The Large Synoptic Survey Telescope (LSST) primary/tertiary (M1M3) mirror cell is a 25-ton, 9-meter x 9-meter x 2- meter steel weldment that supports the 19-ton borosilicate M1M3 monolith mirror on the telescope and acts as the lower vessel of the coating chamber when optically coating the mirror surfaces. The M1M3 telescope mirror cell contract was awarded to CAID Industries, Inc., of Tucson, Arizona in October 2015. After the mirror cell final acceptance in October 2017, the integration of the mirror support system started. The M1M3 cell assembly with the surrogate mirror will take place in a dedicated controlled-environment area at CAID Industries. All components of the mirror support system that were developed and tested by the LSST Telescope and Site M1M3 team at the NOAO offices in Tucson have been moved to CAID premises and have been integrated into the cell by a team of LSST, CAID and Richard F. Caris Mirror lab personnel. After completion of the cell integration and its assembly with the surrogate, a test phase that includes zenith and offzenith testing for the mirror support system will be carried by the LSST team. These tests aim to verify that the active support system components, mirror control, and software are performing as expected and the mirror support system is safe for the next step, the M1M3 cell to borosilicate glass assembly and tests at the RFC Mirror Lab of the University of Arizona.
The Large Synoptic Survey Telescope is an 8.4m telescope now in construction on Cerro Pachón, in Chile. This telescope is designed to conduct a 10-year survey of the southern sky in which it will map the entire night sky every few nights. In order to achieve this goal, the telescope mount has been designed to achieve high accelerations that will allow the system to change the observing field in just 2 seconds. These rapid slews will subject the M1M3 mirror to high inertial and changing gravitational forces that has to be actively compensated for in order to keep the mirror safe, aligned, and properly figured during operations. The LSST M1M3 active support system is composed of six “hard point” actuators and 156 pneumatic actuators. The hard points define the mirror position in the mirror cell (with little or no applied force) and hold that position while observing in order to maintain the alignment of the telescope optics. The pneumatic actuators provide the force-distributed mirror support plus a known (static) figure correction as well as dynamic optical figure optimizations coming from other components of the Active Optics System. Optimizing this mirror support system required the introduction of innovative control concepts in the control loops (Inner and Outer). The Inner Loop involves an extensive pressure control loop to ensure precise force feedback for each pneumatic actuator while the Outer Loop includes telescope motion sensors to provide the real-time feedback to compensate for the changing external inertial and gravitational forces. These optimizations allow the mirror support system to maximize the hard point force-offloading while keeping the glass safe when slewing and during seismic events.
The Large Synoptic Survey Telescope<sup>1</sup> (LSST) is an altitude-azimuth mounted three mirror telescope and camera. The primary (M1) and tertiary (M3) mirrors are integrated into a single, monolithic borosilicate substrate 8.42 m diameter. The annular secondary (M2) mirror is located above the M1M3 mirror and the camera is nested inside the M2. The M1M3 mirror is supported on a mirror cell by two independent systems: one system is for Active Mode and the other for Static Mode. <p> </p>During observing, or Active Mode<sup>2</sup>, the M1M3 mirror is supported by an array of 156 support and figure control actuators consisting of 268 pneumatic cylinders that react to gravity and inertial loads and provide figure error correction. Load cells on the actuators measure forces that are communicated to the M1M3 control system. However, the figure actuators do not define the mirror position. This is defined with six axially stiff linear actuators called hardpoints<sup>3</sup> arranged in a hexapod pattern to restrain rigid body motion of the mirror in a kinematic fashion. By adjusting the length of each hardpoint, the mirror can be adjusted in all six degrees of freedom with respect to the cell. Displacement sensors and load cells on the hardpoints communicate displacements and forces to the control system, which processes the telemetry and issues force corrections to the figure actuators to zero out any loads and moments on the hardpoints. <p> </p>In Static Mode, the M1M3 mirror is no longer supported by figure actuators and the position sensing of the hard point hexapod is inactive. A second support system consisting of 288 wire rope isolators called Static Supports come into play. The static supports mechanically capture the mirror whether in Active or Static Mode and in the event the mirror experiences motion beyond the active motion range in any direction. The static supports also safely support the mirror during seismic events for all elevation angles. In active mode, the static supports do not contact the mirror and thus, do not affect the mirror positioning or figure. <p> </p>This paper focuses on the detailed design, development, testing, integration, and current status of the M1M3 pneumatic figure actuators.
