This PDF file contains the front matter associated with SPIE Proceedings Volume 7739, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Large aspheric primary mirrors are proposed that use hundreds segments that all must be aligned and phased to approximate the desired continuous mirror. We present a method of measuring these concave segments with a Fizeau interferometer where a spherical convex reference surface is held a few millimeters from the aspheric segment. The aspheric shape is accommodated by a small computer generated hologram (CGH). Different segments are measured by replacing the CGH. As a Fizeau test, nearly all of the optical elements and air spaces are common to both the measurement and reference wavefront, so the sensitivities are not tight. Also, since the reference surface of the test plate is common to all tests, this system achieves excellent control for the radius of curvature variation from one part to another. This paper describes the test system design and analysis for such a test, and presents data from a similar 1.4-m test performed at the University of Arizona.

Optics for telescopes - on ground and in space - is getting more and more into complex geometries. Weight reduction and new materials together with aspherical shape and off-axis set-ups increase the need for deterministic processes. With the advent of free-form surfaces having no symmetry at all, a new chapter for fabrication issues is opened. This paper describes our current achievements to combine different fabrication and measurement technologies to cope with the increasing demand in precision and complexity. We will explain our fabrication approach covering the full range from the raw material to the coated and measured component. Several examples of current and recent projects are shown. The variety of materials used ranges from Zerodur® to SiC.

An ultra precision large optics grinding machine, BoX®, was developed and produced at Cranfield University. BoX® offers a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. Grinding high accuracy surfaces with low subsurface damage reduces subsequent polishing time. This efficient grinding process provides the capacity to grind 1.5 m parts. This paper presents an analysis of Astrositall® optical ground parts: a hexagonal 84 m radius of curvature mirror of 1 m across corners and an off-axis 350 mm diameter mirror. The 1 m hexagonal part is representative of segments under study for making extremely large telescope (ELT) segmented mirrors. The second part was machined off-axis to demonstrate free-form fabrication capability. These operations demonstrate the scalability of the rapid grinding process developed for large free-form optics. The use of an error compensation procedure improved an initial ground form accuracy to +/- 1 μm p-v over 1 metre surface. The results highlighted the effect of grinding parameters and machine dynamics on form accuracy and fabrication time.

JSC LZOS under the contract with firm AMOS is carrying out the manufacturing works of Primary and Secondary Mirrors of Devasthal Optical Telescope (DOT) for Aryabhatta Research Institute of Observational Sciences (ARIES). Primary mirror specifications: diameter is 3700 mm, vertex radius is 14639 mm (F/1.96), conical constant is -1.03296, asphericity is 111 microns. Secondary mirror specifications: diameter is 980 mm, vertex radius is 4675 mm (F/1.78), conical constant is -2.79561, asphericity is 47 microns. The current progress status under this project is presented here in the manuscript.

Aspherical surfaces for imaging or spectroscopy are a centerpiece of high-performance optics. Due to the high alignment sensitivity of aspheric surfaces, reference elements and interfaces with a tight geometrical relation to the mirror are as important as the high quality of the optical surface itself. The developed manufacturing method, which accounts for the shape and also for the position of the mirror surfaces, allows controlling and precisely correcting not only the form, but also the alignment of reference marks, interfaces or even other mirrors in the sub-assembly using diamond turning. For Korsch or TMA telescopes it is also possible to diamond turn whole sub-assemblies containing two or more mirrors with a relative position error as low as the machine precision. Reference elements allow the correction of the shape and position of mirrors as well as the position of interfaces for system integration. The presented method opens up a novel manufacturing strategy to enhance the relative positioning accuracy of optic assemblies by one order of magnitude.

The primary mirror of the Giant Magellan Telescope consists of seven 8.4 m segments which are borosilicate honeycomb sandwich mirrors. Fabrication and testing of the off-axis segments is challenging and has led to a number of innovations in manufacturing technology. The polishing system includes an actively stressed lap that follows the shape of the aspheric surface, used for large-scale figuring and smoothing, and a passive "rigid conformal lap" for small-scale figuring and smoothing. Four independent measurement systems support all stages of fabrication and provide redundant measurements of all critical parameters including mirror figure, radius of curvature, off-axis distance and clocking. The first measurement uses a laser tracker to scan the surface, with external references to compensate for rigid body displacements and refractive index variations. The main optical test is a full-aperture interferometric measurement, but it requires an asymmetric null corrector with three elements, including a 3.75 m mirror and a computer-generated hologram, to compensate for the surface's 14 mm departure from the best-fit sphere. Two additional optical tests measure large-scale and small-scale structure, with some overlap. Together these measurements provide high confidence that the segments meet all requirements.

Advanced shapes can now be produced for the corrective optics placed near a reimaged pupil, or even a deformable mirror surface. These surfaces can be improved and even apodization added to improve contrast. In this paper, we describe a special form of Narrow Ion Beam Figuring (NIBF) developed at L-3 Tinsley. In contrast to existing Ion Beam Figuring (IBF) machining schemes, the FWHM beam width is controlled in a much narrower band while still providing high beam currents.

Pending critical spaceborne requirements, including coronagraphic detection of exoplanets, require exceptionally smooth mirror surfaces, aggressive lightweighting, and low-risk cost-effective optical manufacturing methods. Simultaneous development at Schott for production of aggressively lightweighted (>90%) Zerodur^® mirror blanks, and at L-3 Brashear for producing ultra-smooth surfaces on Zerodur^®, will be described. New L-3 techniques for large-mirror optical fabrication include Computer Controlled Optical Surfacing (CCOS) pioneered at L-3 Tinsley, and the world's largest MRF machine in place at L-3 Brashear. We propose that exceptional mirrors for the most critical spaceborne applications can now be produced with the technologies described.

Nanjing Institute of Astronomical Optics & Technology (NIAOT) is investigating two types of sub-aperture polish technique for manufacturing aspheric components in large astronomical telescopes. One technique is computer controlled optical surfacing (CCOS). It removes material by a small polish tool through traditional mechanical and chemical process. The other is ion beam figuring (IBF) technique. It employs a neutralized ion beam to physically sputter material form optical surface. Although the basic mechanism of the two techniques is different, they true share the same mathematical model and fabrication diagram which will be put forward firstly in this paper. Then tool design and material removal function in CCOS will be studied following by a fabrication instance using CCOS. After that some recent progresses achieved in IBF is presented. The last part will focus on the complementary relationship of CCOS and IBF. Using them alternatively optimal combination of surface precision, efficiency and edge control could be obtained. Simulation is provided to support this view and experiment will be done in near future.

The stress polishing method is well suited for the superpolishing of aspheric components for astronomy. The main advantage of this technique is the very high optical quality obtained either on form or on high spatial frequency errors. Furthermore, the roughness can be decreased down to a few angstrom, thanks the classical polishing with a large pitch tool. We describe here the results obtained on the three toric mirrors for the ESO/VLT-SPHERE instrument, dedicated to exoplanet direct imaging. On going work on variable off axis aspherics is presented in the frame of the ESA/ASPIICS-Proba3 mission for solar coronography and applications for Exoplanet detection and solar observations are discussed.

ITT has patented and continues to develop processes to fabricate low-cost borosilicate mirrors that can be used for both ground and space-based optical telescopes. Borosilicate glass is a commodity and is the material of choice for today's flat-panel televisions and monitors. Supply and demand has kept its cost low compared to mirror substrate materials typically found in telescopes. The current technology development is on the path to having the ability to deliver imaging quality optics of up to 1m (scalable to 2m) in diameter in three weeks. For those applications that can accommodate the material properties of borosilicate glasses, this technology has the potential to revolutionize ground and space-based astronomy. ITT Corporation has demonstrated finishing a planar, 0.6m borosilicate, optic to <100 nm-rms. This paper will provide an historical overview of the development in this area with an emphasis on recent technology developments to fabricate a 0.6m parabolic mirror under NASA Earth Science Technology Office (ESTO) grant #NNX09AD61G.

In the last decade a new window for ground-based high energy astrophysics has been opened. It explores the energy band from about 100 GeV to 10 TeV making use of Imaging Atmospheric Cherenkov Telescopes (IACTs). Research in Very High Energy (VHE) gamma-ray astronomy is improving rapidly and thanks to the newest facilities as MAGIC, HESS and VERITAS astronomers and particle physicists are obtaining surprising implications in the theoretical models. New projects have been started as the European Cherenkov Telescope Array (CTA) and the U.S. Advanced Gamma-ray Imaging System (AGIS). The aim is to enhance both the sensitivity and the energy band coverage to perform imaging, photometry and spectroscopy of sources. In this framework, tens of thousands of optical mirror panels have to be manufactured, tested and mounted into the telescopes. Because of this high number of mirrors it is mandatory to develop a technique easily transferable to industrial mass production, but keeping the technical and cost-effectiveness requirements of the next generation of TeV telescopes. In this context the Astronomical Observatory of Brera (INAF-OAB) is investigating a technique for the manufacturing of stiff and lightweight glass mirror panels with modest angular resolution. These panels have a composite sandwich-like structure with two thin glass skins on both sides of a core material; the reflecting skin is optically shaped using an ad-hoc slumping procedure. The technology here presented is particularly attractive for the mass production of cost-effective mirror segments with long radius of curvature like those required in the primary mirrors of the next generation of Cherenkov telescopes. In this paper we present and discuss some relevant results we have obtained from the latest panels realized.

Modeling of the thermal expansion behavior of ZERODUR® for the site conditions of the upcoming Extremely Large Telescope's (ELT's) allows an optimized material selection to yield the best performing ZERODUR® for the mirror substrates. The thermal expansion of glass ceramics is a function of temperature and a function of time, due to the structural relaxation behavior of the materials. The application temperature range of the upcoming ELT projects varies depending on the possible construction site between -13°C and +27°C. Typical temperature change rates during the night are in the range between 0.1°C/h and 0.3°C/h. Such temperature change rates are much smaller than the typical economic laboratory measurement rate, therefore the material behavior under these conditions can not be measured directly. SCHOTT developed a model approach to describe the structural relaxation behavior of ZERODUR®. With this model it is possible to precisely predict the thermal expansion behavior of the individual ZERODUR® material batches at any application temperature profile T(t). This paper presents results of the modeling and shows ZERODUR® material behavior at typical temperature profiles of different applications.

