The Nancy Grace Roman Space Telescope (“Roman”) was prioritized by the 2010 Decadal Survey in Astronomy & Astrophysics and is NASA’s next astrophysics flagship observatory. Launching no earlier than 2026, it will conduct several wide field and time domain surveys, as well as conduct an exoplanet census. Roman’s large field of view, agile survey capabilities, and excellent stability enable these objectives, yet present unique engineering and test challenges. Roman comprises a Spacecraft and the Integrated Payload Assembly (IPA), the latter of which includes the Optical Telescope Assembly (OTA), the primary science Wide Field Instrument, a technology demonstration Coronagraph Instrument, and the Instrument Carrier, which meters the OTA to each instrument. The Spacecraft supports the IPA and includes the Bus, Solar Array Sun Shield, Outer Barrel Assembly, and Deployable Aperture Cover. It provides all required power, attitude control, communications, data storage, and stable thermal control functions as well as shading and straylight protection across the entire field of regard. This paper presents the Observatory as it begins integration and test, as well as describes key test and verification activities.
The Nancy Grace Roman Space Telescope project is NASA's next flagship astrophysics mission to study dark energy, dark matter, and exoplanets along with the innumerable topics that will be enabled by the infrared survey telescope's instruments. The Wide Field Instrument contains a focal plane of 18 newly developed Teledyne H4RG-10 HgCdTe detectors. Roman's focal plane completed its first system level thermal vacuum test at NASA Goddard in 2022, when an increase in dark current compared to component level testing was observed for several detectors. Roman chartered an anomaly review board (ARB) and in collaboration with Teledyne undertook a testing program to help identify possible root cause and select from Roman's spare inventory suitable replacement detectors for devices that had significantly degraded. A possible root cause was determined by the ARB along with recommendations for how to prevent further degradation. We summarize the initial observation of the detector anomaly, present the detector testing strategy to find suitable spares and provide evidence of root cause, share the general findings of the ARB, and show new data showing the improved dark current performance.
REX is a NASA Astrophysics Small Explorer Mission concept to chart the history of cosmic dawn in unprecedented detail in space and time. REX will identify very young galaxies and black holes by means of their powerful Lyman alpha (Lyα) line emission using about 10 narrow-bandpass filters covering about 100 square degrees. The strong line emission identifies samples of the most actively star-forming early galaxies, believed to be the drivers of reionization. Moreover, mapping the distribution and properties of the Lyman alpha emitting population will reveal the distribution of ionized and neutral gas, because neutral gas scatters Lyman alpha light, rendering them difficult to detect. REX will use an 0.5-1m telescope and 1 square degree field of view, tiled with HgCdTe detectors with development heritage from the Nancy Grace Roman Space Telescope. Its large, flexible filter complement will be used in a point-and-stare mode to identify Lyα emitting galaxies at a range of discrete redshift slices spanning the reionization era. In addition to its core reionization surveys, REX brings a new capability of tracing gas emission over large scales at the peak of star and black formation era. We will find millions of the youngest, least massive galaxies in epochs spanning the most active growth period of the universe. Applications will include ionized gas in nearby and distant galaxies, active galactic nuclei, and galaxy clusters. In summary, the REX survey will have the sensitivity and the area coverage to find the sites of earliest galaxy formation and will have the pixel size to enable good localization for follow up of individual galaxies with JWST and future telescopes.
The Nancy Grace Roman Space Telescope (“Roman”) was prioritized by the 2010 Decadal Survey in Astronomy and Astrophysics and is NASA’s next astrophysics flagship Observatory. Launching no earlier than 2026, it will conduct several wide field and time domain surveys, as well as conduct an exoplanet census. Roman’s large field of view, agile survey capabilities, and excellent stability enable these objectives, yet present unique engineering and test challenges. The Roman Observatory comprises a Spacecraft and the Integrated Payload Assembly (IPA), the latter of which includes the Optical Telescope Assembly (OTA), the primary science Wide Field Instrument, a technology demonstration Coronagraph Instrument, and the Instrument Carrier, which meters the OTA to each instrument. The Spacecraft supports the IPA and includes the Bus, Solar Array Sun Shield, Outer Barrel Assembly, and Deployable Aperture Cover. It provides all required power, command handling, attitude control, communications, data storage, and stable thermal control functions as well as shading and straylight protection across the entire field of regard. This paper presents the Observatory as it begins integration and test, as well as describes key test and verification activities.
