Ground-based and Airborne Telescopes IV

Front Matter: Volume 8444

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This PDF file contains the front matter associated with SPIE Proceedings Volume 8444, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The 1.6 m off-axis New Solar Telescope (NST) in Big Bear

Philip R. Goode, Wenda Cao

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The 1.6-m New Solar Telescope (NST) has been used to observe the Sun for more than three years with ever increasing capabilities as its commissioning phase winds down. The NST is the first facility-class solar telescope built in the U.S. in a generation, and it has an off-axis design as is planned for the 4 m Advanced Technology Solar Telescope. Lessons learned will be discussed. Current NST post-focus instrumentation includes adaptive optics (AO) feeding photometric and near-IR polarimetric sytems, as well as an imaging spectrograph. On-going instrumentation projects will be sketched, including Multi-Conjugate AO (MCAO), next generation (dual Fabry- Perot) visible light and near-IR polarimeters and a fully cryogenic spectrograph. Finally, recent observational results illustrating the high resolution capabilities of the NST will be shown.

Applications of infrared techniques in solar telescopes NVST

Yinzhu Li, Fangyu Xu, Shanjie Huang, et al.

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This paper presents the applications of infrared techniques in National Vacuum Solar Telescope(NVST) .We give a brief introduction to infrared thermography for nondestructive evaluation, especially for the measurement of mirror temperature gradient and the dome temperature distribution. The results give us more reference for the Mirror Seeing and Dome Seeing improvement.

Introduction to the Chinese Giant Solar Telescope

Zhong Liu, Yuanyong Deng, Zhenyu Jin, et al.

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In order to detect the fine structures of solar magnetic field and dynamic field, an 8 meter solar telescope has been proposed by Chinese solar community. Due to the advantages of ring structure in polarization detection and thermal control, the current design of CGST (Chinese Giant Solar Telescope) is an 8 meter ring solar telescope. The spatial resolution of CGST is equivalent to an 8 meter diameter telescope, and the light-gathering power equivalent to a 5 meter full aperture telescope. The integrated simulation of optical system and imaging ability such as optical design, MCAO, active maintenance of primary mirror were carried out in this paper. Mechanical system was analyzed by finite element method too. The results of simulation and analysis showed that the current design could meet the demand of most science cases not only in infrared band but also in near infrared band and even in visible band. CGST was proposed by all solar observatories in Chinese Academy of Sciences and several overseas scientists. It is supported by CAS and NSFC (National Natural Science Foundation of China) as a long term astronomical project.

Large-field high-resolution mosaic movies

Robert H. Hammerschlag, Guus Sliepen, Felix C. M. Bettonvil, et al.

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Movies with fields-of-view larger than normal for high-resolution telescopes will give a better understanding of processes on the Sun, such as filament and active region developments and their possible interactions. New active regions can influence, by their emergence, their environment to the extent of possibly serving as an igniter of the eruption of a nearby filament. A method to create a large field-of-view is to join several fields-of-view into a mosaic. Fields are imaged quickly one after another using fast telescope-pointing. Such a pointing cycle has been automated at the Dutch Open Telescope (DOT), a high-resolution solar telescope located on the Canary Island La Palma. The observer can draw with the computer mouse the desired total field in the guider-telescope image of the whole Sun. The guider telescope is equipped with an H-alpha filter and electronic enhancement of contrast in the image for good visibility of filaments and prominences. The number and positions of the subfields are calculated automatically and represented by an array of bright points indicating the subfield centers inside the drawn rectangle of the total field on the computer screen with the whole-sun image. When the exposures start the telescope repeats automatically the sequence of subfields. Automatic production of flats is also programmed including defocusing and fast motion over the solar disk of the image field. For the first time mosaic movies were programmed from stored information on automated telescope motions from one field to the next. The mosaic movies fill the gap between whole-sun images with limited resolution of synoptic telescopes including space instruments and small-field high-cadence movies of high-resolution solar telescopes.

The Advanced Technology Solar Telescope: design and early construction

Joseph P. McMullin, Thomas R. Rimmele, Stephen L. Keil, et al.

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The National Solar Observatory’s (NSO) Advanced Technology Solar Telescope (ATST) is the first large U.S. solar telescope accessible to the worldwide solar physics community to be constructed in more than 30 years. The 4-meter diameter facility will operate over a broad wavelength range (0.35 to 28 μm ), employing adaptive optics systems to achieve diffraction limited imaging and resolve features approximately 20 km on the Sun; the key observational parameters (collecting area, spatial resolution, spectral coverage, polarization accuracy, low scattered light) enable resolution of the theoretically-predicted, fine-scale magnetic features and their dynamics which modulate the radiative output of the sun and drive the release of magnetic energy from the Sun’s atmosphere in the form of flares and coronal mass ejections. In 2010, the ATST received a significant fraction of its funding for construction. In the subsequent two years, the project has hired staff and opened an office on Maui. A number of large industrial contracts have been placed throughout the world to complete the detailed designs and begin constructing the major telescope subsystems. These contracts have included the site development, AandE designs, mirrors, polishing, optic support assemblies, telescope mount and coudé rotator structures, enclosure, thermal and mechanical systems, and high-level software and controls. In addition, design development work on the instrument suite has undergone significant progress; this has included the completion of preliminary design reviews (PDR) for all five facility instruments. Permitting required for physically starting construction on the mountaintop of Haleakalā, Maui has also progressed. This paper will review the ATST goals and specifications, describe each of the major subsystems under construction, and review the contracts and lessons learned during the contracting and early construction phases. Schedules for site construction, key factory testing of major subsystems, and integration, test and commissioning activities will also be discussed.

ATST Enclosure final design and construction plans

Gaizka Murga, Heather Marshall, Javier Ariño, et al.

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The Advanced Technology Solar Telescope (ATST) is a 4-m class solar telescope to be built at the Haleakalā High Altitude Observatory Site in Maui, Hawai'i. It will be the largest solar telescope in the world, with unprecedented abilities to view details of the Sun. Using adaptive optics technology, ATST will be able to provide the sharpest views ever taken of the solar surface. It is expected that the 4-meter class telescope will have a significant impact on the study of stellar magnetic fields, plasma physics and astronomy, allowing scientists to learn even more about the Sun and solarterrestrial interactions. The ATST enclosure is unique in its functionality, as not only it provides protection from adverse weather conditions when not in operation, but it also positions the telescope Aperture Stop which must be accurately aligned so that the primary mirror is fully illuminated, while insolation in other telescope equipment is prevented. The proposed design is based on a multi-sector shutter system arrangement with an innovative crawler drive system (patent pending) assembled on two steel fabricated arch girders. These arch girders are stiffened by a secondary structure and supported on a steel fabricated base ring. The base ring rests on an azimuth mechanism composed of several driven/idling bogies. The outer shape of the enclosure is configured by the secondary structure which supports the cladding and has been selected so as to minimize the solar irradiated surface and reduce shell seeing in early morning hours when the seeing is the best. This paper describes the work performed by AEC IDOM and ATST team to define both the final design of the Enclosure and the construction plan to erect it at the Observatory Site.

Progress making the top end optical assembly (TEOA) for the 4-meter Advanced Technology Solar Telescope

Blaise Canzian, J. Barentine, J. Arendt, et al.

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L-3 Integrated Optical Systems (IOS) Division has been selected by the National Solar Observatory (NSO) to design and produce the Top End Optical Assembly (TEOA) for the 4-meter Advanced Technology Solar Telescope (ATST) to operate at Haleakalā, Maui. ATST will perform to a very high optical performance level in a difficult thermal environment. The TEOA, containing the 0.65-meter silicon carbide secondary mirror and support, mirror thermal management system, mirror positioning and fast tip-tilt system, field stop with thermally managed heat dump, thermally managed Lyot stop, safety interlock and control system, and support frame, operates in the "hot spot" at the prime focus of the ATST and so presents special challenges. In this paper, we describe progress in the L-3 technical approach to meeting these challenges, including silicon carbide off-axis mirror design, fabrication, and high accuracy figuring and polishing all within L-3; mirror support design; the design for stray light control; subsystems for opto-mechanical positioning and high accuracy absolute mirror orientation sensing; Lyot stop design; and thermal management of all design elements to remain close to ambient temperature despite the imposed solar irradiance load.

The azimuth axes mechanisms for the ATST telescope mount assembly

Hans J. Kärcher, Ulrich Weis, Oliver Dreyer, et al.

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The ATST Telescope Mount Assembly uses for the Azimuth axes mechanisms bearing and drive technologies as developed for the machine tool industry. An overview on the ATST mount project and design and its verification by analysis, simulation and tests are given in two separate papers of this conference. This paper describes the main design and accuracy features of the bearing and drive subsystems, their adaption to the ATST mount and their influence on the telescope structural design, and gives a hint to the challenges in the upcoming manufacturing, installation and commissioning phases.

Manufacturing and testing of the large lenses for Dark Energy Survey (DES) at THALES SESO

Denis Fappani, Julien Fourez, Peter Doel, et al.

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After a brief introduction of what is the Dark Energy Survey (DES) project and which optical instrumentation will be used, the presentation will be mainly focused onto the optical production of the large lenses (up to 1m diameter) constituting the DES Camera (DECAM) located at the focal plane of the main observing telescope. Special emphasis will be made onto the optical manufacturing issues and interferometric testing solutions, including compensation of index inhomogeneities, which have been carried out by THALES SESO especially for the biggest entrance lens (very challenging CV/CX meniscus named C1). Through several examples of typical past realizations or future possible ones for different astronomical projects requiring 1m-class optics, the presentation will conclude by a brief over review of the corresponding existing "state of the art" at THALES SESO for these technologies.

The Transneptunian Automated Occultation Survey (TAOS II)

Matthew J. Lehner, Shiang-Yu Wang, Charles A. Alcock, et al.

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The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small ( 1 km diameter) objects in the Solar System and beyond. Such events are very rare (< 10⁻³ events per star per year) and short in duration ( 200 ms), so many stars must be monitored at a high readout cadence. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astron´omico Nacional at San Pedro Martir in Baja California, Mexico. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz.

NGTS: a robotic transit survey to detect Neptune and super-Earth mass planets

Bruno Chazelas, Don Pollacco, Didier Queloz, et al.

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NGTS is a new ground-based transit survey aimed at detecting sub-Neptune sized exoplanets around bright stars. The instrument will be installed at the ESO Paranal observatory in order to benefit from the excellent observing conditions and follow-up synergy with the VLT and E-ELT. It will be a robotic facility composed of 12, 200 mm telescopes equipped with 2Kx2K NIR sensitive detectors. It is built on the legacy of the WASP experience.

Design of a compact wide field telescope for space situational awareness

David Lee, Andrew Born, Philip Parr-Burman, et al.

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The European Space Agency, in the framework of its Space Situational Awareness (SSA) Preparatory Programme, has commissioned a study for a global network of surveillance telescopes to monitor the ever increasing number of objects in Earth orbit. A possible scenario identified by the study is a network of 20 SSA Telescopes located at various observatory sites. This paper presents the conceptual design of a telescope system optimised for wide field, short exposures and fast tracking – all requirements of SSA. The requirements of the SSA telescope will be presented followed by a brief review of potential telescope technologies. Following a trade study analysis a 1 m compact Schmidt telescope design was chosen. This design provides a field of view of 3.4 degrees diameter. The design is achromatic and covers the wavelength range 380 – 900 nm. The sensitivity of the telescope is such that it can monitor the orbital parameters of objects as small as 1 cm in low Earth orbit. This is equivalent to 17^th magnitude in 0.07 seconds at a signal to noise ratio of 5. The telescope is mounted on an Altitude- Azimuth type mount that enables wide coverage of the sky and fast tracking speeds. The entire telescope is contained within a Calotte type enclosure. The camera, detector control, and telescope control system design will also be presented. Systems engineering aspects will be addressed, with particular attention given to the analysis and flow-down of requirements and a practical and pragmatic process of system-level design trade-offs.

OAJ: 2.6m wide field survey telescope

Olivier Pirnay, Vincent Moreau, Grégory Lousberg

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AMOS S.A. is in charge of the development of the telescopes for the "Observatorio Astrofisico de Javalambre" in Spain where a 2.6 m wide field telescope is complemented by an 80 cm telescope. This paper focuses on the 2.6 m telescope Javalambre Survey Telescope (JST): it is combining a large collecting surface with a wide field of view for reaching a vast portion of the sky, which is the most relevant parameter for surveys, while ensuring an optical image quality compatible with the site seeing and a suitable depth in the sky sighting. The major difficulty consists in maintaining the image quality over a 500 mm focal plane. A good design is the result of a thorough multidisciplinary optimization process where the fabrication constraints are a major driving parameter. The complexity of the system led to elaborate innovative solutions for the closed loop control of both image quality and tracking features. The design and the methodology of working are presented in details. The optics fabrication, the integration and acceptance tests are also reviewed.

Design differences between the Pan-STARRS PS1 and PS2 telescopes

Jeffrey S. Morgan, Nicholas Kaiser, Vincent Moreau, et al.

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The PS2 telescope is the second in an array of wide-field telescopes that is being built for the Panoramic-Survey Telescope and Rapid Response System (Pan-STARRS) on Haleakala. The PS2 design has evolved incrementally based on lessons learned from PS1, but these changes should result in significant improvements in image quality, tracking performance in windy conditions, and reductions in scattered light. The optics for this telescope are finished save for their coatings and the fabrication for the telescope structure itself is well on the way towards completion and installation on-site late this year (2012). The most significant differences between the two telescopes include the following: secondary mirror support changes, improvements in the optical polishing, changes in the optical coatings to improve throughput and decrease ghosting, removal of heat sources inside the mirror cell, expansion of the primary mirror figure control system, changes in the baffle designs, and an improved cable wrap design. This paper gives a description of each of these design changes and discusses the motivations for making them.

Ground-based search for the brightest transiting planets with the Multi-site All-Sky CAmeRA: MASCARA

Ignas A. G. Snellen, Remko Stuik, Ramon Navarro, et al.

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The Multi-site All-sky CAmeRA MASCARA is an instrument concept consisting of several stations across the globe, with each station containing a battery of low-cost cameras to monitor the near-entire sky at each location. Once all stations have been installed, MASCARA will be able to provide a nearly 24-hr coverage of the complete dark sky, down to magnitude 8, at sub-minute cadence. Its purpose is to find the brightest transiting exoplanet systems, expected in the V=4-8 magnitude range - currently not probed by space- or ground-based surveys. The bright/nearby transiting planet systems, which MASCARA will discover, will be the key targets for detailed planet atmosphere observations. We present studies on the initial design of a MASCARA station, including the camera housing, domes, and computer equipment, and on the photometric stability of low-cost cameras showing that a precision of 0.3-1% per hour can be readily achieved. We plan to roll out the first MASCARA station before the end of 2013. A 5-station MASCARA can within two years discover up to a dozen of the brightest transiting planet systems in the sky.

LSST secondary mirror assembly baseline design

Douglas R. Neill, William J. Gressler, Jacques Sebag, et al.

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The 3.5-meter diameter Large Synoptic Survey Telescope (LSST) secondary (M2) mirror utilizes a 100mm thick meniscus ULE™ blank completed by Corning Incorporated in 2009. Sub-aperture interferometry will guide the polishing process to meet mirror structure function requirements. The convex asphere is actively supported by 72 axial actuators and 6 tangential links. These tangent links utilize an embedded lever system to meet the requirements. The axial actuators have force limiting devices. The control system utilizes a higher level "outer loop controller" for monitoring and commanding the tangent links and axial actuators. Numerous sensors determine the assembly status. To prevent thermally induced image degradation, the interior air of the M2 cell is conditioned.

Current status of the Hobby-Eberly Telescope wide field upgrade

Gary J. Hill, John A. Booth, Mark E. Cornell, et al.

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

ATST telescope pier

Paul Jeffers, Eric Manuel, Oliver Dreyer, et al.

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The Advanced Technology Solar Telescope (ATST) will be the largest solar telescope in the world with a 4m aperture primary mirror. The off axis nature of the telescope optical layout, has the proportions of an 8 metre class telescope. Accordingly the instrumentation for solar observations a 16m diameter co-rotating laboratory (Coude Rotator) is also located within the telescope pier. The pier has a lower cylindrical profile with an upper conical section to support both the telescope mount with a 9m bearing diameter and contain the 16m diameter Coudé rotator. The performance of this pier cannot be considered in isolation but must account for ancillary equipment, access and initial installation. The Coude rotator structure and bearing system are of similar size to the telescope base structure and therefore this is the proverbial 'ship in a bottle' problem. This paper documents the competing requirements on the pier design and the balancing of these as the design progresses. Also summarized is the evolution of the design from a conceptual traditional reinforced concrete pier to a composite concrete and steel framed design. The stiffness requirements of the steel frame was a unique challenge for both the theoretical performance and overall design strategy considering constructability. The development of design acceptance criteria for the pier is discussed along with interfacing of the AandE firm responsible for the pier design and the telescope designer responsible for the telescope performance.

Design concepts for the EST mount

Hans J. Kärcher, Martin Süss, David Fischer

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The EST has unique an optical layout, with an on-axis Gregorian tube system and the altitude axis behind the M1 mirror unit - a great challenge for the mount designer in regard of balancing. Three different structural design concepts and various alternatives for the bearing and drive systems were investigated. Hydrostatic bearings with direct drives are compared with roller bearings and geared drives. The influence of available bearing and drive technology were investigated by FE calculations, dynamic analysis and end-to-end simulations. The finally recommended design concept is based on large-diameter segmented roller bearings and so-called pinion motors in both axes.

Progress on the structural and mechanical design of the Giant Magellan Telescope

Michael Sheehan, Steve Gunnels, Charles Hull, et al.

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The Giant Magellan Telescope (GMT), one of several next generation Extremely Large Telescopes (ELTs), is a 25.4 meter diameter altitude over azimuth design set to be built at the summit of Cerro Campanas at the Las Campanas Observatory in Chile. The primary mirror consists of 7 individual 8.4 meter diameter segments resulting in an equivalent collecting area of a 21.5 meter diameter single mirror. The telescope structure, optics and instrumentation has a rotating mass of approximately 1250 metric tons and stands approximately 40 meters tall. This paper reports the results of our ongoing preliminary design and development of the GMT structure and its major mechanical and opto-mechanical components. A major recent redesign of the Gregorian Instrument Rotator (GIR) resulted in significant changes to the telescope structure and several mechanisms. Design trade studies of various aspects of the main structure, hydrostatic bearing system, main axes drives, M2 positioner, M3 subsystem and the corrector-ADC subsystem have refined the preliminary design in these areas.

The E-ELT project: the telescope main structure detailed design study

Gianpietro Marchiori, Andrea Busatta, Leonardo Ghedin, et al.

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The European Extremely Large Telescope (E-ELT) is the biggest telescope in the world. Within the Detailed Design activities, ESO has awarded EIE GROUP (European Industrial Engineering) a contract for the Design of the Main Structure to the point where the concept of the telescope has been consolidated, from a construction point of view. All the Design activities have been developed in order to create an integrated system in terms of functionality and performance, while the engineering activities have been performed with the aim of obtaining a telescope that can be built, transported, integrated, with a reduced maintainability.

E-ELT dome for modified baseline design

Armando Bilbao, Gaizka Murga, Celia Gómez

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During the last two years a modified baseline design for the E-ELT was developed. The aim of this revision was both to achieve a significant cost saving and to reduce risk on major items. The primary mirror diameter was slightly reduced to 39 m and the total height of the telescope also decreased accordingly. This paper describes the work performed by IDOM under contract with ESO to review the EELT dome and foundations design to match the modified baseline. Detailed design and construction planning, as well as detailed cost estimates were updated for the 39-metre baseline design. In June 2011, ESO Council formally endorsed this modified design as the E-ELT revised baseline. Key redesign drivers are explained and final redesign details of all major subsystems are outlined. In general, the original compact dome design philosophy is maintained and adapted to the new dimensions. Cost optimisation strategies are applied throughout the detailed design update process. Special attention is also given to some specific new items now included in the modified baseline, such as the special ad-hoc seismic base isolation system for the telescope foundation.

The E-ELT project: the dome design study

G. Marchiori, S. De Lorenzi, A. Busatta

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Further to the re-dimensioning of the E-ELT (European Extremely Large Telescope) telescope to 37 metres, the project of the dome has been completely reviewed, together with the Auxiliary Building and the Foundations. The Dome is now constituted by a structure with a steel hemispherical architecture, 79m.-high, with a 101m.-external pier diameter and a 42m-wide observing slit. These dimensions require the application of technologies for big structures (like stadiums, hangars, etc.) in order to comply with the manufacturing, transport and assembly constrains. The dome is characterized by an agglomerate of mechathronic technologies originated by the long experience matured by EIE in the industrial and astronomical fields. The solutions adopted for the NTT, the VLT, the LBT, the VST and the VISTA have demonstrated, along the years of service, their functionality, as well as their reliability and maintainability. Moreover, innovative technologies have been introduced, especially for what concerns the rotation systems of the Dome, the louvers, the windscreen, etc. The architecture of the control systems has been completed re-formulated, and they are now able to manage in real time all the exigencies of the E-ELT Observatory. All Project phases have been properly analysed and simulated, guaranteeing the completeness of the constructability and the maintainability. The entire work has been developed in close cooperation with ESO Project Team, further to a specific contract.

Seismic design accelerations for the LSST telescope

Douglas R. Neill, Mike Warner, Jacques Sebag

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The Large Synoptic Survey Telescope will be located on a seismically active Chilean mountain. Seismic ground accelerations produce the telescope's most demanding load cases. Consequently, accurate prediction of these accelerations is required. These seismic accelerations, in the form of Peak Spectral Acceleration (PSA), were compared for site specific surveys, the Chilean building codes and measured seismic accelerations. Methods were also investigated for adjusting for variations in damping level and return period. The return period is the average interval of time between occurrences of a specific intensity.

Seismic analysis of the LSST telescope

Douglas R. Neill

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The Large Synoptic Survey Telescope (LSST) will be located on the seismically active Chilean mountain of Cerro Pachón. The accelerations resulting from seismic events produce the most demanding load cases the telescope and its components must withstand. Seismic ground accelerations were applied to a comprehensive finite element analysis (FEA) model which included the telescope, its pier and the mountain top. Response accelerations for specific critical components (camera and secondary mirror assembly) on the telescope were determined by applying seismic accelerations in the form of Power Spectral Densities (PSD) to the FEA model. The PSDs were chosen based on the components design lives. Survival level accelerations were determined utilizing PSDs for seismic events with return periods 10 times the telescope's design life which is equivalent to a 10% chance of occurring over the lifetime. Since the telescope has a design life of 30 years it was analyzed for a return period of 300 years. Operational level seismic accelerations were determined using return periods of 5 times the lifetimes. Since the seismic accelerations provided by the Chilean design codes were provided in the form of Peak Spectral Accelerations (PSA), a method to convert between the two forms was developed. The accelerations are also affected by damping level. The LSST incorporates added damping to meets its rapid slew and settle requirements. This added damping also reduces the components' seismic accelerations. The analysis was repeated for the telescope horizon and zenith pointing. Closed form solutions were utilized to verify the results.

GMT enclosure wind and thermal study

Arash Farahani, Alexy Kolesnikov, Leighton Cochran, et al.

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The GMT (Giant Magellan Telescope) is a large ground-based telescope for astronomical research at optical and infrared wavelengths. The telescope is enclosed inside an Enclosure that rotates to follow the tracking of the telescope. The Enclosure is equipped with adjustable shutters and vents to provide maximum ventilation for thermal control while protecting the telescope from high wind loads, stray light, and severe weather conditions. The project will be built at Las Campanas Observatory in Chile on Cerro Las Campanas. The first part of this paper presents the wind tunnel test data as well as CFD (Computational Fluid Dynamics) study results for the GMT Enclosure. The wind tunnel tests include simulations for: a) Topography, b) Open Enclosure (all the shutters and vents open), and c) Closed Enclosure (all the vents and shutters closed). The CFD modeling was carried out for a wide range of conditions such as low and high wind speeds at various wind directions, and for the fully open and partially open Enclosure. The second part of this paper concerns the thermal effects of the Enclosure steel members. The wind speed and member sizes have been studied in relation to the required time to reach a defined temperature inside the Enclosure. This is one of the key performance characteristics of the Enclosure that can affect "Dome Seeing" significantly. The experimental data and theoretical predications have been used to identify the areas inside the Enclosure that need to be ventilated. The Enclosure thermal control strategy has been determined and an optimized system has been designed based on the final results.

