Aspera is the UV small-satellite mission to detect and map the warm-hot phase gas in nearby galaxy halo. Aspera was chosen as one of NASA's Astrophysics Pioneers missions in 2021 and employs a FUV long-slit spectrograph payload, optimized for low-surface brightness O VI emission line detection at 103-104 nm. The mission incorporates state-of-the-art UV technologies such as high-efficiency micro-channel plates and enhanced LiF coating to achieve a high level of diffuse-source sensitivity of the payload, down to 5.0E-19 erg/s/cm^2/arcsec^2. The combination of the high sensitivity and a 1-degree by 30-arcsecond long-slit field of view enables efficient 2D mapping of diffuse halo gas through step and stare concept observation. Aspera is presently in the critical design phase, with an expected launch date in mid-2025. This work provides a current overview of the Aspera payload design.
Advancements in optical coating methods developed at the Jet Propulsion Laboratory (JPL) now allow for spatial optimization of detector response with respect to a spectrometer system’s optical dispersion. When combined with JPL’s delta-doped, UV detector technology, these patterned coatings will reduce the complexity required for UV instruments while also improving throughput. This technology development offers an innovative solution to the limitations and compromises inherent in existing UV coating technologies. This advancement will result in detectors with high quantum efficiency (QE) in targeted wavelength bands, allowing for more versatile UV–Visible instrumentation.
The integration of a new calibration system into FIREBall-2 (Faint Intergalactic Redshifted Emission Balloon-2) allows in-flight calibration capability for the upcoming Fall 2023 flight. This system is made up of a calibration box that contains zinc and deuterium lamp sources, focusing optics, electronics, and sensors, and a fiber-fed calibration cap with an optical shutter mounted on the spectrograph tank. We discuss how the calibration cap is optimized to be evenly illuminated through nonsequential modeling for the near-UV (200-208nm). Then, we present the pre-flight performance testing results of the calibration system and their implications for in-flight measurements.
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.
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.
Hyperion is a Far-UV (FUV) mission that investigates the birth clouds of stars by probing the nature, extent, and state of H2 at the crucial atomic-to-molecular interstellar medium boundary layer. Hyperion examines the fuel for star formation directly by observing the molecular interface between dense, star-forming clouds, the diffuse interstellar environment, and the stars that arise from these regions. Hyperion observes over the 138.5-161.5 nm spectral range with resolution greater than R==50,000. Mapping faint clouds over large areas of sky requires an efficient, high-etendue spectrometer.
Conventional cross-dispersed Echelle spectrometers suffer from low efficiency (due to the need for a cross-disperser) and limited etendue due to the aberration correction. We describe an efficient high-etendue spectrometer approach that uses a single grating and a 64 mega-pixel array. The spectrometer is a compact f/5 Offner derivative with free-form surfaces and a single diffraction grating.
Ultraviolet (UV, 900−2000Å) spectroscopy simultaneously traces the most common elements (e.g., H, He, O, C, N) in many phases, in the form of ionic, atomic, and molecular lines. UV grating spectrometers hence offer unique insights into astrophysical systems and the impacts of their evolution. This work seeks to understand how we might best optimize certain grating designs for targeted astrophysical tracers. Our work is intended to guide proposers in determining the ideal grating parameters given their specific science objectives. We report on the results of the initial phase of the project, a thorough design phase to determine the ideal grating parameters and electron-beam lithography/potassium hydroxide patterning prescriptions for blazed UV gratings. We use grating simulation software to explore a grating-parameter space and determine the key performance expectations for gratings in next-generation UV space instruments. We present our results for a rough grid in grating-parameter space (blaze angle: ∼30°−76°, grating period: 100−5000 nm). Future work will explore specific cases that include the nominal grating prescriptions for current (e.g., Hyperion, PolStar, LUVOIR) and future mission designs.
This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes and Instrumentation, 2022.
This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes + Instrumentation, 2022.
