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- Front Matter: Volume 9145
- Project Reviews I
- Project Reviews II
- Upgrades to Existing Observatories
- Site Characterization and Testing
- Design of Telescopes for Extreme Environments
- Telescopes to Image Orbiting Objects
- Cherenkov Telescopes I
- Cherenkov Telescopes II
- Airborne Telescopes I
- Airborne Telescopes II
- Airborne Telescopes III
- Telescopes and Arrays for Surveys, Time-domain and Transient Observations I
- Telescopes and Arrays for Surveys, Time-domain and Transient Observations II
- Telescopes and Arrays for Surveys, Time-domain and Transient Observations III
- Telescope Performance Measurement
- Extremely Large Telescopes I
- Extremely Large Telescopes II
- Enabling Technologies for Extremely Large Telescopes I
- Enabling Technologies for Extremely Large Telescopes II
- Telescope Controls
- Segmented Mirror Alignment, Phasing and Wavefront Control
- Millimeter Wavelength Telescopes and Arrays I
- Millimeter Wavelength Telescopes and Arrays II
- Radio Telescopes and Arrays
- Solar Telescopes I
- Solar Telescopes II
- AIV, Commissioning and Early Operations
- Telescope Structures, Bearings and Drives
- Observatory Facilities and Enclosures
- Measurement and Control of Telescope Vibration
- Poster Session
Front Matter: Volume 9145
Front Matter: Volume 9145
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This PDF file contains the front matter associated with SPIE Proceedings Volume 9145, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Project Reviews I
The Large Binocular Telescope: binocular all the time
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The Large Binocular Telescope Observatory is a collaboration between institutions in Arizona, Germany, Italy, Indiana, Minnesota, Ohio and Virginia. The telescope uses two 8.4-m diameter primary mirrors mounted sideby- side on the same AZ-EL mount to produce a collecting area equivalent to an 11.8-meter aperture. Many science observations collect the light from the two sides separately. With the arrival of the second copy of the near-infrared spectrometer and the second copy of the optical spectrometer, the telescope is observing with both apertures a significant fraction of the time. 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. Adaptive optics loops are routinely closed with natural stars on both sides of the telescope for combined beam observations. Twin laser guide star constellations have recently been installed for ground layer adaptive optics observations. Commissioning of new instruments and focal stations for high resolution spectroscopy and near-infrared phased-array imaging is underway.
Ideas for future large single dish radio telescopes
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The existing large single dish radio telescopes of the 100m class (Effelsberg, Green Bank) were built in the 1970s and 1990s. With some active optics they work now down to 3 millimeter wavelength where the atmospheric quality of the site is also a limiting factor. Other smaller single dish telescopes (50m LMT Mexico, 30m IRAM Spain) are located higher and reach sub-millimeter quality, and the much smaller 12m antennas of the ALMA array reach at a very high site the Terahertz region. They use advanced technologies as carbon fiber structures and flexible body control.
We review natural limits to telescope design and use the examples of a number of telescopes for an overview of the available state-of-the-art in design, engineering and technologies. Without considering the scientific justification we then offer suggestions to realize ultimate performance of huge single dish telescopes (up to 160m). We provide an outlook on design options, technological frontiers and cost estimates.
Solaris: a global network of autonomous observatories in the southern hemisphere
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We present Project Solaris, a network of four autonomous observatories in the Southern Hemisphere. The Project's primary goal is to detect and characterize circumbinary planets using the eclipse timing approach. This method requires high-cadence and long time-span photometric coverage of the binaries' eclipses, hence the observatories are located at sites having similar separation in longitude and nearly identical latitudes: South African Astronómical Observatory, Republic of South Africa (Solaris-1 and -2), Siding Spring Observatory, Australia (Solaris-3) and Complejo Astronomico El Leoncito, Argentina (Solaris-4). The headquarters coordinating and monitoring the network is based in Toruń, Poland. All four sites are operational as of December 2013. The instrument and hardware configurations are nearly identical. Each site is equipped with a 0.5-m Ritchey-Chrétien or Schmidt-Cassegrain optical tube assembly mounted on a direct-drive modified German equatorial mount along with a set of instruments. Computer, power and networking components are installed in rack cabinets. Everything is housed in sandwiched fiberglass clamshell 3.5-m diameter robotized domes. The Argentinian site is additionally equipped with a 20-ft office container. We discuss the design requirements of robotic observatories aimed to operate autonomously as a global network with concentration on efficiency, robustness and modularity. We also present a newly introduced spectroscopic mode of operation commissioned on the Solaris-1 telescope. Using a compact échelle spectrograph (20 000 resolution) mounted directly on the imaging train of the telescope, we are able to remotely acquire spectra. A fully robotic spectroscopic mode is planned for 2015.
Deployment of the Hobby-Eberly Telescope wide field upgrade
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The Hobby-Eberly Telescope (HET) is an innovative large telescope located in West Texas at the McDonald Observatory. The HET operates with a fixed segmented primary and has a tracker, which moves the four-mirror optical corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. A major upgrade of the HET is in progress that will substantially increase the pupil size to 10 meters (from 9.2 m) and the field of view to 22 arcminutes (from 4 arcminutes) by replacing the corrector, tracker, and prime focus instrument package. In addition to supporting existing instruments, and a new low resolution spectrograph, this wide field upgrade will feed a revolutionary new integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX§). The upgrade is being installed and this paper discusses the current status.
Project Reviews II
Overview of University of Tokyo Atacama Observatory 6.5m telescope project
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The University of Tokyo Atacama Observatory (TAO) is a project to construct a 6.5-meter telescope optimized for infrared observations at the summit of Co. Chajnantor, 5,640 m altitude. The high altitude and low water vapor (0.5mm in 25% percentile) of the site provide wide wavelength coverage from 0.3 to 38 micron including continuous window from 0.9 to 2.5 micron and new windows at wavelength longer than 25 micron. We report on the design and the current status of the mirror, the telescope, the summit and the base facilities in this paper.
The Cherenkov Telescope Array single-mirror small size telescope project: status and prospects
J. A. Aguilar,
W. Bilnik,
L. Bogacz,
et al.
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The Cherenkov Telescope Array (CTA), the next generation very high energy gamma-ray observatory, will consist of three types of telescopes: large (LST), medium (MST) and small (SST) size telescopes. The small size telescopes are dedicated to the observation of gamma-rays with energy between a few TeV and few hundreds of TeV. The single-mirror small size telescope (SST-1M) is one of several SST designs. It will be equipped with a 4 m-diameter segmented mirror dish and a fully digital camera based on Geiger-mode avalanche photodiodes. Currently, the first prototype of the mechanical structure is under assembly in Poland. In 2014 it will be equipped with 18 mirror facets and a prototype of the camera.
Upgrades to Existing Observatories
Development of a wide field spherical aberration corrector for the Hobby Eberly Telescope: design, fabrication and alignment
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A 4-mirror prime focus corrector is under development to provide seeing-limited images for the 10-m aperture Hobby- Eberly Telescope (HET) over a 22 arcminute wide field of view. The images created by the spherical primary mirror are aberrated with 13 arcmin diameter point spread function. The University of Arizona is developing the 4-mirror wide field corrector to compensate the aberrations from the primary mirror and present seeing limited imaged to the pickoffs for the fiber-fed spectrographs. The requirements for this system pose several challenges, including optical fabrication of the aspheric mirrors, system alignment, and operational mechanical stability. This paper presents current status of the program which covers fabrication of mirrors and structures and pretest result from the alignment of the system.
Conceptual design study to determine optimal enclosure vent configuration for the Maunakea Spectroscopic Explorer (MSE)
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The Maunakea Spectroscopic Explorer (MSE; formerly Next Generation Canada-France-Hawaii Telescope) is a dedicated, 10m aperture, wide-field, fiber-fed multi-object spectroscopic facility proposed as an upgrade to the existing Canada-France-Hawaii Telescope on the summit of Mauna Kea. The enclosure vent configuration design study is the last of three studies to examine the technical feasibility of the proposed MSE baseline concept. The enclosure vent configuration study compares the aero-thermal performance of three enclosure ventilation configurations based on the predicted dome thermal seeing and air flow attenuation over the enclosure aperture opening of a Calotte design derived from computational fluid dynamics simulations. In addition, functional and operation considerations such as access and servicing of the three ventilation configurations is discussed.
The RadioAstron Green Bank Earth Station
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We present the design, commissioning, and initial results of the Green Bank Earth Station (GBES), a RadioAstron data downlink station located at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia. The GBES uses the modernized and refurbished NRAO 140ft telescope. Antenna optics were refurbished with new motors and drives fitted to the secondary mirror positioning system, and the deformable subreflector was refurbished with a new digital controller and new actuators. A new monitor and control system was developed for the 140ft and is based on that of the Green Bank Telescope (GBT), allowing satellite tracking via a simple scheduling block. Tools were developed to automate antenna pointing during tracking. Data from the antenna control systems and logs are retained and delivered with the science and telemetry data for processing at the Astro Space Center (ASC) of the Lebedev Physical Institute (LPI) of the Russian Academy of Sciences and the mission control centre, Lavochkin Association.
Site Characterization and Testing
Assessing VLT-UT science image quality from active optics Shack-Hartmann spot patterns
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A one year database has been gathered from the VLT active optics Shack-Hartmann (S-H) wavefront sensor images taken at each operating focus about every 30 seconds. The VLT telescope control software includes a dedicated code to extract the median full width at half maximum of the unvignetted S-H spots which is used for this study. This code applies a 1-D fit, assuming circular Hartmann spots, which allows to work only on foci equipped with atmospheric dispersion correction, or when the telescopes are observing close to zenith. The S-H image size measured inside the 30m enclosures is compared the outside seeing measured at 6m above ground by the VLT Astronomical Site Monitor (DIMM). A method for correcting DIMM measurements from surface layer turbulence contamination is proposed.
Antarctic observations at long wavelengths with the IRAIT-ITM Telescope at Dome C
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We illustrate the status of the international infra-red telescope IRAIT-ITM, a project developed thanks to an Italian- Spanish-French collaboration and now sited at the Dome C Antarctic base. The telescope and its subsystems were installed at DomeC by a team of Italian and French scientists. The 80 cm telescope is placed on a small snow hill next to a laboratory of astronomy. The operations started in January 2013, with the Nasmyth focal planes equipped with the midinfrared camera AMICA for 1.25 to 25 μm and the sub-millimetre camera CAMISTIC for observation of the sky noise at 200 and 350 μm using a bolometer camera. During 2013 the two winter-overs worked mainly on technological duties, learning how to operate the telescope, while temperatures decreased down to -80°C. The cryogenic systems could be operated respectively at 0.25K and 4K at all times, with satisfactory use of the heat from the compressors of the cryocoolers to the warm-up the laboratory through a closed loop glycol system. The lack of tests and reliability in extreme conditions of some components and difficult access to maintenance hampered regular observations below -50°C. Using the lessons of this first winter, the summer team improves the robustness of the failing systems and ease the access to maintenance. The winter 2014 is the first one with programmed observations. Because of power restrictions, the two instruments are used each one at a time by periods of 2 weeks. The Camistic camera continues to observe the stability of the sky at a fixed altitude in chopping mode and performs skydips. The TCS is being upgraded in order to prepare the next summer season with extensive observations of the sun with Camistic.
Design of Telescopes for Extreme Environments
Kunlun Dark Universe Survey Telescope
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Chinese Antarctic Observatory has been listed as National large research infrastructure during twelfth five-year plan. Kunlun Dark Universe Survey Telescope, one of two major facility of Chinese Antarctic Observatory, is a 2.5-meter optic/infrared telescope and will be built at the Chinese Antarctic Kunlun Station. It is intended to take advantage of the exceptional seeing conditions, as well as the low temperature reducing background for infrared observations. KDUST will adopt an innovative optical system, which can deliver very good image quality over a 2 square degree flat field of view. All of parts of it have been designed carefully to endure the extremely harsh environment. KDUST will be perched on a 14.5-meter-high tower to lift it above the turbulence layer. In this paper, preliminary design and key technology pre-research of KDUST will be introduced.
The AST3 project: Antarctic Survey Telescopes for Dome A
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The AST3 project consists of three large field of view survey telescopes with 680mm primary mirror, mainly for observations of supernovas and extrasolar planets searching from Antarctic Dome A where is very likely to be the best astronomical site on earth for astronomical observations from optical wavelength to thermal infrared and beyond, according to the four years site testing works by CCAA, UNSW and PRIC. The first AST3 was mounted on Dome A in Jan. 2012 and automatically run from March to May 2012. Based on the onsite winterization performance of the first AST3, some improvements such as the usage of high resolution encoders, defrosting method, better thermal control and easier onsite assembly et al were done for the second one. The winterization observation of AST3-2 in Mohe was carried on from Nov. 2013 to Apr. 2014, where is the most northern and coldest part of China with the lowest temperature around -50°. The technical modifications and testing observation results will be given in this paper. The third AST3 will be optimized from optical to thermal infrared aiming diffraction limited imaging with K band. Thus the whole AST3 project will be a good test bench for the development of future larger aperture optical/infrared Antarctic telescopes such as the proposed 2.5m Kunlun Dark Universe Survey Telescope project.
The Greenland Telescope (GLT): antenna status and future plans
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The ALMA North America Prototype Antenna was awarded to the Smithsonian Astrophysical Observatory (SAO) in 2011. SAO and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), SAO’s main partner for this project, are working jointly to relocate the antenna to Greenland to carry out millimeter and submillimeter VLBI observations. This paper presents the work carried out on upgrading the antenna to enable operation in the Arctic climate by the GLT Team to make this challenging project possible, with an emphasis on the unexpected telescope components that had to be either redesigned or changed. Five-years of inactivity, with the antenna laying idle in the desert of New Mexico, coupled with the extreme weather conditions of the selected site in Greenland have it necessary to significantly refurbish the antenna. We found that many components did need to be replaced, such as the antenna support cone, the azimuth bearing, the carbon fiber quadrupod, the hexapod, the HVAC, the tiltmeters, the antenna electronic enclosures housing servo and other drive components, and the cables. We selected Vertex, the original antenna manufacturer, for the main design work, which is in progress. The next coming months will see the major antenna components and subsystems shipped to a site of the US East Coast for test-fitting the major antenna components, which have been retrofitted. The following step will be to ship the components to Greenland to carry out VLBI
New results from the first exoplanet survey in the Canadian High Arctic
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We present new results from the first search for transiting exoplanets undertaken from the High Arctic: the AWCam (Arctic Wide-field Cameras) survey. The survey, which has been operating for 2.5 years, is based at 80 degrees North on Ellesmere Island in the Canadian High Arctic. The small telescopes monitor 70,000 bright stars in a several-hundred square-degree region around Polaris, with milli-magnitude photometric precision, and are capable of discovering giant planets around 10,000 bright, nearby solar-type stars. We present the first longterm monitoring results from the AWCams, including an assessment of the site characteristics and the systems' long-term performance. The High-Arctic site provided excellent survey efficiency, without diurnal windowing and largely uninterrupted by clouds. Useful data was obtained over the entire survey field 71% of the time; the sky was clear 62% of the time. One pristine clear, dark period in winter 2012/13 persisted for 480 hours. In 2012/13 we recorded a period of 480 hours of continuous photometric conditions, attaining 3-4 millimag photometric stability over the entire period. We report the long-term photometric performance of the AWCam systems and detail the discovery of a bright (V=8) low-amplitude eclipsing binary. Finally, we present a concept for an extremely-wide-field arctic survey based on the Evryscope telescope-array design.
Telescopes to Image Orbiting Objects
Ground-based astronomical instrument for planetary protection
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Planetary protection consists of the measurement and characterization of near-earth objects including earth threatening asteroids and earth orbiting debris. The Lockheed Martin STAR Labs in Palo Alto California is developing new astronomical instruments for use in planetary protection. The observation of asteroids is standard for astronomical facilities and there are available instruments designed with this specific science mission in mind. Orbital debris observation and characterization has a somewhat different set of requirements and includes large fields of view with simultaneous spectro-polarimetric data on multiple closely spaced objects. Orbital debris is comprised of spent rocket bodies, rocket fairing covers, paint chips, various satellite components, debris from satellite collisions and explosions and nonoperational satellites. The debris is present in all orbital planes from Low Earth orbit out to the geosynchronous graveyard orbit. We concentrate our effort on the geosynchronous and nearby orbits. This is because typical groundbased astronomical telescopes are built to track at sidereal rates and not at the 1 degree per second rates that are required to track low earth orbiting objects. The orbital debris materials include aluminum, mylar, solar cell materials, composite matrix material and other materials that are used in the fabrication of satellites and launch vehicles. These materials typically have spectral features in different wavebands than asteroids which are mostly composed of materials with molecular absorption bands such as in H2O. This will drive an orbital debris material identification instrument to wavebands and resolutions that are typically not used in asteroid observations.
Space Object Tracking (SPOT) facility
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Lockheed Martin has built a Space Object Tracking (SPOT) facility at our Santa Cruz test site in Northern California. SPOT consists of three 1 meter optical telescopes controlled by a common site management system to individually or cooperatively task each system to observe orbital debris and earth orbiting satellites. The telescopes are mounted in Az/El fork mounts capable of rapid repointing and arc-sec class open loop tracking. Each telescope is installed in a separate clam shell dome and has aft mounted benches to facilitate installing various instrument suites. The telescope domes are mounted on movable rail carts that can be positioned arbitrarily along tracks to provide variable baselines for sparse aperture imaging. The individual telescopes achieved first light in June 2012 and have been used since to observe satellites and orbital debris. Typical observations consist of direct photometric imaging at visible and near infrared wavelengths, and also include spectroscopic and hypertemporal measurements.
Rayleigh beacon adaptive optical systems for atmospheric aberration correction and high rate J-Band trackers for each telescope will be added in 2015. Coherent combinations of the three telescopes as an interferometric imaging array using actively stabilized free space variable delay optical paths and fringe tracking sensors is also planned. The first narrow band (I band) interferometric fringes will be formed in the summer of 2014, with wide band (R, I, H) interferometric imaging occurring by early 2015.
Cherenkov Telescopes I
Status of the Cherenkov Telescope Array Project
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CTA, the Cherenkov Telescope Array, is the next generation ground-based observatory for gamma-ray astronomy in the energy range from 20 GeV to 300 TeV. The CTA project is finishing its preparatory phase, and the pre-production phase will start in 2014. The expected performance of CTA has been assessed using very detailed simulations. The science cases for CTA were established and the key physics programs are defined. A report on the design and prototypes of the different telescopes will be given. Plans for array control, data acquisition and data management are well advanced and will be presented here. Several site candidates for CTA on the Southern and Northern have been evaluated, and a site decision will be taken in 2014.
The ASTRI SST-2M prototype for the Cherenkov Telescope Array: prototype technologies goals and strategies for the future SST
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The Cherenkov Telescope Array (CTA) observatory will represent the next generation of Imaging Atmospheric Cherenkov Telescope. Using a combination of large-, medium-, and small-scale telescopes (LST, MST, SST, respectively), it will explore the Very High Energy domain from a few tens of GeVup to about few hundreds of TeV with unprecedented sensitivity, angular resolution and imaging quality. In this framework, the Italian ASTRI program, led by the Italian National Institute of Astrophysics (INAF) developed a 4-meter class telescope, which will adopt an aplanatic, wide-field, double-reflection optical layout in a Schwarzschild- Couder configuration. Within this program INAF assigned to the consortium between Galbiati Group and EIE Group the construction, assembly and tests activities of the prototype named ASTRI SST-2M. On the basis of the lesson learnt from the prototype, other telescopes will be produced, starting from a re-design phase, in order to optimize performances and the overall costs and production schedule for the CTA-SST telescope. This paper will firstly give an overview of the concept for the SST prototype mount structure. In this contest, the technologies adopted for the design, manufacturing and tests of the entire system will be presented. Moreover, a specific focus on the challenges of the prototype and the strategies associated with it will be provided, in order to outline the near future performance goals for this type of Cherenkov telescopes employed for Gamma ray science.
The ASTRI SST-2M prototype for the Cherenkov Telescope Array: manufacturing of the structure and the mirrors
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The Cherenkov Telescope Array (CTA) observatory will represent the next generation of Imaging Atmospheric Cherenkov Telescopes. Using a combination of large-, medium-, and small-scale telescopes (LST, MST, SST, respectively), it will explore the Very High Energy domain from a few tens of GeV up to few hundreds of TeV with unprecedented sensitivity, angular resolution and imaging quality.
