We present the results of the JUpiter ICy moons Explorer ultraviolet spectrograph (JUICE-UVS) near-earth commissioning performed between June 14th and 25th 2023. JUICE-UVS is a modest power (9 W), compact ultraviolet spectrograph that is the fifth in a series of six such spectrographs designed and built by Southwest Research Institute for ESA and NASA missions. JUICE-UVS includes several innovations in detector, electronics, optics, and software. These innovations include an atomic-layer deposition (ALD) coating on the detector microchannel plates to minimize gain sag as photons are detected during the mission, electronic components able to withstand the harsh Jovian radiation environment, low-scatter optics to minimize the “wings” of the detected interplanetary Lyman-alpha emission, and a programmable histogram data collection mode that maximizes science return while minimizing stored and telemetered data volume. JUICE-UVS also features a high-spatial resolution observation mode, where a small (1/4 the width of nominal) aperture swings into place at the aperture stop and sharpens the instrument focus. Near-earth commissioning activities included measurements of detector dark noise, optimizing detector HV level via observations of the interplanetary Lyman-alpha, and a “sky-spin” observation over the JUICE-UVS 7.5°-long slit while the spacecraft rolled about the high-gain antenna (a “great circle” swath 7.5° wide). Dark rates matched those measured on the ground (approximately 5 Hz/cm2). HV levels were nominal for the operational temperature (approximately 0°C). Observations with the high-spatial resolution aperture confirmed the sharpened focus when compared to nominal observations. The “sky-spin” observation passed through the galactic plane, allowing for the identification of many known UV-bright stars. These stars provide a rough estimate of instrument effective area that will be refined after JUICE passes >2 AU from the sun, enabling 3-axis stabilized pointed observations.
We describe the radiometric performance and ground calibration results of the Europa Clipper Ultraviolet Spectrograph (Europa-UVS). Europa-UVS is a modest power (~8 W) ultraviolet spectrograph that is the sixth in a series of Alice/UVS instruments built by SwRI. Europa-UVS covers a 55-206 nm bandpass with approximately 0.6 nm spectral resolution over a 7.5° field of view with better than 0.25° spatial resolution on-axis. Europa-UVS also features three different observing modes to allow higher-than-normal spatial resolution observing as well as solar occultations of Europa. Both the high spatial resolution and solar occultation observations have reduced sensitivity when compared with nominal observations. Europa-UVS meets all performance requirements with margin, and is the first planetary UV spectrograph to feature a microchannel plate detector with curved borosilicate microchannel plates (expected to be less sensitive to gamma rays than traditional plates). Europa-UVS, like its predecessor JUICE-UVS, incorporates both timetagged pixel list and histogram observing with programmable acquisitions to maximize science return while minimizing data storage and downlink. Europa-UVS will search near Europa for water vapor plumes, examine the composition and structure of Europa’s atmosphere and surface, and characterize Europa's aurora.
Ultraviolet spectroscopy is a powerful method used to study planetary surface composition through reflectance measurements and atmospheric composition through stellar/solar occultations, transits of other planetary bodies, and direct imaging of airglow and auroral emissions. The next generation of ultraviolet spectrographs (UVS) on board ESA’s JUICE (Jupiter icy moons explorer) and NASA’s Europa Clipper missions will perform such measurements of Jupiter and its moons in the early 2030’s. This work presents a compilation of a detailed UV stellar catalog of targets with high intensity in the 52-204 nm region with applications relevant to planetary spectroscopy. These applications include: 1) planning and simulating occultations, including calibration measurements; 2) modeling starlight illumination of dark, nightside planetary surfaces primarily lit by the sky; and 3) studying the origin of diffuse galactic UV light as mapped by existing datasets from Juno-UVS. This catalog also includes information drawn from other resources such as the international ultraviolet explorer (IUE) catalog and SIMBAD. We have constructed spectra at 0.1 nm resolution for over 80,000 targets using Kurucz models and, when available, IUE spectra. We report on our methods for producing the catalog and discuss plans for its implementation during ongoing and upcoming planetary missions.
