Volume-phase holographic gratings (VPHGs) are widely used in astronomical spectrographs due to their adaptability and high diffraction efficiency. Most VPHGs in operation use dichromated gelatin as a recording material, the performance of which is sensitive to the coating and development process, especially in the near-ultraviolet (UV). In this letter, we present the characterization of two UV-blue VPHG prototypes for the BlueMUSE integral field spectrograph on the Very Large Telescope, based on dichromated gelatin and the Bayfol®HX photopolymer film as recording materials. Our measurements show that both prototypes meet the required diffraction efficiency and exhibit similar performance with a wavelength-average exceeding 70% in the 350 to 580 nm range. Deviations from theoretical models increase toward 350 nm, consistent with previous studies on similar gratings. We also report similar performances in terms of spatial uniformity and grating-to-grating consistency. Likewise, no significant differences in wavefront error or scattered light are observed between the prototypes.

The editorial introduces the JATIS Special Section on the SALTUS Probe-Class Mission Concept.

Single Aperture Large Telescope for Universe Studies (SALTUS) is a NASA Astrophysics Probe Explorer (APEX)-class mission concept employing a robust far-infrared pointed space observatory. SALTUS comprises a 14-m inflatable reflector that provides 16× the sensitivity and 4× the angular resolution of Herschel, with a sunshield that radiatively cools the primary to 45 K, along with cryogenic detectors that collectively span the 34 to 660 μm far-infrared spectral range at high and moderate spectral resolutions. The high sensitivity and high spectral resolving power of the SALTUS heterodyne receivers enable both submillimeter and far-infrared observations of trace compounds comprising water and its isotopologues, hydrogen deuteride (HD), and a plethora of molecular species containing carbon, hydrogen, nitrogen, oxygen, phosphorus, or sulfur (CHNOPS), all of which are obscured by the Earth’s atmosphere. The high sensitivity and broadband spectral coverage of the SALTUS far-infrared grating spectrometer enables far-infrared observations of the lattice vibrational spectral signatures of ices and mineral grains contained within a wide variety of solar system targets, including comets, planetary atmospheres, near Enceladus’ plumes, and on the surfaces of icy moons, Jupiter trojans, centaurs, and Kuiper Belt objects. A key objective of SALTUS is to measure HDO/H2O in both Jupiter family and Oort cloud comets. Additional observations will allow us to characterize the water torus around Saturn generated by its icy moon Enceladus, determine the source of stratospheric water in the giant planets, ascertain the time evolution of water on Venus, and search for H2O plumes on Europa, Ganymede, and Callisto. SALTUS will measure HD/H2 in all four giant planets to constrain models of their origin. SALTUS can also measure the abundance of CHNOPS-containing molecules and halides in the atmosphere of Venus and in the comae of comets. We review the extensive amount of solar system science achievable with SALTUS for both the Guaranteed Time Observation and the Guest Observer APEX mission observing programs.

We describe the space observatory architecture and mission design of the Single Aperture Large Telescope for Universe Studies (SALTUS) mission, a National Aeronautics and Space Administration (NASA) Astrophysics Probe Explorer concept. SALTUS will address key far-infrared science using a 14-m diameter <45 K primary reflector (M1) and will provide unprecedented levels of spectral sensitivity for planet, solar system, and galactic evolution studies and cosmic origins. Drawing from Northrop Grumman’s extensive NASA mission heritage, the observatory flight system is based on the LEOStar-3 spacecraft platform to carry the SALTUS Payload. The Payload is comprised of the inflation control system, sunshield module (SM), cold corrector module (CCM), warm instrument electronics module, and primary reflector module (PRM). The 14-m M1 is an off-axis inflatable membrane radiatively cooled by a two-layer sunshield (∼1000 m2 per layer). The CCM corrects for residual aberration from M1 and delivers a focused beam to two instruments—the High-Resolution Receiver (HiRX) and SAFARI-Lite. The CCM and PRM reside atop a truss-based composite deck that also provides a platform for the attitude control system. The SALTUS 5-year mission lifetime is driven by a two-consumable architecture: the propellant system and the inflation control system. The core interface module (CIM), a multi-faceted composite truss structure, provides a load path with high stiffness, mechanical attachment, and thermal separation between the Payload and spacecraft. The SM attaches outside the CIM with its aft end integrating directly to the bus. The spacecraft maintains an attitude off M1’s boresight with respect to the Sun line to facilitate the <45 K thermal environment. SALTUS will reside in a Sun–Earth halo L2 orbit with a maximum Earth slant range of 1.8 million km, thereby reducing orbit transfer delta-v. The instantaneous field of regard provides two continuous 20 deg viewing zones around the ecliptic poles, resulting in full sky coverage in 6 months.

We present an overview of the Milky Way (MW) and nearby galaxy science case for the Single Aperture Large Telescope for Universe Studies (SALTUS) far-infrared (IR) NASA probe-class mission concept. SALTUS offers enormous gains in spatial resolution and spectral sensitivity over previous far-IR missions due to its cold (<40 K) 14-m primary mirror. Key MW and nearby galaxy science goals for SALTUS focus on understanding the role of star formation in feedback in the local universe. In addition to this science case, SALTUS would open a new window to galactic and extragalactic communities in the 2030s, enabling fundamentally new questions to be answered, and would be a far-IR analog to the near- and mid-IR capabilities of the James Webb Space Telescope. We summarize the MW and nearby galaxy science case and plans for notional observing programs in both guaranteed and guest (open) times.

We present an overview of the high-redshift extragalactic science case for the Single Aperture Large Telescope for Universe Studies (SALTUS) far-infrared (IR) National Aeronautics and Space Administration probe-class mission concept. Enabled by its 14-m primary reflector, SALTUS offers enormous gains in spatial resolution and spectral sensitivity over previous far-IR missions. SALTUS would be a versatile observatory capable of responding to the scientific needs of the extragalactic community in the 2030s and a natural follow-on to the near- and mid-IR capabilities of JWST. The key early-universe science goals for SALTUS focus on understanding the role of galactic feedback processes in regulating galaxy growth across cosmic time and charting the rise of metals and dust from the early universe to the present. We summarize these science cases and the performance metrics most relevant for high-redshift observations.

