This PDF file contains the front matter associated with SPIE Proceedings Volume 13094, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The Giant Magellan Telescope (GMT), one of three extremely large telescopes (ELTs) in development, will be located on the summit of Cerro Las Campanas, a peak within the property of the Las Campanas Observatory (LCO) in Chile. The GMT employs seven 8.4m monolithic mirrors as segments to form a single optical surface with an equivalent diameter of 25.4 meters. Developing a new observatory for cutting-edge science operations and a 50-year lifespan poses a variety of design and construction challenges. This paper reports on progress since 2020, including the latest developments for the GMT site master plan, and work completed for the site infrastructure, telescope enclosure, and support facilities. In late 2021, GMTO selected IDOM (Bilbao, Spain) to mature the enclosure from its preliminary reference design through to final design and documents (drawings and specification) for construction. Over the last two years, the designs for enclosure structures, mechanisms, pier seismic isolation system, and related control systems have been refined as they passed through a 60% critical design review in May 2023, and the final design review (FDR) in May 2024. Construction work at the GMTO site started in 2015, and over the past four years has seen completion of the underground utility distribution systems and preparations for start of enclosure construction.

The Sloan Digital Sky Survey V (SDSS-V) Local Volume Mapper (LVM) is an ultra-wide field high spatial resolution IFU survey of the Milky Way, the Magellanic Clouds, and a sample of galaxies in the local volume. Observations are carried out with the LVM Instrument (LVM-I), a specially designed robotic telescope, instrument, and facility located at Las Campanas Observatory (LCO) in Chile. The LVM-I is hosted in a custom-built roll-off type enclosure that protects the hardware, allows for simultaneous observations towards different directions in the sky by the four LVM-I telescopes, provides a thermally controlled stable and clean environment for the LVM-I spectrographs, supplies all necessary utilities (e.g. power, communications, LN2 detector cooling) to the different LVM-I sub-systems, provides environmental telemetry and information, and integrates with the LVM-I control software to operate in an automated fashion. In this paper we discuss the design of the LVM-I enclosure, its construction, and an evaluation of its performance. The LVM-I was successfully integrated on-site and commissioned during the first half of 2023, with the enclosure design and performance meeting its requirements and allowing for the start of the SDSS-V LVM project science operations.

Rubin Observatory Dome was designed and built by EIE GROUP with headquarters in Venice-Mestre, Italy. The Design Phase was completed in February 2016. On-site activities started in the spring of 2017. The Dome is approaching the final completion of testing and integration. The Dome utilizes a steel structure. This supports a bi-parting, two door aperture, a uniquely designed moving Light Windscreen, a Light Baffled Louver System, an overhead bridge crane, a rear access door and numerous platforms. In this paper, we present the status of the final assembly, integration and testing.

The GMT enclosure detail engineering design has been consolidated to confidently face the future construction phase. This final detailed design phase has focused on delivering a cost-effective reliable enclosure that can be efficiently built in Las Campanas remote location providing a resilient integrated system that will house and protect GMT telescope against adverse environmental and seismic conditions. A seamless integration of a wide variety of disciplines including concrete and steel structures, mechanisms, mechanical-electrical-plumbing (MEP), telescope specific utilities, control systems and architectural has been vital to comply with the strict requirements of the project.

Besides, a thorough validation plan has been produced comprising analytical verification, early prototypes, factory and site assembly and testing plans (FAT & SAT), to guarantee performance and reliability of all subsystems at the site. Furthermore, construction procedures, techniques and logistics have been reviewed and considered when developing design key features together with assembly specifications so that the enclosure is constructed at the site in a safe and effective manner.

The telescope Main Structure and the Dome of the ELT are being procured by ESO as an integrated system together with the auxiliary building and the service plants and are supplied by the ACe Consortium. The contract was signed in May 2016 and despite various challenges and obstacles – commercial, technical, and other – the progress that has been achieved to date is significant and tangible. Both the Dome (including Auxiliary Building) and the Telescope Structure have passed Final Design Review; manufacture of the structural elements is approaching completion; the first mechanisms have been tested and delivered to site; and the publicly available footage of the construction speaks for itself. Nevertheless, there is still a long road to completion, with various design optimisations being incorporated as manufacture is ongoing, diligence needed to maintain quality and a significant effort still to be expended in implementing and testing the control system(s) for the mechanisms and services. In this paper we will describe the advancement reached by the project and discuss some technical aspects associated to the design. The status of the design, of the manufacturing and of the construction on site will be described.

The DAG (Dogu Anadolu Gözlemevi) Eastern Anatolia Observatory is an astronomical project fully funded by Turkish Ministry of Development and the Atatürk University of Astrophysics Research Telescope (ATASAM). DAG Observatory is provided with a 4m-class optical and infrared telescope, equipped with secondary (0.76m) and tertiary mirrors which furnish the telescope with two Nasmyth foci. Since 2015, the project has seen the crucial contribution of EIE GROUP in the Design, Production and on-site Installation of the mount structure of the 4m class optical/nearinfrared telescope (DAG Telescope) in contract with AMOS company. EIE GROUP is also the main contractor of the 18.6m-diameter Rotating Building (DAG Dome) at an altitude of 3170m asl on the Erzurum Plateau, Turkey. After completing a full assembly and testing in the factory, the telescope was subsequently disassembled and transported to the final installation site. Now, on-site assembly activities have been completed, and all internal acceptance tests regarding the mount structure have been conducted. This document focuses on the on-site assembly activities of the EIE Group, as well as the related internal pre-commissioning, commissioning, and functional and acceptance tests.

National Astronomical Observatory of Japan (NAOJ) is responsible for procuring the Telescope Structure System (STR) of the Thirty Meter Telescope (TMT) and engaged Mitsubishi Electric Corporation (MELCO) to perform the preliminary/final design and production readiness work since 2012. The final design of the TMT STR was deemed completed through a series of external design reviews covering structural and mechanical, controls, and auxiliary systems such as the Segment Handling System (SHS), Aerial Service Platform (ASP), Elevator (ELV), safety, and the seismic isolation system. TMT STR is currently in the production readiness phase and has already passed the Production Readiness Reviews (PRRs) for major rotating mechanical structures. In this paper we present an overview of the design progress of the TMT STR, matured through extensive studies, performance assessments, and design budgets derived from bottoms-up analyses. Additionally, we discuss prototype activities to mitigate risks to performance and manufacturability of complex designs, along with the current programmatic status of the project.

The Vera C. Rubin Observatory is an integrated survey system, currently under construction in Chile, to accomplish a 10-year optical survey of the southern sky. The 8.4-meter Simonyi Survey Telescope mount is nearing completion and undergoing final verification and performance testing. Since the system is optimized for etendue, the telescope mount slewing performance is particularly critical to overall survey efficiency. For example, this high performance mount is required to slew 3.5 degrees, on the sky, and settle in a 4-second period. Here an account of the mount subsystem is presented and selected dynamic performance results from on-site testing are described.

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) will be a 25-meter optical telescope with a maximum weight of about 2300 t, located on Cerro Las Campanas in Chile. To fulfill the challenging pointing and tracking accuracy requirements, as well as the functionality requirements of the auxiliary subsystems, complex design solutions needed to be developed. To support and validate the design of those subsystems and to provide reliable data and parameter for performance analysis, a variety of prototyping tests have been performed during the design phase. The telescope support consists of a radial spring system that allows thermal decoupling to the concrete foundation, an earthquake damping system as well as frictionless hydrostatic bearings and a high-performance direct drives and control system. Highly accurate and precise mechanical components need to be consistent to gravity-caused structural deformations. This requires special supports to avoid structural overload. These unique supports, especially developed for the GMT have been prototyped. Self-induced vibrations are one of the most disturbing influences on such complex control systems as well as the adaptive optics of the telescope and need to be suppressed or at least reduced wherever possible. Tests have been performed to measure and optimize vibration sources like cable wraps and electronic cabinets. The covers of the primary mirrors with a diameter of more than eight meters were developed and tested in full scale to ensure proper function even in tilted position when the telescope rotates in elevation. Falling object tests have been made to demonstrate the protection of the mirrors. An inflatable wash seal around each mirror has been tested to ensure reliable functionality. The presentation will provide an overview on the subsystem development test activities and show test setups and results of main component tests supporting the subsystems design and analyses.

The National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) located on the summit of Haleakalā, Maui is the largest solar telescope in the world. Housing a 4-meter off-axis primary mirror and a highly advanced adaptive optics system, DKIST is enabling observations of specific regions of the Sun in higher resolution and greater detail than any preexisting ground-based telescope. The DKIST Enclosure Azimuth Mechanism is responsible for accurate positioning of the Enclosure in azimuth and provides a second degree of freedom to the altitude movement of the Enclosure Shutter which enables an overall position accuracy of 19 arcmin point-to-point at the Enclosure Aperture. The mechanism is primarily comprised of sixteen track rail segments, eight driven bogies, and two idler bogies, and it serves as the interface between the fixed support building Ring Girder structure and the rotating Enclosure structure. Visual observations and control system torque data have shown evidence of a loss of contact at the interface between the individual bogie wheels and the track rail. This loss of contact results in imbalanced loading conditions that impact performance and reliability as loads are varied in proportion to the number of wheels in contact. In addition, visual inspections have shown early indications of rolling contact fatigue at specific azimuth locations of the track rails due to high contact stresses. As a result, a project was initiated to improve load sharing and maintain tracking accuracy by minimizing pointing error deviations that result from rail flatness tolerances variations, unanticipated mechanical deformations from load imbalances, and varying control systems demands. In addition, equalizing the load balance will reduce unintended fatigue loading of the structural and mechanical components as well as reduce contact stresses in the rail sections improving overall mechanism reliability. The investigation, implementation, and evaluation of this process is presented herein.

Ground-based telescope observatories are typically located in harsh environments. Due to their location, they are subject to a wide range of severe environmental conditions such as seismic events, strong winds, and large diurnal temperature swings including freeze/thaw cycles. It is common for telescope observatories to experience fatigue and degradation as a result of their unique dynamic use within these harsh environmental conditions. One specific result of this degradation includes rainwater leakage into the rotating telescope enclosure. This water leakage has the potential to cause serious damage to interior components of the telescope enclosure, including the telescope and its sensitive instruments. Innovative techniques for detecting rainwater leakage include the use of a thermal imaging camera in conjunction with an Unmanned Aircraft System (UAS) / drone. Standard RGB photography accompanies thermal integrated analysis to allow a non-invasive peer into the health of the telescope enclosure. The drone and its specialized camera capture visual data to identify any abnormality found and cross reference the thermal anomaly to a physical place on the structure. Traditional techniques used for detection include trained and experienced personnel physically observing the structure alongside the data captured by the drone. Using the 8.2-meter Subaru Telescope on Maunakea in Hawaii as a case study, this paper will present innovative and traditional techniques for detection of rainwater leakage into the rotating telescope enclosure and other sensitive areas. The Subaru Telescope was constructed in the late 1990’s and is starting to experience predictable degradation of the rotating enclosure after 20+ years of use on Maunakea. By utilizing innovative and traditional techniques for rainwater leak detection, the Subaru Telescope will be able to better identify problem areas and start to repair these areas to prevent further degradation. Lessons learned from the experience will better prepare Architects and Engineers for the design of future ground-based telescope observatories.

