This PDF file contains the front matter associated with SPIE Proceedings Volume 12181, including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

This plenary presentation, "Sloan Digital Sky Survey," was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes + Instrumentation 2022.

This plenary presentation, "The x-ray telescope eROSITA on SRG," was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes + Instrumentation 2022.

UV-SCOPE is a mission concept to determine the causes of atmospheric mass loss in exoplanets, investigate the mechanisms driving aerosol formation in hot Jupiters, and study the influence of the stellar environment on atmospheric evolution and habitability. As part of these investigations, the mission will generate a broad-purpose legacy database of time-domain ultraviolet (UV) spectra for nearly 200 stars and planets. The observatory consists of a 60 cm, f/10 telescope paired to a long-slit spectrograph, yielding simultaneous, almost continuous coverage between 1203 Å and 4000 Å, with resolutions ranging from 6000 to 240. The efficient instrument provides throughputs < 4% (far-UV; FUV) and < 15% (near-UV; NUV), comparable to HST/COS and much better than HST/STIS, over the same spectral range. A key design feature is the LiF prism, which serves as a dispersive element and provides high throughput even after accounting for radiation degradation. The use of two delta-doped Electron-Multiplying CCD detectors with UV-optimized, single-layer anti-reflection coatings provides high quantum efficiency and low detector noise. From the Earth-Sun second Lagrangian point, UV-SCOPE will continuously observe planetary transits and stellar variability in the full FUV-to-NUV range, with negligible astrophysical background. All these features make UV-SCOPE the ideal instrument to study exoplanetary atmospheres and the impact of host stars on their planets. UV-SCOPE was proposed to NASA as a Medium Explorer (MidEx) mission for the 2021 Announcement of Opportunity. If approved, the observatory will be developed over a 5-year period. Its primary science mission takes 34 months to complete. The spacecraft carries enough fuel for 6 years of operations.

The Ultraviolet Transient Astronomy Satellite (ULTRASAT) is a space-borne near UV telescope with an unprecedented large field of view (200 deg² ). The mission, led by the Weizmann Institute of Science and the Israel Space Agency in collaboration with DESY (Helmholtz association, Germany) and NASA (USA), is fully funded and expected to be launched to a geostationary transfer orbit in Q2/Q3 of 2025. With a grasp 300 times larger than GALEX, the most sensitive UV satellite to date, ULTRASAT will revolutionize our understanding of the hot transient universe, as well as of flaring galactic sources. We describe the mission payload, the optical design and the choice of materials allowing us to achieve a point spread function of ∼ 10 arcsec across the FoV, and the detector assembly. We detail the mitigation techniques implemented to suppress out-of-band flux and reduce stray light, detector properties including measured quantum efficiency of scout (prototype) detectors, and expected performance (limiting magnitude) for various objects.

Polstar combines, for the first time, the complementary benefits of spectroscopy and polarimetry to probe the complex interface between massive stars and the interstellar medium. Furthermore, it leverages an innovative combination of effective area and time coverage, to reach the diversity of targets necessary to transform our understanding of the ecology of star and planet creation. Detailed knowledge of these bright, yet distant objects, is crucial for understanding the transformation of our galaxy, from the barren landscape of the early Big Bang, into the chemically enriched environment that produced the solar system we call home. Polstar will map stellar wind and magnetospheric structures by uniting time domain, polarimetry and spectroscopy capability in the near- and far-UV (NUV and FUV), which are densely populated with high-opacity resonance lines encoding a rich array of diagnostic information. UV spectropolarimetry is equally important for probing interstellar dust and protoplanetary disks. The instrument combines advances in high reflectivity UV coatings and delta-doped CCDs with high quantum efficiencies to provide dedicated FUV spectropolarimetry for the first time in 25 years. The FUV channel (Ch1), covers 122-200nm at resolution R>30k, while the NUV channel (Ch2) covers 122-320nm at R~140-4,000. The instrumental polarization stability is built to provide signal-to-noise ratios (SNR) for UV polarimetry precision of 1x10^-3 per exposure per resolution element (resel). Precision can be further improved with spectral binning and/or stacking multiple exposures. Polstar spectral resolution in Ch1 is >30x better than WUPPE, with 10x better effective area, while reaching shorter wavelength than WUPPE to access strong lines of species like NIV and SiIV. The 3-year mission of Polstar is 100x longer than WUPPE with orders of magnitude gains in stellar and interstellar observations.

The Lyman-UV imaging spectrograph (LUVIS) is a NASA SMEX mission concept. Here, we describe the basic scientific requirements of LUVIS and instrumental requirements derived from the scientific requirements. Other papers in this conference by Woodruff et al. and Kendrick et al. describe the LUVIS instrument in detail.

This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes and Instrumentation, 2022.

This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes and Instrumentation, 2022.

This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes and Instrumentation, 2022.

We present a proposal for a near-UV space telescope on a ∼70kg micro-satellite with a moderately fast repointing capability and a near real-time alert communication system that has been proposed in response to a call for an ambitious Czech national mission. The mission, which has recently been approved for Phase 0, A, and B1 study shall measure the brightness evolution of kilonovae, resulting from mergers of neutron stars in the near-UV band and thus it shall distinguish between different explosion scenarios. Between the observations of transient sources, the satellite shall perform observations of other targets of interest, a large part of which will be chosen in open competition.

The Polstar NASA medium explorer (MIDEX) design configuration and implementation is strongly driven by the requirement to measure the state of polarization of stellar objects using a space-based sensor. Constraints include, but are not limited to, symmetry of geometry and coatings of the collecting aperture, angle of incidence at optical surfaces, coating uniformity, line of sight jitter and drift, orbit properties, thermal stability, and ground calibration. The Polstar MIDEX will observe scientifically interesting stars. Polstar will simultaneously measure all four Stokes parameters (I, Q, U, V) to high accuracy and precision (~0.001%) of the Stokes vector at high spectral resolving power. The 600-mm diameter aperture telescope images a selected star at the entrance slit of a spectrometer. Polstar offers two spectral channels within one spectrometer: a Far UV 122 nm to 200 nm Channel 1 with R~30K spectral resolving power and a low spectral resolution in Channel 2 channel covering 180 nm to 320 nm with R ~ 120 to 4K and spectroscopy over 115 nm to ~1,000nm. Channel 1 uses a cross-dispersed echelle spectrometer design. Channel 2 achieves its spectral dispersion with a MgF₂ prism disperser. The two channels share a common array detector. The spectrometer includes rotating MgF₂ retarders and a fixed MgF₂ Wollaston prism analyzer to implement a dual beam polarization sensing function. Two orthogonal polarization states are imaged onto the array detector as interleaved echellograms (Channel 1) and as parallel spectra (Channel 2). This paper presents the design resulting from these design constraints and describes the approaches to calibrate the design pre-flight and during flight.

OUL is a wide field imager designed as a small, additional payload to be attached to the Luna 26 mission. The instrument has a field of view of 20° × 20° and provides images with angular resolution 3 arcmin in several far ultraviolet bands, including Lyman-α, He II at 164nm and several continuum bands. The imager is designed to monitor the Earth’s exosphere and the ecliptic (+/-20°) primary at Lyman-α and in the 125-140 nm and 145-170 nm bands. In this contribution, the optical design of the instrument, its mechanical layout and the science program to be implemented will be described.

The mission Ultraviolet Researcher to Investigate the Emergence of Life (URIEL) is designed to carry out low dispersion (600-1,000) UV spectropolarimetry in the 140-400 nm spectral range to investigate the formation of planetary systems, its interaction with stellar winds and search for signatures of prebiotic molecules by remote sensing of small bodies in the Solar System (comets and meteorites) in near Earth orbit. URIEL is conceived as a 50cm primary telescope with a RitcheyChrétien mounting. The telescope is equipped with a single instrument, the ultraviolet spectropolarimeter, whose low dispersion will enable resolving the main spectral features whilst guaranteeing enough flux per resolution element for the Stokes parameters to be measured to an accuracy of 500 ppm in the full range. According to recent calculations based on the chemical analysis of meteorites, this accuracy suffices for the remote detection of alanine by its optical activity at 180 nm in nearby minor bodies. In this sense, URIEL is a pathfinder mission to the technology that will enable remote sensing of amino acids and addressing the source of the chirality imbalance in Earth's bio-molecules.

FURST is a sounding rocket mission designed to acquire the first high quality, full-disk, UV Solar spectra in the range of 1200 - 1800 ̊A. The instrument uses a set of cylindrical optical elements, acting in place of a slit, to collect light from the entire solar disk in combination with a Rowland circle spectrometer, to generate high resolution spectra, ≥2 ×104λ/∆λ, without scanning a slit over the spatial extent of the Sun. The instrument requires absolute radiometric and spectral calibration before and after flight in order to analyze data products and meet science goals. We present an update on the portable calibration system designed to meet ambitious calibration requirements. The system consists of a vacuum chamber, a Pt hollow cathode lamp, collimating optics and NIST calibrated photodiodes. Absolute radiometric calibration of ≤15% and wavelength calibration corresponding to ±3km/s is expected.

JPL’s 2D-doping processes have been proven to exhibit nearly 100% internal QE (i.e. reflection-limited response) from extreme ultraviolet (UV) to the near infrared (NIR). Response can be further optimized and tailored with AR coatings and/or bandpass filters; however, due to silicon’s optical properties, there is no “one size fits all” coating/filter solution that can span the entire UV to NIR wavelength range. Our team has developed a catalog of coating and filter designs suitable for a variety of applications, several of which have already been implemented/deployed. Spectroscopy applications often benefit from a spatially varying detector response optimized according to the instrument’s optical dispersion. Spatially varying the detector response to correspond with instrument dispersion requires that different coatings be applied to different portions of the detector. We have recently demonstrated detectors with a butcher-block style response profile with each portion of the device targeting a specific bandpass—similar to a linear variable filter. This technological advancement is achieved through the intentional and controllable patterning of AR coating(s) on delta-doped arrays. Herein we review implementations/deployments of delta-doped UV detectors with AR and bandpass filter coatings as well as progress on the variable response UV detectors.

We present the status of our imaging and photon counting UV-MCP detector versions, sensitive in the ultraviolet wavelength range. The detectors have a spatial resolution of 2k pixels per axis, are photon counting, have no readout noise and a very low dark rate, making it ideal for photometry and spectroscopy. The detector can be easily adapted to the requirements of different missions, e.g., only the mechanical interfaces and an electrical interface must be defined to integrate the detector, it is relatively lightweight (3 kg) and has a power consumption of only 15 W. For the sealed version of the detector, we are currently testing a sealed detector head with a cesium telluride photocathode in semitransparent mode. The open version of the detector uses a lightweight door mechanism and is currently optimized to use a KBr photocathode. Interesting advances have been made for AlGaN on MgF2 and MgO substrates. A complete h-GaN film could be grown on MgO (0 0 1), and a complete c-GaN film on MgO (1 1 0). Good crystal quality is crucial to obtain a high QE AlGaN photocathode. Finally, the challenges towards a sealed detector head with a diameter of about 8 cm are described. By rotating the detector window on the detector head during the sealing process, we were able to seal the detector. The photocathode in the sealed MCP detector is stable for at least weeks.

In the past two decades, great advances have been made in investigating hard X-rays from accelerated electrons in solar flares. This emission is of interest because the means by which flares so efficiently accelerate particles are still not understood. Observations from the RHESSI spacecraft led to better understanding in the imaging and spectral domains, but presented difficulty for time domain analysis at scales less than ~2 seconds. This leaves the behavior of flare emission at small timescales poorly explored. The NSF-funded IMpulsive Phase Rapid Energetic Solar Spectrometer (IMPRESS) CubeSat is designed specifically to measure hard X-ray emission up to 100 keV from flares at a tens-of-ms cadence. This will provide novel constraints for flare particle acceleration models. IMPRESS is a student-centered collaboration between UMN, MSU, SwRI, and UCSC. This presentation will describe the science, mission concept, and some design specifics for IMPRESS.

The CubeSat solar polarimeter (CUSP) project aims to develop a constellation of two CubeSats orbiting the Earth to measure the linear polarisation of solar flares in the hard x-ray band by means of a Compton scattering polarimeter on board of each satellite. CUSP will allow to study the magnetic reconnection and particle acceleration in the flaring magnetic structures. CUSP is a project approved for a Phase A study by the Italian Space Agency in the framework of the Alcor program aimed to develop CubeSat technologies and missions.

The Sun is a privileged place to study particle acceleration, a fundamental astrophysical problem throughout the universe. The extreme ultra-violet (EUV) contains a number of narrow emission lines formed in all layers of the solar atmosphere whose profiles allow the measurement of plasma properties like density and temperature, along with the presence of non-Maxwellian particle distributions to be diagnosed. The only way to observe is from space, since EUV radiation is absorbed by the Earth’s atmosphere.
Integral field spectroscopy combined with polarimetry is key for the study of the Sun, but the current EUV technology is limiting: the transmission of optical fibers IFUs (integral field units) is low and in-flight effects affect polarisation measurements. The best solution seems to be image slicers. However, this technology has not yet been developed for the EUV spectral range. This communication explores a new highly efficient and compact integral field spectrograph layout based on the application of image slicers combining the surfaces of the IFU with those of the spectrograph, suitable for space applications.

This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at Astronomical Telescopes and Instrumentation, 2022.

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 of 2.5 eV up to 7 keV from 5" pixels, with a hexagonal field of view of 5' equivalent diameter. The main sensor array and its associated detection chain is one of the major sub-systems of the X-IFU instrument, and is the main contributor to X-IFU’s performance. CNES (the French Space Agency) is leading the development of X-IFU; additional major partners are NASA-GFSC, SRON, VTT, APC, NIST, and IRAP. This paper updates the B-phase definition of the X-IFU detection chain. The readout is based on time-division multiplexing (TDM). The different sub-components of the detection chain (the main sensor array, the cold electronics stages, and the warm electronics) require global design optimization in order to achieve the best performance. The detection chain’s sensitivity to the EMI/EMC environment requires detailed analysis and implementation of dedicated design solutions. This paper focuses on these aspects while providing an update to the detection-chain design description.

