Aspera is a NASA-funded UV SmallSat mission designed to detect and map warm-hot phase halo gas around nearby galaxies. The Aspera payload is designed to detect faint diffuse O VI emission at around 103.2 nm, satisfying the sensitivity requirement of 5×10⁻¹⁹ erg/s/cm²/arcsec² over 179 hours of exposure. In this manuscript, we describe the overall payload design of Aspera. The payload comprises two identical co-aligned UV long-slit spectrograph optical channels sharing a common UV-sensitive microchannel plate detector. The design delivers spectral resolution R ∼ 2,000 over the wavelength range of 101 to 106 nm. The field of view of each channel is 1 degree by 30 arcsec, with an effective area of 1.1 cm². The mission is now entering the payload integration and testing phase, with the projected launch-ready date set for late 2025 or early 2026. The mission will be launched into low-Earth orbit via rideshare.

The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall-2) is a UV multi-object spectrograph designed to detect emission from the circumgalactic and circumquasar medium at low redshifts (0.3 < z < 1.0). The FIREBall-2 spectrograph uses a suborbital balloon vehicle to access a stratospheric transmission window centered around 205 nm and is fed by a 1-m primary parabolic mirror and a 2-mirror field corrector that allows an ≈11’ x 35’ field of view. The slit-mask spectrograph can access dozens of galaxy targets per field, with each target spectrum read out on a UV electron-multiplying CCD detector. Following a flight in 2018, several refurbishments and modifications were made to the instrument and telescope to prepare for additional flight opportunities. Here we present an overview of upgrades and improvements made since the previous flight and discuss the 2023 field campaign, which culminated in a flight from Fort Sumner, New Mexico in September, 2023.

The Star-Planet Activity Research CubeSat (SPARCS) is 6U CubeSat whose mission will be to observe low-mass stars in two ultraviolet (UV) bands. SPARCS will provide time-dependent spectral slope, intensity, and evolution of stellar radiation with the goal of understanding the short- and long-term variability of these targets.

Here we summarize the performance of SPARCam, the science camera for SPARCS. SPARCam is a two-detector camera system allowing independent commanding of two delta-doped, UV CCD47-20 detectors, separately optimized for the SPARCS near UV (NUV) and far UV (FUV) bands. The manuscript includes an overview of the UV detectors optimization and performance as well as a brief description of the camera electronics.

SPARCam was developed by the Jet Propulsion Laboratory and delivered to Arizona State University in October 2023.

We present the results of the JUpiter ICy moons Explorer ultraviolet spectrograph (JUICE-UVS) near-earth commissioning performed between June 14th and 25th 2023. JUICE-UVS is a modest power (9 W), compact ultraviolet spectrograph that is the fifth in a series of six such spectrographs designed and built by Southwest Research Institute for ESA and NASA missions. JUICE-UVS includes several innovations in detector, electronics, optics, and software. These innovations include an atomic-layer deposition (ALD) coating on the detector microchannel plates to minimize gain sag as photons are detected during the mission, electronic components able to withstand the harsh Jovian radiation environment, low-scatter optics to minimize the “wings” of the detected interplanetary Lyman-alpha emission, and a programmable histogram data collection mode that maximizes science return while minimizing stored and telemetered data volume. JUICE-UVS also features a high-spatial resolution observation mode, where a small (1/4 the width of nominal) aperture swings into place at the aperture stop and sharpens the instrument focus. Near-earth commissioning activities included measurements of detector dark noise, optimizing detector HV level via observations of the interplanetary Lyman-alpha, and a “sky-spin” observation over the JUICE-UVS 7.5°-long slit while the spacecraft rolled about the high-gain antenna (a “great circle” swath 7.5° wide). Dark rates matched those measured on the ground (approximately 5 Hz/cm²). HV levels were nominal for the operational temperature (approximately 0°C). Observations with the high-spatial resolution aperture confirmed the sharpened focus when compared to nominal observations. The “sky-spin” observation passed through the galactic plane, allowing for the identification of many known UV-bright stars. These stars provide a rough estimate of instrument effective area that will be refined after JUICE passes >2 AU from the sun, enabling 3-axis stabilized pointed observations.

We present a spacecraft and payload system design of a UV space telescope on a ∼130kg micro-satellite mission with a moderately fast repointing capability and near real-time alert communication. The mission, called Quick Ultra-Violet Kilonova surveyor – QUVIK, shall measure the brightness evolution of kilonovae, resulting from mergers of neutron stars simultaneously in the near-UV and far-UV band and thus it shall distinguish between different explosion scenarios. As a secondary objective the mission will also provide unique follow-up capabilities for other transients both in the near- and far-UV bands. The mission was selected for implementation by an ambitious Czech national mission program to promote the development of Czech science and space technology.

The Integral Field Ultraviolet Spectroscopic Experiment sounding rocket is the first far ultraviolet integral field spectrometer. It features an f /16, 0.49 m Cassegrain telescope and a 26-element image slicer feeding 26 holographic gratings, with spectra imaged by the largest cross-strip microchannel plate detector flown in space. The first launch of INFUSE occurred from White Sands Missile Range on October 29th, 2023, and demonstrated spectral multiplexing, successfully detecting ionized gas emission in the XA region of the Cygnus loop. The second launch of INFUSE is projected for spring 2025 to observe the star-forming galaxy NGC 2366 alongside companion NGC 2363. Housed within NGC 2366 is the Mrk 71 region, a prototype for studying highly ionized starburst regions, making NGC 2366 a local analog to Green Pea type galaxies. Several enhancements are planned for INFUSE before this second science flight, including adding an improved baffle to reduce contamination by second order light, improving grating alignment to reduce overlap between different spectrograms, and iriditing several surfaces to reduce scattered geocoronal Ly-α. An additional grating coated with xenon diflouride-enhanced lithium fluoride will also be added to flight qualify a new coating that may support ultraviolet capability on the Habitable Worlds Observatory. The second flight will also feature a ride along mission, the Spectroscopic Ultraviolet Multi-Object Observatory. We report on the results from the first launch as well as outline progress towards preparation for the second flight.

The Spatial Heterodyne Extreme Ultra-Violet Interferometer (SHEUVI) is an instrument developed through the NASA PICASSO program. We present experimental results from the SHEUVI instrument; provide a brief overview and the historical evolution of ARSHS; describe how precipitous results from the SHEUVI effort inspired the instrument design for the recently selected NASA - Astrophysics Research and Analysis (APRA) VUV rocket program; and, discuss how this project has also influenced current design work for future SmallSat/CubeSat mission opportunities.

PETREL (Platform for Extra & Terrestrial Remote Examination with LCTF) is a 50kg class satellite with a 80mm-diameter Ultraviolet Telescope (UVT). The science missions of the UVT system are the discovery of high-energy transients, such as supernovae and gravitational-wave electromagnetic sources. To achieve them, the optical system is optimized to detect near-UV photons between 250 and 300 nm. Within a 30-minutes exposure time per every revolution, it surveys a remarkably wide field as 50 deg^2 with a high sensitivity of 20~ AB magnitude. The Board Unit has an on-board computer, which directly analyzes raw images obtained by a back-illuminated CMOS sensor. The computer can detect transients immediately, so as to alert the transient information to ground within 30 minutes of discovery. We will achieve the first UV survey to explore the transients in their early phase and reveal the underlying physical processes.

Aspera is a NASA Astrophysics Pioneers SmallSat mission designed to study diffuse Ovi emission from the warm-hot phase gas in the halos of nearby galaxies. Its payload consists of two identical Rowland Circle-type long-slit spectrographs, sharing a single MicroChannel plate detector. Each spectrograph channel consists of an off-axis parabola primary mirror and a toroidal diffraction grating optimized for the 1013-1057 Å bandpass. Despite the simple configuration, the optical alignment/integration process for Aspera is challenging due to tight optical alignment tolerances, driven by the compact form factor, and the contamination sensitivity of the Far-Ultraviolet optics and detectors. In this paper, we discuss implementing a novel multi-phase approach to meet these requirements using state-of-the-art optical metrology tools. For coarsely positioning the optics we use a blue-laser 3D scanner while the fine alignment is done with a Zygo interferometer and a custom computer-generated hologram. The detector focus requires iterative in-vacuum alignment using a Vacuum UV collimator. The alignment is done in a controlled cleanroom facility at the University of Arizona.

The MANTIS (Monitoring Activity of Nearby sTars with uv Imaging and Spectroscopy) 16U CubeSat mission, led by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, plans to characterize the high-energy stellar radiation that drives atmospheric photochemistry and escape on extrasolar planets by conducting simultaneous observations of exoplanet host stars at extreme-ultraviolet (100–1200A; EUV), far-ultraviolet (1300–2200A; FUV), near-ultraviolet (2200–3500A; NUV), and visible (3500–10000A; VIS) wavelengths. The science payload's two-telescope design enables simultaneous coverage over the entire UV passband and the first EUV astrophysics capability in over 20 years. An 8.5cm diameter grazing incidence telescope feeds a low-resolution EUV spectrograph while a 14x9cm rectangular Cassegrain telescope feeds a dichroic beamsplitter to divide the light into both an NUV/VIS and FUV channel. The MANTIS design, detector systems, spacecraft bus and mission operations build off of the heritage of the CUTE and SPRITE CubeSats developed by the MANTIS team. This proceeding overviews the design of the MANTIS instrument and general mission concept.

Eos is a mission concept to be proposed to the expected 2025 NASA Small Explorers Announcement of Opportunity (SMEX AO). Eos observes molecular clouds in our galaxy and nearby planet forming disks to understand the link between star and planet formation and molecular hydrogen in galactic star forming regions. Eos does this using very long-slit, high resolution spectroscopy of far ultraviolet (FUV) emission from fluorescent molecular hydrogen (H₂), a powerful and underutilized FUV diagnostic. H₂ is the most abundant molecule in the universe, but is typically observed in the infrared (IR) or inferred via proxies such as CO. Eos will directly observe H₂ via fluorescence, which can be stimulated from a range of sources (shocks, interstellar UV radiation, bright stars, etc). Here we briefly describe the science objectives of Eos, as well as the instrument implementation.

What is the amount of ionizing energy incident on exoplanet atmospheres from their host stars? What is the relationship between white-light flares and this ionizing energy? These are key questions required to link our current archive of hundreds of stellar whitelight flares to the ionizing radiation released during them, and the ramifications of those flares on the survival of exoplanetary atmospheres, particularly for planets orbiting within the habitable zones of low-mass stars. The Small NASA Optical Ultraviolet Telescope (SNOUT) is a proposed Pioneers mission comprised of two co-pointing telescopes: one optimized for EUV wavelengths (comprised of three separate EUV segments) and one for visible wavelengths. SNOUT is designed to measure the quiescent extreme-UV (EUV) emission for 30 mow-mass stars (0.3 - 1 solar masses), covering a range of ages, in three EUV bandpasses. The combined instrument is housed in an ESPA-Grande spacecraft and will launch into low Earth orbit for a one-year baseline mission. SNOUT has a substantial educational and early-career mentoring component; early-career scientists and engineers comprise more than half of the team, including key leadership roles.

The Ultraviolet Explorer (UVEX) mission is built on three scientific pillars: (I) Exploring the low-mass, low-metallicity galaxy frontier; (II) Providing new views of the dynamic universe, and (III) Leaving a broad legacy of modern, deep synoptic surveys. The deep, synoptic all-sky survey includes the Galactic Plane and Magellanic Clouds and achieves depths and resolution matching modern optical/IR surveys with Rubin, Roman, and Euclid. UVEX will follow up the aftermath of GW-detected NS mergers and provide the first rapid UV spectroscopic follow-up of transients. The UVEX payload consists of a single instrument with simultaneous FUV and NUV imaging over a wide (12 deg2) FOV and sensitive R>1000 spectroscopy over a broad band from 1150 – 2650 Å. Placed in a highly elliptical, TESS-like orbit, UVEX achieves low background and high observing efficiency. Frequent ground contacts and rapid slew capability enable UVEX to promptly follow up targets of opportunity, providing the first rapid, deep UV imaging and spectroscopic follow-up capability.

A micro-satellite for wide-field near-UV transient exploration PETREL is presented. The scientific goal is to detect transient sources, such as GW sources accompanied by EM emission, supernovae, and other unknown phenomena in the UV sky, and to reveal the nature of explosive phenomena in the universe through multimessenger observations. PETREL is equipped with an 80 mm refractor coupled with BI-CMOS detector. A powerful OBC automatically processes the received data and searches for orbital transients. If a transient is detected, an alert is immediately sent over the Globalstar network. A 50 kg class micro-satellite bus system is being developed for this mission. A series of functional tests using simulators have verified that the satellite system can detect transient sources in nearby galaxies as designed.

We present Maratus—a proposed 12U cubesat far ultraviolet narrow-band imager, centered on 1350Å to map the circumgalactic medium (CGM). We primarily target O vi emission, likely the brightest tracer of the 10⁵ −10⁶ K gas surrounding galaxies, at z ∼ 0.3. Combining flight-proven hardware with recent technological improvements, we tackle one of the most interesting questions bridging large scale structure and galaxy evolution in our current moment — “How does gas flow into and out of galaxies?” Answering this question is crucial for understanding the regulation of star formation, and the flow of matter, energy, and metals travelling between galaxies and the intergalactic medium. Maratus is a proof of principle instrument that will pave the way for large-scale mapping of the intergalactic medium. Mapping the CGM is identified as a key discovery area in the recent astrophysics decadal report. By using COS-Halos galaxies for our targeted survey, we present the first opportunity to characterize a key metal tracer of the CGM in both emission and absorption.

Type Ia supernovae (SNe Ia) are a cornerstone of modern cosmology. Upcoming missions like the Nancy Grace Roman Telescope are pushing to high redshifts to measure cosmological parameters like the dark energy equation of state. Despite the impressive success of empirically standardizing their luminosities, the explosion mechanism of SNe Ia remains hotly debated; e.g., the mass of the white dwarf (WD) when it explodes and the state of the companion star (degenerate or non-degenerate) are all currently in question.

Early-time UV observations are sensitive to the outermost layers of the ejecta (and least affected by the explosion itself) and show the most diversity for SNe Ia. This makes the UV bandpass an excellent probe to solve these open questions about the nature of these cosmological distance indicators. To achieve this science, we present UVIa, a CubeSat that will be reactive and have simultaneous optical, Near-UV (NUV), and Far-UV (FUV) coverage, takes advantage of state-of-the-art UV coatings, UV-enhanced silicon detectors with whitelight rejection filter, and autonomous observing scheduling, updated regularly based on newly discovered SNe Ia from modern transient surveys.

