In the pursuit of observing fainter astronomical sources and phenomena, a significant challenge in detector development lies in ensuring that these devices can detect each individual photon they receive. By amplifying each incoming photon by several orders of magnitude, electron-multiplying charge-coupled devices (EMCCDs) offer a promising solution to meet this challenge. Although these detectors boast impressive potential, they can be intricate, requiring precise optimization and fine-tuning of their parameters to unlock their full capabilities in the photon-starved regime. The Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall-2) is a stratospheric project that aims to detect and map the low surface brightness environment of galaxies in the ultraviolet (UV) at z∼0.7. As a technology demonstrator for photon-starved astronomy and to advance the technology readiness level of UV EMCCDs, the instrument uses a Teledyne-e2v (T-e2v) EMCCD delta-doped by the Jet Propulsion Laboratory, combined with a NüVü controller. To analyze the detector data and retrieve the device noise contributions, we developed a comprehensive EMCCD model along with DS9 analysis tools to compare the model with the actual data under diverse operating conditions. This allowed us to examine the current performance and limitations of these devices both on the ground and in the stratospheric environment, to unravel the intricacies of these detectors. In addition, we will discuss the development and implementation of an exposure time calculator designed to optimize the end-to-end signal-to-noise ratio under diverse conditions and analyze the different trade-offs associated with such devices. This will be used to explore some EMCCD-related issues encountered on FIREBall-2 and present some recent and potential future upgrade strategies (controller upgrade, red-blocking filter, over-spill register implementation, etc.) to mitigate them.
Transient events exhibit strong UV radiation, but transient activity is not well studied in the UV. Ground-based telescopes have an untapped potential to support space-based UV observations of transients, down to the atmospheric cutoff of roughly 320nm. The Super-LOTIS (Livermore Optical Transient Imaging System) telescope is the first ground-based optical telescope that is being converted for NUV transient science. It will follow up on transient targets identified by the Swift/UVOT instrument, ground-based robotic transient finders, and future space-based missions. It will also have the capacity to conduct its own observations. The development of the Super-LOTIS telescope will provide a model for future ground-based UV surveys. In this paper, we report on the progress to modify the existing camera optics to use a new NUV sensitive camera and filter system.
The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall-2) is a UV multi-object spectrograph designed to detect emission from the circumgalactic and circumquasar medium at low redshifts (0.3 < z < 1.0). The FIREBall-2 spectrograph uses a suborbital balloon vehicle to access a stratospheric transmission window centered around 205 nm and is fed by a 1-m primary parabolic mirror and a 2-mirror field corrector that allows an ≈11’ x 35’ field of view. The slit-mask spectrograph can access dozens of galaxy targets per field, with each target spectrum read out on a UV electron-multiplying CCD detector. Following a flight in 2018, several refurbishments and modifications were made to the instrument and telescope to prepare for additional flight opportunities. Here we present an overview of upgrades and improvements made since the previous flight and discuss the 2023 field campaign, which culminated in a flight from Fort Sumner, New Mexico in September, 2023.
Understanding the noise characteristics of high quantum efficiency silicon-based ultraviolet detectors, developed by the Microdevices Lab at the Jet Propulsion Laboratory, is critical for current and proposed UV missions using these devices. In this paper, we provide an overview of our detector noise characterization test bench that uses delta-doped, photon counting, Electron-multiplying CCDs (EMCCDs) to understand the fundamental noise properties relevant to all silicon CCDs and CMOS arrays. This work attempts to identify the source of the dark current plateau that has been previously measured with photon-counting EMCCDs and is known to be prevalent in other silicon-based arrays. It is suspected that the plateau could be due to a combination of detectable photons in the tail of blackbody radiation of the ambient instrument, low-level light leaks, and a non-temperature-dependent component that varies with substrate voltage. Our innovative test setup delineates the effect of the ambient environment during dark measurements by independently controlling the temperature of the detector and surrounding environment. We present the design of the test setup and preliminary results.
Aspera is a NASA-funded UV SmallSat mission designed to detect and map warm-hot phase halo gas around nearby galaxies. The Aspera payload is designed to detect faint diffuse O VI emission at around 103.2 nm, satisfying the sensitivity requirement of 5×10−19 erg/s/cm2/arcsec2 over 179 hours of exposure. In this manuscript, we describe the overall payload design of Aspera. The payload comprises two identical co-aligned UV long-slit spectrograph optical channels sharing a common UV-sensitive microchannel plate detector. The design delivers spectral resolution R ∼ 2,000 over the wavelength range of 101 to 106 nm. The field of view of each channel is 1 degree by 30 arcsec, with an effective area of 1.1 cm2. The mission is now entering the payload integration and testing phase, with the projected launch-ready date set for late 2025 or early 2026. The mission will be launched into low-Earth orbit via rideshare.
