This PDF file contains the front matter associated with SPIE Proceedings Volume 11821, including the Title Page, Copyright information and Table of Contents

Silicon imagers are ubiquitous in the consumer landscape. With nanoscale engineering, they can become high performance scientific imagers with high sensitivity and extended spectral range response, enabling discoveries and capabilities in space exploration. This allows an opportunity to leverage the enormous investment in these imagers. In this plenary talk, Dr. Shouleh Nikzad will describe how surface engineering enables high performance in detectors, filters, and coating technologies which in turn could enable discoveries in future space missions ranging from CubeSats to flagship. She will also discuss the synergistic way these technologies can be used for terrestrial applications and in particular medical applications.

The Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission is an astrophysics Small Explorer employing ultraviolet spectroscopy (EUV: 80 - 825 Å and FUV: 1280 - 1650 Å) to explore the high-energy radiation environment in the habitable zones around nearby stars. ESCAPE provides the first comprehensive study of the stellar EUV and coronal mass ejection environments which directly impact the habitability of rocky exoplanets. In a 20 month science mission, ESCAPE will provide the essential stellar characterization to identify exoplanetary systems most conducive to habitability and provide a roadmap for NASA's future life-finder missions. ESCAPE accomplishes this goal with roughly two-order-of-magnitude gains in EUV efficiency over previous missions. ESCAPE employs a grazing incidence telescope that feeds an EUV and FUV spectrograph. The ESCAPE science instrument builds on previous ultraviolet and X-ray instrumentation, grazing incidence optical systems, and photon-counting ultraviolet detectors used on NASA astrophysics, heliophysics, and planetary science missions. The ESCAPE spacecraft bus is the versatile and high-heritage Ball Aerospace BCP-Small spacecraft. Data archives will be housed at the Mikulski Archive for Space Telescopes (MAST). ESCAPE is currently completing a NASA Phase A study, and if selected for Phase B development would launch in 2025.

The University of Colorado led Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) small explorer mission concept is designed to measure the extreme- and far-ultraviolet (EUV; 80 - 560 A, 600 - 825 A, FUV; 1280 - 1650 A) irradiance and are activity of exoplanet host stars; essential measurements for assessing the stability of rocky planet atmospheres in the liquid-water habitable zone. The ESCAPE design consists of a fixed optical configuration with a grazing incidence Gregorian, or "Hetterick- Bowyer", telescope feeding grazing and normal incidence spectroscopic channels. The telescope is provided by a joint NASA Marshall Space Flight Center and Smithsonian Astrophysics Observatory team. The grazing incidence gratings have a radial profile and are ruled into single-crystal silicon using electron-beam lithography in the nanofabrication laboratory at Pennsylvania State University. Normal incidence gratings have aberration correcting holographic solutions and are supplied by Horiba Jobin Yvon. Spectra are imaged onto a curved microchannel plate detector supplied by the University of California, Berkeley. ESCAPE utilizes the Ball Aerospace BCP spacecraft. The simple, fixed configuration design of ESCAPE is projected to exceed the effective area of the last major EUV astrophysics spectrograph, EUV E-DS/S, by more than a factor of 50, providing unprecedented sensitivity in this essential bandpass for exoplanet host-star characterization. We report on the ESCAPE design, projected performance and mission implementation plan, as well as the trade studies carried out over Phase A to scope the first NASA EUV astrophysics mission in nearly 30 years. If selected, ESCAPE will launch in Fall 2025.

The GAGG Radiation Instruments (GARI), two identical instruments, are designed to space-qualify new gamma-ray detector technology for space-based astrophysical and defense applications. The detector technology offers improved energy resolution, lower power consumption and reduced size compared to similar systems. Each identical GARI instrument consists of a two cerium-doped gadolinium aluminum gallium garnet (GAGG (Gd3(Al,Ga)5O12 :Ce)) scintillation detectors. The crystals have an energy resolution of 4.2% at 662 keV (specified by the manufacturer) compared to the 6.5% of traditional sodium iodide, and the material has found widespread use in medical imaging applications. GAGG is also unique in the fact that it is rugged (resistant to harsh environments) and one of the few non-hygroscopic scintillators available. GARI’s objective is to study the on-orbit internal activation of the GAGG material and measure the performance of the silicon photomultiplier (SiPM) readouts over its 1-year mission. The combined detectors measure the gamma-ray spectrum over the energy range of 0.02 - 8 MeV. The GARI mission payoff is a space-qualified compact, high-sensitivity gamma-ray spectrometer with improved energy resolution relative to previous sensors. Applicable studies in solar physics and astrophysics include solar flares, Gamma Ray Bursts, novae, supernovae, and the synthesis of the elements. Department of Defense (DoD) and security applications are also possible. Construction of the GARI instruments has been completed, and both instruments are being integrated onto their respective platforms. Both instruments are expected to launch in December of 2021 onboard STP-H7 and STP-H8. This work discusses the objectives, design details and mission concept of operations of the GARI spectrometers.

We present the design of the Spectroscopic Ultraviolet Multi-object Observatory (SUMO), a small satellite mission concept for astrophysics research. SUMO's science instrument is a multi-object spectrograph based on a customized digital micromirror device (DMD). Like other DMD-based spectrographs, SUMO employs parallel imaging and spectroscopic channels. The imaging channel operates in the NUV range and covers a field of view of 2.5 square degrees, with a spatial resolution of 5 arcseconds. The spectrograph channel is designed to achieve a resolving power of R~2500, operating in the range of 140 - 200 nm. The imaging and spectroscopic channels employ a CCD detector and a microchannel plate detector, respectively. Recent advances in satellite bus technology and a wave of successful NASA-funded technology development programs allow SUMO to achieve an effective area comparable to much larger missions of the past.

