This PDF file contains the front matter associated with SPIE Proceedings Volume 10699 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Conventional aluminum-coated mirrors operating at far ultraviolet wavelengths (90–200 nm) utilize protective overcoats of metal fluoride thin films deposited by physical vapor deposition. The use of atomic layer deposition (ALD) holds promise in improving spatial reflectance uniformity and reducing the required thickness of the protective layers. Achieving a stable, pinhole-free, ultrathin (<3 nm) overcoat would allow protected Al mirrors to approach the ideal Al intrinsic reflectivity in the challenging, but spectrally-rich, 90–115 nm range. However, combining ALD methods with high performance evaporated Al layers has technical challenges associated with the formation of undesirable interfacial oxide. To overcome this issue, we demonstrate the use of thermal atomic layer etching (ALE) methods to remove this oxide prior to ALD encapsulation. This paper describes our continuing work to optimize new ALD processes for the metal fluoride materials of MgF₂, AlF₃ and LiF. We also describe new work on low temperature (<200 °C) ALE methods utilizing a fluorination-volatilization approach that has been incorporated into our mirror development efforts. The scalability of this overall approach and the environmental stability of ALD/ALE Al mirrors is discussed in the context of possible future astrophysics applications such as the NASA LUVOIR and HabEx mission concepts. The use of this combined ALE/ALD method may also enable a fabrication platform in space that can renew or reconfigure protective overcoats on Al mirrors on-orbit, as an alternative to other space-based metal coating methods considered previously.

While many materials could be used as IR mirrors, only aluminum has the potential of reaching far into the ultraviolet, as low as 85 nm. Unfortunately, Al oxidizes rapidly when it is exposed to the atmosphere, diminishing the reflectance of bare aluminum mirrors below 200 nm. For terrestrial observations, this is not a large problem, since the Earth’s atmosphere blocks radiation below this wavelength. However, mirrors used in space could use the whole range of aluminum’s reflectance, if a bare, or nearly bare mirror, could be deployed.[1] The compromise to date has been to use a thin UV-transparent, protective barrier composed of magnesium fluoride, lithium fluoride and/or aluminum fluoride. These allow the observation of the Lyman alpha line but light below 110 nm is effectively blocked. We report on our studies of ultrathin fluoride barrier layers and of removable layers which would lie on ultrathin fluoride barriers or directly on the aluminum surface. Removable barriers could be removed shortly before launch or at the mirrors point of use. These removable barriers consist of organic layers like First Contact™ or parylene, inorganic layers like amorphous silicon (a-Si), or a combination of both. We have observed, for example, that ultrathin films of AlF3 (<2.5 nm) are capable of blocking the oxidation of aluminum for several hours in air, long enough to have a removable barrier like First Contact™ applied on their surface. We also report on the effectiveness of ultrathin a-Si as a long-term barrier that may be removable via atomic hydrogen.

Recent technological advances have opened up new instrument capabilities for ultraviolet (UV) astronomy. Of particular interest are advanced deposition processes that have increased the performance of Lithium Fluoride (LiF) overcoated mirrors while mitigating the procedures required for their handling, raising the reflectivity from ∼ 65% to greater than 80% in the Lyman UV (λ > 1000 Å). Traditional magnesium fluride (MgF₂) protected aluminum mirrors have a reflectivity truncated at 1150 Å, missing crucial tracers of warm gas and molecules. The hygroscopic sensitivity of LiF has traditionally added to mission risk and cost. The addition of a thin capping layer of another material (AlF₃, MgF₂) on top of the LiF has been shown to mitigate the degradation by providing a barrier against moisture. These advances open up a new paradigm in UV astronomy by enabling multi-passed optical designs without the crippling 1000 - 1150 Å throughput losses inherent to conventional mirror coatings. We present recent progress in the testing of enhanced lithium fluoride (eLiF) coated optics, and discuss potential instrument concepts for UV astronomy in the next decade.

We present an update to our paper from last year on the design and capabilities of the Ultraviolet Spectrograph (UVS) instrument on the Habitable Exoplanet Observatory (HabEx) concept. The design has been matured to be both more compact and serviceable while delivering all the required capabilities that the original Science Traceability Matrix (STM) demanded. Since last year the project has begun design considerations for a second Architecture for the overall mission, and we present design changes that optimize the performance of the instrument when combined with that Optical Telescope Assembly (OTA). Results of a start at a community driven Design Reference Mission (DRM) are also included to illustrate the anticipated performance of the instrument.

The present paper describes the current baseline optical design of POLLUX, a high-resolution spectropolarimeter for the future LUVOIR mission. The instrument will operate in the ultraviolet (UV) domain from 90 to 390 nm in both spectropolarimetric and pure spectroscopic modes. The working range is split between 3 channels – far (90-124.5 nm), medium (118.5-195 nm) and near (195-390 nm) UV. Each of the channels is composed of a polarimeter followed by an echelle spectrograph consisting of a classical off-axis paraboloid collimator, echelle grating with a high grooves frequency and a cross-disperser grating operating also as a camera. The latter component integrates some advanced technologies: it is a blazed grating with a complex grooves pattern formed by holographic recording, which is manufactured on a freeform surface. One of the key features underlying the current design is the large spectral length of each order ~6 nm, which allows to record wide spectral lines without any discontinuities. The modelling results show that the optical design will provide the required spectral resolving power higher than R ~ 120,000 over the entire working range for a point source object with angular size of 30 mas. It is also shown that with the 15-m primary mirror of the LUVOIR telescope the instrument will provide an effective collecting area up to 38 569 cm² . Such a performance will allow to perform a number of groundbreaking scientific observations. Finally, the future work and the technological risks of the design are discussed in details.

CETUS (“Cosmic Evolution Through Ultraviolet Spectroscopy”) is a mission concept that was selected by NASA for study as a Probe-class mission, meaning a mission whose full life-cycle cost to NASA is between $400M and $1.0B. CETUS is a wide-field UV telescope that will work with other survey telescopes observing at gamma-rays to radio waves to help solve major astrophysical problems. In this paper, we describe how CETUS will make observations of high-energy sources discussed by the 2010 Astrophysics Decadal Survey panel (Astro-2010) including the growth of nuclear black holes and their influence on their surroundings, mergers of neutron-star binaries and their aftermath, supernovae and their progenitors, the flows of matter and energy in the circumgalactic medium. CETUS is well equipped to study these energetic sources. We have chosen instrumentation for CETUS that includes a 1.5-m telescope and two wide-field survey instruments, a near-UV multi-object slit spectrograph (MOS), a near-UV/ far-UV camera. It also has a near-UV/far-UV imaging spectrograph to survey classes of astronomical objects one at a time.

The Colorado Ultraviolet Transit Experiment (CUTE) is a near-UV (NUV), 6U CubeSat designed to characterize the interaction between exoplanetary atmospheres and their host stars. CUTE is dedicated to observing multiple transits of short period planets with a range of masses to measure the transit depths of atomic and molecular nearUV features. These observations will enable us to quantify as a function of wavelength the transit ingress, egress, and depth of exoplanet light curves in order to determine the presence of bow shocks and strong atmospheric mass loss. The CUTE optical system combines a novel rectangular Cassegrain telescope and a holographically-ruled, aberration-correcting diffraction grating. The high-throughput optical system is projected to obtain an average effective area of ≈24 cm² , comparable to previous Explorer class missions (GALEX) in a CubeSat package. This proceeding provides an overview of the science motivation, the final telescope and spacecraft design, and an outline of the mission operation.

A conceptual design of a wide-field near UV transient survey in a 6U CubeSat is presented. Ultraviolet is one of the frontier in the transient astronomy. To open up the discovery region, we are developing a 6U CubeSat for transient exploration. The possible targets will be supernova shock-breakouts, tidal disruption events, and the blue emission from NS-NS mergers in very early phase. If we only focused on nearby/bright sources, the required detection limit is around 20 mag (AB). To avoid the background and optical light, we chose a waveband of 230-280 nm. As an imaging detector, we employ a delta-doped back-illuminated CMOS. In addition to delta doping, the multi-layer coating directly deposited on the detector enables both a high in-band UV QE and the ultra-low optical rejection ratio. Taking into account these specifications, even an 8 cm telescope can achieve the detection limit of 20 magAB. The expected FoV is larger than 60 deg² .

Roughly 40 billion M dwarfs in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs (0.1–0.4 AU). Knowing the UV environments of M dwarf planets will be crucial to understanding their atmospheric composition and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M stars in the far-UV and near-UV, measuring the time-dependent spectral slope, intensity and evolution of low-mass star high-energy radiation.

The Extreme Ultraviolet Imager (EUI) instrument for the Solar Orbiter mission will image the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm) and in the vacuum ultraviolet (121.6 nm) spectral ranges. The development of the EUI instrument has been successfully completed with the optical alignment of its three channels’ telescope, the thermal and mechanical environmental verification, the electrical and software validations, and an end-toend on-ground calibration of the two-units’ flight instrument at the operating wavelengths. The instrument has been delivered and installed on the Solar Orbiter spacecraft, which is now undergoing all preparatory activities before launch.

SUAVE (Solar Ultraviolet Advanced Variability Experiment) is a far UV imaging solar telescope (Lyman Alpha, 121.6 nm, Herzberg continuum, 200-220 nm, etc.) of novel design for ultimate thermal stability and long lasting performances. SUAVE is a 80 mm Ritchey-Chrétien off-axis telescope with SiC mirrors and no entrance window for long and uncompromised observations in the UV (no coatings of mirrors, flux limited to less than 2 solar constants on filters to avoid degradation), associated with an ultimate thermal control (no central obscuration resulting in limited thermal gradients and easier heat evacuation, focus control, stabilization). Design and anticipated performances will be detailed as well as the realization process under way. Tests on a representative breadboard will be performed in 2018 (CNES R&T). SUAVE is the main instrument of the SUITS/SWUSV (Solar Ultraviolet Influence on Troposphere/Stratosphere / Space Weather and Ultraviolet Solar Variability) microsatellite mission.

We describe the stray and scattered light properties of the Juno Ultraviolet Spectrograph (Juno-UVS). Juno-UVS is a modest-powered (9.0 W) instrument that is designed to characterize Jupiter’s auroral emissions and relate them to in situ measurements made by Juno’s particle and wave instruments. A notable scattered light feature has been discovered during UVS operations; a minor solar glint that reveals itself during specific spacecraft orientations when the spin axis is pointed a certain angle away from the sun. This scattered light feature has become more important now that the Juno mission has decided to stay in its 53-day parking orbit instead of transitioning to the planned 14-day science orbit. The impact of the scattered light feature on future instrument operations is discussed.

In this proceeding, we describe the scientific motivation and technical development of the Colorado Highresolution Echelle Stellar Spectrograph (CHESS), focusing on the hardware advancements and testing of components for the fourth and final launch of the payload (CHESS-4). CHESS is a far ultraviolet rocket-borne instrument designed to study the atomic-to-molecular transitions within translucent cloud regions in the interstellar medium. CHESS is an objective echelle spectrograph, which uses a mechanically-ruled echelle and a powered (f/12.4) cross-dispersing grating; it is designed to achieve a resolving power R > 100,000 over the band pass λλ 1000–1600 Å. CHESS-4 utilizes a 40 mm-diameter cross-strip anode readout microchannel plate detector, fabricated by Sensor Sciences LLC, to achieve high spatial resolution with high global count rate capabilities (∼ MHz). An error in the fabrication of the cross disperser limited the achievable resolution on previous launches of the payload to R ∼ 4000. To remedy this for CHESS-4, we physically stress the echelle grating, introducing a shallow toroidal curvature to the surface of the optic. Preliminary laboratory measurements of the resulting spectrum show a factor of 4–5 improvement to the resolving power. Results from final efficiency and reflectivity measurements for the optical components of CHESS-4 are presented, along with the pre-flight laboratory spectra and calibration results. CHESS-4 launched on 17 April 2018 aboard NASA/University of Colorado Boulder sounding rocket mission 36.333 UG. We present flight results for the observation of the γ Ara sightline.

The circumgalactic medium (CGM) plays a critical role in the evolution of galaxy discs, as it hosts important mechanisms regulating their replenishment through inflows and outflows. Besides absorption spectroscopy, mapping of the HI Lyα emission of z>2 CGM is bringing a new perspective with a complete 2- or 3-D mapping. Despite this benefit, data in emission are very scarce in the large time span from z∼2 to the present because of the difficulties inherent to vacuum UV observations. The FIREBall-2 (Faint Intergalactic Redshifted Emission Balloon) instrument has been developed to help fill this gap and is scheduled for launch in September 2018. It has been optimized to provide a bi-dimensional (x, λ) map of the extremely faint diffuse Ly-a HI emission in the CGM at z∼0.7 and has the capability to observe ~200 galaxies and a dozen QSOs in a single night flight. Given its wide field of view (FOV) of 20x40 arcmin2, its angular resolution of 6-10 arcsec and spectral resolution above 1000, FIREBall-2 will bring important insights about the gas distribution in the CGM, and the velocity/temperature fields, and has the potential to bring statistical constraints.
The instrument is a balloon-borne 1m telescope coupled to a UV multi-object spectrograph (MOS) designed to image the CGM in emission via specific spectral lines (Lya, CIV, OVI) redshifted in a narrow UV band [1990 - 2130]A for the nearby universe (0.2< z <1). The optical design relies on a 1.2-meter moving siderostat that stabilizes the beam and reflects the light on a fixed paraboloid which in turn images it at the entrance of the payload. This payload is constituted of a focal corrector followed by a slit Multi-Object Spectrograph (reflective 2400 g/mm holographic aspherical grating located between two Schmidt mirrors). The objects selection is achieved with a series of pre-installed precision mask systems that also feed the fine guidance camera. The detector is a e2v electron multiplying CCD coated and delta-doped by the Jet Propulsion Laboratory. FIREBall-2 is funded by CNES and NASA and is developed in cooperation with a Franco-American consortium composed of LAM, CALTECH, Columbia University, JPL and CST-CNES. In this presentation, we describe the final ground calibration of the instrument. We explain what technical specifications ensue from the scientific goals of the mission and we will then highlight why this optical design has been chosen. The calibration of the instrument (alignment - through focus - distortion) will be presented followed by the analysis of the instrument scientific performances. We will then describe the improvement and the calibration of the ZEMAX-coupled instrument model developed at LAM, based on these final performances. This model is finally used to make an end-to-end prediction of the observations of the emission of the CGM from a large halo in a cosmological simulation.

The Ultraviolet Imager (UVI) instrument is a very challenging imager developed in the frame of the SMILE-ESA mission. The UV camera will consist of a single imaging system targeted at a portion of the Lyman-Birge-Hopfield (LBH) N2 wavelength band. The baseline design of the imager meets the requirements to record snapshots of auroral dynamics with sufficient spatial resolution to measure cusp processes (100 km) under fully sunlit conditions from the specified apogee of the spacecraft. To achieve this goal, the UVI instrument utilizes a combination of four on-axis mirrors with an intensified FUV CMOS based camera. The mirrors will be coated with spectral selective interferometric layers to provide most of the signal filtering. The objective of these filters is to select the scientific waveband between 160 and 180 nm. The combined four mirrors have to give an out-of-band rejection ratio as high as possible to reject light from solar diffusion, dayglow and unwanted atomic lines in a range of 10-8 – 10-9. Different multilayer coatings are considered and optimized according to the π-multilayer equation for different H/L ratio and for different angles of incidence. Our theoretical evaluation shows a modification of the reflectance spectrum as a function of the angle of incidence, so that the optical beams hitting the different mirrors can have different optical properties depending on the optical fields and the distribution of the rays on the pupil. We will evaluate the effect of fields on the spectral throughput of the UVI instrument based on its optical design. This analysis will be done using the Code V ray-trace software and proprietary scripts.

Lynx, one of four strategic mission concepts under study for the 2020 Astrophysics Decadal Survey, will provide leaps in capability over previous and planned X-ray missions, and will provide synergistic observations in the 2030s to a multitude of space- and ground-based observatories across all wavelengths. Lynx will have orders of magnitude improvement in sensitivity, on-axis sub-arcsecond imaging with arcsecond angular resolution over a large field of view, and high-resolution spectroscopy for point-like and extended sources. The Lynx architecture enables a broad range of unique and compelling science, to be carried out mainly through a General Observer Program. This Program is envisioned to include detecting the very first supermassive black holes, revealing the high-energy drivers of galaxy and structure formation, characterizing the mechanisms that govern stellar activity - including effects on planet habitability, and exploring the highest redshift galaxy clusters. An overview and status of the Lynx concept are summarized.

X-ray astronomy critically depends on X-ray optics. The capability of an X-ray telescope is largely determined by the point-spread function (PSF) and the photon-collection area of its mirrors, the same as telescopes in other wavelength bands. Since an X-ray telescope must be operated above the atmosphere in space and that X-rays reflect only at grazing incidence, X-ray mirrors must be both lightweight and thin, both of which add significant technical and engineering challenge to making an X-ray telescope. In this paper we report our effort at NASA Goddard Space Flight Center (GSFC) of developing an approach to making an Xray mirror assembly that can be significantly better than the mirror assembly currently flying on the Chandra X-ray Observatory in each of the three aspects: PSF, effective area per unit mass, and production cost per unit effective area. Our approach is based on the precision polishing of mono-crystalline silicon to fabricate thin and lightweight X-ray mirrors of the highest figure quality and micro-roughness, therefore, having the potential of achieving diffraction-limited X-ray optics. When successfully developed, this approach will make implementable in the 2020s and 2030s many X-ray astronomical missions that are currently on the drawing board, including sounding rocket flights such as OGRE, Explorer class missions such as STAR-X and FORCE, Probe class missions such as AXIS, TAP, and HEX-P, as well as large missions such as Lynx.