In this framework, the Italian ASTRI program, led by the Italian National Institute of Astrophysics (INAF), is currently developing a scientific and technological SST prototype named ASTRI SST-2M; a 4-meter class telescope, it will adopt an aplanatic, wide-field, double-reflection optical layout in a Schwarzschild-Couder configuration.
In this contribution we give an overview of the technological solutions adopted for the ASTRI SST-2M prototype. In particular we focus on the manufacturing of the telescope structure and mirrors. We will also describe early results from tests.
Cherenkov Telescopes II
Medium-sized telescopes for the Cherenkov Telescope Array
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CTA, the Cherenkov Telescope Array, is the next generation ground-based observatory for gamma-ray astronomy in the energy range from 20 GeV to 300 TeV. The sensitivity in the core energy range will be dominated by up to 40 Medium- Sized Telescopes. These telescopes, of Davies-Cotton type with a reflector with a diameter of 12 m, are currently in the prototype phase. A full-size mechanical prototype with drive system has been constructed in Berlin. Different prototype mirrors have been developed, tested and are mounted on the prototype. Two camera types are designed and prototyped. Demonstrator cameras were built and are tested; the integration of these cameras on the prototype is prepared. A report on all aspects of the design, commissioning and performance of the Medium-Sized Telescopes and their main components will be given.
The large size telescope of the Cherenkov Telescope Array
G. Ambrosi,
Y. Awane,
H. Baba,
et al.
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The Cherenkov Telescope Array (CTA) project aims to implement the world’s largest next generation of Very High Energy gamma-ray Imaging Atmospheric Cherenkov Telescopes devoted to the observation from a few tens of GeV to more than 100 TeV. To view the whole sky, two CTA sites are foreseen, one for each hemisphere. The sensitivity at the lowest energy range will be dominated by four Large Size Telescopes, LSTs, located at the center of each array and designed to achieve observations of high red-shift objects with the threshold energy of 20 GeV. The LST is optimized also for transient low energy sources, such as Gamma Ray Bursts (GRB), which require fast repositioning of the telescope. The overall design and the development status of the first LST telescope will be discussed.
Airborne Telescopes I
SOFIA general investigator science program
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SOFIA is a joint project between NASA and DLR, the German Aerospace Center, to provide the worldwide astronomical community with an observatory that offers unique capabilities from visible to far-infrared wavelengths. SOFIA consists of a 2.7-m telescope mounted in a highly modified Boeing 747-SP aircraft, a suite of instruments, and the scientific and operational infrastructure to support the observing program. This paper describes the current status of the observatory and details the General Investigator program. The observatory has recently completed major development activities, and it has transitioned into full operational status. Under the General Investigator program, astronomers submit proposals that are peer reviewed for observation on the facility. We describe the results from the first two cycles of the General Investigator program. We also describe some of the new observational capabilities that will be available for Cycle 3, which will begin in 2015.
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry-BLASTPol: performance and results from the 2012 Antarctic flight
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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 observes polarized light using a total power instrument, photolithographic polarizing grids, and an achromatic half-wave plate to modulate the polarization signal. During its second flight from Antarctica in December 2012, BLASTPol made degree scale maps of linearly polarized dust emission from molecular clouds in three wavebands, centered at 250, 350, and 500 μm. The instrumental performance was an improvement over the 2010 BLASTPol ight, with decreased systematics resulting in a higher number of confirmed polarization vectors. The resultant dataset allows BLASTPol to trace magnetic fields in star-forming regions at scales ranging from cores to entire molecular cloud complexes.
SOFIA pointing history
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The original pointing accuracy requirement of the Stratospheric Observatory for Infrared Astronomy SOFIA was defined
at the beginning of the program in the late 1980s as very challenging 0.2 arcsec rms. The early science flights of the
observatory started in December 2010 and the observatory has reached in the mean time nearly 0.7 arcsec rms, which is
sufficient for most of the SOFIA science instruments. NASA and DLR, the owners of SOFIA, are planning now a future
4 year program to bring the pointing down to the ultimate 0.2 arcsec rms.
This may be the right time to recall the history of the pointing requirement and its verification and the possibility of its
achievement via early computer models and wind tunnel tests, later computer aided end-to-end simulations up to the first
commissioning flights some years ago. The paper recollects the tools used in the different project phases for the
verification of the pointing performance, explains the achievements and may give hints for the planning of the upcoming
final pointing improvement phase.
Airborne Telescopes II
Design and construction of a carbon fiber gondola for the SPIDER balloon-borne telescope
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We introduce the light-weight carbon fiber and aluminum gondola designed for the Spider balloon-borne telescope. Spider is designed to measure the polarization of the Cosmic Microwave Background radiation with unprecedented sensitivity and control of systematics in search of the imprint of inflation: a period of exponential expansion in the early Universe. The requirements of this balloon-borne instrument put tight constrains on the mass budget of the payload. The Spider gondola is designed to house the experiment and guarantee its operational and structural integrity during its balloon-borne flight, while using less than 10% of the total mass of the payload. We present a construction method for the gondola based on carbon fiber reinforced polymer tubes with aluminum inserts and aluminum multi-tube joints. We describe the validation of the model through Finite Element Analysis and mechanical tests.
Pointing control for the SPIDER balloon-borne telescope
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We present the technology and control methods developed for the pointing system of the Spider experiment. Spider is a balloon-borne polarimeter designed to detect the imprint of primordial gravitational waves in the polarization of the Cosmic Microwave Background radiation. We describe the two main components of the telescope’s azimuth drive: the reaction wheel and the motorized pivot. A 13 kHz PI control loop runs on a digital signal processor, with feedback from fibre optic rate gyroscopes. This system can control azimuthal speed with < 0.02 deg/s RMS error. To control elevation, Spider uses stepper-motor-driven linear actuators to rotate the cryostat, which houses the optical instruments, relative to the outer frame. With the velocity in each axis controlled in this way, higher-level control loops on the onboard flight computers can implement the pointing and scanning observation modes required for the experiment. We have accomplished the non-trivial task of scanning a 5000 lb payload sinusoidally in azimuth at a peak acceleration of 0.8 deg/s2, and a peak speed of 6 deg/s. We can do so while reliably achieving sub-arcminute pointing control accuracy.
BLASTbus electronics: general-purpose readout and control for balloon-borne experiments
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We present the second generation BLASTbus electronics. The primary purposes of this system are detector readout, attitude control, and cryogenic housekeeping, for balloon-borne telescopes. Readout of neutron transmutation doped germanium (NTD-Ge) bolometers requires low noise and parallel acquisition of hundreds of analog signals. Controlling a telescope's attitude requires the capability to interface to a wide variety of sensors and motors, and to use them together in a fast, closed loop. To achieve these different goals, the BLASTbus system employs a flexible motherboard-daughterboard architecture. The programmable motherboard features a digital signal processor (DSP) and field-programmable gate array (FPGA), as well as slots for three daughterboards. The daughterboards provide the interface to the outside world, with versions for analog to digital conversion, and optoisolated digital input/output. With the versatility afforded by this design, the BLASTbus also finds uses in cryogenic, thermometry, and power systems. For accurate timing control to tie everything together, the system operates in a fully synchronous manner. BLASTbus electronics have been successfully deployed to the South Pole, and own on stratospheric balloons.
Upgrade of the SOFIA target acquisition and tracking cameras
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The Stratospheric Observatory for Infrared Astronomy (SOFIA) uses three visible range CCD cameras with different optics for target acquisition and tracking. The Wide Field Imager (WFI with 68mm f/2.0 optics) and the Fine Field Imager (FFI with 254mm f/2.8 optics) are mounted on the telescope front ring and are therefore exposed to stratospheric conditions in flight. The Focal Plane Imager (FPI) receives visible light from the 2.5m Cassegrain/Nasmyth telescope via a dichroic tertiary mirror and is mounted inside the pressurized aircraft cabin at typically +20°C. An upgrade of these three imagers is currently in progress. The new FPI was integrated in February 2013 and is operating as SOFIA’s main tracking camera since then. The new FFI and WFI are planned to be integrated in summer of 2015. Andor iXonEM+ DU- 888 cameras will be used in all three imagers to significantly increase the sensitivity compared to the previous CCD sensors. This will allow for tracking on fainter stars, e.g. the new FPI can track on a 16mag star with an integration time of 2 sec. While the FPI uses a commercial off the shelf camera, the cameras for FFI and WFI are extensively modified to withstand the harsh stratospheric environment. The two front ring imagers will also receive new optics to improve the image quality and to provide a stable focus position throughout the temperature range that SOFIA operates in. In this paper we will report on the results of the new FPI and the status of the FFI/WFI upgrade work. This includes the selection and design of the new optics and the design and testing of a prototype camera for the stratosphere. We will also report on preparations to make the new FPI available for scientific measurements.
Airborne Telescopes III
Characterization of InGaAs-based cameras for astronomical applications using a new VIS-NIR-SWIR detector test bench
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A new test bench for detector and camera characterization in the visible and near-infrared spectral range between 350 -2500 nm has been setup at the Max Planck Institute for Solar System Research (MPS). The detector under study is illuminated by an integrating sphere that is fed by a Czerny-Turner monochromator with quasi-monochromatic light. A quartz tungsten halogen lamp is used as a light source for the monochromator. Si- and InGaAs-based photodiodes have been calibrated against secondary reference standards at PTB (Germany), NPL (UK) and NRC (Canada) for precise spectral flux measurements. The test bench allows measurements of fundamental detector properties such as linearity of response, conversion gain, full well capacity, quantum efficiency (QE), fixed pattern noise and pixel response non-uniformity. The article will focus on the commissioning of the test bench and subsequent performance evaluation and characterization of a commercial camera system with a 640 x 480 InGaAs-detector, sensitive between 900 to 1650 nm. The study aimed at the potential use of InGaAs cameras in ground-based and airborne astronomical observations or as target acquisition and tracking cameras in the NIR supporting infrared observations at longer wavelengths, e.g. on SOFIA. An intended future application of the test bench in combination with an appropriate test dewar is the characterization of focal plane assemblies for imaging spectrometers on spacecraft missions, such as the VIS-SWIR channel of MAJIS, the Moons and Jupiter Imaging Spectrometer aboard JUICE (Jupiter Icy Moons Explorer).
Telescopes and Arrays for Surveys, Time-domain and Transient Observations I
The Pan-STARRS Project in 2014
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The Pan-STARRS telescopes are a distributed aperture approach to rapid, multi-color wide-field surveys. The first of these telescopes, a prototype designated PS1, has been in operation now for over three years and has already obtained complete sky coverage of the full 3-π steradians visible from Haleakala in 5 broad passband filters at multiple epochs. On average the PS1 survey has obtained approximately 12 epochs though each filter. The second telescope, designated PS2, has been in its commissioning phase since August 2013 and will begin science operations in the second half of 2014. Several design and fabrication changes in both the telescope and the camera have been implemented in PS2. This talk will describe the science results that have been coming out of the PS1 survey, the design changes implemented on PS2, and the current performance of the PS2 telescope and camera. We will also describe the future missions for the PS1 and PS2 telescopes as of the current year.
The Evryscope: the first full-sky gigapixel-scale telescope
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Current time-domain wide-field sky surveys generally operate with few-degree-sized fields and take many individual images to cover large sky areas each night. We present the design and project status of the Evryscope (“wideseer”), which takes a different approach: using an array of 7cm telescopes to form a single wide-field-of-view pointed at every part of the accessible sky simultaneously and continuously. The Evryscope is a gigapixel-scale imager with a 9060 sq. deg. field of view and has an etendue three times larger than the Pan-STARRS sky survey. The system will search for transiting exoplanets around bright stars, M-dwarfs and white dwarfs, as well as detecting microlensing events, nearby supernovae, and gamma-ray burst afterglows. We present the current project status, including an update on the Evryscope prototype telescopes we have been operating for the last three years in the Canadian High Arctic.
Introduction of Chinese SONG telescope
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SONG (Stellar Oscillation Network Group) is an international project to form a global observing network of eight 1- meter class telescopes. China joined this project and funded one node telescope for this network. By the end of 2013, the Chinese SONG telescope has been installed on the Delinha observing site of Purple Mountain Observatory in Qinghai province. This paper will give the introduction of this telescope, including its optical system, structure and control system. Besides, the preliminary observing performance of the telescope on site will be given in the second part of this paper.
Liverpool Telescope 2: a new robotic facility for time domain astronomy in 2020+
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The robotic 2m Liverpool Telescope, based on the Canary island of La Palma, has a diverse instrument suite and a strong track record in time domain science, with highlights including early time photometry and spectra of supernovae, measurements of the polarization of gamma-ray burst afterglows, and high cadence light curves of transiting extrasolar planets. In the next decade the time domain will become an increasingly prominent part of the astronomical agenda with new facilities such as LSST, SKA, CTA and Gaia, and promised detections of astrophysical gravitational wave and neutrino sources opening new windows on the transient universe. To capitalise on this exciting new era we intend to build Liverpool Telescope 2: a new robotic facility on La Palma dedicated to time domain science. The next generation of survey facilities will discover large numbers of new transient sources, but there will be a pressing need for follow-up observations for scientific exploitation, in particular spectroscopic follow-up. Liverpool Telescope 2 will have a 4-metre aperture, enabling optical/infrared spectroscopy of faint objects. Robotic telescopes are capable of rapid reaction to unpredictable phenomena, and for fast-fading transients like gamma-ray burst afterglows. This rapid reaction enables observations which would be impossible on less agile telescopes of much larger aperture. We intend Liverpool Telescope 2 to have a world-leading response time, with the aim that we will be taking data with a few tens of seconds of receipt of a trigger from a ground- or space-based transient detection facility. We outline here our scientific goals and present the results of our preliminary optical design studies.
Telescopes and Arrays for Surveys, Time-domain and Transient Observations II
Status of the Transneptunian Automated Occultation Survey (TAOS II)
Show abstract
The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small (~1 km diameter) objects in the Kuiper Belt 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 Astronómico Nacional at San Pedro Mártir in Baja California, México. 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. Construction of the site began in the fall of 2013.
MASCARA: the multi-site all-sky CAameRA: concept and first results
Show abstract
MASCARA, the Multi-site All-Sky CAmeRA, will consist of several fully-automated stations distributed across the globe. Its goal is to find exoplanets transiting the brightest stars, in the mV = 4 to 8 magnitude range, currently probed neither by space- nor by ground-based surveys. The nearby transiting planet systems that MASCARA is expected to discover will be key targets for future detailed planet atmosphere observations. The target population for MASCARA consists mostly of hot Jupiters. The main requirement set on MASCARA to detect these planets around stars down to magnitude 8 is to reach a minimum Signal-to-Noise Ratio of 100 within one hour of observation.
Each MASCARA station consists of five low-noise off-the-shelf full-frame CCD cameras, fitted with standard Canon 24 mm , f/1.4 lenses, monitoring the near-entire sky down to magnitude 8 at that location. Measurements have demonstrated that the required Signal-to-Noise Ratio of 100, can be achieved in less than thirty minutes. MASCARA aims at deploying several stations world-wide to provide a nearly continuous coverage of the dark sky, at sub-minute cadence.
While at the faint end MASCARA is limited mainly by photon noise, at the bright end scintillation and red noise become the limiting factors. Instrumental noise sources are reduced by placing the cameras in a fixed orientation and in a temperature controlled environment. By defocusing and allowing stars to drift over the detector, the impact of pixel-to-pixel variations on the photometry are minimized, while taking exposures at fixed sidereal times allows accurate cross-calibration of consecutive nights. The exposure time of 6.4 seconds gives rise to a high data acquisition rate of a MASCARA station, around 500GB per night. In order to minimize data transport and data storage requirements, the raw images are reduced to produce accurate light curves in nearly real time.
The first MASCARA station will be integrated on La Palma during the summer of 2014. MASCARA test
data were taken in July 2013 with one camera targeting the transiting exoplanet HD 189733b. Its brightness of mV = 7:7 is close to the faint end of the MASCARA magnitude range. The 5 - σ detection of the 2.8% deep transit with a 5-minute binning of the data confirms that we will be able to detect 1% transit at the faint end within one hour.
Current status and future plans for the Maunakea Spectroscopic Explorer (MSE)
Show abstract
The Maunakea Spectroscopic Explorer (MSE; formerly ngCFHT) will be a large format wide field spectroscopic facility that replaces the existing 3.6 m Canada-France-Hawaii Telescope. Capable of recording tens of thousands of spectra on faint targets each night, and sustain that pace for years, MSE will be an ideal complement to emerging space- and ground-based imaging survey facilities. The combination of aperture, spectral resolution, and dedicated access to support large surveys makes MSE distinct from any other facilities under development or being planned. We provide an overview of the MSE technical design, organization of the project office, and the core science goals that will help drive MSE for decades.
Wavefront sensing and the active optics system of the dark energy camera
Aaron Roodman,
Kevin Reil,
Chris Davis
Show abstract
Wavefront sensing and the Active Optics System (AOS) of the Dark Energy Camera (DECam) at the CTIO 4-meter Blanco telescope are described. DECam utilizes four pairs of intra/extra-focal CCDs located on the edge of the focal plane for wavefront sensing. Out-of-focus stars are selected, individually fit to a pupil plane Zernike expansion and then collectively analyzed in the time between exposures. The AOS uses this information to control the prime-focus camera’s five degrees of freedom. The AOS is now in routine use, operating with unsupervised control of the focus and camera alignment, both for the Dark Energy Survey and community observing. The design, commissioning and operation of the AOS along with results from the wavefront measurements are described. In particular, wavefront measurements of the complete optical system, including primary mirror aberrations, are shown. Lastly, preliminary results using these wavefront measurements to model the DECam point spread function are presented.
Telescopes and Arrays for Surveys, Time-domain and Transient Observations III
Spectroscopic survey of LAMOST
Show abstract
LAMOST is a special reflecting Schmidt telescope. LAMOST breaks through the bottleneck of the large scale spectroscopic survey observation with both large aperture (effective aperture of 3.6 - 4.9m) and wide field of view (5 degrees). It is an innovative active reflecting Schmidt configuration achieved by changing mirror surface continuously to achieve a series different reflecting Schmidt system in different moments. By using the parallel controllable fiber positioning technique, the focal surface of 1.75 meters in diameter accommodates 4000 optical fibers. Also, LAMOST has 16 spectrographs with 32 CCD cameras. LAMOST is the telescope of the highest spectrum acquiring rate. As a national large scientific project, LAMOST project was proposed formally in 1996. The construction was started in 2001 and completed in 2008. After commission period, LAMOST pilot survey was started in October 2011 and spectroscopic survey began in September 2012. From October 2011 to June 2013, LAMOST has obtained more than 2 million spectra of celestial objects. There are 1.7 million spectra of stars, in which the stellar parameters (effective temperature, surface gravity, metalicitiy and radial velocity) of more than 1 million stars was obtained. In the first period of spectroscopic survey of LAMOST, 5 million of stellar spectra will be obtained and will make substantial contribution to the study of the stellar astrophysics and the structure of the Galaxy, such as the spheroid substructure of the Galaxy, the galactic gravitational potential and the distribution of the dark matter in the Galaxy, the extremely metal poor stars and hypervelocity stars, the 3D extinction in the Galaxy, the structure of thin and thick disks of the Galaxy, and so on.
Baseline design of the LSST telescope mount assembly
Show abstract
The Large Synoptic Survey Telescope (LSST) is an 8.4 meter, 3.5 degree, wide-field survey telescope. The survey mission requires a short slew, settling time of 5 seconds for a 3.5 degree slew. Since it does not include a fast steering mirror, the telescope has stringent vibration limitations during observation. Meeting these requirements will be facilitated by a stiff compact Telescope Mount Assembly (TMA) riding on a robust pier and by added damping. The TMA must also be designed to facilitate maintenance. The design is an altitude over azimuth welded and bolted assembly fabricated from mild steel.
The Maunakea Spectroscopic Explorer: the science driven design rationale
Show abstract
The Maunakea Spectroscopic Explorer (MSE; previously, the Next Generation CFHT) will fill a missing link in the international suite of optical-infra-red facilities in the 2020s, and will provide a key capability for multi-wavelength science, namely: fully dedicated, 10m-class, wide-field spectroscopy of thousands of objects per hour at spectral resolutions ranging from R = 2000 to ≥ 20000. This facility will be provided by upgrading the existing CFHT and expanding the partnership. A Project Office has been established to lead the continued scientific, technical and partnership development and complete a Construction Proposal for the facility. Here, we review the current status of the science development, in particular discussing the mechanisms by which the principal science drivers flow into the technical design, and we discuss how the facility will be optimized to satisfy demanding scientific specifications.