Ultraviolet (UV) spectroscopy is one of the most powerful tools used in a wide range of scientific fields from planetary science to astronomy. We propose a future UV space telescope, LAPYUTA (Life-environmentology, Astronomy, and PlanetarY Ultraviolet Telescope Assembly), selected as a candidate for JAXA’s 6th M-class mission in 2023. Launch is planned for the early 2030s. LAPYUTA will accomplish the following four objectives related to two scientific goals: understanding (1) the habitable environment and (2) the origin of structure and matter in the universe. Objective 1 focuses on the subsurface ocean environments of Jupiter's icy moons and the atmospheric evolution of terrestrial planets. Objective 2 characterizes the atmosphere of the exoplanets around the habitable zone and estimates their surface environment by detecting their exospheric atmosphere. In cosmology and astronomy, Objective 3 tests whether the structures of presentday galaxies contain ubiquitous Ly-α halos and reveals the physical origins of Ly-α halos. Objective 4 elucidates the synthesis process of heavy elements based on observations of ultraviolet radiation from hot gas immediately after neutronstar mergers. LAPYUTA will perform spectroscopic and imaging observations in the far-UV range of 110-190 nm with an effective area of >300 cm2 and a high spatial resolution of 0.1 arcsec. The apogee is 2,000 km, and the perigee is 1,000 km to avoid the influence of the geocorona when observing oxygen and hydrogen atoms and the Earth's radiation belt.

The Johns Hopkins Rocket Group is developing hydrogen absorption cell technology to mitigate the Lyman-alpha emission challenge posed by the geocorona for astronomical photometry in the Lyman ultraviolet spectrum (1000- 1216 Å) from low-Earth orbit. We have assembled a prototype cell from 1.33 SS CFF tube, two (2mm) LiF windows and a tungsten filament. The cell is filled with H₂ to a pressure of 2 torr. The heated filament thermally dissociates the H₂ into its atomic form, which will absorb Lyman-alpha. In theory, the pressure is high enough to collisionaly de-excite the H, thus preventing resonant re-scattering.

We have begun testing and have preliminary results using the Long-slit Imaging Dual Order Spectrograph. Spectral testing of the Lyman-alpha line profiles are vital for advancing hydrogen absorption cell technology in future Lyman ultraviolet missions. These tests can reveal whether or not molecular hydrogen fluorescence is occurring from either electron impact excitation or recombination in higher energy states. Our preliminary results have shown attenuation of the source Lyman-alpha signal by roughly 73% with an associated optical depth of 1.3 and hydrogen column density of 2.2 x 10¹³. Future tests will involve cooling down our lamp/hydrogen cell system as well as testing multiple filament configurations for the most efficient input power possible.

The Hydrogen Emission Line Interferometric eXplorer (HELIX) is a SmallSat mission concept to study the vertical distribution and transport flux of geocoronal hydrogen that is transitioning from Earth’s upper atmosphere into the exosphere. This investigation is conducted using a dual channel, all-reflective Spatial Heterodyne Spectrometer (SHS). A SHS is a type of Fourier Transform Spectrometer that divides incoming light into 2-beams with a diffraction grating that interfere to produce a linear fringe pattern from which spectral power is obtained. The HELIX SHS has a dual ruled grating that is can be simultaneously aligned to observe the Ly-α and Ly-β transitions of hydrogen. It has a spectral resolving power of ~200000 that separates the geocoronal lines from contaminating background emissions and allows exploration of the thermal and non-thermal populations of hydrogen. HELIX is designed for incorporation into a high-heritage SmallSat spacecraft platform that would be launched into low Earth orbit for a 12-month mission. This presentation describes the SHS concept, the mission requirements for HELIX, and the top-level on-orbit performance of the instrument.

In pursuit of maturing high priority UV optics technology for the Habitable Worlds Observatory, we present laboratory reflectivity results and ongoing environmental stability testing of band-selecting filters designed for the Lyman-ultraviolet bandpass (LUV; 90-120 nm) and the far-ultraviolet bandpass (FUV; 120-150 nm), and reflectance uniformity of broadband (90 – 2500 nm) coatings. The band-selecting coatings are multilayer depositions of Al+LiF+SiC+LiF, and LaF3 +AlF3. These narrowband filters were developed in coordination with the Grupo de Óptica de Láminas Delgadas (GOLD) at the Instituto de Óptica-Consejo Superior de Investigaciones Cientificas for the Far- and Lyman-Ultraviolet Imaging Demonstrator (FLUID) sounding rocket payload. Environmental stability tests of Lyman alpha (Ly-α; 121.6 nm) suppressing filters that peak near 105 nm (“F110M”) and 140 nm (“F140M”) were conducted in the optical testing facilities at CU Boulder. Additionally, we present initial UV optics coating development results of MgF₂ capped silicon wafers, and LiF capped aluminum, in collaboration with NASA’s Jet Propulsion Laboratory. These coatings were deposited using atomic layer deposition (ALD) at JPL, to advance the throughput efficiency of MgF₂ protective capping layers for UV optics. Several MgF₂ depositions varying in silicon wafer temperature and dielectric thickness have been fabricated to explore the deposition parameters thoroughly. Exploring deposition uniformity on scales larger than a witness coupon, we also present initial results on the reflectance uniformity of (≤ 6 inches) MgF2/Al ALD coated optics.

The study of solar system bodies in the ultraviolet is often the study of extended sources, including vapor plumes, atmospheres, cometary tails, and planetary surfaces. These objects are traditionally studied with longslit spectrographs that can sample one dimension of spatial information at a time - providing a cross section of the object in question. The Ultraviolet Micromirror Imaging Spectrograph (UMIS) is a new instrument concept that will bring integral-field spectroscopy to the field for the first time, effectively creating a two-dimensional image of the source at every wavelength in the spectral bandpass simultaneously. UMIS is designed around the concept of an image slicer, where a set of angled mirrors at the telescope focal plane dissect the image into sub-regions which are aligned to avoid overlap of spectra on the detector. Unlike conventional image slicers, however, UMIS employs a reconfigurable micromirror array at the focal plane instead of a fixed mirror slicer array. The UMIS micromirror array, provided by Bright Silicon Technologies, consists of 20 × 20 individual mirrors, each actuatable to any angle up to 15 degrees. This new concept overcomes the limitations of a conventional image slicer by enabling the sampling of various sized regions matched to different targets and spectral resolution requirements within a large field-of-view. This proceedings presents the UMIS optical design, concept and development schedule. UMIS is a collaboration of the Planetary Science Institute, The University of Colorado, Boulder, and BAE Systems (formerly Ball Aerospace).

Beyond the lifetime of the Hubble Space Telescope, observational access to the ultraviolet (UV) might be quite limited. Therefore, small missions with short development times are required to bridge the gap to future larger missions in this important wavelength range. Even with the progress in adapting silicon sensors for the UV, single-photon-counting and visible-blind microchannel plate (MCP) detectors can provide a competitive signalto- noise performance, particularly in the far- and extreme-UV, and enable simple instrument designs for small and cheap missions.

Our MCP detector development aims at reaching enhanced sensitivity and increased lifetime with lower size, mass, and power consumption. Therefore, the design comprises (Al)GaN photocathodes with a tunable long-wavelength cut-off, long-life borosilicate MCPs, and a cross-strip anode with an FPGA-based readout.

In this contribution, we report on the overall status of the detector development and give an outlook on the mission prospects.

Understanding the noise characteristics of high quantum efficiency silicon-based ultraviolet detectors, developed by the Microdevices Lab at the Jet Propulsion Laboratory, is critical for current and proposed UV missions using these devices. In this paper, we provide an overview of our detector noise characterization test bench that uses delta-doped, photon counting, Electron-multiplying CCDs (EMCCDs) to understand the fundamental noise properties relevant to all silicon CCDs and CMOS arrays. This work attempts to identify the source of the dark current plateau that has been previously measured with photon-counting EMCCDs and is known to be prevalent in other silicon-based arrays. It is suspected that the plateau could be due to a combination of detectable photons in the tail of blackbody radiation of the ambient instrument, low-level light leaks, and a non-temperature-dependent component that varies with substrate voltage. Our innovative test setup delineates the effect of the ambient environment during dark measurements by independently controlling the temperature of the detector and surrounding environment. We present the design of the test setup and preliminary results.

Astronomy-grade cameras with robust performance and heritage in the space environment have long been costly, substantially limiting capacity for space-based astronomy and creating a resource barrier to access. Additionally, ultraviolet observations have historically been limited by the low-sensitivity of most sensors in this wavelength range. The LUVCam program is designed to address both issues, providing a high-performance, low-cost, UV/optical camera system sufficiently capable to support a wide-array of space-based astronomy missions. LUVCam features a large format, low-noise, large pixel, and high quantum efficiency, commercial-off-the-shelf backside illuminated CMOS sensor, packaged with custom built readout electronics and thermomechanical structure. LUVCam is ITAR-free, and cheap to fabricate, opening up new opportunities for access to space telescopes. LUVCam has reached TRL 6, and has passed qualification testing for operation in low-earth orbit, with competitive performance from 200-900 nm. LUVCam is manifested for multiple near-term orbital missions, including a technology demonstration CubeSat, and a UV transient astronomy SmallSat.

NASA’s Great Observatories Maturation Program (GOMAP) will advance the science definition, technology, and workforce needed for the Habitable Worlds Observatory (HWO) with the goal of a Phase A start by the end of the current decade. GOMAP offers long-term cost and schedule savings compared to the ‘TRL 6 by Preliminary Design Review’ paradigm historically adopted by large NASA missions. Many of the key technologies in the development queue for HWO require the combined activities of 1) facility and process development for validation of technologies at the scale required for HWO and 2) deployment in the ‘real world’ environment of mission Integration and Test prior to on-orbit operations. We present a concept for the Smallsat Technology Accelerated Maturation Platform (STAMP), an integrated facility, laboratory, and instrument prototype development program that could be supported through the GOMAP framework and applied to any of NASA’s Future Great Observatories (FGOs). This brief describes the recommendation for the first entrant into this program, “STAMP-1”, an ESPA Grande-class mission advancing key technologies to enable the ultraviolet capabilities of HWO. STAMP-1 would advance new broadband optical coatings, high-sensitivity ultraviolet detector systems, and multi-object target selection technology to TRL 6 with a flight demonstration. STAMP-1 advances HWO technology on an accelerated timescale, building on current ROSES SAT+APRA programs, reducing cost and schedule risk for HWO while conducting a compelling program of preparatory science and workforce development with direct benefits for HWO mission implementation in the 2030s.

Following the recent reformulation of the Athena mission to meet budgetary and technical constraints, both the scientific case and the instrument design of the Wide Field Imager instrument have been reviewed to reflect the requirements and constraints of the new Athena concept. In this paper, a summary of the updated science case for WFI will be presented, along with an update of the instrument design, the status of critical technologies and future plans for model development.

The Wide Field Imager (WFI), one of two instruments on ESA’s next large X-ray mission Athena, is designed for imaging spectroscopy of X-rays in the range of 0.2 to 15 keV with a large field of view and high count rate capability. The focal plane consists of back-illuminated DEPFET (Depleted p-channel field effect transistor) sensors that have a high radiation tolerance and provide a near Fano-limited energy resolution. To achieve this, a very low noise readout is required, ∼3 electrons ENC at beginning of life is foreseen. This makes the device very susceptible to any radiation induced worsening of the readout noise. The main mechanism of degradation will be the increase of dark current due to displacement damage caused primarily by high energy protons.

To study the expected performance degradation, a prototype detector module with fully representative pixel layout and fabrication technology was irradiated with 62.4 MeV protons at the accelerator facility MedAustron in Wiener Neustadt. A total dose equivalent to 3.3 · 10⁹ 10-MeV protons/cm² was applied in two steps. During, in-between and after the irradiations the detector remained at the operating temperature of 213 K and was fully biased and operated. Data was recorded to analyze the signal of all incident particles.

We report on the increase of dark current after the irradiation and present the current related damage rate at 213 K. The effect of low temperature annealing at 213 , 236 K, 253 K, 273 K, and 289K is presented.

The depleted p-channel field effect transistor is the chosen sensor type for the Wide Field Imager of the Athena mission. It will be used in two types of cameras. One will enable observations of a field of view of 40′ × 40′ by using an array of four 512 × 512 pixel sensors in a 2 × 2 configuration. A second, small one is designed to investigate bright, point-like sources with a time resolution of up to 40 μs. Sensors of final size, layout, and technology were fabricated, assembled and characterised. Also, first results from the flight production are available and confirm the excellent performance. In order to be able to estimate the future performance of degraded detectors, a simulation was developed that takes into account the non-analytical threshold effects on the basis of measurement results. We present the measurement analysis and the comparison of simulated and measured values as well as first attempts to use the Monte Carlo simulation to predict performance results based on noise measurements.

The Athena mission underwent a redefinition phase since July 2022, driven by the imperative to reduce the mission cost for the European Space Agency while maintaining its flagship character. This most notably lead to a modification of the X-ray Integral Field Unit (X-IFU) cryogenic architecture. Passive cooling via radiative panels at spacecraft level (V-grooves) now provides a 50K thermal environment to the X-IFU cryostat. 4K cooling is achieved through a remote active cooler, with a multi-stage Adiabatic Demagnetization Refrigerator delivering the final 50 mK temperature required by the detectors. Amidst these changes, the core concept of the readout chain remains robust, utilizing Transition Edge Sensor microcalorimeters and Time-Division Multiplexing. Noteworthy is the introduction of a slower pixel, enabling an increase in the multiplexing factor (from 34 to 48) without compromising the energy resolution. This mitigates the reduction of the field of view (from 5’ to 4’) while reducing the number of channels and thus the resource demands on the system. In this contribution, we will give an overview of this new instrument architecture, addressing its main functional chains.

The X-ray Integral Field Unit (X-IFU) will be a microcalorimeter instrument on ESA’s Athena X-ray observatory, set to launch around 2037. Athena recently underwent a reformulation exercise resulting in a simplified X-IFU architecture, with a new baseline configuration featuring fewer pixels and readout channels. Newly developed transition edge sensor pixels that are slower and have reduced magnetic field sensitivity have helped enable the new instrument design whilst maintaining flagship quality science. In this paper, we report on the status and plan for continued development of the X-IFU microcalorimeter array. We describe details of the current pixel architecture and performance specifications. We will present the design of the first full scale microcalorimeter arrays that have the necessary flight like electrical and mechanical interfaces for X-IFU. These arrays will undergo testing in a focal-plane assembly (FPA) Development Model (DM) in Europe later in 2024 and serve as a precursor to the X-IFU Engineering Model detector.

