This PDF file contains the front matter associated with SPIE Proceedings Volume 11445, including the Title Page, Copyright information, and Table of Contents.

This Conference Presentation, “The Event Horizon Telescope: the impact of an image and finding Pōwehi,” was recorded for the Astronomical Telescopes + Instrumentation 2020 Digital Forum.

This Conference Presentation, “The National Science Foundation’s Daniel K. Inouye Solar Telescope,” was recorded for the Astronomical Telescopes + Instrumentation 2020 Digital Forum.

One of remarkable features of the University of Tokyo Atacama Observatory (TAO) is an altitude of the site (5,640 m.a.s.l.) While this provides us an excellent condition for astronomical observations, the site development is attended with difficulty due to the hard conditions such as low pressure, low temperature, and limited access. Site preparation for the TAO 6.5 m telescope started in Apr. 2018. Firstly, we have constructed an access road from Pampa la bola plateau (~ 5,000 m.a.s.l) to the summit. It has a width of < 6.5 meter for transportation of telescope parts including the 6.5meter mirror. In order to prevent collapse, angle of side slope is carefully determined based on ground condition and frozen soils. All workers always use oxygen during their work as a measure against hypobaropathy. Since the site temperature in night is lower than 0 degree even in the summer season, it is difficult to ensure quality of foundation concrete if we cast it in-situ. We use pre-cast concrete for the foundation of the telescope, the enclosure, and the support building. The biggest part is the telescope foundation. It has a weight of 600 ton. Considering the transportation to the summit, it is divided into 43 parts and unified at the summit. This is a new trial to make a massive foundation for a large telescope with pre-cast concrete.

The Giant Magellan Telescope (GMT), one of three next-generation extremely large telescopes (ELTs), will have a 25.4- meter diameter effective aperture, and will be located on the summit of Cerro Las Campanas in Chile. Developing a new observatory for cutting-edge science operations and a 50-year lifespan poses a variety of design challenges. This paper discusses the designs that have been adopted in the GMT site master plan, including designs for the site infrastructure, telescope enclosure, and facilities. The GMTO site has been in active construction since 2015, and in the past two years has completed important steps in site development including completion of hard rock excavations for the telescope and enclosure foundations, construction of the underground utility distribution systems, and other infrastructure upgrades to support the current and upcoming construction work.

The Dome of the Extremely Large Telescope (ELT) is under construction at Cerro Armazones, in the Chilean Andes. It is constituted by a concrete pier, with an 86 m diameter concrete wall, and a rotating enclosure on it; the maximum height is about 80 m. The Dome will protect the 40 m class optical telescope, inside it, and must withstand wind speeds of over 40 m/s, as well as strong earthquakes. The whole structure is seismically isolated at the base, for an overall seismic mass of about 35000 t. The rotating enclosure main elements are a truss steel structure, having a base ring and a series of arch girders. It has a hemispherical shape to enhance the aerodynamic behavior and it weighs close to 6500 t. Two slit doors allow the telescope observation, guaranteeing a 42 m wide and 64 m long opening. The enclosure’s Azimuth Rotation Mechanism is constituted by 36 trolleys, installed on the top beam of the concrete pier, on a diameter of 86 m. Cladding covers the Dome structure and it is designed in order to provide proper thermal insulation and to withstand the harsh environmental site conditions. A windscreen, made of four permeable panels, having 42 m span and 10 m height each, protects the Telescope during observation and controls the airflow around it, together with a series of 89 louvers, placed both on the rotating and the fixed part of the Dome. In the Auxiliary Building, which is a ring surrounding the pier, technical rooms to operate and maintain the telescope are hosted. A custom HVAC system controls the temperature with a ±2 °C precision inside the Telescope chamber having about 300000 m3 volume.

The enclosure for the Thirty Meter Telescope (TMT) uses a Calotte-style configuration, chosen for the advantages of a high degree of protection for the telescope, relatively low weight through the use of efficient shell structures, and a balanced shutter mechanical system. This design is unprecedented for large scale telescope enclosures, and introduces significant design, fabrication, construction and operation risks. This paper provides an overview of design development, analysis and testing work that was done to mitigate such risks. Compared to conventional enclosures, the combined moving mass of the cap and shutter represents a greater portion of the enclosure mass, increasing the risk of enclosure vibration impacts on telescope operation. The vibration risk was addressed through development of a self-steering bogie design, bogie spring design and testing, wheel and rail splice design and testing, and slow-speed motion simulation. Risks of rail damage at splices and bogie wheel bearing failures observed on existing observatories were also addressed by bogie and rail joint design. The bogie spring design and test program incorporated elastomeric materials that provide significant damping capability for structural seismic isolation while meeting bogie mechanical design requirements for load distribution and tracking. A novel approach to slow-speed rolling motion simulation in the stick-slip regime was developed with a view to better understand control and vibration impacts. A staged construction analysis and detailed installation sequence was completed, including falsework and erection aids. The activities described above have been performed as part of the recently completed Production Readiness design stage.

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. From the start of the contract, signed in May 2016, major progress has been achieved. During the design phase various challenging technical issues had to be solved, not least given the size of the ELT and the environmental conditions at Cerro Armazones in Chile. As per today the system has been developed, detail designed, reviewed, and is completing the Final Design Review process. Procurement of long lead or schedule critical items was assured by using specific Critical Design Reviews. Manufacturing in Europe and construction in Chile have started and are proceeding, although delays were encountered due to various issues including the Covid-19 pandemic. 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.

Long-term reflectivity and scattering data of MMT primary mirror (M1) coating from 2016 to the present suggest minimal optical degradation, resulting, in part, from periodic wet cleaning of the coating. This extended (approximately four-year) period of coating maintenance and accompanying optical sampling provides a more complete picture of M1 coating performance and of the contribution of periodic cleaning to that performance. Semi-annual, soap-and-water cleanings have helped maintain the coating’s optical quality. Techniques for cotton swab cleaning and for optical sampling of the aluminum coating with a Konica-Minolta CM-600d Spectrophotometer are discussed. These results imply that periodic, well-controlled cleaning has significantly extended the useful life of the 2016 MMT primary mirror coating. With the goal of maintaining a five to six year coating cycle.

The Vera C. Rubin Observatory (Rubin Obs) (formerly Large Synoptic Survey Telescope - LSST) is an 8.4-m telescope, now under construction in Chile. In the last couple of years, the telescope has achieved tremendous progress, though like many other projects, progress has been curtailed for over six months due to the worldwide pandemic. This paper provides the high-level status of each of the telescope's subsystem. The summit facility (Cerro Pachon) and base facility (La Serena) have been substantially completed. The dome is expected to be finished by October of 2021, which will also allow the completion of integration and testing of the Telescope Mount Assembly (TMA). The integration and verification of the TMA is planned to be completed by the end of 2021. The two mirror systems, M1M3 and M2, have been fully tested under interferometers, showing they both satisfy their performance requirement, and both have been received at the summit facility. The M2 mirror has been successfully coated with protected aluminum, which is the first scientific coating produced by the new Rubin coating plant. The M1M3 mirror is planned to be coated with the same plant at the beginning of 2022. The auxiliary telescope and its principal spectrograph instrument, which will allow for real-time atmospheric characterization, has been commissioned. The Rubin environment awareness system (EAS), which includes the DIMM, weather station, all-sky camera, and facility environmental control, is operational. Significant progress has been made on the software for all of the above-mentioned subsystems, as well as the comprehensive telescope control system and the telescope operator interfaces.

The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of <6 million objects, designed to decode the history of the Milky Way, reveal the inner workings of stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the Universe. The Local Volume Mapper (LVM) is one of three surveys that form SDSS-V. LVM will employ a coordinated system of four telescopes feeding three fiber spectrographs at Las Campanas Observatory in Chile. The goal is to map approximately 2500 square degrees of the Galactic plane over the wavelength range 360-980 nm with R~4000 spectral resolution. These observations will reveal for the first time how distinct gaseous environments within the Galaxy interact with each other and with the stellar population, producing the large-scale interstellar medium that we observe. Accurately mapping and calibrating a substantial portion of the sky at this spatial resolution requires a unique type of telescope system. Each of the four LVM telescopes has a diameter of 16 cm, making them considerably smaller and lighter than the instruments they feed. One telescope will host the science IFU containing ~1800 fibers arranged in a close-packed hexagon. Two additional Calibration telescopes will observe fields adjacent to the science IFU, in order to calibrate out terrestrial airglow and other geo-coronal emission. The fourth, Spectrophotometric telescope will make rapid observations of bright stars (typically 12 during a single IFU / Calibration exposure) to correct for telluric absorption lines and overall extinction. The fibers from all three types of telescope will be interspersed in the entrance slits of the spectrographs, allowing for simultaneous science and calibration exposures. Although considerably smaller than the next generation of giants, the LVM telescopes must also operate close to the limits of physical optics, and the geometry and scope of the LVM survey present unique challenges. For example, with this type of telescope at the Las Campanas site, the effects of optical aberrations, diffraction, seeing, and (uncorrected) atmospheric dispersion are all of comparable scale. This, coupled with the need for repeated and reliable measurements over years, leads to some unconventional design choices. This paper presents the preliminary design of the LVM telescope system and discusses the requirements and tradeoffs that led to the baseline choices.

The Next Generation Very Large Array (ngVLA) project to replace the VLA telescope in New Mexico continues to move forward. Concept designs for 15m, 18m, and 6m offset Gregorian antennas based on the Single-piece Rim-supported Composite (SRC) reflector concept have been developed at NRC, the 18m and 6m designs became part of the ngVLA System Reference Design (SRD). The Reference Design array is composed of a main array of 244 x 18m antennas and a short baseline array of 19 x 6m antennas. In the initial design iteration of the 6m antenna, as used in the SRD, was essentially a scaled down version 18m. This design exercise provided a costed concept appropriate for the SRD but did not meet one critical requirement; the ability to close pack the antennas. Following the release of the SRD the team at NRC took a clean piece of paper approach to the 6m antenna design driven by the close packing requirement. This paper will presents the design path from the ngVLA SRD to the latest design.

The Greenland Telescope (GLT), currently located at Thule Air Base, is a 12-m single dish telescope operating at frequencies of 86, 230 and 345 GHz. Since April 2018, the GLT has regularly participated in (sub-)mm VLBI observations of supermassive black holes as part of the Event Horizon Telescope (EHT) and the Global mm VLBI Array (GMVA). We present the status of scientific commissioning activities at the GLT, including most recently the 345 GHz first light and test observations. The antenna surface accuracy has been improved to ~25 microns through panel adjustments aided by photogrammetry, significantly increasing the antenna efficiency. Through all-sky spectral line pointing observations (SiO masers at 86 GHz and CO at 230 and 345 GHz), we have improved the radio pointing accuracy down to <~ 3" at all 3 frequencies. Due to the pandemic, we are in the process of transitioning GLT commissioning and observing activities to remote operations.

Since 2017 LBTO, in partnership with GMTO, has been developing a laser-trussed based metrology system for the active alignment of telescope main optical components to each other and to instruments. The effort has addressed needs of both organizations; LBTO with the opportunity to assess the performance of a new technological approach to telescope alignment, and the GMTO with the opportunity to prototype and field-test a system that has been identified as a crucial "missing link" in the active-optics chain between open-loop modelling and wavefront-sensing for ELT-scale telescopes. Following two years of effort the positive results so far obtained have convinced LBTO, in 2019, to commence to develop an integrated operational active-optics system based on this technological approach. A team drawn from LBTO, Steward Observatory, GMTO, the Wyant College of Optical Sciences and Mersenne Optical Consulting are currently completing the first phase of this Telescope Metrology System (TMS). This paper shall describe the system in detail and report on progress, current status, and future goals.

The Giant Magellan Telescope will be a 25.4-m visible and infrared telescope at Las Campanas Observatory. The optical design consists of 7 8.4-m primary mirror segments that reflect light to 7 secondary mirror segments in a doubly-segmented direct Gregorian configuration. Each mirror pair must be coaligned and co-boresighted. During operations, the alignment of the optical components will deflect due to variations in temperature, gravity-induced structure flexure of the mount, and, on a scale relevant to phasing, vibrations. The doubly-segmented nature and size of the GMT will create a novel set of challenges for initial assembly, integration, and verification and maintaining high-precision alignment of the optical elements during operations. GMT is developing a Telescope Metrology System that uses 3D laser metrology systems to decrease the complexity of alignment and increase observatory efficiency. This paper discusses the 4 subsystems of TMS as well as their operational modes.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) employs an airborne telescope with a 2.7m primary mirror. The telescope structure is composed of carbon fibre with major parts of steel for the suspension and balancing components. It is exposed to harsh environmental conditions and subject to vibration excitation due to aircraft motions and turbulence from the airflow coming into the telescope cavity. To meet pointing requirements and improve image stability there are ongoing efforts on various components of the telescope system, one of which is the implementation of an Active Mass Damping (AMD) control system: Based on accelerometer signals, reaction mass actuators impose forces onto the support structure to dampen the vibration of optical components. The system has been designed, implemented and preliminary tested in the early years of SOFIA’s scientific operation, but concerns about the structural integrity of the primary mirror and new requirements regarding software qualification have prevented the activation and further development for several years. These concerns being addressed, we are now in the process of reactivating the AMD system on the support structure of the primary mirror. Recent ground tests and in-flight jitter measurements indicate that the damping system is very efficient at eliminating the excitation of targeted structural modes of the telescope structure at 40 to 80 Hz and the first bending modes of the primary mirror at 175 Hz, resulting in a significantly improved image quality. This paper presents the analysis of those measurements and discusses options for future development.

High vibrations levels are detrimental to telescope pointing performance. Unfortunately, the true (final) vibration level on the telescope structure can be measured only when the machine is commissioned, i.e. much after the design phase is over. In this context, to reduce engineering risk, it can be useful to assess telescope vibrations very early - also in the preliminary design phase - in order, if needed, to adopt suitable countermeasures (e.g.: vibration damping, structure stiffening, or vibration isolation). This is particularly important in giant telescopes, since their natural frequencies are typically low enough to fall next to many vibration sources (wind, pumps, bogies, electric fans, vortex shedding). EIE developed an integrated procedure to assess the vibration level at the telescope hosted units - mirrors and instruments. The procedure: (i) identifies the relevant vibration sources, (ii) evaluates the vibration level for each source at the generation point, (iii) transfers the vibration from the generation point to the hosted units, and (iv) combines statistically the vibration sources to get the final vibration level. This paper presents EIE integrated procedure for the vibration assessment, and it discusses the most relevant vibration sources to be taken into account in giant telescopes.

