The Compact Doppler Magnetograph (CDM) is a space-qualified, miniaturized Doppler magnetograph, tailored to the requirements of a solar polar mission, and designed to provide photospheric line-of-sight magnetic field and Doppler velocity measurements of the solar surface. CDM is derived from the proven GONG (Global Oscillations Network Group) instrument design (Harvey et al., 1988, 1996), with a space qualified prototype developed for the Solaris solar polar MIDEX mission (Hassler et al., 2020). CDM has roughly 1/3 the mass of current state-of-the-art Doppler magnetographs (e.g., SOHO/MDI, SDO/HMI, SolO/PHI), with greatly increased sensitivity to the magnetic field (B) and Doppler velocity (v) and the capability to perform over an expanded spacecraft orbital velocity range, which is required to fit within the mission design constraints of currently feasible high latitude solar polar missions.
The JUICE (Jupiter ICy moons Explorer) and Europa Ultraviolet Spectrographs (JUICE-UVS and Europa-UVS, respectively) are nearly identical modest-powered (~9W) instruments scheduled to explore the Jovian satellites aboard ESA’s JUICE and NASA’s Europa Clipper missions, respectively. These spectrographs each feature a dedicated door containing a high-resolution aperture stop that reduces the focal ratio of the telescope from f/3 to f/12. The baseline design for this aperture was a 1-cm diameter circle. We compared the optical properties of the baseline 1-cm diameter aperture with a 1-cm by 1-cm square aperture in an effort to increase throughput by 27% while maintaining the native spatial resolution of the spectrograph. The effects of both apertures were analyzed with no appreciable difference in the resulting spatial or spectral resolution. Therefore, the 1-cm by 1-cm square aperture has been implemented in both JUICE- and Europa-UVS.
The impact of gamma radiation on refractive index and transmission was analyzed for several glasses. The goal of the analysis is to quantify the optical performance impact of Jovian electron and proton radiation environments using gamma radiation as a proxy for the Europa Imaging System (EIS) Wide Angle Camera1 (WAC) refractive telescope. The testing was split into two sample sets. The first set of glasses tested are baselined in the current WAC design: BK7G18, Calcium Fluoride, Fused Silica, and LF5G15. Analysis demonstrates no significant change in the refractive index or transmission in BK7G18, Calcium Fluoride, Fused Silica, and LF5G15 when exposed to 1 Mrad of gamma radiation. The second set of glasses tested was two i-line and two radiation resistant glasses from Ohara. Analysis demonstrates no significant change in the refractive index in BAL35Y, PBL25Y, S-BAL25-R, and S-BSL7-R when exposed to 1 Mrad of gamma radiation. Significant loss in transmission was observed for the two i-line glasses (BAL35Y and PBL25Y) when exposed to 1 Mrad of gamma radiation.
NASA's Europa Clipper will carry two cameras as part of the Europa Imaging System (EIS). Both the wide angle camera and narrow angle camera have identical focal plane modules, each containing a CMOS image sensor and patterned optical filter array. The filter array enables multispectral pushbroom imaging in six bands, spanning 380nm to 1000 nm, adding additional science capability for surface characterization and searching for evidence of recent activity. The EIS filter array is monolithic in construction, with all bands coated on a single substrate. Each stripe measures only 320 μm wide-equivalent to 32 pixels on the image sensor-leaving most of the field of view clear for full frame panchromatic imaging. Using photolithography, a mask is applied to the filter substrate and developed, leaving only the desired pattern exposed. The filter is then deposited onto the substrate and the mask removed. This process is repeated for each additional band on the array until all filters have been applied. The filters are then aligned with the image sensor rows using a machined metal housing, placing it as close as possible to the focal plane. As part of a technology development program to qualify them for space flight, several filters have been performance tested for resistance to radiation exposure, thermal cycling, vibration, and dry heat microbial reduction for planetary protection.