In this paper, a kinetic energy recovery system for large telescopes is presented, with the Atacama Large Aperture Submm Telescope (AtLAST) as a possible target application. The system consists of supercapacitors integrated in the DC-link of motor inverters through a bidirectional DC-DC converter. The optimal system design, based on the energy flow analysis within the telescope’s power electronics, is introduced. The proposed system is simulated as part of the telescope’s drives, providing not only a significant reduction in energy consumption of the telescope due to motion, but also remarkably reducing (or shaving) grid power peaks. We find that the system presented here can contribute to making both current and future observatories more sustainable.

Each of the Keck telescopes incorporates a 3” thick layer of grout which serves as the primary load path between the steel azimuth journal—the telescope’s running surface—and the main body of the reinforced concrete pier. Keck has observed increased journal deflections of the Keck 1 telescope under load. These increased deflections affect telescope pointing and can cause azimuth drive faults. Investigation into the source of the deflections found deterioration of the cementitious grout, which is believed caused by a combination of exposure to oil and cyclic loading from the telescope. The JPL team responsible for the Deep Space Network antennas solved a similar issue by changing from a cementitious grout to an oil impervious epoxy grout. Following detailed introduction, history, and background of the issue, this paper presents: material qualification testing of the replacement epoxy grout, procedural validation leading up to a trial repair of a 16-degree section of the Keck 1 pier, and lessons learned from the trial repair which occurred in October 2023—including preliminary performance monitoring. Note: the potential for material creep associated with epoxy grout is one specific area of interest for the new material, which will be monitored and measured for approximately 1 year before a full-scale repair begins in March 2025.

The Greenland Telescope (GLT) currently achieves a blind pointing accuracy of 2" rms, sufficient for 230GHz VLBI operations at Pituffik Space Base. Plans to relocate the antenna to Summit Station are underway to enable observations at ≥690GHz, which requires improving the pointing accuracy due to smaller beam sizes at higher frequencies. Since achieving the ALMA-standard referenced pointing accuracy of less than 1" for single-dish operations is impractical due to limited sensitivity, GLT’s strategy involves real-time adjustments using data from metrology sensors, following the Systematic Pointing Error Model (SPEM) by the antenna manufacturer (Vertex Antennentechnik). This paper highlights our metrology system’s role in predicting pointing corrections through real-time monitoring of inclinometers, linear, and temperature sensors. Additionally, we introduce a night-viable optical guidescope system for astrometric referencing of star-fields, aiming to enhance pointing precision for high-frequency VLBI with the GLT.

In October 2022, there was an accident with the Gemini North Primary Mirror (M1) during routine mirror movements that caused it to come in contact with its washcart. The M1 came into contact with an earthquake restraint on the washcart as it was being moved in preparation for stripping and recoating activities. After the incident, analyses were conducted to determine the extent of the damage and the necessary steps to restore the telescope to normal operations. The extent of the fracture was determined by through visual inspection, and by observing stress polarization within the glass. Due to damage occurring along one of the lateral supports on the M1, it was first necessary to determine a safe method for removal. Grinding and polishing work of the damaged areas was then necessary to secure the glass and remove any stress. It was then necessary to bond a new lateral support to the M1 to prevent higher order aberrations from the asymmetrical support. Since a small change in the location of the support was necessary, a finite element analysis was performed to determine how its new location would affect optical aberrations on the M1. Test samples were produced to verify the performance of the new bond. This paper provides detailed explanations how the Gemini North telescope was returned to normal operations.

During the 2022 Astronomical Telescopes and Instrumentation SPIE, Sener presented a novel concept of a system for cleaning of optical surfaces, initially conceived for ground-based astronomical observatories. The proposed concept is based on laser cleaning, a technology broadly used in industrial application, which has been carefully adjusted to gently cleaning the mirror while guarantee the integrity of the coating and, even more important, the substrate. This paper reports the obtained results during the system tests and presents the conclusions and summarizes the following steps in the product development.

Vera C. Rubin Observatory is the combination of an 8.4-m telescope, a 3.2 gigapixel camera and a sophisticated data pipeline that is now in the final stage of construction/commissioning in Chile. In the last couple of years, every part of the Observatory has gone through tremendous progress. The telescope is fully functional with successful motion tests using metal surrogates on the mirror support systems, the Camera has completed final laboratory performance testing and has been delivered safely to the Observatory and the data pipeline is ready to receive and reduce the first on-sky images. Meanwhile, the Education and Public Outreach team has paved the way to operations by successfully finishing construction and started implementing their full program. The Construction team forecasts completion by mid-2025.

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 Square Kilometre Array Observatory mission is to "build and operate cutting-edge radio telescopes to transform our understanding of the Universe and deliver benefits to society through global collaboration and innovation". It will initially realise this through the construction of the world's largest radio telescope facility, composed of a pair of interferometric arrays, SKA-Low (Australia; 50-350MHz; 74km max baseline) and SKA-Mid (South Africa; 350MHz-15.4GHz; 150km max baseline). With the construction approved in July 2021, and permitting access provided to both sites by December 2022, we describe the high-level construction strategy, in particular, to develop the earliest possible working demonstration of the architecture and then maintain a continuously working and expanding facility that demonstrates the full performance capabilities of the SKA design. We report the current status of the infrastructure development, component manufacture, array deployments and system integration on both sites. We highlight the progress to-date against the planning baselines for budget, schedule and performance to indicate the trajectories for community engagement and early science. We also note the challenges encountered and navigated in the execution of global, large research infrastructure construction as well as the broader impacts for such investments, beyond the planned scientific research.

The Dynamic REd All-sky Monitoring Survey (DREAMS) is a near-infrared fully automated all-sky survey that will be conducted using a custom built 0.5m telescope that will be located at the Australian National University’s Siding Spring Observatory. The telescope feeds 6 individual InGasAs cameras spanning a total field-of-view of 3.8sq.deg using a novel optomechanical design. Here we present the finished details of the telescope construction and its measured performance as well as details of the survey it will perform of the Southern transient sky.

We are carrying out a 1.8-m aperture off-axis telescope project PLANETS. The PLANETS telescope is characterized by using an off-axis mirror to enable us high-contrast imaging and spectroscopy with low-scattering in the optical system. Our major scientific goal is to observe faint emission around a bright body, such as gases surrounding planets and satellites in the solar system (e.g., Jovian satellite Europa’s water plume) as well as exoplanets. Using a new technology of mirror polishing with a robot arm and 3-point drag probe, we performed the polishing of the off-axis primary mirror. We also developed the whiffletree support with warping harness for the primary mirror support. We will assemble the whole PLANETS telescope system and conduct the first light of stars as technical demonstration in Japan within a year. We have begun coordinating with several high-altitude observatory sites in which the PLANETS telescope will be installed after the technical demonstration in Japan.

The National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) is the largest solar telescope in the world, utilizing a 4m off-axis primary mirror sending light to a ∼16m wide rotating multi-instrument coudé laboratory supported by a highly complex active and adaptive optics system, delivering a diffraction limited beam. The resulting mount size, long optical pathways, various moving components, and complex thermal design leaves DKIST with a very tight optical error budget that is susceptible to vibration-related degradation. Prior to and throughout the early stages of DKIST operations, there has been an ongoing survey to identify and address vibration sources affecting the optical path of the telescope. Using data from our High Order Adaptive Optics (HOAO) and Power Spectral Density (PSD) data taken from accelerometers placed throughout the site, we have been able to record and track noteworthy frequencies as they appear throughout various phases of operations. Efforts within the last year have allowed for improvements in this vibration survey with increased monitoring via expansion in both the frequency and scale of data collection. This has enabled us to distinguish and categorize several vibration sources that encompass both high impact individual frequencies and overall noise, in order to prioritize solutions for those with the highest impact on image motion. Components of the DKIST facility thermal system and end consumer internal thermal processes, requisitely located throughout the telescope mount and coud´e in order to remove waste heat from temperature sensitive areas, often prove to be the sources of such vibration. Presented herein are recent examples of sources with significant impact, including the details on how we tracked and identified them, and the solutions that were implemented in order to reduce jitter. As DKIST continues operations, future vibration mitigation efforts will be supported by additional data from other instruments in order to identify opportunities for optimization and further isolate localized vibration within our optics systems.

External environmental conditions lead to thermal deformations of the primary reflector of the 50-m diameter Large Millimeter Telescope Alfonso Serrano (LMT). This paper describes efforts to improve the night-time performance of the telescope at millimeter-wavelengths and allow extension of scientific observations into daylight hours, using the LMT’s active surface to counteract the effects of thermal gradients within the antenna structure. Several approaches to stabilizing the LMT’s thermal behavior will be described, including operation of a ventilation system in the antenna backup structure and a real-time metrology system to measure and correct large-scale, thermally induced, surface deformations.

Computational Fluid Dynamics (CFD) and conjugate heat transfer models have been developed and/or updated to validate thermal requirements for the TMT International Observatory enclosure Heating, Ventilation and Air Conditioning (HVAC) system, azimuth and cap drive systems, interstitial space volume, as well as the Summit Facilities tunnel, mechanical room, utility room, and cooler exhaust. The resulting thermal environment is assessed and linked to performance, wherever applicable.

The Dominion Radio Astrophysical Observatory’s John A. Galt 26m radio telescope serves multiple roles for the Canadian radio astronomy community. The attributes of this telescope make it ideal for spectropolarimetric studies of the interstellar medium, however instrumental conversion between polarization states of the incoming signal can corrupt the astronomical signal as the telescope undergoes various loading conditions. To characterize these effects, a finite element (FE) model of the telescope was constructed, based on available blueprints and supplemented by manual measurements. To validate this FE model, vibration measurements were conducted over four days in September 2022 by NRC-Herzberg engineers. The telescope was instrumented with accelerometers, and vibrations were excited using the step-release and impulse hammer methods. This paper will briefly review the model development and analytical predictions, will describe the instrumentation plan and experimental approach used, and will summarize key results from these tests, in particular the first several vibration modes of the telescope.