Surveys in space and time are key to answering outstanding questions in astrophysics. The power to study very large numbers of stars, galaxies, and transient events over large portions of the sky and different time scales has repeatedly led to new breakthroughs. The Nancy Grace Roman Space Telescope (Roman), NASA’s next Astrophysics Flagship mission, elevates wide field and time domain survey observations to previously inaccessible scales. Roman carries the Wide Field Instrument (WFI), which provides visible to near-infrared imaging and spectroscopy with an unprecedented combination of field-of-view, spatial resolution, and sensitivity. When combined with a highly stable observatory and efficient operations, the WFI allows surveys never before possible. These observations will lead to new discoveries in cosmology, exoplanets, and a very wide array of other astrophysics topics ranging from high redshift galaxies to small bodies in the solar system. This paper provides an overview of Roman survey science, connects this science to the design of the WFI, and provides a status update on WFI hardware build and test.
iLocater is a new, near-infrared, extreme precision radial velocity (EPRV) spectrograph under construction for the dual 8.4m diameter Large Binocular Telescope (LBT). The instrument uses single-mode fibers (SMFs) injected with adaptive optics for illumination. We present the integration process for the spectrograph and cryostat systems, and the laboratory performance testing that has been completed. Testing has included optical performance characterization at ambient and cryogenic temperatures, assessment of cryogenic thermal control of the system (80-100K) at sub-mK level, and instrument detector performance (an H4RG-10). The optimized spectrograph and cryostat system will be delivered to the LBT in 2024.
The Roman Space Telescope Grism and Prism assemblies will allow the wide-field instrument (WFI) to perform slitless, multi-object spectroscopy across the complete field of view. These optical elements play a critical role in the High Latitude Wide Area and High Latitude Time Domain Surveys, which are designed to produce robust spectroscopic redshifts for millions of objects over the mission lifetime. To facilitate the characterization of these assemblies, a dedicated test bed was designed and utilized to perform a wide variety of spectroscopic measurements over the full range of operational wavelengths and field angles. Characterized features include, but are not limited to dispersion magnitude, dispersion clocking, encircled energy, total throughput, and bandpass edges. We present the results of this experimental campaign in which the Grism and Prism assemblies met or exceeded many of their design requirements and discuss measurement limitations.
We present a plan to address the calibration needs of the Wide Field Instrument (WFI) on the Wide Field Infrared Space Telescope (WFIRST), for on on-orbit observations and ground testing. The science mission of WFI is based on a combination of large surveys, a Guest Observer program, and a strong archival research program.
The WFIRST Science Requirements Document delineates several data quality and calibration requirements for the Mission. The Calibration Plan aims to be prescriptive and predictive, discussing which observations will be needed and estimating the total time required to carry out such observations. We discuss these requirements from an instrumental perspective, and identify the measurements, observations, and analysis steps needed to achieve the desired calibration and data quality levels, especially in terms of on-orbit observations..
The Nancy Grace Roman Space Telescope (Roman) formerly known as the Wide-Field Infrared Survey Telescope will answer fundamental questions about the evolution of dark energy over time and expand the catalog of known exoplanets into new regions of parameter space. Using a Hubble-sized mirror and 18 newly developed HgCdTe 4K × 4K photodiode arrays (H4RG-10), the Roman Space Telescope will measure the positions and shapes of hundreds of millions of galaxies, the light curves of thousands of supernovae, and the microlensing signals of over a thousand exoplanets toward the bulge of the Galaxy. These measurements require unprecedented sensitivity and characterization of the Wide Field Instrument, particularly its detectors. The Roman project undertook an extensive detector development program to create focal plane arrays that meet these science requirements. These prototype detectors have been characterized and their performance demonstrated in a relevant space-like environment (thermal vacuum, vibration, acoustic, and radiation testing), advancing the H4RG-10’s technology readiness level (TRL) to TRL-6. We present the performance characteristics of these TRL-6 demonstration devices.
NASA’s Wide Field Infrared Survey Telescope (WFIRST) is being designed to deliver unprecedented capability in dark energy and exoplanet science, and to host a technology demonstration coronagraph for exoplanet imaging and spectroscopy. The observatory design has matured since 2013 [“WFIRST 2.4m Mission Study”, D. Content, SPIE Proc Vol 8860, 2013] and we present a comprehensive description of the WFIRST observatory configuration as refined during formulation phase (AKA the phase-A study). The WFIRST observatory is based on an existing, repurposed 2.4m space telescope coupled with a 288 megapixel near-infrared (0.6 to 2 microns) HgCdTe focal plane array with multiple imaging and spectrographic modes. Together they deliver a 0.28 square degree field of view, which is approximately 100 times larger than the Hubble Space Telescope, and a sensitivity that enables rapid science surveys. In addition, the technology demonstration coronagraph will prove the feasibility of new techniques for exoplanet discovery, imaging, and spectral analysis. A composite truss structure meters both instruments to the telescope assembly, and the instruments and the spacecraft are on-orbit serviceable. We present the current design and summarize key Phase-A trade studies and configuration changes that improved interfaces, improved testability, and reduced technical risk. We provide an overview of our Integrated Modeling results, performed at an unprecedented level for a phase-A study, to illustrate performance margins with respect to static wavefront error, jitter, and thermal drift. Finally, we summarize the results of technology development and peer reviews, demonstrating our progress towards a low-risk flight development and a launch in the middle of the next decade.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant to many astrophysical problems. ACCESS, “Absolute Color Calibration Experiment for Standard Stars”, is a series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration accuracy of 1% and a spectral resolving power of 500 across the 0.35 − 1.7μm bandpass. This paper describes the sub-system testing, payload integration, avionics operations, and data transfer for the ACCESS instrument.