Telescopes suffer from radiative subcooling against the night sky (“low-wind effect”), depending on wind speed, sky exposure and the emissivity of the surface finish. Critical structural elements in the ELT are the spider vanes, the vertical trusses in the telescope tube and the M4 Tower. We present an improved sky temperature model and 3D computational fluid dynamics simulations of the airflow inside the ELT dome with local temperatures and derive the wavefront error map in the pupil from it, using ray tracing. We discuss the optimal shape that M4 can achieve to correct the errors and report the wavefront residuals.

KAGRA is the fourth gravitational wave telescope that forms an international gravitational waves detection network with two Advanced LIGO and one Advanced Virgo telescopes. In addition to many sensitivity enhancement technologies that are generally utilized in these detectors, KAGRA introduces cryogenic technologies and low seismic noise underground environment that are both regarded as the possible technologies to realize the 3rd generation gravitational wave telescopes’ sensitivities that are designed to be about 10 times better than the present gravitational wave telescopes. The KAGRA project has started in 2010, and the designed configuration of KAGRA was mostly finished in 2019 spring after several times operations as an interferometer with a simpler configuration in 2016 and 2018. Finally, KAGRA started its gravitational wave observation in 2020. At present, KAGRA is under improvement to obtain better sensitivity and stability to join the 4th international gravitational waves network detection with Advanced LIGO and Advanced Virgo from hopefully 2022.

Virgo is a gravitational wave detector based on a 3 km long laser interferometer. After a first period of data taking between 2007 and 2011, a major upgrade called Advanced Virgo was prepared starting from 2009. After its implementation and commissioning Advanced Virgo started operation in 2017, joining the Advanced LIGO O2 run. In this period Advanced Virgo contributed to the first detection of gravitational waves from the binary neutron stars merger called GW170814. After a period of improvements and commissioning, in April 2019 Advanced Virgo started a new period of observation in coincidence with Advanced LIGO, during the so-called run O3. In the meantime, a new upgrade called Advanced Virgo Plus is being prepared. The first phase of this upgrade will be implemented at the end of O3 and completed by 2022, when the run O4 is planned to start. A second phase of upgrade is planned to be implemented between 2023 and 2024 and to be completed before the start of O5 in 2025.

The Square Kilometre Array is a global research infrastructure project to construct and operate a radio telescope observatory of unprecedented scale. The first stage of the project’s implementation (SKA1) has concluded its design phase and is about to begin construction in 2021. Composed of two interferometric arrays covering a frequency range of 50-350 MHz in Australia (SKA-LOW) and 350 MHz to 15.4 GHz in South Africa (SKA-MID), the observatory provides sensitivity and resolution which advance the currently available research infrastructure capabilities across a range of scientific frontiers. We describe the design development process for the SKA1, the antenna design and specifications, and the current construction planning and schedule.

Institute of Astronomy, Graduate School of Science, the University of Tokyo is promoting the University of Tokyo Atacama Observatory Project, which is to construct an infrared-optimized 6.5m telescope at the summit of Co. Chajnantor (5640m altitude) in northern Chile. The high altitude and dry climate (PWV-0.5mm) realize transparent atmosphere in the infrared wavelength. The project is now approaching the final phase of the construction. Production of major components are almost completed: Production and preassembly test of a telescope mount and dome enclosure have been completed in Japan, and they are being transported to Chile. Three mirrors, the 6.5m primary, 0.9m secondary, and 1.1m-0.75m tertiary mirrors and their support systems have been all completed and tested in the USA. An aluminizing chamber have been fabricated in China, and its tests have been carried out in Japan. Development of two facility instruments, SWIMS and MIMIZUKU, are also completed. They were transported to the Subaru telescope, successfully saw the first light in 2018, and are confirmed to have the performance as designed. On-site construction work at the summit is now underway. Expansion of a summit access road from the ALMA concession was completed in 2019. Installation of foundation will follow, and then erection of the dome enclosure and a control building. The construction works are delayed by COVID-19, and we expect to complete the dome enclosure by Q3 of 2021. The telescope will be installed inside the dome and see the engineering first light by early 2022.

East Anatolian Observatory’s DAG telescope, with its 4m diameter primary mirror and VIS/IR observation capability, will be located on the Konaklı-Karaya summit at an altitude of 3170 m, near the city of Erzurum, Turkey. Containing both active optics (aO) and adaptive optics (AO) systems, the first light for DAG is expected for the last quarter of 2021. DAG will be equipped with an in-flange derotator – KORAY (K-mirror Optical relAY) that will direct the light to the seeing limited Nasmyth platform containing TROIA (TuRkish adaptive Optics system for Infrared Astronomy). DAG first generation instruments will consist in a 30" FoV near-infrared (NIR) diffraction limited camera and a stellar coronagraph. In his paper, status updates from DAG telescope will be presented in terms of; (i) DAG site, (ii) Site infrastructure, (iii) current status of the observatory building, (iv) DAG optics, (v) current status of the telescope, (vi) current status of enclosure, (vi) current progress of the astronomical instruments, and (viii) status of the Optomechatronics Research Laboratory – OPAL.

The ngVLA is envisaged as an interferometric array with ten times greater sensitivity and spatial resolution than the current VLA and ALMA, operating in the frequency range of 1.2 – 116 GHz. In this talk we provide a project status update and overview of the Reference Design. The Reference Design is a low-technical-risk, costed concept that supports the key science goals for the facility, and forms the technical and cost basis of the ngVLA Astro2020 Decadal Survey proposal.

The Maunakea Spectroscopic Explorer project’s preliminary design phase start coincides with planned and unplanned events in the national and international astronomy landscape. As the decade draws to a close, most MSE participants are undergoing national strategic planning for key future astronomical development. There are processes similar to the Decadal Survey on Astronomy and Astrophysics in the US. Much of the Project Office activities since our last 2018 report have been aligned in supporting these strategic plans. A vital activity related to the Maunakea Observatories (MKO), including the Canada France Hawaii Telescope (CFHT) Corporation and Maunakea Spectroscopic Explorer, is to secure future access to the mountain for astronomy as affected by the current protest over the Thirty Meter Telescope. Much of the MKO activities have been centered on ensuring the long-term success of astronomy on the mountain beyond 2033. However, the most significant unplanned activity has been managing progress through the ongoing COVID pandemic and anticipating its effects on the timeline and efficacy of upcoming national strategic planning recommendations for astronomy among other national priorities. This paper provides a status report of MSE as it enters the preliminary design phase, and our plan to progress and manage changes in an evolving national and international astronomy landscape.

We present the science case, and telescope and instrument designs for our ultra-wide field submillimeter observatory, CCAT-Prime to be sited at a 5600 m elevation site on Cerro Chajnantor in northern Chile. Our science focusses on the study of star and galaxy formation from the epoch of reionization to the present, SZ observations of galaxy clusters, and polarization studies of the CMB and Galactic foregrounds. Our instruments include direct detection polarization-sensitive cameras and spectroscopic imagers, and high spectral resolution heterodyne array receivers. The CCAT-prime telescope is being built by Vertex Antennentechnik GmbH with first light in late 2021.

Water vapour radiometers (WVRs) are critical to both site surveying and site management in microwave and mm-wave very long baseline interferometry (VLBI). We report on the first two years of progress made towards improving the state of water vapour radiometry at HartRAO, South Africa, and the LMT in Mexico, under a SAMexico bilateral programme. We report on progress in the development of low-cost site surveying instruments, multi-purpose cooled receivers, as well as refurbishment and upgrades to existing 22/31 GHz and 215 GHz tipping radiometers.

The ESO’s Extremely Large Telescope (ELT), which green light for construction was given back in December 2014, is now progressing at full speed in its final design and manufacturing stage with only very few procurements remaining to be placed. The construction of the Dome and Main Structure foundations at Cerro Armazones in Chile is well advanced and hardware produced though more than 30 industrial contracts (mostly in Europe) has started to come out of the factories. The four first generation instruments and adaptive optics module are also progressing now towards their final design. Tremendous progress has also been made in gradually incorporating most of the items that were originally deferred to a Phase 2 due to lack of funding. A number of difficulties are encountered, the current COVID-19 pandemic being one of them affecting activities both in Europe and in Chile and putting at risk the target for first light date currently set to end 2025.

The Giant Magellan Telescope project is proceeding with design, fabrication, and site construction. The first two 8.4m primary mirror segments have been completed and placed in storage, three segments are in various stages of grinding and polishing, the sixth segment is in the initial stages of casting, and glass is in hand to cast the seventh segment. An industry contract is in place to complete the design and proceed with fabrication of the telescope structure. Residence buildings and other facilities at the Las Campanas site in Chile are complete. Hard rock excavation of the foundations for the enclosure and telescope pier is complete. Preliminary design of the enclosure has been completed and final design is underway. Seismic isolation system bearings have been tested. A primary mirror segment test cell that will be used to qualify control system components and software is being fabricated. Prototyping continues in several areas, including on-telescope wavefront sensing and control elements, telescope laser metrology, and a subscale Adaptive Secondary Mirror (ASM). Adaptive optics and phasing testbeds are under development. Construction activities were delayed by the global coronavirus pandemic, but work has now resumed.

Located at the Nasmyth Platforms A and B, the Prefocal Stations of the Extremely Large Telescope (ELT) are the last opto-mechanical components before the light from the giant telescope comes to a focus. The mission of the Prefocal Stations are threefold. Firstly, these high-precision opto-mechanical and optical sensing devices propagate the light collected on the telescope into science instruments and other test equipment. Very high optical quality, stability, and low vibration are key characteristics of the deployable M6N and M6C mirrors, that provide the optical propagation function. Secondly, by means of three Sensor Arms, they pick and adapt the light from up to three guide stars for its use in the Acquisition, Guiding and Wavefront Sensing to support the telescope active and adaptive optics. The active optics stabilize the images delivered to the science instruments, despite the constantly changing effects of wind and other disturbances on the telescope, and periodically realign the telescope to keep the adaptive optics working in their operating range. The adaptive optics compensate for the wavefront distortion caused by the atmospheric turbulence by acting on the deformable mirror (M4). Thirdly, the Prefocal Stations provide optical sensing to support phasing of the ELT primary mirrors, diagnostics, and maintenance of the optics. These tasks are performed by the Phasing and Diagnostic Station, which is located on the Coudé path. The functions provided by the Prefocal Stations are critical for the commissioning and operation of the ELT telescope. Here we report on the final design of the Prefocal Stations, with an emphasis on the Prefocal Station Main System.

Large aperture telescopes require active control to maintain focus, collimation, and correct figure errors in the Primary Mirror (M1) due to gravity and thermal deformations. The Giant Magellan Telescope (GMT) M1 active optics subsystem consists of the hardware and software that controls the shape, position, and thermal state of each mirror segment. Pneumatic force actuators support the weight and control the surface figure while linear position actuators control the six solid-body degrees of freedom of each mirror segment. A forced convection system comprised of fan-heat exchanger units control the mean temperature and thermal gradient of each mirror segment. The M1 Subsystem design leverages existing technology and employs innovations driven by more demanding requirements compared to heritage systems. These differences led to the identification of three key GMT project risks: determining if the vibration environment induced by the fan-heat exchanger units and the error in the applied influence functions required to shape the mirror are within image quality budget allocations. The third risk is incorporating damping to the force actuators to meet the seismic requirements. GMT is currently mitigating these risks by integrating a fully functional off-axis M1 Test Cell at the University of Arizona’s Richard F. Caris Mirror Lab. This paper summarizes our requirements and design presented at the M1 Subsystem Preliminary Design Review in June 2019, describes our risk burn-down strategy for the M1 Subsystem, and presents our integration and test progress of the M1 Test Cell.

We present a concept of a millimeter wavefront sensor that allows real-time sensing of the surface of a groundbased millimeter/submillimeter telescope. It is becoming important for ground-based millimeter/submillimeter astronomy to make telescopes larger with keeping their surface accurate. To establish `millimetric adaptive optics (MAO)' that instantaneously corrects the wavefront degradation induced by deformation of telescope optics, our wavefront sensor based on radio interferometry measures changes in excess path lengths from characteristic positions on the primary mirror surface to the focal plane. This plays a fundamental role in planed 50-m class submillimeter telescopes such as LST and AtLAST.

ScotchWeld 2216 is the selected epoxy for the Thirty Meter Telescope primary. The Invar interface components are adhered to the Clearceram segments with this epoxy. The work presented quantifies the bond strength sensitivities for TMT and validates the design. Coupons were subjected to numerous tensile and shear destructive tests. The bond preparation parameters were perturbed, and the sensitivities were evaluated. An attempt at artificial aging of the epoxy bonds was made using cyclical loads and environments. Non-destructive creep testing was evaluated interferometrically with 200mm test articles. Strength was enhanced (33%) by “conditioning” or an elevated cure (100C for 1 hour). The epoxy is strengthened (54%) at the site temperature of 2C. We measured reduced cohesive strengths for thick primer (36% weaker) and for Invar oxide (70% weaker), among other process-related degradations. For artificial aging, cyclical stresses had a minimal impact on strength, but cyclical temperature-humidity tests did significantly reduce strengths (36% weaker). 2216 epoxy exhibits visco-elastic creep in shear. For structural applications, this is unimportant, but for the TMT original design, it resulted in a surface figure degradation (2 nm P-V) over a 9-hour observation window. With alternate epoxies, with much higher Tg’s glass transition temperatures, we saw similar creep responses. 2216 epoxy provides for good strength margins for the TMT design as long as attention to the preparation details is strictly adhered to, and its properties are understood in the context of the overall design performance.

