This PDF file contains the front matter associated with SPIE Proceedings Volume 7733, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Answering well-known fundamental questions is usually regarded as the major goal of science. Discovery of other unknown and fundamental questions is, however, even more important. Recognition that "we didn't know anything" is the basic scientific driver for the next generation. Cosmology indeed enjoys such an exciting epoch. What is the composition of our universe ? This is one of the well-known fundamental questions that philosophers, astronomers and physicists have tried to answer for centuries. Around the end of the last century, cosmologists finally recognized that "We didn't know anything". Except for atoms that comprise slightly less than 5% of the universe, our universe is apparently dominated by unknown components; 23% is the known unknown (dark matter), and 72% is the unknown unknown (dark energy). In the course of answering a known fundamental question, we have discovered an unknown, even more fundamental, question: "What is dark matter? What is dark energy?" There are a variety of realistic particle physics models for dark matter, and its experimental detection may be within reach. On the other hand, it is fair to say that there is no widely accepted theoretical framework to describe the nature of dark energy. This is exactly why astronomical observations will play a key role in unveiling its nature. I will review our current understanding of the "dark sky", and then present on-going Japanese project, SuMIRe, to discover even more unexpected questions.

Over the past decade, sky surveys such as the Sloan Digital Sky Survey (SDSS) have proven the power of large data sets for answering fundamental astrophysical questions. This observational progress, based on a synergy of advances in telescope construction, detectors, and information technology, has had a dramatic impact on nearly all fields of astronomy, and areas of fundamental physics. The next-generation instruments, and the surveys that will be made with them, will maintain this revolutionary progress. The hardware and computational technical challenges and the exciting science opportunities are attracting scientists and engineers from astronomy, optics, low-light-level detectors, high-energy physics, statistics, and computer science. The history of astronomy has taught us repeatedly that there are surprises whenever we view the sky in a new way. This will be particularly true of discoveries emerging from a new generation of sky surveys. Imaging data from large ground-based active optics telescopes with sufficient étendue can address many scientific missions simultaneously. These new investigations will rely on the statistical precision obtainable with billions of objects. For the first time, the full sky will be surveyed deep and fast, opening a new window on a universe of faint moving and distant exploding objects as well as unraveling the mystery of dark energy.

The GTC (Gran Telescopio Canarias) is an optical and IR telescope, with a 10,4 meter segmented primary, installed at the Observatorio del Roque de Los Muchachos (ORM) on the island of La Palma. GTC commissioning started in July 2007 when First Light was achieved. GTC regular scientific operations started at the beginning of 2009 with its first science instrument: OSIRIS, a visible camera with tunable filter and low-resolution multi-object spectroscopic capability. Since that time science operation and telescope and instrument development activities alternate in using the available telescope time. Later in 2010 the second science instrument will be commissioned: CanariCam, a thermal-IR camera and low-resolution spectrograph with polarimetric and coronagraphic capabilities. This paper presents the telescope commissioning process, the problems encountered and shows some of the performance aspects. First science results will also be presented to demonstrate the current capabilities of the GTC facility.

VISTA, the Visible and Infrared Survey Telescope for Astronomy, is a 4-m class 1.65-degree wide field near-IR survey telescope with 0.34 arcsec pixels. VISTA was successfully commissioned and has been making surveys since 15 October 2009, and was formally accepted as a part of ESO's Cerro Paranal Observatory on 10 December 2009. We summarise the design and build process, report on commissioning and the as-built status. The most novel aspects of the system design have proved to all work well. We report the measured on-sky system performance that confirms that VISTA works as expected.

Ludwig-Maximilians-Universitat Munchen operates an astrophysical observatory on the summit of Mt. Wendelstein¹ which will be equipped with a modern 2m-class, robotic telescope. The plan is to operate one of the most efficient robotic 2m telescopes in Europe in order to offer optimal scientific opportunities for our researchers and maintain highest standards for the education of students. The 2m Fraunhofer telescope in its new 8.5m dome has a modern, very compact alt.-azimuth design. Two Nasmyth ports will harbor a wide-field camera (WWFI²), a medium field multi-channel camera (3kk³), a low resolution IFU spectrograph (VIRUSW⁴) and a high resolution spectrograph (upgraded FOCES⁵). All instruments will be simultaneously ready for remote or robotic observations. The telescope is designed as a 3-mirror f/7.8 system and should maintain the excellent (< 0.8" median) seeing of the site1 over a field of view (f.o.v.) of 0.7 deg diameter with a field corrector for the wide field port at optical wavelength. The second port provides a f.o.v. of 60 arcmin² without any corrector optics. It is optimized for simultaneous optical and NIR imaging as well as field spectroscopy and echelle high resolution spectroscopy over the full optical wavelength regime.6 Here we present the design of the telescope as well as the scope and projected time line of the overall project.

The University of Tokyo Atacama Observatory (TAO) is a project to construct a 6.5m infrared-optimized telescope at the summit of Co. Chajnantor, 5,640 m altitude, in northern Chile, promoted by Institute of Astronomy, University of Tokyo. Thanks to the high altitude and low water vapor, continuous window from 0.9 to 2.5μm as well as new windows at wavelength longer than 25μm appears. The site shows extremely low precipitable water vapor of 0.5mm (25 percentile), and fraction of usable night is more than 80%. Measured median seeing is 0".69, which is comparable or better than major observatories over the world. Prior to the 6.5m telescope, a 1m pathfinder telescope called miniTAO is installed and started observations in 2009. Its successes of Paschen α imaging at 1.875 μm and mid-infrared observations at 30μm confirm promising capabilities of the site. The 6.5m telescope is now at a design phase, and two facility instruments are now being constructed, which are a near-infrared imager/multi-object spectrograph with a field of view of 9'.6 and a mid-infrared imager/spectrograph for observations in 2 to 38μm.

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) project has completed its engineering work, and is going to finish commissioning around the end of 2010. The LAMOST telescope is with both large aperture and wide field of view to achieve the large scale spectroscopic survey observation. It is an innovative large aperture meridian active reflecting Schmidt configuration achieved by an active deformable Schmidt mirror, which could not be realized by the traditional optical system. Its primary mirror and active Schmidt mirror are both segmented, and composed of 37 and 24 hexagonal sub-mirrors respectively. A new active optics method succesfully developed in the active deformable Schmidt mirror of LAMOST. It is a conbination of the thin deformable mirror active optics and segmented active optics. This paper presents the optical performance of the telescope of LAMOST during optical test. It is shown that LAMOST project successfully resolving the big technical challenges, and making the progress in active optics and telescope technology.

The Discovery Channel Telescope (DCT) is a 4.3-meter astronomical research telescope being built in northern Arizona as a partnership between Discovery Communications and Lowell Observatory. The telescope will be able to support substantial instrument payloads at Cassegrain, Nasmyth, and prime foci, and high observing cadences. The first-light configuration will be as an f/6.1 Ritchey-Chrétien at Cassegrain with a 30 arc-minute field-of-view. Major facility work is complete, and the telescope is currently in the integration phase with first-light anticipated in 2011. We present an overview of the design and progress to date, and include plans for final integration, commissioning, and early science.

The all sky spectoscopic survey is very important both in extra-galactic and Galactic studies. The Large-Sky-Area Multi-object Fiber Spectroscopic Telescope (LAMOST) has successfully completed its engineering work and inaugurated in October of 2008. Now it is in the commissioning stage. In pursuit of the all sky spectroscopic survey, a southern LAMOST is proposed. Tecnically, the Southern LAMOST will be mainly a copy of present LAMOST in Xinglong, China, which is located at about latitute +40 degrees. Modifications are to be made for much better image quality and thinner optical fibers to match with the better seeing condition in the Southern site. There will be 6000 or 8000 optical fibers used on the focal surface to get the highest spectrum acquiring rate, and will be equipted with about 12 to 16 spectrographs with 24 to 32 CCD cameras. Southern LAMOST is going to be built by international collaboration.

The Large Binocular Telescope (LBT) Observatory is a collaboration between institutions in Arizona, Germany, Italy, Indiana, Minnesota, Ohio and Virginia. The telescope on Mt. Graham in Arizona uses two 8.4-meter diameter primary mirrors mounted side-by-side to produce a collecting area equivalent to an 11.8-meter circular aperture. A unique feature of LBT is that the light from the two primary mirrors can be combined to produce phased-array imaging of an extended field. This cophased imaging along with adaptive optics gives the telescope the diffraction-limited resolution of a 22.65-meter telescope. Binocular imaging with two co-pointed prime focus cameras began in Fall 2007, and science observing continues routinely. We will describe the scientific results and technical challenges of monocular Gregorian focus observations starting in Spring 2008. Commissioning of the first Gregorian spectrometer (LUCIFER1) has been completed with a rigid secondary mirror, and science observations have begun in December 2009. The telescope uses two F/15 adaptive secondaries to correct atmospheric turbulence. The first of these adaptive mirrors has been tested in Italy with the adaptive loop closed, and arrived at the telescope in February 2010. The first adaptive optics images were achieved on-sky in May 2010. The Direct Gregorian focus has been prepared for the arrival of the second Gregorian spectrometer (MODS1).

The Large Synoptic Survey Telescope (LSST) Project is a public-private partnership that is well into the design and development of the complete observatory system to conduct a wide fast deep survey and to process and serve the data. The telescope has a 3-mirror wide field optical system with an 8.4 meter primary, 3.4 meter secondary, and 5 meter tertiary mirror. The reflective optics feed three refractive elements and a 64 cm 3.2 gigapixel camera. The LSST data management system will reduce, transport, alert and archive the roughly 15 terabytes of data produced nightly, and will serve the raw and catalog data accumulating at an average of 7 petabytes per year to the community without any proprietary period. The project has completed several data challenges designed to prototype and test the data management system to significant pre-construction levels. The project continues to attract institutional partners and has acquired non-federal funding sufficient to construct the primary mirror, already in progress at the University of Arizona, build the secondary mirror substrate, completed by Corning, and fund detector prototype efforts, several that have been tested on the sky. A focus of the project is systems engineering, risk reduction through prototyping and major efforts in image simulation and operation simulations. The project has submitted a proposal for construction to the National Science Foundation Major Research Equipment and Facilities Construction (MREFC) program and has prepared project advocacy papers for the National Research Council's Astronomy 2010 Decadal Survey. The project is preparing for a 2012 construction funding authorization.

Pan-STARRS is a highly cost-effective, modular and scalable approach to wide-field optical/NIR imaging. It uses 1.8m telescopes with very large (7 square degree) field of view and revolutionary1.4 billion pixel CCD cameras with low noise and rapid read-out to provide broad-band imaging from 400-1000nm wavelength. The first single telescope system, PS1, has been deployed on Haleakala on Maui, and has been collecting science quality survey data for approximately six months. PS1 will be joined by a second telescope PS2 in approximately 18 months. A four aperture system is planned to become operational following the end of the PS1 mission. This will be able to scan the entire visible sky to approximately 24^th magnitude in less than a week, thereby meeting the goals set out by the NAS 2000 decadal review for a "Large Synoptic Sky Telescope". Here we review the technical design, and give an update on the progress that has been made with the PS1 system.

The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the summit of Cerro Pachón in Chile. The survey mission requires a short slew and settling time of 5 seconds for a 3.5 degree slew. This is significantly faster than similar aperture telescopes. Since the optical system does not include a fast steering mirror the telescope has stringent vibration limitations during observation. Meeting these requirements is facilitated by the compact mount riding on a robust pier which produces high natural frequencies, an advanced control system to minimize vibration excitation and reaction mass dampers. The telescope mount design is an altitude over azimuth welded and bolted assembly fabricated from mild steel. It supports the primary / tertiary mirror cell assembly, the secondary mirror cell assembly and the camera assembly. The mount design enables the removal of these optical assemblies for servicing and recoating. Retractable / deployable platforms have also been provided for accessing the camera on telescope. As a result of the wide field of view, the optical system is unusually susceptible to stray light consequently the mount must incorporate substantial light baffling. The dynamic characteristics of the steel reinforced concrete pier were enhanced by utilizing two different wall thicknesses, an unusually large diameter of 16 meter and anchoring the foundation in unweathered bedrock. The entire pier and mount assembly has been designed to be invariant with azimuth and elevation angle to enhance the effectiveness of the advanced control system.

The 4m Advance Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading ground-based resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. The project has successfully passed its final design review and the Environmental Impact Study for construction of ATST on Haleakala, Maui, HI has been concluded in December of 2009. The project is now entering its construction phase. As its highest priority science driver ATST shall provide high resolution and high sensitivity observations of the dynamic solar magnetic fields throughout the solar atmosphere, including the corona at infrared wavelengths. With its 4 m aperture, ATST will resolve features at 0."03 at visible wavelengths and obtain 0."1 resolution at the magnetically highly sensitive near infrared wavelengths. A high order adaptive optics system delivers a corrected beam to the initial set of state-of-the-art, facility class instrumentation located in the coudé laboratory facility. The initial set of first generation instruments consists of five facility class instruments, including imagers and spectropolarimeters. The high polarimetric sensitivity and accuracy required for measurements of the illusive solar magnetic fields place strong constraints on the polarization analysis and calibration. Development and construction of a fourmeter solar telescope presents many technical challenges, including thermal control of the enclosure, telescope structure and optics and wavefront control. A brief overview of the science goals and observational requirements of the ATST will be given, followed by a summary of the design status of the telescope and its instrumentation, including design status of major subsystems, such as the telescope mount assembly, enclosure, mirror assemblies, and wavefront correction

The European Solar Telescope is a project for a 4-meter class telescope to be located in the Canary Islands. EST is promoted by the European Association for Solar Telescopes (EAST). This is a consortium formed by a number of research organizations from fifteen European countries (Austria, Croatia, Czech Republic, France, Germany, Hungary, Italy, the Netherlands, Norway, Poland, Slovak Republic, Spain, Sweden, Switzerland, and United Kingdom). EST will specialize in high spatial and temporal resolution using diverse instruments that can efficiently produce two-dimensional spectropolarimetric information of the thermal, dynamic and magnetic properties of the plasma over many scale heights in the solar atmosphere. In this contribution, the status of the development of the Design Study of EST is presented, emphasizing the most important aspects of the optical design, mechanical structure, AO and MCAO systems for wavefront correction, instruments and polarization analysis.

India is planning a new solar telescope with an aperture of 2-m for carrying out high resolution studies of the Sun. Site characterization is underway at high altitude locations in the Himalayan mountains. A detailed concept design for NLST (National Large Solar Telescope) has been completed. The optical design of the telescope is optimized for high optical throughput and uses a minimum number of optical elements. A high order AO system is integrated part of the design that works with a modest Fried's parameter of 7-cm to give diffraction limited performance. The telescope will be equipped with a suite of post-focus instruments including a high resolution spectrograph and a polarimeter. NLST will also be used for carrying out stellar observations during the night. The mechanical design of the telescope, building, and the innovative dome is optimized to take advantage of the natural air flush which will help to keep the open telescope in temperature equilibrium. After its completion (planned for 2014), NLST will fill a gap in longitude between the major solar facilities in USA and Europe, and it will be for years the largest solar telescope in the world

In the context of the EST design study for a 4m-class solar telescope and a study for large open-foldable domes of the Dutch Technology Foundation STW, a design is made for the 20 to 30m diameter range. Detailed designs are made for three specific diameter sizes: 23, 28 and 33m. Smaller-size open-foldable domes based on tensioned cloth and in use at the Dutch Open Telescope (7m) and the GREGOR (9m) have proven to be all-weather stable and very effective for good seeing conditions for solar telescopes. The cloth has shown no degradation over the past 14 (DOT) resp. 6 (GREGOR) years of experience and no permanent elongation with the frequent de-tensioning and tensioning during opening and closing. The application of cloth permits a dome design leaving, when opened, the telescope completely free without any structure over the telescope and no massive structures besides or under it. Basis for the new design is the available prestretched stable cloth, which is nowadays produced in much stronger qualities than used for DOT and GREGOR. The larger curvature radius requires larger tension in the cloth, but combination with stronger cloth fits for the upscaling. Calculations show that the steel construction geometries of the GREGOR dome can be upscaled with a few adjustments. Bearings and drives remain within normal sizes. Cost calculations show that open-foldable domes of this size are remarkably lower in price than closed domes. In addition, an interesting option is presented for a semi-transparent windshield of which the position can be adapted to the wind direction. This shield gives an effective wind protection of the region around the primary mirror without disturbing the wind flows above the shield and without stagnant air or big eddies behind it. It is storm safe and the costs are only a fraction of the open-foldable dome costs.

With the integration of a 1-meter Cesic primary mirror the GREGOR telescope pre-commissioning started. This is the first time, that the entire light path has seen sunlight. The pre-commissioning period includes testing of the main optics, adaptive optics, cooling system, and pointing system. This time was also used to install a near-infrared grating spectro-polarimeter and a 2D-spectropolarimeter for the visible range as first-light science instruments. As soon as the final 1.5 meter primary mirror is installed, commissioning will be completed, and an extended phase of science verification will follow. In the near future, GREGOR will be equipped with a multi-conjugate adaptive optics system that is presently under development at KIS.

SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a specially modified Boeing 747SP aircraft with a 2.7- m telescope. Flying above more than 99% of the water vapor in the Earth's atmosphere, SOFIA will enable observations of large regions of the infrared and submillimeter that are normally opaque to terrestrial observatories. A joint project of NASA and DLR, SOFIA has completed a series of major flight tests leading up to the Initial Science Flights this year. In particular, SOFIA has recently completed its first observations through the telescope. This paper gives an overview of the facility and reports on the recent progress in the development of this major astronomical facility including the First Light observations with the FORCAST infrared camera.

The Stratospheric TeraHertz Observatory (STO) is a NASA funded, Long Duration Balloon (LDB) experiment designed to address a key problem in modern astrophysics: understanding the Life Cycle of the Interstellar Medium (ISM). STO will survey a section of the Galactic plane in the dominant interstellar cooling line [C II] (1.9 THz) and the important star formation tracer [N II] (1.46 THz) at ~1 arc minute angular resolution, sufficient to spatially resolve atomic, ionic and molecular clouds at 10 kpc. STO itself has three main components; 1) an 80 cm optical telescope, 2) a THz instrument package, and 3) a gondola [1]. Both the telescope and gondola have flown on previous experiments [2,3]. They have been reoptimized for the current mission. The science flight receiver package will contain four [CII] and four [NII] HEB mixers, coupled to a digital spectrometer. The first engineering test flight of STO was from Ft. Sumner, NM on October 15, 2009. The ~30 day science flight is scheduled for December 2011.