Today's space applications increasingly utilize lightweighted construction concepts, motivated by the demands of manufacturing and functionality, and by economics. Particularly for space optics, mirror stability and stiffness need to be maximized, while mass needs to be minimized. Therefore, mirror materials must possess, besides high material strength and manufacturing versatility, high thermal conductivity combined with low heat capacity and long-term stability against varying thermal loads. Additionally, optical surfaces need to be compatible with reflective coating materials. In order to achieve these requirements, the interplay between material properties and mirror design on one hand, and budgetary constraints on the other must be considered. In this paper, we address these issues by presenting an FEM design study of open and closed-back mirror structures with extremely thin reinforcing ribs, with the goal of obtaining optimal physical and optical characteristics. Furthermore, we show that ECM's carbon-fiber reinforced SiC composite, Cesic^®, and its newly developed, HB-Cesic^® , with their low CTE, low density, and high stiffness, are not only excellent mirror materials, but allow the rapid manufacturing of complex monolithic optical structures at reasonable cost.

There is growing interest within the Astronomical community in the development and use of very large aperture telescopes which will incorporate the latest advancements in optical materials. Two of the most notable of these large size telescope projects, the Thirty Meter Telescope (TMT) and European Extremely Large Telescope (E-ELT), will use mirror segments in the actively controlled primary mirrors. In this paper we present the results of a material characteristics study on Ohara CLEARCERAM^®-Z HS large diameter blanks which includes data on the CTE, CTE uniformity, residual stress and internal quality targeting potential use in the TMT Primary Mirror Segment Banks.

The James Webb Space Telescope (JWST) Optical Telescope Element (OTE) consists of a 6.6 m clear aperture, allreflective, three-mirror anastigmat. The 18-segment primary mirror (PM) presents unique and challenging assembly, integration, alignment and testing requirements. A full aperture center of curvature optical test is performed in cryogenic vacuum conditions at the integrated observatory level to verify PM performance requirements. The Center of Curvature Optical Assembly (CoCOA), designed and being built by ITT satisfies the requirements for this test. The CoCOA contains a multi wave interferometer, patented reflective null lens, actuation for alignment, full in situ calibration capability, coarse and fine alignment sensing systems, as well as a system for monitoring changes in the PM to CoCOA distance. This paper will introduce the systems level architecture and optical layout of the CoCOA and its main subsystems.

The 1.5 m primary ZERODUR® mirror of the solar telescope GREGOR incorporates 420 pockets at the backside for active cooling to avoid the thermal load impact of the sun deteriorating the observation. This design is also under consideration for the 2 m Indian Solar Telescope and for the 4.2 m European Solar Telescope (EST). The tip and tilt M5 mirror of the European Extremely Large Telescope (E-ELT) requires an even more demanding approach in light weighting. The approximately 3 m × 2.4 m elliptical flat mirror is specified to a weight of less than 500 kg. During the successful manufacturing of the GREGOR light weighted mirror, SCHOTT developed a systematic approach for processing such complex and long lead items which are capable for being up-scaled to a dimension of 4 m. In parallel SCHOTT has tested the machining of challenging aspect ratios of rib thickness and pocket height to prove the machinability of the E-ELT M5 design suggestions. The improved data on the bending strengths of ZERODUR® enable aggressive designs for light weighted 4 m class mirrors.

The Giant Magellan Telescope has a 25 meter f/0.7 near-parabolic primary mirror constructed from seven 8.4 meter diameter segments. Several aspects of the interferometric optical test used to guide polishing of the six off-axis segments go beyond the demonstrated state of the art in optical testing. The null corrector is created from two obliquelyilluminated spherical mirrors combined with a computer-generated hologram (the measurement hologram). The larger mirror is 3.75 m in diameter and is supported at the top of a test tower, 23.5 m above the GMT segment. Its size rules out a direct validation of the wavefront produced by the null corrector. We can, however, use a reference hologram placed at an intermediate focus between the two spherical mirrors to measure the wavefront produced by the measurement hologram and the first mirror. This reference hologram is aligned to match the wavefront and thereby becomes the alignment reference for the rest of the system. The position and orientation of the reference hologram, the 3.75 m mirror and the GMT segment are measured with a dedicated laser tracker, leading to an alignment accuracy of about 100 microns over the 24 m dimensions of the test. In addition to the interferometer that measures the GMT segment, a separate interferometer at the center of curvature of the 3.75 m sphere monitors its figure simultaneously with the GMT measurement, allowing active correction and compensation for residual errors. We describe the details of the design, alignment, and use of this unique off-axis optical test.

The most challenging of the metrology needs of multi-objects instruments is the registration of the pupil on the deformable mirror which corrects the wavefront errors. Pick-off mirrors in multi-objects instruments and specially spectrographs (MOS) require accurate positioning and simultaneous viewing of the pupil on the deformable mirror (DM) and the focal plane image on the image slicer at the sub-micron level. A laboratory test prototype simulating the telescope (E-ELT), the beam steering mirror (BSM) and the pupil imaging mirror (PIM), is presented to confirm the correct positioning of the pupil on the DM and to provide the movements of the moveable optical elements to achieve it. The opto-mechanical design and testing of this prototype is shown. The BSM stages (Goniometric cradle, Rotation, & Linear) provide the key mechanical system elements, with precision alignment, resolution, and repeatability . The design and behaviour of the control system is discussed; the ultimate aim of which is to adjust the BSM and PIM to correct for any slight mis-positioning of the pick-off mirror and any temporal drift of all the components to achieve the required alignment. The control system can also cope with flexure effects when required.

Since last years and at present days LZOS, JSC has been producing a range of primary mirrors of astronomical telescopes with diameter more than 1m under contracts with foreign companies. Simultaneous testing of an aspherical surface figure by means of a lens corrector and CGH (computer generated hologram) corrector, testing of the corrector using the CGH allow challenging the task of definite testing of the mirrors surfaces figure. The results of successful figuring of the mirrors with diameter up to 4m like VISTA Project (Southern European Observatory), TNT (Thai National telescope, Australia - Thailand), LCO telescopes (Las Cumbres Observatory, USA) and Russian national projects and meeting these mirrors specifications' requirements are all considered as the sufficient evidence.

The construction of the Southern African Large Telescope (SALT) was largely completed by the end of 2005. At the beginning of 2006, it was realized that the telescope's image quality suffered from optical aberrations, chiefly a focus gradient across the focal plane, but also accompanied by astigmatism and higher order aberrations. In the previous conference in this series, a paper was presented describing the optical system engineering investigation which had been conducted to diagnose the problem. This investigation exonerated the primary mirror as the cause, as well as the science instruments, and was isolated to the interface between the telescope and a major optical sub-system, the spherical aberration corrector (SAC). This is a complex sub-system of four aspheric mirrors which corrects the spherical aberration of the 11-m primary mirror. In the last two years, a solution to this problem was developed which involved removing the SAC from the telescope, installing a modification of the SAC/telescope interface, re-aligning and testing the four SAC mirrors and re-installation on the telescope. This paper describes the plan, discusses the details and shows progress to date and the current status.

This paper will focus on the metrology of multiple complex surfaces that are to be integrated into the KBand Multi- Object Spectrograph (KMOS). KMOS is a multi-field astronomical spectrograph designed for integration with the 8.2m diameter European Southern Observatory Very Large Telescope (VLT). There are 1080 separate optical surfaces in the design, many of them complex freeform surfaces. Optical surfaces were manufactured in aluminium by precision freeform diamond machining. This flexible technique allows the fabrication of extremely complex surfaces with an accuracy of better than 15 nm RMS over a 20 mm aperture, giving the designer great freedom in generating powerful and unorthodox designs. However, the complexity of these freeform surfaces poses a challenge to their accurate characterisation. This paper will discuss in detail the metrology of a specific freeform component in the instrument. The form of these complex astigmatic surfaces was measured using spherical wavefronts by adapting a tilted Twyman-Green Interferometer arrangement. There are eight separate designs for this type of component, each with a different orientation and magnitude of astigmatism. Careful mechanical fixturing is essential to align the astigmatic axis to the test set up. The impact of mechanical tolerances on measurement uncertainty will be discussed in detail.

We have developed a metrology system that is capable of measuring rough ground and polished surfaces alike, has limited sensitivity to the nominal surface shape, and can accommodate surfaces up to 8.4 m in diameter. The system couples a commercial laser tracker with an advanced calibration technique and a system of stability references to mitigate numerous error sources. This system was built to guide loose abrasive grinding and initial polishing of the off-axis primary mirror segments for the Giant Magellan Telescope (GMT), and is also being used to guide the fabrication of the Large Synoptic Survey Telescope primary and tertiary mirrors. In addition to guiding fabrication, the system also works as a verification test for the GMT principal optical interferometric test of the polished mirror segment to corroborate the measurement in several low-order aberrations. A quantitative assessment of the system accuracy is presented, along with measurement results for GMT, including a comparison to the optical interferometric test of the polished surface.8

Aspheric surfaces, such as telescope mirrors, are commonly measured using interferometry with computer generated hologram (CGH) null correctors. The interferometers can be made with high precision and low noise, and CGHs can control wavefront errors to accuracy approaching 1 nm for difficult aspheric surfaces. However, such optical systems are typically poorly suited for high performance imaging. The aspheric surface must be viewed through a CGH that was intentionally designed to introduce many hundreds of waves of aberration. The imaging aberrations create difficulties for the measurements by coupling both geometric and diffraction effects into the measurement. These issues are explored here, and we show how the use of larger holograms can mitigate these effects.

The Hobby-Eberly Telescope (HET) Wide-Field Upgrade (WFU) will be equipped with new metrology systems to actively control the optical alignment of the new four-mirror Wide-Field Corrector (WFC) as it tracks sidereal motion with respect to the fixed primary mirror. These systems include a tip/tilt sensor (TTS), distance measuring interferometers (DMI), guide probes (GP), and wavefront sensors (WFS). While the TTS and DMIs are to monitor the mechanical alignment of the WFC, the WFSs and GPs will produce direct measurement of the optical alignment of the WFC with respect to the HET primary mirror. Together, these systems provide fully redundant alignment and pointing information for the telescope, thereby keeping the WFC in focus and suppressing alignment-driven field aberrations. We describe the current snapshot of these systems and discuss their roles, expected performance, and operation plans.

Aspherical optics are widely used in modern optical telescopes and instrumentation because of their ability to reduce aberrations with a simple optical system. Testing their optical quality through null interferometry is not trivial as reference optics are not available. Computer-Generated Holograms (CGHs) are efficient devices that allow to generate a well-defined optical wavefront. We developed rewritable Computer Generated Holograms for the interferometric test of aspheres based on photochromic layers. These photochromic holograms are cost-effective and the method of production does not need any post exposure process.