The slitless spectrometer plays an important role in the WFIRST mission for the survey of emission-line galaxies. This
will be an unprecedented very wide field, HST quality 3D survey of emission line galaxies1. The concept of the
compound grism as a slitless spectrometer has been presented previously. The presentation briefly discusses the
challenges and solutions of the optical design, and recent specification updates, as well as a brief comparison between
the prototype and the latest design. However, the emphasis of this paper is the progress of the grism prototype: the
fabrication and test of the complicated diffractive optical elements and powered prism, as well as grism assembly
alignment and testing. Especially how to use different tools and methods, such as IR phase shift and wavelength shift
interferometry, to complete the element and assembly tests. The paper also presents very encouraging results from
recent element tests to assembly tests. Finally we briefly touch the path forward plan to test the spectral characteristic,
such as spectral resolution and response.
The current baseline for the Wide-Field Infrared Survey Telescope Astrophysics Focused Telescope Assets (WFIRST/AFTA) instrument includes a single wide-field channel instrument for both imaging and spectroscopy. The only routinely moving part during scientific observations for this wide-field channel is the element wheel (EW) assembly. This filter-wheel assembly will have 8 positions that will be populated with 6 bandpass filters, a blank position, and a grism assembly that will consist of a three-element assembly to disperse the central wavelength undeviated for galaxy redshift surveys. All elements in the EW assembly will be made out of fused silica substrates (110 mm diameter) that will have the appropriate bandpass coatings according to the filter designations (Z087, Y106, J129, H158, F184, W149 and Grism). This paper will present and discuss spectral performance (including spectral transmission and surface-figure wavefront errors ) for a subset of the bandpass filter complement that include filters such as Z087, W149, and Grism. These filter coatings have been procured from three different vendors to assess the most challenging aspects in terms of the in-band throughput (> 95 %), out of band rejection (< 10−4), spatial uniformity (< 1% transmission level) and the cut-on and cut-off slopes (≈ 3% for the filters and 0.3% for the grism coatings).
KEYWORDS: Mirrors, Telescopes, Optical design, Space telescopes, Staring arrays, Sensors, James Webb Space Telescope, Infrared telescopes, Observatories, Ray tracing
The WFIRST-AFTA Wide-Field Infrared Survey Telescope TMA optical design provides 0.28-sq°FOV Wide Field Channel at 0.11” pixel scale, operating at wavelengths between 0.76-2.0μm, including a spectrograph mode (1.35-1.95μm.) An Integral Field Channel provides a discrete 3”x3.15” field at 0.15” sampling.
KEYWORDS: Astrophysics, Space telescopes, Astronomy, Observatories, James Webb Space Telescope, Space operations, Telecommunications, Mars, Telescopes, Asteroids
We describe how availability of new solar electric propulsion (SEP) technology can substantially increase the science capability of space astronomy missions working within the near-UV to far-infrared (UVOIR) spectrum by making dark sky orbits accessible for the first time. We present two case studies in which SEP is used to enable a 700 kg Explorer-class and 7000 kg flagship-class observatory payload to reach an orbit beyond where the zodiacal dust limits observatory sensitivity. The resulting scientific performance advantage relative to a Sun-Earth L2 point (SEL2) orbit is presented and discussed. We find that making SEP available to astrophysics Explorers can enable this small payload program to rival the science performance of much larger long development-time systems. Similarly, we find that astrophysics utilization of high power SEP being developed for the Asteroid Redirect Robotics Mission (ARRM) can have a substantial impact on the sensitivity performance of heavier flagship-class astrophysics payloads such as the UVOIR successor to the James Webb Space Telescope.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant to many astrophysical problems. ACCESS, Absolute Color Calibration Experiment for Standard Stars", is a series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration accuracy of 1% and a spectral resolving power of 500 across the 0.35 - 1.7μm bandpass. This paper describes the payload status, sub-system testing, and data transfer for the ACCESS instrument.
We present the Wide Field Infra-Red Survey Telescope (WFIRST) wide field instrument concept based on the reuse of a
2.4m telescope recently made available to NASA. Two instrument channels are described, a wide field channel
(~0.8x0.4degrees, 300Mpix, imaging and spectroscopy over 0.76-2.0um), and an integral field unit (3x3 arcsec, 1Mpix,
R{2pixel} ~100 over 0.6-2.0um). For this mission concept, the telescope, instruments, and spacecraft are in a
geosynchronous orbit and are designed for serviceability. This instrument can accomplish not only the baseline exoplanet
microlensing, dark energy, and infrared surveys for WFIRST, but can perform at higher angular resolution and with
deeper observations. This enables significant opportunities for more capable general observer programs. The emphasis
on achieving very good imaging stability is maintained from the previous work.