One of the most challenging requirements for the Stratospheric Observatory for Infrared Astronomy (SOFIA) is the pointing stability of 0.2 arcseconds (rms) of its 2.7 m telescope onboard a Boeing 747SP. To support the analysis of pointing disturbances in flight, an EM-CCD camera has been prepared to measure star positions in the focal plane at speeds up to about 400 frames per second. Currently, the camera is planned to be mounted for special engineering flights, a procedure that requires overhead for mechanical work and optical alignment, including star tests on the night sky from the ground. This paper summarizes the status of the project and explores possibilities to mount the camera permanently to the SOFIA telescope. Permanent mounting would make it available for continuous performance monitoring and as a trouble shooting tool if needed. In addition, the camera could serve as a versatile high speed photometer in the visible and very near IR wavelength range for astronomical observations, e.g. for the photometry of stellar occultations and of transits of extra-solar planets.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a 2.5m infrared telescope build into a Boeing 747SP. During observations the telescope will not only be subject to aircraft vibrations and maneuver loads - by opening a large door to give the observatory an unhindered view of the sky, there will also be aerodynamic and aeroacoustic disturbances. A critical factor in the overall telescope performance is the SOFIA Secondary Mirror Assembly. The 35cm silicon carbide mirror is mounted on the Secondary Mirror Mechanism, which has five degrees-of-freedom (rotation about line of sight is blocked) and consists of two parts: The slow moving base for focusing and centering, and on top of that the Tilt Chop Mechanism (TCM) for chopping with a frequency of up to 20Hz and a chop throw of up to 10arcmin. A new controller for the TCM is introduced in this paper in order to meet the stringent performance requirements for the chopper. A state space controller is chosen that combines a feedback path for steady state behavior with a model-based feed forward controller for improved settling time performance. The paper explains the modeling of the TCM via a grey box model approach optimized with system identification data and compares simulated with measured data. Then the structure of the controller is explained and Matlab/Simulink simulations are presented. The simulation results are compared to measurements taken with the real system on ground and finally flight test results with open and closed door are discussed.

During observation flights the telescope structure of the Stratospheric Observatory for Infrared Astronomy (SOFIA) is subject to disturbance excitations over a wide frequency band. The sources can be separated into two groups: inertial excitation caused by vibration of the airborne platform, and aerodynamic excitation that acts on the telescope assembly (TA) through an open port cavity. These disturbance sources constitute a major difference of SOFIA to other ground based and space observatories and achieving the required pointing accuracy of 1 arcsecond cumulative rms or better below 70 Hz in this environment is driving the design of the TA pointing and control system. In the current design it consists of two parts, the rigid body attitude control system and a feed forward based compensator of flexible TA deformation. This paper discusses the characterization and control system tuning of the as-built system. It is a process that integrates the study of the structural dynamic behavior of the TA, the resulting image motion in the focal plane, and the design and implementation of active control systems. Ground tests, which are performed under controlled experimental conditions, and in-flight characterization tests, both leading up to the early science performance capabilities of the observatory, are addressed.

The goal of the Stratospheric Observatory for Infrared Astronomy (SOFIA) is to point its airborne telescope at astronomical targets stable within 0.2 arcseconds (rms). However, the pointing stability will be affected in flight by aircraft vibrations and movements and constantly changing aerodynamic conditions within the open telescope compartment. Model calculations indicate that initially the deviations from targets may be at the order of several arcseconds. The plan is to carefully analyse and characterize all disturbances and then gradually fine tune the telescope's attitude control system to improve the pointing stability. To optically measure how star images change their position in the focal plane, an Andor DU-888 electronmultiplying (EM) CCD camera will be mounted to the telescope instead of its standard tracking camera. The new camera, dubbed Fast Diagnostic Camera (FDC) has been extensively tested and characterized in the laboratory and on ground based telescopes. In ground tests on the SOFIA telescope system it proofed its capabilities by sampling star images with frame rates up to 400 frames per second. From this data the star's location (centroid) in the focal plane can be calculated every 1/400th second and by means of a Fourier transformation, the star's movement power spectrum can be derived for frequencies up to 200 Hz. Eigenfrequencies and the overall shape of the measured spectrum confirm the previous model calculations. With known disturbances introduced to the telescope's fine drive system, the FDC data can be used to determine the system's transfer function. These data, when measured in flight will be critical for the refinement of the attitude control system. Another subsystem of the telescope that was characterized using FDC data was the chopping secondary mirror. By monitoring a star centroid at high speed while chopping, the chopping mechanism and its properties could be analyzed. This paper will describe the EM-CCD camera and its characteristics and will report on the tests that lead up to its first use in a SOFIA flight.

We present the design of a MegaTORTORA telescope (and its prototype, mini-MegaTORTORA, presently in construction at Special Astrophysical Observatory) - modular, multi-purpose, scalable grid of optical cameras based on commercially available objectives and fast CCDs, able to operate with sub-second temporal resolution in both wide-field monitoring regime with all objectives observing different regions of the sky as well as in narrow-field follow-up mode with co-aligned channels and installed color and polarimetric filters for detailed investigation of selected objects, and to change the regime of operation on a sub-second time scale.

During the last years, a number of telescopes and instruments have been dedicated to the follow-up of GRBs: recent studies of the prompt emission (see for instance GRB080319B) and of their afterglows, evidenced a series of phenomena that do not fit very well within the standard fireball model. In those cases, optical observations were fundamental to distinguish among different emission mechanisms and models. In particular, simultaneous observation in various optical filters became essential to understand the physics, and we discovered the need to have a detailed high time resolution follow up. Finally, recent observations of the polarization in GRB 090102 clearly indicate the presence of an ordered magnetic field favoring the electromagnetic outflows models. This is, however, only one case and, in order to detail properly the model, we need a bit of statistics. But, after the Swift launch, the average observed intensity of GRB afterglows showed to be lower than thought before. Robotic telescopes, as demonstrated by REM, ROTSE, TAROT, etc. (but see also the GROND set up) is clearly the winning strategy. Indeed, as we will also briefly discuss later on, the understanding of the prompt emission mechanism depends on the observations covering the first few hundreds seconds since the beginning of the event with high temporal resolution. To tackle these problems and track down a realistic model, we started the conceptual design and phase A study of a 4 meter class, fast-pointing telescope (40 sec on target), equipped with multichannel imagers, from Visible to Near Infrared (Codevisir/Pathos). In the study we explored all the different parts of the project, from the telescope to the instrumental suite to data managing and analysis, to the dome and site issue. Contacts with industry have been fruitful in understanding the actual feasibility of building such a complex machine and no show stoppers have been identified, even if some critical points should be better addressed in the Phase B study. In this paper, we present the main results of the feasibility study we performed.

A number of scientific observations take advantage of the use of robotic, fast pointing telescopes; in particular, fast reacting small telescopes were especially useful for gamma ray burst follow-up which now require better performances and greater telescope size. However, increasing telescope size could imply some limitations in terms of operability and technological solutions. In order to select the best telescope configuration it is necessary to take into account mechanical set up, pointing strategy, wind effects and the resulting effective costs. This paper will investigate and compare the characteristics of traditional alt-az and alt-alt telescope configurations considering also an innovative alt-alt set up to be developed as an alternative to the mainstream layout of present medium class telescopes. In the alt-alt case the system exploits the heritage of larger telescope projects like LBT, coupled with a more traditional fork mounted to match the alt-alt kinematics, so obtaining a more stable machine and minimizing the blind spot limitation.

Current trends in astronomical research necessitate a large number of small to medium sized telescopes be commissioned to support and augment the science goals of larger ground-based observatories and space observatories. The science mission requirements for these telescopes vary widely, yet the critical design requirements for the telescopes are largely consistent across many missions. This paper clarifies the critical functional and performance parameters of a gimbaled telescope system as dictated by three significant classes of telescope missions: laser transmission, wide area surveys and pointed surveys. Within these classifications several specific example science missions are considered from which specific telescope functional requirements are derived. Detailed telescope performance requirements are then evaluated from a systems engineering perspective, highlighting typical performance that may be expected from a modern telescope. Additional commentary is provided on the probable feasibility of upgrading older facilities in contrast to commissioning new telescopes systems. Based on the predictions of the NSF / NOAO sponsored ReSTAR report, it is assumed that the demand for highobservation- volume pointed surveys will increase rapidly within the next ten years. A case is made for the high science value of high gimbal slew rates on the basis of effective throughput in pointed survey applications.

The QUIJOTE CMB experiment aims to characterize the polarization of the CMB in the frequency range 10-30 GHz and large angular scales. It will be installed in the Teide Observatory, following the projects that the Anisotropy of the Cosmic Microwave Background group has developed in the past (Tenerife experiment, IAC-Bartol experiment...) and is running at the present time (VSA, Cosmosomas). The QUIJOTE CMB experiment will consist of two telescopes which will be installed inside a unique enclosure, which is already constructed. The layout of both telescopes is based on an altazimuth mount supporting a primary and a secondary mirror disposed in a offset Gregorian Dragon scheme. The use of industrial-like fabrication techniques, such as sand-mould casting, CNC machining, and laser tracker measuring for alignment, provided the required performances for microwave observation. A fast-track construction scheme, altogether with the use of these fabrication techniques allowed designing and manufacturing the opto-mechanics of the telescope in 14 months prior to delivery for final start-up in December 2008.

We describe a 1p8m f/6 Cassegrain optical system that creates a 1.42° FOV with near diffraction limited images from 400nm to 1100nm with full-field distortion less than 0.01%. The astronomical application for this optical system is the CCD/Transit Instrument with Innovative Instrumentation (CTI-II), designed to produce a highly precise photometric and astrometric survey of a complete strip of sky in the northern hemisphere. We describe the scientific observation program and supporting optical design for the telescope. The all-spherical, five lens field corrector represents a very capable optical system that works well with many other astronomical telescopes such as SDSS, Pan-STARRS, SkyMapper, ESO's VST, the WIYN ODI, and the MMT WFC. In many cases, using a five lens corrector exceeded the optical performance of the original published system designs. Conversely, these and other optical concepts compromised the performance of the CTI-II design. The CTI-II design is similar to many other wide-field telescope and imaging camera designs, thus the design is of potential general use in astronomy.

This paper describes the current status of the Large Millimeter Telescope (LMT), the near-term plans for the telescope and the initial suite of instrumentation. The LMT is a bi-national collaboration between Mexico and the USA, led by the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE) and the University of Massachusetts at Amherst, to construct, commission and operate a 50m-diameter millimeter-wave radio telescope. Construction activities are nearly complete at the 4600m LMT site on the summit of Volcán Sierra Negra, an extinct volcano in the Mexican state of Puebla. Full movement of the telescope, under computer control in both azimuth and elevation, has been achieved. The commissioning and scientific operation of the LMT is divided into two major phases. As part of phase 1, the installation of precision surface segments for millimeter-wave operation within the inner 32m-diameter of the LMT surface is now complete. The alignment of these surface segments is underway. The telescope (in its 32-m diameter format) will be commissioned later this year with first-light scientific observations at 1mm and 3mm expected in early 2011. In phase 2, we will continue the installation and alignment of the remainder of the reflector surface, following which the final commissioning of the full 50-m LMT will take place. The LMT antenna, outfitted with its initial complement of scientific instruments, will be a world-leading scientific research facility for millimeter-wave astronomy.

The Atacama Large Millimeter Array (ALMA) consists of a large number of 12 m diameter antennas that will operate up to 950GHz. The mechanical performances in terms of surface accuracy, pointing stability and residual delay are very tight. The antennas must work at full performances in free air during night and day with also the request to observe the sun. The mechanical performances are affected by all the not repeatable error sources and in particular by the temperature variations and wind component blowing from different directions. The design of the antenna has been done in order to have a very light and stiff structure, in particular all the elevation structure is in carbon fibre with also a very low thermal expansion coefficient, but to achieve the ALMA specification, two different systems able to predict the above error sources have been implemented in the control of the antenna. The first system is composed by a determined number of thermal sensors distributed in the alidade of the antenna (is the only part in steel ) and compensates the elevation axis deformation due to the temperature variation by means of a deformation matrix. The second system is based on two high accuracy inclinometers with a very short recovery time opportunely placed on the antenna and correct the wind induced errors. These innovative systems and instruments have been design and tested in the prototype antenna to the production phase.

We present here the systems aimed to measure and minimize the pointing errors for the Sardinia Radio Telescope: they consist of an optical telescope to measure errors due to the mechanical structure deformations and a lasers system for the errors due to the subreflector displacement. We show here the results of the tests that we have done on the Medicina 32 meters VLBI radio telescope. The measurements demonstrate we can measure the pointing errors of the mechanical structure, with an accuracy of about ~1 arcsec. Moreover, we show the technique to measure the displacement of the subreflector, placed in the SRT at 22 meters from the main mirror, within ±0.1 mm from its optimal position. These measurements show that we can obtain the needed accuracy to correct also the non repeatable pointing errors, which arise on time scale varying from seconds to minutes.

The Atacama Large Millimeter/submillimeter Array (ALMA) is an international facility at an advanced stage of construction in the Atacama region of northern Chile. ALMA will consist of two arrays of high-precision antennas: one made up of twelve 7-meter diameter antennas operating in closely-packed configurations of about 50m in diameter, and the other of up to sixty-four 12-meter antennas arranged in configurations with diameters ranging from about 150 meters to 15 km. There will be four more 12-meter antennas to provide the "zero-spacing" information, which is critical for making accurate images of extended objects. The antennas will be equipped with sensitive millimeter-wave receivers covering most of the frequency range 84 to 950 GHz. State-of-the-art microwave, digital, photonic and software systems will capture the signals, transfer them to the central building and correlate them, while maintaining accurate synchronization. ALMA will provide images of a wide range of astronomical objects with great sensitivity and very high spectral resolution. The images will have much higher "fidelity" than those from existing mm/submm telescopes. This paper gives an update on the status of construction and on progress with the testing and scientific commissioning.

The Square Kilometre Array is intended to be the next-generation radio wavelength observatory. With a Key Science program addressing fundamental physics, astronomy, and astrobiology, the SKA will have a collecting area of up to one million square metres spread over at least 3000 km, providing a sensitivity 50 times higher than the Expanded Very Large Array, and an instantaneous field of view (FoV) of at least several tens of square degrees and possibly 250 square degrees. In this paper, we describe the main features of the SKA, paying attention to the design activities around the world, and outline plans for the final design and phased implementation of the telescope.

The Expanded Very Large Array (EVLA) is an international project to improve the scientific capabilities of the Very Large Array (VLA), an aperture synthesis radio telescope consisting of 27, 25-meter diameter antennas distributed in a Y-shaped configuration on the Plains of San Augustin in west-central New Mexico. The EVLA's major science themes include measuring the strength and topology of magnetic fields, enabling unbiased surveys and imaging of dust-shrouded objects that are obscured at other wavelengths, enabling rapid response to and imaging of rapidly evolving transient sources, and tracking the formation and evolution of objects in the universe. The EVLA's primary technical elements include new or upgraded receivers for continuous frequency coverage from 1 to 50 GHz, new local oscillator, intermediate frequency, and wide bandwidth data transmission systems to carry signals with 16 GHz total bandwidth from each antenna, and a new digital correlator with the capability to process this bandwidth with an unprecedented number of frequency channels for an imaging array. The project also includes a new monitor and control system and new software that will provide telescope ease of use. The project was started in 2001 and is on schedule and within budget. Scientific observations with the new correlator started in March 2010. The structural modifications that convert the VLA antennas to the EVLA design were completed in May 2010. The project will be complete in December 2012 when the last receiver will be installed on an antenna.

The CARMA telescope is a heterogeneous array of 10.4, 6.1 and 3.5 m antennas, with antenna configurations providing spacings from ~3.5 m to 2 km. This heterogeneous array is well suited to imaging a wide range of spatial scales. In compact configurations the heterogeneous array provides high quality short spacing data for aperture synthesis. In extended configurations, the antennas can be paired, with 6.1 and 10.4m antennas making science observations in the 3 mm and 1 mm bands, while 3.5 m antennas are simultaneously observing calibration sources within a few degrees in the 1 cm band. This unique Paired Antenna Calibration System allows us to to correct for atmospheric phase fluctuations and make images at 0.15 arcec resolution in a wide range of atmospheric seeing conditions. In this paper we discuss some results and lessons learned using these heterogeneous observing techniques. These results are relevant to all aperture synthesis arrays, including millimeter/submillimeter wavelength arrays like ALMA, and cm/m wavelength arrays like ATA and SKA.

A dominant problem for large, high precision telescopes is the deformation due to temperature changes in the structure. Even for active surface designs such as the Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT), accurate knowledge of the temperature distribution in the structure is necessary in order to adjust the primary reflector panels and make pointing corrections. The design of thermal management system of the LMT consists of a fully-cladded structure, a forced ventilation system, and a collection of temperature sensors distributed throughout the telescope. During the design, both steady-state and dynamic thermal models were developed to predict the thermal behavior. Additionally, some thermal measurements were taken during construction, before the cladding was installed. Since the structure is now completely enclosed with insulating cladding, it is an excellent candidate for thermal imaging at this stage of the commissioning. Thermal images of the structure are presented, showing the actual temperature distribution of the LMT alidade structure and reflector. The images are taken from a consistent set of positions to show the how the structural temperature distribution evolves over day and night conditions.

Two types of field measurements on the Atacama Submillimeter Telescope Experiment 10-m antenna have been made to diagnose antenna oscillations in strong wind gusts and to reduce pointing errors due to static/quasi-static wind loadings. The measurements with seismic accelerometers on the reflector have been compared with those from axis angle encoders. Our results have confirmed that the dominant wind effects are at low frequencies, and have found that twist and pitching motion of yoke arms are the dominant source of pointing jitters and decrease with frequency along the Kolmogorov slope of -5/3. In the range from about 1 to 10 Hz, the servo-loop excites and dominates pointing error oscillations. For azimuth oscillations, the frontal wind has the largest effects, compared with side- or tail-wind. To improve pointing performance against static/quasi-static wind effects, we have implemented and tested an auxiliary auto-pointingcorrection system with a lookup table compiled from all-sky pointing measurements under strong winds, invoking the Taylor's "frozen turbulence" hypothesis. We have successfully demonstrated that use of upwind data from a nearby anemometer helps to reduce the pointing errors of static wind effects from 2.4 " rms (correction OFF) to 1.2 " rms (correction ON) under a mean wind speed of 9.3 m s^-1.

