This PDF file contains the front matter associated with SPIE Proceedings Volume 12678, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

IXPE, the first observatory dedicated to imaging x-ray polarimetry, was launched on Dec 9, 2021 and is operating successfully. A partnership between NASA and the Italian Space Agencey (ASI) IXPE features three x-ray telescopes each comprised of a mirror module assembly with a polarization sensitive detector at its focus. An extending boom was deployed on orbit to provide the necessary 4 m focal length. A three-axis-stabilized spacecraft provides power, attitude determination and control, and commanding. After one year of observation IXPE has measured statistically significant polarization from almost all the classes of celestial sources that emit X-rays. In the following we describe the IXPE mission, reporting on its performance after 1.5 year of operations. We show the main astrophysical results which are outstanding for a SMEX mission.

The integration of a new calibration system into FIREBall-2 (Faint Intergalactic Redshifted Emission Balloon-2) allows in-flight calibration capability for the upcoming Fall 2023 flight. This system is made up of a calibration box that contains zinc and deuterium lamp sources, focusing optics, electronics, and sensors, and a fiber-fed calibration cap with an optical shutter mounted on the spectrograph tank. We discuss how the calibration cap is optimized to be evenly illuminated through nonsequential modeling for the near-UV (200-208nm). Then, we present the pre-flight performance testing results of the calibration system and their implications for in-flight measurements.

The Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SISTINE) is a rocket-borne imaging spectrograph designed to probe a broad region of the far-ultraviolet (FUV; 976-1272, 1300-1565 Å) emission of nearby stars. The instrument is composed of an f /14 Cassegrain telescope feeding a 2.1x magnifying spectrograph with a blazed, holographically ruled diffraction grating and a powered fold mirror. The telescope optics employ enhanced-lithium fluoride overcoated Al, with the secondary mirror providing the first flight test of hot-deoposition LiF coatings employing an ALD deposited aluminum trifluoride (Al + LiF + AlF₃) capping layer. Spectra are captured on a large-format microchannel plate detector consisting of two 110 x 40 mm segments. The third flight of SISTINE was successfully executed on July 6th, 2022, from Arnhem Space Center (ASC), Northern Territory, Australia. SISTINE-3 successfully obtained FUV spectra of α Centauri A and B, fully resolving the binary pair with a 7” separation on sky. The spectra contain a suite of FUV emission lines crucial for reconstructing the high-energy stellar radiation incident onto planets orbiting solar-mass stars. We present the pre-flight calibration at the University of Colorado Boulder, including predicted performance, effective area, and resolving power; the integration and assembly performed at NASA Wallops Flight Facility (WFF) and ASC; and preliminary science results from the in-flight data.

The SPRITE (The Supernova remnants, Proxies for Re-Ionization Testbed Experiment) 12U CubeSat mission, funded by NASA and led by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, will house the first Far-UV (100-175 nm) long-slit spectrograph with access to the Lyman UV (λ ⪅ 115 nm) and sub-arcminute imaging resolution. SPRITE will map the high energy emission from diffuse gas allowing for the study of star formation feedback in a critical, but rarely studied, Far-UV regime on both stellar and galactic scales. This novel capability is enabled by new UV technologies incorporated into SPRITE’s design. These technologies include more robust, high broadband reflectivity mirror coatings and an ultra-low background photon counting microchannel plate detector. The SPRITE science mission includes weekly calibration observations to characterize the performance of these key UV technologies over time, increasing their technology readiness level (TRL) to 7+ and providing flight heritage essential for future UV flagship space missions such as the Habitable Worlds Observatory (HWO). Currently, SPRITE is in the beginning stages of integration and testing of its flight assembly with a planned delivery date of fall of 2024. This proceeding will overview the current mission status, the schedule for testing and integration prior to launch, and the planned mission operations for SPRITE.

The Far-and Lyman-Ultraviolet Imaging Demonstrator (FLUID) is a rocket-borne multi-band arcsecond-level Ultraviolet (UV) imaging instrument covering four bands between 92 – 193 nm. FLUID will observe nearby galaxies to find and characterize the most massive stars, the primary drivers of the chemical and dynamical evolution of galaxies, and the co-evolution of the surrounding galactic environment. The FLUID short wave channel is designed to suppress efficiency at Lyman alpha wavelengths, while enhancing the reflectivity of shorter wavelengths. Utilizing this technology, FLUID will take the first ever images of local galaxies isolated in the Lyman ultraviolet. As a pathfinder instrument, FLUID will employ and increase TRL of band-selecting UV coatings, and solar-blind UV detector technologies including microchannel plate and solid-state detectors; technologies prioritized in the 2022 NASA Astrophysical Biennial Technology Report. These technologies enable high throughput and high sensitivity observations in four co-aligned UV imaging bands that make up the FLUID instrument. We present the design of FLUID, status on the technology development, and results from initial assembly and calibration of the FLUID instrument.

The INtegral Field Ultraviolet Spectroscopic Experiment (INFUSE), a sounding rocket payload under development by the Colorado Ultraviolet Spectroscopy Program (CUSP), will be the first far ultraviolet (100 nm to 200 nm) Integral Field Spectrograph (IFS) in space. With access to part of the Lyman ultraviolet (100.0 nm to 121.6 nm), INFUSE will be able to study spectral emission lines such as O VI in extended objects at greater spatial resolution and coverage than has previously been possible. An F/16, 0.49 m Cassegrain telescope feeds the instrument. A 26-element image slicer provided by Canon, Inc. forms the basis for the IFS. Each reflective slice acts as a long-slit, creating 26 different channels. Each channel is re-focused and dispersed by one of 26 identical holographic gratings supplied by Horiba JY onto the same 94 x 94 mm cross-strip (XS) microchannel plate detector (MCP). This MCP, provided by Sensor Sciences, will be the largest MCP of its type ever flown in space and will be advancing high event rate photon-counting detector technology for future NASA missions. We discuss the process and results of aligning the telescope and instrument, with a focus on the method by which the 26 gratings are aligned with the image slicer. Additionally, we examine the challenges the large primary mirror presented when being mounted and coated for flight. The first flight of INFUSE is schedule for October 2023 when it will spectroscopically image the XA region of the Cygnus Loop at the interface between the supernova and the ambient ISM, studying shock fronts in the supernova remnant.