We present a novel optical integral field spectrograph (IFS) called the Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES), which will be a facility class instrument within the NASA Exoplanet Exploration Program's High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory. Integral field spectroscopy is ideal for imaging faint exoplanets: it enables spectral characterization of exoplanet atmospheres and can improve contrast by providing chromatic measurements of the target star's point-spread function (PSF). PISCES at the HCIT will be the first IFS to demonstrate imaging spectroscopy in the 10-9 contrast regime required for characterizing exoplanets imaged in scattered light. It is directly relevant as a prototype for IFS science instruments that could fly with the AFTA Coronagraph, the Exoplanet Probe missions currently under study, and/or the ATLAST mission concept. We present the instrument requirements, a baseline design for PISCES, a simulation of its performance, a solution to mitigate spectral crosstalk, experimental verification of our simulator, and the final vacuum compatible opto-mechanical design. PISCES will be assembled and tested at the Goddard Space Flight Center (GSFC), and subsequently delivered and integrated into the HCIT facility. Testing at HCIT will verify the performance of PISCES and its ability to meet the requirements of a space mission, will enable investigations into broadband wavefront control using the IFS as an image plane sensor, and will allow tests of contrast enhancement via multiwavelength differential imaging post-processing. Together with wavefront control and starlight suppression, PISCES is thus a key element for maturing the overall integrated system for a future coronagraphic space mission. PISCES is scheduled to receive first light in the HCIT in 2015.
The Johns Hopkins University sounding rocket group has completed the assembly and calibration of the Far-ultraviolet Off Rowland-circle Telescope for Imaging and Spectroscopy (FORTIS); a sounding rocket borne multi-object spectro-telescope designed to provide spectral coverage of up to 43 separate targets in the 900 - 1800 Angstrom bandpass over a 30′ x 30′ field-of-view. FORTIS is capable of selecting the far-UV brightest regions of the target area by utilizing an autonomous targeting system. Medium resolution (R ~ 400) spectra are recorded in redundant dual-order spectroscopic channels with ~40 cm2 of effective area at 1216 Å. The maiden launch of FORTIS occurred on May 10, 2013 out of the White Sands Missile Range, targeting the extended spiral galaxy M61 and nearby companion NGC 4301. We report on the final flight calibrations of the instrument, as well as the flight results.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant
to many astrophysical problems. ACCESS, “Absolute Color Calibration Experiment for Standard Stars”, is a
series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in
the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from
the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration
accuracy of 1% and a spectral resolving power of 500 across the 0.35−1.7μm bandpass. Achieving a calibration
accuracy of 1% not only requires an accurate calibration transfer from the detector standards to the instrument,
but it also requires characterization and stability of the detector as well as a thermal background that contributes
less than 1% to the flux per resolution element in the near-infrared (1.7μm) spectral region of the ACCESS
bandpass. This paper describes the thermal mechanical design for achieving a low thermal background across
the ACCESS spectral bandpass.
One of the key goals of NASA’s astrophysics program is to answer the question: How did galaxies evolve into the
spirals and elliptical galaxies that we see today? We describe a mission concept called Galaxy Evolution Spectroscopic
Explorer (GESE) to address this question by making a large spectroscopic survey of galaxies at redshift, z~1-2 (lookback
times of 8-10 billion years). GESE is a 1.5-m space telescope with a 3-channel multi-object slit spectrograph that
can obtain spectra of ~400 galaxies per exposure. Together, the 3 channels cover the spectral range, 0.2-1.6 μm at a
resolving power, R~400. (This observed spectral range corresponds to 0.1-0.8 μm in the restframe of a galaxy at a
redshift, z=1 galaxy.) The mission concept takes advantage of two new technological advances: (1) light-weighted, wide
field of view telescope mirrors, and (2) the Digital Micromirror Device (DMD) to be used as a slit generator in a multichannel
(UV, optical, NIR), multi-object slit spectrograph.
The most recent study of the Wide Field Infrared Survey Telescope (WFIRST) mission is based on reuse of an
existing 2.4m telescope. This study was commissioned by NASA to examine the potential science return and cost
effectiveness of WFIRST by using this significantly larger aperture telescope. We review the science program
envisioned by the WFIRST 2012-2013 Science Definition Team (SDT), an overview of the mission concept, and
the telescope design and status. Comparisons against the previous 1.3m and reduced cost 1.1m WFIRST design
concepts are discussed. A significant departure from past point designs is the option for serviceability and the
geostationary orbit location which enables servicing and replacement instrument insertion later during mission
life. Other papers at this conference provide more in depth discussion of the wide field instrument and the optional
exoplanet imaging coronagraph instrument.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant
to many astrophysical problems. ACCESS, “Absolute Color Calibration Experiment for Standard Stars”, is a
series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in
the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from
the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration
accuracy of 1% and a spectral resolving power of 500 across the 0.35-1.7µm bandpass.