Arcus is an innovative MIDEX-class photon-counting X-ray spectroscopy mission. Due to the nature of the sources that Arcus will focus on, observations can be many tens of kiloseconds (ks) long. The resulting spectral images are reconstructed on the ground to remove measured pointing and instrument deflection effects that take place over that time, achieving a higher resolution than would be possible without removing these effects. Arcus’s 12 m focal length grazing incidence optics are separated from the detectors by a 10.8 m long by Ø1.85 m, onorbit deployable boom. This paper describes an implementation of an internal aspect sensor that uses flight tested commercial off the shelf (COTS) components to measure linear deflection from one end of that boom to the other to achieve a better than 22 micron resolution (3σ) correction for that motion, meeting the required performance that Arcus needs to maintain its achieve its imaging resolution.

The Normal-incidence Extreme Ultraviolet Photometer (NExtUP) is a smallsat mission concept designed to measure the EUV radiation conditions of exoplanet host stars, and F-M type stars in general. EUV radiation is absorbed at high altitude in a planetary atmosphere, in the exosphere and upper thermosphere, where the gas can be readily heated to escape temperatures. EUV heating and ionization are the dominant atmospheric loss drivers during most of a planet’s life. There are only a handful of accurately measured EUV stellar fluxes, all dating from Extreme Ultraviolet Explorer (EUVE) observations in the ‘90s. Consequently, current models of stellar EUV emission are uncertain by more than an order of magnitude and dominate uncertainties in planetary atmospheric loss models. NExtUP will use periodic and aperiodic multilayers on off-axis parabolic mirrors and a prime focus microchannel plate detector to image stars in 5 bandpasses between 150 and 900°A down to flux limits two orders of magnitude lower than reached by EUVE. NExtUP may also accomplish a compelling array of secondary science goals, including using line-of-sight absorption measurements to understand the structure of the local interstellar medium, and imaging EUV emission from energetic processes on solar system objects at unprecedented spatial resolution. NExtUP is well within smallsat weight limits, requires no special orbital conditions, and would be flown on a spacecraft supplied by MOOG Industries. It draws on decades of mission heritage expertise at SAO and LASP, including similar instruments successfully launched and operated to observe the Sun.

The Gamow Explorer will use Gamma Ray Bursts (GRBs) to: 1) probe the high redshift universe (z < 6) when the first stars were born, galaxies formed and Hydrogen was reionized; and 2) enable multi-messenger astrophysics by rapidly identifying Electro-Magnetic (IR/Optical/X-ray) counterparts to Gravitational Wave (GW) events. GRBs have been detected out to z ~ 9 and their afterglows are a bright beacon lasting a few days that can be used to observe the spectral fingerprints of the host galaxy and intergalactic medium to map the period of reionization and early metal enrichment. Gamow Explorer is optimized to quickly identify high-z events to trigger follow-up observations with JWST and large ground-based telescopes. A wide field of view Lobster Eye X-ray Telescope (LEXT) will search for GRBs and locate them with arc-minute precision. When a GRB is detected, the rapidly slewing spacecraft will point the 5 photometric channel Photo-z Infra-Red Telescope (PIRT) to identify high redshift (z < 6) long GRBs within 100s and send an alert within 1000s of the GRB trigger. An L2 orbit provides < 95% observing efficiency with pointing optimized for follow up by the James Webb Space Telescope (JWST) and ground observatories. The predicted Gamow Explorer high-z rate is <10 times that of the Neil Gehrels Swift Observatory. The instrument and mission capabilities also enable rapid identification of short GRBs and their afterglows associated with GW events. The Gamow Explorer will be proposed to the 2021 NASA MIDEX call and if approved, launched in 2028.

The Europa Clipper Ultraviolet Spectrograph (Europa-UVS) is the sixth in the line of Alice/UVS spectrographs from Southwest Research Institute (SwRI). The heart of the instrument is a far-UV sensitive microchannel plate detector system. This detector consists of a z-stack of three borosilicate glass microchannel plates, with resistive and secondary emissive layers deposited via an atomic-layer deposition (ALD) process. The resulting detector has orders of magnitude longer lifetime given comparable fluences than previously flown MCP detectors, as well as reduced sensitivity to gamma-ray induced background noise. This detector is also the first instance of a curved borosilicate glass microchannel plate z-stack undergoing thermal vacuum testing in a flight-like environment, raising the TRL of the system to 6. The flight model detector was bench tested at Sensor Sciences and delivered to the Europa-UVS project in July 2020. Further bench tests were undertaken at SwRI after delivery, followed by thermal vacuum testing in December 2020. The results of these tests are presented herein.

We present progress in the development of sealed tube imaging detectors using the cross strip (XS) readout and microchannel plates activated by atomic layer deposition (ALD). Microchannel plate detectors are important tools for photon counting spectroscopy and imaging in astronomical, biological, high energy physics and remote sensing applications ^1-15. Current UV instrument concepts under study for NASA including the Large UV/Optical/IR Surveyor (LUVOIR)¹⁶, the Habitable Exoplanet Imaging Mission (HABEX)¹⁶, and Cosmic Evolution Through UV Spectroscopy (CETUS)16 have also envisaged MCP detector systems. Many of these address sensing beyond 105 nm, and require large area high resolution sealed tube devices for ease of integration and handling. To satisfy these we are implementing high temperature co-fired ceramic (HTCC) cross-strip anode readouts in sealed tubes coupled with encoding electronics that enable high spatial resolution (<20 μm) at low gain (106) and over large formats (5 to 10 cm) with high dynamic range (< 5 MHz). ALD microchannel plates have also been incorporated to deliver stable gain and imaging performance with low background (<0.05 events cm^-2sec^-1) and reduced sensitivity to gamma ray background.

