The enclosure for the Thirty Meter Telescope (TMT) uses a Calotte-style configuration, chosen for the advantages of a high degree of protection for the telescope, relatively low weight through the use of efficient shell structures, and a balanced shutter mechanical system. This design is unprecedented for large scale telescope enclosures, and introduces significant design, fabrication, construction and operation risks. This paper provides an overview of design development, analysis and testing work that was done to mitigate such risks. Compared to conventional enclosures, the combined moving mass of the cap and shutter represents a greater portion of the enclosure mass, increasing the risk of enclosure vibration impacts on telescope operation. The vibration risk was addressed through development of a self-steering bogie design, bogie spring design and testing, wheel and rail splice design and testing, and slow-speed motion simulation. Risks of rail damage at splices and bogie wheel bearing failures observed on existing observatories were also addressed by bogie and rail joint design. The bogie spring design and test program incorporated elastomeric materials that provide significant damping capability for structural seismic isolation while meeting bogie mechanical design requirements for load distribution and tracking. A novel approach to slow-speed rolling motion simulation in the stick-slip regime was developed with a view to better understand control and vibration impacts. A staged construction analysis and detailed installation sequence was completed, including falsework and erection aids. The activities described above have been performed as part of the recently completed Production Readiness design stage.
Optical communication and remote sensing (on the ground and in space) including astronomy requesting high-dynamic range observations are the next frontiers in high-bandwidth communication and civil space surveillance technologies. Each requires very precise glass mirror technology, which has not kept pace with corresponding optical and infrared sensor advances. Consequently communication and remote sensing systems are currently limited by the cost and manufacturing restrictions of their high-quality optics. We are developing a new and interdisciplinary technology for creating extremely lightweight diffractionlimited meta-material-based optical systems with exceptional optical quality spectacularly lower cost and production time — Live-Mirror. Notably such new technology is crucial to the development of dedicated high angular resolution and high-contrast telescope concept – The ExoLife Finder (ELF) Telescope – to the exoplanets studies and related science such as detecting life and even civilizations on Earth-like planets.
The Canada France Hawaii Telescope Corporation (CFHT) plans to repurpose its observatory on the summit of Maunakea and operate a new wide field spectroscopic survey telescope, the Maunakea Spectroscopic Explorer (MSE). MSE will upgrade the observatory with a larger 11.25m aperture telescope and equip it with dedicated instrumentation to capitalize on the site, which has some of the best seeing in the northern hemisphere, and offer its user’s community the ability to do transformative science. The knowledge and experience of the current CFHT staff will contribute greatly to the engineering of this new facility.
MSE will reuse the same building and telescope pier as CFHT. However, it will be necessary to upgrade the support pier to accommodate a bigger telescope and replace the current dome since a wider slit opening of 12.5 meters in diameter is needed. Once the project is completed the new facility will be almost indistinguishable on the outside from the current CFHT observatory. MSE will build upon CFHT’s pioneering work in remote operations, with no staff at the observatory during the night, and use modern technologies to reduce daytime maintenance work.
This paper describes the design approach for redeveloping the CFHT facility for MSE including the infrastructure and equipment considerations required to support and facilitate nighttime observations. The building will be designed so existing equipment and infrastructure can be reused wherever possible while meeting new requirement demands. Past experience and lessons learned will be used to create a modern, optimized, and logical layout of the facility. The purpose of this paper is to provide information to readers involved in the MSE project or organizations involved with the redevelopment of an existing observatory facility for a new mission.
Currently planned massively segmented telescopes like the European Extremely Large Telescope (EELT)1 or the Thirty Meter Telescope (TMT)2, use “Keck-era” optics. Their mirror subapertures create a dynamically rigid primary optical surface from 100’s of 1m-scale few-cm thick mirrors. We suggest that a dedicated telescope for distinguishing reflected exoplanet light from its host star may not follow these design principles. To reduce moving mass and telescope-scattered light, a post-Keck era large telescope could use new technologies that replace this opto-mechanical stiffness with massively parallel active electro-optics and interferometric concepts. This opens the intriguing possibility of building a dedicated ground-based exoplanet telescope with an aperture of 20m at a cost-scale of $100M. This is a compelling reason for exploring what we call “synthetic aperture” or “hybrid optical telescopes.” Even larger apertures that could be an order of magnitude less costly per square meter than comparable Keck-like optics are possible. Here we consider an optical system built from a relatively “floppy” optical structure and scalable interferometrically phased, moderate size (5m diameter), subapertures. This ExoLife Finder (ELF) telescope is sensitive to optical biomarker signals and has the power to map the surfaces of nearby M-dwarf exoplanets on subcontinental scales.