At NASA Goddard Space Flight Center, we consistently produce affordable lightweight sub-arcsecond X-ray mirrors made of directly polished single crystal silicon. Silicon is favored for its high stiffness, low density, high thermal conductivity, zero internal stress, and commercial availability. Our manufacturing process includes traditional grinding, lapping, and polishing methods adapted to X-ray mirror geometry. These mirrors promise to meet the stringent requirements of various planned X-ray telescope missions. Presently, we are refining the many steps involved in our manufacturing process. This paper reports an overview of our mirror manufacturing process and the most recent results.

The NASA Lynx mission concept is under study as a potential successor to the Chandra X-ray Observatory, for launch in the 2030s. Like Chandra, Lynx is to provide 0.5 arcsec half power diameter imaging at 1keV, but with 30 times the collecting area, and sub-arcsec imaging over a 10 arcmin (radius) field-of-view. Adjustable X-ray optics technology represents a potential approach to meet the challenging Lynx requirements by enabling the correction of mirror fabrication figure, mounting induced distortions, and on-orbit correction for variations in the mirror thermal environment. We describe the current state of development of the technology, including summarizing recent test data, development of mirror assembly error budgets, and discussion of the mirror assembly optical design and its anticipated performance.

Many of the key science goals in X-ray astronomy require spectroscopy in the soft energy band, 0.2 - 2.0 keV. The performance requirements placed on spectrometers typically have spectral resolving powers in the thousands with effective areas in the hundreds of square centimeters. Obtaining both of these requirements in a single instrument is a challenge for a variety of reasons. Here, we discuss the development tasks specific to off-plane reflection gratings. We detail the requirements that drive our technical challenges such as fabrication, alignment, and integration. Finally, we summarize recent results of X-ray performance testing demonstrating very high diffraction efficiency and resolving power.

Arcus, a mission proposed as a Medium Size Explorer for high-resolution x-ray spectroscopy, requires unprecedented sensitivities: high resolving power (λ/Δλ >; 2500) and large collecting area (~ 350 cm²). The core instruments on Arcus are Critical-Angle Transmission (CAT) grating spectrometers consisting of hundreds of co-aligned diffraction gratings. The gratings require thorough quality control along the entire manufacturing process: from bare silicon wafers to CAT grating petal assembly. Period variation, grating bar tilt angles, misalignment, and grating film buckling are potential errors of interest which could degrade the performance of the x-ray grating spectrometer. We present progress towards development of metrology techniques to measure and manage aforementioned errors during the entire alignment and integration processes: starting right after fabrication of CAT grating membranes to their assembly into large arrays. A scanning laser reflection tool (SLRT) was developed to measure period variations, alignment, and area percentage of pinched grating bars. An array of four CAT gratings was successfully aligned to satisfy Arcus alignment allocations for a grating window alignment test (GWAT). No discernible signal was found from an effort to measure a ‘half’ diffraction order to characterize stiction between grating bars. A metrology protocol was developed to measure grating bar tilt angle variations and average bar tilt angles relative to the grating surface normal, based on small-angle x-ray scattering (SAXS, Cu-Kα) and an optical surface normal measurement (OSNM) setup. A grating holder was designed with integrated slits to relate independent measurements from two different setups using visible and x-ray beams. Bar tilt variations of 1 degree and average bar tilt angles of ~0.3 degree were observed for seven different CAT grating samples. Bar tilt angle variations induced from buckled grating films were also measured. We discuss implications for a more demanding CAT grating spectrometer for the proposed Lynx X-ray Surveyor mission to be presented to the next Astrophysics Decadal Survey.

The combination of the hot slumping and the Ion Beam Figuring (IBF) technologies can be a very competitive solution for the realization of x-ray optics with excellent imaging capabilities and high throughput. While very thin mirrors segments can be realized by slumping with residual figure errors below few hundreds of nanometres, a non-contact and deterministic process (dependent on dwell time), like IBF, is a very effective post facto correction, as it avoids all the problems due to the handling and the supporting system. In the last years, the two processes were proven compatible with very thin sheet of Eagle XG glasses (0.4 mm thickness). Nevertheless, the fast convergence of the process is a key factor to limit the cost of the mirror plate production. A deeper characterization of removal function stability showed that its repeatability between each run has to be improved for a real enhancement of the process convergence factor. A new algorithm based on de-convolution has been implemented and tested, with important advantages in terms of calculation speed, minimum material removal and optimization possibilities. By analysing the metrological data of test slumped glasses, we showed how the IBF is effective in the correction of figure errors on scales above 8 - 10 mm. An overall figuring time of few hours is required with surface error around 100 nm rms. Thanks to the thickness measurement data, which are performed in transmission mode with an interferometric set-up, we demonstrated that it is possible to disentangle the effective amount of the material removed and the deformations introduced during the process.

We have proposed a new type of X-ray interferometer called Multi Image X-ray Interferometer Module (MIXIM) consisting simply of a grating and an X-ray spectral imaging detector. The baseline concept of MIXIM is a slit camera to obtain the profile of X-ray sources, but aim to get a sub-arcsecond resolution. For that purpose, to avoid blurring of the image by diffraction is a key, and we select X-ray events of which energy satisfies the interferometric condition called Talbot effect. Stacking the images (X-ray interferometric fringes) with the period of the grating is another point of the method, which provides the self image of a grating slit convolved with the profile of the X-ray source. We started an experiment with a micro focus X-ray source, 4.8 μm pitch grating, and an SOI type X-ray detector XRPIX2b with a pixel size of 30 μm. The stacked self image was obtained with a magnification factor of 4.4. We, however, need finer positional resolution for the detector to obtain the self image to a parallel beam, for which the magnification factor must be 1. We thus focused on small pixel size CMOS sensors developed for visible light. We irradiated X-rays to one of such CMOS sensors GSENSE5130 with a pixel size of 4.25 μm, and found enough capability to detect X-rays, i.e., FWHM of 207 eV at 5.9 keV at room temperature. We then employed this sensor and performed an experiment at a 200 m beam line of BL20B2 in the synchrotron facility SPring8. Using a grating with a pitch of 4.8 µm and an opening fraction of f=0.5, we obtained the self image of the grating at the detector distance from the grating of 23 cm and 46 cm and the X-ray energy of 12.4 keV. We also performed an experiment using a 9.6 μm f = 0.2 grating with a detector-grating distance of 92 cm, and obtained higher contrast image of the grating. Note that the slit width of 2.4 μm at 46 cm corresponds to 1.1′′, while that of 1.9 μm at 92 cm does 0.43′′. We suggest several format of possible MIXIM missions, including MIXIM-S for very small satellite of 50cm size, MIXIM-P for parasite use of nominal X-ray observatory employing grazing X-ray telescopes with a focal length of 10 m, and MIXIM-Z in which the grating-detector distance of 100 m is acquired by formation flight or free fryers to yield 0.01” level resolution.

Toward a new era of X-ray astronomy, next generation X-ray optics are indispensable. To meet a demand for telescopes lighter than the foil optics but with a better angular resolution less than 1 arcmin, we are developing micropore X-ray optics based on micromaching technologies. Using sidewalls of micropores through a thin silicon wafer, this type can be the lightest X-ray telescope ever achieved. Two new Japanese missions ORBIS and GEOX will carry this optics. ORBIS is a small X-ray astronomy mission to monitor supermassive blackholes, while GEO-X is a small exploration mission of the Earth’s magnetosphere. Both missions need a ultra light-weight (<1 kg) telescope with moderately good angular resolution (<10 arcmin) at an extremely short focal length (<30 cm). We plan to demonstrate this optics in these two missions around 2020, aiming at future other astronomy and exploration missions.

We report on the design, development and measured performance of the Microchannel plate X-ray optics for the Mercury imaging X-ray spectrometer instrument, due to fly to Mercury on the ESA/JAXA BepiColombo mission in 2018. This paper serves as a progress update, identifying further work to finish the analysis of data from the flight model.

The development of the X-ray optics for ATHENA (Advanced Telescope for High ENergy Astrophysics)[1-4], the selected second large class mission in the ESA Science Programme, is progressing further, in parallel with the payload preparation and the system level studies. The optics technology is based on the Silicon Pore Optics (SPO) [5-48], which utilises the excellent material properties of Silicon and benefits from the extensive investments made in the semiconductor industry. With its pore geometry the SPO is intrinsically very robust and permits the use of very thin mirrors while achieving good angular resolution. In consequence, the specific mass of the resultant ATHENA optics is very low compared to other technologies, and suitable to cope with the imposed environmental requirements. Further technology developments preparing the ATHENA optics are ongoing, addressing additive manufacturing of the telescope structure, the integration and alignment of the mirror assembly, numerical simulators, coating optimisations, metrology, test facilities, studies of proton reflections and meteorite impacts, etc. A detailed Technology Development Plan was elaborated and is regularly being updated, reflecting the progress and the mission evolution. The required series production and integration of the many hundred mirror modules constituting the ATHENA telescope optics is an important consideration and a leading element in the technology development. The developments are guided by ESA, implemented in industry and supported by research institutions. The many ongoing SPO technology development activities aim at demonstrating the readiness of the optics technology at the review deciding the adoption of ATHENA onto the ESA Science flight programme, currently expected for 2021. Technology readiness levels of 5/6 have to be demonstrated for all critical elements, but also the compliance to cost and schedule constraints for the mission.

Silicon Pore Optics (SPO) has been established as a new type of x-ray optics that enables future x-ray observatories such as Athena. SPO is being developed at cosine with the European Space Agency (ESA) and academic and industrial partners. The optics modules are lightweight, yet stiff, high-resolution x-ray optics, that shall allow missions to reach an unprecedentedly large effective area of several square meters, operating in the 0.2 - 12 keV band with an angular resolution better than 5 arc seconds. In this paper we are going to discuss the latest generation production facilities and we are going to present results of the production of mirror modules for a focal length of 12 m, including x-ray test results.

ATHENA (Advanced Telescope for High-ENergy Astrophysics) is the next high-energy astrophysical mission of the European Space Agency. Media Lario leads an industrial and scientific team that has developed a process to align and integrate more than 700 silicon pore optics mirror modules into the ATHENA X-ray telescope. The process is based on the ultra-violet imaging at 218 nm of each mirror module on the focal plane of a 12 m focal length optical bench. Specifically, the position of the centroid of the point spread function produced by each mirror module when illuminated by a collimated plane is used to align each mirror module. Experimental integration tests and correlation with X-ray measurement at the PANTER test facility in Münich have demonstrated that this process meets the accuracy requirement. This technique allows arbitrary integration sequence and mirror module exchangeability. Moreover, it enables monitoring the telescope point spread function during the integration phase.

Within the ATHENA optics technology plan, activities are on-going for demonstrating the feasibility of the mirror module integration. Each mirror module has to be accurately attached to the mirror structure support by means of three isostatic mounts ensuring minimal distortion under environmental loads. This work reports on the status of one of the two parallel activities initiated by ESA to address this demanding task. In this study awarded to the industrial consortium, the integration relies on optical metrology and direct X-ray alignment. For the first or “indirect” method the X-ray alignment results are accurately referenced, by means of a laser tracking system, to optical fiducial targets mounted on the mirror modules and finally linked to the mirror structure coordinate system. With the second or “direct” method the alignment is monitored in the X-ray domain, providing figures of merit directly comparable to the final performance. The paper updates on the laser tracking characterization results of 2 mirror modules, performed at PTB’s X-ray Parallel Beam Facility (XPBF 2.0) at BESSY II. The same 2 mirror modules have then been co-aligned and integrated in a technology demonstrator, with performance verified in full illumination at Panter. The paper provides an overview of the results obtained from the technology development activities.

Lynx is an X-ray mission concept with superb imaging capabilities (< 1arcsec Half Energy Width, HEW) and large throughput (2 m² effective area @1keV). Several approaches are being considered to meet the challenging technological task of the mirror fabrication. Thin and light substrates are necessary to meet mass constraints. Monolithic fused silica shells are a possible solution if their thickness can be maintained to below 4 mm for mirror shells up to 3 m diameter. In this paper we present the opto-mechanical design of the mirror assembly, the technological processes, and the results achieved so far on a prototypal shells under development. In particular, emphasis is placed on the figuring process that is based on direct polishing and on ion beam figuring and on a temporary stiffening structure designed to support the shell during the figuring and polishing operations and to manage the handling of the shell through all phases up to integration into the telescope supporting structure.

The Lynx X-ray Surveyor Mission is one of 4 large missions being studied by NASA Science and Technology Definition Teams as mission concepts to be evaluated by the upcoming 2020 Decadal Survey. By utilizing optics that couple fine angular resolution (<0.5 arcsec HPD) with large effective area (~2 m² at 1 keV), Lynx would enable exploration within a unique scientific parameter space. One of the primary soft X-ray imaging instruments being baselined for this mission concept is the High Definition X-ray Imager, HDXI. This instrument would achieve fine angular resolution imaging over a wide field of view (~ 22 × 22 arcmin, or larger) by using a finely-pixelated silicon sensor array. Silicon sensors enable large-format/small-pixel devices, radiation tolerant designs, and high quantum efficiency across the entire soft X-ray bandpass. To fully exploit the large collecting area of Lynx (~30x Chandra), without X-ray event pile-up, the HDXI will be capable of much faster frame rates than current X-ray imagers. The planned requirements, capabilities, and development status of the HDXI will be described.

Lynx is an x-ray telescope that is one of four large satellite mission concepts currently being studied by NASA to be the next flagship mission. One of Lynx’s three instruments is the Lynx X-ray Microcalorimeter (LXM), an imaging spectrometer placed at the focus of an x-ray optic with 0.5 arc-second angular resolution and approximately 2 m2 area at 1 keV. It will be used for a wide variety of observations, and the driving performance requirements are met through different sub-regions of the array. It will provide an energy resolution of better than 3 eV over the energy range of 0.2 to 7 keV, with pixels sizes that vary in scale from 0.5 to 1 arc-seconds in the inner 5 arc-minute field-of-view, and to 5 arc-seconds in the extended 20 arc-minute field-of-view. The Main Array consists mostly of 1 arc-second pixels in the central 5 arc-minutes with less than 3 eV energy resolution (FWHM) in the energy range of 0.2 to 7 keV. It is enhanced in the inner 1 arc-minute region with 0.5 arc-second pixels that will better sample the point spread function of the X-ray optic. The inner 5 arc-minute region is designed specifically for the observations related to cosmic feedback studies, investigating the interactions of AGN with the local regions surrounding them. The 0.5" pixel size allows detailed studies of winds and jets on a finer angular scale. It is also optimized for spatially resolved measurements of cluster cores. The outer regions of the array are designed to operate during a completely different set of observations. The Extended Array will be utilized for surveys over large regions of the sky, the 20 arc-minute field-of-view making it practical to make observations of the soft diffuse emission from larger scale-structure such as extended galaxies, the outer regions of galaxy groups and clusters and also cosmic filaments. This array is optimized for high energy resolution up to 2 keV through the use of thin (0.5 um) gold absorbers. The Ultra-High-Res Array is designed specifically to enable the study turbulent line broadening around individual through the study of the highly ionized oxygen lines. It is optimized for energy resolution for the oxygen VII and VIII lines, with better than 0.4 eV energy resolution. In this paper we present the design of the baseline configuration and the scientific motivation. We discuss the technologies that are being developed for this instrument, in particular the transition-edge sensor (TES) and metallic magnetic calorimeter (MMC) sensor technologies. We place these technologies in the context of the required energy resolution, energy range, pixel size, and count-rate, as well as strategies for the pixel layout and wiring. We will discuss the use of microwave SQUIDs, HEMT amplifiers, and parametric amplifiers for the read-out and the implications for the cryogenic design. We also describe the design of the full instrument, including the strawman cryogenic design, as well as an estimate for the mass, power and data rate.

NASA commissioned four studies for large astrophysics missions in different wavebands to provide input for the 2020 Decadal Survey of Astronomy and Astrophysics. The X-ray concept under study is called “Lynx”. The Lynx Science and Technology Definition Team has formulated science requirements and we need to evaluate the optical technologies that can meet these requirements. In this context, we present a draft design for a Lynx X-ray grating spectrometer (XGS) using critical-angle transmission (CAT) gratings on a Rowland torus. One of the most important parameters for the achievable spectral resolving power R is the mirror point-spread function (PSF). Different mirror technologies can lead to different PSF characteristics, e.g. the PSF might be dominated by scattering and figure errors or by the misalignment of many different mirror shells. The benefits of using sub-apertures to increase the resolving power could differ widely between different scenarios. Our study avoids mirror-specific assumptions and looks at how we can adjust the design to any of the proposed technologies. Size and placement of the CAT gratings have strong impact on spectral resolving power. We show how gratings can be arranged to meet the Lynx requirements. One consideration is how the presence of gratings impacts the effective area of the zeroth order. We discuss and trade-offs between resolving power and effective area in our design that can be adjusted to match the science requirements.

The Lynx X-ray Grating Spectrograph (XGS) is required to provide high throughput, 4000 cm^2, high resolving power, R>5000, soft X-ray spectroscopy from 0.2-2.0 keV. In this regime of astrophysically important lines, the XGS will probe key science topics such as the distribution of diffuse hot baryons, the feedback environments near supermassive black holes, and the physics of stellar atmospheres and accretion. We present here the conceptual design of an XGS consisting of an array of reflection gratings placed in the off-plane mount. The configuration of the array and the associated detector readout are discussed. Finally, the expected X-ray performance is characterized.

One of the flagship-class missions under study for the Astro 2020 Decadal review is the Lynx x-ray mission. It has significant design heritage to the highly successful Chandra X-ray Observatory. This report will highlight work done by the CAN Consortium of Northrop Grumman, Ball and Harris supporting the mission concept development led by the Lynx Science and Technology Definition Team (STDT) and MSFC Study Office. By comparing the Lynx requirements against the demonstrated performance of the Chandra Observatory, this paper will highlight the high TRL technologies that can be re-used from Chandra and those that will require new development , which impacts the Lynx architecture and development requirements. This paper will also summarize the top level performance budgets, performance predictions and suggestions on the calibration approach.