The Single Aperture Large Telescope for Universe Studies (SALTUS) is a mission concept for a far-infrared observatory developed under the recent Astrophysics Probe Explorer opportunity from the National Aeronautics and Space Administration. The enabling element of the program is a 14-m diameter inflatable primary mirror, M1. Due to its importance to SALTUS and potentially other space observatories, we focus entirely on M1. We present a historical overview of inflatable systems, illustrating that M1 is the logical next step in the evolution of such systems. The process of design and manufacture is addressed. We examine how M1 performs in its environment in terms of the operating temperature, interaction with the solar wind, and shape change due to non-penetrating particles. We investigate the longevity of the inflatant in detail, show that it meets mission lifetime requirements with ample margin, and discuss the development and testing to realize the flight M1.

The Single Aperture Large Telescope for Universe Studies (SALTUS) is a far-infrared space mission concept with unprecedented spatial and spectral resolution. SALTUS consists of a 14-m inflatable primary, providing 16× the sensitivity and 4× the angular resolution of Herschel, and two cryogenic detectors spanning a wavelength range of 34 to 660 μm and spectral resolving power of 300−107. Spectroscopic observations in the far-infrared offer many unique windows into the processes of star and planet formation. These include observations of low-energy water transitions, the H2 mass tracer HD, many CHONS constraining molecules such as NH3 and H2S, and emission lines from the phonon modes of molecular ices. Observing these species will allow us to build a statistical sample of protoplanetary disk masses, characterize the water snowline, identify Kuiper Belt-like debris rings around other stars, and trace the evolution of CHONS from prestellar cores, through to protoplanetary disks and debris disks. We detail several key star and planet formation science goals achievable with SALTUS.

The High-Resolution Receiver (HiRX) is one of two instruments of the Single Aperture Large Telescope for Universe Studies (SALTUS), a mission proposed to NASA’s 2023 Astrophysics Probe Explorer. SALTUS employs a 14 m aperture, leading to a 16-fold increase in collecting area and a factor of 4 increase in the angular resolution with respect to the Herschel Space Telescope. It will be radiatively cooled to ≤45 K and has a planned duration of >5 years. HiRX consists of four bands of cryogenic heterodyne receivers with a high sensitivity and high spectral resolution, being able to observe the gaseous components of objects across the far-IR. HiRX is going to detect water, HD, and other relevant astrophysical lines while resolving them in velocity. HiRX covers the following frequency ranges: Band 1 from 455 to 575 GHz, Band 2 from 1.1 to 2.1 THz, Band 3 from 2.475 to 2.875 THz, and Band 4 for both 4.744 and 5.35 THz. Bands 1 to 3 contain single, high-performance mixers. Band 4 consists of an array of seven hexagonally packed pixels, where the central pixel operates as a heterodyne mixer. Band 1 utilizes superconducting-insulator-superconducting mixers (SIS), whereas Bands 2 to 4 use superconducting hot electron bolometers (HEB) mixers. The local oscillator (LO) system uses frequency-multiplier chains for Bands 1 and 2, and quantum cascade lasers for Bands 3 and 4. Autocorrelator spectrometers are used to process the intermediate frequency (IF) signals from each science band, providing instantaneous frequency coverage of 4 to 8 GHz for Band 1 and 0.5 to 4 GHz for Bands 2 to 4. SALTUS will also fly a chirp transform spectrometer system for high spectral resolution observations in Band 1.

The Single Aperture Large Telescope for Universe Studies (SALTUS) is a deployable space telescope designed to provide the astrophysics community with an extremely large far-infrared (far-IR) space observatory to explore our cosmic origins. The SALTUS observatory can observe thousands of faint astrophysical targets, including the first galaxies, protoplanetary disks in various evolutionary states, and a wide variety of solar system objects. The SALTUS design architecture utilizes radiatively cooled, 14-m diameter unobscured aperture, and cryogenic instruments to enable both high spectral and spatial resolution at unprecedented sensitivity over a wavelength range largely unavailable to any existing ground or space observatories. The unique SALTUS optical design, utilizing a large inflatable off-axis primary mirror, provides superb sensitivity, angular resolution, and imaging performance at far-IR wavelengths over a wide ±0.02 deg×0.02 deg field of view. SALTUS’ design, with its highly compact form factor, allows it to be readily stowed in available launch fairings and subsequently deployed in orbit.

The Single Aperture Large Telescope for Universe Studies (SALTUS) probe mission will provide a powerful far-infrared (far-IR) pointed space observatory to explore our cosmic origins and the possibility of life elsewhere. The observatory employs an innovative deployable 14-m aperture, with a sunshield that will radiatively cool the off-axis primary to <45 K. This cooled primary reflector works in tandem with cryogenic coherent and incoherent instruments that span 34- to 660-μm far-IR range at both high and moderate spectral resolutions. The mission architecture, using proven Northrop Grumman designs, provides visibility to the entire sky every 6 months with ∼35% of the sky observable at any one time. SALTUS’s spectral range is unavailable to any existing ground or current space observatory. SALTUS will have 16× the collecting area and 4× the angular resolution of Herschel and is designed for a lifetime of ≥5 years. The SALTUS science team has proposed a Guaranteed Time Observations program to demonstrate the observatory’s capabilities and, at the same time, address high-priority questions from the Decadal survey that align with NASA’s Astrophysics Roadmap. With a large aperture enabling high spatial resolution and sensitive instruments, SALTUS will offer >80% of its available observing time to Guest Observer programs, providing the science community with powerful capabilities to study the local and distant universe with observations of 1000s of diverse targets such as distant and nearby galaxies, star-forming regions, protoplanetary disks, and solar system objects.

Guest Editors Ettore Del Monte and Todd Veach introduce the Special Section on the STROBE-X Probe-Class Mission Concept.