We describe a mission architecture designed to substantially increase the science capability of the NASA Science
Mission Directorate (SMD) Astrophysics Explorer Program for all AO proposers working within the near-UV to far-infrared
spectrum. We have demonstrated that augmentation of Falcon 9 Explorer launch services with a 13 kW Solar
Electric Propulsion (SEP) stage can deliver a 700 kg science observatory payload to extra-Zodiacal orbit. This new
capability enables up to ~13X increased photometric sensitivity and ~160X increased observing speed relative to a Sun-
Earth L2, Earth-trailing, or Earth orbit with no increase in telescope aperture. All enabling SEP stage technologies for
this launch service augmentation have reached sufficient readiness (TRL-6) for Explorer Program application in
conjunction with the Falcon 9. We demonstrate that enabling Astrophysics Explorers to reach extra-zodiacal orbit will
allow this small payload program to rival the science performance of much larger long development time systems; thus,
providing a means to realize major science objectives while increasing the SMD Astrophysics portfolio diversity and
resiliency to external budget pressure. The SEP technology employed in this study has strong applicability to SMD
Planetary Science community-proposed missions. SEP is a stated flight demonstration priority for NASA's Office of the
Chief Technologist (OCT). This new mission architecture for astrophysics Explorers enables an attractive realization of
joint goals for OCT and SMD with wide applicability across SMD science disciplines.
The New Worlds, New Horizons report released by the Astronomy and Astrophysics Decadal Survey Board in 2010
listed the Wide Field Infrared Survey Telescope (WFIRST) as the highest-priority large space mission for the coming
decade. This observatory will provide wide-field imaging and slitless spectroscopy at near infrared wavelengths. The
scientific goals are to obtain a statistical census of exoplanets using gravitational microlensing, measure the expansion
history of and the growth of structure in the Universe by multiple methods, and perform other astronomical surveys to be
selected through a guest observer program. A Science Definition Team has been established to assist NASA in the
development of a Design Reference Mission that accomplishes this diverse array of science programs with a single
observatory. In this paper we present the current WFIRST payload concept and the expected capabilities for planet
detection. The observatory, with science goals that are complimentary to the Kepler exoplanet transit mission, is
designed to complete the statistical census of planetary systems in the Galaxy, from habitable Earth-mass planets to free
floating planets, including analogs to all of the planets in our Solar System except Mercury. The exoplanet microlensing
survey will observe for 500 days spanning 5 years. This long temporal baseline will enable the determination of the
masses for most detected exoplanets down to 0.1 Earth masses.
The Johns Hopkins University sounding rocket group is entering the final fabrication phase of the Far-ultraviolet Off
Rowland-circle Telescope for Imaging and Spectroscopy (FORTIS); a sounding rocket borne multi-object spectro-telescope
designed to provide spectral coverage of 43 separate targets in the 900 - 1800 Angstrom bandpass over a 30' x 30' field-of-
view. Using "on-the-fly" target acquisition and spectral multiplexing enabled by a GSFC microshutter array, FORTIS
will be capable of observing the brightest regions in the far-UV of nearby low redshift (z ~ 0.002 - 0.02) star forming
galaxies to search for Lyman alpha escape, and to measure the local gas-to-dust ratio. A large area (~ 45 mm x 170 mm)
microchannel plate detector built by Sensor Sciences provides an imaging channel for targeting flanked by two redundant
spectral outrigger channels. The grating is ruled directly onto the secondary mirror to increase efficiency. In this paper, we
discuss the recent progress made in the development and fabrication of FORTIS, as well as the results of early calibration
and characterization of our hardware, including mirror/grating measurements, detector performance, and early operational
tests of the microshutter arrays.
ACCESS, Absolute Color Calibration Experiment for Standard Stars, is a series of rocket-borne sub-orbital
missions and ground-based experiments designed to enable improvements in the precision of the astrophysical
flux scale through the transfer of absolute laboratory detector standards from the National Institute of Standards
and Technology (NIST) to a network of stellar standards with a calibration accuracy of 1% and a spectral resolving
power of 500 across the 0.35.1.7μm bandpass.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant
to many astrophysical problems. Systematic errors associated with problems such as dark energy now compete
with the statistical errors and thus limit our ability to answer fundamental questions in astrophysics.
The ACCESS design, calibration strategy, and an updated preliminary performance estimate are discussed.
The Johns Hopkins University sounding rocket group is building the Far-ultraviolet Off Rowland-circle Telescope for
Imaging and Spectroscopy (FORTIS), which is a Gregorian telescope with rulings on the secondary mirror. FORTIS will
be launched on a sounding rocket from White Sand Missile Range to study the relationship between Lyman alpha escape
and the local gas-to-dust ratio in star forming galaxies with non-zero redshifts. It is designed to acquire images of a 30'
x 30' field and provide fully redundant "on-the-fly" spectral acquisition of 43 separate targets in the field with a bandpass
of 900 - 1800 Angstroms. FORTIS is an enabling scientific and technical activity for future cutting edge far- and near-uv
survey missions seeking to: search for Lyman continuum radiation leaking from star forming galaxies, determine the
epoch of He II reionization and characterize baryon acoustic oscillations using the Lyman forest. In addition to the high
efficiency "two bounce" dual-order spectro-telescope design, FORTIS incorporates a number of innovative technologies
including: an image dissecting microshutter array developed by GSFC; a large area (~ 45 mm x 170 mm) microchannel
plate detector with central imaging and "outrigger" spectral channels provided by Sensor Sciences; and an autonomous
targeting microprocessor incorporating commercially available field programable gate arrays. We discuss progress to date
in developing our pathfinder instrument.