For future astronomical applications we have been developing cross-strip anodes with electronic readouts integrated with large format (≥ 50 mm) sealed tubes and photocathodes covering the UV and optical regimes. These large format devices will be important for the next generation of moderate and large NASA astrophysics instruments under study (e.g. LUVOIR, HabEx, CETUS), as well as ground based focal plane instruments. Microchannel plates (MCPs) are used as electron multipliers in these devices. They amplify the detected photon signal to a charge cloud on order of a million electrons, which is then sensed through the imaging readout. A recent enhancement comes by way of incorporating resistive and secondary emissive layers to borosilicate capillary arrays utilizing atomic layer deposition (ALD) processing techniques. The borosilicate substrates are more robust than traditional MCPs, allowing for large formats (20 x 20 cm), while also supporting 10-micron pores (capillaries). We have successfully integrated this type of MCP into 50 mm aperture sealed tube devices for the first time. These devices show stable, uniform gain, and can provide very good event timing accuracy. Spatial resolution of better than 20 microns can be achieved with these MCPs, providing more than 2k x 2k resolution elements for a 50mm device. Compared with the current generation of MCPs, the ALDborosilicate MCPs have shown an order of magnitude increase in lifetime stability gain retention within the vacuum sealed device and long-term preservation of the photocathode efficiency.

Incom Inc. is developing and commercializing microchannel plate (MCP) electron multiplier devices made from leadfree glass capillary array (GCA) substrates that are functionalized using atomic layer deposition (ALD) thin film coating technology. Notable benefits over conventional lead-oxide based MCP technology are larger MCP size, high and stable gain, low dark counts and gamma-ray sensitivity, improved mechanical and thermal stability, and the unique ability to tune the MCP resistance and electron amplification characteristics over a much wider range and independently from the glass substrate. Incom now routinely produces ALD-GCA-MCPs with 10 and 20 m pore size at MCP dimensions up to 20 cm x 20 cm. ALD-GCA-MCPs are used for photon counting and charged particle detection in analytical instruments, high energy physics, nuclear physics, and space science applications. For future astronomical applications such as LUVOIR, HabEx, and CETUS, large-area, high-performance MCP electron amplifiers are paired with high-performance cross-strip readout systems and integrated into large format (≥ 50 mm sq.) photodetectors operating in the UV and optical regimes. Incom’s large area ALD-MCP-GCA technology is critical for realizing such large format photodetectors. In this paper, we provide a brief update on recent developments addressing the quality of the glass substrate as well as the thermal stability of the MCPs.

Slated to launch in early 2023, Supernova Remnants and Proxies for Re-Ionization Testbed Experiment (SPRITE) is the first NASA funded 12U astrophysics CubeSat payload and the first orbital astrophysics instrument to operate in the windowless Far-ultraviolet (1000 - 1750 Å) since the deployment of HST-COS. SPRITE is an imaging spectrograph with 10 arcsecond angular resolution, breaking new ground with scientific observations enabled by a compact microchannel plate detector system and advanced protected eLiF mirror coatings baselined for the LUVOIR Surveyor. To provide flexibility and customizability the spacecraft bus and spectrograph are all being designed in house at the Laboratory for Atmospheric and Space Physics. SPRITE features several unique mechanical subsystems such as the pump/purge system for the hermetically sealed detector housing, the release mechanism for the detector door, the release mechanism for the solar array, the solar panel design, and compact rectangular telescope. SPRITE's mechanical design meets all science requirements, the CubeSat specific requirements of commercial 12U dispenser systems, and NASA orbital debris limits. We present an overview of the design and development of the mechanical systems and mechanisms for SPRITE prior to the comprehensive design review (CDR).

The INtegral Field Ultraviolet Spectroscopic Experiment (INFUSE), a sounding rocket payload under development at the University of Colorado Laboratory for Atmospheric and Space Physics, will be the first far ultraviolet (1000 - 2000 A° ) integral field spectrograph (IFS) in space. With access to part of the Lyman ultraviolet (1000 - 1216 A° ), INFUSE will study spectral emission lines such as O VI in extended objects at greater spatial resolution and grasp 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 of aligning the instrument, with a focus on the method by which the 26 gratings are aligned with the image slicer. Additionally, we examine the challenges presented by mounting and coating the large primary mirror and the steps taken to ensure that the mirror remains stable in flight. The first flight of INFUSE is projected for Spring 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.

SPRITE, the first NASA-funded 12U CubeSat for astrophysics science, will use an ultraviolet light spectrograph with a photon-counting microchannel plate detector to provide spatial and spectral data on the light observed from low-redshift galaxies, active galactic nuclei, and shocked emission features of supernova remnants in the 1000Å − 1750Å bandpass. This proceedings describes recent progress on the design, implementation, and experimental evaluation of SPRITE’s electrical subsystems, particularly the high voltage power supply required to drive the microchannel plate detector. Measured experimental results for the commercial high voltage power supply module and the electronics board designed and built to control it are presented and discussed. The average voltage and voltage ripple of the high voltage power supply output when driving a resistive load that simulates the load anticipated on orbit due to the detector and a parallel voltage divider are presented. Planned revisions to the SPRITE electronics design are discussed, including modifications to be made to the high voltage power supply control board and the addition of an electronics board to handle all the interfaces between the command and data handling subsystem and the instrument electrical subsystems. SPRITE is planned to launch in early 2023 and will provide on-orbit data for the microchannel plate detector and other technologies onboard that are candidates for use on future large missions.

The Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SIS- TINE) sounding rocket payload is an f /30 imaging spectrograph designed to measure the far ultraviolet (1000 - 1275 and 1300 - 1565 Å) output of exoplanet host stars. The instrument is composed of an f /14 Cassegrain telescope with a 500 mm diameter primary mirror feeding a 2.1x magnifying spectrograph. Light is dispersed by a blazed, holographically ruled grating, reflected off a powered fold mirror, and recorded on a large format microchannel plate (MCP) detector. The instrument incorporates enhanced LiF (eLiF) protected aluminum on the primary, secondary, and fold mirrors. The secondary mirror also has a protective AlF₃ capping layer, applied using atomic layer deposition (ALD). The detector is composed of two windowless 113 x 42 mm segments with cross delay line anodes and CsI photocathodes. The detector utilizes ALD processed borosilicate plates, and additionally serves as a flight test for detectors on future astrophysics missions. The instrument reaches a peak effective area of 99.9 cm2 at 1145 Å. The assembly of SISTINE-2 included the application of new photocathodes to the detector, showing improvements in quantum efficiency after laboratory tests. SISTINE-2 will observe the nearby F star Procyon in late 2021, making the first simultaneous observation from O VI through C IV and setting new empirical constraints on the radiation fields experienced by planets orbiting mid-F stars.