Proc. SPIE. 9911, Modeling, Systems Engineering, and Project Management for Astronomy VI
KEYWORDS: Actuators, Telescopes, Mirrors, 3D modeling, Space telescopes, Finite element methods, Computer aided design, Large Synoptic Survey Telescope, Large Synoptic Survey Telescope, Systems modeling, Solid modeling
During this early stage of construction of the Large Synoptic Survey Telescope (LSST), modeling has become a crucial system engineering process to ensure that the final detailed design of all the sub-systems that compose the telescope meet requirements and interfaces. Modeling includes multiple tools and types of analyses that are performed to address specific technical issues. Three-dimensional (3D) Computeraided Design (CAD) modeling has become central for controlling interfaces between subsystems and identifying potential interferences. The LSST Telescope dynamic requirements are challenging because of the nature of the LSST survey which requires a high cadence of rapid slews and short settling times. The combination of finite element methods (FEM), coupled with control system dynamic analysis, provides a method to validate these specifications. An overview of these modeling activities is reported in this paper including specific cases that illustrate its impact.
This paper describes the status and details of the large synoptic survey telescope<sup>1,2,3</sup> mount assembly (TMA). On June 9<sup>th</sup>, 2014 the contract for the design and build of the large synoptic survey telescope mount assembly (TMA) was awarded to GHESA Ingeniería y Tecnología, S.A. and Asturfeito, S.A. The design successfully passed the preliminary design review on October 2, 2015 and the final design review January 29, 2016. This paper describes the detailed design by subsystem, analytical model results, preparations being taken to complete the fabrication, and the transportation and installation plans to install the mount on Cerro Pachón in Chile. This large project is the culmination of work by many people and the authors would like to thank everyone that has contributed to the success of this project.
At the core of the Large Synoptic Survey Telescope (LSST) three-mirror optical design is the primary/tertiary (M1M3) mirror that combines these two large mirrors onto one monolithic substrate. The M1M3 mirror was spin cast and polished at the Steward Observatory Mirror Lab at The University of Arizona (formerly SOML, now the Richard F. Caris Mirror Lab at the University of Arizona (RFCML)). Final acceptance of the mirror occurred during the year 2015 and the mirror is now in storage while the mirror cell assembly is being fabricated. The M1M3 mirror will be tested at RFCML after integration with its mirror cell before being shipped to Chile.
The Large Synoptic Survey Telescope (LSST) primary/tertiary (M1M3) mirror cell assembly supports both on-telescope operations and off-telescope mirror coating. This assembly consists of the cast borosilicate M1M3 monolith mirror, the mirror support systems, the thermal control system, a stray light baffle ring, a laser tracker interface and the supporting steel structure. During observing the M1M3 mirror is actively supported by pneumatic figure control actuators and positioned by a hexapod. When the active system is not operating the mirror is supported by a separate passive wire rope isolator system. The center of the mirror cell supports a laser tracker which measures the relative position of the camera and secondary mirror for alignment by their hexapods. The mirror cell structure height of 2 meters provides ample internal clearance for installation and maintenance of mirror support and thermal control systems. The mirror cell also functions as the bottom of the vacuum chamber during coating. The M1M3 mirror has been completed and is in storage. The mirror cell structure is presently under construction by CAID Industries. The figure control actuators, hexapod and thermal control system are under developed and will be integrated into the mirror cell assembly by LSST personnel. The entire integrated M1M3 mirror cell assembly will the tested at the Richard F Caris Mirror Lab in Tucson, AZ (formerly Steward Observatory Mirror Lab).
The Large Synoptic Survey Telescope (LSST) has a 10 degrees square field of view which is achieved through a 3 mirror optical system comprised of an 8.4 meter primary, 3.5 meter secondary (M2) and a 5 meter tertiary mirror. The M2 is a 100mm thick meniscus convex asphere. The mirror surface is actively controlled by 72 axial electromechanical actuators (axial actuators). Transverse support is provided by 6 active tangential electromechanical actuators (tangent links). The final design has been completed by Harris Corporation. They are also providing the fabrication, integration and testing of the mirror cell assembly, as well as the figuring of the mirror. The final optical surface will be produced by ion figuring. All the actuators will experience 1 year of simulated life testing to ensure that they can withstand the rigorous demands produced by the LSST survey mission. Harris Corporation is providing optical surface metrology to demonstrate both the quality of the optical surface and the correctablility produced by the axial actuators.