Future X-ray missions such as Lynx require large-format imaging detectors with performance at least as good as the best current-generation devices but with much higher readout rates. We are investigating a Digital CCD detector architecture, under development at MIT Lincoln Laboratory, for use in such missions. This architecture features a CMOS-compatible detector integrated with parallel CMOS signal processing chains. Fast, low-noise amplifiers and highly parallel signal processing provide the high frame-rates required. CMOS-compatibility of the CCD provides low-power charge transfer and signal processing. We report on the performance of CMOS-compatible test CCDs read at rates up to 5 Mpix s⁻¹ (50 times faster than Chandra ACIS CCDs), with transfer clock swings as low as ±1.5 V (power/area < 10% of that of ACIS CCDs). We measure read noise below 6 electrons RMS at 2.5 MHz and X-ray spectral resolution better than 150 eV FWHM at 5.9 keV for single-pixel events. We discuss expected detector radiation tolerance at these relatively high transfer rates. We point out that the high pixel ’aspect ratio’ (depletion-depth : pixel size ≈ 9 : 1) of our test devices is similar to that expected for Lynx detectors, and illustrate some of the implications of this geometry for X-ray performance and noise requirements.

Since 2015, AHEAD (Integrated Activities in the High Energy Astrophysics Domain) has provided a reference framework to bring together Europe's science community. AHEAD is part of the EU Horizon 2020 programme for Research Infrastructures. Its main goal is to integrate the national efforts and keep the European community at the cutting edge of science and technology. AHEAD is offering funding opportunities, also open to participants outside Europe, for transnational visits, workshops and dissemination activities. The landmark for AHEAD is the future large observatory Athena. Significant effort is devoted to improve its design beyond the baseline and improve the related infrastructures. AHEAD is also active in the exploitation of current space missions, providing access to data archives and advanced tools and delivering new products and services. Finally, it supports technology innovation for the benefits of society and new design studies towards the definition of a future gamma-ray mission.

We describe the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X), a probeclass mission concept that will provide an unprecedented view of the X-ray sky, performing timing and spectroscopy over both a broad energy band (0.2–30 keV) and a wide range of timescales from microseconds to years. STROBE-X comprises two narrow-field instruments and a wide field monitor. The soft or low-energy band (0.2–12 keV) is covered by an array of lightweight optics (3-m focal length) that concentrate incident photons onto small solid-state detectors with CCD-level (85–175 eV) energy resolution, 100 ns time resolution, and low background rates. This technology has been fully developed for NICER and will be scaled up to take advantage of the longer focal length of STROBE-X. The higher-energy band (2–30 keV) is covered by large-area, collimated silicon drift detectors that were developed for the European LOFT mission concept. Each instrument will provide an order of magnitude improvement in effective area over its predecessor (NICER in the soft band and RXTE in the hard band). Finally, STROBE-X offers a sensitive wide-field monitor (WFM), both to act as a trigger for pointed observations of X-ray transients and also to provide high duty-cycle, high time-resolution, and high spectral-resolution monitoring of the variable X-ray sky. The WFM will boast approximately 20 times the sensitivity of the RXTE All-Sky Monitor, enabling multi-wavelength and multi-messenger investigations with a large instantaneous field of view. This mission concept will be presented to the 2020 Decadal Survey for consideration.

eXTP is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism. Primary goals are the determination of the equation of state of matter at supra-nuclear density, the measurement of QED effects in highly magnetized star, and the study of accretion in the strong-field regime of gravity. Primary targets include isolated and binary neutron stars, strong magnetic field systems like magnetars, and stellar-mass and supermassive black holes. The mission carries a unique and unprecedented suite of state-of-the-art scientific instruments enabling for the first time ever the simultaneous spectral-timing-polarimetry studies of cosmic sources in the energy range from 0.5-30 keV (and beyond). Key elements of the payload are: the Spectroscopic Focusing Array (SFA) - a set of 9 X-ray optics for a total effective area of ~0.7 m2 and 0.5 m2 at 2 keV and 6 keV respectively, equipped with Silicon Drift Detectors offering 150 eV spectral resolution; the Large Area Detector (LAD) - a deployable set of 640 Silicon Drift Detectors, for a total effective area of ~3.4 m2, and spectral resolution better than 250 eV; the Polarimetry Focusing Array (PFA) – a set of 4 X-ray telescope, for a total effective area of >500 cm2 at 2 keV, equipped with imaging gas pixel photoelectric polarimeters; the Wide Field Monitor (WFM) - a set of 3 coded mask wide field units, equipped with position-sensitive Silicon Drift Detectors, each covering a 90 degrees x 90 degrees field of view. The eXTP international consortium includes major institutions of the Chinese Academy of Sciences and Universities in China, as well as major institutions in several European countries. The predecessor of eXTP, the XTP mission concept, has been selected and funded as one of the missions in the Strategic Pioneering Space Science Program of the Chinese Academy of Sciences since 2011. The strong European participation has ignificantly enhanced the scientific capabilities of eXTP. The planned launch date of the mission is 2025.

The enhanced X-ray Timing and Polarimetry (eXTP) is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism. One of the approaches to obtain large collecting areas is mounting the thermally slumping glass segments (SG) in a nested conical approximation Wolter-I design telescope. In the last two years, we have made a great progress in the research of telescope on the base of thermally slumping glass technology, and successfully fabricated several prototypes for the eXTP SFA mission. This paper intends to provide an overview of the progress. Now we can routinely produce cylindrical glasses with 36-60″ resolution (HPD) and the best mirror produced has an angular resolution of 36″ (HPD). The glass substrates coated with Pt and C layers to obtain high reflectivity of X-ray at 1-10keV, and the reliability of multilayers coating studies are under way as well. The in-situ measurement system and 3-dimention ray-tracing program have developed and can feed measurement data back into the assembly process for improving upon the later mounted mirrors in real time. We fabricated a 3-layer telescope prototype with the diameter of 106mm and focal length of 2000mm, and tested the focusing performance in SSRF, China. The measured HPD is 66″, and W90 is 168″, which meets the requirement of angular resolution of eXTP/SFA.

The eXTP (enhanced X-ray Timing and Polarimetry) mission is a major project of the Chinese Academy of Sciences (CAS) and China National Space Administration (CNSA) currently performing an extended phase A study and proposed for a launch by 2025 in a low-earth orbit. The eXTP scientific payload envisages a suite of instruments (Spectroscopy Focusing Array, Polarimetry Focusing Array, Large Area Detector and Wide Field Monitor) offering unprecedented simultaneous wide-band X-ray spectral, timing and polarimetry sensitivity. A large European consortium is contributing to the eXTP study and it is expected to provide key hardware elements, including a Large Area Detector (LAD). The LAD instrument for eXTP is based on the design originally proposed for the LOFT mission within the ESA context. The eXTP/LAD envisages a deployed 3.4 m² effective area in the 2-30 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors - offering a spectral resolution of up to 200 eV FWHM at 6 keV - and of capillary plate collimators - limiting the field of view to about 1 degree. In this paper we provide an overview of the LAD instrument design, including new elements with respect to the earlier LOFT configuration.

The Advanced Telescope for High Energy Astrophysics (Athena) is a large X-ray observatory which has been selected by the European Space Agency for launch as the second large mission of its Cosmic Vision program. Athena has been designed to address the Hot and Energetic Universe science theme, which aims to reveal hot gas structures and black holes throughout cosmic time, and determine their wider importance for the appearance of the observable Universe. Athena consists of a single, large aperture X-ray telescope based on Silicon Pore Optics (SPO) technology, focussing X-rays onto one of two instruments. The X-ray Integral Field Unit (X-IFU) provides spatially-resolved high resolution spectroscopy, which can be used to map the dynamics and chemical composition of hot diffuse cluster gas in galaxy clusters, and to detect weak absorption and emission features needed to uncovercharacteristic of the hot components of the intergalactic medium. The Wide-Field Imager (WFI) provides spectrally-resolved imaging over a large field of view, as well as high count-rate capability, and will be used, for example, to perform deep and wide X-ray surveys necessary to uncover typical growing black holes in the early Universe at z>6. The mission concept is currently undergoing Phase A study for an eventual launch to the Sun-Earth L2 point using an Ariane 6 launcher. In this presentation, the status of the Athena project and and associated scientific activities will be reviewed.

ATHENA is currently in Phase A, with a view to adoption in 2021. This paper will present the design status for the spacecraft (SC), covering the overall configuration of the SC, as well as the main design features of the main modules. Then the focus will be on the functional and environmental requirements, the thermo-mechanical design and the Assembly, Integration and Test considerations related to the very large Mirror Assembly Module housing the Silicon Pore Optic (SPO) Mirror Modules. Initially functional requirements on the optics accommodation are presented, with the Effective Area and Half Energy Width (HEW) requirements leading to a preliminary HEW budget allocated across the main contributors. This is then used as a reference to derive subsequent requirements and engineering considerations, including: The procedures and technologies under consideration for AIT to achieve the required alignment; stiffness requirements and handling scheme required to constrain deformation under gravity during x-ray testing; temperature control to constrain thermo-elastic deformation during flight; and the capability to focus using the Instrument Switching Mechanism. Next, our best understanding of the launch mechanical environment imposed by the forthcoming Ariane-64 launch vehicle is presented along with the mechanical requirements of the MMs, and the need to minimize shock-loading of the MMs is stressed. Methods to achieve this are presented, including: Modal-tuning of the MAM to act as a low-pass filter during launch shock events; low-shock release-mechanisms; the possibility to deploy a passive vibration solution in the launcher interface plane to reduce loads.

The Wide Field Imager (WFI) instrument for ESA’s next large X-ray mission Athena is designed for imaging and spectroscopy over a large field of view, and high count rate observations up to and beyond 1 Crab source intensity. The other focal plane instrument, the cryogenic X-IFU camera, is designed for high spectral resolution imaging. Both cameras share alternately a mirror system based on silicon pore optics with a focal length of 12 m and unprecedented large effective area. The here described WFI instrument employs DEPFET active pixel sensors together with readout and control ASICs tailored for this project. The WFI DEPFETs are 450 μm thick, fully depleted, back-illuminated silicon active pixel sensors. They provide high quantum efficiency over the 0.2 keV to 15 keV range with state-of-the art spectral resolution and extremely high time resolution compared to previous generations of silicon detectors for Xray astronomy. The focal plane comprises a 'Large Detector Array' (LDA) with over 1 million pixels of 130 um · 130 um size, permitting oversampling of the PSF by a factor >2. The LDA spans a 40 amin · 40 amin large field of view and is complemented by a small 'Fast Detector' (FD) optimized for high count rate applications. In the present phase A of the project, the conceptual design of WFI is defined and the necessary development of technology is performed. Critical subsystems with respect to the development are the detector function and performance, the real-time capability of the on-board signal processing chain, and the ultra-thin large-area optical blocking filter, which has to withstand the acoustic noise loads during launch. Various prototype detectors of smaller size than the LDA detector have been developed and successfully tested for this purpose. The results determine the preliminary design of the detector system for the upcoming engineering model of the camera. With a breadboard of the signal processing chain, the necessary steps for signal correction and filtering are presently tested in particular to evaluate the time needed for this. The modular design of the breadboard is based on the Microsemi RTG4 FPGA as key component for the frame processor. An on-board data reduction is necessary because of the high frame rate and large number of pixels per frame. Otherwise, the signal rate would exceed the available telemetry rate to ground. Tests in acoustic noise facilities, complemented by vibration tests, shall prove that the 17 cm · 17 cm large and 0.18 μm thin optical blocking filter survives the satellite launch without a vacuum enclosure. The filter foil is supported by a mesh made of stainless steel and protected by a filter wheel design that minimizes the loads to the optical blocking filter inside the assembly. Furthermore, the overall design of the instrument and its various subsystems has been further developed. Tradeoffs have been performed to obtain an architecture of the instrument compliant with the requirements to the instrument, especially with respect to energy, time and spatial resolution, quantum efficiency, instrumental background as well as technical budgets like mass, volume, power consumption and radiator area. After completion of the current breadboarding phase, an engineering model of the WFI instrument will be developed and tested. According to the WFI model philosophy, a structural and thermal model as well as a qualification model will be developed and tested before the flight model shall be launched in 2031 to the Lagrangian point L2 in 1.5 million km distance from Earth. The mission lifetime is planned to be four years with a possible five-year extension.

The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of the ESA Athena X-ray observatory. Over a field of view of 5’ equivalent diameter, it will deliver X-ray spectra from 0.2 to 12 keV with a spectral resolution of 2.5 eV up to 7 keV on ∼ 5” pixels. The X-IFU is based on a large format array of super-conducting molybdenum-gold Transition Edge Sensors cooled at ∼ 90 mK, each coupled with an absorber made of gold and bismuth with a pitch of 249 μm. A cryogenic anti-coincidence detector located underneath the prime TES array enables the non X-ray background to be reduced. A bath temperature of ∼ 50 mK is obtained by a series of mechanical coolers combining 15K Pulse Tubes, 4K and 2K Joule-Thomson coolers which pre-cool a sub Kelvin cooler made of a 3He sorption cooler coupled with an Adiabatic Demagnetization Refrigerator. Frequency domain multiplexing enables to read out 40 pixels in one single channel. A photon interacting with an absorber leads to a current pulse, amplified by the readout electronics and whose shape is reconstructed on board to recover its energy with high accuracy. The defocusing capability offered by the Athena movable mirror assembly enables the X-IFU to observe the brightest X-ray sources of the sky (up to Crab-like intensities) by spreading the telescope point spread function over hundreds of pixels. Thus the X-IFU delivers low pile-up, high throughput (< 50%), and typically 10 eV spectral resolution at 1 Crab intensities, i.e. a factor of 10 or more better than Silicon based X-ray detectors. In this paper, the current X-IFU baseline is presented, together with an assessment of its anticipated performance in terms of spectral resolution, background, and count rate capability. The X-IFU baseline configuration will be subject to a preliminary requirement review that is scheduled at the end of 2018.

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 are four DEPFET (Depleted p-channel FET) detectors with a size of 512×512 pixels each. Their size involves challenging demands on the readout process, concerning timing and homogeneity over such large scales. In order to estimate the influence of flight size, smaller prototype sensors of various size, chosen to address the specific problems, were produced and characterized. Both possible readout modes, source follower and drain current readout, were investigated regarding their specific size dependent problems. Time resolution of the particularly stable source follower readout is limited by RC time constants and the fast drain current mode is restricted by inhomogeneities of the pixel matrix, demanding specific properties of the Veritas readout ASIC. To characterize these effects, spectroscopic measurements, showing good performance of the devices, were complemented with electrical ones, enabled by features of the Veritas-ASIC. We characterized the time dependency of the source potential and its influence on signal offset in source follower mode as well as the influence of drain current distribution on detector properties in drain current mode. The limits and capabilities of the current to voltage converter stage were also investigated. Performance measurements on large prototype detectors using photon energies of 5.9 keV show promising results.

The Wide Field Imager (WFI) is one of two focal plane instruments of the Advanced Telescope for High-Energy Astrophysics (Athena), ESA’s next large X-ray observatory, planned for launch in the early 2030’s. In the aimed orbit, a halo orbit around L2, the second Lagrange point of the Sun-Earth system the radiation environment, mainly consisting of solar and cosmic protons, electrons and He-ions, could affect the science performance. Furthermore as additional contribution the unfocused hard X-ray background is taken into account. It is important to understand and estimate the expected instrumental background and to investigate measures, like design modifications or analysis methods, which could improve the expected background level in order to achieve the challenging scientific requirement of < 5×10⁻³ cts/cm²/keV/s. For that purpose, the WFI background working group is investigating possible approaches, which will also be subject to technical feasibility studies. Finally an estimate of the WFI instrumental background for a proposed combination of design optimization and background rejection algorithm is given, showing that WFI is compliant with science background requirements.

The Science Products Module (SPM), a US contribution to the Athena Wide Field Imager, is a highly capable secondary CPU that performs special processing on the science data stream. The SPM will have access to both accepted X-ray events and those that were rejected by the on-board event recognition processing. It will include two software modules. The Transient Analysis Module will perform on-board processing of the science images to identify and characterize variability of the prime target and/or detection of serendipitous transient X-ray sources in the field of view. The Background Analysis Module will perform more sophisticated flagging of potential background events as well as improved background characterization, making use of data that are not telemetered to the ground, to provide improved background maps and spectra. We present the preliminary design of the SPM hardware as well as a brief overview of the software algorithms under development.

The Wide Field Imager (WFI) is one of the two instruments of the ATHENA astrophysics space mission approved by ESA as the second large mission in the Cosmic Vision 2015-2025 Science Programme. The WFI, based on a large array of depleted field effect transistors (DEPFET), will provide imaging in the 0.2-15 keV band over a 40’x40’ field of view, simultaneously with spectrally and time resolved photon counting. The WFI detector is also sensitive to UV/Vis photons, with an electron-hole pair production efficiency in the UV/VIS larger than that for X-ray photons. Optically generated photo-electrons may degrade the spectral resolution as well as change the energy scale by introducing a signal offset. For this reason, the use of X-ray transparent optical blocking filters (OBFs) are needed to allow the observation of X-ray sources that present a UV/Vis bright counterpart. The OBFs design is challenging since one of the two required filters is quite large (~ 160 mm × 160 mm), very thin (< 200 nm), and shall survive the mechanical load during the launch. In this paper, we review the main results of modeling and characterization tests of OBF partially representative samples, performed during the phase A study, to identify the suitable materials, optimize the design, prove that the filters can be launched in atmospheric pressure, and thus demonstrate that the chosen technology can reach the proper technical readiness before mission adoption.