The origin of the cosmic diffuse gamma-ray (CDG) background in the 0.3 – 30 MeV energy range is a mystery that has persisted for over 40 years. The Mini Astrophysical MeV Background Observatory (MAMBO) is a CubeSat mission 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 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. Enabling technologies include the use of compact silicon photomultipliers (SiPMs) for scintillator readout, and a tagged calibration source for real-time gain adjustment. We describe the MAMBO instrument, readout, commercial 12U bus systems, and mission concept in detail, including simulations and laboratory measurements demonstrating the key measurement concept.

The Rockets for Extended-source X-ray Spectroscopy (tREXS) are a funded series of sounding rocket instruments to detect diffuse soft X-ray emission from astrophysical sources. The first launch of tREXS is scheduled for Q4 2021, with a goal to observe the Cygnus Loop supernova remnant. tREXS house a four-channel grating spectrometer that uses passive, mechanical focusers, arrays of reflection gratings, and an extended focal plane based around Teledyne CIS 113 CMOS sensors. We present here an update on the instrument design, build, and calibrations in advance of the launch later this year.

The FOXSI-4 sounding rocket will fly a significantly upgraded instrument in NASA's first solar are campaign. It will deploy direct X-ray focusing optics which have revolutionized our understanding of astrophysical phenomena. For example, they have allowed NuSTAR to provide X-ray imaging and IXPE (scheduled for launch in 2021) to provide X-ray polarization observations with detectors with higher photon rate capability and greater sensitivity than their predecessors. The FOXSI sounding rocket is the first solar dedicated mission using this method and has demonstrated high sensitivity and improved imaging dynamic range with its three successful flights. Although the building blocks are already in place for a FOXSI satellite instrument, further advances are needed to equip the next generation of solar X-ray explorers. FOXSI-4 will develop and implement higher angular resolution optics/detector pairs to investigate fine spatial structures (both bright and faint) in a solar are. FOXSI-4 will use highly polished electroformed Wolter-I mirrors fabricated at the NASA/Marshall Space Flight Center (MSFC), together with finely pixelated Si CMOS sensors and fine-pitch CdTe strip detectors provided by a collaboration with institutes in Japan. FOXSI-4 will also implement a set of novel perforated attenuators that will enable both the low and high energy spectral components to be observed simultaneously in each pixel, even at the high rates expected from a medium (or large) size solar are. The campaign will take place during one of the Parker Solar Probe (PSP) perihelia, allowing coordination between this spacecraft and other instruments which observe the Sun at different wavelengths.

Scheduled to launch in late 2021 the Imaging X-ray Polarimetry Explorer (IXPE) is a Small Explorer Mission designed to open up a new window of investigation -- X-ray polarimetry. The IXPE observatory features 3 identical telescope each consisting of a mirror module assembly with a polarization-sensitive imaging x-ray detector at its focus. An extending beam, deployed on orbit provides the necessary 4 m focal length. The payload sits atop a 3-axis stabilized spacecraft which among other things provides power, attitude determination and control, commanding, and telemetry to the ground. During its 2-year baseline mission, IXPE will conduct precise polarimetry for samples of multiple categories of x-ray sources, with follow-on observations of selected targets. IXPE is a partnership between NASA and the Italian Space Agency (ASI).

The Imaging X-ray Polarization Explorer (IXPE) is a NASA Small Explorer mission to measure the polarization of astrophysical objects in the X-ray (2-8 keV) band set for launch in 2021. The calibration of three three flight optics took place in June-Aug 2020 at the NASA/MSFC Stray Light Test Facility (SLTF), a 100-meter vacuum beam line. One flight telescope (optic + detector: Mirror Module Assembly [MMA] + Detector Unit [DU]) and the flight spare were also calibrated at SLTF. We describe the calibration program and present results, including the measurement of the PSF and effective area of the MMAs at several energies, and the response of the telescope to incident polarized X-rays, including measurement of the Detector Modulation Factor (the response of the telescope to 100% polarized X-rays) and the telescope spurious modulation (response to an unpolarized X-ray source).

The LargE Area Burst Polarimeter (LEAP) will radically improve our understanding of some of the most energetic phenomena in our Universe by exposing the underlying physics that governs astrophysical jets and the extreme environment surrounding newborn compact objects. LEAP will do this by making the highest fidelity polarization measurements to date of the prompt gamma-ray emission from a large sample of Gamma-Ray Bursts (GRBs). The science objectives are met with a single instrument deployed as an external payload on the ISS – a wide FOV Compton polarimeter that measures GRB polarization from 50–500 keV and GRB spectra from ~10 keV to 5 MeV. LEAP measures polarization using seven independent polarimeter modules, each with a 12x12 array of optically isolated high-Z and low-Z scintillation detectors readout by individual PMTs. LEAP is one of two NASA Missions of Opportunity proposals that are currently in a Phase A Concept Study, with a final selection due later this year.

The LargE Area burst Polarimeter (LEAP) is one of two NASA Missions of Opportunity proposals that are currently in a Phase A Concept Study, with a final selection due later this year. It is a wide Field of View (FoV) Compton polarimeter designed to study Gamma-Ray Burst (GRB) polarization over the energy range from 50- 500 keV and to measure GRB spectra in the range from 20 keV - 5 MeV. During the Phase A Concept Study, lab measurements were conducted with a small-scale (5x5) prototype polarimeter module. This included both spectral and polarization measurements with laboratory calibration sources. Here the prototype measurements and the comparisons made with simulations of the prototype detector are described. These results demonstrate the basic functionality of the LEAP design.

Complementary metal–oxide–semiconductor (CMOS) sensors may offer improved performance compared to the charge-coupled devices common in X-ray satellites. We demonstrate x-ray detection in the soft x-ray band (250 to 1700 eV) by a commercially available back-illuminated CMOS sensor using the Advanced Photon Source at Argonne National Laboratory. While operating the device at room temperature, we measure energy resolutions (FWHM) of 48 eV at 250 eV and of 83 eV at 1700 eV, which are comparable to the performance of the CCD on Chandra and Suzaku.

