We measured the reflectivity of an Athena silicon pore optics sample coated with 10-nm thick iridium near the iridium L-edges (L₃ , L₂, and L₁) in a step of 1.5 eV. The derived atomic scattering factor f₂ was similar to a shape of the absorption coefficient μ near L₃ and L₂ obtained by previous x-ray absorption spectroscopy (XAS) measurements. The fine structures of f₂ of L₃ and L₂ can be represented by a strong sharp line referred to as a white line (WL) and two weak lines at center energies of ∼17 and ∼31 eV from each edge energy. The branching ratio (L₃ / L₂) of the WL is >2, which reflects the initial core-electron states available for the L₂ (2p_1/2) and L₃ (2p_3/2) processes, and the ratio remains high to the energy of +7 . 5 eV from WL. The fine structure seen in L₁ also has two weak lines, which were seen in XAS at L₁-edge. Our measurements near L₃, L₂, and L₁ edges demonstrated a different technique to provide atomic structural information as XAS. The ground calibration to measure fine structures near the edges may potentially be simplified using f₂ estimated based on μ.

The design of space missions faces resource limitations that may severely restrict the extent of ground-based calibration programs. Ensuring that the knowledge requirements on key scientific performance are commensurate to the scientific goals of a mission is therefore crucial. In this paper, we describe a method to verify the adequacy of the X-ray effective area calibration requirements and apply it to the mirrors of Athena, the next large-class X-ray observatory of the European Space Agency. It is based on a Monte Carlo algorithm producing a set of energy-dependent mirror effective areas, which describe the limitations in our knowledge of the true performance as embedded in the calibration requirements. Applying this method to a number of simplified astrophysical scenarios related to the “hot and energetic” science themes of Athena, we conclude that the current calibration requirements of the mirror effective area are commensurate to the driving scientific requirements. Our results also stress the need to fulfill, or possibly to exceed the calibration requirements on the relative effective area to ensure fidelity in the reconstruction of X-ray, broad-band spectral features, e.g., those expected from the reflection by relativistic accretion disks around accreting black holes.

The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is designed to identify and characterize gamma rays from extreme explosions and accelerators. The main science themes include supermassive black holes and their connections to neutrinos and cosmic rays; binary neutron star mergers and the relativistic jets they produce; cosmic ray particle acceleration sources including galactic supernovae; continuous monitoring of other astrophysical events and sources over the full sky in this important energy range. AMEGO-X will probe the medium energy gamma-ray band using a single instrument with sensitivity up to an order of magnitude greater than previous telescopes in the energy range 100 keV to 1 GeV that can be only realized in space. During its 3-year baseline mission, AMEGO-X will observe nearly the entire sky every two orbits, building up a sensitive all-sky map of gamma-ray sources and emissions. AMEGO-X was submitted in the recent 2021 NASA MIDEX announcement of opportunity.

The visible emission line coronagraph (VELC) on board the Aditya-L1 mission is an internally occulted reflective coronagraph. It is capable of simultaneous observations of the solar corona in imaging, spectroscopic, and spectropolarimetric modes very close to the solar limb, to 1.05 R _⊙ (R _⊙ – solar radius). Primary mirror (M1) of the VELC receives the light from both the solar disk and the corona up to 3 R _⊙ . In the VELC, occultation happens at the focus of the M1. Secondary mirror (M2) with a central hole size equal to 1.05 R _⊙ is mounted at the focal plane of M1 and serves the purpose of an internal occulter. To meet the proposed science goals of the payload, M1 surface should be super polished with good imaging characteristics. This results in stringent requirements of the surface figure and microroughness on the mirror surface. M1 is an off-axis parabola, so achieving the demanding requirements is quite challenging. At the same time, testing of M1 after development is crucial for evaluating its performance. This paper provides the details of the optical metrology tests carried out on M1 along with the results obtained and their implications on the performance of the VELC.