The University of Tokyo Atacama Observatory (TAO) is a project to build and operate a 6.5m telescope at the summit of Co. Chajnantor (5640 m.a.s.l). This is promoted by the Institute of Astronomy, School of Science, the University of Tokyo in collaboration with many institutes and universities in Japan and Chile. The site construction started in 2018 and was successfully completed by April 2024. An operation support building and an enclosure have already been constructed and are operational at the summit. Electricity is supplied by two generators installed in the operations building. The telescope mount and mirrors have already completed their tests in Japan and the U.S., respectively. They were transported to Chile and wait for the assembly. The first light instruments, NICE and MIMIZUKU, are undergoing final adjustment in Japan and will be transported to Chile as the telescope assembly progresses. The near-infrared instrument SWIMS has completed its open use on the Subaru telescope and returned back to Japan in Aug. 2023 for upgrading for TAO. The near-infrared spectrograph TARdYS, which is being developed in collaboration with Pontificia Universidad Católica de Chile, is also making progress in the development of its optics and detectors. In addition to these, the development of a new optical instrument has been started this year. Allocation of the observing time was also determined. TAO will use approximately 45% of its scientific observation time as project time, 35% as Japan open time for the Japanese community, and 10% as Chilean time for the Chilean community. 5-15% will be provided as paid observing time.

We report on the progress of the CCAT-prime Project: the Fred Young Submillimeter Telescope (FYST), its instrumentation and the associated science program. The FYST system is optimized for wide-field high surface brightness sensitivity in the submillimeter to millimeter-wave telluric windows. Our science program ranges from constraining fundamental properties of the Universe with high frequency CMB polarization studies through studies of reionization, galaxy and structure formation with line-intensity mapping, submillimeter continuum studies and the Sunyaev-Zel’dovich effect to revealing the physics of star formation in the Galaxy through large field, high frequency velocity-resolved spectroscopy and wide-field submillimeter dust polarization studies. These and other studies are enabled by wide-field polarimetric cameras, broad-band imaging spectrometers and heterodyne receiver arrays. FYST first light is expected in early 2025.

The National Science Foundation’s (NSF’s) Daniel K Inouye Solar Telescope (DKIST) is the largest solar telescope in the world; it has and continues to provide the sharpest views ever taken of the solar surface. The telescope has a 4m aperture primary mirror, however, due to the off-axis nature of the optical layout, the telescope mount, enclosure, and observatory have proportions similar to an 8-metre class telescope. The integration of the primary mirror cell to the telescope mount in 2018 was the start of the integration, testing, and commissioning phase of observatory construction. From this point onwards, the integration was a staged process of assembling/integrating sub-systems into the overall observatory system followed by commissioning and verification testing at both the subsystem and system level. DKIST first light initiative was carried out in 2019 with the public release of images in Jan 2020. The observatory officially finished construction in Nov 2021 and moved into the Operations Commissioning Phase which is currently ongoing. This paper provides an overview and discussion of the integration, testing, and commissioning (IT&C) phase of the construction project and the first years of the operations phase. The paper’s perspective is that of the site-based team coordinating the reception and integration of subsystems at the observatory and managing the integration schedule, staff, and budget; this team subsequently transitioned to become the site Technical Operations team at the conclusion of the formal NSF major research infrastructure construction phase. The challenges from logistical, management, and technical perspectives will be highlighted along with strategies that worked and those that did not. Also where appropriate there will be discussion on lessons-learned and what would be done differently. Topics covered in the paper will include (but not be limited to) system incremental capacity relating to staged commissioning, balancing campaign style work patterns of travelers and contractors with local staff, multi-instrument integration, testing time estimation, Band-aids and Bypasses, construction to operations culture and management style.

Three small aperture telescopes (SATs) of Simons Observatory, located at an elevation of 5,200 m in the Atacama Desert in Chile, are designed specifically to target the cosmic microwave background B-mode polarization pattern from primordial gravitational waves. The SATs incorporate over 30,000 transition-edge sensor (TES) bolometers in six spectral bands centered between 27 and 280 GHz. The three SATs were deployed at the site successively from mid 2023 to early 2024 and commissioning has started. In this work, we present an overview of key technologies of the SO SATs . We also report on the current status of the SATs and highlight results in the commissioning observations.

The ASTRI Mini-Array is a collaborative international effort led by the Italian National Institute for Astrophysics (INAF) to develop, build and operate a facility of nine Imaging Atmospheric Cherenkov Telescopes of the four meters class to study astronomical sources emitting very high energy gamma-rays in the TeV spectral band. The ASTRI Mini- Array is currently under construction on the island of Tenerife at the Observatorio del Teide based on a host agreement with the Instituto de Astrofísica de Canarias. The telescopes are alt-azimuthal with an innovative aplanatic dual mirror optical configuration. The first telescope of the ASTRI Mini-Array, named ASTRI-1, was installed at the end of summer 2022. In this paper we report on the results of the opto-mechanical characterization of the telescope. In particular, we analyzed the mechanical behavior of the telescope and we measured the pointing and tracking performance that resulted within the requirements. We tested the procedure to align and focus the panels of the primary mirror automatically. All the software procedures to run the telescope and perform these analyses were also tested.

As the main observational facility of Center for the Gravitational-Wave Universe at Seoul National University, the 7-Dimensional Telescope (7DT) is a multi-telescope system designed to identify electromagnetic (EM) counterparts of gravitational-wave (GW) sources. Consisting of 20 50-cm telescopes along with 40 medium-band filters of 25 nm full width at half maximum, 7DT can obtain spectral mapping images for a large field of view (∼1.25 square degrees). This multi-object spectral imaging capability along with flexible operation, real-time data reduction, and analysis enable 7DT to follow up GW events quickly and to discover EM counterparts with unmatched efficiency. 12 of the 20 planned telescopes are deployed at El Sauce Observatory located at Rio Hurtado Valley in Chile. Since we obtained the first light of 7DT in October 2023, we started its commissioning procedures including examination of bias levels, master flat production, and spectrophotometric standardization. In this talk, we present details of instruments and their set-up, commissioning procedures, and data characteristics of 7DT along with our three-layered surveys which are assumed to be initiated in early 2024.

The US National Science Foundation 4m Daniel K. Inouye Solar Telescope (DKIST) on Haleakala, Maui is the largest solar telescope in the world. DKIST’s superb resolution and polarimetric sensitivity will enable astronomers to explore the origins of solar magnetism, the mechanisms of coronal heating and drivers of flares and coronal mass ejections. DKIST operates as a coronagraph at infrared wavelengths, providing crucial measurements of the magnetic field in the corona. During its Operations Commissioning Phase, DKIST has already conducted a significant number of shared-risk observations for community researchers. The complex raw data are calibrated by the DKIST Data Center located in Boulder and distributed to the science community. We’ll present examples of science results and discuss lessons learned. Ongoing instrument development efforts include, an upgrade of the single-conjugate adaptive optics system to a multi-conjugate AO, the implementation of image slicers for the DL-NIRSP instrument and development of infrared detectors the DL- and CRYO-NIRSP instruments.

SUNRISE III is the third flight of the international stratospheric balloon project Sunrise. The SUNRISE III carries a 1-meter aperture Gregorian telescope and provides a unique platform to perform seeing-free observations at UV-Visible-IR wavelengths. It is designed in the framework of NASA's long-duration balloon program to be launched at ESRANGE, Sweden, and to fly to Canada at float altitudes of 35 – 37 km. For the third flight, the post-focal instrumentation was extensively upgraded to enhance spectro-polarimetric capability; SUSI for 309 – 417 nm, TuMag for 525 nm and 517 nm, and SCIP for 765 – 855 nm. The gondola was also renewed to achieve stable pointing to a target on the solar surface. The team led by NAOJ provided SCIP through international collaboration with the Spanish and German teams. SUNRISE III was launched in July 2022 but was terminated because of a hardware problem. The telescope and instruments were successfully recovered and will be flown again in June 2024.

The Large Millimeter Telescope (LMT) Alfonso Serrano is a bi-national (Mexico and USA) telescope facility constructed on the summit of Sierra Negra, at an altitude of 4600m, in the Mexican state of Puebla. The LMT is a 50-m diameter single-dish radio-telescope designed, constructed and optimized to conduct scientific observations using heterodyne and continuum receivers, as well as VLBI observations, at frequencies between ~70 and 350 GHz. The LMT has an active surface control-system to correct gravitational and thermal deformations of the primary reflector to enable both night-time and daytime observations. We describe the current status and technical performance of the LMT, the instrumentation development program, and an on-going series of engineering and technical upgrades that will increase the optical efficiency and sensitivity of the telescope which will improve the overall scientific productivity and operational efficiency of the LMT.

This paper presents an overview of the SDSS-V Local Volume Mapper (LVM) telescope system. LVM is one of three surveys that form the fifth generation of the Sloan Digital Sky Survey, and it employs a coordinated network of four, 16-cm telescopes feeding three fiber spectrographs at the Las Campanas Observatory. The goal is to spectrally map more than 4000 square degrees of the Galactic plane with 37” spatial resolution and R~4000 spectral resolution over the wavelength range 360-980nm. This corresponds to roughly 50 million individual spectra, which will reveal how distinct gaseous environments within our Galaxy interact with the stellar population, producing the large-scale interstellar medium that we observe.

Accurately mapping and calibrating a substantial portion of the sky in this way requires a unique type of telescope. Each of the four units consists of a two-mirror siderostat in alt-alt configuration feeding an optical breadboard. This produces a fixed, stable focal plane for the fiber IFU and bundle. One telescope hosts the science IFU, while two others observe adjacent dark fields to calibrate geocoronal emission. The fourth telescope makes rapid observations of bright stars to compensate telluric absorption. The entrance slits of the spectrographs intersperse the fibers from all three types of telescope, producing truly simultaneous science and calibration exposures.

After roughly four years of design, development, construction, testing, and commissioning, the LVM telescopes entered regular survey operations in late 2023. We summarize the entire LVM telescope project, from input scientific requirements to the actual performance achieved on-sky.

The MeerKAT+ (MK+) project will extend the current MeerKAT array at the South African Radio Astronomy Observatory (SARAO) site in the Karoo region of South Africa. The South African MeerKAT telescope is a SARAO precursor to the Square Kilometre Array mid-frequency instrument (SKA-MID). The MK+ project is a partnership between SARAO, the Max Planck Society (MPG, MPIfR), and the Istituto Nazionale di Astrofisica (INAF), and is an important milestone towards the SKA-MID array. We will provide details and updates on the MK+ project.

The SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) project aims to detect temperate terrestrial planets transiting nearby ultracool dwarfs, including late M-dwarf stars and brown dwarfs, which are well-suited for atmospheric characterization using the James Webb Space Telescope (JWST) and upcoming giant telescopes like the European Extremely Large Telescope (ELT). Led by the University of Liège, SPECULOOS is conducted in partnership with the University of Cambridge, the University of Birmingham, the Massachusetts Institute of Technology, the University of Bern, and ETH Zurich. The project operates a network of robotic telescopes at two main observatories: SPECULOOS-South in Chile, with four telescopes, and SPECULOOS-North in Tenerife, currently with one telescope (soon to be two). This network is complemented by the SAINT-EX telescope located in San Pedro Mártir, Mexico. In this paper, we review the status of our facilities after five years of operations, the current challenges and development plans, and our latest scientific results.