At the Southern African Large Telescope (SALT), in collaboration with FOGALE Nanotech, we have been testing the recently-developed new generation inductive edge sensors. The Fogale inductive sensor is one technology being evaluated as a possible replacement for the now defunct capacitance-based edge sensing system. We present the results of exhaustive environmental testing of two variants of the inductive sensor. In addition to the environmental testing including RH and temperature cycles, the sensor was tested for sensitivity to dust and metals. We also consider long-term sensor stability, as well as that of the electronics and of the glue used to bond the sensor to its supporting structure. A prototype design for an adjustable mount is presented which will allow for in-plane gap and shear variations present in the primary mirror configuration without adversely disturbing the figure of the individual mirror segments or the measurement accuracy.

An interferometric null Test Method is described for testing convex aspheric surfaces, such as found in secondary mirrors of Cassegrain telescopes or variations thereof such as Mersenne and Ritchey-Chrétien. A family of test designs is described covering a wide range of mirror diameters, radii of curvature, and aspheric shapes as described by conic constants and/or polynomials. The Test Method has been used successfully for testing the convex hyperboloid surface of the 244-mm diameter secondary mirror of the NASA 3-meter IRTF telescope. The Test Method is currently being used to test the 120-mm diameter, convex paraboloid secondary mirrors of the Magdalena Ridge Observatory Interferometer (MROI). Test designs exist on paper for both Keck secondary mirrors (0.53-m and 1.4-m diameter), the HST secondary (0.3-meter diameter), and secondary mirrors of some of the extremely large telescopes of the future, such as the TMT secondary (3.2-m diameter). In typical test embodiments, the simplicity of the Test enables rapid implementation at a fraction of the cost of comparable Hindle-Sphere or Hindle-Simpson tests.

The new giant telescopes can be compared to space projects. They will require ground-based test support equipment to fully characterize the optical sub-system functionalities and performances before costly commissioning on the telescope. The support equipment must be designed to reproduce the telescope or the front optical system's aberrated wavefront. We show that the aberrated wavefront can be generated at low cost by a magnetic liquid deformable mirror. A prototype 91- actuator liquid deformable mirror having a diameter of 33 mm was built and used to simulate the off-axis aberrated CFHT's primary mirror up to 0.5 degrees FOV.

The scanning pentaprism system for testing the 8.4 m off-axis segments for the Giant Magellan Telescope has recently been completed. The system uses a fiber source and a carriage mounted pentaprism to scan a 40 mm collimated beam across the surface of the segment under test. Since the scanning beam is parallel to the optical axis of the parent mirror, it comes to focus on a detector at the telescope's prime focus, where displacement of the spot is proportional to the slope error. A second collimated beam from a stationary reference pentaprism is used to compensate for any changes in the relative positions of the optical components during testing. The optical components are suspended over the mirror on a rail system that can be rotated so that scans can be made across any diameter of the segment. The test is capable of measuring wavefront slope errors to 1 μrad rms, adequate to verify that power, astigmatism, coma, and other low-order aberrations are small enough to be corrected easily at the telescope with the segment's active support system.

The Southern African Large Telescope (SALT) recently (2008) abandoned attempts at using capacitive mirror edge sensors, mainly due to poor performance at a relative humidity above ~60%, a not infrequent occurrence. Different technologies are now being explored for alternative sensors on SALT. In this paper we describe the design and development of a novel prototype optical edge sensor, based on the application of the interferential scanning principle, as used in optical encoders. These prototype sensors were subsequently tested at SAAO and ESO, for potential application on SALT and E-ELT. Environmental tests, conducted in climatic control chambers, looked at temperature and relative humidity sensitivity, long term stability and sensor noise. The temperature sensitivity for height and gap were, respectively, 10nm/°C and 44nm/°C, while for relative humidity they were 4nm/10% and 50nm/10%, respectively. These either met, or were close to, the SALT specification. While there were significant lags in response, this was due to the sensor's relatively large mass (~200 gm per sensor half), which was not optimized. This is likely to improve, should a revised design be developed in future. Impressively the sensor noise was <0.015 nm RMS, over three orders of magnitude better than the specification. Our conclusions are that optical edge sensing is a viable technique for use on segmented mirror telescopes.

Volume phase holographic (VPH) gratings are increasingly being used as diffractive elements in astronomical instruments due to their potential for very high peak diffraction efficiencies and the possibility of a compact instrument design when the gratings are used in transmission. Historically, VPH grating (VPHG) sizes have been limited by the size of manufacturer's holographic recording optics. We report on the design, specification and fabrication of a large, 290 mm × 475 mm elliptically-shaped, mosaic VPHG for the Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph. This high-resolution near-infrared multi-object spectrograph is in construction for the Sloan Digital Sky Survey III (SDSS III). The 1008.6 lines/mm VPHG was designed for optimized performance over a wavelength range from 1.5 to 1.7 μm. A step-and-repeat exposure method was chosen to fabricate a three-segment mosaic on a 305 mm × 508 mm monolithic fused-silica substrate. Specification considerations imposed on the VPHG to assure the mosaic construction will satisfy the end use requirements are discussed. Production issues and test results of the mosaic VPHG are discussed.

The Vector Vortex Coronagraph is a phase-based coronagraph, one of the most efficient in terms of inner working angle, throughput, discovery space, contrast, and simplicity. Using liquid-crystal polymer technology, this new coronagraph has recently been the subject of lab demonstrations in the near-infrared, visible and was also used on sky at the Palomar observatory in the H and K bands (1.65 and 2.2 μm, respectively) to image the brown dwarf companion to HR 7672, and the three extra-solar planets around HR 8799. However, despite these recent successes, the Vector Vortex Coronagraph is, as are most coronagraphs, sensitive to the central obscuration and secondary support structures, low-order aberrations (tip-tilt, focus, etc), bandwidth (chromaticism), and polarization when image-plane wavefront sensing is performed. Here, we consider in detail these sensitivities as a function of the topological charge of the vortex and design features inherent to the manufacturing technology, and show that in practice all of them can be mitigated to meet specific needs.

MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) will be a mid-infrared spectro-interferometer combining the beams of up to four telescopes of the European Southern Observatory Very Large Telescope Interferometer (ESO VLTI), providing phase closure and image reconstruction. Matisse will produce interferometric spectra in the LM and in the N band (2.3 to 13.5 micron) and is as such a successor of MIDI. The instrument will be developed by a consortium consisting of Observatoire de Nice (warm optics), NOVA-ASTRON (cold optics), MPI-A (cryostats) and MPIfR (detectors). Beams of up to four Unit Telescopes or Auxiliary Telescopes (UT - AT) pass the warm pre-optics and in the cold optics all beams recombine on the detector where they create a spectral interference pattern. An innovative MAIT plan drastically shortens the MAIT phase and therefore reduces cost. The MAIT plan comprises the assembly and alignment procedure of about 220 cryogenic optical components for which a mirror mount clip has been developed. Alignment accuracy and stability specifications are of the order of nanometers and arcsec, which requires over 50 degrees of freedom in cryogenic alignment mechanisms for e.g. Tip/Tilt and detector Tip/Tilt/Focus. The design, realization and test results of these mechanisms are presented. A cryogenic electrical switch significantly reduces the complexity of the electronic cabling and improves reliability.

We discuss the C_lover cryostats, which are dry cryostats containing three stages of cooling; a pulse tube cooler, a sorption fridge and a continuous miniature dilution refrigerator. We describe the thermal architecture of the system and present thermal data for the various stages including its performance when tilted.

The Near Infrared Spectrograph (NIRSpec) developed by EADS Astrium GmbH for the European Space Agency (ESA) is a spectrograph covering the 0.6-5.0 μm waveband to fly on the James Webb Space Telescope (JWST). NIRSpec will be primarily operated as a multi-object spectrograph but also includes an integral field unit (IFU) allowing a 3×3 arcsec field of view to be sampled continuously with 0.1 arcsec spatial resolution. The IFU, based on an advanced image slicer concept, is a very compact athermal unit made of aluminium. It contains three 30-element monolithic mirror arrays forming slicer, pupil and slit mirrors, and single-surface image relay and plane fold mirrors, produced using 5-axis diamond-machining techniques. Many of the mirrors have complex surfaces like toric sections with 3rd-order corrections in order to achieve the required performance within a small allowed volume, and could only have been fabricated with the most advanced free-form machining. The mechanical design accommodates the differential expansion between the aluminium IFU and its titanium parent assembly across a 250K drop to operating temperature using an isostatic mounting system. This paper presents the development of the IFU from the design and diamond-machining techniques to the optical and cryogenic testing of the assembled flight model unit.

The Mid Infrared Instrument (MIRI) aboard JWST is equipped with one filter wheel and two dichroic-grating wheel mechanisms to reconfigure the instrument between observing modes such as broad/narrow-band imaging, coronagraphy and low/medium resolution spectroscopy. Key requirements for the three mechanisms with up to 18 optical elements on the wheel include: (1) reliable operation at T = 7 K, (2) high positional accuracy of 4 arcsec, (3) low power dissipation, (4) high vibration capability, (5) functionality at 7 K < T < 300 K and (6) long lifetime (5-10 years). To meet these requirements a space-proven wheel concept consisting of a central MoS2-lubricated integrated ball bearing, a central torque motor for actuation, a ratchet system with monolithic CuBe flexural pivots for precise and powerless positioning and a magnetoresistive position sensor has been implemented. We report here the final performance and lessons-learnt from the successful acceptance test program of the MIRI wheel mechanism flight models. The mechanisms have been meanwhile integrated into the flight model of the MIRI instrument, ready for launch in 2014 by an Ariane 5 rocket.

Infrared radiometers and spectrometers generally use blackbodies for calibration, and with the high accuracy needs of upcoming missions, blackbodies capable of meeting strict accuracy requirements are needed. One such mission, the NASA climate science mission Climate Absolute Radiance and Refractivity Observatory (CLARREO), which will measure Earth's emitted spectral radiance from orbit, has an absolute accuracy requirement of 0.1 K (3σ) at 220 K over most of the thermal infrared. Space Dynamics Laboratory (SDL) has a blackbody design capable of meeting strict modern accuracy requirements. This design is relatively simple to build, was developed for use on the ground or onorbit, and is readily scalable for aperture size and required performance. These-high accuracy blackbodies are currently in use as a ground calibration unit and with a high-altitude balloon instrument. SDL is currently building a prototype blackbody to demonstrate the ability to achieve very high accuracy, and we expect it to have emissivity of ~0.9999 from 1.5 to 50 μm, temperature uncertainties of ~25 mK, and radiance uncertainties of ~10 mK due to temperature gradients. The high emissivity and low thermal gradient uncertainties are achieved through cavity design, while the low temperature uncertainty is attained by including phase change materials such as mercury, gallium, and water in the blackbody. Blackbody temperature sensors are calibrated at the melt points of these materials, which are determined by heating through their melt point. This allows absolute temperature calibration traceable to the SI temperature scale.

