We report on results from the laboratory wide-field phasing testbed that has been constructed to validate the active optics and piston sensing hardware and algorithms to be used on the Giant Magellan Telescope. The GMT is comprised of seven primary (M1) mirror segments, and seven secondary (M2) segments. To maintain a high quality wavefront across the full LTAO field-of-view, telescope aberrations must be controlled at M1 and M2 independently. This will be done on GMT using the 4 off-axis wavefront sensors of the Acquisition, Guiding and Wavefront-sensing System (AGWS). With the double segmented nature of the GMT, the most challenging aberration to control is field-dependent piston, which results from tilts of M1 segments that are compensated by tilts of the corresponding M2 segment. We report here on wavefront sensing experiments conducted with a full-scale prototype AGWS wavefront sensor fed by a GMT optical simulator called the Wide-Field Phasing Testbed (WFPT). With the WFPT we introduce aberrations on M1 and M2, including simulated atmospheric turbulence and a variety of guide-star magnitudes. The AGWS measures the resulting off-axis aberrations, and then corrects the M1 and M2 aberrations. We describe the wavefront reconstructors used to generate the corrections and the performance over a range of conditions.

In the past two years significant forward progress has been achieved in development of Adaptive Optics sensing and control technology needed for the observation modes of the Giant Magellan Telescope1. Most notable is the recent progress in demonstrating the accurate and stable control of segment piston in the diffraction-limited Natural Guide Star AO observation mode. Two NSF-funded testbeds have been successfully operated to validate the control algorithms for active optics, adaptive optics and segment piston in diffraction-limited observation. GMTO also built and operated wavefront sensor prototypes and integrated them with the testbeds. The testing has largely validated the wavefront sensor designs and has retired much of the fabrication and assembly risks. In parallel with the hardware demonstrations, significant progress has been achieved in both NGAO and LTAO control simulations verifying compliance with the required performance in each of these observation modes and thereby supporting the image quality budgets. In the area of design the GMTO Telescope Metrology Subsytem has passed its Preliminary Design Review and the conceptual design of the Adaptive Optics Test Camera has been completed. Finally, a Delta Preliminary Design phase for the LTAO hardware has begun.

The Cherenkov Telescope Array Observatory (CTAO) is the next generation ground-based observatory for gamma-ray astronomy at very high energies. With initially 64 telescopes across two sites, the CTAO will be the world's largest and most sensitive high-energy gamma-ray observatory over energies from 20GeV to 300TeV. With sites at the Roque de los Muchachos Observatory (ORM) on the island of La Palma (Spain) and a southern array at the European Southern Observatory Paranal site in Chile, the CTAO will provide full sky coverage. The CTAO will be one order of magnitude more sensitive than current arrays, have a wider field of view, and have unprecedented accuracy in its detection of highenergy gamma rays dramatically changing our ability to study high energy sources. Development of telescopes and observatory infrastructure for the CTAO is already underway. Three classes of telescope types spread over a large area are required to cover the full the CTAO very-high energy range, and development is underway on all types. Infrastructure is under construction at ORM and increasingly so at Paranal. With its inherent modular architecture, sub-arrays of the eventual final array configuration will become operational in late 2026 with a performance better than existing arrays. The CTAO will continue to increase in performance as more telescopes are added until final completion towards the end of the decade. The CTAO will be the first ground-based gamma-ray observatory open to the worldwide astronomical and particle physics communities as a resource for data from unique, high-energy astronomical observations.

The GMT-Consortium Large Earth Finder (G-CLEF) is the first instrument for the Giant Magellan Telescope (GMT). G-CLEF is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. G-CLEF Flexure Control Camera (FCC) is included as a part in G-CLEF Front End Assembly (GCFEA), which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within GCFEA. FCC consists of an optical bench on which five optical components are installed. The order of the optical train is: a collimator, neutral density filters, a focus analyzer, a reimager and a detector (Andor iKon-L 936 CCD camera). The collimator consists of a triplet lens and receives the beam reflected by a fiber mirror. The neutral density filters make it possible a broad range star brightness as a target or a guide. The focus analyzer is used to measure a focus offset. The reimager focuses the beam from the collimator onto the CCD detector focal plane. The detector module includes a linear translator and a field de-rotator. We performed thermoelastic stress analysis for lenses and their mounts to confirm the physical safety of the lens materials. We also conducted the global structure analysis for various gravitational orientations to verify the image stability requirement during the operation of the telescope and the instrument. In this article, we present the opto-mechanical detailed design of G-CLEF FCC and describe the consequence of the numerical finite element analyses for the design.