In January 2019 SCHOTT has successfully delivered the 4.25 m diameter convex ZERODUR® mirror blank for the secondary mirror (M2) of the extremely large telescope (ELT) of ESO, followed by 4 m ZERODUR® mirror blank for the tertiary mirror (M3) in December 2019. The ELT will be the largest telescope in the world with a primary mirror of 39 m aperture. Additionally to the M2 and M3 blanks all 798 segments of primary mirror M1 and the thin shells for the world’s largest adaptive M4 mirror are made of ZERODUR®. With its 4.25 m physical diameter, the ELT M2 mirror will be the largest convex secondary mirror in the world. The production for the M2 and M3 started with the melting and casting of 4.5 m diameter raw blank. The coefficient of thermal expansion was optimized during ceramization to ZERODUR® TAILORED grade for the application temperature conditions of the ELT on mount Antofagasta in Chile. The installation of a new high accuracy 5 m size CNC grinding center enabled an excellent surface shape accuracy on the functional surface. The sub-surface damage of the back surface and the outer diameter was reduced by means of an acid etching process to increase the lifetime of the bonding interfaces to the support structure. Dedicated handling equipment was designed and build in-house to support the production process. This presentation gives an overview on the tasks and the achieved results of the ELT M2 and M3 ZERODUR® blanks.

The Thirty Meter Telescope (TMT) is expected to reveal the birth of galaxies, planetary surfaces and even the atmospheric composition of exoplanets. The TMT is an optical infrared reflecting telescope that uses very large hydrostatic bearings in the drive units. High precision is required for the sliding surface of the hydrostatic bearing. In the case of TMT, the radius of the hydrostatic bearing of the elevation journal is about 10 meters and it cannot be manufactured as an integral structure, so has a segmented structure. The size of each member of the segmented structure exceeds 10 meters. When high precision machining of about 30 micrometers is performed on the large structure exceeding 10 meters, it may take several days for a single process, which is greatly affected by changes in ambient temperature. Changes in ambient temperature not only cause thermal expansion and contraction of the workpiece, but also cause deformation of the machine tool. There are only a few large machine tools that can process parts over 10 meters in size. We constructed a temperaturecontrolled chamber that covers the large machine tool to prevent ambient temperature fluctuations. We compared the accuracy of machining in a room temperature (variable temperature) environment and machining in a constant temperature environment. This result demonstrates that machining errors can be suppressed in a constant temperature environment. In addition, this paper also shows the results of combining machining and the use of abrasive paper to finish the sliding surface, which improved the surface roughness without deforming the shape of the machined sliding surface. By using these improved machining methods, we were able to establish a precision machining method for large structures.

The Seimei Telescope, a 3.8-m optical and infrared telescope located on the range of Mount Chikurinji in Okayama prefecture of Japan was commissioned in 2019. The Seimei Telescope project was started with the actual commencement of technical development in 2006. Seimei is a segmented-mirror telescope whose primary mirror consists of 18 petal-shaped segments on an ALT-AZ mounting. We will aim at diffraction-limited images with Seimei, by phasing the segments and employing adaptive optics in the future. The telescope tube has a light-weight homologous structure designed with a genetic algorithm. The total moving mass is only 18 000 kg including the two Nasmyth platforms; it can acquire anywhere on sky within 1 min. Current blind pointing accuracy is about 5 arcsec RMS above the altitude of 30 deg. Seimei is a Ritchey-Chretien telescope with two Nasmyth foci of focal ratio of f/6.0, and its optical design is based on that of the WIYN 3.5-m telescope on Kitt Peak, USA. Seimei is operated by Kyoto University with the help of National Astronomical Observatory of Japan (NAOJ). Half of the telescope time is used by Kyoto University, and the remaining time is open to the astronomical community; NAOJ is responsible for the management of the open-use time. Since 2019 February 28, open-use time observations have been made without any serious problems; 140 science night observations are planned for the semester 2021A (from January 4 to June 20, avoiding the Japanese rainy period), with a small amount of engineering time.

The Vera C. Rubin Observatory is a joint NSF and DOE construction project with facilities distributed across multiple sites. These sites include the Summit Facility on Cerro Pachón, Chile; the Base Facility in La Serena, Chile; the Project and Operations Center in Tucson, AZ; the Camera integration and testing laboratories at SLAC National Accelerator Laboratory in Menlo Park, CA; and the data support center based at the National Center for SuperComputing Applications at Urbana-Champaign, IL. The Rubin Observatory construction Project has entered its system integration and testing phase where major subsystem components are coming together and being tested and verified at a system level for the first time. The system integration phase of the Project requires a closely coordinated and organized plan to merge, manage, and be able to adapt the complex set of subsystems and activities across the entire observatory as real effects are discovered. In this paper we present our strategy to successfully complete integration, test and commissioning of the systems making up the Rubin Observatory. We include discussion on (i) our strategy for integration activities and the verification of requirements (ii) a brief summary of construction status at the time of this paper, (iii) early integration activities that are used to mitigate risks including the use of the Rubin Observatory's commissioning camera (ComCam), planning for the integration, testing and verification of the primary science instrument - LSSTCam, and lastly, (v) Science Verification through short concentrated survey-like campaigns. Throughout this paper we identify where key performance metrics are addressed that directly impact the Rubin Observatory's 10{year Legacy Survey of Space and Time (LSST) science capabilities - e.g. image quality, telescope dynamics, alert latency, etc...

The Lowell Observatory Solar Telescope (LOST) will fiber feed sunlight into the EXtreme PREcision Spectrograph (EXPRES) to observe the Sun during the day in an analogous way to stars at night. One main hurdle remains in detecting a terrestrial exoplanet orbiting in the habitable zone of a Sun-like star. The star itself can induce radial velocity jitter of several m/s, completely drowning the minuscule signal from an orbiting planet. Understanding this jitter has proved extremely challenging owing to the fact that the majority of stellar surfaces are unresolved. One star for which this isn’t the case is the Sun. Combining our EXPRES solar spectra with spacecraft data from missions like NASA’s Solar Dynamics Observatory and the recently launched Parker Solar Probe will revolutionize our capability to remove the stellar induced RV jitter, greatly increasing our ability to detect a true Earth analog.

POLARBEAR-2a (PB-2a) is the first of three telescopes comprising the Simons Array, a cosmic microwave background (CMB) polarization observatory sensitive over a wide range of wavelengths and angular scales. The Simons Array will have a broad science reach, including primordial gravitational wave background searches and neutrino physics constraints. PB-2a, which began observing from northern Chile in 2018, has enabled many of the technologies necessary for the full operation of the Simons Array. Here, we describe the first year on-sky characterization and operation of PB-2a along with recent upgrades which improve upon the sensitivity, stability, and operability of the detector array.

Stratospheric balloons offer accessible and affordable platforms for observations in atmosphere-constrained wavelength ranges. At the same time, they can serve as an effective step for technology demonstration towards future space applications of instruments and other hardware. The Stratospheric UV Demonstrator of an Imaging Observatory (STUDIO) is a balloon-borne platform and mission carrying an imaging micro-channel plate (MCP) detector on a 0.5 m aperture telescope. STUDIO is currently planned to fly during the summer turnaround conditions over Esrange, Sweden, in the 2022 season. For details on the ultraviolet (UV) detector, see the contribution of Conti et al. to this symposium.1 The scientific goal of the mission is to survey for variable hot compact stars and flaring M-dwarf stars within the galactic plane. At the same time, the mission acts as a demonstrator for a versatile and scalable astronomical balloon platform as well as for the aforementioned MCP instrument. The gondola is designed to allow the use of different instruments or telescopes. Furthermore, it is designed to serve for several, also longer flights, which are envisioned under the European Stratospheric Balloon Observatory (ESBO) initiative. In this paper, we present the design and current status of manufacturing and testing of the STUDIO platform. We furthermore present the current plans for the flight and observations from Esrange.

The Event Horizon Telescope (EHT) 2017 campaign successfully imaged the black hole shadow for the first time. To achieve this image, we used the very long baseline interferometry (VLBI) technique at the wavelength of 1.3 mm (frequency of 230 GHz) with utilizing eight millimeter- and submillimeter-wavelength telscopes all over the world. For the interferometry, the distance between two telescopes (i.e., baseline length) decides the angular resolution. The EHT telescopes extends near the diameter of the Earth, so together with the short wavelength, it is possible to reach the angular resolution of about 25 micro-arcsec. This resolution is sufficient to image the shadows of nearby supermassive black holes (SMBHs), and indeed, we have succeessfully imaged the shadow of the SMBH at the center of the nearby giant elliptical galaxy M87. In this talk, I will give an overview of the technologies we have used in the EHT 2017 campaign, and also present the plans of the future development.

SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) aims to perform a transit search on the nearest (< 40 pc) ultracool (< 3000K) dwarf stars. The project's main motivation is to discover potentially habitable planets well-suited for detailed atmospheric characterisation with upcoming giant telescopes, like the James Webb Space Telescope (JWST) and European Large Telescope (ELT). The project is based on a network of 1m robotic telescopes, namely the four ones of the SPECULOOS-Southern Observatory (SSO) in Cerro Paranal, Chile, one telescope of the SPECULOOS-Northern Observatory (SNO) in Tenerife, and the SAINTEx telescope in San Pedro Martir, Mexico. The prototype survey of the SPECULOOS project on the 60 cm TRAPPIST telescope (Chile) discovered the TRAPPIST-1 system, composed of seven temperate Earth-sized planets orbiting a nearby (12 pc) Jupiter-sized star. In this paper, we review the current status of SPECULOOS, its first results, the plans for its development, and its connection to the Transiting Exoplanet Survey Satellite (TESS) and JWST.

The Large Millimeter Telescope (LMT) Alfonso Serrano is a 50m-diameter single-dish radio telescope constructed at an altitude of 4600 meters on the summit of Volcan Sierra Negra, an extinct volcano in the Mexican state of Puebla. The LMT is a bi-national scientific collaboration between Mexico and the USA, led by the Instituto Nacional de Astrofisica, Optica y Electronica (INAOE) and the University of Massachusetts at Amherst. The telescope currently operates at wavelengths from 4mm to 1mm, and during the dry winter months the LMT site provides the highest levels of atmospheric transmission and potential future access to submillimeter observing windows. This paper describes the current status and scientific performance of the LMT, the suite of scientific instrumentation and future engineering upgrades that will optimize the optical efficiency of the telescope and increase its scientific productivity.

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne far-infrared telescope that will survey galactic formation history over cosmological time scales with redshifts between 0 and 3.5. EXCLAIM will measure the statistics of brightness fluctuations of redshifted cumulative carbon monoxide and singly ionized carbon line emissions, following an intensity mapping approach. EXCLAIM will couple all-cryogenic optical elements to six μ-Spec spectrometer modules, operating at 420-540 GHz with a spectral resolution of 512 and featuring microwave kinetic inductance detectors. Here, we present an overview of the mission and its development status.

The Next Generation Balloon-Borne Large Aperture Submillimeter Telescope (BLAST-TNG) was a unique instrument for characterizing the polarized submillimeter sky at high-angular resolution. BLAST-TNG flew from the Long Duration Balloon Facility in Antarctica in January 2020. Despite the short flight duration, the instrument worked very well and is providing significant information about each subsystem that will be invaluable for future balloon missions. In this contribution, we discuss the performance of telescope and gondola.

We describe plans for adding a wide-field narrow-band imaging capability to the Dragon y Telephoto Array. Our plans focus on the development of the ‘Dragon y Filter-Tilter', a device which places ultra-narrow bandpass interference filters (Δλ ≈1 nm) in front of each of the lenses that make up the array. The filters are at the entrance pupil of the optical system, rather than in a converging beam, so their performance is not degraded by a converging light cone. This allows Dragon y to image with a spectral bandpass that is an order of magnitude narrower than that of telescopes using conventional narrow-band filters, resulting in a large increase in the contrast and detectability of extended low surface brightness line emission. By tilting the filters, the central wavelength of the transmission curve can be tuned over a range of 7 nm, corresponding to a physical distance range of about 20 Mpc for extragalactic targets. A further benefit of our approach is that it allows off-band observations to be obtained at the same time as on-band observations, so systematic errors introduced by rapid sky variability can be removed with high precision. Taken together, these characteristics should give our imaging system the ability to detect extremely faint low-surface brightness line emission. Future versions of the Dragon y Telephoto Array may have the sensitivity needed to directly image the circumgalactic medium of local galaxies. In this paper, we provide a detailed description of the concept, and present laboratory measurements that are used to verify the key ideas behind the instrument.

The Vera C. Rubin Observatory¹ⁱ is now under construction, on Cerro Pachón, in Chile. Its telescope has an 8.4 m primary tertiary mirror (M1M3), and has been designed to conduct a 10 years survey in which it will map the entire night sky every three nights. The support systems is composed by six Hardpoints and 156 pneumatic actuators. The Hardpoints define the mirror’s position in the mirror cell, and hold that position while observing in order to maintain the alignment of the telescope. The pneumatic actuators provides mirror support and figure correction, from optimizations provided by the Active Optics System (AOS). In order to complete the sky mapping in three nights the telescope mount has been designed to develop high accelerations that will allow it to change the observing field in just 2 seconds. The rapid telescope slews will apply high inertial forces on the mirror that have to be offloaded from the Hardpoints by the mirror's pneumatic actuators. This keeps the mirror safe during operations. For this reason, the support system has been optimized introducing innovative control concepts in both the Outer and Inner Loop, and the individual component. Extensive modeling of the control system dynamics has been developed to simulate and test different control architectures. Inner loop control systems were developed and tested using hardware-in-the-loop simulations which take advantage of the power of the modeling, using the real hardware components. This technique is especially suitable for complex real-time systems and allows for faster development time, with more precise results. The Outer Loop model has been used to tune the Hardpoints off-loading control system. The resulting parameters were used directly in the real system, once integration was completed, and worked as the simulations predicted. Gravity lookup- tables and inertial compensation forces, to counteract the high acceleration from the telescope mount, have also been included in the model. Simulations show the Hardpoints forces are far below their limits. This is particularly important, as we will not have the possibility to test the inertial compensation until the mirror cell is actually installed on the telescope mount. The simulations have provided encouraging results.