This paper describes the design progress of the X ray Integral Field Unit Focal Plane Assembly (X-IFU FPA) for the Athena X-ray observatory. Test results obtained from the Development Model (DM) program are compared to existing numerical models. From these comparisons input to the next FPA Engineering Model (EM) is derived. Measurements have been done to assess the magnetic shielding performance and key thermal properties are verified. A dedicated configuration is used to verify the changes in mechanical dynamic behavior between ambient temperature and after cool-down to assess micro-vibration susceptibility. We conclude with a summary and outlook for the FPA-EM design.

The Athena mission in general and the x-ray integral field unit (X-IFU) instrument in particular are designed to address a wealth of scientific questions related to the science theme of the hot and energetic universe.

X-IFU provides medium spatial resolution and high resolving power by means of a calorimetric detector.

As the X-IFU detector needs to be operated at 50mK, the instrument is contained in a dewar. The aperture cylinder consists of a set of structural and thermal elements that carry and position at correct distances from the detector the first three dewar thermal filters, provide adequate thermal interfaces and protect the filters from contamination.

In this paper, we present the Phase A-B1 contribution of Centre Spatial de Liège (CSL) to the X-IFU consortium. This summarizes to the elaboration of a baseline design for the aperture cylinder, and several demonstration models as a de-risking activity with the intent to increase the aperture cylinder maturity.

This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes + Instrumentation, 2022.

The wide field imager (WFI) for the ATHENA mission will enable the spectroscopic investigation of solid angles up to 40’ in the x-ray regime between 0.2 keV to 15 keV. The required sensors are planed as DEPFET (DEpleted P-channel field-effect transistor) active pixel matrices. These are readout by custom-designed ASICs called VERITAS in a rolling shutter mode. After column parallel processing of the analog signals row-by-row, the resulting pulse heights are multiplexed onto a differential analog line pair. Thus a transmission undisturbed from external influences is achieved. But successive signals can be affected by the limited rise-time of the VERITAS output stage, depending on the signal height, the multiplexing time and the cable length. In order to investigate the impact on the measurements a dedicated cable harness is used during the characterization of a prototype device. The characterizations are performed using either test pulses applied to the VERITAS or with a ⁵⁵Fe calibration source illuminating the whole sensor. Different cable lengths and multiplexing times are tested to determine the influences. In order to deal with this effect a crosstalk correction algorithm is implemented for the analysis of the photon data. The determined crosstalk factors range up to 2.8% for the longest measured cablings of 2 m with the shortest multiplexing time. Using shorter cables and longer multiplexing times these factors can be reduced to below 1%. In all cases the accompanying effects in the data analysis can be corrected using the developed algorithm.

The next generation x-ray observatory ATHENA (advanced telescope for high energy astrophysics) requires an optics with unprecedented performance. It is the combination of low mass, large effective area and good angular resolution that is the challenge of the x-ray optics of such a mission. ATHENA is the second large class mission in the science programme of ESA, and is currently in a reformulation process, following a design-to-cost approach to meet the cost limit of an ESA L-class mission.

The silicon pore optics (SPO) is the mission enabler being specifically developed for ATHENA, in a joint effort by industry, research institutions and ESA. All aspects of the optics are being addressed, from the mirror plates and their coatings, over the mirror modules and their assembly into the ATHENA telescope, to the facilities required to build and test the flight optics, demonstrating performance, robustness, and programmatic compliance.

The SPO technology is currently being matured to the level required for the adoption of the ATHENA mission, i.e., the start of the mission implementation phase. The monocrystalline silicon material and pore structure of the SPO provide these optics with excellent thermal and mechanical properties. Benefiting from technology spin-in from the semiconductor industry, the equipment, processes, and materials used to produce the SPO are highly sophisticated and optimised.

Athena is the European Space Agency’s next flagship x-ray telescope, scheduled for launch in the 2030s. Its 2.5-m diameter mirror will be segmented and comprise more than 600 individual Silicon Pore Optics (SPO) grazing-incidence-angle imagers, called mirror modules. Arranged in concentric annuli and following a Wolter-Schwartzschild design, the mirror modules are made of several tens of primary-secondary mirror pairs, each mirror made of mono-crystalline silicon, coated to increase the collective area of the system, and shaped to bring the incoming photons to a common focus 12 m away. Aiming to deliver a half-energy width of 5”, and an effective area of about 1.4 m2 at 1 keV, the Athena mirror requires several hundred m2 of super-polished surfaces with a roughness of about 0.3 nm and a thickness of just 110 µm. SPO, using the highest-grade double-side polished 300 mm wafers commercially available, were invented for this purpose and have been consistently developed over the last several years to enable next-generation x-ray telescopes like Athena. SPO makes it possible to manufacture cost-effective, high-resolution, large-area x-ray optics by using all the advantages that mono-crystalline silicon and the mass production processes of the semiconductor industry provide. Ahead of important programmatic milestones for Athena, we present the status of the technology, and illustrate not only recent x-ray results but also the progress made on the environmental testing, manufacturing and assembly aspects of the technology.

Several hundreds of Silicon Pore Optics (SPO) mirror modules will be integrated and co-aligned onto the ATHENA (Advanced Telescope for High-ENergy Astrophysics) Mirror Assembly Module (MAM). The integration process has been developed by Media Lario and exploits a full-size optical bench to capture the focal plane image of each mirror module when illuminated by an UV plane wavefront at 218 nm. Each mirror module, handled by a manipulator, focuses the collimated beam onto a CCD camera placed at the 12 m focal position of the ATHENA telescope. The image is processed in real time to calculate the centroid position and overlap it to the centroid of the already integrated Mirror modules. Media Lario with ESA support has designed the Assembly Integration and Test (AIT) facility, able to host the complete ATHENA telescope. The AIT facility is in construction and the 2.6 m Zerodur® parabolic mirror has been accepted for coating and ready to be delivered to Calar Alto Observatory (CAHA, Sierra de Los Filabres, Spain) for the reflective coating application. The building housing the AIT facility is under construction at the Media Lario premises near Milan, Italy, and extends 6.5 m below ground and 17 m above ground. The building also is dimensioned to accommodate the vertical X-ray (Vert-X) test facility. The co-location of these two facilities is strategic for the project and will permit regular checks of the mirror module alignment while the MAM is populated. The MAM will be moved on a rail system connecting the two facilities.

The BEaTriX (Beam Expander Testing X-ray) facility is now operative at the INAF-Osservatorio Astronomico Brera (Merate, Italy). This facility has been specifically designed and built for the X-ray acceptance tests (PSF and Effective Area) of the ATHENA Silicon Pore Optics (SPO) Mirror Modules (MM). The unique setup creates a parallel, monochromatic, large X-ray beam, that fully illuminates the aperture of the MMs, generating an image at the ATHENA focal length of 12 m. This is made possible by a microfocus X-ray source followed by a chain of optical components (a paraboloidal mirror, 2 channel cut monochromators, and an asymmetric silicon crystal) able to expand the X-ray beam to a 6 cm × 17 cm size with a residual divergence of 1.5 arcsec (vertical) × 2.5 arcsec (horizontal). This paper reports the commissioning of the 4.5 keV beam line, and the first light obtained with a Mirror Module.

The X-ray and Cryogenic Facility (XRCF) at the NASA Marshall Space Flight Center (MSFC) is the baselined facility for X-ray testing of the Athena X-ray optics. Here we give an overview of the planned testing, including the XRCF facility and its 500-meter X-ray beamline, the required facility X-ray sources and detectors, testing requirements, and the GSE required for X-ray testing and calibration of the Athena mirror assembly module demonstrator (MAMD), the qualification model mirror (QM), and the flight model mirror (FM). Of special interest is the metrology system needed for the calibration: because the large Athena optic (the Mirror Assembly Module, or MAM) is too large for full illumination in the XRCF 1.5m diameter X-ray beam, the six sectors of the MAM will be tested separately, requiring precise knowledge of the optic and detector positions during the calibration to enable the stitching together of the full MAM point spread function from measurements of the individual sectors.

Silicon pore optic (SPO) mirror modules (MMs) are being developed and produced for ESA’s ATHENA mission. The optics have, and will be, tested at MPEs PANTER x-ray test facility. We present the results obtained from tests performed at the PANTER x-ray test facility for the SPO MM-0050 that was produced to verify the latest optical performance (half energy width (HEW), effective area) of SPOs, supporting the ESA reviews of their optical performance.
The preparations are ongoing at PANTER, ESA, cosine and Media Lario to perform complex opto-thermo-mechanical tests of the two full scale 1/6th sectors of the final ATHENA mirror assembly structure produced by the potential ATHENA primes Airbus Defence and Space and Thales Alenia Space. For these tests a set of three SPO MMs have been produced following the flight configuration. The MMs will be incorporated into the full scale 1/6th sectors to measure the impact of thermal gradients on the thermoelastic deformation of the structure and therefore the HEW performance. A description of the tests is presented here.
PANTER is also involved in the development, testing, and fabrication of the mirror adapter structure (MAS) to support the 2.6-m diameter ATHENA mirror assembly module demonstrators (MAMD) during the planned x-ray tests at XRCF. A description of the PANTER tests and results will be presented in this paper together with a short overview of the MAS MGSE for XRCF.

The future Athena observatory will feature optics with unprecedented collecting area enabled by silicon pore optics technology. In order to achieve the telescope effective area requirements at 1 keV and 7 keV, thin film coatings of iridium with a low-density overcoat are deposited onto the mirror substrates. Assembling the coated silicon pore optics plates into mirror modules for the Athena optics requires wet chemical processing and thermal annealing. While iridium appears to be compatible with the post-coating processes, previous studies have shown degradation of the low-density material. The overcoat layer is particularly critical for the low-energy telescope performance, so several candidate materials (boron carbide, silicon carbide and carbon) have been studied to identify a compatible thin film design. We present the characterisation of x-ray mirror performance using x-ray reflectometry, as well as the measurements of residual film stress with stylus profilometry. Furthermore, we evaluate the effects of post-coating treatment in order to recommend the most suitable overcoat material for the telescope.

This paper is an overview of the Next Generation X-ray Optics effort at NASA’s Goddard Space Flight Center. The objective of the NGXO effort is to develop and mature an X-ray mirror technology that is capable of building and delivering a mirror assembly for flagship missions like Lynx and Probe missions like AXIS, which have been recommended by Astro2020 for implementation in the coming decade(s). The NGXO work encompasses all elements that compose a complete process to design, build, test, and deliver a complete mirror assembly, including optical design, mirror segment fabrication, coating, alignment and bonding to make mirror modules, integration of mirror modules into meta-shells, and integration of meta-shells into a mirror assembly. In addition, the NGXO team also adopts the latest mass-production techniques to ensure that building such a mirror assembly can also meet programmatic, such as schedule and cost, requirements of future missions like Lynx and AXIS.

Numerous scientific questions at the forefront of our modern physical understanding require enhanced x-ray astronomical observations beyond the capabilities of existing x-ray telescopes. These observations demand spaceborne x-ray telescopes of unprecedented imaging power. X-ray focusing optics which are simultaneously light weight and of sufficient quality are presently impossible to realize, given real-world constraints and current manufacturing technology. Our group at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) investigates the development of a x-ray mirror manufacturing process capable of meeting the stringent quality, production time, and cost requirements of the next-generation of x-ray telescopes. This process employs monocrystalline silicon: a lightweight, stiff, thermally conductive, and readily available material which is free of internal stress. These properties combined make silicon a nearly ideal material for thin mirror substrates. Presently, our process is capable of fabricating sub-arcsecond half-power-diameter (HPD) resolution mirror pairs (primary and secondary) at a sub-millimeter mirror thicknesses and of virtually any x-ray optical design (e.g. Wolter-I, Wolter-Schwarzschild, etc.). Further, the substrates include three-dimensional structures on their backsides to aid their alignment and bonding. The mirror substrate surface quality is generally superior to that of the mirrors on the Chandra X-ray Observatory. This paper describes the various manufacturing steps involved in the production of x-ray mirror substrates and a present status report.

An X-ray Observatory, with superb imaging capabilities and with large throughput, has been recognised as a strategic missions in the Astro2020 decadal survey. The traditional solution foreseen for the realisation of very large x-ray mirror modules (diameters above 1 m) is the partition of the optics in azimuthal and radial modules (like Silicon Pore Optics in Athena). Even if this approach solves the initial problem of the procurement and the handling of very large substrates, it moves the difficulties in the second phase, when thousands of segments have to be assembled without degrading their optical performances. On the contrary, a simpler large mirror module design could correspond to less than a few hundred thin monolithic shells. As an example, the complete opto-mechanical design, compliant with the Lynx mass budget and based on fused silica, foresees that the shell thickness ranges between 2 and 4 mm (for mirror shells between 0.4 and 3 m diameter). The conceptual design of such an mirror module could be refined for smaller scale mission, keeping both the advantage of the design simplicity and of the high-resolution capability, achievable through the direct polishing approach. A technology development roadmap for this approach is funded in Italy by ASI and led by INAF-OAB. In this paper, we present the advancements obtained in the development of the different phases of the process and in the realisation of two new single-reflection shells (SR shells), almost representative of the final optical configuration foreseen for the mirror assembly. The first shell will be used to prove the figuring process in a lab-mount, built upon elements of the previous supporting structure concept. The second shell will be hosted in an upgraded lab-mount structure, which guarantees better performances (frequencies, gravity and thermo-elastic response) and which is suitable to test the transfer of the shell to a spider-like configuration.

Versatile Optics for X-ray Imaging (VOXI) is a technology that enables a wide range of missions and opens up new opportunities for scientific research over multiple disciplines including fundamental physics, heliophysics, astrophysics, lunar and planetary science, and laboratory physics. VOXI is well-suited to SmallSats, which have become powerful platforms from which to conduct leading scientific investigations and cutting-edge technology developments at low cost with rapid turn-arounds. At the Center for Astrophysics | Harvard and Smithsonian, in collaboration with other institutions, we have developed VOXI, a Wolter-I Xray telescope with a focal length of < 1.5 m. In this paper we describe the potential of these optics, and the applications for VOXI optics considered to date.

Epoxy has been the preferred agent for x-ray telescope alignment and bonding for many decades. While it may have worked great for thick, stiff Chandra mirrors, its efficacy for thin shell mirrors has proven to be inadequate. We report results of recent experiments with alignment and bonding of silicon x-ray mirrors using silicate bonding sol gel solutions loaded with nanometer-size silica balls—so-called nanosilicate bonds. Strong bonds are obtained even though surfaces were not particularly flat. In this presentation we will show the latest results of bond shear-strength measurements using an Instron industrial tester, and results of preliminary three-point bonds on test mirrors, which mimics the bonding procedure now being used by the Goddard x-ray mirror group. We will also show results of bond line shrinkage experiments and compare to epoxy.