We describe the development status of the first-generation science instruments for the Giant Magellan Telescope (GMT). The first-generation suite includes two infrared and two visible light spectrographs that together will deliver from wide-band imaging to R~200,000 spectroscopy at wavelengths from 0.3 to 5 µm. All four instruments are designed for use with diffraction limited or ground-layer adaptive optics modes. G-CLEF, a visible light echelle designed for broad scientific use and for precision radial velocity measurements, is in fabrication. The other three (GMACS, a wide field multi-object spectrograph; GMTNIRS, a near- to thermal-infrared echelle spectrograph utilizing silicon immersion gratings; and GMTIFS, a near-infrared imager and integral field spectrograph) are in Preliminary Design. The first-generation suite also includes a robotic fiber-feed system called MANIFEST, which enables spectroscopy over the 20 arcmin field of view of the telescope with custom fibers for G-CLEF, GMACS, and GMTNIRS. An additional facility instrument, GMagAO-X, is being developed to provide high-contrast imaging at visible and near-infrared wavelengths and is in Preliminary Design. We also discuss the visible and infrared cameras (called ComCam and AOTC, respectively) that will be used for alignment, verification, and commissioning of the active and adaptive optics modes of the telescope and enable early science activities.

This paper describes the deployment of the GMT-Consortium Large Earth Finder (G-CLEF) at the Clay telescope, one of the two Magellan telescopes, in late 2025, moving to the GMT in 2030. G-CLEF is a fiber-fed, ultra-high stability optical band echelle spectrograph designed for extremely precise stellar radial velocity measurement. On the Magellan Clay telescope, G-CLEF will take spectra with resolution up to ~300,000, fully resolving molecular spectral features and opening totally new discovery space for exoplanet atmosphere composition studies. G@M will also be coupled to the Magellan extreme adaptive optics facility, MagAO-X which will allow it to spatially resolve several exoplanets from their host stars. We provide a system description of the G@M instrument as it will be configured at Magellan. A top-level review of optomechanics, electronics and control systems follows, as well as a description of several risk-reduction exercises the team has undertaken.

The Wide Field Phasing Testbed (WFPT) will be used to test phasing and active optics systems planned for the doubly segmented Giant Magellan Telescope (GMT). The testbed consists of a set of optical relays including segmented and deformable mirrors (DMs) that represent the GMT primary and secondary. Displacements, tilts, and clocking of the GMT M1 and M2 segments generate discontinuous wavefront errors that cannot be accurately reproduced by only continuous-surface deformable mirrors. Therefore, two segmented Piston-Tip-Tilt (PTT) mirror arrays placed at the M1 and M2 conjugate positions augment the DMs to reproduce these wavefronts in the WFPT. They must have large stroke (≥10 µm piston) with high temporal stability (⪅20 nm) to avoid drifts from corrupting the sequential AGWS measurements. They must also have very narrow gaps between the mirror clear apertures to mimic the GMT pupil geometry. The pupil size at the PTT array was scaled to fit hexagonal 17mm mirror segments, producing a pupil of approximately 50.25 mm in diameter. Each of the seven segment assemblies consists of a custom segment base component, to which a set of three piezo actuators are epoxied. We selected lead zirconate titanate (PZT) discrete stack actuators which incorporate strain gauges to allow for closed-loop operation, thus eliminating the hysteresis and creep effects of the actuator. A two-axis flexure is bonded to each piezo, opposite the bonded base. The hexagonal mirror is bonded to the three flexures. The assembly, testing and integration challenges of two arrays completed in June 2022 is discussed.