The X-ray Integral Field Unit (X-IFU) instrument is the high-resolution X-ray spectrometer of the ESA Athena X-ray Observatory. X-IFU will deliver spectra from 0.2 to 12 keV with a spectral resolution requirement of 4 eV (3 eV design goal) up to 7 keV from 5" pixels, with a hexagonal field of view of 4' equivalent diameter. The main sensor array and its associated detection chain is one of the major functional chains of the X-IFU instrument, and is the main contributor to XIFU performance. CNES (Centre National d’Études Spatiales) is the prime contractor for the X-IFU and leads the project development and procurement aspects within the X-IFU Consortium; additional major partners of the main detection chain are NASA-GFSC, SRON, VTT, APC, NIST, IRAP, and IAP. The detection chain design for X-IFU has evolved in the past few years in order to secure the performances and development costs, in the frame of the New Athena mission. New TES pixels are implemented with slower time constant and a reduced sensitivity to magnetic field. The slower time constant directly allows an increase of the MUX factor and a reduction of the number of channels, together with the decrease of the number of proximity electronics boxes, or warm front end electronics (WFEE). The cryostat outer vessel temperature is now a 50 K thermal interface, cooled passively thanks to L-shaped thermal shield (L-grooves). This has a direct impact of the cryo-harness between the 4 K core interface and the WFEE interface. In the past years, we have performed early demonstration on the critical components in order to secure the detection chain design and performances. This paper presents the progress done on early demonstrations (warm electronics, cryo-harness breadboarding,...), while providing an update to the detection-chain design description.

The X-IFU is one of the two instruments of ATHENA, the next ESA large X-ray observatory. It is a cryogenic spectrometer based on an array of TES microcalorimeters. To reduce the particle background, the TES array works in combination with a Cryogenic AntiCoincidence detector (CryoAC). The CryoAC is a 4-pixel detector, based on ~1 cm² silicon absorbers sensed by Ir/Au TES. It is required to have a wide energy bandwidth (from 20 keV to ~1 MeV), high efficiency (< 0.014% missed particles), low dead-time (< 1%) and good time-tagging accuracy (10 μs at 1σ). An end-to-end simulator of the CryoAC detector has been developed both for design and performance assessment, consisting of several modules. First, the in-flight flux of background particles is evaluated by Geant4 simulations. Then, the current flow in the TES is evaluated by solving the electro-thermal equations of microcalorimeters, and the detector output signal is generated by simulating the SQUID FLL dynamics. Finally, the output is analyzed by a high-efficiency trigger algorithm, producing the simulated CryoAC telemetry. Here, we present in detail this end-to-end simulator, and how we are using it to define the new CryoAC baseline configuration in the new Athena context.

Within SRON a first Development Model (DM 1.0) of the X ray Integral Field Unit Focal Plane Assembly (X-IFU FPA) has been designed, realized and tested over the past years. Since the start of the FPA DM 1.0, the X-IFU instrument design has significantly evolved. Moreover, the recent Athena redefinition activities have resulted in a new overall planning in which the Mission Adoption Review (MAR) and X IFU instrument PDR are now foreseen for 2027. To ensure the required experimental feedback for FPA EM conceptual design is available by the time of the PDR an update of the existing FPA DM 1.0, called DM 1.1, is planned which better reflects the evolved instrument design. In the DM 1.1 the existing 4 channel Frequency Domain Multiplexing (FDM) readout is replaced by an 8 channel Time Domain Multiplexing (TDM) differential readout. A small sized TES array is replaced by a flight-sized kpixel array including full on-chip wiring, of which a limited subset is read-out. The interconnections between the main TES array and the SQUID Multiplexer (MUX) chips are realized in a manner which is flight scalable. Superconducting multilayer Niobium flex cables are used to route the TDM signals from the T0 detector stage at nominally 50 mK to the amplifier (AMP) SQUID stages and external interfaces at 2 K.

This work describes the redesign performed on the X ray Integral Field Unit Focal Plane Assembly (X-IFU FPA) Development Model (DM) with a focus on the mechanical modifications of the T0 detector stage. In addition the development progress of several critical interconnection technologies used within the DM 1.1 is described. These include fixation of the main TES array to the metal support, a dedicated wire bonding process of the main TES array to the side panel MUX carrier chips and interconnection of the super-conducting Nb flex cables to the connecting Printed Circuit Boards (PCB).

This paper describes the micro-vibrational characterization of the Development Model (DM) of the X ray Integral Field Unit Focal Plane Assembly (X-IFU FPA) for the Athena X-ray observatory. We discuss the power dissipation occurring when FPA modes are excited. We compare amplitude and phase measured by X-Z accelerometers, thermometers response and the pixels DC baseline signal due to acceleration provided by actuator towards the FPA center of mass. Impact of the micro-vibrations on the thermal stability at the detectors level and the possible degradation on the pixels performance will be discussed in detail.

This paper describes the strategy and planned implementation of the ground calibration of the X-IFU microcalorimeter spectrometer on-board Athena, the X-ray observatory from ESA to be launched after the mid-2030s. X-IFU is the second generation of space microcalorimeter instrument, and its calibration strategy benefits from the experience acquired on the present Japanese-US built Resolve instrument on-board XRISM. This calibration plan takes into account the reformulation of the Athena mission and its instruments that took place in 2022-23. The X-IFU calibration strategy is presented along with the set of X-ray sources needed for the ground calibration and the the definition of the sequences for using them.

The Off-plane Grating Rocket Experiment (OGRE) is a NASA suborbital rocket mission for high-performance X-ray spectroscopy. The nominal payload utilizes lightweight, polished-Si optics fabricated by NASA's Goddard Space Flight Center, a reflection grating array fabricated at Penn State with key industrial collaborations, and an EM-CCD based camera fabricated by XCAM in collaboration with the Open University. In preparation for the nominal mission, we will fly a pathfinder rocket that swaps the polished-Si telescope out for the JET-X telescope. This is one of three telescopes originally made for Spectrum-x-gamma with one currently flying on Swift and one slated for Pathfinder-OGRE, being lent by the Italian Space Agency. Here we report on the progress of the OGRE program, overview of the Pathfinder-OGRE mission, and updates on the nominal payload.

Improved X-ray/UV spectroscopy is needed for studies of exoplanet host systems, the evolution of galaxies, and the physics of extreme astrophysical conditions. Efficient, high-resolution X-ray / UV spectrometers would meet this need, but realizing such instruments, particularly in compact formats like SmallSats, are often gated by the fabrication of a grating that meets the size, shape, diffractive design, and performance requirements of the spectrometer. We report on an effort to make custom, high performance gratings on curved surfaces using electron-beam lithography (EBL). We have made modestly-sized gratings (39 mm X 20 mm) on cylindrical surfaces with sag comparable to that of a grazing-incidence optic (> 1 mm). Our approach uses interferometric measurements of diffracted orders to assess the fidelity of EBL in realizing the desired grating, providing a direct measurement of the technology’s current capabilities and informing development efforts. We also report on the fabrication and testing of a diffractive silicon mirror operating at grazing incidence, as well as an optical design for a test of a novel, two-element spectrometer system.

High resolving power soft x-ray spectroscopy has been confirmed by the Astro2020 Decadal Survey as a highpriority strategic measurement technique with resolving power R = λ/Δλ up to 7500 for some science cases. Examples are the characterization of highly ionized gases in galaxy halos and within and around galaxy clusters, accretion onto supermassive black holes, stellar coronal mass ejections and coronal heating. Arcus, a recently proposed high-resolution x-ray and FUV grating spectrometer Probe class mission, exceeds current capabilities by far, with a minimum R of 2500 (∼ 3500 expected) and effective area up to 500 cm² in the 10-50 Å band, covered by the X-ray Spectrometer (XRS) instrument. The XRS relies on light-weight, high-efficiency, blazed and alignment-insensitive critical-angle transmission (CAT) gratings for dispersion and calls for hundreds of ∼ 30 × 30 mm² gratings. Recent gratings have been fabricated from 200-mm silicon-on-insulator (SOI) wafers using commercial tools from the semiconductor and MEMS industries compatible with volume production. Previously we reported x-ray results from quasi-fully illuminated co-aligned CAT gratings showing record-high R up to 1.3×10⁴ in 18th and 21st diffraction orders at Al-K (∼ 1.5 keV), and diffraction efficiency in agreement with synchrotron measurements and model predictions at O-K. We were recently able to chemically reduce the width of the freestanding, 200 nm-period, ultra-high aspect ratio CAT grating bars post-fabrication, and we report on the resulting increase in diffraction efficiency.

We report on the status of an X-ray optics development effort at Goddard Space Flight Center. The development effort is designed to enable future flagship missions like Lynx in the long term and to support Probe missions and Explorer missions like AXIS, HEX-P, LEM, and STAR-X, in the near term. It takes into consideration the three major work areas of building an X-ray mirror assembly, i.e., technology, engineering, and production, while focusing its resources on developing and maturing a technology based single crystal silicon. Boiled down to the most essentials, the development tackles four major technical areas: fabrication, coating, alignment, and bonding of thin, lightweight mirror segments. The technology is based on single crystal silicon, whose lack of internal stress makes it possible to use many polishing techniques to make the best possible thin, lightweight mirror segments. We will report results achieved with repeated building and testing mirror modules, as well as knowledge and lessons learned in each of the four technical areas.

Lightweight X-ray telescopes with high-angular resolution and a large effective area are essential for elucidating the physical mechanisms behind the evolution of super-massive black holes. To achieve such X-ray telescopes, we are developing X-ray mirrors using carbon fiber reinforced plastic (CFRP); CFRP is a lightweight but strong material that can be processed into a variety of shapes. However, CFRP has a finely textured surface, known as print-through, which is too rough to reflect X-rays effectively. To mitigate the print-through issue, we developed a method to form a thin amorphous nickel phosphide (NiP) layer on the surface of CFRP. The NiP surface was then finished using ultra-precision machining technology to achieve the required surface roughness for X-ray reflection. We fabricated a CFRP plane mirror, and an X-ray reflectivity measurement for the plane mirror using the ISAS X-ray beam line confirmed that the surface roughness was approximately 1.5 nm. Additionally, we made a Wolter-I type mirror and demonstrated that it could focus X-rays. However, the half-power width of the reflected X-ray image was 9.6 arcmin.

The traditional approach for creating very large X-ray mirror modules (with diameters exceeding 1 meter) involves dividing the optics into azimuthal and radial modules, similar to the Silicon Pore Optics used in Athena. While this method addresses the initial challenges of procuring and handling very large substrates, it introduces complexities in the later stages, particularly when thousands of segments must be assembled without compromising their optical performance. In contrast, a simpler design for large mirror modules could involve fewer than a few hundred thin monolithic shells (2-4 mm for mirror shells ranging from 0.4 to 3 meters in diameter). This configuration offers the dual benefits of design simplicity and high-resolution capability, achieved through direct polishing. Additionally, it significantly reduces the polishing time. In Italy, a technology development roadmap for this approach is being funded by ASI and led by INAF-OABrera. In this paper, we present the advancements made in the various phases of this process and in the procurement of new substrates.

The BlackCAT CubeSat is an X-ray coded-aperture-telescope observatory that is expected to launch in 2025. It is designed for observations of bright X-ray sources in the 0.5–20 keV band. The instrument will have a wide field of view (0.85 steradian) and be capable of catching gamma ray bursts (GRBs) from the distant universe, galactic transients, and flares from blazars, while monitoring the X-ray sky. In addition to the primary high-redshift GRB science, BlackCAT can monitor known source variability and search for rare and exciting events including gravitational-wave X-ray counterparts, magnetar flares, supernova shock breakouts, and tidal disruption events. The mission will thus function as a multiwavelength and multi-messenger complement to present and future facilities including LIGO, VIRGO, KAGRA, IceCube, KM3NET, LSST, LOFAR, SKA, and CTA. Rapid notifications of burst positions will be transmitted to the ground via satellite network and then relayed to the GCN. The name BlackCAT is derived from its scientific emphasis on black-holerelated transient events being observed with a coded aperture telescope (CAT). BlackCAT will serve as the scientific payload aboard a commercial 6U CubeSat spacecraft provided by NanoAvionics US. Novel event-driven X-ray hybrid CMOS detectors will form the focal plane array. In addition to carrying out science programs related to distant GRBs, transients, and X-ray sky monitoring, BlackCAT will also serve as a pathfinder for future economical missions combining multiple BlackCAT modules on either a single small satellite or on multiple CubeSats. BlackCAT will also serve as a platform for new X-ray hybrid CMOS detector development. An overview of BlackCAT in its current development state and its current status will be presented.

With the endorsement of the NewAthena (New Advanced Telescope for High ENergy Astrophysics) mission by ESA’s Science Programme Committee in November 2023, the preparations for this next generation X-ray observatory have shifted to a higher gear. Competitive system studies and technology preparation activities are being implemented, aiming to demonstrate readiness for the mission adoption early 2027 and the subsequent mission implementation.

The Silicon Pore Optics (SPO) enables the NewAthena mission, delivering an unprecedented combination of good angular resolution, large effective area and low mass. The SPO technology builds significantly on spin-in from the semiconductor industry and is designed to allow a cost-effective flight optics implementation, compliant with the programmatic requirements of the mission.

The NewAthena X-ray optics is highly modular, consisting of hundreds of compact mirror modules arranged in concentric circles and mounted on a metallic optical bench. All aspects of the optics are being developed in parallel, from the industrial production of the mirror plates, over the highly efficient assembly into mirror modules, to the alignment of the mirror modules and their fixation on the optical bench. Dedicated facilities are being built to measure the performance of the NewAthena X-ray telescope optics, demonstrating their compatibility with the environmental and scientific requirements.

An overview is provided of the activities preparing the implementation of the NewATHENA optics.

The European Space Agency (ESA), cosine and its partners have been developing for 20 years the Silicon Pore Optics (SPO) technology. SPO enables the next generation of space x-ray telescopes, with increased sensitivity and resolution. NewAthena, the New Advanced Telescope for High Energy Astrophysics, has just been endorsed by ESA as one of its Lclass mission, to launch around 2037. NewAthena’s optic is modular and consists of up to 600 mirror modules that form together a ~2.5 m diameter X-ray mirror with a focal length of 12 m and an angular resolution of 9 arc-seconds half-energy width. The total polished mirror surface is ~300 m², which will focus X-rays with an energy of about 0.3 – 10 keV onto two detectors, a wild-field imager (WFI) and an imaging spectrometer (XIFU). Building hundreds of such SPO mirror modules in a cost-efficient and timely manner is a formidable task and subject of a dedicated ESA technology development program.

We present in this paper the status of the optics production and illustrate not only recent X-ray results but also the progress made on the environmental testing, manufacturing and assembly aspects of SPO based optics.

