The Giant Magellan Telescope (GMT) is one of three planned ground-based optical/IR Extremely Large Telescopes (ELTs) that will provide a generational leap in ground-based Optical/IR capability. The GMT Mount is the structural, mechanical, hydraulic, and electronic system that provides the overall framework for mounting and alignment of optics and science instruments, supports payloads and utilities, and provides the three main axes of motion consisting of azimuth, elevation, and Gregorian Instrument Rotator (GIR) rotations. The GMTO Corp. completed in 2019 a multi-stage acquisition process that led to the selection of OHB Digital Connect (ODC, formerly MT-Mechatronics or MTM) and Ingersoll Machine Tools (IMT) to supply the final design, fabrication, and installation of the GMT Mount. The Final Design Review of the Mount subsystem was successfully passed in June 2023. The fabrication of the Mount is split into two phases comprising first the rotating azimuth base structure and secondly the elevation and optical support moving structures. The Mount will be assembled and tested at the IMT factory to the largest feasible assembly state where all three motion axes and critical systems will be functionally tested. The Mount will then be disassembled, shipped, and reassembled and tested at the GMT’s Las Campanas site in Chile. The first phase of fabrication has begun starting with the Azimuth Track Segments. Full factory functional testing of the Hydrostatic Bearing System (HBS), the electric Direct-Drive System, the Earthquake Damping System (EDS), and the Azimuth cable wrap will be completed during the first phase of fabrication. This paper will describe the final design configuration of the Mount, major subassemblies, fabrication and test phasing, fabrication highlights to-date, and an overview of the prototype testing that validated the final design parameters.
The Giant Magellan Telescope (GMT) is one of three planned ground-based optical/IR Extremely Large Telescopes (ELTs) that will provide a generational leap in ground-based Optical/IR capability. The GMTO Corp. completed in 2019 a multi-stage acquisition process that led to the selection of OHB Digital Connect (formerly MT-Mechatronics or MTM) and Ingersoll Machine Tools (IMT) to supply the final design, fabrication, and installation of the GMT Mount. The ~2000 metric ton GMT Mount comprises the telescope structures, mechanisms, and utilities but does not include the optics and science instruments. This paper provides a general overview of the technical scope of the GMT Mount including the key and driving requirements, systems engineering framework, and planned design development. Due to the GMT site location in Chile, the Mount design must accommodate a challenging seismic environment. Major Mount subsystems are also described including the Hydrostatic Bearing System (HBS), Gregorian Instrument Rotator (GIR), and the Azimuth Track and its interface to the telescope Pier. In addition, a summary is presented of the design path forward to the Final Design Review (FDR) from the point of completing the Preliminary Design Review (PDR) in early 2021, including the current status of critical prototyping efforts. Finally, management processes are outlined that are necessary to execute the Mount design-build contract spanning the next 8-9 years.
Management of equipment vibration will be a challenge for the upcoming generation of extremely large telescopes (ELTs) (GMT, TMT, and ESO’s ELT) and is being dealt with proactively by all three projects. We document the approaches, techniques, and future efforts by all three ELTs in their attempts to manage vibration in their telescopes. We detail the approaches to developing component requirements, characterizing vibration sources, simulating telescope structural movements, and approaches to mitigating source vibrations. We illustrate the iterative approach taken by the three observatories with several examples of concrete processes, measurements, and other details of use to future observatories.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing the Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT) which will enter the preliminary design phase in 2016. The GSSM is the tertiary mirror of TMT and consists of the world’s largest flat telescope mirror (approximately 3.4m X 2.4 m X 100mm thick) having an elliptical perimeter positioned with an extremely smooth tracking and pointing mechanism in a gravity-varying environment. In order to prepare for developing this unique mirror system, CIOMP has been developing a 1/4 scale, functionally accurate version of the GSSM prototype during the pre-construction phase of GSSM. The prototype will incorporate the same optomechanical system and servo control system as the GSSM. The size of the prototype mirror is 898.5mm×634mm×12.5mm with an elliptical perimeter. The mirror will be supported axially by an 18 point whiffletree and laterally with a 12 point whiffletree. The main objective of the preconstruction phase includes requirement validation and risk reduction for GSSM and to increase confidence that the challenge of developing the GSSM can be met. The precision mechanism system and the optical mirror polishing and testing have made good progress. CIOMP has completed polishing the mirror, the prototype mechanism is nearly assembled, some testing has been performed, and additional testing is being planned and prepared. A dummy mirror is being integrated into the cell assembly prototype to verify the design, analysis and interface and will be used when testing the prototype positioner tilt and rotation motions. The prototype positioner tilt and rotator structures have been assembled and tested to measure each subsystem’s jitter and dynamic motion. The mirror prototype has been polished and tested to verify the polishing specification requirement and the mirror manufacturing process. The complete assembly, integration and verification of the prototype will be soon finished. Final testing will verify the prototype requirements including mounted mirror surface figure accuracy in 5 different orientations; rotation and tilt motion calibration and pointing precision; motion jitter; and internally generated vibrations. CIOMP has scheduled to complete the prototype by the end of July 2016. CIOMP will get the sufficient test results during the pre-construction phase to prepare to enter the preliminary design for GSSM.
