We present a summary of the Large Millimeter Telescope (LMT) Project and its current status. The LMT is a joint project of the University of Massachusetts (UMass) in the USA and the Instituto Nacional de Astrofisica, Optica y Electronica (INAOE) in Mexico to build a 50m-diameter millimeter-wave telescope. The LMT site is at an altitude of 4600 m atop Volcan Sierra Negra, an extinct volcanic peak in the state of Puebla, Mexico, approximately 100 km east of the city of Puebla. Construction of the antenna steel structure has been completed and the antenna drive system has been installed. Fabrication of the reflector surface is underway. The telescope is expected to be completed in 2008.

The Atacama Large Millimeter/submillimeter Array (ALMA) is an international radio telescope under construction in the Atacama Desert of northern Chile. ALMA will be situated on a high-altitude site at 5000 m elevation which provides excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will be comprised of two key observing components - an array of up to sixty-four 12-m diameter antennas arranged in a multiple configurations ranging in size from 0.15 to ~14 km, and a set of four 12-m and twelve 7-m antennas operating in closely-packed configurations ~50m in diameter (known as the Atacama Compact Array, or ACA), providing both interferometric and total-power astronomical information. High-sensitivity dual-polarization 8 GHz-bandwidth spectral-line and continuum measurements between all antennas will be available from two flexible digital correlators. At the shortest planned wavelength and largest configuration, the angular resolution of ALMA will be 0.005". The instrument will use superconducting (SIS) mixers to provide the lowest possible receiver noise contribution, and special-purpose water vapor radiometers to assist in calibration of atmospheric phase distortions. A complex optical fiber network will transmit the digitized astronomical signals from the antennas to the correlators in the Array Operations Site Technical Building, and post-correlation to the lower-altitude Operations Support Facility (OSF) data archive. Array control, and initial construction and maintenance of the instrument, will also take place at the OSF. ALMA Regional Centers in the US, Europe and Japan will provide the scientific portals for the use of ALMA; a call for early science observations is expected in 2009. In this paper, we present the status of the ALMA project as of mid 2006.

Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is a meridian reflecting Schmidt telescope with an average clear aperture of 4-meter, a focal length of 20-meter and a field of view of 5-degree. It is a national large scientific project in China. The horizontal meridian reflecting Schmidt configuration and with an active Schmidt correcting plate to achieve the special telescope with both wide field of view and large aperture. There are 4000 optical fibers on the focal surface to transfer light of 4000 objects into 16 spectrographs. The project started in 1997. Now it steps into its assembly stage. The general status and progress of LAMOST project is presented in this paper: The key technologies of the project have been tested successfully; the design and manufacturing of the mechanical parts of the telescope have been completed; most segmented mirrors (sub-mirrors) have been polished. Also the first spectrograph, the first three sub-mirrors of Ma (Schmidt plate) with their complete support system, and the first three sub-mirror of the primary mirror are ready for being integrated on the telescope structure

The entire funding has recently been obtained in Belgium for the construction of a 4m Liquid Mirror Telescope. Its prime focus will be equipped with a semi-conventional glass corrector allowing to correct for the TDI effect and a thinned, high quantum efficiency, 4K × 4K pixel equivalent CCD camera. It will be capable of subarcsecond imaging in the i'(760 nm) and possibly r', g' band(s) over a field of ~ 30' in diameter. This facility will be entirely dedicated to a deep photometric and astrometric variability survey over a period of ~ 5 years. In this paper, the working principle of liquid mirror telescopes is first recalled, along with the advantages and disadvantages of the latter over classical telescopes. Several science cases are described. For a good access to one of the galactic poles, the best image quality sites for the ILMT are located either in Northern Chile (latitude near -29°30') or in North-East India (Nainital Hills, latitude near +29°30'). At those geographic latitudes, a deep (i' = 22.5 mag.) survey will approximately cover 90 square degrees at high galactic latitude, which is very useful for gravitational lensing studies as well as for the identification of various classes of interesting galactic and extragalactic objects (cf. microlensed stars, supernovae, clusters, etc.). A description of the telescope, its instrumentation and the handling of the data is also presented.

The Discovery Channel Telescope (DCT) is a 4.2-m telescope being built at a new site near Happy Jack, in northern Arizona. The DCT features a 2-degree-diameter field of view at prime focus and a Ritchey-Chretien (RC) configuration with Cassegrain and Nasmyth focus capability for optical/IR imaging and spectroscopy. Formal groundbreaking at the Happy Jack site for the DCT occurred on 12 July 2005, with construction of major facility elements underway.

LSST will be a large, wide-field groundbased telescope designed to obtain sequential images of the entire visible sky every few nights. The optical design involves a 3-mirror system with an 8.4 m primary, which feeds three refractive correcting elements inside a camera, providing a 10 square degree field of view sampled by a 3 Gpixel focal plane array. The total effective system throughput, AΩ = 319 m² deg², is nearly two orders of magnitude larger than that of any existing facility. The survey will yield contiguous overlapping imaging of 20,000 square degrees of sky in 6 optical bands covering the wavelength regime 320-1060 nm.

VISTA is a 4-m wide field survey telescope with a near infra-red camera and a demanding f/1 primary design now well into its manufacturing phase. We contracted out major items, and generated a coordinated approach to the management of engineering budgets through systems engineering, risks through risk management, and safety through the generation of safety cases. Control of the interfaces and science requirements has been maintained and developed through the current phase. The project is developing the commissioning plan to deliver an effective and safe facility. The current status of VISTA is presented as we move towards the on site integration phase.

The GTC (Gran Telescopio Canarias) is a 10,4 meter segmented telescope, whose integration is currently being completed at the ORM in La Palma, Spain. The GTC is a partnership between Spain, Mexico and the University of Florida. Main science drivers for the GTC are image quality, operational efficiency and reliability. First light is planned for late-2006. The GTC Project, initiated in 1996, is nearly complete in its integration. Groundbreaking was done in 2000. The telescope building and dome were finished by end 2002. The telescope structure was complete in early 2005. Since then this structure is being completed with the rest of the parts, i.e. M1 mirror subcells, M3 tower, main axes encoders and motors, cables, pipes and cable-rotators, electronic cabinets, etc. The mirrors will be installed at the telescope, just before First Light. All the optical elements have been finished and are being prepared to be installed. Three science instruments are being completed to be installed as first generation instruments. Two second-generation instruments, including one exploiting the future Adaptive Optics capabilities of the GTC, are under development.

The four-meter Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. Development of a four-meter solar telescope presents many technical challenges (e.g., thermal control of the enclosure, telescope structure and optics). We give a status report of the ATST project (e.g., system design reviews, instrument PDR, Haleakala site environmental impact statement progress) and summarize the design of the major subsystems, including the telescope mount assembly, enclosure, mirror assemblies, wavefront correction, and instrumentation.

The New Solar Telescope (NST) project at Big Bear Solar Observatory (BBSO) now has all major contracts for design and fabrication in place and construction of components is well underway. NST is a collaboration between BBSO, the Korean Astronomical Observatory (KAO) and Institute for Astronomy (IfA) at the University of Hawaii. The project will install a 1.6-meter, off-axis telescope at BBSO, replacing a number of older solar telescopes. The NST will be located in a recently refurbished dome on the BBSO causeway, which projects 300 meters into the Big Bear Lake. Recent site surveys have confirmed that BBSO is one of the premier solar observing sites in the world. NST will be uniquely equipped to take advantage of the long periods of excellent seeing common at the lake site. An up-to-date progress report will be presented including an overview of the project and details on the current state of the design. The report provides a detailed description of the optical design, the thermal control of the new dome, the optical support structure, the telescope control systems, active and adaptive optics systems, and the post-focus instrumentation for high-resolution spectro-polarimetry.

VERITAS (the Very Energetic Radiation Imaging Telescope Array System) is one of a new generation of ground-based gamma-ray observatories. It is being built by a collaboration of ten institutions from Canada, Ireland, the U.K. and the U.S.A. VERITAS uses the imaging atmospheric Cherenkov technique (IACT) which was developed by the Whipple collaboration using the Whipple 10m telescope. The 10m was the first ground-based gamma-ray telescope to detect both galactic and extragalactic sources of TeV gamma rays. VERITAS is designed to operate in the range from 50 GeV to 50 TeV with optimal sensitivity near 200 GeV; it will effectively overlap with the next generation of space-based gamma-ray telescopes.

EOS Technologies has been commissioned to design and build a unique 2.4m astronomical telescope for the Magdalena Ridge Observatory. This telescope utilizes a high quality primary mirror and cell from a now decommissioned military application. This paper describes the project and gives an overview of the telescope design. The Magdalena Ridge Observatory (MRO) 2.4 meter telescope will be primarily utilized to observe, track, and characterize solar system astronomical targets, Earth satellites, space vehicles, and terrestrial military targets. The telescope's rapid tracking (slew rates are 10^o/sec) will allow it to move to any target and acquire data within one minute of receipt of notice. In this way, the telescope will be used to capitalize on targets of opportunity that occur in asteroid studies (e.g., Near Earth Objects) and in astrophysics, such as gamma ray bursts and other transient phenomena. Planned instrumentation includes a CCD imager, and a low-resolution, wide-band Visible/IR spectrograph (Ryan et al. 2002). Both of these instruments will facilitate characterization studies of asteroids and space objects.

We present the technical status of the Ultra Lightweight Telescope for Research in Astronomy (ULTRA) program. The program is a 3-year Major Research Instrumentation (MRI) program funded by NSF. The MRI is a collaborative effort involving Composite Mirror Applications, Inc. (CMA), University of Kansas, San Diego State University and Dartmouth College. Objectives are to demonstrate the feasibility of carbon fiber reinforced plastic (CFRP) composite mirror technology for ground-based optical telescopes. CMA is spearheading the development of surface replication techniques to produce the optics, fabricating the 1m glass mandrel, and constructing the optical tube assembly (OTA). Presented will be an overview and status of the 1-m mandrel fabrication, optics development, telescope design and CFRP telescope fabrication by CMA for the ULTRA Telescope.

The SkyMapper wide field telescope is currently in production by EOS and is scheduled for first light in Q1 2007. This telescope will produce high quality images over a 3.4 degree diameter flat field for wavebands from 310 nm to 1000 nm. This paper discusses the optical and opto-mechanical design and tolerancing of the SkyMapper Telescope.

The design for robotic telescopes to observe Gamma-Ray Burst (GRB) afterglows and the results of observations are presented. Quickly fading bright GRB flashes and afterglows provide a good tool to study an extremely early universe. However, most large ground-based telescopes cannot afford to follow-up the afterglows and flashes quickly within a few hours since a GRB explosion. We re-modeled the existing middle-class 1.3 m &slasho; telescope of the near infrared band at ISAS in Japan to match for the above requirement. We also set a small telescope of 30 cm diameter with a conventional CCD. These telescopes can monitor afterglows quickly within a few minutes in J, H, Ks and R band with a grism spectrometer.

Ground based gamma-ray telescopes are providing currently key observations to explore the non-thermal universe. The High Energy Stereoscopic System (H.E.S.S.) is a recently commissioned system of four air Cherenkov telescopes observing mainly the southern sky from Namibia at very high energies (VHE) of 100 GeV and above. The data taken during the first two years of operation have unveiled a rich and diverse population of gamma-ray emitters including Pulsar Wind nebulae, the environment of the super-massive black hole in the heart of the Galaxy, shell type supernova remnants, an X-ray binary, so far unidentified Galactic sources, and extragalactic objects mainly of the type of so-called TeV blazars. The extension of H.E.S.S. (Phase II) is already under construction and is scheduled to begin operation in 2007: A large (35 m diameter) Cherenkov telescope is added to the existing 12 m diameter telescopes. The new telescope will extend the energy range towards 20 GeV closing the so far unobserved gap in the energy range between 10 and 100 GeV.

"BOOTES-IR" is the extension of the BOOTES experiment, which has been operating in Southern Spain since 1998, to the near-infrared (nIR). The goal is to follow up the early stage of the gamma ray burst (GRB) afterglow emission in the nIR, as BOOTES does already at optical wavelengths. The scientific case that drives the BOOTES-IR performance is the study of GRBs with the support of spacecraft like HETE-2, INTEGRAL and SWIFT (and GLAST in the future). Given that the afterglow emission in both, the nIR and the optical, in the instances immediately following a GRB, is extremely bright (reached V = 8.9 in one case), it should be possible to detect this prompt emission at nIR wavelengths too. Combined observations by BOOTES-IR and BOOTES-1 and BOOTES-2 since 2006 can allow for real time identification of trustworthy candidates to have a ultra-high redshift (z > 6). It is expected that, few minutes after a GRB, the nIR magnitudes be H ~ 10-15, hence very high quality spectra can be obtained for objects as far as z = 10 by much larger ground-based telescopes. A significant fraction of observing time will be available for other scientific projects of interest, objects relatively bright and variable, like Solar System objects, brown dwarfs, variable stars, planetary nebulae, compact objects in binary systems and blazars.

As the construction of the Subaru Telescope neared the end and the preparation of the first aluminum coating of the primary mirror on the ground floor of the telescope enclosure was in progress in 1997, dust particles blown into the enclosure became a serious issue. The source of the dust particles was mainly volcano cinder rocks in the immediate vicinity of the dome that were crushed through the construction activities, especially by heavy vehicle traffic around the dome. The mitigation measure proposed was to pave the immediate surrounding of the dome. The Subaru dome has a unique design with the special consideration to the airflow through the structure with a few ventilators for the best seeing condition possible. The heat retained by the pavement that may possibly cause thermals was an immediate concern. We examined several types of pavement materials to solve this problem and decided the most suitable materials and method. As a result, we paved the area using asphalt, and were able to improve seeing performance before midnight observation by painting the surface of pavement area white in 2003.