Aspera is an extreme-UV (EUV) Astrophysics small satellite telescope designed to map the warm-hot phase coronal gas around nearby galaxy halos. Theory suggests that this gas is a significant fraction of a galaxy’s halo mass and plays a critical role in its evolution, but its exact role is poorly understood. Aspera observes this warm-hot phase gas via Ovi emission at 1032 °A using four parallel Rowland-Circle-like spectrograph channels in a single payload. Aspera’s robust-and-simple design is inspired by the FUSE spectrograph, but with smaller, four 6.2 cm × 3.7 cm, off-axis parabolic primary mirrors. Aspera is expected to achieve a sensitivity of 4.3×10−19 erg/s/cm2/arcsec2 for diffuse Ovi line emission. This superb sensitivity is enabled by technological advancements over the last decade in UV coatings, gratings, and detectors. Here we present the overall payload design of the Aspera telescope and its expected performance. Aspera is funded by the inaugural 2020 NASA Astrophysics Pioneers program, with a projected launch in late 2024.
Molecular clouds are a crucial stage in the lifecycle of a star, and the far ultraviolet (FUV) spectral range is a prime observation band. Hyperion is an FUV space telescope that investigates the birth clouds of stars using a high-resolution spectrometer. To meet the scientific requirements, we developed and evaluated a spectrometer that covers the 140.5 to 164.5 nm wavelength range with a spectral resolution higher than 30,000. We employed on-axis and on-plane dispersive optic layouts to control the aberration from a large aspect ratio slit (10 arcmin × 2.5 arcsec, aspect ratio R = 240). The cross-dispersion isolates three orders from the échelle grating (n = − 19, −18, and −17), and the subsequent two-mirror freeform imaging optics form a two-dimensional spectral distribution on a 50 mm × 50 mm detector array. The geometrical and spectral performances of this innovative design are evaluated.
The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall-2) is a UV multi-object spectrograph exploring the CGM of galaxies at low redshifts (0.3 < z < 1.0). The science detector is a EMCCD cooled by a Sunpower cryocooler to minimize the noise contributions from dark current. To efficiently remove the heat generated by the cryocooler and other critical hardware, we built a custom water cooling circuit which uses a water/alcohol/ice mixture to regulate temperatures during flight. We report the ground and flight performances of the thermal system during the 2018 campaign and the lessons learned since then. We will discuss the model predictions of the potential impacts of several major upgrades as well as modifications to adapt to those impacts, and the ground performance of the thermal system during the rebuild of FIREBall-2, compared with the model predictions, for the next launch of FIREBall-2 in Fort Sumner in 2020.
The payload of the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2), the second generation of the FIREBall instrument (PI: C. Martin, Caltech), has been calibrated and launched from the NASA Columbia Scientific Balloon Facility in Fort Sumner, New Mexico. FIREBall-2 was launched for the first time on the September 22, 2018, and the payload performed the very first multi-object acquisition from space using a multi-object spectrograph. Our performance-oriented paper presents the calibration and last ground adjustments of FIREBall-2, the in-flight performance assessed based on the flight data, and the predicted instrument’s ultimate sensitivity. This analysis predicts that future flights of FIREBall-2 should be able to detect the HI Lyα resonance line in galaxies at z ∼ 0.67, but will find it challenging to spatially resolve the circumgalactic medium.
Hyperion is a far-UV mission that investigates the birth clouds of stars using a 40 cm aperture telescope feeding an imaging long-slit spectrometer. The science requirements of the mission dictate that the spectrometer covers 140.5- 164.5 nm spectral range with resolution greater than 30,000. We employ smart and efficient design to create a longslit, cross dispersed, echelle spectrometer that utilizes a two-mirror freeform imaging optics. Echelle spectra for n = - 19, -18, and -17 over a 10 arcmin × 2.5 arcsec (length × width) FFOV are imaged onto the focal plane. We simulate the optical performance and the expected spectral efficiency.