High resolving power soft x-ray spectroscopy has been confirmed by the recent Astro2020 Decadal Survey as a high-priority strategic goal with R =λ/Δλ as high as 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, coronal mass ejections and coronal heating. Below the level of an expensive strategic mission, but far exceeding current capabilities, falls the Arcus Grating Explorer mission concept, with a minimum R of 2500 (expected R = 3500) and effective area up to ∼ 300 cm² in the 12-50 Å bandpass. Arcus relies on light-weight, high-efficiency, blazed and alignment-insensitive critical-angle transmission (CAT) gratings for dispersion. The mission calls for hundreds of ∼ 30×30 mm² gratings with a hierarchy of integrated support structures. The most recent CAT gratings have been fabricated from 200 mm silicon-on-insulator wafers using commercial, volume production compatible tools from the semiconductor and MEMS industries. We report x-ray results from quasifully illuminated, co-aligned CAT gratings showing record-high R ∼ 1.3×10⁴ in 18th order at Al-K_α wavelengths, and diffraction efficiency of blazed orders in agreement with pencil beam synchrotron measurements and model predictions at O-K. Tilt of the deep-etched, freestanding grating bars relative to the grating surface is measured and successfully compensated through angular alignment during bonding of the Si gratings to metal frames. We also report on updates to the Arcus resolving power error budget, and on post-fabrication thinning of grating bars, which could lead to increased diffraction efficiency.

It has been known for some time that sputtered low-density coatings deposited under vacuum (e.g. carbon or B4C), applied on top of high-density metallic coatings, can enhance the reflectivity in the soft x-ray band (below ~5 keV). In the last years, we experimented with novel carbonated coatings obtained by dip-liquid deposition, in which a thin film is formed on the surface of a mirror by immersion in a suitable precursor solution. After several attempts with different chemical compounds, we found an optimal candidate both for the reflectivity performance and for the convenience of the deposition process, which is much simpler and inexpensive compared to conventional processes. In particular, such coatings can enhance the soft x-ray response at the reflection angles employed in future telescopes, like ATHENA (ESA), Lynx (NASA) and eXTP (CAS). In this paper we consider the application of dip-liquid overcoatings on conventional coatings (Au, Ir) or in combination with recently proposed chromium overcoatings and their possible uses to enhance the reflectivity of x-ray mirrors at low, medium or higher energies, presenting the first experimental results of x-ray tests on these coatings.

We have developed the capability to optimize a diffraction grating with arbitrary groove density and direction as a function of location. The added degrees of freedom allow additional correction of optical aberrations beyond what is available to holographic recordings. Since the groove direction and density can be independent for all points on the grating, the design is not constrained by the limitations of ensuring that the grooves follow a single parametrized function. The grooves are then written with e-beam fabrication techniques onto a silicon substrate. We present the results from our project to fabricate aberration-correcting gratings using direct writing in silicon. Two gratings were produced as part of this work, one is a demonstration a Fresnel plate to verify that the grating was fabricated as intended. The second grating was designed as part of a Raman spectrograph and provides excellent optical performance over the designed passband.

This presentation "Fabrication of custom astronomical gratings for the next decade (and beyond)," took place during the conference on Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, part of SPIE Astronomical Telescopes + Instrumentation symposium (2022).

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the soft X-ray scientific payload on board the SRG (Spektrum-Roentgen-Gamma) mission. It was successfully launched from Baikonur in July 2019. Following a 101 days cruise phase, SRG reached its final orbit around the Sun-Earth Lagrangian point L2, from where it has carried out already four full-sky surveys. eROSITA is a complex instrument composed of seven identical co-aligned X-ray telescopes with a focal length of 1600mm and an aperture of 350mm. Each telescope is equipped with an independent CCD camera. The cold redundant ITC (Interface and Thermal Controller) manages all seven cameras as well as the thermal control of the telescope and the interface to the spacecraft. The cruise phase of SRG was used to verify that all systems had survived launch and no degradation in the functionality was present. Following that, the main science mission, comprised of an early Calibration and Performance Verification Phase, followed by the all-sky survey. This paper presents the performance of the eROSITA telescope during the first four complete all-sky surveys. It presents the challenges encountered during the telescope operations as well as the operations and mitigation strategies put in place to understand or minimize the effects of the space environment in L2, such as micrometeoroid hits and radiation damage of the detectors.

This presentation, "Updates on SRG/eROSITA background at Sun-Earth L2," took place during the conference on Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, part of SPIE Astronomical Telescopes + Instrumentation symposium (2022).

The imaging x-ray polarimetry explorer (IXPE) was launched on December 9, 2021, from Cape Canaveral into a low-Earth equatorial orbit. The mission, led by NASA in collaboration with the Italian Space Agency (ASI), features three identical telescopes, each with an imaging x-ray photoelectric polarimeter at the focus of an x-ray mirror assembly. Each focal-plane detector includes a set of four calibration sources powered by a ⁵⁵Fe nuclide to monitor the detector’s performance. Of these sources, one produces polarized x-rays at two energies and the remaining three generate unpolarized radiation. Here we present the status of this monitoring program, starting from installation of the flight nuclides before on-ground environmental testing of the observatory through recent on-orbit measurements during science operations.

This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes + Instrumentation, 2022.

This conference presentation was prepared for the conference on Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, part of SPIE Astronomical Telescopes + Instrumentation, 2022.

This conference presentation was prepared for the conference on Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, part of SPIE Astronomical Telescopes + Instrumentation, 2022.

HERMES (high energy rapid modular ensemble of satellites) is a space-borne mission based on a constellation of nano-satellites flying in a low-Earth orbit (LEO). The six 3U CubeSat buses host new miniaturized instruments hosting a hybrid silicon drift detector/GAGG:Ce scintillator photodetector system sensitive to x-rays and gamma-rays. HERMES will probe the temporal emission of bright high-energy transients such as gamma-ray bursts (GRBs), ensuring a fast transient localization (with arcmin-level accuracy) in a field of view of several steradians exploiting the triangulation technique. With a foreseen launch date in late 2023, HERMES transient monitoring represents a keystone capability to complement the next generation of gravitational wave experiments. Moreover, the HERMES constellation will operate in conjunction with the space industry responsive intelligent thermal (SpIRIT) 6U CubeSat, to be launched in early 2023. SpIRIT is an Australian-Italian mission for high-energy astrophysics that will carry in a sun-synchronous orbit (SSO) an actively cooled HERMES detector system payload. On behalf of the HERMES collaboration, in this paper we will illustrate the HERMES and SpIRIT payload design, integration and tests, highlighting the technical solutions adopted to allow a wide-energy-band and sensitive x-ray and gamma-ray detector to be accommodated in a 1U CubeSat volume.

HiZ-GUNDAM is a candidate of future satellite mission for the Japanese competitive M-class mission by ISAS/JAXA to progress a time-domain astronomy and multi-messenger astronomy with gamma-ray burst (GRB) phenomena. The science goals are (1) to probe the early universe with high redshift GRBs at z > 7, and (2) to promote the gravitational wave astronomy with short GRB. HiZ-GUNDAM has been successfully passed a review for pre-project candidate in November 2021, and its team is working on the concept study. We will introduce the sciences and mission overview of HiZ-GUNDAM.

We present the detector performance and early science results from GRBAlpha, a 1U CubeSat mission, which is a technological pathfinder to a future constellation of nanosatellites monitoring gamma-ray bursts (GRBs). GRBAlpha was launched in March 2021 and operates on a 550 km altitude sun-synchronous orbit. The gamma-ray burst detector onboard GRBAlpha consists of a 75×75×5 mm CsI(Tl) scintillator, read out by a dual-channel multi-pixel photon counter (MPPC) setup. It is sensitive in the ∼30−900 keV range. The main goal of GRBAlpha is the in-orbit demonstration of the detector concept, verification of the detector’s lifetime, and measurement of the background level on low-Earth orbit, including regions inside the outer Van Allen radiation belt and in the South Atlantic anomaly. GRBAlpha has already detected five, both long and short, GRBs and two bursts were detected within a time-span of only 8 hours, proving that nanosatellites can be used for routine detection of gamma-ray transients. For one GRB, we were able to obtain a high resolution spectrum and compare it with measurements from the Swift satellite. We find that, due to the variable background, the time fraction of about 67% of the low-Earth polar orbit is suitable for gamma-ray burst detection. One year after launch, the detector

Since transient events, such as gamma-ray bursts (GRBs), can be expected from any direction at any time, their detection and localization is difficult. For localizing transient events, we proposed the Cubesats applied for measuring and localising transients mission (CAMELOT), which will be a fleet of nanosatellites distributed evenly on low Earth orbits. As the first step, we designed a technical demonstration for the CAMELOT mission, named GRBAlpha. Even though this 1U satellite has a reduced size scintillator and different mechanical constraints, all the electronic subsystems and communication protocols are the same. GRBAlpha is operating in orbit since 2021 March 22 and it already detected numerous confirmed GRBs. For further details of the early results and ongoing operations see the related presentation at this conference. After this first success, we continue with the design of the 3U prototype of the CAMELOT satellite, which will host an eight times larger detector system integrated into two walls of the satellite. The main difference is the mechanical constraints of mounting the detector in its casing. While for GRBAlpha the reduced sized scintillator is located on the top (Z+) side of the satellite, for CAMELOT it is located on two of the sides. Since the CubeSat standard does not allow enough lateral extension on the sides, the casing has to be sunk into the satellite where it could interfere with the standard PC/104 stacking. Here, we present a solution on how to integrate the scintillator casing, the uniquely designed electronics and commercially available satellite subsystems.

This conference presentation was prepared for the conference on Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, part of SPIE Astronomical Telescopes + Instrumentation, 2022.

In this paper we describe the characterization of the Glowbug instrument. Glowbug is a gamma-ray telescope for gamma ray bursts (GRBs) and other transients in the 50 keV to 2 MeV band funded by the NASA Astrophysics Research and Analysis (APRA) program. Built by the U.S. Naval Research Laboratory, the instrument will be launched to the International Space Station (ISS) by the Department of Defense (DOD) Space Test Program (STP) in early 2023. Glowbug’s primary science objective is the detection and localization of short GRBs, which are the result of mergers of stellar binaries involving a neutron star with either another neutron star or a black hole. While the instrument is designed to complement existing GRB detection systems, it serves as a technology demonstrator for future networks of sensitive, low-cost gamma-ray transient detectors that provide all-sky coverage and improved localization of such events. Of greatest interest are the binary neutron star systems within the detection horizon of ground-based gravitational-wave interferometers. In a full mission life, Glowbug will detect dozens of short GRBs and provide burst spectra, light curves, and positions for gamma-ray context in multi-wavelength and multi-messenger studies of these merger events. We will present the current state of Glowbug, which will include the hardware development, calibration, environmental testing, simulations, and expected on-orbit sensitivity.

The space-based multi-band astronomical variable objects monitor (SVOM) is a Chinese–French mission due to be launched in 2023. It is composed of four space borne instruments: ECLAIRs, for detecting x-ray and gamma-ray transients; GRM, a gamma-ray spectrometer; VT, a visible telescope and the Microchannel X-ray Telescope (MXT). The MXT’s main goal is to precisely localize, and spectrally characterize x-ray afterglows of gamma-ray bursts. The MXT is a narrow-field-optimised lobster eye x-ray focusing telescope comprising an array of 25 square micro pore optics (MPOs), with a detector-limited field of view of ∼1 square degree, working in the energy band 0.2-10 keV. The SVOM flight model (FM) MXT optic (MOP) was designed, built and initially tested at the University of Leicester and a full calibration of the MOP was completed at the PANTER facility (MPE). It was then integrated in to the full proto flight model (PFM) MXT instrument before it returned to PANTER for the PFM MXT’s full calibration. We present the optic performance as part of the full FM MXT instrument calibration. The response of the telescope was studied at 11 energies from C-K (0.28 keV) to Ge-K (9.89 keV), including measurements of the effective area and the PSF size and shape. The focal length of the instrument was determined and details of the modelling and analysis used to predict the performance are presented. The measurements demonstrate that the actual effective area and PSF are in good agreement with the modelling.

SVOM (space-based multi-band astronomical variable objects monitor) is a mission developed within a Sino-French cooperation context and dedicated to the detection, localization and study of gamma ray bursts (GRBs) and other high-energy transient phenomena. Four instruments, operating in different wavelengths, are implemented on board in order to perform GRB detection and observations. The MXT instrument, developed by the National French Space Agency (CNES) in collaboration with CEA, MPE, IJCLab and the University of Leicester, is dedicated to the observation of GRB afterglows in the soft x-ray band and is one of the four instruments implemented on the Chinese satellite. First the design chosen of this instrument will be described and then the main results of the qualification campaign performed with the development models as EQM or STM and PFM models will be presented, as much at the instrument level as at the SVOM satellite QM level. Then, we will present how flight model design has been updated regarding the qualification campaign results. Furthermore, it will be presented how the performance of this kind of instrument is evaluated or measured through several models at sub system level or at instrument level. Finally, we will provide as a conclusion the main steps which have been achieved for this kind of development and give our main feedback.

The Einstein Probe (EP) is a mission of the Chinese Academy of Sciences (CAS) dedicated to time-domain high-energy astrophysics. Its primary goals are to discover high-energy transients and monitor variable objects. The ESA Science Programme Committee (SPC) approved on 19 June 2018 the participation of ESA to the CAS EP mission as a mission of opportunity. Among other elements, CAS has requested ESA participation for the provision of the mirror modules of the follow-up x-ray telescope (FXT).

FXT is a pair of Wolter-I telescopes operating in the 0.5-10 keV energy range, inheriting the design from eROSITA [2][3]. It provides field of view of about 1 deg diameter. The source localization error will be of 5-15 arcsec depending on the source strength [1]. The FXT is responsible for the quick follow-up observations of the triggered sources and will also observe other interested targets during the all-sky survey at the rest time.

Three FXT mirror modules were produced: structural and thermal model (STM), qualification model (QM) and flight model (FM). Media Lario could leverage on the manufacturing and integration infrastructure still available at its premises from the eROSITA programme [3][4], including the complete set of 54 mandrels needed for the mirror repliforming, property of MPE.