The Large Synoptic Survey Telescope (LSST) primary/tertiary monolithic mirror will be fabricated as a single cast borosilicate substrate that requires an extensive thermal control system. The relatively large coefficient of thermal expansion (CTE) of borosilicate glass requires the thermal system maintain differences throughout the mirror to below 0.1C. The thermal control system is also required to take full advantage of the relatively thin glass sections for good tracking of ambient temperatures. A modified version of the thermal control system utilized on the Magellan telescope primary mirror will provide adequate cooling. This type of system supplies coolant to multiple on-board blowers in the mirror cell. Each blower contains a fan and a heat exchanger supplying conditioned and mildly pressurized air to the mirror cell. The mirror cell then acts as an air plenum which distributes the air through individual nozzles to each honeycomb cell of the mirror. Unlike previous systems, each LSST blower assembly will incorporate individual air temperature and air flow control systems. Since air can be more accurately heated than cooled, the air will be initially slightly overcooled and then reheated electrically to match the ambient air temperature. Based on thermal sensors in the mirror, the optimum cooling air flow rate to balance mirror thermal distortion and mirror seeing will be determined and enforced by the variable speed fans on the blower assemblies. To further equalize the cooling throughout the mirror, the coolant flow system has also been designed to provide inherently equal coolant flow to each blower assembly.

The Gemini Planet Imager (GPi) is an instrument that will mount to either of two nominally identical Telescopes, Gemini North in Hawaii and Gemini South in Chile, to perform direct imaging and spectroscopy of extra-solar planets. This 2,000-kg instrument has stringent mass, center-of-gravity, flexure, and power constraints. The Flexure Sensitive Structure (FSS) supports the main opto-mechanical sub-systems of the GPi which work in series to process and analyse the telescope optical beam. The opto-mechanical sub-systems within the FSS are sensitive to mechanical vibrations, and passive damping strategies were considered to mitigate image jitter. Based on analysis with the system finite element model (FEM) of the GPi, an array of 1-kg tuned mass dampers (TMDs) was identified as an efficient approach to damp the first two FSS flexural modes which are the main sources of jitter. It is estimated that 5% of critical damping can be added to each of these modes with the addition of 23 kg of TMD mass. This estimate is based on installing TMD units on the FSS structural members. TMD mass can be reduced by nearly 50% if the units can be installed on the opto-mechanical sub-systems within the FSS with the highest modal displacements. This paper describes the structural design and vibration response of the FSS, modal test results, and plans for implementation of the TMDs. Modal measurements of the FSS structure were made to validate the FEM and to assess the viability of TMDs for reducing jitter. The test configuration differed from the operational one because some payloads were not present and the structure was mounted to a flexible base. However, this test was valuable for understanding the primary modes that will be addressed with the TMDs and measuring the effective mass of these modes.

Associated to tracking capabilities, the main axes control system of the E-ELT is the first correcting system in the chain of control loops for reducing the image motion (tip/tilt) caused by perturbations on the telescope. The main objective of the closed-loop performance analysis of the axes is to evaluate the trade offs for the choice of control system hardware, i.e. specification and location of the motors and sensors (encoders/tachometers). In addition, it defines the design constraints and requirements (actuator stroke and bandwidth) of other correcting systems in the chain: the field stabilization (M5 unit) and adaptive deformable mirror (M4 unit). In this paper the main axes control analysis of E-ELT is presented and the performance of telescope in face of external perturbations such as wind and imperfections of the drive (cogging/ripple) and sensing (noise) systems is evaluated. The performance metric is the wavefront error at the focal plane which is derived from the mechanical motion of the telescope's optical elements together with their respective optical sensitivities.

Hexapods are finding increased use in telescope applications for positioning large payloads. Engineers from The University of Texas at Austin have been working with engineers from ADS International to develop large, high force, highly precise and controllable hexapod actuators for use on the Wide Field Upgrade (WFU) as part of the Hobby Eberly Telescope Dark Energy Experiment (HETDEX)^‡. These actuators are installed in a hexapod arrangement, supporting the 3000+ kg instrument payload which includes the Wide Field Corrector (WFC), support structure, and other optical/electronic components. In addition to force capability, the actuators need to meet the tracking speed (pointing) requirements for accuracy and the slewing speed (rewind) requirements, allowing as many observations in one night as possible. The hexapod actuator stroke (retraction and extension) was very closely monitored during the design phase to make sure all of the science requirements could be met, while minimizing the risk of damaging the WFC optical hardware in the unlikely event of a hexapod actuator or controller failure. This paper discusses the design trade-offs between stiffness, safety, back-drivability, accuracy, and leading to selection of the motor, high ratio worm gear, roller screw, coupling, end mounts, and other key components.

The Magellan Baade and Clay telescopes regularly produce images of ~0.5" in natural seeing. We review efforts to improve collimation, active optics response, and telescope guiding and pointing to optimize the performance of the telescopes. Procedures have been developed to monitor and analyze image quality delivered by the imaging science instruments. Improved models have been developed to correct for flexure of the telescope and primary mirror under gravity loading. Collimation has been improved using a "two-probe" Shack-Hartman technique to measure field aberrations. Field acquisition performance has been improved by implementing an open loop model for the primary mirror control. Telescope pointing has been improved by regular monitoring and adjustments to improve acquisition times.

A 4-mirror prime focus corrector is under development to provide seeing-limited images for the 10-m aperture Hobby- Eberly Telescope (HET) over a 22 arcminute wide field of view. The HET uses an 11-m fixed elevation segmented spherical primary mirror, with pointing and tracking performed by moving the prime focus instrument package (PFIP) such that it rotates about the virtual center of curvature of the spherical primary mirror. The images created by the spherical primary mirror are aberrated with 13 arcmin diameter point spread function. The University of Arizona is developing the 4-mirror wide field corrector to compensate the aberrations from the primary mirror and present seeing limited imaged to the pickoffs for the fiber-fed spectrographs. The requirements for this system pose several challenges, including optical fabrication of the aspheric mirrors, system alignment, and operational mechanical stability.

The NASA Infrared Telescope Facility is engaged in a long-term program to improve the image quality of the telescope. One element of the program is to minimize the static aberrations. The largest static aberration is spherical aberration, although aberrations caused by zonal polishing rings and support-pad print-through on the primary mirror are also significant. To correct these static wave front errors, a new secondary mirror is being fabricated with a custom, phase compensating surface. Since the as-built optical specifications for the IRTF mirrors have been lost, a configurable multimode instrument was fabricated for use at both the prime and Cassegrain foci to characterize the primary mirror and to measure the wave front errors at both foci. The instrument modes include a focal plane camera, a knife-edge tester, a pupil viewer, a Hartmann wave front sensor, a calibrator, and an on-axis guider. Test results from the prime focus show that the primary mirror has an incorrect conic surface and is poorly supported, which results in a fixed amount of spherical aberration and variable amounts of astigmatism, coma, and trefoil. Cassegrain focal plane results show that the original secondary mirror mount system also induces aberrations. Two new secondary mirrors have been made and at least one of the mirrors will have a custom surface, using ion beam polishing methods, to correct these static aberrations. An analysis is presently underway to determine the optimum compensating surface to be applied by ion beam polishing.

Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Meteorological (cloud cover, temperature, pressure, wind, and humidity) and DIMM seeing data have been obtained at three potential sites, and are compared with identical data taken at the site of the twin Magellan 6.5m telescopes. In addition, measurements of the turbulence profile of the free-atmosphere above LCO have been collected with a MASS/DIMM. Furthermore, we consider photometric quality, light pollution, and precipitable water vapor (PWV). LCO, and Co. Las Campanas in particular, have dark skies, little or no risk of future light pollution, excellent seeing, moderate winds, PWV adequate for mid-IR astronomy during a reasonable fraction of the nights, and a high fraction of clear nights overall. Finally, Co. Las Campanas meets or exceeds all the defined science requirements.

In support of characterization of potential sites for the European Extremely Large Telescope (E-ELT) the European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the astrometeorology group of the Universidad Valparaiso have jointly established an improved understanding of atmospheric precipitable water vapour (PWV) above ESO's La Silla Paranal Observatory. In a first step, 8 years worth of high resolution near-IR spectra taken with VLT-UVES have been statistically analysed to reconstruct the PWV history above Paranal. To this end a radiative transfer model of Earth's atmosphere (BTRAM) developed by ISIS has been used. A median PWV of 2.1 mm is found for Paranal based on UVES data covering the period 2001-2008. Furthermore we conclude that Paranal can serve as a reference site for Northern Chile due to the stable atmospheric conditions in the region. The median offset between Paranal and Armazones is derived to be 0.3 mm, but local arbitrary variations of a few tenths of a mm between the sites have been found by measurement. In order to better understand the systematics involved two dedicated campaigns were conducted in August and November 2009. Several methods for determining the water column were employed, including radiosonde launches, continuous measurements by infrared radiometer, and VLT instruments operating at various wavelengths: CRIRES, UVES, VISIR and X-shooter. In a first for astronomical instruments all methods have been evaluated with respect to the radiosondes, the established standard in atmospheric research. Agreement between the radiosondes and the IR radiometer (IRMA) is excellent while all other astronomical methods covering a wavelength range from 700 - 20000 nm have also been successfully validated in a quantitative manner. All available observations were compared to satellite estimates of water vapour above the observatory in an attempt to ground-truth the satellite data. GOES can successfully be used for site evaluation in a purely statistical approach since agreement with the radiosondes is very good on average. For use as an operational tool at an observatory GOES data are much less suited because of significant deviations depending on atmospheric conditions. We propose to routinely monitor PWV at the VLT and to use it as an operational constraint to guide scheduling of IR observations at Paranal. For the E-ELT we find that a stand-alone high time resolution PWV monitor will be essential for optimizing the scientific output.

Remote turbulence sensing in the first 100m above ground using lunar scintillation has revealed that the seeing measured by regular site monitors can be over-estimated. This explains the well-known discrepancy between the VLT image quality and the seeing measured by the DIMM at Paranal. The concept of "site seeing" needs to be critically reviewed, considering strong dependence of this parameter on the height of site monitors and on the local turbulence in their immediate vicinity. Higher resolution of ground-based telescopes can be reached if we accept that the natural seeing can be better than shown by the DIMMs and that the contribution of telescope and its environment to the seeing can be significant on nights with superb conditions. This is particularly relevant to the wide-angle optical and IR telescopes which do not rely on adaptive optics. Eventually, a wide-angle adaptive optics will remove local and instrumental distortions and will deliver images truly limited by the atmosphere.

In the framework of the E-ELT project a prospecting campaign was launched by the ESO to select the site that will host the next generation of optical telescopes of 42 m diameter. Moroccan Anti-Atlas (Jbel Aklim) was selected as well as other sites (ORM, Ventarrones and Macon) to be a possible potential location that will house the E-ELT. In this paper we first present the reasons for the choice of Jbel Aklim as a E-ELT candidate through various exploration campaigns that we have achieved. The second part concerns description of instruments used. Finally we will present the preliminary results of the meteorological and MASS-DIMM measurements.

A characterization of the optical turbulence vertical distribution and all the main integrated astroclimatic parameters derived from the C²_N and the wind speed profiles above Mt. Graham is presented. The statistic includes measurements related to 43 nights done with a Generalized Scidar (GS) used in standard configuration with a vertical resolution of ~1 km on the whole 20-22 km and with the new technique (HVR-GS) in the first kilometer. The latter achieves a resolution of ~ 20-30 m in this region of the atmosphere. Measurements done in different periods of the year permit us to provide a seasonal variation analysis of the C²_N. A discretized distribution of the typical C²_N profiles useful for the Ground Layer Adaptive Optics (GLAO) simulations is provided and a specific analysis for the LBT Laser Guide Star system ARGOS case is done including the calculation of the 'gray zones' for J, H and K bands. Mt. Graham confirms to be an excellent site with median values of the seeing without dome contribution equal to 0.72", the isoplanatic angle equal to 2.5" and the wavefront coherence time equal to 4.8 msec. We provide a cumulative distribution of the percentage of turbulence developed below H* where H* is included in the (0,1 km) range. We find that 50% of the whole turbulence develops in the first 80 m from the ground. The turbulence decreasing rate is very similar to what has been observed above Mauna Kea.

Atmospheric optical turbulence is the main driver of wavefront distortions which affect optical telescope performance. Therefore, many techniques have been developed to measure the optical turbulence strength along the line of sight. Based on data collected with the MASS (Multi Aperture Scintillation Sensor), we show that a large sample of such measurements can be used to assess the average three dimensional turbulence distribution above ground. The use of, and a more sophisticated instrumental setup for, such turbulence tomography will be discussed.

As part of a program to measure and evaluate atmospheric turbulence on mountains at the most northerly tip of North America, we have deployed two SODARs and a lunar scintillometer at the Polar Environment Atmospheric Research Lab (PEARL) located on a 600m-high ridge near Eureka on Ellesmere Island, at 80° latitude. This paper discusses the program and presents a summary of ground-layer turbulence and seeing measurements from the 2009-10 observing season.

The high altitude Antarctic sites of Dome A and the South Pole offer intriguing locations for future large scale optical astronomical Observatories. The Gattini project was created to measure the optical sky brightness, large area cloud cover and aurora of the winter-time sky above such high altitude Antarctic sites. The Gattini- DomeA camera was installed on the PLATO instrument module as part of the Chinese-led traverse to the highest point on the Antarctic plateau in January 2008. This single automated wide field camera contains a suite of Bessel photometric filters (B, V, R) and a long-pass red filter for the detection and monitoring of OH emission. We have in hand one complete winter-time dataset (2009) from the camera that was recently returned in April 2010. The Gattini-South Pole UV camera is a wide-field optical camera that in 2011 will measure for the first time the UV properties of the winter-time sky above the South Pole dark sector. This unique dataset will consist of frequent images taken in both broadband U and B filters in addition to high resolution (R~5000) long slit spectroscopy over a narrow bandwidth of the central field. The camera is a proof of concept for the 2m-class Antarctic Cosmic Web Imager telescope, a dedicated experiment to directly detect and map the redshifted lyman alpha fluorescence or Cosmic Web emission we believe possible due to the unique geographical qualities of the site. We present the current status of both projects.

For continuous observation at locations that are inhospitable for humans, the desirability of autonomous observatories is self evident. PLATO, the 'PLATeau Observatory' was designed to host an easily configurable instrument suite in the extremely cold conditions on the Antarctic plateau, and can provide up to 1 kW of power for the instruments. Powered by jet fuel and the Sun, PLATO and its instruments have been taking nearly uninterrupted astronomical science and sitetesting data at Dome A, the coldest, highest and driest location¹ on the Antarctic Plateau, since their deployment by the 24th Chinese expedition team in January 2008. At the time of writing, PLATO has delivered a total uptime of 730 days. Following a servicing mission by the 25th Chinese expedition team in 2008-9, PLATO has achieved 100% up-time (520 days) and has been in continuous contact with the rest of the world via its Iridium satellite modems. This paper discusses the performance of the observatory itself, assesses the sources of energy and dissects how the energy is divided between the core observatory functions of instrument power, heating, control and communication.

Dome Fuji, on the Antarctic plateau, is expected to be one of the best sites for infra-red astronomy. In Antarctica, the coldest, driest air on Earth provides the deepest detection limit. Furthermore, the weak atmospheric turbulence above the boundary layer allows for high spatial resolution. We plan to perform site-testing at Dome Fuji during the austral summer of 2010-2011. This will be the first observation to use an optical/infra-red telescope at Dome Fuji. This paper introduces the Antarctic Infra-Red Telescope with a 40cm primary mirror (AIRT40) which will be used in this campaign; it is an infra-red Cassegrain telescope with a fork equatorial mount. AIRT40 will be used for not only site testing (measurement of seeing and sky background) and daytime astronomical observation during this summer campaign, but also for remote scientific observations during the 2012-2014 winter-over campaign. For this purpose, AIRT40 has to work well even at -80 degree Celsius. Therefore, we accounted for the thermal contraction of the materials while designing it, and made it with special parts which were tested in a freezer. For easy operation, many handles for transportation and a polar alignment stage were installed. Moreover, we confirmed that this telescope has enough pointing, tracking, and optical accuracy for the summer campaign through the test observations at Sendai, Japan. Because of these preparations AIRT40 is suited for observations at Dome Fuji. In the 2010-2011 campaign AIRT40 will be used to measure the seeing, infra-red sky background, and to observe Venus.

Prelimenary site testing led by Chinese Center of Antarctic Astronomy (CCAA) shows that the highest point of the Antarctic Plateau Dome A has very clear sky, good seeing, slow wind, low boundary layer and very low precipitable water vapour which make it the best site on earth for optical/IR and sub-mm observations. Chinese Small Telescope ARray (CSTAR) was installed at Dome A in 2008 and have automatically observed for about 3 antarctic winters. The three Antarctic Schmidt telescopes(AST3) with entrance pupil diameter 500mm are the second antarctic project proposed by CCAA and the first AST are being constructed in NIAOT now which is planned to be mounted on Dome A at the beginning of 2011. All the tracking components were tested in the low temperature chamber and an adaptive defrosting method is designed to prevent the frost building up on the schmidt plate.

ICE-T, the International Concordia Explorer Telescope, is under final design by an international consortium led by the Astrophysical Institute Potsdam AIP, Germany, and is intended to be placed at the French-Italian Concordia Station on Dome C in Antarctica. Experience with smaller telescopes at Concordia has shown that under the weather conditions at this site - with mean outside temperatures of -60° to -80° C and temperature changes of 20° in short time intervals - the ice-accumulation on the optical components during observation is a major problem. Also, energy consumption at this site should be minimized because fuel transport to the site is very costly. The paper describes the thermal concept for the telescope where the waste energy of the instrument electronics is used for heating the front surfaces of the Schmidt optics. All other parts of the telescope are protected by an insulated smooth cladding against the harsh outside environment. The effectiveness of the thermal concept is verified by CFD (Computer Fluid Dynamics) calculations.

The CCAT Project is an effort to construct a 25 meter aperture telescope above 5600 meters altitude operating down to wavelengths as short as 200 μm. CCAT has developed some new and innovative approaches to telescope and optics design, added new partners to the project, and has plans for substantially increased activities over the next two years. Begun by Cornell University and the California Institute of Technology, CCAT currently has six national and university partners. Funding has been increased and significant technical activities are underway to investigate the key enabling technologies. Areas of development include telescope optical design, mount design, application of CFRP materials to the telescope, sensing and control of primary mirror segments, and control system architecture. Schedules and budgets for the Project have been updated and an overall approach leading to first light in 2016-2017 has been developed. CCAT promises to have a significant scientific impact on submillimeter astronomy and the prospects for success has never looked better.

The 25-meter Giant Magellan Telescope (GMT) is one of the next generation of extremely large ground-based optical/infrared telescopes. GMT is currently under development by a consortium of major US and international university and research institutions. The telescope will be located at the Las Campanas Observatory in Chile. The GMT Project is mid-way through its Design Development Phase. This paper summarizes the organizational structure and status of the GMT Project and recent progress in the technical development of the various GMT subsystems.