We present the NSX front-end application-specific integrated circuits (ASIC), which has been developed to read charge signals from the High Energy Modular Array and Wide Field Monitor X-ray detectors for the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays mission. The ASIC reads out signals from up to 64 anodes of linear silicon drift detectors (SDDs). When unloaded, the ASIC channel has a charge resolution, expressed in equivalent noise charge (ENC) of ∼2.8 e−. Once connected to the SDD anode, we anticipate, for the 80-keV energy range, an ENC of ∼10.7 e− at a leakage current of 2 pA, which corresponds to a full width half maximum of ∼145 eV at 6 keV once the Fano-limited statistics from charge generation in Si is included. The acquisition is event-triggered, and for events exceeding the threshold, the ASIC measures the peak amplitude and stores it in an analog memory for subsequent readout. The ASIC can also force the measurement of the sub-threshold channels neighboring the triggered channel, including the ones that belong to neighbor chips using bi-directional differential inter-chip communication. Alternatively, the ASIC can measure the amplitudes of all channels at the time of the first detected peak. Additional features include a high-resolution option, a channel power down and skip function, a low-noise pulse generator, a temperature sensor, and the monitoring of the channel analog output and trimmed threshold. The power consumption of the individual channel is ∼590 μW, and when including all shared circuits, it averages to ∼670 μW/channel.

The high-energy modular array (HEMA) is one of three instruments that compose the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X) mission concept. The HEMA is a large-area, high-throughput non-imaging pointed instrument based on the large area detector (LAD) developed as part of the Large Observatory For X-ray Timing (LOFT) mission concept. It is designed for spectral timing measurements of a broad range of sources and provides a transformative increase in sensitivity to X-rays in the energy range of 2 to 30 keV compared with previous instruments, with an effective area of 3.4 m2 at 8.5 keV and an energy resolution of better than 300 at 6 keV in its nominal field of regard.

We give an overview of the science objectives and mission design of the “Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays” observatory, which has been proposed as a NASA probe-class (∼$1.5B) mission in response to the Astro2020 recommendation for an X-ray probe.

The wide-field monitor (WFM) is one of the three instruments on the “Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays” (STROBE-X) mission, which was proposed in response to the National Aeronautics and Space Administration’s 2023 call for a probe-class mission. The WFM is a coded-mask camera system that would be the most scientifically capable wide-angle monitor ever flown. The WFM will anchor X-ray time domain astronomy, at the all-sky level, for the 2030s. The field of view covers one-third of the sky, to 50% mask coding, and the energy sensitivity is 2 to 50 keV. The WFM will identify new X-ray transients for rapid observations with the two pointed instruments of STROBE-X. In addition, the WFM will capture spectral/timing changes in known sources with data of unprecedented quality. WFM data will uniquely advance scientific knowledge for diverse classes in high-energy astrophysics, including X-ray bursts that coincide with gravitational wave detections, gamma-ray bursts (GRBs) and their transition from prompt emission to afterglow, subluminous GRBs that may signal shock breakout in supernovae, state transitions in accreting compact objects and their jets, bright flares in fast X-ray transients, accretion onset in transitional pulsars, and coronal flares from many types of active stars.

The low-energy modular array (LEMA) is one of three instruments that compose the STROBE-X mission concept. The LEMA is a large-effective-area, high-throughput, non-imaging pointed instrument derived from the X-ray timing instrument of the Neutron Star Interior Composition Explorer (NICER) mission. The LEMA is designed for spectral-timing measurements of a variety of celestial X-ray sources, providing a transformative increase in sensitivity to photons in the 0.2 to 12 keV energy range compared with past missions, with an effective area (at 1.5 keV) of 16,000 cm2 and an energy resolution of 85 eV at 1 keV.

Many modern radio telescopes employ an observational strategy that involves maximizing the use of their available spaces (cabins), outfitting them with various receivers at different frequencies to detect incoming signals from the sky simultaneously or individually. The Large Latin American Millimeter Array is a joint venture between Argentina and Brazil consisting of the installation and operation of a 12-m aperture Cassegrain telescope. It features three available cabins for instrumentation and plans to install six single-pixel heterodyne receivers, covering different bandwidths in the 30 to 950 GHz window of the electromagnetic spectrum, in its two lateral Nasmyth cabins at different phases of the project. Therefore, it is crucial not only to design a tertiary optical system that couples the antenna beam to those receivers but also to do it in a scalable way. The primary goal for the design is to simultaneously maximize the antenna efficiency while minimizing optical aberrations for all receivers, both fundamental aspects for the optimal functioning of cutting-edge astronomical instruments. We present the entire design process, starting from the quasi-optical approach based on the propagation of a fundamental Gaussian beam mode, continuing with the validation of the design based on physical optics simulations, and ending with a tolerance analysis of the system. As a result of this process, a frequency-independent tertiary optical system has been achieved for almost all the receivers, which is expected to provide high optical performance for the radio telescope.

The dynamical behavior of opto-mechanical systems is crucial for ensuring the performance in noisy environments. In particular, vibration mitigation is one of the design drivers for pointing and wavefront error requirements. During the initial development stages, the typical design process is based on nominal material properties, geometries, and interface behaviors, resulting in a unique set of frequency response functions. However, this approach lacks robustness and often necessitates extensive redesigns following initial testing or the use of significant margin factors. Conversely, incorporating deviations from the baseline in a statistical manner is computationally heavy and often constrained by confidentiality issues. We give an overview of the most common techniques that can be used in large projects to account for the uncertainty in material properties. We also present a computationally light method aimed at deriving a robust family of system responses via a simple relationship between uncertainties in material properties and system responses. The proposed method is also applicable to models in a modal space representation. We compare a few parametric methodologies that account for material property uncertainties in a rigorous way, showcasing their use with real opto-mechanical systems for both ground and space telescopes. We show that the simplified method yields results comparable to more complex algorithms, offering a practical solution for early-stage design considerations.