LSST Telescope and site status
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The Large Synoptic Survey Telescope (LSST) has recently completed its Final Design Review and the Project is preparing for a 2014 construction authorization. The telescope system design supports the LSST mission to conduct a wide, fast, deep survey via a 3-mirror wide field of view optical design, a 3.2-Gpixel camera, and an automated data processing system. The observatory will be constructed in Chile on the summit of Cerro Pachón. This paper summarizes the status of the Telescope and Site group. This group is tasked with design, analysis, and construction of the summit and base facilities and infrastructure necessary to control the survey, capture the light, and calibrate the data. Several early procurements of major telescope subsystems have been completed and awarded to vendors, including the mirror systems, telescope mount assembly, hexapod and rotator systems, and the summit facility. These early contracts provide for the final design of interfaces based upon vendor specific approaches and will enable swift transition into construction. The status of these subsystems and future LSST plans during construction are presented.
Telescope Performance Measurement
Real-time estimation of differential piston at the LBT
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In this paper, we present and compare different strategies to minimize the effects of telescope vibrations to the differential piston (OPD) for LINC/NIRVANA at the LBT using an accelerometer feedforward compensation approach. We summarize why this technology is of importance for LINC/NIRVANA, but also for future telescopes and instruments. We outline the estimation problem in general and its specifics at the LBT. Model based estimation and broadband filtering techniques can be used to solve the estimation task, each having its own advantages and disadvantages, which will be discussed. Simulation results and measurements at the LBT are shown to motivate and support our choice of the estimation algorithm for the instrument LINC/NIRVANA. We explain our laboratory setup aimed at imitating the vibration behaviour at the LBT in general, and the M2 as main contributor in particular, and we demonstrate the controller's ability to suppress vibrations in the frequency range of 8 Hz to 60 Hz. In this range, telescope vibrations are the most dominant disturbance to the optical path.
For our measurements, we introduce a disturbance time series which has a frequency spectrum comparable to what can be measured at the LBT on a typical night. We show promising experimental results, indicating the ability to suppress differential piston induced by telescope vibrations by a factor of about 5 (RMS), which is significantly better than any currently commissioned system.
Extremely Large Telescopes I
Overview and status of the Giant Magellan Telescope project
Show abstract
The Giant Magellan Telescope (GMT) is a 25.4-m diameter, optical/infrared telescope that is being built by an international consortium of universities and research institutions as one of the next generation of Extremely Large Telescopes. The primary mirror of GMT consists of seven 8.4 m borosilicate honeycomb mirror segments that are optically conjugate to seven corresponding segments in the Gregorian secondary mirror. Fabrication is complete for one primary mirror segment and is underway for the next two. The final focal ratio of the telescope is f/8.2, so that the focal plane has an image scale of 1.02 arcsec/mm. GMT will be commissioned using a fast-steering secondary mirror assembly comprised of conventional, rigid segments to provide seeing-limited observations. A secondary mirror with fully adaptive segments will be used in standard operation to additionally enable ground-layer and diffraction-limited adaptive optics. In the seeing limited mode, GMT will provide a 10 arcmin field of view without field correction. A 20 arcmin field of view will be obtained using a wide-field corrector and atmospheric dispersion compensator. The project has recently completed a series of sub-system and system-level preliminary design reviews and is currently preparing to move into the construction phase. This paper summarizes the technical development of the GMT sub-systems and the current status of the GMT project.
European Extremely Large Telescope: progress report
Show abstract
The European Extremely Large Telescope is a project of the European Southern Observatory to build and operate a 40-m
class optical near-infrared telescope. The telescope design effort is largely concluded and construction contracts are
being placed with industry and academic/research institutes for the various components. The siting of the telescope in
Northern Chile close to the Paranal site allows for an integrated operation of the facility providing significant economies.
The progress of the project in various areas is presented in this paper and references to other papers at this SPIE meeting
are made.
Extremely Large Telescopes II
Design of the Giant Magellan Telescope
Show abstract
The preliminary design of the 25 m Giant Magellan Telescope (GMT) has been completed. This paper describes the design of the optics, structure and mechanisms, together with the rationales that lead to the current design. Analyses that were conducted to verify structure and optical performance are summarized. Science instruments will be mounted within the telescope structure. A common instrument de-rotator is provided to compensate for field rotation caused by the alt-az tracking of the telescope. The various instrument stations and provisions for mounting instruments are described. Post-PDR development plans for the telescope are presented.
Looking beyond 30m-class telescopes: the Colossus project
J. R. Kuhn,
S. V. Berdyugina,
M. Langlois,
et al.
Show abstract
The exponential growth in exoplanet studies is a powerful reason for developing very large optical systems optimized for narrow-field science. Concepts which cross the boundary between fixed aperture telescopes and interferometers, combined with technologies that decrease the system moving mass, can violate the cost and mass scaling laws that make conventional large-aperture telescopes relatively expensive. Here we describe a concept which breaks this scaling relation in a large optical/IR system called “Colossus”1.
Enabling Technologies for Extremely Large Telescopes I
GMT primary mirror support
Charlie Hull
Show abstract
The GMT primary mirror support draws on the heritage developed for the 3.5 m, 6.5 m, and 8.4 m mirrors from the Steward Observatory Mirror Lab. While similar in design philosophy and concept, each successive generation has incorporated refinements based on the experience gained from previous mirrors.
The secondary mirror concept for the European Extremely Large Telescope
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The E-ELT is an active and adaptive 39-m telescope, with an anastigmat optical solution (5 mirrors including two flats), currently being developed by the European Southern Observatory (ESO). The convex 4-metre-class secondary mirror (M2) is a thin Zerodur meniscus passively supported by an 18 point axial whiffletree. A warping harness system allows to correct low order deformations of the M2 Mirror. Laterally the mirror is supported on 12 points along the periphery by pneumatic jacks. Due to its high optical sensitivity and the telescope gravity deflections, the M2 unit needs to allow repositioning the mirror during observation. Considering its exposed position 30m above the primary, the M2 unit has to provide good wind rejection. The M2 concept is described and major performance characteristics are presented.
High volume production trial of mirror segments for the Thirty Meter Telescope
Tetsuji Oota,
Mahito Negishi,
Hirohiko Shinonaga,
et al.
Show abstract
The Thirty Meter Telescope is a next-generation optical/infrared telescope to be constructed on Mauna Kea, Hawaii toward the end of this decade, as an international project. Its 30 m primary mirror consists of 492 off-axis aspheric segmented mirrors. High volume production of hundreds of segments has started in 2013 based on the contract between National Astronomical Observatory of Japan and Canon Inc.. This paper describes the achievements of the high volume production trials. The Stressed Mirror Figuring technique which is established by Keck Telescope engineers is arranged and adopted. To measure the segment surface figure, a novel stitching algorithm is evaluated by experiment. The integration procedure is checked with prototype segment.
Enabling Technologies for Extremely Large Telescopes II
Improved E-ELT subsystem and component specifications, thanks to M1 test facility
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During the last 2 years ESO has operated the “M1 Test Facility”, a test stand consisting of a representative section of the E-ELT primary mirror equipped with 4 complete prototype segment subunits including sensors, actuators and control system. The purpose of the test facility is twofold: it serves to study and get familiar with component and system aspects like calibration, alignment and handling procedures and suitable control strategies on real hardware long before the primary mirror (hereafter M1) components are commissioned. Secondly, and of major benefit to the project, it offered the possibility to evaluate component and subsystem performance and interface issues in a system context in such detail, that issues could be identified early enough to feed back into the subsystem and component specifications. This considerably reduces risk and cost of the production units and allows refocusing the project team on important issues for the follow-up of the production contracts. Experiences are presented in which areas the results of the M1 Test Facility particularly helped to improve subsystem specifications and areas, where additional tests were adopted independent of the main test facility. Presented are the key experiences of the M1 Test Facility which lead to improved specifications or identified the need for additional testing outside of the M1 Test Facility.
New strategies for an extremely large telescope dedicated to extremely high contrast: the Colossus project
Show abstract
Detecting an exoplanetary life signal is extremely challenging with current technology because it requires a sensitive telescope and instrument that can measure the planet's reflected optical and infrared light, while distinguishing this from the star's scattered light and the terrestrial thermal noise background. This requires highly accurate adaptive optics, a coronagraph system, and a specially designed and aligned giant telescope. We present here new strategies for building such a telescope with large circular segments using adaptive optics correction independently for each of these segments prior to cophasing the segments. The foreseen cophasing technique uses focal plane images that allow piston measurements and correction between all the segments. In this context we propose to derive the segment phase error using the inverse approach knowing the segment positions and the single aperture Airy function.
Development of GMT fast steering secondary mirror assembly
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The Giant Magellan Telescope (GMT) is one of Extremely large telescopes, which is 25m in diameter featured with two Gregorian secondary mirrors, an adaptive secondary mirror (ASM) and a fast-steering secondary mirror (FSM). 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. The guiding philosophy in the design of the FSM segment mirror is to minimize development and fabrication risks ensuring a set of secondary mirrors are available on schedule for telescope commissioning and early operations in a seeing limited mode. Each FSM segment contains a tip-tilt capability for fine co-alignment of the telescope subapertures and fast guiding to attenuate telescope wind shake and mount control jitter, thus optimizing the seeing limited performance of the telescope. The final design of the FSM mirror and support system configuration was optimized using finite element analyses and optical performance analyses. The optical surface deformations, image qualities, and structure functions for the gravity print-through cases, thermal gradient effects, and dynamic performances were evaluated. The results indicated that the GMT FSM mirror and its support system will favorably meet the optical performance goals for residual surface error and the FSM surface figure accuracy requirement defined by encircled energy (EE80) in the focal plane. The mirror cell assembly analysis indicated an excellent dynamic stiffness which will support the goal of tip-tilt operation.
Status of E-ELT M5 scale-one demonstrator
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The fifth mirror of the European Extremely Large Telescope optical train is a field stabilization tip/tilt unit responsible for correcting the dynamical tip and tilt caused mainly by wind load on the telescope. A scale-one prototype including the inclined support, the fixed frame and a basic control system was designed and manufactured by NTE-SENER (Spain) and CSEM (Switzerland) as part of the prototyping and design activities. All interfaces to the mirror have been reproduced on a dummy structure reproducing the inertial characteristics of the optical element. The M5 unit is required to have sufficient bandwidth for tip/tilt reference commands coming from the wavefront control system. Such a bandwidth can be achieved using local active damping loop to damp the low frequency mechanical modes before closing a position loop. Prototyping on the M5 unit has been undertaken in order to demonstrate the E-ELT control system architecture, concepts and development standards and to further study active damping strategies. The control system consists of two nested loops: a local damping loop and a position loop. The development of this control system was undertaken following the E-ELT control system development standards in order to determine their applicability and performance and includes hardware selection, communication, synchronization, configuration, and data logging. In this paper we present the current status of the prototype M5 control system and the latest results on the active damping control strategy, in particular the promising results obtained with the method of positive position feedback.
Telescope Controls
CCAT mount control using de-convolution for fast scans
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CCAT will be a 25-meter telescope for submillimeter wavelength astronomy located at an altitude of 5600 meters on
Cerro Chajnantor in northern Chile. This paper presents an overview of the preliminary mount control design. A finite
element model of the structure has been developed and is used to determine the dynamics relevant for mount control.
Controller strategies are presented that are designed to meet challenging wind rejection and fast scan requirements.
Conventional inner loops are used for encoder-based control. Offset requirements are satisfied using innovative
command shaping with feedforward and a two-command path structure. The fast scan requirement is satisfied using a
new approach based on a de-convolution filter. The de-convolution filter uses an estimate of the closed loop response
obtained from test signals. Wind jitter requirements remain a challenge and additional sensors such as accelerometers
and wind pressure sensors may be needed.
Segmented Mirror Alignment, Phasing and Wavefront Control
On-sky measurement accuracy of Keck telescope segment surface errors
Show abstract
We quantify the accuracy of the Keck telescope segment surface figure measurements made on sky by the Phasing Camera System (PCS), a Shack-Hartmann wavefront sensor that uses long integration times to average over the effects of atmospheric turbulence. These measurements are used to determine the settings for warping harnesses that significantly reduce the segment surface errors. When a series of six measurements is performed on the same segment in rapid succession, the Root Mean Square (RMS) segment surface, as reconstructed by 2nd through 4th order Zernike polynomials, is determined with an accuracy of 6.0 ‡ 3.2 nm (error on the mean). However, when we compare measurements on the same segment separated by several hours the inferred surface RMS accuracy is 9.0 ‡ 5.0 nm, or 50% larger. This suggests that there are systematic errors on the order of 7 nm that vary throughout the night. In this paper we investigate and quantify the potential causes of these systematic errors, which together with statistical errors, constitute a fundamental limit for the performance of segment warping harnesses. Such measurements are currently the baseline warping harness inputs for the Thirty Meter Telescope and the European Extremely Large Telescope.
Inductive sensors based on embedded coil technology for nanometric inter-segment position sensing of the E-ELT
Martin Wasmeier,
Josef Hackl,
Samuel Leveque
Show abstract
The primary mirror of the E-ELT consists of a mosaic of 798 hexagonal mirror segments whose relative positions will be measured by 4524 so-called edge sensors. The main properties of these three axes edge sensors are nanometric precision, high linearity, low sensitivity to temperature and humidity fluctuations as well as high reliability. This paper presents the outcome of a development carried out by Micro-Epsilon in the framework of prototype activities launched by the European Southern Observatory several years ago. The performance of inductive sensors based on Embedded Coil Technology are presented as well as results obtained on representative operational conditions.
High performance control of mirror segment actuators for the European Extremely Large Telescope
Show abstract
Segmented primary mirror telescopes require dedicated piston-tip-tilt actuators for optimal optical performance. TNO has developed various prototypes of such actuators, in particular for the E-ELT. In this paper the control results of a specific two-stage prototype will be presented. First, the dynamics of the actuator in interconnection with the to-be-positioned mass has been analyzed, both using frequency response measurements and first principles modeling, resulting in a detailed understanding of the dynamic behavior of the system. Next, feedback controllers for both the fine and the coarse stage have been designed and implemented. Finally, the feedback controlled actuator has been subjected to a realistic tracking experiment; the results have demonstrated that the TNO actuator is able to suppress wind force disturbances and ground vibrations with more than a factor 103, down to 1.4 nm RMS, which is compliant with the requirements.
The Giant Magellan Telescope active optics system
Show abstract
The Giant Magellan Telescope active optics system is required to maintain image quality across a 20 arcminute diameter field of view. To do so, it must control the positions of the primary mirror and secondary mirror segments, and the figures of the primary mirror segments. When operating with its adaptive secondary mirror, the figure of the secondary is also controlled. Wavefront and fast-guiding measurements are made using a set of four probes deployed around the field of view. Through a set of simulations we have determined a set of modes that will be used to control fielddependent aberrations without degeneracies.
Fast optical re-phasing of segmented primary mirrors
Show abstract
For highly segmented primary mirrors, as that of the European Extremely Large Telescope (E-ELT) with its 798 segments, the capability to update regularly the optical phasing solution is essential for robust operations. The duration of standard phasing procedures is driven by the difficulty of maintaining the registration of the image of the primary on the phasing sensor with tolerances of ~0.02% of the mirror diameter. The paper describes a re-phasing procedure with a dynamic range of about ±1.5 microns. This is based on a standard Shack-Hartmann phasing sensor operated at 2 narrow bands filters with wavelength separation of 30%. Controlled registration offsets are applied during the acquisitions, allowing the registration parameters to be estimated from the phasing data. The procedure has been successfully validated at the Gran Telescopio de Canarias (GTC).
Millimeter Wavelength Telescopes and Arrays I
Atacama large millimeter/submillimeter array: progress, status, and development
Stuartt Corder,
Pierre Cox
Show abstract
The Atacama Large Millimeter/submillimeter Array (ALMA) is transitioning from construction to operations. This
connected element array currently operates from wavelengths of 3-mm to 350-um with up to 66 array elements, 54 of
12-m diameter and 12 of 7-m diameter. While the antennas and most of the hardware for the receivers are on site, array
capabilities are still expanding rapidly. In parallel with construction activities, early science observations have been
going on since October 2011. At the time of the meeting, ALMA will be starting Cycle 2, the third cycle of observing,
with many exciting, fundamental results already obtained in the previous two cycles. Having now finished construction,
we review some of the residual issues we are facing in the transition period. We discuss the current status of the project,
array performance, testing, and ongoing development. In short, we will present ALMA: past, present and future.
Design of the optical system for ALMA band 1
Show abstract
This work presents a complete study of the optical system for ALMA band 1, which covers the frequency range from 35 to 50 GHz, with the goal of extending the coverage up to 52GHz. Several options have been explored to comply with the stringent technical specifications, restrictions, and cost constraints. The best solution consists of a corrugated zoned lens, two infrared filters and a spline profiled corrugated horn. The calculated aperture efficiency is better than 75%, while the average noise contribution is lower than 10.3 K. The first prototypes of the system have been constructed and first evaluation results available.
ALMA: the completion of the 25 Europeans antennas: focus on main performances, problems found during erection and lessons learned
Show abstract
The 2013 saw the completion of the Atacama Large Millimeter Array (ALMA). The array consists of 66 antennas and
operates in Chile at the Chajnantor plateau at 5000 m altitude.
25 of the 12 meter diameter antennas have been delivered by the AEM consortium constituted by Thales Alenia Space
France, Thales Alenia Space Italy, European Industrial Engineering (EIE GROUP), and MT Mechatronics.
The purpose of this paper is to present a summary of the results obtained by the antennas during the different test
campaign and a summary of the problems aroused during the erection and the assembly phases and the relative lesson
learned.
The results of the engineering performances and antenna systems, performed during the acceptance phases of the first
antennas, have shown the full correspondence between what was expected during the design phase and what has been
achieved in the final product, with a difference of less than 10% and the trend tends to be conservative.
As for "on sky antennas performances", all the tests done in the 25 antennas showed excellent results. The antenna All
Sky Pointing Error and Offset Pointing Error with and without metrology correction turned to be always excellent. The
Fast Motion Capability with the tracking requirements after a step motion was better than an order of magnitude
compared to the requests.
Four years of on-site activities and the various phases of construction and assembly of 25 antennas have been a major
challenge for the European Consortium. The problems encountered in this phase were many and varied: interfaces
issues, design and foundation problems, manufacturing and assembly errors, electrical installation, shipment delays,
human errors, adverse weather conditions, financial aspects, schedule, etc.
The important is being prepared with an "a priori", that is a risk assessment which helps ensuring the best solution for
the complete customer satisfaction of the scientific and technical requests. Despite the already excellent knowledge in
the field by the companies involved, this period has undoubtedly represented an opportunity for growth and learning. A
better understanding of the problems relates to such large project, will be essential for the future major projects.
Millimeter Wavelength Telescopes and Arrays II
Development of high-accuracy pointing verification for ALMA antenna
Show abstract
Pointing performance of a radio telescope antenna is important in radio astronomical observations to obtain accurate intensity of a target source. The pointing errors of the ALMA ACA antenna are required to be better than 0.6 arcsec rss, which corresponds to 1/10 and 1/20 of the field of view of the ALMA ACA 12-m and 7-m antenna at 950 GHz, respectively. The pointing verification measurements of the ACA antenna were performed using an Optical pointing telescope (OPT) mounted on the antenna backup structure at the ALMA Operations Site Facility at 2900m above the sea level. Pointing errors of these OPT measurements contain three different origins; originated from antenna, originated of atmosphere (optical seeing), and originated of OPT itself. In order to estimate pointing errors of the antenna origin, we need to subtract the components of optical seeing and OPT itself accurately, while we need to add components that cannot be measured in the OPT measurements. The ACA antenna verification test report demonstrated that all the ACA 7-m antenna meets pointing specification of ALMA. However, about one-third of datasets, values of estimated optical seeing is larger than measured pointing errors. We re-examined a procedure to estimate optical seeing, by investigating the property of optical seeing from the high-sampling OPT pointing measurements of long tracking a bright star for 15 minutes. Particularly, we examined the relation between optical seeing and sampling rate derived from Kolmogorov PSD. Our analysis indicated that the optical seeing at ALMA site may have been overestimated in the verification test. We present a new relation between optical seeing and sampling rate proportional to average wind velocity during measurement. We used this new relation to derive the optical seeing and as a result the number of datasets becomes half in which the optical seeing is larger than measured pointing errors. As a result, we successfully develop a new verification method of optical seeing that has high reliability.
What are scientifically valuable developments for ALMA enhancement?