The High-Resolution Energetic X-ray Imager SmallSat Explorer (HSE) is a proposed wide-field, hard X-ray (3-300 keV) coded aperture telescope. Operating a closely tiled array of pixelated CdZnTe (CZT) detectors, HSE seeks to rapidly localize short gamma ray bursts (GRBs) resulting from neutron star and black hole mergers and search for faint undiscovered black hole low mass x-ray binaries. The spectral signatures of these phenomena fall off as a power law, thereby motivating the improvement of HSE’s hard x-ray band coverage at lower energies. This is achievable by tuning HSE’s Nuclear Spectroscopic Telescope Array (NuSTAR) ASIC detector readout and operating in a charge pumping mode. This can extend energy band coverage to as low as 2-3 keV, but requires careful independent tuning of each of the instrument’s ASIC devices. An optimization procedure for efficiently tuning the detector readout via commandable ASIC registers is reported.

Next-generation X-ray observatories, such as the Lynx X-ray Observatory Mission Concept, will require detectors with high quantum efficiency (QE) across the soft X-ray band to observe the faint objects that drive their mission science cases. Hybrid CMOS Detectors (HCDs), a form of active-pixel sensor, are promising candidates for use on these missions because of their faster read-out, lower power consumption, and greater radiation hardness than detectors used in the current generation of X-ray telescopes. In this work, we present QE measurements of a Teledyne H2RG HCD. These measurements were performed using a gas-flow proportional counter as a reference detector to measure the absolute flux incident on the HCD. We find an effective QE of 95:0 ± 1:1% at the Mn ∝/Kβ lines (at 5.9 and 6.5 keV), 98:5 ± 1:8% at the Al Ka line (1.5 keV), and 85:0 ± 2:8% at the O K∝ line (0.52 keV).

The Ultraviolet Transient Astronomical Satellite (ULTRASAT) is a scientific UV space telescope that will operate in geostationary orbit. The mission, targeted to launch in 2024, is led by the Weizmann Institute of Science (WIS) in Israel and the Israel Space Agency (ISA). Deutsches Elektronen Synchrotron (DESY) in Germany is tasked with the development of the UV-sensitive camera at the heart of the telescope. The camera's total sensitive area of ≈90mm x 90mm is built up by four back-side illuminated CMOS sensors, which image a field of view of ≈200 deg². Each sensor has 22:4 megapixels. The Schmidt design of the telescope locates the detector inside the optical path, limiting the overall size of the assembly. As a result, the readout electronics is located in a remote unit outside the telescope. The short focal length of the telescope requires an accurate positioning of the sensors within ±50 μm along the optical axis, with a flatness of ±10 μm. While the telescope will be at around 295K during operations, the sensors are required to be cooled to 200K for dark current reduction. At the same time, the ability to heat the sensors to 343K is required for decontamination. In this paper, we present the preliminary design of the UV sensitive ULTRASAT camera.

The focal-plane camera on the Rockets for Extended-source X-ray Spectroscopy (tREXS) is a large-area detector array that takes advantage of the large-format, 3-side-buttable design of the Teledyne e2v Vega-CIS113 CMOS sensor. This paper discusses the initial design of the focal plane camera, results from testing that identified read noise performance issues, mechanical and electrical challenges of this initial design, and supply chain problems. The changes to the focal plane camera that were made due to these challenges are then presented, along with the final flight camera that has been designed to optimize noise performance and be able to be built within the schedule constraints of the tREXS mission.

Up to 2020, the Chandra ACIS gain has been calibrated using the External Calibration Source (ECS). The ECS consists of an ⁵⁵Fe radioactive source and is placed in the ACIS housing such that all chips are fully illuminated. Since the radioactive source decays over time with a half-life of 2.7 years, count rates are becoming too low for gain calibration. Instead, astrophysical calibration sources will be needed, which do not fill and illuminate the entire field of view. Here, we determine the dominant spatial components of the gain maps through principal component analysis (PCA). We find that, given the noise levels observed today, all ACIS gain maps can be sufficiently described by just a few (often only one) spatial components. We conclude that illuminating a small area is sufficient for gain calibration. We apply this to observations of the astrophysical source Cassiopeia A. The resulting calibration is found to be accurate to 0.6% in at least 68% of the chip area, following the same definition for the calibration accuracy that has been used since launch.

Modern grating manufacturing techniques suffer from inherent issues that limit their peak efficiencies. We describe work in collaboration with the Nanofabrication Lab at Penn State University to design and characterize etched silicon gratings optimized for the extreme (EUV; 10 { 90 nm) and far ultraviolet (FUV; 90 { 180 nm) bandpasses. We develop this technology by fabricating a variety of gratings that operate over these bandpasses. We present analyses for two different grating designs in this work. The first is an FUV echelle that has similar parameters to the grating own on the CHESS sounding rocket. CHESS was an FUV spectrograph that utilized a mechanically ruled echelle grating. We compare the efficiency and in-instrument performance of the gratings, finding a ~ 50% increase in groove efficiency and an 80% decrease in inter-order scatter for the etched gratings compared to their mechanically ruled counterpart. The FUV echelle improvements can ultimately benefit the faint source sensitivity and high-resolution performance of future UV observatories, such as LUVOIR, by reducing the non-uniform inter-order backgrounds that have historically plagued echelle spectrographs. We additionally provide a description of how this lithographic process can be extended to gratings with holographic solutions by discussing our procedure for generating a map of groove traces from holographic recording parameters. This discussion is provided in the context of the creation of a grating sample that was developed in support of the ESCAPE Small Explorer Phase A study.