The New Solar Telescope (NST) is an innovative 1.6-meter, off-axis, open telescope currently being developed and built at the Big Bear Solar Observatory (BBSO). The observatory is situated on a small peninsula in Big Bear Lake, a mountain lake at an altitude of about 2100 m in the San Bernardino Mountains of Southern California. The lake effectively suppresses the boundary layer seeing. Thus, providing consistently very good daytime seeing conditions. BBSO has been identified by the site survey for the Advanced Technology Solar Telescope (ATST) as one of the best sites for solar observations. It is uniquely qualified for long-duration observations requiring high-spatial resolution. This type of observations is typically encountered in solar activity monitoring and space weather forecast. The ATST site survey has collected more than two years of data linking seeing conditions to geographical parameters and local climate. We have integrated these data in a MySQL database and we will use this information in connection with a real-time seeing monitor and weather station to predict the seeing conditions at Big Bear such that scheduling and prioritization of observing programs (e.g., synoptic vs. high-resolution modes) becomes possible.

We present the basic design of the THermal Control System (THCS) for the 1.6-meter New Solar Telescope (NST) at the Big Bear Solar Observatory (BBSO), California. The NST is an off-axis Gregorian telescope with an equatorial mount and an open support structure. Since the telescope optics is exposed to the air, it is imperative to control the local/dome seeing, i.e., temperature fluctuations along the exposed optical path have to be minimized. To accomplish this, a THCS is implemented to monitor the dome environment and interact with the louver system of the dome to optimize instrument performance. In addition, an air knife is used to minimize mirror seeing. All system components have to communicate with the Telescope Control System (TCS), a hierarchical system of computers linking the various aspects of the entire telescope system, e.g., the active mirror control, adaptive optics, dome and telescope tracking, weather station, etc. We will provide an initial thermal model of the dome environment and first measurements taken in the recently replaced BBSO dome.

To get the strategy to confirm image qualities of Subaru Telescope, we have obtained the statistics of seeing measured with auto guider images obtained during scientific observations. In addition to this, we started a regular operation of a stationary DIMM at the Subaru Telescope site. From the data of natural seeing measured with the DIMM, we expect to reveal contributions of telescope vibration, inadequate enclosure ventilation, or optical aberrations including deformation of primary mirror by wind load. The stationary DIMM station consists of one 30 cm diameter DIMM, its enclosure, the local control unit and Linux based control PC. We put our DIMM station at the catwalk of the Subaru enclosure at the level of 12-m from the ground, because the high location from the ground can minimize the influence of ground layer. We describe details of our DIMM station and show seeing data obtained since June 2005 and comparison with the seeing obtained with Subaru auto guider images in order to check whether the enclosure of Subaru Telescope may affect the DIMM to measure the seeing.

The U.S. Naval Observatory Robotic Astrometric Telescope (URAT) project aims at a highly accurate (5 mas), ground-based, all-sky survey. Requirements are presented for the optics and telescope for this 0.85 m aperture, 4.5 degree diameter field-of-view, specialized instrument, which are close to the capability of the industry. The history of the design process is presented as well as astrometric performance evaluations of the toleranced, optical design, with expected wavefront errors included.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is the next generation of airborne astronomical observatories. Funded by the U.S. and German space agencies, SOFIA is scheduled for science flights beginning in late-2008. The observatory consists of a 747-SP modified to accommodate a 2.7-meter telescope with an open port design. Academic and government laboratories spanning both the U.S. and Germany are developing science instruments for SOFIA. Using state-of-the-art technologies, SOFIA will explore the emission of astronomical sources with an unprecedented level of angular resolution (θ[arc-seconds] = 0.1 x wavelength [μm]) and spectral line sensitivity at infrared and sub-millimeter wavelengths. The current status of SOFIA is available from the observatory web site at http://sofia.arc.nasa.gov/ and is updated frequently.

We describe SPIDER, a novel balloon-borne experiment designed to measure the polarization of the Cosmic Microwave Background (CMB) on large angular scales. The primary goal of SPIDER is to detect the faint signature of inflationary gravitational waves in the CMB polarization. The payload consists of six telescopes, each operating in a single frequency band and cooled to 4 K by a common LN/LHe cryostat. The primary optic for each telescope is a 25 cm diameter lens cooled to 4 K. Each telescope feeds an array of antenna coupled, polarization sensitive sub-Kelvin bolometers that covers a 20 degree diameter FOV with diffraction limited resolution. The six focal planes span 70 to 300 GHz in a manner optimized to separate polarized galactic emission from CMB polarization, and together contain over 2300 detectors. Polarization modulation is achieved by rotating a cryogenic half-wave plate in front of the primary optic of each telescope. The cryogenic system is designed for 30 days of operation. Observations will be conducted during the night portions of a mid-latitude, long duration balloon flight which will circumnavigate the globe from Australia. By spinning the payload at 1 rpm with the six telescopes fixed in elevation, SPIDER will map approximately half of the sky at each frequency on each night of the flight.

SUNRISE is an international project for the development, construction, and operation of a balloon-borne solar telescope with an aperture of 1 m, working in the UV/VIS spectral domain. The main scientific goal of SUNRISE is to understand the structure and dynamics of the magnetic field in the atmosphere of the Sun. SUNRISE will provide near diffraction-limited images of the photosphere and chromosphere with an unpredecented resolution down to 35 km on the solar surface at wavelengths around 220 nm. The focal-plane instrumentation consists of a polarization sensitive spectrograph, a Fabry-Perot filter magnetograph, and a phase-diverse filter imager working in the near UV. The first stratospheric long-duration balloon flight of SUNRISE is planned in Summer 2009 from the swedish ESRANGE station. SUNRISE is a joint project of the german Max-Planck-Institut fur Sonnensystemforschung (MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut fur Sonnenphysik (KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, USA, and the spanish IMaX consortium. In this paper we will present an actual update on the mission and give a brief description of its scientific and technological aspects.

Several commercial telecommunication ventures together with a well funded US military program make it a likely possibility that an autonomous, high-altitude, light-than-air (LTA) vehicle which could maneuver and station-keep for weeks to many months will be a reality in a few years. Here I outline how this technology could be used to develop a high-altitude astronomical observing platform which could return high-resolution optical data rivaling those from space-based platforms but at a fraction of the cost.

The 2.5 meter (m) effective diameter telescope on SOFIA - the Stratospheric Observatory for Infrared Astronomy - will operate in an open-port cavity which will be closed below operating altitudes by a cavity-door assembly. When operating, the telescope will view the sky through an aperture defined by an aperture assembly (AA) with a nearly rectangular opening extending 112 inches (2.84 m) in elevation (roll) and 129 inches (3.27 m) in cross-elevation. The aperture will be servo-controlled in roll to track the telescope elevation (EL), and the aircraft heading will be adjusted to maintain the telescope centered on the aperture in cross-elevation (XEL). An upper rigid door (URD) and lower flexible door (LFD) move with the aperture to minimize the opening into the cavity containing the telescope. This paper describes basic parameters of the door system, and estimates possible science impacts of its specification, configuration and planned operation. Topics included are the geometry, expected aerodynamic disturbances, control system, gear life, influences of radiative and diffraction effects on science instrument performance, testing, operational considerations, and development status. As designed, the door system is expected not to limit the performance of science instruments or observatory operational efficiency, but several potential concerns are considered. These include modulation of stray and diffracted radiation, reliability, and maintainability.

The telescope pointing control of the Stratospheric Observatory for Infrared Astronomy (SOFIA) is achieved during science observations by an array of sensors including three imagers, gyroscopes and accelerometers. In addition, throughout alignment and calibration of the telescope assembly, the High-speed Imaging Photometer for Occultation (HIPO) is used as a reference instrument. A summary of the telescope pointing control concept is given and how HIPO is used to calibrate the telescope reference systems on the sky. A method is introduced using simple maneuvers to perform initial alignment of HIPO, the imagers and the gyroscopes by means of single star observations. During the first on sky testing of the SOFIA telescope, these maneuvers were carried out and the alignment could be improved iteratively. The corresponding alignment accuracies are identified considering repeated measurements, environmental and sensor noise. Inertial and non-inertial observations, as well as measurements over the entire operational elevation range provide additional alignment and sensor performance information. Finally, an overview is presented for future improvements in alignment.

The integration of the three main silicon carbide mirrors into the new 1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned during 2006. We expect first light at the end of 2006. A progress report about integration of the optics and mechanics and planning of the commissioning phase of the telescope and post focus instruments will be presented at the meeting. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg, the Astrophysikalische Institut Potsdam, the Institut fur Astronomie Gottingen and additional national and international Partners.

In March 2004, the Commissioning Instrument (CI) for the GTC was accepted in the site of The Gran Telescopio Canarias (GTC) located in La Palma Island, Spain. During the GTC integration phase, the CI will be a diagnostic tool for performance verification. The CI features four operation modes-imaging, pupil imaging, Curvature Wave-front sensing (WFS), and high resolution Shack-Hartmann WFS. The imaging mode permits to qualify the GTC image quality. The Pupil Mode permits estimate the GTC stray light. The segments figure, alignment and cophasing verifications are made with both WFS modes. In this work we describe the Commissioning Instrument and show some tests results obtained during the site acceptance process at the GTC site.

The Large Binocular Telescope (LBT) Project is a collaboration between institutions in Arizona, Germany, Italy, Indiana, Minnesota, Ohio and Virginia. The telescope on Mt. Graham in southeastern 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 coherent imaging along with adaptive optics gives the telescope the diffraction-limited resolution of a 22.65-meter telescope. The first primary mirror was aluminized in April 2005. First light with a single primary mirror and a prime focus imager was achieved in October 2005. We describe here some of the technical challenges met and solved on the way to First Light. The second of two 8.4-meter borosilicate honeycomb primary mirrors has been installed in the telescope in October 2005 and was aluminized in January 2006. Binocular operation with two prime focus cameras is planned for Fall 2006. The telescope uses two F/15 adaptive secondaries to correct atmospheric turbulence. The first of these adaptive mirrors is now being integrated with its electro-mechanics.

The Southern African Large Telescope (SALT) was completed in 2005 and began initial scientific operations in August of that year. Built in just under 6 years and on budget, SALT has been a good example of a successfully managed telescope project where systems engineering disciplines have been applied to good effect. This paper discusses the experiences of completing and commissioning SALT and its first-light instruments and the early scientific operations. Lessons learned in integrating the various telescope subsystems and implementation of the telescope control system are presented. First Light was announced on 1 September 2005 following the installation of the last of the 91 mirror segments and the commissioning of the UV-visible imager, SALTICAM. This was soon followed by the first scientific observations and the beginning of the commissioning phase for the active optics system.

The Large Binocular Telescope is currently equipped with a couple of wide field Prime Focus. The two cameras are optimized for, respectively, the blue and the red portion of the visible spectrum. The history of this project is here sketched up and the current status is shown. The Blue channel is currently working onboard the telescope and provided what has been named the first-light of the telescope in single eye configuration.

The new German solar 1.5 m telescope (GREGOR) will be equipped with an adaptive optic system. GREGOR has a relatively complicated optical scheme with small tolerances. We therefore have to expect certain aberrations due to misalignments and mechanical/optical imperfections. This is why the AO will play an important role as an auxiliary tool for telescope alignment from the very beginning of the commissioning phase. The paper will cover the alignment strategies taking advantage of the AO system.

The National Radio Astronomy Observatory Green Bank Telescope (GBT) is the world's largest fully steerable telescope. The GBT has now been in routine operation for over two years, observing at frequencies up to 50 GHz. In order to deliver the tracking accuracies required at 50 GHz, we solve simultaneously for gravitational and thermal effects in the development of the static pointing and focus tracking models. A precision temperature sensor system then generates additional real-time corrections to compensate for varying thermal gradients in the antenna. Collimation and surface accuracy requirements are met by an active surface control system which combines initial corrections derived from a finite element model of the antenna with additional terms derived from astronomical phase-retrieval holography measurements. The GBT has a rich suite of instrumentation including receivers which cover almost the complete frequency range from ~ 290 MHz to 50 GHz, and backends for spectroscopy, pulsar observing, broadband continuum, very long baseline interferometry and planetary radar reception. A 64-pixel bolometer camera is under development by a consortium including UPenn, NASA-GSFC, NIST, UCardiff and NRAO. Recent software developments include an extremely flexible application which combines traditional interactive observing, scheduling-block based observing and real-time monitoring and data display in a single, convenient interface. In this paper I will summarize the current performance of the GBT, and review some recent science results. I will also describe how plans changed with time, and review some of the lessons learned in the development of the telescope.

The Combined Array for Research in Millimeter-wave Astronomy (CARMA) comprises the millimeter-wave antennas of the Owens Valley Radio Observatory (OVRO), the Berkeley-Illinois-Maryland Association (BIMA) Array, and the new Sunyaev-Zel'dovich Array (SZA). CARMA consists of six 10.4-m, nine 6.1-m, and eventually eight 3.5-m diameter antennas on a site at elevation 2200 m in the Inyo Mountains near Bishop, California. The array will be operated by an association that includes the California Institute of Technology and the Universities of California (Berkeley), Chicago, Illinois (Urbana-Champaign), and Maryland. Observations will be supported at wavelengths of 1 cm, 3 mm, and 1.3 mm, on baselines from 5 m to 2 km. The initial correlator will use field programmable gate array (FPGA) technology to provide all single-polarization cross-correlations on two subarrays of 8 and 15 antennas with a total bandwidth of 8 GHz on the sky. The next generation correlator will correlate the full 23-antenna array in both polarizations. CARMA will support student training, technology development, and front-line astronomical research in a wide range of fields including cosmology, galaxy formation and evolution, star and planet formation, stellar evolution, chemistry of the interstellar medium, and within the Solar System, comets, planets, and the Sun. Commissioning of CARMA began in August 2005, after relocation of the antennas to the new site. The first science observations commenced in April 2006.