We present the optical design and testing of SPRITE, a 12U CubeSat being developed by the Laboratory of Atmospheric and Space Physics (LASP). SPRITE is designed to observe supernova remnants and low redshift galaxies in the far ultraviolet range (1000-1750 Å). SPRITE consists of an 18 x 16 cm parabolic primary mirror, a hyperbolic secondary mirror, an aberration-correcting concave holographic grating, a cylindrical fold mirror, and an advanced borosilicate glass Microchannel Plate (MCP) detector. The grating, secondary mirror (M2) and cylindrical fold mirror (M3) are coated with enhanced reflectivity lithium fluoride (LiF) protected aluminum, or “eLif”, capped with a thin overcoat of MgF₂ for protection of the hygroscopic LiF from water vapor. SPRITE is serving as an orbital testbed for protected eLiF and boroscilicate glass MCP detectors ahead of potential adoption on a future NASA flagship mission, like the Habitable Worlds Observatory (HWO). This paper details the actions taken to protect the optics, as well as the MCP, as they are sensitive to molecular contamination and water vapor. We also detail the experimental setup for monitoring the reflectance of witness samples throughout the SPRITE integration and testing phase. Due to the unique nature of SPRITE, custom hardware for storage and optical testing was required to provide sufficient protection for the sensitive optics and detector. These facilities are essential for proving these new technologies for future flight programs, as well as ensuring SPRITE meets the science requirements. The coatings used on SPRITE’s optics are critical for the development of future large astronomy missions with high throughput down to 1000 angstroms.

The transition from neutral to ionized intergalactic medium (IGM) is one of the key signifiers of cosmic structure formation. The mass and energy flows within galaxies are also dominated by ionization and kinematic processes. The Supernova remnants/Proxies for Reionization and Integrated Testbed Experiment (SPRITE), a 12U CubeSat, will investigate these tracers of galactic and cosmic structure. The innovative optical coatings utilized on SPRITE also allow it to serve as a demonstration testbed for a future large (>6m) ultraviolet/optical/infrared surveyor. We demonstrate that these coatings provide high throughput with low environmental degradation. We also present the results of component-level testing and instrument characterization of the SPRITE instrument.

We present the design of the Spectroscopic Ultraviolet Multi-object Observatory (SUMO) prototype and our plan to deploy this instrument on the INFUSE sounding rocket as an independent fly-along instrument. The SUMO prototype is part of the technology maturation program of SUMO - a mission concept designed for a future small satellite platform. SUMO is designed for astrophysics research in the Far-Ultraviolet (FUV) and Near-Ultraviolet (NUV) regimes encapsulating a wide range of programs, including efforts to understand the processes of star formation and galaxy evolution. Since the last major UV NASA missions, FUSE and GALEX, NASA has invested significantly into technology development for the UV bandpass. As a result, high reflectance mirror coatings and state-of-the-art detectors are now available. These technologies, along with the developed optical design, allow SUMO to achieve effective areas that are comparable to those achieved by FUSE and GALEX, at a fraction of the size and cost. The SUMO prototype consists of an 8 cm Cassegrain telescope and a Digital Micromirror Device (DMD)-based Multi-Object Spectrometer (MOS), with parallel imaging and spectroscopic channels. As part of this work, we are also developing a custom DMD controller, which is suitable for operation in the space environment. Given that current DMD-based spectrographs have been solely ground-based, this will be the first time a DMD-based instrument is deployed in space. Because the SUMO prototype will be deployed as a secondary payload, the spectrograph is also designed for completely autonomous operation. The SUMO prototype is tentatively scheduled for flight in 2025.

Aspera is the UV small-satellite mission to detect and map the warm-hot phase gas in nearby galaxy halo. Aspera was chosen as one of NASA's Astrophysics Pioneers missions in 2021 and employs a FUV long-slit spectrograph payload, optimized for low-surface brightness O VI emission line detection at 103-104 nm. The mission incorporates state-of-the-art UV technologies such as high-efficiency micro-channel plates and enhanced LiF coating to achieve a high level of diffuse-source sensitivity of the payload, down to 5.0E-19 erg/s/cm^2/arcsec^2. The combination of the high sensitivity and a 1-degree by 30-arcsecond long-slit field of view enables efficient 2D mapping of diffuse halo gas through step and stare concept observation. Aspera is presently in the critical design phase, with an expected launch date in mid-2025. This work provides a current overview of the Aspera payload design.

The Imaging X-ray Polarimetry Explorer (IXPE) mission, done in collaboration between NASA and the Italian Space Agency (ASI), has been successfully detecting x-ray polarization from celestial sources for more than one year. This mission comprises three x-ray optics and three x-ray polarization sensitive detectors. Four calibration sources based on ⁵⁵Fe nuclides, one producing polarized radiation (at two energies) and three producing unpolarized radiation, are present on board with each detector. In this contribution we present the in-flight monitoring and calibration of IXPE using these sources, with particular regard to the calibrations of the spectral and polarization response. We also show the monitoring of the optics half-power diameter.

The Arcus Probe mission to be proposed to the NASA Astrophysics Probe Explorer call addresses a range of Astro 2020 Decadal Priority science areas. These include (i) exploring how supermassive black hole accretion and winds vary with luminosity, black hole mass, black hole spin and other parameters, (ii) determining how gas, metals, and dust flow into, though, and out of galaxies, and (iii) probing stellar activity across all stellar types and lifecycles, including exoplanet hosts targeted by current and future NASA habitable planet missions. These science goals, along with a robust General Observer science program, will be achieved using a mission that provides a high-sensitivity soft X-ray spectrometer (XRS) with R=3500 (R⪆2500 req) and an average effective area in the 12-50Å bandpass of 335 cm² (250 cm² req). It will be complemented by a co-aligned UV spectrometer (UVS) working in the 1020-1560Å band with R= 24200 (R⪆17000 req) and ⪆5× the sensitivity of FUSE at O VI (1020Å) that observes simultaneously with the X-ray instrument. Working together, these instruments will enable astronomers to characterize warm and hot plasmas - including hydrogen, helium, and all abundant metals - throughout the Universe, from the halos of galaxies and clusters to the coronae of stars. We present the overall mission plan, including instrumentation, science, and operations for a five-year baseline mission.