Show abstract
The Atacama Large Millimeter/submillimeter Array (ALMA) is already producing a growing number of impressive and scientifically compelling results during its first two years of operation as the most powerful mm/submm interferometer in the world. However, ALMA still has some scientific weak points due to the technological limitations. In order to maintain ALMA as the state-of-the-art facility over the course of its projected life of 30+ years, continuing technical upgrades and developments for new capabilities are essential. We have already performed future development studies and projects for ALMA enhancement, which are the main development focus for the next 5 - 10 years. We should now start the discussion of the technical requirements and the potential science achievable with larger scale developments which are envisioned in the next 10 - 20 years, because it is emphasized that the larger scale project will likely result in higher impact, groundbreaking ALMA science in the year 2034 and beyond.
Radio Telescopes and Arrays
Canadian Hydrogen Intensity Mapping Experiment (CHIME) pathfinder
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A pathfinder version of CHIME (the Canadian Hydrogen Intensity Mapping Experiment) is currently being commissioned at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC. The instrument is a hybrid cylindrical interferometer designed to measure the large scale neutral hydrogen power spectrum across the redshift range 0.8 to 2.5. The power spectrum will be used to measure the baryon acoustic oscillation (BAO) scale across this poorly probed redshift range where dark energy becomes a significant contributor to the evolution of the Universe. The instrument revives the cylinder design in radio astronomy with a wide field survey as a primary goal. Modern low-noise amplifiers and digital processing remove the necessity for the analog beam forming that characterized previous designs. The Pathfinder consists of two cylinders 37m long by 20m wide oriented north-south for a total collecting area of 1,500 square meters. The cylinders are stationary with no moving parts, and form a transit instrument with an instantaneous field of view of ~100 degrees by 1-2 degrees. Each CHIME Pathfinder cylinder has a feedline with 64 dual polarization feeds placed every ~30 cm which Nyquist sample the north-south sky over much of the frequency band. The signals from each dual-polarization feed are independently amplified, filtered to 400-800 MHz, and directly sampled at 800 MSps using 8 bits. The correlator is an FX design, where the Fourier transform channelization is performed in FPGAs, which are interfaced to a set of GPUs that compute the correlation matrix. The CHIME Pathfinder is a 1/10th scale prototype version of CHIME and is designed to detect the BAO feature and constrain the distance-redshift relation. The lessons learned from its implementation will be used to inform and improve the final CHIME design.
Using feed array networks to control distortions in antenna reflector for astrophysical radio-astronomy
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In this paper we present a methodology to calibrate and correct frequency-dependent errors in phased-array antennas with large signal bandwidth and large size. If the receivers are not narrow-band, the hypotheses of constant gain and group delay are not valid. If the frequency responses of the receivers are affected by mismatches, this will also impact directivity. Standard Amplitude and Phase Correction (APC) algorithms will not be effective in this case, and a more advanced complex FIR filtering algorithm is used. A transmitted signal is assumed to be known in order to provide a reference and estimate the optimal calibration coefficients of the FIR filters.
A 200-GHz telescope unit for the QUIJOTE CMB Experiment
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Experiment QUIJOTE (Q-U-I JOint TEnerife) is a scientific collaboration, leaded by the Instituto de Astrofísica de Canarias (IAC), which can measure the polarization of the Cosmic Microwave Background (CMB) in the range of frequency up to 200 GHz, at angular scales of 1°. The project is composed of 2 telescopes and 3 instruments, located in Teide Observatory (Tenerife, Spain).
After the successful delivery of the first telescope (operative since 2012), Idom is currently involved on the turn key supply of the second telescope (phase II). The work started in June 2013 and it will be completed in a challenging period of 12 months (operative at the beginning of July 2014), including design, factory assembly and testing, transport and final commissioning on site.
This second unit will improve the opto-mechanical performance and maintainability. The telescope will have an unlimited rotation capacity in azimuth axis and a range of movement between 25°-95° in elevation axis. An integrated rotary joint will transmit fluid, power and signal to the rotary elements. The pointing and tracking accuracy will be significantly below to specification: 1.76 arcmin and 44 arcsec, respectively.
This project completes Idom´s contribution during phase I, which also comprises the integration and functional tests for the 5 polarimeters of the first instrument in Bilbao headquarters, and the design and supervision of the building which protects both telescopes, including the installation and commissioning of the mechanism for shutters aperture.
Solar Telescopes I
Construction status of the Daniel K. Inouye Solar Telescope
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The Daniel K. Inouye Solar Telescope (DKIST, renamed in December 2013 from the Advanced Technology Solar
Telescope) will be the largest solar facility built when it begins operations in 2019. Designed and developed to meet the
needs of critical high resolution and high sensitivity spectral and polarimetric observations of the Sun, the observatory
will enable key research for the study of solar magnetism and its influence on the solar wind, flares, coronal mass
ejections and solar irradiance variations. The 4-meter class facility will operate over a broad wavelength range (0.38 to
28 microns, initially 0.38 to 5 microns), using a state-of-the-art adaptive optics system to provide diffraction-limited
imaging and the ability to resolve features approximately 25 km on the Sun. Five first-light instruments will be available
at the start of operations: Visible Broadband Imager (VBI; National Solar Observatory), Visible SpectroPolarimeter
(ViSP; NCAR High Altitude Observatory), Visible Tunable Filter (VTF; Kiepenheuer Institut für Sonnenphysik),
Diffraction Limited Near InfraRed SpectroPolarimeter (DL-NIRSP; University of Hawai’i, Institute for Astronomy) and
the Cryogenic Near InfraRed SpectroPolarimeter (Cryo-NIRSP; University of Hawai’i, Institute for Astronomy).
As of mid-2014, the key subsystems have been designed and fabrication is well underway, including the site
construction, which began in December 2012. We provide an update on the development of the facilities both on site at
the Haleakalā Observatories on Maui and the development of components around the world. We present the overall
construction and integration schedule leading to the handover to operations in mid 2019. In addition, we outline the
evolving challenges being met by the project, spanning the full spectrum of issues covering technical, fiscal, and
geographical, that are specific to this project, though with clear counterparts to other large astronomical construction
projects.
The progress of Chinese Giant Solar Telescope
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Chinese Giant Solar Telescope (CGST) is the next generation ground-based solar telescope which was formally listed into the National Plans of Major Science and Technology Infrastructures. We have got series progresses of CGST in the recent years, from site testing to detailed designs. CGST is currently designed to be an 8m Ring Solar Telescope (RST). As an 8-meter solar telescope, the designing of CGST still faces some serious problems, although the ring structure is propitious to the thermo controlling and the high precision magnetic field measuring. The active control and the optical system of CGST are introduced. Then, simulations and the key calculations of the telescope, including the polarization analysis and the thermo calculation result are displayed. The present site testing methods and some results are introduced too. Finally, as the comparison in science and technology, the Chinese space solar telescope plans, such as the Deep Space Solar Observatory (DSO) and its progress are simply introduced.
DKIST enclosure fabrication factory assembly and testing
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After successfully finishing the design of the Advanced Technology Solar Telescope (ATST) Enclosure early in 2012, AEC IDOM, in close collaboration with the ATST Project Office, has successfully fabricated the enclosure’s main components (structure, mechanisms, controls, and cladding), assembled them in the factory, and performed the factory acceptance tests. The factory assembly and testing of the enclosure has allowed the team to verify the correct integration and performance of structures, mechanisms, and controls. Furthermore, the assembly and verification procedures to be used for the enclosure re-assembly at the Haleakala High Altitude Observatory Site have been tested and refined in order to reduce risk during the enclosure site construction, an overall project critical path activity. The Advanced Technology Solar Telescope (ATST), recently renamed as the Daniel K. Inouye Solar Telescope (DKIST) will be the largest solar telescope in the world, with unprecedented abilities to view details of the sun. Using adaptive optics technology, DKIST will be able to provide the sharpest views ever taken of the solar surface, which will allow scientists to learn even more about the Sun and solar-terrestrial interactions. The DKIST Enclosure is unique in that it positions the optical system’s first aperture stop and tracks the sun’s motion with millimeter-level accuracy, protecting observatory components from excess insolation. Its azimuth and altitude systems are driven by mechanisms especially designed to perform smooth operations at tracking speeds.
1.8-M solar telescope in China: the CLST
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For better understanding and forecasting of the solar activity and the corresponding impacts human technologies and life on earth, the high resolution observations for Sun are needed. The Chinese Large Solar Telescope (CLST) with 1.8 m aperture is being built. The CLST is a classic Gregorian configuration telescope with open structure, alt-azimuth mount, retractable dome, and a large mechanical de-rotator. The optical system with all reflective design has the field of view of larger than 3 arc-minute. The 1.8 m primary mirror is a honeycomb sandwiches fused silica lightweight mirror with ULE material and active cooling. The adaptive optics system will be developed to provide the capability for diffraction limited observations at visible wavelengths. The CLST design and development phase began in 2011 and 2012 respectively. We plan for the CLST’s starting of commission in 2017. A multi-wavelength tomographic imaging system with seven wavelengths range from visible to near-infrared wavelength is considered as the first light scientific instruments. In this paper the main system configuration and the corresponding post focal instruments are described. Furthermore, the latest progress and current status of the CLST are also reported.
Solar Telescopes II
Performance verification of the DKIST Mount and Coudé Laboratory
Oliver Dreyer,
Alexei Ippa,
Steffen Seubert,
et al.
Show abstract
The former Advanced Technology Solar Telescope (ATST), now renamed to Daniel K. Inouye Solar Telescope (DKIST) will be the largest solar telescope in the world – with a 4m aperture primary mirror and a 16m diameter co-rotating “Coudé” laboratory located within the telescope pier. Both, the telescope mount and the Coudé laboratory use for their azimuth axis a new kind of bearing technology, so called R-guides, which minimize later maintenance efforts, avoid energy consumption and the risk of oil spill of conventional hydrostatic bearings. The paper describes the integrated modeling approach for the verification of the challenging DKIST jitter requirement of 0.075 arcsec rms with the new bearing system, including initial system engineering guidelines, finite element evaluations, system dynamics and end-to-end jitter simulations, factory tests of subsystems and components, and the commissioning of the trial assembled Coudé table and later the telescope mount.
AIV, Commissioning and Early Operations
The automated planet finder at Lick Observatory
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By July 2014, the Automated Planet Finder (APF) at Lick Observatory on Mount Hamilton will have completed its first year of operation. This facility combines a modern 2.4m computer-controlled telescope with a flexible development environment that enables efficient use of the Levy Spectrometer for high cadence observations. The Levy provides both sub-meter per second radial velocity precision and high efficiency, with a peak total system throughput of 24%. The modern telescope combined with efficient spectrometer routinely yields over 100 observations of 40 stars in a single night, each of which has velocity errors of 0.7 to 1.4 meters per second, all with typical seeing of < 1 arc second full-width-half-maximum (FWHM). The whole observing process is automated using a common application programming interface (API) for inter-process communication which allows scripting to be done in a variety of languages (Python, Tcl, bash, csh, etc.) The flexibility and ease-of-use of the common API allowed the science teams to be directly involved in the automation of the observing process, ensuring that the facility met their requirements. Since November 2013, the APF has been routinely conducting autonomous observations without human intervention.
Status and performance of the Discovery Channel Telescope from commissioning into early science operations
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Lowell Observatory's Discovery Channel Telescope is a 4.3m telescope designed and constructed for optical and near infrared astronomical observation. It is equipped with a cube capable of carrying five instruments and the wave front sensing and guider systems at the f/6.1 RC focus. We report on the overall operations methods for the facility, including coordination of day and night activities, and then cover pointing, and unguided and guided tracking performance of the mount. We also discuss the implementation and performance of the open loop model for, and manual wavefront sensing and correction with the active optics system. We conclude with a report on the early integrated image quality and science performance of the facility using the first science instrument, the Large Monolithic Imager.
Commissioning and science verification of the 2m-Fraunhofer Wendelstein Telescope
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The commissioning of the telescope and its first instrument, a Nasmyth port mounted 0.5 degree CCD mosaic imager, started in November 2013. We will report about the results of astronomical tests of the integrated system including the achieved optical quality across the field of view, pointing and tracking quality and operational experiences with the observatory system. The special design features of this alt-az telescope are its compactness and the low-ghost wide field optics (0.7o f.o.v. diameter), and we will briefly report on the lessons learned especially for these special features. We will present an outlook on the further commissioning including the additional instruments which are all under construction or already finalized.
OAJ 2.6-m survey telescope: assembly, integration, and testing
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AMOS S.A. has developed a 2.6 m wide field telescope for the “Observatorio Astrofisico de Javalambre”. The leading edge performance of this telescope has not only required an extensive work of design, analysis and optimization but also a mastered fabrication process and an appropriate AIV plan. The telescope has successfully passed the factory test and is installed at the observatory on the “Pico del Buitre” in Spain. This paper aims to present the philosophy of the test, the results and the current status after installation. AMOS has gained since more than 30 years a huge experience in testing small and large instruments, including optical testing, alignment, mechanical static, dynamic measurements, system identification, etc. It is this combination of various techniques of measurement that produce accurate and reliable results which are a key element of a successful project.
Telescope Structures, Bearings and Drives
Preliminary design study of the TMT Telescope structure system: overview
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We present an overview of the preliminary design of the Telescope Structure System (STR) of Thirty Meter Telescope (TMT). NAOJ was given responsibility for the TMT STR in early 2012 and engaged Mitsubishi Electric Corporation (MELCO) to take over the preliminary design work. MELCO performed a comprehensive preliminary design study in 2012 and 2013 and the design successfully passed its Preliminary Design Review (PDR) in November 2013 and April 2014. Design optimizations were pursued to better meet the design requirements and improvements were made in the designs of many of the telescope subsystems as follows: 1. 6-legged Top End configuration to support secondary mirror (M2) in order to reduce deformation of the Top End and to keep the same 4% blockage of the full aperture as the previous STR design. 2. “Double Lower Tube” of the elevation (EL) structure to reduce the required stroke of the primary mirror (M1) actuators to compensate the primary mirror cell (M1 Cell) deformation caused during the EL angle change in accordance with the requirements. 3. M1 Segment Handling System (SHS) to be able to make removing and installing 10 Mirror Segment Assemblies per day safely and with ease over M1 area where access of personnel is extremely difficult. This requires semi-automatic sequence operation and a robotic Segment Lifting Fixture (SLF) designed based on the Compliance Control System, developed for controlling industrial robots, with a mechanism to enable precise control within the six degrees of freedom of position control. 4. CO2 snow cleaning system to clean M1 every few weeks that is similar to the mechanical system that has been used at Subaru Telescope. 5. Seismic isolation and restraint systems with respect to safety; the maximum acceleration allowed for M1, M2, tertiary mirror (M3), LGSF, and science instruments in 1,000 year return period earthquakes are defined in the requirements. The Seismic requirements apply to any EL angle, regardless of the operational status of Hydro Static Bearing (HSB) system and stow lock pins. In order to find a practical solution, design optimization study for seismic risk mitigation was carried out extensively, including the performing of dynamic response analyses of the STR system under the time dependent acceleration profile of seven major earthquakes. The work is now moving to the final design phase from April 2014 for two years.
New finite element models and seismic analyses of the telescopes at W.M. Keck Observatory
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On 15 October 2006 a large earthquake damaged both telescopes at Keck observatory resulting in weeks of observing downtime. A significant portion of the downtime was attributed to recovery efforts repairing damage to telescope bearing journals, radial pad support structures and encoder subsystems. Inadequate damping and strength in the seismic restraint design and the lack of break-away features on the azimuth radial pads are key design deficiencies. In May, 2011 a feasibility study was conducted to review several options to enhance the protection of the telescopes with the goal to minimize the time to bring the telescopes back into operation after a large seismic event. At that time it was determined that new finite element models of the telescope structures were required to better understand the telescope responses to design earthquakes required by local governing building codes and the USGS seismic data collected at the site on 15 October 2006. These models were verified by comparing the calculated natural frequencies from the models to the measured frequencies obtained from the servo identification study and comparing the time history responses of the telescopes to the October 2006 seismic data to the actual observed damages. The results of two finite element methods, response spectrum analysis and time history analysis, used to determine seismic demand forces and seismic response of each telescope to the design earthquakes were compared. These models can be used to evaluate alternate seismic restraint design options for both Keck telescopes.
Wheel drives for large telescopes: save the cost and keep the performance over hydrostatic bearings
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The use of steel wheels on steel tracks has been around since steel was invented, and before that it was iron wheels on iron tracks. Not to be made obsolete by the passage of time, this approach for moving large objects is still valid, even optimal, but the detailed techniques for achieving high performance and long life have been much improved. The use of wheel-and-track designs has been very popular in radio astronomy for the largest of the large radio telescopes (RT), including such notables as the 305m Arecibo RT, the 100m telescopes at Effelsberg, Germany (at 3600 tonnes) and the Robert C. Byrd, Greenbank Telescope (GBT, 7600 tonnes) at Greenbank, West Virginia. Of course, the 76m Lovell Telescope at Jodrell Bank is the grandfather of all large aperture radio telescopes that use wheel drives. Smaller sizes include NRAO’s Very Long Baseline Array (VLBA) telescopes at 25m and others. Wheel drives have also been used on large radars of significance such as the 410 tonne Ground Based Radar-Prototype (GBR-P) and the 150 foot (45.7m) Altair Radar, and the 2130 tonne Sea Based X-Band Radar (SBX). There are also many examples of wheel driven communications antennas of 18 meters and larger. All of these instruments have one thing in common: they all use steel wheels that run in a circle on one or more flat, level, steel tracks.
This paper covers issues related to designing for wheel driven systems. The intent is for managing motion to sub arc-second levels, and for this purpose it is primary for the designer to manage measurement and alignment errors, and to establish repeatability through dimensional control, structural and drive stiffness management, adjustability and error management. In a practical sense, there are very few, if any, fabricators that can machine structural and drive components to sufficiently small decimal places to matter. In fact, coming within 2-3 orders of magnitude of the precision needed is about the best that can be expected. Further, it is incumbent on the design team to develop the servo control system features, correction algorithms and structural features in concert with each other. Telescope designers are generally adept at many of these practices, so the scope of this paper is not that, but is limited to those items that pertain to a precision wheel driven system.
Finite element analyses of CCAT preliminary design
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This paper describes the development of the CCAT telescope finite element model (FEM) and the analyses performed to support the preliminary design work. CCAT will be a 25 m diameter telescope operating in the 0.2 to 2 mm wavelength range. It will be located at an elevation of 5600 m on Cerro Chajnantor in Northern Chile, near ALMA. The telescope will be equipped with wide-field cameras and spectrometers mounted at the two Nasmyth foci. The telescope will be inside an enclosure to protect it from wind buffeting, direct solar heating, and bad weather. The main structures of the telescope include a steel Mount and a carbon-fiber-reinforced-plastic (CFRP) primary truss. The finite element model developed in this study was used to perform modal, frequency response, seismic response spectrum, stress, and deflection analyses of telescope. Modal analyses of telescope were performed to compute the structure natural frequencies and mode shapes and to obtain reduced order modal output at selected locations in the telescope structure to support the design of the Mount control system. Modal frequency response analyses were also performed to compute transfer functions at these selected locations. Seismic response spectrum analyses of the telescope subject to the Maximum Likely Earthquake were performed to compute peak accelerations and seismic demand stresses. Stress analyses were performed for gravity load to obtain gravity demand stresses. Deflection analyses for gravity load, thermal load, and differential elevation drive torque were performed so that the CCAT Observatory can verify that the structures meet the stringent telescope surface and pointing error requirements.
Observatory Facilities and Enclosures
Approach to the E-ELT dome and main structure challenges
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The E-ELT as a whole could be classified as an extremely challenging project. More precisely, it should be defined as an array of many different sub-challenges, which comprise technical, logistical and managerial matters. This paper reviews some of these critical challenges, in particular those related to the Dome and the Main Structure, suggesting ways to face them in the most pragmatic way possible. Technical challenges for the Dome and the Main Structure are mainly related to the need to upscale current design standards to an order of magnitude larger design. Trying a direct design escalation is not feasible; it would not work. A design effort is needed to cross hybridize current design standards with technologies coming from other different applications. Innovative design is therefore not a wish but a must. And innovative design comes along with design risk. Design risk needs to be tackled from two angles: on the one hand through thorough design validation analysis and on the other hand through extensive pre-assembly and testing. And, once again, full scale integrated pre-assembly and testing of extremely large subsystems is not always possible. Therefore, defining a comprehensive test plan for critical components, critical subsystems and critical subassemblies becomes essential. Logistical challenges are linked to the erection site. Cerro Armazones is a remote site and this needs to be considered when evaluating transport and erection requirements. But it is not only the remoteness of the site that needs to be considered. The size of both Dome and Main Structure require large construction cranes and a well defined erection plan taking into account pre-assembly strategies, limited plan area utilization, erection sequence, erection stability during intermediate stages and, very specifically, efficient coordination between the Dome and the Main Structure erection processes. Managerial issues pose another set of challenges in this project. Both the size of the project and its special technical characteristics require specific managerial skills. Due to the size of the project it becomes essential to effectively manage and integrate a large number of suppliers and fabricators, of very different nature and geographically distributed. Project management plans need to cope with this situation. Also, extensive on site activities require intensive on site organization in line with large construction management strategies. Finally, the technical edge of the project requires deep technical understanding at management level in order to be able to take sound strategic decisions throughout the project in terms of the overall project quality, cost and schedule.