The Super Pressure Balloon-borne Imaging Telescope (SuperBIT) is a diffraction limited 0.5m optical-to-near-UV telescope launched from New Zealand on NASA’s Super Pressure Balloon (SPB) on April 16, 2023 and flew for 45 nights. There were several communication links used during SuperBIT’s flight to communicate with the telescope from the ground, including Starlink, the Tracking and Data Relay Satellite System (TDRSS), Pilot, and Iridium. While Starlink bandwidth was suitable for TCP-based communications and downlinking, the other links were only capable of supporting UDP-based communications. We designed a file transfer algorithm that downlinked files while detecting missing packets in our downlink and requested them automatically, saving limited bandwidth. We also developed a similar mechanism to upload files as 200-byte commands to SuperBIT. In addition to the downlink and uplink programs, we also created an “autopilot” program to automate observations based on the location, time, and a prioritized list of targets. In this paper, we discuss the communication and observation challenges that were faced and strategies we used to overcome these challenges while operating SuperBIT.

The construction of the ESO’s Extremely Large Telescope (ELT) passed it 50% completion milestone in 2023. There has been good progress on all fronts over the past two years. The construction site at Armazones (Chile) went from a flat landscape dominated by rocks and lean concrete to a mountain top housing finished structural concrete foundations and an 80m-high dome steel structure. In Europe, the manufacturing of the telescope structure is half complete; tens of M1 segments have been polished to excellent optical quality; the M2 mirror is quickly approaching its final figuring accuracy; the M4 adaptive mirror has received all its six Zerodur® thin shells and is progressing to full laboratory integration; the M5 has reached a critical step with the brazing of the six CVD-coated SiC petals; the two large Pre-focal Stations are close to start their final testing; the four instruments are all in final design phase with some having started procurement and more. This paper summarizes the current status of the ESO’s ELT Construction.

The Thirty Meter Telescope (TMT) is an extremely large optical-infrared telescope with diffraction-limited performance that will shape astronomy research for decades from its northern hemisphere vantage point. The TMT International Observatory (TIO) is a public-private-international partnership that unites the scientific, instrumental and industrial communities of Japan, Canada, India and the USA for this endeavor. TIO is part of the US Extremely Large Telescope Program (US-ELTP) that received the top ranking for the ground-based program in the National Academies’ decadal survey report Astro2020. This paper will describe latest progress in TMT’s design and development in all partner countries, the recent NSF Preliminary Design Review, and the many challenges and opportunities of managing a truly global collaboration. The paper will also discuss in depth our completely new approach since 2021 on community engagement in Hawai’i, genuine listening and learning from the native Hawaiian community including hundreds of people who protested against the Project, and our collaborative efforts with the community to build long-term trust and relationships.

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 is part of the United States ELT Program (US-ELTP) which received the top ranking in the National Academies’ ASTRO2020 Decadal Survey. The GMT Project continues to proceed with design, fabrication, and site construction. Our schedule responds to evolving programmatic factors and we are engaged in a process to obtain US federal support for part of the construction and operations scope. Of the seven 8.4m diameter mirror segments comprising the primary mirror, three have been completed with two in storage and with the third undergoing optical testing to demonstrate figure control with the GMT test mirror cell. The remaining four primary mirror segments have been cast and are in various stages of fabrication. The final design of the telescope mount is complete and fabrication is underway. The first off-axis adaptive secondary mirror system is being tested. Results to date from two adaptive optics and phasing testbeds have demonstrated the GMT phasing strategy and continue to be used for risk reduction and component qualification of our wavefront sensing and control strategy. The first generation science instruments are in various stages of development, from design to early fabrication. Hard rock excavation of the foundations for the enclosure and telescope pier is complete, as is the final design of the enclosure. Residence buildings and other facilities and infrastructure needed to support construction at the Las Campanas site in Chile are complete and in operation.

The United States Extremely Large Telescope Program (US-ELTP) is a joint initiative of the organizations building the Giant Magellan Telescope (GMT) and the Thirty Meter Telescope (TMT) and the NSF National Optical and Infrared Astronomy Lab, NOIRLab. The US-ELTP will provide the US astronomical community with open access to observing and archival science with the GMT and TMT via a user services platform supporting the entire lifecycle of scientific inquiry. In this contribution, we summarize the status of the development and design of the program’s components, highlighting key advances and remaining technical challenges, and describing the next steps in bringing this initiative to fruition.

Astronomy is at a turning point in its history and in its relations with the Indigenous peoples who are the generational stewards of land where several of our main observatories are located. The controversy regarding the further development of astronomy facilities on Maunakea is probably the most significant and publicized conflict about the use of such land in the name of science. Thousands have stood in resistance, elders were arrested, and the community is divided. Astronomy’s access to one of its most emblematic sites is at risk. This situation challenges our professional practice, the projects we build on Indigenous lands, and our relationships with the people who live within these lands and with society in general. This paper attempts to share the perspective of the authors on the historical events, including the very recent past, through the lens of our understanding and opinions; to provide transparency, with humility, into our process of introspection and transformation; and to share our hopes and ambitions as leaders from Maunakea Observatories for the future of astronomy in Hawaiʻi, as advocated by the Astro2020 report from the U.S. National Academies of Sciences, Engineering, and Medicine; and to suggest ways for the profession to commit to this long-term vision.

The LIGO gravitational-wave detectors are currently in the middle of the forth observing run, and are routinely detecting multiple gravitational-wave signals from the coalescence of compact objects such as black holes and neutron stars. In this talk I will discuss the technologies that enabled LIGO to reach its unprecedented sensitivity, and the prospects for future improvements.

The Virgo detector contributed to the observations in the O3 observing run and increased its sensitivity from the initial 46 up to 60 Mpc during the run. The detector has undergone to a series of improvements since the end of the O3 observing run in view of O4, as the implementation of an additional recycling cavity at the output of the interferometer – the Signal Recycling cavity (SRC) – to broaden the sensitivity band, the Frequency Dependent Squeezing (FDS) to reduce quantum noise at all frequencies, and a new higher power laser. Some criticality have emerged mainly due to the presence in Virgo of marginally stable recycling cavities with respect to the stable recycling cavities present in the LIGO detectors, which increases the difficulty in controlling the interferometer in presence of defects as those introduced by the high power on the mirrors. This resulted in a delayed joining the O4 run due to a longer than expected commissioning phase. At present the detector is running with a lower laser power (and a lower sensitivity w.r.t. the project design). A new stop of about 2 yr is planned between O4 and O5 starting in 2027, to implement new upgrades (phase II). To improve the stability of the interferometer, we are considering a large upgrade to introduce stable cavities and this will imply heavy infrastructural works also with the minimal design. The aim is to reach a Binary Neutron Star (BNS) sensitivity larger than 100 Mpc. Plans are being made for the post-O5 period as a bridge between 2nd and 3rd generation detectors and a new collaborative effort has born under the name of Virgo nEXT with the aim to keep and push the infrastructure and maintain alive the community.

The primary mirror of ESO’s Extremely Large Telescope contains 798 hexagonal segments, which are equipped with position actuators (PACT) for segment piston-tip-tilt actuation and edge sensors (ES) to measure the relative segment displacements. PACT and ES are used for M1 figure control, i.e. for maintaining the reference shape of the primary mirror. Due to the sheer number of used sensors (4524), ES failures cannot be excluded. In order to minimize the influence of such failures on observations, an automated approach for ES failure handling has been developed. Besides identification of one or more malfunctioning sensors, replacement values for the erroneous sensor signals are calculated and fed back into the figure loop, enabling uninterrupted observations. The figure loop position actuators are hybrid actuators, combining brushless DC motors for a large range of motion with Piezo actuators for high accuracy and fast settling. Motions larger than the Piezo range (∼10μm) are restricted to a maximum velocity of 100μm/s. Since the figure loop is controlled in modal space such a rate limit introduces non-linearities in this large Multi-Input Multi-Output (MIMO) system resulting in cross-coupling of modes and undesirable transient behavior. A custom management scheme for MIMO systems with actuator non-linearities has been developed and successfully tested. It minimizes overshoots and cross-coupling between modes during transitions considering the PACT velocity limitation. In addition, this scheme simplifies closure of the figure loop from any initial condition. This paper covers advancements in both areas. After a brief description of the relevant subsystems, the algorithm to detect faulty ES is introduced. The closely related calculation of ideal replacement values is shown and simulation results illustrate the effectiveness of the Fault Detection, Isolation & Recovery (FDIR) measures for the ELT M1. Then the theory of considering actuator non-linearities in large MIMO systems is introduced. A custom scheme is derived and applied to the ELT M1 Figure Loop. Simulation results and measurements taken with ESO’s seven segment M1 Test Facility are presented.

GMTO has developed a full-scale prototype of the cell that can house an 8.4-meter borosilicate mirror. This test cell is populated with all the active support control hardware and a mass simulator that simulates the mirror weight and the moment of inertia. GMTO has implemented the control software with all the core features needed to operate the active support system. A series of tests have been carried out to verify the functions, performance, and safety of the active support control system. The tests were carried out at several different orientations of the cell to demonstrate that the active support system works with the changing zenith angle and location of the mirror on the telescope mount. This paper describes the results of important safety and dynamic response tests of the active support system.

Astronomy has a long history, and ancient civilizations established calendars based on observations of celestial bodies by eye. Humans continued to observe celestial bodies, but in the 17th century, a major breakthrough was made. This was the invention of the telescope. It made it possible to observe celestial bodies that could not be seen with the naked eye, and it became the foundation of modern science. Since then, astronomical telescopes have evolved from refracting telescopes, which use optical lenses, to reflecting telescopes, which use mirrors. The size and performance of the primary mirror is one of the most important factors in the observing capabilities of a reflecting telescope. The Thirty Meter Telescope (TMT), which is currently under construction, will have the world's largest primary mirror at 30 meters when completed, and is expected to make a significant contribution to the development of astronomy. Ohara supplies the zero-expansion material used for this primary mirror. In this paper, we present the results of measurements and inspections of the coefficient of thermal expansion (CTE), residual stress, bubbles, and foreign matter, etc., for the 357 1.5-meter-long blanks of Ohara CLEARCERAM™-Z produced for the primary mirror of the TMT.