Media Lario produced and integrated the FXT mirror modules, each comprising 54 nested repliformed mirror shells; Max-Planck Institute (MPE) conducted the x-ray optical tests at the PANTER facility, for the acceptance of all the different models. This efficient collaboration enabled the on-time and in-quality delivery of the FXT mirror modules.

The resolve instrument onboard the X-Ray Imaging and Spectroscopy Mission (XRISM) consists of an array of 6 × 6 silicon-thermistor microcalorimeters cooled down to 50 mK and a high-throughput x-ray mirror assembly (XMA) with a focal length of 5.6 m. XRISM is a recovery mission of ASTRO-H/Hitomi, and the Resolve instrument is a rebuild of the ASTRO-H soft x-ray spectrometer (SXS) and the Soft X-ray Telescope (SXT) that achieved energy resolution of ∼5 eV FWHM on orbit, with several important changes based on lessons learned from ASTRO-H. The flight models of the Dewar and the electronics boxes were fabricated and the instrument test and calibration were conducted in 2021. By tuning the cryocooler frequencies, energy resolution better than 4.9 eV FWHM at 6 keV was demonstrated for all 36 pixels and high resolution grade events, as well as energy-scale accuracy better than 2 eV up to 30 keV. The immunity of the detectors to microvibration, electrical conduction, and radiation was evaluated. The instrument was delivered to the spacecraft system in 2022-04 and is under the spacecraft system testing as of writing. The XMA was tested and calibrated separately. Its angular resolution is 1.27′ and the effective area of the mirror itself is 570 cm² at 1 keV and 424 cm² at 6 keV. We report the design and the major changes from the ASTRO-H SXS, the integration, and the results of the instrument test.

Xtend is a soft x-ray imaging telescope developed for the x-ray imaging and spectroscopy mission (XRISM). XRISM is scheduled to be launched in the Japanese fiscal year 2022. Xtend consists of 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. The SXI uses the P-channel, back-illuminated type CCD with an imaging area size of 31mm on a side. The four CCD chips are arranged in a 2×2 grid and can be cooled down to −120 °C with a single-stage Stirling cooler. The XMA nests thin aluminum foils coated with gold in a confocal way with an outer diameter of 45 cm. A pre-collimator is installed in front of the x-ray mirror for the reduction of the stray light. Combining the SXI and XMA with a focal length of 5.6m, a field of view of 38′ × 38′ over the energy range from 0.4 to 13 keV is realized. We have completed the fabrication of the flight model of both SXI and XMA. The performance verification has been successfully conducted in a series of sub-system level tests. We also carried out on-ground calibration measurements and the data analysis is ongoing.

We present a summary of the ground calibration of the x-ray mirror assemblies (XMAs) for the XRISM satellite, that has been performed at the x-ray beamline at NASA’s Goddard Space Flight Center. We used a scan method with a narrow x-ray pencil beam to calibrate both Resolve and Xtend XMAs, at eight different energies. In this paper, we give an overview of the measurement setup, and show the resulting on-axis and off-axis effective area response. Results of imaging performance, stray light, and performance variation across the aperture will be presented in separate publications.

The X-Ray Imaging and Spectroscopy Mission (XRISM) is an x-ray astronomy satellite being developed in collaboration between NASA, JAXA, and ESA, and is scheduled for launch in Japanese fiscal year 2022. The x-ray mirror assembly (XMA) for XRISM has been developed at NASA’s Goddard Space Flight Center (GSFC). Two units were fabricated, one each for a micro-calorimeter array (Resolve) and a CCD array (Xtend). The ground calibration and performance verification measurements for XRISM XMA were taken at the 100-m x-ray beamline at NASA/GSFC. X-ray images at the focal plane were taken by scanning across the entire mirror aperture with a 15 mm×15 mm pencil beam. These measurements were performed at seven different energies including 1.5 keV (Al Kα), 4.5 keV (Ti Kα), 6.4 keV (Fe Kα), 8.0 keV (Cu Kα), 9.4 keV (Pt Lα), 11.1 keV (Pt Lβ), 17.5 keV (Mo Kα). A method for background subtraction was developed using a back-illuminated CCD camera with a 30 mm×30 mm (i.e. 17′×17′) array at the focal plane. Results from the measurements on the imaging performance show a small energy dependence in the angular resolution. We will also present the results of the stray light measurements.

The enhanced x-ray timing and polarimetry mission (eXTP) is a flagship observatory for x-ray timing, spectroscopy and polarimetry developed by an international consortium. Thanks to its very large collecting area, good spectral resolution and unprecedented polarimetry capabilities, eXTP will explore the properties of matter and the propagation of light in the most extreme conditions found in the universe. eXTP will, in addition, be a powerful x-ray observatory. The mission will continuously monitor the x-ray sky, and will enable multi-wavelength and multi-messenger studies. The mission is currently in phase B, which will be completed in the middle of 2022.

The Large Area Detector (LAD) is the high-throughput, spectral-timing instrument onboard the eXTP mission, a flagship mission of the Chinese Academy of Sciences and the China National Space Administration, with a large European participation coordinated by Italy and Spain. The eXTP mission is currently performing its phase B study, with a target launch at the end-2027. The eXTP scientific payload includes four instruments (SFA, PFA, LAD and WFM) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. The LAD instrument is based on the design originally proposed for the LOFT mission. It envisages a deployed 3.2 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 will provide an overview of the LAD instrument design, its current status of development and anticipated performance.

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. The scientific payload of eXTP includes four instruments: the SFA (spectroscopy focusing array) and the PFA (polarimetry focusing array)—led by China —the LAD (large area detector) and the WFM (wide field monitor)—led by Europe (Italy and Spain). They offer a unique simultaneous wide-band x-ray timing and polarimetry sensitivity. The WFM is a wide field x-ray monitor instrument in the 2-50 keV energy range, consisting of an array of six coded mask cameras with a field of view of 180°x90° at an angular resolution of 5 arcmin and four silicon drift detectors in each camera. Its unprecedented combination of large field of view and imaging down to 2 keV will allow eXTP to make important discoveries of the variable and transient x-ray sky and is essential in detecting transient black holes, that are part of the primary science goals of eXTP, so that they can be promptly followed up with other instruments on eXTP and elsewhere.

Supermassive black holes (SMBH) interact with gas in the interstellar and intergalactic media (ISM/IGM) in a process termed “feedback” that is key to the formation and evolution of galaxies and clusters. Characterizing the origins and physical mechanisms governing this feedback requires tracing the propagation of outflowing mass, energy and momentum from the vicinity of the SMBH out to megaparsec scales. Our ability to understand the interplay between feedback and structure evolution across multiple scales, as well as a wide range of other important astrophysical phenomena, depends on diagnostics only available in soft x-ray spectra (10-50 Å). Arcus combines high-resolution, efficient, lightweight x-ray gratings with silicon pore optics to provide R~2500 with an average effective area of ~200 cm², an order of magnitude larger than the Chandra gratings. Flight-proven CCDs and instrument electronics are strong heritage components, while spacecraft and mission operations also reuse highly successful designs.

In this multi-messenger astronomy era, all the observational probes are improving their sensitivities and overall performance. The Focusing on Relativistic universe and Cosmic Evolution (FORCE) mission, the product of a JAXA/NASA collaboration, will reach a 10 times higher sensitivity in the hard X-ray band (E > 10 keV) in comparison with any previous hard x-ray missions, and provide simultaneous soft x-ray coverage. FORCE aims to be launched in the early 2030s, providing a perfect hard x-ray complement to the ESA flagship mission Athena. FORCE will be the most powerful x-ray probe for discovering obscured/hidden black holes and studying high energy particle acceleration in our Universe and will address how relativistic processes in the universe are realized and how these affect cosmic evolution. FORCE, which will operate over 1–79 keV, is equipped with two identical pairs of supermirrors and wideband x-ray imagers. The mirror and imager are connected by a high mechanical stiffness extensible optical bench with alignment monitor systems with a focal length of 12 m. A light-weight silicon mirror with multi-layer coating realizes a high angular resolution of < 15′′ in half-power diameter in the broad bandpass. The imager is a hybrid of a brand-new SOI-CMOS silicon-pixel detector and a CdTe detector responsible for the softer and harder energy bands, respectively. FORCE will play an essential role in the multi-messenger astronomy in the 2030s with its broadband x-ray sensitivity.

The super DIOS mission is a candidate of Japanese future satellite program after 2030’s and this scientific concept has been approved to establish an ISAS/JAXA research group. The main aim of the super DIOS is a x-ray survey to quantify of baryons, over several scales, from the circumgalactic medium around galaxies, cluster outskirts to the warm-hot intergalactic medium along the large cosmic structure by detections of the redshifted emission lines from OVII, OVIII and other ions, for investigating the dynamical state of baryons, including energy flow and metal cycles, in the universe. The super DIOS will have a resolution of 15 arcseconds and 3 kilo-pixels of transition edge sensor (TES) and its micro-wave SQUID multiplexer read-out system. This performance resolves most contaminating x-ray sources and reduces the level of diffuse x-ray background after subtracting point-like sources. The technical achievements of on-board cooling system reached by the Hitomi (ASTRO-H) and XRISM for microcalorimeter provide baseline technology for Super DIOS. We will also have a large scale collaborations with multi wave-length survey projects such as optical and radio survey observations.

GEO-X (GEOspace X-ray imager) is a small satellite mission aiming at visualization of the Earth’s magnetosphere by X-rays and revealing dynamical couplings between solar wind and magnetosphere. In-situ spacecraft have revealed various phenomena in the magnetosphere. In recent years, X-ray astronomy satellite observations discovered soft X-ray emission originated from the magnetosphere. We therefore develop GEO-X by integrating innovative technologies of the wide FOV X-ray instrument and the microsatellite technology for deep space exploration. GEO-X is a 50 kg class microsatellite carrying a novel compact X-ray imaging spectrometer payload. The microsatellite having a large delta v (<700 m/s) to increase an altitude at 40-60 R_E from relatively lowaltitude (e.g., Geo Transfer Orbit) piggyback launch is necessary. We thus combine a 18U Cubesat with the hybrid kick motor composed of liquid N₂O and polyethylene. We also develop a wide FOV (5×5 deg) and a good spatial resolution (10 arcmin) X-ray (0.3-2 keV) imager. We utilize a micromachined X-ray telescope, and a CMOS detector system with an optical blocking filter. We aim to launch the satellite around the 25th solar maximum.

The solar neutron and gamma-ray spectroscopy (SONGS) mission is a 3U CubeSat dedicated for detecting neutrons and gamma-rays associated with intense solar flares. Solar neutron observations have not been in progress because ground-based observations are affected by attenuation in the Earth's atmosphere, and there is no dedicated mission in space at present. Hence, we are now developing in collaboration between science and engineering people at universities, and preparing for launch around 2024 during the next solar maximum. The SONGS carries a novel radiation detector which consists of multi-layered plastic scintillator bars and GAGG(Ce) scintillator array so that it can determine energies for both neutrons and gamma-rays. In total 704 signals from silicon photo-multipliers (SiPMs) are processed by 45 ASICs with very low power consumption, and realized within limited resources. In this presentation, we will describe scientific motivation, mission and instrument overview, and results from the bread-board model (BBM).

We describe the science case, design and expected performances of the X/Gamma-ray Imaging Spectrometer (XGIS), a GRB and transients monitor developed and studied for the THESEUS mission project, capable of covering an exceptionally wide energy band (2 keV – 10 MeV), with imaging capabilities and location accuracy <15 arcmin up to 150 keV over a Field of View of 2sr, a few hundreds eV energy resolution in the X-ray band (<30 keV) and few micro seconds time resolution over the whole energy band. Thanks to a design based on a modular approach, the XGIS can be easily re-scaled and adapted for fitting the available resources and specific scientific objectives of future high-energy astrophysics missions, and especially those aimed at fully exploiting GRBs and high-energy transients for multi-messenger astrophysics and fundamental physics.

STAR-X is a MIDEX mission proposed to NASA in December 2021. Comprising an X-ray telescope (XRT) provided by GSFC and MIT, a UV telescope (UVT) provided by the University of Colorado, and a spacecraft (SC) provided by Ball Aerospace, STAR-X is designed to conduct time-domain survey and to respond rapidly to transient events discovered by other observatories such as LIGO, Rubin LSST, Roman WFIRST, and SKA. STAR-X is a timely response to Astro2020’s recommendation for a space-based, sustaining time-domain and multi-messenger program.

The first three flights of the Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket established the usefulness and feasibility of direct-focusing hard X-ray instruments optimized for the Sun. While the fundamental building blocks of this concept are ready for a spacecraft mission, concurrent development is required to prepare for a subsequent generation of high-energy solar explorers, which will require higher rates and even better angular resolution. The fourth flight of FOXSI features technological advances for high resolution and high rate capability. We are developing high-precision mirror production methods, substrip/subpixel resolution in fine-pitch CdTe sensors, and novel pixelated attenuators (that optimize energy coverage even at high rates). These technologies will be demonstrated in NASA’s first-ever solar flare campaign in March 2024. Multiple payloads will be launched during a solar flare, supporting Parker Solar Probe observations during one of its perihelia.

We have developed a novel x-ray interferometer, multi-image x-ray interferometer module (MIXIM), comprised of a fine aperture mask and an x-ray detector. The angular resolution of this system can be improved with an increase of the distance between two components or a decrease of the aperture size. Although MIXIM has already achieved an angular resolution of less than 0.1” by applying the Talbot effect with a periodic multi-pinhole mask, there remains the issue that its low opening fraction of 1.3% decreases the effective area of the imaging system. Therefore, we newly introduced periodic coded aperture masks which have opening fractions of about 50% instead of the multi-pinhole mask. Conducting an experiment with a 12.4 keV parallel x-ray beam, we successfully demonstrated that the periodic coded aperture could form the self-image, and obtained the x-ray source profile with sub-arcsecond angular resolution by deciphering the coded pattern. The effective area increases about 25 times compared with the multi-pinhole mask by the introduction of the periodic coded aperture masks, which indicates that this novel method can be effective for addressing the problem.