One of the greatest technical challenges of the doubly-segmented Giant Magellan Telescope is the accurate and stable control of segment piston in the diffraction limited observation mode. To address this challenge, in collaboration with the University of Arizona, Smithsonian Astrophysical Observatory and the Istituto Nazionale di Astrofisica, GMTO is executing a project to optimize and validate segment piston control strategies and algorithms using a pair of testbeds. The testbeds provide disturbances to simulate atmospheric turbulence and differential atmospheric dispersion. In addition to the phasing demonstration, the testbeds offer the opportunity to validate hardware designs for the Acquisition & Guiding Wavefront Sensor (AGWS) and the Natural Guide Star Wavefront Sensor (NGWS) and to mitigate their fabrication and assembly risks. Significant progress is reported in the design of the AGWS and NGWS prototypes as well as preliminary test results from the testbeds.

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber-fed, optical echelle spectrograph that will be a first light instrument for the Giant Magellan Telescope (GMT). G-CLEF is a general-purpose echelle spectrograph with precision radial velocity (PRV) capability. The radial velocity (RV) precision goal of G-CLEF is 10 cm/sec; necessary for detection of Earth-sized exoplanets orbiting Solar-type stars in their habitable zone. This imposes challenging stability requirements on the optical mounts and spectrograph support structures especially when considering the instrument's operational environment. G-CLEF's accuracy will be influenced by thermal effects, ambient air pressure, vibration, and micro gravity-vector variations caused by normal telescope slewing. The design and fabrication schedule for the G-CLEF spectrograph and ancillary systems will lead the GMT telescope by approximately 5 years, therefore, we will design and build an interim installation configuration for G-CLEF at Magellan's 6.5m telescopes. This will allow us to complete and commission the spectrograph. During this period, we will collect at least 5 years of data at Magellan from roughly 2025 to 2030. We will also optimize major subsystems including; spectrograph optics and mechanics, vacuum systems, thermal control, and vibration isolation. G-CLEF completed its Critical Design Phase for the GMT configuration in 2018. In this paper, we provide an update on the G-CLEF spectrograph's opto-mechanical design, including the GMT front end assembly. We also provide an update on our current fabrication status including procurement of camera optics, reflective optics, carbon-fiber optical bench, camera optical mounts, and vacuum chamber assembly. We also discuss adaptations required to support the interim deployment at Magellan.

The Wide Field Phasing Testbed will be used to test phasing and active optics systems planned for the doubly segmented Giant Magellan Telescope. The testbed consists of a set of optical relays in which are located segmented and deformable mirrors that represent the GMT M1 and M2 mirrors. The testbed output beam has the GMT’s f/8.16 focal ratio and has a back focal distance large enough to allow using a full-scale prototype of one unit of the Acquisition Guiding and Wavefront Sensing System. The testbed will reproduce the telescope field dependent aberrations that result from misalignment of M1 and M2. Over its 20mm diameter field of view, the testbed will generate aberrations corresponding to the 20′ field of the GMT. A rotating turbulence screen and zero-deviation prisms in the testbed will generate seeing limited images that correspond to typical atmospheric seeing and dispersion conditions expected at the GMT. The software for the testbed is designed to allow connection of the testbed wavefront sensing analysis components to simulations of the testbed optical system, as well as to conform to the planned software interfaces of the GMT’s telescope control system.

The GMT Acquisition Guiding and Wavefront Sensing System (AGWS) is responsible for making the measurements required to keep the optics of the seven-segment GMT coaligned, phased, pointing in the correct direction, and conforming to the correct mirror shape. The AGWS consists of four identical probes that patrol the outer parts of the GMT field of view. Each probe is comprised of two channels, a visible channel for guiding and a J-band dispersed fringe sensor channel used to phase the segmented telescope. The four probes are mounted on the GMT Gregorian Instrument Rotator (GIR) just above the focal plane. A GMT Standard Electronics Cabinet, mounted on the GIR below the probes, houses system electronics. Each probe generates 353 watts and is actively cooled. To preclude the generation of a heat plume, disruptive of telescope seeing, the surface temperatures of the AGWS probes must be held to within ±1 deg C of the GMT enclosure temperature. The AGWS probes are located in a sensitive position on the GMT, just above the Direct Gregorian science instruments. A coolant leak in such a position would be dangerous to these instruments. To mitigate the effects of leaks, we have developed an active cooling system based on NOVEC-7100, an engineered cooling fluid produced by 3M™. The advantage of NOVEC-7100 is that it evaporates rapidly should there be a leak and will not damage sensitive optics or electronics should any liquid reach them. In this paper we describe the AGWS NOVEC-7100 cooling system design and performance.