Vibration mitigation for wind-induced jitter for the Giant Magellan Telescope

Roger M. Glaese, Michael Sheehan

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The Giant Magellan Telescope (GMT) is a planned large terrestrial telescope with a segmented primary mirror with a 24.5 meter overall diameter. Like most terrestrial telescopes, the GMT resides within an enclosure designed to protect the telescope from the elements and to reduce the effects of wind on the optical performance of the telescope. Wind impingement on the telescope causes static deformation and vibration in the telescope structure that affects the alignment and image jitter performance of the telescope. Actively controlled primary mirror segments and a secondary mirror can correct for the static and low frequency portions of the wind effects, but typically the actuators do not have the bandwidth to address higher frequency components of the wind environment. Preliminary analyses on the GMT indicate that the image jitter associated with wind effects meets budgeted allowances but without much margin. Preliminary models show that the bulk of the residual jitter arises from excitation of a small number of modes in the 9 to 12 Hz range. Therefore, as a risk mitigation effort to increase the margin on the wind induced jitter, passive and active vibration mitigation approaches have been examined for the GMT, which will be the focus of this paper. Using a finite element model of the GMT along with wind loading load cases, several passive and active vibration mitigation approaches were analyzed. These approaches include passive approaches such as tuned mass dampers targeting the worst offending modes, and constrained layer damping targeting all of the modes within the troublesome frequency range. Active approaches evaluated include two active damping approaches, one using several reaction mass actuators and the other using active strut type actuators. The results of the study show that although all approaches are successful in reducing the jitter, the active damping approach using reaction mass actuators offers the lightest weight, least implementation impact, and most adaptability of any of the approaches.

Feasibility studies to upgrade the Canada-France-Hawaii Telescope site for the next generation Canada-France-Hawaii Telescope

Kei Szeto, Mathieu Angers, Craig Breckenridge, et al.

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The Next Generation Canada-France-Hawaii Telescope is a dedicated, 10m aperture, wide-field, fiber-fed multiobject spectroscopic facility proposed as an upgrade to the existing Canada-France-Hawaii Telescope on the summit of Mauna Kea. The Next Generation Canada-France-Hawaii Telescope baseline concept assumes the new facility is built on the existing Canada-France-Hawaii Telescope telescope pier and enclosure pier and occupies the same three dimensional exterior “footprint”. Three technical studies have been planned to examine the validity of these assumptions. The technical studies are executed in series as they represent technical decision points in a logical sequence. The three technical studies in succession are: 1. Telescope Pier Study – Load Capacity and Structural Interface, 2. Enclosure Fixed Base Study – Telescope and Enclosure Configuration and Load Capacity and 3. Aero- Thermal Study – Dome Thermal Seeing and Air Flow Attenuation over the Enclosure Aperture Opening. The paper outlines the baseline facility (telescope, spectrograph and enclosure) concept and the status of these studies, and discusses the proposed telescope and enclosure configuration in terms of the redevelopment assumptions. A consolidated feasibility study report will be submitted to the CFHT Board and Science Advisory Committee in the Fall of 2012, with first light for the facility aiming to be in the early 2020s.

The Astronomical Telescope of New York: a new 12-meter astronomical telescope

T. Sebring, R. Junquist, C. Stutzki, et al.

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The Astronomical Corporation of New York has commissioned a study of a 12-meter class telescope to be developed by a group of NY universities. The telescope concept builds on the basic principles established by the Keck telescopes; segmented primary mirror, Ritchey Chretien Nasmyth instrument layout, and light weight structures. New, lightweight, and low cost approaches are proposed for the primary mirror architecture, dome structure and mechanisms, telescope mount approach, and adaptive optics. Work on the design is supported by several NY based corporations and universities. The design offers a substantially larger aperture than any existing Visible/IR wavelength telescope at historically low cost. The concept employs an adaptive secondary mirror and laser guide star adaptive optics. Two First Light instruments are proposed; A High resolution near infrared spectrograph and a near infrared Integral field spectrograph/imager.

Reviewing off-axis telescope concepts: a quest for highest possible dynamic range for photometry and angular resolution

Gil Moretto, Jeff R. Kuhn, Phil R. Goode

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We review off-axis telescope concepts that use unobstructed pupils. Built and prospective telescopes for ground and space astronomy will be presented and discussed. Such concepts offer great advantages in terms of emissivity, throughput, diffraction- limited energy concentration and higher dynamic range. The coronagraphic performance of off-axis telescopes will enable instruments, which are starving for higher dynamic range, for example, those devoted to faint companion detection and solar studies. Smaller telescopes like SOLAR-C (IfA/Haleakala Observatory), and the New Solar Telescope (NST/NJIT/ Big Bear Observatory) are operational and are test beds for the Advanced Technology Solar Telescope (ATST Project) for which site construction is beginning on Haleakala.

Early science results from SOFIA

Erick T. Young, Terry L. Herter, Rolf Güsten, et al.

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SOFIA, the Stratospheric Observatory for Infrared Astronomy, is an airborne observatory with a 2.7-m telescope that is under development by NASA and the German Aerospace Center DLR. From late 2010 and through the end of 2011, SOFIA conducted a series of science demonstration flights, Early Science, using FORCAST (the Faint Object InfraRed Camera for the SOFIA Telescope), HIPO (the High-speed Imaging Photometer for Occultations), and GREAT (the German REceiver for Astronomy at Terahertz frequencies). Flying at altitudes as high as 13.7 km (45,000 ft), SOFIA operates above more than 99.8% of the water vapor in the Earth’s atmosphere, opening up most of the far-infrared and sub-millimeter parts of the spectrum. During Early Science, 30 science missions were flown with results in solar system astronomy, star formation, the interstellar medium, the Galactic Center, and extragalactic studies. Many of these investigations were conducted by the first group of SOFIA General Investigators, demonstrating the operation of SOFIA as a facility for the astronomical community. This paper presents some recent highlights from Early Science.

Active damping of the SOFIA Telescope assembly

Paul J. Keas, Edward Dunham, Ulrich Lampater, et al.

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The NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA) employs a 2.5-meter reflector telescope in a Boeing 747SP. The telescope is housed in an open cavity and is subjected to aeroacoustic and inertial disturbances in flight. To meet pointing requirements, SOFIA must achieve a pointing stability of approximately 0.5 arcseconds RMS. An active damping control system is being developed for SOFIA to reduce image jitter and image degradation due to resonance of the telescope assembly. Our paper discusses the history of the active damping design for SOFIA, from early concepts to the current implementation which has recently completed a ground and flight testing for proof-of-concept. We describe some milestones in the analysis and testing of the telescope assembly which guided the development of the vibration control system. The control synthesis approach and current implementation of the active damping control system is presented. Finally, we summarize the performance observed in early flight tests and the steps that are currently foreseen to completing the development of this system.

Evaluation of the aero-optical properties of the SOFIA cavity by means of computional fluid dynamics and a super fast diagnostic camera

Christian Engfer, Enrico Pfüller, Manuel Wiedemann, et al.

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The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a 2.5 m reflecting telescope housed in an open cavity on board of a Boeing 747SP. During observations, the cavity is exposed to transonic flow conditions. The oncoming boundary layer evolves into a free shear layer being responsible for optical aberrations and for aerodynamic and aeroacoustic disturbances within the cavity. While the aero-acoustical excitation of an airborne telescope can be minimized by using passive flow control devices, the aero-optical properties of the flow are difficult to improve. Hence it is important to know how much the image seen through the SOFIA telescope is perturbed by so called seeing effects. Prior to the SOFIA science fights Computational Fluid Dynamics (CFD) simulations using URANS and DES methods were carried out to determine the flow field within and above the cavity and hence in the optical path in order to provide an assessment of the aero-optical properties under baseline conditions. In addition and for validation purposes, out of focus images have been taken during flight with a Super Fast Diagnostic Camera (SFDC). Depending on the binning factor and the sub-array size, the SFDC is able to take and to read out images at very high frame rates. The paper explains the numerical approach based on CFD to evaluate the aero-optical properties of SOFIA. The CFD data is then compared to the high speed images taken by the SFDC during flight.

Optical characterization of the SOFIA telescope using fast EM-CCD cameras

Enrico Pfüller, Jürgen Wolf, Helen Hall, et al.

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The Stratospheric Observatory for Infrared Astronomy (SOFIA) has recently demonstrated its scientific capabilities in a first series of astronomical observing flights. In parallel, special measurements and engineering flights were conducted aiming at the characterization and the commissioning of the telescope and the complete airborne observatory. To support the characterization measurements, two commercial Andor iXon EM-CCD cameras have been used, a DU-888 dubbed Fast Diagnostic Camera (FDC) running at frame rates up to about 400 fps, and a DU-860 as a Super Fast Diagnostic Camera (SFDC) providing 2000 fps. Both cameras have been mounted to the telescope’s Focal Plane Imager (FPI) flange in lieu of the standard FPI tracking camera. Their fast image sequences have been used to analyze and to improve the telescope’s pointing stability, especially to help tuning active mass dampers that suppress eigenfrequencies in the telescope system, to characterize and to optimize the chopping secondary mirror and to investigate the structure and behavior of the shear layer that forms over the open telescope cavity in flight. In June 2011, a collaboration between the HIPO science instrument team, the MIT’s stellar occultation group and the FDC team, led to the first SOFIA observation of a stellar occultation by the dwarf planet Pluto over the Pacific.

SOFIA observatory performance and characterization

Pasquale Temi, Pamela M. Marcum, Walter E. Miller, et al.

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The Stratospheric Observatory for Infrared Astronomy (SOFIA) has recently concluded a set of engineering flights for Observatory performance evaluation. These in-flight opportunities have been viewed as a first comprehensive assessment of the Observatory's performance and will be used to address the development activity that is planned for 2012, as well as to identify additional Observatory upgrades. A series of 8 SOFIA Characterization And Integration flights have been conducted from June to December 2011. The HIPO science instrument in conjunction with the DSI Super Fast Diagnostic Camera (SFDC) have been used to evaluate pointing stability, including the image motion due to rigid-body and flexible-body telescope modes as well as possible aero-optical image motion. We report on recent improvements in pointing stability by using an Active Mass Damper system installed on Telescope Assembly. Measurements and characterization of the shear layer and cavity seeing, as well as image quality evaluation as a function of wavelength have been performed using the HIPO+FLITECAM Science Instrument conguration (FLIPO). A number of additional tests and measurements have targeted basic Observatory capabilities and requirements including, but not limited to, pointing accuracy, chopper evaluation and imager sensitivity. This paper reports on the data collected during these flights and presents current SOFIA Observatory performance and characterization.

The balloon-borne large-aperture submillimeter telescope for polarimetry-BLASTPol: performance and results from the 2010 Antarctic flight

Enzo Pascale, Peter A. R. Ade, Francesco E. Angilè, et al.

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The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) is a suborbital mapping experiment designed to study the role played by magnetic fields in the star formation process. BLASTPol uses a total power instrument and an achromatic half-wave plate to modulate the polarization signal. During its first flight from Antarctica in December 2010, BLASTPol made degree scale maps of linearly polarized dust emission from molecular clouds in three wavebands centered at 250, 350, and 500 μm. This unprecedented dataset in terms of sky coverage, with sub-arcminute resolution, allows BLASTPol to trace magnetic fields in star-forming regions at scales ranging from cores to entire molecular cloud complexes. A second long-duration flight is scheduled for December 2012.

Optical design and calibration of a medium size telescope prototype for the CTA

Bagmeet Behera, Jürgen Bähr, Sandra Grünewald, et al.

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The Cherenkov Telescope Array (CTA) is designed to make a major improvement in the sensitivity of ground based VHE (Very High Energy, defined as > 20GeV to 100s of TeV) gamma-ray telescopes. Not only will the differential-flux sensitivity be an order of magnitude better than those of the currently operating Cherenkov telescopes, but there will also be significant improvements in the energy, spectral and angular resolution. Delivering these features cost-effectively requires several telescope sizes and designs - a few large size telescopes (23m diameter) are designed for the lowest energies, a large number of small size telescopes (4-7m diameter) to increase the overall collection area which helps at the highest energies and a number of Medium Size Telescopes (MST, 9.5m or 12m diameter, depending on the mirror design) to provide the greatest sensitivity at ∼ 1 TeV. To provide complete sky coverage, CTA will have both a Northern Hemisphere and a Southern Hemisphere site. A prototype for an MST design (currently under development) will be build in Berlin by 2012. This MST prototype has a modified Davies-Cotton design with a tessellated mirror, with individual facets of ∼ 1.2m in diameter. The facets are three-point mounted on the optical support structure, having two powered actuators for alignment adjustments. In addition a number of CCD cameras will be mounted at various positions on the dis and will be used for calibration. Here we present the various optical calibration tasks - optimization of the optical point-spread-function (PSF) and the pointing of this MST prototype, along with initial results.

Development of a mid-sized Schwarzschild-Couder Telescope for the Cherenkov Telescope Array

Robert A. Cameron

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The Cherenkov Telescope Array (CTA) is a ground-based observatory for very high-energy (10 GeV to 100 TeV) gamma rays, planned for operation starting in 2018. It will be an array of dozens of optical telescopes, known as Atmospheric Cherenkov Telescopes (ACTs), of 8 m to 24 m diameter, deployed over an area of more than 1 square km, to detect flashes of Cherenkov light from showers initiated in the Earth's atmosphere by gamma rays. CTA will have improved angular resolution, a wider energy range, larger fields of view and an order of magnitude improvement in sensitivity over current ACT arrays such as H.E.S.S., MAGIC and VERITAS. Several institutions have proposed a research and development program to eventually contribute 36 medium-sized telescopes (9 m to 12 m diameter) to CTA to enhance and optimize its science performance. The program aims to construct a prototype of an innovative, Schwarzschild-Couder telescope (SCT) design that will allow much smaller and less expensive cameras and much larger fields of view than conventional Davies-Cotton designs, and will also include design and testing of camera electronics for the necessary advances in performance, reliability and cost. We report on the progress of the mid-sized SCT development program.

Status and performance of the Discovery Channel Telescope during commissioning

Stephen E. Levine, Thomas A. Bida, Tomas Chylek, et al.

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Lowell Observatory's Discovery Channel Telescope is a 4.3m telescope designed for optical and near infrared astronomical observation. At first light, the telescope will have a cube capable of carrying five instruments and the wave front sensing and guider system at the f/6.1 RC focus. The corrected RC focus field of view is 30’ in diameter. Nasmyth and prime focus can be instrumented subsequently. Early commissioning work with the installed primary mirror and its support system started out using one of the wave front sensing probes mounted at prime focus, and has continued at RC with the recent installation of the secondary mirror. We will report on the on-sky pointing and tracking performance of the telescope, initial assessment of the functionality of the active optics support system, and tests of the early image quality of the telescope and optics. We will also describe the suite of first light instruments, and early science operations.

The Large Binocular Telescope

J. M. Hill, R. F. Green, D. S. Ashby, et al.

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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 borosilicate honeycomb 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 on-sky phasing of the two telescopes in the mid-infrared occurred in October 2010 with the LBTI instrument in Fizeau mode. The telescope control system has been upgraded to allow binocular (2-sided) observations with pairs of instruments. The prime focus cameras (LBC) routinely operate in this mode. Improved collimation and pointing models have been deployed to keep both sides collimated and pointed at the same target. The control system has also been upgraded to allow observations of solar system objects at non-sidereal tracking rates. Science observations are scheduled for 60% of the nights including a significant fraction of adaptive optics imaging with the first adaptive secondary mirror and the FLAO system with natural guide stars. MODS1, a nearUV-optical spectrometer, has been added to the suite of science instruments along with LBC (visible imagers) and LUCI1 (near infrared spectrometer). LMIRcam (2-5 microns) and PISCES (1-2.5 microns) have been used for adaptive optics imaging. The remaining nights are scheduled for telescope and instrument commissioning activities as new instruments arrive. The second of the two F/15 adaptive secondary mirrors has been installed on the telescope in Fall 2011 and has been commissioned on-sky in Spring 2012.

New Fraunhofer Telescope Wendelstein: assembly, installation, and current status

Hans Thiele, Nancy Ageorges, Dirk Kampf, et al.

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Due to the exposed location of the Wendelstein observatory on the steep summit of mount Wendelstein no road exists to transport telescope components and heavy equipment to the observatory in order to install the new 2m Fraunhofer Telescope Wendelstein (FTW) in its new dome. A two step installation concept was therefore followed to mitigate any risks that essential hardware would not work once installed on the mountain. This paper reports on the telescope factory assembly and tests, including on-sky tests, which were performed in early summer 2011 at the factory site to make sure, that the telescope and all essential subsystems are working properly before the telescope would be installed on the mountain. The telescope was disassembled again to be transported to the mountain in summer. Lifting of all structural subsystems and the optics up to the mountain observatory with the help of a heavy lift helicopter will be presented in detail, also looking at specific design drivers, logistic aspects and special tools for installation of the telescope and its mirrors in its new dome. Handling and transport concept for the M1 mirror installation, which also will have to be used when the mirror is disassembled for recoating, are presented. Up to end of 2011 the telescope installation and pre-alignment could be completed including first on-sky tests. The system will undergo a detailed performance test campaign in the first halve of 2012. Current performance results of these commissioning activities will be reported.

VST: from commissioning to science

Pietro Schipani, Massimo Capaccioli, Carmelo Arcidiacono, et al.

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The VLT Survey Telescope (VST) has started the scientific operations on the ESO Paranal observatory after a successful commissioning period. It is currently the largest telescope in the world specially designed for surveying the sky in visible light. The VST is dedicated to survey programmes, supporting the VLT with wide-angle imaging by detecting and pre-characterising sources, which the VLT Unit Telescopes can then observe further.

Commissioning results from the Large Binocular Telescope

Joar G. Brynnel, Norman J. Cushing, Richard F. Green, et al.

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Commissioning of a telescope facility such as the Large Binocular Telescope presents us with unprecedented challenges. The logistical and managerial balance act of scheduling commissioning of telescope, adaptive optics and twelve focal stations with subsequent commissioning of the instruments that populate the focal stations, while still providing for adequate science opportunity with already operational instruments is an equation that is problematic to solve in a way that meets the interests of all stakeholders. This paper presents strategies and priorities applied at the LBTO, and status of telescope commissioning programs. We provide a summary of telescope commissioning results, including a discussion about specific efforts to improve performance of the LBT.

Discovery Channel Telescope active optics system early integration and test

Alexander J. Venetiou, Thomas A. Bida

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The Discovery Channel Telescope (DCT) is a 4.3-meter telescope with a thin meniscus primary mirror (M1) and a honeycomb secondary mirror (M2). The optical design is an f/6.1 Ritchey-Chrétien (RC) with an unvignetted 0.5° Field of View (FoV) at the Cassegrain focus. We describe the design, implementation and performance of the DCT active optics system (AOS). The DCT AOS maintains collimation and controls the figure of the mirror to provide seeing-limited images across the focal plane. To minimize observing overhead, rapid settling times are achieved using a combination of feed-forward and low-bandwidth feedback control using a wavefront sensing system. In 2011, we mounted a Shack-Hartmann wavefront sensor at the prime focus of M1, the Prime Focus Test Assembly (PFTA), to test the AOS with the wavefront sensor, and the feedback loop. The incoming wavefront is decomposed using Zernike polynomials, and the mirror figure is corrected with a set of bending modes. Components of the system that we tested and tuned included the Zernike to Bending Mode transformations. We also started open-loop feed-forward coefficients determination. In early 2012, the PFTA was replaced by M2, and the wavefront sensor moved to its normal location on the Cassegrain instrument assembly. We present early open loop wavefront test results with the full optical system and instrument cube, along with refinements to the overall control loop operating at RC Cassegrain focus.

E-ELT update of project and effect of change to 39m design

Alistair McPherson, Jason Spyromilio, Markus Kissler-Patig, et al.

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During the last year a modified baseline design for the E-ELT has been developed. The aim of this revision was both to achieve a significant cost saving and to reduce risk on major items. The primary mirror diameter was slightly reduced to 39 m and the total height of the telescope also decreased accordingly. This paper describes the work performed by ESO and a variety of contractors to review the EELT design to match the modified baseline. Detailed design and construction planning, as well as detailed cost estimates were updated for the 39-metre baseline design. In June 2011, ESO Council formally endorsed this modified design as the E-ELT revised baseline. The design drivers and balancing cost factors will be described along with the risk reduction measures taken during this phase. This will culminate in the design which has been agreed as being ready to move forward to construction once approval from ESO Council has been achieved.

Thirty Meter Telescope project update

Larry Stepp

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The Thirty Meter Telescope (TMT) is a public-private-international partnership to build an extremely large optical-infrared telescope on the summit of Mauna Kea on the island of Hawai'i. This paper summarizes the design and predicted performance of TMT, and provides updates on the status of the development and prototype testing activities. TMT is currently in its preconstruction phase. The roles of the partner institutions for developing and delivering observatory subsystems are now well defined, the design work is maturing and plans for construction are in place. Current plans are for start of construction in April 2014, with first light including all 492 segments installed by the end of 2021.

Giant Magellan Telescope: overview

Matt Johns, Patrick McCarthy, Keith Raybould, et al.

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The Giant Magellan Telescope (GMT) is a 25-meter optical/infrared extremely large telescope that is being built by an international consortium of universities and research institutions. It will be located at the Las Campanas Observatory, Chile. The GMT primary mirror consists of seven 8.4-m borosilicate honeycomb mirror segments made at the Steward Observatory Mirror Lab (SOML). Six identical off-axis segments and one on-axis segment are arranged on a single nearly-paraboloidal parent surface having an overall focal ratio of f/0.7. The fabrication, testing and verification procedures required to produce the closely-matched off-axis mirror segments were developed during the production of the first mirror. Production of the second and third off-axis segments is underway. GMT incorporates a seven-segment Gregorian adaptive secondary to implement three modes of adaptive-optics operation: natural-guide star AO, laser-tomography AO, and ground-layer AO. A wide-field corrector/ADC is available for use in seeing-limited mode over a 20-arcmin diameter field of view. Up to seven instruments can be mounted simultaneously on the telescope in a large Gregorian Instrument Rotator. Conceptual design studies were completed for six AO and seeing-limited instruments, plus a multi-object fiber feed, and a roadmap for phased deployment of the GMT instrument suite is being developed. The partner institutions have made firm commitments for approximately 45% of the funds required to build the telescope. Project Office efforts are currently focused on advancing the telescope and enclosure design in preparation for subsystem- and system-level preliminary design reviews which are scheduled to be completed in the first half of 2013.

Science with the re-baselined European Extremely Large Telescope

J. Liske, P. Padovani, M. Kissler-Patig

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The modifications to the European Extremely Large Telescope (E-ELT) baseline design were accompanied by an evaluation of their impact on science. We will present the conclusions of this evaluation. The Design Reference Mission served as the benchmark for the evaluation. None of the modifications critically affect the Science Case. In particular, the full instrumentation suite can still be implemented allowing for the full foreseen suite of science cases. The largest impact is induced by the reduced diameter. For a large fraction of the science cases this can be offset by increasing the exposure times by ~20% to 34%. Where spatial resolution is the limiting factor, the limits have to be reduced by 9%. The exoplanet case deserves a special mention: two of the three components of this case (detection of Earth twins by the radial velocity method, and characterisation of the atmospheres of transiting planets) are unaffected; for the third component (direct imaging of Earth-like planets) the same results as for the original baseline can be achieved, but only at 20% smaller distances. Overall, all of the major science cases of the E-ELT can essentially be maintained.

Opacity measurements at Summit Camp on Greenland and PEARL in northern Canada with a 225 GHz tipping radiometer

Keiichi Asada, Pierre L. Martin-Cocher, Chien-Ping Chen, et al.

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We report the first measurements of 225 GHz atmospheric opacity at Summit Camp (Latitude 72°.57 N; Longitude 38°.46 W; Altitude 3250 m) in Greenland and the Polar Environment Atmospheric Research Laboratory (PEARL: Latitude 80°.05 N; Longitude 86°.42 W; Altitude 600 m) in Northern Canada with a tipping radiometer. Summit Camp and PEARL are research stations mostly interested in meteorology and geophysics, and they are potentially excellent sites for astronomical observations at sub-millimeter wavelength. We purchased a tipping radiometer from Radiometer Physics GmbH. After a test run at the summit of Mauna Kea, Hawaii, the radiometer was deployed to PEARL in February 2011, and relocated to Summit Camp in August 2011. The atmospheric opacity has been monitored from February 14th to May 10th, 2011 at PEARL and since August 2011 at Summit Camp. The median values of the measured opacity at PEARL ranged from 0.11 in February to 0.19 in May; Summit Camp varied in the range from 0.04 to 0.18 between August 2011 and May 2012. Summit Camp in Greenland is expected to be an excellent site for sub-millimeter and Terahertz astronomy, and we plan to set up there a 12-m telescope for VLBI and single-dish observations.

Site characterization studies in high plateau of Tibet

Yongqiang Yao, Hongshuai Wang, Liyong Liu, et al.

