This PDF file contains the front matter associated with SPIE Proceedings Volume 7012, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

The GTC (Gran Telescopio Canarias) is an optical/IR telescope, with a 10,4 meter segmented primary, installed at the Observatorio del Roque de Los Muchachos (ORM), at La Palma. Past July 2007 it saw its First Light showing a very promising behaviour. The very good image quality achieved at that an early stage of telescope commissioning is a direct consequence of the quality of its optics, the high performances of its primary mirror control system, and the highly engineered telescope structure and servo system. At present, we are advancing with the telescope commissioning whose first results are presented here. The two Day One science instruments: OSIRIS and CanariCam are being prepared for installation and commissioning on the telescope. Science verification are planned to be initiated by the end of 2008 and regular operation by March 2009.

The Large Binocular Telescope (LBT) Observatory is a collaboration between institutions in Arizona, Germany, Italy, Indiana, Minnesota, Ohio and Virginia. The telescope on Mt. Graham in 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. We will describe the scientific results and technical challenges of monocular prime focus imaging starting in Fall 2006. Binocular imaging with two co-pointed prime focus cameras began in Fall 2007. Installation of a rigid (non-adaptive) secondary mirror occurred in Spring 2008 in time for the arrival of the first Gregorian spectrometer. The telescope will use two F/15 adaptive secondaries to correct atmospheric turbulence. The first of these adaptive mirrors is now being tested in Italy, and is planned to be at the telescope by Summer 2009.

Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is an innovative telescope project with both large aperture (effective in 4 meters) and wide field of view (5 degrees) to achieve the large scale spectroscopic survey observation. It is a horizontal meridian reflecting Schmidt configuration realized by an active deformable Schmidt plate. For achieving such an ambitious project with limited budget, both its primary mirror (6.67m × 6.05m) and Schmidt plate (5.74m × 4.4m) are segmented. LAMOST project is expected to be completed before the end of 2008. The assembly and test of whole telescope and 16 spectrographs with 4000 optical fibers in its focal plane is going to be finished in August of 2008. With just its partial aperture, more than 200 optical fibers and one spectrograph, the scientific commissioning has been done and some preliminary results have been obtained. This paper introduces the progress of LAMOST project during 2007 and 2008, and presents the achievement in its technology which is also useful for the future extremely large telescopes.

The Large Synoptic Survey Telescope Project is a public-private partnership that has successfully completed the Concept Design of its wide-field ground based survey system and started several long-lead construction activities using private funding. The telescope has a 3-mirror wide field optical system with an 8.4 meter primary, 3.4 meter secondary, and 5 meter tertiary mirror. The reflective optics feed three refractive elements and a 64 cm 3.2 gigapixel camera. The telescope will be located on the summit of Cerro Pachón in Chile. The LSST data management system will reduce, transport, alert, archive the roughly 15 terabytes of data produced nightly, and will serve the raw and catalog data accumulating at an average of 7 petabytes per year to the community without any proprietary period. This survey will yield contiguous overlapping imaging of 20,000 square degrees of sky in 6 optical filter bands covering wavelengths from 320 to 1080nm. The project continues to attract institutional partners and has acquired non-federal funding sufficient to construct the primary mirror, already in progress at the University of Arizona, and fund detector prototype efforts, two of the longest lead items in the LSST. The project has submitted a proposal for construction to the National Science Foundation Major Research Equipment and Facilities Construction (MREFC) program and is preparing for a 2011 funding authorization.

Using the array of seven 0.6m antennas in Hawaii, we have conducted short observations on several galaxy clusters through the Sunyaev-Zeldovich effect at 3mm wavelength in 2007. The observations were done with a resolution of 6', and we have chosen the low redshift (z=0.09-0.32) massive clusters to optimize detection. Major contamination to the data comes from instrumental offset and ground pickup. We will demonstrate the results based on a simple on source - off source switching observing scheme. In addition, the performance of a wideband analog 4-lag correlator was also investigated.