The LSST will utilize an Active Optics System to optimize the image quality by controlling the surface figures of the
mirrors (M1M3 and M2) and maintain the relative position of the three optical systems (M1M3 mirror, M2 mirror and
the camera). The mirror surfaces are adjusted by means of figure control actuators that support the mirrors. The relative
rigid body positions of M1M3, M2 and the camera are controlled through hexapods that support the M2 mirror cell
assembly and the camera. The Active Optics System (AOS) is principally operated off of a Look-Up Table (LUT) with
corrections provided by wave front sensors.
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.
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 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.
The 3.5-meter diameter Large Synoptic Survey Telescope (LSST) secondary (M2) mirror utilizes a 100mm thick
meniscus ULE™ blank completed by Corning Incorporated in 2009. Sub-aperture interferometry will guide the
polishing process to meet mirror structure function requirements. The convex asphere is actively supported by 72
axial actuators and 6 tangential links. These tangent links utilize an embedded lever system to meet the
requirements. The axial actuators have force limiting devices. The control system utilizes a higher level "outer loop
controller" for monitoring and commanding the tangent links and axial actuators. Numerous sensors determine the
assembly status. To prevent thermally induced image degradation, the interior air of the M2 cell is conditioned.
The Large Synoptic Survey Telescope (LSST) primary/tertiary (M1M3) mirror cell assembly supports both on-telescope
operations and off-telescope mirror coating. This assembly consists of the M1M3 monolith mirror, the mirror support
systems, the thermal control system, a stray light baffle ring, a laser tracker interface and the supporting steel structure.
During observing the M1M3 mirror is actively supported by figure control actuators and a hexapod. The M1M3 figure
control actuators distribute the load to safely support the glass mirror and actively control its shape. The position of the
mirror relative to the mirror cell is controlled by a set of six hardpoints (displacement controlled actuators) that form a
large hexapod. When the active system is not operating the mirror is supported by a separate passive support system. The
center of the mirror cell supports a laser tracker which measures the relative position of the camera and secondary mirror
for alignment by their hexapods. The mirror cell design height of 2 meters provides ample internal clearance for
installation and maintenance of mirror support and thermal control systems. The mirror cell also functions as the bottom
of the vacuum chamber during coating. Consequently, to withstand the vacuum-induced stress the M1M3 mirror cell
will be fabricated from higher strength steel. The vacuum-induced mirror cell deformations must be isolated from the
mirror support system to prevent overstressing the mirror. This is accomplished by utilizing separate truss support
systems for the top deck and the vacuum boundary.
The very short slew times and resulting high inertial loads imposed upon the Large Synoptic Survey Telescope (LSST) create new challenges to the primary mirror support actuators. Traditionally large borosilicate mirrors are supported by pneumatic systems, which is also the case for the LSST. These force based actuators bear the weight of the mirror and provide active figure correction, but do not define the mirror position. A set of six locating actuators (hardpoints) arranged in a hexapod fashion serve to locate the mirror. The stringent dynamic requirements demand that the force actuators must be able to counteract in real time for dynamic forces on the hardpoints during slewing to prevent excessive hardpoint loads. The support actuators must also maintain the prescribed forces accurately during tracking to maintain acceptable mirror figure. To meet these requirements, candidate pneumatic cylinders incorporating force feedback control and high speed servo valves are being tested using custom instrumentation with automatic data recording. Comparative charts are produced showing details of friction, hysteresis cycles, operating bandwidth, and temperature dependency. Extremely low power actuator controllers are being developed to avoid heat dissipation in critical portions of the mirror and also to allow for increased control capabilities at the actuator level, thus improving safety, performance, and the flexibility of the support system.
The Large Synoptic Survey Telescope (LSST) utilizes an 8.4-meter cast borosilicate primary/tertiary mirror (M1M3).
This mirror system has stringent vibration and stiffness requirements because the LSST optical system does not include a
fast steering mirror and the mission requires a short slew and settling time. The position stability of the M1M3 relative to
the mirror cell is controlled by six displacement controlled actuators (subsequently referred to as "hardpoints") that form
a large hexapod. This design is based largely on previous hardpoints implemented for borosilicate mirror positioning.