The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall-2) is a UV multi-object spectrograph exploring the CGM of galaxies at low redshifts (0.3 < z < 1.0). The science detector is a EMCCD cooled by a Sunpower cryocooler to minimize the noise contributions from dark current. To efficiently remove the heat generated by the cryocooler and other critical hardware, we built a custom water cooling circuit which uses a water/alcohol/ice mixture to regulate temperatures during flight. We report the ground and flight performances of the thermal system during the 2018 campaign and the lessons learned since then. We will discuss the model predictions of the potential impacts of several major upgrades as well as modifications to adapt to those impacts, and the ground performance of the thermal system during the rebuild of FIREBall-2, compared with the model predictions, for the next launch of FIREBall-2 in Fort Sumner in 2020.

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

The Vera C. Rubin Observatory is now under construction on Cerro Pachon in Chile. This ground-based facility is designed to conduct the Legacy Survey of Space and Time (LSST), which is a decade-long time-domain optical survey of the night sky. The system aberrations introduced by temperature gradients, hysteresis and other non-predictable errors can prevent the telescope from delivering a consistently high-quality image over its 3.5 degrees field of view, necessary to the LSST scientific goals. Therefore, the active optics system (AOS) uses a combination of an open-loop and a closed-loop correction. The AOS open-loop is planned to correct for typical gravity variations while the AOS closed-loop will correct the real-time (within 30s) system aberrations. The components used for this task consist mainly of: two mirrors with active support systems (M1M3 and M2), two hexapods and curvature wavefront sensors integrated to the focal plane of the science detector. By the beginning of 2019, both M1 and M3 mirrors had been extensively tested using interferometry techniques, providing necessary measurements to refine our Finite Element models. This will help to achieve higher image quality when integrating all mirrors on the telescope. Progress has also been made on the active optics pipeline, which allows for conversion of the wavefront sensor images into corrective data for the mirrors and hexapods. In this paper, we will present the main results from the mirror testing as well as predicted performance of the AOS using these results. Finally, we will discuss the test plan for commissioning the AOS on the telescope.

The coldest and densest structures of gas and dust in the Universe have unique spectral signatures across the (sub-)millimetre bands (υ ≈30 - 950 GHz). The current generation of single dish facilities has given a glimpse of the potential for discovery, while sub-mm interferometers have presented a high resolution view into the finer details of known targets or in small-area deep fields. However, significant advances in our understanding of such cold and dense structures are now hampered by the limited sensitivity and angular resolution of our sub-mm view of the Universe at larger scales. In this context, we present the case for a new transformational astronomical facility in the 2030s, the Atacama Large Aperture Submillimetre Telescope (AtLAST). AtLAST is a concept for a 50-m-class single dish telescope, with a high throughput provided by a 2 deg - diameter Field of View, located on a high, dry site in the Atacama with good atmospheric transmission up to υ ~1 THz, and fully powered by renewable energy. We envision AtLAST as a facility operated by an international partnership with a suite of instruments to deliver the transformative science that cannot be achieved with current or in-construction observatories. As an 50m-diameter telescope with a full complement of advanced instrumentation, including highly multiplexed high-resolution spectrometers, continuum cameras and integral field units, AtLAST will have mapping speeds hundreds of times greater than current or planned large aperture (< 12m) facilities. By reaching confusion limits below L_* in the distant Universe, resolving low-mass protostellar cores at the distance of the Galactic Centre, and directly mapping both the cold and the hot (the Sunyaev-Zeldovich effect) circumgalactic medium of galaxies, AtLAST will enable a fundamentally new understanding of the sub-mm Universe.

We explore a novel design for “Trip Wire Optics" (TWO), which is a near-Earth object (NEO) detection observatory, arising from the emerging technology of primary objective grating telescopy (the Dittoscope). The design consists of two Schmidt telescopes viewing a large transmission primary objective diffraction grating (POG) at large exodus angle, deployed in a ground based north-south orientation. This document serves to establish a baseline understanding of such an instrument, evaluating the system geometry, light collection efficiency, effects of atmospheric turbulence, and potential for NEO observation. While the atmospheric turbulence precludes diffraction-limited images, the Dittoscope design is no more effected than a conventional telescope and imager. We define a new figure of merit, modified etendue, to compare the light gathering power of a Dittoscope to that of a conventional telescope. We have not succeeded in creating a ground-based imaging survey that collects more light, as measured by modified etendue, with a POG than it did using the same two Schmidt telescopes with conventional imagers. However, the properties of the Dittoscope design differ from conventional surveys, and could potentially be scaled to enormous size. Our evaluation of the POG design suggests it would be more advantageous for applications that require large collection areas for small wavelength ranges (spectroscopy) or to achieve high resolution observations in space.

PANOPTES (Panoptic Astronomical Networked Observatories for a Public Transiting Exoplanets Survey) is a citizen science project that aims to build a collaborative, worldwide network of robots that will survey the night sky for nearby transiting exoplanets. The PANOPTES units are designed to be low-cost, easy to build with a clear set of instructions, and constructed with readily available off-the-shelf hardware. As part of collaborative efforts, we have established an online forum for the PANOPTES community. The forum serves as a platform for everyone involved in PANOPTES to discuss with each other, to help troubleshoot during the build and deployment of a unit, and to provide feedback in improving the design. PANOPTES units have been built by school students, graduate students, astronomy enthusiasts, and citizen scientists from different countries. There are currently 18 units in various stages of deployment across the world, with at least seven more units being planned for construction. The degree of success of the project relies directly on the number of units spread over the world, as light curves from different units in the network will be combined to improve sensitivity and time coverage. In this paper, we provide an overview of the project, its scientific goals, community reach, current status, challenges, and future plans.

Technical activation of newly installed 3.6m optical telescope in March 20l6 paved the way for the routine operation of mechanical systems of telescope and its enclosure at Devasthal. Maintaining and upgrading complex mechanical systems for meeting upcoming technical requirements of telescope, instruments and its enclosure has been an exciting task. Few mechanical systems such as cable anti-twister, telescope cover structure, mechanical locks etc. have been indigenously designed, developed and executed while others are in the pipeline for implementation at site. Telescope’s major mechanical assemblies such as ARISS-octagon, primary mirror cell and secondary mirror cell assembly etc. were disassembled and integrated back in telescope few times for aluminizing missions and for sorting out various problems encountered in the telescope systems. It has served as an important means for training mechanical manpower in various sophisticated assemblies of telescope.

The University of Tokyo Atacama Observatory Project is to construct a 6.5 m infrared-optimized telescope at the summit of Co. Chajnantor (5640 m altitude) in northern Chile. The telescope optics uses a Ritchey-Chretien type layout, with an under-sized secondary mirror to reduce stray light caused by thermal emission from the telescope structure. The primary mirror is a F/1.25 lightweight borosilicate glass (Ohara E6) mirror with honeycomb structure, which is developed by Steward Observatory Richard F. Caris Mirror Lab. The telescope has two Nasmyth foci and two folded-Cassegrain foci, which can be switched by rotating a tertiary mirror. The final focal ratio is 12.2 with a field of view of 25 arcmin in diameter. The telescope mount is a tripod-disk alt-azimuth mount. Both the azimuth and elevation axes are supported by and run on hydrostatic bearings, and they are driven by friction drives with servo motors, which are controlled by the telescope control system. It also controls the hexapod mount of the secondary mirror and the pneumatic actuators of the primary mirror support to keep good image quality during the observation. An off-axis Shack-Hartmann sensor installed in each focus measures the wavefront aberration of the telescope optics, then the misalignment between the secondary and primary mirrors is corrected by adjusting the hexapod mount while other aberrations are corrected by the deformation of the primary mirror. The force distribution of the actuators for correction will be calculated by fitting the wave-front errors with a series of bending modes of the primary mirror.

LOCNES (LOw-Cost NIR Extended Solar telescope) is a solar telescope installed at the TNG (Telescopio Nazionale Galileo). It feeds the light of the Sun into the NIR spectrograph GIANO-B through a 40-m patch of optical fibers. LOCNES has been designed to obtain high signal-to-noise ratio spectra of the Sun as a star with an accurate wavelength calibration through molecular-band cells. This is an entirely new area of investigation that will provide timely results to improve the search of telluric planets with NIR spectrographs such as iSHELL, CARMENES, and GIANO-B. We will extract several disc-integrated activity indicators and average magnetic field measurements for the Sun in the NIR. Eventually, they will be correlated with both the RV of the Sun-as-a -star and the resolved images of the solar disc in visible and NIR. Such an approach will allow for a better understanding of the origin of activity-induced RV variations in the two spectral domains and will help in improving the techniques for their corrections. In this paper, we outline the science drivers for the LOCNES project and its first commissioning results.

Synoptic telescopes are fundamental tools in Solar Physics and Space Weather. Their typical high cadence full-disk observations are pivotal to assess the physical conditions on the Sun and to forecast the evolution in time of those conditions. The TSST (Tor vergata Synoptic Solar Telescope) is a synoptic telescope composed of two main full-disk instruments: an H-alpha Daystar SR-127 telescope and a Magneto Optical Filter (MOF)-based telescope in the Potassium KI at 769.90 nm. The MOF consists in a glass cell containing a Potassium vapor where a longitudinal magnetic field is applied. The MOF-based channel produces full disk Line-of-Sight magnetic field and velocity maps of the solar photosphere at 300 km above the solar surface. In this work, we present the optical setup, the spectral characterization of the MOF-based telescope, and details on the spectral characterization of the MOFs cells which is a required test to obtain calibrated magnetograms and dopplergrams.

This paper describes the design, implementation, and verification of a test-bed for determining the noise temperature of radio antennas operating between 400-800 MHz. The requirements for this test-bed were driven by the HIRAX experiment, which uses antennas with embedded amplification, making system noise characterization difficult in the laboratory. The test-bed consists of two large cylindrical cavities, each containing radio-frequency (RF) absorber held at different temperatures (300K and 77 K), allowing a measurement of system noise temperature through the well-known ‘Y-factor’ method. The apparatus has been constructed at Yale, and over the course of the past year has undergone detailed verification measurements. To date, three preliminary noise temperature measurement sets have been conducted using the system, putting us on track to make the first noise temperature measurements of the HIRAX feed and perform the first analysis of feed repeatability.

Before the transport of a large telescope on site, it is suitable to perform factory tests to guarantee the optical performances. AMOS SA has been awarded of the contract from the design to on-site installation (in Rajasthan) of the 2.5-m Class Telescope for Physical Research Laboratory. The 20-m-focal-length telescope has a Ritchey-Chrétien optical configuration and provides at Cassegrain location one axial port and two side ports. It is equipped with a primary active mirror and a first order adaptive optical system. It operates in the 0.37-4 μm spectral range. The project fulfillment relies on the AMOS multidisciplinary expertise in design and manufacturing of high-accuracy optical, mechanical and opto-mechanical systems. This paper presents the test results carried out at AMOS factory to assess the telescope performances (e.g. active optic control loop, pointing, tracking). It relies on extensive tests on the mount control, and the optical and mechanical sub-systems before assembly.

The addition of multiple “mini-trackers” (MTs) to the Southern African Large Telescope (SALT) would create in effect several four-to-six-meter class telescopes that take advantage of the SALT 10-meter diameter primary mirror’s 35 degree diameter uncorrected field-of-view. These devices, with a 100 square degree patrol area, would provide valuable follow up capability for the large astronomical surveys either in operation (e.g. MeerKAT, eROSITA, Gaia), or expected to begin operations soon (e.g. LSST, SKA, Euclid). A feasibility study was conducted to evaluate the technical practicality associated with the design, fabrication, integration, and testing of a prototype MT for SALT. The study determined that the development of a mini-tracker was indeed feasible, and work has begun on the concept design phase of the project.

Mezzocielo (or "half of the sky") is a concept for a new class of telescopes where a full spherical optical surface is made by filling with a liquid a structure built up with spherical lenses and almost covering an entire sphere. Lenses of the same class of existing ones can be arranged, for example like the faces of a dodecahedron, in order to build up a sphere in the 1 to 4m class in diameter. Liquid with low refractive index and high transparency are available in the electronic and cooling industry and made up devices with strong high order spherical aberrations but consistently identical over basically any direction in the sky simultaneously. An ensemble of moving correctors or a hemispherical array of the same kind of devices can feed a number of detectors lying in the range of the ten of thousands, making modern CMOS the only, today, viable solution to such a kind of futuristic facility.

In the Antofagasta Region in northern Chile the large plateau of Chajnantor, located at more than four thousand meters of altitude, has exceptionally clear skies due to the low humidity in the area, allowing for observations in the sub-/millimeter, infrared and optical ranges. In addition, both its easy access through the international road of Paso Jama and its relative isolation from urban centers, make this area an ideal place for astronomical observations. It is in this area where the Atacama Astronomical Park (AAP) is installed, an initiative that seeks to transform the region into a window to the Universe. The AAP is managed by the non-profit Atacama Astronomical Park Foundation, whose board of directors has the power to directly grant an installation permit to projects that present meritorious applications. After some years of operations of astronomical projects at the Park, the AAP is now moving forward with its vision of an integrated support on enabling infrastructure, so the current and future observatories can focus on their core business: to produce Science. The Park identified key strategic areas of support, namely: communications via fiber optics, centralized power solutions, improvement of the access roads, and a corresponding health, safety and security plan. This paper presents the AAP and describes the progress to fulfill the strategic vision of the Atacama Astronomical Park.

Currently, numerous projects for the study of both outer space and the Earth's surface use mirror optical systems, since they allow working in a wide spectral range. As a rule, three-mirror anastigmats (TMA) are used, however, it is possible to correct four aberrations in some configurations of three-mirror systems without an intermediate image. In order to avoid obscuration, such schemes in a configuration with an off-axis field may be used. In the case of very compact systems, it is necessary to apply fast mirrors, so aspherical surfaces are used. To select the optimal position of an aspherical surface and an equation for describing higher-order and free-form aspherical surfaces, a study is made of higher-order aberrations in systems with various parameters, empirical dependencies are derived that allow one to evaluate the correction capabilities of the schemes. Examples of system designs with an off-axis field are presented.

The ALMA telescope has been producing ground-breaking science since 2011, but it is mostly based on technology from the 2000s. In order to keep ALMA competitive in the coming decade, timely updates are necessary in order to further improve the science output of the telescope in the coming decades. In this contribution, we will present the status of the different projects and studies which constitute the contribution of East Asia to the ALMA Development Program, such as the production of band 1 receivers, the development of band 2 receivers optics, and of the ACA spectrometer. We will also update on the different hardware and software studies towards the implementation of the ALMA Development Roadmap and additional opportunities.