The X-ray integral field unit (X-IFU) proposed for ESA’s Athena X-ray observatory will consist of 3840 transition edge sensor (TES) microcalorimeters optimized for the energy range of 0.2 to 12 keV. The instrument will provide unprecedented spectral resolution of ~ 2.5 eV at energies of up to 7 keV and will accommodate photon fluxes of 10’s mcrab (1000’s cps). Over the past two years the baseline configuration has evolved from the original proposal. The current baseline consists of a uniform large pixel array (LPA) of 5” pixels, AC-biased within their superconducting-to-normal transition and read out using frequency domain multiplexing (FDM). The baseline pixel design is approximately a factor of two times slower than in the original concept. High count-rate accommodation, needed for bright point source observations, is now achieved by defocusing the telescope optic to spread the photons over a larger number of pixels. In this paper we report on Mo/Au TES designs that are being optimized to meet the baseline pixel parameters and performance goals. This includes detailed studies on the optimization of the thermal heat sink and the impact of different TES geometries (including TES size and normal metal feature geometries) on the DC-biased transition shape. We discuss how these geometric effects ultimately impact important performance metrics such as energy resolution, decay time, slew-rate and array scale uniformity. Our Mo/Au TESs have historically been designed and optimized for DC-biased operation, however, the primary readout technology uses an AC drive to bias the TES. Depending upon the drive frequency, the AC bias affects the TES transition shape in two ways. Firstly, due to losses from the bias current coupling to metallic components in close proximity to the TES and secondly introducing fine structure in the transition due to Josephson effects. We present latest pixel design optimizations targeted at mitigating these frequency dependent effects in order to achieve commensurate performance with that obtained in the DC case.

SRON is developing X-ray transition edge sensor (TES) calorimeters arrays, as a backup technology for X-IFU instrument on the ATHENA space observatory. These detectors are based on a superconducting TiAu bilayer TES with critical temperature of 100 mK on a 1 μm thick SiN membrane with Au or Au/Bi absorbers. Number of devices have been fabricated and measured using a Frequency Division Multiplexing (FDM) readout system with 1-5 MHz bias frequencies. We measured IV curves, critical temperature, thermal conductance, noise and also X-ray energy resolution at number of selected bias points. So far our best calorimeter shows 3.9 eV X-ray resolution at 6 keV. Here we present a summary of our results and the latest status of development of X-ray calorimeters at SRON.

We are developing the frequency domain multiplexing (FDM) read-out of transition-edge sensor (TES) microcalorimeters for the X-ray Integral Field Unit (X-IFU) instrument on board of the future European X-Ray observatory Athena. The X-IFU instrument consists of an array of $\sim$3840 TESs with a high quantum efficiency (>90 % at 7 keV) and spectral resolution $\Delta E$=2.5 eV @ 7 keV ($E/\DeltaE\sim$2800). FDM is the baseline readout system for the X-IFU instrument. In FDM, TESs are coupled to a passive LC filter and biased with alternating current (AC bias) at MHz frequencies. Each resonator should be separated beyond their detector thermal response (< 10 kHz) to avoid crosstalk between neighboring resonators. To satisfy the requirement of the X-IFU, a multiplexing factor of 40 pixels/channel in a frequency range from 1 to 5 MHz required. Using high-quality factor LC filters and room temperature electronics developed at SRON and low-noise two-stage SQUID amplifiers provided by VTT, we have recently demonstrated good performance with the FDM readout of Mo/Au TES calorimeters with Au/Bi absorbers. We have achieved a performance requested for the demonstration model (DM) with the single pixel AC bias mode. We have also demonstrated 6-pixel multiplexing with an average energy resolution of 3.4 eV, which is currently limited by non-fundamental issues related to FDM readout in our current lab setup. In parallel to technology developments, we are also constructing a set-up which can be readout 2x40 pixels as the precursor of the DM. In this paper we report on the concept of the focal plane assembly, their requirements, detector performance under FDM scheme, recent results from pre-demonstration model setup and future prospect.

The X-ray Integral Field Unit (X-IFU) is an imaging microcalorimeter being developed for ESA's Athena X-ray observatory to providing high spectral resolution imaging between 0.2-12 keV, with moderate count-rate capability and a large field-of-view. The X-IFU focal plane assembly (FPA) will contain the instrument's large-format transition edge sensor (TES) microcalorimeter array and its superconducting readout electronics, plus a second TES detector, located behind the main sensor array, is used to detect high-energy cosmic rays and secondary particles passing through the sensor array and enable the rejection of false events that they generate in the sensor array's event list. A Kevlar thermal suspension is used to isolate the detectors at 55 mK from the 2 K environment of the X-IFU instrument cryostat's cold stage, while three layers of shielding are used to allow the detector's to achieve their low-noise performance in the expected on-ground and in-flight electromagnetic and microvibration environment. This paper will describe the preliminary design concept of the X-IFU focal plane assembly and its critical technology building blocks.

SQUID Time-Division Multiplexing (TDM) is a technique for the readout of arrays of Transition-Edge Sensors (TESs) for x-ray and gamma-ray science. TDM has been deployed in many recent 250-pixel-scale instruments including at synchrotron light sources and particle-accelerator facilities, as well as in table-top experiments. Two TES spectrometers employing TDM readout will soon be deployed to electron-beam ion-trap facilities. TDM is also under development as a back-up readout option for the X-ray Integral Field Unit (X-IFU) of the Athena satellite mission. The 3,840 TES pixels of the X-IFU will enable efficient, high resolution spectroscopy (2.5 eV FWHM at 7 keV) of extended astrophysical sources. Multiplexing factors of 40 or more sensors per readout column are planned for the X-IFU. To advance the maturity of TDM readout for Athena, we are creating a focal-plane assembly for the readout of 960 TES pixels in a 24 column by 40 row configuration. We will describe the design and experimental progress on this technology demonstrator. In a TDM system, each dc-biased TES has its own first-stage SQUID. Rows of these first-stage-SQUIDs are turned on and off sequentially such that the signal from only one TES at a time per readout column is passed to a series-array SQUID, to a room-temperature preamplifier, and to digital-feedback electronics. Recent implementations of TDM have a row period of 160 ns and non-multiplexed amplifier noise of 0.19 micro-Phi_0/sqrt(Hz) referred to the first-stage SQUID. Some benchmark demonstrations of TDM with x-ray TES sensors include achievement of 2.55 eV FWHM energy resolution at 5.9 keV in a 32-row, 1-column configuration. Here, the fastest slew rates in the TES currents were similar to those of the X-IFU “LPA2” detector model. We have also achieved 2.72 eV FWHM resolution in a 32-row, 6-column configuration that contained 144 high-quality TESs that were similar to the much faster X-IFU “LPA1” pixels. We will describe on-going efforts to read out TDM arrays at the 6x32 scale and larger, as well as efforts to improve the performance of TDM system subcomponents. We will also describe system-level performance metrics such as cross-talk. SQUID Code-Division Multiplexing (CDM) is closely related to TDM but has important performance advantages. CDM and TDM operation are similar with the main difference being that in CDM, all TESs are observed by the multiplexer at all times, with the polarity of the TES signals switched between rows. Because all TESs are observed by the multiplexer at all times, the sqrt(N_rows) noise-aliasing degradation inherent to TDM is eliminated. We are developing flux-summing CDM to be drop-in compatible with existing TDM systems. The most recent CDM implementation has a nonmultiplexed noise level of 0.17 micro-Phi_0/sqrt(Hz) referred to the first-stage SQUID and a row period of 160 ns. We have demonstrated 2.77 eV FWM resolution at 5.9 keV in 32-row, 1-column CDM test.

The background of the ATHENA X-IFU instrument is evaluated by Geant4 simulations. A new, highly detailed, mass model of the X-IFU and of its cryostat has been produced, a new model for the Galactic Cosmic Ray protons in L2 has been developed from satellite data, and a set of physics models tuned to ATHENA needs has been refined through extensive validations against experimental results. We are going to report the latest results in the estimate of the background of the X-IFU instrument, obtained after the update of all the elements of the Geant4 simulations and of the post processing software.

The X-ray Integral Field Unit (X-IFU) is one of the two instruments of the Athena astrophysics space mission approved by ESA in the Cosmic Vision 2015-2025 Science Programme. The X-IFU consists of a large array of transition edge sensor micro-calorimeters that will operate at ~100 mK inside a sophisticated cryostat. A set of thin filters, highly transparent to X-rays, will be mounted on the opening windows of the cryostat thermal shields in order to attenuate the IR radiative load, to attenuate radio frequency electromagnetic interferences, and to protect the detector from contamination. Thermal filters are critical items in the proper operation of the X-IFU detector in space. They need to be strong enough to survive the launch stresses but very thin to be highly transparent to X-rays. They essentially define the detector quantum efficiency at low energies and are fundamental to make the photon shot noise a negligible contribution to the energy resolution budget. In this paper, we review the main results of modeling and characterization tests of the thermal filters performed during the phase A study to identify the suitable materials, optimize the design, and demonstrate that the chosen technology can reach the proper readiness before mission adoption.

We summarize nearly two decades of successful operation of the Chandra High Resolution Camera (HRC). The HRC is a pair of cesium–iodide (CsI) coated microchannel plate X-ray detectors launched in July, 1999, one optimized for widefield imaging (HRC-I) and a second as a readout for X-ray transmission gratings (HRC-S). We discuss the temporal evolution of the performance of the flight instrument, the impact of extended exposure to the charged particle environment of high Earth orbit, and lessons learned from nineteen years of flight operations. We also describe our investigation of new algorithms to remove more efficiently the charged particle background from the science data, as we prepare for another decade of operation.

The Hard X-ray Modulation Telescope (HXMT or also dubbed as Insight-HXMT) is China’s first astronomical satellite. It was launched on 15th June 2017 in JiuQuan, China and is currently in service smoothly. It was designed to perform pointing, scanning and gamma-ray burst (GRB) observations and, based on the Direct Demodulation Method (DDM), the image of the scanned sky region can be reconstructed. Here we introduce the mission and its progresses in aspects of payload, core sciences, ground calibration/facility, ground segment, data archive, software, in-orbit performance, calibration, background model, observations and preliminary results.

NASA's Neutron star Interior Composition Explorer (NICER) progressed smoothly through its final ground-test activities in 2016 and early 2017, in preparation for a spectacular launch and installation on the International Space Station in June 2017. Activation of the payload and initial calibration of its systems followed, rounding out Phase D, Testing and Commissioning, of the mission's development cycle. We describe the final ground verification measurements of NICER's key performance parameters, such as the X-ray Timing Instrument's photon energy resolution and time-stamping accuracy, as well as in-flight effective collecting area, pointing, background, and other calibration efforts. The payload meets all of its design requirements and is poised to deliver new insights in soft X-ray astrophysics; briefly, we touch on early science returns that showcase NICER's unique capabilities.

The Nuclear Spectroscopic Telescope ARray (NuSTAR) has been in orbit for 6 years, and with the calibration data accumulated over that period we have taken a new look at the effective area calibration. The NuSTAR 10-m focal length is achieved using an extendible mast, which flexes due to solar illumination. This results in individual observations sampling a range of off-axis angles rather than a particular off-axis angle. In our new approach, we have split over 50 individual Crab observations into segments at particular off-axis angles. We combine segments from different observations at the same off-axis angle to generate a new set of synthetic spectra, which we use to calibrate the vignetting function of the optics against the canonical Crab spectrum.

The Imaging X-ray Polarimetry Explorer (IXPE) will expand the information space for study of cosmic sources, by adding polarization to the properties (time, energy, and position) observed in x-ray astronomy. Selected in 2017 January as a NASA Astrophysics Small Explorer (SMEX) mission, IXPE will be launched into an equatorial orbit in 2021. The IXPE observatory includes three identical x-ray telescopes, each comprising a 4-m-focal-length (grazing-incidence) mirror module assembly (MMA) and a polarization-sensitive (imaging) detector unit (DU). The optical bench separating the MMAs from the DUs is a deployable boom with a tip/tilt/rotation stage for DU-to-MMA (gang) alignment, similar to the configuration used for the NuSTAR observatory. The IXPE mission will provide scientifically meaningful measurements of the x-ray polarization of a few dozen sources in the 2-8 keV band, over the first two years of the mission. For several bright, extended x-ray sources (pulsar wind nebulae, supernova remnants, and an active-galaxy jet), IXPE observations will produce polarization maps indicating the magnetic structure of the synchrotron emitting regions. For many bright pulsating x-ray sources (isolated pulsars, accreting x-ray pulsars, and magnetars), IXPE observations will produce phase-resolved profiles of the polarization degree and position angle.

ART-XC is an X-ray grazing incidence mirror telescopes array onboard the Spectrum-Roentgen-Gamma (SRG) mission, that is currently scheduled for launch in March 2019. This instrument was developed by the Space Research Institute (IKI) and the All-Russian Scientific Research Institute for Experimental Physics (VNIIEF). The NASA Marshall Space Flight Center (MSFC) has developed and fabricated flight X-ray mirror modules. Each mirror module is aligned with a focal plane CdTe double-sided strip detector which will operate over the energy range of 4−30 keV, with an angular resolution of <1′, a field of view of ~0.3 deg² in double reflection and an expected energy resolution of about 9% at 14 keV. The ART-XC instrument will be used to perform an all-sky survey simultaneously with the other instrument of the SRG mission, eROSITA, operational in a softer energy range 0.3-10 keV. We present an overview of the ARTXC/SRG instrument and an update on the current status of the project.

eROSITA is the main instrument on-board the Russian/German "Spectrum-Roentgen-Gamma" (SRG) mission. It will perform the first imaging all-sky survey in the medium energy band. The development of eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is a national German project, funded by MPG (Max-Planck Gesellschaft), co-funded by DLR (Deutsches Zentrum für Luft- und Raumfahrt) and implemented by MPE (Max-Planck Institut für extraterrestrische Physik) in cooperation with other German institutes and industry. Different from other such extensive and challenging missions, MPE took the responsibility for the overall management, system engineering and product assurance and sub-contracted only specific development tasks, manufacturing and testing for the benefit of small companies. MPE is the architect and the user of this high tech instrument. MPE defined the requirements and verified the requirements. This is a non-standard situation but offers much more flexibility in interpretation of requirements and tailoring of solutions. The implementation of the project was driven by lean management with close cooperation of technical and scientific personnel with pragmatic approaches and extensive testing, supported by the magnitude of inhouse facilities and tools. Potential solutions were discussed, evaluated and selected by mutual agreement. Nonconformances were treated in the same pragmatic way. The paper reports on how eROSITA was made, from design to the realization of the flight model and how it was delivered to and integrated in SRG and how it was tested at the prime contractor. The paper will describe how MPE as a scientific institute managed this challenging project including project management, system engineering and product assurance. The paper will also report on the very positive cooperation but complex communication and negotiations with the prime contractor in Russia.

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is an approved mission for Gamma-Ray Burst (GRB) studies, developed in cooperation between the Chinese National Space Agency (CNSA), the Chinese Academy of Sciences (CAS), the French Space Agency (CNES) and several French laboratories. In the continuity of Swift, SVOM will be a highly versatile astronomy satellite, with built-in multi-wavelength capabilities and rapid slew capability, flexible operations and ground follow-up opening a large discovery area. The paper presents the organization of the program between France and China, the mission and its objectives, the satellite and the payload, the ground segment architecture and finally the operational concept.

The SVOM (Space-based multi-band astronomical Variable Objects Monitor) French-Chinese mission is dedicated to the detection, localization and study of Gamma Ray Bursts (GRBs) and other high-energy transient phenomena. We first present the general description of the French payload composed of the ECLAIRs instrument, dedicated to GRB detection and localization and the MXT instrument, dedicated to GRB follow-up observation in soft X-ray band. Then the paper describes more in detail the design and the performances of the MXT instrument, finally a status of MXT development will be given.

The ASTRO-H mission was designed and developed through an international collaboration of JAXA, NASA, ESA, and the CSA. It was successfully launched on February 17, 2016, and then named Hitomi. During the in-orbit verification phase, the on-board observational instruments functioned as expected. The intricate coolant and refrigeration systems for soft X-ray spectrometer (SXS, a quantum micro-calorimeter) and soft X-ray imager (SXI, an X-ray CCD) also functioned as expected. However, on March 26, 2016, operations were prematurely terminated by a series of abnormal events and mishaps triggered by the attitude control system. These errors led to a fatal event: the loss of the solar panels on the Hitomi mission. The X-ray Astronomy Recovery Mission (or, XARM) is proposed to regain the key scientific advances anticipated by the international collaboration behind Hitomi. XARM will recover this science in the shortest time possible by focusing on one of the main science goals of Hitomi,“Resolving astrophysical problems by precise high-resolution X-ray spectroscopy”.¹ This decision was reached after evaluating the performance of the instruments aboard Hitomi and the mission’s initial scientific results, and considering the landscape of planned international X-ray astrophysics missions in 2020’s and 2030’s. Hitomi opened the door to high-resolution spectroscopy in the X-ray universe. It revealed a number of discrepancies between new observational results and prior theoretical predictions. Yet, the resolution pioneered by Hitomi is also the key to answering these and other fundamental questions. The high spectral resolution realized by XARM will not offer mere refinements; rather, it will enable qualitative leaps in astrophysics and plasma physics. XARM has therefore been given a broad scientific charge: “Revealing material circulation and energy transfer in cosmic plasmas and elucidating evolution of cosmic structures and objects”. To fulfill this charge, four categories of science objectives that were defined for Hitomi will also be pursued by XARM; these include (1) Structure formation of the Universe and evolution of clusters of galaxies; (2) Circulation history of baryonic matters in the Universe; (3) Transport and circulation of energy in the Universe; (4) New science with unprecedented high resolution X-ray spectroscopy. In order to achieve these scientific objectives, XARM will carry a 6 × 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly, and an aligned X-ray CCD camera covering the same energy band and a wider field of view. This paper introduces the science objectives, mission concept, and observing plan of XARM.