KEYWORDS: Galactic astronomy, Camera shutters, Stars, Sensors, Photons, Telescopes, Near ultraviolet, Ionization, Spectroscopy, James Webb Space Telescope
We explore the design of a space mission called Project Lyman that has the goal of quantifying the ionization history of the universe from the present epoch to a redshift of z ~ 3. Observations from WMAP and SDSS show that before a redshift of z (Symbol not available. See manuscript.) 6 the first collapsed objects, possibly dwarf galaxies, emitted Lyman continuum (LyC) radiation shortward of 912 Å that reionized most of the universe. Theoretical estimates of the LyC escape fraction ( fesc ) required from these objects to complete reionization is fesc ~10%. How LyC escapes from galactic environments, whether it induces positive or negative feedback on the local and global collapse of structures, and the role played by clumping, molecules, metallicity and dust are major unanswered theoretical questions, requiring observational constraint. Numerous intervening Lyman limit systems frustrate the detection of LyC from high z objects. They thin below z ~ 3 where there are reportedly a few cases of apparently very high fesc. At low z there are only controversial detections and a handful of upper limits. A wide-field multi-object spectroscopic survey with moderate spectral and spatial resolution can quantify fesc within diverse spatially resolved galactic environments over redshifts with significant evolution in galaxy assemblage and quasar activity. It can also calibrate LyC escape against Lyα escape, providing an essential tool to JWST for probing the beginnings of reionization. We present calculations showing the evolution of the characteristic apparent magnitude of star-forming galaxy luminosity functions at 900 Å, as a function of redshift and assumed escape fraction. These calculations allow us to determine the required aperture for detecting LyC and conduct trade studies to guide technology choices and balance science return against mission cost. Finally we review our efforts to build a pathfinding dual order multi-object spectro/telescope with a (0.5°)2 field-of-view, using a GSFC microshutter array, and crossed delay-line micro-channel plate detector.
The On-board Calibration Monitor (OCM) is being developed as an integral component of the ACCESS instrument
and as a pathfinder for other missions. It provides stable full-aperture illumination of the telescope for
tracking the instrument sensitivity as a function of time. The light source is composed of an ensemble of LED
pairs with central wavelengths that span the spectral range of the instrument and illuminate a diffuser that is
observed by the full optical path. Feedback stabilization of the light source intensity is achieved by photodiode
monitoring of each LED. This stable source will provide real time knowledge of the ACCESS sensitivity throughout
the 5-year duration of the program. The present status of the design and laboratory evaluation of the OCM
system will be presented.
ACCESS is a recently approved rocket-borne payload with a ground-based calibration and performance monitoring
program that is designed to transfer the National Institute of Standards and Technology (NIST) absolute
laboratory standards to the stars with a precision and calibration accuracy of 1% across the 0.35-1.7μm bandpass.
This represents a significant improvement in the absolute and relative astrophysical flux calibration system,
particularly at near-infrared (NIR) wavelengths.
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant
to many astrophysical problems. In particular, the precise calibration of the flux scale across the bandpass
extending from 0.35-1.7 μm is fundamental to the precise determination of dark energy measurements based
on SNeIa photometry.
Since its launch in 1999, the Far Ultraviolet Spectroscopic Explorer (FUSE) has had a profound impact on many areas of astrophysics. Although the prime scientific instrument continues to perform well, numerous hardware failures on the attitude control system, particularly those of gyroscopes and reaction wheels, have made science operations a challenge. As each new obstacle has appeared, it has been overcome, although sometimes with changes in sky coverage capability or modifications to pointing performance. The CalFUSE data pipeline has also undergone major changes to correct for a variety of instrumental effects, and to prepare for the final archiving of the data. We describe the current state of the FUSE satellite and the challenges of operating it with only one reaction wheel and discuss the current performance of the mission and the quality of the science data.
The far ultraviolet spectral region (roughly 900 - 1200 Å) is densely packed with strong atomic, ionic and molecular transitions of astrophysical importance. Many of these transitions provide unique access to the associated species. This spectral region is also technically challenging: optical reflectivities are limited, contamination control requirements are severe and detectors must be windowless. The Far Ultraviolet Spectroscopic Explorer (FUSE) covers the spectral region 905 -1187 Å with a resolution ~ 15 km s-1. The mission, launched in June 1999 and now in its fifth year of science operations, has reaped a rich scientific harvest from this spectral region. This paper will examine the lessons learned from the FUSE mission with the perspective of looking ahead to possible future missions. In order to build on the scientific advances of the FUSE mission, such a mission would require both increased sensitivity and higher spectral resolution. We conclude that achieving these requirements will necessitate, among other advances, new approaches to far ultraviolet mirror coating technology. We also examine the possibility of accessing the far ultraviolet using an ultraviolet observatory designed for longer wavelength ultraviolet radiation.