SSUSI-Lite is an update of an existing sensor, SSUSI. The current generation of Defense Meteorological Satellite Program (DMSP) satellites (Block 5D3) includes a hyperspectral, cross-tracking imaging spectrograph known as the Special Sensor Ultraviolet Spectrographic Imager (SSUSI). SSUSI has been part of the DMSP program since 1990. SSUSI is designed to provide space weather information such as: auroral imagery, ionospheric electron density profiles, and neutral density composition changes. The sensors that are flying today (see http://ssusi.jhuapl.edu) were designed in 1990 - 1992. There have been some significant improvements in flight hardware since then. The SSUSI-Lite instrument is more capable than SSUSI yet consumes ½ the power and is ½ the mass. The total package count (and as a consequence, integration cost and difficulty) was reduced from 7 to 2. The scan mechanism was redesigned and tested and is a factor of 10 better. SSUSI-Lite can be flown as a hosted payload or a rideshare – it only needs about 10 watts and weighs under 10 kg. We will show results from tests of an interesting intensified position sensitive anode pulse counting detector system. We use this approach because the SSUSI sensor operates in the far ultraviolet – from about 110 to 180 nm or 0.11 to 0.18 microns.
KEYWORDS: Sensors, Hyperspectral imaging, Spectrographs, Mirrors, Stray light, Short wave infrared radiation, Signal to noise ratio, Polarization, Telescopes, Space operations
The temporal variability, or phenology, of animals and plants in coastal zone and marine habitats is a function of geography and climatic conditions, of the chemical and physical characteristics of each particular habitat, and of interactions between these organisms. These conditions play an important role in defining the diversity of life. The quantitative study of phenology is required to protect and make wise use of wetland and other coastal resources. We describe a low cost space-borne sensor and mission concept that will enable such studies using high quality, broad band hyperspectral observations of a wide range of habitats at Landsat-class spatial resolution and with a 3 day or better revisit rate, providing high signal to noise observations for aquatic scenes and consistent view geometry for wetland and terrestrial vegetation scenes.
SSUSI-Lite is a far-ultraviolet (115-180nm) hyperspectral imager for monitoring space weather. The SSUSI and GUVI sensors, its predecessors, have demonstrated their value as space weather monitors. SSUSI-Lite is a refresh of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) design that has flown on the Defense Meteorological Satellite Program (DMSP) spacecraft F16 through F19. The refresh updates the 25-year-old design and insures that the next generation of SSUSI/GUVI sensors can be accommodated on any number of potential platforms. SSUSI-Lite maintains the same optical layout as SSUSI, includes updates to key functional elements, and reduces the sensor volume, mass, and power requirements. SSUSI-Lite contains an improved scanner design that results in precise mirror pointing and allows for variable scan profiles. The detector electronics have been redesigned to employ all digital pulse processing. The largest decrease in volume, mass, and power has been obtained by consolidating all control and power electronics into one data processing unit.
We present the design concept of the wavelength calibration system for the Habitable-zone Planet Finder instrument (HPF), a precision radial velocity (RV) spectrograph designed to detect terrestrial-mass planets around M-dwarfs. HPF is a stabilized, fiber-fed, R~50,000 spectrograph operating in the near-infrared (NIR) z/Y/J bands from 0.84 to 1.3 microns. For HPF to achieve 1 m s-1 or better measurement precision, a unique calibration system, stable to several times better precision, will be needed to accurately remove instrumental effects at an unprecedented level in the NIR. The primary wavelength calibration source is a laser frequency comb (LFC), currently in development at NIST Boulder, discussed separately in these proceedings. The LFC will be supplemented by a stabilized single-mode fiber Fabry-Perot interferometer reference source and Uranium-Neon lamp. The HPF calibration system will combine several other new technologies developed by the Penn State Optical-Infrared instrumentation group to improve RV measurement precision including a dynamic optical coupling system that significantly reduces modal noise effects. Each component has been thoroughly tested in the laboratory and has demonstrated significant performance gains over previous NIR calibration systems.
Incomplete and unstable mode population has long complicated the application of optical fiber for transferring star and
calibration light to high precision spectrographs. The need for improved precision calibrators in support of radial velocity
planet surveys has led to the introduction of coherent wavelengths sources using single mode fibers that are then coupled
into multi-mode fibers, further exacerbating this problem. We explore mode scrambling in annealed optical fiber with and
without agitation, as compared to that obtained using octagonal fiber and using an integrating sphere. We observe
improved scrambling with annealed fibers compared to conventional and octagonal fibers.
