The Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission is an astrophysics Small Explorer employing ultraviolet spectroscopy (EUV: 80 to 825 Å and FUV: 1280 to 1650 Å) to explore the high-energy radiation environment in the habitable zones around nearby stars. ESCAPE provides the first comprehensive study of the stellar EUV and coronal mass ejection environments that directly impact the habitability of rocky exoplanets. In a 20-month science mission, ESCAPE will provide the essential stellar characterization to identify exoplanetary systems most conducive to habitability and provide a roadmap for NASA’s future life-finder missions. ESCAPE accomplishes this goal with roughly two-order-of-magnitude gains in EUV efficiency over previous missions. ESCAPE employs a grazing incidence telescope that feeds an EUV and FUV spectrograph. The ESCAPE science instrument builds on previous ultraviolet and x-ray instrumentation, grazing incidence optical systems, and photon-counting ultraviolet detectors used on NASA astrophysics, heliophysics, and planetary science missions. The ESCAPE spacecraft bus is the versatile and high-heritage Ball Aerospace BCP-Small spacecraft. Data archives will be housed at the Mikulski Archive for Space Telescopes.
The Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission is an astrophysics Small Explorer employing ultraviolet spectroscopy (EUV: 80 - 825 Å and FUV: 1280 - 1650 Å) to explore the high-energy radiation environment in the habitable zones around nearby stars. ESCAPE provides the first comprehensive study of the stellar EUV and coronal mass ejection environments which directly impact the habitability of rocky exoplanets. In a 20 month science mission, ESCAPE will provide the essential stellar characterization to identify exoplanetary systems most conducive to habitability and provide a roadmap for NASA's future life-finder missions. ESCAPE accomplishes this goal with roughly two-order-of-magnitude gains in EUV efficiency over previous missions. ESCAPE employs a grazing incidence telescope that feeds an EUV and FUV spectrograph. The ESCAPE science instrument builds on previous ultraviolet and X-ray instrumentation, grazing incidence optical systems, and photon-counting ultraviolet detectors used on NASA astrophysics, heliophysics, and planetary science missions. The ESCAPE spacecraft bus is the versatile and high-heritage Ball Aerospace BCP-Small spacecraft. Data archives will be housed at the Mikulski Archive for Space Telescopes (MAST). ESCAPE is currently completing a NASA Phase A study, and if selected for Phase B development would launch in 2025.
The Normal-incidence Extreme Ultraviolet Photometer (NExtUP) is a smallsat mission concept designed to measure the EUV radiation conditions of exoplanet host stars, and F-M type stars in general. EUV radiation is absorbed at high altitude in a planetary atmosphere, in the exosphere and upper thermosphere, where the gas can be readily heated to escape temperatures. EUV heating and ionization are the dominant atmospheric loss drivers during most of a planet’s life. There are only a handful of accurately measured EUV stellar fluxes, all dating from Extreme Ultraviolet Explorer (EUVE) observations in the ‘90s. Consequently, current models of stellar EUV emission are uncertain by more than an order of magnitude and dominate uncertainties in planetary atmospheric loss models. NExtUP will use periodic and aperiodic multilayers on off-axis parabolic mirrors and a prime focus microchannel plate detector to image stars in 5 bandpasses between 150 and 900°A down to flux limits two orders of magnitude lower than reached by EUVE. NExtUP may also accomplish a compelling array of secondary science goals, including using line-of-sight absorption measurements to understand the structure of the local interstellar medium, and imaging EUV emission from energetic processes on solar system objects at unprecedented spatial resolution. NExtUP is well within smallsat weight limits, requires no special orbital conditions, and would be flown on a spacecraft supplied by MOOG Industries. It draws on decades of mission heritage expertise at SAO and LASP, including similar instruments successfully launched and operated to observe the Sun.
The Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission is an astrophysics Small Explorer employing ultraviolet spectroscopy (EUV: 80 – 825 Å and FUV: 1280 – 1650 Å) to explore the high-energy radiation environment in the habitable zones around nearby stars. ESCAPE provides the first comprehensive study of the stellar EUV and coronal mass ejection environments which directly impact the habitability of rocky exoplanets. In a 21 month science mission, ESCAPE will provide the essential stellar characterization to identify exoplanetary systems most conducive to habitability and provide a roadmap for future life-finder missions. ESCAPE accomplishes this goal with roughly two-order-of-magnitude gains in EUV efficiency over previous missions. ESCAPE employs a grazing incidence telescope that feeds an EUV and FUV spectrograph, building on experience with ultraviolet and X-ray instrumentation, grazing incidence optical systems, and photon-counting ultraviolet detectors. The instrument builds on design and hardware heritage from numerous NASA UV astrophysics, heliophysics, and planetary science missions. The ESCAPE spacecraft bus is the versatile and high-heritage Ball Aerospace BCP-Smallspacecraft. Data archives are housed at the Mikulski Archive for Space Telescopes (MAST).
KEYWORDS: Space telescopes, Stars, Ultraviolet radiation, Magnetism, Telescopes, Planets, Spatial resolution, James Webb Space Telescope, Reflector telescopes, Planetary systems
The solutions to a number of astrophysical problems require access to the ultraviolet, optical, and infrared from space-based facilities, with capabilities beyond those available with Hubble Space Telescope or James Webb Space Telescope. A large ultraviolet-optical-infrared telescope will need to have a large collecting area and milliarcsecond angular resolution capabilities plus highly efficient instruments, providing a revolutionary enhancement in capability. During 2013, the European astronomical community was involved in an exercise to outline the big science that could be achieved with such a facility; the proposal was called EUVO (as per European Ultraviolet-Visible Observatory). Inspired by that work, we describe a proposal on future science and instrumentation to be carried out with a 10-m class telescope.
The various demands on funding agencies make it difficult to sustain the level of expenditure required to provide the
broad range of space astronomy missions that the research community would like to have available. Multi-billion
pound/dollar observatories such Chandra, XMM-Newton and HST have been enormously successful, but JWST has been
delayed and plans for an equivalent large X-ray mission seem to be on-hold. Furthermore, the medium size ESA and
NASA missions provide only a small number of opportunities over the next decade. Much exciting and important
science, by default, will not be done. If satellite mission costs could be reduced significantly, by a factor of 5-10, we
would open up a new parameter space of opportunity that is not currently offered by any agency. Significant
improvement in instrument technology coupled with simplification of optical systems and the development of efficient,
high performance small satellite platforms and ground systems has led to the prospect of the development of some low-cost
opportunities. In this paper, we outline one such possible mission, based on a successful sounding rocket-borne
payload. This comprises a high throughput normal incidence extreme ultraviolet spectrometer, with the design adapted
for accommodation on the SSTL 300 platform. We make use of a segmented diffraction grating to provide an overall
wavelength coverage from ~170-260Å by tuning the multi-layers of the individual elements to different, overlapping
ranges. We outline the capability and science goals of the mission, and how they influence the design and operation of
the satellite platform. We conclude with a discussion of how missions of this type operating both as constellations and
as formation flying sparse apertures, could offer a scientifically viable alternative to monolothic 'great observatory'
missions in the future.
As astronomical observations are pushed to cosmological distances (z>3) the spectral energy distributions of X-ray
objects, AGN for example, will be redshifted into the EUV waveband. Consequently, a wealth of critical spectral
diagnostics, provided by, for example, the Fe L-shell complex and the O VII/VIII lines, will be lost to future planned X-ray
missions (e.g., IXO, Gen-X) if operated at traditional X-ray energies. This opens up a critical gap in performance
located at short EUV wavelengths, where critical X-ray spectral transitions occur in high-z objects. However, normal-incidence
multilayer-grating technology, which performs best precisely at such wavelengths, together with advanced
nanolaminate replication techniques have been developed and are now mature to the point where advanced EUV
instrument designs with performance complementary to IXO and Gen-X are practical. Such EUV instruments could be
flown either independently or as secondary instruments on these X-ray missions. We present here a critical examination
of the limits placed on extragalactic EUV measurements by ISM absorption, the range where high-z measurements are
practical, and the requirements this imposes on next-generation instrument designs. We conclude with a discussion of a
breakthrough technology, nanolaminate replication, which enables such instruments.