In this paper we present optical designs for an entirely new approach to extremely large telescopes and telescopes with spherical primary mirrors. The key feature is a novel optical system referred to as the improved spherical aberration corrector (ISAC). This corrector works exceptionally well for post prime focus applications, as well as for Cassegrain and Couder/Schwarzschild-like optical systems with both spherical primary and spherical secondary mirrors. The Couder/Schwarzschild configuration also adapts to a pancake configuration where the telescope is physically shorter than its aperture.

The enclosure design for the Thirty-Meter Telescope is now in final design phase. The focus of design activities now turns to developing details and strategies enabling efficient manufacturing, construction and operations of the enclosure on the selected Mauna Kea site. This paper provides an overview of the enclosure design and an outline of the proposed construction plan.

Status of the Feasibility Study of E-ELT, the ESO 42 m Extreme Large Telescope, with emphasis on the Dome architecture and erection. The Dome is a hemispherical shape concept servomechanism 86 m high, with an external diameter of 108 m and a 45 m wide Observing Slit. Such dimensions require the application of big structure technologies (like stadium, hangar etc), in order to comply with manufacturing, transport and assembly constrains. The mentioned technology must be fitted with mechanical and control system constrains required by this kind of servo-system. Mechanisms inside the Dome must be sufficiently light and stiff, and composite materials meet the above mentioned requirements. The management of the whole mass is extremely important for the services and power consumption. This paper describes how the above mentioned problems were handled during the E-ELT Dome Feed study.

As a continuation of the Preliminary Design of the Dome for the European Extremely Large Telescope (E-ELT) proposed by IDOM, the Detail Design for the E-ELT Dome has been developed with the objective of optimizing the design to minimize the manufacturing, erection and operation costs. The proposed design is based on a hemispherical dome tightly fitted to the dome design volume to minimize the enclosed volume and consequently the cost. The large observing slit, large as compared to the dome diameter, is covered by means of two horizontal biparting doors. This paper summarizes the most significative changes in the design and the approach followed by IDOM for the detailed design process, with emphasis in the construction process. The design work presented in this paper has been performed under contract with the European Southern Observatory (ESO).

The 25 meter aperture Cornell Caltech Atacama Telescope (CCAT) will provide an enormous increase in sensitivity in the submillimeter bands compared to existing observatories, provided it can establish and maintain excellent image quality. To accomplish this at a very low cost, it is necessary to conduct accurate engineering trades, including the most effective segment and wavefront sensing and control approach, to determine the best method for continuously maintaining wavefront quality in the operational environment. We describe an integrated structural/optical/controls model that provides accurate performance prediction. We also detail the analysis methods used to quantify critical design trades.

The Giant Magellan Telescope (GMT) Mirror cells provide positioning, support, with active optics compensation, and thermal control of the seven 8.4 meter primary mirror segments. Each mirror cell is a large steel welded structure, and in the case of the outer off axis segments, is designed to be interchangeable for any one of the 6 possible mirror positions. The mirror support and active optics compensation are provided through a series of single axis and three axis pneumatic actuators that control the force used to support the mirror at a total of 165 positions and allows for support of the mirror in any one of the six positions. Mirror positioning is provided by a stiff hexapod actuator system between the mirror and the mirror cell. Mirror thermal control is provided by a series of fans that pressurize the mirror cell and condition the air before it is directed into the mirror through 1700 nozzles.

Latest progress on Tinsley methods are described for faster stress mirror polishing of the Thirty Meter Telescope primary mirror segments. These methods are outlined, and full scale segment data results are presented. The Tinsley SMP process complements additional processes at ITT Industries Space Systems, with the potential to effectively optically finish all TMT segments.

The 25-m aperture Cornell Caltech Atacama Telescope (CCAT) will have a primary mirror that is divided into 162 individual segments, each of which is equipped with 3 positioning actuators. This paper presents a mathematical description of the telescope, its actuators and sensors, and uses it to derive control laws for figure maintenance. A Kalman Filter-based Optical State Estimator is used to continuously estimate the aberrations of the telescope; these are used in a state-feedback controller to maintain image quality. This approach provides the means to correct for the optical effects of errors that occur in un-actuated degrees of freedom, such as lateral translations of the segments. The control laws are exercised in Monte Carlo and simulation analysis, to bound the closed-loop performance of the telescope and to conduct control design trades.

CCAT will be a 25 m diameter submillimeter-wave telescope that will operate inside a dome located on Cerro Chajnantor in the Atacama Desert. The telescope must have high aperture efficiency at a wavelength of 350 microns and good performance out to a wavelength of 200 microns. A conceptual design for a carbon fiber reinforced plastic (CFRP) truss and primary reflector support truss has been developed. This design yields a telescope with a net ½ wave front error of <10 microns using a lookup table to adjust the segment actuators to compensate for gravitational deflections. Minor corrections may be required to compensate for the expected 20 C temperature excursions. These can be handled using a coarse lookup table.

The segments in the Keck telescopes are routinely phased using a Shack-Hartmann wavefront sensor with subapertures that span adjacent segments. However, one potential limitation to the absolute accuracy of this technique is that it relies on a lenslet array (or a single lens plus a prism array) to form the subimages. These optics have the potential to introduce wavefront errors and stray reflections at the subaperture level that will bias the phasing measurement. We present laboratory data to quantify this effect, using measured errors from Keck and two other lenslet arrays. In addition, as part of the design of the Thirty Meter Telescope Alignment and Phasing System we present a preliminary investigation of a lenslet-free approach that relies on Fresnel diffraction to form the subimages at the CCD. Such a technique has several advantages, including the elimination of lenslet aberrations.

This paper presents a recent progress in designing a nanometer-accurate inductive-type of edge sensor. A new technology of Direct Deposit on Glass (DDG) has been developed. The DDG technology also has high rate of reproducibility and is suitable for the mass production and still be a very cost-effective solution. The sensor designs are fully optimized using mechanical and EM modeling for specific metrology needs. We discuss briefly on various electronic architectures and their impacts on the maintainability of the system. We conclude the paper by showing the experimental results.

Control of primary segmented mirror of an extremely large telescope with large number of actuators and sensors and multiple control loops is a complex problem. The designer of the M1 unit is confronted to the dilemma of trade-off between the relatively though performance requirements and the robust stability of the control loops. Another difficulty arises from the contradictory requirements of the stiffness of the segment support system and position actuators for wind rejection on one hand and vibration mitigation on other hand. The presence of low frequency mechanical modes of the back structure and possible interaction of the large number of control loops through such structure could be a limiting factor for achieving the required control bandwidths. To address these issues a better understanding of dynamical behavior of segmented mirror is necessary. This paper addresses the trade-offs on dynamical aspects of the M1 segmented mirror and the robust stability conditions of various control loops.

The Thirty Meter Telescope has 492 primary mirror segments, each incorporated into a Primary Segment Assembly (PSA), each of which in turn has three actuators that control piston, tip, and tilt, for a total of 1476 actuators. Each actuator has a servo loop that controls small motions (nanometers) and large motions (millimeters). Candidate actuators were designed and tested that fall into the categories of "hard" and "soft," depending on the offload spring stiffness relative to the PSA structural stiffness. Dynamics models for each type of actuator are presented, which respectively use piezo-electric transducers and voice coils. Servo design and analysis are presented that include assessments of stability, performance, robustness, and control structure interaction. The analysis is presented for a single PSA on a rigid base, and then using Zernike approximations the analysis is repeated for 492 mirror segments on a flexible mirror cell. Servo requirements include low-frequency stiffness, needed for wind rejection; reduced control structure interaction, specified by a bound on the sensitivity function; and mid-frequency damping, needed to reduce vibration transmission. The last of these requirements, vibration reduction, was found to be an important distinguishing characteristic for actuator selection. Hard actuators have little inherent damping, which is improved using PZT shunt circuits and force feedback, but still these improvements were found to result in less damping than is provided by the soft actuator. Results of the servo analysis were used for an actuator down-select study.

Finite element models (FEMs) are being used extensively in the design of the Thirty Meter Telescope (TMT). One such use is in the design and analysis of the Primary Segment Assembly (PSA). Each PSA supports one primary mirror segment on the mirror cell, as well as three actuators, which are used to control three degrees of freedom - tip, tilt, and piston - of the mirror segment. The dynamic response of the PSA is important for two reasons: it affects the response of the mirror to fluctuating wind forces, and high-Q modes limit the bandwidth of the control loops which drive the actuators, and impact vibration transmissivity, thereby degrading image quality. We have completed a series of tests on a prototype PSA, in which the dynamic response was tested. We report on the test methods used to measure the dynamic response of the PSA alone and with candidate actuators installed, and we present comparisons between the measured response and FEM predictions. There is good agreement between FEM predictions and measured response over the frequency range within which the dynamic response is critical to control system design.

The largest optical telescope in the world will be the E-ELT. Its primary mirror will be 42m in diameter. This mirror will consist of 984 hexagonal segments that are all individually supported. Each mirror will be controlled in six DOF while local shaping of the segments is provided by so called warping harnesses. These will correct for focus, astigmatism and trefoil. Hence a mirror with an extreme diameter to thickness ratio of almost 30 is obtained. Its support structure must guarantee a maximum surface form error of 30 nm rms independent of the segment attitude. Furthermore its stiffness to mass ratio must allow natural frequencies of 50Hz or higher to obtain sufficient bandwidth for the actuators that control the piston and tip/tilt of the segment. Designing such structure is a challenge that has been successfully completed. Three prototypes have been built and are about to be delivered to ESO. This paper discusses the main performance requirements and how they could be transferred into an elegant structure design. Furthermore an overview will be given on the main performance parameters in order to see whether the present design can be further optimized.

The Wind Evaluation Breadboard (WEB) is a primary mirror and telescope simulator formed by seven aluminium segments, including position sensors, electromechanical support systems and support structures. WEB has been developed to evaluate technologies for primary mirror wavefront control and to evaluate the performance of the control of wind buffeting disturbance on ELT segmented mirrors. For this purpose WEB electro-mechanical set-up simulates the real operational constrains applied to large segmented mirrors. This paper describes the WEB assembly, integration and verification, the instrument characterisation and close loop control design, including the dynamical characterization of the instrument and the control architecture. The performance of the new technologies developed for position sensing, acting and controlling is evaluated. The integration of the instrument in the observatory and the results of the first experiments are summarised, with different wind conditions, elevation and azimuth angles of incidence. Conclusions are extracted with respect the wind rejection performance and the control strategy for an ELT. WEB has been designed and developed by IAC, ESO, ALTRAN and JUPASA, with the integration of subsystems of FOGALE and TNO.

The primary mirror control system for the Thirty Meter Telescope (TMT) maintains the alignment of the 492 segments in the presence of both quasi-static (gravity and thermal) and dynamic disturbances due to unsteady wind loads. The latter results in a desired control bandwidth of 1Hz at high spatial frequencies. The achievable bandwidth is limited by robustness to (i) uncertain telescope structural dynamics (control-structure interaction) and (ii) small perturbations in the ill-conditioned influence matrix that relates segment edge sensor response to actuator commands. Both of these effects are considered herein using models of TMT. The former is explored through multivariable sensitivity analysis on a reduced-order Zernike-basis representation of the structural dynamics. The interaction matrix ("A-matrix") uncertainty has been analyzed theoretically elsewhere, and is examined here for realistic amplitude perturbations due to segment and sensor installation errors, and gravity and thermal induced segment motion. The primary influence of A-matrix uncertainty is on the control of "focusmode"; this is the least observable mode, measurable only through the edge-sensor (gap-dependent) sensitivity to the dihedral angle between segments. Accurately estimating focus-mode will require updating the A-matrix as a function of the measured gap. A-matrix uncertainty also results in a higher gain-margin requirement for focus-mode, and hence the A-matrix and CSI robustness need to be understood simultaneously. Based on the robustness analysis, the desired 1 Hz bandwidth is achievable in the presence of uncertainty for all except the lowest spatial-frequency response patterns of the primary mirror.

While the ultimate proof of telescope performance is in the quality and amount of science it is able to produce, commissioning results give a good and in-depth indication of how well a telescope facility actually performs, both in terms of sub-system commissioning and on-sky commissioning. Results from LBT commissioning activities are presented, along with lessons learned and a discussion of the challenges for future commissioning required to prepare the LBT for true Binocular Operation and ultimately interferometric operations.

VISTA¹ is an infrared survey telescope which delivers 0.5 arc second images over a 1.65 degree diameter unvignetted field of view. The project was split into separate work-packages, which after successful individual acceptance, were integrated by the project office. The main mechanical integration is the matching up of two sides of a controlled interface and should be a straightforward process. This covers the mounting of the M2 Hexapod, the installation of the M2 mirror assembly onto the M2 Hexapod, the M1 attachment to the M1 support system components and installation of the instrument mass simulator. The second stage of this integration is the mechanical alignment of the optical elements (i.e. M1 & M2) to the telescope mechanical axis. This is achieved through use of jigs and alignment equipment combined with the inbuilt adjustment in both the M2 on it's Hexapod and the manual adjustment of the M1 on its positional definers. This then leaves the telescope in a state ready to start optical commissioning using a Shack Hartman wavefront sensor. This paper deals with the mechanical integration and alignment of the telescope components up to the start of optical commissioning. There will be discussion of the build-up of information through the separate component acceptance details, to the equipment methodology, preparation and actual integration of the different systems. There will also be discussion of lessons learned.

The initial operation of the Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT) main axis servo system showed promising results, with subarcsecond RMS performance even without a complete drive system. Since that time, there has been substantial progress in the commissioning of the system. For example, the alignment and grouting of the elevation axis gear rims is completed and all motors have been installed. This has allowed full-speed operation in both axes and has enabled some tuning of the servo system. The digital control architecture of the LMT allows direct measurement of the frequency response function of the system. Further, it allows the rate loop and position loop to be configured either as a classical proportional-integral (PI) controller or as a model-based (e.g., LQG) state-space controller. Finally, the architecture permits additional special-purpose control features to be implemented, including friction compensation and lookup table feedforward to reduce nonlinear effects. The measured FRF results are presented, and have been applied to tuning of the control system, with a resulting improvement in performance. Results are presented for the LMT main axis slewing, pointing, and tracking performance. Additionally, results are presented from initial experiments in applying lookup table feedforward to improve performance in crossing joints in the azimuth track.

For large telescopes, management of axis friction presents a significant challenge. In some cases, this is avoided or minimized in the design stage by employing hydrostatic bearings. However, the main axis servo systems of many large telescopes must cope with bearing or wheel friction. This friction affects or limits servo control performance in several ways. The most obvious is the stick-slip limit cycle that is characteristic of trying to hold position with an integrating control system in the presence of friction. If it is not taken into account, friction also introduces effects into the state estimation in model-based controllers. There are several standard approaches to friction compensation. These include dithering (introducing a noise signal to the drive motors), direct Coulomb friction compensation (sending an additional torque based on the rate command), and adaptive techniques based on monitoring of the final drive velocities. In this work, we experimentally compare different friction compensation approaches on the static positioning performance of the Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT). Single and double integrator systems are investigated, as well as direct Coulomb friction compensation.

Large thin meniscus mirrors use force-controlled shape actuators to obtain the required optical performance. The shape actuators can be interpreted as an advancement of classical mirror supports as whiffle trees or iso-static levers, which worked purely mechanical. The paper develops, after a short historical overview, the theoretical background of mirror mechanics. Different combinations of force-controlled shape actuators with mechanical, hydraulic or pneumatic whiffle trees or iso-static levers are analyzed in regard of their impact on optical performance, dynamic and control behavior. The investigations were the basis for the choice of the shape actuator system for the E-ELT M2, executed by MT Mechatronics under an ESO contract in 2008-09.

The VISTA Telescope¹ is obtaining superb survey images. The M1 support system is essential to image quality and uses astatic pneumatic supports to balance the M1 against the varying effects of gravity and wind, with four axes being actively controlled via software and CANbus. The system also applies externally determined active optics force patterns. The mechanical, electronic, software and control design and as-built operation of the system are described, with the practical design points discussed.

The Large Synoptic Survey Telescope (LSST) primary/tertiary (M1M3) mirror cell assembly supports both on-telescope operations and off-telescope mirror coating. This assembly consists of the M1M3 monolith mirror, the mirror support systems, the thermal control system, a stray light baffle ring, a laser tracker interface and the supporting steel structure. During observing the M1M3 mirror is actively supported by figure control actuators and a hexapod. The M1M3 figure control actuators distribute the load to safely support the glass mirror and actively control its shape. The position of the mirror relative to the mirror cell is controlled by a set of six hardpoints (displacement controlled actuators) that form a large hexapod. When the active system is not operating the mirror is supported by a separate passive support system. The center of the mirror cell supports a laser tracker which measures the relative position of the camera and secondary mirror for alignment by their hexapods. The mirror cell design height of 2 meters provides ample internal clearance for installation and maintenance of mirror support and thermal control systems. The mirror cell also functions as the bottom of the vacuum chamber during coating. Consequently, to withstand the vacuum-induced stress the M1M3 mirror cell will be fabricated from higher strength steel. The vacuum-induced mirror cell deformations must be isolated from the mirror support system to prevent overstressing the mirror. This is accomplished by utilizing separate truss support systems for the top deck and the vacuum boundary.

Secondary mirrors for large ground-based telescopes often require positioning systems with payload capacities around 1000 kg, relative accuracies within a few micrometers, and resonant frequencies above 15 Hz. A suitable six-legged parallel manipulator, or hexapod, has been developed for sub-micron level positioning of large optical payloads in six degrees of freedom. This 1000 kg class hexapod has tip/tilt rotational ranges of ±1800 arcsec, relative accuracies within 1%, and resolutions of better than ±0.2 arcsec, along with a piston translational range of ±30 mm, relative accuracy within 1%, and resolution of better than ±1 μm. The center of rotation of the system may be placed at an arbitrary location within the overall range limitations. The axial stiffness of each of the six actuators tested greater than 100 N/μm. The actuators use high precision roller screws and employ two degree of freedom universal end-joints. The preload on the joints eliminates backlash due to transitions from tension to compression and maintains friction moment of <10 Nm. An additional rotational degree of freedom is allowed in the body of the actuator to achieve the proper kinematic constraints for the motion platform. The actuators have power-off hold capability to protect against power loss and reduce heat dissipation. Overall heat dissipation has been measured and techniques have been studied to reduce its impact. The paper describes the actuator design and hexapod performance in support of planned use in ground test and validation of the James Webb Space Telescope.

Hexapod systems (6 legged Stewart Platforms), offer advantages in accuracy over other positioning systems and are finding applications in numerous telescopes. However, instruments with increased sophistication for modern telescopes continue to grow in size and required positioning accuracy. This paper details an alternative hexapod configuration and design approach, particularly focused on relatively large, high precision hexapod systems supporting high mass payloads. The new configuration improves accuracy, reduces actuator mass, simplifies design, and reduces system cost but requires modest additional control algorithm sophistication.

