The Giant Magellan Telescope, with a 25.4m primary and operating from the ultraviolet to the long wave infrared, is being built as one of the next-generation Extremely Large Telescopes. The size of the GMT and its doubly segmented design create a unique set of challenges for telescope alignment, from initial alignment during the assembly, integration, verification and commissioning phase to operational alignment between and during the telescope exposures. GMT therefore includes a Telescope Metrology System (TMS) that uses networks of laser trackers and absolute and differential distance-measuring interferometers for improved alignment efficiency and phasing of the mirror segments. The TMS has successfully passed its Preliminary Design Review and entered the Final Design phase. In this paper we present the current design and expected performance of the GMT TMS.
The Giant Magellan Telescope has a seven-segment Adaptive Secondary Mirror (ASM) System that must meet stringent surface error performance requirements while tracking and offloading. The first hexapod of the M2 Positioner has been constructed and tested by AdOptica using an attocube-based laser truss as a truth sensor. Modeling, analysis, test results are presented, including an actuator model, control structure interaction analysis, attocube sensor and actuator noise models, modal identification, and performance measurements. The test results show that the 10nm RMS surface error requirement due to actuator-based noise sources is verified.
The 25.4m diameter Giant Magellan Telescope utilizes a segmented adaptive secondary mirror subsystem (ASMS) for correction of atmospheric wavefront error (r0=7cm), wind-induced telescope vibrations up to 17m/s wind speed, and M1 and M2 segment alignment errors. The ASMS is composed of seven ASM segments. Each is a 1.05m diameter concave circular segment with a 2mm thick face sheet that is driven by 675 voice coil motor motors to provide wave front and phasing control. The face sheet surface figure can be updated at up to 2kHz with a -3dB bandwidth greater than 800Hz. The ASMS is integrated to the top end of the telescope by actively controlled 6 DOF hexapods. Each hexapod provides 7Hz position control to maintain the alignment within the capture range of the wave front control system. The first off-axis ASM segment is currently being manufactured by the AdOptica Consortium and their subcontractors. The Zerodur Reference Body, Zerodur face sheet, and major structural components have been manufactured and integrated. Structural and dynamic testing of the ASM primary load path has been completed. A phasing testbed is in the build stage that utilizes the single ASM segment, edge sensors, and a reference frame to simulate the phasing of an array of 4 ASM segments. This document presents an overview of the ASMS design and the results of the manufacturing, assembly and testing of the first ASM segment.
The Giant Magellan Telescope will be a 25.4-m visible and infrared telescope at Las Campanas Observatory in Chile. The initial alignment of this doubly segmented telescope will be challenging, particularly when mapping coordinate systems together. To ease the complications of alignment, a laser tracker network has been developed to accurately determine the coordinate systems of subsystems and tie them into a reference coordinate system to ensure a successful and efficient first photons phase of the telescope. This paper will discuss the simulations that have been run to date of this laser tracker network and our general initial alignment strategy.
The Giant Magellan Telescope will be a 25.4-m visible and infrared telescope at Las Campanas Observatory. The optical design consists of 7 8.4-m primary mirror segments that reflect light to 7 secondary mirror segments in a doubly segmented direct Gregorian configuration. GMT is developing a Telescope Metrology System (TMS) to decrease the complexity of alignment and increase observatory efficiency. The TMS has been developed to Preliminary Design Review level. A prototyping, modelling, and analysis effort has been completed. All components of the system were matured, and the edge-sensing strategy was significantly revised. This paper describes the current TMS design.
The Giant Magellan Telescope will be a 25.4-m visible and infrared telescope at Las Campanas Observatory. The optical design consists of 7 8.4-m primary mirror segments that reflect light to 7 secondary mirror segments in a doubly-segmented direct Gregorian configuration. Each mirror pair must be coaligned and co-boresighted. During operations, the alignment of the optical components will deflect due to variations in temperature, gravity-induced structure flexure of the mount, and, on a scale relevant to phasing, vibrations. The doubly-segmented nature and size of the GMT will create a novel set of challenges for initial assembly, integration, and verification and maintaining high-precision alignment of the optical elements during operations. GMT is developing a Telescope Metrology System that uses 3D laser metrology systems to decrease the complexity of alignment and increase observatory efficiency. This paper discusses the 4 subsystems of TMS as well as their operational modes.
The Giant Magellan Telescope (GMT) will feature two Gregorian secondary mirrors, an adaptive secondary mirror (ASM) and a fast-steering secondary mirror (FSM). The FSM has an effective diameter of 3.2 m and consists of seven 1.1 m diameter circular segments, which are conjugated 1:1 to the seven 8.4m segments of the primary. Each FSM segment contains a tip-tilt capability for fast guiding to attenuate telescope wind shake and mount control jitter. This tiptilt capability thus enhances performance of the telescope in the seeing limited observation mode. The tip-tilt motion of the mirror is produced by three piezo actuators. In this paper we present a simulation model of the tip-tilt system which focuses on the piezo-actuators. The model includes hysteresis effects in the piezo elements and the position feedback control loop.
