition with zero-voltage on the individual piezo elements and with the full holding force available to provide nanometer stability, no matter where it is along its travel range. The NEXLINE^® stage is equipped with capacitive sensors for the closed loop mode. The piezo modules are specially designed for cryogenic application.

This paper describes the mechanical design of the KMOS pick-off arms and the way in which the design is driven by combinations of requirements. The use of a recirculating linear bearing in a cryogenic environment is novel and the qualification of this component is described. Novel use is made of a single leadscrew with two leads to move optical components at different speeds to maintain the optical path length. Cryogenic flexure, repeatability and torque tests are described.

The CTU (Cryogenics Translation Unit) is a low range (±1 mm) high resolution (<50 nm) translation unit to be used at cryogenic temperature (20K). The unit is a multipurpose device capable of fine closed loop positioning. This device can be used as active element in IR Instrumentation for compensating thermo-elastic deformation moving optical elements or sensors. CTU motion system is based in thin flexures deformation to assure repeatability and moves in closed loop mode by means of a fine linear actuator and a calibrated non contact capacitive sensor. This paper describes main design features, how cryogenic testing of main requirements was carried out (including methodologies used for calibration and submicron verification), tested performances, and main lesson learned during the development.

A cryogenic Fourier transform infrared spectrometer (Cryo-FTS) was developed for the Low Background Infrared (LBIR) facility at the National Institute of Standards and Technology (NIST). This spectrometer was developed for the Missile Defense Agency Transfer Radiometer (MDXR) that will be used to calibrate infrared sources that cannot be transported to NIST for calibration. When used inside the MDXR, the Cryo-FTS provides relative spectral measurements with a repeatability better than 1 % over the spectral range from 3 μm to 15 μm and at a spectral resolution of 0.6 cm^-1. This level of performance is enabled by the use of an advancec real-time resampling method. The compact interferometer uses a compensated Michelson configuration and has an operating temperature range between 10 K and 340 K with very low static beam redirection (< 215 μrad). The interferometer uses flat mirrors and a KBr beamsplitter and compensator. This optics maintains low wavefront distortion for infrared beams of up to 2 cm diameter and 5 mrad divergence. It integrates a digitally servo-controlled porchswing mechanism to provide an accurate and repeatable optical path difference and is supported by a Wavefront Alignment (WA) system to correct for wavefront residual tilt in real time using a fibre optic coupled metrology system. The interferometer provides modulation efficiency of better than 44% with limited power dissipation (< 2.8 W) during operation.

ASTRON is involved in the development and realization of various optical astronomical instruments for ground-based as well as space telescopes, with a focus on near- and mid-infrared instrumentation. ASTRON has developed, among others, cryogenic optics for the first generation ESO VLT and VLTI instruments VISIR, MIDI and the SPIFFI 2K-camera for SINFONI. Currently under construction are MIRI for the James Webb Space Telescope and X-shooter for the second generation ESO VLT instrumentation, while the initial design of several ELT instruments has started. Mounting optics is always a compromise between firmly fixing the optics and preventing stresses within the optics. The fixing should ensure mechanical stability and thus accurate positioning in various gravity orientations, temperature ranges, during launch, transport or earthquake. On the other hand, the fixings can induce deformations and sometimes birefringence in the optics and thus cause optical errors. Even cracking or breaking of the optics is a risk, especially at the cryogenic temperatures required in instruments for infrared astronomy, where differential expansion of various materials amounts easily to several millimetres per meter. Special kinematic mounts are therefore needed to ensure both accurate positioning and low stress. Though ASTRON is involved in the full realization of instruments from initial design to commissioning, this paper concentrates on the opto-mechanical design of optics mountings, especially for large transmission optics in cryogenic circumstances. It describes the development of temperature-invariant ("a-thermal"), kinematic designs and how they are implemented in instruments such as SPIFFI and X-shooter.

An infrared instrument used for observation has to keep the detector and optical components in a very cold environment during operation. However, because of maintenance, upgrades, and other routine work, there are situations that require the instrument to be warmed-up and then cooled-down again. At Subaru Observatory, our MOIRCS infrared instrument has required warm-up and cool-down several times a year for routine maintenance and filter replacement. The MOIRCS instrument has a large heat capacity and cool-down using only the closed cycle cooler is impractical due to the huge amount of time it would require. To address this problem Subaru engineers have created a mechanism to allow PRE-COOLING of the instrument via liquid nitrogen - allowing for a much faster pre-cool process. Even with liquid nitrogen, the pre-cool process requires 10 tanks and almost a week of continual monitoring in order to reach the desired target temperature. It is very difficult to work for such a long period of time at the oxygen starved summit of Mauna Kea (4205 meters),and issues of man-power and scheduling conflicts only add to the problems. To address these concerns Subaru developed an automated pre-cooling system which works continuously and remotely at the summit. The strategy was to have basic functionality for pre-cooling and user friendly interface. i.e. (1) Continuous cooling until the target temperature is reached by automated liquid nitrogen tank exchanges and precision temperature control by automated changes to the liquid nitrogen flow. (2) Remote monitoring and control of all parameter setting by Web browser as user interface (UI). The goal of the Subaru pre-cooling system was to make it both inexpensive and quick to implement by using existing technologies. The original goal (to cut down on labor and precision temperature control) has been attained through several pre-cooling and software/hardware modification cycles. We will report on the progress and status of our pre-cooling experiences in this presentation.