Juno is a spacecraft in polar orbit around Jupiter, and one of its objectives is to explore the Jovian magnetosphere. Charged particles trapped along the Jovian magnetic field lines may generate auroral emission. The Juno magnetospheric payload is designed to measure the charged particle distributions in the Jovian magnetosphere while remote sensing the related UV-auroral emissions. The ultraviolet spectrograph on Juno (Juno-UVS) is a photon-counting imaging spectrograph designed to observe Jupiter’s prominent far-UV auroral emissions in the 68 to 210 nm spectral range. This work presents an improvement on the wavelength and radiometric calibration of Juno-UVS. Ground calibration measurements were reanalyzed by expanding the spectral database ultimately used to produce the instrument spectral pixel size map. This significantly improves the wavelength assignation, up to 4 nm at the longer wavelengths, compared with the previous calibration. Dedicated Juno-UVS observation sequences were made to evaluate the slit-dependent radiometric calibration, which was revised accordingly. This work highlights a slight slit-dependent variation in the radiometric calibration. An additional radiometric correction was established at wavelengths greater than 160 nm using some of UVS’s brightest recorded stellar spectra.
We describe the radiometric performance and ground calibration results of the JUpiter ICy moons Explorer Ultraviolet Spectrograph (JUICE-UVS) instrument. JUICE-UVS is a modest power (8 W) ultraviolet spectrograph that is the fifth in a series of Alice/UVS instruments built by Southwest Research Institute. JUICE-UVS covers a 50-204 nm bandpass with 0.4 nm spectral resolution over a 7.5° field of view with better than 0.3° spatial resolution. JUICE-UVS also features three different observing modes to allow higher-than-nominal spatial resolution observing as well as solar occultations in the Jupiter system. JUICE-UVS meets all performance requirements with margin, and is the first planetary UV spectrograph to feature a microchannel plate detector with an atomic layer deposition (ALD) coating to minimize in-flight gain loss due to accumulated fluence. JUICE-UVS also features both a time-tagged pixel list observing mode and a programmable histogram mode to maximize observational flexibility and data management. During the main JUICE mission, JUICE-UVS will explore the atmospheres and surfaces of the Galilean satellites, examine the dynamics of Jupiter’s upper atmosphere from pole to equator, and investigate the Jupiter-Io connection through observations of the Io torus.
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 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) timescales, as well as longer timescales from minutes to hours during each close approach to Jupiter. This variability has required a multipronged 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).
With the imminent launch of the JWST, the field of thermal-infrared (TIR) astronomy will enjoy a revolution. It is easy to imagine that all areas of infrared (IR) astronomy will be greatly advanced, but perhaps impossible to conceive of the new vistas that will be opened. To allow both follow-up JWST observations and a continuance of work started on the ground-based 8m’s, we continue to plan the science cases and instrument design for a TIR imager and spectrometer for early operation on the TMT. We present the current status of our science cases and the instrumentation plans, harnessing expertise across the TMT partnership. This instrument will be proposed by the MICHI team as a second-generation instrument in any upcoming calls for proposals.
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.
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%.
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.
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).
The Lunar Reconnaissance Orbiter’s (LRO) Lyman Alpha Mapping Project (LAMP) is a lightweight (6.1 kg), lowpower (4.5 W), ultraviolet spectrograph based on the Alice instruments aboard the European Space Agency’s Rosetta spacecraft and NASA’s New Horizons spacecraft. Its primary job is to identify and localize exposed water frost in permanently shadowed regions (PSRs) near the Moon’s poles, and to characterize landforms and albedos in PSRs. LRO launched on June 18, 2009 and reached lunar orbit four days later. LAMP operated with its failsafe door closed for its first seven years in flight. The failsafe door was opened in October 2016 to increase light throughput during dayside operations at the expense of no longer having the capacity to take further dark observations and slightly more operational complexity to avoid saturating the instrument. This one-time irreversible operation was approved after extensive review, and was conducted flawlessly. The increased throughput allows measurement of dayside hydration in one orbit, instead of averaging multiple orbits together to reach enough signal-to-noise. The new measurement mode allows greater time resolution of dayside water migration for improved investigations into the source and loss processes on the lunar surface. LAMP performance and optical characteristics after the failsafe door opening are described herein, including the new effective area, wavelength solution, and resolution.