The Far-UV Off Rowland-circle Telescope for Imaging and Spectroscopy (FORTIS) has been successful in maturing technologies for carrying out multi-object spectroscopy in the far-UV, including: the successful implementation of the Next Generation of Microshutter Arrays; large-area microchannel plate refetectors; and an aspheric dual-order" holographically ruled diffraction grating with curved, variably-spaced grooves with a laminar (rectangular) profile. These optical elements were used to construct an efficient and minimalist two-bounce" spectro-telescope in a Gregorian configuration. However, the susceptibility to Lyman alpha (Ly) scatter inherent to the dual order design has been found to be intractably problematic, motivating our move to an Off-Axis" design. OAxFORTIS will mitigate its susceptibility to Ly by enclosing the optical path, so the detector only receives light from the grating. The new design reduces the collecting area by a factor of 2, but the overall effective area can be regained and improved through the use of new high efficiency reflective coatings, and with the use of a blazed diffraction grating. This latter key technology has been enabled by recent advancements in creating very high efficiency blazed gratings with impressive smoothness using electron beam lithography and chemical etching to create grooves in crystalline silicon. Here we discuss the derivation for the OAxFORTIS grating solution as well as methods used to transform the FORTIS holographic grating recording parameters (following the formalism of Noda et al.1974a,b), into curved and variably-spaced rulings required to drive the electron beam lithography write-head in three dimensions. We will also discuss the process for selecting silicon wafers with the proper orientation of the crystalline planes and give an update on our fabrication preparations.

The Ultraviolet Micromirror Imaging Spectrograph (UMIS) will be the first UV integral field spectrograph (IFS) to use micro-electro-mechanical systems (MEMS) micromirrors, specifically in the form of two-axis analog micromirror arrays (AMAs). This novel application of AMAs will increase both the flexibility and spectral multiplexing efficiency of UMIS relative to currently available instruments. AMAs are already a widely used technology in telecommunications; this study investigated and proved their suitability for high performance scientific instrumentation. Suitability was determined through evaluation of the individual micromirror component on a custom optical bench set up. The following metrics were evaluated: temporal stability, thermal drift and stability, large-scale linear response and pointing precision. The tests demonstrated that under conditions of 20C - 40C the micromirror's temporal stability, thermal stability, large-scale linear response and pointing precision were stable within the required range. The micromirror's performance, as measured in this experiment, meets the requirements specified in UMIS design and indicates feasibility for future flight instruments. We present the experiment test setup and results in the context of the development of the UMIS testbed instrument.

Observations of astronomical objects in the far ultraviolet (FUV wavelengths span 900-1800 A) from earth's orbit has been impeded due to bright Lyman- geocoronal emission. The Johns Hopkins Rocket Group is developing a hydrogen absorption cell that would act as a narrow band Lyman- rejection filter to enable space-based photometric observation in bandpasses that span over the Lyman ultraviolet region shortward of the geocoronal line. While this technology has been applied to various planetary missions with single element photomultiplier detectors it has yet to be used on near earth orbiting satellites with a multi-element detector. We are working to develop a cell that could be easily incorporated into future Lyman ultraviolet missions. The prototype cell is a low-pressure (~few torr) chamber sealed between a pair of MgF2 windows allowing transmission down to 1150 A. It is filled with molecular hydrogen that is converted to its neutral atomic form in the presence of a hot tungsten lament, which allows for the absorption of the Lyman- photons. Molecular hydrogen is stored in a fully saturated non-evaporable getter module (St707TM), which allows the cell pressure to be increased under a modest application of heat (a 20 degree rise from room temperature has produced a rise in pressure from 0.6 to 10 torr). Testing is now underway using a vacuum ultraviolet monochromator to characterize the cell optical depth to Lyman- photons as functions of pressure and tungsten filament current. We will present these results, along with a discussion of enabled science in broadband photometric applications.

We are presenting the result of the microshutter arrays for multi-object spectroscopy. Microshutter arrays are MEMS technology devices that are 2D programmable field masks for object selection in the sparsely populated fields. This next generation microshutters are based on the first generation of the microshutter arrays developed for the James Webb Space Telescope Near-Infrared Spectrometer (JWST NIRSpec) we developed new fabrication process that allowed to build fully electrostatic microshutter arrays. The microshutter arrays based on this new development have been successfully demonstrated in the FORTIS project sounding rocket flight. We are currently in the process of expanding the fabrication process to large format microshutter arrays designed for the use on the future NASA flagship missions such as HabEx and LUVOIR.

Diffraction gratings used in ultraviolet astronomical spectrographs have been made using mechanical ruling or interference lithography. However, required performance for newly developed EUV (10-90 nm) and FUV (100-180 nm) spectrographs can benefit from groove densities, blaze angles, and low-scatter enabled with electron-beam lithography patterning and chemical etching. We report on the fabrication of custom grating prototypes developed at the Nanofabrication Laboratory at Penn State University. The gratings in development for the ESCAPE NASA Small Explorer (Univ. of Colorado/Boulder) involve writing specific patterns of curved grooves with variable line density on flat substrates. The design of the grating within the DEUCE sounding rocket payload involves writing straight grooves on a spherically curved substrate. All gratings are subsequently etched to achieve the specified blaze in the silicon. These efforts are enabling new applications in the field of astronomical UV spectroscopy.

We outline progress in the development of novel perforated X-ray attenuators for fine-pitch (50{400 mm) spectro- scopic X-ray detectors composed of hundreds or thousands of pixels. Simple attenuators made of solid slabs of material drastically suppress the low energy signal which can reduce the scientific value of observations. By contrast, perforated attenuators can be designed to suit the shape and intensity of the expected incident spectrum, thus allowing a wider spectral range to be reliably measured. This is achieved by fabricating regions of different thicknesses on spatial scales smaller than the pixels and replicated over grids of hundreds or thousands of pixels. Perforated attenuators can enhance the scientific value of observations because they can enable multiple physical processes that dominate different regions of the X-ray spectrum to be observed simultaneously, e.g. lower energy thermal and higher energy non-thermal processes in solar flares. For this reason, a perforated attenuator will be own onboard the FOXSI-4 sounding rocket as part of a solar are campaign. In this paper we describe specific designs and fabrication methods and demonstrate the concept by measuring the transmission profiles of a number of prototypes. We conclude that such designs can be reliably produced with current fabrication techniques including microlithography and macroporous silicon technology, and can achieve transmission profiles desirable for solar are observations. Work described in this paper is the subject of pending patents.