We present a design for an active telescope for space astronomy. The telescope is capable of both exoplanet work and general astronomy over wavelengths from ∼100 nm up to 5 μm. The primary mirror is 6 m in diameter, formed by 16 mirror segments that are precisely phased and supported on rigid body actuators and with segment optical surface figures fine-tuned using surface figure actuators. The active primary forms a large deformable mirror (DM) with wavefront error (WFE) correction at the entrance pupil. Thus the largest source of WFE can be removed at the source and is corrected over the entire field of view. This enables diffraction-limited performance at 400 nm and a more efficient optical system over a broader wavelength range than could be achieved by a small DM at a downstream relayed pupil. The telescope is passively cooled to below 100 K at Sun–Earth L2, enabling astronomical-background-limited observations out to 5 μm. Launched on a SpaceX Starship or alternatively National Aeronautics and Space Administration’s Space Launch System, the telescope requires minimal deployments. A 72-m-diameter starshade provides a contrast ratio better than 10 ^{− 10} for exoplanet science. Near the visible region, with a 108% working bandwidth from 300 to 1000 nm, a working distance of 120 Mm provides a 51-mas inner working angle (IWA). This band can be moved to shorter or longer wavelengths by adjusting the starshade range from the telescope. Our first-ever thermal analysis of such a starshade shows that a temperature below 100 K can be achieved over a broad range of observing directions, permitting the possibility of working into the infrared. We model the yield in exoplanets that can be observed. A starshade and associated spectrograph offer significant advantages for exoplanet characterization. They enable a much broader instantaneous spectral bandwidth (here 108%) than current coronagraphs (∼10 % to 20% bandwidth), allow both polarizations to be observed simultaneously, and have higher throughput. The IWA is twice as small as can be achieved with a coronagraph and there is no outer working angle. These differences are particularly pronounced in the UV, where coronagraph performance would be strongly affected by throughput losses, wavefront aberrations, Fresnel polarization effects at surfaces, and thermal instability.

A typical inflatable reflector for space application consists of two thin membranes with a parabolic shape. It is critical to understand the interaction of the inflatable and the micrometeoroid environment to which it is exposed. This interaction leads to a series of penetrations of the inflatable membrane on the entrance and exit of the impacting particle, creating a pathway for gas to escape. To increase the fidelity of the of the estimated damage that will be incurred, we examine the literature for descriptions of micrometeoroid fragmentation and present a theoretical formulation for the damage caused by an impacting particle to the entrance and exit membranes. This theory is compared with an initial set of hyper-velocity tests for micrometeoroid-sized particles on thin film membranes. We use the results of these tests to produce a predictive model. This model is applied to estimate the damage rate near the 1 AU location and output predictions for the effectiveness of a micrometeoroid shield to reduce the damage on the lenticular and effectively optimize its lifetime. Finally, we apply the kinetic theory of gasses to develop expressions for the expenditure of gas over a specified mission lifetime due to penetrations. Although we examine the specific case of an inflated lenticular protected by extra membrane layers, our predictive model can be applied to any gossamer structure composed of polyimide membranes.

Earth is the only known habitable planet and it serves as a testbed to benchmark the observations of temperate and more Earth-like exoplanets. It is required to observe the disk-integrated signatures of Earth for a large range of phase angles, resembling the observations of an exoplanet. In this work, an acousto-optic tunable filter (AOTF)-based experiment is designed to observe the spectro-polarimetric signatures of Earth. The results of spectroscopic and polarimetric laboratory calibration are presented here along with a brief overview of a possible instrument configuration. Based on the results of the spectro-polarimetric calibration, simulations are carried out to optimize the instrument design for the expected signal levels for various observing conditions. The usefulness of an AOTF-based spectro-polarimeter is established from this study, and it is found that, in the present configuration, the instrument can achieve a polarimetric accuracy of <0.3 % for linear polarization for an integration time of 100 ms or larger. The design configuration of the instrument and the planning of conducting such observations from Lunar orbit are discussed.

We present Hyperion, a mission concept recently proposed to the December 2021 NASA Medium Explorer announcement of opportunity. Hyperion explores the formation and destruction of molecular clouds and planet-forming disks in nearby star-forming regions of the Milky Way. It does this using long-slit high-resolution spectroscopy of emission from fluorescing molecular hydrogen, which is a powerful far-ultraviolet (FUV) diagnostic. Molecular hydrogen (H₂) is the most abundant molecule in the universe and a key ingredient for star and planet formation but is typically not observed directly because its symmetric atomic structure and lack of a dipole moment mean there are no spectral lines at visible wavelengths and few in the infrared. Hyperion uses molecular hydrogen’s wealth of FUV emission lines to achieve three science objectives: (1) determining how star formation is related to molecular hydrogen formation and destruction at the boundaries of molecular clouds, (2) determining how quickly and by what process massive star feedback disperses molecular clouds, and (3) determining the mechanism driving the evolution of planet-forming disks around young solar-analog stars. Hyperion conducts this science using a straightforward, highly efficient, single-channel instrument design. Hyperion’s instrument consists of a 48-cm primary mirror with an f/5 focal ratio. The spectrometer has two modes, both covering 138.5- to 161.5-nm bandpasses. A low resolution mode has a spectral resolution of R ≥ 10,000 with a slit length of 65 arcmin, whereas the high-resolution mode has a spectral resolution of R ≥ 50,000 over a slit length of 5 armin. Hyperion occupies a 2-week-long high-earth lunar resonance TESS-like orbit and conducts 2 weeks of planned observations per orbit, with time for downlinks and calibrations. Hyperion was reviewed as category I, which is the highest rating possible but was not selected.