The Jovian system is the focus of multiple current and future NASA and ESA missions, but dangerously high radiation levels surrounding the planet make operations of instruments sensitive to high energy electrons or gamma rays problematic. Microchannel plate (MCP) detectors have been the detectors of choice in planetary ultraviolet spectrographs for decades. However, the same properties that give these detectors high response to vacuum ultraviolet photons also make them sensitive to high energy electrons and gamma rays. The success of ultraviolet investigations in the Jovian system depends on effectively shielding these MCP detectors to protect them as much as possible from this withering radiation. The design of such shielding hinges on our understanding of the response of MCP detectors to the high energy electrons and gamma rays found there. To this end, Southwest Research Institute and Massachusetts Institute of Technology collaborated in 2012-13 to measure the response of a flight-spare microchannel plate detector to a beam of high energy electrons. The detector response was measured at multiple beam energies ranging from 0.5-2.5 MeV and multiple currents. This response was then checked with MCNP6, a radiation transport simulation tool, to determine the secondary gamma rays produced by the primary electrons striking the detector window. We report on the measurement approach and the inferred electron and gamma sensitivities.
We report our progress toward optimizing backside-illuminated silicon P-type intrinsic N-type complementary metal oxide semiconductor devices developed by Teledyne Imaging Sensors (TIS) for far-ultraviolet (UV) planetary science applications. This project was motivated by initial measurements at Southwest Research Institute of the far-UV responsivity of backside-illuminated silicon PIN photodiode test structures, which revealed a promising QE in the 100 to 200 nm range. Our effort to advance the capabilities of thinned silicon wafers capitalizes on recent innovations in molecular beam epitaxy (MBE) doping processes. Key achievements to date include the following: (1) representative silicon test wafers were fabricated by TIS, and set up for MBE processing at MIT Lincoln Laboratory; (2) preliminary far-UV detector QE simulation runs were completed to aid MBE layer design; (3) detector fabrication was completed through the pre-MBE step; and (4) initial testing of the MBE doping process was performed on monitoring wafers, with detailed quality assessments.
Solar glint suppression is an important consideration in the design of compact photon-counting ultraviolet spectrographs. Southwest Research Institute developed the Lyman Alpha Mapping Project for the Lunar Reconnaissance Orbiter (launch in 2009), and the Ultraviolet Spectrograph on Juno (Juno-UVS, launch in 2011). Both of these compact spectrographs revealed minor solar glints in flight that did not appear in pre-launch analyses. These glints only appeared when their respective spacecraft were operating outside primary science mission parameters. Post-facto scattered light analysis verifies the geometries at which these glints occurred and why they were not caught during ground testing or nominal mission operations. The limitations of standard baffle design at near-grazing angles are discussed, as well as the importance of including surface scatter properties in standard stray light analyses when determining solar keep-out efficiency. In particular, the scattered light analysis of these two instruments shows that standard "one bounce" assumptions in baffle design are not always enough to prevent scattered sunlight from reaching the instrument focal plane. Future builds, such as JUICE-UVS, will implement improved scattered and stray light modeling early in the design phase to enhance capabilities in extended mission science phases, as well as optimize solar keep out volume.
Four compact planetary ultraviolet spectrographs have been built by Southwest Research Institute and successfully operated on different planetary missions. These spectrographs underwent a series of ground radiometric calibrations before delivery to their respective spacecraft. In three of the four cases, the in-flight measured sensitivity was approximately 50% lower than the ground measurement. Recent tests in the Southwest Research Institute Ultraviolet Radiometric Calibration Facility (UV-RCF) explain the discrepancy between ground and flight results. Revised ground calibration results are presented for the Rosetta-Alice, New Horizons-Alice, the Lunar Reconnaissance Orbiter Lyman- Alpha Mapping Project, and Juno-Ultraviolet Spectrograph (UVS) and are then compared to the original ground and flight calibrations. The improved understanding of the calibration system reported here will result in improved ground calibration of the upcoming Jupiter Icy Moons Explorer (JUICE)-UVS.
Heritage wide-field ultraviolet imagers have observed large (~30°) fields-of-view, but suffer from relatively poor (~0.6°) spatial resolution. Improvements in mirror design and fabrication technology allow for a new two-mirror design that preserves a large (40°x20°) field-of-view, while improving spatial resolution by nearly a factor of ten to 0.07° while imaging onto a flat focal surface. Such an imager has uses in a number of ultraviolet astronomical applications, including plasmaspheric imaging and monitoring of the interplanetary medium.