The GMT Acquisition, Guidance and Wavefront Sensing System (AGWS) is responsible for making the measurements required to keep the optics of the seven-segment Giant Magellan Telescope coaligned, phased, pointed correctly and properly figured. Each AGWS probe includes several mechanisms to enable the probe to access and accurately track guide stars within its patrol field. Mechanism performance is crucial to the overall performance of the AGWS as they must be able to handle the large mass of the probe while operating over the wide GMT operational temperature and dynamic motion ranges. Prototyping test results have demonstrated compliance with challenging AGWS requirements.

The GMT-Consortium Large Earth Finder (G-CLEF), one of the first light instruments for the Giant Magellan Telescope (GMT), is a fiber-fed, high-resolution echelle spectrograph. G-CLEF is expected to proceed towards fabrication in the coming months. In this paper, we present the current, pre-construction G-CLEF optical design, with an emphasis on the innovative features derived for the spectrograph fiber-feed, the implementation of a volume-phase holographic (VPH)- based cross disperser with enhanced blue throughput and our novel solutions for a multi-colored exposure meter and a flat-fielding system.

The GMT-Consortium Large Earth Finder (G-CLEF) is one of the first instrument for the Giant Magellan Telescope (GMT). The G-CLEF is a fiber fed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. The G-CLEF Flexure Control Camera (FCC) is included as a part in the G-CLEF Front End Assembly (GCFEA), which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within the GCFEA. The five optical components constituting the FCC are aligned on a common optical bench. The order of the optical train is: a collimator, neutral density filters, a focus analyzer, a reimaging camera barrel, and a detector module. The collimator receives the beam reflected by the fiber mirror and consists of a triplet lens. The neutral density filters are located just after the collimator to make it possible a broad range star brightness as a target or a guide. The tent prism focus analyzer is positioned at a pupil produced by the collimator and is used to measure a focus offset. The reimaging camera barrel includes two pairs of doublet lenses to focus the beam onto the CCD focal plane. The detector module is composed of a linear translator and a field de-rotator. In this article, we present the optical and mechanical detailed designs of the G-CLEF FCC.

The Giant Magellan Telescope’s Acquisition, Guiding, and Wavefront Sensing System (AGWS) is comprised of four identical probes, each containing 11 axes of precision control. The largest of the mechanisms carries a mass of nearly 500kg. The mechanisms are diverse in type, including a voice coil actuated tip-tilt mirror, a rotary harmonic drive, high accuracy and precision lenslet rotation stages and ballscrew driven linear stages. To meet image quality, positioning, and tracking requirements, these mechanisms and their EtherCATcontrolled servos are designed for stiffness. Employing inductive tape encoders, they must position and track to 10um precision with minimal backlash, over velocities ranging from ~10mm/sec to essentially zero, where stiction becomes significant. We will present the designs of the mechanisms, highlighting key features, design trades, and preliminary prototyping results.