APEX, the Atacama Pathfinder Experiment, has been successfully commissioned and is in operation now. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the world's outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of 17-18 μm makes APEX suitable for observations up to 200 μm, through all atmospheric submm windows accessible from the ground.

Science studies made by the Large Synoptic Survey Telescope will reach systematic limits in nearly all cases. Requirements for accurate photometric measurements are particularly challenging. Advantage will be taken of the rapid cadence and pace of the LSST survey to use celestial sources to monitor stability and uniformity of photometric data. A new technique using a tunable laser is being developed to calibrate the wavelength dependence of the total telescope and camera system throughput. Spectroscopic measurements of atmospheric extinction and emission will be made continuously to allow the broad-band optical flux observed in the instrument to be corrected to flux at the top of the atmosphere. Calibrations with celestial sources will be compared to instrumental and atmospheric calibrations.

From 2006 to 2008, all sub-mirrors and instruments of LAMOST will be installed gradually until fully completion. Before all sub-mirrors and instruments installed, LAMOST team planed a temporary scheme in order to do some testing observations. The plan will start from the beginning of 2007, and the part LAMOST will have 3×3 Mirrors (3 sub Ma and 3 sub Mb) with 1.25 degree field, and 250 fibers on its focal plane at that time. We are planning a set of observations during the engineering process, which includes small amount of stars. The spectral resolution will be 10000 and 2000, and the amount of spectra in the data set will reach several thousands. By using these data, we can improve our techniques of automated reduction and analyzing. For example, in order to test our software, physical parameters of a small proportion of stars such as Vr, Teff, log g, [Fe/H], [α/Fe] should be compared with Sloan Digital Sky Survey (SDSS). If the results are precise enough, the parameters of more stars could be applied to do some research, such as searching for star stream, studying star clusters in our Galaxy, and searching for poor-metal star etc.

Dome C, located on the Antarctic Plateau, is expected to be one of the best sites for ground-based astronomical observations at infrared wavelengths. Its high elevation, equivalent to 3800 m of a temperate site, and the very low temperatures (down to -90°C), reduce dramatically the background thermal emission from both the instrument and the sky; the very dry and cold environment makes the atmospheric windows more transparent, wide and stable than in any ground-based temperate site. The Antarctic Multiband Infrared Camera (AMICA), mounted at the focal plane of the IRAIT telescope, is designed to perform astronomical observations at near- and mid-infrared wavelengths from Dome C. In order to fully exploit the above-mentioned excellent site conditions, a set of optimized infrared filters covering the 2 - 25 microns region has been defined as a result of a careful analysis. In the first step, the bands of interest were identified on the basis of the scientific requirements and the opportunities offered by the site. The fundamental scientific parameters, as the central wavelength, the bandwidth, the isophotal magnitude were then computed for each filter, in such a way to optimize the camera performances.

In this paper we present the characterization of some of the principal meteorological parameters extended over 25 km from the ground and over two years (2003 and 2004) above the Antarctic site of Dome C. The data set is composed by 'analyses' provided by the General Circulation Model (GCM) of the European Center for Medium Weather Forecasts (ECMWF) and they are part of the catalog MARS. A monthly and seasonal (summer and winter time) statistical analysis of the results is presented. The Richardson number is calculated for each month of the year over 25 km to study the stability/instability of the atmosphere. This permits us to trace a map indicating where and when the optical turbulence has the highest probability to be triggered on the whole troposphere, tropopause and stratosphere. We finally try to predict the best expected isoplanatic angle and wavefront coherence time (θ_0,max and a τ_0,max) employing the Richardson number maps, the wind speed profiles and simple analytical models of C_N² vertical profiles.

The MMT all-sky camera is a low-cost, wide-angle camera system that takes images of the sky every 10 seconds, day and night. It is based on an Adirondack Video Astronomy StellaCam II video camera and utilizes an auto-iris fish-eye lens to allow safe operation under all lighting conditions, even direct sunlight. This combined with the anti-blooming characteristics of the StellaCam's detector allows useful images to be obtained during sunny days as well as brightly moonlit nights. Under dark skies the system can detect stars as faint as 6th magnitude as well as very thin cirrus and low surface brightness zodiacal features such as gegenschein. The total hardware cost of the system was less than $3500 including computer and framegrabber card, a fraction of the cost of comparable systems utilizing traditional CCD cameras.

The high plateaus in west China (Tibet) may provide good candidate sites possibly for ELT projects. According to satellite weather data, we found that a certain area in Tibet shows potentiality for good astronomical observations with less cloud coverage. We have explored through west Tibet to watch its topography in summer, 2004. We reanalyze meteorological data collected by GAME-Tibet project. We have started weather monitor in two candidate sites in west China; Oma in western area of Tibet and Karasu near the western boundary of China. Monitoring observations using modern astronomical site-testing techniques such as a DIMM and an IR cloud monitor camera will be started to catch up continuous monitoring of seeing and cloud coverage.

The simulation of the optical turbulence (OT) for astronomical applications obtained with non-hydrostatic atmospherical models at meso-scale presents, with respect to measurements, some advantages. Among these: (1) the possibility to provide 3D C²_N maps above a region of a few tens of kilometers around a telescope. (2) the possibility to simulate the turbulence 'where' and 'when' it is desired without the need of long and expensive site testing campaigns done with several instruments. (3) the possibility to forecast the optical turbulence, goal considered a 'chimera' by all astronomers and fundamental element for the implementation of the flexible scheduling, crucial operation mode for the success of new class of telescopes (D > 10 m). The future of the ground-based astronomy relies upon the potentialities and feasibility of the ELTs. Our ability in knowing, controlling and 'managing' the effects of the turbulence on such a new generation telescopes and facilities are determinant to assure their competitiveness with respect to the space astronomy. In the past several studies have been carried out proving the feasibility of the simulation of realistic C²_N profiles above astronomical sites. The European Community (FP6 Program) decided recently to fund a Project aiming, from one side, to prove the feasibility of the OT forecasts and the ability of meso-scale models in discriminating astronomical sites from optical turbulence point of view and, from the other side, to boost the development of this discipline at the borderline between the astrophysics and the meteorology. In this contribution I will present the scientific and technological goals of this project, the challenges for the ground-based astronomy that are related to the success of such a project and the international synergies that have been joint to optimize the results.

We present a proposal for an 8.4 metre off-axis optical/IR telescope to be located at Dome C, Antarctica. LAPCAT will use a mirror identical to the offset segment recently cast for the Giant Magellan Telescope (GMT) as a completely unobscured f/2.1 primary. With a cooled deformable Gregorian secondary in a dewar following prime focus, LAPCAT will allow for diffraction-limited imaging with only a single reflecting surface at ~220K, and thus the lowest possible thermal background obtainable on earth. The exceptionally low atmospheric turbulence above Dome C enables very high contrast imaging in the thermal infrared, and diffraction limited imaging extending to optical wavelengths (20 mas at 800 nm, where Strehl ratios > 60% are projected). As an example, a deep 5 μm exoplanet imaging survey to complement current radial velocity methods could take advantage of both the low background and pupil remapping methods for apodization enabled by the clear aperture. Many new, young, giant planets (≥ 3M_J at 1 Gyr) would be detected in orbits ≥ 5 AU out to 20 pc. By providing a test bed for many of the GMT technologies in an Antarctic environment, LAPCAT also paves the way for the eventual construction of a second GMT at Dome C. Such a telescope would have unparalleled capabilities compared both to other ELTs in temperate sites and to JWST.

We describe a large-angle survey for fast, optical transients: gamma ray bursts (GRBs), supernovae (SNe), lensed and transiting planets, AGNs and serendipitously found objects. The principal science goals are to obtain light curves for all transients and to obtain redshifts of GRBs and orphan afterglows. The array is called Xian. In conjunction with the gamma-ray satellites, ECLAIRs/SVOM and GLAST, the data will be used to study sources from z=0.1 to >6. The telescope array has 400 Schmidt telescopes, each with ~20 sq. degree focal planes and apertures of ~0.5 meters. The passively cooled, multiple CCD arrays have a total of 16000x16000 pixels, up to 13 readout channels per 1K x 4K CCD and work in TDI mode. The system provides continuous coverage of the circumpolar sky, from the Antarctic plateau, every few seconds. Images averaged over longer time intervals allow searches for the host galaxies of the detected transients, as well as for fainter, longer timescale transients. Complete, data at high time resolution are only stored for selected objects. The telescopes are fixed and use a single filter: there are few (or no) moving parts. Expected detection rates are 0.3 GRBs afterglows per day, >100 orphan afterglows per day and >0.1 blue flashes per day from Type II or Type Ib/c supernovae. On-site computers compare successive images and trigger follow-up observations of selected objects with a co-sited, well-instrumented telescope (optical, IR; spectroscopy, photometry, polarimetry), for rapid follow-up of transients. Precursor arrays with 20-100 square degrees are planned for the purpose of developing trigger software, testing observing strategies and deriving good cost estimates for a full set of telescope units.

Thanks to exceptional coldness, low sky brightness and low content of water vapour of the above atmosphere Dome C, one of the three highest peaks of the large Antarctic plateau, is likely to be the best site on Earth for thermal infrared observations (2.3-300 μm) as well as for the far infrared range (30 μm-1mm). IRAIT (International Robotic Antarctic Infrared Telescope) will be the first European Infrared telescope operating at Dome C. It will be delivered to Antarctica at the end of 2006, will reach Dome C at the end of 2007 and the first winter-over operation will start in spring 2008. IRAIT will offer a unique opportunity for astronomers to test and verify the astronomical quality of the site and it will be a useful test-instrument for a new generation of Antarctic telescopes and focal plane instrumentations. We give here a general overview of the project and of the logistics and transportation options adopted to facilitate the installation of IRAIT at Dome C. We summarize the results of the electrical, electronics and networking tests and of the sky polarization measurements carried out at Dome C during the 2005-2006 summer-campaign. We also present the 25 cm optical telescope (small-IRAIT project) that will installed at Dome C during the Antarctic summer 2006-2007 and that will start observations during the 2007 Antarctic winter when a member of the IRAIT collaboration will join the Italian-French Dome C winter-over team.

The Antarctic Plateau offers unique opportunities for ground-based Infrared Astronomy. AMICA (Antarctic Multiband Infrared CAmera) is an instrument designed to perform astronomical imaging from Dome-C in the near- (1 - 5 μm) and mid- (5 - 27 μm) infrared wavelength regions. The camera consists of two channels, equipped with a Raytheon InSb 256 array detector and a DRS MF-128 Si:As IBC array detector, cryocooled at 35 and 7 K respectively. Cryogenic devices will move a filter wheel and a sliding mirror, used to feed alternatively the two detectors. Fast control and readout, synchronized with the chopping secondary mirror of the telescope, will be required because of the large background expected at these wavelengths, especially beyond 10 μm. An environmental control system is needed to ensure the correct start-up, shut-down and housekeeping of the camera. The main technical challenge is represented by the extreme environmental conditions of Dome C (T about -90 °C, p around 640 mbar) and the need for a complete automatization of the overall system. AMICA will be mounted at the Nasmyth focus of the 80 cm IRAIT telescope and will perform survey-mode automatic observations of selected regions of the Southern sky. The first goal will be a direct estimate of the observational quality of this new highly promising site for Infrared Astronomy. In addition, IRAIT, equipped with AMICA, is expected to provide a significant improvement in the knowledge of fundamental astrophysical processes, such as the late stages of stellar evolution (especially AGB and post-AGB stars) and the star formation.

The Large-Sky-Area Multi-object Fiber Spectroscopic Telescope (LAMOST) put forward by Shou-guan Wang and Ding-qiang Su is a special reflecting Schmidt telescope with the spherical mirror fixed and the correcting plate acts as both correcting plate and tractor. The correcting plate is installed on an alt-azimuth mounting and its aspherical figure is variable to meet the requirement for eliminate the spherical aberration of the spherical primary mirror when it is at variant orientations during the observation course and for different sky area. With LAMOST, both large aperture and large field of view can been obtained. Benefited from the LAMOST design and practice, a LAMOST-type telescope for full-sky survey is conceived for the Antarctic. Because of the favorable seeing condition and all-winter continuous observation, a telescope with aperture of the 2-m could be equivalent to the 4-m LAMOST. We preliminarily considered a 2-m telescope with a primary focus and a Cassegrain focus. The f-ratio of 5 and FOV 3-degree for the primary focus, and f-ratio of 15 and 8 minutes FOV with the diffraction limited image for the Cassegrain focus. In this paper, the scientific goals, the optical system of the telescope, particular material and technique which are applicable under the extreme low temperature condition at the Antarctic are described.

We present preliminary results of a comparison of possible Antarctic telescope locations based on the results of a regional climate model. The simulation results include predictions for temperature, wind speed, seeing, precipitable water vapor, and cloud cover. The domain of the simulation is the entire Antarctic continent for the 2004 winter season. By incorporating lateral forcing, our simulation captures the effects of weather systems that can affect even the interior regions of the Antarctic plateau. The simulation also shows maritime air advection into the plateau interior. We find the model predictions are generally in good agreement with measurements made at the South Pole and Dome C. The simulation results suggest that the Dome F and Dome A regions are potentially very good sites and are generally superior to Dome C.