The exponential growth in exoplanets studies and related science such as detecting life and even civilizations on Earth-like planets requires high angular resolution and high-contrast observations. Such appealing sciences cases are a powerful reason for developing a dedicated high contrast telescope concept – The ExoLife Finder (ELF) Telescope. Here we describe the ELF overall optical concept, its preliminary Adaptive Optics concept and a novel and revolutionary technology to produce mirrors making use of force-sensor-actuator elements that are 3D-printed onto very thin slumped glass-sandwich elements of fire-polished glass – a very precise aspherical optical surface dedicated to high contrast measurements.
The Canada-France-Hawaii-Telescope Corporation (CFHT) plans to repurpose its observatory on the summit of Maunakea and operate a (60 segment) 11.25m aperture wide field spectroscopic survey telescope, the Maunakea Spectroscopic Explorer (MSE). The prime focus telescope will be equipped with dedicated instrumentation to take advantage of one of the best sites in the northern hemisphere and offer its users the ability to perform large surveys. Central themes of the development plan are reusing and upgrading wherever possible. MSE will reuse the CFHT site and build upon the existing observatory infrastructure, using the same building and telescope pier as CFHT, while minimizing environmental impact on the summit. MSE will require structural support upgrades to the building to meet the latest building seismic code requirements and accommodate a new larger telescope and upgraded enclosure. It will be necessary to replace the current dome since a larger slit opening is needed for a larger telescope. MSE will use a thermal management system to remove heat generated by loads from the building, flush excess heat from lower levels, and maintain the observing environment temperature. This paper describes the design approach for redeveloping the CFHT facility for MSE. Once the project is completed the new facility will be almost indistinguishable on the outside from the current CFHT observatory. Past experience and lessons learned from CFHT staff and the astronomical community will be used to create a modern, optimized, and transformative scientific data collecting machine.
The Maunakea Spectroscopic Explorer is designed to be the largest non-ELT optical/NIR astronomical telescope, and will be a fully dedicated facility for multi-object spectroscopy over a broad range of spectral resolutions. The MSE design has progressed from feasibility concept into its current baseline design where the system configuration of main systems such as telescope, enclosure, summit facilities and instrument are fully defined. This paper will describe the engineering development of the main systems, and discuss the trade studies to determine the optimal telescope and multiplexing designs and how their findings are incorporated in the current baseline design.
KEYWORDS: Telescopes, Optical instrument design, Control systems, Structural design, Safety, Control systems design, Finite element methods, Space telescopes, Earthquakes, Thirty Meter Telescope
The Thirty Meter Telescope (TMT) project has revised the reference optical configuration from an Aplanatic Gregorian
to a Ritchey-Chrétien design. This paper describes the revised telescope structural design and outlines the design
methodology for achieving the dynamic performance requirements derived from the image jitter error budget. The usage
of transfer function tools which incorporate the telescope structure system dynamic characteristics and the control
system properties is described along with the optimization process for the integrated system. Progress on the structural
design for seismic considerations is presented. Moreover, mechanical design progress on the mount control system
hardware such as the hydrostatic bearings and drive motors, cable wraps and safety system hardware such as brakes and
absorbers are also presented.
KEYWORDS: Telescopes, Optical instrument design, Earthquakes, Mirrors, Systems modeling, Space telescopes, Astronomy, Finite element methods, Complex systems, Thirty Meter Telescope
This paper documents the methods used for the seismic design and analysis of the Thirty Meter Telescope (TMT)2. The
seismic analysis includes response spectrum and nonlinear time history methods. Several seismic restraint design options
are considered, both linear and nonlinear, and the seismic performance is presented for these options. The paper
addresses several issues specific to large optical telescope seismic design and analysis: generation of appropriate
response spectra and time histories; use of operational and survival level earthquakes; selection of damping coefficients;
use of reduced degree of freedom models and their calibration with more detailed models; and local response spectra for
telescope-mounted systems.