ASTE is a 10-m submillimeter telescope operating in Atacama desert in northern Chile since 2002 by NAOJ and collaborators. Thanks to the excellent observing condition at the telescope site, ASTE has been producing numerous astronomical results from star forming regions, Galactic center, Magellanic clouds, nearby galaxies, and galaxy clusters. There has been three major improvements during the years 2007-2008: continuum camera "AzTEC", new SIS receiver "CATS345", and a wide-band spectrometer "WHSF". AzTEC is a 144 element bolometer array at 270 GHz, developed by University of Massachusetts and collaborators. The mapping speed reaches 10-30 arcmin²/hr/mJy². CATS345 is a side-band separation (2SB) SIS receiver developed by University of Tokyo and NAOJ. The IF bandwidth is 4 GHz with side-band rejection ratio better than 10 dB. We have achieved the typical system noise temperature of 200-400 K (SSB) within 330-360 GHz, the best value being 150 K (SSB) at the frequency of ¹²CO(J=3-2) at 345 GHz under a typical weather condition. The new spectrometer WHSF employs of an FX type auto-correlator, ultra-high speed sampler, and digital signal transmitter. It can be operated in two modes; 4096 MHz band-width × 2 IFs or 2048 MHz band-width × 4 IFs, both with 4096 channels in spectral resolution.

As the Large Millimeter Telescope (LMT) has continued to progress towards scientific operations, some preliminary commissioning of the telescope control system has taken place. We present the architecture of the LMT control system along with initial commissioning results of the LMT servo and drive system. The LMT azimuth drive system is a wheel-on-track mechanism with sixteen individually driven wheels on a circular track. The elevation drive system consists of two main gear arcs, each driven by two pinions. All twenty of the drives (sixteen in azimuth and four in elevation) consist of a motor and a gearbox. These drives are controlled by a fully digital servo system that is divided into a drive control unit which consists of the servo amplifiers and an embedded PLC that implements torque sharing and safety interlocks, and an antenna control unit that implements the servo control loops and astronomical tracking. The results of the initial commissioning of the LMT servo and drive system include full range motion in azimuth and elevation, azimuth track welding effects, elevation gear rims alignment effects, elevation balance, friction contribution to servo errors, and initial tracking accuracy.

AMOS SA has been awarded of the contract for the design, manufacturing, assembly, tests and on site installation (Nainital, Devasthal site at 2540 mm altitude) of the 3,6 m Optical Telescope for ARIES (Aryabhatta Research Institute of Observational Sciences), Nainital (India). This paper describes the opto-mechanical design of this telescope and presents the solutions adopted by AMOS to meet the specific requirements. The telescope has a Ritchey-Chrétien optical configuration with a Cassegrain focus equipped with one axial port and two side ports. The primary mirror is a meniscus active mirror.

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

Las Cumbres Observatory Global Telescope (LCOGT) is redefining the function of robotic telescopes by deploying 0.4 meter telescopes that act as a highly networked intelligent instrument. The 0.4 meter telescopes, (P4) are optimized for quick and accurate object acquisition and tracking. This minimizes response time and enables the leveraging of the instrument. A single P4 can independently execute multiple science programs concurrently or team up with other P4s for deeper or multi-color observations of a single target. The intelligent control software will optimize the observation schedule for each individual telescope and the entire network. LCOGT is deploying 6 networked clusters consisting of four P4s around the world, providing capacity and versatility beyond the classical observatory. Each P4 has zero slippage, no backlash friction systems, and is currently achieving 20 deg/s slewing. Blind pointing is currently 8 arcsec RMS. Using the AG acquisition routine, the drive will have repeatable pointing to within 0.6 arcsec within 12 seconds from anywhere on the sky. Other features include wind buffet correction, rapid thermalization, dual autoguiders, novel scanning flat fielding device, large 20 kg instrument capacity, high speed instrument changer, and a stiff split ring mount.

The eSMA ("expanded SMA") combines the SMA, JCMT and CSO into a single facility, providing enhanced sensitivity and spatial resolution owing to the increased collecting area at the longest baselines. Until ALMA early science observing (2011), the eSMA will be the facility capable of the highest angular resolution observations at 345 GHz. The gain in sensitivity and resolution will bring new insights in a variety of fields, such as protoplanetary/ transition disks, high-mass star formation, solar system bodies, nearby and high-z galaxies. Therefore the eSMA is an important facility to prepare the grounds for ALMA and train scientists in the techniques. Over the last two years, and especially since November 2006, there has been substantial progress toward making the eSMA into a working interferometer. In particular, (i) new 345-GHz receivers, that match the capabilities of the SMA system, were installed at the JCMT and CSO; (ii) numerous tests have been performed for receiver, correlator and baseline calibrations in order to determine and take into account the effects arising from the differences between the three types of antennas; (iii) First fringes at 345 GHz were obtained on August 30 2007, and the array has entered the science-verification stage. We report on the characteristics of the eSMA and its measured performance at 230 GHz and that expected at 345 GHz. We also present the results of the commissioning and some initial science-verification observations, including the first absorption measurement of the C/CO ratio in a galaxy at z=0.89, located along the line of sight to the lensed quasar PKS 1830-211, and on the imaging of the vibrationally excited HCN line towards IRC+10216.