Shull et al. have asserted that the contribution of stars, relative to quasars, to the metagalactic
background radiation that ionizes most of the baryons in the universe
remains almost completely unknown at all epochs. The potential to
directly quantify this contribution at low redshift has recently become
possible with the identification by GALEX of large numbers of
sparsely distributed faint ultraviolet galaxies. Neither STIS nor
FUSE nor GALEX have the ability to efficiently survey these sparse
fields and directly measure the Lyman continuum radiation that may leak
into the low redshift (z < 0.4) intergalactic medium. We present
here a design for a new type of far ultraviolet spectrograph, one that
is more sensitive, covers wider fields, and can provide spectra and
images of a large number of objects simultaneously, called the
Far-ultraviolet Off Rowland-circle Telescope for Imaging and
Spectroscopy (FORTIS). We intend to use a sounding rocket flight to
validate the new instrument with a simple long-slit observation of the
starburst populations in the galaxy M83. If however, the long-slit
were replaced with microshutter array, this design could isolate the
chains of blue galaxies found by GALEX over an ~30' diameter
field-of-view and directly address the Lyman continuum problem in a
long duration orbital mission. Thus, our development of the sounding
rocket instrument is a pathfinder to a new wide field spectroscopic
technology for enabling the potential discovery of the long
hypothesized but elusive Lyman continuum radiation that is thought to leak from low redshift galaxies and contribute to the ionization of the universe.
PRIME (The Primordial Explorer) is a proposed Explorer-class mission. It will carry out a deep sky survey from space in four near-infrared bands between ~0.9-3.5 μm. It surveys a quarter of the sky to AB magnitude of ~24, which is ~600 times deeper than 2MASS and ~ five million times deeper than COBE at long wavelengths. Deeper surveys in selected sky regions are also planned. PRIME will reach an epoch during which the first quasars, galaxies and clusters of galaxies were formed in the early universe, map the large-scale structure of the dark matter, discover Type-Ia supernovae to be used in measuring the acceleration of the expanding universe, and detect thousands of brown dwarfs and even Jupiter-size planets in the vicinity of the solar system. Most of these objects are so rare that they may be identified only in large and deep surveys. PRIME will serve as the precursor for the Next Generation Space Telescope (NGST), supplying rare targets for its spectroscopy and deep imaging. It is more than capable of providing targets for the largest ground-based telescopes (10-30m). Combining PRIME with other surveys (SDSS, GALEX) will yield the largest astronomical database ever built.
KEYWORDS: Satellites, Space operations, Observatories, Data archive systems, Astronomy, Control systems, Gyroscopes, Space telescopes, Telescopes, Stars
The Far Ultraviolet Spectroscopic Explorer satellite (FUSE)
is a NASA Origins mission launched on 1999 June 24 and
operated from the Johns Hopkins University Homewood campus in
Baltimore, MD. FUSE consists of four aligned telescopes feeding
twin far-ultraviolet spectrographs that achieve a spectral
resolution of R=20,000 over the 905-1187 Å spectral region.
This makes FUSE complementary to the Hubble Space Telescope
and of broad general interest to the astronomical community.
FUSE is operated as a general-purpose observatory with
proposals evaluated and selected by NASA.
The FUSE mission concept evolved dramatically over time. The
version of FUSE that was built and flown was born out of the
"faster, better, cheaper" era, which drove not only the
mission development but also plans for operations. Fixed price
contracts, a commercial spacecraft, and operations in the
University environment were all parts of the low cost strategy.
The satellite performs most functions autonomously, with ground
contacts limited typically to seven 12-minute contacts per
day through a dedicated ground station. All support functions
are managed by a staff of 40 scientists and engineers located at
Johns Hopkins. In this configuration, we have been able to achieve
close to 30% average on-target science efficiency. In short, FUSE is a successful example of the "faster, better, cheaper" philosophy.
The Far Ultraviolet Spectroscopic Explorer is a NASA Origins mission
launched in June 1999 to obtain high-resolution spectra of astronomical sources at far-ultraviolet wavelengths. The science objectives require the satellite to provide inertial pointing at arbitrary positions on the sky with sub-arcsecond accuracy and stability. The requirements were met using a combination of ring-laser gyroscopes, three-axis magnetometers, and a fine error sensor for attitude knowledge, and reaction wheels for attitude control. Magnetic torquer bars are used for momentum management of the reaction wheels, and coarse sun sensors for safe mode pointing.
The gyroscopes are packaged as two coaligned inertial reference units of three orthogonal gyroscopes each. There are four reaction wheels: three oriented along orthogonal axes, the fourth skewed at equal angles (54.7°) with respect to the others. Early in the mission the gyroscopes began showing signs of aging more rapidly than expected, and one failed after two years of operation. In addition, two of the orthogonal wheels failed in late 2001. The flight software has been modified to employ the torquer bars in
conjunction with the two remaining wheels to provide fine pointing control. Additional new flight software is under development to provide attitude control if both gyroscopes fail on one or more axes.