High-energy astrophysics missions demand cutting-edge technologies to assure their maximum observational capabilities. This study explores multilayer coatings for X-ray mirrors, specifically assessing their potential applications for the NewAthena mission and other possible future high-energy missions. Our work emphasizes the design parameters crucial for enhancing mirror performance and investigates the experimental challenges related to the fabrication and performance evaluation of multilayer coatings. We present various concept designs for both soft and hard X-ray focusing telescopes, incorporating simple single-layer and bilayer coatings, with a particular focus on linear and depth-graded multilayer coatings. Leveraging state-of-the-art understanding and modeling of relevant effects influencing telescope performance enables a realistic extension of coating designs to higher energies. The implications of our findings not only endorse the use of multilayer coatings for the NewAthena mission but also offer insights into the broader landscape of future high-energy astrophysics missions.

Future mission X-ray optics are regularly tested and calibrated at the PANTER X-ray test facility of the Max- Planck-Institute for Extraterrestrial Physics. The ATHENA mission has just completed a science and hardware redefinition phase as the NewATHENA mission. During this one-and-a-half-year redefinition phase, the development of the baseline Silicon Pore Optics SPOs continued, resulting in the fabrication of the first SPO mirror modules with all the NewATHENA characteristics (dimensions, rib spacing, and coating). At PANTER, these NewATHENA SPOs will be measured and characterized. This characterization comprises half energy widths of the on- and off-axis point spread function. Furthermore, effective area measurements covering the energy range of NewATHENA will be performed. We provide an overview of the results obtained from measurements during a test campaign in January 2024 of the SPO MM-0058, the first representative NewATHENA row-08 mirror module.

The Einstein Probe (EP), launched successfully on January 9, 2024, is a space mission dedicated to X-ray time-domain astrophysics with a broad range of scientific goals. EP carries a wide-field X-ray telescope to monitor the soft X-ray sky in 0.5–4 keV with a 3600 square-degree field-of-view and a narrow-field X-ray telescope for follow-up observations in 0.3–10 keV and precise source locating. The satellite is currently in the commissioning phase, undertaking in-orbit tests and calibration of the spacecraft and payloads, and tests for the data telemetry and space-ground communication. The test and calibration results achieved so far show that the spacecraft and instruments are working normally, and all the performances meet the requirements of the project design. EP is expected to start normal science operations from late June or early July, 2024.

What do medical imaging and astronomy have in common? Whether it is detecting tumors or observing colliding neutron stars, both fields can benefit from the same sensor technology. When observing radiation in the MeVband (0.1-100 MeV) from celestial sources, one faces challenges like low flux, limited interaction probability, three energy loss processes, and a high background radiation rate. Present MeV-band observatories suffer from poor sensitivity, and new state-of the-art detector technology will be a key contributor to improve sensitivity of future observatories. The detector group at DTU Space has developed a 3D CdZnTe drift strip detector technology to meet the demands of future high-energy detectors. This advancement also shows potential application for emerging Low Dose Molecular Breast Imaging (LD-MBI) systems for breast cancer diagnosis. In this study, we present the results of the novel large area 3D CZT drift strip detectors (4×4×0.5 cm³) developed in a collaboration between DTU Space and Kromek. We find the spatial resolution of these modules to be < 0.6mm in the x- and z-axis, and we measure the spectral resolutions to be < 7% FWHM at 122 keV, < 1.4% FWHM at 661.6 keV, and 1% FWHM above 1460 keV.

As the Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory completes a quarter century of on orbit operations, it continues to perform well and produce spectacular scientific results. The response of ACIS has evolved over the lifetime of the observatory due to radiation damage, molecular contamination, changing particle environment, and aging of the spacecraft in general. We present highlights from the instrument team’s monitoring program and our expectations for the future of ACIS. Performance changes on ACIS continue to be manageable, and do not indicate any limitations on ACIS lifetime. We examine aspects of the design and operation of ACIS that have impacted its long lifetime with lessons learned for future instruments.

The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) was a solar X-ray mission that observed the Sun at X-ray and gamma-ray wavelengths for 16 years, with an energy range covering 3 keV – 17 MeV. RHESSI instrumentation consisted of nine cryocooled, segmented, germanium detectors. We report on the performance of these detectors over the course of 16 years of science operations in a mid-latitude, low-Earth orbit environment. We assess the evolution of the energy gain and energy calibration for each detector, the segmentation status of the detectors over time, and the effectiveness of detector annealing in restoring performance. We highlight some of the challenges associated with determining the calibration over such a long on-orbit time period. These results provide valuable context for future X-ray and gamma-ray space missions.

The X-Ray Imaging and Spectroscopy Mission (XRISM) project at JAXA officially started in 2018. Following the development of onboard components, the proto-flight test was conducted from 2021 to 2023 at JAXA Tsukuba Space Center. The spacecraft was launched from JAXA Tanegashima Space Center on September 7, 2023 (JST), and onboard components, including the science instruments, were activated during the in-orbit commissioning phase. Following the previous report in 2020, we report the spacecraft ground tests, the launch operation, in-orbit operations, and the status and plan of initial and subsequent guest observations.

The initial on-orbit checkout of the soft X-ray spectroscopic system on board the XRISM satellite is summarized. The satellite was launched on September 6, 2023 (UT) and has been undergoing initial checkout since then. Immediately after the launch, the cryocoolers were turned on and their operation was established. The first cycle of the adiabatic demagnetization refrigerator was performed on Oct. 9th, 2023, to transition the sensor to steady-state operational temperature conditions. Subsequently, the filter wheel, which supports energy calibration, was started up. The energy scale is highly sensitive to the temperature environment around the sensor and its analog electronics. The gain correction was established by referring to the calibration X-ray line. For an optimization of the cooler frequencies, we took data including the noise spectra by scanning the cooler frequencies, and selected a good frequency pair in the on-orbit environment. At the last stage of the checkout, the gate valve, which protects the inside of the Dewar from outside air pressure at launch, was attempted to be opened to bring the system to a state where it is ready for regular operations but was failed.

Xtend is one of the two telescopes onboard the X-ray imaging and spectroscopy mission (XRISM), which was launched on September 7th, 2023. Xtend comprises the Soft X-ray Imager (SXI), an X-ray CCD camera, and the X-ray Mirror Assembly (XMA), a thin-foil-nested conically approximated Wolter-I optics. A large field of view of 38′ × 38′ over the energy range from 0.4 to 13 keV is realized by the combination of the SXI and XMA with a focal length of 5.6 m. The SXI employs four P-channel, back-illuminated type CCDs with a thick depletion layer of 200 μm. The four CCD chips are arranged in a 2×2 grid and cooled down to −110°C with a single-stage Stirling cooler. Before the launch of XRISM, we conducted a month-long spacecraft thermal vacuum test. The performance verification of the SXI was successfully carried out in a course of multiple thermal cycles of the spacecraft. About a month after the launch of XRISM, the SXI was carefully activated and the soundness of its functionality was checked by a step-by-step process. Commissioning observations followed the initial operation. We here present pre- and post-launch results verifying the Xtend performance. All the in-orbit performances are consistent with those measured on ground and satisfy the mission requirement. Extensive calibration studies are ongoing.

We present the design and performance of the XRISM Soft X-Ray Spectrometer Resolve, successfully launched on a JAXA H-IIA rocket September 7, 2023. The instrument uses a 36-pixel array of microcalorimeters at the focus of a grazing-incidence x-ray mirror. The instrument has achieved an energy resolution of 4.5 eV (FWHM) at 6. The overall cooling chain was designed to provide a lifetime of at least 3 years in orbit and operate without liquid helium to provide redundancy and the longest operational lifetime for the instrument. Early indications that the cryogen lifetime will exceed 4 years. X-rays are focused onto the array with a high-throughput grazing incidence X-ray Mirror Assembly with over 200 nested two-stage X-ray reflectors. A series of onboard X-ray calibrations sources allow simultaneous energy scale calibration lines simultaneously while observing celestial sources. The inflight performance of Resolve will be described along with a summary of the scientific capabilities.

The Resolve instrument was launched on-board the XRISM observatory in early September 2023. The Resolve spectrometer is based on a high-sensitivity X-ray calorimeter detector system that has been successfully deployed in many ground and sub-orbital spectrometers. However, the Resolve instrument will be the first long-term implementation in space. The instrument will provide essential diagnostics for nearly every class of X-ray emitting objects, from the atmosphere of Jupiter to the outskirts of galaxy clusters, without degradation for spatially extended objects. The Resolve detector system consists of a 36-pixel microcalorimeter array operated at a heat-sink temperature of 50mK. In pre-flight testing, the detector system demonstrated a resolving power of better than 1300 at 6 keV with a simultaneous bandpass from below 0.3 keV to above 12 keV and a timing precision better than 100 μs. An anti-coincidence detector placed directly behind the microcalorimeter array effectively suppresses background. The detector energy-resolution budget included terms for interference from the Resolve cooling system and the spacecraft. Additional terms for energy-scale stability, on-orbit effects, and use of mid-grade events were also included, predicting an end-of-life, on-orbit performance for high and mid-grade events that meets the requirement of 7 eV FWHM at 6 keV. Here we discuss the actual on-orbit performance of the Resolve detector system and compare this to performance in pre-flight testing, on-orbit predictions, and the almost identical Hitomi/SXS instrument. We will also discuss the on-orbit gain stability, any additional on-orbit interference, and measurements of the on-orbit background.

The in-orbit performance verification and calibration of the X-ray Mirror Assembly (XMA) on the XRISM satellite are ongoing. The optical performance of the XMA is being measured with bright point-like or bright small enough sources in orbit. This paper reports the preliminary results for the XMA of Resolve (Resolve- XMA). The in-orbit on-axis and off-axis (1.8′–9′ away from the aimpoint) Point Spread Function (PSF) of the Resolve-XMA were measured using 3C 273 and Cyg X-2, respectively. No significant changes were found in the PSF compared to on-ground results, indicating that the Resolve-XMA is functioning as expected (HPD ∼ 1.3′). For the Effective Area (EA) calibration, XRISM observed 3C 273 alongside other satellites. The Resolve spectrum of 3C 273 is well reproduced by an absorbed power law. While the best-fit photon index is consistent with that measured by NuSTAR, the flux is 5% higher than the NuSTAR measurement. In-orbit stray light observation was conducted with Crab at 60′ off from the aimpoint, and a signature of stray light on Resolve was detected. The observation of Resolve optical search has not yet been performed, and GX 3+1 has been proposed as the target.

XRISM (X-ray Imaging and Spectroscopy Mission) is an X-ray astronomy satellite developed in collaboration with JAXA, NASA and ESA. It successfully launched on Sept. 7, 2023. Two complementary X-ray telescopes, Resolve and Xtend are on-board XRISM. Resolve uses the pixelized X-ray micro calorimeter developed by NASA/GSFC and has very high energy resolution of 5 eV. On the other hand, Xtend uses an X-ray CCD camera as its focal plane detector which has high spatial resolution and a wide field of view. We evaluated the performance of the X-ray Mirror Assembly (XMA) for Xtend using data observed during the commissioning and PV phases of XRISM. To verify the imaging performance, the Point Spread Functions (PSF) generated from the observations of NGC 4151 and PDS 456 were compared with the ground-calibration results. The results show that the imaging performance of Xtend-XMA is not significantly different from that of the ground calibration, and that it meet the requirement. The effective area was verified by comparing the results of simultaneous observations of 3C 273 by XRISM and four X-ray astronomy satellites (Chandra, XMM-Newton, NuSTAR, and Swift). The results of the fitting of the X-ray spectrum of Xtend show no significant difference from the results of other satellites, suggesting the effective area used for fitting is correct. The on-axis position on the detector was estimated from the intensity of the Abell 2029 observations at four off-axis angles. The on-axis is about 40 arcsec away from the aim point, and the decrease in effective area at the aim point is less than 1%. Stray light observations of the Crab Nebula at 60 arcmin off-axis were obtained at two different satellite roll angles. The stray light intensity obtained at each roll angle was significantly different, verifying the dependence of the stray light on the roll angle.

The X-Ray Imaging and Spectroscopy Mission (XRISM) is an international X-ray observatory developed by Japan Aerospace Exploration Agency (JAXA) and National Aeronautics and Space Administration (NASA) in collaboration with European Space Agency (ESA), successfully launched in September 2023. Since the early stage of the project, the XRISM science operations team (SOT) was organized independently of the spacecraft bus system and mission instrument development teams, having prepared for the in-orbit science operations to maximize the scientific outputs. During about half year for the initial operation phase after launch, operations for the mission instruments were started, and the quick-look and the pipeline processes were carried out by SOT in order to check the functions of the instruments. After transition to the nominal operation phase, we started the target observations in the performance verification phase, whose short and long-term observation plans are considered by SOT, including planning the target of opportunity observations. The information on the observation modes of the mission instruments and the status of the data processing is maintained collectively in database synchronized between JAXA and NASA. We also performed the performance verification and optimization activities which provide the well-calibrated data, appropriate tools, and analysis methods for the users and established a help desk that supports the XRISM data analysis. The publicly solicited observation for the guest observer will be started from August or September 2024. These daily science operations are being carried out by dedicated scientists belonging to JAXA in collaboration with the other SOT members, the mission operations team and the instrument teams. This paper will introduce the ground system for the XRISM science operations and report on the activities of the SOT from the launch to today and plans for future science operations.

The XRISM is the newly born X-ray satellite led by JAXA and NASA in collaboration with ESA, aiming to perform high-resolution spectroscopy of many astronomical X-ray objects. In the era of multi-messenger astronomy, where observations are performed in various wavelengths and include neutrino and gravitational data, it is important for the observatories to assign precise time of photons. To achieve the science goals of the XRISM mission, an absolute timing accuracy of 1.0 ms is required for the Resolve. The timing system, including both onboard instruments and off-line data-processing tools, is designed to meet this requirement. Following the lessons of the previous X-ray mission of Hitomi, comprehensive list of items that affect the accuracy of the timing are listed together with the timing error budget. During the system design and verification phases on the ground, all elements are controlled and verified to be within the budgets at the component level. After the launch of the satellite on 7 September 2023, in the initial commissioning phase, the overall timing performance of the timing system is scheduled to be confirmed to satisfy the timing requirements using a millisecond pulsar. The XRISM spacecraft carries the GPS receiver and the timing system uses the GPS signals in the nominal operation mode. In this presentation, we summarize the detailed design of the timing system of the XRISM, and the results of the timing verification tests both on ground and in orbit in the nominal operation mode. Detailed results on the failure mode of the GPS receiver will be presented in another presentation.