A new family of 2 mirror wide field unobscured telescopes have been designed. They are of compact "Schiefspiegler", off axis Cassegrain geometry, incorporating aspheres, tilted and decentered secondary, and tilted focal surfaces. These additional optimization variables allow control of the tilt of the focal surface. Designs range from f/5 to f/16, and provide fully baffled, all reflecting systems with no color, moderately wide diffraction limited fields of view with unobscured aperture MTF. The systems are well suited for use as visual telescopes, CCD camera or high resolution wide field collimator and IR scene projector. The nCUB designs provide a focal surface normal to the gut ray for visual use. The tCUB designs provide collimator telescopes with focal surfaces tilted so that any light reflected from the reticle is eliminated and with it Narcissus. Instead, this reflection can be used to provide a uniform "background" irradiance field. Simple interferometric tests allow straightforward element figuring and system alignment. Examples will be described and compared to current designs. Manufacturing, testing and mounting of the optical system will be briefly discussed.

Lund Observatory is presently designing and constructing a robotic telescope dedicated to studies of the Earth's albedo by measuring the ratio between the intensity of the dark and bright sides of the Moon. The telescope will operate both in broadband and narrow-band modes over the entire visible wavelength range and will transmit observational results back to the operation team over the Internet. Design challenges, in particular related to choice of CCD and stray light suppression, are described, together with the design of the optics, control system, and enclosure. Finally we present results from laboratory tests. The telescope will go into operation in the first half of 2011.

The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design, with an 8.4-meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary feeding a refractive camera design with 3 lenses (0.69-1.55m) and a set of broadband filters/corrector lenses. Performance is excellent over a 9.6 square degree field and ultraviolet to near infrared wavelengths. We describe the image quality error budget analysis methodology which includes effects from optical and optomechanical considerations such as index inhomogeneity, fabrication and null-testing error, temperature gradients, gravity, pressure, stress, birefringence, and vibration.

LCOGT are currently building and deploying a worldwide network of at least fifteen 1-meter and twenty-four 0.4-meter telescopes to three sites in each hemisphere, enabling extended, redundant and optimally continuous coverage of time variable or transient sources. Each site will support two or more 1m telescopes and four or more 0.4m telescopes. All telescope classes provide a full range of optical narrow-band and broad-band UBVRI and ugriZY imaging filters. All telescopes are being equipped with a moving light-bar flatfielding system called Lambert. The 1m network is intended primarily for science observing while the 0.4m network additionally provides educational opportunities to participating schools and institutes. The global network is designed to accommodate multiple science, educational and rapid response capabilities. For LCOGT, the network IS the telescope.

To obtain high resolution infrared image, both low photon efficiency and long wavelength of infrared light requires enough large aperture telescope, but large aperture vacuum windows can hardly achieve high optical quality, so open structure becomes the only viable choice for large infrared solar telescope. In addition to the effects of atmospheric turbulence, open solar telescopes suffer from the heating of the optics by sunlight, especially primary mirror heating. These factors cause the image to shiver and become blurred, and increase infrared observing noise. Since blowing air across the front surface of the primary mirror doesn't have the necessary heat transfer coefficient to remove the absorbed heat load, it must be cooled down to maintained at a temperature between 0K and 2K below ambient air temperature to reduce the effects of turbulence. This paper will introduce some cooling methods and simulation results of primary mirror in large infrared solar telescope. On the other hand, mirror material with nice thermal conductivity can reduce the temperature difference between mirror surface and air, and mirror surface polishing at infrared wavelength can be comparatively easier than at visible wavelength, so it is possible to select low cost metal mirror as primary mirror of infrared solar telescope. To analyze the technical feasibility of metal mirror serving as primary mirror, this paper also give some polishing results of aluminum mirror with electroless nickel coating.

A study is presented for the realization of the heat stop for the 4-m European Solar Telescope EST, whose feasibility study will be completed in 2011. EST is an on-axis Gregorian telescope, equipped with a four-meter diameter primary mirror and primary focal length of about six meters. The heat stop, positioned at the primary focus, must be able to remove a heat load of 13 kW, while maintaining its surfaces very close to room temperature, to avoid the onset of seeing. In order to remove the heat, three configurations have been taken into consideration: 1) a flat 45° inclined heat rejecter, 2) a 45° conical heat rejecter and 3) a heat trap (made of a conical heat rejecter and a cylindrical heat absorber). All devices include an air removal system to avoid the formation of thermal plumes.

New Jersey Institute of Technology, in collaboration with the University of Hawaii and the Korea Astronomy & Space Science Institute, has successfully developed and installed a 1.6 m clear aperture, off-axis New Solar Telescope (NST) at the Big Bear Solar Observatory. The NST will be the largest aperture solar telescope in the world until the 4 m Advanced Technology Solar Telescope (ATST) and 4 m European Solar Telescope (EST) begin operation in the next decade. Meanwhile, the NST will be the largest off-axis telescope before the 8.4 m segmented Giant Magellan Telescope (GMT) comes on-line. The NST is configured as an off-axis Gregorian system consisting of a parabolic primary, prime focus field stop and heat reflector, elliptical secondary and diagonal flats. The primary mirror is made of Zerodur from Schott and figured to a final residual error of 16 nm rms by Steward Observatory Mirror Lab. The final focal ratio is f/52. The 180 circular opening in the field stop defines the maximal square field-of-view. The working wavelength range will cover 0.4 to 1.7 μm in the Coud´e Lab two floors beneath the telescope, and all wavelengths including far infrared at the Nasmyth focus on an optical bench attached to the side of the telescope structure. First-light scientific observations have been attained at the Nasmyth focus and in the Coud´e Lab. This paper presents a detailed description of installation and alignment of the NST. First-light observational results are also shown to demonstrate the validity of the NST optical alignment.

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. This paper summarizes the work performed by IDOM, in the concept design of Transfer Optics system comprising the optomechanics and seeing control of the optical train and surrounding area. Additionally, the possibility of using the Transfer Optics system to compensate the field rotation is currently under study. This work has been performed with the support of the Seventh Framework Programme (FP7) of the European Union.

As part of a larger project for measuring various aspects of foldable domes in the context of EST and with support of the Dutch Technology Foundation STW, we have collected over a year of continuous temperature and humidity measurements, both inside and outside the domes of the Dutch Open Telescope (DOT) on La Palma⁵ and the GREGOR telescope on Tenerife.⁶ In addition, we have measured the wind field around each dome. Although the structure of both domes is similar, the DOT dome has a single layer of cloth, and is situated on top of an open tower. In contrast, the GREGOR dome has a double layer of cloth, and is situated on top of a tower-shaped building. These differences result in large differences in temperature and humidity insulation when the dome is closed. We will present the changes in temperature and humidity one can expect for each dome within one day, and the statistics for the variations throughout a year. In addition, we will show that the main advantage of a foldable dome is the near instantaneous equilibration of the air inside the volume originally enclosed by the dome and that of the environment outside the dome. This property allows one to operate a telescope without needing expensive air conditioning and dome skin temperature control in order to limit dome and shell seeing effects. The measurements give also information about the weather fluctuations at the sites of the domes. It was observed that on small time scales the temperature fluctuations are significantly greater during the day than during the night.

The European Solar Telescope (EST) is a 4-m class solar telescope, which is currently in the conceptual design phase. EST will be located in the Canary Islands and aims at observations with high spectral, spatial and temporal resolution of the solar photosphere and chromosphere. The main purpose of the enclosure is to protect the telescope and instruments from severe weather conditions. An enclosure is also often needed for reducing wind buffeting on the telescope and primary mirror cell, but on the other hand enclosures are generally considered to degrade local seeing. In this contribution we will present the conceptual design of the enclosure for EST. Two different concepts have been studied in more detail: the first being a dome concept with vent gates to enhance local flushing, the other being a retractable enclosure, with an optional windshield. Technically both alternatives seem feasible, but we conclude that the retractable enclosure is the less risky solution, since it allows easier local seeing control and allows the use of a reflecting heat stop in the primary focus. A windshield is effective in reducing wind load on the primary mirror; although preliminary analysis indicate that there are feasible solutions to keep the deformation caused by wind buffeting within the requirements.

EST (European Solar Telescope) is a 4-m class solar telescope, which is currently in the conceptual design phase. EST will be located in the Canary Islands and will aim at high spectral, spatial and temporal resolution observations in the photosphere and chromosphere, using a suite of instruments that can produce efficiently two-dimensional spectropolarimetric information of the thermal, dynamic and magnetic properties of the plasma over many scale heights. The pier is defined as the construction that supports the telescope and the enclosure. It needs a certain height to minimize daytime ground turbulence. At the bottom of the pier a large instrument lab is located, 16 m in diameter and 10 m high. To the pier is attached a service building that accommodates all auxiliary services, possibly together with a separate building. Solid concrete- and open framework piers are compared, in terms of stability, thermal properties and flow characteristics and building structures in terms of construction issues. FE and CFD analysis are used to give qualitative insight in the differences between the alternatives. The preferred alternative is a cone shaped pier surrounded by an open framework.

The Multi-Application Solar Telescope (MAST) is a 50 cm diameter class telescope to be installed by AMOS on the Udaipur Solar Observatory's Island on the Lake Fatehsagar in India. Despite its limited size, the telescope is expected to be competitive with respect to worldwide large and costly projects thanks to its versatility regarding science goals and due to its demanding optomechanical and thermal specification. This paper describes the latest, on-going and forthcoming activities, including factory assembly, integration and testing, followed by on-site installation and commissioning activities. Emphasis is put on the highly demanding thermal control of the telescope, showing development and results for the specific techniques employed on this purpose. Other key features also depicted are the unusual tracking and alignment control solutions on such a specific science target like the Sun.

The European Solar Telescope (EST) is a pan-european project (with 29 partners, plus 7 collaborating institutions, from 14 countries) for the conceptual design study of a 4-meter class solar telescope promoted by the European Association for Solar Telescopes (EAST) to be located in the Canary Islands. The telescope, in the conceptual study, provides a Coudé focus with an F/50 telecentric beam. It is diffraction-limited in a FOV of 1 arcmin and it will be optimized in throughput for several instruments observing simultaneously in a spectral range from 0.39 μm to 2.3 μm. Its innovative concept integrates an optical transfer stage assembling multiconjugated adaptive optics with optical field de-rotation and with a perfect balance of the whole system in terms of polarization being time and wavelength invariant.

The telescope of the Stratospheric Observatory for Infrared Astronomy (SOFIA) has three target acquisition and tracking cameras, the Wide Field Imager (WFI), Fine Field Imager (FFI) and Focal Plane Imager (FPI). All three cameras use Thompson TH7888A CCD sensors (now offered by e2v) which are quite suitable in terms of their geometry and readout speed. However, their quantum efficiency and dark current rate are not comparable to newer CCD sensors now widely used in astronomy. The Deutsches SOFIA Institut (DSI) under contract of the German Aerospace Center (DLR) has therefore initiated an upgrade project of the cameras with high-sensitivity and low dark current CCD sensors, the e2v CCD47-20 BI AIMO. The back-illuminated architecture allows for high quantum efficiency, while the inverted mode operation lowers the dark current significantly. Both features enable the cameras to use fainter stars for tracking. The expected improvements in sensitivity range between 1.2 and 2.5 stellar magnitudes for the three cameras. In this paper we present results of laboratory and on-sky tests with the new sensor, obtained with a commercial camera platform.

After 8 years of development, the telescope of the Stratospheric Observatory for Infrared Astronomy, SOFIA has been integrated into the aircraft and has just started with the first observation test flights. Due to its rather unique environment in the open port of a Boeing 747SP, the telescope optics of SOFIA is exposed to extreme aero-acoustic excitations. The telescope pointing system is equipped with several design features, such as a vibration isolation system, a flexible body control system and - potentially - active mass dampers, to handle excitations in different frequency ranges. Final performance features of these systems will only be available after the first test flights, which will happen in the first half of 2010. A progress report is presented and describes the recent achievements as well as the status of the telescope, and gives an update of the SOFIA pointing system, and the planned commissioning tests.

The SOFIA airborne observatory flies in the lower stratosphere above more than 99.9% of the Earth's water vapor. As low as this residual water vapor is, it will still affect SOFIA's infrared and sub-millimeter astronomical observations. As a result, a heterodyne instrument operating at 183 GHz will be used to measure the integrated water vapor overburden in flight. The accuracy of the measured precipitable water vapor must be 2 microns or better, 3 sigma, and measured at least once a minute. This presentation will cover the design and the measured laboratory performance of this instrument, and will discuss other options for determining the water vapor overburden during the SOFIA Early Science shared-risk period.

The balloon-borne PIPER instrument will observe the polarization in the cosmic microwave background (CMB) at 200, 270, 350, and 600 GHz. Two co-pointed telescopes are placed inside a 3000 L liquid helium dewar and cooled to 1.5 K. The telescopes are arranged so that one measures Stokes parameters Q and V while the other measures U and V . Each telescope consists of a variable-delay polarization modulator (VPM) as the primary optical element, two off-axis mirrors, a folding flat, and re-imaging optics with off-axis lenses that focus each of the orthogonal linear polarization signals through an analyzer grid and onto two bolometer arrays (one for each polarization state). A cold Lyot stop is imaged onto the VPM to define the entrance pupil of the telescope. Each telescope has a 6° × 4.7° field-of-view.

Off-axis telescopes with unobstructed pupils offer great advantages in terms of emissivity, throughput, and diffractionlimited energy concentration. For most telescope designs, implementation of an off-axis configuration imposes enormous penalties in terms of cost, optical difficulty and performance, and for this reason off-axis telescopes are rarely constructed. However, for the reflective Schmidt design, implementation of an off-axis configuration is very straightforward, and involves only a modest optical penalty. Moreover, the reflective Schmidt gets particular benefits, avoiding the obstruction of its large focal plane and support column, and gaining a highly accessible, gravity-invariant prime focus, capable of accommodating very large instrumentation. We present an off-axis f/8 reflective Schmidt design for the proposed 'KDUST' Chinese infrared telescope at Dome A on the Antarctic plateau, which offers simultaneous diffraction-limited NIR imaging over 1°, and close to diffraction-limited imaging out to 2° for fibre-fed NIR spectroscopy.

The spatial frequencies accessible with a non-redundant mask (NRM) are fixed by the relative positions of the sub-apertures over the telescope pupil. In this paper we present several iterative algorithms for constructing nonredundant sub-apertures configurations. We use the triple correlation of a pre-existing set of n sub-apertures in order to find if, and where, a supplementary n+1th sub-aperture can be placed. As several possible locations may be found, we propose 3 different criteria to choose among them. Favoring the positions that are the closest to the center of mass of the sub-apertures ends up finding configurations similar to those described by Golay. The 2 other criteria aim at favoring higher spatial frequencies. The possibility of working with pupils of different radii in order to obtain a better coverage is briefly explored. The comparison between the configurations found with the 3 algorithms is done by computing for each of them the radial density of the spatial frequencys coverage and the total flux collected by the sub-apertures. An algebraic expression of the diffraction patterns associated to these configurations is given.

We designed the optics supporting structure (OSS) of a 3.8 m segmented mirror telescope by applying genetic algorithm optimization. The telescope is the first segmented mirror telescope in Japan whose primary mirror consists of 18 petal shaped segment mirrors. The whole mirror is supported by 54 actuators (3 actuators per each segment). In order to realize light-weight and stiff telescope structure, we have adopted full truss structure as OSS of the telescope. We optimized its design by a newly developed software program incorporating genetic algorithm. The program automatically generates new OSS design step-by-step by optimizing the OSS parameters for realizing both light-weight structure and homologous deformation of the mirror surface supported by the OSS against the telescope elevation change simultaneously. The program successfully generated an ultra light-weight OSS design whose weight is only 8 tons including the optical elements and actuators (4 tons) with an eigen frequency of 9.5 Hz. The deviations of the 54 nodes from their original configuration of the designed OSS are less than 100 μm in the range of elevation angle 20 - 90 degrees. A real model of the OSS is under test construction. We also report the results of static test and deformation performance of this OSS model.

Korea Astronomy and Space Science Institute (KASI) has officially started a project to construct an astronomical widefield survey system, namely KMTNet (Korea Micro-lensing Telescope Network), from January 2009. Its primary scientific goal is to discover numerous extra-solar planets, especially earth-mass planets, using the gravitational microlensing technique. This goal requires continuous photometric observations with high cadence of about 10 minutes for tens of millions of stars in dense fields toward the Galactic bulge. KMTNet will comprise three identical systems at southern observatories with different time zones. Each observing system consists of a 1.6 m wide-field optical telescope and a 20k by 20k mosaic CCD camera, which covers a 2 by 2 degrees square field of view. In this proceeding, we present technical specifications, designs and fabrication schedule of the KMTNet system.

A dismountable and portable telescope with a primary mirror of 250 mm in diameter and a numerical aperture of 5.6, is presented. The telescope has a all-spheric catadioptric optical design, consisting of a spherical primary and a group of spherical lenses, where the last surface is aluminized, as a secondary mirror. The group of lenses corrects all the optical aberrations, including the spherical introduced by the primary and the chromatic ones. The telescope has a very compact design, with a physical length of 600mm. This fact, joint with the allspherical design, make it a ligth portable and easy to align instrument: when dismounted it can be contained in a suitcase sizing 580x440x140 mm and the spherical surface for all the mirrors and lenses makes easy the final alignment of the optical train. We discuss here in detail the optical design and the realized prototype and will show the results, both in terms of theoretical and effective performances.

Telescope is a very important tool for astronomers to survey and study the stellar stars and astronomical phenomena. The performance of a telescope is its capability to track the observing objects and keep the image on the field of view during the observing period. All these functions will be achieved by telescope mount, including mount control system. The mount is to support the mirror cell and keep the mirror cell position stability. Meanwhile, with the help of control system, the mount acts as tracker of the observing objects. So, for a telescope, the mount and its control system play an important role during the telescope operation. This paper gives an introduction of a mount structure designed for a 2.5m optical/infrared telescope and the corresponding control system. Some of preliminary test results are also given in this paper.

The DEdicated MONitor of EXotransits (DEMONEX) is a low-cost, 0.5 meter, robotic telescope assembled mostly from commercially-available parts. The primary goal of DEMONEX is to monitor bright stars hosting transiting planets in order to provide a homogeneous data set of precise relative photometry for all transiting systems visible from its location at Winer Observatory in Sonoita, Arizona. This photometry will be used to refine the planetary parameters, search for additional planets via transit timing variations, place limits on the emission of the planet from secondary eclipses, and search for additional transiting planets in some systems. Despite its modest size, DEMONEX achieves a signal-to-noise ratio per transit that is comparable to that obtained with larger, 1m-class telescopes, because of its short readout time and high z-band quantum efficiency. However, the main advantage of DEMONEX is that it can be used every night for transit follow-up. With the 39 known transiting planets visible from Winer Observatory, over 90% of all nights have at least one full event to observe. We describe the hardware, and the scheduling, observing, and data reduction software, and we present some results from the first two years of operation. Synoptic surveys coming online will undoubtedly uncover a plethora of variable objects which will require inexpensive, robotic, dedicated telescopes to adequately characterize. The outline followed and lessons learned from this project will be broadly applicable for constructing such facilities.