Recent data have shown that Dome C, on the Antarctic plateau, is an exceptional site for astronomy, with atmospheric conditions superior to those at any existing mid-latitude site. Dome C, however, may not be the best site on the Antarctic plateau for every kind of astronomy. The highest point of the plateau is Dome A, some 800 m higher than Dome C. It should experience colder atmospheric temperatures, lower wind speeds, and a turbulent boundary layer that is confined closer to the ground. The Dome A site was first visited in January 2005 via an overland traverse, conducted by the Polar Research Institute of China. The PRIC plans to return to the site to establish a permanently manned station within the next decade. The University of New South Wales, in collaboration with a number of international institutions, is currently developing a remote automated site testing observatory for deployment to Dome A in the 2007/8 austral summer as part of the International Polar Year. This self-powered observatory will be equipped with a suite of site testing instruments measuring turbulence, optical and infrared sky background, and sub-millimetre transparency. We present here a discussion of the objectives of the site testing campaign and the planned configuration of the observatory.

The brightness of the night sky at an astronomical site is one of the principal factors that determine the quality of available optical observing time. At any site the optical night sky is always brightened with airglow, zodiacal light, integrated starlight, diffuse Galactic light and extra-galactic light. Further brightening can be caused by scattered sunlight, aurorae, moonlight and artificial sources. Dome C exhibits many characteristics that are extremely favourable to optical and IR astronomy; however, at this stage few measurements have been made of the brightness of the optical night sky. Nigel is a fibre-fed UV/visible grating spectrograph with a thermoelectrically cooled 256 × 1024 pixel CCD camera, and is designed to measure the twilight and night sky brightness at Dome C from 250 nm to 900 nm. We present details of the design, calibration and installation of Nigel in the AASTINO laboratory at Dome C, together with a summary of the known properties of the Dome C sky.

The Gattini cameras are two site testing instruments for the measurement of optical sky brightness, large area cloud cover and auroral detection of the night sky above the high altitude Dome C site in Antarctica. The cameras have been in operation since January 2006. The cameras are transit in nature and are virtually identical, both adopting Apogee Alta ccd detectors. The camera called Gattini-SBC images a 6 degree field centred on the South Pole, an elevation of 75° at the Dome C site. The camera takes repeated images of the same 6 degree field in the Sloan g' band (centred on 477nm) and, by adopting a lens with sufficiently long focal length, one can integrate the sky background photons and directly compare to the equivalent values of the stars within the field. The second camera, called Gattini-allsky, incorporates a fish-eye lens and images ~110 degree field centred on local zenith. By taking frequent images of the night sky we will obtain long term cloud cover statistics, measure the sky background intensity as a function of solar and lunar altitude and phase and directly measure the spatial extent of bright aurora if present and when they occur. An overview of the project is presented together with preliminary results from data taken since operation of the cameras in January 2006.

A survey of northwest Africa and southern Spain (including the Canary Islands) has been carried out using satellite data from the Meteosat Operational Service (in geostationary orbit at 0^o longitude). The study was funded by European Southern Observatory (ESO) as part of the site survey effort for the Overwhelmingly Large Telescope (OWL), recently re-baselined as the European Extremely Large Telescope (E-ELT). Cloud cover and water vapor were surveyed over the area 20^oN to 40^oN and 20^oW to 10^oE using satellite data for the 7-year period January 1996 to December 2002. The study included a calibration of the Upper Tropospheric Humidity (UTH) for Meteosat-5, an aerial analysis of cloud cover and precipitable water vapor (PWV) and a verification of the satellite cloud cover using ground-based observations of sky conditions derived from extinction measurements made at the Observatorio del Roque de los Muchachos (ORM) on La Palma. In view of the importance of establishing the accuracy of the satellite method, a summary of results from earlier verification studies has been included in the relevant section.

We present the results of vertical profiles of refractive index structure constant C_n²(h) measurements made at the 1-m telescope, La Silla Observatory (ESO,Chile) using the generalized SCIDAR technique. Observations took place during July, August, November, 2002 and February 2003. The instrumentation, computer interface and a preliminary reduction software were provided by the Imperial College (London) scientific group. We describe the SCIDAR image processing technique and two inverting methods. The first, proposed by the Imperial College group, is based on the Tikhonov regularization and the second, on use at Nice University, is based on maximum entropy. Performances of both methods agree well. The profile integrals are compared to simultaneous DIMM seeing measurements made at La Silla Observatory.

The Thirty Meter Telescope (TMT) project is currently testing six remote sites as candidates for the final location of the telescope. Each site has several instruments, including seeing monitors, weather stations, and turbulence profile measuring systems, each of which is computer controlled. As the sites are remote (usually hours from the nearest town), they requires a system that can control the operations of all the varied subsystems, keep the systems safe from damage and recover from errors during operation. The robotic system must also be robust enough to operate without human intervention and when internet connections are lost. It is also critical that a data archiving system diligently records all data as gathered. This paper is a discussion of the TMT site testing robotic computer system as implemented.

The project for the proposed Large Synoptic Survey Telescope (LSST) performed more than two years of data collection, site evaluation, and analysis to support the selection of its prime site. LSST assessment was based on using an existing site with existing infrastructure and historical performance information. A large and diverse set of comparative information was compiled for potential sites using results from other site campaigns, measurements from existing large telescopes, new astro-climate measurements, logistical and feasibility information, and from existing satellite and climate databases. Several analyses were performed on these data including the assessment of survey performance using the LSST operation simulator. An independent site selection committee of experts provided recommendations to the Project leading to three finalist sites, one in Mexico, and two in northern Chile. The finalist sites were assessed thoroughly with additional data collection from all-sky cameras and site proposals. Cerro Pachon in Chile was selected to be the site for LSST after a difficult decision between the high quality final candidates. This paper describes the data, analysis and approach used to support the site evaluation.

Differential Image Motion Monitors (DIMMs) have become the industry standard for astronomical site characterization. The calibration of DIMMs is generally considered to be routine, but we show that particular care must be paid to this issue if high accuracy measurements are to be achieved. In a side by side comparison of several DIMMs, we demonstrate that with proper calibration we can characterize the seeing to better than ±0.02 arcseconds.

The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope being designed for high spatial, spectral and temporal resolution, as well as IR and low-scattered light observations. The overall limit of performance of the telescope is strongly influenced by the qualities of the site at which it is located. Six sites were tested with a seeing monitor and a sky brightness instrument for 1.5 to 2 years. The sites were Big Bear (California), Haleakala (Hawaii), La Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak (New Mexico), and San Pedro Martir (Baja California, Mexico). In this paper we will describe the methods and results of the site survey, which chose Haleakala as the location of the ATST.

We are developing a new type of lidar for measuring range profiles of atmospheric optical turbulence. The lidar is based on a measurement concept that is immune to artifacts caused by effects such as vibration or defocus. Four different types of analysis and experiment have all shown that a turbulence lidar that can be built from commercially available components will attain a demanding set of performance goals. The lidar is currently being built, with testing scheduled for August 2006.

Adaptive optics devices in astronomy compensate the distortions introduced by the atmosphere in the quality and resolution of images taken by ground-based telescopes. The proper knowledge of the spatial and temporal behaviour of the atmospheric turbulence is crutial for optimizing the design of multiconjugate adaptive optics systems to satisfy the excellent image quality requirements of the new generation of large and extremelly large telescopes. Atmospheric turbulence monitoring is being carried out at astronomical sites using different techniques, being generalized SCIDAR one of the most popular. Generalized SCIDAR technique provides enough information to derive the vertical structure of the atmospheric turbulence (C²_N(h)) as well as the velocity of the turbulent layers (V_tur(h)). In this work, we present a new and automatic method to derive V_tur(h) from generalized SCIDAR data based on wavelet analysis.

Roque de los Muchachos Observatory (ORM) at La Palma (Canary Islands) is one of the two top sites selected for hosting the future European Large Telescope (ELT) (http://www.eso.org/projects/e-elt/), the other being Paranal (in Chile). Meteorological and seeing conditions are crucial for the site selection. New concepts related to geophysical properties (seismicity and microsismicity), local climate variability, the presence of aerosols, atmospheric conditions related to the optical turbulence (tropospheric and ground wind regimes) have recently been introduced for selecting sites for a new generation of Extremely Large Telescopes (Munoz-Tunon 2002, Munoz-Tunon et al. 2003 a, 2003 b; Varela et al., 2002; Varela & Munoz-Tunon, 2004; Varela et al., 2004 a, 2004 b) and also for telescope design and feasibility studies for adaptive optics. Wind speed at 200 mbar is one of the key parameters proposed for characterizing atmospheric turbulence above the Observatory (Sarazin & Tokovinin, 2002, Garcia-Lorenzo et al., 2005). A lower average 200 mbar wind speed is obtained at the ORM in comparison with other astronomical sites; furthermore, the ORM ranks first in in suitability for adaptive optics suitability (Garcia-Lorenzo et al., 2005). The usefulness of this value might be conditional on the continuity of the wind value and wind direction from the upper troposphere to the ground level. With this motivation we are undertaking a study of tropospheric and ground winds at several observing sites.

We discuss the use of the water vapour radiometry technique for atmospheric phase correction as applied to the Atacama Large Millimetre Array (ALMA). The atmospheric conditions derived from site test instrumentation are summarised, and the nature of the phase correction problem quantified. We then present calculations of the expected errors in the radiometrically-corrected atmospheric phase, based on estimates of the radiometer sensitivity. These results indicate how well we need to know the atmospheric structure in order to make accurate phase estimates, and have implications for the meteorological instruments needed on the site. Finally we present the results of simulations of daytime turbulence on the site, and use these to predict the phase fluctuations due to wet and dry air, and discuss their implications for phase correction at Chajnantor.

The Thirty Meter Telescope (TMT) site testing programme is evaluating the use of sonic anemometers as a means of measuring the optical turbulence at the level of its MASS/DIMM telescopes (7m). Tests were performed where sonic anemometers were directly compared against a differenced fine wire thermocouple system. We also show here that fine wire thermocouples produce turbulence measurements comparable to those from a traditional microthermal probe system.

As part of the Thirty Meter Telescope (TMT) site testing program, several instruments have been deployed to characterize the turbulence profiles of the candidate sites. To make such measurements in the boundary layer (height < 1,000m) we have installed several SODARs. Initially conceived to make 3-dimensional wind speed profiles, this instrument is also capable of measuring the temperature fluctuation constant C²_T. Such a measurement requires calibration to become quantitative. We present in this paper a new calibration method that relies on additional kinetic heat flux measurements. This method is the first method to be fully portable to any other SODARs and does not rely on another turbulence profiler for cross calibration. This method will be used to calibrate all TMT SODAR data.

We present the details of an experimental apparatus built to explore wavefront distortion and its mitigation when an optical beam passes from one thermal environment into another. The experiment simulates a situation within the Advanced Technology Solar Telescope (ATST) baseline design where the beam travels from an ambient-temperature environment into a thermostatically controlled "room temperature" environment. We found that an 8°C temperature difference between the two environments introduces about 125 nm rms of wavefront distortion. A double air curtain (one on each side of the boundary) reduces this to about 30 nm rms. We also showed that the high-order (>1300 DoF) adaptive optics system which is integral to the ATST design will be able to further reduce this to about 5 nm rms, well within our initial error budget.

We present a study of the impact of short term variations (up to hours) of the physical conditions at a site on the atmospheric seeing conditions. This study includes ground layer seeing estimates through the use of computational fluid dynamics (CFD) simulations as well as observational data originating from the site testing program of the Thirty-Meter-Telescope (TMT). We discuss a case scenario and compare this and general trends to the CFD predictions.

With Euro50 as a convenient telescope laboratory, the Euro50 team has continued development aiming at a European extremely large telescope (ELT). Here, we give a progress report. The needs of science and instrumentation are briefly discussed as is the importance of photometric stability and precision. Results are reported from work on integrated modelling. Details are given concerning point-spread functions (PSFs) obtained with and without adaptive optics (AO). Our results are rather encouraging concerning AO photometry and compensation of edge sensor noise as well as regarding seeing-limited ELT operation. The current status of our development of large deformable mirrors is shown. Low-cost actuators and deflection sensors have been developed as have hierarchic control algorithms. Fabrication of large thin mirror blanks as well as polishing and handling of thin mirrors has been studied experimentally. Regarding adaptive optics, we discuss differential refraction and the limitations imposed by dispersive optical path differences (OPDs) and dispersive anisoplanatism. We report on progress in laser guide star (LGS) performance and a real-time online experiment in multi-conjugate AO (MCAO). We discuss ELTs, high-resolution spectroscopy and pupil slicing with and without use of AO. Finally, we present some recent studies of ELT enclosure options.

The science case for the next generation of Extremely Large Telescopes (ELTs) covers a huge range of astronomical topics and requires a wide range of capabilities. Here we describe top-level requirements on an ELT, which were derived from some of the key science cases identified by European astronomers. After a brief summary of these science cases we discuss the requirements on the ELT system in terms of several parameters, including wavelength range, field of view, image quality etc. We discuss the science driver that sets the limits on each parameter. We also discuss specific requirements on instrumentation, site and adaptive optics. In several cases, detailed simulated observations will be required in order to set the requirements. While the example science cases provide a useful guide, we also note that an important goal is to develop a facility that covers a broad parameter space, and maintains flexibility in order to adapt to new scientific directions.