Meteors carry important and indispensable information about the interplanetary environment, which can be used to understand the origin and evolution of our solar system. We have developed a multi-station meteor monitoring (M3) system that can observe almost the entire sky and detect meteors automatically, and it determines their trajectories. They are highly extensible to construct a large-scale network. Each station consists of a waterproof casing, a wide field-of-view lens with a complementary metal oxide semiconductor camera, and a supporting computer. The camera has a built-in GPS module for accurately timing the meteoroid’s entry into the atmosphere (accurate to 1 μs), which is the most prominent characteristic compared with other existing meteor monitoring devices. We have also developed a software package that can efficiently identify and measure meteors appearing in the real-time video stream and compute the orbits of meteoroids in the solar system via multi-station observations. During the Geminid meteor shower in 2021, the M3 system was tested at two stations (∼55 km apart) in the suburbs of Beijing. The test results show that the astrometric accuracy is ∼0.3 to 0.4 arcmin. About 800 meteors were detected by these two stations. A total of 473 meteors have their orbits calculated by our software, and 377 of them belong to the Geminid meteoroid stream. Our M3 system will be further tested and upgraded, and it will be used to construct a large monitoring network in China in the future.

We introduce a new model named the regional spherical harmonic model aimed at enhancing the pointing accuracy of alt-azimuth telescopes. Considering that the pointing accuracy of telescopes is influenced by a combination of mechanical and environmental errors, a mathematical model combining spherical harmonics and Fourier series is proposed to address the issue of data discontinuities observed during the observation process. In addition, a regional modeling approach was incorporated to further refine the accuracy. The model was validated using multi-day actual observation data from the Changchun 1-m diameter Cassegrain telescope with an alt-azimuth mounting (Changchun 1-m Telescope). Compared with classical pointing models, the proposed method significantly improves the pointing accuracy after calibration. The azimuth pointing accuracy reached 1.899 arcseconds, and the elevation pointing accuracy reached 0.913 arcseconds.

The Wide Area Linear Optical Polarimeter North is an optical polarimeter designed for the needs of the Polar-Areas Stellar Imaging in Polarimetry High-Accuracy Experiment survey. It will be installed on the 1.3-m telescope at the Skinakas Observatory in Crete, Greece. After commissioning, it will measure the 30×30 arcmin2 polarization of millions of stars at high galactic latitude, aiming to measure hundreds of stars per square degree. The astronomical filter used in the instrument is a modified, polarimetrically neutral broadband Sloan Digital Sky Survey-r. This instrument will be a pioneering one due to its large field of view (FoV) of and high-accuracy polarimetry measurements. The accuracy and sensitivity of the instrument in polarization fraction will be at the 0.1% and 0.05% levels, respectively. Four separate 4k×4k charge-coupled devices will be used as the instrument detectors, each imaging one of the 0-, 45-, 90-, and 135-deg polarized FoV separately, therefore making the instrument a four-channel, one-shot polarimeter. Here, we present the overall optical design of the instrument, emphasizing the aspects of the instrument that are different from Wide Area Linear Optical Polarimeter South. We also present a customized design of filters appropriate for polarimetry along with details on the management of the instrument size and its polarimetric calibration.

The Taiji program aims to achieve space gravitational wave interferometry measurement through quasi-equilateral triangle satellite groups and explore major phenomena in the universe. We detail the design and wavefront test of the space gravitational wave detection telescope, which is one of the core payloads of the Taiji program. It features an all-glass-ceramics structure aiming for an optical path stability of ≤1 pm/Hz1/2. The telescope, with a 400-mm aperture and an off-axis reflective optical system, comprises two large glass-ceramics components, easing assembly and connectivity challenges. The weight of the telescope is 19 kg, which meets the ≤20 kg system requirement. Ground wavefront test methods were optimized using a “hanging-ear” support approach. Under 1 g gravity, the wavefront error of the system is 0.018λ [root mean square (RMS), λ=1064 nm], and considering processing, assembly, and in-orbit temperature conditions, the space environment system wavefront distortion RMS is ∼0.045λ (λ/22), meeting the RMS ≤λ/20 requirement. This design and testing method lay the groundwork for subsequent assembly and in-orbit application of the telescope, providing key technical support for the implementation of the Taiji program.

Silver-based telescope mirrors excel in the visible infrared but require protective coatings to overcome low durability. A single-layer of aluminum oxide (AlOx) deposited through atomic layer deposition (ALD) using trimethylaluminum and water (H2O) at low temperatures (∼60°C) protects the silver without adversely impacting the optical performance of the mirrors, but in environmental tests under high humidity at high temperatures, they degrade quickly. This paper compares the performance of AlOx-protected silver-based mirrors using two oxygen precursors: H2O and pure ozone (PO). Initially comparable, the reflectance of the PO-prepared samples shows a 17% improvement over those prepared with H2O after environmental testing.

MezzoCielo telescope aims to be a revolutionary optical instrument, designed to exhibit a field of view of around 104 square degrees. As such, it will be able to carry out whole-sky patrolling, which could be exploited, for instance, to track space debris or localize transient phenomena. From an optical stand-point, the telescope is a monocentric lens, composed by an outer glass shell enclosing an inner cavity filled with optical fluid (having proper refractive index for light convergence). From a mechanical point of view, instead, given the limitations related to manufacture large glass elements having high performance, the adoption of a segmented structure, presenting, for example, a platonic solid-like shape, is required. In this paper, the main aspects concerning the sizing of such frame (chosen to be a dodecahedral one) and the thermo-mechanical analysis of the lenses support system assembly, both analytical and numerical, will be presented. In particular, it will be shown how the lenses will be able to operate with little temperature difference across their volume independently from the surrounding conditions and the way in which the telescope can withstand external low temperatures without manifesting high thermal stresses, while maintaining, at the same time, constant focal length. Subsequently, a birefringence investigation, carried out to select the more appropriate lens shape, will be described. From our analysis, pentagonal-shape lenses turn out to be the most suitable ones for the MezzoCielo application.