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) Parkes Radio Telescope, Australia, has been in operation since 1961. It is a 64-metre parabolic antenna, with receiver systems capable of observing from 700-MHz to 26 GHz with bandwidths up to 3 GHz, and it is part of the CSIRO Australia Telescope National Facility (ATNF). Parkes has continued to be at the forefront of radio astronomy and technology research, having had many improvements, which enabled unprecedented surveys of atomic hydrogen in the Southern sky, and helped discover approximately half the known population of pulsars, as well as discovering Fast Radio Bursts. Parkes was recognised as a Square Kilometre Array (SKA) Pathfinder in 2016, on the basis of Phased Array and Wideband Feed technology development. I will present a summary of the current status of the capabilities, and its science yield, in the context of the developments of SKA oriented technology. This includes the ultra-wideband low frequency receiver, a high frequency counterpart, and a cyrogenically cooled phased array feed.

Absolute flux calibration of standard stars, traceable to the International System of Units (SI) standards, is essential for 21st century astrophysics. Dark energy investigations that rely on observations of Type Ia supernovae and precise photometric redshifts of weakly lensed galaxies require a minimum uncertainty of 0.5% (k=1) in the absolute color calibration. Other areas of astronomy and astrophysics, e.g. fundamental stellar astrophysics, will also benefit. In the era of large telescopes and all sky surveys, well-calibrated standard stars that do not saturate, are available over the whole sky, and extend to fainter magnitudes are needed. Our collaboration, NIST Stars, has developed a novel, fully SI-traceable laboratory calibration strategy that will enable achieving the demanding 0.5% requirement which we shall describe here. We discuss our results from a pilot study to determine the top-of-the-atmosphere absolute spectral irradiance of bright stars and the next steps.

The Near-Earth Object Survey TELescope- NEOSTEL telescope is based on the Fly-Eye design developed by OHB-Italia that it is also the prime contractor and the technical coordinator of a multinational consortium that develops and deploys its first unit. The Italian INAF institute supports OHB-Italia in the integration and testing phase of the NEOSTEL telescope within the NEOSTED (Near-Earth Object Survey TElescope Development) program. NEOSTEL is an optical telescope, 1-meter class primary mirror, that splits the image into 16 CCD cameras mounted on as many objectives (Secondary Optics Tubes-SOTs). Each channel optically works as a single unit of a multi-telescope, and it is equipped with a camera. The NEOSTEL CCD camera is under development within the ESA ASTROCAD program. The 1180mm entrance aperture and the performance of the ASTROCAD camera shall allow scanning two-thirds of the visible sky about three times per night, detecting NEOs down to apparent magnitudes 21.5. ESA, in collaboration with the Italian Space Agency (ASI) identified the location for the installation of the first NEOSTEL prototype on top of the Mount Mufara on the Madonie Chain in Sicily.

The LCT project aims to refurbish the CSO telescope, move it from Maunakea to Chajnantor, in Chile, and operate it scientifically for 10 years. The relocation of the telescope involves a variety of changes in the working conditions, which demands in-depth mechanical analysis. To conduct the required studies, an FEM model of the entire telescope has been developed, together with CFD tools. This paper introduces the LCT project, presents the full-FEM model, its validation, and the first steps towards these analyses. Preliminary results of the simulations of the telescope, considering the working conditions at the Plateau, are also shown.

The robotic 2-metre Liverpool Telescope (LT), located at Roque de los Muchachos, La Palma, has seen great success in its <15 year lifetime. In particular the facility thrives in time domain astronomy, responding rapidly to triggers from Swift and efficiently conducting a wide variety of science with its intelligent scheduler. The New Robotic Telescope (NRT) will be a 4-metre class, rapid response, autonomous telescope joining the Liverpool Telescope on La Palma in ~2025. The NRT will slew to targets and start observations within 30 seconds of receipt of a trigger, allowing us to observe faint and rapidly fading transient sources that no other optical facility can capture. The NRT will be the world’s largest optical robotic telescope. Its novel, first-generation instrumentation suite will be designed to conduct spectroscopic, polarimetric and photometric observations driven by user requirements.

The SPEED project aims at developing and testing key recipes for high-contrast imaging at small angular separations with unfriendly telescope apertures. SPEED combines optimized segmented aperture coronagraphy, dual-deformable mirrors wavefront control and shaping architecture for creating a dark hole in the scientific image by deformable mirror (DM) actuation. The challenge is to overcome the various fundamental limitations for quasi-static speckle calibration at very small angular separations. We report on the progress made in elaborating an accurate simulated model of our instrument in preparation for the wavefront control and wavefront shaping strategy with a multi-DM setup.

The ngVLA Front End concept has six separate cryogenically-cooled, dual polarization receiver bands, each with an integral feed horn. The upper five bands (2–5) are co-located within a single compact cryostat, while the lowestfrequency band (1) occupies a second cryostat of similar volume and mass. For optimum performance at higher frequencies, waveguide-bandwidth (~1.66:1) receivers are used above 12 GHz, with axially-corrugated feed horns for high aperture efficiency and low spillover. Below 12 GHz, wideband (~3.5:1) receivers and feed horns are used to reduce receiver count, total mass, and cost, with modest trades in sensitivity. Ongoing work includes development of wideband feed horns, windows, low-noise amplifiers (LNAs) and couplers for Bands 1–2, design or procurement of orthomode transducers (OMTs) and LNAs for Bands 3–6, and detailed mechanical design of the conceptual Front End cryostats and receiver/feed/window subassemblies. Accurate simulations of sensitivity (AEFF/TSYS) versus frequency and antenna elevation will be shown, based on modeled or measured component data and the simulated performance of the antenna optics.

There are many astronomical, interferometric and space situational awareness applications for single and multiple 2-meter aperture optical and infrared mobile telescopes that are low cost, can be easily transported and quickly deployed at a variety of sites. A design concept is presented for a trailermounted 2-meter telescope with a novel micro-enclosure that allows the telescope to be moved and deployed quickly for observations. The telescope is protected from adverse weather using a weatherproof telescope tube instead of a conventional dome or enclosure. It has Cassegrain, Nasmyth and coudé foci suitable for astronomical, interferometric, space situational awareness, and laser communications applications, and is designed for replication at low cost. An initial implementation is being developed to explore the performance of such a telescope using re-purposed primary and secondary mirrors and other components from the MAGNUM telescope.

The Atacama Large Millimeter Array is an array made of 64 antennas, observing the Universe in the sub-millimeter wavelength range. As technical leader of the consortium dedicated to the design and construction of the European antennas, EIE is in a unique position to evaluate possible improvements of the design. EIE has initiated an internal development, to evaluate to what extent it is possible to increase the dish diameter of the antenna, while keeping the surface and pointing accuracy achieved with ALMA. This paper presents the results of such activity.

The ELT is a project led by the European Southern Observatory (ESO) for a 40-m class optical, near- and mid-infrared, ground-based telescope. When it will enter into operation, the ESO ELT will be the largest and most powerful optical telescope ever built. It will not only offer unrivalled light collecting power, but also exceedingly sharp images, thanks to its ability to compensate for the adverse effect of atmospheric turbulence on image sharpness. The basic optical solution for the ESO ELT is a folded three-mirror anastigmat, using a 39-m segmented primary mirror (M1), a 4-m convex secondary mirror (M2), and a 4-m concave tertiary mirror (M3), all active. Folding is provided by two additional flat mirrors sending the beams to either Nasmyth foci along the elevation axis of the telescope. The folding arrangement (flat M4 and M5 mirrors) is conceived to provide conveniently located flat surfaces for an adaptive shell (M4) and field stabilization (M5). The M5 Mirror and M5 Cell contracts started in 2019. Both sub-units are currently designed by the selected contractors. While the cell is still in an early design phase, the mirror design is in the final phase and the manufacturing of the blank has already started. With the focus on the M5 mirror, we flow down the key requirements to the cell and the mirror and highlight the main characteristics of the current design, discussing the challenges of mirror manufacturing. Finally, we conclude with the current status and an overview of the coming milestones.

The ELT M4 is the telescope-facility adaptive unit for the European ELT. Final design and construction were awarded in 2015 to AdOptica, a consortium of Microgate and ADS International; on-site delivery is planned for 2024. The unit is based on a monolithic, structural reference body manufactured by Mersen Boostec. The flat thin mirror, controlled using the contactless voice-coil-motor based technology, is split in 6 segments produced by Safran Reosc. The M4 unit is ready for integration: we report here the results of the construction and component level testing, introducing also the forthcoming integration and system-level tests.

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

The next generation Extremely Large Telescopes (ELTs) are promising a profound transformation of our understanding of the universe through large-scale surveys of a myriad of previously unseen astronomical objects across cosmic space-time. For such surveys, the ELTs will need a super-efficient field corrector (FC) that can expand their field of view over a broad wavelength range, thus enabling multi-object spectroscopy using multiple back-end instruments. Arrayed Wide-Angle Camera System (AWACS) is built on the segmented FC architecture that can break the limits of monolithic design in scaling to the ELTs and beyond. AWACS accomplishes desired field expansion via a suite of small cost-effective electro-opto-mechanical units over a telescope’s focal surface that compensates for telescope field aberrations and atmospheric dispersion, locally and simultaneously. We constructed a dual-unit proof-of-concept AWACS and tested the adaptive aberration correction on sky as detailed in this paper.

Ice rich permafrost is observed at Chajnantor volcano (5,640m a.s.l.) on the University of Tokyo Atacama Observatory (TAO) site. Presence or absence of the permafrost is considered to be requested quite different engineering skills for their infrastructures. Lower altitude boundary is reported to be above 5,079m a.s.l. and maximum active (thawing) layer is 14cm. Minimal seasonal temperature variation, small active layer thickness as the consequences of low numbers of thawing and freezing degree days. Diurnal amplitude results in freeze-thaw cycles only near the surface. Severe frost shattering occurs near the ground surface, producing a dusty, fine-material horizon called a hyper-cryogenic layer. The importance of the snow-covered season for providing great protection for surface energy penetration. Many permafrost hazards are expecting in this construction site such as frost heaving, subsiding, mass movements, erosion, chemical weathering, frost shattering, embankment instability, and

The Daniel K. Inouye Solar Telescope (DKIST) will be the largest solar telescope in the world, housing a 4 meter primary mirror that will enable observation of specific regions of the sun in higher resolution and greater detail than any existing telescope. The DKIST Facility Thermal Systems is comprised of various systems and components that contribute to maintaining an appropriate thermal environment for solar observation. One of these systems is the Carousel Cooling System, which contributes to active control of the Enclosure thermal environment. This system is intended to actively maintain the Enclosure exterior at, or just below, ambient temperature through a system of plate heat exchangers. These heat exchangers, termed plate coils, are designed to reject solar radiation from the Enclosure cladding in order to mitigate dome seeing effects caused by turbulent air of dissimilar temperatures. Per DKIST's specifications, OMEGA Thermo Products fabricated 232 type 304 stainless steel plate coils that are categorized into 104 different dimensions. These are in the process of being installed on the following sections of the Enclosure: Aperture Stop, Shutter, Arches and Vent Gates. This has further complicated installation as each section yields different requirements for lifting, integrating, mounting, and piping the various plate coils. Presented here is a review of the installation progress and future planning for the Carousel Cooling System.

PLANETS will be a 1.8-m off-axis telescope combined with contrast enhancement techniques, enabling us to observe faint emissions in the vicinity of bright objects. This “high dynamic-range” capability is largely dependent upon precision of telescope optics as well as atmospheric distortion. We present feasibility study of monitoring water plumes on Europa, neutral torus close to Enceladus, and ionosphere on Mars using PLANETS telescope. To test feasibility of high dynamic-range observation under actual conditions of wavefront error, we modeled propagation of light though the system based on Fraunhofer calculation taking into account for wavefront error made by atmospheric distortion and by primary mirror figure error. Then point spread function is calculated for several cases of figure errors under use of adaptive optics. The modeling result predicts that the moderate or high-precision primary mirror is mandatory to accomplish the high dynamic-range observation. We also present the latest design of PLANETS, especially focus on the support structures of primary mirror. We employ 36-point whiffletrees with 33 warping harnesses for axial support, and 24-point Schwesinger support for lateral support. The active support system is expected to reduce pre-polished RMS error from 1.51 μm to 0.66 μm corresponding to 70% reduction in total volume of final polish. The laboratory experiment using one third part of prototype whiffletrees shows supporting force RMS repeatability < 0.005 kgf, and drive hysteresis < 0.7% of load range, which are precise enough to control or to keep the primary mirror figure.

The purpose of this study is expressing advances in design stages for in flange optical field derotator system for 4 meters DAG Telescope. In-Flange Derotator KORAY (K-mirror OpticalRelAY) is designed, analysed and manufactured to meet the specifications of DAG telescope. DAG telescope, situated at Erzurum/Karakaya summit at 3150m altitude, is the first Turkish optical telescope with VIS(Visible) and IR (Infrared) observation capability. DAG, designed by Turkish engineers at FMV Isik University, is also the largest telescope (4m diameter) in Turkey and in European continent. Being one of the 2023 vision projects; the first light of DAG is expected to take place in 2021. This purpose brings some real-life challenges such as design limitations, material selection and electronic integration.

The entire system of the LAMOST ((Large Sky Area Multi-Object Fiber Spectroscopic Telescope) requires high positioning accuracy of the fiber positioning unit. In order to acquire accurately target celestial objects, fiber view metrology system for positioners can efficiently and accurately detect thousands of fiber spots simultaneously in a large scale is required. The traditional method mainly used the "back-illumination method" for detection. With the advent of 8k*6k high-resolution CMOS cameras, fiber position detection based on the "front-illumination method" becomes feasible. This paper mainly studies the fiber position detection based on the "front-end illumination image processing method". The image is preprocessed first, and then the edge detection of a large number of fiber target points in the image is performed. Considering the constant radius of the white ceramic head where the fiber is located, the article proposes a "front-illuminated" image algorithm based on radius-based Hough space conversion and optimal radius error center search. This algorithm improves the speed and accuracy of fiber pixel coordinate detection. At the same time, it can be coordinated and compared with the "back-illuminated method" to further optimize and improve the detection accuracy of the fiber position.