David Sahnow, Alessandra Aloisi, K. Azalee Bostroem, John Debes, Justin Ely, Philip Hodge, Gerard Kriss, Derck Massa, Cristina Oliveira, Rachel Osten, Steven Osterman, Steven Penton, Charles Proffitt, Julia Roman-Duval, Paule Sonnentrucker
The Far Ultraviolet (FUV) detector of the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST)
uses a large-format, two-segment microchannel plate detector with a Cross Delay-Line anode. Since the installation of
COS into HST in 2009, the detector’s properties have continually evolved, and changes to both sensitivity and
microchannel plate gain have been observed. In order to maximize the lifetime of the detector, we have been monitoring
its local properties as a function of time, cumulative exposure, and other factors, and we have constructed models to
predict its future evolution. These models will allow us to actively manage the microchannel plate high voltage levels
and the location of the spectra on the detector in order to extend its life without limiting its scientific use. We are also
tracking the global sensitivity of the detector, which has been decreasing since installation; the rate of degradation has
been found to vary with time, and appears to be correlated with solar activity.
We present a conceptual design for a high-resolution optical spectrograph appropriate for mounting at Cassegrain on a large aperture telescope. The design is based on our work for the Gemini High Resolution Optical Spectrograph (CUGHOS) project. Our design places the spectrograph at Cassegrain focus to maximize throughput and blue wavelength coverage, delivering R=40,000 resolving power over a continuous 320–1050 nm waveband with throughputs twice those of current instruments. The optical design uses a two-arm, cross-dispersed echelle format with each arm optimized to maximize efficiency. A fixed image slicer is used to minimize optics sizes. The principal challenge for the instrument design is to minimize flexure and degradation of the optical image. To ensure image stability, our opto-mechanical design combines a cost-effective, passively stable bench employing a honeycomb aluminum structure with active flexure control. The active flexure compensation consists of hexapod mounts for each focal plane with full 6-axis range of motion capability to correct for focus and beam displacement. We verified instrument performance using an integrated model that couples the optical and mechanical design to image performance. The full end-to-end modeling of the system under gravitational, thermal, and vibrational perturbations shows that deflections of the optical beam at the focal plane are <29 μm per exposure under the worst case scenario (<10 μm for most orientations), with final correction to 5 μm or better using open-loop active control to meet the stability requirement. The design elements and high fidelity modeling process are generally applicable to instruments requiring high stability under a varying gravity vector.
We present the scientific motivation and conceptual design for the recently funded Habitable-zone Planet Finder (HPF), a stabilized fiber-fed near-infrared (NIR) spectrograph for the 10 meter class Hobby-Eberly Telescope (HET) that will be capable of discovering low mass planets around M dwarfs. The HPF will cover the NIR Y and J bands to enable precise radial velocities to be obtained on mid M dwarfs, and enable the detection of low mass planets around these stars. The conceptual design is comprised of a cryostat cooled to 200K, a dual fiber-feed with a science and calibration fiber, a gold coated mosaic echelle grating, and a Teledyne Hawaii-2RG (H2RG) *NIR detector with a 1.7μm cutoff. A uranium-neon hollow-cathode lamp is the baseline wavelength calibration source, and we are actively testing laser frequency combs to enable even higher radial velocity precision. We will present the overall instrument system design and integration with the HET, and discuss major system challenges, key choices, and ongoing research and development projects to mitigate risk. We also discuss the ongoing process of target selection for the HPF survey.
David Sahnow, Alessandra Aloisi, K. Azalee Bostroem, John Debes, Julia Duval, Justin Ely, Philip Hodge, Gerard Kriss, Kevin Lindsay, Derck Massa, Cristina Oliveira, Rachel Osten, Steven Osterman, Steven Penton, Charles Proffitt, Paule Sonnentrucker, Brian York
The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope in May 2009, and has been
collecting ultraviolet spectra since then. The Far Ultraviolet channel of COS uses an efficient optical design and a two-segment,
large-format Cross Delay Line microchannel plate detector to obtain spectra at medium and low resolution in
the far ultraviolet. While the overall instrument performance has been excellent, several long-term trends in performance
have been noted and are being addressed. These include a slow decrease in overall sensitivity, which is independent of
the illumination and may be due to a degradation of the photocathode with time.