The key factor influencing the size of future radio aperture synthesis telescope projects is the cost of the antenna dish and its drive and axis system. A good drive and axis system is of vital importance to the antenna performance as it is directly related to the antenna pointing and tracking accuracy. In this paper, various different drive systems have been investigated and, finally, a compact, modular, scalable, combined elevation and azimuth drive and axis unit design is presented. In this proposed design, the elevation drive and axis component shares virtually all parts with the azimuth drive and axis component and many commercial off-the-shelf parts are used for both axis and drive linkage. This design can also assure the required pointing and tracking accuracy is met. Since it is a self contained unit, the assembly, installation, and maintenance are further simplified, resulting in overall lower cost.

Radio telescopes with much more larger aperture collect much more signals and therefore sought after by astronomers. The primary reflecting antenna is traditionally segmented and perfectly optically aligned at the central altitude among the whole observation sky area for minimizing the gravitational deformation during operation and passively open-loop maintained at any other altitude. A new laser segmentation sensing and maintaining method based on normal deflection angle measurement is proposed in this paper. After the introduction of the theory, the method is simulated and tested on a special prototype of radio panel segmentation system. It provides real-time monitoring and measurement of the global segmentation status of all panels and is proved to be a high accurate, high efficient and low cost method. Finally several conclusions are reached.

Large radio-telescopes requiring accurate 'blind' pointing accuracy are often equipped with dedicated metrology systems in order to correct for structural deformations. We present here a novel tiltmeter concept conceived specifically to compensate for the fast, wind-induced deformations occurring on such large structures. This instrument combines the typical accuracy and resolution of geodetic devices with an unique capability of recovering quickly from large saturations: this condition often occurs during fast slewing of the antenna. Moreover, the device features a reduced sensitivity to in-plane accelerations. All this allows its installation in favorable positions concerning the observability of the structural deformations to be detected and corrected, thus simplifying the processing from raw instrument data to the pointing correction to be applied. The instrument has been subjected to a thorough characterization and qualification process, by means of extensive tests both in the lab, using a dedicated testbench, and on the ALMA-EU antenna prototype. This activity allowed assessing other critical aspects for the final application, in particular easiness of installation, simplicity of mechanical and electrical interfaces, robustness, reliability and very limited maintenance requirements. The device will be installed on the ALMA-EU production antennas.

We have recently equipped the 34-meter DSS-28 radio telescope at the Goldstone Deep Space Communications Complex with a novel wide bandwidth radiometer and digital signal processor as part of the Goldstone Apple Valley Radio Telescope (GAVRT) educational outreach program operated by the Jet Propulsion Laboratory and the Lewis Center for Educational Research. The system employs a cryogenically cooled wide bandwidth quad-ridge feed and InP low noise amplifiers to achieve excellent noise performance from 2.7 to 14 GHz; a fractional bandwidth better than 4:1. Four independently tunable dual-polarization receivers each down-convert a 2 GHz block to baseband, providing access to 8 GHz of instantaneous bandwidth. A flexible FPGA-based signal processor has been constructed using CASPER FPGA hardware and tools to take advantage of this enormous bandwidth. This system demonstrates many of the enabling wide bandwidth technologies that will be crucial to maximizing the utility of future large centimeter-wavelength arrays, in particular the Square Kilometer Array. The GAVRT program has previously used narrow bandwidth total power radiometers to study flux variability of quasars and the outer planets. The versatility of DSS-28 will enable other projects including spectroscopy and SETI. Finally, the wide instantaneous bandwidth available makes this system uniquely suited for studying transient radio pulses. A configuration of the digital signal processor has been developed which provides the capability of recording a burst of raw baseband voltage data triggered by a real-time incoherent dedispersion system which is very sensitive to pulses from a known source, such as the Crab Nebula pulsar.

Optical telescopes and cameras are often used to determine the initial pointing model for radio antennas. After this initial determination, the optical systems are typically not used. The Combined Array for Research in Millimeter-wave Astronomy (CARMA) has implemented optical oset pointing as a standard calibration option for science observations. We report on the proof of concept testing, the method, and the typical improvements obtained over traditional radio pointing. We conclude with a brief discussion of future directions, which may oer further improved pointing at CARMA and at other facilities that require increased pointing accuracy.

The planned Square Kilometer Array (SKA) includes three thousand 15m antennas. The radio flux density from the sun is stronger, so that a solar array, such as Frequency-Agile Solar Radiotelescope (FASR) with hundreds of dishes can have smaller dish size. Therefore, light weight, low cost dish design is of vital importance. The reflecting surface supported by an antenna back-up structure, generally, should have an RMS surface error less than λ/20 (λ_. is the operating wavelength). For resisting gravitational, wind, and ice-snow loadings, an antenna dish also requires reasonable mode frequencies. In this paper, different low cost small or medium back-up structure designs are discussed, including double-layer truss design and prestressed dish design. Based on discussion, an innovative light weight, prestressed back-up structure is proposed for small or medium aperture antennas. Example of a small 4.5m aperture dish design working below 3GHz is presented. This design is a one-layer prestressed truss structure with low weight, ease installation, and low manufacture cost. Structural analysis and modal extraction results show the structure is much stiffer than the same structure without prestressed loading.

The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint project between astronomical organizations in Europe, North America, and East Asia, in collaboration with the Republic of Chile. ALMA will consist of at least 54 twelve-meter antennas operating in the millimeter and sub-millimeter wavelength range. It will be located at an altitude above 5000m in the Chajnantor Plateau in northern Chile. There are 192 antenna foundations under construction at ALMA's Array Operations Site (AOS). Interchangeability between foundations will permit a variety of array configurations. Foundations provide the physical interface to the bedrock, as well as to the underground signal and power cable conduits. To achieve ALMA's precision requirements, the antenna pointing angular error budget is strict with anticipated non-repeatable error on the order of a few arc seconds. This level of precision imposes rigorous requirements on antenna foundations. The objective of this study is to demonstrate the methodology of precision tilt measurements combined with finite element simulation predictions to portray the qualitative nature of the antenna foundation surface deformation. Characteristics of foundation surface tilt have been examined in detail. Although the actual foundation has demonstrated much less resistance to tilt than the finite element representation, the simulation has predicted some key characteristics of the tilt pattern. The large deviations from the ideal have incited speculations into the compliance of materials, ambiguities in the construction, thermal effects and several other aspects described herein. This research has served as groundwork to characterize ALMA's foundation surface behavior on a micro-degree level and to identify subsequent studies to pursue. This in turn has contributed to the diagnosis of antenna pointing anomalies.

The performance of single dish radio antennas or telescopes is depending on the surface accuracy of the reflectors in the beam path and the focus/pointing errors induced by deviations/misalignment of the reflectors from a desired direction. For multiple dish VLBI arrays an additional mechanical effect, the path length stability, is a further source of performance degradation. For application at higher frequencies environmental influences as wind and temperature have to be considered additionally to the usually required manufacturing and alignment accuracies. Active measurement ("metrology") of the antenna deformations and their compensation by "active optics" (AO) respectively "flexible body compensation" (FBC) are established methods. For the path length errors AO or FBC are up to now not established methods. The paper describes how to handle the path length errors and the related metrology analogues to the established methods used for surface and focus/pointing error corrections.

High angular resolution observations are essential to understand a variety of astrophysical phenomena. The resolution of millimeter wave interferometers is limited by large and rapid differential atmospheric delay fluctuations. At the Combined Array for Research in Millimeter-wave Astronomy (CARMA) we have employed a Paired Antenna Calibration System (C-PACS) for atmospheric phase compensation in the extended array configurations (up to 2 km baselines). We present a description of C-PACS and its application. We also present successful atmospheric delay corrections applied to science observations with dramatic improvements in sensitivity and angular resolution.

The ATST scientific instruments are located on benches installed on a large diameter rotating coud lab floor. The light path from the telescope to the instruments is greater than 38 meters and passes from external ambient conditions to the 'shirt-sleeve' environment of the coudé lab. In order to minimize any contribution to local seeing or wavefront distortion, two strategies are implemented. First, an air curtain is installed where the beam passes from ambient conditions to the lab space and second, the coudé lab environmental conditions are tightly controlled. This paper presents the design parameters of the environmental conditions, the basis of each design parameter, an overview of the equipment and components of the system planned to control those conditions, and the thermal and computational fluid dynamic analyses that have been performed in support of the system as designed.

This paper describes the outcome of a survey reviewing commercially available state-of-the-art high-cooling power 2- stage cryocooler systems for a potential use in powerful scientific instruments for ground-based astronomy. We present the development of a dedicated test-bed as well as vibration and performance measurements on different 2-stage refrigerator systems. As a result of this investigation program, one system was selected as ESO's new standard 20 K closed cycle cooler offering substantial advantages in flexibility and orientation insensitivity along with best compromise for a low vibration device with high cooling power. The new cryocooler type was integrated with VLT instrumentation. A concept for a comprehensive vibration test program at VLT is presented in order to define admissible vibration spectra for future instrumentation.

Wind is a well known performance detractor for telescope pointing. Increasing the size of the telescope increase the aeroelastic effect onto the performances of the telescope. A dome is often used for larger telescopes to minimize those interactions. Rapid pointing telescope requires rapid domes, which usually are heavy drawing their cost not negligible respect to the overall amount of budget required. For this reason fast telescope's dome are usually fully deployed leaving the telescope unprotected from the wind. This paper wants to show a modification of the fully foldable tents in order to realize a partially foldable light-weighted tent able to follow the alt-az fast movement of a large scale telescope protecting it from aeroelastic loading without interacting with the dynamic of the main system. The alt-az movement of the telescope is decoupled from an azimuth rotation of the full tent and an alt motion of the two shells. In this way it is possible to work with a fully emyspherical tent and aan opened window for the observations.

Between February and April 2009 a number of ultrasonic anemometers, temperature probes and dust sensors were operated inside the CTIO Blanco telescope dome. These sensors were distributed in a way that temperature and 3 dimensional wind speeds were monitored along the line of sight of the telescope. During telescope operations, occasional seeing measurements were obtained using the Mosaic CCD imager and the CTIO site monitoring MASS-DIMM system. In addition, also a Lunar Scintillometer (LuSci) was operated over the course of a few nights inside the dome. We describe the instrumental setup and first preliminary results on the linkage of the atmospheric conditions inside the dome to the overall image quality.

Strategies for thermal control of the 6.5-meter diameter borosilicate honeycomb primary (M1) mirror at the MMT Observatory have included: 1) direct control of ventilation system chiller setpoints by the telescope operator, 2) semiautomated control of chiller setpoints, using a fixed offset from the ambient temperature, and 3) most recently, an automated temperature controller for conditioned air. Details of this automated controller, including the integration of multiple chillers, heat exchangers, and temperature/dew point sensors, are presented here. Constraints and sanity checks for thermal control are also discussed, including: 1) mirror and hardware safety, 2) aluminum coating preservation, and 3) optimization of M1 thermal conditions for science acquisition by minimizing both air-to-glass temperature differences, which cause mirror seeing, and internal glass temperature gradients, which cause wavefront errors. Consideration is given to special operating conditions, such as high dew and frost points. Precise temperature control of conditioned ventilation air as delivered to the M1 mirror cell is also discussed. The performance of the new automated controller is assessed and compared to previous control strategies. Finally, suggestions are made for further refinement of the M1 mirror thermal control system and related algorithms.

Wind loading can be a detrimental source of vibration and deflection for any large terrestrial optical telescope. The Hobby-Eberly Telescope* (HET) in the Davis Mountains of West Texas is undergoing a Wide Field Upgrade (WFU) in support of the Dark Energy Experiment‡ (HETDEX) that will greatly increase the size of the instrumentation subjected to operating wind speeds of up to 20.1 m/s (45 mph). A non-trivial consideration for this telescope (or others) is to quantify the wind loads and resulting deflections of telescope structures induced under normal operating conditions so that appropriate design changes can be made. A quasi-static computational fluid dynamics (CFD) model was generated using wind speeds collected on-site as inputs to characterize dynamic wind forces on telescope structures under various conditions. The CFD model was refined until predicted wind speed and direction inside the dome agreed with experimental data. The dynamic wind forces were then used in static loading analysis to determine maximum deflections under typical operating conditions. This approach also allows for exploration of operating parameters without impact to the observation schedule of the telescope. With optimum combinations of parameters (i.e. dome orientation, tracker position, and louver deployment), deflections due to current wind conditions can be significantly reduced. Furthermore, the upper limit for operating wind speed could be increased, provided these parameters are monitored closely. This translates into increased image quality and observing time.

The image motion (tip/tilt) of the telescope is dominated by two types of perturbations: a) atmospheric b) wind load. The wind load effect on E-ELT can be an order of magnitude higher than the atmospheric effect. Part of the image motion due to the wind load on the telescope structure is corrected by the main axis control system (mainly large amplitude, low frequency errors). The residual tip/tilt is reduced by M5 and M4 mirror units. M5 with its large stroke and relative low bandwidth (higher than main axes) corrects for large amplitude and low frequency part of the image motion and M4 unit takes the higher frequency parts with smaller stroke availability. In this paper the two stage control strategy of the E-ELT field stabilization is introduced. The performance of the telescope due to the wind load and in the presence of the major imperfections in the control system is presented.

A large structural weldment has been designed to serve as the new star tracker bridge for the Wide Field Upgrade to the Hobby-Eberly Telescope at McDonald Observatory in support of the Hobby-Eberly Telescope Dark Energy Experiment^‡. The modeling approach, analysis techniques and design details will be of interest to designers of large structures where stiffness is the primary design driver. The design includes detailed structural analysis using finite element models to maximize natural frequency response and limit deflections and light obscuration. Considerable fabrication challenges are overcome to allow integration of precision hardware required for positioning the corrector optics to a precision of less than 5 microns along the 4-meter travel range. Detailed descriptions of the bridge geometry, analysis results and challenging fabrication issues are discussed.

The University of Texas, Center for Electromechanics (UT-CEM) is making a major upgrade to the robotic tracking system on the Hobby Eberly Telescope (HET) as part of theWide Field Upgrade (WFU). The upgrade focuses on a seven-fold increase in payload and necessitated a complete redesign of all tracker supporting structure and motion control systems, including the tracker bridge, ten drive systems, carriage frames, a hexapod, and many other subsystems. The cost and sensitivity of the scientific payload, coupled with the tracker system mass increase, necessitated major upgrades to personnel and hardware safety systems. To optimize kinematic design of the entire tracker, UT-CEM developed novel uses of constraints and drivers to interface with a commercially available CAD package (SolidWorks). For example, to optimize volume usage and minimize obscuration, the CAD software was exercised to accurately determine tracker/hexapod operational space needed to meet science requirements. To verify hexapod controller models, actuator travel requirements were graphically measured and compared to well defined equations of motion for Stewart platforms. To ensure critical hardware safety during various failure modes, UT-CEM engineers developed Visual Basic drivers to interface with the CAD software and quickly tabulate distance measurements between critical pieces of optical hardware and adjacent components for thousands of possible hexapod configurations. These advances and techniques, applicable to any challenging robotic system design, are documented and describe new ways to use commercially available software tools to more clearly define hardware requirements and help insure safe operation.

The Hobby-Eberly Telescope (HET) is an innovative large telescope of 9.2 meter aperture, located in West Texas at the McDonald Observatory (MDO). The HET operates with a fixed segmented primary and has a tracker which moves the four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. A major upgrade of the HET is in progress that will increase the pupil size to 10 meters and the field of view to 22' by replacing the corrector, tracker and prime focus instrument package. In addition to supporting the existing suite of instruments, this wide field upgrade will feed a revolutionary new integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX^‡). This paper discusses the current status of this upgrade.

The Wide Field Upgrade presents a five-fold increase in mass for the Hobby-Eberly Telescope's* tracker system. The design of the Hobby-Eberly Telescope places the Prime Focus Instrument Package (PFIP) at a thirty-five degree angle from horizontal. The PFIP and its associated hardware have historically been positioned along this uphill axis (referred to as the telescope's Y-axis) by a single screw-type actuator. Several factors, including increased payload mass and design for minimal light obscuration, have led to the design of a new and novel configuration for the Y-axis screw-drive as part of the tracker system upgrade. Typical screw-drive designs in this load and travel class (approximately 50 kilonewtons traveling a distance of 4 meters) utilize a stationary screw with the payload translating with the moving nut component. The new configuration employs a stationary nut and translating roller screw affixed to the moving payload, resulting in a unique drive system design. Additionally, a second cable-actuated servo drive (adapted from a system currently in use on the Southern African Large Telescope) will operate in tandem with the screw-drive in order to significantly improve telescope safety through the presence of redundant load-bearing systems. Details of the mechanical design, analysis, and topology of each servo drive system are presented in this paper, along with discussion of the issues such a configuration presents in the areas of controls, operational and failure modes, and positioning accuracy. Findings and results from investigations of alternative telescope safety systems, including deformable crash barriers, are also included.

The V. M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory is undergoing a number of improvements in preparation for the delivery of the Dark Energy Camera. The program includes upgrades having potential to deliver gains in image quality and stability. To this end, we have renovated the support structure of the primary mirror, incorporating innovations to improve both the radial support performance and the registration of the mirror and telescope top end. The resulting opto-mechanical condition of the telescope is described. We also describe some improvements to the environmental control. Upgrades to the telescope control system and measurements of the dome environment are described in separate papers in this conference.

To enable the Hobby-Eberly Telescope Wide Field Upgrade, the University of Texas Center for Electromechanics and McDonald Observatory are developing a precision tracker system - a 15,000 kg robot to position a 3,100 kg payload within 10 microns of a desired dynamic track. Performance requirements to meet science needs and safety requirements that emerged from detailed Failure Modes and Effects Analysis resulted in a system of 14 precision controlled actuators and 100 additional analog and digital devices (primarily sensors and safety limit switches). This level of system complexity and emphasis on fail-safe operation is typical of large modern telescopes and numerous industrial applications. Due to this complexity, demanding accuracy requirements, and stringent safety requirements, a highly versatile and easily configurable centralized control system that easily links with modeling and simulation tools during the hardware and software design process was deemed essential. The Matlab/Simulink simulation environment, coupled with dSPACE controller hardware, was selected for controls development and realization. The dSPACE real-time operating system collects sensor information; motor commands are transmitted over a PROFIBUS network to servo amplifiers and drive motor status is received over the same network. Custom designed position feedback loops, supplemented by feed forward force commands for enhanced performance, and algorithms to accommodate self-locking gearboxes (for safety), reside in dSPACE. To interface the dSPACE controller directly to absolute Heidenhain sensors with EnDat 2.2 protocol, a custom communication board was developed. This paper covers details of software and hardware, design choices and analysis, and supporting simulations (primarily Simulink).