Arcus is a high-resolution soft X-ray and far-ultraviolet spectroscopy mission being developed for submission to NASA’s inaugural Astrophysics Probe solicitation. Arcus makes simultaneous observations in these two critical wavelength regimes to address a broad range of science questions highlighted by the 2020 Astronomy and Astrophysics Decadal Survey, from the temperature and composition of the missing baryons in the intergalactic medium to the evolution of stars and their influence on orbiting planets. This proceeding presents the science motivation for and performance of the Arcus UltraViolet spectrograph (UVS). UVS comprises a 60 cm, off-axis Cassegrain telescope feeding an imaging spectrograph operating over the 970 – 1580 ˚A bandpass. The instrument employs two interchangeable diffraction gratings to provide medium-resolution spectroscopy (R ⪆ 20,000 in two grating modes centered at approximately 1110 and 1390 ˚A, respectively). The spectra are recorded on an open-face, photon-counting microchannel plate detector. The instrument design achieves an end-to-end sensitivity ⪆ 10 times that of the Far-Ultraviolet Spectroscopic Explorer over the key 1020 – 1150 ˚A range and offers arcsecond-level angular resolution spectral imaging over a six arcminute long slit for observations of extended sources. We describe example science investigations for FUV spectroscopy on Arcus, the resultant instrument design and predicted performance, and simulated data from potential Guest Observer programs with Arcus.

The Arcus Probe is designed to measure the feedback cycle of material into and out of galaxies, and the inter-relation between these flows and the central black holes that drive many of these processes. Arcus consists of a high-resolution x-ray spectrometer (led by the Smithsonian Astrophysics Observatory; SAO) with a companion medium resolution (R ~ 24,500) far-ultraviolet imaging spectrograph covering the 970 - 1580 Å bandpass. The Arcus Ultraviolet Spectrograph (UVS) is designed in part to be a sucessor to the successful FUSE mission, with more than five-times the sensitivity in the essential Lyman UV, including rest-frame O VI 1032 ˚A, than any previous medium resolution spectroscopic instrument. The instrument consists of a 60 cm off-axis Cassegrain telescope feeding a two-channel spectrograph, with the spectra recorded on an open-face microchannel plate detector. The channels each consist of a medium resolution grating mounted to a grating selector: the G110M (970 - 1280 Å, optimized for 1000 - 1280 Å) and the G140M (1195 - 1580 Å). The Arcus UVS is led by the University of Colorado Laboratory for Atmospheric and Space Physics (LASP) and incorporates several technologies developed in the more than two decades since F USE, and matured on previous CU-LASP flight programs, including enhanced lithium fluoride protected aluminum mirror coatings (eLiF) and large-format borosilicate glass MCPs. We describe the recent development and TRL advancement of these enabling technologies, and then outline the UVS instrument and projected performance.

HEX-P is a probe-class mission concept that will combine high angular resolution (⪅ 5 ′′ at 6 keV) x-ray imaging and broad energy sensitivity (0.2 − 80 keV) to enable revolutionary new insights into black holes, neutron stars, and other extreme environments powering the high energy universe. HEX-P prioritizes broad band imagery and high resolution simultaneously, providing a wealth of information not possible with any other planned or operating observatory. HEX-P achieves its breakthrough performance by combining technologies developed by experienced partners: high resolution low energy imagery with silicon segmented mirrors provided by the Goddard Space Flight Center (GSFC, Greenbelt, MD); state of the art high energy imagery from nickel shell mirror technology developed by Media Lario (Bosisio Parini, Italy) and the National Institute for Astrophysics (INAF, Merate, Italy) through a contribution from the Italian Space Agency (ASI, Rome, Italy); high speed, high resolution Depleted P-Channel Field Effect Transistor (DEPFET) detectors through a contribution from the Max Planck Institute for Extraterrestrial Physics (MPE, Garching, Germany); photon counting high energy detectors from the NuSTAR team at the California Institute of Technology (Caltech, Pasadena CA); and a spacecraft and payload structure with a 20 m deployable boom developed by Northrop Grumman (Falls Church, VA).

CIS221-X is the first in a new generation of monolithic CMOS image sensors optimized for soft x-ray applications. The pixels are built on 35 μm thick, high-resistivity epitaxial silicon and feature Deep Depletion Extension (DDE) implants, facilitating over depletion by reverse substrate bias. When cooled to -40 °C, CIS221-X reports a readout noise of 3.3 e- RMS and 12.4 ± 0.06 e-/pixel/s of dark current. The 40μm pixels experience near-zero image lag. Following per-pixel gain correction, an energy resolution of 130 ± 0.4 eV FWHM has been measured at 5.9 keV. In the 0.3 – 1.8 keV energy range, the sensor achieves a quantum efficiency of above 80%. Radiation tests have shown that both the readout noise and dark current increase with total ionising dose and that the OBF can help to mitigate the increase in dark current. The measured electro-optical parameters and the preliminary ionising radiation results strongly support the use of the CIS221-X in soft x-ray applications.

Our group is currently testing large format high frame rate low noise deep-depletion CCD detectors developed by MIT Lincoln Laboratory for future x-ray missions, such as AXIS. This new generation of detectors makes use of pJFET transistors for output signal readout which results in much lower noise than commonly used MOSFET-based circuits. It also incorporates single-level polysilicon gate structure enabling fast charge transfer with very low clock amplitude. We achieved the level of noise of two electrons rms at 2 MHz rate with six frames/s readout, bringing performance level close to the requirements of AXIS mission. Trying to improve parallel speed we encountered an unexpected phenomenon related to interaction between bias substrate and state of inversion near the CCD gates. This effect reveals an important trade space for selecting mode of operation for large x-ray CCD arrays.