KEYWORDS: Mirrors, Telescopes, Actuators, Space telescopes, Off axis mirrors, Integrated modeling, Interfaces, Optical instrument design, Phase transfer function, Control systems
The Fast-Steering Secondary Mirror (FSM) of Giant Magellan Telescope (GMT) consists of seven 1.1m diameter segments with effective diameter of 3.2m. Each segment is held by three axial supports and a central lateral support with a vacuum system for pressure compensation. Both on-axis and off-axis mirror segments are optimized under various design considerations. Each FSM segment contains a tip-tilt capability for guiding to attenuate telescope wind shake and mount control jitter. The design of the FSM mirror and support system configuration was optimized using finite element analyses and optical performance analyses. The design of the mirror cell assembly will be performed including sub-assembly parts consisting of axial supports, lateral support, breakaway mechanism, seismic restraints, and pressure seal. . In this paper, the mechanical results and optical performance results are addressed for the optimized FSM mirror and mirror cell assembly, the design considerations are addressed, and performance prediction results are discussed in detail with respect to the specifications
The Fast-steering Secondary Mirror (FSM) of Giant Magellan Telescope (GMT) consists of seven 1.1 m diameter circular segments with an effective diameter of 3.2 m, which are conjugated 1:1 to the seven 8.4 m segments of the primary. Each FSM segment contains a tip-tilt capability for fast guiding to attenuate telescope wind shake and mount control jitter by adapting axial support actuators. Breakaway System (BAS) is installed for protecting FSM from seismic overload or other unknown shocks in the axial support. When an earthquake or other unknown shocks come in, the springs in the BAS should limit the force along the axial support axis not to damage the mirror. We tested a single BAS in the lab by changing the input force to the BAS in a resolution of 10 N and measuring the displacement of the system. In this paper, we present experimental results from changing the input force gradually. We will discuss the detailed characteristics of the BAS in this report.
The Giant Magellan Telescope (GMT) will be equipped with two Gregorian secondary mirrors: a fast-steering mirror (FSM) system for seeing-limited operations and an adaptive secondary mirror (ASM) for adaptive optics observing modes. The FSM has an effective diameter of 3.2 m and is comprised of seven 1.1 m diameter circular segments, which are conjugated 1:1 to the seven 8.4m segments of the primary. Each FSM segment has a tip-tilt capability for fast guiding to attenuate telescope wind shake and jitter. To verify the tip-tilt performance at various orientations, we performed tiptilt tests using a conceptual prototype of the FSM (FSMP) which was developed at KASI for R&D of key technologies for FSM. In this paper, we present configuration, methodology, results, and lessons from the FSMP test which will be considered in the development of FSM.
The Fast Steering Secondary Mirror (FSM) for the Giant Magellan Telescope (GMT) will have seven 1.05 m diameter circular segments and rapid tip-tilt capability to stabilize images under wind loading. In this paper, we report on the assembly, integration, and test (AIT) plan for this complex opto-mechanical system. Each fast-steering mirror segment has optical, mechanical, and electrical components that support tip-tilt capability for fine coalignment and fast guiding to attenuate wind shake and jitter. The components include polished and lightweighted mirror, lateral support, axial support assembly, seismic restraints, and mirror cell. All components will be assembled, integrated and tested to the required mechanical and optical tolerances following a concrete plan. Prior to assembly, fiducial references on all components and subassemblies will be located by three-dimensional coordinate measurement machines to assist with assembly and initial alignment. All electronics components are also installed at designed locations. We will integrate subassemblies within the required tolerances using precision tooling and jigs. Performance tests of both static and dynamic properties will be conducted in different orientations, including facing down, horizontal pointing, and intermediate angles using custom tools. In addition, the FSM must be capable of being easily and safely removed from the top-end assemble and recoated during maintenance. In this paper, we describe preliminary AIT plan including our test approach, equipment list, and test configuration for the FSM segments.
The Giant Magellan Telescope (GMT) will be equipped with two Gregorian secondary mirrors; a fast-steering secondary mirror (FSM) for seeing-limited operations and an adaptive secondary mirror (ASM) for adaptive optics observing modes. The FSM has an effective diameter of 3.2 m and is comprised of seven 1.1 m diameter circular segments, which are conjugated 1:1 to the seven 8.4m segments of the primary mirror. Each FSM segment has a tip-tilt capability for fast guiding to attenuate telescope wind shake and jitter. The FSM is mounted on a two-stage positioning system; a macro-cell that positions the entire FSM segments as an assembly and seven hexapod actuators that position and drive the individual FSM segments. In this paper, we present a technical overview of the FSM development status. More details in each area of development will be presented in other papers by the FSM team.
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