A research and development activity on image slicer systems for integral field spectroscopy has grown in the last years. It allows the simultaneous observation on the same detector matrix of two-dimensional sky maps and a spectral decomposition of light reducing the observation times. Today, image slicers lead to possible applications on future instrumentation for ground-based and space telescopes, covering a spectral domain ranging from blue to mid-IR wavelengths. Since 2001, the Centre de Recherche Astrophysique de Lyon has designed, manufactured, integrated and tested six different breadboards using advanced image slicers. These breadboards are based on different optical designs (three or two mirror arrays or a combination of mirrors and mini-lens arrays). All these designs will be presented. Furthermore, all manufacturing methods will be described. Some use classical polishing approach on Zerodur with an assembling by molecular adhesion. Others are made of metal with monolithic or segmented optical elements and state-of-the-art diamond turning machines. Then all individual tests (roughness, shape and reflectivity) and system performances (alignment and quality image) will be summarized. We will conclude with a comparison between these different breadboards by choosing the most suitable solution for the projects.

The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design, with an 8.4- meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary feeding a camera system that includes a set of broad-band filters and refractive corrector lenses to produce a flat focal plane with a field of view of 9.6 square degrees. Optical design of the camera lenses and filters is integrated with optical design of telescope mirrors to optimize performance, resulting in excellent image quality over the entire field from ultra-violet to near infra-red wavelengths. The LSST camera optics design consists of three refractive lenses with clear aperture diameters of 1.55 m, 1.10 m and 0.69 m and six interchangeable, broad-band, filters with clear aperture diameters of 0.75 m. We describe the methodology for fabricating, coating, mounting and testing these lenses and filters, and we present the results of detailed tolerance analyses, demonstrating that the camera optics will perform to the specifications required to meet their performance goals.

The LSST camera is a tightly packaged, hermetically-sealed system that is cantilevered into the main beam of the LSST telescope. It is comprised of three refractive lenses, on-board storage for five large filters, a high-precision shutter, and a cryostat that houses the 3.2 giga-pixel CCD focal plane along with its support electronics. The physically large optics and focal plane demand large structural elements to support them, but the overall size of the camera and its components must be minimized to reduce impact on the image stability. Also, focal plane and optics motions must be minimized to reduce systematic errors in image reconstruction. Design and analysis for the camera body and cryostat will be detailed.

In traditional seeing-limited observations the spectrograph aperture scales with telescope aperture, driving sizes and costs to enormous proportions. We propose a new solution to the seeing-limited spectrograph problem. A massively fiber-sliced congfiguration feeds a set of small diffraction-limited spectrographs. We present a prototype, tunable, J-band, diffraction grating, designed specifically for Astronomical applications: The grating sits at the heart of a spectrograph, no bigger than a few inches on a side. Throughput requirements dictate using tens-of-thousands of spectrographs on a single 10 to 30 meter telescope. A full system would cost significantly less than typical instruments on 10m or 30m telescopes.

Waveguide image-slicer prototypes with resolutions up to 310.000 for the fiber fed PEPSI echelle spectrograph at the LBT and single waveguide thicknesses of down to 30 μm have been manufactured. The waveguides were macroscopically prepared, stacked up to an order of 7 and thinned back to square stack cross sections. A high filling ratio was achieved by realizing homogenous adhesive gaps of 4.6 μm, using index matching adhesives for TIR within the waveguides. The image-slicer stacks can be used in immersion mode and are miniaturized to be implemented in a set of four, measurements indicate an overall efficiency of above 80% for them.

The reliability of active optic for telescopes and instrumentation is now good enough to make them available for day to day use in working observatories. Future telescopes and their associated instruments will benefit from this technology to offer innovative concepts, optimal performance and improved reliability. An optical design of the multi-objects spectrograph EAGLE using, active surfaces, is detailed in this article. The first active component is a steering mirror, included in the target acquisition system, able to compensate for large astigmatism variations due to the variable off-axis design. This innovative design also includes two variable curvature mirrors authorising focus compensation and adding a zoom facility. A complete description of these active mirrors mechanical principle is presented, from elasticity theory to opto-mechanical design. The prototypes of these active mirrors with their complete test bench are detailed.

Our OPTICON JRA6 research line developed a 4 year study of non conventional uses of Volume Grating Holographic Gratings (VPHG). The final results are witnessed by the construction of a bench prototype of tunable grating and a tunable filters. This realization has all the characteristics of robustness and versatility to be worth extending its use to existing of future FOSC camera spectrograph. The adjustable bending of the in/out-coming beam allows broadband VPHG to exploits the superblaze efficiency curve in dispersing mode and thick grating, to act as narrow passband filter.

Volume phase holographic gratings (VPHGs) are becoming an interesting alternative to the ruled gratings in modern astronomical instrumentation. Photochromic materials with thermal stability are good candidates for the development of holographic optical elements and in particular for VPHGs. VPHGs based on photochromic materials can be written and erased many times without the degradation of the material; moreover the material does not need any developing process after the exposure, making the writing process very simple. We have already studied photochromic materials for this aim in the framework of the JRA6 (Opticon Project, FP6) and we found that large modulations of the refractive index can be achieved using diarylethene polymers. Going from the materials characterization to technology, substrates with larger thickness and good optical properties are required. Herein we present the development of new technique to tailor the thickness of the photochromic films in two ranges: 5 - 30 micron and 700 - 1000 micron. The former are suitable for the development of broadband VPHGs, whereas the latter are suitable for narrow band tunable filters application. Details on the optical properties of the films are reported. Finally, a holographic set-up based on an Ar+ laser has been optimized in order to write the gratings.

Integral Field Spectroscopy (IFS) provides a spectrum simultaneously for each spatial sample of an extended two-dimensional field. Basically, the IFS is located in a telescope focal plane and is composed by an Integral Field Unit (IFU or image slicer) and a spectrograph. The IFU acts as a coupler between the telescope and the spectrograph by reformatting optically a rectangular field into a quasi-continuous pseudo-slit located at the entrance focal plane of the spectrograph. The Integral Field Units (IFUs) are presently limited either by their cost/risk (when manufactured with classical glass polishing techniques) or by their performances (when constituted by metallic components). Recent innovative methods, developed conjointly by LAM (Laboratoire d'Astrophysique de Marseille, France) and WinLight Optics (Marseille, France), allow reaching high performances (accurate roughness, sharp edges, surface form, etc.) with standard glass manufactured components while saving costs and time by an order of magnitude compared with classical techniques. Last developments (in term of design and manufacturing) and applications are presented in details in this article.