The Euclid mission is currently being developed within the European Space Agency's Cosmic Vision Program. The five year mission will survey the entire extragalactic sky (~ 20 000 deg²) with the aim of constraining the nature of dark energy and dark matter. The spacecraft's payload consists of two instruments: one imaging instrument, which has both a visible and a near-infrared channel, and one spectroscopic instrument operating in the near-infrared wavelength regime. The two channels of the imaging instrument, the Visible Imaging Channel (VIS) and the Near-Infrared Imaging Photometer Channel (NIP), will focus on the weak lensing science probe. The large survey area and the need to not only image each patch of sky in multiple bands, but also in multiple dithers, requires over 640 000 operations of the NIP channel's filter wheel mechanism. With a 127 mm diameter and a mass of ~ 330 g per element, these brittle infrared filters dictate highly demanding requirements on this single-point-failure mechanism. To accommodate the large filters the wheel must have an outer diameter of ~ 400 mm, which will result in significant loads being applied to the bearing assembly during launch. The centrally driven titanium filter wheel will house the infrared filters in specially designed mounts. Both stepper motor and brushless DC drive systems are being considered and tested for this mechanism. This paper presents the design considerations and details the first prototyping campaign of this mechanism. The design and finite element analysis of the filter mounting concept are also presented.

TNO, together with its partners Micromega and SRON, have designed a cryogenic scanning mechanism for use in the SAFARI Fourier Transform Spectrometer (FTS) on board of the SPICA mission. The optics of the FTS scanning mechanism (FTSM) consists of two back-to-back cat's-eyes. The optics are mounted on a central "back-bone" tube which houses all the important mechatronic parts: the magnetic bearing linear guiding system, a magnetic linear motor serving as the OPD actuator, internal metrology with nanometer resolution, and a launch lock. A magnetic bearing is employed to enable a large scanning stroke in a small volume. It supports the optics in a free-floating way with no friction, or other non-linearities, enabling sub-nanometer accuracy within a single stage with a stroke of -4 mm to +31.5 mm. Because the FTSM will be used at cryogenic temperatures of 4 Kelvin, the main structure and optics are all constructed from 6061 Aluminum. The overall outside dimensions of the FTSM are: 393 x 130 x 125 mm, and the mass is 2.2 kg.

The Sardinia Radio Telescope (SRT) is a 64 meters (diameter) single dish radioantenna which is in the building phase in Italy. One of the most challenging characteristics of SRT is its capability to observe up to a frequency of 100 GHz thanks to its main reflector active surface. The active surface is composed by 1008 panels and 1116 mechanical actuators which may modify the segmented shape of the main reflector making possible the correction for wavefront distortions induced by the gravitational and thermal deformations. In order to observe at a frequency of 100 GHz the surface shape must be accurate below of a value of 150 μm r.m.s.. This value may be reached during the initial alignement phase using the microwave holography but it cannot be maintained during the scientific operations because of the (dynamical) deformations. In order to permit the observations at any time, a system able to measure the surface deformations with the necessary accuracy and a time-response of few minutes (the time-scale of the deformations) must be operative. We propose here three simple and robust methods to measure the relative deformations of the segmented panels with respect to an initial aligned surface (reference surface). The ultimate choice on which one of the three systems will operate on SRT will be taken after final testing on all of them. Prototypes of each system have been realized and two of them have been also successfully tested on the active optics radiotelescope of Noto (Italy). The test on the third system will be done in the next few months.

The complexity and size of instruments for next generation telescopes demands innovative approaches to existing problems. Within this framework, we present MAPS; a Micro Autonomous Positioning System for mirror deployment in an E-ELT instrument such as EAGLE. The micro-robots have a 25mmx25mm footprint and utilise RF communications and small rechargeable batteries to be completely wireless. Coarse positioning and fine alignment is achieved through the use of miniature gear motors and gearheads. Positional information is determined externally and corrective motions relayed to the robots. This paper reports on the challenges which such a system presents, current developments, and areas of expected future research.

We report on the technological achievements of our latest Starbug prototypes and their implications for smart focal plane fiber positioning applications for wide-field astronomy. The Starbugs are innovative self-motile miniature robotic devices that can simultaneously and independently position fibers or payloads over a field plate located at the telescope's focal plane. The Starbugs concept overcomes many of the limitations associated with the traditional 'pick and place' positioners where a robot places fixed buttons onto the field plate. The new Starbug prototypes use piezoelectric actuators and have the following features: (i) new 'lift-and-step' method (discrete step) for accurate positioning over different surfaces; and (ii) operate in an inverted hanging position underneath a transparent field plate, removing the need for fibercable retractors. In this paper, we present aspects of the Starbug prototypes, including the theoretical model, mechanical design, experimental setup, algorithms, performance and applications for astronomical instrumentation.

The two antenna transporters of the ALMA Observatory are used to relocate 12-meter antennas and to move them between low (3000m) and high altitude site (5000m). When analyzing the dynamic response of the transporters to road ripple of critical height and inter-distance, it turned out that transporter accelerations exceeding the seismic accelerations cannot be excluded. This is considered as a remote risk however with possibly catastrophic consequences for the equipped antennas. The problem was analyzed by ESO experts for dynamic simulations and an additional damping system was designed to limit the loads to acceptable values. This paper describes the design of the additional damping system including its concept, the model-based design using dynamic simulations and verification tests on site.

Generally, panels of radio telescopes are mainly shaped in trapezoid and each is supported/positioned by four adjustors beneath its vertexes. Such configuration of panel supporting system is essentially hyper-static, and the panel is overconstrained from a kinematic point of view. When the panel is to be adjusted and/or actuated, it will suffer stress from its adjusters and hence its shape is to be distorted. This situation is not desirable for high precision panels, such as glass based panels especially used for sub-millimeter and shorter wavelength telescopes with active optics/active panel technology. This paper began with a general overview of panel patterns and panel supports of existing radio telescopes. Thereby, we proposed a preferable master-slave active surface concept for triangular and/or hexagonal panel pattern. In addition, we carry out panel error sensitivity analysis for all the 6 degrees of freedom (DOF) of a panel to identify what DOFs are most sensitive for an active surface. And afterwards, based on the error sensitivity analysis, we suggested an innovative parallel-series concept hexapod well fitted for an active panel to correct for all of its 6 rigid errors. A demonstration active surface using the master-slave concept and the hexapod manifested a great save in cost, where only 486 precision actuators are needed for 438 panels, which is 37% of those actuators needed by classic segmented mirror active optics. Further, we put forward a swaying-arm based design concept for the related connecting joints between panels, which ensures that all the panels attached on to it free from over-constraints when they are positioned and/or actuated. Principle and performance of the swaying-arm connecting mechanism are elaborated before a practical cablemesh based prototype active surface is presented with comprehensive finite element analysis and simulation.

After suffering from serious problems in the course of the SiC 1.5m M1 manufacturing, the existing design of the M1, it's cell and the associated mirror cooling system was investigated in terms of modification efforts to be compatible for a different M1 substrate (Zerodur). The analysis included the system requirements, the M1 design, the M1 support system, the M1 cooling system as well as the M1 cell. The investigations resulting in a modified design of the above mentioned system. Driven by the choice of material, different requirements became design driving factors. The consequences on the detail design of the M1 Mirror as well as on the support system and the cooling system are presented.

The Large Synoptic Survey Telescope (LSST) utilizes an 8.4-meter cast borosilicate primary/tertiary mirror (M1M3). This mirror system has stringent vibration and stiffness requirements because the LSST optical system does not include a fast steering mirror and the mission requires a short slew and settling time. The position stability of the M1M3 relative to the mirror cell is controlled by six displacement controlled actuators (subsequently referred to as "hardpoints") that form a large hexapod. This design is based largely on previous hardpoints implemented for borosilicate mirror positioning. Traditionally, all dynamic forces applied to these mirrors are reacted through their hardpoints. Consequently, the characteristics of these hardpoints critically affect the ability of the telescope to meet the stringent dynamic requirements without overstressing the mirror. The hardpoints must have a high stiffness of 120 N/um in the axial direction, while protecting the mirror by limiting the loads in all six degrees of freedom. The non-axial direction loads are limited by flexures. The axial loads are limited by a pneumatic breakaway mechanism. Since the hardpoints react the dynamic mirror loads, the axial breakaway force may limit the telescope's slewing accelerations. The travel of the breakaway mechanism must accommodate the transfer of the mirror from its active supports to its static supports. The hardpoint positioning mechanism must have sufficient travel and resolution to properly position the mirror relative to the mirror cell. Fulfilling these functions also requires numerous sensors, including a precision axial load cell which is paramount in determining the figure control actuator forces.

The drive and bearing technologies have a major impact on the static and dynamic performance of steerable structures such as telescope and dome. Merging drive and bearing system into friction drive mechanical devices (bogie) can reduce the complexity and cost of the design. In the framework of ELT design study (European FP6) a breadboard test setup was realized to test and evaluate the static and dynamic behavior of such bogies. In this paper some of the characterization test results are presented. Characterization of the bogies and the setup structure in the frequency domain, quantification and measure of the most important parameters of the friction forces, the control of the bogies and the tracking performance of the test setup are among the main results discussed in this paper.

The Magdalena Ridge Interferometer (MROI) is a project which comprises an optical array of up to ten relocatable 1.4m telescopes arranged in a "Y" configuration. Each of these telescopes will be housed inside a Unit Telescope Enclosure (UTE) which can be lifted and moved onto any of 28 stations. This paper presents a general description of how the constraints imposed by the requirements for the close-pack configuration and relocatability led to the design of an innovative, compact and light-weight enclosure of small diameter and high structural strength. The unique internal layout gives sufficient space inside to house, not only to house the telescope mount, but also associated electronics, nasmyth table opto-mechanical equipment and beam relay system interface.

Deformable mirrors actuated by smart structures are promising devices for next generation astronomical instrumentation. Thermal activated Shape Memory Alloys are materials able to recover their original shape, after an external deformation, if heated above a characteristic temperature. If the recovery of the shape is completely or partially prevented by the presence of constraints, the material can generate recovery stress. Thanks to this feature, these materials can be positively exploited in Smart Structures if properly embedded into host materials. This paper will show the technological processes developed for an efficient use of SMA-based actuators embedded in smart structures tailored to astronomical instrumentation. In particular the analysis of the interface with the host material. Some possible modeling approaches to the actuators behavior will be addressed taking into account trade-offs between detailed analysis and overall performance prediction as a function of the computational time. We developed a combined Finite Element and Raytracing analysis devoted to a parametric performance predictions of a SMA based substrate applicable to deformable mirrors. We took in detail into account the possibility to change the focal length of the mirror keeping a satisfactory image quality. Finally a possible approach with some preliminary results for an efficient control system for the strongly non-linear SMA actuators will be presented.