We report on the development of metal-dielectric bandpass filters that can be integrated with back-illuminated CMOS imaging sensors for operation at far ultraviolet wavelengths (FUV, 90-200 nm). These coatings utilize previous developments in atomic layer deposition (ALD) processes for transparent dielectric materials which are combined with evaporated aluminum layers in multilayer structures. Planar coatings can produce an FUV bandpass response that allows broadband silicon imaging sensors to operate with visible and solar blindness. We describe the fabrication and optical characterization of these coatings, and describe the development of delta-doped detectors integrating these coatings that are motivated by the performance requirements of the NASA astrophysics mission Ultraviolet Explorer (UVEX), currently undergoing a Phase A concept study. We also describe the extension of this concept to include graded thickness dielectric layers deposited by ALD. We show that a graded lateral thickness can be engineered in a variety of thermal ALD processes by depositing into a shallow horizontal cavity. This allows for the fabrication of detector-integrated filter coatings with a spatially-varying response that can be matched to the spectral dispersion of the planned UVEX spectrograph channel. Prototype graded coatings are demonstrated over areas up to 4 x 4 cm, and characterized for optical performance and environmental stability.

Advancements in optical coating methods developed at the Jet Propulsion Laboratory (JPL) now allow for spatial optimization of detector response with respect to a spectrometer system’s optical dispersion. When combined with JPL’s delta-doped, UV detector technology, these patterned coatings will reduce the complexity required for UV instruments while also improving throughput. This technology development offers an innovative solution to the limitations and compromises inherent in existing UV coating technologies. This advancement will result in detectors with high quantum efficiency (QE) in targeted wavelength bands, allowing for more versatile UV–Visible instrumentation.

Slitless spectrometers can provide both spatial and spectral information of extended objects, such as the Sun, in a single snapshot. The data, however, require unfolding of overlapping spatial and spectral information. Thanks to advances in computer processing speeds, there have been several techniques developed to complete the spatial/spectral unfolding, unlocking the full capability of slitless spectrometers for solar observations. The goal of this talk is to give an overview of the capability of such instruments and demonstrate their usefulness in the next decade of solar observatories and beyond.

XPOL-III is a recently developed 180 nm CMOS VLSI ASIC integrating more than 100K pixels at 50um pitch in a total active area of 15 X 15 mm² . Each channel directly samples the charge collected at its own anode and holds it for readout through the built-in, low noise spectroscopic electronics chain. A global control circuit allows for the reconstruction of the spatial distribution of the event charge and the suppression from the readout stream of those pixels below a programmable signal threshold. XPOL-III inherits from previous generations of this ASIC, and extends its predecessor’s performances in terms of readout speed and response uniformity, making XPOL-III a suitable option for high resolution, low noise, high data throughput X-ray detectors. Implementing a single photon detection architecture, XPOL-III provides accurate timing, energy and position resolved measurements when coupled to a proper photon to charge converter. We spot the principles of operation of XPOL-III and summarize the preliminary test results when integrated in its original context, the Gas Pixel Detector (GPD), the same detector class currently at the focus of the Imaging X-ray Polarimetry Explorer (IXPE) telescopes.

The novel Speedster-EXD550 is a 550×550-pixel x-ray Hybrid CMOS Detector (HCD) with event-driven readout capabilities and 40-micron pixel pitch. In event-driven readout mode, only the pixels that contain sufficient liberated charge from the absorption of an x-ray will be read out. Event-driven readout allows for even faster readout speed than other HCDs, reaching readout speeds up to 10,000 frames/sec. The high frame rate of the Speedster-EXD550 is desirable for future missions as the effects of dark current and x-ray pile-up will be reduced. The readout circuitry within the ROIC for the Speedster-EXD550 contains a high-gain capacitive transimpedance amplifier, in-pixel correlated double sampling, and an in-pixel comparator enabling event-driven readout. The Speedster-EXD550 also utilizes column-parallel on-chip digitization. The ability of the Speedster-EXD550 will be demonstrated on BlackCAT, a funded NASA CubeSat mission. Testing and characterization of the Speedster-EXD550 has been done by the Penn State High Energy Astrophysics Detector and Instrumentation lab in both full-frame and event-driven readout modes. A radioactive 55Fe source was used for the measurements presented. Here, we discuss the methods and recent results for the characterization of the Speedster-EXD550 dark current, read noise, gain, and gain variation.

The NuSTAR (Nuclear Spectroscopic Telescope Array) mission launched in 2012, and it has successfully deployed the first orbiting telescopes to focus light in the high-energy x-ray range (3 - 79 keV), providing a wealth of new information about the sources of high-energy x-rays. Follow-up missions such as the proposed HEX-P, BEST, and FORCE could perform a deeper black hole census providing a more refined measurement of black hole spins, allowing for greater knowledge about supermassive black holes. These missions are motivated by recent breakthroughs in hard x-ray mirror technologies where mirrors made of monolithic silicon segments and mirrors made directly or through replication of shells demonstrate the feasibility of making hard x-ray mirrors with angular resolutions of five to ten arc seconds Half Power Diameter (HPD) compared to NuSTAR’s one arc minute HPD. Such a high angular resolution requires matched detectors (higher pixel density) to fully benefit from the achievable improved spatial resolution. In the above framework, the development of the HEXID ASIC, embedding is a novel pixelated front-end suitable for reading out a finely segmented CZT sensor, is presented. The required large dynamic range (from 2 keV to 180 keV) and low input noise (ENC ⪅ 20 e⁻) together with a small pixel size (150 μm) pose several design challenges in chip implementation. The chosen architecture of the front-end circuit and in-pixel processing blocks, together with the readout architecture of the registered signals and other adopted design solutions, driven by the quoted requirements, will be reviewed.

The current stage of the project aims to develop a cutting-edge Next-Generation Microshutter Array (NGMSA) device as a spaceflight-qualified field object selector mask for multi-object spectroscopy (MOS). This technological goal is defined by the expectation by the strategic space flight missions large format field selector masks. We present the status of the NGMSA large format arrays from technology readiness level from 3 to 5. The preceding cycle of the development resulted in demonstration of the small format NGMSA technology in the Far-ultraviolet Off Rowland-circle Telescope for Imaging and Spectroscopy (FORTIS) sounding rocket flight. It opened the path to the next stage of the large format arrays. We report on the current status of the arrays fabrication, functional and optical testing, integration and the plans to scalability of the individual devices into the focal plane assembly.