Simulations indicate that the pointing requirements will still be met, though with some decrease in observing efficiency. We will describe the new attitude control system, compare performance characteristics before and after the reaction wheel failures, and
present predicted performance without gyroscopes.
The FUSE satellite employs innovative techniques for autonomous target acquisitions and fine pointing control. One of two Fine Error Sensors, incorporated in the optical path of the science instrument, provide the Instrument Data System computer with images, for target identification, and field star centroids, for fine pointing information to the spacecraft attitude control system. A suite of 'toolbox' functions has been developed to locate stars, selected and track on 'unknown' guide stars from the image, identify the star field, track preselected 'known' guide stars, follow moving targets, and provide pointing optimizations to fine- tune the centering of a target. After a maneuver to a new field, initial attitude is determined by identifying stars found in a 20' X 20' image. Identification is done by matching stars with an uploaded table of up to 200 objects selected from the Hubble Space Telescope (HST) Guide Star Catalog (GSC), ranging from V equals 9 to 13.5 mag., and typically covering a one degree field around the target. During identification, tracking is performed on unidentified stars in the image to prevent the satellite from drifting. A corrective slew is then commanded to place the target at the desired position. Tracking is then resumed on preselected guide stars. If desired, further fine alignment of the science apertures is performed by a target peakup using the FUV detectors. We discuss the target acquisition process; end-to- end performance; and problems encountered due to the limitations of the small field of view of the FES, HST GSC errors, and stray light in the telescope baffles.
The Far Ultraviolet Spectroscopic Explorer mission imposes stringent requirements on the satellite attitude control system. Target acquisition accuracy and target tracking stability must each be no greater than 0.5 arcseconds FWHM. The data required by the attitude control system to meet these requirements are provided by two redundant Fine Error Sensors. Each Fine Error Sensor operates as a slit-jaw camera that provides either complete images of the star-field around the line of sight of the telescope, or centroided positions of selected guide stars in the field of view. The satellite pointing requirements must be met over a wide dynamic range of target or guide star brightness, for both sparse and crowded starfields, and for targets that may be either point sources or extended objects. We will describe the operational characteristics of the FES and present data on its performance. We also discuss the optical, mechanical, thermal, and electronic design challenges encountered in meeting the mission requirements, and how they were addressed in the context of a very tight development schedule.
The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched on June 24, 1999. FUSE is designed to make high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 angstrom). Its high effective area, low background and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. FUSE has now been in orbit for one year. We discuss the accomplishments of the FUSE mission during this time, and look ahead to the future now that normal operations are under way.
The Far Ultraviolet Spectroscopic Explorer (FUSE) is a NASA astrophysics satellite designed to produce high resolution spectra in the far-ultraviolet (90.5-118.7 nm bandpass) with a high effective area (20-70 cm2) and low background detector. It was launched on a three-year mission in June 1999 aboard a Boeing Delta II rocket. The satellite has been performing routine science observations since December 1999. FUSE contains four co-aligned, normal incidence, off-axis parabolic primary mirrors which illuminate separate Rowland circle spectrograph channels equipped with holographically ruled diffraction gratings and microchannel plate detectors. Fine error sensors (slit jaw cameras) operating in the visible on two of the channels are used for target acquisition and guiding. The FUSE mission was first proposed in the late 1980s, and experienced several major conceptual changes prior to fabrication, assembly, and testing, which lasted from 1996 through 1999. During the program, we realized both positive and negative aspects to our design and processes that may apply to other space missions using telescopes and spectrographs. The specific topics we address are requirements, design, component specification, integration, and verification. We also discuss on-orbit alignment and focus. These activities were complicated by unexpected levels of motion between the optical elements, and the logistical problems associated with limited ground contact passes in low Earth orbit. We have developed methods to characterize the motions and mitigate their resultant effects on the science data through a combination of observing techniques and modifications to the data reduction software.
The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched into orbit on June 24, 1999. FUSE is now making high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 angstroms). Its high effective area, low background, and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. In this paper, we describe the on- orbit performance of the FUSE satellite during its first nine months of operation, including measurements of sensitivity and resolution.
The FUSE is an astrophysics satellite designed to make observations at high spectral resolving power in the 90.5- 118.7 nm bandpass. This NASA Origins mission will address many important astrophysical problems, including the variations in the deuterium/hydrogen ratio in the Milky Way and in extragalactic clouds, the kinematics and distribution of O5+ and other hot gas species in the Galactic disk and halo, the properties of molecular hydrogen in interstellar clouds having a wide variety of temperatures and densities, and the properties of stellar and planetary atmospheres. Between August 1997 and January 1999 an extensive series of vacuum optical test was conducted, first with the spectrograph alone and then with the full satellite in flight-like conditions. Numerous UV spectra were obtained and found to be consistent with performance requirements. We also obtained visible light images with the fine error sensor camera, whose performance will be critical for meeting the demanding pointing requirements of FUSE. In this paper we present estimates of the performance of the instrument, including spectral resolution, line shapes, and effective area. We also present data on the visible light performance of the FES.
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