Deformable mirrors actuated by smart structures are promising devices for next generation astronomical instrumentation. The piezo technology and in particular piezoceramics is currently among the most investigated structural materials. Fragility makes Ceramic materials extremely vulnerable to accidental breakage during bonding and embedding processes and limits the ability to comply to curved surfaces (typical of mirrors). Moreover lead-based piezoceramics typically have relevant additional masses. To overcome these limitations, we studied the applicability of composites piezoceramics actuators to smart structures with these purposes. We developed a combined Finite Element and Raytracing analysis devoted to a parametric performance predictions of a smart Piezocomposites based substrate applicable to deformable mirrors. We took in detail into account the possibility to change the focal length of the mirror keeping a satisfactory image quality. In this paper we present a specific type of Piezocomposite actuators and numerical/experimental techniques purposely developed to integrate them into smart structures. We evaluated numerical and experimental results comparing bonding and embedding of these devices.

The solar telescope EST is currently in the conceptual design phase. It is planned to be build on the Canary Islands until end of the decade. It is specialized on polarimetric observations and will provide high spatial and spectral observations of the different solar atmospheric layers. The diameter of the primary mirror blank is 4.2m. Different types of mirror shapes were investigated with respect to thermal and mechanical characteristics. To remove the absorbed heat an air cooling system from the back side will be applied. Additional an air flushing system will remove remaining warm air from the front side. A major problem of a large open telescope will be the wind load. Results of the investigations will be shown. To achieve optimal optical performance an active support system is planned. The primary mirror cell needs to be stiff enough to support the primary mirror without deformation at strong wind in case of the open telescope option, but sufficient room for the active support system and cooling system below the backside of the mirror is also required. Preliminary designs and analysis results will be presented.

The Large Synoptic Survey Telescope (LSST) flat-fields must repeatedly trace not only the spatial response variations, but also the chromatic response through the entire optical system, with an accuracy driven by the photometric requirements for the LSST survey data. This places challenging requirements on the LSST Calibration Dome Screen, which must uniformly illuminate the 8.4-meter diameter telescope pupil over its 3.5-degree field of view at desired monochromatic wavelengths in a way that allows the measurement of the total system throughput from entrance pupil to the digitization of charge in the camera electronics. This includes the reflectivity of the mirrors, transmission of the refractive optics and filters, the quantum efficiency of the sensors in the camera, and the gain and linearity of the sensor read-out electronics. The baseline design uses a single tunable laser and includes an array of discrete projectors. The projected flux of light produced by the screen must fill the entire telescope pupil and provide uniform illumination to 1% at the focal plane and to within 0.25% over any optical trajectory within 0.5 degrees of each other. The wavelength of light is tunable across the LSST bandpass from 320 nm to 1080 nm. The screen also includes a broad-band ("white") light source with known Spectral Energy Density (SED) that spans the same range of wavelengths.

Design-to-cost exercises and innovative design have resulted in remarkably high performing half-meter class wide field astronomical telescopes. This approach is being extended to meter+ class telescopes with further innovation on mounts and optics. Custom motors, drives and bearings have been developed to keep performance up and cost down. We will also report on a concurrent engineering campaign with Brashear Optics to ensure optical performance while maintaining the highest value for primary mirrors in our line of meter (and larger) class astronomical telescopes.

The performance of the C-ring telescope mount rivals other designs in stiffness, tracking, simplicity, lack of field rotation, mechanical size and operating envelope. Issues relating to cost, fabrication, and complexity have suppressed the prevalence of the C-ring mount. The Las Cumbres Observatory Global Telescope (LCOGT) robotic C-ring telescope mounts, built for its network of 1.0m and 0.4m telescopes, solve many of these issues. The design yields a scalable mount with performance capabilities well suited for telescopes located at the best astronomical sites in the world at a low cost. Pointing has been demonstrated to be under 7 arc-sec RMS. Unguided tracking performance is 0.6 arc-sec for 1 minute and 2 arc-sec for 15 minutes. Slew speeds of 10deg/sec are reliably used with sub-second settling times. The mount coupled with the 1.0m telescope yields a well damped 16 Hz system. Axes are driven with zero backlash direct drive motors with a 0.01 arc-sec resolution. High system bandwidth yields superb disturbance rejection making it ideal for open air operation. Drive and bearings are maintenance free and feature a novel "bug cover" to seal them from wear and damage. Low costs are achieved with the drive/feedback configuration, structure design, and fabrication techniques, as well minimizing operating and maintenance.

Scientific performance specifications, a necessity for ease of commissioning and minimal maintenance, and a desire for automated sensing and remote collimation have led to novel designs and features in LCOGT's one-meter Optical Tube Assembly (OTA). We discuss the design and performance of the quasi-RC optical system with 18 point whiffletree and radial hub mount. Position probes and IR temperature sensors on the primary and secondary mirrors give feedback for active collimation and thermal control. A carbon fiber/epoxy composite truss, with unique spherical node connections, mounts to parallel and offset Invar vanes. A flexure based, closed loop, 3-DOF secondary mirror mechanism is used for tip/tilt collimation. The optics and deflections of the OTA components were iteratively designed for passive collimation with a changing gravity vector. We present the FEA predictions, measured deflections, and measured hysteresis for many of the components. Vibration modes, amplitudes, and damping of the system are presented with an FFT frequency analysis. Thermal CTE effects on loading and focal position are quantified. All of these system effects are then related to the overall scientific performance of the 1.0 m telescope.

The Discovery Channel Telescope (DCT) is a 4.3-meter telescope designed for dual optical configurations, featuring an f/6.1 Ritchey-Chretien prescription with a 0.5° field-of-view, and a corrected f/2.3 prime focus with a 2° field-of-view. The DCT Active Optics System (AOS) maintains collimation and mirror figure to provide seeing limited images across the focal planes and rapid settling times to minimize observing overhead, using a combination of feed-forward and lowbandwidth feedback control via wavefront sensing. Collimation is maintained by tip-tilt-piston control of the M2 assembly and articulating M1 within its cell, taking advantage of the 120 degree-of-freedom support used for figure control. We present an overview of the AOS design and principles of operation, and a summary of progress and results to date.

The hexapod is a parallel kinematic manipulator that is the minimum arrangement for independent control of six degrees of freedom. Advancing needs for hexapod performance, capacity and configurations have driven development of highly capable new actuator designs. This paper describes new compact hexapod design proposals for high load capacity, and corresponding hexapod actuator only mechanisms suitable for integration as structural motion elements in next-generation telescope designs. These actuators provide up to 90 000N load capability while preserving sub-micrometer positional capability and in-position stability. The design is optimized for low power dissipation and incorporates novel encoders direct manufactured with the nut flange to achieve more than 100000 increments per revolution. In the hexapod design we choose cardan joints for the actuator that have axis offsets to provide optimized stiffness. The additional computational requirements for offset axes are readily solved by advanced kinematic algorithms and modern hardware. The paper also describes the hexapod controller concept with individual actuator designs, which allows the integration of hexapod actuators into the main telescope structure to reduce mass and provide the telescope designer more design freedom in the incorporation of these types of motion systems. An adaptive software package was developed including collision control feature for real-time safety during hexapod movements.

The close-pack array of the MROI necessitated an original design for the Unit Telescope Enclosure (UTE) at Magdalena Ridge Observatory. The Magdalena Ridge Observatory Interferometer (MROI) is a project which comprises an array of up to ten (10) 1.4m diameter mirror telescopes arranged in a "Y" configuration. Each of these telescopes will be housed inside a Unit Telescope Enclosure (UTE) which are relocatable onto any of 28 stations. The most compact configuration includes all ten telescopes, several of which are at a relative distance of less than 8m center to center from each other. Since the minimum angle of the field of regard is 30° with respect to the horizon, it is difficult to prevent optical blockage caused by adjacent UTEs in this compact array. This paper presents the design constraints inherent in meeting the requirement for the close-pack array. An innovative design enclosure was created which incorporates an unique dome/observing aperture system. The description of this system focuses on how the field of regard requirement led to an unique and highly innovative concept that had to be able to operate in the harsh environmental conditions encountered at an altitude of 10,460ft (3,188m). Finally, we describe the wide use of composites materials and structures (e.g. glass/carbon fibres, sandwich panels etc.) on the aperture system which represents the only way to guarantee adequate thermal and environmental protection, compactness, structural stability and limited power consumption due to reduced mass.

Astronomical optics are often exposed to moisture and dust in observatory environments, which frequently compromises their high-performance coatings. Suitable protective layers to resist dust and moisture accumulation would be extremely advantageous, but have received scant attention thus far. Hydrophobic and scratch-resistant coatings, developed primarily for opthalmic use, exhibit several attractive properties for astronomical optics. We examine the properties of one such coating and its applicability to astronomical mirrors and lenses. This includes efficiency of dust removal, abrasion resistance, moisture resistance, ease of stripping, and transmission across a wide wavelength range.

Rugate designs for the realization of notch filters are well known in the literature. The required deposition of gradient index layers is difficult to manufacture. In our approach we apply the equivalent index theory to replace the gradient index profile of a notch filter design. We produce single and multiple notch filters with plasma ion-assisted deposition and broad-band optical monitoring. As examples, a 500nm notch filter for the GREGOR telescope and a 589nm notch filter for the GALACSI instrument of the VLT are discussed. Additionally, a 4-line multiple notch filter and a 218nm notch filter made for fluorescence spectroscopy applications are presented.

Context. Dark fringe interferometry in the thermal infrared is one way to detect directly a planet orbiting a star, and so to characterize the planet's atmosphere through spectroscopy. This method demands a phase shift of π1 in one arm of the interferometer. In order to detect various bio-tracers gases, a broad wavelength range (6-18 μm)^2-3 is necessary, therefore an achromatic phase shift of π is required. The achromatic device presented here is a phase shifter made of two cellular mirrors, in which each cell induces a specific phase shift. Aims. We wish to demonstrate that this theoretical concept is experimentally valid. We present in this paper the setup and the very first results. Methods. In a first step, we have consolidated the theoretical ground and in a second step we developed an optical bench in the visible domain to test the concept and measure the performances of this device. Results. The preliminary experimental tests show evidences that such a device is working as expected in terms of nulling and achromatism: in spite of an error on one cell of the prototype, it provides a nulling of 2.10^-3 at one wavelength, and this value is close to the expected value. Besides, a nulling of 1.10^-2 in a 450 to 750 nm bandwidth: a hint that a perfect device should be achromatic.