KEYWORDS: Telescopes, Space telescopes, Mirrors, Diagnostics, Adaptive optics, Electronics, Near field optics, Laser safety, Optical benches, Thirty Meter Telescope
The Thirty Meter Telescope (TMT) will implement a Laser Guide Star Facility (LGSF), which will generate up to nine
Na laser beams in at least four distinct asterisms. The TMT LGSF conceptual design is based upon three 50W solid state,
continuous wave, sum frequency 589 nm lasers and conventional beam transport optics. In this paper, we provide an
update to the TMT LGSF conceptual design. The LGSF top end and the beam transfer optics have been significantly
redesigned to compensate for the TMT telescope top end flexure, to adapt for the new TMT Ritchey-Chretien optical
design, to reduce the number of optical surfaces and to reduce the mass and volume. Finally, the laser service enclosure
has been relocated within the telescope azimuth structure. This will permit the lasers to operate with a fixed gravity
vector, but also requires further changes in the beam transport optical path.
The Thirty Meter Telescope (TMT) project has chosen a reference configuration with the telescope elevation axis above the primary mirror. The TMT telescope design has a segmented primary mirror, with 738 segments, nominally 1.2 m across corners, and it uses an articulated tertiary mirror to feed science light to predefined instrument positions on two large Nasmyth platforms. This paper outlines the development of the telescope structural design to meet the motion requirements related to the image quality error budget. The usage of opto-structural performance evaluation tools such as Merit Function Routine are described in addition with the optimization techniques used during the telescope structure design development.
KEYWORDS: Telescopes, Mirrors, Adaptive optics, Space telescopes, Optical instrument design, Point spread functions, Silicon carbide, Sensors, Stars, Control systems
A design is proposed for a 20 m Canadian Very Large Optical Telescope (VLOT). This design meets the science, schedule, and availability requirements of the Canadian astronomical community. The telescope could be operational by early in the next decade to complement the science discoveries of the Next Generation Space Telescope (NGST) and Atacama Large Millimeter Array (ALMA). This design is suitable for location on the Mauna Kea summit ridge, and could replace the current 3.6 m CFHT telescope. The telescope structure provides room for two vertically oriented Nasmyth instruments, implements a very stiff monocoque mirror cell, and offers a short and direct load path to the telescope mount. A Calotte style dome structure offers many advantages over current designs including lower and more even power requirements, and a circular aperture that will better protect the telescope structure from wind buffeting. The science requirements are presented, and the telescope optical design, primary mirror pupil segmentation options, including hexagonal segments and a radial segment design with a central 8 m mirror, are considered. Point spread function plots and encircled energy calculations show that there is no significant diffraction performance difference between the options except that hexagonal segments in the 1 m point-to-point range appear to deliver poorer PSF's as compared to 2 m and larger segments. Plans for implementation of a Matlab based integrated telescope model are discussed. A summary of adaptive optics system issues for large telescopes is presented along with plans for future research in AO.
An enclosure design concept is proposed for a large ground-based optical telescope in the 20- to 30-metre class. The proposed configuration differs from the enclosures for existing large telescopes. Current large telescope enclosure designs have inherent inefficiencies which may be substantially magnified if these designs are scaled. Dynamic analysis studies show that motion requirements for the mechanical components of existing enclosures may be too stringent for next-generation enclosures and that these requirements should be revisited. The proposed enclosure design uses a spherical base structure with a rotating inclined cap. This design improves upon some of the mechanical, structural and operational inefficiencies of current spherical enclosures with conventional shutters. The design also offers potential advantages in the protection of the telescope from wind buffeting forces. Wind loading is expected to be one of the most significant factors governing the design of a next-generation large telescope. The enclosure design includes features which are expected to improve the air flow characteristics in and around the enclosure. Preliminary computational fluid dynamics (CFD) studies have been performed in order to analyze the effect of various enclosure details and components on the flow patterns. Future comparative and detailed CFD studies on the enclosure and telescope are proposed. A plan for practical validation of the results of CFD analysis is presented, in order to better understand the benefits of CFD in predicting the effects of wind buffeting on next-generation large telescopes.
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