The cadmium zinc TElluride Radiation Imager, or TERI, is an instrument to space-qualify large-volume 4×4×1.5 cm3 pixelated CdZnTe (CZT) detector technology. The CZT’s anode is composed of a 22×22 array of pixels, whereas the cathode is planar. TERI contains four of those crystals with each pixel having an energy range of 40 keV up to 3 MeV with a resolution of 1.3% full-width-at-half maximum at 662 keV all while operating in room temperature. As the detectors are 3D position sensitive, TERI can Compton image events. TERI is fitted with a coded-aperture mask, which permits imaging of low-energy photons in the photoelectric regime. TERI’s primary mission is to space-qualify large-volume CZT and measure its degradation due to radiation damage in a space environment. Its secondary mission includes detecting and localizing astrophysical gamma-ray transients. TERI is manifested in the Department of Defense’s STP-H10 mission for launch to the International Space Station in early 2025.

Space telescopes play a key role in the exploration of our universe, from imaging planets to gathering spectra of distant stars. To date, all space telescopes are manufactured on Earth and launched into orbit, with their size constrained by the diameter of the launcher’s payload fairing. This approach sets a hard limit on the telescope light collection ability, which determines its resolution and contrast. The Fluidic Telescope (FLUTE) project proposes to overcome launch constraints through the in-space creation of large liquid mirrors by utilizing interfacial physics under microgravity conditions. We present the design of experiments for the creation and measurement of spherical liquid mirrors under microgravity and their successful execution in parabolic flights. We describe the design of the mechanical apparatus and experimental methods used to pin, constrain, and control liquid gallium alloy and ionic liquid, as well as the optical technique used to reconstruct their surfaces in situ using Shack–Hartmann wavefront sensing. The results validate our experimental approach and show that the surfaces obtained under microgravity are indeed spherical, as expected from theory, though parabolic flight conditions prohibit optical-grade liquid surfaces. This set of experiments is a key milestone in maturing the FLUTE approach toward future extremely large liquid space telescopes.

With the aim of improving the star tracking performance of ground-based telescopes, we deal with the design of model predictive control architecture so as to properly lead their axes while mitigating possible external disturbances affecting the control task. The proposed architecture is composed of two layers, namely, (i) a trajectory generator that determines, based on the astronomic computation, the telescope position and speed references to be tracked while ensuring that all the telescope physical constraints, in terms of speed and acceleration, are never violated; (ii) an model predictive control (MPC) controller that guarantees the optimal tracking of the desired reference behavior by providing the torque inputs for telescope axes for the achievement of star observation task. The control architecture is tailored for the tracking control problem of Telescopio Nazionale Galileo (TNG), located at La Palma (Spain). To this end, by leveraging real data measurements in specific operative scenarios, a 12-order linear system describing the TNG dynamics is identified, via the non-iterative subspace method, for the design of the second layer. Validation results confirm the goodness of the dynamical model in predicting the TNG behavior within the operative range of (80 and 90 deg) altitude position. The effectiveness of the proposed MPC-based control architecture is proven via an ad-hoc virtual testing simulation platform implemented in MATLAB and Simulink and tailored for the identified TNG model. Virtual testing results, involving the real scientific target TYC 1731-916-1, confirm the capability of the proposed solution in ensuring optimal star tracking while mitigating the wind external disturbances forces. Finally, a comparison analysis w.r.t. the state-of-the-art control approaches, i.e., Linear-Quadratic-Gaussian and Proportional-Integrator-Derivative controller, and a robustness analysis w.r.t. the model mismatch between the MPC prediction model and the simulated TNG dynamics are provided to disclose the improved tracking performance achievable via the proposed MPC-based control architecture.

Spider is a balloon-borne instrument designed to map the cosmic microwave background at degree-angular scales in the presence of Galactic foregrounds. Spider has mapped a large sky area in the Southern Hemisphere using more than 2000 transition-edge sensors (TESs) during two NASA Long Duration Balloon flights above the Antarctic continent. During its first flight in January 2015, Spider was observed in the 95- and 150-GHz frequency bands, setting constraints on the B-mode signature of primordial gravitational waves. Its second flight in the 2022–2023 season added new receivers at 280 GHz, each using an array of TESs coupled to the sky through feedhorns formed from stacks of silicon wafers. These receivers are optimized to produce deep maps of polarized Galactic dust emission over a large sky area, providing a unique data set with lasting value to the field. We describe the instrument’s performance during Spider’s second flight, focusing on the performance of the 280-GHz receivers. We include details on the flight, in-band optical loading at float, and an early analysis of detector noise.

Astronomy and Space Domain Awareness are limited by the size of available telescope optics, the cost for which scales steeply due to the exquisitely ground and polished primary mirrors, typically made of glass or other lightweight substrates. Liquid mirrors (LMs) may break this unfavorable cost scaling. When rotated at a constant angular velocity, it has been shown that fluid surfaces take the form of a paraboloid, which can function as a primary mirror. However, current LMs cannot slew or tilt off-zenith due to gravity, greatly limiting the viewing area in the sky. To overcome these limitations while also enabling low-cost, very-large-aperture telescopes, the Defense Advanced Research Projects Agency launched the Zenith program. Zenith is developing entirely new LM design-for-build approaches that can create large optical surfaces without rotation and maintain the optical quality during tilt and slew by correcting transient liquid surface aberrations in real time. The development of these new designs is being supported by multi-physics models, materials, surface and field controls, and structures. We discuss key and fundamental aspects of four new design and modeling approaches for this new class of LMs, and the software and simulation tools developed by the Zenith program to design tiltable and size-scalable liquid mirrors.