This paper work reports the results of the Preliminary Design Phase of the Floating Sphere Telescope that has been presented during the AOMATT in Xi'an, China, November 2005. The FST represents a new design for the realization of an ELT with a 40-metre primary mirror. The innovative concept of the structure and the sub-systems that constitute it as well as the use of new materials and technologies allow to obtain an instrument able to comply with very extreme specifications for structure such as ELTs. The structure allows to improve the stiffness to weight ratio of the structure, to introduce higher damping while maintaining under control the construction and maintenance costs. In comparison with the previous study, the following steps have been implemented: • Refining and optimizing the structural design and the FEA model, in particular we have included a realistic model of the constraint provided by the fluid used for flotation by characterization of its viscous and elastic properties in order to estimate the additional modal damping introduced by the flotation as function of fluid properties and geometry. • Designed (and introduced in the FEA model) various types of drives such as friction drives, tensioned ropes in "hexapod" configuration, "gravity" drives (moving ballast) and combinations of them to evaluate potential tracking performances • Designed the necessary connections for various types of utilities (power, data, cooling) • Included in the structural design a more elaborate optical design to satisfy specific science requirements (e.g. multiconjugate AO)

The Thirty Meter Telescope (TMT) Project will design and build a thirty-meter diameter telescope for research in astronomy at optical and infrared wavelengths. TMT is a partnership between the University of California, Caltech, Association of Canadian Universities for Research in Astronomy (ACURA), and the Association of Universities for Research in Astronomy (AURA). The TMT design and development phase is funded and work is underway. We include a high level description of the design of the telescope and its planned adaptive optics and science instrumentation. The organizational structure of the project is summarized along with the schedule of key milestones in the design. We are carrying out key conceptual and cost reviews in 2006 and will be prepared to begin construction in 2009, with first light in 2015.

The Giant Magellan Telescope (GMT) is being developed by a consortium of universities and research institutions to address the science goals set forth in the National Academy of Sciences most recent Decadal Survey. The telescope will be located in northern Chile and used for astronomical research at wavelengths from the atmospheric UV cut-off through the mid-IR. The GMT is designed with a segmented primary mirror consisting of seven 8.4 meter diameter mirrors and will have a collecting area equal to a filled aperture 21.9 meter telescope and the diffraction limited performance of a 24.5 meter telescope in the IR. The design builds on technology in the areas of structures, mirror fabrication, adaptive optics, and instrumentation developed for the current generation 6.5 m and 8.4 m telescopes. The GMT Project has recently completed its Conceptual Design Phase. This paper summarizes the telescope and enclosure concepts, site evaluation, and the GMT program.

Over the next decade, we can expect that some imaging of extrasolar planets will be possible with the high-resolution LBT and present 8 m class telescopes. But it will be limited by sensitivity and contrast ratio to self-luminous planets of the nearest young stars. When the Giant Magellan Telescope (GMT) comes on-line, it will have because of much larger light grasp and sharper PSF, the potential for imaging many new planets as well as, for the first time, imaging planets of known msini. It will also be capable of starting atmospheric studies through spectrophotometry. The full angular resolution of the GMT (that of D=24 m filled aperture) will be exploited with coronagraphy and nulling interferometry. The new coronagraphic technique of phase apodization being pioneered at the MMT will enable very high contrast at angular separations ≥3λ/D. To reach the highest contrast levels, the AO system is being designed not to minimize wavefront error, but to shape the corrected wavefront so as to cancel speckles in the search region. Interferometric measurements of complex amplitude in the focal plane make this possible, regardless of whether the speckles originate from errors in diffraction or phase. New control algorithms are being developed to minimize the decorrelation time as well as the intensity of residual speckles, so that they average out to the smoothest possible background halo. In this way, detections at 1.65 μm at the 5σ level of planets at 10^-8 contrast at 50 mas separation should be possible. The low background AO system of the GMT, made with its deformable secondary, will allow also high contrast imaging with high sensitivity at 5 μm, down to 100 mas separation.

The concept for Chinese Future Giant Telescope (CFGT) with 30-m aperture has been around for several years, although the requirements for control system are still far from completed and conclusive at this stage. Since the project was proposed more study on a number of key issues relevant to the control system has been conducted. In particular the mount control system for the giant telescope has been put forward under exploration. With our ongoing 4-m LAMOST telescope just underwent a successful mount drive test the LAMOST control group has become more knowledgeable with hands on experience that would be quite useful for mount drive design of even large telescope. This paper focuses on the mount control system design for CFGT telescope in general. Particular aspects such as the effect of large moment of inertia with ultra low-speed and multi-disturbance are included. Friction drive is opted for both historical and economical reasons. Drive stiffness and servo control parameters optimization are discussed based on the workshop test with LAMOST mount that could possibly be mapped to CFGT.

Cornell, California Institute of Technology (Caltech), and Jet Propulsion Lab (JPL) have joined together to study development of a 25 meter sub-millimeter telescope (CCAT) on a high peak in the Atacama region of northern Chile, where the atmosphere is so dry as to permit observation at wavelengths as short as 200 μm. The telescope is designed to deliver high efficiency images at that wavelength with a total one-half wavefront error of about 10 μm. With a 20 arc min field of view, CCAT will be able to accommodate large format bolometer arrays and will excel at carrying out surveys as well as resolving structures to the 2 arc sec resolution level. The telescope will be an ideal complement to ALMA. Initial instrumentation will include both a wide field bolometer camera and a medium resolution spectrograph. Studies of the major telescope subsystems have been performed as part of an initial Feasibility Concept Study. Novel aspects of the telescope design include kinematic mounting and active positioning of primary mirror segments, high bandwidth secondary mirror segment motion control for chopping, a Calotte style dome of 50 meter diameter, a mount capable of efficient scanning modes of operation, and some new approaches to panel manufacture. Analysis of telescope performance and of key subsystems will be presented to illustrate the technical feasibility and pragmatic cost of CCAT. Project plans include an Engineering Concept Design phase followed by detailed design and development. First Light is planned for early 2012.

The Square Kilometre Array (SKA) is the future centimeter- and meter-wavelength telescope with a sensitivity about 50 times higher than present instruments. Its Key Science Projects are (a) Astrobiology including planetary formation within protoplanetary disks; (b) Testing theories of gravitation using an array of pulsars to search for gravitational waves and relativistic binaries to probe the strong-field regime; (c) The origin and evolution of cosmic magnetism, both within the Galaxy and in intergalactic space, via an all-sky grid of magnetic field measurements; (d) The end of the Dark Ages, involving searches for a neutral hydrogen signature, the first supermassive black holes, and the first metal-rich systems; and (e) A hydrogen census to a redshift z greater than or equal to 1 from which to study the evolution of galaxies, dark matter, and dark energy. The SKA will operate at wavelengths from 1.2 cm to 3 m (0.1-25 GHz), providing milliarcsecond resolution at the shortest wavelengths. Its instantaneous field of view will be about 1° (20 cm wavelength), with many simultaneous beams on the sky. The Reference Design is composed of a large number of small dish antennas, building upon an original US proposal. In order to obtain these capabilities at a reasonable cost, significant engineering investments are being made in antennas, wideband feeds and receivers, and signal processing; aperture arrays (phased feeds) are also being investigated in Europe for the lower frequencies. Candidate sites are in Argentina, Australia, China, and South Africa, with a short list of acceptable sites anticipated late in 2006.

The large submillimeter telescope (LST) is a proposed wide-field, 30m-class telescope operating from a ground-based site in the relatively unexplored 0.2 - 1mm waveband. The telescope will be equipped with imaging and spectroscopic instrumentation to allow astronomers to probe the earliest evolutionary stages of galaxies, stars and planets. It is intended to operate the telescope in the 200μm atmospheric window, giving access to unique science; probing the peak emission from the cosmic far-IR/submm background and proto-stellar cores. The wide field-of-view and superb image fidelity will be perfect for large-scale surveys of the sky, such as entire giant molecular clouds and of fields of dusty galaxies at early epochs. It will therefore be an ideal complement to new generation interferometers (such as ALMA). In this paper we present an update on the science case and outline initial designs for both the telescope and instrumentation.

The Cornell Caltech Atacama Telescope (CCAT) is a 25m-class sub-millimeter radio telescope capable of operating from 300GHz up to 1.5 THz. The CCAT optical design is an f/8 Ritchey-Chretien (RC) system in a dual Nasmyth focus configuration and a 20 arc-min FOV (diffraction limited imaging performance better than 0.31" at the edge of the field). The large FOV is capable to accommodate up to 1200x1200 (Nyquist Sampled) Pixels at 200 microns, with better than 96% Strehl ratio. The telescope pedestal assembly is a counterbalanced elevation over azimuth design. The main reflector surface is segmented and actively controlled to attain diffraction-limited operation up to 200 microns. A flat Mirror located behind the main reflector vertex provides the optical path relay to either of the two Nasmyth platforms and to a bent-Cassegrain focus for surface calibration. We present the imaging characteristics of the CCAT over the 20arc-min FOV at 200 microns at the Nasmyth focal plane, as well as the positioning sensitivity analysis of CCAT's 3.2m-diameter sub-reflector given in terms of the telescope optical performance, antenna pointing requirements and sub-reflector chopping characteristics.

In designing and building extreme large optical telescopes of sizes above 10m main aperture diameter, the effort for protecting the telescope against environmental influences gets remarkable large in engineering efforts as well as in costs. Large radio telescopes of similar size are built in "exposed" design, which means, that the protections for the sensitive components are integrated into the telescope itself. Long ranging experience even for sub-millimeter wavelength radio telescopes is available. Why not thinking the unthinkable and design exposed extreme large optical telescopes? The paper describes methods to protect the optics, to protect the structures and mechanics, and to overcome the wind and temperature induced disturbances during operations. It shows also means to integrate large and comfortable rooms for the science instruments with free access during operations into the protected area of the telescope.

The Giant Magellan Telescope (GMT) is a collaborative effort between universities and research institutions to build a next-generation extremely large telescope for astronomical research at optical and infrared wavelengths. The GMT enclosure is cylindrical in shape and stands approximately 65 meters high. The telescope rotates independently of the enclosure down to a minimum elevation angle of 25°. This paper covers the decisions made during the conceptual design phase of the GMT enclosure, including an understanding of the facilities systems.

Design of an extremely large optical telescope poses many technical challenges. One of these challenges includes the design of an enclosure that meets the necessary functional requirements while minimizing the financial cost. This study describes the conceptual design of the Thirty Meter Telescope enclosure. Initially, four general enclosure styles were considered including calotte, dome-shutter, carousel and co-rotating enclosure styles. Progressively detailed comparative studies were completed to evaluate the structural, mechanical, aerodynamic, thermal and operational characteristics of the candidates, and the associated capital and operational costs. As a result, the calotte enclosure was selected as the preferred configuration to carry forward through the conceptual design phase. Continuing design and analysis have brought all of the major calotte enclosure subsystems to a conceptual design level.

Cornell University and California Institute of Technology are currently studying the feasibility of constructing a 25 meter telescope to operate down to 200 micron wavelength to be sited on a high peak in the Atacama region of Chile. An enclosure dome is required to protect the telescope from wind, solar heating, snow, and dust. A diameter of 50 meters at the equator is anticipated, larger than any existing opening telescope enclosure. A review of various approaches indicates that a "calotte" type design, which uses two rotational axes to achieve full sky pointing, is structurally and dynamically superior to other large enclosure approaches. The calotte design is balanced about both axes of rotation and features a circular aperture which provides optimal isolation from the wind. The nearly continuous spherical shell lends itself to efficient space frame type structural form. An initial conceptual design was developed, including structures, bearings, and drive systems. Analysis of these components was performed which illustrates the feasibility of the chosen approach and provides indications of areas of critical risk in further development.

By the end of the XXth century, the development of new technologies, such as segmented mirrors and adaptive optics, allowed an increase in the maximum feasible diameter of telescopes with diffraction limited resolution. The technological limit for the diameter of new generation telescopes is not clear yet and several feasibility studies have been carried out. In Europe, after some previous studies performed by the ESO (OWL) and the University of Lund in Sweden (EURO50), the design study for the European Extremely Large Telescope has been launched supported by the European Community (Framework Programme 6, ELT Design Study, contract No 011863). In the context of this design study, the IAC (Instituto Astrofisico de Canarias) as responsible for the design of the enclosure of the giant telescope, organized a call for ideas in order to find a third alternative for this system (to the two previously developed EURO50 and OWL), in which enterprises and individuals were invited to participate. This paper presents the enclosure concept presented to the contest by IDOM, the Eyelid System for Telescope Protection, which was one of the two ideas selected by the jury. The system basically consists of two structures that can be kept apart during observation - providing the required aperture for light gathering - and closed (joined) when the observation is finished.

For the demand of astronomical limitation observations, such as exploring extra-terrestrial planets, black hole accretion disk and jet in the near-infrared and optical wave band, extremely large telescopes (optical and infrared) have become the principal ground-based astronomical instrumentation. With the maturation of interferometric imaging theory, the borderline between new generation ground-based extremely large telescope and interferometric array for aperture synthesis imaging is increasingly going blurring and the only differences in their technical methods and characteristics are also gradually disappearing. This report introduces some fruitful study results on the next generation ground-based extremely large telescopes, especially the results about the PSF and MTF of the telescope system and the interferometric imaging reconstruction arithmetic. The results not only can be used in the design of large interferometric array for aperture synthesis imaging but also adaptable to the design of single aperture telescope. On the foundation of our results, we bring forward a new concept ground-based extremely large telescope - 30m Ring Interferometric Telescope (30mRIT). It has the direct imaging ability and resolution like single aperture telescope, and it also can image with high resolution like the aperture synthesis imaging mode. The 30mRIT project is remarkably different from the conventional ground-base telescopes and its pivotal techniques have got the support of CAS and China NSF.