As one of the preliminary research projects of Chinese ELT, 30m RIT--Ring Interferometric Telescope are being simulated and tentatively designed by Yunnan Astronomical Observatory, CAS. The simulations of 30m RIT are mainly included as follows: PSF transform and the image quality at limited photons mode, active control mode of the primary ring mirror, the phasing mode of 30m segmented ring mirror, the turbulent atmosphere and adaptive optics etc. This paper also introduces some tentative design results of 30m RIT, such as the optical design, the conceptual design of the enclosure. The astronomical experiments at seeing limited case and diffraction limited case are introduced in this paper too. A ring aperture mask was put on the entrance pupil of a one meter telescope, real astronomical objects were observed by this "ring telescope" and reconstructed by high resolution imaging techniques such as speckle masking, iterative shift and add methods. The diffraction imaging ability and the full u-v coverage property of a ring aperture were proved by these astronomical experiments.

We present the status of the Sardinia Radio Telescope (SRT) project, a new general purpose, fully steerable 64 m diameter parabolic radiotelescope capable to operate with high efficiency in the 0.3-116 GHz frequency range. The instrument is the result of a scientific and technical collaboration among three Structures of the Italian National Institute for Astrophysics (INAF): the Institute of Radio Astronomy of Bologna, the Cagliari Astronomy Observatory (in Sardinia,) and the Arcetri Astrophysical Observatory in Florence. Funding agencies are the Italian Ministry of Education and Scientific Research, the Sardinia Regional Government, and the Italian Space Agency (ASI,) that has recently rejoined the project. The telescope site is about 35 km North of Cagliari. The radio telescope has a shaped Gregorian optical configuration with a 7.9 m diameter secondary mirror and supplementary Beam-WaveGuide (BWG) mirrors. With four possible focal positions (primary, Gregorian, and two BWGs), SRT will be able to allocate up to 20 remotely controllable receivers. One of the most advanced technical features of the SRT is the active surface: the primary mirror will be composed by 1008 panels supported by electromechanical actuators digitally controlled to compensate for gravitational deformations. With the completion of the foundation on spring 2006 the SRT project entered its final construction phase. This paper reports on the latest advances on the SRT project.

The Infrared Imaging System (IRIS) is a 0.8 m telescope equipped with a 1024×1024 pixels near-infrared camera using a HAWAII-1 detector array. IRIS will be located at the Cerro Armazones Observatory in Chile that is operated by the Ruhr University Bochum jointly with the Universidad Catolica del Norte in Antofagasta. The system is specifically designed to survey star forming regions and to search for deeply embedded variable young stars.

Vibration is becoming a more important element in design of telescope structures as these structures become larger and more compliant and include higher bandwidth actuation systems. This paper describes vibration damping methods available for current and future implementation and compares their effectiveness for a model of the Large Synoptic Survey Telescope (LSST), a structure that is actually stiffer than most large telescopes. Although facility and mount design, structural stiffening and occasionally vibration isolation have been adequate in telescopes built to date, vibration damping offers a mass-efficient means of reducing vibration response, whether the vibration results from external wind disturbances, telescope slewing, or other internal disturbances from translating or rotating components. The paper presents several damping techniques including constrained layer viscoelastics, viscous and magnetorheological (MR) fluid devices, passive and active piezoelectric dampers, tuned mass dampers (vibration absorbers) and active resonant dampers. Basic architectures and practical implementation considerations are discussed and expected performance is assessed using a finite element model of the LSST. With a goal of reducing settling time during the telescope's surveys, and considering practicalities of integration with the telescope structure, two damping methods were identified as most appropriate: passive tuned mass dampers and active electromagnetic resonant dampers.

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, PDR, Haleakalä 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 European Solar Telescope (EST) is a project for a large aperture (3-5 meters) ground-based telescope, to be located in the Canary Islands. EST will be optimized for studies of magnetic coupling between the deep photosphere and upper chromosphere. This will require diagnostics of the thermal, dynamic and magnetic properties of the plasma over many scale heights, by using multiple wavelength imaging, spectroscopy and spectropolarimetry. The design of EST will strongly emphasize the use of a large number of visible and near-infrared instruments simultaneously. To achieve these goals, EST will specialize in high spatial and temporal resolution using instruments that can efficiently produce twodimensional spectral information. In this communication, the present situation of the design is outlined, as well as the expected future phases and scheduling.