We present the status of on-going detector development efforts for our joint NASA/Centre National d’Études Spatiales balloon-borne UV multiobject spectrograph, the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2; FB-2). FB-2 demonstrates a UV detector technology, the delta-doped electron-multiplying CCD (EMCCD), in a low-risk suborbital environment, to prove the performance of EMCCDs for future space missions and technology readiness level advancement. EMCCDs can be used in photon-counting mode to achieve extremely low readout noise (<1 electron). Our testing has focused on reducing clock-induced-charge (CIC) through wave shaping and well-depth optimization with a Nüvü V2 CCCP controller, measuring CIC at 0.001 e − / pixel / frame. This optimization also includes methods for reducing dark current, via cooling, and substrate voltage levels. We discuss the challenges of removing cosmic rays, which are also amplified by these detectors, as well as a data reduction pipeline designed for our noise measurement objectives. FB-2 flew in 2018, providing the first time an EMCCD, was used for UV observations in the stratosphere. FB-2 is currently being built up to fly again in 2020, and improvements are being made to the EMCCD to continue optimizing its performance for better noise control.
The Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall-2, FB-2) is designed to discover and map faint UV emission from the circumgalactic medium around low redshift galaxies (z ~ 0.3 (C IV); z ~ 0.7 (Lyα); z ~ 1.0 (O VI)). FIREBall-2's first launch, on September 22nd 2018 out of Ft. Sumner, NM, was abruptly cut short due to a hole that developed in the balloon. FIREBall-2 was unable to observe above its minimum require altitude (25 km; nominal: 32 km) for its shortest required time (2 hours; nominal: 8+ hours). The shape of the deflated balloon, as well as a concurrent full moon close to our observed target field, revealed a severe, off-axis scattered light path directly to the UV science detector. Additional damage to FB-2 added complications to the ongoing effort to prepare FB-2 for a quick re-flight. Upon landing, several mirrors in the optical chain, including the two large telescope mirrors, were damaged, resulting in chunks of material broken off the sides and reflecting surfaces. The magnifying optical element, called the focal corrector, was discovered to be misaligned beyond tolerance after the 2018 flight, with one of its two mirrors damaged from the landing impact. We describe the steps taken thus far to mitigate the damage to the optics, as well as procedures and results from the ongoing efforts to re-align the focal corrector and spectrograph optics. We report the throughput of the spectrograph before and after the 2018 flight and plans for improving it. Finally, we describe several methods by which we address the scattered light issues seen from FIREBall-2's 2018 campaign and present the current status of FB-2 to fly during the summer campaign in Palestine, TX in 2020.
In this talk, I will describe briefly the telescope, instrument, and flight of the Faint Intergalactic medium Redshifted Emission Balloon (FIREBall-2). FIREBall-2 is a UV multi-object spectrograph fed by a 1 meter parabola mirror. The instrument was designed to observe 4 pre-selected fields and uses a UV optimized delta-doped EMCCD. The telescope flew on September 22, 2018 from Fort Sumner, NM, as part of the fall CSBF balloon campaign. The telescope collected data for several night hours before being cut down. I will describe the testing, flight, and hardware performance with an emphasis on the in flight performance of the instrument, including resolution, throughput, and the overall operation of the UV optimized EMCCD. Additional talks will be presented on other aspects of the flight and data.