Future high-resolution x-ray imaging missions at both strategic (Probe and Great Observatory) and smaller scales require mega-pixel focal planes with high frame rates and near-theoretical spectroscopic performance. We report test results from advanced charge-coupled devices (CCDs) developed at MIT Lincoln Laboratory for such missions. These devices incorporate two new technologies already demonstrated in small devices: a single-polysilicon gate structure enabling efficient, low-power charge transfer, and a low-noise pJFET output amplifier capable of < 3 electrons RMS noise at megahertz pixel rates. Here we report results from the first application of these technologies in a prototype large format (2k x 1k pixel, 5 x 2.5 cm²) frame transfer CCD with eight parallel outputs. In architecture, total area, and pixel count this device meets requirements for strategic missions. First measurements of noise, charge transfer efficiency and spectral resolution and achieved frame-rate are compared with requirements of candidate missions. Next steps toward maturation of this technology are briefly discussed.

In the early 2030s, ESAs new x-ray observatory, Athena, is scheduled to be launched. It will carry two main instruments, one of which is the x-ray integral field unit (X-IFU), an x-ray imaging spectrometer, which will consist of an array of several thousand transition-edge sensors (TESs) with a proposed energy resolution of 2.5 eV for photon energies up to 7 keV. At SRON we develop the backup TES array based on Ti/Au bilayers with a transition temperature just below 100 mK. In this contribution we will give a broad overview of the properties and capabilities of these state-of-the-art detectors. Over the years we have fabricated and studied a large number of detectors with various geometries, providing us with a good understanding of how to precisely control the properties of our detectors. We are able to accurately vary the most important detector properties, such as the normal resistance, thermal conductance and critical temperature. This allows us to finely tune our detectors to meet the demands of various applications. The detectors have demonstrated excellent energy resolutions of below 1.8 eV for 5.9 keV x-rays. By tuning the properties of the devices, they can be optimally matched to various read-out schemes using both AC and DC biasing. The next step is to increase the size of our TES arrays from our current kilo-pixel arrays towards the full-sized array for X-IFU.

We are developing an x-ray CMOS detector for the GEO-X (GEOspace x-ray imager) mission that will perform soft x-ray (≤2 keV) imaging spectroscopy of Earth’s magnetosphere using a micro satellite. The mission instrument consists of a MEMS x-ray mirror and a focal plane detector. For the latter, we need a sensor with fine positional resolution and moderate energy resolution in the energy band of 0.3 to 2 keV. Because we observe the day-side structure of the earth’s magnetosphere, visible-light background must be decreased by shortening the integration time for readout. To satisfy the above requirements, a high-speed x-ray CMOS sensor is being evaluated as a primary candidate for the detector. We adopt back-side illuminated sensors that have been originally developed for visible-light or UV imaging. The sensors have different specification in terms of the thickness of epitaxial wafer and specific resistance. Irradiating sensors with monochromatic x-rays from ⁵⁵Fe, we obtained the energy resolution of 205 and 227 eV (FWHM) depending on the sensor type for single pixel events at 6 keV by cooling down the sensor to −15°C. On the other hand, we found that the pulse height of the events whose charges spread over multiple pixels are significantly lower than that of single pixel events in some chips. Then we selected the chips that shows better charge collection efficiency as flight candidate. Radiation tolerance of the sensor, especially in terms of total dose effect, is investigated with 100 MeV proton. The amount of dose ranges up to 100 krad depending on position in the sensor. In spite of the excessive dose compared with 10 krad/yr in the expected highly elliptical orbit, Mn Kα and Kβ are well resolved. The amount of degradation of energy resolution is less than 50 eV up to 10 krad, which ensures that we will be able to track and calibrate the change of the line width in orbit We also utilize multi-color x-rays to investigate spectroscopic performance in the energy band of 0.5 to 7 keV. Multiple lines below 1 keV are resolved and energy resolutions are evaluated as well as linearity performance.

An X-ray interferometer is a promising technology to achieve an unprecedentedly high-spatial resolution, which provides us further understandings of astrophysical objects and the Universe. The most critical key to realize a space telescope of X-ray interferometry is downsizing the optics, and one method for that is to develop an X-ray sensor with high position accuracy that can detect narrow X-ray interference fringes. For this purpose, we are developing a position-sensitive X-ray sensor by applying the Transition-Edge Sensor (TES) technology. We designed a prototype sensor as two Ti/Au (40/90 nm) TES pixels (140 × 140 μm) connected by a single oblong Au absorber (1400 μm × 20 μm × 1 μm) aiming the sub-micrometer position accuracy. Depending on an X-ray incident position, a photon energy is divided into the two TES pixels causing individual pulses. By measuring the difference of rising edges of the two pulses, we can determine the photon-incident position. We fabricated the prototype sensor, and performed an X-ray irradiation experiment by using an ⁵⁵Fe radioactive source. As a result, we successfully detected pulses with different trigger times which reflect different rising edges up to ∼ 5 μsec, corresponding to the X-ray photon incident positions up to ∼ 0.5 mm from the center of the absorber. Here, the position accuracy depends on the accuracy of determining the rising edges. The response of our sensor is observed as ∼ 0.5 mm/5 μsec, indicating that a sub-micrometer position determination could be achieved by observing rising edges with nsec accuracy as a future prospect. In this paper, we introduce the design, fabrication, and X-ray irradiation experiment of this new position-sensitive X-ray sensor.

A science goal of many future x-ray observatories is mapping the cosmic web through deep exposures of faint diffuse sources. Such observations require low background and the best possible knowledge of the remaining unrejected background. The dominant contribution to the background above 1-2 keV is from Galactic cosmic ray protons. Their flux and spectrum are modulated by the solar cycle but also by solar activity on shorter timescales. Understanding this variability may prove crucial to reducing background uncertainty for ESA’s Athena x-ray observatory and other missions with large collecting area. We examine the variability of the particle background as measured by ACIS on the Chandra x-ray observatory and compare that variability to that measured by the alpha magnetic spectrometer (AMS), a precision particle detector on the ISS. We show that cosmic ray proton variability measured by AMS is well matched to the ACIS background and can be used to estimate proton energies responsible for the background. We discuss how this can inform future missions.

There is a growing interest in the science uniquely enabled by observations in the MeV range, particularly in light of multi-messenger astrophysics. The Compton Pair (ComPair) telescope, a prototype of the AMEGO Probe-class concept, consists of four subsystems that together detect and characterize gamma rays in the MeV regime. A double-sided strip silicon Tracker gives a precise measure of the first Compton scatter interaction and tracks pair-conversion products. A novel cadmium zinc telluride (CZT) detector with excellent position and energy resolution beneath the Tracker detects the Compton-scattered photons. A thick cesium iodide (CsI) calorimeter contains the high-energy Compton and pair events. The instrument is surrounded by a plastic anti-coincidence (ACD) detector to veto the cosmic-ray background. In this work, we will give an overview of the science motivation and a description of the prototype development and performance.

Hard-x/soft gamma-rays are probes of the most powerful phenomena in the universe. Unlike soft x-ray astrophysics, this band has benefited less from the technological advancement due to the difficulty to absorb this radiation and to the lack of focusing instrumentation. For these reasons the quest for innovative soft gamma-ray instrumentation is pressing and their effective recognition and realization are urgent. In this context, and in the framework of the AHEAD project, funded by the European Commission, the ASTENA experiment was proposed as an innovative mission concept to face some of the most debated questions in hard x-/gamma-ray astronomy. This effort will be done through the use of instruments based on groundbreaking technologies, capable of providing unprecedented broad energy passband in a wide field of view, high sensitivity observations and, at the same time, sub-arcminute localization of gamma-ray sources and polarimetric measurement. In this paper we describe the instruments on board ASTENA, the technologies involved, the performances achievable with their exploitation and their level of readiness.

Observing cosmic sources in the medium-energy gamma-ray regime (~0.4 – 10 MeV) requires an efficient instrument with good angular resolution and background rejection. Artificial single-crystal diamond detectors (SCDDs) have comparable energy ranges, energy resolution, and threshold levels as traditional silicon solid-state detectors (SSDs), but with faster rise times (~1 ns), improved radiation hardness, and are generally insensitive to light and temperature. Here we present work preliminary to the pairing of artificial single-crystal diamond detectors (SCDDs) with CeBr₃ calorimeters to produce a prototype Compton telescope.

In this paper we describe ProtoGECCO–a prototype instrument for the Galactic Explorer with a Coded aperture mask and Compton Telescope (GECCO). ProtoGECCO is comprised of two main imaging calorimeters. The top calorimeter is an array of cadmium zinc telluride (CZT); the bottom calorimeter is an array of high-light yield Gd₃Al₂Ga₃O₁₂:Ce (GAGG) fingers with silicon photomultiplier (SiPM) readout. The calorimeters are surrounded by a thallium-doped cesium iodide (CsI:Tl) active shield. ProtoGECCO employs the techniques of both coded aperture imaging and a Compton telescope. The main goals of the prototype are to further develop the instrument technology, thereby raising the technical readiness level (TRL), and to fly on a high-altitude balloon from Fort Sumner, NM. The results of this work are directly applicable to future space instruments that require detectors with large area; excellent spatial, energy, and angular resolution; and high detection efficiency. Such future missions will address problems in the MeV domain of gamma-ray astronomy—one of the most underexplored windows on the universe.

Hard x-/soft gamma-ray astronomy (>100 keV) is a crucial field for the study of important astrophysical phenomena such as the 511 keV positron annihilation line in the galactic center region and its origin, gamma-ray bursts, soft gamma-ray repeaters, nuclear lines from SN explosions and more. However, several key questions in this field require sensitivity and angular resolution that are hardly achievable with present technology. A new generation of instruments suitable to focus hard x-/soft gamma-rays is necessary to overcome the technological limitations of current direct-viewing telescopes. One solution is using Laue lenses based on Bragg’s diffraction in a transmission configuration. To date, this technology is in an advanced stage of development and further efforts are being made in order to significantly increase its technology readiness level (TRL). To this end, massive production of suitable crystals is required, as well as an improvement of the capability of their alignment. Such a technological improvement could be exploited in stratospheric balloon experiments and, ultimately, in space missions with a telescope of about 20 m focal length, capable of focusing over a broad energy pass-band. We present the latest technological developments of the TRILL (technological readiness increase for Laue lenses) project, supported by ASI, devoted to the advancement of the technological readiness of Laue lenses. We show the method we developed for preparing suitable bent germanium and silicon crystals and the latest advancements in crystals alignment technology.

The origin of the cosmic diffuse gamma-ray (CDG) background in the 0.3–10 MeV energy range is a mystery that has persisted for over 40 years. The Mini Astrophysical MeV Background Observatory (MAMBO) is a new CubeSat mission under development at Los Alamos National Laboratory with the goal of addressing this longstanding puzzle. The concept is motivated by the fact that, since the MeV CDG is relatively bright, only a small detector is required to make high-quality measurements of it. Indeed, the sensitivity of space-based gamma-ray instruments to the CDG is limited not by size, but by the locally generated instrumental background produced by interactions of energetic particles in spacecraft materials. Comparatively tiny CubeSat platforms provide a uniquely quiet environment relative to previous MeV gamma-ray science missions. The MAMBO mission will provide the best measurements ever made of the MeV CDG spectrum and angular distribution, utilizing two key innovations: 1) low instrumental background on a 12U CubeSat platform; and 2) an innovative shielded spectrometer design that simultaneously measures signal and background. Los Alamos is partnering with commercial vendors for the 12U CubeSat bus and ground station network, which we expect will become a new paradigm for low-cost, fast-turnaround space science missions. We describe the MAMBO instrument and mission concept in detail and present the expected scientific return.

The POLAR-2 gamma-ray burst (GRB) polarimetry mission is a follow-up of the successful POLAR mission which has collected data during 6 months on board the Chinese Tiangong-2 spacelab in 2016-2017. From the polarization studies on 14 GRBs, POLAR measured an overall low polarization as well as an unexpected complexity in the time evolution of the polarization during a GRB. These results indicate that measurements with a significantly improved precision are required. Furthermore, with the recent discovery of gravitational waves and their connection to GRBs warrant a high precision GRB polarimeter capable of both providing high precision polarization measurements as well as detecting very weak GRBs. The POLAR-2 polarimeter, based on the same Compton scattering measurement principle as POLAR, but with an extended energy range and an order of magnitude larger overall effective area for polarization events. The instrument, proposed and being developed by a Swiss, Chinese, Polish and German c

The gamma-ray polarimeter experiment (GRAPE) is a NASA-funded high-altitude scientific balloon experiment. For over a decade, GRAPE has been developing wide field of view (FoV) scintillator-based Compton polarimeters designed to measure gamma-ray polarization from GRBs over the energy range of 50-500 keV. A variant of a GRAPE design was tested in flight in 2011 and 2014. A new design is scheduled to fly in Fort Sumner, New Mexico in August of 2023. The new design of GRAPE incorporates an assemblage of 245 optically isolated high-Z and low-Z scintillators each read out by individual silicon photomultipliers (SiPMs) and arranged in a 3-dimensional 7x7x5 cuboid layout which provides moderate imaging capabilities. The cube design of GRAPE is expected to improve performance with respect to previous GRAPE missions by eliminating optical cross-talk and using the instrument’s imaging capability to reduce instrument background. To standardize the development process for the flight instrument, select optimal technology to optimize the design features, and build a framework for the analysis and simulation of the 245 detector instrument, a small-scale prototype instrument of the cube design was developed and studied in the lab using simulations and lab measurements of unpolarized sources. The results of these studies are presented here along with an overview of the 7x7x5 flight instrument and mission.

We are developing a novel Bragg reflection x-ray polarimeter using hot plastic deformation of silicon wafers. A Bragg reflection polarimeter has the advantage of simple principle and large modulation factor but suffers from the disadvantage of a narrow detectable energy band and difficulty to focus an incident beam. We overcome these disadvantages by bending a silicon wafer at high temperature. The bent Bragg reflection polarimeter have a wide energy band using different angles on the wafer and enable focusing. We have succeeded in measuring x-ray polarization with this method for the first time using a sample optic made from a 4-inch silicon (100) wafer.

Ultraviolet spectroscopy is a key element in the multi-wavelength approach to astronomy. Echelle spectroscopy provides high resolution and broad wavelength coverage and is a frequent choice for optical spectroscopy. However, it has limitations when applied to ultraviolet applications, particularly in the far ultraviolet, at wavelengths shortward of the MgF2 cutoff at ~ 1150 Å. I present an approach to provide echelle spectroscopy at these short wavelengths, enabling aberration control with only two optics post-telescope, by using gratings with curved and variable line-space grooves.