We present the manufacturing and first results from testing and characterising the SWIFT image slicer. The SWIFT image slicer design is based on the MPE-3D and SPIFFI image slicers. It uses plane mirrors to slice the input field but through a novel, de-magnifying design, using a mosaic of spherical lenses, it achieves a considerable de-magnification. Classical polishing techniques can be applied to manufacture both plane and spherical surfaces with very high surface accuracy and quality reducing aberrations and scattered light. The SWIFT image slicer was manufactured over a 18 months period and was delivered to Oxford in September 2007. The commissioning of the SWIFT instrument will take place in August/September 2008.

AstroPhotonica Europa (APE) is a partnership to exploit photonic principles for astronomy and related areas, using and enriching the existing research and industrial infrastructure. The primary goal is to make instruments for future telescopes such as the Extremely Large Telescopes (ELTs) and ground- and space-based interferometry affordable and practicable by exploiting photonic principles. This paper describes the aims of the partnership, its constitution and its plans.

Collaboration between Kaiser Optical Systems, Inc. and the Department of Physics and Astronomy at Johns Hopkins University has resulted in the construction of volume phase holographic (VPH) transmission gratings that were subsequently tested in a cryogenic environment. VPH gratings were built on two popular optical glasses and subjected to temperatures near 100 Kelvin. Test conditions, observations and results are reported. Design considerations for optimizing VPH grating performance in cold environment is discussed.

A new class of astronomical telescope with a primary objective grating (POG) has been studied as an alternative to mirrors. Nineteenth century POG telescopes suffered from low resolution and ambiguity of overlapping spectra as well as background noise. The present design uses a conventional secondary spectrograph to disambiguate all objects while enjoying a very wide instantaneous field-of-view, up to 40°. The POG competes with mirrors, in part, because diffraction gratings provide the very chromatic dispersion that mirrors defeat. The resulting telescope deals effectively with long-standing restrictions on multiple object spectrographs (MOS). The combination of a POG operating in the first-order, coupled to a spectrographic astronomical telescope, isolates spectra from all objects in the free spectral range of the primary. First disclosed as a concept in year 2002, a physical proof-of-principle is now reported. The miniature laboratory model used a 50 mm plane grating primary and was able to disambiguate between objects appearing at angular resolutions of 55 arcseconds and spectral spacings of 0.15 nm. Astronomical performance is a matter of increasing instrument size. A POG configured according to our specifications has no moving parts during observations and is extensible to any length that can be held flat to tolerances approaching float glass. The resulting telescope could record over one million spectra per night of objects in a line of right ascension. The novel MOS does not require pre-imaging to start acquisition of uncharted star fields. Problems are anticipated in calibration and integration time. We propose means to ameliorate them.

We are developing single-crystalline silicon micromirror arrays (MMA) for future generation infrared multiobject spectroscopy (IR MOS). The micromirrors are 100μm × 200μm in size and can be tilted by electrostatic actuation yielding a tilt-angle of 20°. Arrays of 5x5 micromirrors were gold-coated and tested at below 100K. The coated and uncoated micromirrors are optically flat (peak-to-valley deformation < λ/20 for λ > 1μm) at room temperature and in cryogenic environment. Successful actuation has been done at room temperature and at temperatures below 100K. Large arrays of 200x100 micromirrors are being fabricated and an actuation scheme for extremely large arrays has been developed.

We have conducted extensive tests of both transmission and focal ratio degradation (FRD) on two integral field units currently in use on the VIRUS-P integral field spectrograph. VIRUS-P is a prototype for the VIRUS instrument proposed for the Hobby-Eberly Telescope at McDonald Observatory. All tests have been conducted at an input f-ratio of F/3.65 and with an 18% central obscuration in order to simulate optical conditions on the HET. Transmission measurements were conducted with narrow-band interference filters (FWHM: 10 nm) at 10 discrete wavelengths (337 to 600 nm), while FRD tests were made at 365 nm, 400 nm and 600 nm. The influence of wavelength, end immersion, fiber type and length on both FRD and transmission is explored. Most notably, we find no wavelength dependence on FRD down to 365 nm. All fibers tested are within the VIRUS instrument specifications for both FRD and transmission. We present the details of our differential FRD testing method and explain a simple and robust technique of aligning the test bench and optical fiber axes to within ±0.1 degrees.

We have developed an alternative FRD empirical model for the parallel laser beam technique which can accommodate contributions from both scattering and modal diffusion. It is consistent with scattering inducing a Lorentzian contribution and modal diffusion inducing a Gaussian contribution. The convolution of these two functions produces a Voigt function which is shown to better simulate the observed behavior of the FRD distribution and provides a greatly improved fit over the standard Gaussian fitting approach. The Voigt model can also be used to quantify the amount of energy displaced by FRD, therefore allowing astronomical instrument scientists to identify, quantify and potentially minimize the various sources of FRD, and optimise the fiber and instrument performance.

Echidna is a fiber positioner designed and built by the Anglo-Australian Observatory using novel technology to position 400 fibers in the prime focus field of the Subaru telescope. The fibers feed two near infrared OH-suppression spectrographs, the whole project being known as Fiber Multi Object Spectrograph (FMOS). In order to accommodate the large number of the fibers in the physically limited area, a new fiber positioning method is developed. Stand-alone tests of the positioner at sea level confirm its performance is fully satisfactory. Initial results and prospects of the on-sky commissioning tests of the positioner are also described.