The solar telescope GREGOR is under construction on the canary island Tenerife. A large effort was made to thermally characterize the telescope during the design phase. The image quality is very sensitive to differences between ambient and structure or main mirror temperatures. Tests with the GREGOR telescope structure and an integrated dummy mirror were made to investigate the distribution and temporal behavior of the temperature of the telescope and main mirror.

The solar submillimeter-wave telescope (SST) is the only one of its kind dedicated to solar continuous observations. Two radiometers at 0.740 mm (405 GHz), and four at 1.415 mm (212 GHz) are placed in the Cassegrain focal plane of the 1.5-m dish at El Leoncito high altitude site, San Juan, Argentina. The aperture efficiencies are close to design predictions: 20% and 35% for 2 and 4 arcminutes beam sizes at 405 and 212 GHz, respectively. The positioner absolute pointing accuracy is 10 arcseconds. Spectral coverage is complemented by ground-based mid-infrared telescopes developed for high cadence observations in the continuum 10 micron band (30 THz), using small apertures and room-temperature microbolometer cameras. Using the system, a new solar burst spectral component was discovered, exhibiting fluxes increasing for smaller wavelengths, separated from the well known microwave component. Rapid sub-second pulsations are common for all bursts. The pulsations onset times of appear to be connected to the launch times of CMEs. Active regions are brighter for shorter submillimeter-waves. Mid-IR bright regions are found closely associated with calcium plages and magnetic structures near the solar photosphere. Intense and rapid 10 micron brightening was detected on active centers in association with weak flares. These results raise challenging difficulties for interpretation.

It was in the years around 1970 that during site-test campaigns for JOSO masts were erected up till 30 m height with sensors at several heights for the measurement of temperature fluctuations. Cornelis (Kees) Zwaan discovered that the fluctuations decrease drastically at heights from about 15 m and upward when there is some wind. The conclusion from this experience was the open telescope principle: the telescope should be completely free in the air 15 m or more above the ground. The Dutch Open Telescope (DOT) was the pioneering demonstrator of the open-telescope technology. Now that larger high-resolution telescopes come in view, it is time to analyze again the principle: (i) the essentials for proper working of the open principle; (ii) the differences with nighttime observations particularly concerning the seeing; (iii) the design consequences for the new generation of high-resolution solar telescopes.

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, allowing excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will contain an array of up to sixty-four 12-m diameter high-precision antennas arranged in multiple configurations ranging in size from 150 meters up to ~15 km, and a set of four 12-m and twelve 7-m antennas operating in closely packed configurations ~50m in diameter. The instrument will provide both interferometric and total-power astronomical information on high-energy electrons, molecular gas and dust in solar system, our Galaxy, and the nearby and high-redshift universe. In this paper we outline the scientific drivers, technical challenges and construction status of ALMA.

The Atacama Compact Array (ACA) is an array composed of twelve 7-m dishes and four 12-m dishes. The ACA is designed for use as a part of the ALMA (Atacama Large Millimeter / Submillimeter Array) to provide high fidelity imaging capability for large extended objects. Basic parameters of the array configuration of the ACA were selected based on the analysis of the sensitivity in uv plane for mosaicing observations with the ACA and the ALMA. For detailed design of the sub-array with 7-m dishes (7-m Array), we adopted the compact spiral concept, which realizes higher uv response at the short uv spacings and better sidelobe performance. To satisfy the sky coverage requirement, the north-south elongation is needed. The 7-m Array was designed to have two configurations, one (Inner Array) is a compact spiral array with small north-south elongation (× 1.1) and the other (NS Array) is a dedicated configuration with large north-south elongation (× 1.7). In actual design, inner 6 antenna pads are shared by both configurations because of construction constraints.

The development process of the ALMA project from its first prototype phase to the present one of serial production, has stimulated the development of concepts of innovative engineering and manufacturing design. The technologies adopted such as the large use of composite materials, motorizations without contact (Direct Drive) etc., have allowed to obtain extreme performances with reference to the scientific/environmental context. ALMA technologies represent a new gateway for the astrophysical applications of the future.

The first European ALMA production antenna is in the final stage of manufacturing and pre-assembly. Precommissioning of parts of this antenna will start soon. The series production is partly ongoing or in the final stage of preparation. Design features of the European ALMA antennas w.r.t. to manufacturing, assembly and integration in Europe and on site, the status of the manufacturing works and pre-commissioning are presented. An outlook to the next steps of the realization of the antennas is given.

In the ALMA project, in order to achieve the specification, very important is the use of a metrology instrument able to correct the non repeatable errors. Errors induced by wind or temperature variations inside the structure that are non systematic have to be predicted and corrected by an active system. During design phase, CFD and thermal analyses have been performed in order to identify the whole behaviour of the structure and the relative corrections formulas. Innovative instruments and layout have been studied from the prototype to the production phase.