The Resolve instrument aboard the X-ray Imaging and Spectroscopy Mission (XRISM) is a 36-pixel microcalorimeter spectrometer that provides non-dispersive spectroscopy with 5 eV spectral resolution in the soft x-ray waveband. Resolve has a requirement to provide absolute energy-scale calibration of ± 2 eV from 0.3–12 keV. In this manuscript we describe our ground calibration strategy and results of a subset of the ground calibration campaigns, including a discussion of improvements in the energy scale ground calibration compared to Hitomi’s. These improvements include calibration of the low-energy band below 4 keV with the instrument in the flight dewar and the dewar aperture door open, which was not performed for Hitomi, and thorough measurements over an extended high-energy waveband to 22 keV. We also developed an improved technique for gain calibration of ‘mid-res’ secondary events, which have suppressed gain due to proximity to a preceding x-ray event (18-70 ms) on the same pixel. We provide an assessment of how well these pre-launch gain scales correct on-orbit data and discuss approaches for updating the gain curves. Energy-scale calibration approaches for future space-based instruments, including the X-ray Integral Field Unit (X-IFU) on Athena and the microcalorimeter spectrometer proposed for the Line Emission Mapper (LEM), have heritage in the calibration of XRISM. We briefly comment on lessons learned from Resolve calibration that are relevant for these future instruments.

High spatial- and spectral-resolution X-ray capabilities are essential for future strategic missions to address the key priorities set forth by the 2020 Decadal Survey on Astronomy and Astrophysics. These missions will require megapixel X-ray imaging detectors more capable than any available today, providing frame rates at least a factor of 20 faster and pixel aspect ratios twice as large, while retaining the low noise and excellent spectral performance of current sensors.

We summarize recent results from our NASA-funded technology development program to develop imaging sensors required for future strategic missions, and describe the prototype CCD sensor we are developing for AXIS, the Advanced X-ray Imaging Satellite mission concept recently proposed in response to NASA’s Astrophysics Probe Explorer call. We have designed and are fabricating at MIT Lincoln Laboratory a 16-output, 1440 x 1440 pixel frame-store CCD to serve as a form/fit/function prototype for AXIS. This sensor incorporates the low-voltage, single-polysilicon gate and low-noise pJFET technologies we have proven in previous work. Our goal is to demonstrate a device meeting or exceeding the noise, spectral resolution and frame-rate requirements of AXIS when operated with the Multi-channel Readout Chip developed by our team at Stanford University. We also describe our strategy for optimizing CCD output amplifier architecture and design for even lower noise and faster readout for AXIS and subsequent high-energy astrophysics missions.

Bringing artificial intelligence (AI) alongside next-generation X-ray imaging detectors, including CCDs and DEPFET sensors, enhances their sensitivity to achieve many of the flagship science cases targeted by future X-ray observatories, based upon low surface brightness and high redshift sources. Machine learning algorithms operating on the raw frame-level data provide enhanced identification of background vs. astrophysical X-ray events, by considering all of the signals in the context within which they appear within each frame. We have developed prototype machine learning algorithms to identify valid X-ray and cosmic-ray induced background events, trained and tested upon a suite of realistic end-to-end simulations that trace the interaction of cosmic ray particles and their secondaries through the spacecraft and detector. These algorithms demonstrate that AI can reduce the unrejected instrumental background by up to 41.5 per cent compared with traditional filtering methods. Alongside AI algorithms to reduce the instrumental background, next-generation event reconstruction methods, based upon fitting physically-motivated Gaussian models of the charge clouds produced by events within the detector, promise increased accuracy and spectral resolution of the lowest energy photon events.

The DarkNESS CubeSat will deploy skipper-CCDs, the most sensitive silicon detectors to date, on a nano-satellite to study the diffuse X-ray background in the Milky Way and search for Dark Matter (DM). DM is an abundant, but invisible, presence in our Universe. It dictates how galaxies were initially formed and influences their dynamics today. The total mass of DM in the universe is known to be five times that of ordinary matter, but its true nature remains elusive, and its identity is one of the biggest questions in science today. We will search for DM by mapping the Galaxy's diffuse X-ray spectrum using an array of skipper-CCDs on a nanosatellite in LEO. This will address the experimental conundrum associated with the observation of an unidentified 3.5~keV X-ray line, potentially produced from the decay of a DM particle. The mission will also perform a direct search for low-mass, strongly-interacting DM candidate particles that would not penetrate the Earth’s atmosphere and are therefore inaccessible to terrestrial DM experiments

Traditional cosmic ray filtering algorithms used in X-ray imaging detectors aboard space telescopes perform event reconstruction based on the properties of activated pixels above a certain energy threshold, within 3×3 or 5×5 pixel sliding windows. This approach can reject up to 98% of the cosmic ray background. However, the remaining unrejected background constitutes a significant impediment to studies of low surface brightness objects, which are especially prevalent in the high-redshift universe. The main limitation of the traditional filtering algorithms is their ignorance of the long-range contextual information present in image frames. This becomes particularly problematic when analyzing signals created by secondary particles produced during interactions of cosmic rays with body of the detector. Such signals may look identical to the energy deposition left by X-ray photons, when one considers only the properties within the small sliding window. Additional information is present, however, in the spatial and energy correlations between signals in different parts of the same frame, which can be accessed by modern machine learning (ML) techniques. In this work, we continue the development of an ML-based pipeline for cosmic ray background mitigation. Our latest method consist of two stages: first, a frame classification neural network is used to create class activation maps (CAM), localizing all events within the frame; second, after event reconstruction, a random forest classifier, using features obtained from CAMs, is used to separate X-ray and cosmic ray features. The method delivers > 40% relative improvement over traditional filtering in background rejection in standard 0.3-10 keV energy range, at the expense of only a small (< 2%) level of lost X-ray signal. Our method also provides a convenient way to tune the cosmic ray rejection threshold to adapt to a user’s specific scientific needs.

The Lunar Electromagnetic Monitor in X-rays (LEM-X) is an imager for X-ray Astronomy to be installed on the surface of the Moon, is funded by the Italian Ministero dell’Università e della Ricerca Scientifica and lead by the Istituto Nazionale di Astrofisica in the framework of the Italian “Piano Nazionale di Ripresa e Resilienza”. The building block of LEM-X is represented by a pair of coded aperture cameras, each one built around four large-area linear Silicon Drift Detectors and able to image the sky within a field of view of ~1 sr with a source location accuracy of ~1 arcmin, while at the same time reaching a spectral resolution better than 350 eV FWHM at 6 keV. The LEM-X instrument preliminarily envisages about seven such camera pairs, arranged on a dome-like structure on the surface of the Moon, to reach a sensitivity better than 5 mCrab in 50 ks and 1 Crab in 1 s in the 2 – 50 keV energy band. In this contribution we describe the design of LEM-X, we discuss the scientific performance and we report the status of the instrument development.

SVOM (Space based Variable Object Monitor) is a Chinese-French mission dedicated to the study of the most luminous explosions in the Universe: Gamma-Ray Bursts. This observatory for time-domain astrophysics is due for launch on June 24th 2024. Among the four space borne instruments is the Micro-channel X-ray Telescope (MXT). The MXT is a focusing X-ray telescope, based on “lobster-eye” optics, whose main goal is to improve the localization of transient sources, as well as to measure their timing and spectral properties. The MXT camera is implementing a 256 × 256 pixels pnCCD detector, sensitive in the 0.2-10 keV energy range. The spectral performance of the MXT instrument was measured in 2021 during the calibration campaign at the MPE PANTER X-ray facility and the End-to-End testing during the vacuum and thermal tests of the full satellite in the SECM Shanghai integration facility. SVOM is in a low-Earth orbit crossing the South Atlantic Anomaly, and the MXT will thus be submitted to irradiation, in particular from protons, that will cause radiation damage. To anticipate the evolution of the MXT performances over its three years mission lifetime, a spare flight model of the MXT detector plane has been irradiated with 50 MeV protons at the Arronax cyclotron facility, and then installed and characterized at the X-ray Metrology beamline of the SOLEIL Synchrotron in June 2023.

This paper presents the results of calibration campaigns to infer the performances of the MXT instrument over the lifetime of the SVOM mission.

Hot Universe Baryon Surveyor (HUBS) is proposed as a dedicated probe of hot gas in galaxy ecosystems, which is beyond the capabilities of current X-ray observatories but holds a key to understanding galaxy evolution. It employs a non-dispersive spectrometer based on TES microcalorimeters, enabling both high-resolution spectroscopy and imaging. In this contribution, we briefly describe the progress on the development of TES microcalorimeters for HUBS, as well as that of supporting key technologies including frequency-division multiplexing readout electronics, cryocoolers and adiabatic demagnetization refrigerator, and wide-field X-ray optics. We also show the design of a pathfinder experiment (DIXE), which is being considered for inclusion in the science portfolio of the China Space Station, not only to advance the TRLs of the key technologies for HUBS, but to conduct a high-resolution X-ray spectroscopic survey for the first time.

The Large Area Detector (LAD) is the high-throughput, spectral-timing instrument designed for the eXTP (enhanced Xray Timing and Polarimetry) mission, a major project of the Chinese Academy of Sciences and China National Space Administration. The eXTP science case involves the study of matter under extreme conditions of gravity, density and magnetism. The eXTP mission is currently performing a phase B study, expected to be completed by the end of 2024. The target launch date is end-2029. Until recently, the eXTP scientific payload included four instruments (Spectroscopy Focusing Array, Polarimetry Focusing Array, Large Area Detector and Wide Field Monitor) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. The mission designed was however rescoped in early 2024 to meet the programmatic requirements of a final mission adoption in the context of the Chinese Academy of Sciences. Negotiations are still ongoing at agency level to assess the feasibility of a European participation to the payload implementation, by providing the LAD and WFM instruments, through a European Consortium composed of institutes from Italy, Spain, Austria, Czech Republic, Denmark, France, Germany, Netherlands, Poland, Switzerland and Turkey. At the time of writing, the LAD instrument is thus a scientific payload proposed for inclusion on eXTP. The LAD instrument for eXTP is based on the design originally proposed for the LOFT mission within the ESA-M3 context. The eXTP/LAD envisages a deployed >3 m² effective area in the 2-30 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors - offering a spectral resolution of up to 200 eV FWHM at 6 keV - and of capillary plate collimators - limiting the field of view to about 1 degree. In this paper we provide an overview of the LAD instrument design and the status of its maturity when approaching nearly the end of its phase B study.

The eXTP (enhanced X-ray Timing and Polarimetry) mission is a major project of the Chinese Academy of Sciences (CAS), with a large involvement of Europe. Its scientific payload includes four instruments: SFA (Spectroscopy Focusing Array), PFA (Polarimetry Focusing Array), LAD (Large Area Detector) and WFM (Wide Field Monitor). They offer an unprecedented simultaneous wide-band Xray timing and polarimetry sensitivity. A large European consortium is contributing to the eXTP study, both for the science and the instrumentation. Europe is expected to provide two of the four instruments: LAD and WFM; the LAD is led by Italy and the WFM by Spain. The WFM for eXTP is based on the design originally proposed for the LOFT ESA M3 mission, that underwent a Phase A feasibility study. It will be a wide field of view X-ray monitor instrument working in the 2-50 keV energy range, achieved with large-area Silicon Drift Detectors (SDDs), similar to the ones used for the LAD but with better spatial resolution. The WFM will consist of 3 pairs of coded mask cameras with a total combined field of view (FoV) of 90x180 degrees at zero response and a source localisation accuracy of ~1 arc min. The main goal of the WFM onboard eXTP is to provide triggers for the target of opportunity observations of the narrow field of view instruments (SFA, PFA and LAD), in order to perform the core science observation programme, dedicated to the study of matter under extreme conditions of density, gravity and magnetism. In addition, the unprecedented combination of large field of view and imaging capability, down to 2 keV, of the WFM will allow eXTP to make important discoveries of the variable and transient X-ray sky, and provide X-ray coverage of a broad range of astrophysical objects covered under 'observatory science', such as gamma-ray bursts, fast radio bursts, gravitational wave electromagnetic counterparts. In this paper we provide an overview of the WFM instrument, explaining its design, configuration, and anticipated performance. Right now, eXTP is in phase B2, after a successful I-SRR (Instrument System Requirements Review). It is waiting for the adoption of the whole eXTP mission in China. Details about the current work in Phase B2, including the manufacturing and testing of the demonstration models of the WFM subsystems, will be presented, paying also a special emphasis on the collaboration with space dedicated industrial partners.

HERMES (High Energy Rapid Modular Ensemble of Satellites) Pathfinder is a space-borne mission based on a constellation of six nano-satellites flying in a low-Earth orbit (LEO). The 3U CubeSats, to be launched in early 2025, host miniaturized instruments with a hybrid Silicon Drift Detector/GAGG:Ce scintillator photodetector system, sensitive to X-rays and gamma-rays in a large energy band. HERMES will operate in conjunction with Australian Space Industry Responsive Intelligent Thermal (SpIRIT) 6U CubeSat, launched in December 2023. HERMES will probe the temporal emission of bright high-energy transients such as Gamma-Ray Bursts (GRBs), ensuring a fast transient localization in a field of view of several steradians exploiting the triangulation technique. HERMES intrinsically modular transient monitoring experiment represents a keystone capability to complement the next generation of gravitational wave experiments. In this paper we outline the scientific case, development and programmatic status of the mission.

HiZ-GUNDAM is a future satellite mission whose mission concept was approved by ISAS/JAXA, and it is one of the future satellite candidates of JAXA’s competitive medium-class mission. HiZ-GUNDAM will lead time-domain astronomy in 2030s, and its key sciences are (1) exploration of the early universe with high-redshift gamma-ray bursts, and (2) contribution to the multi-messenger astronomy. Two mission payloads are aboard HiZ-GUNDAM to realize these two scientific issues. The wide field X-ray monitors which consist of Lobster Eye optics array and focal imaging sensor, monitor ~0.5 steradian field of view in 0.5–4 keV energy range. The near infrared telescope with an aperture size of 30 cm in diameter performs simultaneous 5-band photometric observation in 0.5–2.5 μm wavelength with Koester’s prism for X-ray transients discovered by Wide Field X-ray Monitor. In this paper, we introduce the mission overview of HiZ-GUNDAM while the information contained herein may change in future studies.

The HiZ-GUNDAM mission is one of the candidates for the JAXA’s competitive M-class missions. HiZ-GUNDAM revolutionizes our understanding of the high redshift universe and promotes multi-messenger astronomy. Combining a highly sensitive wide-field X-ray monitor, a near-infrared telescope, and autonomous spacecraft slew capability makes a powerful machine to hunt interesting X-ray transients and immediately identify their counterparts in near-infrared. The Wide Field X-ray Monitor (WFXM) is the main instrument to search for the transients in the soft X-ray band. WFXM comprises lobster-eye optics (LEO) and pnCCD as an X-ray imager. LEO has a size of 40 mm x 40 mm and a radius of curvature of 600 mm. We are planning to use the LEO manufactured by Photonis Inc. One WFXM module has three by three LEOs, which cover a field of view of 12 deg x 12 deg. The current baseline design is composed of 16 modules to cover 0.7 sr sky. The candidate focal imager is the pnCCD detector by PNSensor Inc. We will present the current status and prospects of the WFXM.