X-Ray collimators based on MCPs (Micro Channel Plates) are composed of glass capillaries in a dense array. It is a known technology capable of producing large areas with high aspect-ratio holes; however, the choice of glass for the collimator material has some drawbacks. These collimator perform poorly at energies above <10 keV. We are developing MCPs for this energy range by adding a wall-coating that is comprised of a conformal several-micrometerthick metal layer. All fabrication used techniques can be applied to large area glass capillary arrays. The main micro-fabrication challenge is that glass capillary arrays have extreme high aspect ratios, which requires that all fabrication methods have to be optimized for these aspect ratios. The fabrication sequence is a two-step process: (i) coating of array walls by metal ALD (atomic layer deposition) and (ii) metal (we use gold and copper) electroplating. We successfully develop homogenous Pt coating by ALD. Since ALD is an inherently slow process; depositing thick conducting films is extremely time-consuming. However, electroplating requires a good conducting film. A 200 nm thick highly conducting film can be plated within 20 min. Ni is a standard starting layer for gold or copper electroplating The combination of Pt ALD acting as a starting catalyst for the electroless nickel then enables to possibility of electroplating various thick metal coatings. Copper and gold films were electroplated onto the Ni conformally covering the MCP walls. One possible application of these metal coated MCPs would be the large area detector for the STROBE-X (Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays) mission, a probe-class mission concept currently under consideration by NASAke.

We describe two techniques to verify and improve the energy calibration of pixelated solid-state X-ray detectors by specifically analyzing multiple-pixel events. There are two primary types of multiple-pixel events. In fluorescent events, some of the incident photon energy is re-emitted as a Cd or Te characteristic X-ray, with mean free path (~80-200 μm) comparable to the pixel pitch. Deposition of the fluorescence photon commonly occurs in an adjacent pixel. Isolating fluorescent double-pixel events provides low-energy (<15 keV) escape lines not intrinsic to the source. These lines reveal that the non-linearity of the gain at low energies is larger than previously thought, and can now be corrected. In charge-shared events, the cloud of deposited charge from one incident photon spreads across pixel boundaries. This causes charge loss due to variation in applied field strength within inter-pixel regions. The charge loss is a smooth function of the ratio between component energies, with more loss seen when a photon hits closer to the boundary and its energy is more evenly split. Characterization of this energy-split-dependent loss lets us extrapolate ‘split event’ behavior below the signal threshold. We can then verify consistency of the non-linear gain calibration at the lowest energies.

The thermal analysis of the SPRITE astrophysics CubeSat will be presented. As a far-UV instrument with a precision telescope, thermal control is essential to maintain instrument focus as well as to limit molecular contamination on the optics. A thermal model was created in Thermal Desktop to simulate the conductive and radiative heat transfer effects the components will experience during the mission. Mission specific orbital and attitude parameters were also incorporated to increase model fidelity. Several model parameters were created to simulate the most extreme temperature variations SPRITE would experience. A 'cold' case and a 'hot' case were created for charging and science attitudes, utilizing the bounds of recorded Earth albedo, solar flux, and IR Planetshine values. The results of these models are presented and outline the passive and active thermal control steps that will be employed by the SPRITE team to meet requirements.

The Colorado Ultraviolet Transit Experiment (CUTE) is a 6U cubesat housing a Cassegrain telescope and a nea rultraviolet (NUV) spectrograph designed to study the composition and mass-loss rates of exoplanet atmospheres. This instrument covers a bandpass of 250 - 330 nm with a peak effective area of ~28 cm² and a resolving power of ~2000. The instrument focal plane consists of a back illuminated CCD driven by clocking and readout electronics developed at the Laboratory for Atmospheric and Space Physics (LASP). Special consideration is given to achieving low noise readout due to typical observation signal levels and time constraints of exoplanet transit observations. Additionally, the electronics driving the CCD are space constrained and designed to fit in a cubesat 1/2U volume. Prior to installation in the flight instrument the detector system parameters are optimized and characterized at LASP in a custom ultraviolet detector test chamber. Engineering and technical details including system gain, quantum efficiency, and read noise are discussed. We present the development, optimization, and characterization results of the CCD and associated readout electronics developed for the CUTE instrument.

The Rockets for Extended-source X-ray Spectroscopy (tREXS) are a series of NASA funded suborbital rockets that will make large field-of-view observations of the diffuse soft X-ray emission from the Cygnus Loop and Vela supernova remnants. The tREXS focal plane camera is made up of an array of 11 Vega-CIS113 CMOS detectors, with a 12th as the zero-order detector. To optimize the performance of the camera, a test setup was developed where a single CMOS detector can be characterized to determine which settings have the highest impact on detector performance characteristics such as readout noise. This paper will discuss this test setup, the initial testing that has occurred using an engineering grade detector, and the initial results on how changing bias potentials and pixel timings impact the readout noise. Improvements that will be made to the final focal plane camera electronics based on the findings in the initial testing will also be discussed.

The Rocket for Extended-Source X-ray Spectroscopy (tREXS) is a suborbital rocket payload that is designed to obtain the most highly resolved soft X-ray emission spectrum from the Cygnus Loop to date. This research will discuss the development and implementation of a guidance system that will replace the traditional pointing mechanism for a sub-orbital payload. Normally the pointing requirement for a sub-orbital flight is achieved using a NSROC altitude control system, which uses an ST5000 star tracker co-aligned with the X-ray optic. In tREXS design there is not space to use this star tracker; therefore, a design has been made that utilizes a side looking ST5000 to acquire the target field and an aspect camera for fine pointing. The aspect camera will stream frames of the target star field, that will be processed by the guidance algorithm. The algorithm will relay where to position the payload to target the Cygnus Loop.