We report our progress toward optimizing backside-illuminated silicon PIN CMOS devices developed by Teledyne Imaging Sensors (TIS) for far-UV planetary science applications. This project was motivated by initial measurements at Southwest Research Institute (SwRI) of the far-UV responsivity of backside-illuminated silicon PIN photodiode test structures described in Bai et al., SPIE, 2008, which revealed a promising QE in the 100-200 nm range as reported in Davis et al., SPIE, 2012. Our effort to advance the capabilities of thinned silicon wafers capitalizes on recent innovations in molecular beam epitaxy (MBE) doping processes. Key achievements to date include: 1) Representative silicon test wafers were fabricated by TIS, and set up for MBE processing at MIT Lincoln Laboratory (LL); 2) Preliminary far-UV detector QE simulation runs were completed to aid MBE layer design; 3) Detector fabrication was completed through the pre-MBE step; and 4) Initial testing of the MBE doping process was performed on monitoring wafers, with detailed quality assessments. Early results suggest that potential challenges in optimizing the UV-sensitivity of silicon PIN type CMOS devices, compared with similar UV enhancement methods established for CCDs, have been mitigated through our newly developed methods. We will discuss the potential advantages of our approach and briefly describe future development steps.
The Extreme Ultraviolet Imager (IMAGE/EUV) aboard NASA's IMAGE mission studied the distribution of singly
ionized helium (He+) in the Earth's plasmasphere by imaging its emission at 30.4 nm. This instrument consisted of three
separate camera heads, each with a 28° field-of-view, with 0.6°resolution. We describe an improved imaging system
that can simultaneously image a 40° field-of-view with 0.45° resolution utilizing only one compact camera head and
detector. This improved imager also increases sensitivity over the heritage EUV imager by a factor of four due to
improvements in optical coatings, detector technology, and a larger entrance aperture.
The Southwest Research Institute Ultraviolet Reflectance Chamber (SwURC) is a highly capable UV reflectometer
chamber and data acquisition system designed to provide bidirectional scattering data of various surfaces and
materials. The chamber provides laboratory-based UV reflectance measurements of water frost/ice, lunar soils,
simulants, and analogs to support interpretation of UV reflectance data from the Lyman Alpha Mapping Project
(LAMP) Lunar Reconnaissance Orbiter (LRO). A deuterium lamp illuminates a monochromator with a nominal
wavelength range of 115 nm to 210 nm. The detector scans emission angles -85° to +85°in the principal plane. Liquid
nitrogen passed through the sample mount enables constant refrigeration of tray temperatures down to 78 K to form
water ice and other volatile samples. The SwURC can be configured to examine a wide range of samples and
materials through the use of custom removable sample trays, connectors, and holders. Calibration reference standard
measurements reported here include Al/MgF2 coated mirrors for specular reflection and Fluorilon for diffuse
reflectances. This calibration work is a precursor to reports of experiments measuring the far-UV reflectance of water
frost, lunar simulants, and Apollo soil sample 10084 in support of LRO-LAMP.
We present a description of the Juno ultraviolet spectrograph (Juno-UVS) and results from its in-flight commissioning
performed between December 5th and 13th 2011 and its first periodic maintenance between October 10th and 12th 2012.
Juno-UVS is a modest power (9.0 W) ultraviolet spectrograph based on the Alice instruments now in flight aboard the
European Space Agency’s Rosetta spacecraft, NASA’s New Horizons spacecraft, and the LAMP instrument aboard
NASA’s Lunar Reconnaissance Orbiter. However, unlike the other Alice spectrographs, Juno-UVS sits aboard a spin
stabilized spacecraft. The Juno-UVS scan mirror allows for pointing of the slit approximately ±30° from the spacecraft
spin plane. This ability gives Juno-UVS access to half the sky at any given spacecraft orientation. The planned 2 rpm
spin rate for the primary mission results in integration times per 0.2° spatial resolution element per spin of only ~17 ms.
Thus, for calibration purposes, data were retrieved from many spins and then remapped and co-added to build up
exposure times on bright stars to measure the effective area, spatial resolution, scan mirror pointing positions, etc. The
primary job of Juno-UVS will be to characterize Jupiter’s UV auroral emissions and relate them to in-situ particle
measurements. The ability to point the slit will make operations more flexible, allowing Juno-UVS to observe the
atmospheric footprints of magnetic field lines through which Juno flies, giving a direct connection between energetic
particle measurements on the spacecraft and the far-ultraviolet emissions produced by Jupiter’s atmosphere in response
to those particles.