HiZ-GUNDAM is a future satellite mission for gamma-ray burst observations. One of the mission instruments is the wide-field X-ray monitor with a field of view (FoV) of 0.6 steradian at 0.4–4.0 keV, consisting of Lobster Eye Optics (LEO) and pnCCD image sensors. LEOs need to be spatially well-aligned to achieve both of wide FoV and fine position accuracy of < 3 arcmin. To address this challenge, we explored an alignment method with X-rays and developed an optical frame. This study reports on the evaluation of the optical frame, our alignment method, and x-ray performance of the optical system.

We have been developing X-ray optics for a fourth FOXSI (Focusing Optics X-ray Solar Imager) sounding rocket experiment, FOXSI-4. We fabricated two types of X-ray optics, soft X-ray optics (SXR) and hard X-ray optics (HXR), specified for soft and hard X-ray observations. We conducted X-ray irradiation tests to evaluate X-ray performances such as angular resolution and effective area. For the Flight Model (FM) SXR, the resultant angular resolution in Half Power Diameter (HPD) is 16 ± 2 / 14 ± 2 arcseconds at 2.7 / 4.5 keV for the best images, respectively and no significant energy dependence in HPD is seen. The observed effective area was reproduced within an accuracy of 10% by using our original ray-tracing simulator considering all of the SXR components in the 1.5-16 keV range at the smallest off-axis angle. Subsequently, both FM mirror module assemblies were integrated into a sounding rocket in combination with detectors and the vibration tests were performed for the whole sounding rocket system. Finally, FOXSI-4 was successfully launched on April 17, 2024 (UTC), and the sounding rocket and the data were also recovered successfully.

The Decadal Survey on Astronomy and Astrophysics 2020 issued in 2021 by the National Academies delivered strong recommendations for NASA to consider future missions to complement detections of gravitational waves and neutrinos with electromagnetic observations in space, and more generally to sustain its fleet of missions that contribute to the science enabled by multi-messenger and time-domain astronomy. In this presentation we discuss the current technology investments by NASA in this vibrant field, including detector development, infrastructure, suborbital experiments, and small satellites.

HEX-P is a probe-class mission concept that combines the power of high angular resolution with broad bandpass coverage to provide the necessary leap in capabilities to address the important astrophysical questions of the next decade. HEX-P achieves its breakthrough performance by combining technologies developed by experienced partners and international collaborations. HEX-P will be launched into L1 for a high observing efficiency, and to meet the science goals the payload consists of a suite of three co-aligned X-ray telescopes designed to cover the 0.2 - 80 keV bandpass where accretion is at its peak. The High Energy Telescope (HET) has an effective bandpass of 2-80 keV, and the Low Energy Telescope (LET) an effective bandpass of 0.2-20 keV. The combination of bandpass and high observing efficiency delivers a powerful General Observer platform for a broad science that services a wide community base. The baseline mission is 5 years, with 30% of t

The Arcus Probe mission addresses a wide range of Astro2020 Decadal and NASA Science Mission Directorate Priority science areas, and is designed to explore astrophysical feedback across all mass scales. Arcus' three baseline science goals include: (i) Characterizing the drivers of accretion-powered feedback in supermassive black holes, (ii) Quantifying how feedback at all scales drives galaxy evolution and large-scale structure, including the tenuous cosmic web, and (iii) Analyzing stellar feedback from exoplanetary to galactic scales, including its effects on exoplanet environments targeted by current and future NASA missions. These science goals, along with a robust General Observer program, will be achieved using a mission that provides a high-sensitivity soft (10-60Å) X-ray spectrometer (XRS), working simultaneously with a co-aligned UV spectrometer (UVS; 970-1580Å). Arcus enables compelling baseline science and provides the broader astronomy community a revolutionary tool to characterize the full ionization range of warm and hot plasmas - including hydrogen, helium, and all abundant metals - in the Universe, from the halos of galaxies and clusters to the coronae of stars.

The Line Emission Mapper (LEM) is a Probe mission concept developed in response to NASA’s Astrophysics Probe Explorer (APEX) Announcement of Opportunity. LEM has a single science instrument composed of a large-area, wide-field X-ray optic and a microcalorimeter X-ray imaging spectrometer in the focal plane. LEM is optimized to observe low-surface-brightness diffuse X-ray emission over a 30′ equivalent diameter field of view with 1.3 and 2.5 eV spectral resolution in the 0.2−2.0 keV band. Our primary scientific objective is to map the thermal, kinetic, and elemental properties of the diffuse gas in the extended X-ray halos of galaxies, the outskirts of galaxy clusters, the filamentary structures between these clusters, the Milky Way star-formation regions, the Galactic halo, and supernova remnants in the Milky Way and Local Group. The combination of a wide-field optic with 18′′ angular resolution end-to-end and a microcalorimeter array with 1.3 eV spectral resolution in a 5′ × 5′ inner array (2.5 eV outside of that) offers unprecedented sensitivity to extended low-surface-brightness X-ray emission. This allows us to study feedback processes, gas dynamics, and metal enrichment over seven orders of magnitude in spatial scales, from parsecs to tens of megaparsecs. LEM will spend approximately 11% of its five-year prime science mission performing an All-Sky Survey, the first all-sky X-ray survey at high spectral resolution. The remainder of the five-year science mission will be divided between directed science (30%) and competed General Observer science (70%). LEM and the NewAthena/XIFU are highly complementary, with LEM’s optimization for soft X-rays, large FOV, 1.3 eV spectral resolution, and large grasp balancing the NewAthena/X-IFU’s broadband sensitivity, large effective area, and unprecedented spectral resolving power at 6 keV. In this presentation, we will provide an overview of the mission architecture, the directed science driving the mission design, and the broad scope these capabilities offer to the entire astrophysics community.

The Advanced X-ray Imaging Satellite (AXIS), a concept recently submitted to NASA’s Astrophysics Probe Explorer competition, will offer low-background, arcsecond-resolution imaging in the 0.3–10 keV band across a 450-arcmin2 field of view, with an effective area at 1 keV of at least 4200 cm². AXIS will bring X-ray astronomy back to the forefront of modern mainstream astrophysics, reaching equivalent depths in X-rays to many of the major facilities of the 2030’s (e.g., JWST, Roman, Rubin, ngVLA, LISA) to address the most important questions identified by the Astro2020 Decadal Survey. Here, we present an update on the status of AXIS.

The Spectroscopic Time-Resolving Observatory for Broadband X-rays (STROBE-X) is a proposed NASA Astrophysics Probe-class mission. STROBE-X is a time domain and multi-messenger mission designed to provide an unparalleled laboratory for probing strong gravity and the behavior of matter in extreme environments. The instrument suite encompasses a wide-field monitor and two pointed instruments to provide transient discovery and the capability for rapid follow-up with broadband (0.2–30 keV), high time resolution spectroscopy. Over 10,000 pointed observations will be conducted each year and STROBE-X will be able to slew to targets within minutes in response to transients triggered by on-board or ground alerts. Here, we present an overview of the STROBE-X science drivers, mission design, and instrument complement.

The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket experiment enables hard-X-ray solar observations with high angular resolution, high energy resolution, and high sensitivity using the direct imaging method. The fourth flight, FOXSI-4, aimed for the first-ever focusing imaging spectroscopic observation of a medium to large solar flare in hard X-rays and launched in spring 2024 as part of NASA’s sounding rocket solar flare campaign. For resolving structures in the footpoints and the loop-top of a solar flare, the hard X-ray telescopes, which consist of focal plane detectors and Wolter-I mirrors, are required for high angular resolution of 3 arcseconds with high-count-rate photon detection.

We developed wide-gap CdTe Double-sided Strip Detectors (CdTe-DSDs) for the hard X-ray focal plane detector, which achieved an energy resolution of 1 keV (FWHM) and a high position resolution of 30 Μm with high detection efficiency. We also developed a new onboard data acquisition (DAQ) system with a Raspberry Pi, an FPGA board SPMU-001, and a SpaceWire interface for controlling all CdTe-DSDs and realizing fast readout of the observation data whose counting rate is estimated to be 5000 counts per second. The observation data is written in a 128 MB data ring buffer region for temporary storage. The software in the Raspberry Pi controls each detector by the commands from a ground-based computer and simultaneously reads the data at 0.6 Mbps for storage in the DAQ. Some essential data for operation, for example, light curves, energy spectrum, and the status of the DAQ system, is sent to the ground-based computer through the onboard control system.

THESEUS is a space mission concept that is undergoing a Phase A study by ESA as a candidate M7 mission. The mission aims at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. The mission will exploit high-redshift GRBs for cosmology and allow the identification and study of the electromagnetic counterparts to sources of gravitational waves, which will be routinely detected in the ’30s by next-generation facilities like aLIGO/aVirgo, LISA, KAGRA, and Einstein Telescope (ET), as well as of most classes of X/gamma-ray transient sources. As such, THESEUS will secure ideal synergies with virtually all electromagnetic facilities of the near future like, e.g., LSST, ELT, TMT, SKA, CTA, ATHENA. These breakthrough scientific objectives will be achieved by an unprecedented combination of X/gamma-ray monitors and an on-board NIR telescope.

The LargE Area burst Polarimeter (LEAP) is a proposed Compton scattering polarimeter that will, for the first time, measure the level of polarization for a significant number of GRBs with sufficient sensitivity to determine the magnetic field structure, composition, energy dissipation mechanism of GRB jets, and determine the prompt emission mechanism of GRBs. Once approved, LEAP will be deployed as an external payload on the International Space Station (ISS) where it will measure GRB polarization over the energy range from 50–1000 keV, perform GRB spectroscopy from 20 keV to 6 MeV, and self-sufficiently determine the source direction. LEAP is uniquely suited to fill a critical gap in our knowledge regarding GRBs, by exposing the underlying physics that governs astrophysical jets and the extreme environment surrounding newborn compact objects.

The KOYOH satellite, launched on December 1, 2023, aboard a SpaceX Falcon 9 rocket from Vandenberg Space Force Base, is a 50-kg class microsatellite designed to advance the understanding of short gamma-ray bursts (GRBs) and their association with gravitational wave (GW) events. The satellite operates in a Sun-Synchronous Orbit (SSO), equipped with the Transient Localization Experiment (T-LEX) and the Gamma-ray Detector (KGD). T-LEX, a wide-field X-ray imaging detector, and KGD, a wide-field gamma-ray detector, are designed to detect and localize GRBs and other high-energy transients. Following its launch and initial deployment, the satellite successfully established communication links and confirmed the operational status of its subsystems. Initial telemetry data verified the deployment of the Solar Array Paddles (SAP) and correct orientation towards the Sun. The satellite’s power systems were confirmed to be functioning nominally. Subsequent tests established the functionality of the mission instruments. The KGD exhibited a count rate of about 300-500 counts/sec at low latitudes, while T-LEX showed a count rate of approximately 200-300 counts/sec in total. These initial results confirm the successful detection of X-ray and gamma-ray photons by both instruments in orbit. This paper details the design, launch, initial operations, and early mission results of the KOYOH satellite, highlighting its contributions to multi-messenger astronomy.

GEO-X (GEOspace X-ray imager) is a small satellite mission to visualize the Earth’s magnetosphere through Solar Wind Charge eXchange (SWCX). SWCX is known as soft X-ray emissions generated by the charge exchange between highly charged-state heavy ions and neutral atoms in the Earth’s exosphere. The GEO-X satellite is aimed to be launched during the upcoming solar maximum around 2025-2027 and is planned to be injected to a low-latitude orbit which allows visualization of the magnetosphere from outside the magnetosphere. The satellite will carry a light-weight X-ray imaging spectrometer, dramatically improving the size and weight of those onboard past X-ray astronomy satellites.

BurstCube is a 6U (10 x 20 x 30 cm) CubeSat designed to detect gamma-ray bursts (GRBs) and enable multimessenger observations, scheduled to launch in early 2024. BurstCube science is informed by the coincident detection of GRB 170817A and gravitational wave (GW) 170817, which confirmed compact binary mergers as progenitors for GRBs. Future coincident detections will also provide important context to the GW measurements - namely constraining the neutron star equation of state and testing fundamental physics, while also probing the origin of GRB prompt emission. Full sky coverage in the gamma-ray regime is needed to increase the likelihood of such measurements. Once in orbit, BurstCube will expand sky coverage while rapidly providing public alerts and localization information to the community using the Tracking and Data Relay Satellite (TDRS) and General Coordinates Network (GCN). This work will describe the current status of the mission, as well as an outline of post-launch operations, performance, and science goals.

The upper atmosphere at the altitude of 60–110 km, the mesosphere and lower thermosphere (MLT), has the least observational data of all atmospheres due to the difficulties of in-situ observations. Previous studies demonstrated that atmospheric occultation of cosmic X-ray sources is an effective technique to investigate the MLT. Aiming to measure the atmospheric density of the MLT continuously, we are developing an X-ray camera, “Soipix for observing Upper atmosphere as Iss experiment Mission (SUIM)”, dedicated to atmospheric observations. SUIM will be installed on the exposed area of the International Space Station (ISS) and face the ram direction of the ISS to point toward the Earth rim. Observing the cosmic X-ray background (CXB) transmitted through the atmosphere, we will measure the absorption column density via spectroscopy and thus obtain the density of the upper atmosphere. The X-ray camera is composed of a slit collimator and two X-ray SOI-CMOS pixel sensors (SOIPIX), and will stand on its own and make observations, controlled by a CPU-embedded FPGA “Zynq”. We plan to install the SUIM payload on the ISS in 2025 during the solar maximum. In this paper, we report the overview and the development status of this project.

Chronos is a X-ray observatory concept capable of “hour-level” follow up observations of transient alerts in 2030s’ multi-messenger astronomy, with 0.3–40+ keV wide X-ray band-width and 250–300 nm ultra-violet (UV) coverage. The mission has a good hard X-ray imaging spectroscopy with > 9′ field of view, the soft X-ray imager with > 30′ field of view, and the UV imager with > 7° field of view. Aiming at launch in mid-2030s, the mission is designed to provide wide-band spectroscopy of time dependent high-energy phenomena. The low background and large effective area in the hard X-ray band also make it good at observing diffuse hard X-ray emissions, such as many TeV sources which will be newly found in 2030s.

We have, at last, an observatory dedicated to X-ray polarimetry that has been operational since December 9th, 2021. The Imaging X-ray Polarimetry Explorer (IXPE) is a NASA SMEX mission, in partnership with ASI, based on three X-ray telescopes, each equipped with a polarization-sensitive detector in the focus. An extending boom was deployed in orbit, positioning the detectors at the optimal distance from the optics, which have a 4-meter focal length. The spacecraft is three-axis stabilized, providing power, attitude determination and control, transmission, and commanding capabilities.