A summary of the optical coatings for the spectral range from 50 to 200 nm that can be prepared at GOLD is presented. This spectral range, named here far and extreme ultraviolet (FUV/EUV), is characterized by the high absorption of almost all materials and the strong dependence of their optical properties on the deposition parameters and on the exposure of the samples to the atmosphere. Broadband mirrors and narrowband filters were prepared in an ultra high vacuum system where in situ FUV/EUV reflectometry is available. In this work we summarize the main aspects concerning in situ performance and ageing of these coatings. Broadband mirrors composed of Al/MgF₂, SiC, B and Al/MgF₂/SiC cover the FUV/EUV spectral range from 50 to 200 nm. Above the transparency cutoff of MgF₂ (115 nm), transmittance filters based on Al/MgF₂ multilayers have been developed peaked at wavelengths as short as 120 nm. An example is shown centered at 124 nm with a peak transmittance of 27% and a FWHM of 12 nm for a fresh coating. Below 115 nm, a research on reflectance filters has recently started with very promising results on filters peaked at ~83 nm, close to the OII spectral line. Fresh filters with 27% peak reflectance at normal incidence and a FWHM of 14 nm have been obtained. These novel reflectance filters based on Al, Yb and SiO must still demonstrate stability over time. The developed coatings have a potential application in the field of astronomical observations.

SAGEM has developed a line of product specific to the large-sized parts. The means available make it possible today to coat substrates of dimensions going until 1m50. Current developments address coating of substrate up to 2m20. A specific focus has been held on the wavefront deformation due to the coating. Principle contributors of this deformation are introduced and analyzed as well as some experimental results.

Near-infrared bandpass filters are commonly designed & manufactured using vacuum-evaporated films of Silicon and Silicon Monoxide. However the transparency of these filters is limited by optical absorption in the films when producing filters for wavelengths below 1200nm approximately. This work reports improvements in NIR filter transparency achieved by exploiting recent advances in magnetron sputtering technology. Sputtered silicon compound films have been used to demonstrate efficient bandpass filters for astronomy applications at wavelengths below 1000nm. This process technology allows a new selection of film materials to be used in design of NIR bandpass filters, with transmission and thermal drift characteristics which differ from conventional evaporated coatings. The spectral location of the bandpass is controlled by a non-optical method, which avoids the complex optical monitoring configurations normally required. The speed and flexibility of this process also offers a potential solution for projects which require small batches of custom NIR optical filters. Highly durable filters are obtained without elevated process temperature, which would otherwise be required in conventional evaporation processes. This avoids heating filter substrates which may be sensitive to thermal cycling effects. Attenuation of sidebands to T<0.0001 is reported across the spectral range of common sensor devices. The thermal sensitivity for cryostat applications is characterised and compared to conventional evaporated optical coatings. This method has been applied to 975nm & 985nm bandpass filters for use on VISTA project instrumentation. It also offers improvements for filters at longer wavelengths in the range 1000nm-5000nm. Some examples are reported in this region.

Mirrors with large aperture, high asphericity and tight shape tolerances are indispensable for modern astronomical telescope. This pressing demand provides new challenges on optical fabrication. Paper here presents a 2.5m CNC machine which has been designed and constructed in Nanjing Institute of Astronomical Optics & Technology (NIAOT). Mechanical layout of 2.5m OFM is first studied basing on analyzing fabrication requirements. Equipped with six motion axes, it can process parts up to 2500mm in diameter. Rotary symmetrical component can be finished under cylindrical coordinates and Cartesian coordinates are applied for off-axis workpiece. Then control system using CAN field bus is discussed. This control architecture offers many characteristics, such as high openness, expansibility and flexibility. Since 2.5m OFM is developed to combine faculties of grinding, lapping and polishing, we arrange a series of tests for each function. Now a 1.1m hexagonal mirror is carried for grinding. Polishing test using sub-aperture tool and active stressed lap will be programmed later.

A 450mm diameter active stressed lap has been developed in NIAOT by 2003. We design a new lap in 2007. This paper puts on emphases on introducing the new deforming control system of the lap. Aiming at the control characteristic of the lap, a new kind of digital deforming controller is designed. The controller consists of 3 parts: computer signal disposing, motor driving and force sensor signal disposing. Intelligent numeral PID method is applied in the controller instead of traditional PID. In the end, the result of new deformation are given.

This paper describes a major advance in the post-treatment of diamond-turned surfaces to remove repetitive micro-structure; a result which could have a major beneficial impact on fabrication of Walter-type X-ray mandrels, and metal mirrors. Diamond-turning is highly deterministic and versatile in producing axially-symmetric forms, and through fast-tool servos, non-axially symmetric, free-form and micro-structured surfaces. However, the fine turning marks left in the metal surface limit performance. In this paper, we describe how fluid-jet polishing under CNC control can be used to eliminate these structures, without significantly degrading the surface roughness or form produced by the prior turning operation.

In the LAMOST project, the unit-holes on the Focal Plane Plate are the final installation location of the optical fiber positioning system. Theirs precision will influence the observation efficiency of the LAMOST. For the unique requirements, the unit-holes on the Focal Plane Plate are composed by a series of tiny angle dimensional holes which dimensional angle are between 16' to 2.5°. According to these requirements, the measurement of the tiny angle dimensional holes for the unit-holes needs to less than 3'. And all the unit-holes point to the virtual sphere center of the Focal Plane Plate. To that end, the angle departure of the unit-holes axis is changed to the distance from the virtual sphere center of Focal Plane Plate to the unit-holes axis. That is the better way to evaluate the technical requirements of the dimensional angle errors. In the measuring process, common measuring methods do not fit for the tiny angle dimensional hole by CMM(coordinate measurement machine). An extraordinary way to solve this problem is to insert a measuring stick into a unit-hole, with a target ball on the stick. Then measure the low point of the ball center and pull out the stick for the high station of center. Finally, calculate the two points for the unit-hole axis to get the angle departure. But on the other hand, use this methods will bring extra errors for the measuring stick and the target ball. For better analysis this question, a series experiments are mentioned in this paper, which testify that the influence of the measure implement is little. With increasing the distance between the low point and the high point position in the measuring process should enhance the accuracy of dimensional angle measurement.