Ultraviolet (UV, 900−2000Å) spectroscopy simultaneously traces the most common elements (e.g., H, He, O, C, N) in many phases, in the form of ionic, atomic, and molecular lines. UV grating spectrometers hence offer unique insights into astrophysical systems and the impacts of their evolution. This work seeks to understand how we might best optimize certain grating designs for targeted astrophysical tracers. Our work is intended to guide proposers in determining the ideal grating parameters given their specific science objectives. We report on the results of the initial phase of the project, a thorough design phase to determine the ideal grating parameters and electron-beam lithography/potassium hydroxide patterning prescriptions for blazed UV gratings. We use grating simulation software to explore a grating-parameter space and determine the key performance expectations for gratings in next-generation UV space instruments. We present our results for a rough grid in grating-parameter space (blaze angle: ∼30°−76°, grating period: 100−5000 nm). Future work will explore specific cases that include the nominal grating prescriptions for current (e.g., Hyperion, PolStar, LUVOIR) and future mission designs.

We are developing the design for the Lyman-Ultraviolet (LUV) Imaging Spectrograph, LUVIS to propose for a small explorer (SMEX) mission. LUVIS will provide true long slit (six arc minute) imaging spectroscopic capability with large spectral resolving power, R. Minimizing the number of optical components to the required minimum of three enables large spectral throughput. The design uses a two-mirror Cassegrain Ritchey-Chretien Optical Telescope assembly (OTA), a single optic Rowland-like spectrometer, and a windowless 50 x 127 mm curved microchannel plate (MCP). The design is optimized over the 102 to 140 nm spectral range providing spectral imaging at R ~ 20K in a single exposure. Lyman-β enhanced Al + LiF mirror and grating coatings with the LiF protected with an atomic layer deposition (ALD) fluoride encapsulating overcoat provide high throughput over that spectral range. Line-of-sight (LOS) jitter control utilizes time-tag photon arrival to compensate field position jitter by re-registering pixel location in post-processing as well as tip/tilt active control of the secondary mirror of the OTA. This paper will describe the design as well as some of the key design trades that defined the design.

The World Space Observatory–Ultraviolet mission (Spektr-UF, WSO-UV) is an efficient multipurpose orbital observatory for high- and low-resolution spectroscopy, high sensitivity imaging and slitless spectroscopy in the ultraviolet wavelength range. It will open new opportunities in (exo)planetary science, extragalactic astronomy, stellar astrophysics and cosmology. The observatory is based on a complex of scientific instruments including the T-170M telescope (aperture 170 cm), spectrographs and imagers. The payload should be ready in 2025. We briefly describe the current status of the mission.

The advantages of an astrophysical UV telescope on the moon surface and a number of scientific tasks are discussed. An approach to build an astronomical 20-30 cm UV telescope at the future international lunar research station is presented. It is suggested to use a slewing mirror to repoint the moon-based telescope and to switch between filters and detectors. The first small telescope at the ILRS can be considered as a step towards the development of technologies for moon-based astronomical observations.

The Lyman UV imaging spectrograph (LUVIS) accomplishes priority UV science contained in the budget of a SMEXclass mission. LUVIS consists of a 0.5-m f/24 Cassegrain optical telescope assembly feeding a UV/ far-UV spectrometer. LUVIS has a long 6 arcmin slit enabling spectral imaging and is optimized for 102-140 nm with a resolving power of 20,000 on a micro-channel plate detector with a CsI photocathode. The light gathering power is designed to reach galaxies with near-UV fluxes as low as 10^-14 erg/s/cm² /Å (and lower with long time exposures). The design approach encompasses a simple but elegant optical design, minimum number of reflective surfaces, limited mechanisms, and an orbit minimizing fuel requirements while offering operational advantages. All components are already at a high technology readiness level further reducing technical and cost risk to meet a SMEX budget with healthy cost reserves.

ULTRASAT is a scientific satellite carrying a near UV telescope with high sensitivity and large field of view. The mission, led by the Weizmann Institute of Science and the Israeli Space Agency in collaboration with Deutsches Elektronen-Synchrotron (DESY), is expected to be launched in 2025 by NASA. ULTRASAT will revolutionize our understanding of the high energy transient universe and will have a broad scientific impact across the fields of gravitational wave (GW) sources, supernovae, variable and flare stars, active galactic nuclei, tidal disruption events, compact objects, and galaxies.

The ULTRASAT camera, developed by DESY, is based on a custom imager, developed by Analog Value and Tower Semiconductors, and manufactured by Tower Semiconductor in Israel. The focal plane array is composed of four independent sensors with an effective area of ~45×45 mm² each, providing graceful degradation capabilities. Each sensor array has ~22,450M pixels, with pixel size of 9.5×9.5 μm². The sensor implements backside illumination and an anti-reflective coating optimized for the wavelength range 230 to 290nm, achieving high quantum efficiency of >60%. Low dark noise of i_d<0.026 e/sec/pixel is needed to meet the required sensitivity. This is achieved by both operating at -73°C, and by a special design including advanced pixel architecture, optical trench between the array of pixels and surrounding circuits and a low noise design of the digital electronics. High dynamic range (HDR) capability is achieved by dual gain 5T pixels. The design of the sensor includes one analog to digital converter (ADC) per column architecture and low voltage differential signal (LVDS) output buffers. The operation is controlled by a dedicated microcontroller and configuration registers. The design employs techniques for mitigating space radiation effects, enabling an operation lifetime of six years in GEO.

This paper describes the design of the sensor and its target performance. The performance that was achieved will be described in future publications.

The far ultraviolet (FUV, 91.2 nm to 180 nm) is the wavelength region with the greatest density of absorption and emission lines. However, despite of being one of the most exciting parts of the astrophysical spectrum, FUV missions are rare, partly due to the need for an instrument with a windowless, open-face detector.

TINI, the Tuebingen-IIA Nebula Investigator, is a proposed space mission that addresses this unique wavelength range with a 12U imaging spectrograph tailored for observations of diffuse sources like nebulae or the ISM. It features a field-of-view of 0.7° with 13" spatial resolution and a spectral resolution of 0.8Å (resolving power R≈2000). The mission is led by the Indian Institute of Astrophysics, where the instrument is developed. The detectors are a contribution by the University of Tübingen.

This publication provides a brief overview of the scientific goals, the instrument, and the planned mission concept.

Based on the science case for the SMEX ESCAPE mission, a normal incidence EUV mirror mission would be an interesting follow on. Our provisional SmallSat/CubeSat design has a 1 m diameter primary deployable mirror. The mirror would be coated with multilayers for normal incidence EUV reflectivity. The deployable mirror substrate is a shape memory alloy (SMA). The SMA needs to be over coated with a material that can be polished and then smoothed further. The combination that worked well on an aluminum cylinder is a high phosphorous content electroless nickel (eNiP) super-polished and then coated with carbon nitride (CNx). The multilayers were deposited on the eNiP+CNx stack. We report here our progress toward putting in place the pieces for a proof of concept. We discuss a scale up of previous return to shape on sheets of NiTi and the ray tracing results that demonstrate a sufficient return to shape of 1 micron. Furthermore, corrections post deployment are possible if desired.

WSO-UV is the coming mission for ultraviolet astronomy. The telescope is equipped with instrumentation for imaging and spectroscopy in the 115 nm-315 nm spectral range. The far ultraviolet imager on board WSO-UV will obtain 100 mas angular resolution images from geosynchronous orbit in five far UV bands within the 115 nm-175 nm spectral range. Additionally, it will be equipped with prisms to obtain slit-less spectroscopy with dispersion 500 around the relevant spectral lines (Lyman-a, CII at 134 nm and CIV at 155 nm). A laboratory for vacuum ultraviolet optics has been developed in the premises of the Universidad Complutense de Madrid to test the optical performance of the channel. An optical emulator of the WSO-UV beam has been developed to fit within the modular vacuum chamber. An MCP detector with an optical architecture similar to the flight detector has been produced specifically for the tests. In this presentation, we describe the laboratory set-up and the optical emulator developed for the tests.

Ultraviolet spectroscopy is a powerful method used to study planetary surface composition through reflectance measurements and atmospheric composition through stellar/solar occultations, transits of other planetary bodies, and direct imaging of airglow and auroral emissions. The next generation of ultraviolet spectrographs (UVS) on board ESA’s JUICE (Jupiter icy moons explorer) and NASA’s Europa Clipper missions will perform such measurements of Jupiter and its moons in the early 2030’s. This work presents a compilation of a detailed UV stellar catalog of targets with high intensity in the 52-204 nm region with applications relevant to planetary spectroscopy. These applications include: 1) planning and simulating occultations, including calibration measurements; 2) modeling starlight illumination of dark, nightside planetary surfaces primarily lit by the sky; and 3) studying the origin of diffuse galactic UV light as mapped by existing datasets from Juno-UVS. This catalog also includes information drawn from other resources such as the international ultraviolet explorer (IUE) catalog and SIMBAD. We have constructed spectra at 0.1 nm resolution for over 80,000 targets using Kurucz models and, when available, IUE spectra. We report on our methods for producing the catalog and discuss plans for its implementation during ongoing and upcoming planetary missions.

In order to prolong the life of the detector in the FUV channel of the cosmic origins spectrograph (COS) on the Hubble Space Telescope (HST), the positions of the spectra are adjusted by offsetting targets in the cross-dispersion direction. Since the installation of COS in 2009, five lifetime positions (LPs) have been used, and a sixth is scheduled to be commissioned in late 2022. The location of each LP is chosen based on both the evolving detector gain sag and the optical properties of the spectrograph. The COS optical design was optimized for use at its initial lifetime position (LP1), and offsetting the spectra introduces aberrations which affect the spectral resolution. In order to understand the effects of these aberrations on the data quality, optical models have been constructed in order to predict the performance of the spectrograph over the permissible range of target offsets and grating focus values. This modeling work, and how it is used in combination with on-orbit data when determining where to locate new lifetime positions, is discussed.

We describe the radiometric performance and ground calibration results of the Europa Clipper Ultraviolet Spectrograph (Europa-UVS). Europa-UVS is a modest power (~8 W) ultraviolet spectrograph that is the sixth in a series of Alice/UVS instruments built by SwRI. Europa-UVS covers a 55-206 nm bandpass with approximately 0.6 nm spectral resolution over a 7.5° field of view with better than 0.25° spatial resolution on-axis. Europa-UVS also features three different observing modes to allow higher-than-normal spatial resolution observing as well as solar occultations of Europa. Both the high spatial resolution and solar occultation observations have reduced sensitivity when compared with nominal observations. Europa-UVS meets all performance requirements with margin, and is the first planetary UV spectrograph to feature a microchannel plate detector with curved borosilicate microchannel plates (expected to be less sensitive to gamma rays than traditional plates). Europa-UVS, like its predecessor JUICE-UVS, incorporates both timetagged pixel list and histogram observing with programmable acquisitions to maximize science return while minimizing data storage and downlink. Europa-UVS will search near Europa for water vapor plumes, examine the composition and structure of Europa’s atmosphere and surface, and characterize Europa's aurora.

The Polstar Mission uses time domain FUV and NUV spectropolarimetric observations to provide insight into how our galaxy became able to support a solar system like ours. Polstar will study the evolution of massive stars, including the inter-stellar dust and gas that they interact with and the dynamics of protoplanetary disks and lower resolution near UV (180nm – 320 nm) to study interstellar reddening mechanism. Polstar will simultaneously measure at high spectral resolving power all four Stokes parameters (I, Q, U, V)^T to high accuracy (0.001) with a precision better than 0.0001 using an instrument comprising a modulator with rotating MgF₂ retarders and a fixed MgF₂ Wollaston prism analyzer that concurrently measures the two orthogonal polarizations of the retarder modulated signal at six optimized rotational angles on a common detector. The output of the Wollaston prism either directly enters an echelle spectrograph, which provides spectral resolution of ~30K with a wavelength range from 122 nm to 200 nm, or is reflected to a prism spectrograph, which provides spectral resolution ranging from 140– 4000 with a wavelength range from 180 nm to 320 nm. In this paper we outline the instrument calibration approach to obtain the Mueller matrices over the full wavelength range that permit us to determine the Stokes parameters, and to spectrally calibrate the instrument. We also describe the ground support equipment for calibration.

Four evaporated, thin-film Al samples protected by a thin (29±2 nm) aluminum fluoride (AlF₃) overcoat stored in dry (dew point 276K ), 327 K air over a period of 2500 hours exhibited no significant changes in the thickness of the protective AlF₃ layer nor growth in aluminum oxide as observed by variable-angled, spectroscopic ellipsometry. Two of the samples had AlF₃ evaporated at T>200°C, two without substrate heating. No difference in aging was noted amongst the samples. Since many months may elapse between fabrication and launch of the completed observatory, this result contributes to understanding the boundaries in temperature and humidity separating negligible changes in fluoride-containing optical components from unacceptable degradation. While negligible changes in thicknesses were observed, there were changes in the ellipsometric data, psi and delta, with time. In this study, we also present our use of an effective medium approximation model in understanding changes in the fluoride layer with aging. The observed changes in SE parameters are here interpreted as changes in void fraction, though the presence of some water was not ruled out. Apparent void fraction fell by a factor of two by the end of the 2500 hours. The decreasing void fraction suggests that the films might be becoming more compact with time. Other surface sensitive techniques such as AFM are needed to narrow down possible explanations for observed changes.