The EUV waveband includes critical spectral features containing diagnostic information often not available at other
wavelengths, and the bulk of radiation from million degree plasmas is emitted in the EUV. Such plasmas are ubiquitous,
and examples include white dwarf photospheres; accretion phenomena in young stars, CVs and AGN; stellar coronae;
and the ISM of our galaxy and of others. However, sensitive high-resolution spectroscopy is required to resolve and
identify source and ISM spectral features unambiguously, and to measure line profiles and Doppler shifts. This allows
exploitation of the full range of plasma diagnostic techniques developed in laboratory and solar physics. The J-PEX
high-resolution EUV spectrometer has made a breakthrough in capability with an effective area of 7 cm2 (220-250 Å)
and resolving power of 4000, which exceed EUVE by factors of 7 and 20 respectively, and cover a range beyond the
170-Å cutoff of the Chandra LETG. J-PEX has flown successfully twice on NASA sounding rockets, but NASA has
approved no new orbital EUV mission. It is time for one. Here we describe the scientific case for high-resolution EUV
spectroscopy, summarize the technology that makes practical such measurements, and present concepts for a ~3-month
orbital mission and for larger missions.
The World Space Observatory - Ultraviolet (WSO-UV) is a space astronomy project led by Russia, with contributions
from China, Germany, Italy, Spain, United Kingdom and a number of other countries in the world. WSO-UV consists of
a 1.7-meter diameter telescope and three focal plane science instruments. The Long Slit Spectrograph instrument on-board
WSO-UV will produce moderate spectral resolution (R=1000-2500) spectra in the 102nm ~ 320nm wavelength
range along a slit of 75 arcsec in length and 1 arcsec in width. The spatial resolution of the instrument will be ~1 arcsec.
A two-channel scheme is proposed to optimize performance, with each of these using a Rowland Circle optical design
with Microchannel Plate detectors in the focal plane. We will discuss the detailed design of the spectrograph and its
expected performance in this paper.
Since hot 100,000-1,000,000K gas in stars radiates predominantly at EUV and soft X-ray wavelengths, observations in
these bands provide important diagnostics of the physical conditions in hot photospheres, stellar coronae and stellar
winds. However, such studies are only able to examine the bulk of material, without being able to separate out the
several gas components present. Radial velocity diagnostics have been used frequently in the UV and visible bands to
distinguish different emission or absorption components in stellar spectra. Now, developments in grating and instrument
technology provide a first opportunity to extend this technique into the EUV. Based on capabilities of the improved JPEX
spectrometer (reported elsewhere in this volume), this paper reports on the key science that might be carried out
with such an instrument; both as a sounding rocket payload and longer duration mission.
APEX is a proposed mission for a Small Explorer (SMEX) satellite. The instrument is a suite of 8 near-normal incidence EUV spectrometers and is the outgrowth of 17 years of research at NRL on multilayer coatings and holographic ion-etched diffraction gratings. A prototype spectrometer has been flown successfully on a sounding rocket. We have examined different multilayer and gratings designs and produced a configuration optimized for the proposed science. APEX will achieve a peak effective area of at least 30-50 cm2 in the range 90-275 Å with resolution ~10,000, significant improvements on Chandra and EUVE.
APEX is a proposed mission for a Small Explorer (SMEX) satellite. APEX will investigate the density, temperature, composition, magnetic field, structure, and dynamics of hot astrophysical plasmas (log T = ~5-7), which emit the bulk of their radiation at EUV wavelengths and produce critical spectral diagnostics not found at other wavelengths. APEX addresses basic questions of stellar evolution and galactic structure through high-resolution spectroscopy of white dwarf stars, cataclysmic variables, the local interstellar medium, and stellar coronae. Thus APEX complements the Chandra, Newton-XMM, FUSE, and CHIPS missions. The instrument is a suite of 8 near-normal incidence spectrometers (~90-275 Angstroms, resolving power ~10,000, effective area 30-50 cm2) each of which employs a multilayer-coated ion-etched blazed diffraction grating and a microchannel plate detector of high quantum efficiency and high spatial resolution. The instrument is mounted on a 3-axis stabilized commercial spacecraft bus with a precision pointing system. The spacecraft is launched by a Taurus vehicle, and payload size and weight fit comfortably within limits for the 2210 fairing. Of order 100 targets will be observed over the baseline mission of 2 years. These are selected carefully to maximize scientific return, and all were detected in the EUVE and the ROSAT WFC surveys.