Stellar coronagraphy is a key technology for current and future instruments for exoplanet imaging and spectroscopy, both on the ground and in space. We pursue the research on coronagraphs based on circular phase masks and report in this paper on recent advances in terms of the trade between spectral bandwidth and achievable contrast. Circular phase masks combined with colored apodizations prove to be promising options in such coronagraphic systems to reach high contrast gains within the search area over a wide band of wavelengths.

We are developing high performance mid-infrared (especially 30-40μm wavelength regions) multilayer interference filters with mechanical strength and robustness for thermal cycling toward cryogenic infrared astronomical missions. Multilayer interference filters enable us to design a wide variety of spectral response by controlling refractive index and thickness of each layer. However, in mid- and far-infrared (MIR/FIR) regions, there are a few optical materials so that we can only use limited refractive index values to design filters, which makes difficult to realize high performance filters. It is also difficult to deposit thick layers required for MIR/FIR multilayer filters. Furthermore, deposition of two materials, which have different coefficients of thermal expansion, makes filters fragile for thermal cycling. To clear these problems, we introduce sub-wavelength structures (SWS) for controlling the refractive index. Then, only one material is necessary for fabricating filters, which enables us to fabricate filters with mechanical strength and robustness for thermal cycling. According to the effective medium approximation (EMA) theory, the refractive index of randomly mixing materials in sub-wavelength scale is controllable by changing the ratio of mixing materials. However, it is not clear that EMA can be applied to such simple SWS, periodic cylindrical holes on a bulk material, which is easily fabricated by photolithography. In order to verify the controllability of refractive index by simple SWS, we have fabricated simple SWS on a silicon substrate and measured its transmittance. Comparing measured transmittance with theoretical transmittance calculated by EMA, we confirm that EMA can be applied to simple SWS fabricated by photolithography.

Black and spectrally selective surfaces are important in optical systems. The proper selection of these surfaces is essential to create or maintain system performance. A critical first step in selection of surfaces is to understand the performance requirements for contrast and stray light. A well-defined performance specification accompanied by stray light modeling is important to understand how the system behaves. Without both of these, the selection of surfaces is very difficult. Practical considerations in choosing spectrally selective and tailored emissivity surfaces for a range of ultraviolet/optical/infrared telescopes and instruments are given. The Bidirectional Reflectance Data Function (BRDF) of a surface is the most useful characterization in assessing the optical properties of surfaces. Data on long-term surface durability characteristics necessary for end of life optical predictions are also critical.

The Key Technology Network (KTN) within the OPTICON programme has been developing a roadmap for the technology needed to meet the challenges of optical and infrared astronomy over the next few years, with particular emphasis on the requirements of Extremely Large Telescopes. The process and methodology so far will be described, along with the most recent roadmap. The roadmap shows the expected progression of ground-based astronomy facilities and the technological developments which will be required to realise these new facilities. The roadmap highlights the key stages in the development of these technologies. In some areas, such as conventional optics, gradual developments in areas such as light-weighting of optics will slowly be adopted into future instruments. In other areas, such as large area IR detectors, more rapid progress can be expected as new processing techniques allow larger and faster arrays. Finally, other areas such as integrated photonics have the potential to revolutionise astronomical instrumentation. Future plans are outlined, in particular our intention to look at longer term development and disruptive technologies.

In this publication we present the results of a detailed study into directly written multimode waveguides for astronomical applications. We show that waveguides up to 100 ìm across can be inscribed with the cumulative heating form of this technique. The waveguides have 2 concentric guiding regions which are elliptical; a core that has an average ellipticity of 1.1±0.1 and an outer cladding with an ellipticity of 0.15±0.03. It was demonstrated that the ellipticity of the waveguides could be reduced by creating "structured" waveguides which consist of several waveguides stacked together. The 7 mm long waveguides demonstrated insertion losses at 800 nm as low as 39% when light was launched and collected by a standard multimode fibre (50 ìm core diameter and numerical aperture of 0.12), which is representative of the fibres currently used on astronomical installations. More importantly, we show for the first time that structured waveguides designed to have outer cladding regions which match the dimensions of the core of the launch and collection fibers, have lower insertion losses than structured waveguides designed to have matching core dimensions. It is believed that by moving to longer wavelengths of operation and exploring other structuring and beam shaping techniques it may be possible to reduce the losses even further and make these waveguides of practical use for astronomy.

Fibre modal noise occurs in high spectral resolution, high signal-to-noise applications. It imposes fundamental limits upon the photometric accuracy of state-of-the-art fibre-spectrograph systems. In order to maximize the performance of current and future instruments it is therefore essential to predict fibre modal noise. Explicitly theoretical approaches are often restricted to specific cases, therefore this paper focuses on the conditions relevant to astronomy. The goal of this work is to derive a reliable model which can be used for the optimization of future spectrograph designs. We give a description of experimental investigations undertaken in Durham, displaying preliminary results. The first laboratory tests of a square fibre have shown modal noise characteristics that are interestingly similar to standard circular fibre.

Astrophotonics offers a solution to some of the problems of building instruments for the next generation of telescopes through the use of photonic devices to miniaturise and simplify instruments. It has already proved its worth in interferometry over the last decade and is now being applied to nightsky background suppression. Astrophotonics offers a radically different approach to highly-multiplexed spectroscopy to the benefit of galaxy surveys such as are required to determine the evolution of the cosmic equation of state. The Astrophotonica Europa partnership funded by the EU via OPTICON is undertaking a wide-ranging survey of the technological opportunities and their applicability to high-priority astrophysical goals of the next generation of observatories. Here we summarise some of the conclusions.

Supercontinuum white light sources (SCLS) are intense, spatially coherent laser sources with a very broad and flat spectral energy distribution which have very quickly found ubiquitous use in optical laboratories. As photonics is now providing more and more applications for astronomical instrumentation, the possible use of SCLS as a calibration light source for spectroscopy has been tested. A standard industrial SCLS was coupled to the calibration unit of the PMAS integral field spectrophotometer and compared directly to the PMAS standard tungsten filament lamp that is normally used for calibration exposures. We report on comparative measurements concerning flux, spectral energy distribution, and temporal stability.

Diverse field spectroscopy is a new concept in which any part of a field can be optically captured and send to the entrance slit of a spectrograph. It is more general than integral field spectroscopy, multi-object spectroscopy and even multi-integral-field spectroscopy which combine the two as in the KMOS instrument. In diverse field spectroscopy, point sources and extended sources are simultaneously optically captured in an optimal way that fully use the spectrograph for only the regions of interest; as opposed to multi-integral-field spectroscopy where rectangular or square fields are fully captured, the capturing mechanism will follow the complex shapes of the sources removing any useless field which can then be use for other sources instead or permit to observe larger sources. Optical switches can be programmed to transmit any subset of the spatial elements of a field to the spectrograph. We present the different optical designs of switches that we made, some using micromirrors arrays, others small lenses. We also present conceptual designs of low cost projects for Échelle spectrographs as the SALT HRS and for the FMOS spectrographs on SUBARU. A critical aspect of the designs is to minimize the cost so that the switches can be mass-produced while maintaining high optical performances. A general discussion will be made of the relation between the total cost of the switch system plus spectrograph and the multiplex advantage with respect to an integral-field spectrograph giving the same performances.

The wavefront reconstruction accuracy in Shack Hartmann sensor based adaptive optics system depends on accurate centroiding and phase estimation from measured slope values. Monte Carlo simulations of vector matrix multiply and Fourier phase estimation methods show fluctuations in the value of wavefront reconstruction accuracy leading to inconsistency. In this paper, it is shown that these fluctuations can be minimized and high wavefront reconstruction accuracy can be maintained consistently by applying a dither signal on the Shack Hartmann lenslet array. The information of the dither signal to be applied can be obtained from the wavefronts of the past.

Earth's atmosphere represents a turbulent, turbid refractive element for every ground-based telescope. We describe the significantly enhanced and optimized operation of observatories supported by the combination of a lidar and spectrophotometer that allows accurate, provable measurement of and correction for direction-, wavelength- and timedependent astronomical extinction. The data provided by this instrument suite enables atmospheric extinction correction leading to "sub-1%" imaging photometric precision, and attaining the fundamental photon noise limit. In addition, this facility-class instrument suite provides quantitative atmospheric data over the dome of the sky that allows robust realtime decision-making about the photometric quality of a night, enabling more efficient queue-based, service, and observer-determined telescope utilization. With operational certainty, marginal photometric time can be redirected to other programs, allowing useful data to be acquired. Significantly enhanced utility and efficiency in the operation of telescopes result in improved benefit-to-cost for ground-based observatories. We propose that this level of decision-making will make large-area imaging photometric surveys, such as Pan-STARRS and the future LSST both more effective in terms of photometry and in the use of telescopes generally. The atmospheric data will indicate when angular or temporal changes in atmospheric transmission could have significant effect across the rather wide fields-of-view of these telescopes. We further propose that implementation of this type of instrument suite for direct measurement of Earth's atmosphere will enable observing programs complementary to those currently requiring space-based observations to achieve the required measurement precision, such as ground-based versions of the Kepler Survey or the Joint Dark Energy Mission.

The OPTIMOS-EVE instrument proposed for the E-ELT aims to use the maximum field of view available to the E-ELT in the limit of natural or ground-layer-corrected seeing for high multiplex fibre-fed multi-object spectroscopy in the visible and near-IR. At the bare nasmyth focus of the telescope, this field corresponds to a focal plane 2.3m in diameter, with a plate-scale of ~3mm/arcsec. The required positioning accuracy that is implied by seeing limited performance at this plate-scale brings the system into the range of performances of commercial off-the-shelf robots that are commonly used in industrial manufacturing processes. The cost-benefits that may be realized through such an approach must be offset against the robot performance, and the ease with which a useful software system can be implemented. We therefore investigate whether the use of such a system is indeed feasible for OPTIMOS-EVE, and the possibilities of extending this approach to other instruments that are currently in the planning stage.

Temporal spectral astronomy or time resolved astronomy is the study of astrophysical phenomena that show spectral variability on very short timescales. These timescales are often too short to be resolved by current astronomical equipment. The lack of detailed observations in this area keeps important theoretical descriptions of astronomical events unclear or incomplete. To resolve this, instruments with very high spectral resolution and fast read-out speeds are needed. Photonic devices such as fibre Bragg gratings (FBGs) offer potential advantages. The use of Bragg gratings in optical fibres allows for very high spectral resolution and the stability and precision needed for the observation of the fast variation of one particular spectral line, with the potential to observe multiple spectral lines at once. Here, we present the concept for a fibre Bragg grating based instrument specifically for temporal spectral astronomy and we discuss the different profiles of FBGs for such applications.