We investigate the potential of photonic lantern (PL) fiber-fed spectrometers for two-dimensional spectroastrometry. Spectroastrometry, a technique for studying small angular scales by measuring centroid shifts as a function of wavelength, is typically conducted using long-slit spectrographs. However, slit-based spectroastrometry requires observations with multiple position angles to measure two-dimensional spectroastrometric signals. In a typical configuration of PL-fed spectrometers, light from the focal plane is coupled into the few-moded PL, which is then split into several single-mode outputs, with the relative intensities containing astrometric information. The single-moded beams can be fed into a high-resolution spectrometer to measure wavelength-dependent centroid shifts. We perform numerical simulations of a standard six-port PL and demonstrate its capability of measuring spectroastrometric signals. The effects of photon noise, wavefront errors, and chromaticity are investigated. When the PL is designed to have large linear responses to tip tilts at the wavelengths of interest, the centroid shifts can be efficiently measured. Furthermore, we provide mock observations of detecting accreting protoplanets. PL spectroastrometry is potentially a simple and efficient technique for detecting spectroastrometric signals.

We have been developing an X-ray imaging system, multi-image X-ray interferometer module (MIXIM), to achieve a high angular resolution with a compact system size. MIXIM is comprised of a mask with equally spaced apertures and an X-ray detector. The aperture size and the mask-detector distance determine the system’s angular resolution. Although a smaller aperture gives a better resolution, the degree of improvement is limited by a diffraction effect. MIXIM circumvents this problem by utilizing the Talbot effect. Our experiment with the previous model equipped with a multi-pinhole mask obtained an angular resolution of 0.5″ with a mask-detector distance of 92 cm. A major downside of the multi-pinhole mask is, however, that it has a very low opening fraction, which results in a very low effective area. Here, we newly adopt a multiple coded aperture (MCA) mask, an array of coded aperture patterns. Our proof-of-concept experiment demonstrates that the Talbot effect works even for the MCA mask with a high opening fraction of ∼50% at 12.4 keV. Consequently, the new MIXIM realizes ∼25 times as large an effective area as that of the previous model while maintaining a high angular resolution of 0.2″ and a compact size of ∼1.5 m.

The Mexico-UK Submillimeter Camera for AsTronomy (MUSCAT) is a continuum camera in the 1.1-mm band for the Large Millimeter Telescope (LMT), with 1458 lumped-element kinetic inductance detectors distributed across six arrays. Installed on the telescope at the end of 2021, we present the characterization of the detector beams of four of the six arrays based on the beam map observations of bright point sources developed during the first commissioning campaign between February and June 2022. With all the observations, we estimate the average positions of each detector with an average error in azimuth of less than 0.70 arcsec and less than 1.05 arcsec in elevation. From the positions, we created the coadded maps of all the detectors, from which we selected only eight observations to calculate the mean beam width of MUSCAT-LMT, of 6.32±0.36 arcsec⁡×5.78±0.19 arcsec. By stacking the maps, we identify the sidelobes with three main structures whose amplitudes are ∼3% with respect to the main beam.

Spectroastrometry, which measures wavelength-dependent shifts in the center of light, is well-suited for studying objects whose morphology changes with wavelength at very high angular resolutions. Photonic lantern (PL)-fed spectrometers have the potential to enable the measurement of spectroastrometric signals because the relative intensities between the PL output SMFs contain spatial information on the input scene. To use PL output spectra for spectroastrometric measurements, it is important to understand the wavelength-dependent behaviors of PL outputs and develop methods to calibrate the effects of time-varying wavefront errors in ground-based observations. We present experimental characterizations of the three-port PL on the SCExAO testbed at the Subaru Telescope. We develop spectral response models of the PL and verify the behaviors with lab experiments. We find the sinusoidal behavior of astrometric sensitivity of the three-port PL as a function of wavelength, as expected from numerical simulations. Furthermore, we compare experimental and numerically simulated coupling maps and discuss their potential use for offsetting pointing errors. We then present a method of building PL spectral response models (solving for the transfer matrices as a function of wavelength) using coupling maps, which can be used for further calibration strategies.

The Exoplanet Transmission Spectroscopy Imager (ETSI) amalgamates a low-resolution slitless prism spectrometer with custom multi-band filters to simultaneously image 15 spectral bandpasses between 430 and 975 nm with an average spectral resolution of R=λ/δλ∼20. ETSI requires only moderate telescope apertures (∼2 m), is capable of characterizing an exoplanet atmosphere in as little as a single transit, enabling the selection of the most interesting targets for further characterization with other ground and space-based observatories, and is also well suited to multi-band observations of other variable and transient objects. This enables a new technique, common-path multi-band imaging, used to observe transmission spectra of exoplanets transiting bright (V<14 magnitude) stars. ETSI is capable of near photon-limited observations, with a systematic noise floor on par with the Hubble Space Telescope and below the Earth’s atmospheric amplitude scintillation noise limit. We report the as-built instrument optical and optomechanical design, detectors, control system, telescope hardware and software interfaces, and data reduction pipeline. A summary of ETSI’s science capabilities and the initial results are also included.

Cross-dispersed echelle spectrographs (CDESs) are a fundamental tool for modern astronomy. Their spectral power relies on the echelle pupil size and collimator focal length. Due to this, seeing-limited ground-based observatories often require large instrument sizes to achieve high spectral resolutions. With the advent of large-aperture telescopes and the unrelenting demand for high resolution, the prevailing trajectory of these instruments leans toward escalating in both size and complexity. However, it is important to explore miniaturization strategies for CDESs, which are particularly valuable for space-based instruments where size, weight, and power are crucial. Miniaturization also offers benefits for ground-based instruments, enabling the use of compact, high-resolution CDES systems in lab setups for academic use and as cost-effective solutions for small to medium telescopes in professional observatories. Although there exist miniaturization strategies and designs such as the double pass with a three-mirror anastigmat, they can be challenging to implement due to their sensitivity to alignment. We present a first approach design of a CDES using a Cassegrain collimator. This approach effectively has a reduction in instrument footprint while achieving high spectral power, when compared with the three-fold design. We also performed a sensitivity analysis for the alignment of this design and showed that at a smaller scale, the design does not offer added complexity when compared with the three-fold design.