Errors in grating fabrication contribute to ghosting and reduce efficiency, decreasing the signal-to-noise ratio of observations. It has historically been challenging to quantify fabrication errors across large areas using common tools such as scanning electron microscopes due to time and automation constraints. Interferometry allows for direct, large area measurement of these characteristics as a metric for success. We present interferometric measurements of laminar which have been used to characterize and optimize EBL tool error (“stitch error”) over large areas and detail future measurements of the impact of KOH etching on the groove placement accuracy. Additionally we comment on future work replicating EBL gratings via nanoimprint lithography.

We present laboratory reflectivity results of two novel optical filters designed for the Lyman ultraviolet bandpass (LUV; 90-120 nm) and the far ultraviolet bandpass (FUV; 120-150 nm). These filters were developed in coordination with the Grupo de Óptica de Láminas Delgadas (GOLD) at the Instituto de Óptica-Consejo Superior de Investigaciones Cientìficas for the Far- and Lyman-Ultraviolet Imaging Demonstrator (FLUID) sounding rocket payload. In addition to maturing high priority band-selecting UV filter technology, FLUID will measure the LUV and far ultraviolet (FUV; 120-200 nm) morphologies of nearby galaxies in four imaging bands to provide local analogs for JWST observations of high redshift galaxies. Images in the LUV will be used to make the first ever morphological classifications of local galaxies in this bandpass. FLUID comprises four f /28.7 Cassegrain telescopes with ⪅3 arcsecond angular resolution over a 20 arcminute wide field-of-view. Each telescope receives a unique band-defining filter covering the LUV through FUV (approximately 15 nm FWHM band centered on 105 nm, and 20 nm FWHM bands centered on 140 nm, 160 nm, or 180 nm). These filters are multilayer reflectance filters, and were developed by GOLD in collaboration with CU Boulder. Evaluation of the F140M filter and the Lyman alpha (Ly-α; 121.6 nm) suppressing F110M filter witness samples, as well as the secondary and primary mirrors, were completed with optical testing facilities at both GOLD and CU. We present the measured efficiencies of the F110M optics, which all demonstrate reflectivites ⪅3% at Ly-α while maintaining ⪆40% reflectivity at 105 nm, and the F140M optics, which show show peak reflectivities for 140 nm greater than 87%. These values are used to estimate the performance of the FLUID instrument in this band. Additionally we will conduct further testing of all four filters, as well as testing age and environmental stability of the filters over the course of the project.

In this paper we discuss the testing setup, characterization, and applications of hollow core fiber optics designed to transmit light in the far-ultraviolet (FUV; λ ⪅ 200 nm). These hollow core fibers were developed at the University of Bath in collaboration with the University of Colorado (CU) Laboratory for Atmospheric and Space Physics (LASP) for potential use in a multiplexed spectrometer for future planetary science instruments. We present an update on the nitrogen-purged test chamber used for throughput and bend loss testing. We find that these fibers exhibit less than 3 dB loss at λ = 170 nm at a bend angle of 90 degrees and a 27 mm radius of curvature. The net transmission of the 20 cm fiber sample in this bend configuration remains greater than 10% for three of the four fiber samples tested, meeting initial requirements for a future prototype fiber-fed instrument. Two of the four fibers tested exceeded 30% transmission. We present these results in detail and provide an update on the development of the Testbed for Fiber-Fed Instrumentation (TUFFI) prototype in development at CU-LASP.

Next-Generation Microshutter Arrays (NGMSA) are customizable multi-aperture spectrograph slit masks manufactured by Goddard Spaceflight Center (GSFC) that have an advanced pure electrical actuation and latching mode, which is considerably more robust than the scanning magnetic actuation and electric latching method used by the first generation MSA devices on JWST’s NIRSpec. These first-generation devices were found to have an average open-to-closed contrast ratio of approximately 66,000 at visible and near-infrared wavelengths (Kutyrev et al. 2008). NGMSA have been baselined in the multi-object UV spectroscopic designs for Habitable Worlds Observatory (HWO) and other Explorer missions. Consequently, the near-UV contrast of these devices as a function of input focal ratio is of great interest. Here we present an update to the contrast evaluation apparatus first reported in Carter et al. (2021), but with an improved doublet projection and imaging optical train. Overall spherical aberration is considerably reduced, and the analysis of a prototype flight array yields significantly higher contrast than found in that initial work, emphasizing the need for high quality projection and imaging optics for precise contrast measurements. There is a clear monotonically increasing relationship between contrast and f/#. At ratios slower than f/15 we find single slit contrast ratios in excess of 100,000 using Hg emission line source at 1849 and 2537 Å and with a narrowband filtered continuum D2 lamp at 3004 Å. The contrast using a 2214 Å filter with the D2 lamp was somewhat lower (⪆ 60,000) but may have contributions from chromatic aberration in the quartz optics and out-of-band leakage in the interference filters. Requirements for enabling the measurement of NGMSA contrast in the vacuum ultraviolet below approximately 1800 Å are addressed.

The FUV detector for the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope is a limited resource and must be managed carefully in order to prolong its life. This includes implementing multiple Lifetime Positions (LPs) in order to have spectra fall at different positions on the detector and adjusting the high voltage to minimize the extracted charge. The detector model used to predict how the gain evolves with time has become more sophisticated since launch and is used for both short and long-term planning. One limitation of the model is our incomplete understanding of how the response of a region on the detector is affected by factors such as the applied high voltage, shape of the pulse height distribution, modal gain, and previous usage. With more than fourteen years’ worth of data available for analysis, we can now improve our understanding of the effects of these items and enhance our predictive capabilities. We will discuss our investigation of how they affect the model and address the possibility that we may be able to recover data from heavily gain sagged regions of the detector.

We describe the post-delivery performance testing of the JUpiter ICy moons Explorer Ultraviolet Spectrograph (JUICE-UVS). JUICE-UVS is a modest power (8 W) ultraviolet imaging spectrograph that is the fifth in a series of Alice/UVS instruments built by Southwest Research Institute (SwRI). JUICE-UVS covers a 50-204 nm bandpass with 0.4 nm spectral resolution over a 7.5° field of view with better than 0.3° spatial resolution. JUICE-UVS will explore the Galilean satellites, examine the dynamics of Jupiter’s upper atmosphere from pole to equator, and investigate the Jupiter-Io connection through observations of the Io torus. JUICE-UVS underwent an extensive ground testing campaign at strategic points during the JUICE integration-and-testing over the course of four years and four countries on three continents. High voltage operations were enabled via the usage of specially designed Optical Ground Support Equipment (OGSE) that attached to the spacecraft for key tests. All performance requirements continue to be met, and there is no observable performance degradation after all spacecraft environmental testing and transport activities. In particular, the microchannel plate detector has similar sensitivity and dark rates as measured during pre-delivery testing. Testing of optical witness samples removed during key tests indicates the instrument optical throughput is unchanged. In-flight calibrations planned for shortly after launch will further confirm the performance of JUICE-UVS.