X-ray Astronomy Recovery Mission (XARM) scheduled to be launched in early 2020’s carries two soft X-ray telescopes. One is Resolve consisting of a soft X-ray mirror and a micro calorimeter array, and the other is Soft X-ray Imaging Telescope (Xtend), a combination of an X-ray mirror assembly (XMA) and an X-ray CCD camera (SXI). Xtend covers a field of view (FOV) of 38′ × 38′ , much larger than that of Resolve (3′ × 3 ′ ) with moderate energy resolution in the energy band from 0.4 keV to 13 keV, which is similar to that of Resolve (from 0.3 keV to 12 keV). Simultaneous observations of both telescopes provide complimentary data of X-ray sources in their FOV. In particular, monitoring X-ray sources outside the Resolve FOV but inside the Xtend FOV is important to enhance the reliability of super high resolution spectra obtained with Resolve. Xtend is also expected to be one of the best instruments for low surface brightness X-ray emissions with its low non X-ray background level, which is comparable to that of Suzaku XIS. The design of Xtend is almost identical to those of Soft X-ray Telescope (SXT) and Soft X-ray Imager (SXI) both on board the Hitomi satellite. However, several mandatory updates are included. Updates for the CCD chips are verified with experiment using test CCD chips before finalizing the design of the flight model CCD. Fabrication of the foils for XMA has started, and flight model production of the SXI is almost ready.

The Resolve instrument onboard the X-ray Astronomy Recovery Mission (XARM) consists of an array of 6x6 silicon-thermistor microcalorimeters cooled down to 50 mK and a high-throughput X-ray mirror assembly with a focal length of 5.6 m. The XARM is a recovery mission of ASTRO-H/Hitomi, and is developed by international collaboration of Japan, USA, and Europe. The Soft X-ray Spectrometer (SXS) onboard Hitomi demonstrated high resolution X-ray spectroscopy of ~ 5 eV FWHM in orbit for most of the microcalorimeter pixels. The Resolve instrument is planned to mostly be a copy of the Hitomi SXS and Soft X-ray Telescope designs, though several changes are planned based on the lessons learned of Hitomi. The energy resolution budget of the microcalorimeters is updated, reflecting the Hitomi SXS results. We report the current status of the Resolve instrument.

The Einstein Probe (EP) is a small satellite dedicated to time-domain astronomy to monitor the sky in the soft X-ray band. It is a mission led by the Chinese Academy of Sciences and developed in its space science programme with international collaboration. Its wide-field imaging capability is achieved by using established technology of the micro-pore lobster-eye X-ray focusing optics. Complementary to this is deep X-ray follow-up capability enabled by a Wolter-I type X-ray telescope. EP is also capable of fast transient alerts triggering and downlink, aiming at multi-wavelength follow-up observations by the world-wide community. EP will enable systematic survey and characterisation of high-energy transients at unprecedented sensitivity, spatial resolution, grasp and monitoring cadence. Its scientific goals are mainly concerned with discovering new or rare types of transients, including tidal disruption events, supernova shock breakouts, high-redshift GRBs, and of particular interest, electromagnetic sources of gravitational wave events.

Arcus, a Medium Explorer (MIDEX) mission, was selected by NASA for a Phase A study in August 2017. The observatory provides high-resolution soft X-ray spectroscopy in the 12-50 Å bandpass with unprecedented sensitivity: effective areas of >350 cm^2 and spectral resolution >2500 at the energies of O VII and O VIII for z=0-0.3. The Arcus key science goals are (1) to measure the effects of structure formation imprinted upon the hot baryons that are predicted to lie in extended halos around galaxies, groups, and clusters, (2) to trace the propagation of outflowing mass, energy, and momentum from the vicinity of the black hole to extragalactic scales as a measure of their feedback and (3) to explore how stars, circumstellar disks and exoplanet atmospheres form and evolve. Arcus relies upon the same 12m focal length grazing-incidence silicon pore X-ray optics (SPO) that ESA has developed for the Athena mission; the focal length is achieved on orbit via an extendable optical bench. The focused X-rays from these optics are diffracted by high-efficiency Critical-Angle Transmission (CAT) gratings, and the results are imaged with flight-proven CCD detectors and electronics. The power and telemetry requirements on the spacecraft are modest. Arcus will be launched into an ~ 7 day 4:1 lunar resonance orbit, resulting in high observing efficiency, low particle background and a favorable thermal environment. Mission operations are straightforward, as most observations will be long (~100 ksec), uninterrupted, and pre-planned. The baseline science mission will be completed in <2 years, although the margin on all consumables allows for 5+ years of operation.

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a NASA sounding rocket instrument designed to obtain spatially resolved soft X-ray spectra of the solar atmosphere in the 6–24 Å (0.5–2.0 keV) range. The instrument consists of a single shell Wolter Type-I telescope, a slit, and a spectrometer comprising a matched pair of grazing incidence parabolic mirrors and a planar varied-line space diffraction grating. The instrument is designed to achieve a 50 mÅ spectral resolution and 5 arcsecond spatial resolution along a ±4-arcminute long slit, and launch is planned for 2019. We report on the status and our approaches for fabrication and alignment for this novel optical system. The telescope and spectrometer mirrors are replicated nickel shells, and are currently being fabricated at the NASA Marshall Space Flight Center. The diffraction grating is currently under development by the Massachusetts Institute of Technology (MIT); because of the strong line spacing variation across the grating, it will be fabricated through e-beam lithography.

We are working on an updated program of the future Japanese X-ray satellite mission DIOS (Diffuse Intergalactic Oxygen Surveyor), called Super DIOS. We keep the main aim of searching for dark baryons in the form of warmhot intergalactic medium (WHIM) with high-resolution X-ray spectroscopy. The mission will detect redshifted emission lines from OVII, OVIII and other ions, leading to an overall understanding of the physical nature and spatial distribution of dark baryons as a function of cosmological timescale. We are working on the conceptual design of the satellite and onboard instruments, with a provisional launch time in the early 2030s. The major changes will be improved angular resolution of the X-ray telescope and increased number of TES calorimeter pixels. Super DIOS will have a 10-arcsecond resolution and a few tens of thousand TES pixels. Most contaminating X-ray sources will be resolved, and the level of diffuse X-ray background will be reduced after subtraction of point sources. This will give us very high sensitivity to map out the WHIM in emission. The status of the spacecraft study will be presented: the development plan of TES calorimeters, on-board cooling system, X- ray telescope, and the satellite system. The previous study results for DIOS and technical achievements reached by the Hitomi (ASTRO-H) mission provide baseline technology for Super DIOS. We will also consider large scale international collaboration for all the on-board instruments.

AXIS is a probe-class concept under study for submission to the 2020 Decadal survey. AXIS will extend and enhance the science of high angular resolution x-ray imaging and spectroscopy in the next decade with ∼ 0.3 00 angular resolution over a 70 radius field of view and an order of magnitude more collecting area than Chandra in the 0.3−12 keV band with a cost consistent with a probe. These capabilities are made possible by precision-polished lightweight single-crystal silicon optics achieving both high angular resolution and large collecting area, and next generation small-pixel silicon detectors adequately sampling the point spread function and allowing timing science and preventing pile up with high read-out rate. We have selected a low earth orbit to enable rapid target of opportunity response, similar to Swift, with a high observing efficiency, low detector background and long detector life. The combination opens a wide variety of new and exciting science such as: (1) measuring the event horizon scale structure in AGN accretion disks and the spins of supermassive black holes through observations of gravitationally-microlensed quasars; (ii) determining AGN and starburst feedback in galaxies and galaxy clusters through direct imaging of winds and interaction of jets and via spatially resolved imaging of galaxies at high-z; (iii) fueling of AGN by probing the Bondi radius of over 20 nearby galaxies; (iv) hierarchical structure formation and the SMBH merger rate through measurement of the occurrence rate of dual AGN and occupation fraction of SMBHs; (v) advancing SNR physics and galaxy ecology through large detailed samples of SNR in nearby galaxies; (vi) measuring the Cosmic Web through its connection to cluster outskirts; (vii) a wide variety of time domain science including rapid response to targets of opportunity. With a nominal 2028 launch, AXIS benefits from natural synergies with the ELTs, LSST, ALMA, WFIRST and ATHENA. The AXIS team welcomes input and feedback from the community in preparation for the 2020 Decadal review.

Within the AHEAD consortium a mission concept named ASTENA (Advanced Surveyor of Transient Events and Nuclear Astrophysics) is proposed to address the top-priority themes identified by the AHEAD Science Advisory Group: Gamma-Ray Bursts and Nuclear Astrophysics. GRBs are among the most intriguing phenomena of the Universe, which thanks to their vast luminosities can be used to probe the first billion years of cosmic history, i.e. the era of first stars and black-holes. In spite of great advancements in the GRB astronomy since the BeppoSAX discovery of afterglows, several issues concerning both the prompt emission and the afterglow are still open. Concerning the prompt emission, for example, the emission mechanism of the radiation and the energy dissipation site (internal shocks? external shocks? photosphere?) are far from being understood. What is required is an accurate determination of the photon spectrum from few keV up to tens of MeV, and importantly, a measurement of the polarization of the radiation. The emission of the afterglow has been deeply investigated with Swift in the energy band from 0.5 to 10 keV, showing that an understanding of the origin of the emission mechanism requires spectral information extending to much higher energies, as already suggested by a few studies at < 60 keV (e.g., Kouveliotou et al. 2013, ApJ 779, L1). Landmark progress on this issue therefore requires polarization capabilities and a passband extending well beyond 60 keV. Concerning nuclear astrophysics, a fundamental issue concerns the origin of the 511 keV positron annihilation line discovered with INTEGRAL/SPI in the Galactic center. According to the INTEGRAL results the emission is diffuse, but the poor imaging capability of INTEGRAL (at the best with a resolution of 12 arcmin with ISGRI) does not allow one to establish whether what appears diffuse is indeed the superposition of the emission from point-like sources, such as micro-quasars. The important role played by micro-quasars as sources of positron annihilation line emission has also been established with INTEGRAL (Siegert et al. 2016, Nature 531, 341). Another open issue in nuclear astrophysics concerns the determination and understanding of the nuclear burning processes in Type-1a supernovae. This requires a study of the intensity and time behavior of the expected lines emitted by the heavy elements produced in supernova explosions. Instrument concept to address the IWG requirements. With the above considerations in mind, we propose to perform a feasibility study of a configuration of two instruments: a) a wide field monitor/spectrometer (WFM/S), with a passband from 1 keV to 20 MeV, made of a suitable number of detection modules, each consisting of an array of long bars of scintillator with very small cross section, and readout from both sides with solid state thin detectors (e.g. Silicon Drift Detectors, SDD). One of the SDD is used as soft X-ray Position Sensitive Detector. A possible crystal material is CsI(Tl), but also other faster crystals such as LSO(Ce) or CeBr3 should be examined. The detector modules are coupled to a light coded mask, for obtaining a GRB localization accuracy of order of ~1 arcmin between 1 and 30/50 keV. The number of modules, equipped with collimators, should be sufficient to achieve the required sensitivity to GRBs. The order of magnitude of the total detection area is 18000 cm2. The modules are slightly misaligned with each other tin order o achieve a wide FOV (> 1 sr). b) a narrow field telescope (NFT), made of a broad-band Laue lens (50 – 600/700 keV) of a 20 m focal length, based on the exploitation of bent crystals, like those under development in Ferrara (FOV= 3.5 arcmin, angular resolution ≈20”). The NFT is coupled to a high efficiency (>80% above 600 keV) focal plane position sensitive detector, with 3D spatial resolution of at least 300 µm in the (X,Y) plane, fine spectroscopic response (1% @511 keV) and with polarization sensitivity. With the WFM/S, we expect to accurately determine the energy spectrum of GRB prompt emission in the broadest band ever achieved with a single instrument, to measure the gamma-ray polarization of, at least, the brightest GRBs and to search for electromagnetic counterparts of Gravitational Wave events. In addition, with adequate scintillator bars and fast electronics, the Lorentz invariance for the brightest events can be tested. With the NFT, which is >~100 times more sensitive at a few hundred keV than any other past or planned mission, we can carry out for the first time a long-sought study of the afterglow spectrum of GRBs up to high energies (600/700 keV), including its polarization level. We can also establish, thanks to its high angular resolution (about 20”), whether the 511 keV positron annihilation line is due to the superposition of emission from point-like sources. In addition, we can address many Legacy Science topics mentioned in the Call, such as the origin of the high energy emission from magnetars, the first determination of the spectrum of blazars out to z~8 in between the two Synchrotron and Compton bumps, the determination of the sources that give rise to the gamma-ray diffuse background. For example, one could determine the high-energy cutoff from spectra of relatively bright AGN and study how this depends on the physics of the accretion (e.g. BH mass, Eddington ratio). We emphasize that the unprecedented sensitivity of the NFT and the combination with the WFM/S implies a large discovery space of this configuration. Moreover, such an instrument concept, thanks to the lightweight of the Laue lens and compactness of the wide field instrument, is expected to be within the limits imposed by an ESA Medium Size Mission.

The High-Energy X-ray Probe (HEX-P) is a probe-class mission concept that will extend the reach of broadband (2-200 keV) X-ray observations, with 40 times the sensitivity of any previous mission in the 10-80 keV band and 10,000 times the sensitivity of any previous mission in the 80-200 keV band. HEX-P addresses key NASA science goals and is an important complement to ESA's L-class Athena mission. Working in coordination with Athena HEX-P will provide continuum measurements that are essential for interpreting Athena spectra. With angular resolution improved by more than an order of magnitude relative to NuSTAR, HEX-P will carry out an independent program aimed at addressing questions unique to the high energy X-ray band, such as the nature of the source that powers Active Galactic Nuclei, the evolution of black holes in obscured environments, and understanding of how compact binary systems form, evolve and influence galactic systems. With heritage from NuSTAR, HEX-P can be executed within the next decade with a budget less than double that of a Medium class Explorer (MIDEX) mission.

The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket experiment aims to investigate fundamental questions about the high-energy Sun through direct imaging and spectroscopy of hard X-rays. The experiment utilizes Wolter-I type nested hard X-ray mirrors and fine-pitch semiconductor detectors, which are separated by a 2m focal length. Tol date, FOXSI has had two successful flights, on 2012 November 02 and 2014 December 11, demonstrating that the technology can measure small-scale energy releases (microflares and aggregated nanoflares) from the solar corona. The third flight for FOXSI is scheduled for August 2018. Significant improvements have been made on the FOXSI instrumentation, including upgraded optic modules with more nested mirror shells; specially designed collimators to mitigate the number of single bounce photons (ie., ghost rays) reaching the focal plane detector; and fine-pitch double-sided CdTe strip detectors to replace some of the Si-based hard X-ray detectors for better efficiency for hard X-rays. Furthermore, a CMOS based soft X-ray (SXR) instrument, “Phoenix”, will be added to FOXSI-3 by replacing one hard X-ray detector with a photon-counting SXR sensor. This will enable evaluation of the Sun via imaging spectroscopy simultaneously over a large X-ray energy range covering soft to hard X-rays. This paper will describe the overall instrument design of the FOXSI-3 experiment, which will be sensitive to solar soft and hard X-rays in the 1 – 20 keV range, as well as give a summary of insightful results and lessons from the first two flights. Possible observations for FOXSI-3 will also be discussed.

FORCE is a 1.2 tonnes small mission dedicated for wide-band fine-imaging x-ray observation. It covers from 1 to 80 keV with a good angular resolution of 15′′ half-power-diameter. It is proposed to be launched around mid2020s and designed to reach a limiting sensitivity as good as F_X(10 − 40 keV) = 3 × 10⁻¹⁵ erg cm⁻² s ⁻¹ keV⁻¹ within 1 Ms. This number is one order of magnitude better than current best one. With its high-sensitivity wideband coverage, FORCE will probe the new science field of “missing BHs”, searching for families of black holes of which populations and evolutions are not well known. Other point-source and diffuse-source sciences are also considered. FORCE will also provide the “hard x-ray coverage” to forthcoming large soft x-ray observatories.

X-ray Hybrid CMOS Detectors (HCDs) have advantages over X-ray CCDs due to their higher readout rate abilities, flexible readout, inherent radiation hardness, and low power, which make them more suitable for the next generation large-area X-ray telescope missions. The Penn State high energy astronomy laboratory has been working on the development and characterization of HCDs in collaboration with Teledyne Imaging Sensors (TIS). A custom-made H2RG detector with 36 μm pixel pitch and 18 μm ROIC shows an improved performance over standard H1RG detectors, primarily due to a reduced level of inter-pixel capacitance crosstalk (IPC). However, the energy resolution and the noise of the detector and readout system are still limited when utilizing a SIDECAR at non-cryogenic temperatures. We characterized an H2RG detector with a Cryo-SIDECAR readout and controller, and we find an improved energy resolution of ∼2.7 % at 5.9 keV and read noise of ∼6.5 e- . Detections of the ∼0.525 keV Oxygen Kα and ∼0.277 keV Carbon Kα lines with this detector display an improved sensitivity level at lower energies. This detector was successfully flown on NASA’s first water recovery sounding rocket flight on April 4th, 2018. We have also been developing several new HCDs with potential applications for future X-ray astronomy missions. We are characterizing the performance of small-pixel HCDs (12.5 μm pitch), which are important for the development of a next-generation high-resolution imager with HCDs. The latest results on these small pixel detectors has shown them to have the best read noise and energy resolution to-date for any X-ray HCD, with a measured 5.5 e- read noise for a detector with in-pixel correlated double sampling. Event recognition in HCDs is another exciting prospect. We characterized a 64 × 64 pixel prototype Speedster-EXD detector that uses comparators in each pixel to read out only those pixels having detectable signal, thereby providing an order of magnitude improvement in the effective readout rate. Currently, we are working on the development of a large area Speedster-EXD with a 550 × 550 pixel array. HCDs can also be utilized as a large FOV instrument to study the prompt and afterglow emissions of GRBs and detect black hole transients. In this context, we are characterizing a Lobster-HCD system for future CubeSat experiments. This paper briefly presents these new developments and experimental results.