GMT site: facilities and enclosure design overview
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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. This paper provides an update and overview of the ongoing efforts for the GMT site, infrastructure, facilities and enclosure design. The paper provides insight of the proposed systems, trade studies and approach resulting in the current design solution.
The Observatorio Astrofísico de Javalambre: engineering of observatory facilities and physical infrastructure, goals, and current status
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The Observatorio Astrofísico de Javalambre in Spain is a new astronomical facility particularly conceived for carrying out large sky surveys with two unprecedented telescopes of unusually large fields of view: the JST/T250, a 2.55m telescope of 3deg field of view, and the JAST/T80, an 83cm telescope of 2deg field of view. The most immediate objective of the two telescopes for the next years is carrying out two unique photometric surveys of several thousands square degrees, J-PAS[9][14][16] and J-PLUS [14][16], each of them with a wide range of scientific applications, like e.g. large structure cosmology and Dark Energy, galaxy evolution, supernovae, Milky Way structure, exoplanets, among many others. To do that, JST and JAST will be equipped with panoramic cameras under development within the J-PAS collaboration, JPCam and T80Cam respectively, which make use of large format (~ 10k x 10k) CCDs covering the entire focal plane. This paper describes in detail the engineering development of the overall facilities and infrastructures for the robotic observatory and a global overview of current status and future actions to perform from engineering point of view.
Measurement and Control of Telescope Vibration
VLTI-UT vibrations effort and performances
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The ESO Very Large Telescope Interferometer (VLTI) using the Unit Telescope (UT) was strongly affected by vibrations since the first observations. Investigation by ESO on that subject had started in 2007, with a considerable effort since mid 2008. An important number of investigations on various sub-systems (On telescope: Guiding, Passive supports, Train Coude, insulation of electronics cabinets; On Instruments: dedicated campaign on each instruments with a special attention on the ones equipped with Close Cycle Cooler) were realized. Vibrations were not only recorded and analyzed using the usual accelerometers but also using on use sub-systems as InfRared Image Sensor (IRIS) and Multiple Applications Curvature Adaptive Optics (MACAO) and using a specific tool developed for vibrations measurements Mirror vibrAtion Metrology systeM for the Unit Telescope (MAMMUT). Those tools and systems have been used in order to improve the knowledge on telescope by finding sources. The sources whenever it was possible were damped. As known for years, instruments are still the principal sources of vibrations, for the majority of the UT. A special test in which 2 UTs instruments were completely shut down was realized to determine the minimum Optical Path Length (OPL) achievable. Vibrations is now a part of the instruments interface document and during the installation of any new instrument (KMOS) or system (AOF) a test campaign is realized. As a result some modifications (damping of CCC) can be asked in case of non-compliance. To ensure good operational conditions, levels of vibrations are regularly recorded to control any environmental change.
Implementation of an active vibration damping system for the SOFIA telescope assembly
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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 image stability goal for SOFIA is 0.2 arc-seconds. An active damping control system is being developed for SOFIA to reduce image jitter and degradation due to resonance of the telescope assembly. We describe the vibration control system design and implementation in hardware and software. The system’s unique features enabling system testing, control system design, and online health monitoring will also be presented.
Equipment vibration budget for the TMT
Show abstract
Vibration from equipment mounted on the telescope and in summit support buildings has been a source of performance degradation at existing observatories, for adaptive optics performance in particular. To ensure that that the total optical performance degradation due to vibration is less than the corresponding optical error budget allocation, a vibration budget has been created that specifies allowable force levels from each source of vibration in the observatory (e.g., pumps, chillers, cryocoolers, etc.). In addition to its primary purpose, the vibration budget allows us to make design trade-offs, specify isolation requirements for equipment, and tighten or widen individual equipment vibration specifications as necessary. Defining this budget relies on two types of information: (i) vibration transmission analysis that determines the optical consequences that result from forces applied at different locations in the Observatory and at different frequencies; and (ii) initial estimates for plausible source amplitudes in order to allocate force budgets to different sources in the most realistic and cost-effective manner. The transmission of vibration from sources through to their optical consequences uses the finite element model of the telescope structure, including primary mirror seg- ment models and control loops. Both the image jitter and higher-order deformations due to M1 segment motion are included, along with the spatial- and temporal-correctability by the adaptive optics system. Measurements to support estimates of plausible soil transmissibility are described in a companion paper. As the detailed design progresses and more information is available regarding what is achievable at realistic cost, the vibration budget will be refined.
Poster Session
Modeling and simulation of a 6-DOF parallel platform for telescope secondary mirror
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The 6-DOF parallel platform in this paper is a kind of Stewart platform. It can be used as supporting structure for telescope secondary mirror. In order to adapt the special dynamic environment of the telescope secondary mirror and to be installed in extremely narrow space, a unique parallel platform is designed. PSS Stewart platform and SPS Stewart platform are analyzed and compared. Then the PSS Stewart platform is chosen for detailed design. The virtual prototyping model of the parallel platform is built. The model is used for the analysis and calculation of multi-body dynamics. With the help of ANSYS, the finite element model of the platform is built and then the analysis is performed. According to the above analysis the experimental prototype of the platform is built.
Active optics operations at the Large Binocular Telescope
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The Large Binocular Telescope (LBT) has three pairs of Active Optics (aO) systems used to collimate the telescope. We will describe the aO systems and their uses at the various focal stations, discuss their similarities and differences, and evaluate and compare their operational performances (i.e. with guide stars having different distances from the optical axis and guide stars of various brightness). We will also describe their performance with differing seeing conditions.
A laser tracker active optics system for the Large Binocular Telescope
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The Large Binocular Telescope consists of two 8.4m telescopes on a common mount. Its current active optics system uses measured mechanical deflections of its optics to compensate for misalignment due to changes in telescope elevation angle and analysis of stellar images to calculate compensating optic displacements. The process is iterated until the inferred wavefront is within tolerance. Due to the asymmetry of the distribution of thermal mass of the telescope structure, thermal gradients during the night cause the current active optics alignment system to require extra iterations to achieve alignment. A system is proposed which uses a laser tracker to measure optic misalignment resulting from the additional thermal influence. This provides a single measurement of relative optic misalignment and reduces the number of iterations required to achieve collimation. A single laser tracker location can be used to measure the rigid body locations of the primary mirror, secondary mirror, prime focus camera, and flat tertiary mirror for both telescopes. A set of reference points on the telescope structure provides a common coordinate system for measurements of optic locations on each side and to assist with binocular copointing. The laser tracker measures the displacement of the optics relative to their locations measured when the telescope is in collimation. Practical considerations integrating the system with the telescope will be discussed, as well as its expected performance.
Active optics control development at the LBT
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The Large Binocular Telescope (LBT) is built around two 8.4 m-diameter primary mirrors placed with a centerline separation of 14.4 m in a common altitude/azimuth mount. Each side of the telescope can utilize a deployable prime focus instrument; alternatively, the beam can be directed to a Gregorian instrument by utilizing a deployable secondary mirror. The direct-Gregorian beam can be intercepted and redirected to several bent-Gregorian instruments by utilizing a deployable tertiary mirror. Two of the available bent-Gregorian instruments are interferometers, capable of coherently combining the beams from the two sides of the telescope. Active optics can utilize as many as 26 linearly independent degrees of freedom to position the primary, secondary and tertiary mirrors to control optical collimation while the telescope operates in its numerous observing modes. Additionally, by applying differential forces at 160 locations on each primary mirror, active optics controls the primary mirror figure. The authors explore the challenges associated with collimation and primary mirror figure control at the LBT and outline the ongoing related development aimed at optimizing image quality and preparing the telescope for interferometric operations.
Challenges of the opto-mechanical conceptual design of a small far-IR balloon experiment
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Astronomers require more and more precise instruments for their observations. Here we describe the challenges encountered in the optical and mechanical designs of the CIDRE (Campagne d’Identification du Deutérium par Réception hEtérodyne) project, which was to be flown on a high altitude balloon at 40 km. The project aimed to measure the transitions of the HD molecule at 2.675 THz band and some other THz lines in our galaxy. The astronomers asked to fly the biggest possible telescope in a standard balloon gondola, and required high pointing accuracy (7 arcsec). In January 2014, the technical project, including the optical and mechanical designs, was evaluated to be of excellent standard, but, for all that, the project was cancelled because of financial constraints. Nevertheless the phase A study allowed us to identify the optical and mechanical challenges of balloon projects and we were able to come up with a simple design, that fulfilled all the requirements. The 900 mm primary mirror and the rest of the optics were designed to be supported by a sandwich-panel composite structure with carbon epoxy skins and aluminum honeycomb core to improve the mechanical stiffness and the thermal behavior of the instrument without increasing its mass or its complexity.
In this paper, we describe the optical design and the mechanical structure of the instrument. Finite element analysis is carried out to estimate the gravitational flexure and the thermal deformations, which can both harm the pointing accuracy and the performances of the instrument. These simulations show that the proposed design would fulfill the different requirements (pointing accuracy, landing survival as well as the dynamic behavior).
Attitude determination for balloon-borne experiments
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An attitude determination system for balloon-borne experiments is presented. The system provides pointing information in azimuth and elevation for instruments flying on stratospheric balloons over Antarctica. In-flight attitude is given by the real-time combination of readings from star cameras, a magnetometer, sun sensors, GPS, gyroscopes, tilt sensors and an elevation encoder. Post-flight attitude reconstruction is determined from star camera solutions, interpolated by the gyroscopes using an extended Kalman Filter. The multi-sensor system was employed by the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol), an experiment that measures polarized thermal emission from interstellar dust clouds. A similar system was designed for the upcoming flight of Spider, a Cosmic Microwave Background polarization experiment. The pointing requirements for these experiments are discussed, as well as the challenges in designing attitude reconstruction systems for high altitude balloon flights. In the 2010 and 2012 BLASTPol flights from McMurdo Station, Antarctica, the system demonstrated an accuracy of < 5’ rms in-flight, and < 5” rms post-flight.
Environmental testing for new SOFIA flight hardware
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New flight hardware for the Stratospheric Observatory for Infrared Astronomy (SOFIA) has to be tested to prove its safety and functionality and to measure its performance under flight conditions. Although it is not expected to experience critical issues inside the pressurized cabin with close-to-normal conditions, all equipment has to be tested for safety margins in case of a decompression event and/or for unusual high temperatures, e.g. inside an electronic unit caused by a malfunction as well as unusual high ambient temperatures inside the cabin, when the aircraft is parked in a desert. For equipment mounted on the cavity side of the telescope, stratospheric conditions apply, i.e., temperatures from -40 °C to -60°C and an air pressure of about 0.1 bar. Besides safety aspects as not to endanger personnel or equipment, new hardware inside the cavity has to function and to perform to specifications under such conditions. To perform these tests, an environmental test laboratory was set up at the SOFIA Science Center at the NASA Ames Research Center, including a thermal vacuum chamber, temperature measurement equipment, and a control and data logging workstation. This paper gives an overview of the test and measurement equipment, shows results from the commissioning and characterization of the thermal vacuum chamber, and presents examples of the component tests that were performed so far. To test the focus position stability of optics when cooling them to stratospheric temperatures, an auto-collimation device has been developed. We will present its design and results from measurements on commercial off-the-shelf optics as candidates for the new Wide Field Imager for SOFIA as an example.
BRRISON IR Camera (BIRC)
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BIRC is a multispectral infrared imager designed to operate in 8 bandpasses between 2.5 and 5.0 μm utilizing a cryocooled
HgCdTe detector and Ø80 cm telescope. The instrument was flown on a ballooncraft platform and operated in a
near-space environment. BIRC was designed to measure the water and CO2 emissions from the comet ISON. The system
produces an f/4 image over a field of view of 3 arcminutes, and employs shift/co-add algorithms to observe dim objects.
An innovative thermal design holds the system components in separate vacuum and atmospheric zones which are
independent of the neighboring instrument deck. This paper summarizes the design, test and integration of the BIRC
instrument.
A prototype for the real-time analysis of the Cherenkov Telescope Array
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The Cherenkov Telescope Array (CTA) observatory will be one of the biggest ground-based very-high-energy (VHE) γ-
ray observatory. CTA will achieve a factor of 10 improvement in sensitivity from some tens of GeV to beyond 100 TeV
with respect to existing telescopes.
The CTA observatory will be capable of issuing alerts on variable and transient sources to maximize the scientific return.
To capture these phenomena during their evolution and for effective communication to the astrophysical community,
speed is crucial. This requires a system with a reliable automated trigger that can issue alerts immediately upon detection
of γ-ray flares. This will be accomplished by means of a Real-Time Analysis (RTA) pipeline, a key system of the CTA
observatory. The latency and sensitivity requirements of the alarm system impose a challenge because of the anticipated
large data rate, between 0.5 and 8 GB/s. As a consequence, substantial efforts toward the optimization of highthroughput
computing service are envisioned.
For these reasons our working group has started the development of a prototype of the Real-Time Analysis pipeline. The
main goals of this prototype are to test: (i) a set of frameworks and design patterns useful for the inter-process
communication between software processes running on memory; (ii) the sustainability of the foreseen CTA data rate in
terms of data throughput with different hardware (e.g. accelerators) and software configurations, (iii) the reuse of nonreal-
time algorithms or how much we need to simplify algorithms to be compliant with CTA requirements, (iv) interface
issues between the different CTA systems. In this work we focus on goals (i) and (ii).
SST-GATE telescope: an innovative dual-mirror prototype for the Cherenkov Telescope Array
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The Observatoire de Paris is involved in the Cherenkov Telescope Array (CTA) project by designing and constructing on
the site of Meudon a Small Size Telescope prototype, named SST-GATE, in collaboration with the CHEC team
(Compact High Energy Camera) which is providing the camera. The telescope structure is based on the Schwarzschild-
Couder optical design which has never been adopted before in the design of a ground-based telescope. This concept
allows a larger field of view and cheaper and smaller telescope and camera design with improved performance compared
to the Davies-Cotton design traditionally used in very high energy gamma-ray telescopes.
The SST-GATE telescope has been designed with the prime objectives of being light, versatile and simple to assemble with a minimal maintenance cost. This papers aims at reviewing the SST-GATE telescope structure from mechanics to optics along with the control command architecture; several innovative developments implemented within the design are discussed. Updates of the project status and perspectives are made.
SST dual-mirror telescopes for the Cherenkov Telescope Array
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The Cherenkov Telescope Array (CTA) is an international collaboration that aims to create the world's foremost very high energy gamma-ray observatory, composed of large, medium and small size telescopes (SST). The SSTs will be the most numerous telescopes on site and will focus on capturing the rarer highest energy photons. Three prototypes of SST are designed and currently under construction; two of them, ASTRI and SST-GATE, have been designed, based on a dual-mirror Schwarzschild-Couder (SC) design which has never been built before for any astronomical observation. The SC optical design allows for a small plate scale, a wide field of view and a lightweight cameras aiming to minimize the cost of SST telescopes in order to increase their number in the array.
The aim of this article is to report the progress of the two telescope projects prototyping telescope structures and cameras for the Small Size Telescopes for CTA. After a discussion of the CTA project and its scientific objectives, the performance of the SC design is described, with focus on the specific designs of SST-GATE and ASTRI telescopes. The design of both prototypes and their progress is reported in the current prototyping phase. The designs of Cherenkov cameras, CHEC and ASTRI, to be mounted on these telescopes are discussed and progresses are reported.
Performance of the small size telescope sub-array of the Cherenkov Telescope Array observatory
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The southern part of the Cherenkov Telescope Array (CTA) observatory will consist of at least three types of telescopes: large size, medium size and small size telescopes. Massive Monte Carlo simulations have been performed using the European Grid Infrastructure to analyze the performance of this array. We present the results of these simulations for a sub-array of small size telescopes of the Davies-Cotton type. Such a telescope, called SST-1M, is currently being proposed for the CTA observatory by a group of Polish and Swiss institutions. SST-1M will have a mirror of 4m diameter and it will be equipped with a fully digital camera based on silicon photodetectors. We present the analysis of the sub-array sensitivity, angular resolution, and energy resolution to demonstrate the fulfillment of the requirements of the CTA Consortium. To verify the results obtained in numerical simulations a construction of a mini array of five SST-1M telescopes is planned. We also present the performance of such a mini array and discuss the prospects of its scientific program.
Status of the photomultiplier-based FlashCam camera for the Cherenkov Telescope Array
G. Pühlhofer,
C. Bauer,
F. Eisenkolb,
et al.
Show abstract
The FlashCam project is preparing a camera prototype around a fully digital FADC-based readout system, for the medium sized telescopes (MST) of the Cherenkov Telescope Array (CTA). The FlashCam design is the first fully digital readout system for Cherenkov cameras, based on commercial FADCs and FPGAs as key components for digitization and triggering, and a high performance camera server as back end. It provides the option to easily implement different types of trigger algorithms as well as digitization and readout scenarios using identical hardware, by simply changing the firmware on the FPGAs. The readout of the front end modules into the camera server is Ethernet-based using standard Ethernet switches and a custom, raw Ethernet protocol. In the current implementation of the system, data transfer and back end processing rates of 3.8 GB/s and 2.4 GB/s have been achieved, respectively. Together with the dead-time-free front end event buffering on the FPGAs, this permits the cameras to operate at trigger rates of up to several ten kHz. In the horizontal architecture of FlashCam, the photon detector plane (PDP), consisting of photon detectors, preamplifiers, high voltage-, control-, and monitoring systems, is a self-contained unit, mechanically detached from the front end modules. It interfaces to the digital readout system via analogue signal transmission. The horizontal integration of FlashCam is expected not only to be more cost efficient, it also allows PDPs with different types of photon detectors to be adapted to the FlashCam readout system. By now, a 144-pixel mini-camera" setup, fully equipped with photomultipliers, PDP electronics, and digitization/ trigger electronics, has been realized and extensively tested. Preparations for a full-scale, 1764 pixel camera mechanics and a cooling system are ongoing. The paper describes the status of the project.
Schwarzschild-Couder Telescope for The Cherenkov Telescope Array
Kevin J. Meagher
Show abstract
The Cherenkov Telescope Array (CTA) is the next major ground-based observatory for gamma-ray astronomy. With CTA gamma-ray sources will be studied in the very-high energy gamma-ray range of a few tens of GeV to 100TeV with up to ten times better sensitivity than available with current generation instruments. We discuss the proposed US contribution to CTA that comprises imaging atmospheric Cherenkov telescope with Schwarzschild-Couder (SC) optics. Key features of the SC telescope are a wide field of view of eight degrees, a finely pixelated camera with silicon photomultipliers as photon detectors, and a compact and power efficient 1 GS/s readout. The progress in both the optical system and camera development are discussed in this paper.
Thermal design and performance of the balloon-borne large aperture submillimeter telescope for polarimetry BLASTPol
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We present the thermal model of the Balloon-borne Large-Aperture Submillimeter Telescope for Polarimetry (BLASTPol). This instrument was successfully own in two circumpolar flights from McMurdo, Antarctica in 2010 and 2012. During these two flights, BLASTPol obtained unprecedented information about the magnetic field in molecular clouds through the measurement of the polarized thermal emission of interstellar dust grains. The thermal design of the experiment addresses the stability and control of the payload necessary for this kind of measurement. We describe the thermal modeling of the payload including the sun-shielding strategy. We present the in-flight thermal performance of the instrument and compare the predictions of the model with the temperatures registered during the flight. We describe the difficulties of modeling the thermal behavior of the balloon-borne platform and establish landmarks that can be used in the design of future balloon-borne instruments.