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The site survey in western China has been carried out since 2003. Remote studies and local surveys are performed, and Oma site, Ali area in southwest Tibet, has been selected in 2005 to make site testing measurements. The monitoring results show that Ali area can be the best choice for astronomical observations over the East Asian regions. A new site in Ali has been identified and begun construction in 2010 for small telescopes and detailed site characterization. This paper reviews the long term site survey, presents site characteristics in Tibet, and introduces current status of the new Ali observatory.

New instruments to calibrate atmospheric transmission

Peter Zimmer, John T. McGraw, Daniel C. Zirzow, et al.

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Changing atmospheric transmission accounts for the largest systematic errors limiting photometric measurement precision and accuracy for ground-based telescopes. While considerable resources have been devoted to correcting the effects of the atmosphere on image resolution, the effects on precision photometry have largely been ignored. To correct for the transmission of the atmosphere requires direct measurements of the wavelength-dependent transmission in the same direction and time that the supported photometric telescope is acquiring its data. We describe a multi-wavelength lidar, the Facility Lidar for Astronomical Measurement of Extinction (FLAME) that observes the stable upper stratosphere, and the Astronomical Extinction Spectrophotometer (AESoP), a spectrophotometer that creates and maintains NIST absolute standard stars. The combination of these two instruments enables high photometric precision of both the stellar spectra and atmospheric transmission. The throughput of both FLAME and AESoP are calibrated to NIST radiometric standards. This inexpensive and replicable instrument suite provides the lidar-determined monochromatic transmission of Earth’s atmosphere at visible and near-infrared wavelengths to better than 0.25% per airmass and the wavelength-dependent transparency to better than 1% uncertainty per minute. These atmospheric data are merged to create a metadata stream that allows throughput corrections from data acquired at the time of the scientific observations to be applied to broadband and spectrophotometric scientific data. This new technique replaces the classical use of nightly mean atmospheric extinction coefficients, which invoke a stationary and plane-parallel atmosphere and ultimately limit ground-based all-sky photometry to 1% - 2% precision.

The Greenland Telescope

Paul Grimes, Raymond Blundell

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In the spring of 2010, the Academia Sinica Institute of Astronomy and Astrophysics, and the Smithsonian Astrophysical Observatory, acquired the ALMA North America prototype antenna – a state-of-the-art 12-m diameter dish designed for submillimeter astronomy. Together with the MIT-Haystack Observatory and the National Radio Astronomy Observatory, the plan is to retrofit this antenna for cold-weather operation and equip it with a suite of instruments designed for a variety of scientific experiments and observations. The primary scientific goal is to image the shadow of the Super-Massive Black Hole in M87 in order to test Einstein’s theory of relativity under extreme gravity. This requires the highest angular resolution, which can only be achieved by linking this antenna with others already in place to form a telescope almost the size of the Earth. We are therefore developing plans to install this antenna at the peak of the Greenland ice-sheet. This location will produce an equivalent North-South separation of almost 9,000 km when linked to the ALMA telescope in Northern Chile, and an East-West separation of about 6,000 km when linked to SAO and ASIAA’s Submillimeter Array on Mauna Kea, Hawaii, and will provide an angular resolution almost 1000 times higher than that of the most powerful optical telescopes. Given the quality of the atmosphere at the proposed telescope location, we also plan to make observations in the atmospheric windows at 1.3 and 1.5 THz. We will present plans to retrofit the telescope for cold-weather operation, and discuss potential instrumentation and projected time-line.

Status of the first Antarctic survey telescopes for Dome A

Zhengyang Li, Xiangyan Yuan, Xiangqun Cui, et al.

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The preliminary site testing carried out since the beginning of 2008 shows the Antarctic Dome A is very likely to be the best astronomical site on earth even better than Dome C and suitable for observations ranging from optical wavelength to infrared and sub-millimeter. After the Chinese Small Telescope Array (CSTAR) which is composed of four small fixed telescopes with diameter of 145mm and mounted on Dome A in 2008 for site testing and variable star monitor, three Antarctic Survey Telescopes (AST3) were proposed for observations of supernovas and extrasolar planets searching. AST3 is composed of 3 large field of view catadioptric telescopes with 500mm entrance diameter and G, R, I filter for each. The telescopes can point and track autonomously along with a light and foldable dome to keep the snow and icing build up. A precise auto-focusing mechanism is designed to make the telescope work at the right focus under large temperature difference. The control and tracking components and assembly were successfully tested at from normal temperature down to -80 Celsius degree. Testing observations of the first AST3 showed it can deliver good and uniform images over the field of 8 square degrees. The first telescope was successfully mounted on Dome A in Jan. 2012 and the automatic observations were started from Mar. 2012.

Ukpik: testbed for a miniaturized robotic astronomical observatory on a high Arctic mountain

Eric Steinbring, Brian Leckie, Tim Hardy, et al.

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Mountains along the northwestern coast of Ellesmere Island, Canada, possess the highest peaks nearest the Pole. This geography, combined with an atmospheric thermal inversion restricted to below ~1000 m during much of the long arctic night, provides excellent opportunities for uninterrupted cloud-free astronomy - provided the challenges of these incredibly remote locations can be overcome. We present a miniaturized robotic observatory for deployment on a High Arctic mountaintop. This system tested the operability of precise optical instruments during winter, and the logistics of installation and maintenance during summer. It is called Ukpik after the Inuktitut name for the snowy owl, and was deployed at two sites accessible only by helicopter, each north of 82 degrees latitude; one on rock at 1100 m elevation and another on a glacier at 1600 m. The instrument suite included at first an all-sky-viewing camera, with the later addition of a small telescope to monitor Polaris, both protected by a retractable weather-proof enclosure. Expanding this to include a narrow-field drift-scanning camera for studying extra-solar planet transits was also investigated, but not implemented. An unique restriction was that all had to be run on batteries recharged primarily by a wind turbine. Supplementary power came from a methanol fuel-cell electrical generator. Communications were via the Iridium satellite network. The system design, and lessons learned from three years of operation are discussed, along with prospects for time-domain astronomy from isolated, high-elevation polar mountaintops.

The Gattini South Pole UV experiment

Anna M. Moore, Sara Ahmed, Michael C. B. Ashley, et al.

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The Gattini South Pole UV experiment (Gattini SPUV) was deployed to the South Pole dark sector in February 2010 and has recently completed a highly successful first season of winter time observations. The experiment has, for the first time ever, measured and categorized the optical night sky brightness at the very blue wavelengths. The experiment consists of a remotely operated 6” aperture custom designed telescope. The telescope feeds a blue sensitive imager with 4 degree field of view that contains a bank of 3 filters: SDSS g’, Bessel U and a custom “super U” filter specifically designed to probe the sky emission at wavelengths approaching the atmospheric cut-off. The filters are continually cycled with exposure times ranging from 30 to 300 seconds throughout the winter period. The telescope, in addition, feeds a 2 degree long slit VPH grating spectrograph with R~1000. The bandwidth is 350-450nm. The spectra are recorded simultaneously with the imager exposures. The experiment is designed for low temperature Antarctic operation and resides on the roof of the MAPO building in the South Pole Antarctic sector. The primary science goals are to categorize the Antarctic winter-time sky background at the very bluest of wavelengths as a pathfinder for the Antarctic Cosmic Web Imager. We present a technical overview of the experiment and results from the first winter season.

PLATO-R: a new concept for Antarctic science

Michael C. B. Ashley, Yael Augarten, Colin S. Bonner, et al.

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PLATO-R is an autonomous, robotic observatory that can be deployed anywhere on the Antarctic plateau by Twin Otter aircraft. It provides heat, data acquisition, communications, and up to 1kW of electric power to support astronomical and other experiments throughout the year. PLATO-R was deployed in 2012 January to Ridge A, believed to be the site with the lowest precipitable water vapour (and hence the best atmospheric transmission at terahertz frequencies) on earth.^1-4 PLATO-R improves upon previous PLATO designs that were built into ten-foot shipping containers by being much smaller and lighter, allowing it to be field-deployable within 2-3 days by a crew of four.

Canada-France-Hawaii Telescope image quality improvement initiative: thermal assay of the observing environment

Karun Thanjavur, Kevin Ho, Sarah Gajadhar, et al.

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As part of the image quality (IQ) assessment and improvement initiative being carried out at the 3.6m Canada France Hawaii Telescope (CFHT) on Mauna Kea, Hawaii, our objective in the work reported here is to obtain a systematic assay of thermal sources within the dome and in the summit environment around the observatory, and therefore mitigate their contributions to convective instability leading to 'dome seeing'. Toward this, we undertook a nighttime overflight to capture thermal images with a calibrated infrared camera of the outer structures of CFHT and the neighboring observatories on the summit ridge, as well as of a significant area of the surrounding terrain. The same thermal camera was then used to image heat sources within the dome. Using a convective heat transfer model, all these measured surface temperatures were converted to heat fluxes, and thus used to build a thermal assay of the dome. In addition, using button type temperature loggers, we simultaneously recorded the nighttime dome skin temperatures of CFHT and two other observatories over a weeklong period to evaluate nighttime supercooling of the dome skin due to radiation to the cold night sky. As a complementary goal we compared the efficacy of different paints and coatings used in observatories to minimize this effect. Though similar studies have been carried out at other observatories, the results are rarely available in published literature. Therefore, here we explain our methodologies, along with a detailed discussion of our results and inferences to serve as a useful resource to the larger observing community.

New optical telescope projects at Devasthal Observatory

Ram Sagar, Brijesh Kumar, Amitesh Omar, et al.

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Devasthal, located in the Kumaun region of Himalayas is emerging as one of the best optical astronomy site in the continent. The minimum recorded ground level atmospheric seeing at the site is 0.006 with median value at 1.001. Currently, a 1.3-m fast (f/4) wide field-of-view (660) optical telescope is operating at the site. In near future, a 4-m liquid mirror telescope in collaboration with Belgium and Canada, and a 3.6-m optical telescope in collaboration with Belgium are expected to be installed in 2013. The telescopes will be operated by Aryabhatta Research Institute of Observational Sciences. The first instruments on the 3.6-m telescope will be in-house designed and assembled faint object spectrograph and camera. The second generation instruments will be including a large field-of-view optical imager, high resolution optical spectrograph, integral field unit and an optical near-infrared spectrograph. The 1.3-m telescope is primarily used for wide field photometry imaging while the liquid mirror telescope will see a time bound operation to image half a degree wide strip in the galactic plane. There will be an aluminizing plant at the site to coat mirrors of sizes up to 3.7 m. The Devasthal Observatory and its geographical importance in between major astronomical observatories makes it important for time critical observations requiring continuous monitoring of variable and transient objects from ground based observatories. The site characteristics, its expansions plans and first results from the existing telescope are presented.

Towards a national astronomy observatory for the United Arab Emirates

S. Els, J. Maree, S. Al Marri, et al.

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The Emirates Institute for Advanced Science and Technology (EIAST) investigated the possibility to setup an astronomical research and outreach center within the United Arab Emirates. The main goals of such a new institution are to raise interest in space research and to ultimately develop a significant research community within the UAE. Such an astronomy center will also require appropriate observatory facilities. In this paper current concepts of such a possible national UAE astronomy observatory will be outlined, and the findings of an initial survey for suitable locations to host the telescopic facilities within the UAE are presented.

The 3,6 m Indo-Belgian Devasthal Optical Telescope: general description

Nathalie Ninane, Carlo Flebus, Brijesh Kumar

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AMOS SA has been awarded of the contract for the design, manufacturing, assembly, tests and on site installation (Devasthal, Nainital in central Himalayan region) of the 3.6 m Indo-Belgian Devasthal Optical Telescope (IDOT). The telescope has Ritchey-Chrétien optical configuration with one axial and two side Cassegrain ports. The meniscus primary mirror is active and it is supported by pneumatic actuators. The azimuth axis system is equipped with hydrostatic bearing. The telescope was completely assembled and tested in AMOS workshop. This step is completed and successful. The telescope is now ready for shipment to Nainital. This paper describes the telescope and summarizes the test results performed at AMOS to demonstrate that the telescope satisfies the main system requirements.

Manufacturing optics of a 2.5m telescope

F. Poutriquet, P. Plainchamp, J. Billet, et al.

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Over the past few years, Sagem REOSC has designed, manufactured and tested a 2.5m ALT/AZ telescope and its complete observatory. The next stage - integration - should occur in 2012. The aim of this paper is to develop the different stages of the project from technical and management's point of view. The telescope is a 2.5m-class telescope with an aperture of F/8. It is composed of a 2.5m primary mirror made of Zerodur©, a silica secondary mirror and a rotating tertiary mirror that allows pointing at Nasmyth foci. In addition, a wide field corrector can be adapted either at Cassegrain focus or at Nasmyth focus. Results achieved on the realization of such optics will be presented. An emphasis on the concurrent engineering and the problem solving approach will also be presented.

E-ELT optomechanics: overview

M. Cayrel

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The E-ELT is a project led by the European Southern Observatory (ESO) for a 40-m class optical, near- and midinfrared, ground-based telescope. When it will enter into operation, the E-ELT will be the largest and most powerful optical telescope ever built. It will not only offer unrivalled light collecting power, but also exceedingly sharp images, thanks to its ability to compensate for the adverse effect of atmospheric turbulence on image sharpness. The basic optical solution for the EELT is a folded three-mirror anastigmat, using a 39-m segmented primary mirror (M1), a 4-m convex secondary mirror (M2), and a 4-m concave tertiary mirror (M3), all active. Folding is provided by two additional flat mirrors sending the beams to either Nasmyth foci along the elevation axis of the telescope. The folding arrangement (flat M4 and M5 mirrors) is conceived to provide conveniently located flat surfaces for an adaptive shell (M4) and field stabilization (M5). That paper provides an overview of the specifications, design, and expected performance of the E-ELT optical systems.

E-ELT M1 test facility

M. Dimmler, J. Marrero, S. Leveque, et al.

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During the advanced design phase of the European Extremely Large Telescope (E-ELT) several critical components have been prototyped. During the last year some of them have been tested in dedicated test stands. In particular, a representative section of the E-ELT primary mirror has been assembled with 2 active and 2 passive segments. This test stand is equipped with complete prototype segment subunits, i.e. including support mechanisms, glass segments, edge sensors, position actuators as well as additional metrology for monitoring. The purpose is to test various procedures such as calibration, alignment and handling and to study control strategies. In addition the achievable component and subsystem performances are evaluated, and interface issues are identified. In this paper an overview of the activities related to the E-ELT M1 Test Facility will be given. Experiences and test results are presented.

Active damping strategies for control of the E-ELT field stabilization mirror

B. Sedghi, M. Dimmler, M. Mueller

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The fifth mirror unit (M5) of the E-ELT is a field stabilization unit responsible to correct for the dynamical tip and tilt caused mainly due to the wind load on the telescope. The unit is composed of: i) an electromechanical subunit, and ii) an elliptical mirror with a size of approximately 2.4 by 3-m. The M5 unit has been designed and prototyped using a three point support for the mirror actuated by piezo actuators without the need of a counter weight system. To be able to meet the requirements of the telescope, i.e. sufficient wavefront rejection capability, the unit shall exhibit a sufficient bandwidth for tip/tilt reference commands. In the presence of the low damped mechanical resonant modes, such a bandwidth can be guaranteed thanks to an active damping loop. In this paper, different active damping strategies for the M5 unit are presented. The efficiency of the approaches are analyzed using a detailed model of the unit. On a scale-one prototype active damping was implemented and the efficiency was demonstrated.

Development of a fast steering secondary mirror prototype for the Giant Magellan Telescope

Myung K. Cho, Andrew Corredor, Christoph Dribusch, et al.

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The Giant Magellan Telescope (GMT) will be a 25m class telescope currently in the design and development phase. The GMT will be a Gregorian telescope and equipped with a fast-steering secondary mirror (FSM). This secondary mirror is 3.2 m in diameter and built as seven 1.1 m diameter circular segments conjugated 1:1 to the seven 8.4m segments of the primary. The prototype of FSM (FSMP) development effort is led by the Korea Astronomy and Space Science Institute (KASI) with several collaborators in Korea, and the National Optical Astronomy Observatory (NOAO) in USA. The FSM has a tip-tilt feature to compensate image motions from the telescope structure jitters and the wind buffeting. For its dynamic performance, each of the FSM segments is designed in a lightweight mirror. Support system of the lightweight mirror consists of three axial actuators, one lateral support at the center, and a vacuum system. A parametric design study to optimize the FSM mirror configuration was performed. In this trade study, the optical image qualities and structure functions for the axial and lateral gravity print-through cases, thermal gradient effects, and dynamic performances will be discussed.

Repairing stress induced cracks in the Keck primary mirror segments

Dennis McBride, John S. Hudek, Sergey Panteleev

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Stress induced cracks have developed in the Zerodur glass at bonded supports for the primary mirror segments of the W.M. Keck Observatory telescopes. This has been a slow process that has advanced over the 20 year life of the telescopes. All mirror segments exhibit cracks to varying degrees. The number and severity of cracks has now reached a stage at which repairs are mandatory. A project is under way to determine the root causes of the cracks, and to develop a repair strategy. New supports and bonding methods are being designed and tested that will replace all of the original supports.

Alignment algorithms for the Thirty Meter Telescope

Gary Chanan

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A variety of algorithms utilized in the alignment of segmented telescopes were developed for and implemented on the Keck telescopes in the 1990s. The algorithms associated with the Keck segmented primary mirrors are very similar to those that will be used for the Thirty Meter Telescope (TMT). However, there are alignment or related wavefront measurement tasks associated with the TMT secondary and tertiary mirrors for which the corresponding Keck algorithms either did not exist or are not adequate for TMT. We discuss two particular algorithms associated with the TMT secondary and tertiary mirrors.

Phasing metrology system for the GMT

D. Scott Acton, Antonin Bouchez

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The Giant Magellan Telescope (GMT) is a 25.4 m diameter ground-based segmented Gregorian telescope, composed of 7 8.4 meter diameter primary mirror segments, and 7 1 meter diameter adaptive secondary mirror segments. Co-phasing of the integrated optical system will be partially achieved by making real-time measurements of the wavefront of an offaxis guide star. However, slowly varying aberrations due to thermal and gravitational effects, as well as wind buffeting, will make it difficult to maintain alignment using real-time optical measurements alone. Consequently, we are proposing internal metrology systems to maintain the relative alignment of the optical elements. In this paper we describe a differential capacitive edge sensing system to maintain the relative alignment of the adaptive secondary mirror reference bodies. We also propose an interferometric system for sensing of the relative displacements of primary mirror segments.

Performance prediction of the fast steering secondary mirror for the Giant Magellan Telescope

Myung Cho, Andrew Corredor, Christoph Dribusch, et al.

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The Giant Magellan Telescope (GMT) Fast-steering secondary mirror (FSM) is one of the GMT two Gregorian secondary mirrors. The FSM is 3.2 m in diameter and built as seven 1.1 m diameter circular segments conjugated 1:1 to the seven 8.4m segments of the primary. A parametric study and optimization of the FSM mirror blank and central lateral flexure design were performed. For the optimized FSM configuration, the optical image qualities and structure functions for the axial and lateral gravity print-through cases, thermal gradient effects, and dynamic performances will be discussed. This paper reports performance predictions of the optimized FSM. To validate our lateral flexure design concept, mechanical and optical tests were conducted on test mirrors installed with two different lateral flexures.

Dynamics, active optics, and scale effects in future extremely large telescopes

Renaud Bastaits, Bilal Mokrani, Goncalo Rodrigues, et al.

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This paper examines the active optics of future large segmented telescopes from the point of view of dynamic simulation and control. The first part of the paper is devoted to the modelling of the mirror. The model has a moderate size and separates the quasi-static behavior of the mirror (primary response) from the dynamic response (secondary or residual response). The second part of the paper is devoted to control. The control strategy considers explicitly the primary response of the telescope through a singular value controller. The control-structure interaction is addressed with the general robustness theory of multivariable feedback systems, where the secondary response is considered as uncertainty. This approach is very fast and allows extensive parametric studies. The study is illustrated with an example involving 90 segments, 270 inputs, and 654 outputs.

The development of the actuator prototypes for the active reflector of FAST

QiMing Wang, MingChang Wu, Ming Zhu, et al.

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Upon its completion, the Five-hundred-meter Aperture Spherical radio Telescope (FAST) will be the largest single dish radio telescope ever in the world. The construction has been initiated in March 2011 in Guizhou province of China. The whole construction process is expected to be completed in September 2016, with duration of 5.5 years. With an aperture of 500 meters and an illumination aperture of 300 meters, the active reflector is one of the most important parts of FAST. The reflector is composed of a ring beam, a cable net and thousands of panels, tie-down cables, actuators and anchors. For the observation process of source switching and source tracking, the parabola shape of the reflector is achieved by drawing back of the tie-down cables by the actuators. The motion performance and the reliability of the actuators are of great importance to the telescope. In this paper, the motion models of the actuators are analyzed for the observation process of source switching and source tracking. Several design schemes are proposed, including mechanical and hydraulic design. The electric, mechanical and hydraulic characteristics of these designs are discussed. Related experimental studies are performed to investigate the electric and mechanical performances of these actuator prototypes. Based on the analysis and test results, a final type of actuator will be optimally concluded to meet the requirements of the reflector of FAST.

Design, development, and manufacturing of highly advanced and cost effective aluminium sputtering plant for large area telescopic mirrors.

Rajeev R. Pillai, Sanjith K. K., K. Mohanachandran, et al.

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The design, development and manufacturing of a fully automated and cost effective aluminum sputtering unit for the deposition of aluminum on large area telescopic mirrors (maximum diameter of 3600mm) is presented here. The unit employs DC planar magnetron sputtering for the deposition process. A large area glow discharge unit is also designed for the pre-cleaning of the mirrors prior to aluminum coating. A special kinematic support structure with rotation is designed to support heavy mirrors of large area to minimize the deflection of the mirrors during deposition process. A custom designed 'mask' is employed in the magnetron system to improve the thickness uniformity within <±3%. The adhesion, thickness uniformity and reflectivity properties are studied in detail to validate the sputtering plant. Special fixtures have been designed for the system to accommodate smaller mirrors and studies have been conducted for the coatings and reported in the paper. The unit was successfully tested at HHV facility in Bangalore and will be installed at the ARIES Facility, Nainital.

The Australian SKA Pathfinder

Antony E. Schinckel, John D. Bunton, Tim J. Cornwell, et al.

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The Australian Square Kilometre Array Pathfinder (ASKAP) will be the fastest cm-wave survey radio-telescope and is under construction on the new Murchison Radio-astronomy Observatory (MRO) in Western Australia. ASKAP consists of 36 12-meter 3-axis antennas, each with a large chequerboard phased array feed (PAF) operating from 0.7 to 1.8 GHz, and digital beamformer preceding the correlator. The PAF has 94 dual-polarization elements (188 receivers) and the beamformer will provide about 36 beams (at 1.4 GHz) to produce a 30 square degree field of view, allowing rapid, deep surveys of the entire visible sky. As well as a large field of view ASKAP has high spectral resolution across the 304 MHz of bandwidth processed at any one time generating a large data-rate (30Gb/sec in to the imaging system) that requires real-time processing of the data. To minimise this processing and maximise the field of view for long observations the antenna incorporates a third axis, which keeps the PAF field of view and sidelobes fixed relative to the sky. This largely eliminates time varying artefact in the data that is processed. The MRO is 315 kilometres north-east of Geraldton, in Western Australia’s Mid West region. The primary infrastructure construction for ASKAP and other telescopes hosted at the Murchison Radio-astronomy Observatory has now been completed by CSIRO, the MRO manager, including installation of the fibre connection from the MRO site to Perth via Geraldton. The radio-quietness of the region is protected by the Mid West Radio Quiet Zone, implemented by the Australian Federal Government, out to a radius of 260km surrounding the MRO.

LOFAR, the low frequency array

R. C. Vermeulen

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LOFAR, the Low Frequency Array, is a next-generation radio telescope designed by ASTRON, with antenna stations concentrated in the north of the Netherlands and currently spread into Germany, France, Sweden and the United Kingdom; plans for more LOFAR stations exist in several other countries. Utilizing a novel, phased-array design, LOFAR is optimized for the largely unexplored low frequency range between 30 and 240 MHz. Digital beam-forming techniques make the LOFAR system agile and allow for rapid re-pointing of the telescopes as well as the potential for multiple simultaneous observations. Processing (e.g. cross-correlation) takes place in the LOFAR BlueGene/P supercomputer, and associated post-processing facilities. With its dense core (inner few km) array and long (more than 1000 km) interferometric baselines, LOFAR reaches unparalleled sensitivity and resolution in the low frequency radio regime. The International LOFAR Telescope (ILT) is now issuing its first call for observing projects that will be peer reviewed and selected for observing starting in December. Part of the allocations will be made on the basis of a fully Open Skies policy; there are also reserved fractions assigned by national consortia in return for contributions from their country to the ILT. In this invited talk, the gradually expanding complement of operationally verified observing modes and capabilities are reviewed, and some of the exciting first astronomical results are presented.