We have developed SOIPIXs based on the CMOS SOI technology for the future X-ray astronomical satellite. SOIPIXs has the event trigger output function implemented in each pixel offers microsecond time resolution and its event trigger function enables to separate celestial X-rays and non-X-ray background by combining the anticoincidence system and to reduce the non-X-ray background that dominates the high X-ray energy band above 5-10 keV. A fully depleted SOIPIXs with a 300-500 um thick depletion layer and back illumination offers wide band coverage of 0.3-40 keV. In order to use XRPIXs in space environment, to investigate the radiation hardness of XRPIXs is important because semiconductor detectors such as XRPIXs and CCDs are damaged by interacting with many cosmic rays which are composed primarily energy protons in orbit. The damage causes the increase of dark current and the degradation of the performance such as the energy resolution of XRPIXs. To evaluate the radiation hardness of XRPIXs, we have carried out the radiation damage test at the heavy ion medical accelerator (HIMAC) in Japan. For this experiment, we used the XRPIX2b-FZ (Takeda et al, 2015) which was the front illuminated XRPIX with 300um thick depletion layer. XRPIX2b-FZ has 144 x 144 pixels and the pixel size is 30um x 30 um. We installed XRPIX2b-FZ in the vacuum chamber and cooled it around -80 C degree. The proton beam flux was much strong for our purpose of this experiment, we set the 3 um thick Au film as a scatterers in the cubic flange in front of vacuum chamber in order to reduce the beam flux. We introduced the scattered proton beam to the two direction of the downstream of the beam line, and one was irradiated to XRPIX2b-FZ in the vacuum chamber and the other was irradiated to the faraday cup connected to the cubic flange to monitor the scattered beam flux. We also obtained the total doze of proton beam using the faraday cup. We irradiated the proton beam to XRPIX2b-FZ until the total irradiation dose reached 10 krad while increasing the irradiation dose and evaluated the performance such as leak current, gain and energy resolution using X-ray from 109 Cd after the proton irradiation of 1 rad, 400 rad, 1 k rad, 4 k rad, and 10 krad. From above experimental results, we found that the gain and the energy resolution was degraded by 0.2 % and 10 % respectively with 400 rad whose equivalent time in orbit was 3.5 years, and the gain and energy resolution became worse by 0.8 % and 32 % respectively after irradiation of 4k rad. We investigated the reason of the degradation of the energy resolution and found the degradation was mainly caused by the increasing the read out noise. We also found the number of bad pixels clearly increased by about 10 times after the irradiation of 10 krad.

D2R1 (Dimension 2 revision 1) is the most recent development of CdTe based X-ray detectors within a series of highly successful imaging spectrometers CALISTE. The detector consists of a CdTe crystal which is directly connected to a low-noise readout ASIC by a flip-chip bonding process. The reduced stray capacitance in combination with an adapted ASIC design results in a superior energy resolution of 584 eV FWHM at 60 keV. The 16x16 pixel array with a 300um pixel pitch constitutes a 4.8x4.8 mm^2 detector surface on a 750um thick crystal. Such fine-pitched hard X-ray detectors show not only an improved spatial resolution but also an improved spectral resolution at soft and medium energies. A slightly diminishing spectral resolution is only observed for energies that are large enough to increase the split ratio significantly. X-ray polarimetry based on incoherent scattering also benefits from the improved spectral and spatial resolution. Furthermore, the sensitivity for polarimetric measurements that uses only a single detector unit is greatly enhanced because of an increased efficiency for detecting Compton scattered events: within smaller pixel structures, the position of the incoherent scattering and the position of the scattered photon absorption are less likely within the same pixel and can be therefore detected individually. After a description of the new ASIC concept we are presenting laboratory measurements that were realized with several different detector modules in order to verify their spectral and spatial properties. The home made ASIC of D2R1 is based on a Charge Sensitive Amplifier (CSA) in combination with a Multi Correlated Double Sampling method: the continuous sampled outputs of the CSA are averaged on -chip before and after an event detection. The difference of these two values represent the signal height of the detected event. The ASIC exhibit very good performance and the Equivalent Noise Charge is as low as 29 electors rms, making them perfectly suitable to read semiconductor detectors of any kind and any bias polarity. In order to investigate the spectral and spatial properties the focus of the data analysis is put on the event split ratio and its dependence with energy. The determination of the virtual pixel size for single events, i.e. the region within a pixel that results in a single event detection, is key for a proper understanding of the evolution of the spectral and spatial resolution with energy. While split events decrease the spectral performance because of added noise contributions of multiple readout channels, they increase the spatial resolution by allowing a center-of-mass calculation with a sub-pixel resolution. The virtual pixel size for single, double, triple, and quadruple events are estimated with an analytical model which is verified by measurements at different energies (5.6 keV, 13.9 keV, 60 keV, 122 keV and 245 keV). Finally, the polarimetric performance of D2R1 is examined via detailed simulations. The wide accessible energy range between 2-250 keV and the fast timing capabilities complete D2R1 to suite a variety of different applications. Excellent spatial, spectral, and timing capabilities in the medium and hard X-ray range are key parameters for future X-ray missions. All these properties are well combined within the D2R1 concept.

Since 2009, CEA have started a long term program to achieve the collective realisation of a large (32x32 pixels) μ-Calorimeters camera for X-ray Astrophysics. This camera is based on silicon doped sensors with Composite Tantalum absorber readout thanks to HEMT/SiGe based Cryo-Electronics. The goal of this development is to achieve a spectral resolution of about 2eV@6keV in a thermal budget of ∼ 1μW@50mK for over 4000 pixels. In the course of this R and D program, we have started a deep system approach and developed various technics to achieve a compact Focal Plane Array (hereafter FPA) design. In this paper, we present most of these technics. Some are dedicated to high impedance sensors such as Silicon doped sensors or High resistivity TES (NbSi HRTES) and other may of much more general use for Astronomical Sub-K spatial instruments. We will present here the status of our development and our FPA integration technics.

e-ASTROGAM is a concept for a breakthrough observatory space mission carrying a γ-ray telescope dedicated to the study of the non-thermal Universe in the photon energy range from 0.15 MeV to 3 GeV. The lower energy limit can be pushed down to energies as low as 30 keV for gamma-ray burst detection with the calorimeter. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with remarkable polarimetric capability. Thanks to its performance in the MeV–GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous and current generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will be a major player of the multiwavelength, multimessenger time-domain astronomy of the 2030s, and provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LISA, LIGO, Virgo, KAGRA, the Einstein Telescope and the Cosmic Explorer, IceCube-Gen2 and KM3NeT, SKA, ALMA, JWST, E-ELT, LSST, Athena, and the Cherenkov Telescope Array.

The Compton Spectrometer and Imager (COSI) is a compact Compton telescope which is inherently sensitive to gamma-ray polarization in the energy range of 0.2-2.0 MeV. A long duration gamma-ray burst, GRB 160530A, was detected by COSI during its 2016 COSI’s balloon flight. The polarization of GRB 160530A was constrained based on the distribution of azimuthal scattering angles from each incident photon inside COSI’s germanium detector array.¹ In order to determine COSI’s polarization response and to identify systematic deviations from an ideal sinusoidal modulation, the polarization performance of COSI was validated in the laboratory prior to the 2016. A partially polarized beam was created by scattered emission from a radioactive source off a scintillator. In addition, measurements and simulations of unpolarized radioactive sources were compared to validate our capability of capturing the instrument systematics in the simulations. No statistically significant differences exist between the measured and simulated modulations and polarization angle, where the upper bound on the systematic error is 3%-4%.² In this talk, I will present the measurements used to validate COSI’s polarimetric performance. Furthermore, I will use these results to estimate the minimum detectable polarization levels for current and future COSI missions.

The Advanced Energetic Pair Telescope (AdEPT), a future NASA/GSFC MIDEX mission, is being developed to perform high-sensitivity medium-energy (5–200 MeV) astronomy and revolutionary gamma-ray polarization measurements. The enabling technology for AdEPT is the ThreeDimensional Track Imager (3-DTI), a large volume gaseous time projection chamber with 2- dimentional micro-well detector (MWD) readout. The low density and high spatial resolution of the 3-DTI allows AdEPT to achieve high angular resolution (~0.5° at 67.5 MeV) and, for the first time, exceptional gamma-ray polarization sensitivity. These capabilities enable a wide range of scientific discovery potential for AdEPT. The key science goals of the AdEPT mission include: 1) Explore fundamental processes of particle acceleration in active astrophysical objects, 2) Reveal the magnetic field configuration of the most energetic accelerators in the Universe, 3) Explore the origins and acceleration of cosmic rays and the Galactic MeV diffuse emission, 4) Search for dark matter in the Galactic center, and 5) Test relativity with polarization measurements. We report on the latest developments of the MWDs for the 3-DTI.

The ASTENA mission, conceived within the AHEAD framework, consists of two coaligned instruments, a broad band Wide Field Monitor/Spectrometer WFM/S and a broad band Narrow Field Telescope (NFT). In the NFT a large geometric area Laue lens (3 m maximum diameter with a 20 m focal length) allows to focus the radiation of the 50 - 700 keV energy pass-band. Differently from other proposed Laue lenses in the past, the NFT is made of optimized thickness bent crystal tiles, made with Silicon (for the lower energy part of the lens pass-band) and Germanium (dedicated to the upper energy threshold). With these assumption we have optimized the NFT Field of View (FoV) to 3.5 arcmin with the angular resolution of 20”. The Laue lens is coupled with a high efficiency (>80% above 600 keV) focal plane position sensitive detector, with 3D spatial resolution of at least 300 µm in the (X,Y) plane and fine spectroscopic response (1% @511 keV) and with polarization sensitivity. In this SPIE contribution we will discuss the NFI geometry simulated with the MEGAlib toolkit and we will discuss its performances by simulating broad band and narrow energy typical sources, giving finally the instrument performances.

The Gamma Ray Polarimeter Experiment (GRAPE) is designed to investigate gamma-ray bursts (GRB) in the important energy range of 50-500 keV. Our eventual goal is to fly GRAPE on a long duration balloon (LDB) platform to collect data on a significant sample of GRBs. Our experience with two balloon flights (in 2011 and 2014), coupled with further design efforts focused on orbital payloads, has led to an improved polarimeter concept that represents a natural evolution of the current design. The new concept employs a large number of small (2 cm3 ), optically-isolated scintillator cubes, each of which is read out by its own silicon photomultiplier (SiPM). These cubes are stacked in an arrangement that allows the determination of event interaction locations in three dimensions. The resulting three-dimensional location data provides a moderate level of Compton imaging capability (1σ angular resolution of 10-15). This level of imaging can be used to significantly reduce the instrumental background by limiting the impact of the cosmic diffuse flux, dramatically improving the polarization sensitivity. Here we shall describe this concept, some results from initial laboratory studies, and the expected performance parameters. We are currently working to optimize this design in preparation for a prototype balloon flight in the summer of 2020. Our long-term goal (pending acquisition of continued funding) is to fly a prototype balloon payload in the summer of 2020 and to be prepared for a first long duration balloon (LDB) flight at the end of 2021.

We propose a fleet of nanosatellites to perform an all-sky monitoring and timing based localisation of gamma-ray transients. The fleet of at least nine 3U cubesats shall be equipped with large and thin CsI(Tl) scintillator based soft gamma-ray detectors read out by multi-pixel photon counters. For bright short gamma-ray bursts (GRBs), by cross-correlating their light curves, the fleet shall be able to determine the time difference of the arriving GRB signal between the satellites and thus determine the source position with an accuracy of ∼ 100 . This requirement demands precise time synchronization and accurate time stamping of the detected gamma-ray photons, which will be achieved by using on-board GPS receivers. Rapid follow up observations at other wavelengths require the capability for fast, nearly simultaneous downlink of data using a global inter-satellite communication network. In terms of all-sky coverage, the proposed fleet will outperform all GRB monitoring missions.

HERMES (High Energy Rapid Modular Ensemble of Satellites) is a mission concept based on a swarm of nano-satellites in low Earth orbit, hosting simple but fast scintillators to probe the X-ray emission of bright high-energy transients. The three main scientific objectives of HERMES are: 1) the accurate and prompt localisation of bright hard X-ray/soft gamma-ray transients such as Gamma-Ray Bursts (GRBs). Fast high energy transients are among the likely electromagnetic counterparts of the gravitational wave events (GWE) recently discovered by Advanced LIGO/Virgo, and of the Fast Radio Burst. 2) Open the window of timing down to a fraction of micro-seconds at X-ray energies, and thus investigate for the first time the micro-second structure of GRBs. 3) Test quantum space-time scenarios by measuring the delay time between GRB photons of different energy. A technologic pathfinder has been recently funded by Italian Ministry of University and Research.

SAGE (SagnAc interferometer for Gravitational wavE) is a fast track project for a space observatory based on multiple 12-U CubeSats in geostationary orbit. The objective of this project is to create a Sagnac interferometer with 73 000 km circular arms. The geometry of the interferometer makes it especially sensitive to circularly polarized gravitational waves at frequency close to 1Hz. The nature of the Sagnac measurement makes it almost insensitive to position error, allowing spacecrafts in ballistic trajectory. The light source and recombination units of the interferometer are based on compact fibered technologies, without the need of an optical bench. The main limitation would come from non-gravitational acceleration of the spacecraft. However, conditionally upon our ability to post-process the effect of solar wind, solar pressure and thermal expansion, we would detect gravitational waves with strains down to 10⁻²¹ over a few days of observation.

The Cosmic Origins Spectrograph (COS) has been collecting data since soon after its installation on the Hubble Space Telescope in May 2009. The two-segment microchannel plate-based detector for the FUV channel is subject to gain sag, and eventually a permanent loss of efficiency at the locations where the largest number of counts have fallen. The initial strategy for the use of the detector was to maximize the scientific productivity of the instrument over the five-year design lifetime. This has been accomplished by periodically adjusting the high voltage and moving the spectra to a different location on the detector in order to spread the damage on the detector and thus minimize gain sag. The instrument is now well past this point and performing well, so in late 2016 we began to investigate ways to extend the life of the detector for as long as possible without seriously affecting the scientific performance. As a result of these studies, we adopted a new lifetime extension strategy when the spectra were moved to Lifetime Position 4 (LP4) in October 2017, and placed restrictions on the G130M observing modes that put Lyman-α airglow lines on the detector. Central wavelengths 1300, 1309, 1318, and 1327 are no longer permitted to illuminate Segment B of the detector, and G130M/1291 is permitted on that segment only for FP-POS values 3 and 4 in order to concentrate the damage to the detector. These changes limit the damage from gain sag “holes” due to airglow to only two locations on the detector, rather than the twenty at the previous LPs. In addition, we modified our previous approach of increasing the high voltage or changing LPs before any hole experienced a sensitivity loss of 5%, and will permit the two G130M/1291 holes to become permanently sagged, thus creating a new detector gap. Science programs that require wavelength coverage near the rest-frame Lyman-α region (1216 Å) can be executed at LP3. Observations with other gratings remain unaffected, but the wavelength coverage on Segment B for a single exposure will now include gaps due to the gain sag holes from the G130M/1291 observations. Models of gain loss as a function of exposure suggest that by adopting this strategy and giving up these small regions of the detector, we will be able to use LP4 productively for six or more years, as opposed to the ~2.5 years that was available at previous positions.

The Lunar Ultraviolet Cosmic Imager (LUCI) is an innovative all-spherical mirrors telescope, proposed to fly as a scientific UV imaging payload on a lunar mission in collaboration with Indian Aerospace Company-TeamIndus, Axiom Research Labs Pvt. Ltd. Observations from the Moon provide a unique opportunity to observe the sky from a stable platform far above the Earths atmosphere. LUCI will observe at a fixed elevation angle and will detect stars in the near ultraviolet (200-320 nm) to a limiting magnitude of 12 AB, with a field of view of around 0.5 degrees. The primary science goal is to search for transient sources and flag them for further study. The instrument has been assembled in the class 1000 clean room at the M.G.K Menon Laboratory for Space Sciences. Here we will describe the optomechanical assembly procedures we have carried out during the optical alignment and integration of the payload. Opto-mechanical alignment of the instrument was carried out by using alignment telescope cum autocollimator (for coarse alignment) and ZYGO interferometer (fine alignment). We will also discuss the ground calibration tests performed on the assembled telescope. The results from the ground calibration activities will help in establishing the full calibration matrix of the instrument once operational.

Chromospheric LAyer Spectro-Polarimeter (CLASP2) is our next sounding rocket experiment after the success of Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP1). CLASP2 is scheduled to launch in 2019, and aims to achieve high precision measurements (< 0.1 %) of the linear and circular polarizations in the Mg ii h and k lines near the 280 nm, whose line cores originate in the upper solar chromosphere. The CLASP2 spectro-polarimeter follows very successful design concept of the CLASP1 instrument with the minimal modification. A new grating was fabricated with the same radius of curvature as the CLASP1 grating, but with a different ruling density. This allows us to essentially reuse the CLASP1 mechanical structures and layout of the optics. However, because the observing wavelength of CLASP2 is twice longer than that of CLASP1, a magnifier optical system was newly added in front of the cameras to double the focal length of CLASP2 and to maintain the same wavelength resolution as CLASP1 (0.01 nm). Meanwhile, a careful optical alignment of the spectro-polarimeter is required to reach the 0.01 nm wavelength resolution. Therefore, we established an efficient alignment procedure for the CLASP2 spectro-polarimeter based on an experience of CLASP1. Here, we explain in detail the methods for achieving the optical alignment of the CLASP2 spectro-polarimeter and discuss our results by comparing with the performance requirements.