Development of a 30-cm submillimeter-wave telescope for the operation at Dome Fuji in Antarctica
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We have developed a 30-cm submillimeter-wave telescope intended to survey the Milky Way in 500 GHz emission lines at the Dome Fuji station in Antarctic plateau. Transportability and low power consumption are required while keeping low system noise temperature for the operation in Antarctica. The telescope is designed to be divided into five components and to operate with less than 2.5 kW of electric power. Its receiver noise temperature is less than 85 K in SSB at 461 and 492 GHz. We succeeded in operating the telescope at -30◦C in laboratory that is a typical temperature of the Dome Fuji in summer.
Wide field corrector for the KMTNet telescope
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We present the design, assembly, alignment, and verification process of the wide field corrector for the Korea Microlensing Telescope Network (KMTNet) 1.6 meter optical telescope. The optical configuration of the KMTNet telescope is prime focus, having a wide field corrector and the CCD camera on the topside of Optical Tube Assembly (OTA). The corrector is made of four lenses designed to have all spherical surfaces, being the largest one of 552 mm physical diameter. Combining with a purely parabolic primary mirror, this optical design makes easier to fabricate, to align, and to test the wide field optics. The centering process of the optics in the lens cell was performed on a precision rotary table using an indicator. After the centering, we mounted three large and heavy lenses on each cell by injecting the continuous Room Temperature Vulcanizing (RTV) silicon rubber bonding via a syringe.
Stress polishing demonstrator for ELT M1 segments and industrialization
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After two years of research and development under ESO support, LAM and Thales SESO present the results of their experiment for the fast and accurate polishing under stress of ELT 1.5 meter segments as well as the industrialization approach for mass production. Based on stress polishing, this manufacturing method requires the conception of a warping harness able to generate extremely accurate bending of the optical surface of the segments during the polishing. The conception of the warping harness is based on finite element analysis and allowed a fine tuning of each geometrical parameter of the system in order to fit an error budget of 25nm RMS over 300μm of bending peak to valley. The optimisation approach uses the simulated influence functions to extract the system eigenmodes and characterise the performance. The same approach is used for the full characterisation of the system itself. The warping harness has been manufactured, integrated and assembled with the Zerodur 1.5 meter segment on the LAM 2.5meter POLARIS polishing facility. The experiment consists in a cross check of optical and mechanical measurements of the mirrors bending in order to develop a blind process, ie to bypass the optical measurement during the final industrial process. This article describes the optical and mechanical measurements, the influence functions and eigenmodes of the system and the full performance characterisation of the warping harness.
The INdoor turbulENce SEnsor (INTENSE) instrument
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Optical system performances can be affected by local optical turbulence created by its surrounding environment (telescope dome, clean room, atmospheric surface layer). We present our new instrument INTENSE (INdoor TurbulENce SEnsor) dedicated to this local optical turbulence characterization. INTENSE consists of using several parallel laser beams separated by non-redundant baselines between 0.05 and 2.5m and measuring Angle-of-Arrival fluctuations from spots displacements on a CCD. We present detailed characterization of instrumental noise and first results for the characterization of the turbulence inside clean rooms for optical testing and integration.
Approaches to the interferometric test of large flat mirrors: the case of the adaptive M4 for E-ELT
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A particular example of meter class flat mirrors is the adaptive M4 Unit of E-ELT, a deformable six petals mirror of 2.4m in diameter. We studied different approaches to the calibration and certification of M4, in a trade-off between stitching and full aperture measurements. Possibilities to test the mirror with a macro-stitching concept, both in normal and grazing incidence have been considered. Approaches reported in the literature, as the Ritchey-Common or the external Fizeau, and different beam expander setups, varying the collimating mirror and the nulling system, both on-axis and off-axis, have been deeply studied to understand performances and sensitivities to fabrication errors, alignment errors and environmental effects.
Design and development status of the University of Tokyo Atacama Observatory 6.5m telescope
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We here summarize the design and the current fabrication status for the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. The TAO telescope is operated at one of the best sites for infrared observations, at the summit of Co. Chajnantor in Chile, and is optimized for infrared observations. The telescope mount, mirrors, and mirror support systems are now at the final design phase. The mechanical and optical designs are done by following and referring to those of the Magellan telescopes, MMT, and Large Binocular Telescope. The final focal ratio is 12.2. The field-of-view is as wide as 25 arcmin in diameter and the plate scale is 2.75 arcsec mm−1.
The F/1.25 light-weighted borosilicate (Ohara E6) honeycomb primary mirror is adopted and being fabricated by the Steward Observatory Mirror Laboratory. The primary mirror is supported by 104 loadspreaders bonded to the back surface of the mirror and 6 adjustable hardpoints. The mirror is actively controlled by adjusting the actuator forces based on the realtime wavefront measurement. The actuators are optimized for operation at high altitude of the site, 5640-m above the sea level, by considering the low temperature and low air pressure. The mirror is held in the primary mirror cell which is used as a part of the vacuum chamber when the mirror surface is aluminized without being detached from the cell.
The pupil is set at the secondary mirror to minimize infrared radiation into instruments. The telescope has two Nasmyth foci for near-infrared and mid-infrared facility instruments (SWIMS and MIMIZUKU, respectively) and one folded-Caseggrain focus for carry-in instruments. At each focus, autoguider and wavefront measurement systems are attached to achieve seeing-limited image quality.
The telescope mount is designed as a tripod-disk type alt-azimuth mount. Both the azimuthal and elevation axes are supported by and run on the hydrostatic bearings. Friction drives are selected for these axis drives. The telescope mount structure and primary mirror support as well as the mirrors are under thermal control and maintained at ambient air temperature to minimize the mirror seeing.
Progress on the New York State Observatory: a new 12-meter astronomical telescope
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Over the past two years, the New York Astronomical Corporation (NYAC), the business arm of the Astronomical Society of New York (ASNY), has continued planning and technical studies toward construction of a 12-meter class optical telescope for the use of all New York universities and research institutions. Four significant technical studies have been performed investigating design opportunities for the facility, the dome, the telescope optics, and the telescope mount. The studies were funded by NYAC and performed by companies who have provided these subsystems for large astronomical telescopes in the past. In each case, innovative and cost effective approaches were identified, developed, analyzed, and initial cost estimates developed. As a group, the studies show promise that this telescope could be built at historically low prices. As the project continues forward, NYAC intends to broaden the collaboration, pursue funding, to continue to develop the telescope and instrument designs, and to further define the scientific mission. The vision of a historically large telescope dedicated to all New York institutions continues to grow and find new adherents.
Astroclimate at Jbel Aklim site in Moroccan anti-atlas: 2008-2010 seeing and isoplanatic angle statistics from the E-ELT site testing data
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In this paper we present an analysis of the statistical and temporal properties of seeing and isoplanatic angle measurements obtained with combined Differential Image Motion Monitor (DIMM) and Multi-Aperture Scintillation Sensor (MASS) at Jbel Aklim candidate site for the Eauropean Extremely Large Telescope (E-ELT). These data have been collected from February 2008 to Jun 2010. The overall seeing statistics for Jbel Aklim site are presented, broken into total seeing, free atmosphere seeing and isoplanatic angle, and ground-layer seeing (difference between the total and free-atmosphere seeing). We examine the statistical distributions of seeing measurements and investigate annual and nightly behavior. The properties of the seeing measurements are discussed in terms of the geography and meteorological conditions at Jbel Aklim site.
E-ELT seeing and isoplanatic angle: comparison of Aklim site and El Roque de Los Muchachos Observatory
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The new Extremely Large Telescope projects need accurate evaluation of the candidate sites. In this work we present the seeing, free seeing and isoplanatic angle comparison between Aklim site located in Moroccan Anti- Atlas at the geographic coordinates 30°7'39" N, 08 18'39" W, and the Observatorio del Roque de Los Muchachos (ORM), located in La Palma, Canary Islands, at 28°45'00 N, 17°53”10 W, the both sites are pre-selected to house the E-ELT. In this work we present the seeing statistics of (Ɛ), the free seeing (Ɛ free) and the isoplanatic angle ϴ0 measurements at each site, statistics of the mentioned parameters are obtained from the whole data recorded from 09 May 2008 to 09 November 2009 using the Multi Aperture Scintillation Sensor (MASS) - Differential Image Motion Monitor (DIMM) system, compare the common data between the tow sites, more representative results and statistics are shown hereafter.
A new generalized differential image motion monitor
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We present first results of a new instrument, the Generalized Differential Image Motion Monitor (GDIMM), aiming at monitoring parameters of the optical turbulence (seeing, isoplanatic angle, coherence time and outer scale). GDIMM is based on a small telescope equipped with a 3-holes mask at its entrance pupil. The seeing is measured by the classical DIMM technique using two sub-pupils of the mask (6 cm diameter separated by a distance of 20 cm), the isoplanatic angle is estimated from scintillation through the third sub-pupil (its diameter is 10 cm, with a central obstruction of 4 cm). The coherence time is deduced from the temporal structure function of the angle of arrival (AA) fluctuations, thanks to the high-speed sampling rate of the camera. And the difference of the motion variances from sub-apertures of different diameters makes it possible to estimate the outer scale. GDIMM is a compact and portable instrument, and can be remotely controlled by an operator. We show in this paper the first results of test campaigns obtained in 2013 and 2014 at Nice observatory and the Plateau de Calern (France). Comparison with simultaneous data obtained with the Generalized Seeing Monitor (GSM) are also presented.
Monitoring atmospheric turbulence profiles with high vertical resolution using PML/PBL instrument
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Wide-Field Adaptive Optics (WFAO) have been proposed for the next generation of telescopes. In order to be efficient, correction using WFAO require knowledge of atmospheric turbulence parameters. The structure constant of index-of-refraction fluctuations (C2 N ) being one of them. Indirect methods implemented in instruments as SCIDAR, MASS, SLODAR, CO-SLIDAR and MOSP have been proposed to measure C2 N (h) pro le through different layers of the atmosphere. A new monitor called the Profiler of Moon Limb (PML) is presented. In this instrument, C2 N (h) pro les are retrieved from the transverse covariance via minimization of a maximum likelihood criterion under positivity constraint using an iterative gradient method. An other approach using a regularization method (RM) is also studied. Instrument errors are mainly related to the detection of the Moon limb position and are mostly due to photon noise. Numerical simulations have been used to evaluate the error on the extracted pro le and its propagation from the detection to the inverse technique.
Phase characteristics of the ALMA 3-km baseline data
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We present the phase characteristics study of the Atacama Large Millimeter / submillimeter Array (ALMA) long (up to 3 km) baseline, which is the longest baseline tested so far using ALMA. The data consist of long time-scale (10 20 minutes) measurements on a strong point source (i.e., bright quasar) at various frequency bands (bands 3, 6, and 7, which correspond to the frequencies of about 88 GHz, 232 GHz, and 336 GHz) Water vapor radiometer (WVR) phase correction works well even at long baselines, and the efficiency is better at higher PWV (< 1mm) condition, consistent with the past studies. We calculate the spatial structure function of phase fluctuation, and display that the phase fluctuation (i.e., rms phase) increases as a function of baseline length, and some data sets show turn-over around several hundred meters to km and being almost constant at longer baselines. This is the first millimeter / submillimeter structure function at this long baseline length, and to show the turn-over of the structure function. Furthermore, the observation of the turn-over indicates that even if the ALMA baseline length extends to the planned longest baseline of 15 km, fringes will be detected at a similar rms phase fluctuation as that at a few km baseline lengths. We also calculate the coherence time using the 3 km baseline data, and the results indicate that the coherence time for band 3 is longer than 400 seconds in most of the data (both in the raw and WVR-corrected data) For bands 6 and 7, WVR-corrected data have about twice longer coherence time, but it is better to use fast switching method to avoid the coherence loss.
Optical turbulence profiling with SloDAR in the Canadian High Arctic
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The Earth's polar regions offer unique advantages for ground-based astronomical observations with its cold and dry climate, long periods of darkness, and the potential for exquisite image quality. We present preliminary results from a site-testing campaign during nighttime from October to November 2012 at the Polar Environment Atmospheric Research Laboratory (PEARL), on a 610-m high ridge near the Eureka weatherstation on Ellesmere Island, Canada. A Shack-Hartmann wavefront sensor was employed, using the Slope Detection and Ranging (SloDAR) method. This instrument (Mieda et al, this conference) was designed to measure the altitude, strength and variability of atmospheric turbulence, in particular for operation under Arctic conditions. First SloDAR optical turbulence profiles above PEARL show roughly half of the optical turbulence confined to the boundary layer, below about 1 km, with the majority of the remainder in one or two thin layers between 2 km and 5 km, or above. The median seeing during this campaign was measured to be 0.65 arcsec.
SLODAR instrument for characterizing an Arctic site: overview of the experimental method, design, and performance
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We present the development of a portable SLODAR (SLOpe Detection and Ranging) instrument to measure the vertical atmosphere profile using several different telescopes (14”, 16”, and 20” aperture) and at varying worldwide sites. In particular, the portability and feasibility of this instrument motivated us to operate it at Ellesmere Island in the Canadian High Arctic. We discuss the SLODAR technique, the design of the instrument, and the results of the performance tests in the lab. The results of the Arctic site testing measurements in October and November 2012 are discussed by Maire et. al. (this conference).1
Calibration systems for LSST
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The Large Synoptic Survey Telescope (LSST) relies on a set of calibration systems to achieve the survey photometric performances over a wide range of observing conditions. Its purpose is to consistently and accurately measure the observatory instrumental response and the atmospheric transparency during LSST observing. The instrumental response calibration will be performed regularly to monitor any variation of the transmission during the duration of the survey. The atmospheric data will be acquired nightly and processed to atmospheric models. In this paper, we describe the calibration screen system that will be used to perform the instrumental response calibration and the atmospheric calibration system including the auxiliary telescope dedicated to the acquisition of spectral data to determine the atmospheric transmission.
Reliability-centered maintenance for ground-based large optical telescopes and radio antenna arrays
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In the last years, EIE GROUP has been more and more involved in large optical telescopes and radio antennas array projects. In this frame, the paper describes a fundamental aspect of the Logistic Support Analysis (LSA) process, that is the application of the Reliability-Centered Maintenance (RCM) methodology for the generation of maintenance plans for ground-based large optical telescopes and radio antennas arrays. This helps maintenance engineers to make sure that the telescopes continue to work properly, doing what their users require them to do in their present operating conditions. The main objective of the RCM process is to establish the complete maintenance regime, with the safe minimum required maintenance, carried out without any risk to personnel, telescope and subsystems. At the same time, a correct application of the RCM allows to increase the cost effectiveness, telescope uptime and items availability, and to provide greater understanding of the level of risk that the organization is managing. At the same time, engineers shall make a great effort since the initial phase of the project to obtain a telescope requiring easy maintenance activities and simple replacement of the major assemblies, taking special care on the accesses design and items location, implementation and design of special lifting equipment and handling devices for the heavy items. This maintenance engineering framework is based on seven points, which lead to the main steps of the RCM program. The initial steps of the RCM process consist of: system selection and data collection (MTBF, MTTR, etc.), definition of system boundaries and operating context, telescope description with the use of functional block diagrams, and the running of a FMECA to address the dominant causes of equipment failure and to lay down the Critical Items List. In the second part of the process the RCM logic is applied, which helps to determine the appropriate maintenance tasks for each identified failure mode. Once the logic is completed for all the analyzed items, the resulting Maintenance Program is compiled in order to preserve all the system important functions and to rationalize the tasks periodicities. Lastly, the RCM is kept alive throughout the entire life of the telescope, where the effectiveness of the maintenance is constantly reviewed and adjusted on the basis of the “lesson learned”. In addition to the RCM analysis methodology, a second basic concept is applied for the telescope maintenance: to design and install components in such a manner to restore a failure and to perform servicing procedures as close as possible to the telescope, maximizing the replacement of Line Replaceable Units (LRUs) or Shop Replaceable Units (SRUs), rather than repair on-equipment.
Wavefront coding applied to a two-mirror telescope
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A wave-front coded imaging system is an optical-digital method for aberration control. Wave-front coding technology incorporates an aspheric element in the optical system in order to capture a coded image and by digital processing decode it to obtain the final image. The WFC system is very insensitive to defocus-like aberrations and thereby becomes a tool in the aberration balancing for telescope systems. We propose WFC technology to be implemented in a two spherical mirror telescope. In this work we present the design and simulation of the proposed telescope, trade-offs encountered in the design process and aspects of the image restoration.
Three wide-field telescopes with spherical primary mirrors
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This paper presents three optical designs based on the work of Maurice Paul. Paul's three-mirror anastigmats produce well-corrected, distortion-free fields of view. His design equations can be solved for a spherical primary mirror with one limitation: the image field is curved. Adding all-spherical refractive field-flattening optics yields well-corrected, flat image-fields of two degrees angular diameter or more. These designs can be scaled to very large telescopes with current technology.
Simultaneous ultra-high contrast imaging and determination of time-dependent, non-common path aberrations in the presence of detector noise
Show abstract
Ground-based ultra-high contrast imaging, as required for direct imaging of exoplanets and other solar systems, is limited by difficulty of separating the planetary emission from the effects of optical aberrations that are not compensated by the adaptive optics (AO) system, so-called non-common path aberrations" (NCPAs). Simultaneous (~ millisecond) exposures by the science camera and the AO system enable the use of “phase diversity" to estimate both the NCPAs and the scene via a processing procedure first described by the author (R. Frazin 2013, ApJ, 767, article id. 21).This method is fully compatible with more standard concepts used in long-exposure high-contrast imaging, such as angular differential imaging and spectral deconvolution. Long-exposure methods find time-dependent NCPAs, such as those caused by vibrations, particularly challenging. Here, an NCPA of the form of α cos(k•r-ωt + ∂) is considered. It is shown that, when sampled at millisecond time-scales, the image plane data are sensitive to arg(α), ∂ and ω, and, therefore such NCPAs can be simultaneously estimated with the scene. Simulations of observations with ms exposure times are reported. These simulations include substantial detector noise and a sinusoidal NCPA that places a speckle exactly at the location of a planet. Simulations show that the effects of detector noise can be mitigated by mixing exposures of various lengths, allowing estimation of the planet's brightness.
Integration and commissioning of the China SONG Telescope Tracking System
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China SONG telescope would achieve the goal for long time continuous, uninterrupted, full automatic observation and
works in the diffraction limit condition, what's more, it must realize 0.3 arc second tracking precision without guide star.
This paper describes the integration and fine-tuning of the China SONG Drive Systems. It discusses the different problems
encountered during the integration and commissioning. The servo model that was used to simulate the problems and to find
new solutions is described as well as test results and advanced analysis methods.
Fly's Eye camera system: optical imaging using a hexapod platform
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The Fly's Eye Project is a high resolution, high coverage time-domain survey in multiple optical passbands: our goal is to
cover the entire visible sky above the 30° horizontal altitude with a cadence of ~3 min. Imaging is going to be
performed by 19 wide-field cameras mounted on a hexapod platform resembling a fly’s eye. Using a hexapod developed
and built by our team allows us to create a highly fault-tolerant instrument that uses the sky as a reference to define its
own tracking motion. The virtual axis of the platform is automatically aligned with the Earth’s rotational axis; therefore
the same mechanics can be used independently from the geographical location of the device. Its enclosure makes it
capable of autonomous observing and withstanding harsh environmental conditions. We briefly introduce the electrical,
mechanical and optical design concepts of the instrument and summarize our early results, focusing on sidereal tracking.
Due to the hexapod design and hence the construction is independent from the actual location, it is considerably easier to
build, install and operate a network of such devices around the world.
Observational performance of the KMTNet
Show abstract
Korea Astronomy and Space Science Institute have been developing the Korea Microlensing Telescope Network aka KMTNet consists of three identical 1.6-m wide-field optical telescopes. Each telescope covers 2 deg by 2 deg FOV with an 18k by 18k mosaic CCD camera to discover Earth mass extrasolar planets using a microlensing method. A predefined 4 deg by 4 deg Bulge area will be monitored for 24-hours with the help of almost equally located three southern observatories: Cerro Tololo Inter-American Observatory in Chile, South African Astronomical Observatory in South Africa and Siding-Spring Observatory in Australia. One of the required photometric performances of the system to accomplish its scientific goal is to secure 1% of magnitude uncertainty in the range of 13 < I < 18 at the heavily crowded Galactic bulge area. To minimize the blending effect and to maximize the photometric accuracy in the photometric process, we use the difference image analysis method for a data reduction pipeline that requires precise alignment and constant point spread function profile in the observed images. In this paper we present the test observation results and verify the observational performance of the first telescope installed at CTIO. From the test observation we obtained a pointing accuracy of 8.5 arcsec RMS, an open loop tracking accuracy of 0.166 arcsec for two minutes without autoguiding, a delivered image quality of 0.86, 0.86, 0.93, 0.98 arcsec in I, R, V, B–bands, and a photometric error of 1% for the stars with 17.0 magnitude in I-band using a prescience CCD camera which has a quantum efficiency of 30%.