Finding a contract vehicle that balances the concerns of the customer and the contractor in a development project can be difficult. The customer wants a low price and an early delivery, with as few surprises as possible as the project progresses. The contractor wants sufficient cost and schedule to cover risk. Both want to clearly define what each party will provide. Many program offices do not want to award cost plus contracts because their funding sources will not allow it, their boards do not want an open ended commitment, and they feel like they lose financial control of the project. A fixed price incentive contract, with a mutually agreed upon target cost, provides the owner with visibility into the project and input into the execution of the project, encourages both parties to save costs, and stimulates a collaborative atmosphere by aligning the respective interests of customers and contractors.
While the concept of wavefront decomposition is a foundation of active optics systems, the choice of basis functions for
mirror figure control is divided. The common functions are Zernike polynomials, ubiquitously used for wavefront
descriptions, and bending (also called minimum energy or vibration) modes which offer optimal performance. We
present a look at the comparative performance between the two approaches, and discuss an implementation approach
which seeks to combine much of the analytic and interface simplicity of Zernike polynomials with the improved
performance of bending modes.
The Discovery Channel Telescope (DCT) is a 4.3-meter telescope designed for dual optical configurations, featuring an
f/6.1, 0.5° FoV, Ritchey-Chretien prescription, and a corrected f/2.3, 2° FoV, prime focus. The DCT is expected to
typically deliver sub-arcsecond images, with a telescope and local seeing contribution of <0.28" FWHM at the R-C
focus and <0.38" FWHM at the prime focus. The Delivered Image Quality (DIQ) budget considers errors from design
residuals, manufacturing, environmental effects, and control system limitations. We present an overview of the
analytical methods used, including sensitivity analysis for determining collimation effects, and a summary of
contributors to the overall system performance.
The Discovery Channel Telescope (DCT) is a 4.3-meter astronomical research telescope being built in northern Arizona
as a partnership between Discovery Communications and Lowell Observatory. The telescope will be able to support
substantial instrument payloads at Cassegrain, Nasmyth, and prime foci, and high observing cadences. The first-light
configuration will be as an f/6.1 Ritchey-Chrétien at Cassegrain with a 30 arc-minute field-of-view. Major facility work
is complete, and the telescope is currently in the integration phase with first-light anticipated in 2011. We present an
overview of the design and progress to date, and include plans for final integration, commissioning, and early science.
The Discovery Channel Telescope (DCT) is a 4.3-meter telescope designed for dual optical configurations, featuring an
f/6.1 Ritchey-Chretien prescription with a 0.5° field-of-view, and a corrected f/2.3 prime focus with a 2° field-of-view.
The DCT Active Optics System (AOS) maintains collimation and mirror figure to provide seeing limited images across
the focal planes and rapid settling times to minimize observing overhead, using a combination of feed-forward and lowbandwidth
feedback control via wavefront sensing. Collimation is maintained by tip-tilt-piston control of the M2
assembly and articulating M1 within its cell, taking advantage of the 120 degree-of-freedom support used for figure
control. We present an overview of the AOS design and principles of operation, and a summary of progress and results
to date.
The Discovery Channel Telescope is a 4.2-meter clear aperture telescope undertaken by the Lowell Observatory in
Flagstaff, Arizona. It will feature an interchangeable secondary assembly to allow the use of either a prime focus
instrument or a secondary mirror. In addition, it will have an active optical system and provisions for a wide range of
instruments. This paper describes the design of the telescope mount and drive systems. Particular challenges associated
with the design include: consideration for the weight of the 3500 lb Prime Focus Assembly (PFA) instrument;
interchangeable secondary assemblies; and providing thermal and mechanical stability in between updates to maintain
alignment between optical elements.
The Discovery Channel Telescope (DCT) is a 4.2-m telescope being built at a new site near Happy Jack, in northern Arizona. The DCT features a 2-degree-diameter field of view at prime focus and a Ritchey-Chretien (RC) configuration with Cassegrain and Nasmyth focus capability for optical/IR imaging and spectroscopy. Formal groundbreaking at the Happy Jack site for the DCT occurred on 12 July 2005, with construction of major facility elements underway.
The 4.2 m Discovery Channel Telescope requirements create interesting challenges for the Mount mechanical and control system design. The wide field of view survey telescope incorporates two operational foci: prime focus and cassegrain, either one must be available during any night's observing. The mission for observing requires fast slewing / offsets between each exposure with fast settling times to maintain the mission requirements. The prime focus arrangement includes a dedicated camera on the spider assembly and the cassegrain configuration includes a secondary mirror at the spider assembly with a dedicated instrument located at the cassegrain focus. This requirement challenges the design team to incorporate a prime focus / secondary mirror flipping mechanism within the secondary spider. The configuration requires a substantial prime focus and cassegrain payload with long focal distances creating a large inertia on the altitude axis. These are a few of the interesting challenges that are presented in this paper along with the design, trade-offs of different solutions, and the recommended design for the telescope Mount.
The success of giant telescopes is dependant not only in the optics design but also in the mechanics and electromechanics configurations. This paper addresses some of the key aspects of mechanical designs that impact this success. Areas investigated include methods for mitigating pointing errors caused by wind, thermal and gravity deflections; bearing and drive selection; and servo control issues. To reduce the cost of the telescope mount, it is hoped that conventional mechanical designs can be used to accomplish the high level of performance needed in the structure and drives area.
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