Astronomical space telescopes to study astrophysical phenomena from the far-ultraviolet (FUV) to the near infrared (NIR) will require mirror coatings with high reflectance over this entire spectral region. While coatings for the optical and NIR part of the spectrum are fairly well developed with proven performance, the FUV presents significant challenges. The U.S. Naval Research Laboratory (NRL) has developed a processing system based on an electron beam-generated plasma that provides for controlled fluorination and/or etching of surfaces with near monolayer precision and minimal changes to surface morphology. In this paper, we report recent results of samples treated in the NRL Large Area Plasma Processing System (LAPPS) where restoration of the high intrinsic reflectance in the FUV spectral range have been observed of aluminum (Al) mirrors protected with a magnesium di-fluoride (MgF2) overcoat. This paper will also extend these studies to other un-protected Al mirrors protected to demonstrate the capability of LAPPS to simultaneously etch the native oxide layer from bare Al and passivate the surface with fluorine, leading to marked enhancements in FUV reflectance. Laboratory test data and optical diagnostic techniques used to verify surface scattering and durability of selected coatings will be presented. Finally, we will discuss the scalability of the LAPPS etching process in order to realize these high-reflectivity coatings on mirror segments as large as those proposed for the Large Ultraviolet, Optical, and Infrared (LUVOIR) astronomical telescope system (1+meter class).

As it is rich in spectral lines emitted by plasma between 10000 K and 20 MK, the vacuum ultraviolet (VUV - 17 to 200 nm) solar spectrum is extremely valuable for instruments that study the physics of the solar atmosphere. We present multilayer coatings with simultaneous broadband reflectance in the two spectral ranges of 16.9 nm to 21.5 nm and 46.3 nm to 127.5 nm. The coatings are based on Mo/Si multilayers with a thin capping layer of boron carbide (B₄C). Samples were produced and their reflectance measured. Their performance in terms of resistance to high temperatures and low micro-roughness was also assessed by measurement. Our study shows that a coating with the characteristics required by next generation spectrometers for studies of the solar atmosphere is feasible.

Europa-UVS plans to characterize the Europan exosphere by performing solar occultation measurements at key points during the Europa Clipper mission. Observing the Sun from Jovian space requires a system with high dynamic range. The high end of the dynamic range of the Europa-UVS MCP-XDL detector is limited by dead time effects and is rated at ~ 300 kHz, corresponding to a <1.2 μs dead time requirement. The global count rate is estimated to exceed this upper limit by a factor of two during solar occultation measurements, due to the dramatic increase in solar photon flux towards the high end (> 150 nm) of the Europa-UVS bandpass (55-210 nm). To reduce the input photon flux in the Europa-UVS optical train, we propose applying a thin MgF₂ overcoat on the heritage bare gold solar port mirror adopted from the New Horizons Alice solar occultation channel and the JUICE-UVS solar port. The MgF₂ layer, with the distinct advantage as the standard coating on the other heritage optics for Europa-UVS, suppresses the reflectance of the solar port mirror, especially above 140 nm, compensating the solar photon flux increase. The decrease in reflectance has been modeled using Fresnel reflectance theory and verified experimentally by comparing reflectance of Au and MgF₂-Au mirrors. With the implementation of the MgF₂ layer together with a reduction in the solar port aperture size, we predict global count rates that are well-matched to the 300 kHz threshold of the Europa-UVS detector.

“Chromospheric LAyer Spectro-Polarimeter (CLASP2)” is the next sounding rocket experiment of the “Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP)” that succeeded in observing for the first time the linear polarization spectra in the hydrogen Lyman-α line (121.6 nm) and is scheduled to be launched in 2019. In CLASP2, we will carry out full Stokes-vector spectropolarimetric observations in the Mg ii h and k lines near 280 nm with the spectro-polarimeter (SP), while imaging observations in the Lyman-α line will be conducted with the slitjaw optics (SJ). For the wavelength selection of CLASP2, the primary mirror of the telescope uses a new dual-band pass cold mirror coating targeting both at 121.6 nm and 280 nm. Therefore, we have to perform again the alignment of the telescope after the installation of the recoated primary mirror. Before unmounting the primary mirror from the telescope structure, we measured the wave-front error (WFE) of the telescope. The measured WFE map was consistent with what we had before the CLASP flight, clearly indicating that the telescope alignment has been maintained even after the flight. After the re-coated primary mirror was installed the WFE was measured, and coma aberration was found to be larger. Finally, the secondary mirror shim adjustments were carried out based on the WFE measurements. In CLASP2 telescope, we improved a fitting method of WFE map (applying 8th terms circular Zernike polynomial fitting instead of 37th terms circular Zernike fitting) and the improved method enables to achieve better performance than CLASP telescope. Indeed, WFE map obtained after the final shim adjustment indicated that the required specification (< 5.5 μm RMS spot radius) that is more stringent than CLASP telescope was met.

The Juno mission is a NASA New Frontiers mission, orbiting Jupiter since 4 July 2016 and placed on a 53-day period, highly elliptical, polar orbit. The Ultraviolet Spectrograph onboard Juno (Juno-UVS) is a photoncounting imaging spectrograph, designed to cover the 68-210 nm spectral range.¹ This range includes the H₂ bands and the Lyman series produced in Jupiter’s far-ultraviolet (FUV) auroras. The purpose of Juno-UVS is to study Jupiter’s auroras from the unique vantage point above both poles allowed by Juno’s orbit, and to provide a wider auroral context for the in-situ particle and field instruments on Juno. Because of the 2 rpm spin of Juno, UVS nominally observes 7.5°x360° swaths of the sky during each spin of the spacecraft. The spatial resolutions along the slit and across the slit, i.e. in the spin direction, are respectively 0.16° and 0.2° , while the filled-slit spectral resolution is ∼1.3 nm.² UVS borrows heavily from previous instruments led by Southwest Research Institute (New-Horizons and Rosetta Alices, LRO-LAMP), major improvements are: (i) an extensive radiation shielding; (ii) a scan mirror which allows targeting specific auroral features; and (iii) an improved cross-delay line readout scheme of the microchannel plate (MCP) detector. The ability offered by the scan mirror combined with Juno’s spin allows UVS access to half of the sky during every spacecraft rotation. This pointing flexibility, combined with the changing spin-axis of the spacecraft since launch, has allowed UVS to map 99 % of the sky in the 68-210 nm range. This paper describes the substantial number of spectra that have been used to monitor the health of the instrument over the course of the mission. More than 5800 spectra of mainly O, A, and B spectral-type stars in the V-magnitude range of ∼0-7 have been extracted to date. Selected stars among this list are used to calibrate the UVS instrument. This paper describes how previous spectral databases from the International Ultraviolet Explorer have been refined and adapted for UVS’ calibration purposes, in combination with observations from the Hubble Space Telescope. The retrieved effective area of the instrument peaks around 0.28 at ∼125 nm, with uncertainties lower than 10%.

The Colorado Ultraviolet Transit Experiment (CUTE) is a 6U NASA CubeSat carrying a low-resolution (R ≈ 3000), near-ultraviolet (255 – 330 nm) spectrograph fed by a rectangular primary Cassegrain. CUTE, is planned for launch in spring 2020 and it will monitor transiting extra-solar planets to study atmospheric escape. We present here the CUTE data simulator, which is a versatile tool easily adaptable to any other mission performing singleslit spectroscopy and carrying on-board a CCD detector. We complemented the data simulator with a data reduction pipeline capable of performing a rough reduction of the simulated data. This pipeline will then be updated once the final CUTE data reduction pipeline will be fully developed. We further briefly discuss our plans for the development of a CUTE data reduction pipeline. The data simulator will be used to inform the target selection, improve the preliminary signal-to-noise calculator, test the impact on the data of deviations from the nominal instrument characteristics, identify the best spacecraft orientation for the observation of each target and construct synthetic data to train the science team in the data analysis prior to launch.

Reflectometry is one of the widely used method to study rough optical surfaces. Here we present results of first measurement of mirror samples of T-170M Primary Mirror. These measurements were made by using compact HOROS-S instrument for 3D Bidirectional reflectance distribution function (BRDF) determination constructed by Jena Fraunhofer Institute of Applied Optics.

Two instruments aboard the Solar Orbiter mission, the Extreme Ultraviolet Imager and the Metis coronagraph, are using cameras of similar design to obtain images in the Lyman alpha line of hydrogen at 121.6 nm. Each of these cameras is based on an APS sensor used as readout of a single microchannel plate intensifier unit whose output current is converted into visible light photons through a phosphor screen. Before integration on the respective instruments, both detector’s flight models have been characterized and calibrated. In this paper, we describe the two camera systems, the results of qualification tests, and report their performance characteristics.

The WSO-UV project is an efficient multipurpose orbital observatory for high sensitivity imaging. The imaging instrument Field Camera Unit (FCU) onboard WSO-UV will be the first UV camera to be flown to a geosynchronous orbit. The observatory is planned to operate for at least five years and perhaps longer. WSO-UV will open new opportunities in planetary science, stellar astrophysics, extragalactic astronomy and cosmology. This paper provides an information on updated FCU instrument.

The European Space Agency’s (ESA’s) Rosetta mission to comet 67P/Churyumov-Gerasimenko, launched 2004, carried the first in the Southwest Research Institute’s (SwRI’s) Alice series of ultraviolet imaging spectrographs. Subsequent iterations of the instrument are currently operational on NASA’s New Horizons, Lunar Reconnaissance Orbiter (LRO) and Juno missions, launched 2006, 2009 and 2011, respectively, and two further versions of the spectrograph are in development at SwRI for flight on ESA’s JUICE mission to the Jovian system (Phase C) and NASA’s Europa Clipper mission (Phase B). While the basic optical design is similar for all versions of the instrument, developments in microchannel plate (MCP) detector and electronics technology have enhanced the scientific return of the more recent Alice spectrographs, with some corresponding increase in the mass and power of the system. Here, we describe a reevaluation of the Rosetta-Alice (R-Alice) instrument design based on updated technology, lessons learned from subsequent Alice-type instrument development, and a “wish list” of suggested improvements in instrument performance provided by the R-Alice Science Team. The resulting instrument design, which we designate R-Alice II, would form the baseline concept for an ultraviolet instrument proposed by the SwRI UVS/Alice team for future Rosetta-type missions.

This paper summarizes our current instrument prototyping efforts of miniature near-UV imaging spectro-polarimeters to probe the thermodynamics and magnetism of the solar Chromosphere and Transition Region. This includes our high altitude balloon piggyback instruments DIMS-RADIANCE and DIMS-STOUT, which are scheduled to fly in 2018. These payloads are CubeSat sized instruments designed around commercial off-the-shelf miniaturized spectrographs. Additionally we detail a new optical concept and proposed CubeSat mission called SolarCube. This instrument will be capable of “snapshot polarimetry” with simultaneous 2D imaging, spectroscopy, and linear polarization without mechanisms or scanning. This concept utilizes an integral field unit, diffraction grating, and unique polarization sensitive detector. The design, capabilities, current prototyping efforts, and future plans are discussed. The design goal is to observe the spatially resolved polarization signature of the Mg II h-k doublet at 280nm over the full solar disk.

The Cosmic Evolution Through UV Spectroscopy (CETUS) concept^1-3 enables parallel observations by the UV multiobject spectrometer (MOS) and near-UV/far-UV camera which operate simultaneously but independently with their separate field of views. The near-UV MOS can target up to 100 objects at a time without confusion with nearby sources or background zodiacal light. This multiplexing will allow over 100,000 galaxies to be observed over a typical mission lifetime. The MOS includes a next-generation micro-shutter array (NGMSA), an efficient aspheric Offner-like spectrometer design with a convex grating, and nanotube light traps for suppressing unwanted wavelengths. The NUV/FUV Camera has the capability to image in a range of sub-bands from 115-400 nm at the same time the MOS is operating at 180-350 nm. The UV camera has a similar Offner-like relay, selectable filters, and two separate detectors to optimize observing in either the far-UV (115-175 nm) or the near-UV (180-400 nm) utilizing a CsI Micro-Channel Plate detector (MCP) and a CCD respectively.

The Juno Ultraviolet Spectrograph (Juno-UVS) is a remote-sensing science instrument onboard the Juno spacecraft that has been in polar orbit around Jupiter since July 2016. Juno-UVS measures photon events in the ultraviolet from about 68 to 210 nm. It is primarily used to observe emission from the Jovian aurorae, but is also sensitive to other sources such as UV-bright stars, sky background Lyman-alpha emission, and reflected sunlight. However, Juno-UVS is also sensitive to the effects of penetrating high-energy radiation, which results in elevated count rates as measured by the instrument detector array. This radiation presents a challenge for efficiently planning the acquisition of mission science data, as data volume is a valuable (and finite) resource that can quickly be filled when the spacecraft periodically passes through regions of high radiation. This background radiation has been found to vary significantly on both short (spacecraft spin-modulated) time scales, as well as longer timescales from minutes to hours during each close approach to Jupiter. This variability has required a multi-pronged approach in the operation planning of hardware (such as dynamic instrument voltage adjustment) as well as onboard software (such as utilizing data quality factors for the selective storage of science data). We present an overview of these current mitigation/optimization techniques and planning strategies used for this instrument, which will likely also be useful for the development and operations of future instruments within high radiation space environments (e.g., the ESA JUICE mission or NASA’s Europa Clipper).

POLLUX is a high-resolution, UV spectropolarimeter proposed for the 15-meter primary mirror option of LUVOIR1 . The instrument Phase 0 study is supported by the French Space Agency (CNES) and performed by a consortium of European scientists. POLLUX has been designed to deliver high-resolution spectroscopy (R ≥ 120,000) over a broad spectral range (90-390 nm). Its unique spectropolarimetric capabilities will open-up a vast new parameter space, in particular in the unexplored UV domain and in a regime where high-resolution observations with current facilities in the visible domain are severely photon starved. POLLUX will address a range of questions at the core of the LUVOIR Science portfolio. The combination of high resolution and broad coverage of the UV bandpass will resolve narrow UV emission and absorption lines originating in diffuse media, thus permitting the study of the baryon cycle over cosmic time: from galaxies forming stars out of interstellar gas and grains, and stars forming planets, to the various forms of feedback into the interstellar and intergalactic medium (ISM and IGM), and active galactic nuclei (AGN). UV circular and linear polarimetry will reveal the magnetic fields for a wide variety of objects for the first time, from AGN outflows to a diverse range of stars, stellar explosions (both supernovae and their remnants), the ISM and IGM. It will enable detection of polarized light reflected from exoplanets (or their circumplanetary material and moons), characterization of the magnetospheres of stars and planets (and their interactions), and measurements of the influence of magnetic fields at the (inter)galactic scale. In this paper, we outline the key science cases of POLLUX, together with its high-level technical requirements. The instrument design, its estimated performances, and the required technology development are presented in a separated proceeding² .

The importance of high performance interference bandpass filters in the UV is growing recently. For the CETUS project a set of bandpass filters with a clear aperture of 70 mm is required centered at the wavelengths 215.5 nm / 256.5 nm / 297.5 nm / 338.5 nm / 379.5 nm with a FWHM of 41 nm and blocked as good as possible up to 1100 nm. We present a design study based on all-dielectric hard sputtered coatings on colorglass substrates for the wavelengths 297.5 nm / 338.5 nm / 379.5 nm. The colorglass substrates where chosen to suppress ghost images by reflection on the exit face and to improve the blocking in the required range. For the wavelengths 215.5 nm and 256.5 nm a conventionally evaporated design of metal-dielectric Fabry-Perot stacks was chosen on fused silica substrates. We comment on how system requirements are leading to filter specifications and show theoretical spectra of the chosen filter designs.

The Pesit/IIA Observatory for the Night Sky(PIONS) is a near UV imaging telescope to be flown on a small satellite. The instrument is a 150mm RC telescope that covers a wavelength range of 180-280 nm. We are using an intensified CMOS detector with a solar blind photocathode, to be operated in photon counting mode. The telescope has a wide field of view of 3 degrees and an angular resolution of 13”. We plan to point the telescope to scan the sky continuously along the sun pointing axis to look for variable UV sources such as flare stars, AGNs, and other transient events. We can detect objects as faint as 21 magnitude and perform their photometric analysis. Since the aperture and the effective area of the telescope are comparatively small, it can be pointed to relatively brighter parts of the UV sky which were not accessible to larger mission due to detector limitations.

The World Space Observatory, Ultraviolet (WSO-UV), is a Russian-Spanish space mission born as a response to the growing up demand for UV facilities by the astronomical community. It is the only 2-meter class on-orbit telescope in the after-HST epoch fully devoted to UV observations in the spectral domain of 115-310 nm. This paper provides an information on instrumentation status in 2018 and on the forthcoming Call for the Core Program application.

Microchannel plate sensors are widely used as photon counting imagers in many applications, including, astronomy, high energy physics, and remote sensing. Potential future NASA observatories with ultraviolet instruments, such as LUVOIR and HABEX, will require large area detectors (8k × 8k pixels) with large dynamic range (≥1 kHz/resel), high quantum efficiency (75% peak), and very low backgrounds (≤0.1 cts/sec/cm² ). New microchannel plate technology combining borosilicate glass microcapillary arrays with high efficiency materials applied by atomic layer deposition are being developed with these goals in mind. Detectors with these microchannel plates can be made in large formats (up to 400 cm² ) with focal plane matching, have high spatial resolution (<20μm), are radiation hard, and have very low background rates (<0.05 events/sec/cm² ) with no readout noise. Typical sensors make use of high efficiency photocathodes in open faced detectors (< 110 nm range) or in ultra-high vacuum sealed tube devices (>110 nm range). New photocathodes, such as GaN and hybrid bialkali/alkali halide, have high quantum efficiencies over broadband wavelengths. Cross-strip anodes are well suited for large format detectors with high spatial resolution and high dynamic range requirements. Improvements to detector anodes and readout electronics have resulted in better spatial resolution (10×), output event rate (100×), and temporal resolution (1000×), all the while operating at lower gain (10×). Combining these developments can have a significant impact to potential future NASA sub-orbital and satellite instruments.