The Faint Intergalactic-medium Redshifted Emission Balloon (FB-2), a collaborative NASA/CNES suborbital balloon telescope, targets the mapping of faint UV emissions from the circumgalactic medium around low-redshift galaxies. The initial September 2018 flight encountered challenges, including a balloon breach and subsequent damage during landing, impacting the two large telescope mirrors and the critical focal corrector. Likely due to landing shock, the focal corrector experienced misalignment beyond tolerance, necessitating reevaluation and realignment. This paper outlines a comprehensive approach to realigning the focal corrector using a computer-generated hologram (CGH) and a Zygo interferometer for feedback. The CGH enables precise alignment corrections in various degrees of freedom, while interferometer feedback aids in reducing aberrations. The paper details the methodology for optical alignment, surface measurement, and performance evaluation of the focal corrector, emphasizing its successful integration into the FB-2 spectrograph in early 2023 for the September 2023 flight.
Aspera is a NASA Astrophysics Pioneers SmallSat mission designed to study diffuse Ovi emission from the warm-hot phase gas in the halos of nearby galaxies. Its payload consists of two identical Rowland Circle-type long-slit spectrographs, sharing a single MicroChannel plate detector. Each spectrograph channel consists of an off-axis parabola primary mirror and a toroidal diffraction grating optimized for the 1013-1057 Å bandpass. Despite the simple configuration, the optical alignment/integration process for Aspera is challenging due to tight optical alignment tolerances, driven by the compact form factor, and the contamination sensitivity of the Far-Ultraviolet optics and detectors. In this paper, we discuss implementing a novel multi-phase approach to meet these requirements using state-of-the-art optical metrology tools. For coarsely positioning the optics we use a blue-laser 3D scanner while the fine alignment is done with a Zygo interferometer and a custom computer-generated hologram. The detector focus requires iterative in-vacuum alignment using a Vacuum UV collimator. The alignment is done in a controlled cleanroom facility at the University of Arizona.
Aspera is a NASA Pioneers SmallSat mission designed to detect and map the O VI emission (1032 Å) through long-slit spectroscopy in the halos of nearby galaxies for the first time. The spectrograph utilizes toroidal gratings with multilayer coatings of aluminum, lithium fluoride, and magnesium fluoride that optimize their throughput in the extreme ultraviolet EUV waveband of 1030 to 1040 Å. We discuss the grating verification test setup design, including optical alignment and reference measurement setup. We also present grating testing and grating efficiency simulation results using the target grating groove profile and the multi-layer coatings.
Aspera is a NASA Pioneers Mission designed to measure faint OVI emission around nearby galaxies with unprecedented sensitivity. The SmallSat payload consists of two identical co-aligned spectrographs, both operating in the Far Ultraviolet (FUV) between 1030−1040 Å. Missions operating at FUV wavelengths are particularly sensitive to contamination, as short wavelengths are easily scattered and absorbed by contaminants deposited on payload optical surfaces. A strict contamination control plan is critical to avoiding a severe loss in FUV throughput. Aspera contamination control efforts have been tailored to fit within the scope of a sub-Class D mission, a challenge that has become increasingly relevant as advances in FUV optics/detectors drive an uptick in smaller platform, contamination sensitive UV payloads. Contamination monitoring is used to audit the cleanroom environment, avoid outgassing contaminants under vacuum, and assess contaminant levels on payload optics. We present a detailed contamination budget through the mission end of life as well as our ongoing contamination monitoring efforts. We discuss protocols implemented for minimizing contamination-related performance degradation.
We present the integration of a new calibration system into the Faint Intergalactic-medium Redshifted Emission Balloon-2 (FIREBall-2), which added in-flight calibration capability for the recent September 2023 flight. This system is composed of a calibration source box containing zinc and deuterium lamp sources, focusing optics, electronics, 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 non-sequential modeling for the near-UV (191 to 221 nm) for spectrograph slit mask position calibration, electron multiplying charged-coupled device (EMCCD) gain amplification verification, and wavelength calibration. Then, we present the pre-flight performance testing results of the calibration system and their implications for in-flight measurements. FIREBall-2 flew in 2023, but did not collect calibration data due to early termination of the flight.