Ground-based Extremely Large Telescopes with aperture diameters of 30-60 m will reach their ultimate imaging capabilities by means of Adaptive Optics (AO) systems. One of the fundamental limitations of AO systems working with Natural Guide Stars (NGSs) is very low sky coverage, especially in the visible. The use of laser guide stars (LGSs) created at a finite distance above the telescope aperture could, in principle, relax this limitation, but owing to proximity of the LGSs, a problem of their imaging through the telescope optics arises. To resolve the LGS re-imaging problem, one may adopt the virtual wavefront sensing concept, which employs two wavefront sensors (WFSs): the primary WFS located in the first available telescope focus for measuring wavefront errors induced by atmospheric turbulence and, possibly by the first deformable mirror (DM), and a test-source WFS located at the final telescope focus for measuring contributions from additional DMs. To verify the virtual WFS concept, an optical system has been designed for an experimental setup. It contains three artificial reference sources; a beam splitter forming reference-source arm and test-source arm, atmospheric module with three phase screens followed by a scaled model of a 10-m telescope with two DMs positioned in two separate arms and conjugated to different heights. A single WFS module combining images from the two arms plays a role of the primary and test WFSs. An acquisition camera is employed to monitor image correction made with two DMs. The foundation of the virtual WFS concept is described and its two approaches are outlined in relation to the optical design of the setup. The validity of the experimental verification under the simplified conditions is discussed together with further work addressing the critical issues of the concept, which have not been covered in the present experiment.

The capability of the adaptive optics to correct for the segmentation error is analyzed in terms of the residual wavefront RMS and the power spectral density of the phase. The analytical model and the end-to-end simulation give qualitatively equal results justifying the significance of the geometrical matching between segmentation geometry and the actuators/subaperture distribution of the adaptive optics. We also show that the design of the wavefront sensor is rather critical.

The All-Sky camera used in the LSST and TMT site testing campaigns is described and some early results are shown. The All-Sky camera takes images of the entire visible hemisphere of sky every 30s in blue, red, Y and Z filters giving enhanced contrast for the detection of clouds, airglow and the near-infrared. Animation is used to show movement of clouds. An additional narrow band filter is centered on the most prominent line of the sodium vapor lamp spectra and is used to monitor any man-made light pollution near the site. The camera also detects aircraft lights and contrails, satellites, meteor(ite)s, local light polluters, and can be used for stellar extinction monitoring and for photometry of transient astronomical objects. For outreach and education the All-Sky camera can show wandering planets, diurnal rotation of the sky, the zodiacal light, and similar astronomical basics.

The Cornell Caltech Atacama Telescope (CCAT) is a 25m far infrared telescope in the conceptual design phase. Its primary mirror is composed of a set of panels supported by a space truss. The primary and secondary mirror arrangement resembles the reflector and quadrapod arrangement seen in many radio telescopes, but with shallower primary mirror geometry. In addition, the optical layout calls for a close spacing between the tertiary mirror and the Nasmyth and bent Cassegrain instruments. The mount design is driven by the spacing of the optical elements, the presence of the Nasmyth and bent Cassegrain ports, and the size of the primary mirror truss. This paper examines the mechanical and control system design solutions provided in response to the challenges posed by the optical requirements. These solutions include tradeoffs in structure, drive, and control system design.

The Thirty Meter Telescope (TMT) project has chosen a reference configuration with the telescope elevation axis above the primary mirror. The TMT telescope design has a segmented primary mirror, with 738 segments, nominally 1.2 m across corners, and it uses an articulated tertiary mirror to feed science light to predefined instrument positions on two large Nasmyth platforms. This paper outlines the development of the telescope structural design to meet the motion requirements related to the image quality error budget. The usage of opto-structural performance evaluation tools such as Merit Function Routine are described in addition with the optimization techniques used during the telescope structure design development.

This paper examines the use of Stressed Mirror Polishing for rapid and low cost fabrication of the large number of mirror segments required for the TMT primary mirror. Prior experience fabricating Keck mirror segments is used as a starting point. Specific refinements are made to processes and tooling for faster and more economical fabrication of segments ready for Ion Beam Figuring. Analytical calculations, finite element analyses, design trades, and stressing fixture conceptual designs are presented. Feasibility of Stressed Mirror Polishing is demonstrated and recommendations for further work are given.

The Thirty Meter Telescope project will design and build a thirty-meter diameter telescope for research in astronomy at optical and infrared wavelengths. The highly segmented primary mirror will use edge sensors to align and stabilize the relative piston, tip, and tilt degrees of freedom of the segments. We describe an edge sensor conceptual design and relate the sensor errors to the performance of the telescope as whole. We discuss the sensor calibration, installation, maintenance, and reliability.

The Thirty Meter Telescope (TMT) is a collaborative project between the California Institute of Technology (CIT), the University of California (UC), the Association of Universities for Research in Astronomy (AURA), and the Association of Canadian Universities for Research in Astronomy (ACURA). In order for the Thirty Meter Telescope (TMT) to achieve the required optical performance, each of its 738 primary mirror segments must be positioned relative to adjacent segments with nanometer-level accuracy. Three in plane degrees of freedom are controlled via a passive Segment Support Assembly which is described in another paper presented at this conference (paper 6273-45). The remaining three out of plane degrees of freedom, tip, tilt, and piston, are controlled via three actuators for each segment. Because of its size and the shear number of actuators, TMT will require an actuator design, departing from that used on the Keck telescopes, its successful predecessor. Sensitivity to wind loads and structural vibrations, the large dynamic range, low operating power, and extremely reliable operation, all achieved at an affordable unit cost, are the most demanding design requirements. This paper describes a concept that successfully meets the TMT requirements, along with analysis and performance predictions. The actuator concept is based on a prototype actuator developed for the California Extremely Large Telescope (CELT) project. It relies on techniques that achieve the required accuracy while providing a substantial amount of vibration attenuation and damping. A development plan consisting of a series of prototype actuators is envisioned to verify cost, reliability, and performance before mass production is initiated. The first prototype (P₁) of this development plan is now being built and should complete initial testing by the end of 2^nd QTR 06.

Currently, a number of astrophysical institutes all over the world are working on the design of Extremely Large Telescopes (ELT). Due to the enormous size of the primary mirror these telescopes make use of segmented mirrors. These segments have to be positioned with respect to each other with nanometer accuracy in spite of all kind of external disturbances such as wind loads, thermal loads, deformation of the base frame, varying orientation with respect to the field of gravity, etc. Janssen Precision Engineering (JPE) developed a revolutionary position actuator called the HiPAC which is able to fulfill the demanding requirements for this kind of actuators. The actuator is based on an integrated system of a pneumatic actuator, an electric voice coil and smart control strategy and has the following features: high positioning accuracy performance due to play-free and frictionless actuation; high reliability and maintenance free operation due to flexure-based frictionless guiding; system behavior is constant in time, because no parts affected by wear are used in the actuator; low cost, because no highly accurate machined parts required to reach high end performance; the position actuator acts as an integrated vibration isolator which isolates the segmented mirrors from external vibrations induced in the telescope frame; In this paper the design, simulation and measurements of the HiPAC actuator will be presented.

The Thirty Meter Telescope (TMT) is a collaborative project between the California Institute of Technology (CIT), the University of California (UC), the Association of Universities for Research in Astronomy (AURA), and the Association of Canadian Universities for Research in Astronomy (ACURA). The Alignment and Phasing System (APS) for the Thirty Meter Telescope will be a Shack-Hartmann type camera that will provide a variety of measurements for telescope alignment, including segment tip/tilt and piston, segment figure, secondary and tertiary figure, and overall primary/secondary/tertiary alignment. The APS will be modeled after the Phasing Camera System (PCS), which performed most, but not all, of these tasks for the Keck Telescopes. We describe the functions of the APS, including a novel supplemental approach to measuring and adjusting the segment figures, which treats the segment aberrations as global variables.

The Cornell Caltech Atacama Sub-millimeter Telescope (CCAT) is proposed to have 25m-diameter primary segmented active surface capable of diffraction-limited operation in the wavelength range between 200 microns to 1mm. The active surface design layout is composed of 162 "pie-shaped" segments, each fitted with three actuators that provide piston and tilt/tip control for segment positioning and orientation. We present a performance analysis for five types of segment positioning errors, e.g., piston, tilt/tips, radial and azimuth displacements, and twist errors. From these only the first two, segment piston and tilt/tip errors, are directly controllable by the actuator system. Segment tilt/tip motions may indirectly compensate radial and azimuth segment positioning errors. Residual segment twists introduce quadric phase distribution errors across the face of the segments that cannot be compensated by a simple 3-actuator/segment active surface control system. We have obtained Ruze's coefficients that relate the standard deviation of each segment positioning error type with the overall Strehl ratio of the telescope at 200 microns.

In the technological development for the ELTs, one of the key activities is the phasing and alignment of the primary mirror segments. To achieve the phasing accuracy of a small fraction of the wavelength, an optical sensor is required. In 2005 has been demonstrated that the Pyramid Wavefront Sensor can be employed in closed loop to correct simultaneously piston, tip and tilt errors of segmented mirror. The Pyramid Phasing Sensor (PYPS) is based on the sensing of phase step on the segment edges; this kind of phasing sensors have the common limitation of the signal ambiguity induced by the phase periodicity of πδ/λ on the mirror surface step δ, when the wavelength λ is used for the sensing. In this paper we briefly describe three different techniques that allow to solve the phase ambiguity with PYPS. As first we present experimental results on the two wavelengths closed loop procedure proposed by Esposito in 2001; in the laboratory test the multi-wavelength procedure allowed to exceed the sensor capture range of ±λ/2 and simultaneously retrieve the differential piston of the 32 mirror segments starting from random positions in a 3.2 λ wavefront range, the maximum allowed by the mirror stroke. Then we propose two new techniques based respectively on the segment and wavelength sweep. The Segment Sweep Technique (SST) has been successfully applied during the experimental tests of PYPS at the William Herschel Telescope, when 13 segments of the NAOMI DM has been phased starting from a random position in a 15λ range. The Wavelength Sweep Technique (WST) has been subject of preliminary tests in the Arcetri laboratories in order to prove the concept. Each technique has different capture range, accuracy and operation time, so that each can solve different tasks required to an optical phasing sensor in the ELT application. More in detail the WST and SST could be used combined for the first mirror phasing when the calibration required for the closed loop operations are not yet available. Then the closed loop capture range can be extended from ±λ/2 to ±10λ with the multi-wavelength closed loop technique.

In a framework of ELT design study our group is building an Active Phasing Experiment (APE), the main goals of which is to demonstrate the non-adaptive wavefront control scheme and technology for Extremely Large Telescope (ELT). The experiment includes verification and test of different phasing sensors and integration of a phasing wavefront sensor into a global scheme of segmented telescope active control. After a sufficient number of tests in the laboratory APE will be mounted and tested on sky at a Nasmyth focus of a VLT unit telescope. The paper presents APE as a demonstrator of particular aspects of ELT and provides a general understanding concerning the strategy of segmented mirrors active control.

The purpose of the Active Phasing Experiment, designed under the lead of ESO, is to validate wavefront control concepts for ELT class telescopes. This instrument includes an Active Segmented Mirror, located in a pupil image. It will be mounted at a Nasmyth focus of one of the Unit Telescopes of the ESO VLT. APE contains four different types of phasing sensors, which are developed by Istituto Nazionale di Astrofisica in Arcetri, Instituto Astrofisica Canarias, Laboratoire d'Astrophysique de Marseille and ESO. These phasing sensors can be compared simultaneously under identical optical and environmental conditions. All sensors receive telecentric F/15 beams with identical optical quality and intensity. Each phasing sensor can measure segmentation errors of the active segmented mirror and correct them in closed loop. The phasing process is supervised by an Internal Metrology system developed by FOGALE Nanotech and capable of measuring piston steps with an accuracy of a few nanometers. The Active Phasing Experiment is equipped with a turbulence generator to simulate atmospheric seeing between 0.45 and 0.85 arcsec in the laboratory. In addition, the Active Phasing Experiment is designed to control simultaneously with the phasing corrections the guiding and the active optics of one of the VLT Unit Telescopes. This activity is supported by the European Community (Framework Programme 6, ELT Design Study, contract No 011863).

This paper presents a non-contact, optical metrology system that allows to measure the pistons and tip/tilt angles of a compact-sized, flat segmented mirror, with nanometer resolution, from a long working distance of a few meters. The system is developed in the scope of the APE project (Active Phasing Experiment), and will be installed on the Very Large Telescope (VLT). It will serve for two purposes: (1) as the sensor within the closed loop control of the mirror segments, and (2) as internal reference metrology to qualify the accuracy of different types of phasing cameras that will be developed and tested within the scope of the APE project. The sensor is based on the concept on instantaneous phase shifting, low-coherence, dual wavelength interferometry. By simultaneously acquiring four interferograms at phase shifts of 90° the system is inherently very insensitive to vibrations. Working at two wavelengths allows absolute distance measurements within the range of half the synthetic wavelength, i.e. in our case within a range of about 25 μm. The concept of low coherence interferometry avoids phase contributions of parasitic reflections and speckle effects. The low coherent light sources are two superluminescent diodes emitting at visible (red) wavelengths with coherence lengths in the range of 25 μm that can be increased by spectral filtering. Dual wavelengths measurements are performed at a rate of 20 Hz. The targeted accuracy is better than 5 nm rms (wavefront). The paper starts with a description of the system architecture. The different subsystems (light source, interferometer core with phase modulator and signal decoder, computer) are discussed. After having presented the optical design, the paper provides a closer look to the measurement and calibration algorithms. Finally, the paper presents the experimental setup and the "first fringes" obtained in the laboratory.