The PANOPTES project: discovering exoplanets with low-cost digital cameras
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The Panoptic Astronomical Networked OPtical observatory for Transiting Exoplanets Survey (PANOPTES, www.projectpanoptes.org) project is aimed at identifying transiting exoplanets using a wide network of low-cost imaging units. Each unit consists of two commercial digital single lens reflex (DSLR) cameras equipped with 85mm F1.4 lenses, mounted on a small equatorial mount. At a few $1000s per unit, the system offers a uniquely advantageous survey eficiency for the cost, and can easily be assembled by amateur astronomers or students. Three generations of prototype units have so far been tested, and the baseline unit design, which optimizes robustness, simplicity and cost, is now ready to be duplicated. We describe the hardware and software for the PANOPTES project, focusing on key challenging aspects of the project. We show that obtaining high precision photometric measurements with commercial DSLR color cameras is possible, using a PSF-matching algorithm we developed for this project. On-sky tests show that percent-level photometric precision is achieved in 1 min with a single camera. We also discuss hardware choices aimed at optimizing system robustness while maintaining adequate cost. PANOPTES is both an outreach project and a scientifically compelling survey for transiting exoplanets. In its current phase, experienced PANOPTES members are deploying a limited number of units, acquiring the experience necessary to run the network. A much wider community will then be able to participate to the project, with schools and citizen scientists integrating their units in the network.
Dome shutter failure causes longest shutdown (67-nights) ever recorded by CFHT Observatory
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The dome shutter drive system for the CFHT observatory experienced two, separate, catastrophic failures recently (15 DEC 11) and (14 APR 12); leading to a full-blown, company-wide investigation to understand and determine the root cause of both failures. Multiple resources were utilized to detect and reveal clues to help determine the cause of failure. Former colleagues were consulted, video footage investigated, ammeter plots dissected, solid models developed, forensic analysis of failed parts performed, controller mock-up established; all in an attempt to gather data, better understand the system, and develop a clear path solution to resurrect the shutter and return it to normal operation. My paper will attempt to describe in detail the problems encountered, investigations performed, analysis developed, and solutions integrated.
Design development of a deployable tertiary mirror for Keck
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The University of California Observatories will design and construct a deployable tertiary mirror (named K1DM3) for the Keck 1 telescope, which will complement technical and scientific advances in the area of time-domain astronomy. The K1DM3 device will enable astronomers to swap between any of the foci on Keck 1 in under 2 minutes, both to monitor varying sources (e.g. stars orbiting the Galactic center) and catch rapidly fading sources (e.g. supernovae, flares, gamma-ray bursts). In this paper, we report on the design development during our in-progress Preliminary Design phase. The design consists of a passive wiffle tree axial support system and a diaphragm lateral support system with a 5 arcminute field-of-view mirror. The mirror assembly is inserted into the light path with an actuation system and it relies on a kinematic mechanism for achieving repeatable, precise positioning. This project, funded by an NSF MRI grant, aspires to complete by the end of 2016.
Planning the installation of the dark energy spectroscopic instrument on the Mayall Telescope
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The KPNO Nicholas U. Mayall 4-meter telescope is to be the host facility for the Dark Energy Spectroscopic Instrument (DESI). DESI will record broadband spectra simultaneously for 5000 objects distributed over a 3-degree diameter field of view; it will record the spectra of approximately 20 million galaxies and quasi-stellar objects during a five-year survey. This survey will improve the combined precision of measurement on the dark energy equation of state today (w0) and its evolution with redshift (wa) by approximately a factor of ten over existing spectroscopy baryon acoustic oscillation surveys (e.g., BOSS1) in both co-moving volume surveyed and number of galaxies mapped. Installation of DESI on the telescope is a complex procedure, involving a complete replacement of the telescope top end, routing of massive fiber cables, and installation of banks of spectrographs in an environmentally-controlled lab area within the dome. Furthermore, assembly of the instrument and major subsystems must be carried out on-site given their size and complexity. A detailed installation plan is being developed early in the project in order to ensure that DESI and its subsystems are designed so they can be safely and efficiently installed, and to ensure that all telescope and facility modifications required to enable installation are identified and completed in time.
A laser guide star system for LAMOST
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The closed-loop correction must be carry out before observation of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) to eliminate the low-frequency errors. A natural guide star S-H sensor in the focal plane of LAMOST is used to conduct wave-front sensing. The designed limiting magnitude of the S-H sensor is 10th magnitude, and the beacon must be located in the center of field of view, or slightly deviated from the center. The survey time of LAMOST is 2 hours before and after transit, wherefore the active optical correction should be completed within half of an hour, so it is necessary to make the wave-front sensing time as short as possible. Since the magnitude of guide star and atmospheric seeing have important effect on the efficiency of wave-front sensing, 9th magnitude or brighter stars are adopted in operation. For 9th magnitude stars, sky coverage will be about 100%, but at most of time, the beacons are not located in the center of field of view, so we propose to design a laser guide system based on Rayleigh scattering to provide a beacon whose brightness is equivalent to a 7th or 8th magnitude star and to launch the beacon in the center of field of view at any observational sky. In this paper, we describe the optical design of the implementation involved a laser system with 532nm in wavelength, beam diagnostics, a launch telescope with 350mm in diameter, and receiving system.
Upgradation progress of 13.7m millimeter radio telescope reflector surface maintenance test
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The real-time maintenance sensor for the active reflector is one of the key technologies for the active reflector upgradation plan of 13.7m millimeter radio telescope from Purple Mountain Observatory, China. A new type of maintenance integration sensor based on PSD and laser module based on normal angle and distance detection is proposed in this paper. After the brief introduction of the maintenance theory of the radio telescope segmented primary reflector, the method is simulated and tested on the real backup panel from the telescope in the active reflector lab in Nanjing Institute of Astronomical Optics and Technology, China. The method is proved to be a high accurate, engineering feasible for that real-time maintenance of the whole primary. Finally some conclusions are reached.
Save our secondary: recovering a broken 1.3-m mirror
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In an inauspicious start to the ultimately very successful installation of the Dark Energy Camera on the V. M. Blanco 4- m telescope at CTIO, the light-weighted Cer-Vit 1.3-m-diameter secondary mirror suffered an accident in which it fell onto its apex. This punched out a central plug of glass and destroyed the focus and tip/tilt mechanism. However, the mirror proved fully recoverable, without degraded performance. This paper describes the efforts through which the mirror was repaired and the tip/tilt mechanism rebuilt and upgraded. The telescope re-entered full service as a Ritchey- Chrétien platform in October of 2013.
The Mercator telescope: relevance, status, and future
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In todays era of ever growing telescope apertures, there remains a specific niche for meter-class telescopes, provided they are equipped with efficient and dedicated instruments. In case these telescopes have permanent and long-term availability, they turn out very useful for intensive monitoring campaigns over a large range of time-scales. Flexible scheduling and time allocation allow small telescopes to rapidly seize new opportunities or provide immediate follow-up observations to complement data from large ground-based or space-borne facilities. The Mercator telescope, a 1.2-m telescope, installed at the Roque de Los Muchachos Observatory on La Palma (Canary Islands, Spain), successfully targets this niche of intensive monitoring and flexible scheduling. Mercator is already in operation since 2001 and has seen several upgrades in the mean time. In this contribution we give an update about the actual telescope status and its performance. We also present the Mercator instrument suite that currently consists of two instruments. The workhorse instrument is HERMES, a very efficient and stable fibre-fed high-resolution spectrograph. Recently, the MAIA imager was commissioned. This is a three- channel photometric instrument that observes a large field simultaneously in the different color bands. The MAIA detectors are unique 6k x 2k frame transfer devices which also allow for fast and continuous monitoring of variable phenomena.We discuss two important upcoming upgrades: a long-awaited automatic mirror cover and, more importantly, an entirely new telescope control system (TCS). This TCS is based on modern PLC technology, and relies on OPC UA and EtherCAT communication. Only commercially off-the-shelve hardware will be used for controlling the telescope. As a test case and as a precursor of the full TCS, such PLC systems are already deployed at Mercator to steer the Nasmyth mirror mechanism and to control the MAIA instrument. Finally, we also give an overview of the exploitation scheme of the telescope, the scheduling software that we developed to guarantee that time series or time-critical observations can be acquired in an efficient way, and how this all serves the most important research themes for Mercator, mainly in the domain of stellar astrophysics.
Concept and implementation of a virtual image slicer at the VLT
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The concept of "Virtual Image Slicer" was developed and implemented at the Very Large Telescope (VLT). The Virtual Image Slicer consists in elongating the stars in a given direction by the use of the Active Optics of the telescope. Alignment of the major axis of the elongated star along the entrance slit of the spectrograph allows to increase the total signal collected in a single (polarimetric) spectrum by a factor of up to 100 or more relative to a perfectly shaped image for bright sources.
Laboratory performance testing, installation, and commissioning of the wide field upgrade tracker for the Hobby-Eberly Telescope
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A major upgrade of the HET is in process that increases the pupil size to 10 meters and the field of view to 22’ by replacing the four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of astronomical targets. To support the new payload a new Tracker, comprising 13 axes, and weighing 20 tons, was designed, built and tested at the University of Texas Center for Electromechanics, in Austin, Texas. It was then disassembled and installed on the HET. Structural modifications were performed on the upper hexagon of the telescope structure to support the net increase of 15% to the total mass of the system and maintain fundamental mode performance of 5Hz. Testing in the laboratory, as well as subsequent commissioning tests on the HET, confirm that the Tracker will position the payload to acquire and track within the specified +/-9.5um de-center, +/-15um de-focus, and +/-4.4 arc-sec tip/tilt requirement*.
Turkey's next big science project: DAG the 4 meter telescope
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The DAG (Turkish for Eastern Anatolia Observatory) 4-m telescope project has been formally launched in
2012, being fully funded by the Government of Turkey. This new observatory is to be located on a 3170 m
altitude ridge near the town of Erzurum in Eastern Anatolia. First light is scheduled for late 2017. The
DAG team’s baseline design of the telescope consists of a Ritchey-Chretien type with alt-az mount, a focal
length of 56 m and a field of view up to 30 arcmin. Multiple instruments will be located at the Nasmyth
foci. The optical specifications of the telescope are set by DAG team for diffraction limited performance
with active and adaptive optics. Modern mirror control technologies will allow defining in a most cost
effective way the figuring requirements of the optical surfaces: the low order figuring errors of the
combined optical train constituted of M1-M2-M3 are defined in terms of Zernike coefficients and referred
to the M1 surface area. The high order figuring errors are defined using the phase structure functions.
Daytime chilling of the closed enclosure volume and natural ventilation through suitable openings during
observations will be used to ensure optimal mirror and dome seeing. A design of a ground layer adaptive
optics (GLAO) subsystem is developed concurrently with the telescope. In this paper, main design aspects,
the optical design and expected performance analysis of the telescope will be presented.
Challenges in operating an Arctic telescope
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We describe our seven year experience and the specific technical and environmental challenges we had to overcome while operating a telescope in the High Arctic, at the Eureka Weather Station, during the polar winter. The facility and the solutions implemented for remote control and maintenance are presented. We also summarize the observational challenges encountered in making precise and reliable star-photometric observations at sea-level.
LSST telescope integration and tests
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The Large Synoptic Survey Telescope (LSST) Telescope integration and test plan is phased to ensure that subsystems and services are available to support the integration flow. It begins with the summit facility construction and shows how the major subsystems feed into the activities through final testing. In order to minimize the amount of hardware mated for the first time during that period, the approach is to favor all hardware mated and pre-tested at vendors’ facilities with associated hardware and software prior to delivery onsite. The integration and test plan exploits the diffraction limited on-axis image quality of the three-mirror design. In addition, fiducials will be used during optical acceptance testing at vendors’ facilities to capture the optical axis geometry of each optical element. These fiducials will be used during the integration and tests sequence to facilitate the telescope optical alignment. In this paper, we describe the major steps of the LSST telescope integration and test sequence prior to the start of commissioning with the science camera.
Tuning a 2.4-meter telescope... blindfolded
Show abstract
Just as the 2.4 meter Automated Planet Finder (APF) commenced its final shakedown, three significant events occurred: uncontrolled telescope oscillations while tracking, liquidation of the telescope vendor’s primary facility, and the expiration of the vendor warranty. Left with scant documentation, few external resources to draw upon, and limited direct local expertise, University of California Observatories (UCO) embarked on an initiative to stabilize the telescope control system at a minimal internal cost. This paper covers the problems encountered, our solutions, and the compromises made when the budget could not support a complete remedy. Specific topics include: measurement and alignment of linear encoder signals, and custom electronics developed to enable precise alignment of the read heads and adjustment of the interpolation electronics; the use of sensitive accelerometers to isolate and diagnose sources of vibration, and to provide immediate feedback on the stability of the servo tuning; procedures used to adjust the servo control loop, and the observable effects of parameter adjustments; assessment and validation of the performance on-sky.
Design and implementation of coating hardware for the Hobby-Eberly Telescope wide-field corrector
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A major upgrade of the HET is in progress that will substantially increase the pupil size to 10 meters and the field of view to 22 arc-minutes by replacing the spherical aberration corrector. The new Wide Field Corrector is a 4-element assembly weighing 750kg and measuring 1.34 meters diameter by 2.1 meter in length. Special fixtures were required in order to support the mirrors of the Wide-Field Corrector and adapt them to the coaters chamber, during the vacuum coating process. For the 1 meter-class mirrors, the only suitable support interface was located on a 80mm wide cylindrical surface on the periphery of each mirror. The vacuum compatible system had to support the mirrors with the surface facing downward, and accommodate thermal ranges from ambient to 100C without inducing stresses in the substrate. The fixture also had to accommodate washing, as well as support of witness samples during testing and production runs, and provide masking for alignment fixtures in the center apertures of each mirror. Design principles, materials, implementation details, as well as lessons learned are covered*.
SPEED: the segmented pupil experiment for exoplanet detection
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Searching for nearby exoplanets with direct imaging is one of the major scientific drivers for both space and groundbased programs. While the second generation of dedicated high-contrast instruments on 8-m class telescopes is about to greatly expand the sample of directly imaged planets, exploring the planetary parameter space to hitherto-unseen regions ideally down to Terrestrial planets is a major technological challenge for the forthcoming decades. This requires increasing spatial resolution and significantly improving high contrast imaging capabilities at close angular separations. Segmented telescopes offer a practical path toward dramatically enlarging telescope diameter from the ground (ELTs), or achieving optimal diameter in space. However, translating current technological advances in the domain of highcontrast imaging for monolithic apertures to the case of segmented apertures is far from trivial. SPEED – the segmented pupil experiment for exoplanet detection – is a new instrumental facility in development at the Lagrange laboratory for enabling strategies and technologies for high-contrast instrumentation with segmented telescopes. SPEED combines wavefront control including precision segment phasing architectures, wavefront shaping using two sequential high order deformable mirrors for both phase and amplitude control, and advanced coronagraphy struggled to very close angular separations (PIAACMC). SPEED represents significant investments and technology developments towards the ELT area and future spatial missions, and will offer an ideal cocoon to pave the road of technological progress in both phasing and high-contrast domains with complex/irregular apertures. In this paper, we describe the overall design and philosophy of the SPEED bench.
The integrated motion measurement simulation for SOFIA
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The Stratospheric Observatory for Infrared Astronomy SOFIA consists of a B747-SP aircraft, which carries aloft a 2.7-meter reflecting telescope. The image stability goal for SOFIA is 0:2 arc-seconds rms. The performance of the telescope structure is affected by elastic vibrations induced by aeroacoustic and suspension disturbances. Active compensation of such disturbances requires a fast way of estimating the structural motion. Integrated navigation systems are examples of such estimation systems. However they employ a rigid body assumption. A possible extension of these systems to an elastic structure is shown by different authors for one dimensional beam structures taking into account the eigenmodes of the structural system. The rigid body motion as well as the flexible modes of the telescope assembly, however, are coupled among the three axes. Extending a special mathematical approach to three dimensional structures, the aspect of a modal observer based on integrated motion measurement is simulated for SOFIA. It is in general a fusion of different measurement methods by using their benefits and blinding out their disadvantages. There are no mass and stillness properties needed directly in this approach. However, the knowledge of modal properties of the structure is necessary for the implementation of this method. A finite-element model is chosen as a basis to extract the modal properties of the structure.
Measuring transmission and forces from observatory equipment vibration
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We describe measurements of both the vibration forces imparted by various types of observatory equipment, and the transmission of these forces through the soil, foundations and telescope pier. These are key uncertainties both in understanding how to mitigate vibration at existing observatories and for developing a vibration budget in the design of future observatories such as the Thirty Meter Telescope. Typical vibration surveys have measured only the resulting motion (acceleration); however, this depends on both the source and the system being excited (for example, isolating equipment results in less force being transmitted, but greater motion of the equipment itself). Instead, here we (a) apply a known force input to the pier from a shaker and measure the response at different locations, and (b) use isolator properties combined with measured acceleration to infer the forces applied by various equipment directly. The soil foundation and pier transmission can then be combined with a finite element model based vibration transmission analysis to estimate the optical consequences. Estimates of plausible source levels supports the development of a vibration budget for TMT that allocates allowable forces to the sources of vibration; this is described in a companion paper.
Accelerometer-based position reconstruction for the feedforward compensation of fast telescope vibrations in the E-ELT/MICADO
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The amount of image motion caused by vibrations of the telescope structure increases with the size of the telescope. Compensating the effects of structural vibrations in the optical path will be a major design question for adaptive optics (AO) systems in future extremely large telescopes like the E-ELT. A promising control system architecture is the recently developed Dual-Loop-Approach, with a feedforward loop based on accelerometer measurements, compensating for the vibrations in addition to the classical AO feedback loop compensating for atmospheric turbulences. We present our efforts to develop sophisticated estimation and control algorithms for this feedforward loop. The major task from a control engineering point of view is reconstructing the position of the vibrating elements from accelerometer measurements highly deteriorated by low-frequency drift and highfrequency noise. The algorithms are evaluated and compared using a realistic Tip-Tilt-Vibration laboratory test setup. Position reconstruction for a realistic 8 Hz structural resonance with an error of only 4% is achieved. Our ultimate goal is to achieve longer and more sensitive wavefront sensor (WFS) integrations by permitting a smaller bandwidth of the AO feedback loop in the E-ELT/MICADO.
ALMA band 10 (787-950 GHz) first astronomical fringes
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The Atacama Large Millimeter/submillimeter Array (ALMA) Band 10 receiver covering 787 to 950 GHz is the highest frequency receiver of the ten bands envisioned for the ALMA Front End system. The Band 10 receivers have been undergoing installation and commissioning since 2012. After the Band 10 receiver tuning scripts (Josephson currents suppression, LO power optimization) and operation procedures had been developed and implemented, astronomical verification procedures (radio pointing, focus, beam squint, and end-to-end spectroscopic verification) were established in single dish mode at the ALMA Operations Support Facility (OSF; 2900 m elevation). Subsequently, the first Band 10 astronomical fringes were achieved at the Array Operations Site in October 2013 (AOS; 5000 m elevation). This is the highest frequency ever achieved by a radio interferometer and opens up a new window into submillimeter astrophysics.
A holography receiver for the Atacama Large millimeter/submillimeter array antenna and the measured surface deformation
Hitoshi Kiuchi,
Masumi Yamada,
Masahiro Sugimoto,
et al.
Show abstract
A holography receiver has been developed for both ALMA antennas (12m and 7m). ALMA had no holography receivers for the 7m antenna. It required high-accuracy, despite small size and light weight for easy installation with a limited working area. The ALMA antennas are also used for daytime observations. The antenna deformation strongly depends on ambient temperature and sun exposure. It is essential to know the daytime antenna deformation for success of the ALMA observation. The purpose of the project is to provide a holography receiver that can measure the diurnal and the seasonal antenna deformation.