After two and a half years of observation, IXPE has detected positive polarization from nearly all classes of celestial sources that emit X-rays. In this report, we describe the IXPE mission, detailing the performance of the scientific instrumentation after 2.5 years of operation. We also present the main astrophysical results and a few examples of scientific performance during flight.

The Compton Spectrometer and Imager (COSI) is a NASA funded Small Explorer (SMEX) mission slated to launch in 2027. COSI will house a wide-field gamma-ray telescope designed to survey the entire sky in the 0.2-5 MeV range. Using germanium detectors, the instrument will provide imaging, spectroscopy, and polarimetry of astrophysical sources with excellent energy resolution and degree-scale localization capabilities. In addition to the main instrument, COSI will fly with a student collaboration project known as the Background and Transient Observer (BTO). BTO will extend the COSI bandpass to energies lower than 200 keV, thus enabling spectral analysis across the shared band of 30 keV–2 MeV range. The BTO instrument will consist of two NaI scintillators and student-designed readout electronics. Using spectral information from both the COSI and BTO instruments, physics such as the energy peak turnover in gamma-ray bursts, the characteristics of magnetar flares, and the event frequency of a range of transient phenomena will be constrained. In this paper, we present the expected science returnables from BTO and comment on the shared returnables from the COSI and BTO missions. We include simulations of gamma-ray bursts, magnetar giant flares, and terrestrial gamma-ray flashes using BTO’s spectral response. Additionally, we estimate BTO’s gamma-ray burst detection rate and find that BTO will detect ∼100–150 gamma-ray bursts per year, with at least 10% of the events being sGRB.

The Gamma-Ray Polarimeter Experiment (GRAPE) is a high-altitude balloon experiment designed for polarization studies of transient sources with a long-term goal of observing Gamma-Ray Bursts (GRBs) aboard a series of Long Duration Balloon flights (LDBs). Polarization studies of GRB prompt emission is necessary to constrain existing physics models describing the radiation processes and magnetic field structures of astrophysical jets. GRAPE is a wide field of view (FoV) Compton polarimeter measuring γ-ray polarization in the 50-500 keV energy range with a broad range (20 keV – 3 MeV) for spectroscopy. The novel 3-dimensional geometry of the current design provides GRAPE with Compton imaging in addition to polarization capabilities. The instrument consists of 245 optically isolated SiPM coupled to either high-Z (GAGG:Ce) or low-Z (para-Terphenyl) scintillator arranged in a 7x7x5 cuboid structure. At the center of the scintillator array two low-Z detectors contain a ~25 nCi Co-60 calibration source for onboard calibrations. A test flight of this design was flown on August 27, 2023, from Fort Sumner, NM to validate the scientific capability of the instrument design. We will report on res

Many questions posed in the Astro2020 Decadal survey in both the New Messengers and New Physics and the Cosmic Ecosystems science themes require a gamma-ray mission with capabilities exceeding those of existing (e.g. Fermi, Swift) and planned (e.g. COSI) observatories. ComPair, the Compton Pair telescope, is a prototype of such a next-generation gamma-ray mission. It had its inaugural balloon flight from Ft. Sumner, New Mexico in August 2023. To continue the goals of the ComPair project to develop technologies that will enable a future gamma-ray mission, the next generation of ComPair (ComPair-2) will be upgraded to increase the sensitivity and low-energy transient capabilities of the instrument. These advancements are enabled by AstroPix, a silicon monolithic active pixel sensor, in the tracker and custom dual-gain silicon photomultipliers and front-end electronics in the calorimeter. This effort builds on design work for the All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) concept that was submitted the 2021 MIDEX Announcement of Opportunity. Here we describe the ComPair-2 prototype design and integration and testing plans to advance the readiness level of these novel technologies.

The CUbesat Solar Polarimeter (CUSP) project is a future CubeSat mission orbiting the Earth aimed to measure the linear polarization of solar flares in the hard X-ray band, by means of a Compton scattering polarimeter. CUSP will allow us to study the magnetic reconnection and particle acceleration in the flaring magnetic structures of our star. The project is in the framework of the Italian Space Agency Alcor Program, which aims to develop new CubeSat missions. CUSP is approved for a Phase B study that will last for 12 months, starting in mid-2024. We report on the current status of the CUSP mission project as the outcome of the Phase A.

GRAMS (Gamma-Ray and AntiMatter Survey) is a next-generation proposed balloon-borne/satellite-based mission aimed at high sensitivity MeV gamma-ray astrophysical observations and background-free indirect dark matter search via hadronic antiparticles. The main detector of GRAMS is a meter-scale liquid argon time projection chamber (LArTPC). The adoption of liquid argon as detector material allows us to produce an unprecedentedly large effective area instrument both for cosmic MeV gamma rays of 0.5-20 MeV and antiparticles of dark matter origin. This large effective area, which will exceed 1000 cm2, is necessary for measuring faint gamma-ray signals of nuclear line emissions from energetic phenomena such as supernovae as well as for observing short-duration transient objects including gamma-ray bursts with high photon statistics. In this talk, we present the mission concept and design, the current proof-of-concept studies using prototype LArTPCs, and an engineering balloon flight conducted in 2023.

We are planning to launch a 50kg-class satellite named INSPIRE, equipped with a small, high-performance Hybrid Compton Camera (HCC) for MeV gamma-ray astronomy.Since the launch of the COMPTEL satellite in 1991, there have been limited observations in the MeV gamma-ray band. However, this energy range is crucial for studying nucleosynthesis processes. INSPIRE aims to conduct a wide-area survey of nuclear gamma rays from the galactic plane and includes gamma-ray observations of solar flares as one of its objectives. Equipped with a hybrid Compton camera (HCC) system, INSPIRE can perform simultaneous X-ray and gamma-ray imaging. This is achieved by integrating the features of both Compton and pinhole cameras within a single detector system. The system includes two sensor layers of large-area Silicon Photomultiplier (SiPM) arrays, optically coupled with GAGG scintillators. This configuration enables simultaneous imaging of gamma rays from 30 to 200 keV in pinhole mode and from 200 to 3000 keV in Compton mode. Its intrinsic efficiency and angular resolution are comparable to those of COMPTEL.The INSPIRE satellite is being developed as the successor to PETREL, which is currently being prepared for launch, with a planned launch in 2027.

MeV gamma-ray observations provide unique information about nucleosynthesis, diffusion in our galaxy, low-energy cosmic rays, particle acceleration, and other phenomena. However, the detection sensitivity in this band is significantly lower than that in other bands due to a large background contamination. To address this issue, we are developing an electron-tracking Compton camera (ETCC) with powerful background rejection tools based on Compton recoil electron tracks. This will enable future observations to be conducted with greater sensitivity. We have successfully demonstrated the detection technology and performance of the ETCC with two balloon experiments. We are preparing for the next balloon flight, SMILE-3, to observe galactic diffusion gamma rays and some bright celestial objects.

Aspera is a NASA Pioneers Mission designed to measure faint OVI emission around nearby galaxies with unprecedented sensitivity. The SmallSat payload consists of two identical co-aligned spectrographs, both operating in the Far Ultraviolet (FUV) between 1030−1040 Å. Missions operating at FUV wavelengths are particularly sensitive to contamination, as short wavelengths are easily scattered and absorbed by contaminants deposited on payload optical surfaces. A strict contamination control plan is critical to avoiding a severe loss in FUV throughput. Aspera contamination control efforts have been tailored to fit within the scope of a sub-Class D mission, a challenge that has become increasingly relevant as advances in FUV optics/detectors drive an uptick in smaller platform, contamination sensitive UV payloads. Contamination monitoring is used to audit the cleanroom environment, avoid outgassing contaminants under vacuum, and assess contaminant levels on payload optics. We present a detailed contamination budget through the mission end of life as well as our ongoing contamination monitoring efforts. We discuss protocols implemented for minimizing contamination-related performance degradation.

The balloon-borne UV telescope Faint Intergalactic Red-shifted Emission Balloon (FIREBall-2) was launched from Fort Sumner, NM on September 25, 2023, for its second attempted flight. The flight was unexpectedly terminated at 10 hours due to a mechanical issue, and no science data was obtained; however, this short flight provided an excellent opportunity to test the in-flight communications system. Testing the communication system pre-flight was challenging, and an accurate simulation of signal reception and communication errors expected during flight was not possible. From launch to landing, only a single packet was dropped. Had the flight continued for the expected duration, the success up to early termination gives confidence that the communications systems would have continued to meet our expectations. While this test was highly successful, some areas for improvement were identified and will be addressed before FIREBall-2’s next flight.

FIREBall-2 is a Balloon-Borne UV telescope designed to observe faint UV emission from the circumgalactic medium around low redshift galaxies (z 0.3 - 1.0). FIREBall-2 employs a 1m telescope with a multi-object spectrograph, custom-designed slit-masks and a delta-doped EMCCD detector. FIREBall-2 achieves steady 1-2” pointing with a CNES-provided coarse guidance system complemented by a fine guidance system which provides real time, on-sky feedback with an sCMOS camera embedded within the spectrograph enclosure. The guider system provides a live video stream, computes translational and rotational offsets and sends high rate (30 Hz) gondola pointing error corrections, while also handling slit mask selection and in-flight optimization of the image focus and PSF. We review the current state of the system after testing and use during FIREBall-2’s 2018 and 2023 campaigns and discuss its performance, challenges and development of its hardware and software functions ahead of its next flight campaign.

The Faint Intergalactic-medium Redshifted Emission Balloon (FB-2), a collaborative NASA/CNES suborbital balloon telescope, targets the mapping of faint UV emissions from the circumgalactic medium around low-redshift galaxies. The initial September 2018 flight encountered challenges, including a balloon breach and subsequent damage during landing, impacting the two large telescope mirrors and the critical focal corrector. Likely due to landing shock, the focal corrector experienced misalignment beyond tolerance, necessitating reevaluation and realignment. This paper outlines a comprehensive approach to realigning the focal corrector using a computer-generated hologram (CGH) and a Zygo interferometer for feedback. The CGH enables precise alignment corrections in various degrees of freedom, while interferometer feedback aids in reducing aberrations. The paper details the methodology for optical alignment, surface measurement, and performance evaluation of the focal corrector, emphasizing its successful integration into the FB-2 spectrograph in early 2023 for the September 2023 flight.

Aspera is a NASA Pioneers SmallSat mission designed to detect and map the O VI emission (1032 Å) through long-slit spectroscopy in the halos of nearby galaxies for the first time. The spectrograph utilizes toroidal gratings with multilayer coatings of aluminum, lithium fluoride, and magnesium fluoride that optimize their throughput in the extreme ultraviolet EUV waveband of 1030 to 1040 Å. We discuss the grating verification test setup design, including optical alignment and reference measurement setup. We also present grating testing and grating efficiency simulation results using the target grating groove profile and the multi-layer coatings.

A small UV imager named HI (Hydrogen Imager) is under development to observe the hydrogen coma of a long-period comet or Interstellar object from space. The instrument will be aboard one of the probes for ESA's Comet Interceptor mission, scheduled for launch in 2029. This mission will remain at the Sun-Earth Second Lagrange Point (SEL2) until an optimal target (a reachable long-period comet or interstellar object) is detected through ground observation. During the cruise from SEL2 to the target, HI will observe the cometary hydrogen coma, which emits Lyman-alpha (wavelength 121.6 nm) through the resonance scattering of solar light. Additionally, during the closest approach phase, lasting several tens of hours, HI will measure Lyman-alpha emissions from both hydrogen and deuterium in the coma using switchable gas filters. The optical design, filters, and detector of HI are optimized for observing Lyman-alpha, with dimensions smaller than 100 mm × 100 mm × 250 mm and power consumption less than 9 W. The mirrors are coated with Al/MgF2 to enhance UV reflectance and maintain reflectivity during ground operations before launch. Two gas filters containing hydrogen and deuterium molecules, respectively, are installed to deduce the hydrogen/deuterium brightness ratio of the coma. A Z-stacked MCP detector assembled with a resistive anode is used, without a photocathode, to prevent degradation during ground operations.

The Cosmic Origins Spectrograph (COS) was installed on the Hubble Space Telescope (HST) in 2009. The majority of science spectra are taken with the Far Ultraviolet (FUV) channel, which uses a cross delay line detector. This detector is subject to gain sag, which causes its sensitivity to decrease at locations where counts have fallen. Increasing the high voltage can be used to compensate for this effect, but when the voltage limit is reached, the spectra are moved to a different Lifetime Position (LP) by offsetting them in the cross-dispersion direction on the two-dimensional detector. However, since the optical design was optimized for the initial spectral position, other LPs show a change in the shape of the point spread function, with distortions that lead to a loss of resolution.

In anticipation of a move to a seventh lifetime position (LP7) in ~2025, we have conducted exploratory work to model the instrument performance over the full range of possible positions for the spectra on the detector. This effort includes (1) optical modeling of the spectrograph; (2) creating simulated science spectra and evaluating the resolving power and other spectral properties at a range of positions; (3) evaluating the detector properties at potential lifetime positions while considering mechanical limitations of the hardware; and (4) reserving sufficient space for later LPs. We have used this information to formulate preliminary plans for moving to the next position, which includes identifying which observing modes should be adjusted, and providing our initial thoughts on future Lifetime Positions.

This article describes the development of a space-based near-Ultraviolet (NUV) spectrograph, focusing on the intricate fabrication and meticulous evaluation of an optical slit employing advanced techniques such as optical lithography and deep reactive ion etching (DRIE). The fabrication process entails a precise definition of the slit pattern on silicon wafer substrates through optical lithography, followed by the transfer of the pattern into the substrate material using DRIE. The resultant optical slit boasts sub-angstrom surface roughness and nanometer-scale slit width uniformity, essential for achieving superior spectrographic performance. Through comprehensive evaluation methodologies, including interferometry and spectrophotometry, the optical slit’s spectral resolution, throughput, and stray light rejection are rigorously examined. These breakthroughs promise to elevate the sensitivity, resolution, and dependability of space-based NUV spectrographic instruments, enabling deeper exploration of celestial phenomena and cosmic evolution.

We present an update on the development of the Spectroscopic Ultraviolet Multi-object Observatory (SUMO) concept and Prototype. Specific development includes telescope design and manufacturing, mechanical design, procurement of optics, controller development, and preliminary laboratory testing. The SUMO Prototype is part of the technology maturation program of SUMO, a mission concept designed for a small/medium-sized satellite platform, and 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 designed for completely autonomous operation in the near-ultraviolet (NUV) regime. This research encapsulates 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 regime. 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 also will develop a custom DMD controller, which is suitable for operation in the space environment. This controller works with a custom-developed object selection code, which performs multi-object spectroscopy in real-time. The SUMO Prototype is tentatively scheduled for flight in Spring 2025 aboard the INFUSE sounding rocket.