The RAEGE VLBI 2010 radiotelescope design

Eberhard Sust, José Antonio López Fernández

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The goal of the RAEGE (Red Atlantica Estaciones Geodinamicas Espaciales) project is the establishment of a Spanish-Portuguese network of geodynamical and spatial geodesy stations by the installation and operation of four fundamental geodetic / astronomical stations provided with radio telescopes located at - Yebes, close to Madrid / Spain - Tenerife, Canary Islands / Spain - Santa Maria, Azores Islands / Portugal. VLBI 2010 radiotelescopes are belonging to a new generation of radiotelescopes suitable for high precision geodetical earth observation and measurements, that shall allow to built up a high precision global reference system. The design of the radiotelescopes has been finished by MT Mechatronics in summer 2011 and currently three radiotelescopes are being manufactured. The first one is scheduled for installation in summer 2012 at Yebes Observatory close to Madrid.

Architecture of the metrology for the SRT

Tonino Pisanu, Franco Buffa, Gian Luigi Deiana, et al.

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The Sardinia Radio Telescope (SRT) Metrology team is planning to install an initial group of devices on the new 64 meters radio-telescope. These devices will be devoted for the realization of the antenna deformation control system: an electronic inclinometer able to monitor the alidade deformations and a Position Sensing Device (PSD) able to map the antenna secondary mirror (M2) displacements and tilts. The inclinometer will be used to map the rail conditions, the azimuthal axis inclination and the thermal effects on the alidade structure. The PSD will be used to measure the secondary mirror displacements induced by the gravity and by the thermal deformations that produce shifts and tilts with respect to its ideal optical alignment. The PSD will be traced by diode laser installed on a mechanically stable position inside the elevation equipment room. The inclinometer has been tested in laboratory with the aim to compare its performances with a reference measurement system. The PSD and the laser have been characterized by a long-term tests to assess their stability and accuracy, thus simulating the open air conditions that will be experienced by the device during its operative life. M2 may move freely in space thanks to a six axis actuator system (hexapod). The PSD measurements are processed by a hexapod kinematic model (HKM) to evaluate the correct actuator elongations, thus closing the control loop. The sensors will be acquired and recorded by a dedicated PC installed in the Alidade equipment room and connected to the sensors via the Ethernet network.

Requirements and considerations of the surface error control for the active reflector of FAST

MingChang Wu, QiMing Wang, XueDong Gu, et al.

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The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is currently under construction at a Karst depression in the Guizhou province of China. The active reflector of the telescope is composed of 4395 triangular panels laid on a cable-net structure. The aperture of the spherical surface is 500 meters, with open angle of about 110~120 degrees. Acting as the nodes of the reflector, the joint of these panels are adjusted by 2235 down-tie cables drawn by actuators. The RMS error of the parabola reflector is expected to be 5mm. To form the parabola shape of the reflector, for each of the actuators, a minimal working stroke of 950mm is required, with maximal speed of 1.6mm/s at the load of 50kN. Considering the elastic deformation of the down-tie cable and other factors, a positioning error within 0.25mm is required for the actuators. In this paper, the base formula for the motion of a general actuator at a typical observation time is studied analytically. The results are used to estimate the control error of the actuators and the pointing error of the whole reflector. Based on the designed error budgets, a statistical method is employed to estimate the overall surface error of the parabola reflector. The overall surface error is a comprehensive result of the panel design error, panel fabrication error, thermal deformation error, panel wind load induced error, cable-net error, installation error, measurement and control error etc. The results may be used as a reference in the measurement and control of the active reflector when in operation.

The Sardinia Radio Telescope (SRT) optical alignment

Martin Süss, Dietmar Koch, Heiko Paluszek

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The Sardinia Radio Telescope (SRT) is the largest radio telescope recently built in Europe – a 64m Radio Telescope designed to operate in a wavelength regime down to 1mm. The SRT is designed in a classical Gregorian configuration, allowing access to the primary mirror focus (F1), the Gregorian focus (F2) as well as a further translation to different F3 using a beam waveguide system and an automated change between different F3 receiver positions. The primary mirror M1, 64m in diameter, is composed by 1008 individual panels. The surface can be actively controlled. It’s surface, as well as the one of the 8 m Gregorian subreflector, needed to be adjusted after panel mounting at the Sardinia site. The measurement technique used is photogrammetry. In case of the large scale M1 a dedicated combination of a large scale and a small scale approach was developed to achieve extremely high accuracy on the large scale dimension. The measurement/ alignment efforts were carried out in 2010 and 2011, with a final completion in spring 2012. The results obtained are presented and discussed. The overall alignment approach also included the absolute adjustments of M2 to M1 and the alignments of M3, M4 and M5. M3 is a rotating mirror guiding the RF beam to M4 or M5, depending on the operational scenario. These adjustments are based on Lasertracker measurements and have been carried out in an integrated approach.

Final tests and performances verification of the European ALMA Antennas

Gianpietro Marchiori, Francesco Rampini

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The Atacama Large Millimeter Array (ALMA) is under erection in Northern Chile. The array consists of a large number (up to 64) of 12 m diameter antennas and a number of smaller antennas, to be operated on the Chajnantor plateau at 5000 m altitude. The antennas will operate up to 950 GHz so that their mechanical performances, in terms of surface accuracy, pointing precision and dimensional stability, are very tight. The AEM consortium constituted by Thales Alenia Space France, Thales Alenia Space Italy, European Industrial Engineering (EIE GROUP), and MT Mechatronics is assembling and testing the 25 antennas. As of today, the first set of antennas have been delivered to ALMA for science. During the test phase with ESO and ALMA, the European antennas have shown excellent performances ensuring the specification requirements widely. The purpose of this paper is to present the different results obtained during the test campaign: surface accuracy, pointing error, fast motion capability and residual delay. Very important was also the test phases that led to the validation of the FE model showing that the antenna is working with a good margin than predicted at design level thanks also to the assembly and integration techniques.

ALMA system verification

Richard Sramek, Koh-Ichiro Morita, Masahiro Sugimoto, et al.

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The ALMA aperture synthesis radio telescope is under construction in northern Chile. This paper presents the organization and process of ALMA System Verification. The purpose of System Verification is to measure the performance of the integrated instrument with respect to the ALMA System Technical Requirements. The System Technical Requirements flow down from the Science Requirements of the telescope and are intended to guide the design of the array and set the standards for technical performance. The process of System Verification will help determine how well the ALMA telescope meets its science goals. Some verification results are discussed.

The CCAT 25m diameter submillimeter-wave telescope

David Woody, Steve Padin, Eric Chauvin, et al.

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CCAT will be a 25 m diameter telescope operating in the 2 to 0.2 mm wavelength range. It will be located at an altitude of 5600 m on Cerro Chajnantor in Northern Chile. The telescope will be equipped with wide-field, multi-color cameras for surveys and multi-object spectrometers for spectroscopic follow up. Several innovations have been developed to meet the <0.5 arcsec pointing error and 10 μm surface error requirements while keeping within the modest budget appropriate for radio telescopes.

High performance holography mapping with the LMT

David R. Smith, Kamal Souccar

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When making holography measurements on a large telescope, there are many factors that make it difficult to obtain a consistent map. Two of these factors are variations of the satellite and temperature-induced deformations of the reflecting surface. The former requires frequent returns to the center of the map to check the satellite and the latter requires that the map be completed rapidly and at night. While holography mapping has traditionally been performed using point-by-point or raster scanning, these methods involve substantial overhead in the frequent movements back to the center of the map. In performing holography maps of the Large Millimeter Telescope (LMT) for the first light campaign, the observing team proposed a radial scanning approach. This strategy has the advantage that every scan passes through the center of the map. However, such a scan results in a disproportionate amount of telescope time near the center region. To achieve more uniform coverage, the team proposed a velocity profile that is inversely proportional to the distance from the center of the map. Because the velocity profile is defined with respect to position rather than time, this new approach required an extension of the existing parametric scanning capabilities at the LMT. The high axis rates resulting from this velocity profile present additional challenges. This paper describes the implementation and performance results for holography maps that use a radial scan pattern with a position-dependent velocity profile at the LMT. Both theoretical and experimental results are presented.

Photonic local oscillator technics for large-scale interferometers

H. Kiuchi, M. Saito, S. Iguchi

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In signal transmission through optical fiber, cable length delay fluctuation accompanied by chromatic and polarization-mode dispersion affects the coherence of distributed signals. To maintain signal coherence, it is very important to generate very-high-frequency signals with minimum phase noise and transmission loss. In a photonic local signal generation/distribution system with a microwave-photonic signal generator and a real-time microwave-photonic signal phase stabilizer that we developed as an alternative photonic LO system for ALMA (Atacama Large Millimeter/sub-millimeter Array), signals are transmitted in the form of frequency difference between two coherent light waves, effectively maintaining the coherence of distributed reference signals. Through the development of the real-time phase stabilizer, we discovered that the system would be further improved with the introduction of a post-processing scheme phase stabilizer and confirmed its effectiveness by experiments.

Precision attitude control for the BETTII balloon-borne interferometer

Dominic J. Benford, Dale J. Fixsen, Stephen A. Rinehart, et al.

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The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter baseline far-infrared interferometer to fly on a high altitude balloon. Operating at wavelengths of 30-90 microns, BETTII will obtain spatial and spectral information on science targets at angular resolutions down to less than half an arcsecond, a capability unmatched by other far-infrared facilities. This requires attitude control of the gondola at the several arcsecond level, and phase correction of the gondola attitude at a level of less than a tenth of an arcsecond, great challenges for a lightweight balloon-borne system. We have designed a precision attitude determination system to provide gondola attitude knowledge at a level of 2 milliarcseconds at rates up to 100Hz, with accurate absolute attitude determination at the half arcsecond level at rates of up to 10Hz. A multi-stage control system involving rigid body motion and tip-tiltpiston correction provides precision pointing stability to the level required for the far-infrared instrument to perform its spatial/spectral interferometry in an open-loop control. We present key aspects of the design of the attitude determination and control and its development status.

First technological steps toward opening a near-IR window at stratospheric altitudes

Fernando Pedichini, Mauro Centrone, Dario Lorenzetti, et al.

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The possibility to open a near-IR window at stratospheric altitude is crucial for a large variety of astronomical issues, from cosmology to the star formation processes. Up to now, one of the main issue is the role of the OH and thermal sky emission that are rising the sky background level when such observations are performed through ground based telescopes. We present the results of our technological activity aimed at affording some critical aspects typical of balloon flights. In particular, the obtained performances of prototype systems for rough and fine tracking will be illustrated. Both these systems constitute a high precision device (≤ 1 arcsec) for pointing and tracking light telescopes on board stratospheric balloons. We give the details concerning the optical and mechanical layout, as well as the detector and the control system. We demonstrate how such devices, when used at the focal plane of enough large telescopes(2-4m, F/10), may be capable to provide diffraction limited images in the near infrared bands. We have also developed a prototypal single channel photometer NISBA (Near Infrared Sky Background at Arctic pole), working in the H band (1.65 μm), able to evaluate, during a high-latitude balloon flight, how OH emission affects the sky background during the arctic night. The laboratory tests and performance on sky are presented and analyzed.

SOFIA in operation: telescope performance during the basic science flights

Hans J. Kärcher, Jörg Wagner, Alfred Krabbe, et al.

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The Stratospheric Observatory for Infrared Astronomy SOFIA started in December 2010 with the first series of science flights, and has successfully completed about 38 science missions until fall 2011. The science instruments flown included HIPO, FORCAST, GREAT and FLITECAM. Beside their scientific results (see related papers in these proceedings) the flights delivered an extensive data base which is now used for the telescope performance characterization and the operational optimization of the telescope in its unique environment. In this progress report we summarize recent achievements of the observatory as well as the status of the telescope and give an update of the SOFIA pointing system completed by intended future pointing optimization activities.

A new backup secondary mirror for SOFIA

Michael Lachenmann, Martin J. Burgdorf, Jürgen Wolf, et al.

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The telescope of the Stratospheric Observatory for Infrared Astronomy (SOFIA) is a Cassegrain design with a convex, hyperbolic secondary mirror. It is 352 mm in diameter, was made from silicon carbide and weighs only 1.9 kg. As this material is brittle, and the secondary mirror is indispensable to observations with SOFIA, a backup with the same mass and moments of inertia was made of aluminium in 2004. This mirror, however, allows diffraction-limited observations only above 20 μm and it produces double peaked images. In this paper we discuss the requirements for a new backup secondary mirror that can be employed also at near-infrared and even visible wavelengths and describe the most important aspects of the manufacturing process. The starting point of our analysis was a high-precision measurement of the surface properties of the existing aluminium secondary mirror, using the NANOMEFOS technique, which was recently developed by TNO in Delft, the Netherlands. With the exact shape of the mirror as input for a Zemax model we could reproduce the results of actual measurements of its optical performance that had been carried out on SOFIA in 2004. Based on these findings we determined then the specifications to be fulfilled by a new backup secondary mirror in order to meet the requirements on improved optical performance. Finally, we discuss the dynamic deformation of the aluminium mirror during chopping motions.

Upgrade of the SOFIA target acquisition and tracking cameras

Manuel Wiedemann, Jürgen Wolf, Hans-Peter Roeser

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The Stratospheric Observatory for Infrared Astronomy (SOFIA) uses three CCD cameras with different optics for target acquisition and tracking. The Wide Field Imager (WFI with 68 mm optics) and the Fine Field Imager (FFI with 254 mm optics) are mounted on the telescope front ring and are therefore exposed to stratospheric conditions in flight. The Focal Plane Imager (FPI) receives the visible light from the 2.5 meter telescope and is mounted inside the pressurized aircraft cabin at ca. 20°C. It is planned to replace all three imagers' CCD sensors with commercial Andor iXon cameras to significantly increase the sensitivity allowing for tracking on fainter stars. Andor cameras were temporarily mounted on the FPI flange as stand-alone systems to optically measure the telescope's pointing stability and the performance of various telescope sub-systems during engineering flights. Three DU-888 cameras will now be integrated in SOFIA's telescope system, so their image data can be used for target acquisition and tracking. To replace the WFI and FFI, the cameras will also need to be tested under stratospheric conditions, to ensure that they can be operated safely and without degradation of performance. In this paper we will report about the results of the environmental tests with the cameras, the integration of the camera in the SOFIA tracker and the current status of the upgrade project.

The 3,6 m Indo-Belgian Devasthal Optical Telescope: assembly, integration and tests at AMOS

Nathalie Ninane, Christian Bastin, Jonathan de Ville, et al.

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AMOS SA has been awarded of the contract for the design, manufacturing, assembly, tests and on site installation (Devasthal, Nainital in central Himalayan region) of the 3.6 m Indo-Belgian Devasthal Optical Telescope (IDOT). The telescope has a Ritchey-Chrétien optical configuration with a Cassegrain focus equipped with one axial port and two side ports. The meniscus primary mirror is active and is supported by pneumatic actuators. The mount is an Alt-Az type with for the azimuth axis a 5 m diameter hydrostatic track. The telescope was completely assembled and tested in AMOS workshop. This step is completed and successful. The telescope is now ready for shipment to Nainital. This paper describes the test campaign at sub-system and system level that has taken place to demonstrate that the telescope satisfies the main system requirements. Besides of the functionality of the telescope, the units interacting with the image quality or the tracking performance were plenty tested. Some selected tests directly connected to the performance of the telescope are also looked specifically in this paper.

First tests of the compact low scattered-light 2m-Wendelstein Fraunhofer Telescope

Ulrich Hopp, Ralf Bender, Frank Grupp, et al.

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The integration of the 2m Fraunhofer telescope started in August 2011 at the Mt. Wendelstein observatory. The logistics of the project are a key problem of the integration as the observatory has no road access. All large or heavy components inlcuding the primary mirror were successfully delivered by helicopter. Meanwhile, they are integrated in the telescope. The special design features of this alt-az telescope are its compactness and the low-ghost wide field optics (0.7 deg. f.o.v. diameter). We will briefly report on tests of the building and of the telescope system before the telescope moved to the mountain. The integration at the observatory and the first astronomical performances tests of the telescopes are discussed, and a brief update on the status of its instruments is presented. We comment on the cleaning and recoating strategy for the primary mirror based on sample tests.

SALT's transition to science operations

David A. H. Buckley, J. C. Coetzee, Steven M. Crawford, et al.

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The Southern African Large Telescope (SALT) began its re-commissioning phase in April 2011 following the completion of remedial engineering work on the telescope and the major science instrument, the Robert Stobie Spectrograph (RSS). The engineering work required modifications to the spherical aberration corrector, in order to improve the telescope’s image quality, and RSS, to improve its throughput. Positive test results included delivery of sub-arcsecond images, essentially meeting the original telescope image quality specifications and exhibiting none of the previous field-dependent aberrations, while the RSS has shown greatly improved efficiency performance. SALT has since transitioned to science operations, as from 1 September 2011, following the first open call for charged science proposals from the SALT partners. This paper discusses the current performance of SALT and it First Generation instruments, some initial science results, the proposal process and the operational model for the telescope.

The QUIJOTE-CMB experiment: studying the polarisation of the galactic and cosmological microwave emissions

J. A. Rubiño-Martín, R. Rebolo, M. Aguiar, et al.

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The QUIJOTE (Q-U-I JOint Tenerife) CMB Experiment will operate at the Teide Observatory with the aim of characterizing the polarisation of the CMB and other processes of Galactic and extragalactic emission in the frequency range of 10-40GHz and at large and medium angular scales. The first of the two QUIJOTE telescopes and the first multi-frequency (10-30GHz) instrument are already built and have been tested in the laboratory. QUIJOTE-CMB will be a valuable complement at low frequencies for the Planck mission, and will have the required sensitivity to detect a primordial gravitational-wave component if the tensor-to-scalar ratio is larger than r = 0.05.

The next generation of the Canada-France-Hawaii Telescope: science requirements and survey strategies

Alan McConnachie, Patrick Côté, David Crampton, et al.

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A concept study is underway to upgrade the existing 3.6 meter Canada-France-Hawaii Telescope (CFHT) to a 10 meter class, wide-field, dedicated, spectroscopic facility, which will be the sole astronomical resource capable of obtaining deep, spectroscopic follow-up data to the wealth of photometric and astrometric surveys planned for the next decade, and which is designed to tackle driving science questions on the formation of the Milky Way galaxy and the characterization and nature of dark energy. This unique facility will operate at low (R ∼ 2000), intermediate (R ∼ 6000) and high (R ∼ 20000) resolutions over the wavelength range 370 ≤ λ≤ 1300nm, and will obtain up to 3200 simultaneous spectra per pointing over a 1.5 square degree field. Unlike all other proposed or planned wide field spectroscopic facilities, this “Next Generation CFHT” will combine the power of a 10m aperture with exquisite observing conditions and a mandate for dedicated spectroscopic studies to enable transformative science programs in fields as diverse as exoplanetary host characterization, the interstellar medium, stars and stellar astrophysics, the Milky Way galaxy, the Local Group, nearby galaxies and clusters, galaxy evolution, the inter-galactic medium, dark energy and cosmology. A new collaboration must be formed to make this necessary facility into a reality, and currently nearly 60 scientists from 11 different communities - Australia, Brazil, Canada, China, France, Hawaii, India, Japan, South Korea, Taiwan, USA - are involved in defining the science requirements and survey strategies. Here, we discuss the origins of this project, its motivations, the key science and its flow-down requirements. An accompanying article describes the technical studies completed to date. The final concept study will be submitted to the CFHT Board and Science Advisory Committee in Fall 2012, with first light for the facility aiming to be in the early 2020s.

The optics and detector-simulation of the air fluorescence telescope FAMOUS for the detection of cosmic rays

Tim Niggemann, Thomas Hebbeker, Markus Lauscher, et al.

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A sophisticated method for the observation of ultra-high-energy cosmic rays (UHECRs) is the fluorescence detection technique of extensive air showers (EAS). FAMOUS will be a small fluorescence telescope, instrumented with silicon photomultipliers (SiPMs) as highly-sensitive light detectors. In comparison to photomultiplier tubes, SiPMs promise to have a higher photon-detection-efficiency. An increase in sensitivity allows to detect more distant and lower energy showers which will contribute to an enrichment of the current understanding of the development of EAS and the chemical composition of UHECRs.

Experimental characterization of the turbulence inside the dome and in the surface layer

Aziz Ziad, Dali-Ali Wassila, Julien Borgnino, et al.

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We present the concept of a new instrument dedicated to modeling turbulence inside the dome and in the surface layer. It consists of using parallel laser beams separated by non redundant baselines between 0.1 and 2-3m and measuring Angle-of-Arrival (AA) fluctuations from spots displacements on a CCD. We use weighted least-square method to fit the measured AA longitudinal and transverse covariances with theoretical forms deduced from the usual models of turbulence. Then, the whole parameters characterizing this turbulence are provided from a complete spatio-temporal analysis of AA fluctuations. Thus, the surface layer turbulence energy in terms of C²_N constant is provided from the AA structure function as in the DIMM instrument.

Seeing trends from deployable Shack-Hartmann wavefront sensors, MMT Observatory, Arizona, USA

J. Duane Gibson, G. Grant Williams, Thomas Trebisky

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Deployable Shack-Hartmann wavefront sensors (WFS) for the f/5 and f/9 secondary configurations have been used at the 6.5-meter MMT Observatory (MMTO) since 2003. Probe mirrors for these WFS's are moved into the optical path of the telescope between scientific observations multiple times each night. Results from the wavefront measurements are then used to bend the primary mirror (M1) and to reposition the secondary mirror (M2) to correct for wavefront errors. In addition to measuring the optical wavefront error, the Shack-Hartmann data are used to determine the delivered seeing using the measured spot sizes. This study attempts to analyze the more than 75,000 WFS measurements and associated seeing values obtained at the MMTO since 2003. The overall WFS data reduction and analysis procedure is discussed. This data analysis includes: 1) finding the spots in each image, 2) centroiding the spots, 3) measuring a point-spread function, 4) determining an average spot width and a derived seeing value, and 5) computing the best-fit Zernike polynomial coefficients. Wavefront slopes are calculated from spot displacements and wavefront aberrations are fit with a 19-term Zernike polynomial. As part of this study, the WFS-derived seeing values are correlated with other observing parameters, such as mirror-air temperature contrasts. Finally, seasonal climate and local weather (e.g., prevailing wind direction) effects on astronomical seeing are evaluated.

An updated T-series thermocouple measurement system for high-accuracy temperature measurements of the MMT primary mirror

D. Clark, J. D. Gibson

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Starting in 2009, MMTO began design and installation of a new set of electronics to measure a set of radiallydistributed type T thermocouples installed after the primary mirror polishing was completed. These thermocouples are arranged in both single measurement points and as thermopiles for differential temperature sensing. Since the goal of the primary mirror temperature control system is to minimize mirror seeing and mirror figure errors induced by temperature variation across the primary mirror, it depends on excellent accuracy from the temperature sensing system. The new electronics encompass on-board cold-junction compensation, real-time ITS-90 curve fitting, and Ethernet connectivity to the data servers running in the MMTO software infrastructure. We describe the hardware design, system wiring, and software used in this system.

A spectropolarimetric focal station for the ESO E-ELT

Klaus G. Strassmeier, Igor DiVarano, Ilya Ilyin, et al.

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We present a conceptual design for a spectropolarimetric focal station for ESO's European Extremely Large Telescope (E-ELT). It uses the intermediate f/4.4 focus, the only symmetric focus of the telescope. A dual channel, full Stokesvector polarimeter provides on-axis light for the wavelength range 380-1600nm to up to two spectrographs simultaneously via two pairs of fibers. With such spectropolarimetric capability and a proper spectrograph for the optical and the near infrared wavelengths, the E-ELT would be able to provide the full parameter space of an incoming wavefront. Because of the on-axis entrance location of the polarimeter collimator and an entrance aperture of just 1.3 arcsec, the expected poor image quality of the intermediate telescope focus is not directly relevant.

Performance of industrial scale production of ZERODUR mirrors with diameter of 1.5 m proves readiness for the ELT M1 segments

Thomas Westerhoff, Peter Hartmann, Ralf Jedamzik, et al.

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The two Extremely Large Telescopes under discussion, the Thirty Meter Telescope and the European Extremely Large Telescope, will use a multitude of hexagonal shaped mirror segments to achieve the large aperture of 30 m and 39 m, respectively. The proper functionality of both telescopes will strongly depend upon the variation of material properties between individual segments. SCHOTT has a well proven experience in production of mirror substrates for segmented telescopes. Today five of the world's six segmented telescopes are using ZERODUR® as mirror substrate material. Since 2003 SCHOTT delivered more than 260 mirrors of 1.5 m in diameter for industrial application not related to astronomy. In this paper the achievements during the serial production of those are presented for specified material properties and dimensional parameters. The presentation includes data on the fulfillment of the CTE specification, the achieved tolerances on surface figure and flatness and other geometrical quality parameters. The data to be presented will demonstrate the excellent reproducibility of ZERODUR®'s material properties and its manufacturing process. The production capabilities at SCHOTT for the successful delivery in time of the multitude of ZERODUR® segments are presented and discussed. They will demonstrate that ZERODUR® is well prepared for the demands of industrial scale production for the two large segmented ELT's in quality, quantity, and in the requested time period.