EUVE and the ROSAT WFC have left a tremendous legacy in astrophysics at EUV wavelengths. More recently, Chandra and XMM-Newton have demonstrated at X-ray wavelengths the power of high-resolution astronomical spectroscopy, which allows the identification of weak emission lines, the measurement of Doppler shifts and line profiles, and the detection of narrow absorption features. This leads to a thorough understanding of the density, temperature, abundance, magnetic, and dynamic structure of astrophysical plasmas. However, the termination of the EUVE mission has left a gap in spectral coverage at crucial EUV wavelengths (~100-300 Å), where hot (105 - 108 K) plasmas radiate most strongly and produce critical spectral diagnostics. CHIPS will fill this hole only partially as it is optimized for diffuse emission and has only moderate resolution (R~150). For discrete sources, we have successfully flown a follow-on instrument to the EUVE spectrometer (Aeff ~ 1 cm2, R ~ 400), the high-resolution spectrometer J-PEX (Aeff ~ 3 cm2, R ~ 3000). Here we build on the J-PEX prototype and present a strawman design for an orbiting spectroscopic observatory, APEX, a SMEX-class instrument containing a suite of 8 spectrometers that together achieve both high effective area (Aeff > 10 cm2) and high spectral resolution (R ~ 10,000) over the range 100-300 Å. We also discuss alternate configurations for shorter and longer wavelengths.
We report on the successful sounding rocket flight of the high resolution (R=3000-4000) J-PEX EUV spectrometer. J-PEX is a novel normal incidence instrument, which combines the focusing and dispersive elements of the spectrometer into a single optical element, a multilayer-coated grating. The high spectral resolution achieved has had to be matched by unprecedented high spatial resolution in the imaging microchannel plate detector used to record the data. We illustrate the performance of the complete instrument through an analysis of the 220-245Å spectrum of the white dwarf G191-B2B obtained with a 300 second exposure. The high resolution allows us to detect a low-density ionized helium component along the line of sight to the star and individual absorption lines from heavier elements in the photosphere.
Martin Barstow, L. Binette, Noah Brosch, F.Z. Cheng, Michel Dennefeld, A.I. de Castro, H. Haubold, K.A. van der Hucht, N. Kappelmann, P. Martinez, A. Moisheev, I. Pagano, Erez Ribak, J. Sahade, B. Shustov, J.-E. Solheim, W. Wamsteker, K. Werner, Helmut Becker-Ross, Stefan Florek
The World Space Observatory is an unconventional space project proceeding via distributed studies. The present design, verified for feasibility, consists of a 1.7-meter telescope operating at the second Largangian point of the Earth-Sun system. The focal plane instruments consist of three UV spectrometers covering the spectral band from Lyman alpha to the atmospheric cutoff with R~55,000 and offering long-slit capability over the same band with R~1,000. In addition, a number of UV and optical imagers view adjacent fields to that sampled by the spectrometers. Their performance compares well with that of HST/ACS and the spectral capabilities of WSO rival those of HST/COS.
The WSO, as presently conceived, will be constructed and operated with the same distributed philosophy. This will allow as many groups and countries to participate, each contributing as much as feasible but allowing multi-national participation. Although designed originally with a conservative approach, the WSO embodies some innovative ideas and will allow a world-class mission to be realized with a moderate budget.
We have fabricated the four flight gratings for a sounding rocket high-resolution spectrometer using a holographic ion-etching technique. The gratings are spherical (4000-mm radius of curvature), large (160 mm x 90 mm), and have a laminar groove profile of high density (3600 grooves/mm). They have been coated with a high-reflectance multilayer of Mo5C/Si/Mo2Si. Using an atomic force microscope, we examined the surface characteristics before and after multilayer coating. The average roughness is approximately 2-3A rms after coating, somewhat smoothened by the multilayer. Using synchrotron radiation, we completed an efficiency calibration map of each grating over the wavelength range 225-245A. At an angle of incidence of 5 degree(s) and a wavelength of 234A, the average efficiency peaks in the first inside order at 10.3+/- 0.6% for Grating 1, 7.3+/- 0.9% for Grating 6, 7.2+/- 1.2% for Grating 3, and 9.0+/- 1.5% for Grating 4. These values exceed all previously published results for a high density grating. The first order groove efficiency for Grating 1 is 34.4+/- 1.9%, in good agreement with the best value obtained from similar test gratings and close to the theoretical limit of 40.5%.