This paper, presented on behalf of the Large Millimeter Telescope (LMT) project team, describes the status and near-term plans for the telescope and its initial instrumentation. The LMT is a bi-national collaboration between Mexico and the USA, led by the Instituto Nacional de Astrofísica, Optica y Electronica (INAOE) and the University of Massachusetts at Amherst, to construct, commission and operate a 50m-diameter millimeter-wave radio telescope. Construction activities are nearly complete at the 4600m LMT site on the summit of Sierra Negra, an extinct volcano in the Mexican state of Puebla. Full movement of the telescope, under computer control in both azimuth and elevation, has been achieved. First-light at centimeter wavelengths on astronomical sources was obtained in November 2006. Installation of precision surface segments for millimeter-wave operation is underway, with the inner 32m-diameter of the surface now complete and ready to be used to obtain first light at millimeter wavelengths in 2008. Installation of the remainder of the reflector will continue during the next year and be completed in 2009 for final commissioning of the antenna. The full LMT antenna, outfitted with its initial complement of scientific instruments, will be a world-leading scientific research facility for millimeter-wave astronomy.

This paper devotes to the working space analysis of the main positioning system of FAST cabin suspension, a flexible-cable-driven parallel manipulator. The problem formulation is deduced through equilibrium analysis of the cabin platform and suspension cables, which changes subsequently into a nonlinear constrained optimization intending a uniform allocation of the six cable tension force. The analysis verifies the accessibility of focus cabin to the whole focus surface. The optimization investigates the orientation of the focus cabin under equilibrium and the optimal cable forces, as well as elaborates their importance in the finite element modeling of the cable-cabin system and the respective layout designs of the rotator, Stewart stabilizer and capstan motors. In the end, the influences of the tower height and the position of mass center of the focus cabin on the optimization results are discussed.

China has embarked on a project to build the world's largest radio telescope, the Five hundred meter Aperture Spherical Telescope (FAST), in a karst depression in southwest Guizhou Province. The telescope is of a modified Arecibo type. We suggest an active main reflector that is spherical in the neutral state but the illuminated aperture of 300m in diameter would be adjusted into a proper paraboloid such that a simple feed could be used at its focus, since the "spherical correction" has be done on the ground. The feed cabin at the focus is supported and driven directly by cables controlled by computer, which avoids a heavy and expensive feed supporting system. Newly developed method and technology for determining the spatial position of 2400 nodes on the main reflector of the FAST are introduced in this paper. Base on the measurements of the position of node under which the down cable are linked, a loop feedback control enables accurately driving the spherical reflector deformed to paraboloid. The key technique of this implementation is the precise measurement of 2400 nodes. In this article, we introduce the scheme of simplified photogrammetry aiming at no lateral shift situation; we analyse the influence of lateral shift; and considering lateral shift, we propose a scheme using rotation platform plus double-eye camera to accomplish the dynamic measurement of the reflector. The result of analysis and testing shows the feasibility and effectivity of the scheme of measurement.

Reflector surface deformation due to wind loading on the Nobeyama 45-m antenna has been measured with four LED lamps on the surface at r = 20 m and two CCD cameras on the central hub as it rotates in azimuth with elevation angles of 90 and 11 degrees. The side-wind loading of 8.4 m s^-1 caused a tilt of 12 arcseconds and an astigmatic deformation of 0.8 mm. The front- and back-wind loading of 9.9 m s^-1 induced a vertical displacement variation of 2.3 mm. These largescale surface deformation profiles have been compared with those of finite element calculations and coefficients of axial force and yaw moment predicted by a JPL wind tunnel data excerpt.

A wind pressures PSD measured on the Gemini South Telescope was applied to the FEA model of the LSST telescope to determine the RMS motions of the principal optical systems. These motions were then converted to the time domain. The time domain motions were analyzed in the ZEMAX® software to determine the wind induced image degradation. This degradation was shown to be tolerable.

The Wind Evaluation Breadboard (WEB) for the European Extremely Large Telescope (ELT) is a primary mirror and telescope simulator formed by seven segments simulators, including position sensors, electromechanical support systems and support structures. The purpose of the WEB is to evaluate the performance of the control of wind buffeting disturbance on ELT segmented mirrors using an electro-mechanical set-up which simulates the real operational constrains applied to large segmented mirrors. The instrument has been designed and developed by IAC, ALTRAN, JUPASA and ESO, with FOGALE responsible of the Edge Sensors, and TNO of the Position Actuators. This paper describes the mechanical design and analysis, the control architecture, the dynamic model generated based on the Finite Element Model and the close loop performance achieved in simulations. A comparison in control performance between segments modal control and actuators local control is also presented.