We describe here the optical design, mechanical project and the manufacturing of a mechanically reconfigurable spherical slicing mirror. We made use of nowadays commonly available mechanical cutting techniques (wire spark-erosion) to obtain single blades (slices) shaped with profile close to the optical sag specification. Blades so constructed are ready to be optically finished with standard optical workshop techniques. We present here the results obtained from metrology made on the first constructive phase of the system before to start the final optical polishing phase.

This paper summarizes the main aspects of the design and qualification test results of the ALMA Amplitude Calibration Device Robotic Arm (ACD). The design aspects of the ACD, including a detailed description of the components selected to achieve the expected performances are presented in the first part of the paper. Also the system performances results measured in the first prototype units are summarized at the last part of the paper.

We present our recent developments towards the construction of a large, thin, single-piece mirror for adaptive optics (AO). Our current research program aims to have completed fabrication and testing of a 1m diameter, nickel coated carbon-fibre reinforced cyanate ester resin mirror by the last quarter of 2009. This composite mirror material is being developed to provide a lightweight and robust alternative to thin glass shell mirrors, with the challenge of future large deformable mirrors such as the 2.5m M4 on the E-ELT in mind. A detailed analysis of the material properties of test mirror samples is being performed at the University of Birmingham (UK), the first results of which are discussed and presented here. We discuss the project progress achieved so far, including fabrication of the 1m flat moulds for the replication process, manufacturing and testing methods for 20 cm diameter sample mirrors and system simulations.

This paper present the results of a diamond turning study of a rapidly solidified aluminium 6061 alloy grade, known as RSA6061. It is shown that this small grain material can be diamond turned to smaller roughness values than standard AA6061 aluminium grades. Also, the results are nearly as good as nickel plated surfaces, but the RSA6061 has the advantage that no additional production steps are needed and that no bi-metallic bending or delamination can occur in a thermally changing environment, e.g. when cooling to cryogenic temperature. Therefore, RSA6061 is a good material for optical applications in the visual spectrum.

Initiated in 1968 by the first order of the Max-Planck-Institute in Heidelberg the successful history of ZERODUR^® continues now since 40 years. ZERODUR^® zero expansion glass ceramic from SCHOTT has been the material of choice in astronomy for decades, thanks to its special properties such as its extremely high thermal and mechanical stability. Today most of the major modern optical telescopes of the 4 m class and of the 8 m to 10 m class are equipped with ZERODUR^®. For the future several Extremely Large Telescope (ELT) projects are in development, which are designed with even larger primary mirrors ranging from 30 m to 42 m. Also here ZERODUR^® is under consideration. A historical review, the actual status of developments and an outlook to the future is given in this paper.

The Naval Research Laboratory (NRL) has been exploring the use of meter class telescopes using Carbon Fiber Reinforced Polymer (CFRP) material for support structure and optics, resulting in over an order of magnitude reduction in weight over traditional steel and glass telescopes. In conjunction with Composite Mirror Applications (CMA), for the past three years this program has proceeded from conceptual phase to prototype development. In this paper we will review the various stages of this program. We will also present the status of our 0.4 meter and 1.4 meter telescopes. Experimental results from these developments and testing will be shown.

Highly stable but lightweight structural materials are essential for the realization of spaceborne optical instruments, for example telescopes. In terms of optical performance, usually tight tolerances on the absolute spacing between telescope mirrors have to be maintained from integration on ground to operation in final orbit. Furthermore, a certain stability of the telescope structure must typically be ensured in the measurement band. Particular challenging requirements have to be met for the LISA Mission (Laser Interferometer Space Antenna), where the spacing between primary and secondary mirror must be stable to a few picometers. Only few materials offer sufficient thermal stability to provide such performance. Candidates are for example Zerodur and Carbon-Fiber Reinforced Plastic (CFRP), where the latter is preferred in terms of mechanical stiffness and robustness. We are currently investigating the suitability of CFRP with respect to the LISA requirements by characterization of its dimensional stability with heterodyne laser interferometry. The special, highly symmetric interferometer setup offers a noise level of 2 pm/√Hz at 0.1Hz and above, and therefore represents a unique tool for this purpose. Various procedures for the determination of the coefficient of thermal expansion (CTE) have been investigated, both on a test sample with negative CTE, as well as on a CFRP tube specifically tuned to provide a theoretical zero expansion in the axial dimension.

In millimeter wavelength telescope design and construction, there have been a number of mysterious failures of simple CFRF-metal joints. Telescope designers have not had satisfactory interpretations of these failures. In this paper, factors which may influence the failure of joints are discussed. These include stress concentration, material creep, joint fatigue, reasons related to chemical process and manufacture process. Extrapolation formulas for material creep, joint fatigue, and differential thermal stresses are derived in this paper. Detailed chemical and manufacturing factors are also discussed. All these issues are the causes of a number of early failures under a loading which is significantly lower than the strength of adhesives used. For ensuring reliability of a precision instrument structure joint, the designer should have a thorough understanding of all these factors.

The upper part of the European Extremely Large Telescope (E-ELT) altitude structure is one of the most critical areas of the telescope's structure. This part hosts sensitive optical elements of the telescope. Its structural performance has a major impact on the whole system. The most critical requirements are low optical path obscuration, high static and dynamic performance (high specific modulus), high mechanical safety (high specific strength), low wind cross section and low weight. Composite materials are ideally suited to meet these requirements. This study is carried out in order to quantify the relative advantage of composite material over mild steel, in terms of performance and costs. The mechanical behavior of the steel structure can be easily improved with a structure manufactured with composite materials. This structure is significantly lighter than the steel one and reduces relative displacements between primary and secondary mirror. Consequently, optical performance is improved, assembly process is simplified and transport cost is reduced.