The Hot Universe Baryon Surveyor (HUBS) mission aims at addressing the long-standing ”missing baryon problem” in astrophysics and cosmology. Observationally, it is realized that the detectable amount of baryonic matter (i.e., normal matter, as opposed to dark matter) in the present-day universe is significantly less than that in the early universe. Theoretically, it is postulated that such "missing” baryons are present in diffuse gas of very low density and high temperature around and between galaxies. The gas would radiate soft x-ray, but the signal is thought to be too weak to be detected by the current generation of x-ray observing facilities. HUBS plans to take advantage of the superior (photon) energy resolution of microcalorimeters, to increase the signal-to-noise ratio of detections through narrow-band imaging and to perform high-resolution x-ray spectroscopy, as the spectrum of the radiation is expected to be dominated by emission lines. The HUBS mission and the associated development of microcalorimeters are briefly described in this work.

BlackCAT is a NASA CubeSat mission planned to be launch-ready in early 2025. Using a wide-field telescope, this 6U CubeSat will monitor the soft x-ray sky, searching for high-redshift Gamma-Ray Bursts (GRBs), gravitational-wave counterparts, and other transient events. After detecting burst events, BlackCAT will be capable of transmitting rapid alerts to enable prompt follow-up observations. The instrument is composed of a coded-aperture telescope using an array of event-driven x-ray Hybrid CMOS Detectors (HCDs) in its focal plane. In this paper, we provide a brief update on the design and status of the mission.

The origin of the Cosmic Diffuse Gamma-ray (CDG) background in the 0.3 to 30 MeV energy range is a mystery that has persisted for 50 years. The best existing measurements have large systematic uncertainties, and the latest theoretical models based on emission from active galactic nuclei and supernovae differ significantly from these data below 1 MeV. The Mini Astrophysical MeV Background Observatory (MAMBO) is a new CubeSat mission under development at Los Alamos National Laboratory with the goal of making high-quality measurements of the MeV CDG to help solve this puzzle. The concept is motivated by the fact that, since the MeV CDG is relatively bright, only a small detector is required to make high-quality measurements of it. Indeed, the sensitivity of space-based gamma-ray instruments to the MeV CDG is limited not by size, but by the locally generated instrumental background produced by interactions of energetic particles in spacecraft materials. Comparatively tiny CubeSat platforms provide a uniquely quiet environment relative to previous gamma-ray science missions. The MAMBO mission will provide the best measurements ever made of the MeV CDG spectrum and angular distribution, utilizing two key innovations: 1) low instrumental background on a 12U CubeSat platform; and 2) an innovative shielded spectrometer design that simultaneously measures signal and background. Los Alamos is partnering with commercial vendors for the 12U CubeSat bus and ground station network, which we expect will become a new paradigm for low-cost, fast-turnaround space science missions. We present calibration and test results for the payload and simulations of the expected scientific return.

The Rocket Experiment Demonstration of a Soft X-ray Polarimeter (REDSoX) is a NASA-funded sounding rocket instrument that can make the first measurement of the linear X-ray polarization of an extragalactic source in the 0.2-0.4 keV band. We employ multilayer-coated mirrors as Bragg reflectors at the Brewster angle. By matching the dispersion of a dispersive spectrometer using critical angle transmission gratings to three laterally graded multilayer mirrors (LGMLs), we achieve polarization modulation factors over 90%. We will describe new prototyping work as well as extensions of the design for an orbital version. This work is supported in part by NASA grant 80NSSC23K0644.

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket mission that completed a successful flight from the White Sands Missile Range on July 30, 2021. MaGIXS captured spatially resolved soft X-ray spectra from portions of two solar active regions during its roughly 5-minute flight. The instrument was originally designed as a grazing incidence slit spectrograph but flew in a slit-less configuration that produced overlapping spectroheliograms. For the second flight, MaGIXS-2, the instrument has been reconfigured to a more simplified optical layout that reuses the Wolter-I telescope and blazed varied-line space reflective grating. The field stop at the telescope focal plane and the finite conjugate spectrometer mirror pair have been removed – the telescope now directly feeds the grating. Additionally, an identical but new 2k x 1k CCD camera has been built for this flight. The MaGIXS-2 data product will again be overlapping spectroheliograms of at least one solar active region, but with improved resolution, a larger field of view and increased effective area. Here we present the updated instrument layout, the expected performance, the integration and calibration approach, and proposed future improvements, including the implementation of additional complimentary spectral diagnostics.

The GAGG Radiation Instrument (GARI) is designed to space-qualify a compact, high-sensitivity gamma-ray spectrometer for astrophysical and defense applications and has completed over one year of operations on the International Space Station (ISS). The on-orbit activation of the GAGG crystal induced by the radiation background was measured. Characteristic gamma-ray lines present in the on-orbit spectra were compared to ground-based tests for identification. The radiation background, including the particle-induced internal activation of the crystal, affects the sensitivity of the instrument. We also show the degradation in the performance of the silicon photomultiplier (SiPM) readout (known to be sensitive to radiation damage). Results shown here will be useful in predicting the performance of larger instruments that use GAGG scintillator technology for gamma-ray spectroscopy.