The primary, secondary and tertiary mirrors of the Thirty Meter Telescope (TMT), taken together, have approximately 12,000 degrees of freedom in optical alignment. The Alignment and Phasing System (APS) will use starlight and a variety of Shack-Hartmann based measurement techniques to position the segment pistons, tips, and tilts, segment figures, secondary rigid body motion, secondary figure and the tertiary figure to correctly align the TMT. We present a conceptual design of the APS including the requirements, alignment modes, predicted performance, software architecture, and an optical design.

The purpose of the Active Phasing Experiment, designed under the lead of ESO, is to study new phasing technologies and to validate wavefront control concepts for Extremely Large Telescopes. The Active Phasing Experiment is currently tested in the laboratory at the ESO headquarters and will be tested on sky at a Nasmyth focus of a VLT unit telescope at the end of 2008. The test bench contains four different phasing sensors which are tested in parallel to compare them under the same conditions. They have been developed by Istituto Nazionale di Astrofisica in Florenze, Instituto Astrofisica Canarias in Tenerife, Laboratoire d'Astrophysique de Marseille and ESO. It includes also an Active Segmented Mirror which simulates the segmentation of a primary mirror. A non-contact optical metrology has been developed by Fogale Nanotech to control it. The VLT focus and the VLT atmospheric conditions are simulated in the laboratory with a turbulence generator producing a seeing between 0.45 and 0.85 arcsec. Once installed on a VLT unit telescope, the control system of the Active Phasing Experiment will be able to control the phasing of the ASM, but also the guiding and the active optics of the VLT. This proceeding gives a brief summary of the opto-mechanical aspects of the Active Phasing experiment, describes its control system and gives an analysis of the preliminary results obtained in the laboratory.

The out-of-plane degrees of freedom (piston, tip, and tilt) of each of the 492 segments in the Thirty Meter Telescope primary mirror will be actively controlled using three actuators per segment and two edge sensors along each intersegment gap. We address two important topics for this system: edge sensor design, and the correction of fabrication and installation errors. The primary mirror segments are passively constrained in the three lateral degrees of freedom. We evaluate the segment lateral motions due to the changing gravity vector and temperature, using site temperature and wind data, thermal modeling, and finite-element analysis. Sensor fabrication and installation errors combined with these lateral motions will induce errors in the sensor readings. We evaluate these errors for a capacitive sensor design as a function of dihedral angle sensitivity. We also describe operational scenarios for using the Alignment and Phasing System to correct the sensor readings for errors associated with fabrication and installation.

To meet the 10 µm RMS half wavefront error requirement for the 25 m diameter Cornell Caltech Atacama Telescope (CCAT), active control of the approximately 200 primary mirror panels is required. The CCAT baseline design includes carbon fiber aluminum honeycomb sandwich mirror panels. Distortions of the panels due to thermal gradients, gravity and the mounting scheme need to be taken into consideration in the control system design. We have modeled the primary mirror surface as both flat and curved surfaces and have investigated mirror controllability with a variety of sensor types and positions. To study different mirror segmentation schemes and find acceptable sensor configurations, we have created a software package that supports multiple segment shapes and reconfigurable panel sizing and orientation. It includes extensible sensor types and flexible positioning. Inclusion of panel and truss deformations allows modeling the effects of thermal and gravity distortions on mirror controllability. Flat mirrors and curved mirrors with the correct prescription give similar results for controlled modes, but show significant differences in the unsensed flat mirror modes. Both flat and curved mirror models show that sensing schemes that work well with rigid, thermally stable panels will not control a mirror with deformable panels. Sensors external to the mirror surface such as absolute distance measurement systems or Shack-Hartmann type sensors are required to deal with panel deformations. Using a combination of segment based sensors and external sensors we have created a promising prototype control system for the CCAT telescope.

This paper presents a non-contact optical metrology measuring the pistons and tip/tilt angles of the 61 hexagonal segments of a compact-sized segmented mirror. The instrument has been developed within the scope of a design study for a European Extremely Large Telescope (E-ELT). It is used as reference sensor for cophasing of the mirror segments in closed loop control. The mirror shape is also measured by different types of stellar light-based phasing cameras whose performances will be evaluated with regard to a future E-ELT. Following a description of the system architecture, the second part of the paper presents experimental results demonstrating the level of precision: 0.48nm RMS in piston and 0.074 μrad RMS in tip and tilt.