We developed an aspheric convex 33-cm diameter secondary mirror of the Hiroshima University 1.5-m Ritchy-Chretien telescope using Zero-expansion Pore-free ceramics, which has physical properties (thermal expansion, stiffness, thermal conductance, etc.) comparable with or better than existing zero-expansion glasses. After high-precision grinding, polishing, and coating aluminum and silicon monoxide, we obtained the sufficient optical reflecting surface with a figure error within λ/10 and a roughness of about 3 nm rms. The mirror has been attached on the telescope and we confirmed its sufficient performance through a Hartmann test. To date it has shown a good performance in our application and we suggest that this ceramic material has a potential to be used for astronomical telescopes and related area.

LAMOST is a quasi-meridian reflecting Schmidt telescope, which consists of a reflecting Schmidt corrector M_A, a spherical primary mirror M_B and a focal plane. The telescope with its optical axis tilted by an angle of 25° to the horizon tracks the celestial objects by the movements of M_A to make the light throughout aim at M_B, and M_B mirror consists of 37 spherical segments hanged upside down on the truss which tilted by about 25° to the horizon. This paper presents a design of M_B sub-mirror segment handling manipulator for LAMOST, carries out a simulation analysis, presents an engineering program and describes the program's design principles and ideas. The manipulator including grab, declutch, elevation, stretch, pitching, rotation, automatic control and several other parts, and the control system can coordinate all these movements so that each segment can be located installed and handled precisely. In the structural design process the stiffness and positioning accuracy problems have been taken full account of.

Annular subaperture interferometric method has provided an alternative solution to testing rotationally symmetric aspheric surfaces with low cost and flexibility. However, some new challenges, particularly in the motion and algorithm components, appear when applied to large aspheric surfaces with large departure in the practical engineering. Based on our previously reported annular subaperture reconstruction algorithm with Zernike annular polynomials and matrix method, and the experimental results for an approximate 130-mm diameter and f/2 parabolic mirror, an experimental investigation by testing an approximate 302-mm diameter and f/1.7 parabolic mirror with the complementary annular subaperture interferometric method is presented. We have focused on full-aperture reconstruction accuracy, and discuss some error effects and limitations of testing larger aspheric surfaces with the annular subaperture method. Some considerations about testing sector segment with complementary sector subapertures are provided.

A procedure has been developed to compute static aberrations after the PSF measured with the lucky imaging technique, using a nearby star as the point source to probe the optical system. This PSF is iteratively turned into a phase map at the pupil using the Gerchberg-Saxton algorithm, and then converted to the adequate actuation information for a deformable mirror having low actuator number but large stroke capability. The main advantage of this procedure is related with the capability of correcting static aberration at the specific pointing direction and without the need of a wavefront sensor.

The Large Millimeter Telescope (LMT) at Cerro La Negra in Central Mexico is currently being fitted out with optical, mechanical and control systems. The tertiary mirror is a 1.1 x 1.7m ellipse, mounted on a positioner which provides tracking in elevation and 180° image direction switching between detectors. Installation and alignment of mirror and positioner must be achieved with high accuracy in a construction-site environment, at an altitude of 4600m. Alignment equipment should be intuitive to use, easy to install, and have minimum interference with other site tasks. Alignment will be achieved with small diameter, well-collimated laser beams, pre-aligned to the telescope elevation and primary reflector (optic) axes. Although a total station and laser tracker are available, the laser beam method has theoretically higher accuracy, gives faster, more intuitive results and requires no time-sharing with the former instruments. This paper describes the alignment concept, equipment to be used, pre-installation testing, and alignment procedures to be carried out at the telescope.

Camera calibration is the important step for the stereo vision measurement system. The accuracy of the calibration affects the accuracy of the vision measurement system. The calibration is realized with a planar pattern. The pattern has some spot array with high precision. Stereo vision measurement system captures the images of the calibration pattern at several different orientations. The parameter model is modified as the polynomial model to describe the lens distortion. The calibration experiment demonstrates that the error of 3-D reconstruction is 0.020mm.

We experimentally demonstrate that a stabilized femtosecond frequency comb can be applied as a tool for distance measurement. The scheme is based on optical interference between individual pulses in a Michelson type interferometer. The cross-correlation functions between individual pulses with a distance of around 15 meter and 30 meter are observed and analysed.

Frequency and distance metrology have been revolutionized with the arrival of stabilized frequency comb lasers. We discuss several aspects of distance metrology specially the contribution of the dispersion in by air.

The application of freeform diamond machining techniques to the manufacture of precision optics for astronomical instrumentation has opened up a wide range of exciting new design possibilities. Freeform surfaces, not limited by symmetry considerations, and complex multi-faceted mirror arrays can be precisely machined. This capability has removed many constraints from the design process and has enabled the fulfilment of radical instrument designs. However, this flexibility poses a significant challenge for component characterisation. Accurate measurement of the form accuracy of surfaces lacking symmetry is particularly difficult using standard interferometric techniques. Furthermore, the accurate 3 dimensional characterisation of complex multi-faceted components presents an added challenge. The authors describe techniques that have been applied to the measurement of complex surfaces in Integral Field Units (IFUs). In particular, we present novel approaches for the measurement of the form of complex non-radially symmetric surfaces to an accuracy of a few nanometres. These measurements use a Twyman-Green Interferometer configured in a variety of non-standard arrangements. In addition, the authors consider the difficulties in the measurement of multifaceted surfaces, and the accurate determination of the geometric relations between these surfaces. The authors discuss the use of confocal gauge techniques in the characterisation of these surfaces.