Vacuum photodetectors have a long history in ultraviolet (UV) sensing for both astronomy and remote sensing. One of the main advantages of this technology is the ability to use solar blind photocathodes to enable high sensitivity measurements of astronomical and atmospheric sources of Far UV (FUV) and Deep UV (DUV) emission in environments with high visible light (VIS) backgrounds. The use of microchannel plates (MCP) in vacuum photodetectors also allows single photon sensitivity for extremely weak signals. However, these detectors have typically suffered from lower Quantum Efficiency (QE) than their solid-state alternatives. Recent advances in photocathode technology have resulted in significant increases in QE for several UV sensitive photocathodes. We present test results of next generation high QE photocathodes appropriate for use in a wide range of FUV and DUV astronomy and remote sensing. A newly developed opaque Cesium Iodide (CsI) photocathode deposited on microchannel plates and sealed into vacuum photodetectors with a Magnesium Fluoride (MgF₂) input window demonstrates QE of < 16% @ 130 nm. An optimized transmission mode solar blind (SB) alkali-telluride photocathode demonstrates 29% peak QE and 10³ to 10⁸ suppression of NUV and visible light, a significant improvement over previous alkali-telluride photocathodes. Finally, we present data from a new high QE S20 alkali-antimonide photocathode with < 40% QE at 254 nm, suitable for instruments requiring wideband DUV through VIS coverage. Improvements in collection efficiency of vacuum photodetector MCPs from 60% to 90% will also be presented, providing a further 50% boost to detective QE.

Efficient mirrors with high reflectivity over the ultra-violet, optical, and infra-red (UVOIR) spectral range are essential components in future space-based observatories. Aluminum mirrors with fluoride-based protective layers are commonly the baseline UV coating technology; these mirrors have been proven to be stable, reliable, and with long flight heritage. However, despite their optical performance to date, their reflectivity is still insufficient for future large telescope instrumentation in which several reflections are required.

Recently, a novel passivation procedure based on the exposure of bare Al to a fluorine containing electron beam generated plasma has been presented [1,2]. This research is framed in a collaboration between Goddard Space Flight Center (GSFC) and the U.S. Naval Research Laboratory (NRL), with plasma treatment carried out in NRL’s large area plasma processing system (LAPPS) using aluminum coated glass samples produced at GSFC coating facilities. The passivation of the bare Al is accomplished by using an electron-beam generated plasma produced in a fluorine-containing background to simultaneously remove the native oxide layer while promoting the formation of an AlF₃ passivation layer with tunable thickness. Importantly, this new treatment uses benign precursors (SF₆) and is performed at room temperature. In this work, details of the plasma process and in situ surface monitoring with spectroscopic ellipsometry are discussed. This novel procedure has demonstrated improved Al mirrors with state of the art far-ultraviolet (FUV) (λ = 90-200 nm) reflectivity (e.g. R=91% at 121.6 nm) paired with an excellent thickness control of the Al protective layer.

This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes + Instrumentation, 2022.

This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes + Instrumentation, 2022.

The planetary extreme ultraviolet spectrometer (PLUS) is a project funded by the Italian Space Agency focused on the development of an extreme (EUV) and far-ultraviolet (FUV) high-performance spectrograph, which adopts a dual channel optical scheme. Thanks to an optimized layout based on the use of variable line space (VLS) gratings in an off-Rowland configuration, high spectral and spatial resolution are achieved. The efficiency improvement is obtained by the optimization of the coatings on the optical components. Improved detection limit, shorter observations integration time and unprecedented performance in terms of dynamic range will be achieved by the use of high resolution/dynamic range solar blind photon counting detectors. The photon counting detectors will be based on a micro-channel plate (MCP) coupled with an application specific integrated circuit (ASIC) read out system.

The data processing methods for AstroSat’s UVIT instrument and the software implementations that have been developed over the past few years will be presented. The instrument calibration is discussed in other work. Source magnitude extraction is calibrated with respect to a curve of growth analysis (COG) where the COG calibration is described in Ref. 2. UVIT images require corrections for geometric distortion, flat-field illumination, and spacecraft drift, which is carried out with the UVIT-customized software package CCDLAB. A description of the usage of the CCDLAB Pipeline for UVIT data reduction from Level 1 raw data to completed science images was presented in Ref. 4. The astrometry has been improved recently by incorporating the Gaia DR2 catalog and developing a new algorithm for coordinate matching. CCDLAB was upgraded in 2020 to produce exposure maps for the entire field of view. New methods for source extraction for crowded fields have now been added to the CCDLAB Pipeline. Other new updates will be discussed.

The UVIT instrument on AstroSat has carried out a survey of our neighboring Andromeda galaxy, with a set of 19 fields to cover its large angular extent. The survey is complete in the FUV F148W filter, and about halfcomplete in FUV F169M, FUV F172M, NUV N219M and NUV N279N filters. The NUV coverage is incomplete due to failure of the NUV detector partway through the AstroSat mission. The survey and its scientific results are reviewed, with emphasis on the most recent results. From the Andromeda survey, catalogs of point sources in the FUV and NUV filters have been created. Young stars have been detected in the bulge. FUV and NUV counterparts of the X-ray sources in Andromeda were identified and are predominantly globular clusters. Clusters from the HST/Pan-Andromeda Hubble Treasury (PHAT), which covers a large part of the NE half of the galaxy, have been identified in UVIT FUV and NUV and characterized using their multi-band FUV to IR photometry. FUV variable stars have been identified in Andromeda observations with exposures separated by a few years, and cross-matched with hot stars. The Andromeda bulge has been characterized in FUV and NUV wavelengths for the first time, including measurement of structural parameters and modelling of the star formation and metallicity history of the bulge.

The far ultraviolet (FUV, 100-200 nm wavelengths) contains plenty of spectral lines for key targets of the astrophysics, solar physics, and atmospheric physics communities. Imaging at spectral lines like O VI (103.2, 103.8 nm), H Lyman α (121.6 nm), N V (123.8, 124.2 nm), O I (130.4, 135.6 nm), C IV (155 nm), etc., will enable address important targets for the above communities, which is reinforced by the very limited access to such imaging so far. Hence LUMOS instrument of LUVOIR (Large Ultraviolet Optical Infrared Surveyor, large space telescope concept) proposed imaging emission features, such as outer planet auroras at H₂ Werner bands to map CH₄ absorption, for which LUMOS would use a FUV imaging channel operating with narrow- and medium- band filters. The GOLD group has been investigating narrowband mirrors that are tuned at the desired FUV spectral line(s) as candidate coatings for imaging space instrumentation. It developed Al/LiF/SiC/LiF coatings that can be tuned at the shortest end of the FUV, 100 nm, which enables mirrors peaked at H Lyman β (102.6 nm) or at the O VI doublet. Furthermore, such coatings can be designed to reject the ubiquitous H Lyman α, where they can be made to reflect below 1%. The group is also investigating on narrowband mirrors based on multilayers that alternate two fluorides, such as AlF₃/LaF₃. These coatings can be tuned at the desired FUV wavelength longer than 120 nm. The proceeding presents a summary of the main results on these two sorts of coatings, which can cover the full FUV with narrowband MLs.

The Star-planet activity research CubeSat (SPARCS) is a 6U CubeSat mission focused on dual channel, SPARCS farUV (153-171 nm) and near-UV (260-300 nm), photometric monitoring of nearby M-stars. These data will advance our understanding of the typical day-to-day UV environments around M stars and how these conditions evolve over the stars’ multibillion-year lifespans; critical factors that constrain the potential habitability of planets orbiting M stars, informing the search for life in the galaxy. This paper lays out the detailed plan for the SPARCS science payload assembly, integration, and testing (AIT), including the optical calibration and performance measurement methods for the science telescope, thermal vacuum bakeouts for part cleaning, ongoing contamination monitoring methods, and spectral performance measurements of the assembled payload camera. We will provide updates on AIT proceedings at ASU and the SPARCS thermal vacuum chamber (TVAC) test facility built for UV CubeSat missions at Arizona State University’s School of Earth and space exploration.

The star-planet activity research CubeSat (SPARCS) is a small space telescope tasked with monitoring sunspots and flares of M-type stars in near ultra-violet (NUV) and far-ultraviolet (FUV) wavelengths. The SPARCS instrument is approaching its critical design review (CDR), and the team is moving forward with assembly integration and test (AI&T) plans for the payload and spacecraft. This paper focuses on the SPARCS thermal vacuum (TVAC) testing facility and thermal testing plan for the payload. The SPARCS TVAC testing chamber has been developed at Arizona State University (ASU) to provide a clean and relevant thermal environment for testing CubeSats and their payloads. The chamber can perform long-duration bakeouts at +80°C for cleaning and monitoring volatile and condensable contaminants with a thermal quartz crystal microbalance (TQCM) and a residual gas analyzer (RGA). These capabilities allow the SPARCS team to control and monitor the cleanliness of the test environment. An FUV monochromator is mounted to the side of the chamber, providing a calibrated light source to test and calibrate the payload. The SPARCS payload will be the first instrument tested in this chamber and demonstrate the capabilities of the SPARCS TVAC Test Facility. The team will verify the payload’s thermal capabilities, such as heating critical surfaces to expel contaminants and cooling the detectors for imaging. The thermal test plan details thermal cycling, hot/cold dwells, thermal balance, and instrument operations through the test. The SPARCS payload TVAC test aims to verify various performance requirements before integration with the spacecraft.

Solar flares are some of the most energetic events in the solar system and can be studied to investigate the physics of plasmas and stellar processes. One interesting aspect of solar flares is the presence of accelerated (nonthermal) particles, whose signatures appear in solar flare hard x-ray emissions. Debate has been ongoing since the early days of the space age as to how these particles are accelerated, and one way to probe relevant acceleration mechanisms is by investigating short-timescale (tens of milliseconds) variations in solar flare hard x-ray flux. The impulsive phase rapid energetic solar spectrometer (IMPRESS) CubeSat mission aims to measure these fast hard x-ray variations. In order to produce the best possible science data from this mission, we characterize the IMPRESS scintillator detectors using Geant4 Monte Carlo models. We show that the Geant4 Monte Carlo detector model is consistent with an analytical model. We find that Geant4 simulations of x-ray and optical interactions explain observed features in experimental data, but do not completely account for our measured energy resolution. We further show that nonuniform light collection leads to double-peak behavior at the 662 keV ¹³⁷Cs photopeak and can be corrected in Geant4 models and likely in the lab.

The solar ultraviolet imaging telescope (SUIT) is an imaging telescope on-board the Aditya-L1 satellite, which is India’s maiden space mission dedicated solely to solar observations. The spatially resolved, high cadence observations are designed to be taken in eleven science filters with full width half maxima ranging between 0.1–58 nm and spread over the near-ultraviolet (NUV) domain of the solar spectrum (200–400 nm). The huge incoming solar flux, limited by the linearity regime performance of the charge coupled device (CCD) as well as the thermal operational constraints, mandate the use of an entrance aperture filter, the thermal filter (TF), for SUIT. The design of this filter is, further, constrained by exposure time and enhanced emission of the sun during eruptive events. From performance perspective, the TF reflects ∼50% of the incident radiation and allows only 0.1–0.45% of the incoming flux to pass within 200–400 nm. The transmission on either side of the operational range is satisfactorily reduced, so as to ensure minimum unwanted light leaking into the imaging system. Therefore, the TF plays a significant role in increasing the photometric efficiency as well as maintaining the operational temperature of the telescope. To the best of our knowledge, this is the first time any attempt of designing and manufacturing any such rejection filter aiming optimized performance in the NUV range is being done for a space-based imaging solar telescope. The choice of materials for substrate and coating for the filter poses several challenges in terms of contamination, corrosion/ oxidation, durability during manufacturing process, long-term exposure to harsh space environment as well as formation of pinholes. The transmission and reflection profiles of the fabricated TF is satisfactory to meet our design and technical constraints. The TF is also qualified for various environmental and radiation conditions. The transmission of the TF is seen to be well within our allowed margins (±10% of the design value) even after being exposed to these qualification tests.

The solar transition region ultraviolet explorer (STRUVE) is a proposed CubeSat mission with a slit-scanning, full-Stokes spectropolarimeter that will observe the Sun with a spectral range of about 259 to 281 nm. STRUVE addresses two main high-level science objectives: 1) understand the magneto-fluid conditions at the base of the corona and the build-up and release of magnetic energy; and 2) understand how the magnetic and plasma properties at the base of the solar corona vary between open and closed magnetic structures. This paper aims to illustrate the flow down of requirements from the mission science objectives to design requirements while also giving an overview of the design developed from the concept study. The derived requirements from the science objectives are the primary functions STRUVE will need to perform to capture the needed data for the mission. The overview of the mission design will delve into the mission operations and give an overview of the STRUVE instrument and spacecraft. Links between the requirements and mission design are made, pointing out how critical requirements are being met. Throughout the paper, trade studies are presented showing the rationale behind many of the critical design choices made in developing STRUVE for the concept study

The solar transition region ultraviolet explorer (STRUVE) is a proposed CubeSat mission to study the magnetic field in the solar atmosphere from the photosphere up to the top of the chromosphere. The STRUVE instrument is a full-Stokes spectro-polarimeter and observes a region of the near-UV that contains the well-known Mg II h- and k-lines as well as a number of Fe I- and Fe II-lines that sample many heights in the atmosphere. In order to accurately determine the magnetic field strength and orientation, STRUVE has sub-arcsecond yaw and pitch pointing stability requirements to suppress crosstalk between Stokes parameters. One of our concept study priorities is addressing the fine pointing requirements to demonstrate mission feasibility. This paper provides an overview of the STRUVE CubeSat and related background, the main sources of jitter and our ADCS solutions. We present several studies that provide rationale for pointing system design choices and review tools that have been developed to demonstrate system capabilities.

The wide field imager (WFI) is one of the two focal plane instruments on-board the Athena x-ray astronomy mission, the second large-class mission of the European Space Agency. Athena is planned to be launched in 2034 and will be stationed in Lagrange point L1, from where it will perform observations in the x-ray spectrum, from 0.2 keV to 15 keV. The frame processing module (FPM) is part of the detector electronics (DE) of the Athena WFI, which has the main task of reading out the WFI detector array, digitizing it, performing real-time frame processing, and event extraction, using offset correction and threshold maps. The high number of 512×512 pixels on each large detector (LD), the fast readout cycle (5 ms) and the complex sequence of digital signals required to read out the WFI detectors present some stringent design requirements on the electronics used in the FPM as well as on the programmable logic implemented in the selected field programmable gate array (FPGA). This paper describes the hardware design of the FPM and the preliminary engineering model that has already been manufactured. Given the criticality of the FPM, this early development model already includes most of the flight-like electronics based on state-of-the-art radiation hard ADCs, FPGAs and SSRAM memories. Specific design challenges are addressed related to the electronic implementation of the FPM, which already fulfils most of the design rules according the ECSS standards.