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX ^‡)at the University of Texas McDonald Observatory will deploy the Visible Integral-Field Replicable Unit Spectrograph (VIRUS) to survey large areas of sky. VIRUS consists of up to 192 spectrographs deployed as 96 units. VIRUS units are fiber-fed and are housed in four enclosures making up the VIRUS Support Structure (VSS). Initial design studies established an optimal array size and an upper and lower bound on their placement relative to the existing telescope structure. Tradeoffs considering IFU (optical fiber) length, support structure mass and ease of maintenance have resulted in placement of four 3 × 8 arrays of spectrograph pairs, about mid-point in elevation relative to the fixed HET structure. Because of the desire to minimize impact on the modal performance of the HET, the VSS is required to be an independent, selfsupporting structure and will only be coupled at the base of the telescope. Analysis shows that it is possible to utilize the existing azimuth drives of the telescope, through this coupling, which will greatly simplify the design and reduce cost. Each array is contained in an insulated enclosure that will control thermal load by means of heat exchangers and use of facility coolant supply. Access for installation and maintenance on the top, front, and rear of the enclosures must be provided. The design and analysis presented in this paper must provide an optimum balance in meeting the stringent requirements for science and facility constraints such as cost, weight, access, and safety.

The LSST project has updated the all-sky IR camera that was installed on Cerro Pachón in Chile to continue its investigations in cloud monitoring and quantifying photometric conditions. The objective is to provide the survey scheduler with real-time measured conditions of the sky/clouds, including high cirrus to better optimize the observing strategy. This paper describes the changes done to improve the detection performance of the first generation system and presents comparison results of visible and IR images.

The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the AstroMeteorology group at the Universidad de Valparaiso collaborated on a project to understand the precipitable water vapour (PWV) over the La Silla Paranal Observatory. Both La Silla and Paranal were studied with the goal of using them as reference sites to evaluate potential E-ELT sites. As ground-based infrared astronomy matures, our understanding of the atmospheric conditions over the observatories becomes paramount, specifically water vapour since it is the principle source of atmospheric opacity at infrared wavelengths. Several years of archival optical spectra (FEROS) have been analysed to reconstruct the PWV history above La Silla using an atmospheric radiative transfer model (BTRAM) developed by ISIS. In order to better understand the systematics involved, a dedicated atmospheric water vapour measurement campaign was conducted in May 2009 in close collaboration with Las Campanas observatory and the GMT site testing team. Several methods of determining the water column were employed, including radiosonde launches, continuous measurements by infrared radiometers (IRMA), a compact echelle spectrograph (BACHES) and several high-resolution optical echelle spectrographs (FEROS, HARPS and MIKE). All available observations were compared to concurrent satellite estimates of water vapour in an attempt to ground-truth the satellite data. We present a comparison of the methods used, and results from the archival study and measurement campaign. A mean PWV of 3.4 ± 2.4 mm is found for La Silla using FEROS data covering the period 2005-2009. Important lessons on the strengths and limitations of satellite data are presented. The value of a stand-alone high time resolution PWV monitor has been demonstrated in the context of parallel observations from Las Campanas and La Silla.

Snodar is a high resolution acoustic radar designed specifically for profiling the atmospheric boundary layer on the high Antarctic plateau. Snodar profiles the atmospheric temperature structure function constant to a vertical resolution of 1 m or better with a minimum sample height of 8 m. The maximum sampling height is dependent on atmospheric conditions but is typically at least 100 m. Snodar uses a unique in-situ intensity calibration method that allows the instrument to be autonomously recalibrated throughout the year. The instrument is initially intensity calibrated against tower-mounted differential microthermal sensors. A calibration sphere is located in the near-field of the antenna to provide a fixed echo of known intensity, allowing the instrument to be continuously re-calibrated once deployed. This allows snow accumulation, transducer wear and system changes due to temperature to be monitored. Year-round power and communications are provided by the PLATO facility. This allows processed data to be downloaded every 6 hours while raw data is stored on-site for collection the following summer. Over 4 million processed samples have been downloaded through PLATO to date. We present signal attenuation from accumulation of snow and ice on Snodar's parabolic reflector during the 2009 at Dome A.

In this paper the Paranal Surface Layer characterization is presented. Causes, physics and behavior of the SL above Paranal surface are discussed. The analysis is developed using data from different turbulence profilers operated during several campaigns between 2007 and 2009. Instruments used are SL-SLODAR, DIMM, Elevated DIMM, MASS, Lunar Scintillometer and Ultrasonic Anemometers with temperature sensors positioned at different strategic heights.

In this contribution we present how the mesoscale model Meso-Nh model together with the Astro-Meso-Nh and a set of diagnostic tools allow for a full 3D investigation of the C²_N and derived integrated astroclimatic parameters. The possibility to study simultaneously 3D fields of meteorological and astroclimatic parameters permits us to provide a comprehensive understanding of the characteristics of the atmospheric flow as well as the physical mechanisms that produce them. To illustrate the different diagnostics and their potentialities, we investigated one night and looked at instantaneous fields of meteorologic and astroclimatic parameters. To show the potentialities of this tool for applications in an Observatory we ran the model above sites with very different optical turbulence (OT) distributions: the antarctic plateau (Dome C, Dome A, South Pole) and a mid-latitude site (Mt. Graham, Arizona). We put particular emphasis on the 2D maps of integrated astroclimatic parameters (such as seeing, isoplanatic angles, ...) and to the possibility to calculate them in different slabs (having what ever thickness) at different heights in the troposhere. The latter option is particularly useful for the seeing. For this reason this is an useful tool of prediction and investigation of the turbulence structure and it can support the optimization of the AO, GLAO and MCAO systems running at the focus of the ground-based telescopes. The examples we provide put clearly in evidence that different astroclimatic sites present different OT behaviors. Besides, our tool allowed us for discriminating these sites.

Atmospherical mesoscale models can offer unique potentialities to characterize and discriminate potential astronomical sites. Our team has recently completely validated the Meso-Nh model above Dome C (Lascaux et al. 2009, 2010). Using all the measurements of C²_N profiles (15 nights) performed so far at Dome C during the winter time (Trinquet et al. 2008) we proved that the model can reconstruct, on rich statistical samples, reliable values of all the three most important parameters characterizing the turbulence features of an antarctic site: the surface layer thickness, the seeing in the free atmosphere and in the surface layer. Using the same Meso-Nh model configuration validated above Dome C, an extended study is now on-going for other sites above the antarctic plateau, more precisely South Pole and Dome A. In this contribution we present the most important results obtained in the model validation process and the results obtained in the comparison between different astronomical sites above the internal plateau. The Meso-Nh model confirms its ability in discriminating between different optical turbulence behaviors, and there is evidence that the three sites have different characteristics regarding the seeing and the surface layer thickness. We highlight that this study provides the first homogeneous estimate, done with comparable statistics, of the optical turbulence developed in the whole 20-22 km above the ground at Dome C, South Pole and Dome A.

The performances of a modern telescope and its safety are dependent on the presence of atmospheric dust. The TNG telescope at ORM (Canary Islands) was one of the first sites monitored on a continuous basis by an automatic dust monitor. This paper presents the analysis of about 10 years of atmospheric dust content collected at the ORM using the TNG facilities. We have detected particles of 0.3, 0.5, 1.0, 3.0, 5.0 and 10.0 μm size. In this study particles of 0.5 and 5.0 μm measured at Paranal Observatory (Chile) are also compared to those similar at TNG. The seasonal behavior of the particles content in the atmosphere is compared between the two sites. The contribution of the dust emissivity to the sky brightness in the NIR is computed for the first time. To complete this study we defined the aerosol mass critical limit to be used as a safety limit for the observations. We found a limit of 12 μg m^-3 as total mass of (0.5 + 5.0) μm particles.

Seeing measurements are crucial for the optimum design of (multi-conjugate) adaptive optics systems operating at solar telescopes. For the design study of the 4-meter European Solar Telescope, to be located in the Canary Islands, several instruments have been constructed and operated, at the Observatorio del Roque de los Muchachos (La Palma) and at the Observatorio del Teide (Tenerife), to measure the properties of the ground layer and medium-high altitude turbulence. Several units of short (42.34 cm) and two long (323.06 cm) scintillometer bars are, or are to be, installed at both observatories. In addition to them, two wide-field wavefront sensors will be attached to the optical beams of the Swedish tower, on La Palma, and of the German VTT, on Tenerife, simultaneously used with the normal operation of the telescopes. These wavefront sensors are of Shack-Hartmann type with ~1 arcminute field of view. In this contribution, the instruments setup and their performance are described.

The futures large telescopes will be certainly equipped with Multi-Conjugate Adaptive Optics systems. The optimization of the performances of these techniques requires a precise specification of the different components of these systems. Major of these technical specifications are related to the atmospheric turbulence particularly the structure constante of the refractive index C²_n(h) and the outer scale L₀(h). New techniques based on the moon limb observation for the monitoring of the C²_n(h) and L₀(h) profiles with high vertical resolution will be presented.

The content of precipitable water vapor (PWV) in the atmosphere is very important for astronomy in the infrared and radio (sub-millimeter) spectral regions. Therefore, the astrometeorology group has developed different methods to derive this value from measurements and making forecasts using a meteorological model. The goal is use that model to predict the atmospheric conditions and support the scheduling of astronomical observations. At ESO, several means to determine PWV over the observatories have been used, such as IR-radiometers (IRMA), optical and infrared spectrographs as well as estimates using data from GOES-12 satellite. Using all of these remote sensing methods a study undertaken to compare the accuracy of these PWV measurements to the simultaneous in-situ measurements provided by radiosondes. Four dedicated campaigns were conducted during the months of May, July, August and November of 2009 at the La Silla, APEX and Paranal observatory sites. In addition, the astrometeorological group employs the WRF meteorological model with the goal of simulating the state of the atmosphere (every 6 hours) and forecasting the PWV. With these simulations, plus satellite images, radiosonde campaign data can be classified synoptically and at the same time the model can be validated with respect to PWV.

There is growing interest in measuring seeing at existing and prospective telescope sites. Several methods exist to quantify seeing, one among them is by measuring the scintillation of solar or lunar light using a photodiode. A shadow band ranger (SHABAR) analyses the covariance of the signals from an array of such photodiodes, which allows for the spatial resolution of the index of refraction above the SHABAR device. This allows one to estimate the index of refraction structure parameter as a function of height, C²_n(h). Although a SHABAR has a limited range compared to a differential image motion monitor (DIMM) or the latest wavefront sensors, the advantage is that it does not need telescope optics to work. A SHABAR device can be made very compact and can operate independent of other instruments. We describe the design of such a SHABAR device with six photodiodes that can operate virtually indefinitely without requiring human intervention. An inversion algorithm is used to convert the raw scintillation signals of the photodiodes to the desired C²_n(h) profile and a value for the Fried parameter r₀ at height zero. We show that it is possible to perform inversions of 10 s periods in real time on relatively low-end hardware, such as an Intel Atom based computer, which allows the results to be presented live to astronomers, who can use this information to help make decisions about their observation schedule.

Nigel is a fiber-fed UV/visible grating spectrograph with a thermoelectrically-cooled 256×1024 pixel CCD camera, designed to measure the twilight and night sky brightness from 300nm to 850 nm. Nigel has three pairs of fibers, each with a field-of-view with an angular diameter of 25 degrees, pointing in three fixed positions towards the sky. The bare fibers are exposed to the sky with no additional optics. The instrument was deployed at Dome A, Antarctica in January 2009 as part of the PLATO (PLATeau Observatory) robotic observatory. During the 2009 winter, Nigel made approximately six months of continuous observations of the sky, with typically 104 deadtime between exposures. The resulting spectra provide quantitative information on the sky brightness, the auroral contribution, and the water vapour content of the atmosphere. We present details of the design, construction and calibration of the Nigel spectrometer, as well some sample spectra from a preliminary analysis.

Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Atmospheric precipitable water vapor (PWV) adversely impacts mid-IR astronomy through reduced transparency and increased background. Prior to the GMT site testing effort, little was known regarding the PWV characteristics at LCO and therefore, a multi-pronged approach was used to ensure the determination of the fraction of the time suitable for mid-IR observations. High time resolution monitoring was achieved with an Infrared Radiometer for Millimeter Astronomy (IRMA) from the University of Lethbridge deployed at LCO since September of 2007. Absolute calibrations via the robust Brault method (described in Thomas-Osip et al.¹) are provided by the Magellan Inamori Kyocera Echelle (MIKE), mounted on the Clay 6.5-m telescope on a timescale of several per month. We find that conditions suitable for mid-IR astronomy (PWV < 1.5 mm) are concentrated in the southern winter and spring months. Nearly 40% of clear time during these seasons have PWV < 1.5mm. Approximately 10% of these nights meet our PWV requirement for the entire night.

Cerro Las Campanas located at Las Campanas Observatory in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Seeing data have been obtained at three potential sites, and are compared with identical data taken at the site of the twin Magellan 6.5m telescopes. In addition, measurements of the turbulence profile of the free-atmosphere have been collected. Co. Las Camapanas and the Magellan site are nearly identical in their seeing statistics, and apparently their average ground-layer characteristics.

Modern optical and infrared astronomical sites are getting used to a flexible way of operation, namely queue modes, allowing astronomical observations in the most appropriate weather conditions for each specific observing scientific program. The forecast of weather conditions is then a mandatory issue to plan in advance the observations queue for each night in order to exploit efficiently the astronomical facilities with the largest high quality data output for scientific exploitation. The precipitable water vapour is the parameter accounting for the infrared (IR) quality of an astronomical site. The temporal fluctuation of this parameter drastically affects the quality of the IR data recorded at ground telescopes. An optical/IR telescope needs the forecasting of the precipitable water vapour for a proper queue scheduling of IR observations. The Roque de los Muchachos Observatory (ORM) on the island of La Palma (Spain) presents an abrupt topography which difficult the forecasting at this astronomical site. We discuss the performance of a mesoscale numerical weather model (WRF, Weather Research and Forecasting) applied to ORM region including the comparison with local precipitable water vapour estimations from GPS (Global Positioning System).

We present a characterization of meteorological parameters: Wind and direction speed, temperature, relative humidity and pressure. Data set is provided by the system of NCEP/NCAR Re-analysis. The statistical treatment of data will cover the years between 2003 and 2006 for the Observatory Oukaïmeden. An analysis of monthly, seasonal, and annual results is presented. We calculated the Richardson number for each month of the year. In addition, this paper describes a comparison between balloon-sounding made at different stations and coincident model-based meteorological analysis. The comparison allows the assessment reliability of the analysis in studied period.

As part of the conceptual and preliminary design processes of the Extremely Large Telescope (ELT), the ELT site-testing team at Morocco has spent the last two years measuring the atmospheric properties at Aklim site as another 4 candidate mountains in North and South hemisphere, Aklim is the per-selected site for the ELT, is located in Moroccan Anti-Atlas at the geographic coordinates 30°7'39" N, 08°18'39" W. In this paper we present the isoplanatic angle θ₀ and the isopistonic angle θ_p, measurements at Aklim site, statistics of the mentioned parameters are obtained from the whole data recorded from April 2008 to December 2009 using the Multi Aperture Scintillation Sensor (MASS) - Differential Image Motion Monitor (DIMM) system, more representative results and statistics are shown hereafter.

The Concordia Base in Dome C, Antarctica, is an extremely promising site for photometric astronomy due to the 3- month long night during the Antarctic winter, favorable weather conditions, and low scintillation. The ASTEP project (Antarctic Search for Transiting ExoPlanets) is a pilot project which seeks to identify transiting planets and understand the limits of visible photometry from this site. ASTEP 400 is an optical 40cm telescope with a field of view of 1° x 1°. The expected photometric sensitivity is 1E-3, per hour for at least 1,000 stars. The optical design guarantees high homogeneity of the PSF sizes in the field of view. The use of carbon fibers in the telescope structure guarantees high stability. The focal optics and the detectors are enclosed in a thermally regulated box which withstands extremely low temperatures. The telescope designed to run at -80°C (-110°F) was set up at Dome C during the southern summer 2009- 2010. It began its nightly observations in March 2010.

The International Concordia Explorer Telescope (ICE-T) is two 60cm wide-field robotic Schmidt telescopes optimized for high-precision CCD photometry in two separate bandpasses. The project is under final design by an international consortium led by the Astrophysical Institute Potsdam, Germany, and was foreseen to be placed at the French-Italian Concordia Station on Dome C in Antarctica. Its core scientific objective would be to detect and investigate the combined effects of extra-solar planets, stellar magnetic activity and non-radial pulsations on the structure and evolution of stars. We present the optical, the mechanical, and the electronic design of the telescope and lay out the operational constraints for its search for extrasolar planets and magnetic stellar activity.

The extreme environment of Antarctic greatly benefits astronomical observations. Site testing works already show the excellent seeing and transmission on Dome C. And the higher, colder inland plateau Dome A is widely predicted as even better astronomical site than Dome C. Preliminary site testing carried out since the beginning of 2008 shows that Dome A has lower boundary layer and lower precipitable water vapour. Now the automated seeing monitor is urgently needed to quantify the site's optical character which is necessary for the telescope design and deployment. We modify the commercial telescopes with diameter of 35cm to function as site testing DIMM and make it monitor both seeing and isoplanatic angle at the same time automatically on Dome A at different height. Part of the processed data will be transferred back by Iridium satellite network every day. The first DIMM will be deployed on Dome A in early 2011.

As science makes progress, proposing new discoveries every day, it is more and more interesting for the astronomical world to perform sub-millimeter observations from very suitable terrestrial sites, due to the purity of the air, as well as to other environmental factors. A site with these characteristics has been identified in the area of Dome C in the South Pole. The problems, both technical and logistic, that the installation of a radioantenna in the South Pole imposes, are easily understandable. Proceeding at the same rate as the progress of science, also the technological and industrial capacities improve, so that it is possible to overcome all the problems that the realization of a sub-millimeter Observatory in the South Pole implies. This paper aims at summarizing the Preliminary Feasibility Study of the AST (Antarctic Sub-millimeter Telescope) Radioantenna that is intended to be installed at Dome C.