The pentaprism test is based on the property of a paraboloidal surface where all rays parallel to the optical axis will go through its focal point. We have developed a scanning pentaprism system that exploits this geometry to measure off-axis paraboloidal mirrors such as those for the Giant Magellan Telescope primary mirror. Extension of the pentaprism test to off-axis mirrors requires special attention to field effects that can be ignored in the measurement of an axisymmetric mirror. The test was demonstrated on a 1. -m diameter off-axis mirror and proved to have about 50nm rms surface accuracy. This paper gives detailed performance results for the measurement of the 1.7 m mirror, and designs and analysis for the test of the GMT segments.

Surface measurements represent a significant part of the cost for manufacturing large aspheric optics. Both polished and rough ground surfaces must be measured with high precision and spatial resolution. We have developed a system that couples a commercial laser tracker with an advanced calibration technique and a system of external references. This system was built to measure the off-axis primary mirror segments for the Giant Magellan Telescope where it will guide loose abrasive grinding and initial polishing. The system is further expected to corroborate the optical interferometric tests of the completed mirrors, in several low-order aberrations. The design, analysis, calibration, and measured performance of this system will be presented.

In an effort to reduce the amount of time spent focusing the telescope and to improve the quality of the focus, a new procedure has been investigated and implemented at the Canada-France-Hawaii Telescope (CFHT). The new procedure is based on a paper by Tokovinin and Heathcote and requires only two out-of-focus images to determine the best focus for the telescope. Using only two images provides a great time savings over the five or more images required for a standard through-focus sequence. In addition, it has been found that this method is significantly less sensitive to seeing variations than the traditional through-focus procedure, so the quality of the resulting focus is better. Finally, the new procedure relies on a second moment calculation and so is computationally easier and more robust than methods using a FWHM calculation. The new method has been implemented for WIRCam for the past 18 months, for MegaPrime for the past year, and has recently been implemented for ESPaDOnS.

With the advent of Queue observing at the Canada-France-Hawaii Telescope (CFHT), much emphasis has been placed on minimizing the overheads in the observing process. Ensuring telescope focus is a necessary overhead, but taking the focus sequences required to keep focus during the night adds significant time. In order to nearly eliminate this overhead without sacrificing good telescope focus, the necessary focus position for each instrument has been modeled as a function of telescope temperature and position on the sky. The correct focus position is calculated instead of measured, so focus updates are practically instantaneous. The model coefficients are updated with new data regularly. Automatic focus using calculated focus positions has been implemented for MegaCam, WIRCam and ESPaDOnS.

The basic principle of the linear phase retrieval (LPR) method is introduced. It is found that in small phase condition, the odd and even parts of phase aberration can be obtained uniquely with a simple linear calculation method. The difference between a single measured image with aberration and the calibrated image with inherent aberration are used to retrieve aberration phases. In this paper, the principle of LPR and its application in close-loop AO system are introduced in vector-matrix format, which is a kind of linear calculation and is suitable for real-time calculation. Although the LPR method is limited for small aberrations only, it is suitable to use as a wavefront sensor in close-loop adaptive optical system. The performances of the LPR method are tested in a close-loop adaptive optics system with PZT deformable mirror. The experiment results show that the LPR method can be performed in real time and achieve good capabilities.

Up to now, optical design of astronomical instrumentation has been based onto "classical" surfaces, i.e. plano surfaces, spherical surfaces, and some classes of aspheric surfaces. More complex surfaces (like cylinders), are used from time to time to correct for aberrations. A new class of more general surfaces, i.e. non-rotationally symmetrical and completely "free-form" surfaces have been recently introduced. Their use in astronomy, however, has not widely used so far. We propose a new layout for an anamorphic collimator based onto two "free-form" cylinder surfaces, giving diffraction limited images. This collimator can be used to create an elliptical pupil, and allows reducing size of optical systems, too. Two interesting cases of application in astronomy are shown: a very-high resolution spectrograph for large telescopes, and an interferometer cavity to test large plano optics.

Visible Light Laser Guidestar Experiments (ViLLaGEs) is a new Micro-Electro Mechanical Systems (MEMS) based visible-wavelength adaptive optics (AO) testbed on the Nickel 1-meter telescope at Lick Observatory. Closed loop Natural Guide Star (NGS) experiments were successfully carried out during engineering during the fall of 2007. This is a major evolutionary step, signaling the movement of AO technologies into visible light with a MEMS mirror. With on-sky Strehls in I-band of greater than 20% during second light tests, the science possibilities have become evident. Described here is the advanced engineering used in the design and construction of the ViLLaGEs system, comparing it to the LickAO infrared system, and a discussion of Nickel dome infrastructural improvements necessary for this system. A significant portion of the engineering discussion revolves around the sizable effort that went towards eliminating flexure. Then, we detail upgrades to ViLLaGEs to make it a facility class instrument. These upgrades will focus on Nyquist sampling the diffraction limited point spread function during open loop operations, motorization and automation for technician level alignments, adding dithering capabilities and changes for near infrared science.

This paper explores one Arc PMSM for Direct Drive Telescope tracking system. By the Arc PMSM, we can very easily manufacture one direct drive system for large telescope. Direct drive system has many advantages over more traditionally used friction and rack/pinion drive. The advantages include high stiffness, no friction, easy alignment and low maintenance. The paper discusses the design process of the Arc PMSM, especially the methods to reduce the torque ripple.

The 6.5m MMT telescope currently has three focal configurations. The f/5 optical configuration has a system of optical baffles to prevent stray light from entering the focal plane. The system consists of a cone baffle supported on the secondary (M2) structure and set of concentric rings suspended between the secondary and the primary (M1). This paper reviews the optical configurations, mechanical design, alignment, installation, and measured performance of the system.