Large segmented mirrors require efficient co-phasing techniques in order to avoid the image degradation due to segments misalignment. DIPSI (Diffraction Image Phase Sensing Instrument) is an instrument developed by IAC, GRANTECAN and LAM. This instrument is being integrated in the Active Phasing Experiment (APE), aimed at testing different phasing techniques for an Extremely Large Telescope. This paper describes the mathematical solution for determining piston and tip-tilt simultaneously from the DIPSI images. A complete set of simulations is included to study the residual errors. Residual errors are bigger when piston and tip-tilt are combined (three degrees of freedom).

One of the major issues in new Extremely Large Telescopes is the phasing of their primary segmented mirror. A cophasing sensor is mandatory to achieve the ultimate resolution of the telescope. Phase diversity (PD) is a light-hardware cophasing technique. In this paper, we show that this technique is suited to segmented pupil instruments, such as the E-ELT.

We present an analytical description of the diffraction halo created by optical aberrations randomly distributed over hexagonal segments of a segmented mirror. We do not restrict ourselves to the piston and tip-tilt errors only, but show that the halo from any type of the aberration can be described in a general form. We also study the ability of the high order adaptive optics to correct for this type of aberrations. These effects are especially critical for application of the high contrast imaging with extremely large segmented telescopes.

The shape correction of the mirrors is a crucial operation to obtain diffraction limited images in actively controlled telescopes. If the mirror is not monolithic, the segmentation errors introduced by piston, tip and tilt of the segments are superimposed on the continuous aberrations. In the case of a sensor based on the measurement of the wave front slopes, like the Shack-Hartmann wave front sensor, an algorithm which allows separating the different contributions is necessary for a proper correction. In the framework of the Active Phasing Experiment (APE) carried out at ESO, we have developed a simple algorithm which can be applied to compute the aberrations and the tip-tilt coefficients using the information obtained with a Shack-Hartmann sensor. It is based on the construction of an orthogonal base in the space of the wave front slope functions. The description of the algorithm and its performance in the cases of low-order aberrations superimposed on tip-tilt misalignment of the segments are reported. A particular application of this technique in the case of the European Extremely Large Telescope (E-ELT) is discussed and the expected upper limits for the residual errors after correction are estimated.

The largest telescopes (ELT) involve a highly segmented primary mirror. The monitoring of the mirror shape use thousands of sensors, located on segment edges, which measure the relative piston, tip and tilt of all segments. Today, telescopes with segmented primary mirrors use capacitance-based edge sensors. Although this technology offers excellent metrological performances, its practical use is limited by the intrinsic sensitivity to humidity, dust and condensation, whose effect exceeds the requirements for future ELTs. Being specialized in both capacitive and inductive metrology, Fogale nanotech has developed a novel concept of edge sensors using the inductive technology, which does not suffer from humidity, condensation, and dust effects. Cost effective sensor with specific layout, associated electronics, demonstrated metrological performance (sub-nanometer resolution and nanometer stability) that outperforms the capacitive concept.

In the framework of the Active Phasing Experiment (APE), four different phasing techniques are tested. The ZErnike Unit for Segment phasing sensor (ZEUS) is integrated on the APE bench. APE has been tested in the laboratory before it will be installed on one of the Nasmyth platform of a Very Large Telescope (VLT) Unit Telescope to perform on sky tests. The ZEUS phasing sensor concept has its origins in the Mach-Zehnder interferometer equipped with a spatial filter in its focal plane. In this paper, the ZEUS phasing sensor is described together with its theoretical background and deployment within the APE experiment. The algorithms and its elements used to reconstruct the wavefront are described. Finally, the preliminary results obtained in the laboratory are presented.

The EELT is a project led by ESO on behalf of its 14 member states. The project is in Phase B (detailed design), a 3-year, 57.2 M activity that will result in a Proposal for Construction by June 2010. The requirements for the basic reference design, starting point for the current phase, were defined through a community process that led to the convergence of earlier concepts into a single European project: a 42m adaptive telescope based on a novel 5-mirror design that is scheduled to have first light in 2017. This paper reports on the status of the Phase B activities, on the basic reference design development, and on the progress of the science case and Design Reference Mission.

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, and the Association of Canadian Universities for Research in Astronomy (ACURA). The $80 million TMT design and development phase is fully funded and Preliminary Design is in progress. An additional $300 million has been pledged towards early TMT construction which will commence in 2009. We include a high level description of the design of the telescope and its planned adaptive optics and science instrumentation. The schedule of key milestones for completing the design and construction is summarized.