We report on the continued development of multilayer optical coatings on back-illuminated silicon imaging sensors in order to enhance the functionality of such systems at ultraviolet wavelengths. This includes the development metal-dielectric filter structures to enable solar-blind operation, and graded thickness coatings to tune the spatial response of a detector system to the dispersion of a spectrometer. Such systems can maintain the high internal quantum efficiency afforded by the delta-doping process utilized at NASA JPL, while also providing long-wavelength rejection or a spatially optimized efficiency (or both). We present the characterization of CCD and CMOS image sensors incorporating these processes, and describe the atomic layer deposition coating processes. Such detectors are currently being developed for ground-based high energy physics applications as well as NASA orbital astrophysics instruments operating at wavelengths shorter than 200 nm.

We describe new results from the ALD application of fluoride mirror coatings that offer high performance over the UV bandpass (90 -235 nm). Such coatings provide an alternative to PVD and have broad applications in the UV, particularly for UV astronomy. The fabrication process is carried out at the JPL Microdevices Lab, beginning with an optically thick layer of evaporated Al which is capped with an ALD protective fluoride layer, such as LiF. Capping the Al is necessary because it otherwise oxidizes quickly and loses significant reflectance. Immediately before applying the ALD protective thin film we use atomic layer etching (ALE) to remove any native oxides that manifested after Al deposition. FUV reflectivity measurements are conducted in the vacuum ultraviolet space hardware characterization facilities at the University of Colorado at Boulder. We present the results of reflectivity testing of five samples from 90 to 230 nm; samples include Al+LiF (3), Al+LiF+MgF₂ (1), and Al+LiF+LiF₃ (1). We vary the number of ALE and ALD cycles across several Al+LiF samples to begin exploring the optimal amount of etching and film thickness. Preliminary results confirm <80% reflectivity at 1200 Å with one Al+LiF sample yielding 86 ± 2%. Future work will include testing how layer thickness and ALD deposition temperature impact FUV reflectivity with a focus on optimizing reflectivity below Lyβ.

Observing cosmic sources in the medium-energy gamma-ray regime (~0.4 - 10 MeV) requires highly efficient instruments with high angular resolution and robust background rejection. Artificial single-crystal diamond detectors (SCDDs) are comparable to traditional silicon solid-state detectors (SSDs) in terms of energy range, energy resolution, and threshold levels. However, they exceed SSD performance with faster rise times, improved radiation hardness, and insensitivity to light and temperature. CeBr₃ scintillator is a high density, high Z material with fast rise times and good energy resolution ( 4% FWHM at 662 keV) make it a promising gammaray calorimeter. Here, we outline ongoing work by Southwest Research Institute (SwRI) to develop readout and data acquisition electronics to characterize SCDDs. Additional work is ongoing at Los Alamos National Laboratory to characterize CeBr3 scintillator detectors that are read out with silicon photomultipliers (SiPMs). Currently, an off the shelf ASIC system from PETsys Electronics (TOFPET2 ASIC),¹ developed for time-of-flight (ToF) positron emission tomography (PET), is used to record the CeBr₃ data. After characterization of the CeBr₃ and SCDDs, we plan to bring them together to form a prototype Compton telescope. Performance of the prototype will benchmark simulations of a functional Compton Telescope to predict the sensitivity of an optimized instrument for a satellite platform.

Arcus is an innovative MIDEX-class X-ray spectroscopy mission with 12 m focal length grazing incidence optics. The instrument has a 10.8 m long by Ø1.85 m, 4-longeron coilable boom with an enclosing sock. The boom, designed and built by Northrop Grumman, is included to enable launch in a fairing that is shorter than the operational length of the instrument. This paper outlines the process to select the boom type, design it to meet Arcus requirements, construct a flight-like engineering model, and test it to the expected environments. The team demonstrated that the 4-sided Arcus coilable boom offers a stiff, thermally stable platform that is precisely and repeatably deployable with a high packing density (compact stowage). This low-cost and low-risk solution permits the Arcus orbital X-ray observatory to use a focal length that greatly exceeds the limitations of the launch vehicle fairings. We offer comparisons to other boom designs, outline the design of this boom, its predecessors, the design of the sock, its deployment performance, and the results of its environmental testing.

Microshutter arrays are powerful tools enabling simultaneous spectroscopy of multiple objects within a single, crowded field-of-view. This technology is currently employed on the James Webb Space Telescope, and next-generation arrays are being proposed for future flagship missions such as LUVOIR and HabEx. For these future large missions, it is important to fully characterize the performance of the next-generation microshutter arrays in the lab, particularly in the ultraviolet range not probed with JWST. To this end, we have developed a laboratory testbed to measure the contrast between opened and closed shutters achievable with these devices.

Next-generation X-ray imaging missions require fast, low-noise detectors that can survive the harsh environment of space without significant loss of performance. As part of a detector development effort toward a mission such as Lynx, we report on the effects of proton exposure on the spectral performance, dark current and charge transfer efficiency of a back illuminated MIT Lincoln Laboratory CCID93. The CCD has 8 micron pixels and can be clocked with 2.5MHz pixel speeds with CMOS compatible voltage swings. The 40 MeV proton dose is chosen to represent typical on orbit exposure. Variations with charge injection, temperature, and clocking speed are explored. These results are compared with those of the front illuminated version of the same device.

Since its installation on the Hubble Space Telescope in 2009, the Cosmic Origins Spectrograph (COS) has obtained thousands of spectra in the ultraviolet. Most of these observations have used the far ultraviolet (FUV) channel. The microchannel plates in the FUV detector are subject to gain sag, resulting in a loss of sensitivity as a function of time, so the spectra are regularly repositioned to mitigate this effect. The original operations concept allowed space for spectra to be placed at five separate Lifetime Positions (LPs) on the detector, and the last of these will become operational in October 2021. Recent investigations into extending the operations of COS beyond 2025 have led to the realization that the instrument is capable of supporting additional LPs if operational changes are adopted. As a result, we have begun planning for taking data at LP6, which will use an area on the detector originally thought to be unavailable, beginning in 2022. Exploratory work for this effort began in late 2020, and additional characterization and calibration will continue over the next year. Here we discuss our plans for operating COS at LP6 and beyond.