The GMT-Consortium Large Earth Finder (G-CLEF) will be part of the first generation instrumentation suite for the Giant Magellan Telescope (GMT). G-CLEF is a general purpose echelle spectrograph operating in the optical passband with precision radial velocity (PRV) capability. The measurement precision goal of G-CLEF is 10 cm/sec; necessary for the detection of Earth analogues. This goal imposes challenging stability requirements on the optical mounts and spectrograph support structures especially when considering the instrument’s operational environment. G-CLEF’s accuracy will be influenced by changes in temperature and ambient air pressure, vibration, and micro gravity-vector variations caused by normal telescope motions. For these reasons we have chosen to enclose G-CLEF’s spectrograph in a wellinsulated, vibration-isolated vacuum chamber in a gravity invariant location on GMT’s azimuth platform. Additional design constraints posed by the GMT telescope include; a limited space envelope, a thermal leakage ceiling, and a maximum weight allowance. Other factors, such as manufacturability, serviceability, available technology, and budget are also significant design drivers. G-CLEF will complete its Critical Design phase in mid-2018. In this paper, we discuss the design of GCLEF’s optical mounts and support structures including the choice of a low-CTE carbon-fiber optical bench. We discuss the vacuum chamber and vacuum systems. We discuss the design of G-CLEF’s insulated enclosure and thermal control systems which simultaneously maintain the spectrograph at milli-Kelvin level stability and limit thermal leakage into the telescope dome. Also discussed are micro gravity-vector variations caused by normal telescope slewing, their uncorrected influence on image motion, and how they are dealt with in the design. We discuss G-CLEF’s front-end assembly and fiber-feed system as well as other interface, integration and servicing challenges presented by the telescope, enclosure, and neighboring instrumentation. This work has been supported by the GMTO Corporation, a non-profit organization operated on behalf of an international consortium of universities and institutions: Arizona State University, Astronomy Australia Ltd, the Australian National University, the Carnegie Institution for Science, Harvard University, the Korea Astronomy and Space Science Institute, the São Paulo Research Foundation, the Smithsonian Institution, the University of Texas at Austin, Texas AM University, the University of Arizona, and the University of Chicago.

The Acquisition Guiding and Wavefront Sensing System (AGWS) is responsible for making the measurements required to keep the optics of the seven-segment GMT coaligned, phased, pointing in the correct direction, and conforming to the correct mirror shape. The AGWS consists of four identical probes that patrol the outer parts of the GMT field of view. Each probe is comprised of two channels. The visible channel contains optics that can provide high-speed full aperture guiding, segment guiding, or Shack-Hartmann wavefront sensing feeding an EMCCD camera. In natural seeing operations, these probes feed the GMT active optics system. In ground layer AO mode, they are the primary wavefront sensors. The second channel, used for phasing the seven segments in diffraction limited operation, contains J-band dispersed fringe sensor optics feeding a SAPHIRA IR e-APD array. We present the system architecture, and an overview of requirements, optical, mechanical and electrical designs.

The GMT-Consortium Large Earth Finder (G-CLEF) will be part of the first generation instrumentation suite for the Giant Magellan Telescope (GMT). G-CLEF will be a general purpose optical passband echelle spectrograph with a precision radial velocity (PRV) capability of 10 cm/sec, a requirement necessary for the detection of Earth analogues. The instrument will be particularly sensitive to thermal effects and the necessary stability cannot be achieved through the use of low CTE materials alone. It is the combination of low CTE materials and exquisite thermal control which will enable the instrument to achieve its precision requirements. G-CLEF will complete its Critical Design phase in mid-2018. In this paper, we discuss the precision thermal control systems which enable milli-Kelvin-level stability of the spectrograph and its red and blue focal planes. The measurement electronics and thermal control strategies used in the spectrograph are described. Of particular importance is the development of a continuous LN2 flow cryo-cooler system used to maintain the focal planes at stable cryogenic operational temperatures. This system has been validated with a prototyping effort completed during the instrument's design phase. We also review G-CLEF's insulated enclosure which simultaneously maintains the spectrograph a stable temperature and limits the maximum thermal leakage into the telescope dome. This work has been supported by the GMTO Corporation, a non-profit organization operated on behalf of an international consortium of universities and institutions: Arizona State University, Astronomy Australia Ltd, the Australian National University, the Carnegie Institution for Science, Harvard University, the Korea Astronomy and Space Science Institute, the Sao Paulo Research Foundation, the Smithsonian Institution, the University of Texas at Austin, Texas A&M University, the University of Arizona, and the University of Chicago.

The GMT-Consortium Large Earth Finder (G-CLEF) is an instrument that is being designed to exceed the state-of-the-art radial velocity (RV) precision achievable with the current generation of stellar velocimeters. It is simultaneously being designed to enable a wide range of scientific programs, prominently by operating to blue wavelengths (< 3500Å). G-CLEF will be the first light facility instrument on the Giant Magellan Telescope (GMT) when the GMT is commissioned in 2023. G-CLEF is a fiber-fed, vacuum-enclosed spectrograph with an asymmetric white pupil echelle design. We discuss several innovative structural, optical and control system features that differentiate G-CLEF from previous precision RV instruments.