E-ELT project: geotechnical investigation at Cerro Armazones

Paolo Ghiretti, Volker Heinz, Daniela Pollak, et al.

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The design and construction of large telescopes include significant geotechnical challenges. In order to guarantee reliable and stable operations, a giant telescope like the European - Extremely Large Telescope (E-ELT) requires a foundation performance according to the level of accuracy of the other telescope's components. This paper describes the main geological and geotechnical activities conducted on site along with the studies completed in specialized geotechnical laboratories with the objective to achieve a thorough characterization of the ground conditions. This study shows that, the properties of the foundation materials are appropriate to guarantee a good performance of the E-ELT.

Technological developments toward the small size telescopes of the Cherenkov Telescope Array

R. Canestrari, T. Greenshaw, G. Pareschi, et al.

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In the last two decades a new window for ground-based high energy astrophysics has been opened. This explores the energy band from about 100 GeV to 10 TeV by making use of Imaging Atmospheric Cherenkov Telescopes (IACTs). Research in Very High Energy (VHE) gamma-ray astronomy is progressing rapidly and, thanks to the newest facilities such as MAGIC, HESS and VERITAS, astronomers and particle physicists are obtaining data with far-reaching implications for theoretical models. The Cherenkov Telescope Array (CTA) is the ambitious international next-generation facility for gamma-ray astronomy and astrophysics that aims to provide a sensitivity of a factor of 10 higher than current instruments, extend the energy band coverage from below 50 GeV to above 100 TeV, and improve significantly the energy and angular resolution to allow precise imaging, photometry and spectroscopy of sources. To achieve this, an extended array composed of nearly 100 telescopes of large, medium and small dimensions is under development. Those telescopes will be optimized to cover the low, intermediate and high energy regimes, respectively. In this paper, we focus our attention on the Small Size Telescopes (SSTs): these will be installed on the CTA southern hemisphere site and will cover an area of up to 10 km². The energy range over which the SSTs will be sensitive is from around 1 TeV to several hundreds of TeV. The status of the optical and mechanical designs of these telescopes is presented and discussed. Comments are also made on the focal surface instruments under development for the SSTs.

SST-GATE: an innovative telescope for very high energy astronomy

Philippe Laporte, Jean-Laurent Dournaux, Hélène Sol, et al.

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The Cherenkov Telescope Array (CTA) is an international collaboration that aims to create the world's largest (ever) Very High Energy gamma-ray telescope array, consisting of more than 100 telescopes covering an area of several square kilometers to observe the electromagnetic showers generated by incoming cosmic gamma-rays with very high energies (from a few tens of GeV up to over 100 TeV). Observing such sources requires - amongst many other things - a large FoV (Field of View). In the framework of CTA, SST-GATE (Small Size Telescope - GAmma-ray Telescope Elements) aims to investigate and to build one of the two first CTA prototypes based on the Schwarzschild-Couder (SC) optical design that delivers a FoV close to 10 degrees in diameter. To achieve the required performance per unit cost, many improvements in mirror manufacturing and in other technologies are required. We present in this paper the current status of our project. After a brief introduction of the very high energy context, we present the opto-mechanical design, discuss the technological tradeoffs and explain the electronics philosophy that will ensure the telescopes cost is minimised without limiting its capabilities. We then describe the software nedeed to operate the telescope and conclude by presenting the expected telescope performance and some management considerations.

A new era for the 2-4 meters class observatories: an innovative integrated system telescope-dome

G. Marchiori, A. Busatta, S. De Lorenzi, et al.

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The experience and the lessons learned gained in two decades of activity in astronomical industry in projects like NTT, VLT, LBT, VST VISTA and finally E-ELT brought to study a flexible fully integrated system which could address every astronomic institute to approach astronomy with a complete self standing facility including a dome, a telescope with 2 to 4 meters class optics and relative instruments with which it is possible to match the desired science cases and objectives. This paper describes the aspects of the flexibility which is so important to adapt the design to the specifications in order to fulfil the institutes science goals in the least time possible through the latest design tools such as CAD CAE FEM etc and the best and more cost effective technology experienced along the projects mentioned before.

Low-frequency high-sensitivity horizontal monolithic folded-pendulum as sensor in the automatic control of ground-based and space telescopes

F. Acernese, R. De Rosa, G. Giordano, et al.

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This paper describes a new mechanical implementation of a monolithic folded pendulum based inertial sensor, configurable as seismometer and as accelerometer. The sensor is a compact, light, fully scalable, tunable in frequency (< 100mHz), with large measurement band (10⁻⁶ Hz ÷ 10Hz) and high quality factor (Q > 1500 in air) instrument, with immunity to environmental noises guaranteed by an integrated laser optical readout. The measured sensitivity curve is in very good agreement with the theoretical one (10⁻¹²m/√Hz) in the band (0.1 ÷ 10Hz). Although its natural application is in the fields of earthquake engineering and geophysics, its performances make it suitable also for applications as sensor in the control of inertial platforms for interferometric detectors of gravitational waves, where a residual horizontal motion better than 10⁻¹⁵m/√Hz in the band 0.01 ÷ 100Hz is a requirement, and in the control of the mechanical support systems of ground-based or space telescopes.

Herzberg Institute of Astrophysics' vibration measurement capabilities with applications to astronomical instrumentation

P. W. G. Byrnes

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The Herzberg Institute of Astrophysics, Astronomy Technology Research Group's vibration measurement capabilities include modal test via impulse hammer or electrodynamic exciter, structural response monitoring via piezoelectric accelerometers, and data acquisition via LabVIEW virtual instruments. This paper will review our existing capabilities, and give examples of past and future applications relevant to astronomical instrumentation.

ALMA temporal phase stability and the effectiveness of water vapor radiometer

Satoki Matsushita, Koh-Ichiro Morita, Denis Barkats, et al.

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We present the temporal phase stability of the entire ALMA system. We first verified the temporal phase stability: We observed a strong quasar for a long time (a few tens of minutes), derived the temporal structure function after the atmospheric phase correction using the water vapor radiometers (WVRs), and confirmed that the phase stability of all the baselines reached the ALMA specification. We then verified frequency transfer between bands: We observed a bright quasar and switched between the two frequency bands, and confirmed that the phase returned to the original values within the phase fluctuation. In addition to these results, we also studied the effectiveness of the WVR phase correction at various frequencies, baseline lengths, and weather conditions.

ALMA array element astronomical verification

S. Asayama, L. B. G. Knee, P. G. Calisse, et al.

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The Atacama Large Millimeter/submillimeter Array (ALMA) will consist of at least 54 twelve-meter antennas and 12 seven-meter antennas operating as an aperture synthesis array in the (sub)millimeter wavelength range. The ALMA System Integration Science Team (SIST) is a group of scientists and data analysts whose primary task is to verify and characterize the astronomical performance of array elements as single dish and interferometric systems. The full set of tasks is required for the initial construction phase verification of every array element, and these can be divided roughly into fundamental antenna performance tests (verification of antenna surface accuracy, basic tracking, switching, and on-the-fly rastering) and astronomical radio verification tasks (radio pointing, focus, basic interferometry, and end-to-end spectroscopic verification). These activities occur both at the Operations Support Facility (just below 3000 m elevation) and at the Array Operations Site at 5000 m.

Trajectory generation for parametric rotating scan patterns at the LMT

David R. Smith, Kamal Souccar

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As main axis controllers for large, high precision telescopes have become more sophisticated, astronomers are developing new approaches to observing. Rather than merely pointing at a particular set of coordinates and tracking to account for the rotation of the Earth or for the ephemeris of the source, these new observing techniques often call for a telescope to scan in a pattern around the nominal source coordinates. These motions are conducted at higher rates and accelerations than traditional single point or raster maps, which introduces additional complexity into the control. Additionally, these motions must work in conjunction with an existing trajectory generator. This paper describes how a general parametric rotating scan pattern has been implemented at the Large Millimeter Telescope (LMT). The desired motion is combined with the existing trajectory generator and allows the addition of a parametric scan pattern, defined for each axis. The pattern can also be continuously rotated at a constant rate as the system tracks the source. The development allows for any parametric scan pattern, and the particular case of a continuously rotating Lissajous pattern is addressed in detail.

Atacama compact array antennas

M. Saito, J. Inatani, K. Nakanishi, et al.

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The ACA (Atacama Compact Array) system is an important element of ALMA and consists of four ACA 12-m antennas and twelve ACA 7-m antennas. The ACA system aims to acquire the total power data with four 12-m antennas and the short baseline interferometer data with 7-m antennas. The ACA system also increases reliability of the interferometer maps of astronomical sources larger than the field view of the 12-m antenna. The science performance of these antennas has been extensively verified at OSF (operation support facility) at an elevation of 2900 m in Atacama desert in northern Chile since 2007. The pointing performance has been verified with a dedicated optical pointing telescope, the servo performance is tested with angle encoders, and the surface accuracy has been measured with a radio holography method. Both ACA 12-m antennas and 7-m antennas have been successfully demonstrated to meet the very stringent ALMA specifications.

Very large millimeter/submillimeter array toward search for 2nd Earth

Satoru Iguchi, Masao Saito

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ALMA (Atacama Large Millimeter/submillimeter Array) is a revolutionary radio telescope and its early scientific operation has just started. It is expected that ALMA will resolve several cosmic questions and will give us a new cosmic view. Our passion for astronomy naturally goes beyond ALMA because we believe that the 21st-century astronomy should pursue the new scientific frontier. In this conference, we propose a project of the future radio telescope to search for habitable planets and finally detect 2nd Earth as a migratable planet. Detection of 2nd Earth is one of the ultimate dreams not only for astronomers but also for every human being. To directly detect 2nd Earth, we have to carefully design the sensitivity and angular resolution of the telescope by conducting trade-off analysis between the confusion limit and the minimum detectable temperature. The result of the sensitivity analysis is derived assuming an array that has sixty-four (64) 50-m antennas with 25-;μm surface accuracy mainly located within the area of 300 km (up to 3000 km), dual-polarization SSB receivers with the best noise temperature performance achieved by ALMA or better, and IF bandwidth of 128 or 256 GHz.. We temporarily name this telescope "Very Large Millimeter/Submillimeter Array (VLMSA)". Since this sensitivity is extremely high, we can have a lot of chances to study the galaxy, star formation, cosmology and of course the new scientific frontier.

ACA phase calibration scheme with the ALMA water vapor radiometers

Yoshiharu Asaki, Satoki Matsushita, Koh-Ichiro Morita, et al.

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In Atacama Large Millimeter/submillimeter Array (ALMA) commissioning and science verification we have conducted a series of experiments of a novel phase calibration scheme for Atacama Compact Array (ACA). In this scheme water vapor radiometers (WVRs) devoted to measurements of tropospheric water vapor content are attached to ACA’s four total-power array (TP Array) antennas surrounding the 7 m dish interferometer array (7 m Array). The excess path length (EPL) due to the water vapor variations aloft is fitted to a simple two-dimensional slope using WVR measurements. Interferometric phase fluctuations for each baseline of the 7 m Array are obtained from differences of EPL inferred from the two-dimensional slope and subtracted from the interferometric phases. In the experiments we used nine ALMA 12-m antennas. Eight of them were closely located in a 70-m square region, forming a compact array like ACA. We supposed the most four outsiders to be the TP Array while the inner 4 antennas were supposed to be the 7 m Array, so that this phase correction scheme (planar-fit) was tested and compared with the WVR phase correction. We estimated residual root-mean-square (RMS) phases for 17- to 41-m baselines after the planar-fit phase correction, and found that this scheme reduces the RMS phase to a 70 – 90 % level. The planar-fit phase correction was proved to be promising for ACA, and how high or low PWV this scheme effectively works in ACA is an important item to be clarified.

Functional safety for the Advanced Technology Solar Telescope

Scott Bulau, Timothy R. Williams

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Since inception, the Advanced Technology Solar Telescope (ATST) has planned to implement a facility-wide functional safety system to protect personnel from harm and prevent damage to the facility or environment. The ATST will deploy an integrated safety-related control system (SRCS) to achieve functional safety throughout the facility rather than relying on individual facility subsystems to provide safety functions on an ad hoc basis. The Global Interlock System (GIS) is an independent, distributed, facility-wide, safety-related control system, comprised of commercial off-the-shelf (COTS) programmable controllers that monitor, evaluate, and control hazardous energy and conditions throughout the facility that arise during operation and maintenance. The GIS has been designed to utilize recent advances in technology for functional safety plus revised national and international standards that allow for a distributed architecture using programmable controllers over a local area network instead of traditional hard-wired safety functions, while providing an equivalent or even greater level of safety. Programmable controllers provide an ideal platform for controlling the often complex interrelationships between subsystems in a modern astronomical facility, such as the ATST. A large, complex hard-wired relay control system is no longer needed. This type of system also offers greater flexibility during development and integration in addition to providing for expanded capability into the future. The GIS features fault detection, self-diagnostics, and redundant communications that will lead to decreased maintenance time and increased availability of the facility.

Facility level thermal systems for the Advanced Technology Solar Telescope

LeEllen Phelps, Gaizka Murga, Mark Fraser, et al.

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The management and control of the local aero-thermal environment is critical for success of the Advanced Technology Solar Telescope (ATST). In addition to minimizing disturbances to local seeing, the facility thermal systems must meet stringent energy efficiency requirements to minimize impact on the surrounding environment and meet federal requirements along with operational budgetary constraints. This paper describes the major facility thermal equipment and systems to be implemented along with associated energy management features. The systems presented include the central plant, the climate control systems for the computer room and coudé laboratory, the carousel cooling system which actively controls the surface temperature of the rotating telescope enclosure, and the systems used for active and passive ventilation of the telescope chamber.

Stray light and polarimetry considerations for the COSMO K-Coronagraph

Alfred G. de Wijn, Joan T. Burkepile, Steven Tomczyk, et al.

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The COSMO K-Coronagraph is scheduled to replace the aging Mk4 K-Coronameter at the Mauna Loa Solar Observatory of the National Center for Atmospheric Research in 2013. We present briefly the science objectives and derived requirements, and the optical design. We single out two topics for more in-depth discussion: stray light, and performance of the camera and polarimeter.

Quasi-static wavefront control for the Advanced Technology Solar Telescope

Luke C. Johnson, R. Upton, T. Rimmele, et al.

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The Advanced Technology Solar Telescope (ATST) requires active control of quasi-static telescope aberrations in order to meet image quality standards set by its science requirements. Wavefront control is managed by the Telescope Control System, with many telescope subsystems playing key roles. We present the design of the ATST quasi-static wavefront and alignment control architecture and the algorithms used to control its four active mirrors. Two control algorithms are presented, one that minimizes force on M1 actuators and another that employs a neutral-pointing constraint on M2 to reduce pointing error. We also present simulations that generate typical daily active mirror trajectories which correct optical misalignments due to changing gravitational and thermal loads.

Optical design of the COSMO large coronagraph

Dennis Gallagher, Steven Tomczyk, Haiying Zhang, et al.

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The Coronal Solar Magnetism Observatory (COSMO) is a facility dedicated to measuring magnetic fields in the corona and chromosphere of the Sun. It will be located on a mountaintop in the Hawaiian Islands and will replace the current Mauna Loa Solar Observatory (MLSO). COSMO will employ a suite of instruments to determine the magnetic field and plasma conditions in the solar atmosphere and will enhance the value of data collected by other observatories on the ground (SOLIS, ATST, FASR) and in space (SDO, Hinode, SOHO, GOES, STEREO, DSCOVR, Solar Probe+, Solar Orbiter). The dynamics and energy flow in the corona are dominated by magnetic fields. To understand the formation of Coronal Mass Ejections (CMEs), their relation to other forms of solar activity, and their progression out into the solar wind requires measurements of coronal magnetic fields. The COSMO suite includes the Large Coronagraph (LC), the Chromosphere and Prominence Magnetometer (ChroMag) and the K-Coronagraph. The Large Coronagraph will employ a 1.5 meter fuse silica singlet lens and birefringent filters to measure magnetic fields out to two solar radii. It will observe over a wide range of wavelengths from 500 to 1100 nm providing the capability of observing a number of coronal, chromospheric, and photospheric emission lines. Of particular importance to measuring coronal magnetic fields are the forbidden emission lines of Fe XIII at 1074.7 nm and 1079.8 nm. These lines are faint and require the very large aperture. NCAR and NSF have provided funding to bring the COSMO Large Coronagraph to a preliminary design review (PDR) state by the end of 2013.

Behavior of a horizontal air curtain subjected to a vertical pressure gradient

James Linden, LeEllen Phelps

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We present the details on an experiment to investigate the behavior of an air curtain that is subjected to a transverse pressure gradient. The setup simulates the conditions that will be present in the Advanced Technology Solar Telescope (ATST), a 4-meter solar observatory that will be built on Haleakala, Hawaii. A test rig was built to replicate the region at which the optical path crosses a temperature and pressure boundary between the telescope mount region, which is at the ambient temperature and pressure, and a warmer, pressurized lab space directly below. Use of an air curtain in place of an optically-transmitting window at the interface would allow science observations at a wider range of scientific wavelengths. With the air curtain exhibiting transitional flow behavior across the boundary, and applied pressure gradients of up to 6.5 Pa, we found that the air curtain was able to hold a pressure gradient of 0.25 Pa. As the applied pressure was increased, transient turbulent regions formed at the interface, and predictable flow behavior only occurred in the region closest to the air curtain blower. Computer modeling is used to validate the test data, identify laminar regions of the air curtain where minimal image distortion would occur, and explore the relationship between the applied pressure, effective pressure difference, and air curtain profile.

ATST telescope mount: machine tool or telescope

Paul Jeffers, Günter Stolz, Giovanni Bonomi, et al.

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The Advanced Technology Solar Telescope (ATST) will be the largest solar telescope in the world, and will be able to provide the sharpest views ever taken of the solar surface. The telescope has a 4m aperture primary mirror, however due to the off axis nature of the optical layout, the telescope mount has proportions similar to an 8 meter class telescope. The technology normally used in this class of telescope is well understood in the telescope community and has been successfully implemented in numerous projects. The world of large machine tools has developed in a separate realm with similar levels of performance requirement but different boundary conditions. In addition the competitive nature of private industry has encouraged development and usage of more cost effective solutions both in initial capital cost and thru-life operating cost. Telescope mounts move relatively slowly with requirements for high stability under external environmental influences such as wind buffeting. Large machine tools operate under high speed requirements coupled with high application of force through the machine but with little or no external environmental influences. The benefits of these parallel development paths and the ATST system requirements are being combined in the ATST Telescope Mount Assembly (TMA). The process of balancing the system requirements with new technologies is based on the experience of the ATST project team, Ingersoll Machine Tools who are the main contractor for the TMA and MT Mechatronics who are their design subcontractors. This paper highlights a number of these proven technologies from the commercially driven machine tool world that are being introduced to the TMA design. Also the challenges of integrating and ensuring that the differences in application requirements are accounted for in the design are discussed.

Performance introduction of a 2.5m telescope mount

Guomin Wang, Bozhong Gu, Shihai Yang, et al.

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In recent years, Nanjing Institute of Astronomical Optics and Technology (NIAOT) has made several telescopes for observatories all around the world. In 2011 NIAOT just finished the development of a 2.5m optical/infrared telescope mount. First part of this paper is to introduce the mount structure and their adjustment work. Second part is to give an introduction of the mount performance test methods and test results finished on NIAOT workshop.

Installation and verification of high precision mechanics in concrete structures at the example of ALMA antenna interfaces

Volker Heinz, Max Kraus, Eduardo Orellana

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For the ALMA interferometer at the array operation facility near San Pedro de Atacama at 5.000 meters asl 192 concrete antenna foundations had to be equipped with coupling points for 66 antennas. These antennas will be frequently moved between the foundations and placed on these interfaces without further adjustment. To position the ALMA antennas with the required accuracy, high precision inserts need to be installed in previously casted concrete foundations. Very tight mechanical tolerances have to be applied to civil structures, with standard tolerances of not less than millimeters. This is extremely difficult considering the material (mortar and steel in a concrete slab) to be used and the environmental conditions on site. Special tools had to be designed and an installation and alignment procedure developed, tested and improved. Important was to have a robust process, which allows highest precision installation without major re-machining for approx 600 interface blocks. Installation material, which could cope with the conditions, was specially tested for these requirements. The geometry of the interface and other parameters such as horizontal and vertical stiffness must be verified after the installation. Special metrology tools to measure reliable at micron level at high altitude had been selected. The experience and knowledge acquired will be beneficial for the installation of any opto-mechanical device in civil engineering structures, such as telescope and dome track rails, but also in optical interferometer installations. Metrology requirements and environmental conditions in most of these cases are equally challenging.

E-ELT telescope main structure

Alfredo Orden Martínez, Angel Dilla Martínez, Noelia Ballesteros Pérez, et al.

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The European Extra Large Telescope is ESO's biggest astronomical telescope project. The E-ELT is an active and adaptive telescope. It has an astigmatic optical solution (five mirrors, including two flat ones). The telescope structure is of alt-azimuth type able to support a primary mirror with an equivalent diameter of 40 m. The telescope will be installed in a high-seismicity zone, in Cerro Armazones, Antofagasta Region, Chile, at an altitude of 3046 metres above sea level. This has significantly affected the boundary conditions and safety aspects considered during the project. The scope of the paper describes the Telescope Main Structure configuration developed by Empresarios Agrupados (Spain) during the FEED Studies performed from June 2009 to July 2011 in the frame of ESO Contracts. Most of the solutions implemented were extrapolated from existing installations in which Empresarios Agrupados has participated, adjusting for the extra large size of this new telescope.

Testing, characterization, and control of a multi-axis, high precision drive system for the Hobby-Eberly Telescope Wide Field Upgrade

Ian M. Soukup, Joseph H. Beno, Gary J. Hill, et al.

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A multi-axis, high precision drive system has been designed and developed for the Wide Field Upgrade to the Hobby- Eberly Telescope at McDonald Observatory. Design, performance and controls details will be of interest to designers of large scale, high precision robotic motion devices. The drive system positions the 20-ton star tracker to a precision of less than 5 microns along each axis and is capable of 4 meters of X/Y travel, 0.3 meters of hexapod actuator travel, and 46 degrees of rho rotation. The positioning accuracy of the new drive system is achieved through the use of highprecision drive hardware in addition to a meticulously tuned high-precision controller. A comprehensive understanding of the drive structure, disturbances, and drive behavior was necessary to develop the high-precision controller. Thorough testing has characterized manufacture defects, structural deflections, sensor error, and other parametric uncertainty. Positioning control through predictive algorithms that analytically compensate for measured disturbances has been developed as a result of drive testing and characterization. The drive structure and drive dynamics are described as well as key results discovered from testing and modeling. Controller techniques and development of the predictive algorithms are discussed. Performance results are included, illustrating recent performance of several axes of the drive system. This paper describes testing that occurred at the Center for Electromechanics in Austin Texas.

Enclosure rotation on the Large Binocular Telescope

James Howard, Robert Meeks, David Ashby, et al.

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After several years of operation the enclosure rotation system of the LBT is exhibiting wear and other performance issues that may impact operations. This paper reviews the system design and assumptions used, describes the current performance and observed symptoms, and discusses recent improvements made to improve performance and reliability. The rotating enclosure of the LBT is a 2200 ton structure riding on four bogies with a total of 20 wheels. Identified deficiencies include wheel bearing capacities, bogie misalignment, and rail loading. These are partially due to excess enclosure weight, which was supposed to be 1600 tons, but also due to design errors. The most serious problem was the failure of several wheel bearings. The bearings were not designed for field serviceability, so a crash program began to determine how to replace them. This got us back on sky quickly, but a review of the engineering calculations identified an error which led to the use of undersized bearings. A method of installing a larger bearing was found, and these have been installed. One set of bogie wheels are misaligned so severely the structure makes loud popping and banging noises when the direction of building rotation changes. The bogie needs to be rotated about its vertical axis, but there was no provision in the design for this. The circular rail the bogies roll on is wearing faster than expected. The rails are extremely difficult to replace, so the short term plan is to study the problem.