CCAT will be a 25 m diameter, submillimeter-wave telescope. It will be located on Cerro Chajnantor in the Atacama Desert, near ALMA. CCAT will be an on-axis, Ritchey-Chrétien design with an active primary to compensate gravitational deformations. The primary mirror will have 162 segments, each with ~0.5 × 0.5 m reflecting tiles on a ~2×2 m, insulated, carbon-fiber-reinforced-plastic subframe. CCAT will be equipped with wide-field, multi-color cameras and multi-object spectrometers at its Nasmyth foci. These instruments will cover all the atmospheric windows in the λ = 0.2 to 2 mm range. The field of view at the Nasmyth foci will be 1°, so CCAT will be able to support cameras with a few ×10⁴ detectors (spaced 2 beamwidths) at λ = 1 mm to a few ×10⁶ detectors (spaced half a beamwidth) at λ = 350 μm. Single instruments of this size are probably impractical, so we will break the field into smaller pieces, with a separate sub-field camera for each piece. The cameras will require some relay optics to couple the fairly slow beam from the telescope to the detectors. A reflective relay for 1° field of view is too large to be practical, so we plan to use a compact, cold, refractive relay in each sub-field camera.

The Giant Magellan Telescope (GMT) is an optical-infrared 25 Meter ELT to be located in Chile. It is being designed and constructed by a group of U.S. and international universities and research institutions¹. Structural performance of large telescopes can be enhanced significantly with the added stiffness that results from distributing loads to many points in the structure. In defining the two rotating assemblies in an altitude-over-azimuth mount more than a kinematic set of constraints can lead to hydrostatic bearing oil film failure due to unintended forces that result from runner bearing irregularities. High Frequency Over Constraint (HFOC) increases stiffness without risk of oil film failure. It was used successfully on the Magellan 6.5 Meter Telescopes. GMT will employ this and two additional methods to enhance stiffness at frequencies from DC wind up through the telescope primary mode frequencies of ~11 Hz. This will be achieved without excessive hydrostatic bearing pad forces. Detailed discussion of GMT's hydrostatic constraints, azimuth track and optics support structure (OSS) runner bearing illustrations, and performance criteria are provided for the design.

In order to validate various assumptions about the operating environment of the Thirty Meter Telescope (TMT), to validate the modeling packages being used to guide the design work for the TMT and to directly investigate the expected operation of several subsystems we have embarked on an extensive campaign of environmental measurements at the Keck telescopes. We have measured and characterized the vibration environment around the observatory floor and at certain locations on the telescope over a range of operating conditions. Similarly the acoustic environment around the telescope and primary mirror has been characterized for frequencies above 2 Hz. The internal and external wind and temperature fields are being measured using combined sonic anemometer and PRT sensors. We are measuring the telescope position error and drive torque signals in order to investigate the wind induced telescope motions. A scintillometer mounted on the telescope is measuring the optical turbulence inside the telescope tube. This experimental work is supplemented by an extensive analysis of telescope and engineering sensor log files and measurements, primarily those of accelerometers located on the main telescope optics, primary mirror segment edge sensor error signals (residuals), telescope structure temperature measurements and the telescope status information.

Segmentation of telescope's primary mirror creates quasi-static speckles in an image. These speckles are impediment for the detection of faint structures around stars, for instance exoplanets. An elaborated postprocessing method is required to improve the detection level. The Stochastic Speckle Discrimination (SSD) method developed for this purpose uses statistical variability of intensity to distinguish between planets and speckles. To calculate the efficiency of SSD we derive analytical expressions for mean and standard deviation of point spread function (PSF) produced by segmented pupil. The expressions are general for any point in the image plane, but there is a difference in statistical behavior for the central point and for the off-axis point. In particular we show that a modified Rician distribution is inapplicable to describe on-axis intensity. In the last section we calculate the level of primary mirror phasing required for the efficient use of SSD.

Telescope with much larger primary can collect much more light and it is always pursued by the astronomers. Instead of using a monolithic primary, more and more large telescopes, which are now planed or in construction, invariably adopted segmented primary mirror. Therefore, how to sense and phase the primary mirror is the key technology. Unlike edge sensors, which need careful calibrations, dispersed Hartmann sensor (DHS) is non-contact method using broadband point light sources, and it can estimate piston by the two-direction spectrum formed by the transmissive grating's dispersion and lenslet array. Thus it can realize the combination of co-focusing and co-phasing. In this paper, we introduce the design of our dispersed Hartmann sensor together with its principle. We also manufacture a DHS sensor and do real tests on our existing segmented mirror optics platform. Finally some conclusions are given based on the test results.

The Active Phasing Experiment (APE) was designed to test four different phasing techniques and to validate wavefront control concepts for Extremely Large Telescopes. One of the sensors is the ZErnike Unit for Segment phasing (ZEUS), which was successfully tested on-sky along with the rest of the APE experiment at one of the Nasmyth platforms of the Very Large Telescope (VLT) in 2009. During the four observing campaigns, multiple results were obtained in open-loop and in closed-loop at different wavelengths. We present in this paper an analysis of the multi-wavelength data in terms of piston measurement precision at the edges of the segments and on the reconstructed wavefront, and an analysis of the evolution of these errors in successive closed-loop runs at different wavelengths. This work demonstrates how the applied multi-wavelength algorithm leads to convergence, allowing phasing of segments with piston errors of several microns.

European Extremely Large Telescope (E-ELT) based in 984 primary mirror segments achieving required optical performance; they must position relatively to adjacent segments with relative nanometer accuracy. CESA designed M1 Position Actuators (PACT) to comply with demanding performance requirements of EELT. Three PACT are located under each segment controlling three out of the plane degrees of freedom (tip, tilt, piston). To achieve a high linear accuracy in long operational displacements, PACT uses two stages in series. First stage based on Voice Coil Actuator (VCA) to achieve high accuracies in very short travel ranges, while second stage based on Brushless DC Motor (BLDC) provides large stroke ranges and allows positioning the first stage closer to the demanded position. A BLDC motor is used achieving a continuous smoothly movement compared to sudden jumps of a stepper. A gear box attached to the motor allows a high reduction of power consumption and provides a great challenge for sizing. PACT space envelope was reduced by means of two flat springs fixed to VCA. Its main characteristic is a low linear axial stiffness. To achieve best performance for PACT, sensors have been included in both stages. A rotary encoder is included in BLDC stage to close position/velocity control loop. An incremental optical encoder measures PACT travel range with relative nanometer accuracy and used to close the position loop of the whole actuator movement. For this purpose, four different optical sensors with different gratings will be evaluated. Control strategy show different internal closed loops that work together to achieve required performance.

The Discovery Channel Telescope (DCT) is a project of Lowell Observatory, undertaken with support from Discovery Communications, Inc., to design and construct a 4-meter class telescope and support facility on a site approximately 40 miles southeast of Flagstaff, AZ. Lowell Observatory contracted with Dynavac of Hingham, MA to design and build an optical coating system for the DCT optics. The DCT Optical Coating System includes a mechanical roughing pump, two high-vacuum cryogenic pumps, a Meissner trap, evaporative filament aluminum deposition system, LabView software and PLC-based control system, and all ancillary support equipment. The system was installed at the site and acceptance testing was completed in October 2009. The Optical Coating System achieved near perfect reflectivity performance, thickness uniformity of 1000 angstroms ±10%, and adhesion conforming to MIL-F-48616, Section 4.6.8.1. This paper discusses the design and analysis of the coating system, the process of transportation and assembly as well as testing results.

We present the current status of the University of Tokyo Atacama 1.0-m telescope constructed at the summit of Co. Chajnantor (5,640 m) in Atacama, Chile, which is an optical/infrared telescope at the world's highest site. The telescope is an f/12 Ritchey-Chretien type with a field of view of 10 arcmin. It is installed in a 6-m dome and is controlled from the operation room in a container separated from the dome. The engineering first light observation was carried out in March 2009, and the astronomical observations have been carried out since June 2009. The pointing of the telescope is as accurate as 2.4 arcsec (RMS), showing good tracking accuracy of 0.2 arcsec for 60-s observation without guiding. The Hartmann constant is 0.19 arcsec and the image quality of the telescope is satisfactory for scientific observations. The best PSF obtained is 0.5 arcsec (FWHM) in optical, which demonstrates that the summit of Co. Chajnantor is one of the best seeing site in the world. Also the excellent atmospheric transmission in infrared wavelength at the site is proved by successful observations carried out by the ANIR near-infrared camera and the MAX38 mid-infrared instrument. In the near future, the operation room will be connected to the base support facility at San Pedro de Atacama for remote observation.

The VLT Survey Telescope is a f/5.5 modified Ritchey-Chretien imaging telescope, which is being installed at the ESO-Paranal Observatory. It will provide a one square degree corrected field of view to perform surveyprojects in the wavelength range from UV to I band. In this paper we describe the opto-mechanical alignment procedure of the 2.61m primary mirror, the secondary and correctors lenses onto the mechanical structure of the telescope. The alignment procedure does not rely on the mechanical precision of the mirrors. It will be achieved using ad-hoc alignment tools, described in the paper, which allows the spatial determination of optical axes (and focuses where necessary) of the optical components with respect to the axis defined by the rotation of a laser beam mounted on the instrument bearing.

The Large Binocular Telescope's hydrostatic bearing system is operational, and tuning for optimal performance is currently underway. This low friction system allows for the precise control of the 700 ton telescope at temperatures ranging from -20°C to +25°C. It was a challenge to meet the performance requirements on such a massive telescope with a wide range of operating temperatures. This required changes to the original design, including significantly improving oil temperature control, and adding variable capillary resistors to allow for precise flow control to each pocket on each bearing. We will present a system description and report on lessons learned.

The VST telescope is going to be commissioned in Paranal, together with its main sub-systems, such as the Image Analysis and Auto-Guiding system. A preliminary work of fine tuning of each sub-system has been performed in Italy before their shipping to Paranal, where they are waiting for the telescope AIV to be completed in a way to start the final commissioning of the overall system. Each unit has been extensively characterized and tested, with particular care to the Active Optics Shack-Hartmann sensor and to the Auto-Guiding arm. We describe here the phases concerning the integration and test of all the VST Auxiliary Units performed in Italy before their shipping to Paranal.

We present the results from the commisioning of the first three off-axis Acquisition, Guiding and Wavefront Sensing Units on the Large Binocular Telescope. In particular we report on the performance of the units with respect to image quality, optical efficiency and scattered light. We also present the procedure for calibrating the stage coordinate system astrometrically to the focal plane coordinates of the telescope as well as the positional performance of the system. The first of a total of four units was mounted on the telescope in October 2007 and in the mean time three units have been mounted on the telescope. The units have been used for commisioning of the focal stations as well as for scientific observations since the end of 2008 with LUCIFER-I, the near-IR images and MOS spectrograph

The Atacama Large Millimeter/submillimeter Array (ALMA) is a joint project between astronomical organizations in Europe, North America, and East Asia, in collaboration with the Republic of Chile. ALMA will consist of at least 54 twelve-meter antennas and 12 seven-meter antennas operating as an interferometer in the millimeter and sub-millimeter wavelength range. It will be located at an altitude above 5000m in the Chilean Atacama desert. As part of the ALMA construction phase the Assembly, Verification and Integration (AIV) team receives antennas and instrumentation from Integrated Product Teams (IPTs), verifies that the sub-systems perform as expected, performs the assembly and integration of the scientific instrumentation and verifies that functional and performance requirements are met. This paper aims to describe those aspects related to the AIV Engineering team, its role within the 4-station AIV process, the different phases the group underwent, lessons learned and potential space for improvement. AIV Engineering initially focused on the preparation of the necessary site infrastructure for AIV activities, on the purchase of tools and equipment and on the first ALMA system installations. With the first antennas arriving on site the team started to gather experience with AIV Station 1 beacon holography measurements for the assessment of the overall antenna surface quality, and with optical pointing to confirm the antenna pointing and tracking capabilities. With the arrival of the first receiver AIV Station 2 was developed which focuses on the installation of electrical and cryogenic systems and incrementally establishes the full connectivity of the antenna as an observing platform. Further antenna deliveries then allowed to refine the related procedures, develop staff expertise and to transition towards a more routine production process. Stations 3 and 4 deal with verification of the antenna with integrated electronics by the AIV Science Team and is not covered directly in this paper. It is believed that both continuous improvement and the clear definition of the AIV 4-station model were key factors in achieving the goal of bringing the antennas into a state that is well enough characterized in order to smoothly start commissioning activities.

The Discovery Channel Telescope (DCT) is a project of Lowell Observatory, undertaken with support from Discovery Communications, Inc., to design and construct a 4-meter class telescope and support facility on a site approximately 40 miles southeast of Flagstaff, Arizona. The Discovery Channel Telescope Enclosure was completed in November, 2009. The DCT Enclosure is an octagonal steel structure with insulated composite panel skin. The structure rotates on sixteen compliant bogie assemblies attached to the stationary facility. The shutter is composed of two independently actuated, bi-parting structures that provide a viewing aperture. To improve seeing, the skin is covered with adhesive aluminum foil tape and the enclosed observing area is passively ventilated via rollup doors. The observing area can also be actively ventilated using a downdraft fan, and there are provisions for upgrades to active air conditioning. The enclosure also includes operational equipment such as a bridge crane, personnel lift, and access platforms. This paper discusses some of the design trades as well as the construction challenges and lessons learned by the DCT Project, its designer M3 Engineering and Technology Corporation (M3), and its general contractor, Building and Engineering Contractors, Southwest (BEC Southwest).

This paper gives a summary on control strategies and algorithms for contemporary large astronomical optical telescopes. The study lays emphasis on high precision tracking for large astronomical optical telescopes with large inertia, ultra-low speed and multi-disturbance. The control strategies and algorithms of some telescopes based on direct drive or friction drive are analyzed carefully. Finally, the future development in this field is presented.

This paper is intended primarily for the LAMOST UCAM CCD systems. The illustrations given here show the prototype LAMOST UCAM systems. Designed as a universal CCD controller, the UCAM system has variety options of readout modes, sampling speeds, binning options and charge clean. Its main components, architecture and technical design are introduced here. Some important performance characteristics about the UCAM controller and the e2v-203-82 CCD (4K by 4K, blue CCD) are tested under laboratory conditions, such as readout noise and gain at different sampling modes and readout speeds, CTE, dark current, QE, and fringing. Perfect CTE and less than 3 electrons / pixel system readout noise prove that the UCAM CCD controller system meets the requirement of the LAMOST telescope.

LAMOST is a kind of special reflecting Schmidt telescope which solved the problem to achieve both wide FOV and large aperture on one telescope. This feature makes it competitive to do the large sky area survey work. According to the configuration, the focal plate of this kind of telescope will perform three main motions: derotation, tilt and focusing. Normally the focal plate will be supported at a certain height above ground. China has launched the astronomy research at Antarctic Dome A and planned to set up a LAMOST-style telescope there. Considering the harsh environment and terrible remote transportation, a kind of simple and compact support structure of focal plate is proposed in this paper aiming at light weight, easy installation and easy adjustment, based on the review of LAMOST experiments. The calculation and simulation results show that the compact support structure can meet the system requirements.

A high precision, dual drive system has been designed and developed for the Wide Field Upgrade to the Hobby-Eberly Telescope* at McDonald Observatory in support of the Hobby-Eberly Telescope Dark Energy Experiment^‡. Analysis, design and controls details will be of interest to designers of large scale, high precision robotic motion devices. The drive system positions the 19,000 kg star tracker to a precision of less than 5 microns along its 4-meter travel. While positioning requirements remain essentially equal to the existing HET, tracker mass increases by a factor greater than 5. The 10.5-meter long tracker is driven at each end by planetary roller screws, each having two distinct drive sources dictated by the desired operation: one slowly rotates the screw when tracking celestial objects and the second rotates the nut for rapid displacements. Key results of the roller screw rotordynamics analysis are presented. A description of the complex bearing arrangement providing required degrees of freedom as well as the impact of a detailed Failure Modes and Effects Analysis addressing necessary safety systems is also presented. Finite element analysis results demonstrate how mechanical springs increase the telescope's natural frequency response by 22 percent. The critical analysis and resulting design is provided.

We describe the design and performance of an improved hardpoint for the primary mirror cell of the Large Binocular Telescope. Six hardpoints define the position and orientation of the primary mirror and are key elements of the active optics system. After several years of operation, various undesirable characteristics of the original hardpoints were identified. A new deign was developed that provides higher stiffness, greater repeatability, and better overall performance. We describe the design features and present preliminary performance data from lab testing and initial operation in the telescope.

The Large Area Multi-Object Spectroscopic Telescope (LAMOST) is a meridian reflecting Schmidt telescope with a 40m optical axis between the reflecting Schmidt plate and the spherical primary mirror. In the middle is located the spherical focal plane, through which there are corresponding 4000+ unit mounting holes for the fibers, and on its back, there attached a support truss adapted from Serrurier concept. The mechanical stabilization of the focal plane system naturally has magnificent impact on the observation efficiency of the LAMOST. A comprehensive Finite Element Model of the focal plane system has been built to evaluate thermally induced degradation of its mechanical accuracy using the nodal modification technique within ANSYS, and diverse temperature load cases have been considered on the Finite Element model and related thermal analyses have been carried out to investigate thermal deformation of the focal plane. Subsequently the calculated deflection of the working surface has been extracted and reconstructed with least square fitting in MATLAB. The results show that temperature change around the telescope has little effect on the performance of the focal plane within temperature variation requirements of the LAMOST. The methods of modeling and analyzing used in this research are informative for future large telescope projects.

Off-axis systems in radio and infrared wavelengths have obvious advantages in suppressing aperture blockage and background noise. Therefore, the signal-to-noise ratio as well as system gain is improved. However, an off-axis optical system involves complex aberrations which limit its field of view. This paper provides an overview of aberrations in axial symmetric and off-axis optical systems. As the system deviates from an axial symmetric one, system aberrations become more and more complicated. In a general two mirror off-axis focusing system, the field of view is nearly zero. Even for off-axis system with an equivalent parabola, the field of view is still very small as the linear astigmatism dominates the system. An optimized off-axis system is one in which the linear astigmatism and cross polarization-free conditions are met. In this optimized system, coma aberration is dominant, so that the field of view is still limited. The field of view of an optimized off-axis system can be improved using a simple coma corrector system.

The laser tracker allows the precise determination of positions of surfaces in three dimensions over volumes exceeding 30 m radius from the tracker head. At the Large Binocular Telescope a laser tracker has recently been employed for the initial alignment of all telescope optics in the right hand side (DX) bent Gregorian optical train. In this paper the particular approach to alignment of optical elements employed during this campaign is discussed in detail, together with results and expected accuracies. Subsequent to this "mechanical alignment" the telescope was taken "onsky" and a subsequent "optical alignment" using a Shack-Hartman wavefront sensor with stellar sources took place. Ongoing activities include using the laser tracker to measure elevation and thermally induced displacements of individual optical elements.