Large segmented mirrors require efficient co-phasing techniques in order to avoid the image degradation due to segments misalignment. For this purpose in the last few years new co-phasing techniques have been developed in collaboration with several European institutes. The Active Phasing Experiment (APE) will be a technical instrument aimed at testing different phasing techniques for an Extremely Large Telescope (ELT). A mirror composed of 61 hexagonal segments will be conjugated to the primary mirror of the VLT (Very Large Telescope). Each segment can be moved in piston, tip and tilt. Three new types of co-phasing sensors dedicated to the measurement of segmentation errors will be tested, evaluated and compared: ZEUS (Zernike Unit for Segment phasing) developed by LAM and IAC, PYPS (PYramid Phase Sensor) developed by INAF/ARCETRI, and DIPSI (Diffraction Image Phase Sensing Instrument) developed by IAC, GRANTECAN and LAM. This experiment will first run in the laboratory with point-like polychromatic sources and a turbulence generator. In a second step, it will be mounted at the Nasmyth platform focus of a VLT unit telescope. This paper describes the scientific concept of DIPSI, its optomechanical design, the signal analysis to retrieve segment piston and tip-tilt, the multiwavelength algorithm to increase the capture range, and the multiple segmentation case, including both simulation and laboratory tests results.

The purpose of the Active Phasing Experiment, designed at ESO, is to validate wavefront control concepts for ELT class telescopes. This instrument includes an Active Segmented Mirror, located in a pupil image. It will be mounted at a Nasmyth focus of one of the unit telescopes of the ESO VLT. The Active Phasing Experiment will compare four types of phasing sensor. One of them is based on the Shack-Hartmann principle. The lenslets in the array will be placed on intersegment borders for the measurement of piston steps, as well and inside the subapertures defined by the segments for the measurement of local slopes generated by the segments and the telescope optics. The paper describes the design of the sensor optics and the lenslet array, and discusses the expected performance of the sensor under laboratory conditions and in the telescope.

We describe the ZEUS phasing camera for future extremely large telescopes (ELTs) based on the Zernike phase contrast method. A prototype instrument is under construction for implementation in the Active Phasing Experiment (APE), a VLT test bed scheduled for operation in 2007. The paper describes theoretical aspects of the method and its experimental validation, as well as the instrumental implementation for APE. Aspects of its implementation in an ELT are also discussed. While the classical Zernike method uses a phase mask with diameter approximately equal to the Airy disk, we employ a mask the size of the seeing disk. This allows us to overcome the problems related to atmospheric turbulence, whose low spatial frequency phase errors are much larger than the co-phasing errors to be measured. The thickness (OPD) of the mask can be set to lambda/4 - as in the classical case - for maximum signal strength, but for initial phasing where phase errors are much larger than the sensor's linear range (+/-lambda/4), a thinner mask produces a cleaner signal more easily exploitable, leaving the signal analysis more robust. A multi wavelength approach is implemented in order to extend the capture range of the sensor, and the ultimate precision is reached using an iterative approach. End-to-end simulations indicating an achievable precision within the required precision will be shown.

As is known to all, the LAMOST active optics wavefront test is realized by Shack-Hartmann Wavefront Sensor. But because of the characteristics and difficulties of the LAMOST, it is the key problem in the design of LAMOST Shack-Hartmann Wavefront Sensor to select and decide the sampling point number corresponding to one segment of LAMOST. In this paper we mainly discuss the sampling point number experiment by simulating different numbers of Shack-Hartmann sampling points from one LAMOST segment based on the Large Aperture Active Optics Experiment Telescope Device, which is briefly introduced with LAMOST. After the introduction, the main contents of this article are given including the following three experimental analysis parts. The first experimental analysis is the active optics tests, active optics close loop corrections and comparisons among experiments with different sampling point numbers. The second is the fitting and correction of the low-frequency aberration items existing in the system with about twenty sampling points. The last is that the low-frequency aberrations such as astigmatism and defocus are generated and then corrected with only twenty sampling points after close loop correction with all sampling points. Finally some primary conclusions of LAMOST Shack-Hartmann Wavefront Sensor sampling point number are reached and given.

The goal of investigation is to estimate the quality of the mirror-lens telescope (MLT) consisting of the afocal two-mirror system (ATS) and the lens. Such combination can decrease size and mass of the telescope. This aspect greatly influences the application of device in the outer space. Optical computer programs used nowadays do not allow calculating oblique beams in the systems with surfaces defined parametrically. In the work the task of calculation of oblique beams in such kind of systems was solved and the computer program was composed.

The 10-m class Southern African Large Telescope (SALT) at Sutherland, South Africa, was inaugurated in November 2005, following completion of all its major sub-systems. It is the largest single optical telescope in the southern hemisphere. The SAMS (Segment Alignment Measurement System) is a unique capacitive edge sensing solution for the active alignment of the SALT primary mirror. Twelve thin film edge sensors are bonded directly onto the edges of each of the 91 segments, with heat-generating control electronics housed remotely in temperature-controlled enclosures. The SAMS is capable of measuring the tip/tilt and piston of each segment, as well as the change in global radius of curvature, a mode normally undetected by such a system. The primary objective was to build a system that offered an excellent cost-to-performance ratio without sacrificing measurement accuracy, a very necessary requirement because of the scale and number of sensors required for large segmented mirrors. This paper describes the results obtained during the commissioning and calibration of the completed system.

The aperture of future Extremely Large Telescopes will be composed of hundreds of individual segments which require the development of new robust phasing techniques based on the concept of pupil plane detection. The misalignments of the segments produce amplitude variations at the location of the segment edges recorded on the phasing camera. To analyze the signals which contain the information about the segmentation error, the position of the segment borders on a CCD image must be determined with a sub-pixel accuracy. In the framework of the Active Phasing Experiment (APE) carried out at ESO, we have developed two methods to retrieve the segmented pattern. One is based on the Hough transform and the other one on the correlation of the images with a hexagonal pattern. After a description of both methods, we shall present the results achieved so far with simulations. Finally, the performances of the two methods will be compared. This project forms part of the ELT Design Study and is supported by the European Commission, within Framework Programme 6, contract No 011863.

VISTA is a survey telescope which will deliver 0.5 arc second images over a 2 degree diameter unvignetted field of view. The Telescope Work Package which includes both the Mount and M1 support system is being designed and built by VertexRSI. The Contract includes an extensive factory test programme after full assembly of the telescope systems. The main optical elements in projects this size are ordered early so that they are ready for integration with the telescope on site. This means that testing of the telescope with its optics in the factory environment is rarely possible. So to try and avoid problems during site integration, the scope and extent of hardware and control system factory testing is significant and should be suitably in-depth. This paper describes the metrology and testing carried out to date in the factory environment. In addition the axis control system was simulated using Matlab-Simulink models. The models were also used as the basis of software verification using hardware-in-the-loop tests in a model-based development process. This development process and subsequent factory testing is described in some detail, and covers the mount axes and the M1 support system. In conclusion this paper discusses the perceived usefulness of the extent of the factory testing employed and how this is expected to mesh with the process of telescope and optics integration on site.

LAMOST experiment set is a special reflecting Schmidt telescope set up at the camps of NIAOT (Nanjing Institute of Astronomical Optics & Technology). Its optical configuration and tracking formulas are given. The difference between LAMOST experiment set and general alt-azimuth telescope is analyzed. The method for getting pointing error data from ST-7 CCD image is discussed. A TPOINT like approach for the pointing model was chosen. The procedure for the development of the model is described. As result we got 4.35" rms accuracies.

The Large Binocular Telescope Observatory (LBT) encoded their elevation and azimuth axis with Farrand Inductosyn tape encoders. The authors present the unique design requirements to achieve high precision tracking and pointing. This paper describes the mechanical hardware used to meet these goals. The telescope elevation axis uses two tapes to encode 14m diameter tracks machined into the optical support structure. Each elevation tape is encoded with two custom read heads machined to fit the surfaces. The read heads are mounted on spring loaded flexures with rollers to insure consistent alignment of the heads to the tapes and to allow for radial run out. The azimuth is encoded with two tapes set end to end. Four custom read heads have been installed on similar flexures. The tape mounting hardware has been designed to maintain uniform and constant tension over the lifetime of the tape. We also describe the equipment and procedures used during installation to insure uniform tension of the tape in the track.

When constructed on the summit of Haleakala on the island of Maui, Hawaii, the Advanced Technology Solar Telescope (ATST) will be the world's largest solar telescope. The ATST is a unique design that utilizes a state-of-the-art off-axis Gregorian optical layout with five reflecting mirrors delivering light to a Nasmyth instrument rotator, and nine reflecting mirrors delivering light to an instrument suite located on a large diameter rotating coude lab. The design of the telescope mount structure, which supports and positions the mirrors and scientific instruments, has presented noteworthy challenges to the ATST engineering staff. Several novel design solutions, as well as adaptations of existing telescope technologies to the ATST application, are presented in this paper. Also shown are plans for the control system and drives of the structure.

Telescope enclosure design is based on an increasingly standard set of criteria. Enclosures must provide failsafe protection in a harsh environment for an irreplaceable piece of equipment; must allow effective air flushing to minimize local seeing while still attenuating wind-induced vibration of the telescope; must reliably operate so that the dome is never the reason for observatory down time; must provide access to utilities, lifting devices and support facilities; and they must be affordable within the overall project budget. The enclosure for the Advanced Technology Solar Telescope (ATST) has to satisfy all these challenging requirements plus one more. To eliminate so-called external dome seeing, the exterior surfaces of the enclosure must be maintained at or just below ambient air temperature while being subjected to the full solar loading of an observing day. Further complicating the design of the ATST enclosure and support facilities are the environmental sensitivities and high construction costs at the selected site - the summit of Haleakala on the island of Maui, Hawaii. Previous development work has determined an appropriate enclosure shape to minimize solar exposure while allowing effective interior flushing, and has demonstrated the feasibility of controlling the exterior skin temperature with an active cooling system. This paper presents the evolution of the design since site selection and how the enclosure and associated thermal systems have been tailored to the particular climatic and terrain conditions of the site. Also discussed are load-reduction strategies that have been identified through thermal modeling, CFD modeling, and other analyses to refine and economize the thermal control systems.

The conceptual design of a sliding enclosure, which allows open air operation at night, has been completed for the ESO 100m telescope (OWL). The design has been performed both using classical structural design and using an interesting technology based on supporting the beams with low pressure air cushions (Tensairity), which allows enormous savings in structural material and therefore in costs. Implications of the sliding hangar on the project are discussed; the radome concept as architectural alternative is taken in consideration and compared from the performance point of view.

The Cornell Caltech Atacama Telescope (CCAT) is a joint project to design and construct a 25-meter class submillimeter telescope in the Atacama region of northern Chile. The conceptual design and cost analysis done by M3 Engineering and Technology Corporation (M3) incorporates a cost trade-off of three optional sites and a baseline design of the facilities at Cerro Chajnantor. The details covered in this paper provide the final concept design of the CCAT facility, the decisions and rationale of the design process as well as a critical risk assessment of building at high altitude sites.

A cable-suspended parallel robot utilizes the basic idea of Stewart platform but replaces parallel links with cables and linear actuators with winches. It has many advantages over a conventional crane. The concept of applying a cable-suspended parallel robot into the construction and maintenance of giant telescope is presented in this paper. Compared with the mass and travel of the moving platform of the robot, the mass and deformation of the cables can be disregarded. Based on the premises, the kinematic and dynamic models of the robot are built. Through simulation, the inertia and gravity of moving platform are found to have dominant effect on the dynamic characteristic of the robot, while the dynamics of actuators can be disregarded, so a simplified dynamic model applicable to real-time control is obtained. Moreover, according to control-law partitioning approach and optimization theory, a workspace model-based controller is proposed considering the characteristic that the cables can only pull but not push. The simulation results indicate that the controller possesses good accuracy in pose and speed tracking, and keeps the cables in reliable tension by maintaining the minimum strain above a certain given value, thus ensures smooth motion and accurate localization for moving platform.

The USNO 61" (1.55 m) astrometric reflector was state-of-the-art when it entered service in 1964. However, with a relatively small aperture, it now has limited research capability because it can not observe faint objects. The current facility, including dome and pier, offers significant resources upon which to build a larger telescope. Preliminary estimates indicate that a 3.5 m telescope could be retrofitted into the dome at a cost of ~$10-15 million; about half the cost of building on a new site. USNO has contracted with an engineering firm to perform a feasibility study of such a telescope upgrade, the results of which are summarized.

The Subaru Telescope has been operated smoothly for eight years after its first light. With the advent of instruments with high spatial resolution such as the adaptive optics, elongation of images has been noticed towards specific azimuth (AZ) and elevation (EL). With accelerometers with high time resolution, we detected vibrations of the telescope and could attribute the elongation of images to the vibrations. The detected vibrations are at 3.6 Hz and at 7-9 Hz in AZ direction and at 5-6 Hz in EL direction. Image motion due to these vibrations is 0.4 arcsec peak-to-peak at maximum, which is not negligible compared to image motion of 0.063 arcsec rms in quiescent state. The motion, which can not be canceled with the auto guider, results in elongation of images. The 3.6 Hz vibration in AZ direction is only excited while culmination EL of above 80 degrees. The 7-9 Hz vibration in AZ direction and the 5-6 Hz vibration in EL direction are excited by periodic errors in incremental encoders which are used to measure velocity of telescope rotation. We investigated possibilities to reduce the vibrations with tuning control loops of the AZ and EL axes.