I will present on-going detector developments in our joint NASA/CNES balloon-borne UV multi-object spectrograph, FIREBall-2, the Faint Intergalactic Redshifted Emission Balloon. FIREBall-2 is a path finding mission to test new technology (EMCCDs) and make new constraints on the temperature and density of this gas. This instrument has been designed to detect faint emission from the circumgalactic medium (CGM) around low redshift galaxies (z ~ 0.7). One major change from FIREBall-1 has been the use of a delta-doped Electron Multiplying CCD (EMCCD). EMCCDs can be used in photon-counting (PC) mode to achieve extremely low readout noise (< 1 electron). Our testing initially focused on reducing clock-induced-charge (CIC) through wave shaping and well depth optimisation with a NuVu CCD Controller for Counting Photons (CCCP). This optimisation also includes methods for reducing dark current, via cooling, and exploring substrate voltage levels. I will present some of our dark current results from laboratory testing. We recently launched FIREBall-2 from Fort Sumner, New Mexico on September 22nd, 2018. This was the first time an EMCCD has been used for UV/optical observations in flight! I will present performance data from the flight including cosmic ray rate measurements, and some of our preliminary on-sky UV results using our data reduction.
Here we discuss advances in UV technology over the last decade, with an emphasis on photon counting, low noise, high efficiency detectors in sub-orbital programs. We focus on the use of innovative UV detectors in a NASA astrophysics balloon telescope, FIREBall-2, which successfully flew in the Fall of 2018. The FIREBall-2 telescope is designed to make observations of distant galaxies to understand more about how they evolve by looking for diffuse hydrogen in the galactic halo. The payload utilizes a 1.0-meter class telescope with an ultraviolet multi-object spectrograph and is a joint collaboration between Caltech, JPL, LAM, CNES, Columbia, the University of Arizona, and NASA. The improved detector technology that was tested on FIREBall-2 can be applied to any UV mission. We discuss the results of the flight and detector performance. We will also discuss the utility of sub-orbital platforms (both balloon payloads and rockets) for testing new technologies and proof-of-concept scientific ideas.
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.
Exciting concepts are under development for flagship, probe class, explorer class, and suborbital class NASA missions in the ultraviolet/optical spectral range. These missions will depend on high-performance silicon detector arrays being delivered affordably and in high numbers. To that end, we have advanced delta-doping technology to high-throughput and high-yield wafer-scale processing, encompassing a multitude of state-of-the-art silicon-based detector formats and designs. We have embarked on a number of field observations, instrument integrations, and independent evaluations of delta-doped arrays. We present recent data and innovations from JPL’s Advanced Detectors and Systems Program, including two-dimensional doping technology, JPL’s end-to-end postfabrication processing of high-performance UV/optical/NIR arrays and advanced coatings for detectors. While this paper is primarily intended to provide an overview of past work, developments are identified and discussed throughout. Additionally, we present examples of past, in-progress, and planned observations and deployments of delta-doped arrays.
We report on multilayer high efficiency antireflection coating (ARC) design and development for use at UV wavelengths on CCDs and other Si-based detectors. We have previously demonstrated a set of single-layer coatings, which achieve >50% quantum efficiency (QE) in four bands from 130 to 300 nm. We now present multilayer coating designs that significantly outperform our previous work between 195 and 215 nm. Using up to 11 layers, we present several model designs to reach QE above 80%. We also demonstrate the successful performance of 5 and 11 layer ARCs on silicon and fused silica substrates. Finally, we present a five-layer coating deposited onto a thinned, delta-doped CCD and demonstrate external QE greater than 60% between 202 and 208 nm, with a peak of 67.6% at 206 nm.
We present the latest developments in our joint NASA/CNES suborbital project. This project is a balloon-borne UV multi-object spectrograph, which has been designed to detect faint emission from the circumgalactic medium (CGM) around low redshift galaxies. One major change from FIREBall-1 has been the use of a delta-doped Electron Multiplying CCD (EMCCD). EMCCDs can be used in photon-counting (PC) mode to achieve extremely low readout noise (¡ 1e-). Our testing initially focused on reducing clock-induced-charge (CIC) through wave shaping and well depth optimisation with the CCD Controller for Counting Photons (CCCP) from Nüvü. This optimisation also includes methods for reducing dark current, via cooling and substrate voltage adjustment. We present result of laboratory noise measurements including dark current. Furthermore, we will briefly present some initial results from our first set of on-sky observations using a delta-doped EMCCD on the 200 inch telescope at Palomar using the Palomar Cosmic Web Imager (PCWI).