Aspera is a NASA-funded UV SmallSat Mission in development with a projected launch in 2025. The goal of the mission is to detect and map warm-hot gas in the circumgalactic medium of nearby galaxies traced by the Ovi emission line at 103.2 nm. To that goal, Aspera will conduct long-exposure observations at one or more spatial fields around each target galaxy, employing two long-slit spectrographs. Spectra from both channels are focused on a single micro-channel plate detector. In preparation of the mission’s launch, we are developing a data reduction pipeline, the goal of which is to reconstruct a calibrated 3D IFU-like data cube by combining the photon event lists obtained during each observation for a given target galaxy. In this proceedings paper, we present an outline for the data reduction pipeline and describe the data flow through the processing of science observations. We will further discuss individual steps to be applied to the data during the processing and show how our final data cubes shall be reconstructed. Finally, we will present our planned data products and discuss how simulations of the Aspera data cubes are being used to develop the pipeline.
The warm-hot phase coronal gas, known as the circumgalactic matter (CGM), around galaxy halos plays a critical role in the evolution of galaxies. However, the morphology of the CGM is poorly understood as it is difficult to detect the extreme-UV (EUV) emission from this diffuse gas. Aspera, a small satellite telescope, is designed to map the EUV emission from the CGM of nearby galaxies. In order to achieve high observation efficiency, the payload has a unique dual-channel optical layout sharing a Microchannel plate (MCP) detector. The spectroscopy layout benchmarked the Rowland Circle ( OAP + slit + curved diffractive optics) and adopted a special coating to enhance reflectivity at EUV (~103.2 nm). The unique dual-channel layout requires co-pointing alignment of both channels and tight tolerance of each channel alignment. We reviewed the tolerance and sensitivity analyses of the optical system. The comprehensive Monte Carlo simulation provides the required alignment accuracy, and we proposed appropriate alignment plans using the interferometer and computer-generated hologram (CGH). The proposed alignment strategy is available for quantitative and decomposed evaluation of misalignin
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.
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.
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.
The solar ultraviolet imaging telescope (SUIT) is an imaging telescope on-board the Aditya-L1 satellite, which is India’s maiden space mission dedicated solely to solar observations. The spatially resolved, high cadence observations are designed to be taken in eleven science filters with full width half maxima ranging between 0.1–58 nm and spread over the near-ultraviolet (NUV) domain of the solar spectrum (200–400 nm). The huge incoming solar flux, limited by the linearity regime performance of the charge coupled device (CCD) as well as the thermal operational constraints, mandate the use of an entrance aperture filter, the thermal filter (TF), for SUIT. The design of this filter is, further, constrained by exposure time and enhanced emission of the sun during eruptive events. From performance perspective, the TF reflects ∼50% of the incident radiation and allows only 0.1–0.45% of the incoming flux to pass within 200–400 nm. The transmission on either side of the operational range is satisfactorily reduced, so as to ensure minimum unwanted light leaking into the imaging system. Therefore, the TF plays a significant role in increasing the photometric efficiency as well as maintaining the operational temperature of the telescope. To the best of our knowledge, this is the first time any attempt of designing and manufacturing any such rejection filter aiming optimized performance in the NUV range is being done for a space-based imaging solar telescope. The choice of materials for substrate and coating for the filter poses several challenges in terms of contamination, corrosion/ oxidation, durability during manufacturing process, long-term exposure to harsh space environment as well as formation of pinholes. The transmission and reflection profiles of the fabricated TF is satisfactory to meet our design and technical constraints. The TF is also qualified for various environmental and radiation conditions. The transmission of the TF is seen to be well within our allowed margins (±10% of the design value) even after being exposed to these qualification tests.
This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes and Instrumentation, 2022.
We present a comprehensive stray light analysis and mitigation strategy for the FIREBall-2 UV telescope. Using non-sequential 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 post-flight 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.
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.
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.
KEYWORDS: Space operations, Ultraviolet radiation, Space telescopes, Telescopes, Space telescopes, Solar processes, Sensors, X-ray imaging, Plasma, Ions, Magnetosphere
The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard the Aditya-L1 spacecraft, the first dedicated solar mission of the Indian Space Research Organization (ISRO), which will be put in a halo orbit at the Sun-Earth Langrage point (L1). SUIT has an off-axis Ritchey–Chrétien configuration with a combination of 11 narrow and broad bandpass filters which will be used for full-disk solar imaging in the Ultravoilet (UV) wavelength range 200-400 nm. It will provide near simultaneous observations of lower and middle layers of the solar atmosphere, namely the Photosphere and Chromosphere. These observations will help to improve our understanding of coupling and dynamics of various layers of the solar atmosphere, mechanisms responsible for stability, dynamics and eruption of solar prominences and Coronal Mass ejections, and possible causes of solar irradiance variability in the Near and Middle UV regions, which is of central interest for assessing the Sun’s influence on climate.
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