We describe the development of an imaging microchannel plate detector for a new class of high resolution EUV spectrometer. The detector incorporates a front MCP coated with a CsI photocathode to enhance quantum efficiency, while the rear MCP, supplied by Photonis SAS for a European Space Agency Technology Research Program, represents one of the first uses of a 6 micron pore device in astronomy. The detector uses a unique design of charge division anode, the Vernier readout, enabling it to deliver a spatial resolution better than 15 microns FWHM. The detector forms an integral component of J- PEX, a sounding rocket EUV spectrometer operating at near- normal incidence, using multilayer coated gratings to deliver a resolution and effective area 10 times that of EUVE in the 225 - 245 angstrom band.
The Chandra X-ray Observatory was successfully launched on July 23, 1999, and subsequently began an intensive calibration phase. We present preliminary results from in- flight calibration of the low energy response of the High Resolution Camera Spectroscopic readout (HRC-S) combined with the Low Energy Transmission Grating (LETG) aboard Chandra. These instruments comprise the Low Energy Transmission Grating Spectrometer (LETGS). For this calibration study, we employ a pure hydrogen non-LTE white dwarf emission model (Teff equals 25000 K and log g equals 9.0) for comparison with the Chandra observations of Sirius B. Pre-flight calibration of the LETGS effective area was conducted only at wavelengths shortward of 45 angstroms (E > 0.277 keV). Our Sirius B analysis shows that the HRC-S quantum efficiency (QE) model assumed for longer wavelengths overestimates the effective area on average by a factor of 1.6. We derive a correction to the low energy HRC-S QE model to match the predicted and observed Sirius B spectra over the wavelength range of 45 - 185 angstroms. We make an independent test of our results by comparing a Chandra LETGS observation of HZ 43 with pure hydrogen model atmosphere predictions and find good agreement.
The main design features and the early findings of the Rosat XUV wide field camera (WFC) are discussed. The most important data on the WFC telescope and detectors are presented. The WFC operational features, observing efficiency, filter performance, thermal performance star tracker performance, and single-event upsets are discussed. The first WFC images are compared with preflight calibration data.
Results of the calibration program performed on flight and flight-spare detectors for the Rosat Wide Field Camera (WFC) are presented. The result of an accelerated life test on a development model detector assembled to flight standard are summarized. Imaging tests demonstrate that the lookup table technique for removing distortion works efficiency with low differential nonlinearity. No undesirable 'chicken wire' effects are seen in the images, and the detector resolution matches the on-axis performance of the telescope and is constant across the field of view. Peaks in efficiency occur at 10.2, 20, and 100 eV and mimima at 13 and 45 eV. The secondary 13 eV minimum is correlated with the onset of two-electron photoemission. The mean change in gain as a function of photon energy in the EUV band is much less rapid than in the soft X-ray band.
The ROSAT project is an international collaboration between the Federal Republic of Germany, the United Kingdom, and the United States. The satellite, due to be launched in June 1990, carries a payload of two coaligned imaging telescopes: the German X-Ray Telescope (XRT), which operates in the soft x-ray band (0.1 to 2 keV or 6 to 100 A), and the UK Wide Field Camera (WFC), which operates in the XUV band (0.02 to 0.2 keV or 60 to 600 A). ROSAT will perform two main tasks in its anticipated two to four year lifetime: a six-month all-sky survey in the soft x ray and XUV bands followed by a program of pointed observations for detailed studies of thousands of individual targets. In this paper we review the
design and performance of the WFC. The instrument is a grazing incidence telescope comprising a set of three nested, Wolter-Schwarzschild Type I, gold-coated aluminum mirrors with a microchannel plate detector at their common focus. Thin plastic and metal film filters define the wavelength passbands.
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