The Giant Magellan Telescope (GMT) is being developed by a consortium of major US and international educational and research institutions. The 25 meter next-generation telescope will be located at Las Campanas Observatory in Chile. The project has completed the conceptual design of the telescope and enclosure and is currently in the Design Development Phase leading up to construction. Various refinements have been made to the telescope structure since the Conceptual Design. These include the modification of the upper truss structure to reduce image blur due to wind shake and the design of a 9 meter rotator for large Gregorian instruments. An integral field spectrograph has been added to the candidate list of first-generation instruments. The primary mirror for GMT consists of seven 8.4 meter diameter segments. The first of the six, highly aspheric, off-axis segments has been cast and generated at the University of Arizona SOML with completion of the mirror expected in 2009. The metrology for polishing the segments is currently being installed in the new test tower at SOML. Verification tests that independently measure the mirror figure have been designed and are also being implemented. This paper summarizes the overall design and recent progress in the technical development of GMT and in characterizing the site.

The baseline design for the enclosure of the E-ELT is based on a spherical dome concept. This dome is tightly fitted to the TRV so that its surface, the enclosed volume and consequently the system overall cost are minimized. The large slit that is required for observation-as compared to the enclosure volume-, much larger than in smaller telescopes, poses a big challenge to the design. This affects the slit covering system design, for which dynamic issues must be carefully considered in order to prevent operation problems, as well as the dome structure and other mechanisms such as the windscreen and the crane, that have to cover a large 45m span. This paper presents a design that solves all these difficulties in both a cost-effective and reliable way. The design work presented in this paper has been performed under contract with the European Southern Observatory.

The design of the calotte enclosure for the Thirty-Meter Telescope is currently in the preliminary design phase. Key aspects of the design include an efficient structural/mechanical form, repetition of components, modular construction, and operational efficiency. This paper includes an overall description of the enclosure design, as well as a description of the major structural and mechanical subsystems. The enclosure incorporates features that influence the thermal and aerodynamic environment of the telescope including ventilation openings and wind deflecting features. Other key considerations of the preliminary design include the constructability and maintainability of a dynamic structure of this scale at a remote mountain site.

FAST is an Arecibo-type antenna with 3 outstanding aspects: the unique karst depression as the site; the active main reflector which corrects spherical aberration on the ground to achieve full polarization and wide band without involving complex feed system; and the light focus cabin driven by cables and servomechanism plus a parallel robot as secondary adjustable system to carry the most precise parts of the receivers. These design features will enable FAST to jumpstart many of science goals, such as HI neutral hydrogen line survey, pulsar survey, largest station in VLBI network, spectral line observations and Search for alien's technologies. The feasibility studies for FAST have been carried out for 14 years, being supported by Chinese and world astronomical communities. Funding for Project FAST has been approved by the National Development and Reform commission NDRC in July of 2007 with a capital budget ~ 600 millions RMB and a project time of 5.5 years from the foundation.

The European Extremely Large Telescope (E-ELT) is a 42-m class optical telescope with a segmented primary mirror composed of 984 segments which is currently being studied by ESO (European Southern Observatory). The segment support system combines a series of mechanical whiffletrees for the axial support, a central diaphragm for lateral support and a torsional constrainer. These elements are fixed to a common moving frame which is actively moved by means of three actuators in piston and tip-tilt in order to keep the whole primary mirror in phase. The moving frame is fixed to the segments subcells, which properly attach the segments to the cell structure, by means of special flexures, allowing large axial alignment capability combined with high lateral stiffness. This paper describes the development of the support system for the primary mirror segments of the E-ELT, which has been specified for a high stiffness and eigenfrequencies, 60Hz for axial modes and 40Hz for lateral ones.

A study is presented of the impact on science data from extremely large telescopes of a transformation of wavelength base for optimization of actuator architecture from 2 200 to 1 250 nm. From the optical path difference (OPD) data for Euro50, we transform to E-ELT OPDs. We compute the corresponding power spectrum, in which we simulate a higher actuator density via high-pass filtering to convert from K to J band actuator-pitch optimization. From the modified power spectrum we derive the correspondingly modified OPDs, PSFs and Strehl ratios. A massive improvement is demonstrated resulting from converting from AO@K to AO@J. This result is followed up by model-based E-ELT imaging in a field in a galactic disc at a distance of 4 Mpc. The improvements in image quality, background and limiting magnitude are very large as are the increases in photometric precision derived from the field imaging. Further, the great science benefit and large opportunities provided by partial AO is demonstrated. In conclusion, while admittedly challenging, pushing AO optimization to wavelengths as short as possible is of prime concern for the science output of ELTs.