AXIS is a Probe-class mission concept that will provide high-throughput, high-spatial-resolution x-ray spectral imaging, enabling transformative studies of high-energy astrophysical phenomena. To take advantage of the advanced optics and avoid photon pile-up, the AXIS focal plane requires detectors with readout rates at least 20 times faster than previous soft x-ray imaging spectrometers flying aboard missions such as Chandra and Suzaku, while retaining the low noise, excellent spectral performance, and low power requirements of those instruments. We present the design of the AXIS high-speed x-ray camera, which baselines large-format MIT Lincoln Laboratory CCDs employing low-noise pJFET output amplifiers and a single-layer polysilicon gate structure that allows fast, low-power clocking. These detectors are combined with an integrated high-speed, low-noise ASIC readout chip from Stanford University that provides better performance than conventional discrete solutions at a fraction of their power consumption and footprint. Our complementary front-end electronics concept employs state of the art digital video waveform capture and advanced signal processing to deliver low noise at high speed. We review the current performance of this technology, highlighting recent improvements on prototype devices that achieve excellent noise characteristics at the required readout rate. We present measurements of the CCD spectral response across the AXIS energy band, augmenting lab measurements with detector simulations that help us understand sources of charge loss and evaluate the quality of the CCD backside passivation technique. We show that our technology is on a path that will meet our requirements and enable AXIS to achieve world-class science.

Over the past several years, research and development surrounding hollow-core optical fibers has produced intriguing designs that feature low attenuation and precise polarization control. We present findings of polarization effects in symmetric, tapered, negative curvature fibers. The tested fibers feature twenty-two inner tubes that are much smaller than those in previous designs. Our tests involve transmitting light of varying wavelengths and linear polarization states through the fiber and imaging the fiber output with a microscopic camera. The camera that observes the transmitted light is positioned on a setup that can bend the fiber to observe any intensity or mode shape due to the bending, including any polarization dependence. These fibers may provide excellent polarization stability without the need for more complex designs, like those with nesting or asymmetric capillaries.

Ultraviolet (UV, 900−2000 Å) astrophysics plays a vital role in studying exoplanets and evaluating their potential habitability. One approach to understanding exoplanetary habitability is through the study of their absorption spectra, which can reveal not only the chemical composition and physical properties (e.g., mass-loss rate) of their atmosphere but also the UV environment around the host star. Using grating simulation software, we explored a grating-parameter space (blaze angle, grating period) to optimize the design parameters of a UV grating designed for observing key spectral features (e.g., H i, O i, C ii, etc.) in exoplanetary atmospheres. We use interferometric measurements to determine the grating’s groove placement accuracy, groove uniformity, and limiting resolution; and other metrology techniques to characterize the surface roughness. We quantify the expected performance of our UV gratings using these measurements. This work is part of an effort to leverage trends found between measured UV grating performance and the grating’s intrinsic, fabricated characteristics to estimate the expected performance of UV gratings as we fabricate larger gratings.

The Supernova remnants Proxies for reIonization Testbed Experiment (SPRITE) CubeSat is designed to map shock emission in supernova remnants and determine the escape fraction of hydrogen ionizing radiation in star-forming galaxies. As a secondary objective, SPRITE will track the stability of new advanced ‘eLiF’ mirror coatings and Micro Channel Plate (MCP) detector over the mission’s lifetime as they are sensitive to molecular contamination, especially from organic compounds, silicones, as well as exposure to water vapor. As a result, a thorough cleaning procedure was created to prepare the components for flight assembly. This system contains two ovens that are able to operate independently of one another. One operates at approximately 3 torr with a nitrogen purge, while the other operates at 10^-6 torr and funnels contaminants into a liquid nitrogen cold trap. Typically, parts are baked in the low-vacuum oven for three to four days before being transferred to the high-vacuum oven to bake for an additional three to four days where the liquid nitrogen and Residual Gas Analyzer (RGA) measurements are checked daily. This process allows parts to outgas in a controlled environment, rather than exposing the optics to molecular contaminants during integration and while on-orbit (throughout the mission lifetime). This paper will detail the fabrication of the custom vacuum bakeout system and the associated procedures used to bake components at high vacuum. This vacuum bakeout setup is inexpensive and sufficient to meet the contamination control needs of sensitive missions like SPRITE, within the limited budgets of CubeSat and SmallSat missions.

Building on the successful launch and operation of the Imaging X-ray Polarimetry Explorer (IXPE) mission,1 the Italian National Institute for Nuclear Physics (INFN) has initiated an R&D program to develop the next generation of Gas Pixel Detectors (GPDs) for X-ray polarimetry.2 To support this effort, a Bake and Fill System (BFS) was designed, integrated, and tested. The complex BFS architecture consists of various subsystems, including gas distribution and purification, thermal control, vacuum generation, leak detection and residual gas analysis (RGA), high voltage supply, scientific data acquisition, and x-ray generation (both with passive and active sources). We also implemented remote monitoring and logging of the system status and relevant environmental data. The BFS facility was successfully used to test the detector’s sub-components, fill the GPDs with several gas mixtures at different fill pressures, and conduct functional and performance acceptance tests of the detectors even before their final sealing. The BFS’s successful implementation has demonstrated its potential to support extensive qualification campaigns of detector components, besides being a reliable production facility for flight, sealed GPDs for future space missions in X-ray polarimetry. The development and utilization of the BFS represent an important step towards the production of cutting-edge X-ray polarimeters, which have a wide range of applications in astronomy and astrophysics.

HEX-P is an x-ray probe-class mission concept that will combine high angular resolution (⪅15 arcsec) with broad band spectral coverage (0.2 - 80 keV) to enable revolutionary new insights into the important astrophysical questions of the next decade identified by the 2020 Decadal Survey. Sensitivity is key to the instrument performance and estimating the background a crucial step in the development of the design and prediction of the instrument performance. The HEX-P orbit is at L1, and since L1 has hosted no prior missions with x-ray coverage that can be used to estimate the background level, the particle background has to be simulated. We present here the simulations done to evaluate the contribution to the background from charged particles, which show that the high energy background is dominated by hadronic activation in the detector mass and prompt leptons. To reduce the additional Cosmic X-ray Background (CXB), which is non-charged, the instruments are fitted with apertures and blocking plates of a graded-Z material to attenuate the CXB to a level an order of magnitude below the requirement.