Traditionally, all dynamic forces applied to these mirrors are reacted through their hardpoints. Consequently, the
characteristics of these hardpoints critically affect the ability of the telescope to meet the stringent dynamic requirements
without overstressing the mirror. The hardpoints must have a high stiffness of 120 N/um in the axial direction, while
protecting the mirror by limiting the loads in all six degrees of freedom. The non-axial direction loads are limited by
flexures. The axial loads are limited by a pneumatic breakaway mechanism. Since the hardpoints react the dynamic
mirror loads, the axial breakaway force may limit the telescope's slewing accelerations. The travel of the breakaway
mechanism must accommodate the transfer of the mirror from its active supports to its static supports. The hardpoint
positioning mechanism must have sufficient travel and resolution to properly position the mirror relative to the mirror
cell. Fulfilling these functions also requires numerous sensors, including a precision axial load cell which is paramount
in determining the figure control actuator forces.
As astronomical instruments have increased in complexity, cost and production time, sharing a major instrument
between telescopes has become an attractive alternative to duplication. This requires solving technical and logistical
problems of transportation, transferring operational support knowledge between on-site staffs, and developing effective
responses to in-service problems at a different site. The infrared camera NEWFIRM has been operated for two years on
the 4-m Mayall telescope of Kitt Peak National Observatory in Arizona. We have recently temporarily moved it to the 4-
m Blanco telescope of Cerro Tololo Interamerican Observatory in Chile for a limited period of operation. We describe
here our solutions to the challenges involved in relocating this major in-service cryogenic instrument, with an emphasis
on "lessons learned" to date.
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.
Atmospheric turbulence compensation via adaptive optics (AO) will be essential for achieving most objectives of the
TMT science case. The performance requirements for the initial implementation of the observatory's facility AO system
include diffraction-limited performance in the near IR with 50 per cent sky coverage at the galactic pole. This capability
will be achieved via an order 60x60 multi-conjugate AO system (NFIRAOS) with two deformable mirrors optically
conjugate to ranges of 0 and 12 km, six high-order wavefront sensors observing laser guide stars in the mesospheric
sodium layer, and up to three low-order, IR, natural guide star wavefront sensors located within each client instrument.
The associated laser guide star facility (LGSF) will consist of 3 50W class, solid state, sum frequency lasers,
conventional beam transport optics, and a launch telescope located behind the TMT secondary mirror.
In this paper, we report on the progress made in designing, modeling, and validating these systems and their components
over the last two years. This includes work on the overall layout and detailed opto-mechanical designs of NFIRAOS and
the LGSF; reliable wavefront sensing methods for use with elongated and time-varying sodium laser guide stars;
developing and validating a robust tip/tilt control architecture and its components; computationally efficient algorithms
for very high order wavefront control; detailed AO system modeling and performance optimization incorporating all of
these effects; and a range of supporting lab/field tests and component prototyping activities at TMT partners. Further
details may be found in the additional papers on each of the above topics.
The High-resolution Near-infrared Spectrograph (HRNIRS) concept for the Gemini telescopes combines a seeing-limited R ~ 70000 cross-dispersed mode and a MCAO-fed near diffraction-limited R ~ 20000 multi-object mode into a single compact instrument operating over the 0.9-5.5μm range. We describe the mechanical design, emphasizing the challenging design requirements and how they were met. The approach of developing the optical and mechanical designs in concert and utilizing proven working concepts from the Gemini Near Infra-Red Spectrograph were key elements of the design philosophy. Liang, et al. provides a detailed discussion of the optical design, Hinkle, et al. describes the science cases and requirements as well as a general overview, and Eikenberry, et al. describes the systems engineering and performance aspects of HRNIRS.
The Thirty Meter Telescope (TMT) project is a partnership between ACURA, AURA, Caltech, and the University of California. The design calls for a 3.6 m diameter secondary mirror and an elliptical tertiary mirror measuring more than 4 m along its major axis. Each mirror will weigh more than two metric tons and must be articulated to compensate for deformation of the telescope structure. The support and control of these "smaller optics" pose significant challenges for
the designers. We present conceptual designs for active and passive figure control and articulation of these optics.