Nulling interferometry is one of the most promising technologies for imaging exoplanets within stellar habitable zones. The use of photonics for carrying out nulling interferometry enables the contrast and separation required for exoplanet detection. So far, two key issues limiting current-generation photonic nullers have been identified: phase variations and chromaticity within the beam combiner. The use of tricouplers addresses both limitations, delivering a broadband and achromatic null together with phase measurements for fringe tracking. We present a derivation of the transfer matrix of the tricoupler, including its chromatic behavior, and our 3D design of a fully symmetric tricoupler, built upon a previous design proposed for the guided-light interferometric nulling technology instrument. It enables a broadband null with symmetric, baseline-phase-dependent splitting into a pair of bright channels when inputs are in antiphase. Within some design trade space, either the science signal or the fringe tracking ability can be prioritized. We also present a tapered-waveguide 180-deg-phase shifter with a phase variation of 0.6 deg in the 14-to-1.7-μm band, producing a near-achromatic differential phase between beams for optimal operation of the tricoupler nulling stage. Both devices can be integrated to deliver a deep, broadband null together with a real-time fringe phase metrology signal.

We report the fabrication of a binary-phase proof-of-concept astronomical diffraction grating embedded in a quartz substrate via reactive ion plasma etching. This grating operates at the first diffraction order within the 450 to 750 nm wavelength band. It features 1400-nm-deep, 188-nm-wide binary grooves at a 566-nm pitch, or 1767 lines/mm groove density, over a 25.4 × 25.4 mm² area. A high depth-to-width ratio ( ∼ 8 ∶ 1 in this case) is one of the keys to near-theoretical diffraction efficiency being attained by the fabricated grating (94% at center wavelength and 70% at band edges) over a broad bandpass (>200 nm). This performance is also attributed to high-resolution micro-lithographic electron-beam patterning and anisotropic reactive ion etching process fabrication techniques. These types of binary gratings can potentially be high-throughput alternatives to Volume-Phase Holographic Gratings (VPHGs) for general spectroscopic applications. When scaled to appropriate sizes for astronomy, such gratings can serve as main or cross dispersion elements in low-, medium-, and high-resolution spectrographs not only in ground-based telescopes but also in those subject to challenging environmental conditions such as in space observatories.

The large binocular telescope (LBT) can spectrally characterize faint objects from the ultraviolet (UV) to the near infrared (NIR) using two instruments, such as multiobjects double spectrograph (MODS) and LBT utility camera in the infrared (LUCI), which are pairs of imagers and spectrographs. Although LUCI can cover the NIR bands (0.9 to 2.4 μm), we currently need to use both LUCIs at the same time with existing gratings and filters. We report on the design and initial construction of a modular system called mask-oriented breadboard implementation for unscrambling spectra (MOBIUS) that enables a single LUCI to produce a full NIR spectrum (0.9 to 2.4 μm) in a single exposure. MOBIUS is a Littrow type spectrograph that is installed within the limited space of exchangeable mask frame space of LUCI. This plug-in concept requires no modification to the current instrument while dispersing the input slit perpendicular to the dispersion direction of the gratings in LUCI. With MOBIUS, we can utilize a slit length up to 2.3 arcsecond to acquire zJHK spectra without mixing orders at the LUCI image plane. In binocular observations with the LBT, a MODS spectrograph will be used with a LUCI + MOBIUS to acquire spectra across the full optical NIR wavelength range from 0.3 to 2.4 μm simultaneously. This will benefit studies of transient sources from rotating asteroids in our solar system to gamma-ray bursts, as well as anything with broad spectral features or unknown redshifts. The design process, tolerances, and initial table-top testing results to verify the operation of MOBIUS are presented in this work.