ALMA fast switching phase calibration on long baselines
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We present results of feasibility studies of Atacama Large Millimeter/submillimeter Array (ALMA) interferom-
eter phase calibration scheme combined with the Fast Switching (FS) phase referencing and the Water Vapor
Radiometer (WVR) phase correction (FS+WVR phase correction). With FS scheme, ALMA antennas observe
a scientific target source and a nearby calibrator by turn very quickly. Because interferometer phase errors of the
target due to the water vapor contents commonly exist in those of the calibrator, the target phase is corrected
with the calibrator phase. We have demonstrated the FS+WVR phase correction for ALMA with baselines up to
2.7 km for various switching cycle times and separations between sources. For instance, in the case of sources with
the 1° separation, root-mean-square phases of the target were reduced from 300 to 40 microns in path length for
1 km baselines, and the target interferometer phases could be stabilized to an ALMA specification requirement
level for the interferometer phase stability. We also analytically evaluated the root-mean-square phase corrected
with the FS+WVR phase correction to predict the performance as a function of the separation and switching
cycle time.
GMT enclosure structure and mechanism design
Show abstract
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 Campánas at the Las Campánas Observatory in Chile. This paper describes the current status of the GMT enclosure structure and mechanisms design as it evolves in the current preliminary design phase.
Building information modeling (BIM) approach to the GMT Project
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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 Campánas at the Las Campánas Observatory in Chile. The paper describes the use of Building Information Modeling (BIM) for the GMT project.
Design of mirror coating facility for The University of Tokyo Atacama Observatory 6.5m telescope
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The telescope of the University of Tokyo Atacama Observatory has a 6.5-m primary mirror in diameter. In order to fabricate the reflecting film initially and to maintain its performance over a long period, we have mirror coating facility on site. We have chosen to leave the primary mirror in its cell with the mirror support system intact. Two major advantages of leaving the mirror in its cell are that the mirror does not have to be lifted or handled and the support system does not have to be removed or reinstalled for coating. The facility consists of a clean booth for stripping of the old film, an evaporation coating chamber, and a cart with a lifter for handling the primary mirror. A conventional evaporation system with a metal pre-wetted filament array is adopted for achieving various optical requests. The coating equipment has also a function of fabrication for film on secondary and tertiary mirrors.
Baseline design and requirements for the LSST rotating enclosure (dome)
Show abstract
The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the Cerro Pachón summit in Chile. As a result of the wide field of view, its optical system is unusually susceptible to stray light; consequently besides protecting the telescope from the environment the rotating enclosure (Dome) also provides indispensible light baffling. All dome vents are covered with light baffles which simultaneously provide both essential dome flushing and stray light attenuation. The wind screen also (and primarily) functions as a light screen providing only a minimum clear aperture. Since the dome must operate continuously, and the drives produce significant heat, they are located on the fixed lower enclosure to facilitate glycol water cooling. To accommodate day time thermal control, a duct system channels cooling air provided by the facility when the dome is in its parked position.
Design of enclosure and support facilities for the University of Tokyo Atacama Observatory 6.5-m Telescope
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A basic design of enclosure and support facilities for the University of Tokyo Atacama observatory (TAO) 6.5-m telescope is described in this paper. The enclosure facility has a carousel shape with an open-space near the ground surface. The upper carousel rotates independently of the telescope. Horizontally opened slit doors, a dozen ventilation windows, wind and moon shields, and an overhead bridge-crane are equipped. For safety reasons, most of maintenance walkways are placed inside of the enclosure facility. An observation floor of the enclosure facility is connected to the support facility via a bridge for maintenance of observation instruments and a primary mirror of the telescope. Air inside of the enclosure and support facilities is exhausted to an underground tunnel.
SKA mid-frequency aperture array thermal analysis for South Africa
Show abstract
SKA (Square Kilometre Array) is a radio telescope that will have a collecting area of a square kilometer. The Mid frequency range receivers of SKA will be located in the Karoo desert in South Africa. Several designs of enclosures are proposed to protect the antenna arrays and electronics against the harsh environment. Thermal analyses by Computational Fluid Dynamics are performed on the different designs of antenna enclosures to determine their effect on the maximum temperatures and the temperature stability of the receivers.
The SRT inclinometer for monitoring the rail and the thermal gradient effects on the alidade structure
Show abstract
Here we present the hardware and software of the inclinometer chosen to be installed on the SRT alidade. This is a commercial device which basically uses two pendulum-like sensors to measure two angles from which the antenna pointing errors can be easily inferred. Such an inclinometer was installed on the plane of the SRT alidade close to the antenna elevation axis to measure the azimuth and elevation axis tilts due to the not-perfect flatness of the rail and to the temperature gradient effects on the alidade steel beams. Last summer some tests were carried out during night time, allowing first to check the inclinometer in a measurement set-up aboard on SRT, and then, to monitor the axis tilt due mainly to the rail roughness. Several measurements were recorded by the inclinometer, while the antenna was moving at constant speed in the azimuth direction for a 360-degrees rotation. The results showed a good agreement with those we got during the laboratory tests, and the rail turned out to be plan within the expected accuracy, which means a resulting pointing error of about ±2 arc-sec. Finally inclinometer measurements and astronomical observations have been performed all at once. The inclinometer measurements and the antenna pointing offsets due mainly to thermal effects have been recorded, while SRT was observing at 23 GHz toward a circumpolar calibrator source for many hours after the sunrise. A good agreement between the two set of measurement has been found as will be shown here following.
Sardinia aperture array demonstrator
Show abstract
We present a project aimed at realizing an Italian aperture array demonstrator constituted by prototypical Vivaldi antennas designed to operate at radio frequencies below 500 MHz. We focus on an array composed of a core plus a few satellite phased-array stations to be installed at the Sardinia Radio Telescope (SRT) site. The antenna elements are mobile and thus it will be possible to investigate the performance in terms of both uv-coverage and synthesized resolution resulting from different configurations of the array.
QUIJOTE-CMB experiment: a technical overview
M. R. Pérez-de-Taoro,
M. Aguiar-González,
R. Génova-Santos,
et al.
Show abstract
The QUIJOTE-CMB experiment (Q-U-I JOint TEnerife CMB experiment) is an ambitious project to obtain polarization measurements of the sky microwave emission in the 10 to 47 GHz range. With this aim, a pair of 2,5μm telescopes and three instruments are being sited at the Teide Observatory, in Tenerife (Canary Islands, Spain). The first telescope and the first instrument (the MFI: Multi Frequency Instrument) are both already operating in the band from 10 to 20 GHz, since November 2012. The second telescope and the second instrument (TGI: Thirty GHz instrument) is planned to be in
commissioning by the end of summer 2014, covering the range of 26 to 36 GHz. After that, a third instrument named FGI (Forty GHz instrument) will be designed and manufactured to complete the sky survey in the frequency range from 37 to 47 GHz. In this paper we present an overview of the whole project current status, from the technical point of view.
A PSD (position sensing device) to map the shift and tilt of the SRT secondary mirror
Show abstract
The Sardinia Radio Telescope (SRT) Metrology team has started to install the 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 secondary mirror (M2) displacements and tilts. The inclinometer is 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 it s ideal optical alignment. The PSD will be traced by a laser diode installed on a mechanically stable position inside the vertex room. Preliminarly we decided to characterize excursion range of M2, in order to know if the PSD measuring range of about +/- 10 mm is enough for our purposes. We designed, built and tested an optical measuring device, based on commercial CMOS with a wider measurement range of +/- 40 mm and with a resolution of around 0.1 mm. After a laboratory characterization at the 23 meters real distance, the PSD and the laser have been installed in the antenna. In this paper we show the results of the measurements performed by moving the antenna in elevation.
Calibrating CHIME: a new radio interferometer to probe dark energy
Laura B. Newburgh,
Graeme E. Addison,
Mandana Amiri,
et al.
Show abstract
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral hydrogen in the frequency range 400 { 800MHz over half of the sky, producing a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 { 2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that will yield constraints on the BAO power spectrum and provide a test-bed for our calibration scheme. I will discuss the CHIME calibration requirements and describe instrumentation we are developing to meet these requirements.
Latest progress of LAMOST primary co-phasing experiment in NIAOT, China
Show abstract
Extremely large telescopes with more and more large apertures are pursued, proposed and constructed by astronomers and technicians all over the world in the coming next years to satisfy the great demand of scientific progress. Segmented mirror active optics is the most important technology to co-phase the large primary for optically perfect segmentation. Based the experimental platform and test work in Nanjing Institute of Astronomical Optics and Technology in China, we introduce the latest co-phasing progress on fine segment support, edge sensor and close-loop co-phasing correction in China in this paper. Finally some conclusions are given based on the test results.
SALT segmented primary mirror: inductive edge sensors
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The development of an inductive edge sensor is in process for the control of the Southern African Large Telescope’s (SALT)1 segmented mirror primary. The original capacitive edge sensing system was not capable of maintaining the figure of the primary mirror due to excessive noise and a severe sensitivity to humidity despite exhaustive attempts at characterisation1. The prototype of the inductive edge sensor has progressed to a mature industrialised version that is in the process of being installed and commissioned on SALT. The performance of the sensor in response to temperature and RH is very good with a maximum error of 10nm typical after temperature compensation. The noise and control characteristics of the array have been simulated in order to establish the maximum cumulative error and error rate tolerable for the SALT specific case. It has been established through simulation that over the expected 5 day alignment cycle, a maximum cumulative error of 30nm can be tolerated.
Research progress of co-phasing inductance edge sensor for Chinese extremely large telescope
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Edge sensor is one of the most important technologies for the extremely large segmented primary telescopes like Keck, Thirty Meter Telescope (TMT), European Extremely Large Telescope (E-ELT) and Chinese Future Giant Telescope (CFGT) for control of out-of-plane degrees of freedom. Different from the capacity edge sensor from Keck and TMT, one kind of an inductance edge sensor is proposed and applied with the similar principle and configuration, fine aligned and tested in this paper to try to realize the same co-focusing or co-phasing maintenance purpose and high accuracy of relative piston and tip/tilt degrees of freedom of the segments. The sensor is also considered and modified to much more sensitive to dihedral angle between the neighboring segments. Finally some preliminary conclusions are reached.
Active control of the Chinese Giant Solar Telescope
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The Chinese Giant Solar Telescope (CGST) is the next generation solar telescope of China with diameter of 8 meter. The unique feature of CGST is that its primary is a ring, which facilitates the polarization detection and thermal control. In its present design and development phase, two primary mirror patterns are considered. For one thing, the primary mirror is expected to construct with mosaic mirror with 24 trapezoidal (or petal) segments, for another thing, a monolithic mirror is also a candidate for its primary mirror. Both of them depend on active control technique to maintain the optical quality of the ring mirror. As a solar telescope, the working conditions of the CGST are quite different from those of the stellar telescopes. To avoid the image deterioration due to the mirror seeing and dome seeing, especially in the case of the concentration of flux in a solar telescope, large aperture solar projects prefer to adopt open telescopes and open domes. In this circumstance, higher wind loads act on the primary mirror directly, which will cause position errors and figure errors of the primary with matters worse than those of the current 10-meter stellar telescopes with dome protect. Therefore, it gives new challenges to the active control capability, telescope structure design, and wind shielding design. In this paper, the study progress of active control of CGST for its mosaic and monolithic mirror are presented, and the wind effects on such two primary mirrors are also investigated.
An innovative telescope control system architecture for SST-GATE telescopes at the CTA Observatory
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SST-GATE (Small Size Telescope - GAmma-ray Telescope Elements) is a 4-metre telescope designed as a prototype for the Small Size Telescopes (SST) of the Cherenkov Telescope Array (CTA), a major facility for the very high energy gamma-ray astronomy of the next three decades. In this 100-telescope array there will be 70 SSTs, involving a design with an industrial view aiming at long-term service, low maintenance effort and reduced costs. More than a prototype, SST-GATE is also a fully functional telescope that shall be usable by scientists and students at the Observatoire de Meudon for 30 years. The Telescope Control System (TCS) is designed to work either as an element of a large array driven by an array controller or in a stand-alone mode with a remote workstation. Hence it is built to be autonomous with versatile interfacing; as an example, pointing and tracking —the main functions of the telescope— are managed onboard, including astronomical transformations, geometrical transformations (e.g. telescope bending model) and drive control. The core hardware is a CompactRIO (cRIO) featuring a real-time operating system and an FPGA. In this paper, we present an overview of the current status of the TCS. We especially focus on three items: the pointing computation implemented in the FPGA of the cRIO —using CORDIC algorithms— since it enables an optimisation of the hardware resources; data flow management based on OPCUA with its specific implementation on the cRIO; and the use of an EtherCAT field-bus for its ability to provide real-time data exchanges with the sensors and actuators distributed throughout the telescope.
TCS software for the SONG telescope
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Stellar Observations Network Group, SONG, is a Danish led international collaboration project to construct a global network of small 1m telescope around the globe. The second 1 meter SONG node telescope designed by NIAOT is installed at Delingha site in west China.
TCS hardware is based on PC, UMAC, tape encoder, motor and driver. TCS software is developed in powerful Qt Creator environment under stable Debian 6.0 operation system. The design rules are modularity and simplification. Several software modules work together to realize telescope usual function . Tracking algorithm is comprised of two parts. One is UMAC motion program, another is tracking thread in PC program. Communication between TCS and OCS is complicated. The method to process remote command is described.
TCS hardware is based on PC, UMAC, tape encoder, motor and driver. TCS software is developed in powerful Qt Creator environment under stable Debian 6.0 operation system. The design rules are modularity and simplification. Several software modules work together to realize telescope usual function . Tracking algorithm is comprised of two parts. One is UMAC motion program, another is tracking thread in PC program. Communication between TCS and OCS is complicated. The method to process remote command is described.
A new telescope control system for the Telescopio Nazionale Galileo: I – derotators
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Telescopio Nazionale Galileo (TNG) is a 4m class active optics telescope at the observatory of Roque de Los Muchachos. In the framework of keeping optimum performances during observation and continuous reliability the telescope control system (TCS) of the TNG is going through a deep upgrade after nearly 20 years of service. The original glass encoders and bulb lamp heads are substituted with modern steel scale drums and scanning units. The obsolete electronic racks and computers for the control loops are replaced with modern and compact commercial drivers with a net improvement in the tracking error RMS. In order to minimize the impact on the number of nights lost during the mechanical and electronic changes in the TCS the new TCS is developed and tested in parallel to the existing one and three steps will be taken to achieve the full upgrade. We describe here the first step affecting the mechanical derotators at the Nasmyth foci.
System identification and interval analysis of the Green Bank Telescope structure and servo system
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To conduct astronomical observations during windy days and increase the time available for exploration with the Green Bank Telescope (GBT) it is necessary to reduce the sensitivity of the telescope structure to wind forces. A promising approach is to design an advanced robust control system for wind induced vibration attenuation. As a first step it is necessary to (1) model analytically the structure and the servo system of the telescope and (2) validate the model through systems identification experiments. This paper presents the results of the identification experiments of the structure and the servo system along with the subsequent interval analysis.
An iterative model-based cogging compensator for the Green Bank Telescope servo system
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This paper outlines an anti-cogging methodology and summarizes the current state of motor cogging cancellation on the Green Bank Telescope (GBT). An iterative, model-based algorithm is developed for finding the anticogging signal which yields rapid convergence. This method fills a gap in present methodologies in that it can serve as a drop-in cogging solution which operates in the presence of unknown structural dynamics as well as with an existing feedback controller. The algorithm is described and demonstrated on a 40 HP DC brushed motor test bed and also on the GBT’s elevation axis motors. Results and implementation experience from deploying the algorithm on a motor test bed and on the GBT are discussed.
Keck telescope mount control redesign to improve short move performance
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The Keck I and II telescopes have been operational respectively since 1990 and 1996. Operational improvements are
sought to decrease the settling time in response to short moves. The structural response of the open loop system has been
re-identified and the mount control design has been re-examined. Changes to the mount control compensators and
command shaping architecture have been proposed in order to achieve improved response. Results from these studies are
presented, both theoretical and experimental.
Seismic analysis of the 4-meter telescope SST-GATE for the Cherenkov Telescope Array
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The Cherenkov Telescope Array (CTA) project aims to create a next generation Very High Energy (VHE)γ-ray
telescope array, devoted to the observation in a wide band of energy, from a few tens of GeV to more than 100 TeV.
Two sites are foreseen to view the whole sky, with the main one in the Southern Hemisphere where about 100 telescopes
of three different classes, related to the specific energy region to be investigated, will be installed. Among these, the
Small Size class of Telescopes, SSTs, are 4-meter telescopes and are devoted to the highest energy region, from 1 TeV to
beyond 100 TeV.
Some of these sites considered for CTA exhibit strong seismic constraints. At the Observatoire de Paris, we have
designed a prototype of a Small Size Telescope named SST-GATE, based on the dual-mirror Schwarzschild-Couder
optical formula, which was never before implemented in the design of a Cherenkov telescope. The integration of this
telescope on the site of the Observatoire de Paris is currently in progress.
Technical solutions exist in the literature to protect structures from dynamic loads caused by earthquakes without
increasing the mass and cost of the structure. This paper presents a state of the art of these techniques by keeping in mind
that the operational performance of the telescope should not be compromised. The preliminary seismic analysis of SSTGATE
performed by the finite element method is described before.
Two-motor direct drive control for elevation axis of telescope
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Two-motor application has become a very attractive filed in important field which high performance is permitted to
achieve of position, speed, and acceleration. In the elevation axis of telescope control system, two-motor direct drive is
proposed to enhance the high performance of tracking control system. Although there are several dominant strengths
such as low size of motors and high torsional structural dynamics, the synchronization control of two motors is a very
difficult and important. In this paper, a multi-loop control technique base master-slave current control is used to
synchronize two motors, including current control loop, speed control loop and position control loop. First, the direct
drive function of two motors is modeled. Compared of single motor direct control system, the resonance frequency of
two motor control systems is same; while the anti-resonance frequency of two motors control system is 1.414 times than
those of sing motor system. Because of rigid coupling for direct drive, the speed of two motor of the system is same, and
the synchronization of torque for motors is critical. The current master-slave control technique is effective to synchronize
the torque, which the current loop of the master motors is tracked the other slave motor. The speed feedback into the
input of current loop of the master motors. The experiments test the performance of the two motors drive system. The
random tracking error is 0.0119" for the line trajectory of 0.01°/s.
Simple modeling of hydrostatic bearings
Charlie Hull
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Hydrostatic bearings are a key component for many large telescopes due to their high load bearing capacity, stiffness and low friction. A simple technique is presented to model these bearings to understand the effects of geometry, oil viscosity, flow control, temperature, etc. on the bearings behavior.
Design of the planets telescope structure
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The planets telescope structure is a hybrid off-axis design that uses a carbon truss to support the secondary mirror and an aluminum base to support the primary mirror and provide an interface to the declination rotation axis. This paper describes the development of the optical support structure of the telescope, which required an integrated model to predict closed-loop optical metrics in the presence of wind loading. The integrated model combined a finite element model, the optical prescription, a control model and measured wind loading.
The Giant Magellan telescope (GMT): Gregorian instrument rotator bearing
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The Giant Magellan Telescope (GMT) is an optical-infrared 25 Meter ELT to be located in Chile. It is being designed and constructed by a group of U.S. and international universities and research institutions. The Gregorian Instrument Rotator (GIR) for GMT will be a structural-mechanical assembly 9.4 meters in diameter and 6.9 meters long. The complete assembly including structure, instruments and mechanisms has a rotating mass of 117,000 kg. It will be supported by a unique bearing system using high-capacity precision industrial rollers. The rollers will support the GIR via two large hardened and ground runner bearings integral with the structure. The bearing system includes an upper axial bearing with (8) rollers and an upper and lower radial bearing, each using (10) identical rollers. The bearing system will have the advantages of adjustability, low friction, low noise (jitter), and low cost. The rollers have a manufacturer-rated capacity 4 times greater than their maximum working load in GMT. It is important that the hardened runner bearings have a life in this application comfortably greater than the life of the GIR in the telescope. A test was devised and executed to confirm the life of the runner bearing surface (track) and to characterize the bearing friction. The bearing system design and test details and results are described.
Structural analysis and modifications to the V. M. Blanco telescope for dark energy camera (DECam) installation
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To substantially upgrade the Blanco telescope a new Dark Energy Camera (DECam)5 was developed. The Blanco telescope was commissioned in 1974 before the benefits of modern heavy instruments were foreseen. Consequently, the mass of DECam is greater than the original instrument payload. DECam was installed on the Blanco in 20121, 2. The telescope mount was rebalanced about the declination assembly by redesigning the Cassegrain cage to accommodate a significant increase in balancing mass. Finite element analysis was used to both determine the structural integrity of the new telescope configuration and to predict the effects of this added mass on the relative displacement between the primary and secondary mirrors. The counterweight system is described.