We discuss the Maunakea Spectroscopic Explorer (MSE) Acquisition and Guide (A and G) System conceptual focal plane hardware and operational requirements and pay detailed attention to the A and G system’s three CMOS cameras’ areas and sensitivities needed to assure a high success rate in acquiring suitable guide stars. Ways to provide auxiliary functions, including the measurement of defocus and misalignment of the telescope optics, are also discussed.

The New Robotic Telescope (NRT) will be the largest fully robotic telescope in the world (4-m class). The primary mirror (M1) will be comprised of 18 independent 960 mm hexagonal segments with an actively controlled position to maintain the shape of the optical surface. The secondary mirror (M2) will be a lightweighted circular mirror of 1270 mm of diameter. This contribution presents the conceptual design and preliminary results of the M1 segment support assembly and a first study of two lightweighted substrate candidates for the M2 mirror.

The wide field survey telescope (WFST) is a 2.5 meter optical telescope that is currently under construction in China. Designed with a large field of view (FOV) of 3 degrees in diameter and equipped with a 0.75 gigapixel mosaic CCD camera, the telescope will be mainly used for high sensitivity time-domain imaging surveys across the northern sky. The optical design for WFST features an advanced primary-focus assembly (PFA) housing five corrector lenses, an atmospheric dispersion corrector, filters of six bands, and the CCD camera. Stray light rejection performance is crucial for WFST to achieve an optimal sensitivity and maximize its scientific outputs. The primary-focus geometry of WFST helps to reduce the celestial background compared with a Cassegrain geometry, but the wide FOV imposes additional difficulty in stray light control and suppression. In this paper, the stray light behavior of WFST is carefully modeled by establishing a detailed opto-mechanical model of the telescope, assigning proper surface properties, and launching ray tracing simulations for a variety of scenarios. Important stray light paths including ghost effect and first-order scatterings are identified. Stray light mitigation measures including baffle and mask designs are proposed and optimized based on the stray light analysis results, which show promising suppression capability.

The Vera C. Rubin Observatory is currently under construction on Cerro Pachón, in Chile. It was designed to conduct a 10-year multi-band survey of the southern sky with frequent re-visits (with both an intra- and extra-night cadence) to identify transient and moving objects. The mirror cell assembly was designed in Tucson, Arizona by the Rubin Observatory engineering department, and was tested twice in Tucson. The first testing campaign was performed at CAID industries, where the mirror cell was fabricated, using a steel mirror surrogate that has the same geometry and mass of the glass mirror2,4. The glass mirror is a single monolith that contains both the primary and tertiary mirrors on a single substrate. The testing results confirmed that the mirror support system was performing within the design specifications, and that it was safe to install the glass mirror on the cell. The second test campaign was performed at the Richard F. Caris Mirror Lab of the University of Arizona using the actual glass mirror16. This test campaign was performed under the test tower, which contains a vibration insensitive interferometer to measure mirror figure. This confirmed the mirror support system could achieve proper optical surface figure control for both primary and tertiary mirrors. After successful test campaigns at CAID, and the mirror Lab, the mirror cell assembly was disassembled, packed and shipped to the Rubin Observatory site at the Cerro Pachón summit in Chile. Upon arrival, the mirror cell has been integrated with the mirror surrogate once again to perform the third test campaign that confirmed the system has arrived safe and operational to the summit. This integrated system will be tested on the telescope mount assembly to verify that it still meets it requirements under the effects of variations in gravitational orientation, and dynamic (slewing) loads.

The SUNRISE Chromospheric Infrared spectroPolarimeter (SCIP) is a balloon-borne long-slit spectrograph for SUNRISE III to precisely measure magnetic fields in the solar atmosphere. The scan mirror mechanism (SMM) is installed in the optical path to the entrance slit of the SCIP to move solar images focused on the slit for 2-dimensional mapping. The SMM is required to have (1) the tilt stability better than 0.035″ (3σ) on the sky angle for the diffraction-limited spatial resolution of 0.2″, (2) step response shorter than 32 msec for rapid scanning observations, and (3) good linearity (i.e. step uniformity) over the entire field-of-view (60″x60″). To achieve these performances, we have developed a flight-model mechanism and its electronics, in which the mirror tilt is controlled by electromagnetic actuators with a closed-loop feedback logic with tilt angles from gap-based capacitance sensors. Several optical measurements on the optical bench verified that the mechanism meets the requirements. In particular, the tilt stability achives better than 0.012″ (3σ). Thermal cycling and thermal vacuum tests have been completed to demonstrate the performance in the vacuum and the operational temperature range expected in the balloon flight. We found a small temperature dependence in the step uniformity and this dependence will be corrected to have 2-demensional maps with the sub-arcsec spatial accuracy in the data post-processing.

The Gran Telescopio Canarias (GTC) has been recently equipped with the Main Cassegrain Focal Station (CG-Set), composed of an Instrument Rotator (IR) and the corresponding Acquisition, Guiding and Wavefront Sensing (AGWS) system. A shutter protects the Science Instrument during maintenance operations. IDOM was awarded in November 2017 the supply of this equipment, covering its design, manufacturing, assembly and commissioning of the CG-Set. The equipment was transported to the Observatorio del Roque de los Muchachos (ORM) in December 2019. The Site Acceptance Tests were successfully completed in January 2020. The final installation on the telescope has been carried out at the end of November 2020. The Cassegrain Station features a compact and lightweight design with an innovative cable wrap solution. This design results in a smooth and precise movement, whilst guarantees good access to relevant components, simplifying the maintainability. The CG-Set permits a range of movement of the Instrument Rotator of ±270º, providing a tracking accuracy better than 7 arcsec. The AGWS Mechanics provides the required pointing and focusing capabilities, using a reference star to accurately correct the telescope drives and optics. The Cassegrain Focal Station is remotely commanded from the Telescope Control System (GCS) during normal operation and from the Local Control System (LCS) supplied by IDOM for maintenance. For this purpose, two mobile HMIs can be connected at different locations. The Local Interlock and Safety System (LISS) communicates with the Telescope Interlock and Safety System (ISS) to guarantee safe operation of the CG-Set on both local and remote operation. This system is accommodated in an active thermally controlled electronic cabinet The project has been financed by both Spanish and Canary Governments (European Regional Development Funds).

High precision calibration is essential for the new generation of radio interferometers looking for Baryon Acoustic Oscillation signatures in neutral hydrogen emissions which is a signal buried in foregrounds. Yet, differences in instrument design and non-redundancies in the subsystems consisting such instruments can pose great challenges to proper calibration. For instance, Canadian Hydrogen Intensity Mapping Experiment (CHIME) offers a large instantaneous field of view with fast mapping speed with a sensitivity equivalent to a single dish in terms of total collecting area. However, the calibration of its 1000+ individual receivers poses major obstacle to harness the full capability of the new technology. In future instruments, it is planned to use redundancy at the level required for science experiments (typically below 1%). Although, this idea is against the traditional knowledge of having the radio receivers accurate to 1/20th of the observed wavelength, we plan to meet this goal by solving the redundancy issue in the front-end subsystems using precise metrology and alignment methods. To achieve this goal, we work on a 2-element interferometer called Deep Dish Development Array (D3A), with a targeted precision of 1/1000th of a wavelength at 300 MHz, located at Dominion Radio Astrophysical Observatory, located in Penticton, BC, Canada. The D3A will serve as test bed for dish prototyping, composite dish repeatability, antennae back ends which can be scaled to larger arrays without sacrificing the precision. The two dishes are made out of fiber glass composite and measured in the shop condition and in the field after fabrication. The relative pointing accuracy was obtained as 0.02°. The elevation axes of the dishes were placed in East-West direction within 0.04° of error. The surface RMS error was obtained as 0.389 mm which meets the 1/1000th of observation wavelength. RMS error due to temperature variation and assembly error on the dishes were obtained at 1 mm. This article presents the metrology principles applied to obtain the results and challenges. The tests performed in D3A will be implemented in Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) and the Canadian Hydrogen Observatory and Radio Transient Detector (CHORD).

The DREAMS telescope is currently under construction at the Siding Spring Observatory. Once completed, the 0.5m telescope will be the fastest infrared surveyor in the southern hemisphere and one of the best tool available for transient astronomy. The Opto-mechnical design is fully custom and consists of two distinct sections: The telescope tube assembly and the instrument optical relay that feeds the light into six InGaAs cameras. We present here, the details of the mechanical design of the telescope.

WEAVE is a new wide-field multi-object spectroscopy (MOS) facility proposed for the prime focus of the 4.2m William Herschel Telescope. The facility comprises a new 2-degree field-of-view Prime Focus Corrector (PFC) with a 1000-multiplex fibre positioner, a small number of individually deployable integral field units, and a large single integral field unit (IFU). The IFUs and the MOS fibres can be used to feed a dual-beam spectrograph that will provide full coverage of the majority of the visible spectrum in a single exposure at a spectral resolution of ~5000 or modest wavelength coverage in both arms at a resolution ~20000. In order to compensate the field rotation, the Prime Focus Rotator (PFR) is assembled in between the WEAVE Fiber Positioner (system that positions the fibers in the focal plane) and with the Central Can (contains the Prime Focus corrector optics) on the William Herschel Telescope (WHT). The Prime Focus Rotator must provide a rotation degree of freedom for the Fibre Positioner with a high bending stiffness (causing a deflection smaller than 0.008° between interface flanges) adding the minimum mass possible to the system (less than 700kg). This is easily identified as the main design driver to be considered. The Prime Focus Rotator positions the Fibre Positioner to an accuracy of 5 arcsec when tracking and guides all the fibres and other power and control lines through a cable wrap, for which the available space is limited. IDOM proposal to comply with these coupled requirements consists of an optimized structural system with a slightly preloaded cross roller bearing providing the highest possible stiffness to weight ratio. The rotation is driven by means of a direct drive motor powered by a servo drive. For the Cable Wrap, a compact design based on a concept previously developed by IDOM for the Folded Cassegrain Sets the GTC was proposed.

The Vera C. Rubin Observatory Primary Tertiary Mirror (M1M3), together with the fully-assembled mirror support system, underwent two optical testing campaigns at the University of Arizona Richard F. Caris Mirror Lab. The objectives of the testing campaigns were: (1) optimizing the M1M3 surfaces with support forces, and (2) characterizing how the surfaces respond to actuator forces, including measuring the bending modes and single actuator influence functions. Both objectives were successfully achieved. The differences between the measured bending modes and the Finite Element Analysis (FEA) predicted modes were shown to be less than a few percent. The surface optimizations routinely resulted in Root-Mean-Square (RMS) surface errors below 30 nm for M1 and M3, simultaneously. The entire system was shown to be robust and repeatable. In this paper, we present the results of the optical testing and the analyses performed using the data acquired.

Heat rejecter (HR) is a critical component of large aperture solar telescopes. It has the double task of acting as a Field Stop, to select the solar region to be studied, and as a heat rejecter to reduce the thermal load in the subsequent optics and keep the temperature of all internal surfaces within a few degrees of the ambient temperature. This last request is necessary to avoid the onset of internal convective air plumes and the subsequent generation of internal seeing. Since the thermal flux at the primary focus of a 4-m class telescope, as the European Solar Telescope (EST), is expected to be of the order of several MW=m², even considering high HR reflectivity, the residual thermal load is conceivably high and a suitable Cooling Systems must be considered. Among the available cooling techniques, the most promising, and already applied in critical conditions such as for nuclear fusion reactor divertor, is the Multiple Jet Impingement (MJI) techniques. To fulfill the technological challenge of the HR for the next generation 4-m class European Solar Telescope (EST), a new prototype for the 1.5 meters GREGOR solar telescope has been developed as technological proof of concept. With the aim of testing this technique, a prototype of HR was realized to be mounted at the 1.5 meters GREGOR solar telescope at the at the Teide Observatory (Canary Islands, Spain). We present the HR thermal-hydraulic design based on the expected thermal load on the GREGOR primary focal plane (⋍ 1500W) and the constraints on the HR temperature. The MJI technology consists in a series of nozzles impinging the liquid coolant on the backside of the field stop hot wall. The high cooling capabilities of MJI relies on the high Reynolds numbers achievable, even with modest velocity flow. In this work we describe our efforts to design, fabricate and test the prototype of an HR to characterize the MJI technology. More in detail, we show the results of the hydraulic and thermal tests carried out in the opto-electronics laboratory of the Physics Department of the University of Rome Tor Vergata.

During the last few years we have been working on a modernization plan for the Telescopio Nazionale Galileo (TNG) Control System^1,2. On October 2019 we had the opportunity to execute the first step of this process. The telescope was going to be stopped for one month due to M1 mirror being aluminized, so we could change the azimuth control system, that had been thoroughly tested during the summer, with no additional observational time loss. In this paper we present the new control system based on the CompactRIO platform from National Instruments, the switching process between the old and the new control systems, and a performance comparison between them.

The servo control algorithms of the TNG, developed in the nineties, have been working for more than 20 years with no major updates. The original hardware was based on a VME-bus based platform running a real time operating system, a rather popular choice for similar applications at the time. Recently, the obsolescence of the hardware and the lack of spares pushed the observatory towards a complete replacement of the electronics that is now being implemented in steps, respecting the basic requirement of never stopping the observatory night operations. Within the framework of this major hardware work, we are taking the opportunity to review and update the existing control schemes. This servo control update, crucial for the telescope performance, envisages a new study from scratch of the controlled plant, including a re-identification of the main axes transfer functions and a re-design of the control filters in the two nested position and speed loops. The ongoing work is described, including preliminary results in the case study of the azimuth axis and our plans for possible further improvements.

The axes servo control of optical telescopes and antennas acts in two typical phases: the slew to a new target and the subsequent accurate tracking of the source. Although the tracking error minimization is paramount, a good design of the slewing phase is needed as well. In fact, saturations of velocity and acceleration can easily occur during telescope slew, introducing non-linearities in the control system which may lead to undesired behaviors. Also, sudden accelerations may trigger vibrations of the telescope structure, which may increase the slew time or even prevent a stable target acquisition. In this paper, a command pre-processor is adopted to provide recursively a valid path to reach the assigned target, never exceeding the specified rate and acceleration limits. Different generation methods are considered, with different degrees of smoothness and slewing time. Numerical simulations show their main features in different test cases, for both radio and optical telescopes.