Conventional PbO-based Microchannel Plates (MCPs) are known to experience large drops in gain as a function of extracted charge, with a particularly large drop known as a “burn-in” period that occurs in the first 1 C/cm² of extracted charge. Incom has developed ALD-GCA-MCPs that use Atomic Layer Deposition (ALD) to coat Glass Capillary Arrays (GCAs) of a base glass in order to make MCPs. In this way, the electrical and mechanical properties of the MCPs are separated. One advantage of this is that Incom can make MCPs out of various types of glass, such as aluminosilicate, which is substantially free of alkalis that can migrate in the glass matrix and change the electrical properties of the MCPs. This process has enabled Incom, using their proprietary C14 glass, to make MCPs that have much longer device lifetimes. The goal of these experiments was to compare the lifetime performance of Incom MCPs to PbO MCPs, as well as to compare the performance of ALD-GCA-MCPs made out of two types of glass substrates: C14 glass and an alkali-containing C5 glass. The MCP made with C14 glass had a gain of 1E4 at 950 V after 300 C/cm² extracted charge, and no spatial variations in gain out to at least 23 C/cm². The MCPs made of C5 glass exhibited imaging defects after 3 C/cm². The gain of the PbO MCP fell to 1E3 at 950 V after 110 C/cm².

Arcus is a concept for a probe class mission to deliver high-resolution FUV and x-ray spectroscopy. For x-rays, it combines cost-effective Silicon Pore Optics (SPO) with high-throughput Critical-Angle Transmission (CAT) gratings to achieve R⪆ 3000 in a bandpass from 12-50 Å. We show in detail how the x-ray and the UV spectrographs (XRS and UVS) on Arcus will be aligned to each other. For XRS we present ray-tracing studies to derive performance characteristics such as the spectral resolving power and effective area, study the effect of misalignments on the performance, and conclude that most tolerances can be achieved with mechanical means alone. We also present an estimate of the expected on-orbit background.

The Advanced X-ray Imaging Satellite (AXIS) is a Probe-class concept that will build on the legacy of the Chandra x-ray Observatory by providing low-background, arcsecond-resolution in the 0.3-10 keV band across a 450 arcminute² field of view, with an order of magnitude improvement in sensitivity. AXIS utilizes breakthroughs in the construction of lightweight segmented x-ray optics using single-crystal silicon, and developments in the fabrication of large-format, small-pixel, high readout rate CCD detectors with good spectral resolution, allowing a robust and cost-effective design. Further, AXIS will be responsive to target-of-opportunity alerts and, with onboard transient detection, will be a powerful facility for studying the time-varying x-ray universe, following on from the legacy of the Neil Gehrels (Swift) x-ray observatory that revolutionized studies of the transient x-ray Universe. In this paper, we present an overview of AXIS, highlighting the prime science objectives driving the AXIS concept and how the observatory design will achieve these objectives.

SPRITE is a NASA far-UV telescope and spectrograph being designed and assembled at the Laboratory for Atmospheric and Space Physics (LASP). SPRITE’s mission is UV astrophysics in the 1000 - 1750 Angstroms spectral regime. SPRITE will observe low-redshift galaxies, as well as supernova remnants in the Milky Way. SPRITE’s complex science payload is extremely constrained by the volume allocation of the 12U CubeSat form factor. Our solution to deal with SPRITE's volume constraints, is to fabricate solar panels with a high fill factor. With only three deployable single-hinge panels and one body-mounted panel, SPRITE is able to generate 8.5 to 9.7 Watts of power when fully illuminated, using 45 Azur Space AG30A solar cell assemblies. SPRITE is currently finishing the integration and testing phase of its program, with a launch manifested for August 2024.

HEX-P is a probe-class mission concept that will combine high angular resolution (⪅15 arcsec) x-ray imaging with broad band spectral coverage (0.2-80 keV) to enable revolutionary new insights into important astrophysical questions identified by the 2020 Decadal Survey. The bandpass is achieved with a 20-meter focal length provided by an extendable boom from Northrop Grumman, Deployables, and a metrology system is required to measure the bench-to-bench deflections and reconstruct the point spread function. We describe the metrology system derived from NuSTAR, which is a laser metrology system monitoring the motion, normal to the optical axis, of the bench carrying the optics relative to the focal plane with a resolution better than 50 micrometers. We also describe the boom and show that the metrology system is well matched to the predicted behavior of the boom and capable of meeting the angular requirement.

Evaluating Wolter-like x-ray mirror prescriptions via ray tracing is useful for selecting and optimizing the right mirror prescriptions for a specified application. Moreover, incorporating real metrology data into a ray trace and simulating Point Spread Functions (PSF) allow for performance predictions representative of real manufacturing errors and tolerances. In fulfillment of an internship project, an x-ray ray trace routine using a Monte-Carlo method has been developed to examine different Wolter-like prescriptions and characterize their theoretical performances over a specified field of view. This routine includes the ability to use real metrology data to evaluate the impact of figure error on imaging performance. As a test case, the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) Wolter-I mirror prescription and an equivalent Wolter-Schwarzschild prescriptions were traced and imaging performance of a specified field of view were mapped. Here we present the approach used in this routine, showcase example results, and discuss future goals for expanding the routine to address azimuthally varying figure errors and surface roughness.

The Johns Hopkins Rocket Group is advancing Hydrogen Absorption Cell technology to filter geocoronal emissions from Earth's atmosphere. Our innovation, a low-pressure chamber converting molecular hydrogen into its atomic form, is designed to integrate seamlessly into future Lyman ultraviolet missions. Currently, we are engineering this cell to interface with the Long-slit Imaging Dual Order Spectrograph (LIDOS) for comprehensive testing, focusing on stray light detection. This research aims to leverage this technology for photometric measurements and assess its suitability with a spectrograph in future mission concepts.

Arcus is a proposed pointed x-ray and UV Probe mission which will observe targets across the sky for extended periods of time. Total observation times for targets range from a few ks to 2 Ms, nearly all of which can be performed in a series of discontinuous exposures throughout the mission. The mission is also designed with a requirement to respond to Target of Opportunity (ToO) triggers within four hours. Arcus will not carry an all-sky monitor, and therefore new commands must be formulated on the ground and uploaded once a ToO trigger is received. We present the Arcus Operations Simulator (OpSim). This consists of the Observation Planning tool (ObsPlan), which will plan (and re-plan) the entire observing mission within minutes, accounting for relevant observatory restrictions, and the ToO tool (ToOT) which automatically rejects or approves ToO triggers, will rapidly notify Mission Operations (MOps), and will trigger ObsPlan to create and transmit an updated observation plan within 20 minutes. This software is modular and easily extensible and therefore may be of use for other pointed missions for creating their own observing plans.