ZERODUR® production for the Extremely Large Telescope mirror substrates concludes in 2024. The ELT M1 substrate blank contract is by far the largest serial production ever undertaken for an astronomical telescope, as well as for SCHOTT ZERODUR® manufacturing. The production results demonstrate the maturity and reproducibility of the production process in terms of material properties and dimensional processing capabilities. The installed ZERODUR® manufacturing capacities enabled a continuous ELT M1 blank production on high quality level in parallel to an extraordinary increase in ZERODUR® demand of the IC Lithography equipment industry. This paper reflects the SCHOTT contribution to the ELT. It reviews the excellent data on the coefficient of thermal expansion and the dimensional characteristics achieved for the complete set of 949 M1 segment blanks, vastly better than specified.

The Extremely Large Telescope (ELT) hosts two Prefocal Stations, one on each of its Nasmyth Platforms A and B. Both units will alternately distribute the light collected by the telescope’s giant optical system into the science instruments and other test equipment, deliver the focal surface images and pupil images of three natural guide stars for acquisition, guiding and wavefront sensing purposes and provide optical sensing to support phasing of the ELT primary mirrors, diagnostics, and maintenance of the optics as part of the Phasing and Diagnostics Station (supplied by ESO). As the subsystems were being assembled, the integration and verification activities proceeded gradually, following the typical V-process model approach. The full PFS Main System test without the M6 optics, which are being tested on their mirror mounts separately at the polisher premises, is now coming to its end and the overall system is ready for final testing.

The European Extremely Large Telescope (ELT) is a first-of-its-kind project, putting together a range of unique engineering challenges. The performances of its mirror cells are particularly demanding, and their verification has required the development of innovative methodologies. This paper addresses the developed verification methodologies for the most critical performances of the Secondary and Tertiary Mirror Cells (M2 and M3) and the Fifth Mirror Cell (M5). Concerning the monolithic 4-meter class M2 and M3 Cells, that is the maximum surface error (SFE) allowed in operational conditions. The SFE due to manufacturing and integration tolerances is singularly complex to evaluate, and testing is required to ensure compliance of the Cell supports as built. Moreover, such testing must be performed with a non-reflective Dummy Mirror. Hence, a methodology to obtain the SFE from the forces measured on all Mirror supports was developed. The application of uncertainty reduction techniques was essential to obtain reliable conclusions. The M5 Cell supports the largest fast steering mirror (2.7 by 2.2 metres) ever employed in a telescope. The most challenging performances regarding dynamic response are its control bandwidth above 10 Hz, a phase lag below 30 degrees up to 4 Hz, and a cross-coupling below 1% between degrees of freedom. After investigations with an actuator prototype, a method based on application of optimised frequency sweep commands was selected. The test setup was designed to avoid artificial resonant modes, and dedicated postprocessing methods to extract the frequency response were developed. This paper describes in detail the SFE verification methodology for the M2 and M3 Cells, and the tip-tilt capability verification for the M5 Cell. The obtained test results are presented and discussed.

The Hydrostatic Bearing System (HBS) is one of the core assemblies of the Giant Magellan Telescope mount. It supports the high dead loads of the moving parts of the entire telescope while providing a stick slip free rotation in the main axes. It is capable of compensating for structural deformations while maintaining a thin oil film layer between the moving parts. Hydraulic groups have been designed to provide the kinematic compliance required to keep the bearing loads almost constant, even under geometrical deviations. The complete development of the bearing was supported by Finite Element Analysis (FEA) for various aspects. FEA was used to predict the deformation of the bearings and tracks under hydraulic loading down to the micrometer level in order to verify one of the major contributors to the oil film budget. On the other hand, FEA was taken to perform quasi static deformation analyses of the entire telescope for gravity load cases and verify alignment of optical elements and provide the basis for the levelling and tilting feature sizing of the HBS. Furthermore, a comprehensive seismic analysis was performed with various loads. The results were a driver for the hydraulic schematic. In addition to the FEA, a dynamic simulation was carried out to analyze the dynamic effects of wind loads and the effects of load variations when bearing pads pass geometrical deviations of the tracks. In the end, a good balance was found between stiffness and limited disturbances. Careful leakage analyses were performes and taken into account in the design optimization to minimize the risk of oil contamination. This was achieved by a combination of oil suction, active scrapers, seals and by guiding measures to lead back the remaining oil to the main oil return system.

The Giant Magellan Telescope (GMT) will be installed at Las Campanas summit in the Atacama Desert (Chile), one of the highest seismicity areas worldwide. To protect the telescope high value optical systems and instrumentation a seismic isolation system (SIS) has been devised. The SIS has a double function, to provide a high stiffness during normal observation for an accurate tracking while allowing the telescope to move freely during an earthquake filtering the seismic ground accelerations transmitted to the telescope, mirrors, and instruments. To achieve these two opposite functionalities a combined SIS comprising single friction pendulums, viscous dampers, fuses, a recentering system and a health and safety monitoring system has been designed. The system has been validated through early prototypes and OpenSees Finite Element Models (FEM) considering multiple non-linearities as well of construction tolerances, uplift and accidental torsion effects.

In October 2023, TMT International Observatory contracted AMOS to develop the Secondary Mirror Support System and Positioner (M2SSP). The M2SSP was identified by TIO as a critical sub-system for which early design would substantially reduce technical, schedule and cost risks to the overall TMT project development plan. In this paper, we present the preliminary design of the M2SSP elaborated by AMOS to comply with the demanding performance requirements imposed by the operational cases and the environment of TMT. The M2SSP is composed of a semi-active mirror support assembly (M2CA) and a positioner (M2POS) that consists of a hexapod with tracking capabilities.

MSE is a massively multiplexed spectroscopic survey facility that will replace the Canada-France-Hawaii-Telescope in the coming decade. This 12-m plus telescope, with its 1.5-2.0 square degree field-of-view, will observe 18,720 astronomical targets at every pointing with nominal specifications including: wavelength range equal to 360 nm through 1.8 microns (H-band); low/moderate resolution (R=3,000/7,000) or high resolution (R=30,000). MSE will contribute to nearly every field of astrophysics across all spatial scales, from individual stars to the largest scale structures in the Universe, including (i) the ultimate Gaia follow-up facility for understanding the chemistry and dynamics of the Milky Way, including the outer disk and faint stellar halo (ii) galaxy formation and evolution at cosmic noon, (iii) derivation of the mass of the neutrino and insights into inflationary physics through a cosmological redshift survey that probes a large volume of the Universe. The instrument suite, dedicated to large-scale surveys, will enable MSE to collect massive data, equivalent to a full SDSS Legacy Survey every several weeks. We present an update to the MSE specifications, requirements and technology.

The ground-based Stage-4 Cosmic Microwave Background Experiment (CMB-S4) is a forefront scientific endeavor aimed at mapping the cosmic microwave background (CMB) with unprecedented sensitivity. The cosmic microwave background is the afterglow of the Big Bang and provides crucial insights into the origin and evolution of the universe. CMB-S4 will enhance our understanding of the universe's history, from the highest energy density at the moment of the Big Bang to the formation and evolution of cosmic structures up to the present day.

CMB-S4 is a collaborative effort proposed to be jointly pursued by the U.S. Department of Energy, the National Science Foundation, and international partners. CMB-S4 will deploy the largest arrays of superconducting microwave detectors ever built. The receiver cryostats will be integrated into three different types of highly optimized survey telescopes.

The paper briefly describes the main elements of the proposed CMB-S4 construction project and the key technologies required to build the survey telescopes. The CMB-S4 project management organization is designed as a unified single project integrating the complex organization and support from the two funding agencies. A possible project schedule is introduced, which maps out mass-producing large quantities of superconducting detector wafers, superconducting readout electronics, and testing of final focus module assemblies.

In this paper, we describe the wide-field spectroscopic survey telescope (WST) project. WST is a 12-metre wide-field spectroscopic survey telescope with simultaneous operation of a large field-of-view (3 sq. degree), high-multiplex (20,000) multi-object spectrograph (MOS), with both a low and high-resolution modes, and a giant 3×3 arcmin² integral field spectrograph (IFS). In scientific capability, these specifications place WST far ahead of existing and planned facilities. In only 5 years of operation, the MOS would target 250 million galaxies and 25 million stars at low spectral resolution, plus 2 million stars at high resolution. Without need for pre-imaged targets, the IFS would deliver 4 billion spectra offering many serendipitous discoveries. Given the current investment in deep imaging surveys and noting the diagnostic power of spectroscopy, WST will fill a crucial gap in astronomical capability and work in synergy with future ground and space-based facilities. We show how it can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; the origin of stars and planets; and time domain and multi-messenger astrophysics. WST’s uniquely rich dataset may yield unforeseen discoveries in many of these areas. The telescope and instruments are designed as an integrated system and will mostly use existing technology, with the aim to minimise the carbon footprint and environmental impact. We will propose WST as the next European Southern Observatory (ESO) project after completion of the 39-metre ELT.

DAG, the 4-meter VIS/NIR telescope and the observatory, reached foreseen first light status at last: the enclosure acceptance is completed; to finalize the opto-mechanical alignment and pointing/tracking, the telescope mirrors have been exposed to heavens in absence of instrumentation. On the optical train; the two instruments that make the telescope distinctive, namely KORAY (the optical derotator) and flexible concept TROIA (ExAO) systems are characterized at the laboratory, and are anxiously waiting to be installed at their blessed location of mission – the diffraction limited Nasmyth platform along with the PLACID stellar coronagraph and DIRAC (NIR camera). We felt that PLACID, which is not yet lead star got jealous; so with the funding provided by the RACE-GO (ERC Project), within just after 60 days of its first mission, it will undergo for a technical makeover to a K-Band instrument. We now have a dilemma, the vacant seeing Nasmyth platform – the landlord- is still waiting for a cutting-edge tenant. Thus, the paper not only presents the telescope and its instrumentation, but also reserves a dedicated section for possible co-operations/collaborations to take place on the seeing Nasmyth platform.

Our article “Optical system for extremely large spectroscopic survey telescope” has been accepted on December 26, 2023, published online on March 7, 2024, and will be published in July 2024 Vol. 67 No. 7: 279511 in Sci. China-Phys. Mech. Astron. In this article, a pure reflecting optical system with a novel strip lensm (lens-prism) atmospheric dispersion corrector (S-ADC) is used, breaking through the glass material size limit of the lens atmospheric dispersion corrector, making possibility to have an aperture of 16 meters and a field of view 2.5 degrees for the spectral survey telescope. This paper gives a brief introduction to the previous article first, and then presents the progress of four important issues that were not discussed in depth in the previous article: (1) The study of Integrated Field Unit (IFU) observation of the galaxy extended sources in coudé focus; (2) The support structure and fabrication test of S-ADC; (3) A new special method of optical fiber positioning unit to resolve the problem of chief ray not perpendicular to the focal plane. (4) The preliminary telescope structure. Finally, this paper proposes to develop a spectroscopic survey telescope with a diameter of 14.5 meters. Its Nasmyth focus with a focal ratio of 4 or 3.5, a field of view diameter of 2.5 degrees (or 2 degrees), equipped with about 50,000 optical fibers, is mainly used for spectral survey of point sources. The coudé focus is used for integrated field spectral observation of extended sources (galaxies, etc.) with 4 arc-minutes and 2 arc-minutes field of view in diameter, equipped with about 50,000 or even more optical fibers. We refer to this Telescope simply as ESST (Extremely large Spectroscopic Survey Telescope).