The wide field imager (WFI) is one of two instruments of the x-ray advanced telescope for high-energy astrophysics (Athena) mission selected by ESA. The WFI instrument uses a camera with a DEPFET sensor, Detector electronics (DE) to control the camera, and additional electronics units to communicate with the spacecraft on-board-computer (OBC). The spacecraft event time (SCET) is generated on the OBC and synchronized with ground. The SCET timing synchronization between the OBC and the sensor photon detection presents particular challenges. The science user requirement of the absolute knowledge error of the WFI time stamp relative to the OBC clock is 5 µs with a confidence level of 99.73%. In this paper, we present the WFI timing distribution implementation. The three main contributors of the timing distribution are: (1) time delays and jitter between OBC and DE, (2) internal delays of the DE, and (3) delay between a photon capture and the time stamping in the DE. The first contributor is the most critical and two solving methods are identified. The first method uses only the timecode of the SpaceWire (SpW) communication network, and the second method uses a combination of pulse-per-second (PPS) signal and SpW network. SpW network standard was published in 2003 and few missions such as ESA solar orbiter use it exclusively for time distribution. In our analysis, we found that using the second method with a PPS signal, delays contribution is in order of nanoseconds.

The Wide Field Imager (WFI), one of two complementary instruments on board ESA’s next large X-ray mission Athena, combines state-of-the-art resolution spectroscopy with a large field of view and high count rate capability. Centerpiece of the WFI instrument is the large detector assembly consisting of four DEPFET (Depleted p-channel field effect transistor) sensors with a size of 512×512 pixels each, and one fast detector with a size of 64×64 pixels. They are planned to be operated in drain current readout mode, which enables fast readout rates but is sensitive to inhomogeneities of the drain currents. These inhomogeneities arise from the sheer size of the DEPFET sensor matrix and are originated in the spatial distribution of wafer properties and process parameters. We characterized the drain current distribution of a large detector lab module (one quadrant of the large detector assembly, 512×512 pixels) out of the pre-flight production of Athena’s WFI DEPFET detectors. In order to better understand the origin of the current spread we measured I-V characteristics of all pixels and extracted the channel length modulation parameters, threshold voltages and transconductance values of the external (gm) and internal (gq) gate of the individual pixels of the detector in operational conditions. This is enabled by features of the VERITAS readout ASIC.

The wide field imager for the Athena x-ray telescope is composed of two back side illuminated detectors using DEPFET sensors operated in rolling shutter readout mode: a large detector array featuring four sensors with 512×512 pixels each and a small detector that facilitates the high count rate capability of the WFI for the investigation of bright, point-like sources. Both sensors were fabricated in full size featuring the pixel layout, fabrication technology and readout mode chosen in a preceding prototyping phase. We present the spectroscopic performance of these flight-like detectors for different photon energies in the relevant part of the targeted energy range from 0.2 keV to 15 keV with respect to the timing requirements of the instrument. For 5.9 keV photons generated by an ⁵⁵Fe source the spectral performance expressed as full width at half maximum of the emission peak in the spectrum is 126.0 eV for the large detector and 129.1 eV for the fast detector. A preliminary analysis of the camera’s signal chain also allows for a first prediction of the performance in space at the end of the nominal operation phase.

In this paper we describe the current development state of the Athena X-IFU instrument control unit and its application software. Athena is a ESA large mission scheduled for launch in the early 2030s, that has reached the instrument requirement review phase. Not all of the needed functionalities are frozen yet, but the baseline concept and implementation will be described. While the hardware part will be based on well developed solution, some of the software functionalities, in particular the OBCP engine, will need to be developed and qualified. We will describe our approach for development and testing. The X-IFU instrument will use a Spacewire network for communications with the platform and internally between the ICU and the other subsystems, with the ICU providing the routing capabilities for housekeeping telemetry and telecommand as well as the scientific data. We will describe some aspects of the implementation of such a network.

The x-ray integral field unit (X-IFU) is one of the two instruments of ESA’s ATHENA space mission. It is a cryogenic x-ray spectro-imager with an unprecedented 2.5 eV resolution up to 7 keV. We present the development of the demonstrator model (DM) of X-IFU’s warm front-end electronics (WFEE). X-IFU will have around 2400 cryogenic micro-calorimeters divided into 72 time-division multiplexed (TDM) channels. The main functions of the WFEE are providing the biasing currents for the detectors and two SQUID stages and to amplify the SQUIDs output signals. Each channel requires 5 current sources (quasi-DC DACs) and a fully differential low-noise voltage amplifier (LNA). The DACs can be written and read via an I2C bus. The active component of the WFEE is the AwaXe ASIC, which was specifically designed for this project and integrates current DACs and LNAs for two TDM channels. The WFEE has also to provide housekeeping signals for power supply voltage, and on-chip ASIC temperature. Both, the final expected performances of the instrument and the general specifications of a space mission, impose strong requirements on the WFEE in terms of thermal stability, mechanical design, radiation hardness, raw performance and reliability. To validate some of these requirements, a demonstrator model of the WFEE is currently being developed to be integrated in a full readout chain for lab testing. In this paper we will discuss the PCB and mechanical assembly designs of the WFEE demonstrator model in preparation of the ATHENA space mission.

The X-IFU is one of the two instruments of the ESA ATHENA mission, offering an unprecedented high spectral resolution. In the detection and readout chain of the X-IFU, the first warm stage is the WFEE subsystem. It mainly includes low-noise amplifiers and current sources to read out and bias cryogenic stages. Based on the development of four previous versions of the ASICs dedicated to the WFEE, a new version has been recently developed to transfer analogue functions to a thinner SiGe technology node of 130 nm. This paper updates the development of this new ASIC.

X-ray telescopes opened up a new window into the high-energy universe. However, the last generation of these telescopes encountered an unexpected problem: their optics focused not only x-rays but low-energy (so called soft) protons as well. These protons are very hard to model and can not be distinguished from x-rays. For example, 40% of XMM-Newton observations is significantly contaminated by soft proton induced background flares. In order to minimize the background from such low-energy protons the advanced telescope for high energy astrophysics (ATHENA) satellite introduced a novel concept, the so called charged particle diverter (CPD). It is an array of magnets in a Hallbach design, which deflects protons below 76 keV before they would hit the wide field imager (WFI) detector. In this work, we investigate the effect of scattering of the deflected protons with the CPD walls and the inner surfaces of the WFI detector assembly. Such scattered protons can loose energy, change direction and still hit the WFI. In order to adopt the most realistic instrument model, we imported the CAD model of both the CPD and the WFI focal plane assembly. Soft protons corresponding to ≈2.5 hours of exposure to the L1 solar wind are simulated in this work. The inhomogeneous magnetic field of the CPD is included in the simulation. We present a preliminary estimate of the WFI residual background induced by soft proton secondary scattering, in the case of the optical blocking filter present in the field of view. A first investigation of the volumes responsible for scattering the protons back into the field of view is reported.

The X-IFU is one of the two instruments onboard the Athena x-ray observatory, a large ESA mission to be launched in the 2030 decade. The instrument is based on a large TES-array able to perform simultaneous high-grade energy spectroscopy and imaging. The challenging scientific goals of the instrument also require the reduction of the particle background level. This is obtained by combining the large array with a TES-based cryogenic anticoincidence detector (CryoAC), which allows to veto the unwanted events. One of the key elements of the CryoAC system is the trigger logic, an algorithm able to identify the events measured by the CryoAC detector. The requirements for the CryoAC lead to the development of a sophisticated algorithm capable of achieving the required trade-off between conflicting parameters, such as trigger efficiency and dead-time, with precise time-tagging and pile-up identification. The trigger logic is based on a finite state machine and it is able to identify, in addition to the pulse-shaped events, particular conditions such as the saturation of the CryoAC detector. Due to the peculiar CryoAC pulses features and timing, the developed algorithm is based on derivatives of the signal evaluated by moving averages computed in six contiguous sliding windows, updated at every sample. The algorithm has been tested with a sequence of simulated data stream, showing the compliance with the requirements.

The focal plane of Athena’s WFI consists of spectroscopic single photon x-ray detectors that contain arrays of DEPFETs (Depleted P-channel field-effect transistor) as well as ASICs that are used for steering, readout and analog signal shaping. These components have to be examined regarding the effect of ionizing radiation. A total ionizing dose (TID) test was done with prototype detector modules with 64×64 DEPFETs and one SWITCHER and VERITAS ASIC each. The current design of the WFI detector head features a proton shield equivalent to 4 cm of aluminum in order to prevent a strong increase of leakage current in the fully depleted 450 µm thick bulk of the sensor. This keeps the expected doses and dose rates during the nominal mission relatively low (~5 Gy). It is nevertheless important to study the current system in a dedicated TID test in order to exclude unforeseen effects and to study any radiation related changes that can have an effect on the very sensitive readout chain and the detector performance. The combination of low doses, low dose rates, low operating temperature (<-60°C) but high sensitivity on small changes of the threshold voltages represent somehow unusual boundary conditions in comparison to TID tests for standard radiation hard electronic components. Under these circumstances it was found beneficial to do the test in our own laboratory with an x-ray source in order to realize irradiation during nominal operation conditions. Furthermore, it facilitated to take annealing effects into account. Reasonably accurate dosimetry is achieved by measuring the x-ray spectrum and intensity with the device under test. After irradiation to a total dose of 14 Gy and subsequent annealing the threshold voltage of the DEPFETs were shifted by a mean value of 80 mV, the performance remained unchanged apart from a slight increase in readout noise by 10%.

The last generation of x-ray focusing telescopes operating outside the Earth’s radiation belt discovered that optics were able to focus not only astrophysical x-ray photons, but also low-energy heliophysical protons entering the field of view (FOV). This “soft proton” contamination affects around 40% of the observation time of XMM-Newton. The ATHENA charged particle diverter (CPD) was designed to use magnetic fields to move these soft protons away from the FOV of the detectors, separating the background-contributing ions in the focused beam from the photons of interest. These magnetically deflected protons can hit other parts of the payload and scatter back to the focal plane instruments. Evaluating the impact of this secondary scattering with accurate simulations is essential for the CPD scientific assessment. However, while Geant4 simulations of grazing soft proton scattering on x-ray mirrors have been recently validated, the scattering on the unpolished surfaces of the payload (e.g. the baffle or the diverter itself) is still to be verified with experimental results. Moreover, the roughness structure can affect the energy and angle of the scattered protons, with a scattering efficiency depending on the specific target volume. Using atomic force microscopy to take nanometer-scale surface roughness measurements from different materials and coating samples, we use Geant4 together with the CADMesh library to shoot protons at these very detailed surface roughness models to understand the effects of different material surface roughnesses, coatings, and compositions on proton energy deposition and scattering angles. We compare and validate the simulation results with laboratory experiments, and propose a framework for future proton scattering experiments.

The X-IFU (x-ray integral field unit) onboard the large ESA mission Athena (advanced telescope for high energy astrophysics), planned to be launched in the mid 2030s, will be a cryogenic x-ray imaging spectrometer operating at 55 mK. It will provide unprecedented spatially resolved high-resolution spectroscopy (2.5 eV FWHM up to 7 keV) in the 0.2-12 keV energy range thanks to its array of TES (transition edge sensors) microcalorimeters of more than 2k pixel. The detection chain of the instrument is developed by an international collaboration: the detector array by NASA/GSFC, the cold electronics by NIST, the cold amplifier by VTT, the WFEE (warm front-end electronics) by APC, the DRE (digital readout electronics) by IRAP and a focal plane assembly by SRON. To assess the operation of the complete readout chain of the X-IFU, a 50 mK test bench based on a kilo-pixel array of microcalorimeters from NASA/GSFC has been developed at IRAP in collaboration with CNES. Validation of the test bench has been performed with an intermediate detection chain entirely from NIST and Goddard. Next planned activities include the integration of DRE and WFEE prototypes in order to perform an end-to-end demonstration of a complete X-IFU detection chain.

The X-ray Integral Field Unit (X-IFU) instrument to be on board the future ESA mission Athena X-ray Observatory is a cryogenic micro-calorimeter array of Transition Edge Sensor (TES) detectors aimed at providing spatially resolved high-resolution spectroscopy. As a part of the on-board Event Processor (EP), the reconstruction software will provide the energy, spatial location and arrival time of the incoming X-ray photons hitting the detector and inducing current pulses on it. Being the standard optimal filtering technique the chosen baseline reconstruction algorithm, a particular modification of this technique based on a truncation of the filter in the Time Domain (equivalent to 0-padding the pulse signal) was previously studied on simulated data, proving a better energy resolution results at a lower computational cost. However, the 0-padding technique also showed a larger sensitivity to instrumental conditions, making essential the analysis of its behaviour over real laboratory data. A comparative analysis of X-IFU-like TES laboratory data from NASA and NIST (at different instrumental conditions) with both the 0-padding filter and the standard optimal filters reconstruction shows that, once the corrections for the baseline drift and the jitter (phase introduced by the sampling rate) have been performed, the resolution values obtained using 0-padding are systematically lower than those of the standard filter of the same length and comparable or even lower to the values provided by the full-length filter. The shorter length of the 0-padding filter would be an additional benefit, reducing the computational cost of the reconstruction process.

The advanced telescope for high energy astrophysics (Athena) is an ESA X-ray observatory mission to address the hot and energetic universe theme. The instrument consists of a single x-ray telescope, supported by a large area mirror/ lens based on silicon pore optics technology, which will focus the photon flux alternatively onto two different instruments, 12m away: the wide field imager (WFI) and the x-ray integral field unit (X-IFU). The process of switching the focus between the two instruments is produced by a large hexapod structure that is able to change the pointing of the main mirror and the focus plane position, according to strict operational requirements. In order to verify that the mirror optical axis is perfectly aligned with each of the instruments, the telescope shall be supported by an optical on-board metrology system (OBM) that is able to estimate the telescope pointing with accuracy better than 0.5 arcsec.
The Athena OBM system currently under development is based on the concept of a projective metrology where a pattern of active fiducials point sources is imaged onto an array detector. The position and orientation of the imaged pattern provides the necessary information to reconstruct the fiducial displacements with respect to the calibrated reference points, thus allowing obtaining an estimate of the pointing absolute knowledge error. In the present implementation, the fiducials shall be located close to the instrument’s detectors and will be imaged by a specially designed camera system located at the center of the Athena mirror. In this paper we will present the overall architecture and requirements of the metrology system under development for the Athena x-ray observatory mission.