The 8-meter mirror production capacity at the University of Arizona is well known. As the Arizona Stadium facility is occupied with giant mirrors, we have developed capability for grinding, polishing, and testing 4-m mirrors in the large optics shop in the College of Optical Sciences. Several outstanding capabilities for optics up to 4.3 meters in diameter are in place: A 4.3-m computer controlled grinding and polishing machine allows efficient figuring of steeply aspheric and nonaxisymmetric surfaces. Interferometry (IR and visible wavelengths) and surface profilometry making novel use of a laser tracker allows quick, accurate in-process measurements from a movable platform on a 30-m vertical tower. A 2-meter class flat measured with a 1-m vibration insensitive Fizeau interferometer and scanning pentaprism system; stitching of 1-m sub-apertures provides complete surface data with the technology ready for extension to the 4 m level. These methods were proven successful by completion of several optics including the 4.3-m Discovery Channel Telescope primary mirror. The 10 cm thick ULE substrate was ground and polished to 16 nm rms accuracy, corresponding to 80% encircled energy in 0.073 arc-second, after removing low order bending modes. The successful completion of the DCT mirror demonstrates the engineering and performance of the support system, ability to finish large aspheric surfaces using computer controlled polishing, and accuracy verification of surface measurements. In addition to the DCT mirror, a 2-meter class flat was produced to an unprecedented accuracy of <10 nm-rms, demonstrating the combined 1-m Fizeau interferometer and scanning pentaprism measurement techniques.

We evaluated depth of subsurface damage on a ground surface of the ultra low expansion glass-ceramics CLEARCERAMR®-Z HS (CC-Z HS) by Ohara Inc., which is one of the candidates for material for segmented mirrors of the Thirty Meter Telescope. We made polishing spots of Magnetorheological Finishing on the ground surface of CC-Z HS and measured exposed subsurface damage features on the spot surface. We also studied on hydrofluoric acid etching of the CC-Z HS ground surface, which is expected to be an effective method to remove a subsurface damage layer compared with time-consuming polishing. We etched small ground surfaces of CC-Z HS and evaluated its uniformity.

More and more astronomical telescopes use carbon fiber reinforced composites (CFRP). CFRP has high stiffness, high strength, and low thermal expansion. However, they are not isotropic in performance. Their properties are direction dependent. This paper discusses, in detail, the structural and thermal properties of carbon fiber structure members, such as tubes, plates, and honeycomb sandwich structures. Comparisons are provided both from the structural point of view and from the thermal point of view.

To reduce the cost and increase the feasibility of the astronomical optical telescope, modern large optical telescope is normally required to be as light as possible. Therefore lightweight mirror is always pursued by large telescopes development. In this paper, a new type lightweight optical mirror blank, the evaluation of its technical feasibility and the reduction of cost are introduced. For the purpose of applying active optics with this lightweight mirror blank, the structural analysis, thermal analysis and optical performance simulation by the finite element method have been presented.

Successful launch and imagery from the Herschel Space Telescope has demonstrated a nominally in focus telescope. There still remains a discrepancy between the prediction and measurement of the telescope back focal length prior to launch. New material strain data has been applied to the structural/optical model of the telescope. The new data significantly closed the gap between the previous optical test measurement and prediction. However, a discrepancy still exists. Model results and techniques will be presented and discussed.

This paper summarizes a comparison of pre- and post-flight optical performance on optical components (mostly mirrors) from the Corrective Optics Space Telescope Axial Replacement (COSTAR) instrument and the Wide Field Planetary Camera 2 (WF/PC 2) pickoff mirror. These measurements were carried out after both the COSTAR and WF/PC 2 were retrieved from the Hubble Space Telescope in May of 2009 and returned to GSFC in July of 2009. Both of these instruments had a highly UV-reflecting coating of Al with a MgF2 layer on top for protection on their reflecting optics. We studied these in order to document the aging process on these coatings while in space for more than 15.5 years. When compared to data before flight and witness coupons kept on the ground, we find a severely degraded UV performance for the coatings that flew in space, particularly at the Lyman-α wavelength. Based on similar observations seen earlier on the WF/PC1 POM, the current degradation, of the latest optical components removed from HST, are a result of outgassing of substances such as hydrocarbons and silicone from nearby hardware on the spacecraft and UV light that photo-polymerize those materials on the mirror surfaces.

Future space missions, such as SPICA and DARWIN, require large, light-weighted, and stiff mirrors with excellent stability. During the past years, ECM fabricated a number of light-weighted mirrors. However, future large missions require further advances with light-weighting, pushing this technology to the limit possible with recently developed composite materials, new fabrication processes, and innovative designs. In 2009, ECM took steps in this direction by fabricating successfully an ultra-lightweighted HB-Cesic^® mirror demonstrator 1 m in size. We demonstrated that HB-Cesic^®, due to its extreme light-weighting capability and manufacturing versatility, combined with high stiffness, high mechanical strength, and low CTE at cryogenic temperatures, is able to fully meet the requirements of future large cryogenic space mirrors. In this paper we describe the fabrication process of this demonstrator and its physical characteristics.

During the past two years, ECM, Germany, together with Mitsubishi Electric Corporation (MELCO), Japan, developed a new carbon-fiber-reinforced SiC material, called HB-Cesic^®, which possesses superior mechanical and thermal cryogenic properties compared to traditional Cesic^®. This combination makes HB-Cesic^® an excellent choice for large cryogenic mirrors, which will be required for future scientific space missions, such as SPICA and DARWIN. ESA contracted Thales Alenia Space (TAS), France, to design a super-lightweighted HB-Cesic^® mirror with a diameter of 600 mm, isostatic fixations, and a special astigmatism compensation device (ACD) for mirror shape control. The mirror was manufactured by ECM, polished and coated by Société Européenne de Systèmes Optiques (SESO), France, and tested to cryogenic temperatures by TAS. The measured wave-front error at ambient and cryogenic temperatures demonstrated the excellent homogeneity of HB-Cesic^® and TAS' expertise in mirror mounting. Furthermore, when thermally actuated, the ACD exhibited perfect control of the mirror shape. This success confirmed HB-Cesic^®'s superior material properties and its applicability to future cryogenic space mirrors. In this paper we describe the design and fabrication process of this cryogenic mirror and give test results at ambient and cryogenic temperatures.

Ultra-lightweight and high-accuracy CFRP (carbon fiber reinforced plastics) mirrors for space telescopes were fabricated to demonstrate their feasibility for light wavelength applications. The CTE (coefficient of thermal expansion) of the all- CFRP sandwich panels was tailored to be smaller than 1×10^-7/K. The surface accuracy of mirrors of 150 mm in diameter was 1.8 um RMS as fabricated and the surface smoothness was improved to 20 nm RMS by using a replica technique. Moisture expansion was considered the largest in un-predictable surface preciseness errors. The moisture expansion affected not only homologous shape change but also out-of-plane distortion especially in unsymmetrical compositions. Dimensional stability due to the moisture expansion was compared with a structural mathematical model.

CFRP (Carbon Fiber Reinforced Plastics) is the ideal material for space based mirror due to its low thermal expansion, and high specific modulus. To expand the use of CFRP, we investigated the long-term stability of CFRP under humid environment. CFRP mirror was made as precise as possible by using special class of material and adopting particular design techniques. Dimensional stability of CFRP mirror was evaluated by nano-scale measurement. The factors which cause out-of-plane deformation of the mirror is discussed.

The European Solar Telescope (EST) is a European collaborative project to build a 4m class solar telescope in the Canary Islands, which is now in its design study phase. The telescope will provide diffraction limited performance for several instruments observing simultaneously at the Coudé focus at different wavelengths. A multi-conjugated adaptive optics system composed of a tip-tilt mirror and several deformable mirrors will be integrated in the telescope optical path. The secondary mirror system is composed of the mirror itself (Ø800mm), the alignment drives and the cooling system needed to remove the solar heat load from the mirror. During the design study the feasibility to provide fast tip-tilt capabilities at the secondary mirror to work as the adaptive optics tip-tilt mirror is also being evaluated.

During the experimental process of the spatial point's position detection, we analyze the advantages and disadvantages of the classical method, and propose an improved method. First, we interpolate the point's data to increase the size of the image. Then use the Zernike moment to detect the edge of the point. Finally, we obtain a coordinate of the center of the point by using the ellipse fitting algorithm, and take this coordinate as the position of the spatial point. Experimental results in laboratory show that, the proposed detection method on sub-pixel level is realized to detect the spatial point's position with high-accuracy. And experimental results of relative measurement with 100 meters outdoor show that, the repeatable accuracy of this method can reach 0.12 pixel during the day and 0.05 pixel at night.

A new method of attitude measurement of the calibration target based on machine vision is proposed in this paper. Firstly, the internal parameters and external parameters of the CCD camera are calibrated by using the feature points on the calibration target. Secondly, shoot the calibration target in different positions and gather any different image information. Finally, measure the calibration target's attitude through reconstructing the positions of those feature points which on the calibration target. Experiment results show that the standard deviation of the attitude measurement errors is less than 10 arc-second. This method is an effective high-precision space attitude measurement algorithm which can meet the engineering requirements.

The method of 3D reconstruction from multi-view of the object with single camera is proposed in this paper. The images of the planar pattern from different views are captured by the single camera. The internal and external parameters of the camera are calculated precisely with Two-stage camera calibration method. On this basis, the image points of calibration pattern can be matched and reconstructed. Experimental results show that: the flatness of reconstructed planar pattern is about 0.006mm; the position error of sign is about 0.012mm. The proposed method is high-accuracy, simple, flexible and effective.

We discuss the use of a Faro Arm - a portable coordinate measuring machine - in the re-alignment and testing of the Southern African Large Telescope's Spherical Aberration Corrector. In pushing this versatile tool to its limits, we have arrived at a better understanding of its true capabilities and developed ways to compensate for some of its weaknesses. It is possible to achieve excellent results (~5 microns) when making relative measurements and keeping the Arm's orientation relatively constant. The Faro is also extremely useful in providing live feedback while making fine adjustments. However, single measurements of the same position are considerably less reliable (~50 microns) when the Arm is operated in widely different orientations. If the latter is unavoidable, one may largely counteract this by taking continuous streams of measurements (1000 readings) for a given point while exercising the Arm as much as possible in order to average the encoder errors. Various other techniques and accessories that we have found useful, as well as some painful lessons, are described here and a few examples are given to demonstrate how we have used a Faro Arm in our challenging optical alignment project.