We describe vacuum ultraviolet sensitivity measurements of a new high performance silicon-based CMOS sensor from
Teledyne Imaging Sensors. These sensors do not require the high voltages of MCP detectors, making them a lower mass
and power alternative to the more mature MCP technology. These devices demonstrate up to 40 percent quantum
efficiency at vacuum ultraviolet wavelengths, either meeting or greatly exceeding 10 percent quantum efficiency across
the entire 100-200 nm wavelength region. As with similar visible sensitive devices, backside illumination results in a
higher quantum efficiency than frontside illumination. Measurements of the vacuum ultraviolet sensitivity of the
Teledyne silicon PIN detectors were made by directing a known intensity of ultraviolet light at discrete wavelengths onto
the test detectors and reading out the resulting photocurrent. The sensitivity of the detector at a given wavelength was
then calculated from the intensity and wavelength of the incoming light and the relative photodiode to NIST-traceable
calibration diode active areas. A custom electromechanical interface was developed to make these measurements within
the SwRI Vacuum Radiometric Calibration Chamber. While still in the single pixel stage, full 1K × 1K focal plane
arrays are possible using existing CMOS readout electronics and hold great promise for inclusion in future spaceflight
instrument concepts.
The Lyman Alpha Mapping Project (LAMP) is a lightweight (6.1 kg), low-power (4.5 W), ultraviolet spectrograph based
on the Alice instruments now in flight aboard the European Space Agency's Rosetta spacecraft and NASA's New
Horizons spacecraft. Its primary job on NASA's Lunar Reconnaissance Orbiter (LRO) is to identify and localize
exposed water frost in permanently shadowed regions (PSRs) near the Moon's poles, and to characterize landforms and
albedos in PSRs. In this paper we describe the in-flight radiometric performance and commissioning results and
compare them to ground calibration measurements.
We describe the radiometric performance and ground calibration results of the Juno mission's Ultraviolet Spectrograph
(Juno-UVS) flight model. Juno-UVS is a modest power (9.0 W) ultraviolet spectrograph based on the Alice instruments
now in flight aboard the European Space Agency's Rosetta spacecraft, NASA's New Horizons spacecraft, and the LAMP
instrument aboard NASA's Lunar Reconnaissance Orbiter. Its primary job will be to characterize Jupiter's UV auroral
emissions and relate them to in situ particle measurements.
Southwest Research Institute's (SwRI's) "ALICE" line of ultraviolet spectrographs (UVS) is founded on a lightweight,
low power, and highly versatile instrument design. Generally small changes in detector photocathode, pixel size, slit
shape, optical coatings, pinhole aperture implementations, and other minor tweaks have enabled a wide variety of
applications for the ALICE design, including investigations of comets (Rosetta-ALICE), Pluto (New Horizons-ALICE),
the Moon (Lunar Reconnaissance Orbiter (LRO)-Lyman Alpha Mapping Project (LAMP)), and Jupiter (Juno-UVS).
ALICE's high capability and our experience with high radiation environment and outer solar system requirements make
this UVS a good choice for future planetary mission concepts.
We describe the pre-flight radiometric performance and calibration results of the Lunar Reconnaissance Orbiter's
Lyman Alpha Mapping Project (LRO/LAMP) flight model. LAMP is a lightweight (6.1 kg), low-power (4.5 W),
ultraviolet spectrograph based on the ALICE instruments now in flight aboard the European Space Agency's Rosetta
spacecraft and NASA's New Horizons spacecraft. Its primary job will be to identify and localize exposed water frost in
permanently shadowed regions (PSRs), and to characterize landforms and albedos in PSRs. Detailed radiometric
performance results of the LAMP flight model are presented and discussed.
The Echelon-cross-Echelle Spectrograph (EXES) will provide the Stratospheric Observatory for Infrared Astronomy (SOFIA) with high spectral resolution capabilities in the mid-infrared. EXES will have a maximum spectral resolving power of 100,000 along with lower resolution options (R=10,000; R=3000). EXES on SOFIA will provide sensitivity and spectral resolution never before available from an orbital or sub-orbital platform. Because of the wealth of molecular features in the EXES spectral range, 4.5 to 28.3 μm, and the dramatic reduction in telluric atmospheric interfence provided by SOFIA, EXES will be particularly relevant for studies of the solar system, star formation and the interstellar medium. We report on the EXES design and current status, provide descriptions of observing modes and sensitivity estimates, discuss the calibration and likely data products, and describe the potential gains of incorporating a 1024 × 1024, low-background, Si:As detector array.