KOSMOS is a low-resolution, long-slit, optical spectrograph that has been upgraded at the University of Washington for its move from Kitt Peak National Observatory’s Mayall 4-m telescope to the Apache Point Observatory’s ARC 3.5-m telescope. One of the additions to KOSMOS is a slitviewer, which requires the fabrication of reflective slits, as KOSMOS previously used matte slits machined via wire electrical discharge machining. We explore an innovative method of slit fabrication using nanofabrication methods and compare the slit edge roughness, width uniformity, and the resulting scattering of the new fabricated slits to the original slits. We find the kerf surface of the chemically etched reflective silicon slits are generally smoother than the machined matte slits, with an upper limit average roughness of 0.42 ± 0.03 μm versus 1.06 ± 0.04 μm, respectively. The etched slits have width standard deviations of 6 ± 3 μm versus 10 ± 6 μm, respectively. The scattering for the chemically etched slits is higher than that of the machined slits, showing that the reflectivity is the major contributor to scattering, not the roughness. This scattering, however, can be effectively reduced to zero with proper background subtraction. As slit widths increase, scattering increases for both types of slits, as expected. Future work will consist of testing and comparing the throughput and spectrophotometric data quality of these nanofabricated slits to the machined slits with on-sky data, in addition to making the etched slits more robust against breakage and finalizing the slit manufacturing process.

We evaluate the single event tolerance of the x-ray silicon-on-insulator (SOI) pixel sensor named XRPIX, developed for the future x-ray astronomical satellite FORCE. In this work, we measure the cross-section of single event upset (SEU) of the shift register on XRPIX by irradiating heavy ion beams with linear energy transfer (LET) ranging from 0.022 to 68 MeV / ( mg/cm² ) . From the SEU cross-section curve, the saturation cross-section and threshold LET are successfully obtained to be 3.4−0.9+2.9×10−10 cm2/bit and 7.3−3.5+1.9 MeV/(mg/cm2), respectively. Using these values, the SEU rate in orbit is estimated to be ≲ 0.1 event / year primarily due to the secondary particles induced by cosmic-ray protons. This SEU rate of the shift register on XRPIX is negligible in the FORCE orbit.

We present a study of a sample pixelated cadmium zinc telluride (CZT) detector using CZT purchased from Redlen Technologies. We demonstrate that the material shows good uniformity across the 2 cm × 2 cm × 3 mm crystal in terms of leakage current, gain, and spectral resolution. We find that the detector produces very good spectral resolution for energies up to at least 105 keV, achieving a full-width at half-maxima of 450 eV at 14 keV up to 880 eV at 105 keV using only single-pixel events. Though our analysis of spectra including multiple-pixel events is somewhat limited, we also produce a spectrum including events in which photon energy is deposited across two adjacent pixels. We find that this degrades the energy resolution by up to 30%, but this result can likely be improved using more rigorous calibrations. Additionally, we investigate depth-of-interaction effects, showing that spectral resolution can be improved by 3% to 7% for energies between 86 and 105 keV by removing events beyond a certain depth. Performing this cut reduces efficiency, removing 13% to 21% of photons from the resulting spectral lines.

We present an overview of the NuSTAR non x-ray background. This is dominated by proton scattering in the detector and surrounding material as well as activation lines from of material in the detector and its housing. We also discuss contributions from the solar component (when the Sun is active), and the impact of short-lived radiation belts on the NuSTAR background and activation in the detectors.

The article presents statistics of the astronomical seeing at the Maidanak Observatory in Uzbekistan. Astronomical seeing measurements were performed using a differential image motion monitor. In the period 2018 to 2021, a total number of 204 night observations were carried out. The median zenith seeing for the entire period of observations was found to be 0.69″ (arcseconds). The results were compared with those obtained in the previous measurement period of 1996 to 2003. The comparison shows very small differences between the two measurement sets in the monthly and yearly median values. The best seeing was observed in October, but it was November according to the previous measurements. The best year in terms of seeing was 2019 with its median value 0.65″ and the worst seeing observed in 2021 (0.71″).