The 3,6 m Indo-Belgian Devasthal Optical Telescope: the hydrostatic azimuth bearing

Jonathan de Ville, Maxime Piérard, Christian Bastin

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AMOS SA has been awarded of the contract for the design, manufacturing, assembly, tests and on site installation (Devasthal, Nainital in central Himalayan region) of the 3.6 m Indo-Belgian Devasthal Optical Telescope (IDOT). 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 mount is an Alt-Az type with for the azimuth axis a 5 m diameter hydrostatic track. This paper presents the solution adopted by AMOS to meet the specific requirements for the azimuth axis. The track is designed to be able to control the positioning of the telescope around the azimuth axis with an accuracy of 0.05 arc second for all tracking configurations. The challenge came from this tight accuracy with a mass in rotation weighting 125 tons. The azimuth track was mounted and tested in AMOS workshop; the tests and performances are also discussed.

Telescope positioning and drive system based on magnetic bearings, technical challenges and possible applications in optical stellar interferometry

Roland Lemke, Hans J. Kärcher, Lothar Noethe

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The paper describes the envisaged positioning and drive system for telescopes of the 2m class, gives some basic analysis for power consumption and positioning performance and proposes next steps for verification of the concept. A possible application could be in optical stellar interferometry where an additional delay could be spared if the positioning performance is better than 10nm. Fast re-positioning of the telescopes should allow for multiple baselines during one observing night giving the opportunity to obtain high spatial stellar images with high time resolution.

Enclosure design for the ARIES 3.6m optical telescope

A. K. Pandey, Vishal Shukla, Tarun Bangia, et al.

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A 3.6-m, f/9 optical telescope is planned to be installed at Devasthal, India (Latitude:29° 21' 40'' N, Longitude: 79° 41' 04'' E, Altitude: 2450 m above msl). The telescope has Cassegrain focus and alt-azimuth mount. The design of the telescope enclosure and the auxiliary building includes a fixed base enclosure, a telescope pier, a rotating dome structure, an auxiliary building, ventilation and component handling systems. The design is optimized for thermal, mechanical, structural, as well as for telescope installation and maintenance requirements. The design aims to provide seeing limited images within the telescope enclosure. This paper presents design of the 3.6m telescope enclosure.

An innovative alt-alt telescope for small observatories and amateur astronomers

M. Riva, S. Basso, R. Canestrari, et al.

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This paper want to show an innovative amateur oriented telescope with an unconventional alt-alt conguration. The goal is to make a telescope with good optical quality reducing production costs by adopting a gimbal based mounting to develop an alt-alt conguration suitable for a telescope. Reduce costs while preserving the optical quality is a necessary condition to allow small groups of amateur astronomers, schools and cultural clubs, with reduced economic resources, to acquire an astronomical instrument that encourages learning and advancing astrophysical knowledge. This unconventional mechanism for the realization of a telescope alt-alt provides signicant advantages. The traditional rotary motors coupled with expensive precision bearings are replaced with two simple linear actuators coupled to a properly preloaded gimbal joint and the cell becomes the primary structure of the telescope. A second advantage would be secured by mechanical simplicity evident in the easy portability of the instrument. The frame alt-alt has some limitations on the horizon pointing but does not show the zenith blind spot of the alt-az mount. A dedicated alt-alt pointing and tracking model is under development to be compatible with commercial telescope softwares and with the proposed new mounting.

Prototype enclosure design for the Korea Microlensing Telescope Network (KMTNet)

N. Kappler, L. Kappler, W. M. Poteet, et al.

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TBR Construction and Engineering (TBR) has under development for the Korea Astronomy and Space Science Institute (KASI), a project to provide three 1.6 meter optical telescopes observatories in three southern countries: Chile, South Africa, and Australia. The contracting team has chosen to develop a full scale prototype of the observatory. This will become a functional assembly and testing facility for all three project telescopes in Tucson, Arizona. This prototyping concept is meant to allow the optics team to make changes to the observatory as needed for the scientific mission while minimizing the expense of making changes in remote countries.

Initial alignment and commissioning plan for the LSST

William J. Gressler, Jacques Sebag, Chuck Claver

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The planned construction and completion of the Large Synoptic Survey Telescope (LSST) Project consists of phased activities. The initial telescope construction period will transition to a multi-year commissioning phase, which will conclude with final hand off to science operations. The initial telescope alignment will utilize laser tracker fiducials and nodal aberration theory (NAT) to demonstrate Engineering First Light with a three-mirror optical system and test camera, prior to the integration of the science camera. This plan exploits the diffraction limited on-axis image quality of the three-mirror design. Commissioning consists of final integration of the three LSST subsystems (Telescope, Camera, and Data Management), followed by on-sky science verification to show compliance with the survey performance specifications.

Dark energy camera installation at CTIO: overview

Timothy M. Abbott, Freddy Muñoz, Alistair R. Walker, et al.

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The Dark Energy Camera (DECam) has been installed on the V. M. Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. This major upgrade to the facility has required numerous modifications to the telescope and improvements in observatory infrastructure. The telescope prime focus assembly has been entirely replaced, and the f/8 secondary change procedure radically changed. The heavier instrument means that telescope balance has been significantly modified. The telescope control system has been upgraded. NOAO has established a data transport system to efficiently move DECam's output to the NCSA for processing. The observatory has integrated the DECam highpressure, two-phase cryogenic cooling system into its operations and converted the Coudé room into an environmentally-controlled instrument handling facility incorporating a high quality cleanroom. New procedures to ensure the safety of personnel and equipment have been introduced.

Dark Energy Camera installation at CTIO: technical challenges

Freddy Muñoz A., Andrés Montane, Roberto Tighe, et al.

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The Dark Energy Camera (DECam) is a new prime focus, wide-field imager for the V. M. Blanco 4-m telescope at CTIO. Instrumentation includes large, five-lens optical corrector mounted on hexapod mechanism for fine adjustment, filters, and a 519 Megapixel camera vessel; all integrated in a cage similar to the existing telescope prime focus structure. Currently Blanco allows a flip of this structure such that the f/8 secondary mirror, mounted on the back of the cage, points towards the primary mirror for Ritchey-Chretien observations. DECam will maintain this capability by attaching the existing F/8 mirror cell to the front of the new cage. Installation of this 8,600 kg instrument required the removal from the telescope of the primary mirror, the removal of the old prime focus assembly, and fine adjustment of large, over-constrained mechanisms followed by reassembly. A large facility shutdown was scheduled for this upgrade and several tools, fixtures, monitoring systems and procedures were developed in order to identify and then recover the optical alignment of the system, to control the distribution of stresses during tuning of the installation and to maintain the balance of the telescope with significant added mass. The final goal has been to maintain high performance of the telescope for both the existing f/8 Ritchey-Chretien focus mounted instruments and the new DECam instrument now in commissioning. The challenges presented in handling large elements, real-time monitoring, alignment, verification and feedback are described.

Korea Microlensing Telescope Network: science cases

Byeong-Gon Park, Seung-Lee Kim, Jae Woo Lee, et al.

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We present the science cases with the Korea Microlensing Telescope Network (KMTNet) which consists of three widefield 1.6 m telescopes distributed in Chile, South Africa, and Australia, respectively, providing unique continuous sky coverage with the three telescopes. The primary scientific goal of the KMTNet project is to explore the structure and diversity of planetary systems and variable objects. Since the system is mainly optimized to conduct gravitational microlensing surveys, it will enable detections of very low-mass exoplanets, potentially down to the mass of Mars that are inaccessible by other ground-based techniques. In addition to the primary science, it is possible to conduct a variety of other observational programs with the KMTNet system, including photometric studies of nearby galaxies and galaxy clusters, discovery of supernovae and their follow-up observations, and observations of near-Earth objects. We expect synergies between the KMTNet project with other similar or complementary projects in the southern sky, such as SkyMapper.

Design and development of a wide field telescope

Il Moon, Sangon Lee, Juhee Lim, et al.

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A prototype of large wide field telescope is a Cassegrain telescope which covers 2° field of view with two hyperbolic mirrors, a 0.5 m primary mirror and a 0.2 m secondary mirror with multiple correction lenses. To fulfill the optical and mechanical performance requirements in design and development phase extensive finite element analyses using NX NASTRAN and optical analyses with CODE V and PCFRINGE have been conducted for the structure of optical system. Analyses include static deformation (gravity and thermal), frequency, dynamic response analysis, and optical performance evaluations for minimum optical deformation. Image motion is also calculated based on line of sight sensitivity equations integrated in finite element models. A parametric process was performed for the design optimization to produce highest fundamental frequency for a given weight, as well as to deal with the normal concerns about global performance.

Achieving high precision photometry for transiting exoplanets with a low cost robotic DSLR-based imaging system

Olivier Guyon, Frantz Martinache

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We describe a low cost high precision photometric imaging system, which has been in robotic operation for one and half year on the Mauna Loa observatory (Hawaii). The system, which can be easily duplicated, is composed of commercially available components, offers a 150 sq deg field with two 70mm entrance apertures, and 6-band simultaneous photometry at a 0.01 Hz sampling. The detectors are low-cost commercial 3-color CMOS array, which we show is an attractive costeffective choice for high precision transit photometry. We describe the design of the system and show early results. A new data processing technique was developed to overcome pixelization and color errors. We show that this technique, which can also be applied on non-color imaging systems, essentially removes pixelization errors in the photometric signal, and we demonstrate on-sky photometric precision approaching fundamental error sources (photon noise and atmospheric scintillation). We conclude that our approach is ideally suited for exoplanet transit survey with multiple units. We show that in this scenario, the success metric is purely cost per etendue, which is at less than $10000s per square meter square degree for our system.

An active surface upgrade for the Delingha 13.7-m Radio Telescope

Dehua Yang, Yong Zhang, Guohua Zhou, et al.

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An upgrade program is proposed for the Delingha 13.7-m radio telescope to implement active surface for multi-beam observation at 3 mm wavelength. The upgrade involves three critical development aspects. One is the displacement actuator, which must fit the existing position, space and connections of the panels and backup structure, meanwhile, must be as compact and lightweighted as possible. The second is that a new sub-reflector is necessitated by the multi-beam observation, where a new hyperbolic surface figure is optimized. The third, more crucial and difficult, is to realize active control of the actuators and real-time closed-loop of the full active surface. This paper is to present the progress of the development work, test and experiments associated with the three areas. With one of the spare panels of the telescope, an experiment system is carried out with six sets of actuator and control electronics. Another experiment system of a novel laser-based closed-loop measurement concept is also conducted with four smaller dummy panels. Both experiment setups have output expected results and further experiments are going on with them. In this paper, based on the two experiments, we will describe the special design and test of the actuator, including the design of its special mounting and connecting mechanisms. The design and manufacture and measurement of the new hyperbolic sub-reflector will be detailed as well as the principle, simulation and realization of the laser-based measurement system. Besides, the control strategy of the large scale use of the hundreds of actuators and EMI suppression are also covered.

Development of a compact precision linear actuator for the active surface upgrade of the Delingha 13.7-m radio telescope

Guohua Zhou, Aihua Li, Dehua Yang, et al.

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The Delingha 13.7-m radio telescope is to be upgraded with an active surface for multi-beam observation at 3 mm wavelength. Its primary reflector is paved with 72 aluminum panels which are originally supported by 480 fixtures. One of the critical tasks associated with the upgrade program is development of precision linear displacement actuators to replace the panel fixtures hence to Listed first in the upgrade program is actively drive and position the panels. The linear actuator is required to fit the existing positions, dimensions and connections of the panels and the backup structure, also implicitly required to be as compact and lightweighted as possible. This paper is to report in detail the development and experiment of the compact, folded, precision linear actuator according to given technique requirements and constraints, including the description of the flexible adaption of the fixture of the actuators and the special design of the connecting mechanism with the panels. The experiment system is established with one of the spare panels of the telescope, and six sets of actuator and control electronics are included for driving the panel. This paper will present the test results measured on a single actuator prototype as well as the actuators working together in the spare panel experiment. The test results prove that the actuator manifests positioning accuracy of microns and load capacity of 12 kg. The related connection and electronics design of the actuator also meets the requirements of the update program of the telescope.

Upgrading the TNT Telescope: remote observing and future perspectives

G. Di Rico, M. Fiaschi, G. Valentini, et al.

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The Teramo Normale Telescope (TNT) is a 0.72 m telescope operating at the INAF-Teramo since the 1994. At the end of 2011, the whole system has been completely upgraded in order to improve the overall performance of the instrument and to allow safe and full remote observations, without the need of local operators. The main results of this work is setting up a reliable and modern system in a short while, and at the same time paving the way to further steps towards the development of a fully robotic observatory. Starting by a general overview of the system we describe the most important upgraded components and the possible next developments.

ESPRESSO: design and analysis of a Coudé-train for a stable and efficient simultaneous optical feeding from the four VLT unit telescopes

Alexandre Cabral, André Moitinho, João Coelho, et al.

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ESPRESSO is a fiber-fed, cross-dispersed, high-resolution, echelle spectrograph. Being the first purpose of ESPRESSO to develop a competitive and innovative high-resolution spectrograph to fully exploit the VLT (Very Large Telescope), and allow new science, it is important to develop the VLT array concept bearing in mind the need to obtain the highest stability, while preserving its best efficiency. This high-resolution ultra-stable spectrograph will be installed in the VLT at the Combined Coudé Laboratory (CCL), fed by four Coudé Trains, which brings the light from the Nasmyth platforms of the four VLT Unit Telescopes to the CCL. A previous trade-off analysis, considering the use of mirrors, prisms, lenses or fibers and several possible combinations of them, pointed towards a Full Optics solution, using only conventional optics to launch the light from the telescope into the front-end unit. In this case, the system is composed of a set of prisms and lenses to deliver a pupil and an image in the CCL, including an Atmospheric Dispersion Compensator. In this paper, we present the optical design of the Coudé Trains, the opto-mechanical concept, the main characteristics and expected performances.

Recent performance improvements for the Large Binocular Telescope primary mirror system

Robert L. Meeks, David Ashby, Chris Biddick, et al.

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Over the last several years the primary mirror cell systems for the Large Binocular Telescope have been upgraded to improve on-sky performance and observing efficiency. We describe improvements made to the support actuators and mirror positioning system and explain how those changes have led to better performance and contributed to increased reliability. Both systems have been substantially redesigned and remanufactured to allow the LBT primary mirror systems to meet extremely precise performance requirements over a very broad temperature range. We also discuss the mirror ventilation and thermal monitoring system and review its current status and potential upgrades to improve its performance.

Modernization of the 1 meter Swope and 2.5 meter Du Pont telescopes at Las Campanas Observatory

Frank Perez, Alan Bagish, Greg Bredthauer, et al.

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The Observatories of the Carnegie Institution for Science have operated the 1 and 2.5-meter telescopes since the early 1970s with only minor changes to the original control systems. We discuss the replacement of the original 4004 microprocessor- based telescope control system with modern high-speed servo controllers and motors, absolute main axis encoders, modern closed-loop controls and PC-based main operating software. We also discuss the original relay-based interlock systems that have been replaced with Programmable Logic Controllers (PLC) and have been interfaced into the new telescope control system. The modernization of both telescopes also includes many hardware upgrades to allow for remote observing and scripted automatic observations. These upgrades also include the modernization of shutter drives, windscreens and dome controls to improve the reliability and safety required for remote observing from an existing facility.

A happy conclusion to the SALT image quality saga

Lisa A. Crause, Darragh E. O'Donoghue, James E. O'Connor, et al.

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Images obtained with the Southern African Large Telescope (SALT) during its commissioning phase showed degradation due to a large focus gradient and a variety of other optical aberrations. An extensive forensic investigation eventually traced the problem to the mechanical interface between the telescope and the secondary optics that form the Spherical Aberration Corrector (SAC). The SAC was brought down from the telescope in 2009 April, the problematic interface was replaced and the four corrector mirrors were optically tested and re-aligned. The surface figures of the SAC mirrors were confirmed to be within specification and a full system test following the re-alignment process yielded a RMS wavefront error of just 0.15 waves. The SAC was re-installed on the tracker in 2010 August and aligned with respect to the payload and primary mirror. Subsequent on-sky tests produced alarming results which were due to spurious signals being sent to the tracker by the auto-collimator, the instrument responsible for controlling the attitude of the SAC with respect to the primary mirror. Once this minor issue was resolved, we obtained uniform 1.1 arcsecond star images over the full 10 arcminute field of view of the telescope.

Facility calibration unit of Hobby Eberly Telescope wide field upgrade

Hanshin Lee, Gary J. Hill, Brian L. Vattiat, et al.

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The Hobby-Eberly Telescope (HET) Wide-Field Upgrade (WFU) will be equipped with new Facility Calibration Unit (FCU). The FCU is in support of VIRUS and the facility instruments and consists of the head and source box. The FCU head, connected to the source box through two liquid light guides, is attached to the bottom of the WFU Wide-Field Corrector (WFC) and can be deployed into the beam to inject calibration light through the WFC whenever calibration is needed. A set of Fresnel lenses is used in the FCU head to mimic the caustics of M1 as much as possible to re-produce the telescope’s focal plane illumination pattern. Various imaging/non-imaging optical components (e.g. Compound Parabolic Concentrators, cone reflectors, condenser lenses) are used for efficient coupling between different types of calibration lamps and light guides, covering wavelengths from 350nm to 1800nm. In addition, we developed an efficient and tunable Light-Emitting Diode (LED) based source and coupler for UV and Visible spectral flat field calibration. This paper presents the designs, prototypes, and as-built components / subsystems of the FCU.

Solid telescopes for interferometric enhancement of existing telescopes

Alberto Riva, Mario Gai

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This paper describes a concept study for a simple and cost effective approach to upgrade of existing infrastructures. A conventional monolithic telescope can be endowed with a set of identical small telescopes combined coherently to enhance the resolution. The solid telescope represent a convenient solution for a simple and replicated small telescope. The solid telescope is intrinsically suited to be used in diffraction limited mode down to visible wavelengths. This may allow a viable dual feed mode for both guiding and phase referenced imaging. In this paper we analyze some of the critical engineering aspects and outline a possible implementation approach.

Optics and the mechanical system of the 62-cm telescope at the Severo Díaz Galindo Observatory in Guadalajara, Jalisco, México

Eduardo de la Fuente, J. Manuel Nuñez, Salvador Zazueta, et al.

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We present the results of a modification performed in the optical system of the 62 cm telescope (f/14.32) at observatory “Severo Díaz Galindo” Universidad de Guadalajara, Mexico. This modification consists of a change of distance between the primary and secondary mirrors from 1020 to 1135 mm. With this, a change in the image plane from 5200 mm to 600 mm, measured from the vertex of the primary mirror, is obtained. The latter allow to get the first astronomical images of The Telescope. This modification was necessary because alignment errors, such as distance between primary and secondary mirrors in the original system were presented. Besides, the telescope has a new accurate and adequate mechanical system installed on November 2011. Details and the first images obtained, are here presented.

Folded Cassegrain sets of the Gran Telescopio Canarias (GTC)

Alberto Gomez, Rubén Sanquirce, Gaizka Murga, et al.

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The Gran Telescopio Canarias (GTC) has been recently received two Folded Cassegrain Sets (FC-Sets) composed of an instrument rotator and the corresponding Acquisition and Guiding (AG) optomechanics. IDOM has been the responsible for the design, manufacturing, assembly and commissioning of the two units of FC-Sets. The design combines a compact layout of the mechanical system, enhanced by an innovative cable wrap design, resulting in a smooth and precise movement, whilst guaranteeing good access to important components and maximizing the maintainability. The custom design of the cable wrap as an evolution of the rolling loop type eliminates the need for a cable chain static housing, minimizing weight and impact on the telescope tube. The AG Mechanics provides the required pointing and focusing capabilities in a compact configuration. In January 2010, IDOM is awarded the design and procurement of the two FC-Sets. The final design is approved by GRANTECAN and the fabrication process starts in Nov 2011. The assembly and commissioning of both units are completed in April 2011. Once the Factory Acceptance Tests finishes in Dec 2011, all the elements are delivered to the Observatorio del Roque de los Muchachos (ORM). The Site Acceptance Tests are completed in Feb 2012.

Design, testing, and installation of a high-precision hexapod for the Hobby-Eberly Telescope dark energy experiment (HETDEX)

Joseph J. Zierer, Joseph H. Beno, Damon A. Weeks, et al.

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Engineers from The University of Texas at Austin Center for Electromechanics and McDonald Observatory have designed, built, and laboratory tested a high payload capacity, precision hexapod for use on the Hobby-Eberly telescope as part of the HETDEX Wide Field Upgrade (WFU). The hexapod supports the 4200 kg payload which includes the wide field corrector, support structure, and other optical/electronic components. This paper provides a recap of the hexapod actuator mechanical and electrical design including a discussion on the methods used to help determine the actuator travel to prevent the hexapod payload from hitting any adjacent, stationary hardware. The paper describes in detail the tooling and methods used to assemble the full hexapod, including many of the structures and components which are supported on the upper hexapod frame. Additionally, details are provided on the installation of the hexapod onto the new tracker bridge, including design decisions that were made to accommodate the lift capacity of the Hobby- Eberly Telescope dome crane. Laboratory testing results will be presented verifying that the performance goals for the hexapod, including positioning, actuator travel, and speeds have all been achieved. This paper may be of interest to mechanical and electrical engineers responsible for the design and operations of precision hardware on large, ground based telescopes. In summary, the hexapod development cycle from the initial hexapod actuator performance requirements and design, to the deployment and testing on the newly designed HET tracker system is all discussed, including lessons learned through the process.

Prototype pipeline for LSST wavefront sensing and reconstruction

Charles F. Claver, Srinivasan Chandrasekharan, Ming Liang, et al.

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The Large Synoptic Survey Telescope (LSST) uses an Active Optics System (AOS) to maintain system alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from 4 curvature based wavefront sensors located on the corners of the inscribed square within the 3.5 degree field of view. Each wavefront sensor is a split detector such that the halves are 1mm on either side of focus. In this paper we describe the development of the Active Optics Pipeline prototype that simulates processing the raw image data from the wavefront sensors through to wavefront estimation on to the active optics corrective actions. We also describe various wavefront estimation algorithms under development for the LSST active optics system. The algorithms proposed are comprised of the Zernike compensation routine which improve the accuracy of the wavefront estimate. Algorithm development has been aided by a bench top optical simulator which we also describe. The current software prototype combines MATLAB modules for image processing, tomographic reconstruction, atmospheric turbulence and Zemax for optical ray-tracing to simulate the closed loop behavior of the LSST AOS. We describe the overall simulation model and results for image processing using simulated images and initial results of the wavefront estimation algorithms.

Active optics in Large Synoptic Survey Telescope

Ming Liang, Victor Krabbendam, Charles F. Claver, et al.

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The Large Synoptic Survey Telescope (LSST) has a 3.5º field of view and F/1.2 focus that makes the performance quite sensitive to the perturbations of misalignments and mirror surface deformations. In order to maintain the image quality, LSST has an active optics system (AOS) to measure and correct those perturbations in a closed loop. The perturbed wavefront errors are measured by the wavefront sensors (WFS) located at the four corners of the focal plane. The perturbations are solved by the non-linear least square algorithm by minimizing the rms variation of the measured and baseline designed wavefront errors. Then the correction is realized by applying the inverse of the perturbations to the optical system. In this paper, we will describe the correction processing in the LSST AOS. We also will discuss the application of the algorithm, the properties of the sensitivity matrix and the stabilities of the correction. A simulation model, using ZEMAX as a ray tracing engine and MATLAB as an analysis platform, is set up to simulate the testing and correction loop of the LSST AOS. Several simulation examples and results are presented.

Keck 1 deployable tertiary mirror (K1DM3)

J. Xavier Prochaska, Christoph Pistor, Gerald Cabak, et al.

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We aim to build a new tertiary mirror (M3) and its mount for the 10 m Keck I (K1) telescope at the W. M. Keck Observatory (WMKO) to make its full observational capabilities available for time-sensitive scientific programs.. In contrast to the existing tertiary mirror and mount, the device will rapidly deploy and rotate the mirror to any instrument at a Nasmyth focus or, as desired, stow the mirror out of the light path to permit observations at the Cassegrain focus. In this manner, the K1 deployable tertiary mirror (K1DM3) will enable observations with any of the K1 instruments on any given night, and at any given time. The K1DM3 device will be integrated within the K1 telescope control system and WMKO has committed to a new operations model that takes full advantage of this new capability.

Metrology systems of Hobby-Eberly Telescope wide field upgrade

Hanshin Lee, Gary J. Hill, Mark E. Cornell, et al.