Solaris is a scientific and technological project aimed at the development of a smart Solar monitoring system at high radio frequencies, based on single-dish imaging techniques. It combines the implementation of dedicated and interchangeable high-frequency receivers on existing small single-dish radio telescope systems (1.5/2.6m class) available in our laboratories and in Antarctica, to be adapted for Solar observations. Solaris can perform Solar imaging observations nearly 20h/day during Antarctic summer with optimal sky opacity, and it will be the only Solar facility offering continuous monitoring at 100GHz. In perspective, our system could be implemented also in the Northern hemisphere to offer unprecedented Solar radio monitoring and imaging for the whole year.

The Large Fiber Array Spectroscopic Telescope (LFAST) will provide a large, scalable collecting area, equivalent to or greater than other ELTs under construction, at a much reduced cost. LFAST will carry out scientific investigations that require spectroscopy with high-signal-to-noise or of faint objects. LFAST is an array telescope, combining light from hundreds of 0.76m diameter prime focus telescopes into a single fiber-fed spectrograph. Twenty telescopes will be mounted on a common alt-az mount, and we are currently constructing the first prototype twenty-unit system. In this talk we will present status and updates from the first 2.5 years of the LFAST project, and describe plans for large arrays, including a 200-unit system in the next few years and a 2,640 unit system in the future.

The next-generation Event Horizon Telescope (ngEHT) will be a transformative upgrade to the Event Horizon Telescope (EHT), capable of making real-time and time-lapse movies of supermassive black holes on event horizon scales. These movies will resolve complex structure and dynamics in the immediate vicinity of the event horizon, bringing into focus not just the persistent strong-field gravity features predicted by General Relativity (GR), but details of active accretion and relativistic jet-launching that drive large scale structure in the Universe. This effort builds upon recent results by the EHT: the first image of M87’s supermassive black hole and its magnetic field structure, as well as resolved images of Sgr A*, the central black hole at the heart of the Milky Way.

The Atacama Large Aperture Submm Telescope (AtLAST) is a concept for a novel 50-meter class single-dish telescope operating at sub-millimeter and millimeter wavelengths (30-950 GHz). The telescope will provide an unprecedentedly wide field of view (FoV) of 1-2 degree diameter with a large receiver cabin housing six major instruments in Nasmyth and Cassegrain positions. The high observing frequencies, combined with the scanning operation movements with up to 3deg/second, place high demands on the accuracy and stability of the optical and structural components. The design features the introduction of a rocking chair type mount with an isostatically decoupled main reflector backup structure and an active main reflector surface with a high precision metrology system. The planned site location is in the Chilean Atacama Desert at approximately 5050 meters above sea level, near Llano de Chajnantor. This paper gives an overview of the optical, structural, and mechanical design concepts. It explains the flow-down from key science requirements to technical design decisions as well as showing design analogies from other existing large radio, (sub-)mm, and optical telescopes.

The upcoming large astronomical telescopes are trending towards the Segmented Primary Mirror due to technological advancements & manufacturing feasibility. We have designed a wide-field optical IR spectroscopic survey telescope that can deliver spectra of several millions of astronomical sources. The baseline design of this telescope is a 6.2 m segmented primary mirror with hexagonal mirror segments of 1.44m size, intersegment Edge sensors, and soft positioning actuators. The telescope is designed to provide a 2.5deg FOV achieved through a system of wide field corrector lenses with a design residual ~0.2". Also, it delivers an f/3.61 beam suitable for directly feeding optical fibres. A mechanical concept of the telescope is designed with a truss-based mirror cell to support the segmented primary mirror and keep the deformation to a minimum. As the primary mirror is segmented, the deformation due to different disturbances like wind, vibration and thermal effects must be corrected to a nanometer accuracy to make it act like a monolithic primary mirror. This is achieved through an active control system using three actuators and six inter-segment edge sensors. A simulation tool, codeSMT, is built based on the state-space model of a soft actuator with Multiple-Input Multiple-Output (MIMO) capability to incorporate dynamic wind disturbance from the IAO Hanle site and vibration effects. A detailed error multiplier analysis is performed numerically using this tool and is in good agreement with analytical calculations. A parameter sensitivity analysis is performed to fine-tune the primary mirror control system variables. This paper presents the Optical, Mechanical and Active Control system design approach of a 6.2m wide-field telescope currently under conceptual design.

The Argus Array will be the first large optical telescope capable of exploring the entire sky simultaneously. Consisting of 900 small-aperture telescopes with ultra-low-noise detectors multiplexed into a 55 GPix array, Argus will have the equivalent collecting area of a 5m telescope but will explore the sky in a very different way from conventional survey telescopes. Each Argus exposure covers 8,000 square degrees with a sampling of 1.4"/pixel; this enormous field of view allows the Array to achieve deep imaging by observing every part of the sky at cadences as fast as one second – for 6-10 hours each night. Realtime transient detection systems will process the incoming images at TB/sec speeds on a high-speed GPU cluster. Over five years, the Array will build a publicly-available, two-color, million-epoch movie of the northern sky, giving the astronomical community the unprecedented ability to follow the evolution of every deep time-variable source across the sky simultaneously. We will detail the current status of the Argus project, including construction plans and first results from the on-sky Argus Pathfinder hardware and software prototype system.

The Gravitational-wave Optical Transient Observer (GOTO) is a project dedicated to identifying optical counterparts to gravitational-wave detections using a network of dedicated, wide-field telescopes. After almost a decade of design, construction, and commissioning work, the GOTO network is now fully operational with two antipodal sites: La Palma in the Canary Islands and Siding Spring in Australia. Both sites host two independent robotic mounts, each with a field-of-view of 44 square degrees formed by an array of eight 40cm telescopes, resulting in an instantaneous 88 square degree field-of-view per site. All four telescopes operate as a single integrated network, with the ultimate aim of surveying the entire sky every 2–3 days and allowing near-24-hour response to transient events within a minute of their detection. In the modern era of transient astronomy, automated telescopes like GOTO form a vital link between multi-messenger discovery facilities and in-depth follow-up by larger telescopes. GOTO is already producing a wide range of scientific results, assisted by an efficient discovery pipeline and a successful citizen science project: Kilonova Seekers.

Here we present a concept for a mobile, completely off-grid, robotic observatory for rapid deployment and observational support. This 1-meter aperture, 3-degree FOV telescope employs state-of-the-art commercial instrumentation such that it not only supports satellite orbit cataloging but also closely spaced object detection/ characterization at atmospheric seeing limits, i.e. sub-arcsecond pixels vs. more traditional cataloging systems’ 2-3 arcsecond pixels. Its relatively large étendue, high throughput, and up to 50 deg/s slew speeds provides for high survey speeds, be it for lost space debris or astronomical transients. We will detail the design and simulated performance of this Deployable, Attritable Optical (DAO) system. Furthermore, each system will employ US Space Force developed observatory control software called SensorKit, a completely open-source software that enables robotic operation and, if desired for SDA purposes, communication with the Unified Data Library. Scheduling, tasking, data processing and dissemination and more are a part of the US Space Force MACHINA program, presented separately in these proceedings.

Time domain astronomy is revolutionizing our understanding of the universe. One of the biggest issues with the flood of temporal data is following up on the plethora of discoveries. There just is not enough telescope time available to observe the new objects in detail, especially spectroscopically. Building a new 3 meter class telescope is very expensive, but a telescope that size would be ideal to observe a large fraction of the objects. We propose to create a custom 3 meter telescope, using 1 meter mirrors mounted on the same telescope frame. Each mirror would feed a dedicated fiber optic, and the whole telescope would be designed to be easily replicable and maintainable, as well as have high optical throughput and be fully automated. Once the first "multiple telescope telescope" has been commissioned, multiple copies would be built and stationed around the world, creating a new network of spectroscopic telescopes that can continually monitor the sky. Versions of this technology could be used to build 6 or 8 meter telescopes for far less than a single monolithic mirror.

The Hobby-Eberly Telescope (HET) is an innovative 10m-class telescope that operates with a fixed-altitude segmented spherical primary mirror (M1) while a tracker, located at the top of the telescope, moves the prime-focus spherical aberration corrector (SAC) and instrument package in order to track the sidereal and non-sidereal motions of celestial objects. In 2016, we completed the wide-field upgrade of the telescope, which includes the Wide-Field Corrector (WFC), the tracker, the prime focus instrument package, and all electromechanical hardware and telescope control software. Post the upgrade, we have been monitoring the imaging performance of the telescope through the in-situ metrology systems. These systems highlight weak spots of the telescope facility in imaging performance and provide quantitative guidance to specific facility repair and/or upgrades to further improve the HET’s overall performance. This paper discusses our long-range (7yrs) datasets, specific analysis techniques used, and current outcomes of this investigative effort in the context of specific facility improvement and upgrade plans.

COALA (COphasing and ALignment Aid) is an instrument aimed to measure the relative alignment and piston of any three adjacent segments of the primary mirror of the GTC during day without using stellar light. The main driver in conceiving COALA has been the increase overall operation efficiency of GTC permitting to recover the telescope alignment after exchanging recoated segments without the constraints of weather and seeing conditions imposed by the current alignment/phasing procedures using focal plane WFS illuminated with stellar light. This instrument is a 6 sub-apertures wavefront sensor built around a Ø350mm telescope. Three sub apertures are used to measured tip-tilt between segments as in a Shack-Hartmann WFS. The other three sub-apertures include chromatic dispersion prisms that permit to measure a chromatically dispersed diffraction image of apertures placed between segments, the analysis of that images permits to measure the relative piston between segments within 8μm range without ambiguity. For using the instrument, a quasi-punctual white light source is placed in the telescope focus to generate a collimated beam. COALA analyze the wavefront of that collimated beam generated by the telescope. COALA is attached to the telescope dome in an alt-azimuthal mount. Combined motion of COALA and telescope mounts permit that the subapertures of COALA can scan the full aperture of the telescope without the need of an intruder mechanical system in front of the primary mirror. COALA has been installed in the GTC in October 2023, and the commissioning tasks are ongoing. This paper describes the design of the instrument and the results obtained during commissioning.