The Subaru telescope had its astronomical first light in January 1999 and has been stably operated since the common use started in December 2000. The telescope is mounted on an alt-azimuth structure. The structure of 550 tons is supported by six hydrostatic oil pads which lift the structure by 50 microns. The azimuth (Az) and elevation (El) axes are driven by direct-drive linear motors, ensuring very smooth pointing and tracking operations. The Az rail consists of eight circular arc pieces. They were installed in January 1997 with a peak-to-peak level of within 0.1mm. However at a later time, vertical undulations of the Az rail were found to be more than 0.2 mm peak-to-peak at some locations where the telescope structure in the rest position applies load. Open-loop tracking accuracy of the telescope, which was about 2 arcsec RMS on the sky, was found to be due to the undulations of the Az rail. We made a table to correct telescope pointings due to the undulations. It has made open-loop tracking accuracy better than 0.2arcsec RMS. Since then, we have been monitoring the flatness of the Az rail. So far the undulations have not changed.

The James Clerk Maxwell Telescope (JCMT) on the summit of Mauna Kea is currently undergoing significant structural upgrade in order to accommodate the new generation instrument SCUBA-2 (Submillimeter Common-User Bolometric Array) which is being developed by the United Kingdom Astronomy Technology Centre (UK ATC). This four tonne instrument will be located at the Nasmyth focus of the telescope and will require five large auxiliary external warm mirrors to be installed on the telescope structure and in the receiver cabin along with dedicated automatically deployable tertiary mirror. The carousel of the observatory building as well as the original telescope structure was not designed for an instrument of this mass and complexity. The whole left Nasmyth platform of the telescope has to be removed and rebuilt in order to accommodate the instrument, its support structure and the warm optics. The floor of the observatory has to be reinforced and fitted with rail system and a scissor lift in order to handle the installation of the instrument on the telescope and removal from the telescope for maintenance. Details are given of particular challenges associated with handling, mechanical interfacing, optical alignment, design of the external warm mirrors mounts and the tertiary mirror deployment mechanism for SCUBA-2.

The CTIO V. M. Blanco 4-m telescope is to be the host facility for the Dark Energy Survey (DES), a large area optical survey intended to measure the dark energy equation of state parameter, w, to a precision of ˜ 5%. The survey is expected to take 5 years and use a new 520 megapixel CCD prime focus imaging system: the Dark Energy Camera (DECam). In preparation for the arrival of DECam, we plan numerous upgrades to the telescope, including a new telescope control system optimized for programmed and queued survey observations, modifications to the telescope itself to improve reliability and performance, extended real-time telemetry of site and facility characteristics, and a distributed observer interface allowing for on- and off-site observations and real time quality control. These upgrades are specifically motivated by the scientific goals of the DES but will also improve community use of the telescope.

The Gran Telescopio Canarias (GTC) is a 10m segmented mirror telescope that is under construction at the Observatorio del Roque de los Muchachos (Spain) and that is expected to have first light during 2006. The telescope mechanics is comprised of the telescope structure, bearings, motors, encoders, brakes, cable wraps and counterweights and also the Nasmyth instrument rotators and the tertiary mirror drives. The structure of the telescope was assembled at site between 2003 and 2005 and the rest of the systems are being assembled and tested during 2005 and 2006. This paper presents the process of the assembly of the telescope mechanics, the problems presented and the lessons learned during it, and the results of the tests performed.

The Large Synoptic Survey Telescope (LSST), ref 1, is a large (8.4M) wide-field (3.5 degree) survey telescope. The wide-field of view is accomplished by a three mirror system combined with a three lens camera. The tertiary mirror is inscribed in the primary mirror and the two will be fabricated as a single unit. The camera is located in front of the secondary mirror, which is in a conventional location. This configuration, along with the small f# of 1.23 produces a very compact system relative to similar aperture telescopes. The survey mission of the telescope requires a short slew and settling time of 5 seconds for a 3.5 degree slew. This is significantly faster than most similar aperture telescopes. Meeting this requirement is facilitated by the compact configuration which produces high natural frequencies and low moments of inertia. Maintainability also demands that the mount allow for the removal of all optical components for coating.

Periodic vortex shedding from a 12-m parabola antenna has been found in the wind of 9 m s^-1 and an attack angle of 26 degrees. The measurements have been made at the NRAO VLA site. The periodic yaw motion of an elevation axis has been detected with linear gauges mounted on a reference structure that was built in each side of the yoke. It has also been observed in the angle difference of two encoders installed at both ends of the elevation axis. The frequency of yaw motion was 0.15 Hz. The same periodicities have been found in both the wind direction and wind velocity measured with an ultrasonic anemometer in the wake downstream of the antenna. Such periodicities have been seen in neither common displacement of the bearing housings nor rotation of the elevation axis. The Reynolds number of the flow was 6 x 10⁶ (hypercritical), suggesting the vortex shedding be periodic, which is consistent with our observations. The Strouhal number of parabola has been found to be 0.19 that is comparable to those of cylinder, inverse triangle, and other similar geometric shapes. The coefficient for oscillatory lateral force exerted on the antenna by shedding vortices has been estimated to be about 1.

A 0.4 meter lightweight telescope has been developed as a prototype for a future 1.4 meter telescope to be implemented at the Naval Prototype Optical Interferometer (NPOI). Using carbon fiber construction for all components, including optics, an order of magnitude reduction in weight is easily obtainable, with the estimated weight of the 1.4 meter telescope being less than 300 pounds. However, lightweight composite materials traditionally offer certain drawbacks, such as different material behavior and vibration characteristics from conventional materials and difficulty in obtaining optical surface quality. This paper describes the characterization of the mechanical properties of the advanced materials used in the construction of these telescopes and includes measurements of the optical figure obtained with carbon fiber construction.

The Arcminute Microkelvin Imager Small Array (AMI-SA) has recently begun scientific observations. This paper describes the design of the AMI-SA, a new radio interferometer that will carry out a survey of galaxy clusters using the Sunyaev-Zel'dovich (SZ) effect. AMI-SA consists of ten 3.7 m antennas with baselines in the range 5-20 m. The relatively wide synthesised beam of 3'.4 improves the sensitivity to the extended features of galaxy clusters. The AMI-SA is located at Cambridge, UK and observes at 12-18 GHz. Commercially available dishes were used for the primary antennas and a novel rolled-edge Cassegrain system was developed to improve the aperture efficiency. A low system temperature of 25 K required for an SZ survey is achieved by cooled low-noise receivers. A high IF band of 6-12 GHz was adopted to realize broadband IF components. The path differences between antennas are corrected by a broad-band path compensator and signals are cross-correlated by a cost-effective broadband analogue lag correlator that synthesizes eight frequency channels. The effects of radio sources that contaminate the SZ effect will be removed by simultaneous observation with a separate long-baseline interferometer. As part of the AMI program, the Ryle Telescope is currently undergoing a major upgrade; the AMI Large Array (AMI-LA) will be an eight-element interferometer with 12.8 m dishes. It will observe over the same band at the same site and much of the back-end electronics are common with the AMI-SA.

A concept is presented for a global network of robotically operated 2m-class telescopes, operating as a single globally distributed observatory, for follow-up from the emerging generation of gigapixel focal plane survey telescopes and the investigation of time-domain phenomena. The concept is developed from a model of approximately fifteen networked telescopes of varying apertures and instrumentation compliments, and an exploration of the operating principles of the network. A network architecture is presented which is able to deliver the remote operational support of this network. The operating requirements of the unit telescope design are developed.

We are implementing the second-generation CCD/Transit Instrument (CTI-II), a unique 1.8-m imaging astrometric and photometric telescope. We discuss design aspects of CTI-II, including the optical system, structure, focal plane mosaic and the detector readout system that allows precise astrometric and photometric measurements. The scientific design drivers for the imaging telescope include discovery and measurement of motion and distance for late M, L and T stars, synoptic photometric monitoring of active galactic nuclei (AGN), and discovery and near real-time spectroscopic followup of distant supernovae and AGN outbursts. These projects drive the design of the wide field-of-view stationary telescope that employs the time-delay and integrate (TDI) readout mode for CCD detectors to produce a deep, multicolor image of the sky every clear night. Nightly observation of the same strip of the sky produces the time domain photometric and repeated astrometric measurements required by the science drivers. The telescope, its focal plane mosaic and the data system all incorporate unique and innovative elements that support an unbiased survey of the sky with intensive time-domain sampling. We review these aspects of the project, and describe steps taken to support the astrometric and photometric precision required by the scientific mission of the telescope.

The HET is a modified Arecibo-style telescope with a segmented spherical primary and a four-mirror spherical aberration corrector (SAC). Objects are tracked by driving the SAC along the focal sphere of the primary. In the original design of the telescope the alignment of the SAC was to be maintained passively. In practice, this could not be done to specifications, leading to degraded imaging quality. We have developed a metrology system to actively control the alignment of the SAC. An autocollimator maintains the optical axis of the SAC normal to the primary mirror beneath it. An absolute distance measuring interferometer (DMI) monitors the SAC/primary mirror distance, maintaining focus. Both systems work at a wavelength of 1.5 microns, well above the operating wavelength of current or planned science instruments and therefore do not interfere with observations. The performance of the system is measured via Hartmann testing. Several upgrades are implemented in the primary mirror control system, including calibration of individual edge sensors, new control system software, and a new method of setting and controlling the overall radius of curvature of the primary array. New techniques were developed to efficiently piston the segments onto the proper sphere radius.

A major performance upgrade for the Hobby-Eberly Telescope (HET) is in the conceptual design phase. The extensive upgrade will include a wide field optical corrector, a new HET tracker with increased payload capacity, and improved telescope pointing and tracking accuracy. The improvements will support the HET Dark Energy Experiment (HETDEX), which seeks to characterize the evolution of dark energy by mapping the imprint of baryonic oscillations on the large scale structure of the Universe. HETDEX will use the increased field-of-view and payload to feed an array of approximately 145 fiber-fed spectrometers, called VIRUS for "Visible Integral field Replicable Unit Spectrograph". The new corrector will have a science field-of-view diameter of 18 arcminutes, in contrast to the original corrector's 4 arcminute field, a twenty-fold increase in area. A new HET tracker with increased payload capacity will be designed to support the wide field corrector. Improved pointing and tracking will be accomplished using new autocollimation and distance measuring metrology combined with real-time wavefront sensing and correction. The upgrade will maintain operation of the current suite of facility instruments, consisting of low, medium, and high resolution spectrometers.

European VLBI is undergoing a rapid development. On one hand electronic or e-VLBI is changing the very nature of the European VLBI Network (EVN), on the other hand a dramatically increased time resolution will enable the EVN to image vast areas of sky at unprecedented resolution. The resulting increase of data volumes will require new calibration tools and new ways of computing, storing and distributing data products.

The design of the National Radio Astronomy Observatory's Expanded Very Large Array (EVLA) project is approaching completion. Four of the twenty-seven antennas have been upgraded into the final configuration. The 2200 miles of fiber optic cables have been installed underground and are functional. The master oscillator and the round trip phase hardware have been operating uninterrupted since November 2003. Hundreds of hours of test observations have been performed as we start the task of characterizing the upgraded system. This paper discusses the results of this testing and describes the techniques used to maintain phase coherence of the EVLA LO chain and of the new wideband receivers. The enhancements to the VLA system include a new local oscillator (LO) system, a fiber optic LO distribution system, and a digital round trip phase measurement system. The phase requirement for the LO system requires that the long term phase drift slope be less than 6.0 picoseconds per 30 minutes at 40 GHz and be maintained across the entire array. To accomplish this, a near real time continuous measurement is made of the phase delay in the fiber optic cable distributing the LO reference signals to each antenna. This information is used by the correlator to set the phase on each of the baselines in the array.

The Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. Development of this four-meter off-axis solar telescope has presented many optical design challenges including: • support of both Nasmyth and flexible coude lab instrumentation, • incorporation of an integrated adaptive optics system, • thermal control of optics, and • optical alignment of multiple off-axis conics. This paper gives an overview of the optical design, error budgeting, and the performance modeling done to ensure the telescope will satisfy its optical performance requirements.

The last decade has seen significant interest in wide field of view (FOV) telescopes for sky survey and space surveillance applications. Prompted by this interest, a multitude of wide-field designs have emerged. While all designs result from optimization of competing constraints, one of the more controversial design choices is whether such telescopes require flat or curved focal planes. For imaging applications, curved focal planes are not an obvious choice. Thirty years ago with mostly analytic design tools, the solution to wide-field image quality appeared to be curved focal planes. Today however, with computer aided optimization, high image quality can be achieved over flat focal surfaces. For most designs, the small gains in performance offered by curved focal planes are more than offset by the complexities and cost of curved CCDs. Modern design techniques incorporating reflective and refractive correctors appear to make a curved focal surface an unnecessary complication. Examination of seven current, wide FOV projects (SDSS, MMT, DCT, LSST, PanStarrs, HyperSuprime and DARPA SST) suggests there is little to be gained from a curved focal plane. The one exception might be the HyperSuprime instrument where performance goals are severely stressing refractive prime-focus corrector capabilities.

Since the launch of the Hubble Space Telescope there has been widespread popular interest in astronomy. A further series of events, most notably the recent Deep Impact mission and Mars oppositions have served to fuel further interest. As a result more and more amateurs are coming into astronomy as a practical hobby. At the same time more sophisticated optical equipment is becoming available as the price to performance ratio become more favourable. As a result larger and better optical telescopes are now in use by amateurs. We also have the explosive growth in digital imaging technologies. In addition to displacing photographic film as the preferred image capture modality it has made the capture of high quality astronomical imagery more accessible to a wider segment of the astronomy community. However, this customer requirement has also had an impact on telescope design. There has become a greater imperative for wide flat image fields in these telescopes to take advantage of the ongoing advances in CCD imaging technology. As a result of these market drivers designers of consumer astronomical telescopes are now producing state of the art designs that result in wide, flat fields with optimal spatial and chromatic aberrations. Whilst some of these designs are not scalable to the larger apertures required for professional ground and airborne telescope use there are some that are eminently suited to make this transition.