TEXES is a versatile mid-infrared spectrograph, which has been used on the NASA IRTF since 2000. It is capable of high spectral resolution (R ≈ 100,000), which is well suited for observations of interstellar and circumstellar molecules and ions, as well as molecules in planetary and stellar atmospheres. It has been installed on Gemini North where its point source sensitivity is expected to improve by a factor of 7, and its angular resolution will improve by 8/3.
TEXES, the Texas Echelon Cross Echelle Spectrograph, is a versatile mid-infrared (5-25 μm) spectrograph that can be used in several operating modes: high resolution cross-dispersed, with a resolving power of R = 50-100,000; medium resolution long-slit, with R~15,000; low resolution long-slit, with R~3000; source acquisition imaging; and pupil imaging.
The design of TEXES is unique in several respects. The primary disperser is a variation on an echelon, a steeply and coarsely blazed (R10 with 0.3 inch groove spacing), 36 inch long, diamond-machined aluminum grating. The cross disperser is an R4 echelle used in low order at R2, with the grooves acting as corner reflectors. Cold mechanisms allow the echelon to be bypassed to use the cross disperser in long-slit mode. A first-order grating can be inserted in front of the echelle for lower resolution. In addition, the low resolution grating can be turned face-on to act as a mirror allowing source-acquisition imaging and pupil viewing.
TEXES has been used for 8 nights on the McDonald Observatory 2.7m and 45 nights on the NASA IRTF 3m telescopes over the last 2 1/2 years. Sources observed include planets and planetary satellites, stellar atmospheres, circumstellar outflows and disks, and molecular clouds and HII regions in the Milky Way and external galaxies.
TEXES, the Texas Echelon Cross Echelle Spectrograph, is an ideal instrument to study molecular clouds at a spectral resolving power of 100,000 between 5 and 25 μm. In many molecular clouds, high extinction often means that no visible stars are available for off-axis guiding. At a resolving power of 100,000, only the very brightest sources can be observed while guiding on the power in the dispersed IR spectra.
We present the design of a high-speed on-axis guider for TEXES operating at 3.65 μm, a wavelength outside the spectrometer operating band where many of the target sources are still detectable for imaging. We use a new technology gold nanomesh resonant IR filter/mirror from EDTEK, that transmits 3.65 μm light to the guide detector with a peak transmittance of 60% while reflecting light from 5 μm long-ward with 98% efficiency to the dispersing elements in the spectrograph. A PC controls clocking patterns for the CRC-463 detector from Raytheon Infrared Operations and the analog to digital conversion of signals with a 14 bit A/D card. Image centroiding is done in software and then offsets are sent to the telescope for pointing adjustments or tip-tilt corrections when a tip-tilt secondary is available.
This system is a prototype designed to test the feasibility of a similar guider for EXES, the Echelon Cross Echelle Spectrograph, mounted on SOFIA, the Stratospheric Observatory for Infrared Astronomy.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) will provide new opportunities for high spectral resolution observations in the mid-infrared. To take advantage of these opportunities, we are developing EXES, the Echelon-Cross-Echelle Spectrograph. EXES will operate from 4.5 microns to 28.5 microns and achieve a velocity resolution of 3 km/s for λ < 10 μm. EXES will be a versatile instrument with three spectroscopic modes: cross-dispersed with R~105; long-slit with R~104; and long-slit with R~3000. The unique aspect of EXES is the high-resolution capability provided by a 1 meter echelon grating and a 256 by 256 low-background Si:As IBC detector. Much of the design and operation of EXES has already been validated by the performance of a very similar ground-based instrument, the Texas Echelon-Cross-Echelle Spectrograph (TEXES). We present here a summary of the EXES design and current status; a brief description of ground-based, high spectral resolution, mid-infrared results; and a look ahead to the possible science using SOFIA and EXES.
We are developing a high spectral resolution grating spectrograph as a PI instrument for the Stratospheric Observatory for Infrared Astronomy. The Echelon-Cross- Echelle Spectrograph (EXES) will operate at 5.5 - 28.5 micrometers in three spectroscopic modes: R approximately 105, 2 X 104, and 4000. We use an echelon, a coarsely ruled, steeply blazed diffraction grating to achieve high resolution. Cross-dispersion is done with an echelle used at relatively low order. The detector is a 256 X 256 pixel Si:As IBC array. A very similar instrument, the Texas Echelon-Cross-Echelle Spectrograph (TEXES), has had a successful telescope run at the McDonald Observatory. We give here a progress report on the design of EXES and the status of TEXES.
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