The new general detector controller, 2nd generation (NGCII) is in development for the first-generation instruments of the extremely large telescope (ELT) as well as new instruments for the very large telescope (VLT). Building on experience with previous European Southern Observatory (ESO) detector controllers, a modular system based on the MicroTCA.4 industrial standard, is designed to control a variety of infrared and visible light scientific and wavefront sensor detectors. This article presents the early development stages of NGCII hardware and firmware from the decision to start an all-new design to first tests with detectors and readout integrated circuits.

The X-ray Integral Field Unit (X-IFU) is an instrument of European Space Agency’s future NewAthena space observatory, with the goal to provide high-energy resolution (<4 eV at X-ray energies up to 7 keV) and high-spatial resolution (9 in.) spectroscopic imaging over the X-ray energy range from 200 eV to 12 keV, by means of an array of ∼1500 transition-edge sensors (TESs) read out via superconducting quantum interference device time-division multiplexing (TDM). A TDM-based laboratory test bed has been assembled at Netherlands Institute for Space Research, hosting an array of 75×75 μm2 TESs that are read out via 2-column × 32-row TDM. A system component that is critical to high-performance operation is the wiring harness that connects the room-temperature electronics to the cryogenic readout componentry. We report here on our characterization of such a test bed, whose harness has a length close to what was envisioned for X-IFU, which allowed us to achieve a co-added energy resolution at a level of 2.7-eV full width half maximum at 6 keV via 32-row readout. In addition, we provide an outlook on the integration of TDM readout into the X-IFU focal plane assembly development model.

Starshade is one of the technologies that will enable the observation and characterization of small planets around nearby stars through direct imaging. Extensive models have been developed to describe a starshade’s optical performance and noise budget in exoplanet imaging. The Starshade Exoplanet Data Challenge was designed to validate this noise budget and evaluate the capabilities of image-processing techniques by inviting community participating teams to analyze >1000 simulated images of hypothetical exoplanetary systems observed through a starshade. Because the starshade would suppress the starlight so well, the dominant noise source remaining in the images becomes the exozodiacal disks and their structures. We summarize the techniques used by the participating teams and compare their findings with the truth. With an independent component analysis to remove the background, ∼70% of the inner planets (close to the inner working angle) have been detected along with ∼30% of the outer planets. Planet detection becomes more difficult in the cases of higher disk inclination as the false negative and false positive counts increase. Interestingly, we found little difference in the planet detection rate between 10−10 and 10−9 instrument contrast, confirming that the dominant limitations are from the astrophysical background and not the performance of the starshade. A non-parametric background calibration scheme, such as the independent component analysis reported here, results in a mean residual of 10% the background brightness. This background estimation error leads to substantial false positives and negatives and systematic bias in the planet flux estimation and should be included in the estimation of the planet detection signal-to-noise ratio for imaging using a starshade and also a coronagraph that delivers exozodi-limited imaging. These results corroborate the starshade noise budget and provide new insight into background calibration that will be useful for anticipating the science capabilities of future high-contrast imaging space missions.

To answer the new challenges imposed by the most recent exoplanet space missions, testing and calibrating high-precision photometric instruments requires a highly stable illumination system, which is a great challenge when the mission’s required photometric stability is a few parts per million for long observation periods. Traditional calibration sources do not fulfill the stability requirements of the most demanding missions. It is necessary to use additional methods to compensate for flux fluctuations. This study introduces a new method, using a digital micromirror device (DMD) as an intensity light modulator. DMD is a micro-electromechanical device developed by Texas Instruments, which consists of a two-dimensional array of micromirrors. Each micromirror can be individually tilted between two positions. By controlling the state of each micromirror, it is possible to control the flux of light that goes in a particular direction. This technology enables fast modulation speeds, with high precision and broadband capabilities. This study presents an exploratory work on the technical feasibility of using DMDs to compensate for light source fluctuations, accurately modulating the beam coming from a Halogen (QTH) source. We developed a proof-of-concept method able to reduce light source fluctuations from ±1.3% to ±0.1%, based on a simple open loop methodology.

We present the design and validation of a variable temperature cryogenic blackbody source, hereinafter called a cold load, that will be used to characterize detectors to be deployed by cosmic microwave background stage 4 (CMB-S4), the next-generation ground-based cosmic microwave background (CMB) experiment. Although cold loads have been used for detector characterization by previous CMB experiments, this cold load has three innovative design features: (1) the ability to operate from the 1-K stage of a dilution refrigerator (DR), (2) a He3 gas-gap heat switch to reduce cooling time, and (3) the ability to couple small external optical signals to measure detector optical time constants under low optical loading. The efficacy of this design was validated using a 150-GHz detector array previously deployed by the Spider experiment. Thermal tests showed that the cold load can be heated to temperatures required for characterizing CMB-S4’s detectors without significantly impacting the temperatures of other cryogenic stages when mounted to the DR’s 1-K stage. In addition, optical tests demonstrated that external signals can be coupled to a detector array through the cold load without imparting a significant optical load on the detectors, which will enable measurements of the CMB-S4 detectors’ optical time constants.

We present a method of centroiding undersampled point spread functions (PSFs) that may be useful, especially when dithering is not an option. If the profile of the expected PSF is known fairly well through the characterization of the telescope and detector used for observing, one can simulate the undersampled PSF at many positions on a simulated pixel grid. The true centroid positions are known because the PSFs are simulated, and so, one can match up each undersampled PSF image to its true centroid location, thus forming a lookup table. One then assigns the centroid position of an observed PSF to the position associated with the PSF in the lookup table that has the smallest squared residual with respect to the observed PSF. We examine a few PSF sizes and demonstrate that the lookup table provides better centroid positions compared to a traditional curve-fitting algorithm when the PSFs are undersampled, even in the presence of noise. The lookup table can also outperform a traditional curve-fitting algorithm in the case of PSFs with a very low signal-to-noise ratio, even if the PSFs are not undersampled.