More and more astronomical instruments have been installed in extreme environment such as Antarctica because of good seeing. However it’s not good for electromechanical system of astronomical telescope due to the harsh environment. This paper presents the study of the unanticipated states of direct drive system of extremely large telescope in extreme environment. The unanticipated states which are short of priori knowledge will degrade the reliability of monitor system significantly and put the self-diagnosis system into trouble.

Aiming at the lack of prior information and the characterization difficulties of unanticipated state detection in the drive systems of astronomical telescope, the paper proposes a Multi-layer General Process Model for the recognition of telescope drive system state. Firstly, based on the prior information of state recognition, this paper refines the classification of anticipated state and unanticipated state. Then, focusing on the comprehensive description of the state of the telescope drive system, a Multi-layer General Process Model for the recognition of unanticipated state is established. Finally, the model is evaluated by using an example of Antarctica Survey Telescope drive system and excellent results have been obtained. The study of unanticipated state is the deepening and upgrading of anticipated, and it is an extension of fault diagnosis technology.

The New Robotic Telescope is designed to conduct rapid target follow-up within 30 seconds of an ‘alert’ from survey facilities. To achieve this will require a quick settling time requirement for the mount structure and the mirrors. This means the structure shall be designed to be sufficiently rigid to achieve the mirror position within the ‘settle time’ after a quick slew operation. An optimization analysis using the finite element model is developed to conceptually design the mount structure that meets the mechanical and more importantly the NRT science requirements. The main objective of this study is to determine the required locked rotor resonance frequency (LRF) that provides enough rigidity for the telescope dynamic performance while minimizing the structural mass and cost.

Twenty-five 12-meter diameter antennas were delivered by the National Radio Astronomy Observatory (NRAO) to the Atacama Large Millimeter Array (ALMA) Observatory. Astronomical holography (astroholography) surface measurements conducted from 2011 through 2014 established that on some antennas the reflector surface error surpassed the specified error limit of 25μm because of an excessive thermal dependence. This paper summarizes the testing and analysis efforts to identify the root-cause of the primary surface error thermal dependence and the resulting design efforts, which lead to the development of a prototype and a subsequent production wall system that satisfactorily minimizes the primary surface thermal difference.

CSTAR (Chinese Small Telescope Array) was installed in Dome A in 2008 and moved back to China in 2012. In order to fully use wide-field and multi-band features of CSTAR, the CSTAR telescope was updated with it is installed on an equatorial. The updated CSTAR telescope is named by CSTAR2 telescope. The servo system and solutions for harsh environment are presented in this paper to make sure the whole telescope work smoothly at Dome A. Meanwhile, the pointing and tracking results obtained during the commissioning test are described.

The Main Structure (MS) of the Extremely Large Telescope (ELT) is a 40 m class optical, near and mid-infrared telescope, under construction at Cerro Armazones, in the Chilean Andes. The MS is characterized by an Alt-Azimuth mounting weighting about 3700 t. It is divided in three major sub-systems: the Azimuth tracks, fixed to a concrete pier, which sustain the whole telescope weight; the Azimuth Structure, which allows the rotation around the vertical axis and sustain the Altitude Structure; the Altitude Structure, which allows the rotation around the horizontal axis. The MS consists in a steel space-frame structure, highly optimized to guarantee dynamical requirements and system level performances in general, not least pointing stability and tracking capabilities, reducing the rotating mass as much as possible. A fundamental design constraint has been the need for minimizing repeatable and non-repeatable deflections, particularly for the Altitude Structure, that hosts the segmented M1 mirror unit and all the main optics. Care has also been taken to guarantee survival conditions, particularly in the design of an effective seismic isolation system, capable to adequately limit Hosted Units (HU) accelerations and deformations. Finally, the major design challenge, in general, has been the need to design the system, having its overall dimensions and masses characteristics of large civil structures, like modern steel buildings and sports arenas, in order to be compatible with the strict requirements typical of extremely high precision machines and telescopes.

The Large Millimeter Telescope Alfonso Serrano (LMT) is a 50m-diameter radio telescope for millimeter-wave astronomy. In this paper we describe a number of initiatives underway to upgrade the antenna systems and permit scientific observations during daylight hours. We summarize recent efforts to characterize the thermal gradients that occur within the LMT structure and to identify important modes of surface deformation. The mitigation program involves use of the LMT's active surface to counteract the effects of measured thermal gradients within the antenna structure. It also includes active measures such as the installation of a ventilation system in the antenna backup structure. Prospects for additional active metrology measurements of the antenna surface for real-time surface corrections are also discussed.

The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a planned interferometric radio telescope array that will ultimately consist of 1024 close packed 6 m dishes that will be deployed at the SKA South Africa site. HIRAX will survey the majority of the southern sky to measure baryon acoustic oscillations (BAO) using the 21 cm hyperfine transition of neutral hydrogen. It will operate between 400-800 MHz with 391 kHz resolution, corresponding to a redshift range of 0:8 < z < 2:5 and a minimum Δz/z of ~0.003 (frequency resolution 500 < R < 1000). One of the primary science goals of HIRAX is to constrain the dark energy equation of state by measuring the BAO scale as a function of redshift over a cosmologically significant range. Achieving this goal places stringent requirements on the mechanical and optical design of the HIRAX instrument which are described in this paper. This includes the simulations used to optimize the mechanical and electromagnetic characteristics of the instrument, including the dish focal ratio, receiver support mechanism, and instrument cabling. As a result of these simulations, the dish focal ratio has been reduced to 0.23 to reduce inter-dish crosstalk, the feed support mechanism has been redesigned as a wide (35 cm diam.) central column, and the feed design has been modified to allow the cabling for the receiver to pass directly along the symmetry axis of the feed and dish in order to eliminate beam asymmetries and reduce sidelobe amplitudes. The beams from these full-instrument simulations are also used in an astrophysical m-mode analysis pipeline which is used to evaluate cosmological constraints and determine potential systematic contamination due to physical non-redundancies of the array elements. This end-to-end simulation pipeline was used to inform the dish manufacturing and assembly specifications which will guide the production and construction of the first-stage HIRAX 256-element array.

The windscreen of the Subaru Telescope, which had been installed to prevent strong wind from directly hitting the telescope, was damaged and dropped out during the night operation at around 12:40 am, April 10, 2017. After that all observations at Subaru Telescope have been forced to be done without the windscreen. Due to the lack of the windscreen, the telescope would vibrate with strong wind, and the shape of the primary mirror would be deformed, thus the star image would become worse. Here we have investigated the effect of the lack of the windscreen statistically. The seeing at zenith at 500 nm was calculated from the FWHM of the star image obtained from the HSC on-site analysis software, and compared with the DIMM seeing at the east ridge of Maunakea simultaneously. Although the median seeing value varied by ~0.100 each year, the median seeing of DIMM before and after the incident is almost the same value (0.6100 and 0.6400), while the median seeing of HSC after the incident is ~0.0700 larger than before (0.6800 to 0.7500). The wind speeds at the telescope top ring, telescope center section, and outside the dome roof were investigated from the telescope telemetry data, and the correlations with the seeing were also investigated. Although the wind speed outside the dome did not change significantly before and after the incident, it was found that the wind speed inside the dome increased after the incident. Although it is not clear whether the degradation of the HSC seeing can be attributed to the absence of the windscreen, the seeing values over the last three years have statistically become ~10% worse than before.

The Near Earth Object Survey TELescope (NEOSTEL, also known as “FlyEye”), is a survey telescope developed in the framework of the Space Situational Awareness (SSA) program of the European Space Agency. NEOSTEL is dedicated to the detection of Near-Earth Objects sized 40m, and it is designed to provide an early-warning signal with a maximum delay of three days from detection to the alert generation. A first unit of this innovative telescope will be installed in Italy, on top of the Monte Mufara, within the “Madonie” Natural Park, Sicily region. The detection capabilities and the quality of service required by NEOSTEL pose new challenges to the design and construction of the dome and the observatory. In particular, the combination of fast telescope slewing and equatorial mount configuration makes the requests to the enclosure rotation extremely demanding. The site orography imposes an optimization of the entire observatory, in order to minimize the environmental impact of the infrastructure, while providing at the same time all the infrastructural elements which are necessary to operate and maintain the telescope. In this paper we present the first results of the optimized layout of the infrastructure, a description of the facility and in particular we outline the main technical characteristics of the dome and of the maintenance equipment.

The telescope of the University of Tokyo Atacama Observatory has a primary mirror with a diameter in 6.5m. In order to fabricate the reflecting film initially on the mirror surface and to maintain its optical performance over a long period, a mirror{coating facility will be installed in operation building beside enclosure of the telescope at the summit of Co. Chajnantor (5,640m). The facility consists of mirror coating chamber, cleaning unit for stripping off the old film and clean-up the mirror, and a cart with a lifter for handling the primary mirror cell. Almost all equipment, including the main chamber, was completed by early 2020 and engaged as a mirror coating facility. In order to optimize the coating parameters, comprehensive performance tests were carried out (without primary mirror cell which plays a role of a part of chamber). The evaluation items are how long it takes to reach the target vacuum level and parameters of the current, voltage, and application time during ion bombardment and aluminization. Through iterating test, we were able to obtain each parameter that ultimately met the requirements of the TAO telescope mirror.

The SOAR telescope was designed to have a bare Aluminum coating. This coating is performed in the Gemini-South sputtering facility. Two coatings have been done on the SOAR mirror (2004 and 2009). On both occasions, the reflectivity obtained for the UV-blue were lower than the reflectivity of the nominal bare Aluminum. Various tests have been done during 2018 and 2019, in order to reach a higher reflectivity in the UV, including changes in the coating recipe. We report here the progress to date, the performance that we have reached and the problems we have faced in this 8-meter coating facility.

Since the University of Tokyo Atacama Observatory (TAO) is located in extremely high altitude (5,640 m.a.s.l.), safety management is one of the most important issues for the project. We have developed safety management program for work at the site in order to prevent medical illness for humans. In this program all staff have to take medical examinations such as Electrocardiogram and Hipobaria before their work starts. The results are reviewed by medical doctor. Only authorized staff can be permitted to work at the site. During stay in site, all staff need to always use oxygen supply because there is only half of the oxygen at the site. It is also important to understand physical workload at the site. Our safety staff reviews it and determines necessary resting time for each worker, e.g. great load works need to work 50 minutes and rest 10 minutes. In addition to low air pressure, very low temperature, extremely high UV radiation, and extremely dry atmosphere should be concerned. Our program requests all staff to use winter clothes, sunblock and UV protection sunglasses and a lot of potable water consumption. Keep communication is also very important to secure the safety. Normal telephone communication is not available as well as internet connectivity. We have established satellite communication as well as UHF internal communication for general works and safety coordination with other observatories in Atacama area.

The novel 9.7m Schwarzschild-Couder Telescope (SCT), utilizing aspheric dual-mirror optical system, has been constructed as a prototype medium size x-ray telescope for the Cherenkov Telescope Array (CTA) observatory. The prototype SCT (pSCT) is designed to achieve simultaneously the wide (≥ 8°) field of view and the superior imaging resolution (0.067 per pixel) to significantly improve scientific capabilities of the observatory in conducting the sky surveys, the follow-up observations of multi-messenger transients with poorly known initial localization and the morphology studies of x-ray sources with angular extent. In this submission, we describe the hardware and software implementations of the telescope optical system as well as the methods specifically developed to align its complex optical system, in which both primary and secondary mirrors are segmented. The pSCT has detected Crab Nebula in June 2020 during ongoing commissioning, which was delayed due to worldwide pandemic and is not yet completed. Verification of pSCT performance is continuing and further improvement of optical alignment is anticipated.

During the LAMOST observation, to accurately align a large number of fibers with the target star positions, we used a closed-loop feedback system based on visual measurement in fiber positioner operation mode. The fiber was illuminated at the end of the spectrometer and the fiber light spots on the other end of the focal plane could be captured by the metrology system for positioning. The system can have a larger field of view and a single measurement can cover thousands of fibers. The metrology accuracy which is based on camera accurate calibration, is critical in the fiber positioning system. In general, calibration of a standard camera requires a reference surface with a known precise position marker and covering the camera's field of view. Theoretically, it is necessary to design a standard target surface that covers the camera's field of view to calibrate the camera's error. However, it is not realistic to manufacture and install a large standard target that meets the accuracy requirement. To ensure that the camera calibration error is within the limited range, and the fiber positioner can obtain higher positioning accuracy, we use the focal plane unit hole to insert a dedicated reference unit to serve as its calibration reference. In this paper, a reference fiber unit structure was designed according to the requirements of closedloop positioning. Through the test experiment on the reference fibers, it was finally verified that the reference fiber unit meets the accuracy requirements of closed-loop control.

To carry out astronomical observations in the molecule rich 3 mm window the Green Bank Telescope (GBT) compensates for gravitational and weather induced deformations of its primary reflector. Terrestrial laser scanners (TLSs) offer a fast and reliable means of measuring these deformations, but their use has been limited to measuring gravitational deformations thus far due to the large systematics inherent to their construction. The laser antenna surface scanning instrument (LASSI) on the GBT uses a TLS to measure weather induced deformations. The LASSI removes the TLS systematics by taking the difference between scans. We use the active surface (AS) on the GBT to validate this strategy and find that the LASSI can accurately measure deformations corresponding to different Zernike polynomials with amplitudes between 60 μm and 550 μm. We estimate that the wavefront error introduced by the LASSI to the surface is 100 ± 30 μm, root-mean-squared (rms), which would result in a total surface error of 250 μm rms. This suggests that using the LASSI to measure, and the AS to correct, for weather induced deformations is a viable method to efficiently carry-out day time 3 mm observations with the GBT.