The primary mirror (M1) of the Hobby Eberly Telescope (HET) consists of 91 mirror segments in a regular hexagonal shape. The M1’s center of curvature can be accessed from the top of a 90ft-tall tower, located just outside the HET dome. The current alignment metrology system in this tower, called the Center of Curvature Alignment System (CCAS), provides alignment metrology necessary to bring the 91 segments into a single smooth 11-meter diameter spherical surface. This critical function is at risk due to the obsolescence and deficiencies of the aging system. The upgrade includes a suite of advanced metrology instruments to provide improved alignment precision and metrology. In particular, the upgrade features a new dispersed fringe sensing (DFS) device capable of measuring the piston error of all 240 segment edges across the HET’s 11m primary mirror in a single-shot exposure based on wavelength multiplexing, arrayed diffractive components, and spatial filters. This paper summarizes the electro-opto-mechanical design of the system and other design features to be implemented in the upgrade.

The Sardinia Radio Telescope performance upgrade is completed and now it has the capabilities to scan the universe up to a maximum radio frequency of 116 GHz, corresponding to a wavelength of 2.6mm. Nevertheless, observing at the highest frequencies for which SRT has been designed, requires a tighter control of the pointing and main reflector surface accuracy than before. This is possible through the mitigation of effects produced by environmental loads that were previously negligible. Therefore, a new metrology system, called SMS, has been implemented to face the new challenges. This paper aims to provide a description of strategies conceived to use the SMS system instrumentation, in order to achieve the planned functional objectives.

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 advantage of large optical telescopes from the ground for high-contrast direct imaging relies on achieving exquisite control of the incident optical wavefront. Since the exoplanet problem almost always has a bright star within a small field of view there are usually ample photons for measuring the atmospheric and telescopedistorted wavefront. A 5-year ERA Chair-funded Laboratory for Innovation in Opto-Mechanics (LIOM) has just begun at the Instituto de Astrof´ısica de Canarias (IAC). Measuring the wavefront using Machine Learning techniques in combination with a photonic lantern offers the possibility of fully common-mode wavefront sensing for combining the Fizeau telescope sub-apertures to minimize scattered light and to perform accurate wavefront nulling (“dark spot” or “vortex” nulling) in the image plane. Here we describe our progress in implementing this approach through numerical and laboratory simulation.

The Alignment and Phasing System (APS) of the Thirty Meter Telescope (TMT) will use Shack-Hartmann-type measurements to determine the alignment of the telescope mirrors as well as the relative alignment and shapes of the segments of the primary mirror (M1). These measurements are required to be made with high accuracy in order for the telescope to produce diffraction-limited images. As TMT commissioning time will be limited, full performance must also be achieved as quickly as possible, and routine operations times need to be minimized. From the earliest stages of the design, the TMT APS team has therefore emphasized work that ensures that APS will work as well and as close to out of the box as possible and reduces the associated risks. APS is based on the Phasing Camera System (PCS) with more than 60 years of combined operation between the two telescopes of the W. M. Keck Observatory. In addition to the vast experience available from this heritage, there has been a great deal of effort on algorithm and software development, analytical studies and simulations, experiments, and prototyping. Here, we describe some of these efforts and explain why we are confident that this critical subsystem of TMT will achieve its goals.

For a segmented mirror telescope, the desired resolution can only be achieved when all the segments are precisely co-aligned, co-focused and co-phased. The process of minimization of the piston errors is called co-phasing, which is one of the most stringent tasks in handling the segmented mirror telescope. The OTF based phasing technique samples light from the center of the segments, which is re-imaged on the detector plane, forming a fringed PSF. The Fourier transform of the PSF gives the OTF, which carries information about the piston and tip/tilt errors of the segments. The phase part (PTF) of the OTF can be primarily utilized to extract segment tip-tilt and piston errors lesser than ±λ/4, whereas, the magnitude part (MTF) can provide piston measurements up to a few hundreds of micron. To study the OTF technique in detail, we have developed a Python-based simulation code, that can generate realistic PSF images for the OTF based phasing system under practical conditions. It takes into consideration all the external effects, such as the stellar magnitude and spectral type, atmospheric turbulence and extinction, losses due to optics, and various noises. The OTF is also affected by the segment tip/tilt errors, and hence we have studied the effects of cross-talk between piston and tip/tilt errors on the measurements. In addition to these simulations, we have also conducted laboratory experiments so that the simulation results can be validated. In this paper, we present the results of our extensive simulations as well as experimentation.

The Atacama Large Aperture Submillimeter Telescope (AtLAST) aims to be the premier next generation large diameter (50-meter) single dish observatory capable of observations across the millimeter/sub-millimeter spectrum, from 30 to 950 GHz. The large primary mirror diameter, the 2-degree field of view and its large 4.7-meter focal surface give AtLAST a high throughput (aperture size times field of view) and grasp (throughput times spectral reach), with the ability to illuminate > O(10⁷) detectors. The optical design concept for AtLAST consists of a numerically optimized two-mirror Ritchey-Chrétien system with an additional flat folding mirror, which enables a quick selection among its planned six instrument positions. We present the optical design concept and discuss the expected optical performance of AtLAST. We then present design concepts that can be implemented in the receiver and instrument optics to correct for astigmatism and mitigate the high degree of curvature of the focal surface in order to recover significant fractions of the geometric field of view at sub-millimeter wavelengths.

The Vera C. Rubin Observatory is reaching the final stages of its construction and integration, advancing towards its 10-year Legacy Survey of Space and Time (LSST). One of the key milestones was the installation of the M1M3 Mirror Cell Assembly onto the Simonyi Survey Telescope’s (SST) Telescope Mount Assembly (TMA). The Cell Assembly actively supports the primary/tertiary mirror (M1M3), playing a crucial role in maintaining the glass safe and ensuring image quality. However, before the mirror glass installation, the Cell Assembly was installed on the TMA while supporting a steel surrogate M1M3 mirror. This surrogate closely mimics the glass mirror’s mass, center of gravity, and geometry. The M1M3 cell and surrogate were tested under conditions that simulate rapid field changes in the sky, which are essential for the observatory’s ambitious sky mapping schedule. These tests, extending from 1-100% of designed telescope slew velocities/accelerations, assessed the M1M3 active mirror support system, including the force balance system’s performance, the hardpoint behaviors, and the efficacy of the pneumatic figure control actuators. Preliminary results suggest the system meets operational requirements, ensuring safety and effectiveness at full speed.

Dome-C in the Antarctic Plateau is a privileged site for Astronomy, with one of the lowest concentrations of water vapor in the world, providing a pristine atmospheric window for IR observations. Together with the long winter nights, this allows for extended continuous observational campaigns. At the Concordia Station, ASTEP has taken advantage of the weather and long nights to observe long-period transiting exoplanets for over a decade. With the Cryoscope Pathfinder we now plan to take advantage of the dark IR window between 2.35 and 2.55𝜇m. The unique design of Cryoscope Pathfinder is optimized for a very wide field of view and very thermal background. It is a cryogenic 0.26 m telescope designed for observations in K-dark with a field of view of 16 deg^2. This is the first step for a much more ambitious project, the full scale 1-meter class Cryoscope telescope, with a field of view of 50 deg^2. The initial science drivers are the study of exoplanets and of the infrared transient sky, where it will play a major role in the localization of gravitational wave sources. Furthermore, many other science topics will be enabled by Cryoscope and through synergies with other surveys.

The European Solar Telescope (EST) will be Europe’s most ambitious ground-based infrastructure in solar physics. It will have a primary mirror with a diameter of 4.2m, which will make it the largest in Europe, and of identical aperture as the largest solar telescope available worldwide, namely the Daniel K. Inouye Telescope (DKIST) installed at the Haleakala summit, Hawai'i. EST will have two main characteristics devoted to maximising the scientific return. First, the telescope’s optical path will be polarisation-free using pairs of mirrors that compensate for instrumental polarisation. Second, the telescope will be designed together with a complete instrument suite with imaging and spectrograph instruments. EST will also bring many new technologies, such as a multi-conjugate adaptive optics system and integral field spectro-polarimeters. This contribution presents the conceptual design of the infrared (1 to 1.8 microns) integral field spectropolarimeter. The instrument will have an integral field unit composed of a mirror-based image slicer as input to a Czerny-Turner spectrograph. It will have a polarimeter to record the polarisation state of light on a dual-beam configuration to ensure high-precision spectro-polarimetry.

The M2 secondary mirror of the Vera C. Rubin Observatory, scheduled to be commissioned on-sky in 2024, will be the first active secondary mirror of 3.5m diameter in operation. Its substantial dimensions and advanced functionalities place it in league with the secondary mirrors of the upcoming 30m class telescopes. Characterizing its performance serves as a critical step towards comprehending and controlling the optics of the next generation of Extremely Large Telescopes (ELTs). This study focuses on testing and validating the M2 cell in the Observatory’s integration hall and at the Telescope Mount Assembly (TMA). We also report on the integration steps of the M2 cell onto the TMA itself, including installing the light baffle. During the testing campaign, the M2 cell is equipped with an aluminum mirror surrogate for safety reasons regarding the glass mirror. To ensure integrity when the thin glass mirror (10cm) is installed onto the telescope, the M2 support system must be actively controlled during any M2 cell movement. This prompted the development of a dedicated control system to enable closed loop mode for transporting the M2 cell with the glass mirror from the integration hall to the telescope. The tests in the integration hall were conducted with the M2 cell mounted on a rotating cart, allowing different orientations with respect to gravity as it will experience on the telescope. Upon reaching the telescope, static and dynamic tests are conducted at progressively higher telescope performance, increasing slewing speed, acceleration, and jerk. A significant novelty introduced by Rubin to astronomical instrumentation is the Verification & Validation architecture as part of the model-based Systems Engineering approach where requirements, test procedures and executions are merged into an interlaced and dynamic flow. This report presents the experimental results from the distinct test campaigns covering a wide range of M2 cell functionalities. These include characterization of actuator behavior in terms of maximum stroke and force limits, evaluation of closed-loop (active) and open-loop (passive) support system operation for the M2, system settling time and Force Balance response to different slewing speeds of the telescope.

The Gregor Infrared Spectrograph (GRIS) is installed at the Gregor telescope at Observatorio del Teide, Spain. The instrument started observations in 2012 and underwent several upgrades in the following years. Currently, it is experiencing the most significant upgrade so far, which includes, among other things, adding two optical channels to perform simultaneous multi-wavelength observations. One of the elements we need to modify to optimise the performance of the instrument on all the new spectral channels is the Polarisation Module Unit (PMU). In this contribution, we want to present our theoretical analysis, laboratory experiments, and first-light results related to the new version of the PMU. This new version and many of the improved capabilities of the instrument will be offered to the community gradually during 2024.