The construction of the BEaTriX (Beam Expander Testing X-ray) facility is ongoing at INAF/Osservatorio astronomico di Brera. The facility will generate a broad (170 x 60 mm² ), uniform and low-divergent (1.5 arcsec HEW) X-ray beam within a small lab (∼ 9 x 18 m² ), using an X-ray microfocus source, a paraboloidal mirror, a monochromation system based on a combination of symmetrically cut and asymmetrically-cut crystals in Bragg diffraction configuration. Once completed, BEaTriX can be used to test the Silicon Pore Optics modules of the ATHENA X-ray observatory, as well as other optics, like the ones of the Arcus mission. The facility is designed to operate at 1.49 keV and 4.51 keV, by using two fixed beam lines, equipped with the necessary optical elements. The first beam line to be completed will be at 4.51 keV and will prove the BEaTriX concept. Silicon crystals are used at this energy and four symmetric diffractions, with appropriate tilt of some crystals, will provide the spectral filtering at the required level to return the desired divergence. Owing to the quite short range necessary to obtain a parallel beam with this setup, a low vacuum level (10-3 mbar) can be used without a significant beam extinction. In addition to a modular vacuum approach, the low vacuum will allow us to reduce the time required to evacuate the tank, thus enabling to demonstrate a test rate that will match the ATHENA SPO production of 3 MM/day. In this paper, we report the design of the facility and the construction progress.

Given the unprecedented effective area, the new ATHENA Silicon Pore Optics (SPO) focusing technology, the dynamic and variable L2 environment, where no X-ray mission has flown up to date, a dedicated Geant4 simulation campaign is needed to evaluate the impact of low energy protons scattering on the ATHENA mirror surface and the induced residual background level on its X-ray detectors. The Geant4 mass model of ATHENA SPO is built as part of the ESA AREMBES project activities using the BoGEMMS framework. An SPO mirror module row is the atomic unit of the mass model, allowing the simulation of the full structure by means of 20 independent runs, one for each row. No reflecting coating is applied in the model: this simplification implies small differences (few percentages) in the proton flux, while reducing the number of volumes composing the mass model and the consequent simulation processing time. Thanks to the BoGEMMS configuration files, both single pores, mirror modules or the entire SPO row can be built with the same Geant4 geometry. The conical approximation used for the Si plates transmits 20% less photons than the actual SPO design, simulated with a ray-tracing code. Assuming the same transmission reduction for protons, a 20% uncertainty can be accepted given the overall uncertainties of the input fluxes. Both Remizovich, in its elastic approximation, and Coulomb single scattering Geant4 models are used in the interaction of mono-energetic proton beams with a single SPO pore. The scattering efficiency for the first model is almost twice the efficiency obtained with the latter but for both cases we obtain similar polar and azimuthal angular distributions, with about 70-75% of scatterings generated by single or double reflections. The soft proton flux modelled for the plasma sheet region is used as input for the simulation of soft proton funneling by the full SPO mass model. A much weaker soft proton vignetting than the one observed by XMM-Newton EPIC detectors is generated by ATHENA mirrors. The residual soft proton flux reaching the focal plane, defined as a 15 cm radius, is 10⁴ times lower than the input L2 soft proton population entering the mirror, at the same energy, with rates comparable or higher than the ones observed in XMM EPIC-pn most intense soft proton flares.

We present the expected coating performance based on design and simulations, tested coating performance evaluated by means of X-ray reflectometry and short and long term stability of several materials considered as coating options for the X-ray mirrors of the ATHENA mission. As part of this study we also report on the compatibility of the X-ray reflecting coatings to the industrial processes involved in the assembly of mirror modules using Silicon Pore Optics technology.

Silicon Pore Optics (SPO) provide high angular resolution with low effective area density as required for the Advanced Telescope for High Energy Astrophysics (Athena). The x-ray telescope consists of several hundreds of SPO mirror modules mounted in a telescope structure. During the development of the SPO technology, specific requirements of a future mass production have been considered right from the beginning. We present an updated analysis of the time and resources required for the Athena flight programme. A preliminary timeline for building and commissioning the required infrastructure, and for flight model production and integration of the mirror modules, is presented.

The ATHENA (Advanced Telescope for High Energy Astrophysics) X-ray observatory is an ESA-selected L2 class mission. In the proposed configuration, the optical assembly has a diameter of 2.2 m with an effective area of 1.4 m² at 1 keV, 0.25 m² at 6 keV, and requires an angular resolution of 5 arcsec. To meet the requirements of effective area and angular resolution, the technology of Silicon Pore Optics (SPO) was selected for the optics implementation. The ATHENA’s optic assembly requires hundreds of SPOs mirror modules (MMs), obtained by stacking wedged and ribbed silicon wafer plates onto silicon mandrels to form the Wolter-I configuration. Different factors can contribute to limit the imaging performances of SPOs, such as i) diffraction through the pore apertures, ii) plate deformations due to fabrication errors and surface roughness, iii) alignment errors among plates in an MM, and iv) co-focality errors within the MMs assembly. In order to determine the fabrication and assembling tolerances, the impact of these contributions needs to be assessed prior to manufacturing. A set of simulation tools responding to this need was developed in the framework of the ESA-financed projects SIMPOSIuM and ASPHEA. In this paper, we present the performance simulation obtained for the recentlyproposed ATHENA configuration in terms of effective area, and we provide a simulation of the diffractive effects in a pair of SPO MMs. Finally, we present an updated sizing of magnetic diverter (a Halbach array) and the magnetic fields levels that can be reached in order to deviate the most energetic protons out of the detector field.

We describe recent advances in backside passivation of large-format charge-coupled devices (CCDs) fabricated on 200- mm diameter wafers. These CCDs utilize direct oxide bonding and molecular-beam epitaxial (MBE) growth to enable high quantum efficiency in the ultraviolet (UV) and soft X-ray bands. In particular, the development of low-temperature MBE growth techniques and oxide bonding processes, which can withstand MBE processing, are described. Several highperformance large-format CCD designs were successfully back-illuminated using the presented process and excellent quantum efficiency (QE) and dark current are measured on these devices. Reflection-limited QE is measured from 200 nm to 800 nm, and dark current of less than 1e- /pixel/sec is measured at 40°C for a 9.5 μm pixel.

We fabricated X-ray mirrors from carbon-fiber-reinforced-plastic (CFRP) with a tightly nested design for X-ray satellites. The mirror shape is Wolter type-I quadrant shell geometry with a diameter of 200 mm and a focal length of 12 m. The mirror substrates were successfully formed with a rms error of about 1 μm. Through a replication process, a smooth surface was obtained on the CFRP substrate. We are developing a positioning method of thin mirrors in a telescope housing. It is found that a piezo-linear motor is very useful to adjust the mirror position with accuracy of sub μm. The CFRP mirrors were evaluated by using 20 keV X-ray pencil beam at BL20B2 in SPring-8 synchrotron radiation facility. The HPD of the mirrors was estimated to be about 2.3 arc-minutes. The spread of X-ray image would be caused by small waviness on the mirror surface after replication.

McXtrace is a general, highly modular, X-ray tracing open source software package for simulating X-ray optics. While initially intended for simulating synchrotron beamlines, it has recently found use in astrophysics. Here it is being used to evaluate the projected performance of X-ray telescope designs. We present the software add-on toolbox ”AstroX” to McXtrace containing all of the common optical elements found in satellite based X-ray telescopes. In addition, the toolbox contains detector and source models relevant for astronomical applications. As an added benefit, users may exploit the heritage of McXtrace and use its beamline elements, to simulate characterization measurements of optical elements. McXtrace AstroX allows for simulation of X-rays telescopes based on different optical concepts such as nested mirror shells and Silicon Pore Optics technology. In this study we present examples of McXtrace AstroX use for ATHENA-, and NuSTAR-like telescope concepts.

The progress of X-ray Optics joint research activity of the European Union Horizon 2020 AHEAD project is presented here covering the X-ray optic technologies that are currently being worked on in Europe. These are the Kirkpatrick Baez, lobster eye micropore (SVOM, SMILE), slumped glass, and silicon pore (ATHENA, ARCUS) optics technologies. In this activity detailed comparisons of the measurements, of the different optics produced by the participating optics groups, obtained mainly at the MPEs PANTER X-ray test facility, are compared with simulations. In preparation for the ATHENA mission a study has been made to design the BEaTRiX X-ray test facility for testing individual silicon pore optics mirror modules, and the realization of the facility is now on going. A zone plate collimating optics developed for PANTER is being studied, optimized, and tested at PANTER. This zone plate will be used for characterising a high quality optics module in a parallel beam to verify the BEaTriX performance. Several of the measurements and selected results are presented here.

The Off-plane Grating Rocket Experiment (OGRE) is a soft X-ray spectroscopy suborbital rocket payload scheduled for launch in Q3 2020 from Wallops Flight Facility. The payload will serve as a testbed for several key technologies which can help achieve the desired performance increases for the next generation of X-ray spectrographs and other space-based missions: monocrystalline silicon X-ray mirrors developed at NASA Goddard Space Flight Center, reflection gratings manufactured at The Pennsylvania State University, and electron-multiplying CCDs developed by the Open University and XCAM Ltd. With these three technologies, OGRE hopes to obtain the highest-resolution on-sky soft X-ray spectrum to date. We discuss the optical design of the OGRE payload.

Performance of X-ray reflectors affects that of X-ray mirrors. Modern X-ray mirrors have thousands of reflectors to gain large effective area. Evaluation of the reflectors is an important process in production of the mirrors. A diffraction pattern dominates reflector image when the parallel optical beam illuminates the reflector along its optical axis because the reflectors are used at grazing incident angles of around 1 deg and their effective width are 1–10 mm. A diffraction pattern from the entire reflector surface can be acquired at once with the aid of a lens. The diffraction pattern holds information of the surface profiles of the reflectors. To quantitatively evaluate the reflectors with the diffraction pattern, we created a diffraction pattern model by the wave optics with the ideal surface profile and fitted it to data. As a result, a correlation between fitting residual and the normal vector distribution of the surface profile was found. With our method, the reflectors can be evaluated and sorted out more efficiently.

Thin film coated mirrors enable pioneering observations of X-rays and soft gamma rays. The performance of the reflective mirrors is key in expanding knowledge of the hot and energetic Universe. A critical part of maturing the optics technology is firstly, to establish a smooth surface and interface of the selected materials and, secondly, to obtain an in-depth understanding of the contamination in the thin films and ultimately, to ensure long-term stability. The aim of this study is to investigate the chemical composition, roughness and stability of boron carbide and iridium thin films and the effects of nitrogen incorporation.

The X-ray imaging with Micro-Pore Optic (MPO) plates can provide huge field of view with light mass, which will be applied for the Wide-field X-ray telescope (WXT), one of the two payloads onboard China’s Einstein Probe (EP) mission. Since each MPO plate has millions of micro square pores with width of 20 μm which actually behave as honeycomb materials, the mechanical properties of the MPO plates will be much more complex than normal optical glass as homogeneous material. This work estimated the mechanical properties of MPO plates, provided an equivalent mechanical properties as homogeneous material to greatly simplify the Finite-Element Analysis (FEA). Three basic material properties of MPO plates - relative density, effective elastic stiffness (Young’s module) and the effective Poisson’s ratio are estimated and preliminary validated with FEA simulations.

Recent advances in the fabrication of silicon mirrors and their alignment and integration methods make it possible to build large-area, lightweight, high-resolution x-ray telescopes with arc-second angular resolution. Such a telescope, having simultaneously arc-second resolution and large (> 1 m² ) collecting area, has never been built before and it will revolutionize high energy astronomy. For such optics, the challenges are twofold: fabrication of high quality mirror segments and precise integration of thousands of these mirrors to a common sharp focus. In this paper, we address the technology for the mirror integration carried out at Goddard Space Flight Center and report the recent result of making such high-resolution optics. We address the crucial technology components: positioning a mirror, measuring its focus, adjusting its mount pointsto optimize the focus, bonding the mirror, and co-alignment of mirrors. We also present the latest x-ray test results that demonstrate the efficacy of such methods and address areas for further improvement. Presently, mirrors built this way have a resolution of 2²-3² HPD (half-ower diameter).

We present the development of the reflective coating by magnetron sputtering deposition onto precisely-fabricated thin X-ray mirrors. Our goal is to remove distortion induced by the coating and then keep their surface profiles. We first addressed the uniform coating to minimize the distortion by introducing a mask to control the spatial distribution of the coating thickness. The uniformity was finally achieved within ±1%. We next tried a platinum single-layer coating on a glass substrate with a dimension of 200 mm × 125 mm. The distortion caused by the frontside coating with a thickness of 320 Å was found to be at most ∼ 1 μm, smaller than the previous results obtained from the non-uniform coating. We then carried out the platinum coating with the same amount of the thickness on the backside surface of the glass substrate. The surface profile of the glass substrate was fully recovered, indicating that the residual stress was successfully balanced by the backside coating. Furthermore, we tried to an iridium single-layer coating with a thickness of 150 Åon the silicon mirrors. The frontside coating caused the degradation of the imaging quality by 7.5 arcsec in half-power width. However, the backside coating with the same amount of the thickness reduced this degradation to be 3.4 arcsec. Finally, an additional backside coating with a thickness of 100 Å and the annealing to relax the residual stress were found to eliminate the distortion completely; the final degradation of the imaging quality was only 0.4 arcsec.

Segmented X-ray telescope mirrors fabricated from thin silicon substrates are being developed by a group at the NASA Goddard Space Flight Center for future generation telescopes such as the Lynx mission concept. The Goddard team has demonstrated high precision silicon mirrors with high angular resolution (~1’’) manufactured by a simple, low cost process. However, the required high-Z optical coatings on mirror front surfaces are difficult to deposit without significant compressive thin film stress, which threatens to distort mirrors and negate the benefits of the high quality substrates. Coating stress reduction methods have been investigated by several groups, but none to date have reported success on real mirrors to the required tolerances. In this paper, we report a new method for correcting mirrors with stress-induced distortion which utilizes a micro-patterned silicon oxide layer on the mirror’s back side. Due to the excellent lithographic precision of the patterning process, we demonstrate stress compensation control to a precision of ~0.3%. The proposed process is simple and inexpensive due to the relatively large pattern features on the photomask. The correction process has been tested on flat silicon wafers with 30 nm-thick chrome coatings under compressive stress and achieved surface slope improvements of a factor of ~80. We have also successfully compensated two iridium-coated silicon mirrors provided by the Goddard group. The RMS slope errors on coated mirrors after compensation were only degraded by ~0.06 arc-seconds RMS axial slope compared to the initial uncoated state.

Recently, the X-ray optics community has been developing technology for high angular resolution, large collecting area X-ray telescopes such as the Lynx mission concept. To meet the high collecting area requirements of such telescope concepts, research is being conducted on thin, segmented optics. The precision mounting posts that fixture and align segmented optics must be the correct length to sub-micron accuracy to satisfy the angular resolution goals of such a concept. Mirror distortion caused by adhesive shrinkage at mount points on the mirror surface also needs to be controlled to micron-radian tolerances. We report on two solutions to these problems. Set-and-forget adjustable length optical mounting posts have been developed to control mirror spacer length. The actuator consists of a metal cylinder with a cylindrical neck cut halfway along the length. To change the length of this actuator, an axial force is applied and the neck is momentarily heated to the plastic deformation temperature via resistive heating. All of the plastic deformation that occurs becomes permanent after cooling. Both compression and expansion of these actuators has been demonstrated in steps ranging from 6 nm to several microns. This paper will describe an experimental setup, show, and discuss data. Additionally, a stress relief technique to reduce mirror distortion caused by shrinkage of the adhesive bond to the actuator is proposed and demonstrated by modelling.

The eXTP (enhanced X-ray Timing and Polarimetry) mission is a major project of the Chinese Academy of Sciences (CAS) and China National Space Administration (CNSA) currently performing an extended phase A study and proposed for a launch by 2025 in a low-earth orbit. The eXTP scientific payload envisages a suite of instruments (Spectroscopy Focusing Array, Polarimetry Focusing Array, Large Area Detector and Wide Field Monitor) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. A large European consortium is contributing to the eXTP study and it is expected to provide key hardware elements, including a Wide Field Monitor (WFM). The WFM instrument for eXTP is based on the design originally proposed for the LOFT mission within the ESA context. The eXTP/WFM envisages a wide field X-ray monitor system in the 2-50 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors. The WFM will consist of 3 pairs of coded mask cameras with a total combined Field of View (FoV) of 90×180 degrees at zero response and a source localization accuracy of ~1 arcmin. In this paper we provide an overview of the WFM instrument design, including new elements with respect to the earlier LOFT configuration, and anticipated performance.

The large Halo orbit in L2 of the ATHENA mission will expose the spacecraft (SC) to a significant flux of charged particles which is expected to overlap with the energy range of the instruments. This is a source of measurement background that needs to be minimized as much as possible to achieve the strict requirements of the mission. The need to know and mitigate this type of background has been identified as critical, and has led to a number of technology development activities which are progressing in parallel to the Phase A activities. Particularly, this paper details the status of the on-going activities to develop a set of charged particle diverters whose goal is to reduce the background generated by soft-protons which are focused by the Silicon Pore Optics (SPO) mirror modules towards the instrument detectors. This paper explains the considerations leading to an accommodation of the charged particle diverters close to the instruments in the Science Instrument Module (SIM), and details the analytical approach followed to choose the massoptimal location for the case of a uniform magnetic field Halbach design. The case of graded (non-uniform) magnetic fields is also explained in an effort to further decrease the mass. Preliminary magnetic field maps are presented as a proxy to compare the mass from different options. Finally, the first engineering models, manufacturing and test plans are presented which are the focus of a technology development activity aiming at the validation of the technologies involved up to TRL5.