We present a laboratory analysis of the use of a 19-core photonic lantern (PL) in combination with neural network (NN) algorithms as an efficient focal plane wavefront sensor (FP-WFS) for adaptive optics (AO), measuring wavefront errors (WFE) such as low wind effect (LWE), Zernike modes, and Kolmogorov phase maps. The aberrated wavefronts were experimentally simulated using a spatial light modulator with combinations of different phase maps in both the approximately linear regime (average incident RMS WFE of 0.88 rad) and in the nonlinear regime (average incident RMS WFE of 1.5 rad). Results were analyzed using an NN to determine the transfer function of the relationship between the incident WFE at the input modes at the multimode input of the PL and the intensity distribution output at the multicore fiber outputs end of the PL. The root mean square error (RMSE) of the reconstruction of petal and LWE modes were just 2.87×10−2 rad and 2.07×10−1 rad respectively, in the nonlinear regime. The reconstruction RMSE for Zernike combinations ranged from 5.67×10−2 rad to 8.43×10−1 rad, depending on the number of Zernike terms and incident RMS WFE employed. These results demonstrate the promising potential of PLs as an innovative FP-WFS in conjunction with NNs.

The Giant Magellan Telescope will use laser tomography adaptive optics to correct for atmospheric turbulence using artificial guide stars created in the sodium layer of the atmosphere (altitude ≈90 km). The sodium layer has appreciable thickness (≈11 km), which results in the laser guide star being an elongated cylinder shape. Wavefront sensing with a Shack–Hartmann is challenging as subapertures located further away from the laser launch position image an increasingly elongated perspective of the laser guide star. Large detectors can be used to adequately pack and sample the images on the detector; however, this increases readout noise and limits the design space available for the wavefront sensor. To tackle this challenge, we propose an original solution based on nano-engineered meta-optics tailored to produce a spatially varying anamorphic image scale compression. We present meta-lenslet array designs that can deliver ≈100% of the full anamorphic image size reduction required for focal lengths down to 8 mm and a greater than 50% image size reduction for focal lengths down to 2 mm. This will allow for greatly improved sampling of the available information across the whole wavefront sensor while being a viable design within the limits of current-generation fabrication facilities.

With the commencement of the development of the Habitable Worlds Observatory, it is imperative that the community has an understanding of (1) the stability requirements for the observatory to inform the design and (2) the gains expected from post-processing to inform observing scenarios and science yield estimates. We demonstrate that a previously developed, photon-efficient dark zone maintenance (DZM) algorithm that corrects quasi-static wavefront error drifts using only science images is compatible with traditional post-processing techniques. Further, we augment the DZM algorithm to estimate the coherent and incoherent light separately and introduce three novel post-processing techniques that leverage the concurrent estimation of coherent and incoherent light. With the DZM algorithm implemented on the High-contrast imager for Complex Aperture Telescopes testbed at the Space Telescope Science Institute, artificial drifts are injected as a random walk on a set of deformable mirrors and are corrected with DZM. We present an injected fake planet recovered in post-processing using a variety of techniques, such as angular differential imaging (ADI), and three additional techniques: incoherent accumulated imaging, software-based coherent differential imaging, and coherent reference differential imaging. All post-processing techniques can recover an injected planet at the same contrast level as the dark zone background contrast (∼8×10−8), and the ADI technique is shown to recover a 4×10−8 planet in a 8×10−8 dark zone. For a space-based observatory, this would mean that, if the instrument can reach a contrast level, we can maintain it and recover a planet that is undetectable in a single frame.

Active optics technology is pivotal in the development of next-generation large-aperture telescopes. The Four-Meter Telescope independently developed by the Institute of Optics and Electronics, under the Chinese Academy of Sciences, was completed and put into operation by the end of 2021. To maintain excellent imaging quality, it includes an active primary mirror with 110 active actuators. During active optics control, there are some innovation characteristics. First, the active optics system is operated using a combination of the look-up-table method and the real-time correction method. Second, the active optics and adaptive optics are united to eliminate the distortion caused by structural deformation and atmospheric turbulence. Third, our proposed control strategy based on the compensation plane method and constrained least-squares algorithm are applied in the real-time correction. We described the compositions and function principles of the active optics system for the Four-Meter Telescope. In addition, current star observation results are reported. The observation results show that the average FWHM results of the star images for different elevation angles are 0.6 to 0.8 arcsec after active optics correction, which indicates that the convergence results of active optics systems closely match the seeing conditions of the local observation site. The FWHM for the long-exposure image can reach 0.44 and 0.55 arcsec in x and y directions, respectively.

The large apertures of the upcoming generation of Giant Segmented Mirror Telescopes will enable unprecedented angular resolutions that scale as ∝λ/D and higher sensitivities that scale as D4 for point sources corrected by adaptive optics (AO). However, all will have pupil segmentation caused by mechanical struts holding up the secondary mirror (European Extremely Large Telescope and Thirty Meter Telescope) or intrinsically, by design, as in the Giant Magellan Telescope (GMT). These gaps will be separated by more than a typical atmospheric coherence length (Fried Parameter). The pupil fragmentation at scales larger than the typical atmospheric coherence length, combined with wavefront sensors with weak or ambiguous sensitivity to differential piston, can introduce differential piston areas of the wavefront known as “petal modes.” Commonly used wavefront sensors, such as a pyramid wavefront sensor, also struggle with phase wrapping caused by >λ/2 differential piston wavefront error (WFE). We have developed the holographic dispersed fringe sensor (HDFS), a single pupil-plane optic that employs holography to interfere the dispersed light from each segment onto different spatial locations in the focal plane to sense and correct differential piston between the segments. This allows for a very high and linear dynamic piston sensing range of approximately ±10 μm. We have begun the initial attempts at phasing a segmented pupil utilizing the HDFS on the High Contrast Adaptive optics phasing Testbed (HCAT) and the Extreme Magellan Adaptive Optics instrument (MagAO-X) at the University of Arizona. In addition, we have demonstrated the use of the HDFS as a differential piston sensor on-sky for the first time. We were able to phase each segment to within ±λ/11.3 residual piston WFE (at λ=800 nm) of a reference segment and achieved ∼50 nm RMS residual piston WFE across the aperture in poor seeing conditions.