The 2.6m VST telescope is in installation phase in the ESO observatory of Cerro Paranal. After preliminary tests in Europe performed jointly by INAF and ESO the tracking system was considered at the readiness level to be shipped to Chile. The motion control system has already been reintegrated in Chile and is operational again. The final tuning is going to be performed after the integration of all the telescope subsystems, still in progress. Therefore here the focus is especially on tests performed in Italy. This paper describes the solutions adopted for the telescope main axes control as well as the preliminary tracking results. Available test data are related to encoder feedback. Tests have been performed tracking coordinates of virtual objects. A comprehensive test case to evaluate the performance of different controllers was needed to proceed in a systematic way. A tracking map derived from the VLT commissioning experience has been used, spanning all the different conditions for axes positions and speeds, including meridian crossing and tracking near the blind spot.

The VST telescope is equipped with an active optics system based on a wavefront sensor, a set of axial actuators to change the primary mirror shape and a secondary mirror positioner stage. The secondary mirror positioning capability allows the correction of defocus and coma optical aberrations, mainly caused by incorrect relative positions of the optics. The secondary mirror positioner is a 6-6 Stewart platform (also called "hexapod"). It is a parallel robot with a mobile platform moved by 6 linear actuators acting simultaneously. This paper describes the secondary mirror support system and the current status of the work.

Telescope is a very important tool for astronomers to survey and study the stellar stars and astronomical phenomena. The performance of a telescope is its capability to track the observing objects and keep the image on the field of view during the observing period. All these functions will be achieved by telescope mount, including mount control system. The mount is to support the mirror cell and keep the mirror cell position stability. Meanwhile, with the help of control system, the mount acts as tracker of the observing objects. So, for a telescope, the mount and its control system play an important role during the telescope operation. This paper introduces the structure design and analysis of the mount system of a 2.5m optical/infrared telescope, such as azimuth axis, elevation axis, M2 positioning system, M3 positioning system, and so on. Especially, an innovative support and escape mechanism of M3 will be proposed and analysed in this paper.

For an astronomical telescope mount, having a high stiffness to support the mirror cell and instruments is its basic function. Traditionally, the mount is composed of azimuth base, azimuth axis, fork, altitude axis, tube, top-ring, etc. On the other hand, telescope will be driven to track the observing objects during operation. So, for the mechanical structure design engineer, finding a high stiffness-to-weight ratio mount is the main task. Finite element method (FEM) is a powerful tool to help structure design engineer to achieve this goal. ANSYS is one of these kinds of finite element method software. In this paper, with the help of ANSYS, the static and dynamic analysis, calculation and optimization of a 2.5m telescope mount will be given. The FEM results show that the structure, designed for 2.5m telescope, is feasible and reliable and have a high stiffness-to-weight ratio to meet the optical demands.

Dome C and A of the Antarctic plateau is considered to be the best astronomical site on the earth because of extremely cold, dry weather, low wind speed and atmospheric turbulence overhead. CSTAR (Chinese Small Telescope ARray), which is composed of four small telescopes with 100mm clear aperture, has been accomplished in August and shipped to Antarctic at November 2007. Then, from the Zhongshan station, Chinese traverse team sledged it by snow tractor to Dome A through about 20 days hard trip and erected in January 2008. In this paper, the vibration proof design of packing box of CSTAR is introduced based on vibration theory and the analysis of power spectrum density is done to verify parameter selection. Finally, transport experiment is done to prove that packing box is suitable for the inclement and various transport condition.

The reflector of FAST (Five-hundred-meter Aperture Sphere Telescope) is a net mesh structure and can be considered as a flexible parallel motion mechanism array which can form the varying paraboloid surface by controlling the motion of the net mesh nodes. As a parallel mechanism, the motion of the nodes are coupled together. In order to release the coupling, or to estimate the surface error of the reflector, the motion of FAST 30m Model was simulated combined with ADAMS and SIMULINK. The net mesh mechanism was modeled as springs and spheres with mass in ADAMS software. To control the large amount of actuators, and to analyze the motion of the net mesh motion mechanism, a control model in SIMULINK has been built, which includes astronomical plan, actuator controlling and surface analysis. The model can be used as the test tool of the actuator control strategy and optimization for the net mesh structure. With the combined simulation, the amount of the couple phenomenon is estimated precisely. The paraboloid shape forming and moving in the observing course is simulated, and the variation of the surface error of the reflector and the forces of each cable are given. By the simulation, it can be concluded that the couple effect is small in the FAST 30m Model, and such a method can be applied to the FAST prototype.

FAST is an Arecibo type large radio telescope with 500 meters aperture reflector, which is composed of about 4600 triangle panels. The panels and back structures are installed on the spring cable meshes. FAST adopts the active reflection structure to change the spherical difference, which will form a simultaneous parabola with aperture of 300 meters. To test the feasibility of this new type reflector structure, a FAST model of 30 meters aperture was constructed in 2005. In this paper, the structure of the model is introduced, which includes a circle supporting girder of 30 meters in diameter, 252 panel back structures, 472 main cables, and 145 sets of control cables, nodes, actuators and anchors. The structural design and analysis are processed for these compositions, and the test results of the model reflector are given. The work of the paper will provide a significant reference for the primary design of FAST reflector.

Friction drive is used in some large astronomical telescopes in recent years. Comparing to the direct drive, friction drive train consists of more buildup parts. Usually, the friction drive train consists of motor-tachometer unit, coupling, reducer, driving roller, big wheel, encoder and encoder coupling. Normally, these buildup parts will introduce somewhat errors to the drive system. Some of them are random error and some of them are systematic error. For the random error, the effective way is to estimate their contributions and try to find proper way to decrease its influence. For the systematic error, the useful way is to analyse and test them quantitively, and then feedback the error to the control system to correct them. The main task of this paper is to analyse these error sources and find out their characteristics, such as random error, systematic error and contributions. The methods or equations used in the analysis will be also presented detail in this paper.