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The Hobby-Eberly Telescope (HET) Wide-Field Upgrade (WFU) will be equipped with new closed-loop metrology systems to actively control the optical alignment of the new four-mirror Wide-Field Corrector (WFC) as it tracks sidereal motion with respect to the fixed primary mirror. These systems include a tip/tilt camera (TTCam), distance measuring interferometers (DMI), guide probes (GP), and wavefront sensors (WFS). While the TTCam and DMIs are to monitor the mechanical alignment of the WFC, the WFSs and GPs will produce direct measurement of the optical alignment of the WFC with respect to the HET primary mirror. Together, these systems provide fully redundant alignment and pointing information for the telescope, thereby keeping the WFC in focus and suppressing alignment driven field aberrations. In addition to these closed-loop metrology systems, we will have a pupil viewing camera (PVCam) and a calibration wavefront sensor (CWFS). The PVCam will be used for occasional reflectance measurement of the HET primary mirror segments in the standard R,G,B colors. The CWFS will provide the reference wavefront signal against which the other two WFS are calibrated. We describe the current snapshot of these systems and discuss lab/on-sky performance test results of the systems.

Optics derotator servo control system for SONG Telescope

Jin Xu, Changzhi Ren, Yu Ye

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The Stellar Oscillations Network Group (SONG) is an initiative which aims at designing and building a groundbased network of 1m telescopes dedicated to the study of phenomena occurring in the time domain. Chinese standard node of SONG is an Alt-Az Telescope of F/37 with 1m diameter. Optics derotator control system of SONG telescope adopts the development model of "Industrial Computer + UMAC Motion Controller + Servo Motor".¹ Industrial computer is the core processing part of the motion control, motion control card(UMAC) is in charge of the details on the motion control, Servo amplifier accepts the control commands from UMAC, and drives the servo motor. The position feedback information comes from the encoder, to form a closed loop control system. This paper describes in detail hardware design and software design for the optics derotator servo control system. In terms of hardware design, the principle, structure, and control algorithm of servo system based on optics derotator are analyzed and explored. In terms of software design, the paper proposes the architecture of the system software based on Object-Oriented Programming.

Active optical control system design of the SONG-China Telescope

Yu Ye, Songfeng Kou, Dongsheng Niu, et al.

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The standard SONG node structure of control system is presented. The active optical control system of the project is a distributed system, and a host computer and a slave intelligent controller are included. The host control computer collects the information from wave front sensor and sends commands to the slave computer to realize a closed loop model. For intelligent controller, a programmable logic controller (PLC) system is used. This system combines with industrial personal computer (IPC) and PLC to make up a control system with powerful and reliable.

The 3,6m Indo-Belgian Devasthal Optical: the active M1 mirror support

Maxime Pierard, Carlo Flebus, Nathalie Ninane

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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 Indo-Belgian Devasthal Optical Telescope (IDOT). The primary mirror is a meniscus active mirror. This paper describes the opto-mechanical design of the M1 unit and provides some test results performed on sky to demonstrate the proper functioning of the active system.

Synchronous redundant control algorithm in the telescope drive system

Changzhi Ren, Yong Niu, Xiaoli Song, et al.

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The modern large telescope is endowed with advanced imaging systems and active optics, resulting in very high peak angular resolution. The drive systems for the telescope must consequently be able to guarantee a tracking accuracy better than the telescope angular resolution, in spite of unbalanced and sudden loads such as wind gusts and in spite of a structure that, because of its size, can not be infinitely stiff, which puts forward a great challenge to the telescope' drive system. Modern telescope's drive system is complicated, which performance and reliability directly affect the telescope tracking performance and reliability. Redundant technology is one of the effective ways to improve the security of the system. This paper will introduce one redundant synchronous control method for direct drive torque motor of large diameter telescope drive system, which can effectively improve the telescope drive system tracking precision and improve the reliability, stability and anti-jamming ability.

The M2&M3 positioning control systems of a 2.5m telescope

Yu Ye, Chong Pei, Zhiyong Zhang, et al.

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The 2.5m optical/infrared telescope is an F/8 telescope comprising one Cassegrain foci, two Nasmyth foci and two student Nasmyth foci. This paper presents a brief description of the physical structure, conceptual design, hardware implementing measure and software structure in the positioning control system of M₂&M₃. The graphical user interface application (Qt) is adopted to design the software. During the full working range the M₂ focus and decenter achieve the positioning repeatability is better than ±4μm and the M₂ tilt is better than 10 μrad. The M₃ angular positioning and locking accuracy is better than 10 arcsec and repeatability is better than 2 arcsec RMS.

Progress of the active reflector antenna using laser angle metrology system

Yong Zhang, Jie Zhang, Dehua Yang, et al.

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An active reflector is one of the key technologies for constructing large telescopes, especially for the millimeter/sub-millimeter radio telescopes. This report presents a new and substantial progress on the efficient laser angle metrology system for the active reflector antenna of the large radio telescopes, with a plenty of experiments based on a four-panel prototype system constructed by Nanjing Institute of Astronomical Optics and Technology (NIAOT). The test results prove that this technology is workable for sub-millimeter radio telescopes both in accuracy and time-response. Thus it can be applied to the reconstruction of the active reflector antenna in China and play a central role in promoting the new area of sub-mm radio astronomy.

The active optics system of the VST: concepts and results

Pietro Schipani, Demetrio Magrin, Lothar Noethe, et al.

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The active optics system of the VLT Survey Telescope (VST) adopts a positioning system for the secondary mirror, a system to support and modify the shape of the 2.6-m primary mirror, and a Shack-Hartmann wavefront sensor. This paper describes the concepts of the VST active optics and the commissioning of the whole system on the ESO's Paranal Observatory.

Performance comparison between two active support schemes for 1-m primary mirror

Dongsheng Niu, Guomin Wang, Bozhong Gu

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Active support scheme may decide the deformation of the optical surface figure of the primary mirror. Two active support schemes have been designed for 1-m primary mirror, and the performance of each support scheme is conducted. Finite element analysis (FEA) is employed to analyze the optical surface figures of the primary mirror, and optimizations are carried out by using ANSYS for each support scheme to obtain the locations of the axial support. When the locations are determined, axial support force sensitivities are calculated for the two support schemes in a case that a single axial support has a force error of 0.5N. The correction ability of the active support system for both of support schemes are analyzed when an arbitrary axial support is failure. Several low order Zernike modes are modeled with MATLAB procedure, and active optics corrections are applied to these modes for the two active supports. Thermal deformation of the mirror is also corrected for the two schemes.

Design, development, and testing of the DCT Cassegrain instrument support assembly

Thomas A. Bida, Edward W. Dunham, Ralph A. Nye, et al.

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The 4.3m Discovery Channel Telescope delivers an f/6.1 unvignetted 0.5° field to its RC focal plane. In order to support guiding, wavefront sensing, and instrument installations, a Cassegrain instrument support assembly has been developed which includes a facility guider and wavefront sensor package (GWAVES) and multiple interfaces for instrumentation. A 2-element, all-spherical, fused-silica corrector compensates for field curvature and astigmatism over the 0.5° FOV, while reducing ghost pupil reflections to minimal levels. Dual roving GWAVES camera probes pick off stars in the outer annulus of the corrected field, providing simultaneous guiding and wavefront sensing for telescope operations. The instrument cube supports 5 co-mounted instruments with rapid feed selection via deployable fold mirrors. The corrected beam passes through a dual filter wheel before imaging with the 6K x 6K single CCD of the Large Monolithic Imager (LMI). We describe key development strategies for the DCT Cassegrain instrument assembly and GWAVES, including construction of a prime focus test assembly with wavefront sensor utilized in fall 2011 to begin characterization of the DCT primary mirror support. We also report on 2012 on-sky test results of wavefront sensing, guiding, and imaging with the integrated Cassegrain cube.

Experience of primary surface alignment for the LMT using a laser tracker in a non-metrology environment

David M. Gale

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The 50-metre Large Millimeter Telescope (LMT) successfully completed first light observations in June 2011, operating with an initial 32.5-metre diameter collecting area. This reduced-area primary surface consists of 84 reflector panels measuring approximately 3x5m. During the construction phase, individual panels were assembled and adjusted to the specified rms surface error off-site, then installed and aligned on the antenna using a total station. Prior to first-light observations, panels were fine-tuned in piston, tip-tilt and twist using full-surface holography measurements to direct the movement of electromechanical actuators located at the four corners of each panel. In preparation for the next observing season the 32.5m primary is being refurbished and re-aligned on-site, using a commercial laser tracker for surface adjustment of each panel. For this task we have opted for the transfer of panels from the antenna surface to the telescope basement for adjustment, offering an enclosed environment with stable temperature, followed by reinstallation and measurement on the open-air antenna surface at night. In this paper we present our experiences on the use of a laser tracker to conduct panel surface measurement and adjustment on-site, at an isolated location 4,700m (15,000ft) above sea level and in the absence of dedicated metrology facilities. In section 2 we present the primary surface concept deployed at the LMT. Section 3 discusses the laser tracker equipment and data processing for panel surface measurement. Section 4 describes the panel adjustment process carried out in the site basement and presents examples of indoor panel metrology using the laser tracker. In section 5, we present our experiences to date of open-air measurement of panels installed on the antenna. Some conclusions are offered in section 6.

Using a laser tracker for active alignment on the Large Binocular Telescope

A. Rakich

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The Large Binocular Telescope (LBT) currently achieves collimation using a combination of collimation models and closed-loop active correction schemes. Shack Hartmann wavefront sensors with off-axis guide stars are used for Gregorian modes, and a closed-loop correction scheme is used for the prime-focus cameras. While in general this combination serves to produce alignment residuals well below a good seeing limit within a few minutes of obtaining a given target field, the uniquely asymmetrical structure of the LBT is prone to producing large deflections of the telescope optics when the ambient temperature is changing unusually rapidly. These deflections are difficult to model satisfactorily, and are an ongoing source of inefficiency in telescope operations. Furthermore, none of the current approaches to telescope collimation are particularly "piston aware"; a situation that needs to be improved on now that the LBT is commencing operations with the first of its beam combining instruments, LBTI. The laser tracker is a metrology instrument capable of automatically measuring optical element positions with better than 100 micron precision within a spherical volume of 30 m radius centered on the tracker head. With the ability to directly measure optics into position to this accuracy built into the Telescope Control System (TCS), the LBT would always be starting observations from a point of near-collimation, the component telescopes would be co-pointed, and the OPD would be well within the capture range of the beam combining instrument's internal phasing systems. This paper describes first results from engineering investigations into using the laser tracker to automatically align the optics on the LBT.

Generic misalignment aberration patterns and the subspace of benign misalignment

Paul L. Schechter, Rebecca Sobel Levinson

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Q1: Why deploy N wavefront sensors on a three mirror anastigmat (TMA) and not N + 1? Q2: Why measure M Zernike coefficients and not M + 1? Q3: Why control L rigid body degrees of freedom (total) on the secondary and tertiary and not L + 1? The usual answer: “We did a lot of ray tracing and N, M, and L seemed OK.” We show how straightforward results from aberration theory may be used to address these questions. We consider, in particular, the case of a three mirror anastigmat.

The VST alignment: strategy and results

Pietro Schipani, Lothar Noethe, Konrad Kuijken, et al.

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In a wide-field telescope like the VST, the requirements for alignment are tighter than for traditional instruments. The same amount of misalignment can be negligible in traditional telescopes with fields of some arc minutes, but unacceptable when the field is one order of magnitude larger. We describe the alignment procedure implemented during the telescope commissioning on the Paranal ESO's observatory, as well as the final results.

Test system for a Shack-Hartmann sensor based telescope alignment demonstrated at the 40cm Wendelstein Telescope

Stephanie Bogner, M. Becker, Frank Grupp, et al.

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A commercial Shack-Hartman wavefront sensor is being used in a test setup installed at the Wendelstein 40 cm telescope to test methods for telescope alignment based on reverse optimization. Measured low-order Zernike wave-fronts are being used to determine the misalignment of the telescopes optical elements. Then a procedure to optimize wave-front performance by aligning the telescope secondary mirror is applied. The setup contains a collimating optical system, the Shack-Hartman sensor and a guiding and acquisition camera.

An improved collimation algorithm for the Large Binocular Telescope using source extractor and an on-the-fly reconstructor

Douglas L. Miller, Andrew Rakich, Torsten Leibold

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A recent upgrade of the LBTO’s Wavefront Reconstruction algorithm in the Active Optics system has proven to reduce the collimation time by a substantial amount and to provide a much more stable telescope collimation as observing conditions change. The new reconstruction algorithm uses Source Extractor to detect the spots in a Shack-Hartmann wavefront sensor camera image. With information about which Shack spots are detected, a reconstructor matrix is calculated on-the-fly that only includes the illuminated sub-apertures. This drastically improves the wavefront reconstruction for a highly aberrated wavefront when many sub-apertures contain no information. This is generally the situation at the beginning of the night when the collimation of the telescope is set only from models rather than on-sky information and occasionally when a new observational target is acquired. Similarly, the undersized tertiary mirror can cause vignetting of the pupil seen by the Shack-Hartmann wavefront sensor for far off-axis guide stars and again some sub-apertures have no wavefront information. We will present a brief description of the Active Optics system used at the Gregorian focal stations at the LBTO, discuss the original wavefront reconstruction algorithm, describe the new Source Extractor algorithm and compare the performance of these two approaches in several conditions (low signal to noise, highly aberrated wavefront, vignetted pupil, poor seeing).

Features of a laser metrology subsystem for astrometric telescopes

Alberto Riva, Mario Gai, Mario G. Lattanzi

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In astrometric instrumentation a laser subsystem may be used for precise metrology of instrumental response. Such subsystems do not require diraction limited imaging, but can be tailored to specic application needs. We describe an interferometric arrangement for high precision monitoring of telescope line of sight and evaluate its performance as a function of some design parameters. We deduce that good sensitivity can be achieved over a signicant range of e.g. focusing conditions, provided proper cautions are adopted for detection and data processing.

Conceptual design of a 5-m terahertz telescope at Dome A

Dehua Yang, Hai Wang, Yong Zhang, et al.

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A 5-meter terahertz telescope is proposed by the Chinese Center for Antarctic Astronomy (CCAA) for the East Antarctica site of the Dome A plateau. The Dome A 5-m terahertz telescope (DATE 5) will be operated at sub-millimeter waveband taking the unique advantage of the transparent atmospheric windows between 200 and 350 μm wavelengths at Dome A. A preliminary design has been conducted according to the given technical requirements and the special environmental conditions at Dome A. A symmetric R-C Cassegrain optical system is designed for the telescope, with a primary f-ratio of 0.4 and a wide field of view of 10 arcmin. The magnification of the sub-reflector is 9.4, leading to the final focal ratio of 3.76 and the focus 0.2 m below the vertex of the primary reflector. To ensure surface accuracy of the reflectors precise as small as 10 um RMS, we consider using Carbon Fiber Reinforced Plastics (CFRP) to build the backup structure (BUS) of the primary reflector and the sub-reflector itself. An alt-azimuthal mounting is adopted and a tall base structure beneath the telescope is set up to lift the telescope above the low atmosphere turbulent layer. All the mechanics, as well as control electronics, are strictly designed to fit the lower temperature operation in the Dome A environment. This paper is to generally present the mentioned systematic optical, structural and electronic design of the DATE 5 telescope.

New Exoplanet Surveys in the Canadian High Arctic at 80 Degrees North

Nicholas M. Law, Suresh Sivanandam, Richard Murowinski, et al.

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Observations from near the Eureka station on Ellesmere Island, in the Canadian High Arctic at 80° North, benefit from 24-hour darkness combined with dark skies and long cloud-free periods during the winter. Our first astronomical surveys conducted at the site are aimed at transiting exoplanets; compared to mid-latitude sites, the continuous darkness during the Arctic winter greatly improves the survey’s detection effciency for longer-period transiting planets. We detail the design, construction, and testing of the first two instruments: a robotic telescope, and a set of very wide-field imaging cameras. The 0.5m Dunlap Institute Arctic Telescope has a 0.8-square-degree field of view and is designed to search for potentially habitable exoplanets around low-mass stars. The very wide field cameras have several-hundred-square-degree fields of view pointed at Polaris, are designed to search for transiting planets around bright stars, and were tested at the site in February 2012. Finally, we present a conceptual design for the Compound Arctic Telescope Survey (CATS), a multiplexed transient and transit search system which can produce a 10,000-square-degree snapshot image every few minutes throughout the Arctic winter.

An off-axis telescope concept for Antarctic astronomy

Gil Moretto, Nicolas Epchtein, Maud Langlois, et al.

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The Antarctic plateau offers exceptional atmospheric and environmental conditions for astronomical observations over a wide range of wavelengths and uniquely favorable to infrared astronomy. Exceptional low sky brightness throughout the near- and mid-infrared and a telescope facility complying with the highest possible dynamic range for photometry, angular resolution and the widefield leads to the possibility of a modest-sized 2m off-axis telescope achieving comparable sensitivity to that of a larger ground-based 8-10m class telescope or a same sized space-based ones.

The package cushioning design of the first AST3 and its dynamics analysis

Haikun Wen, Xuefei Gong, Ru Zhang

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Dome A has been considered as one of the best observation sites on the earth. The First AST3(three Antarctic Survey Telescopes) is on its way to Dome A by the 28th Chinese National Antarctic research expedition. It will be the largest Optic telescope in Dome A after assembling and testing in this austral summer. Firstly, this paper reports the method of collecting the vibration and shock data from ShangHai to Dome A and analyses the data. Secondly, the package cushioning design of the first AST3 is introduced in this paper according to the vibration and shock data. Finally, the paper introduces the result of the dynamics analysis of the design and a test was done to verify the performance of the package cushioning design. The dynamics analysis and the test indicate that the package cushioning design can meet the demand of the Antarctic inland transportation.

Nonlinear disturbance to Large Optical Antarctic Telescope

Shihai Yang

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Large Optical Antarctic Telescope, LOAT hereafter, is a new research hotspot nowadays. For example, a 2.5m KDUST, e.g. Kunlun Dark UniverSe Telescope is on anvil. It's difficult for main axis of large telescope tracking system to track the target precisely with ultra-low speed because of nonlinear disturbances due to unique ultra-low temperature. This paper presents these nonlinear disturbances.

Where is Ridge A?

Geoff Sims, Craig Kulesa, Michael C. B. Ashley, et al.

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First identied in 2009 as the site with the lowest precipitable water and best terahertz transmission on Earth, Ridge A is located approximately 150 km south of Dome A, Antarctica. To further rene this optimum location prior to deployment in 2012 of a robotic THz observatory, we have modelled the atmospheric transmission as a function of location over a 1,000,000 km square grid using three years of data from the Microwave Humidity Sounder on the NOAA-18 satellite. The modelling identies a broad area of exceptionally low water vapour close to the 4,000 metre elevation contour, reaching below 100 microns for extended periods of time.

Two years of polar winter observations with the ASTEP400 telescope

L. Abe, J.-P. Rivet, A. Agabi, et al.

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The ASTEP program is dedicated to exo-planet transit search from the Concordia Station located at Dome C, Antarctica. It comprises two instruments: a fixed 10cm refractor pointed toward the celestial South Pole, and a 400mm Newton telescope with a 1x1 degree field of view. This work focuses on the latter instrument. It has been installed in November 2009, and has been observing since then during the two polar winters 2010 and 2011. After presenting the main science observing programs, we review the telescope installation, performance, and describe its operating conditions as well as the data reduction and handling strategy. The resulting lightcurves are generally very stable and of excellent quality, as shown by continuous observations of WASP-19 that we present here.

HETDEX tracker control system design and implementation

Joseph H. Beno, Richard Hayes, Ron Leck, et al.

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To enable the Hobby-Eberly Telescope Dark Energy Experiment, The University of Texas at Austin Center for Electromechanics and McDonald Observatory developed a precision tracker and control system – an 18,000 kg robot to position a 3,100 kg payload within 10 microns of a desired dynamic track. Performance requirements to meet science needs and safety requirements that emerged from detailed Failure Modes and Effects Analysis resulted in a system of 13 precision controlled actuators and 100 additional analog and digital devices (primarily sensors and safety limit switches). Due to this complexity, demanding accuracy requirements, and stringent safety requirements, two independent control systems were developed. First, a versatile and easily configurable centralized control system that links with modeling and simulation tools during the hardware and software design process was deemed essential for normal operation including motion control. A second, parallel, control system, the Hardware Fault Controller (HFC) provides independent monitoring and fault control through a dedicated microcontroller to force a safe, controlled shutdown of the entire system in the event a fault is detected. Motion controls were developed in a Matlab-Simulink simulation environment, and coupled with dSPACE controller hardware. The dSPACE real-time operating system collects sensor information; motor commands are transmitted over a PROFIBUS network to servo amplifiers and drive motor status is received over the same network. To interface the dSPACE controller directly to absolute Heidenhain sensors with EnDat 2.2 protocol, a custom communication board was developed. This paper covers details of operational control software, the HFC, algorithms, tuning, debugging, testing, and lessons learned.

An upgrade to the telescope control system (TCS) for the Canada-France-Hawaii Telescope

K. K. Y. Ho, W. Cruise, J. Thomas

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The Canada-France-Hawaii Telescope (CFHT) has been in operation since 1979. The Telescope Control System (TCS) has undergone software changes since the beginning of science operation but the original hardware has largely been untouched except for an upgrade to the time system and host computer. Telescope performance has not been an issue although some improvements are desirable. However, parts obsolescence will become a problem as the telescope enters it third decade of operation. Although there are sufficient spare parts currently, many are no longer readily available. Some critical components, such as encoders and VME CPU boards are no longer available. The TCS upgrade project addresses the obsolete and obsolescent issues to ensure operational capability through 2025. It seeks to modernize and simplify the electronics and to take advantages of the advancement made in stand-alone servo controllers.

Automation of the OAN/SPM 1.5-meter Johnson telescope for operations with RATIR

Alan M. Watson, Michael G. Richer, Joshua S. Bloom, et al.

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The Reionization And Transients Infra-Red (RATIR) camera is intended for robotic operation on the 1.5-meter Harold Johnson telescope of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. This paper describes the work we have carried out to successfully automate the telescope and prepare it for RATIR. One novelty is our use of real-time absolute astrometry from the finder telescopes to point and guide the main telescope.

Control system for the first three Antarctic Survey Telescopes (AST3-1)

Xiaoyan Li, Daxing Wang, Lingzhe Xu, et al.

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The first Three Antarctic Survey Telescope (AST3-1), a 50/68cm Schmidt-like equatorial-mount telescope, is the first automated Chinese telescope operating on the Antarctic plateau. It is planned to be in operations at Dome A, the highest peak on the Antarctic plateau, in 2012. The telescope is unmanned during night-time operations in the Austral winter. The telescope optics and mechanics, as well as the motors and position sensors, are exposed to a very harsh environment. The mechanics is enclosed with a foldable tent-like dome to prevent snow, diamond dust and ice. While the drive boxes, most circuit, power supply and computers are located inside the warm instrumental cabin. This article describes the challenges the telescope control system encountered in night-time operations, such as the power supply limit, the harsh meteorological condition, unattended testing, automatic operation, remote control and telemetry, etc. Some solutions are also discussed in this paper, which are applied on the AST3-1 and waiting for validation. AST3-1 is also an exploration of a larger telescope on the Antarctic.

Development of an EtherCAT enabled digital servo controller for the Green Bank Telescope

Peter G. Whiteis, Melinda J. Mello

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EtherCAT (Ethernet for Control Automation Technology) is gaining wide spread popularity in the automation industry as a real time field bus based on low cost, Ethernet hardware. EtherCAT maximizes use of 100Mbps Ethernet hardware by using a collision free ring topology, efficient Ethernet frame utilization (> 95%), and data exchange "on the fly". These characteristics enable EtherCAT to achieve Master to Slave node data exchange rates of > 1000 Hz. The Green Bank Telescope, commissioned in 2000, utilizes an analog control system for motion control of 8 elevation and 16 azimuth motors. This architecture, while sufficient for observations at frequencies up to 50GHz, has significant limitations for the current scientific goals of observing at 115GHz. Accordingly, the Green Bank staff has embarked on a servo upgrade project to develop a digital servo system which accommodates development and implementation of advanced control algorithms. This paper describes how the new control system requirements, use of existing infrastructure and budget constraints led us to define a distributed motion control architecture where EtherCAT real-time Ethernet was selected as the communication bus. Finally, design details are provided that describe how NRAO developed a custom EtherCAT-enabled motor controller interface for the GBT's legacy motor drives in order to provide technical benefits and flexibility not available in commercial products.

Design and development of telescope control system and software for the 50/80 cm Schmidt telescope

T. S. Kumar, R. N. Banavar

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In this paper, we describe the details of telescope controller design for the 50/80 cm Schmidt telescope at the Aryabhatta Research Institute of observational sciencES. The GUI based software for commanding the telescope is developed in Visual C++. The hardware architecture features a distributed network of microcontrollers over CAN. The basic functionality can also be implemented using the dedicated RS232 port per board. The controller is able to perform with negligible rms velocity errors. At fine speeds limit cycles are exhibited due to nonlinear friction. At speeds over 3.90 × 10^-02 radians/sec, the PI controller performs with peak errors less than 1%.