CMB-S4, the next-generation CMB observatory, will deploy hundreds of thousands of detectors to enable mapping the millimeter-wavelength sky with unprecedented speed. The large aperture telescopes for CMB-S4 consist of six-meter diameter crossed Dragone designs and a five-meter diameter three-mirror anastigmat. The two-mirror crossed Dragone design requires astigmatism corrections in the refractive optics to achieve diffraction-limited performance. We present biconic lens corrections for the CMB-S4 crossed Dragone camera optics and compare these designs to the camera optics for the three mirror anastigmat, as the optical designs of the cameras for these telescopes are being prototyped.

The European Solar Telescope (EST) is a 4-m class-solar telescope that will become part of the next generation of groundbased facilities. Located at the “Observatorio del Roque de los Muchachos” in La Palma (Spain), it will be aimed to study the magnetic connectivity of the solar atmosphere with high spatial and temporal resolution. The EST optical design has been optimized during the preliminary design phase to maximize throughput, balance the instrumental polarization and to reduce the image rotation due to the change in orientation during operation. The optical system consists of a 4.2m active primary mirror located above the elevation axis to ensure natural air flushing and minimize local seeing degradation and a secondary mirror assembled as an Adaptive Secondary Mirror (ASM). Both arranged in an on-axis Gregorian configuration to deliver an aplanatic secondary focal plane. These are followed by four fold mirrors, which will be upgraded to deformable mirrors and are conjugated to different layers of the atmosphere. These, together with the ASM, M7 and two wavefront sensors, will make up the Multi-Conjugate Adaptive Optics system. Finally, a dioptric system, housed in a vacuum vessel, transfers the light to the science focus, which will be delivered to the Scientific Instrumentation by a dedicated distribution system. EST ultimately provides a diffraction-limited telecentric F/50 science focal plane covering a FOV of 90×90 arcsec² over a wavelength range from 380nm to 2300nm. Along the contribution, details about the preliminary optical design of EST and its subassemblies will be presented. The expected performance is also discussed.

The New Robotic Telescope (NRT) is an autonomous telescope that can operate multiple instruments at the Cassegrain focal station and the straight-through port. The optical beam is directed to the ports by a fold mirror subsystem in the focal station assembly. The fold mirror is elliptical in shape, manufactured by Instituto Nazionale di Astrofisica (INAF), and polished down to RMS surface deformation of λ/20. An optomechanical analysis is performed to simulate the effect of gravity over the mirror surface deformation and the results have been compared to the interferometry plots to optimize the Ion Beam Figuring (IBF) process to polish the mirror aperture. The mirror assembly is supported by a bipod flexure design to reduce surface deformation under gravity and thermal loads. There are three sets of bipod elements and a central support in the quasi-kinematic support structure. Using wire EDM, the bipods were manufactured precisely as one piece. Following careful preparation and the development of multiple glue jigs to ensure an even glue thickness, the bipods, and central pads are glued to the mirror, and multiple experimental tests have been performed to ensure the glue layer's strength and durability. Other components of the mirror assembly, such as the mirror cell, mirror stand, and moving platform, are being machined out of INVAR, assembled, and mounted on the linear stage and a rotary stage before being installed over the mechanism platform in the A&G box. The design and manufacturing of the mirror assembly, including the gluing process, will be summarised as part of this article.

The ELT M1 Local Coherencer is a non-contact metrology system aimed to simultaneously measure the relative pistons on the six sides of a target M1 segment with respect to neighbouring ones (reference segments) with an accuracy below 300nm in a range of ±250μm while it is supported by the M1 Segment Manipulator hanging from the M1 Segment Crane. For this purpose, the Local Coherencer is equipped with six Sensing Modules integrating a patented partially coherent light interferometer, an absolute tip-tilt sensor, a fine alignment system to orient the system normal to the reference segment and a coarse alignment detection system composed of a distance sensor and a border visualisation camera. The Preliminary Design described in a precedent paper has been further optimized to provide a better performance of the interferometer: a superluminiscent led (SLED) with a higher brilliance and spatial coherence has been selected to enhance the radiometry and contrast, the optical layout has been optimized to improve both the radiometric and wavefront degradation performance, additionally a detector with a bigger sensor area has been integrated to avoid the need of an afocal system to fit the output beam, thus further reducing the number of elements inducing beam degradation. As a part of the Final Design effort, an Early Unit of a Sensing Module has been built and tested to validate the expected performance, check the correct operation of the three measurement systems contained in the system as well as the local alignment system and tests the latency of the measurements. This paper describes the Final Design and the first results obtained with the aforementioned Early Unit of the Sensing Module.

The Dragonfly Spectral Line Mapper is a mosaic telescope comprising 120 Canon telephoto lenses, based on the design of the Dragonfly Telephoto Array. With a wide field of view, and the addition of the “Dragonfly Filter-Tilter” instrumentation holding ultra narrow bandpass filters in front of each lens, the Dragonfly Spectral Line mapper is optimized for ultra low surface brightness imaging of visible wavelength line emission. The Dragonfly Spectral Line Mapper was constructed and commissioned in four phases from March 2022 to November 2023. During this time, four individual mounts of 30 lenses each were constructed and commissioned. The commissioning of the telescope included the deployment of the “Dragonfly StarChaser” which carries out image stabilization corrections in the telephoto lens, to enable hour-long exposures to be taken. In addition, we introduced new instrumentation such as a film to cover the optics to keep the filters clean. Here we describe the updated design of the complete 120-lens array, and the implementation of the instrumentation described above. Additionally, we present updated characterization of the cameras and filter transmission for the full array. Finally, we reflect on the construction and commissioning process of the complete 120-lens array Dragonfly Spectral Line Mapper, and remark on the feasibility of a larger 1000-lens array.

The Vera C. Rubin Observatory is nearing completion, and we are embarking on a campaign to optimize the image quality during its upcoming 10-year optical survey. Here, we present the tools and methods we are implementing to disentangle and quantify the different sources of image degradation, as well as our plans to correct and mitigate as many of these different contributions to seeing as possible. The tools include an on-site Differential Image Motion Monitor (DIMM) for measuring atmospheric seeing, multiple 2D and 3D sonic anemometers for measuring in-dome wind speed and turbulence, and direct dome seeing monitors. We also implement a guider mode that allows data to be taken at 9Hz over small regions and a stuttered and streaked imaging mode that allows us to measure mount tracking and jitter and perform atmospheric tomography. Additionally, we use curvature wavefront sensing to estimate the residual wavefront error to support the telescope’s alignment and focus. This is the same algorithm that we will use for the Simonyi Survey Telescope. Many of these tools, as well as additional techniques to quantify the contribution of astigmatism to seeing, have been tested at the Auxiliary Telescope (AuxTel). This 1.2m telescope acts as a pathfinder for the Rubin Observatory. We present initial results and the creation of an image quality budget table for AuxTel to characterize and monitor significant sources of image quality degradation. We then discuss plans for implementing these techniques on the 8.4m Simonyi Survey Telescope.

The Dragonfly Spectral Line Mapper is an innovative all-refracting telescope designed to carry out ultra-low surface brightness wide-field mapping of visible wavelength line emission. Equipped with ultranarrowband (0.8nm bandwidth) filters mounted in Dragonfly Filter-Tilter instrumentation, the Dragonfly Spectral Line Mapper maps Hα, [NⅡ]λ6583, and [OⅢ]λ5007 line emission produced by structures with sizes ranging from ∼1 to 1000kpc in the local Universe. These spatial scales encompass that of the exceedingly diffuse and faintly radiating circumgalactic medium, which is singularly difficult to detect with conventional mirror-based telescope instrumentation. Extremely careful control of systematics is required to directly image these large scale structures, necessitating high fidelity sky background subtraction, wavelength calibration, and specialized flat-fielding methods. In this paper, we discuss the on-sky performance of the Dragonfly Spectral Line Mapper with these methods in place.

The signal induced by a temperate, terrestrial planet orbiting a Sun-like star is an order of magnitude smaller than the host stars’ intrinsic variability. Understanding stellar activity is, therefore, a fundamental obstacle in confirming the smallest exoplanets. We present the Lowell Observatory Solar Telescope (LOST), a solar feed for the EXtreme PREcision Spectrometer (EXPRES) at the 4.3-m Lowell Discovery Telescope (LDT). EXPRES is one of the newest high-resolution spectrographs that accurately measure extreme radial velocity. With LOST/EXPRES, we observe disk-integrated sunlight autonomously throughout the day. In clear conditions, we achieve a R ∼ 137, 500 optical spectrum of the Sun with a signal-to-noise of 500 in ∼ 150s. Data is reduced using the standard EXPRES pipeline with minimal modification to ensure the data are comparable to the observations of other stars with the LDT. During the first three years of operation, we find a daily RMS of 71cm/s. Additionally, having two EPRV spectrometers located in Arizona gives us an unprecedented opportunity to benchmark the performance of these planet-finders. We find a RMS of just 55cm/s when comparing data taken simultaneously with EXPRES and NEID.

The Super-pressure Balloon-borne Imaging Telescope (SuperBIT) was a diffraction limited 0.5m optical-to-near-UV telescope that was designed to study dark matter via cluster weak lensing. SuperBIT launched from Wanaka, New Zealand via NASA’s super-pressure balloon (SPB) technology on April 16, 2023 and remained in the stratosphere for 40 days. During the flight, SuperBIT obtained multi-band images for 30 science targets; data analysis to produce shear measurements for each target is ongoing. SuperBIT’s pointing system comprised three nested frames that stablized the entire telescope within 0.34 arcseconds rms, plus a back-end tip-tilt mirror that achieved focal plane image stability of 0.055 arcseconds rms during 300 second exposures. The power system reached full charge every day and never dropped below 30% at night. All components remained within their temperature limits, and actively controlled components remained within a standard deviation of ∼0.1K of their set point. In this paper we provide an overview of the flight trajectory behaviour and flight operations. The first two days of the flight were used for payload characterization and telescope alignment after which all night time was dedicated to science observations. Target scheduling was performed by an on-board “Autopilot” system which tracked available targets and prioritized completing targets over starting new targets. SuperBIT was the first balloon telescope to fly a Starlink dish to enable high-bandwidth communications with the payload. Prior to flight termination, two Data Retrieval System modules were deployed to provide a redundant data recovery method.

The US Extremely Large Telescope Program (US-ELTP) is a joint initiative of the organizations building the Giant Magellan Telescope (GMT) and the Thirty Meter Telescope (TMT), and the NSF National Optical- Infrared Astronomy Research Laboratory (NOIRLab). The US-ELTP will enable all U.S. astronomers to carry out transformational research that fully leverages the diverse capabilities of both the GMT and TMT, as well as the two-hemisphere system. In this paper, we present an overview of the program’s scientific goals, the high-level roles and responsibilities of the US-ELTP partners, and the operating modalities of the joint program, including science and engineering operations for science investigators and archival research support.

The Primary Mirror Cont