We present a comprehensive stray light analysis and mitigation strategy for the FIREBall-2 ultraviolet balloon telescope. Using nonsequential optical modeling, we identified the most problematic stray light paths, which impacted telescope performance during the 2018 flight campaign. After confirming the correspondence between the simulation results and postflight calibration measurements of stray light contributions, a system of baffles was designed to minimize stray light contamination. The baffles were fabricated and coated to maximize stray light collection ability. Once completed, the baffles will be integrated into FIREBall-2 and tested for performance preceding the upcoming flight campaign. Given our analysis results, we anticipate a substantial reduction in the effects of stray light.

Detector modeling is becoming more and more critical for the development of new instruments in scientific space missions and ground-based experiments. Modeling tools are often developed from scratch by each individual project and not necessarily shared for reuse by a wider community. To foster knowledge transfer, reusability, and reliability in the instrumentation community, we developed Pyxel, a framework for the simulation of scientific detectors and instruments. Pyxel is an open-source and collaborative project, based on Python, developed as an easy-to-use tool that can host and pipeline any kind of detector effect model. Recently, Pyxel has achieved a new milestone: the public release and launch of version 1.0, which simplified third-party contributions and improved ease of use even further. Since its launch, Pyxel has been experiencing a growing user community and is being used to simulate a variety of detectors. We give a tour of Pyxel’s version 1.0 changes and new features, including a new interface, parallel computing, and new detectors and models. We continue with an example of using Pyxel as a tool for model optimization and calibration. Finally, we describe an example of how Pyxel and its features can be used to develop a full-scale end-to-end instrument simulator.

The next generation of giant ground and space telescopes will have the light-collecting power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of the Giant Segment Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are optimized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance and, as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the innovative comprehensive adaptive optics and coronagraph test instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We describe the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. We detail the error budget of the CACTI system, review its operation and calibration procedures, and discuss its current status. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the raw intensity and slopes map signal processing methods. This experiment was repeated for a modulation radius of 1.6 and 3.25 λ / D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned.

We explore the capabilities of large segmented telescopes with active and adaptive optics, with a particular focus on a system view, which includes use of approaches that are routine for current large ground-based telescopes. Using a physically motivated order-of-magnitude model, we show that continuous control of telescope misalignments using adjustable optics in an exoplanet imaging instrument significantly relaxes stability requirements for the entire observatory. We start with the recent analysis by Nemati et al., (2020, JATIS 6, id. 039002), which asserts that small monolithic mirrors have an engineering advantage over larger segmented mirrors when it comes to obtaining images stable enough for direct exoplanet imaging and characterization, i.e., picometer stability. When we fold these results into our model of closed-loop operations and properly partition engineering challenges by optimizing error budget allocations, we find that even for the most sensitive modes, allowable drifts are actually of the order of nanometer over an hour, well within easily engineered tolerances. While this order-of-magnitude analysis does not include full end-to-end modeling or proper engineering margins, it showcases the importance of considering continuous wavefront sensing and control when discussing the feasibility of future exoplanet missions. We also quantify how large segmented architectures, in spite of appearing more complex at the observatory level, facilitate closed-loop operations due to their large photon collection abilities. We place our work in the context of larger discussions on aperture size that highlight a more fundamental challenge: the deeper uncertainties in performance of an exo-earth characterizing telescope primarily reside in our knowledge of the frequency of exo-earths; the effects of geological age on the resulting atmospheres; and, most importantly, on the likelihood of detectable life arising on such planets. A mission that sets out to establish whether we are alone among the nearby stars must adopt a mission architecture that is resilient against such intrinsic uncertainties: uncertainties that only direct observations can resolve. Large apertures enabled by segmented telescope designs historically have demonstrated such resilience.

Future planned space telescopes, such as the IR/O/UV Large Telescope, recommended by Astro2020 will be used to directly image exo-Earths. They will employ high-order wavefront sensing and control (HOWFSC) to correct static and slow wavefront errors in the image plane to achieve contrasts better than 10⁹. Our work evaluates the computational requirements for HOWFSC algorithms and compares these to the capabilities of processors that are expected to be available during mission development. We find that HOWFSC creates unprecedented requirements for space-based computational power, such as the ∼10¹³ floating-point operations necessary to generate the dark hole, based on the Large UV/Optical/IR (LUVOIR) study. In our worst-case estimates, maintaining an LUVOIR-size dark hole at 10¹⁰ contrast might require up to several orders of magnitude more computational throughput than available on the most advanced radiation-hardened processor.

Erratum corrects an error related to Figs. 1 and 2.