The Gemini Near-Infrared Spectrograph (GNIRS) supports a variety of observing modes over the 1-5 μm wavelength
region, matched to the infrared-optimized performance of the Gemini 8-m telescopes. We describe the optical,
mechanical, and thermal design of the instrument, with an emphasis on challenging design requirements and how they
were met. We also discuss the integration and test procedures used.
The High-Resolution Near-InfraRed Spectrograph (HRNIRS) concept for the Gemini telescopes combines a seeing limited R ~ 70000 cross-dispersed mode and an MCAO-fed near diffraction-limited R ~ 30000 multi-object mode into a single compact instrument operating over the 1 - 5 μm range. The HRNIRS concept was developed in response to proposals issued through the Aspen instrument process by Gemini. Here we review the science drivers and key functional requirements. We present a general overview of the instrument and estimate the limiting performance.
The Thirty Meter Telescope (TMT) will utilize adaptive optics to achieve near diffraction-limited images in the near-infrared using both natural and laser guide stars. The Laser Guide Star Facility (LGSF) will project up to eight Na laser beacons to generate guide stars in the Earth's Na layer at 90 - 110 km altitude. The LGSF will generate at least four distinct laser guide star patterns (asterisms) of different geometry and angular diameter to meet the requirements of the specific adaptive optics modules for the TMT instruments. We describe the baseline concept for this facility, which draws on the heritage from the systems being installed at the Gemini telescopes. Major subsystems include the laser itself and its enclosure, the optics for transferring the laser beams up the telescope structure and the asterism generator and launch telescope, both mounted behind the TMT secondary mirror. We also discuss operational issues, particularly the required safety interlocks, and potential future upgrades to higher laser powers and precompensation of the projected laser beacons using an uplink adaptive optics system.
The James Clerk Maxwell Telescope (JCMT) on the summit of Mauna Kea is currently undergoing significant
structural upgrade in order to accommodate the new generation instrument SCUBA-2 (Submillimeter Common-User
Bolometric Array) which is being developed by the United Kingdom Astronomy Technology Centre (UK ATC). This
four tonne instrument will be located at the Nasmyth focus of the telescope and will require five large auxiliary external
warm mirrors to be installed on the telescope structure and in the receiver cabin along with dedicated automatically
deployable tertiary mirror. The carousel of the observatory building as well as the original telescope structure was not
designed for an instrument of this mass and complexity. The whole left Nasmyth platform of the telescope has to be
removed and rebuilt in order to accommodate the instrument, its support structure and the warm optics. The floor of the
observatory has to be reinforced and fitted with rail system and a scissor lift in order to handle the installation of the
instrument on the telescope and removal from the telescope for maintenance. Details are given of particular challenges
associated with handling, mechanical interfacing, optical alignment, design of the external warm mirrors mounts and the
tertiary mirror deployment mechanism for SCUBA-2.
The NEWFIRM program will provide a widefield IR imaging system optimized for survey programs on the NOAO 4-m telescopes in Arizona and Chile. The camera images a 28 x 28 arcminute field of view over 1-2.4 microns wavelength range with a 4K x 4K pixel array mosaic. We present an overview of camera design features including optics design, manufacture, and mounting; control of internal flexure between input and output focal planes; mosaic array mount design; and thermal design. We also discuss the status of other projects within the program: array control electronics, observation and pipeline reduction software, and production of the science grade array complement. The program is progressing satisfactorily and we expect to deliver the system to the northern 4-m telescope in 2005.
We present case studies on the application of passive compensation in two large astronomical instruments: the Gemini Near Infrared Spectrograph (GNIRS), including actual performance, and the NOAO Extremely Wide Field Infrared Mosaic (NEWFIRM) camera. Image motion due to gravity flexure is a problem in large astronomical instruments. We present solutions for two different cases using passive mechanical compensation of the optical train. For the Gemini Near Infrared Spectrograph (GNIRS), articulation of a single sensitive optic is used. Adjustable cantilevered weights, designed to respond to specific gravity components, are employed to drive tilt flexures connected to the collimator mirror. An additional requirement is that cryocooler vibration must not dynamically excite this mirror. Performance testing of the complete instrument shows that image motion has been satisfactorily compensated. Some image blur due to dynamic excitation by the cryocoolers was noted. A successful damping scheme has been developed experimentally. For the NOAO Extremely Wide Field Infrared Mosaic camera (NEWFIRM), the entire optical support structure is mechanically tuned to deflect and rotate precisely as a rigid body relative to the telescope focal plane. This causes the optical train to remain pointed at a fixed position in the focal plane, minimizing image motion on the science detector. This instrument is still in fabrication.