Fireball (Faint Intergalactic Redshifted Emission Balloon) is a NASA/CNES balloon-borne experiment to study the faint diffuse circumgalactic medium from the line emissions in the ultraviolet (200 nm) above 37 km flight altitude. Fireball relies on a Multi Object Spectrograph (MOS) that takes full advantage of the new high QE, low noise 13 μm pixels UV EMCCD. The MOS is fed by a 1 meter diameter parabola with an extended field (1000 arcmin2) using a highly aspherized two mirror corrector. All the optical train is working at F/2.5 to maintain a high signal to noise ratio. The spectrograph (R~ 2200 and 1.5 arcsec FWHM) is based on two identical Schmidt systems acting as collimator and camera sharing a 2400 g/mm aspherized reflective Schmidt grating. This grating is manufactured from active optics methods by double replication technique of a metal deformable matrix whose active clear aperture is built-in to a rigid elliptical contour. The payload and gondola are presently under integration at LAM. We will present the alignment procedure and the as-built optic performances of the Fireball instrument.
The Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall-2) is an experiment designed to observe low density emission from HI, CIV, and OVI in the circum-galactic medium around low-redshift galaxies. To detect this diffuse emission, we use a high-efficiency photon-counting EMCCD as part of FIREBall-2's detector. The flight camera system includes a custom printed circuit board, a mechanical cryo-cooler, zeolite and charcoal getters, and a Nüvü controller, for fast read-out speeds and waveform shaping. Here we report on overall detector system performance, including pressure and temperature stability. We describe dark current and CIC measurements at several temperatures and substrate voltages, with the flight set-up.
We present an overview of the detector for the upcoming Faint Intergalactic Red-shifted Emission Balloon (FIREBall-2) experiment, with a particular focus on the development of device-integrated optical coatings and detector quantum efficiency (QE). FIREBall-2 is designed to measure emission from the strong resonance lines of HI, OVI, and CIV, all red-shifted to 195-225 nm window; its detector is a delta-doped electron multiplying charge coupled device (EM-CCD). Delta-doped arrays, invented at JPL, achieve 100% internal QE from the UV through the visible. External losses due to reflection (~70% in some UV regions) can be mitigated with antireflection coatings (ARCs). Using atomic layer deposition (ALD), thin-film optical filters are incorporated with existing detector technologies. ALD offers nanometer-scale control over film thickness and interface quality, allowing for precision growth of multilayer films. Several AR coatings, including single and multi-layer designs, were tested for FIREBall-2. QE measurements match modeled transmittance behavior remarkably well, showing improved performance in the target wavelength range. Also under development are ALD coatings to enhance QE for a variety of spectral regions throughout the UV (90-320 nm) and visible (320-1000 nm) range both for space-based imaging and spectroscopy as well as for ground-based telescopes.
The Faint Intergalactic Redshifted Emission Balloon (FIREBall) is a NASA/CNES balloon-borne ultraviolet multi-object spectrograph designed to observe the diffuse gas around galaxies (the circumgalactic medium) via line emission redshifted to ~205 nm. FIREBall uses a ultraviolet-optimized delta doped e2v CCD201 with a custom designed high efficiency five layer anti-reflection coating. This combination achieves very high quantum efficiency (QE) and photon-counting capability, a first for a CCD detector in this wavelength range. We also present new work on red blocking mirror coatings to reduce red leak.
We describe recent progress in the development of anti-reflection coatings for use at UV wavelengths on CCDs
and other Si-based detectors. We have previously demonstrated a set of coatings which are able to achieve
greater than 50% QE in 4 bands from 130nm to greater than 300nm. We now present new refinements of these
AR-coatings which will improve performance in a narrower bandpass by 50% over previous work. Successful test
films have been made to optimize transmission at 190nm, reaching 80% potential transmission.
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