Upgrading the MMT primary mirror actuator test stand: a unique vehicle for evaluating EtherCAT as a future I/O standard for systems

Dusty Clark, Skip Schaller

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The MMT Observatory (MMTO) uses a complex system of pneumatic actuators to support the telescope's 6.5m primary mirror. For operational checkout after repair and to collect calibration data for use in the primary mirror support control software, the Steward Observatory Mirror Lab (SOML) built a test stand that accurately measures the output forces and moments from the actuator using a 6-DOF (degree of freedom) work plate. The electronics and software provided by SOML are outdated and needed replacing. In this report, we discuss the selection of EtherCAT as the data-acquisition hardware, the software development required, and the some aspects of using the test stand in the lab.

MMT nightly tracking logs: a web-enabled database for continuous evaluation of tracking performance

D. Clark, J. D. Gibson, D. Porter, et al.

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Over the past few years, the MMT Observatory has developed a number of web browser front ends for operation interfaces and staff access to internal databases. Among these is a facility for viewed reduced tracking logs in both time series and FFTs for convenient examination of tracking performance. Part of the back-end software also keeps the tracking data in a searchable database, allowing data over long periods of time to be collected and analyzed to look for trends, the influence of environmental factors on tracking, and help detect tracking degradation in a timely manner.

Pointing and tracking results of the VST telescope

Pietro Schipani, Carmelo Arcidiacono, Javier Argomedo, et al.

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The VLT Survey Telescope (VST) is the latest telescope installed at ESO’s Paranal Observatory in northern Chile. The exceptional quality of this site imposes tight requirements on the telescope performance in terms of pointing modeling and tracking. This paper describes the control strategy and the results obtained during the commissioning of the telescope.

Design and fabrication of three 1.6-meter telescopes for the Korea Microlensing Telescope Network (KMTNet)

W. M. Poteet, H. K. Cauthen, N. Kappler, et al.

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The KMTNet telescope Project, sponsored by The Korea Astronomy and Space Science Institute (KASI), is fabricating three wide-field equatorial mount telescopes of 1.6 meter aperture to conduct continuous observations of the Galactic bulge region to search for extra-solar planets. Southern latitude sites secured for these telescopes are SAAO (South Africa), CTIO (Chile), and SSO (Australia). A prime-focus configuration, along with a four-lens corrector achieves the 2.8 degree diagonal FOV. The basic mechanical design utilizes a scaled-up version of the successful 2MASS Telescopes built by the authors in the late 1990's. Scaling up of components has presented challenges requiring several iterations of the detailed mechanical analysis as well as the optical analysis due to interaction with mounting assemblies for the optical components. A flexure-style focus mechanism, driven by three precision actuators, moves the entire headring assembly and provides real-time focus capability, and active primary mirror cooling is implemented for the Zerodur primary. KMTNet engineering specifications are met with the current design, which uses Comsoft's Legacy PCTCS for control. A complete operational telescope and enclosure are scheduled for installation in Tucson, AZ prior to shipping the first hardware to CTIO in order to verify tracking, optical characteristics at various attitudes, and overall observatory functionality. The cameras, being fabricated by The Ohio State University Department of Astronomy, Imaging Sciences Laboratory (ISL), are proceeding in parallel with the telescope fabrication, and that interface is now fixed. Specifics of the mechanical and optical design are presented, along with the current fabrication progress and testing protocols.

Introduction of Chinese SONG Telescope

Guomin Wang, Songfeng Kou, Dongsheng Niu, et al.

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SONG is initiated by Danish to design, build, and utilize a global network of eight 1-meter class telescopes to be operated as a whole-Earth telescope. China has joined the international SONG project in 2009 and will build one 1-meter telescope as the node of SONG global network in China. Now the telescope is during the period of building. This paper will give an introduction of Chinese SONG telescope, including telescope requirements, telescope design and other information.

Perspectives of astronomy in Kazakhstan: from new ground-based telescopes to space ones

Ch. T. Omarov, Zh. Sh. Zhantayev

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Astronomical observations in Kazakhstan are carried out for over 60 years. The advantage of the geographical location makes it possible to set and conduct programs of stationary ground-based observations, that from the most observatories of other countries are difficult or impossible. However outdated technical condition of scientific equipment, which include ground-based optical telescopes, poses a direct problem to the development of astronomy in Kazakhstan. In addition, observational data in the other spectral bands from space telescopes are needed. Therefore, in order to create a modern experimental astrophysical base today in Kazakhstan two projects are being put forward in the frame of national space program: 1) a new optical telescope with a primary mirror 3.6 meters (completed in 2016), and 2) participation in the international space project "World Space Observatory -Ultraviolet" that to be launched in 2014.

Deployment status of the Las Cumbres Observatory Global Telescope

A. J. Pickles, W. Rosing, J. Martinez, et al.

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Our global network of telescopes is designed to provide maximally available optical monitoring of time variable sources, from solar system to extra-galactic objects, and ranging in brightness from about 7-20m. We are providing a distributed network with varied apertures but homogeneous instrumentation: optical imaging, with spectroscopic capabilities. A key component is a single centralized process that accepts (in real time) and schedules TAC approved observing requests across the network; then continuously updates schedules based on status, weather and other availability criteria. Requests range from occasional to continuous monitoring, at slow to high-speed cadences (imaging and fast photometry), and includes rapid response to targets of opportunity. Each node of the network must be fully autonomous, with software agents to control and monitor all functions, to provide auto-recovery as necessary, and to announce their status and capabilities up the control structure. Real-time monitoring or interaction by humans should be infrequent. Equipment is designed to be reliable over long periods to minimize hands-on maintenance, by local or LCOGT staff. Our first 1m deployment was to McDonald Obs. in April 2012. Eight more 1m telescopes are close to deployment to complete the Southern ring, scheduled by end-2012.

The microwave holography system for the Sardinia Radio Telescope

G. Serra, P. Bolli, G. Busonera, et al.

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Microwave holography is a well-established technique for mapping surface errors of large reflector antennas, particularly those designed to operate at high frequencies. We present here a holography system based on the interferometric method for mapping the primary reflector surface of the Sardinia Radio Telescope (SRT). SRT is a new 64-m-diameter antenna located in Sardinia, Italy, equipped with an active surface and designed to operate up to 115 GHz. The system consists mainly of two radio frequency low-noise coherent channels, designed to receive Ku-band digital TV signals from geostationary satellites. Two commercial prime focus low-noise block converters are installed on the radio telescope under test and on a small reference antenna, respectively. Then the signals are amplified, filtered and downconverted to baseband. An innovative digital back-end based on FPGA technology has been implemented to digitize two 5 MHz-band signals and calculate their cross-correlation in real-time. This is carried out by using a 16-bit resolution ADCs and a FPGA reaching very large amplitude dynamic range and reducing post-processing time. The final holography data analysis is performed by CLIC data reduction software developed within the Institut de Radioastronomie Millimétrique (IRAM, Grenoble, France). The system was successfully tested during several holography measurement campaigns, recently performed at the Medicina 32-m radio telescope. Two 65-by-65 maps, using an on-the-fly raster scan with on-source phase calibration, were performed pointing the radio telescope at 38 degrees elevation towards EUTELSAT 7A satellite. The high SNR (greater than 60 dB) and the good phase stability led to get an accuracy on the surface error maps better than 150 μm RMS.

Structural optimization of the outer ring of FAST Telescope

Xin-yu Zhang, Hui Li, Shi-mo Yang

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The two-axis steering mechanism installed in the FAST focus cabin can be seen as a universal joint consisting of two ring beams and makes role in the process of real-time adjustment of the receiver orientation. The outer ring of the mechanism is a large-span curve beam with strict mass and rigidity requirements. The aim of this paper is to develop a simple and effective method for constructing a truss-shape structure for the outer ring under the upper-limit constraints of certain structural weight and mid-span deflection. Two truss configurations for weight minimization problems are presented. One assumes consistent beam height. The second design proposes varying heights along the ring. Analytical deflections are given based on the theory of thin-walled beam in combination of bending and torsion. In numerical optimization of the structure, some key geometrical parameters are selected to be optimized. The optimization is subsequently achieved by the steepest descent method, which is based on the sensitivity analysis of the variables (reduced to be dimensionless) in each iteration. Several sets of initial conditions for optimization have been generated randomly. Corresponding optimum results have small mutual deviations. Finally a comparison of the two designs considering stiffness-to-mass ratios is given in the numerical examples.

Experimental study on the damping of FAST cabin suspension system

Hui Li, Jing-hai Sun, Xin-yu Zhang, et al.

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The focus cabin suspension of the FAST telescope has structurally weak-stiffness dynamics with low damping performance, which makes it quite sensitive to wind-induced vibrations. A reasonable estimation about the damping is very important for the control performance evaluation of the prototype. It is a quite difficult task as the telescope is no at available yet. In the paper, a preliminary analysis is first made on the aerodynamic damping. Then a series of experimental models are tested for measuring the total damping. The scales of these models range from 10m to 50m in diameter while 6 test parameters are specially designed to check the damping sensitivity. The Ibrahim time domain (ITD) method is employed to identify the damping from the measured cabin response. The identification results indicate that the lowest damping ratio of the models is about 0.2%~0.4%. Friction-type cabin-cable joint seems to have main influence on the system damping.

Control algorithm for the petal-shape segmented-mirror telescope with 18 mirrors

Atsushi Shimono, Fumihide Iwamuro, Mikio Kurita, et al.

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A 3.8 m segmented telescope is planned to be built at the Okayama Astrophysical Observatory by the joint program among Kyoto university, Nagoya university, NAOJ, and Nano-Optonics Energy Inc. This is the world’s first optical-infrared telescope whose primary mirror is composed of “petal-shaped” segment mirrors. To investigate the best layout of the displacement sensors as well as to study the control algorithm, we have developed a simulation software for the segmented petaloid mirrors. This simulator calculates the vertical position differences between the segments at the 60 displacement sensors based on the three-dimensional movements of the 54 actuators, and enables us to test the control algorithms under various conditions including random noise on the displacement sensors, random movement errors of the actuators, and unexpected lateral shifts of the segments. The outputs of the simulator are not only the phase error of the primary mirror but also the PSF image, taking the structure function of the optical surfaces into account. Using a singular value decomposition method, we found that the 18 petal-shaped segments are controllable within the required displacement errors of 15 nm under the following three conditions: 1) the displacement measurement sensors are placed in staggered fashion between segments, 2) the displacement measurement sensors are axisymmetrically placed with respect to the optical axis, and 3) the relative lateral shift and rotation of each segment are less than 500 μm and 0.05 degree, respectively. In this report, the control algorithm, requirements for the layout of the displacement measurement sensors, and the simulated performance will be presented.

How to calibrate edge sensors on segmented mirror telescopes

Chris Shelton, Lewis C. Roberts Jr.

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The next generation of large ground based telescopes use segmented mirrors. Sensors mounted on the edge of the segments measure the relative heights of the segments. The segments are actively controlled in height by three actuators per segment, but lateral motion is only passively constrained. Thus there will be some small change in the gap and shear between segments as changing telescope orientation and temperature make small distortions in the telescope structure. These "in-plane" motions place an additional performance burden on the edge sensors, and on the precision with which they must be mounted relative to the optical surface. In addition, both the scaling and offset of sensor edge height readings also vary with changes in gap. Our method for correcting the in-plane motion induced errors in the primary mirror has three parts. First, the edge sensors are modified to report segment-to-segment gap, as well as the height difference, to make the in-plane segment positions observable. Second, the mirror segments are phased optically, at a set of zenith angles and temperatures, to give a set of "measured sensor readings". Finally, during observing, a calibration procedure combines these data into "desired sensor readings" which are optimal for the current telescope state. We have included this calibration process in a control loop model of the Thirty Meter Telescope primary mirror control system. We present our calibration method and the model.

Outdoors phasing progress of dispersed fringe sensing technology in NIAOT, China

Yong Zhang, Xiangqun Cui, Genrong Liu, et al.

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A telescope with a larger primary mirror can collect much more light and resolve objects much better than one with a smaller mirror, and so the larger version is always pursued by astronomers and astronomical technicians. Instead of using a monolithic primary mirror, more and more large telescopes, which are currently being planned or in construction, have adopted a segmented primary mirror design. Therefore, how to sense and phase such a primary mirror is a key issue for the future of extremely large optical/infrared telescopes. The Dispersed Fringe Sensor is a non-contact method using broadband point light sources and it can estimate the piston by the two-directional spectrum formed by the transmissive grating's dispersion and lenslet array. In this paper we introduce you the current research progress of the successful design, construction and alignment of our dispersed Hartmann sensors together with its design principles and simulations for indoor segmented mirror experiment system and outdoor segmented mirror experiment system. We also conduct many successful real phasing tests and phasing corrections in the visible waveband using our existing indoor and outdoor segmented mirror optics platform. Finally, some conclusions are reached based on the test and correction of experimental results.

The new TNG-DIMM: calibrations and first data analysis

Emilio Molinari, A. G. de Gurtubai, A. della Valle, et al.

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Since 2011 a new differential image motion monitor (DIMM) works at Roque de los Muchachos Observatory close to Telescopio Nazionale Galileo (TNG). The purpose of this instrument is to provide useful information about the optical turbulence for the astronomical observations at TNG. We present the instrument and the first statistical results including a relationship between the principal components analysis of local-ground atmospheric parameters and seeing.

Atmospheric turbulence measurements at Ali Observatory, Tibet

Liyong Liu, Yongqiang Yao, Jean Vernin, et al.

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The atmospheric turbulence characteristics are important to evaluate the quality of ground-based astronomical observatory. In order to characterize Ali observatory, Tibet. we have developed a single star Scidar (SSS) system, which is able to continuously monitor the vertical profiles of both optical turbulence and wind speed. The main SSS configuration includes a 40cm telescope and a CCD camera for fast sampling the star scintillation pattern. The SSS technique analyzes the scintillation patterns in real time, by computing the spatial auto-correlation and at least two cross-correlation images, and retrieves both C² _n (h) and V (h) vertical profiles from the ground up to 30km. This paper presents the first turbulence measurements with SSS at Ali observatory in October, 2011. We have successfully obtained the profiles of optical turbulence and wind speed, as well as the key parameters for adaptive optics, such as seeing, coherence time, and isoplanatic angle. The favourable results indicate that Ali observatory can be an excellent astronomical observatory.

Dust concentration and soil properties at the TMT candidate sites

S. G. Els, R. Riddle, M. Schöck, et al.

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During the site testing campaign for the Thirty Meter Telescope (TMT) in addition to the optical conditions of the atmosphere, measurements of the soil surface properties were obtained also. The dust concentration in the air was measured by means of dust sensors which were mounted underneath the mount of the site monitoring telescopes. The ground head fluxes and soil temperatures were measured several centimeters into the ground. On Cerro Armazones it was also possible to conduct an experiment to measure heat conduction of the soil. In this paper, all of these measurements are described, the results and their potential use is summarized.

Surface layer turbulence measurements on the LSST site El Peñon using microthermal sensors and the lunar scintillometer LuSci

J. Sebag, P. Zimmer, J. Turner, et al.

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Results from determining the optical turbulence profile (OTP) on the LSST site, El Peñon, located on Cerro Pachón (Chile) are presented. El Peñón appears to be an excellent observatory site with a surface layer seeing contribution on the order of 0.15” with most of this seeing being produced below 20m. These measurements also helped to confirm that the telescope is elevated high enough above ground. As part of the LSST site characterization campaign, microthermal measurements were taken in order to determine the contribution of the surface layer turbulence to the atmospheric seeing. Such measurements are commonly used for this purpose where pairs of microthermal sensors mounted on a tower measure atmospheric temperature differences. In addition, the lunar scintillometer LuSci was installed on El Peñon for short campaigns near full moon for the same purpose. LuSci is a turbulence profiler based on measuring spatial correlation of moonlight scintillations. The comparison of the results from both instruments during simultaneous data acquisition showed a remarkable temporal correlation and very similar mean OTPs.

Overview of Site Monitoring at the SAAO

T. Pickering, S. M. Crawford, L. Catala, et al.

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We present a comprehensive review of the first two years of a site monitoring campaign at the South African Astronomical Observatory (SAAO) located outside Sutherland, South Africa. This campaign is in support of the Southern African Large Telescope (SALT), a 11-metre, fixed-elevation, optical telescope located at SAAO . The heart of this observing campaign involves continuous monitoring of the site by a MASS-DIMM instrument. The MASS-DIMM has been in routine use since March 2010 and its operation is now fully automated. At the beginning of this campaign, simultaneous observations were also made by a SLODAR instrument, which allows high resolution observations of the lower atmosphere. In August 2011 a two week campaign was carried out with a two-channel Generalized Seeing Monitor (GSM) telescope along with a lunar limb profiler (Profileur Bord Lunaire; PBL). Combined with the MASS-DIMM data these observations provide multiple independent measurements of atmospheric turbulence as a function of height. They also help improve the calibration of our site for more direct comparison to other major astronomical observatories. Our results so far indicate that the atmospheric conditions at the SAAO Sutherland site have deteriorated compared to past measurements. The ground layer accounts for the majority of the integrated seeing, while the free atmosphere seeing is comparable with other major sites.

Evaluations of new atmospheric windows at thirty micron wavelengths for astronomy

Takashi Miyata, Shigeyuki Sako, Takafumi Kamizuka, et al.

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Thirty micron has remained one of unexplored frontiers of ground-based astronomical observations. Recent developments of extreme high sites including the Chajnantor TAO site (5,640m) enable us to access the this wavelengths from the ground. The expected transmittance seems clear enough for astronomical observations, but practical evaluations based on astronomical data has not been carried out yet. We have analyzed images obtained at the 31.7 micron with a mid-infrared camera MAX38 attached on a mini-TAO 1.0-meter telescope. 109 images of a star IRC+10420 and 11,114 images of the sky have been reduced. Clear relationship between the measured photocurrents and the perceptible water vapor has been found. Simple estimation of the photocurrents with of the ATRAN model gives good agreements with the measurements, indicating that the ATRAN model reproduce the atmospheric transmittance reasonably well. This also supports our assumption that the scaling factor 0.85 of the PVW at the Chajnantor TAO site to the PWV at the APEX. The average transmittance in the 31.7 micron is achieved to be over 20% when the PWV below 0.6 mm. In some cases clear degradation up to 10% in the transmittance is found. It may be caused by droplets of liquid or iced water with a size over 10 micron although the causes are not exactly specified. Diurnal time variations of the sky photocurrents are also investigated. The sky is sometimes bright and usually unstable in the twilight time. On the other hand the sky around the noontime does not show clear difference from the night sky. It may suggest that the observing condition at the thirty micron windows remain good even in the daytime.

Atmospheric seeing measurements obtained with MISOLFA in the framework of the PICARD Mission

R. Ikhlef, T. Corbard, A. Irbah, et al.

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PICARD is a space mission launched in June 2010 to study mainly the geometry of the Sun. The PICARD mission has a ground program consisting mostly in four instruments based at the Calern Observatory (Observatoire de la Cˆote d’Azur). They allow recording simultaneous solar images and various atmospheric data from ground. The ground instruments consist in the qualification model of the PICARD space instrument (SODISM II: Solar Diameter Imager and Surface Mapper), standard sun-photometers, a pyranometer for estimating a global sky quality index, and MISOLFA a generalized daytime seeing monitor. Indeed, astrometric observations of the Sun using ground-based telescopes need an accurate modeling of optical effects induced by atmospheric turbulence. MISOLFA is founded on the observation of Angle-of-Arrival (AA) fluctuations and allows us to analyze atmospheric turbulence optical effects on measurements performed by SODISM II. It gives estimations of the coherence parameters characterizing wave-fronts degraded by the atmospheric turbulence (Fried parameter r₀, size of the isoplanatic patch, the spatial coherence outer scale L₀ and atmospheric correlation times). We present in this paper simulations showing how the Fried parameter infered from MISOLFA records can be used to interpret radius measurements extracted from SODISM II images. We show an example of daily and monthly evolution of r₀ and present its statistics over 2 years at Calern Observatory with a global mean value of 3.5cm.

Optical system of Chinese SONG Telescope

Songfeng Kou, Genrong Liu, Guomin Wang

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The paper reports optical system of a 1 meter diameter telescope dedicated to Stellar Observations Network Group (SONG) for the National Astronomical Observatories, CAS. SONG is an international cooperative project, Optimize the design for Asteroseismology purposes. According to the prototype of SONG, Chinese SONG telescope includes Cassegrain telescope, Nasmyth platform, Coudé train, Coudé focal plane, Shack-Hartmann wavefront sensor and spectrograph. The telescope will provide a field of view of 65 arcsec at the Nasmyth F/36.67 focus, 10 arcsec at the F/6 Coudé focus. The rotating tertiary mirror directs the light to the two Nasmyth foci, one for Shack-Hartmann wavefront sensor, the other for Nasmyth platform and spectrograph.

Design of an off-axis optical reflecting system

Y. V. Bazhanov, V. B. Vlahko

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Existing off-axial optical systems aberration theories are based on series expansion of optical path function (eikonal function). Numerical evaluations, conducted in this paper, have shown, that the most accurate results are obtained with theory, based on series expansion of exact ray-tracing equations, where expressions for high-order aberration coefficients include expressions for low order ones. We have used that very method in our search of optimal decision for off-axis optical reflective telescope systems.

Dome flat-field system for 1.3-m Araki Telescope

Tomohiro Yoshikawa, Yuji Ikeda, Naofumi Fujishiro, et al.

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We report the system/optics design and performance of the dome flat-field system for the Araki Telescope, a 1.3- m optical/near-infrared telescope at Koyama Astronomical Observatory in Japan. A variety of instruments are attached to the telescope. The optical imager, which is intended to search for exoplanets, requires an illumination flatness within 1% on the focal plane over the 17-arcmin FOV. Illumination flatness at both the pupil plane and the focal plane of the telescope is essential for calibration of the transmittance of the optical system. We devised an optical design for the flat-field system that satisfies illumination flatness at both the focal and pupil planes using the non-sequential ray tracing software LightTools. We considered far-field illumination pattern of the lamps, scattering surface reflectance distribution of the screen, telescope structure, primary/secondary mirrors, and mirror baffles. We achieved a flat illumination distribution of 0.9% at the focal plane. The systems performance was tested by comparison with a cloud-flat frame, which was derived by imaging cloud cover illuminated by city lights. The calibration data for the dome flat-field system agree well with the cloud-flat frame within 1% for the g′ and i′ bands of the imager, but the r0 band data does not meet the requirement (less than or equal to 2). Moreover, various instruments require a focal plane illuminance ranging over three orders of magnitude. We used six high-power (60W) halogen lamps; the output power is remotely controlled by a thyristor-driven dimmer and a bypass circuit to an autotransformer.

Fast and compact wide-field Gregorian telescope

Mehdi Bahrami, Alexander V. Goncharov

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A traditional Gregorian telescope features an intermediate focus, which makes the system longer than an equivalent fnumber Cassegrain design. One could shorten the Gregorian system by inserting a flat mirror before the secondary mirror. We explore the potential of this compact configuration for sky survey imaging with relaxed requirements for angular resolution. A 0.5 m f/1.4 telescope with 4 deg full field is presented. The modified design consists of two elliptical mirrors and a folding flat in between. A plano-convex field flattener is used near the focal plane. The telescope optical performance is analyzed and possible improvements are discussed based on aberration balancing. A special emphasis is given to stay light analysis and baffle designs are considered.

Optical design for amateur reflecting telescopes based on tilted axial-symmetrical planoidal mirror

Sergey A. Chuprakov

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Two-mirrors aplanatic optical design for amateur telescopes up to 0.5m class is described. The optical system is low cost, easy for adjusting, fast and large field of view can be used for visual and astrophotography. The method for calculation of baffles for straight light protection is described. The optical performances and sample shots for the builted device are presented. Keywords: two-mirrors system, all-reflecting schmidt system, aplanatic system, protection from straight light, baffles, obscuration, wide-field, telescopes for amateurs.

Preliminary optical design for the WEAVE two-degree prime focus corrector

Tibor Agócs, Don Carlos Abrams, Diego Cano Infantes, et al.

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We present the preliminary optical design for a new two-degree refractive prime focus corrector for the 4.2m William Herschel Telescope optimised for the wide-field multi-object spectrograph, WEAVE (WHT Enhanced Area Velocity Explorer). From the two conceptual designs described previously [1], the counter-rotating atmospheric dispersion corrector approach was selected and further optimized to meet the flat image surface requirement. The preliminary design provides good polychromatic image quality. The PSF does not exceed 0.6 arcsec (80% encircled energy) over a wavelength range from 370 to 1000nm covering a two degree FOV for zenith angles up to 65 degrees. We describe the corrector's performance and the trade-off between telecentricity and the requirement for a flat image surface. We present the results of the tolerance and thermal analyses, ghost and scattered light calculations and the finite element analysis that are necessary to establish the PSF error budget for the corrector.

Ground-based and Airborne Telescopes IV

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