Wide field-of-view, high-resolution near-infrared cameras on 4-m class telescopes have been identified by the astronomical community as critical instrumentation needs in the era of 8-m and larger telescopes. Acting as survey instruments, they will provide the input source discoveries for large-telescope follow-up observations. The NOAO Extremely Wide Field Infrared Mosaic (NEWFIRM) imaging instrument will serve this need within the US system of facilities. NEWFIRM is being designed for the National Optical Astronomy Observatory (NOAO) 4-m telescopes (Mayall at KPNO and Blanco at CTIO). NEWFIRM covers a 28 x 28 arcmin field of view over the 1-2.4 μm wavelength range with a 4k x 4k pixel detector mosaic assembled from 2k x 2k modules. Pixel scale is 0.4 arcsec/pixel. Data pipelining and archiving are integral elements of the instrument system. We present the science drivers for NEWFIRM, and describe its optical, mechanical, electronic, and software components. By the time this paper is presented, NEWFIRM will be in the preliminary design stage, with first light expected on the Mayall telescope in 2005.
The Large Binocular Telescope (LBT) under construction on Mount Graham, Arizona is a unique instrument which supports two 8.4-meter primary mirrors on the same mount. This unique optical support structure configuration presented new challenges in the design and construction of the telescope enclosure building. The LBT is a project managed by Steward Observatory at the University of Arizona and Arcetri Observatory in Italy. This paper discusses the design and analysis of the steel structure that encloses the telescope, including solutions to the problems presented by the design criteria.
The SOAR telescope dome is a 20 meter diameter 5/8 spherical structure built on a rotating steel frame with an over the top nesting shutter and covered with a fiberglass panel system. The insulated fiberglass panel system can be self- supporting and is typically used for radomes on ground based tracking systems. The enclosed observing area is ventilated using a down draft ventilation system. The rotating steel frame is comprised of a ring beam and dual arch girders to provide support to the panel system sections and guide the shutter. The dual door shutter incorporates a unique differential drive system that reduces the complexity of the control system. The dome, shutter and windscreen `track' the telescope for maximum wind protection. The dome rotates on sixteen fixed compliant bogie assemblies. The dome is designed for assembly in sections off the facility and lifted into place for minimal impact on assembly of other telescope systems. The expected cost of the complete dome; including structure, drives, and controls is under 1.7 million. The details covered in this paper are the initial trade-offs and rationale required by SOAR to define the dome, the detailed design performed by M3 Engineering and Technology, and the choices made during the design.
In order to encourage adequate dome ventilation to reduce or eliminate dome seeing at the 3.8 m United Kingdom Infrared Telescope (UKIRT), a dome ventilation system (DVS) was designed to be installed in the lower dome skirt. The modifications to the dome for the new DVS apertures consisted of installing a reinforcing frame containing an insulated rollup door and adjustable louvers. This paper describes the finite element structural analysis of the reinforcing frame, the detailed design of the frame hardware, the design of the programmable language control (PLC) system for controlling the opening and closing of the rollup doors, and the fabrication and installation of a prototype frame assembly. To date, a prototype assembly has been installed that confirms the design, and fifteen production assemblies are currently under fabrication for installation by September 1996.
Four lightweight solid contoured back mirror shapes (a double arch, a single arch, a modified single arch, and a double concave mirror) and a cellular sandwich lightweight meniscus mirror, have been considered for the primary mirror of the Space Infrared Telescope Facility (SIRTF). A parametric design study using these shapes for the SIRTF 40 inch primary mirror with a focal ratio f/2 is presented. Evaluations of the optical performance and fundamental frequency analyses are performed to compare relative merits of each mirror configuration. Included in these are structural, optical, and frequency analyses for (1) different back contour shapes, (2) different number and location of the support points, and (3) two gravity orientations (ZENITH and HORIZON positions). The finite element program NASTRAN is used to obtain the structural deflections of the optical surface. For wavefront error analysis, FRINGE and PCFRINGE programs are used to evaluate the optical performance. A scaling law relating the optical and structural performance for various mirror contoured back shapes is developed.