We describe a system being developed for measuring the shapes of the mirrors of the Fred Young Submillimeter Telescope (FYST), now under construction for the CCAT Observatory. “Holographic” antenna-measuring techniques are an efficient and accurate way of measuring the surfaces of large millimeter-wave telescopes and they have the advantage of measuring the wave-front errors of the whole system under operational conditions, e.g. at night on an exposed site. Applying this to FYST, however, presents significant challenges because of the high accuracy needed, the fact that the telescope consists of two large off-axis mirrors, and a requirement that measurements can be made without personnel present. We use a high-frequency (~300GHz) source which is relatively close to the telescope aperture (<1/100th of the Fresnel distance) to minimize atmospheric effects. The main receiver is in the receiver cabin and can be moved under remote control to different positions, so that the wave-front errors in different parts of the focal plane can be measured. A second receiver placed on the yoke provides a phase reference. The signals are combined in a digital cross-correlation spectrometer. Scanning the telescope provides a map of the complex beam pattern. The surface errors are found by inference, i.e. we make models of the reflectors with errors and calculate the patterns expected, and then iterate to find the best match to the data. To do this we have developed a fast and accurate method for calculating the patterns using the Kirchhoff-Fresnel formulation. This paper presents details of the design and outlines the results from simulations of the measurement and inference process. These indicate that a measurement accuracy of ~3μm rms is achievable.

The Cherenkov Telescope Array (CTA) is the next generation of ground-based gamma-ray observatory. The observatory will consist of two arrays, one located in the southern hemisphere (Paranal, Chile) and the other in the northern hemisphere (Canary Island, Spain), covering the whole sky in the range of observation. More than 100 telescopes are planned to be in operation for as long as 30 years, which motivated the development of a continuous condition monitoring of the individual telescopes. The main goal of the monitoring is to detect degradation and failures before critical damages occur. Two approaches are considered: the structure monitoring system, in which the Eigenfrequencies of the telescope and their damping rates are measured and monitored; and the drive monitoring, in which the power spectra of rotating components are measured during telescope movements. The structure monitoring concept system was applied to the prototype Medium Size telescope (MST) prototype of CTA in Berlin during late 2018 and in 2019, and the first results are presented here. The system showed reasonable stability during periods, in which the telescope structure was unchanged. The system was also capable to detect mechanical changes, e.g. varying tension in the steel ropes of the camera support structure. The successful implementation of the structure monitoring system supports the decision of implementing the system in all future MSTs.

LAMOST, as the astronomical telescope with the highest spectrum acquisition efficiency in the world, requires high positioning accuracy, the maximum allowable positioning error is only 40μm. Due to various aberrations, the general photogrammetry system cannot meet the requirements of detecting high-precision optical fiber positioning errors. In this study, we proposed a double telecentric measurement system to detect accurately the actual position of fiber positioner by taking advantage of ultra-low distortion and ultra-wide depth of field of telecentric lens. In this paper, the main sources of telecentric lens distortion were analyzed, and the calibration method of polynomial calibration model and dot matrix calibration target was adopted, and the validity of the five parameters obtained by calibration is verified by experiments. The experimental results showed that all optical fibers reached the target after two steps of approximation, and the errors met the positioning requirements.

We present here the results of an OOF holography campaign recently performed at the SRT observing a high flux density radio source as the W3(OH) water maser by using the K-band 7 feeds Focal Plan Array receiver centered at 22.23 GHz. The resulting OOF maps (0.2 times 0.2 deg extent) of the SRT radiation pattern allowed to retrieve the gravitational large scale deformation on the aperture plane at 65 deg elevation.

The recently commissioned Dark Energy Spectroscopic Instrument (DESI) will measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope delivers light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We describe the use of a Faro Laser Tracker with custom hardware and software tools for alignment during integration of DESI’s focal plane. The focal plane is approximately one meter in diameter and consists primarily of ten radially symmetrical focal plane segments (“petals”) which were individually installed into the telescope. The nominal clearance between petals is 600 microns, and an alignment accuracy of 100 microns and 0.01 degrees was targeted. Alignment of the petals to their targeted locations on the telescope was accomplished by adjusting a purpose-built alignment structure with 14 degrees of freedom using feedback from the laser tracker, which measured the locations of retroreflectors attached to both the petal and the telescope and whose positions relative to key features were precisely known. These measurements were used to infer the locations of aligning features in both structures, which were in turn used to calculate the adjustments necessary to bring the system into alignment. Once alignment was achieved to within acceptable tolerances, each petal was installed while monitoring building movement due to wind and thermal variations.

How much light from the astronomical object actually reaches the focal plane of a telescope? To what extent the sensitivity can be extended to both ends of the visible wavelengths – ultraviolet (UV) and infrared (IR) – as much as possible from the ground? And how to maintain good throughput of the telescope optics? In this report, we make a simplified model to show effect in the reflectivity change of the telescope mirror from the recoating and cleaning versus degradation focusing on a segmented primary mirror of a telescope. The better understandings and monitoring of these competing factors will help fine tune the scheduling of the in-situ cleaning such as CO₂ cleaning. By maintaining the high throughput of the optics, it becomes more feasible to catch rare atmospheric condition whenever it becomes available for very sensitive UV or IR observations during Moon’s dark and bright phases, respectively. The degradation not recoverable by the cleaning is reset by replacing dirty segments with freshly coated ones. The importance of regular in-situ cleaning is evident when it takes long time to replace the large number of freshly coated segments. It is important to clean the entire aperture as much as possible when a wet condition is forecast; for once the contamination settles on the surface, CO₂ cleaning alone won’t be able to recover good surface characteristics of reflectivity, scattering, and emissivity.

Vibration measurements at the Gemini South observatory were conducted in February 2020, in order to experimentally determine acceleration transfer functions between the instrument support structure and key locations on the telescope, including the optics. An electrodynamic exciter was used to impart known dynamic forces into the telescope structure. Acceleration responses were measured at numerous locations on the telescope, including on M1 and M2, using the facility Vibration Monitoring System (VMS) accelerometers. This paper describes the equipment, the experimental approach, and will summarize initial results from these tests.

The Herzberg Astronomy and Astrophysics Research Centre has established a comprehensive and versatile vibration measurement capability. In recent years, HAA personnel have executed a number of diverse vibration measurement projects, including recent vibration transmission measurements at Gemini South. In this paper we describe the HAA’s vibration measurement capabilities, including the equipment and experimental approaches that have been used. We will provide some illustrative examples of recent applications and results, and highlight plans for further development of our capabilities.

The present work provides analysis of the ELT M4 control system interaction with the deformable mirror supporting structure. The aim is the verification of the system robustness in terms of both stability and performance. The results of the analysis suggested the opportunity to improve the system dynamic behavior through the addition of damping on the system supporting structure. The solution adopted has been the introduction of active damping using six proof mass actuators (PMAs) placed on the ELT M4 reference body (RB). The effectiveness of this solution, which is now part of the ELT M4 final design, is proved through numerical simulations. Moreover, the PMA design together with some experimental tests performed on a pre-series device will be presented.

Due to the high complexity of the system and the variety of influencing factors of large astronomical telescopes, the current control system could be improved largely. It’s difficult for traditional automatic control technologies to ensure reliable and highly efficient operation. The key problem is such a system which needs to consider not only the various internal factors but also the various external factors. In addition, some factors are difficult to be digitized. Thus, it’s hard to make mathematical models to represent such complex and dynamic systems. The first goal of this project is to construct a software experimental platform for the intelligentization. The second goal is to develop an intelligent reliability management system, and an optimization system for observation quality. These application systems will be running using the historical data of LAMOST operation. The evaluation of such systems will be based on the simulation of these data.

The Simons Observatory (SO) will be a cosmic microwave background (CMB) survey experiment with three small-aperture telescopes (SATs) and one large-aperture telescope, which will observe from the Atacama Desert in Chile. In total, SO will field over 60,000 bolometers in six spectral bands centered between 27 and 280 GHz. The SATs are designed to target the primordial B-mode polarization signal. The SATs adopt a three metamaterial anti-reflection coated Silicon lens refractor design each with a 42 cm aperture and 35 degree field-of-view. We discuss the optics design development and optimization process of the SAT refractor system and warm baffling.

The SKA LOW telescope is an interferometer composed of 512 stations. Each station consists of 256 electronically steered antennas. The Low Frequency Aperture Array is the portion of the SKA-LOW telescope including the antennas and the related electronics. The LFAA signal processing chain amplifies, transports and combines the signals from the antennas composing each station into a coherent beam. Beamforming is performed in the frequency domain, with stringent requirements on bandpass flatness, linearity in a RFI contaminated spectral region, and allowed signal degradation. We adopted an architecture including a highly optimized oversampled polyphase filterbank for channelization, and a distributed network beamformer. The system has been validated as part of the Aperture Array Verification System, a single station operating at the SKA site in Western Australia.

A novel version of digital hardware Italian Tile Processing Module (ITPM) 1.6 has been released for the Low-Frequency Aperture Array (LFAA) component of the Square Kilometre Array (SKA). This back-end includes two plugged-in main blocks, as an analog device , the Pre-ADU board, and an Analog to Digital Unit (ADU), a 6U board containing sixteen dual-inputs Analog to Digital Converters and two Field Programmable Gate Array (FPGA) devices, capable of digitizing and processing 32 RF input signals (50-650 MHz). We present the main features of the upgrade of the board compared to previous versions: there are new and high performance components improving processing capability, mechanical changes matching the design of the housing sub-rack and finally a general reduction of the overall power consumption. The ITPM ADU 1.6 version, now in engineering phase together with its sub-rack system, is currently the last prototype before the design of the industrial line for mass production, necessary for the LFAA deployment. Results of system performances will be presented.

The ALMA 2030 Development Roadmap defines the long-term scientific objectives and serves as a guide for the development activity for the upgrade of hardware, software, and analysis tools in order to enhance the future observing capabilities of ALMA. A working group was established to define a set of consistent system level technical goals in order to guide the ongoing and future ALMA technical development effort. The working group has prepared an updated set of technical goals for Front-end and Digitizer products to enable the scientific needs as stipulated in the ALMA 2030 Development Roadmap. This manuscript describes the working group’s considerations of system trade-offs and feasibility studies and presents tentative specifications arrived at for some of the key technical requirement goals.

The coudé lab is one of the central components of the Coudé Environmental Systems (CES) at the Daniel K. Inouye Solar Telescope (DKIST). The scientific instruments for DKIST are located on benches inside the coudé lab. The light path from the telescope to the coudé lab goes from ambient to conditioned space, therefore, in order to minimize local seeing or wave front distortion, the CES was designed. The CES is composed of the Air Knife and equipment that condition the coudé lab to the desired cleanliness, temperature, and humidity design parameters. The Air Knife uses an air curtain to divide the external ambient space from the conditioned coudé lab through a series of fan operated and filtered ducted assemblies. The coudé lab is conditioned using filtered air handling units, makeup air handling units, a HEPA filter plenum ceiling, floor dampers, and humidifiers. The installed CES equipment shall be tested and results shall be presented to determine whether the design parameters

Measurement campaigns of radio frequency interferences (RFIs) represent a fundamental aspect to optimize data collected by radio astronomical observations. In order to monitor the state of unwanted man-made signals, every radio telescope needs to have a radio frequency map in the frequencies range of its receivers. The Sardinia Aperture Array Demonstrator (SAD) is an Italian aperture array demonstrator composed of prototypical Vivaldi antennas designed to work at frequencies below 500 MHz. The antennas are located at the Sardinia Radio Telescope (SRT) site and they are arranged with a versatile approach that is able to provide different array configurations. In this paper, we present the results of measurement campaigns conducted with the SAD antennas at the SRT observing site with the aim to monitor the evolution of RFI scenario from 2016 to date. The signal acquisition chain and the software tool used for RFI detection are, also, presented.

The BLAST Observatory is a proposed super-pressure balloon-borne polarimeter designed for a future ultra- long duration balloon campaign from Wanaka, New Zealand. To maximize scientific output while staying within the stringent super-pressure weight envelope, BLAST will feature new 1.8m off-axis optical system contained within a lightweight monocoque structure gondola. The payload will incorporate a 300 L ⁴He cryogenic receiver which will cool 8,274 microwave kinetic inductance detectors (MKIDs) to 100mK through the use of an adiabatic demagnetization refrigerator (ADR) in combination with a ³He sorption refrigerator all backed by a liquid helium pumped pot operating at 2 K. The detector readout utilizes a new Xilinx RFSOC-based system which will run the next-generation of the BLAST-TNG KIDPy software. With this instrument we aim to answer outstanding questions about dust dynamics as well as provide community access to the polarized submillimeter sky made possible by high-altitude observing unrestricted by atmospheric transmission. The BLAST Observatory is designed for a minimum 31-day flight of which 70% will be dedicated to observations for BLAST scientific goals and the remaining 30% will be open to proposals from the wider astronomical community through a shared-risk proposals program.

Space debris are human-made objects, of variable sizes and shapes, that orbit the Earth or reenter the atmosphere. They represent a serious problem for every active spacecraft and satellite, due to the high risk of collision and consequently the generation of new debris. One of the main segments of the Space Situational Awareness program regards space surveillance and tracking activities, with procedures for tracking resident space objects, using a sensor network composed by radars, telescopes and lasers. In this way, it is possible to collect data in order to catalogue and perform orbit predictions of objects orbiting the Earth, with the aim of avoiding collisions between them. One of the Italian radars for space and surveillance tracking functions is represented by the BIRALET system, an acronym which stands for Bistatic Radar for LEO Tracking. This radar operates in P-band at 410-415 MHz, is a bi-static configuration composed of a transmitting 7-meter antenna and the SRT (Sardinia Radio Telescope) as receiver, with a baseline of about 20 km. The Sardinia Radio Telescope is a 64-meter fully steerable wheel-and-track antenna, located near San Basilio (Cagliari, Sardinia, Italy). It represents a flexible instrument used for radio astronomy and space science studies, developed to work in a wide frequency range between 300 MHz and 110 GHz. In this paper, we present a review of the status of the SRT for space debris observation. In particular, we describe three possible system configurations, in order to perform Doppler shift and range measurements. In particular, we present a simplified solution based on a spectrum analyzer as a back-end that permits only Doppler shift measurements. Another more complex solution for Doppler shift measurements, is based on the electronic Red Pitaya board. For the Red Pitaya we developed also a dedicated signal acquisition chain with a down-conversion circuit, in order to shift the received signal in the frequency range of the board. Finally, a more complex solution that allows range and range rate measurements, based on the National Instrument USRP board as a back-end. For future developments, we present the possibility to improve our system, using a C-band Phased Array Feed as a receiver.