SPRITE (Supernova Remnants and Proxies for Reionization Testbed Experiment) is a 12U CubeSat mission funded by NASA and led by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder. The payload will house the first sub-arcminute resolution Far-Ultraviolet (FUV) long-slit spectrograph with access to the Lyman UV (912 − 1216 Å), enabled by new enhanced lithium fluoride coatings and an ultra-low-noise photon-counting microchannel plate (MCP) detector. The scientific mission has two main components: constraining the escape fraction of ionizing Lyman-Continuum (LyC) radiation from low-redshift galaxies (0.14 ≤ z ≤ 0.4) and measuring feedback from nearby star forming regions and supernova remnants. Enabling the scientific mission are two distinct observing modes. For the faintest sources, we will operate the MCP detector in photon-counting mode. For brighter sources, we will operate the MCP in an accumulation / integration mode. For extended sources we will collate multiple pointings of the long slit, stepping across the field of view in a ‘push broom’ mapping to create 3D spectroscopic cubes. SPRITE will also take weekly calibration data to characterize the degradation of the coatings and detector. We present these observing modes along with the data acquisition and processing pipeline required to enable scientific analysis on the ground.

Feedback from massive stars through their host galaxies is a crucial driver of galaxy evolution, energizing and enriching the interstellar medium (ISM) and circumgalactic medium (CGM). Massive stars also emit ionizing radiation, a fraction of which escapes into the intergalactic medium. The Supernova Remnants and Proxies for Reionization Testbed Experiment (SPRITE) is a 12U CubeSat that will observe these processes in the far-ultraviolet in local galaxies through two independent but related science surveys. SPRITE is the first independent far-UV orbital spectroscopic mission in over 20 years, and the first orbital instrument capable of sub-arcminute imaging spectroscopy in the Lyman ultraviolet (91 < λ < 120 nm). We present the results of ground testing of the SPRITE flight instrument and characterize its projected on-orbit performance. We also demonstrate the capabilities of SPRITE’s unique technological developments, including advanced UV optical coatings and a low-background microchannel plate detector, providing flight heritage for Habitable Worlds Observatory (HWO) and other future missions.

ULTRASAT is a near-ultraviolet imaging satellite with a wide field of view (200 square degrees) and a planned launch in late 2027. It is an international partnership led by Israel (Israel Space Agency and Weizmann Institute of Science) in partnership with the United States (NASA) and Germany (DESY). ULTRASAT will provide high cadence observations and rapid target-of-opportunity response, providing a powerful capability for time-domain and multimessenger astrophysics (TDAMM), and will have scientific applications from solar system studies to cosmology. This proceedings paper includes the content of a poster presented at the 2024 SPIE Astronomical Telescopes and Instruments meeting, describing briefly the ULTRASAT science drivers and capabilities; NASA’s roles in the ULTRASAT project; and how ULTRASAT fits with NASA scientific priorities. It also includes an expanded summary of the United States Participating Scientist Program for ULTRASAT.

The Spectroscopic Investigation of Nebular Gas (SING), a near-ultraviolet (NUV) spectrograph, operates from 1400 Å to 2700 Å with a 3.7 Å spectral resolution and 1.33′ spatial resolution. Its primary objective is to study various sky regions such as interstellar medium (ISM), hot gas in supernova remnants (SNR), warm gas in planetary nebulae, and cold gas in molecular clouds. It has a 298-mm aperture telescope feeding a long slit UV spectrograph with a dumbbell slit and holographic grating. SING is designed to be mounted on a stable space platform for scanning mode of observation. This article summarizes SING’s design, calibration, and initial performance.

We discuss the final assembly, integration, and testing of the Star-Planet Activity Research CubeSat. SPARCS is a 6U CubeSat mission designed to monitor the dual-channel, far-UV (153-176 nm) and near-UV (258-308 nm) photometric activity of nearby low mass stars to advance our understanding of their evolution, activity, and the habitability of surrounding exoplanets. This paper details the assembly of the SPARCS instrument and the testing process to characterize and validate the performance of the payload prior to spacecraft integration. To test SPARCS, we have established a customized CubeSat AIT laboratory and thermal vacuum chamber at ASU equipped to handle CubeSats requiring meticulous contamination control for work in the FUV. After a brief overview of these facilities and the testing plan, we will detail the methods and data used to verify the performance of SPARCS and generate calibration products to reduce raw flight data to high-quality science products. The result will be the delivery of the first highly sensitive FUV astrophysics CubeSat which will inform exoplanet environments and future observations of these systems by facilities like the Habitable Worlds Observatory.

The Start-Planet Activity Research CubeSat (SPARCS) is a NASA-funded mission led by Arizona State University, devoted to characterizing the UV emission of low-mass stars. During its nominal one-year mission, SPARCS will observe close to 20 low-mass stars, with the goal of understanding their short and long-term UV variability. SPARCS will be ready for launch in 2025. SPARCS’ payload is a 9-cm telescope paired with two delta-doped charge-coupled devices (CCDs). The data calibration converts the raw instrument counts into an average flux within the two ultraviolet bands (153 - 171 nm, 258 - 308 nm). While the system is only weakly sensitive in the infrared, the target stars are very bright at long wavelengths. This requires careful correction of the data for out-of-band emission. The system is being fully characterized on the ground to provide supporting calibration data. The calibration uses observations of very stable white dwarfs to achieve the 10% photometric accuracy requirement in both bands.

The Carruthers Geocorona Observatory is a NASA Heliophysics mission designed to study the variability of Earth’s hydrogen exosphere. Launching in 2025, the Carruthers GeoCoronal Imager (GCI) will observe the exosphere at Far Ultraviolet wavelengths from an Earth-Sun L1 vantage point. The GCI consists of two coaligned imagers that simultaneously provide both wide field observations of the entire exosphere, in addition to high spatial resolution observations near the Earth’s limb. The optical prescription for both the narrow field imager (NFI) and wide field imager (WFI) is discussed, including critical analyses that were performed during the design phase of the project. A deterministic alignment approach was adopted to verify performances of the imagers at visible wavelengths prior to verification in the vacuum ultraviolet. The details of this alignment plan, along with opto-mechanical considerations and requirements are discussed in detail. Finally, we discuss the imaging performance of the system in the ultraviolet utilizing a ground calibration facility previously developed for another NASA spaceflight mission.

The CASTOR mission is a wide-field, nearly diffraction-limited, 1m-diameter space telescope that is under development by the Canadian Space Agency. The telescope is being optimized for wide-field imaging at UV/blue-optical wavelengths, but also features low- and medium-resolution spectroscopic capabilities covering the 150 to 400 nm region, as well as three precision photometers for observations of exoplanet transits. In this paper, we briefly describe the current design of the mission, including payload layout, instrument suite, bus, orbit and observing plans. A companion paper provides a short description of CASTOR’s science mission and capabilities within the international landscape.

The Spektr-UF/WSO UV is a 1.7 m class ultraviolet observatory equipped with instrumentation for high spectral resolution and long slit low spectral resolution spectroscopy within a range of 115 and 315 nm. In addition, it is provided with an imaging instrument, the Field Camera Unit (FCU) composed by two independent channels: the near ultraviolet (NUV) channel operating at 174 and 305 nm, and the Far Ultraviolet (FUV) channel which can perform high resolution images and low dispersion spectra in the 115 to 176 nm spectral range. The detector for the FUV channel is provided by Spain, as part of its contribution to the project. Herein, the results of the qualification campaigns (quantum efficiency, photon counting uniformity, count rate linearity, spot uniformity, spatial stability or temporal uniformity) of the flight and spare detectors for the mission are presented.

Pollux is a project of UV spectropolarimeter proposed as a European contribution for the planned NASA-led Habitable Worlds Observatory. In the present study we consider design options for four spectral channels. The two main channels operate in the range of 118-472 nm. We consider a few design options depending on the hosting telescope size and the approach to correct the aberrations in the camera part and show that the resolving power of R > 90’000 is reachable. In addition, we study 2 other channels: a visible and near infrared spectropolarimeter, which could reach up to 1050 nm or 1800 nm depending on the detector choice, and a far UV channel operating in the range of 100-120 nm. We also provide two design options with different resolution and main disperser type for these channels.

Planned for the launch in late 20s Spektr-UF space observatory, being created in Russia, is designed to obtain images and spectra of space objects in the ultraviolet region of the electromagnetic spectrum (115 – 310 nm). Here we briefly describe the current status of the mission.

The space mission "Spektr-UF" (Spectrum Ultraviolet, another name is World Space Observatory-Ultraviolet) is aimed to create a large space telescope to work in the UV wavelength domain (115 - 310 nm). In the Federal Space Program of Russia the launch of the project is scheduled for 2029. The observatory includes a 170 cm aperture telescope capable of high-resolution spectroscopy and long slit low-resolution spectroscopy with the WUVS (WSO-UV Spectrographs) instrument. Moreover UV imaging will be available with the Field Camera Unit (FCU) instrument. Here we provide a brief description on updated FCU instrument and its current status.

The Ultraviolet Explore (UXEX) mission is a wide-field two band imager with a long multi-width slit spectrometer to study the dynamic ultraviolet universe. The UVEX mission will provide an all-sky survey in the ultraviolet to complement Rubin, Euclid, and Roman operating in the optical/infrared. The telescope will be capable of deep imaging and spectroscopic follow-up within hours of an event for study of targets of opportunity. The telescope optical design provides a continuous 5.0°×3.5° Field of View (FoV) that achieves an rms spot radius of <10 μm. The optical design is a compact unobstructed freeform f/2.7 Three Mirror Anastigmat (TMA) with a 75 cm virtual entrance pupil. The all-reflective design is driven to support imaging into the far UV down to 115 nm. The telescope provides light to three instrument channels: a NUV imager (200 - 260 nm), a FUV imager (130 - 190 nm), and a Long-Slit Spectrometer (LSS) operating over the entire wavelength range (115 – 265 nm). The spectrometer is an all-reflective re-imager based on an Offner-Chrisp design where the secondary convex mirror is the dispersing element. The spectrometer has a 2° long-slit length with three discrete slit widths of 2′′, 4′′, and 8′′ wide. With a 2′′ slit width, the spectrometer has a spectral resolving power of 1400 - 3200 from 115 - 265 nm wavelength range.

The 2175 Å bump shows considerable variations in its strength, width, and central wavelength when observed along different sightlines in the Milky Way and other galaxies. These variations offer valuable insights into the composition, size distribution, and processing of interstellar dust grains along different sightlines. This paper introduces a mission concept called UVESS (Ultra Violet Extinction Sky Survey) aimed at exploring the composition of the interstellar medium (ISM) within both the Milky Way and nearby Local Group Galaxies by mapping the variation of UV extinction curve slopes and the 2175 Å feature across a majority of the sky to gain insights into the makeup of the ISM. Recent advancements in UV instrumentation and technologies pave the way for the development of high-throughput instruments in compact form factors. In this paper, we outline mission science goals and instrument concept tailored for a small satellite-based platform dedicated to the study of UV extinction.

CASTOR, for the Cosmological Advanced Survey Telescope for Optical and Ultraviolet Research, is a widefield space telescope that is under active development by the Canadian Space Agency (CSA). This 1m telescope will produce panoramic imaging of the UV/optical (150-550 nm) sky delivering HST-like image quality over a wide field of view (0.25 sq. deg.), in three filters simultaneously. CASTOR will be optimized for wide-field surveys, although the telescope may also feature low- and medium-resolution spectroscopic capabilities. The paper will describe CASTOR’s unique capabilities within the astronomical landscape in the coming decade, and present highlights from a recently completed Phase 0 study that defined the science mission, including 14 “Legacy Surveys” that span a wide range of fields: including Dark Energy and Weak Lensing; Time Domain and Multi-messenger Astronomy; Galaxy Evolution and AGNs; Star Formation and more.

Our current understanding of cosmology is largely shaped by Type Ia supernovae (SNe Ia), the detonations of carbon-oxygen white dwarves (WDs). SNe Ia are powerful standard candles due to their uniform peak luminosities which decay predictably. SNe Ia progenitor system architecture is highly debated, as none have been observed pre- and post-detonation. Within the first few days after detonation, critical progenitor signatures are preserved in the ultraviolet (UV) bandpass. We present the optical design of UVIa, a proposed 12U CubeSat capable of simultaneous measurements in the far-UV, near-UV, and u-band. Double-offset Cassegrain telescopes were designed to image onto CMOS detectors. We discuss the benefits and challenges associated with double-offset telescopes. UVIa additionally serves as a technology demonstration platform for several cutting-edge UV technologies. The optical design of UVIa enables early-time observations of SNe Ia and serves as a pathfinder for future UV transient telescopes.

JAXA recently selected LAPYUTA (Life-environmentology, Astronomy, and PlanetarY Ultraviolet Telescope Assembly) as a candidate for JAXA's Small Scale Program No. 6 to be launched by Epsilon in ~2032. We will accomplish the following four objectives: #1 Solar System, #2 Exoplanets, #3 Galaxies, #4 the origin of heavy elements. To achieve these scientific objectives, LAPYUTA aims to carry out spectroscopy with a large effective area (>300 cm2) and a high spatial resolution (0.1 arc-sec) and imaging in far ultraviolet spectral range (110-190 nm). A high dispersion spectrograph with a spectral resolution of > 40000 is required, especially for observing exospheres of terrestrial (Earth-like) exoplanets. We are considering the design of the Spectrograph with High dispersion Echelle grating for the Terrestrial (exo-)planetary Atmosphere (SHETA) as an instrument. In this presentation, we introduce the scientific objective and the conceptual design of the SHETA instrument.

SOLAR-C is a Japanese solar physics mission with contributions from the United States and European countries. It features the EUV High-Throughput Spectroscopic Telescope (EUVST) for EUV spectroscopy in a wide temperature range (104–107 K). The optical system’s innovation omits an aperture filter, using only a 28 cm off-axis parabolic primary mirror and a diffraction grating assembly composed of two different gratings, resulting in an effective area ten times larger than the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. This design offers exceptionally high spatial (0.4 arcseconds) and temporal (1 second) resolutions for EUV-UV imaging spectroscopy across a broad wavelength range (170–212 Å, 464–522 Å, 558–610 Å, 719–847 Å, 928–1043 Å, 1115–1221 Å) within a 100×100 arcsecond field of view. A trade-off study focusing on manufacturability successfully eased the specifications of one grating. This presentation reports the latest optical design, optical alignment policy, sensitivity analysis result, and the current spatial resolution error budget plan.