Typical radio telescopes have the primary reflector surface which is composed of several single panels that have dimensions of a meter a side. The manufacturing of these radio panels yield a micrometric precision over the volume on the single panel, hence the surface roughness of the panels can be measured with very high accuracy by means of the low coherence interferometry (LCI) technique which reaches micrometric spatial and depth resolution and has the advantage of being contact-less. We have developed a multi-channel partially coherent light interferometer to realize non contact 3D surface topography. The technique is based on the LCI principle, for which a bi-dimensional sensor - a CMOS - has been developed to directly acquire images. Tri-dimensional measures are recovered with a single scanning along the depth direction in a millimetric range, and every single pixel of the bi-dimensional sensor measures a point on the object, this allows a fast analysis in real time on square centimeter areas. In this paper we show the results obtained by applying the LCI technique method to analyze the surface roughness of the panels of a large radio antenna of 64 m of width and used for astronomical observations at 100 GHz; by measuring their 3D structure at micrometric resolution it is possible to verify their fabrication errors.

The Large Synoptic Survey Telescope (LSST) utilizes a three-mirror design in which the primary (M1) and tertiary (M3) mirrors are two concentric aspheric surfaces on one monolithic substrate. The substrate material is Ohara E6 borosilicate glass, in a honeycomb sandwich configuration, currently in production at The University of Arizona's Steward Observatory Mirror Lab. In addition to the normal requirements for smooth surfaces of the appropriate prescriptions, the alignment of the two surfaces must be accurately measured and controlled in the production lab. Both the pointing and centration of the two optical axes are important parameters, in addition to the axial spacing of the two vertices. This paper describes the basic metrology systems for each surface, with particular attention to the alignment of the two surfaces. These surfaces are aspheric enough to require null correctors for each wavefront. Both M1 and M3 are concave surfaces with both non-zero conic constants and higher-order terms (6th order for M1 and both 6th and 8th orders for M3). M1 is hyperboloidal and can utilize a standard Offner null corrector. M3 is an oblate ellipsoid, so has positive spherical aberration. We have chosen to place a phase-etched computer-generated hologram (CGH) between the mirror surface and the center-of-curvature (CoC), whereas the M1 null lens is beyond the CoC. One relatively new metrology tool is the laser tracker, which is relied upon to measure the alignment and spacings. A separate laser tracker system will be used to measure both surfaces during loose abrasive grinding and initial polishing.

The Advanced Wavefront Sensing and Control Testbed (AWCT) is built as a versatile facility for developing and demonstrating, in hardware, the future technologies of wavefront sensing and control algorithms for active optical systems. The testbed includes a source projector for a broadband point-source and a suite of extended scene targets, a dispersed fringe sensor, a Shack-Hartmann camera, and an imaging camera capable of phase retrieval wavefront sensing. The testbed also provides two easily accessible conjugated pupil planes which can accommodate active optical devices such as fast steering mirror, deformable mirror, and segmented mirrors. In this paper, we describe the testbed optical design, testbed configurations and capabilities, as well as the initial results from the testbed hardware integrations and tests.

Phase retrieval is an image-based wavefront sensing process, used to recover phase information from defocused stellar images. Phase retrieval has proven to be useful for diagnosis of optical aberrations in space telescopes, calibration of adaptive optics systems, and is intended for use in aligning and phasing the James Webb Space Telescope. This paper describes a robust and accurate phase retrieval algorithm for wavefront sensing, which has been successfully demonstrated on a variety of testbeds and telescopes. Key features, such as image preprocessing, diversity adaptation, and prior phase nulling, are described and compared to other methods. Results demonstrate high accuracy and high dynamic range wavefront sensing.

Optical cophasing has a key role in ensuring that segmented mirror telescopes reach their best performance. To measure and correct segments misalignment it is necessary to have a wavefront sensor (WFS) in the telescope optical path. All the cophasing WFS suffer the phase ambiguity problem that limits the piston error measurements to a unit of wavelength. To overcome this problem we have developed a new cophasing technique based on the wavelength sweep. This paper will present the results of laboratory and on-sky tests of this technique, comparing them with the expected performance obtained in a previous work through numerical simulations. The laboratory test was carried out on the Active Phasing Experiment bench at ESO premises in Garching. We measured wavefront piston errors up to 15μm with an accuracy better than 0.25μm on a pupil conjugate segmented mirror using the Pyramid Phasing Sensor (PYPS) and a commercial tunable filter. We tested the possibility of propagating the differential piston measurements over the segmented mirror to cophase it, obtaining a residual surface error less than 0.2μm rms. The first on-sky test of the WST was carried out at William Hershel Telescope (WHT) using the NAOMI segmented mirror. We checked the effects of atmospheric turbulence on the measurements of large piston errors up to 15um wavefront and it was obtained an accuracy of 0.5μm, which is in agreement with simulation.

The key factor, which influences the size of future radio aperture synthesis telescope projects, is the cost of the antenna dish. Lower antenna dish cost will allow more antennas to be built, providing more baselines and improving the telescope sensitivity and image quality. In this paper, various methods of lowering the dish structure cost, including using pre-stressed beam members, are discussed and, finally, an innovative low cost small antenna dish is proposed which relies mostly on commercial off-the-shelf components.

The 2.6-m primary mirror of the VST telescope is equipped with an active optics system in order to correct low-order aberrations, constantly monitoring the optical quality of the image and controlling the relative position and the shape of the optical elements. Periodically an image analyser calculates the deviation of the image from the best quality. VST is equipped with both a Shack-Hartmann in the probe system and a curvature sensor embedded in the OmegaCAM instrument. The telescope control software decomposes the deviation into single optical contributions and calculates the force correction that each active element has to perform to achieve the optimal quality. The set of correction forces, one for each axial actuator, is computed by the telescope central computer and transmitted to the local control unit of the primary mirror system for execution. The most important element of the VST active optics is the primary mirror, with its active support system located within the primary mirror cell structure. The primary mirror support system is composed by an axial and a lateral independent systems and includes an earthquake safety system. The system is described and the results of the qualification test campaign are discussed.

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, caused by incorrect relative positions of the two mirrors arising from the deformation of the telescope tube and of the optical train under the effect of gravity and thermal espansion. Periodically the image analyser calculates the deviation of the image from the best quality and the telescope control software decomposes the deviation into the single optical contributions. The new position and orientation of the secondary mirror is computed by the telescope control software and transmitted to the secondary mirror support system for execution. The secondary mirror positioner is a hexapod, i.e. a parallel robot with a mobile platform moved by six linear actuators acting simultaneously. This paper describes the secondary mirror support system and the qualification test campaign performed both in laboratory and at the telescope.

The VST primary mirror is a 2.6-m meniscus made of Astro-Sitall. An active optics system is implemented to correct surface errors due to manufacturing or induced by gravity and temperature changes. The primary mirror is axially supported by 84 supports disposed in four concentric rings. Three of the supports, symmetrically placed and much stiffer than the other ones, define the axial plane of the primary mirror acting as fixed points. The remaining 81 supports are force controlled actuators, used to change the shape of the mirror according to wavefront measurements in closed loop operation, or to a look-up table in open loop. This paper describes the solutions adopted for the axial actuator, as well as the test campaign to assess their performance and degree of reliability.

We studied the thermal effects on the 32 m diameter radio-telescope managed by the Institute of Radio Astronomy (IRA), Medicina, Bologna, Italy. The preliminary results show that thermal gradients deteriorate the pointing performance of the antenna. Data has been collected by using: a) two inclinometers mounted near the elevation bearing and on the central part of the alidade structure; b) a non contact laser alignment optical system capable of measuring the secondary mirror position; c) twenty thermal sensors mounted on the alidade trusses. Two series of measurements were made, the first series was performed by placing the antenna in stow position, the second series was performed while tracking a circumpolar astronomical source. When the antenna was in stow position we observed a strong correlation between the inclinometer measurements and the differential temperature. The latter was measured with the sensors located on the South and North sides of the alidade, thus indicating that the inclinometers track well the thermal deformation of the alidade. When the antenna pointed at the source we measured: pointing errors, the inclination of the alidade, the temperature of the alidade components and the subreflector position. The pointing errors measured on-source were 15-20 arcsec greater than those measured with the inclinometer.

The very short slew times and resulting high inertial loads imposed upon the Large Synoptic Survey Telescope (LSST) create new challenges to the primary mirror support actuators. Traditionally large borosilicate mirrors are supported by pneumatic systems, which is also the case for the LSST. These force based actuators bear the weight of the mirror and provide active figure correction, but do not define the mirror position. A set of six locating actuators (hardpoints) arranged in a hexapod fashion serve to locate the mirror. The stringent dynamic requirements demand that the force actuators must be able to counteract in real time for dynamic forces on the hardpoints during slewing to prevent excessive hardpoint loads. The support actuators must also maintain the prescribed forces accurately during tracking to maintain acceptable mirror figure. To meet these requirements, candidate pneumatic cylinders incorporating force feedback control and high speed servo valves are being tested using custom instrumentation with automatic data recording. Comparative charts are produced showing details of friction, hysteresis cycles, operating bandwidth, and temperature dependency. Extremely low power actuator controllers are being developed to avoid heat dissipation in critical portions of the mirror and also to allow for increased control capabilities at the actuator level, thus improving safety, performance, and the flexibility of the support system.

Magdalena Ridge Observatory Interferometer (MROI) comprises an array of up to ten (10) 1.4m diameter mirror telescopes. Each of these ten telescopes will be housed inside a Unit Telescope Enclosure (UTE) which can be relocated, with the telescope inside, to any of 28 stations arranged in a "Y" configuration. These stations comprise fixed foundations with utility and data connections. There are four standard array configurations, the most compact of which one has less than 350 mm of space between the enclosures. This paper describes the relocation systems that were evaluated, including a rail based system, wheels or trolley fixed to the bottom of the enclosure, and various lifting mechanisms, all of which were analyzed to determine their performances related to the requirements. Eventually a relocation system utilizing a modified reachstacker (a transporter used to handle freight containers) has been selected. The reachstacker is capable of manoeuvring between and around the enclosures, is capable of lifting the combined weight of the enclosure with the telescope (40tons), and can manoeuvre the enclosure with minimal vibrations. A rigorous testing procedure has been performed to determine the vibrations induced in a dummy load in order to guarantee the safety of optics that must remain on the nasmyth table during the relocation. Finally we describe the lifting system, constituted by hydraulic jacks and locating pins, designed to lift and lower the enclosure and telescope during the precise positioning of the telescopes in the various stations.

As direct drive technology is finding their way into telescope drive designs for its many advantages, it would push to more reliable and cheaper solutions for future telescope complex motion system. However, the telescope drive system based on the direct drive technology is one high integrated electromechanical system, which one complex electromechanical design method is adopted to improve the efficiency, reliability and quality of the system during the design and manufacture circle. The telescope is one ultra-exact, ultra-speed, high precision and huge inertial instrument, which the direct torque motor adopted by the telescope drive system is different from traditional motor. This paper explores the design process and some simulation results are discussed.