In addition, the detector microchannel plates are showing severe gain sag in the regions where the most photons have
fallen. As a result, we are in the process of moving the spectra to a new, nearly pristine, location on the detector. This
will be the first of several additional lifetime positions which will allow us to collect high-quality spectra for many years
to come. We will discuss the factors that led to our decision on where to move next and our progress in moving there,
including details of the enabling and calibration activities which are being performed at the new location, and the
anticipated performance. We will also address strategies that will be implemented in order to prolong the life at this and
subsequent positions.
Radial velocity (RV) surveys supported by high precision wavelength references (notably ThAr lamps and I2 cells) have
successfully identified hundreds of exoplanets; however, as the search for exoplanets moves to cooler, lower mass stars,
the optimum wave band for observation for these objects moves into the near infrared (NIR) and new wavelength
standards are required. To address this need we are following up our successful deployment of an H band(1.45-1.7μm)
laser frequency comb based wavelength reference with a comb working in the Y and J bands (0.98-1.3μm). This comb
will be optimized for use with a 50,000 resolution NIR spectrograph such as the Penn State Habitable Zone Planet
Finder. We present design and performance details of the current Y+J band comb.
The color dependence of the measured decline of the on-orbit sensitivity of the FUV channel of the HST Cosmic Origins
Spectrograph (HST-COS) indicated the principal loss mechanism to be degradation of the cesium iodide (CsI)
photocathode of the open-faced FUV detector. A possible cause of this degradation is contamination by atomic oxygen
(AO), prompting an investigation of the interaction of AO with CsI. To address this question, opaque CsI photocathodes
were deposited on stainless steel substrates employing the same deposition techniques and parameters used for the
photocathodes of the HST-COS FUV detector. The as-deposited FUV quantum efficiency of these photocathodes was
measured in the 117-174 nm range. Several of the photocathodes were exposed to varying levels of thermalized, atomic
oxygen (AO) fluence (produced via an RF plasma). The post AO exposure QE's were measured and the degradation of
sensitivity versus wavelength and AO fluence are presented.
The Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) uses a large-format cross delay line
(XDL) detector in its Far Ultraviolet (FUV) channel. While obtaining spectra, light falls non-uniformly on the detector
due to the optical design and the spectral properties of the object being observed; in particular, bright emission lines
from geocoronal Lyman-alpha can fall on the detector in more than 20 locations. As a result, some areas of the detector
have received a much greater exposure than others. This non-uniform illumination has led to a time- and position-dependent
change in the gain of the microchannel plates, which causes variations in the overall detector performance.
We will discuss the effects of this gain sag on the science data, and discuss mitigation strategies which are being
implemented in order to maximize the detector lifetime.
The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope (HST) during Servicing
Mission 4 (SM4) in May 2009. COS is designed to obtain spectra of faint objects at moderate spectral resolution (R >
16,000) in two channels: FUV, covering wavelengths from 1150 to 1450 Å; and NUV, covering 1700 - 3200 Å. Two
low resolution gratings (R > 1500) cover the < 900 - 2050 Å (FUV) and 1650 - 3200 Å (NUV) wavelength regions. An
imaging capability is also available on the NUV channel.
As part of the Hubble Servicing Mission Observatory Verification (SMOV) program, an extensive period of checkout,
fine-tuning and preliminary characterization began after the installation of COS. The COS SMOV program was a
cooperative effort between the Space Telescope Science Institute and the Instrument Definition Team based at the
University of Colorado. Nearly 2800 COS exposures in 34 separate observing programs were obtained during the course
of SMOV. Early activities included an initial instrument functional checkout, turn-on and initial characterization of the
detectors, NUV and FUV channel focus and alignment, and target acquisition verification and assessment. Once this
initial period was completed, science-related calibrations and verifications were performed in order to prepare the
instrument for normal science operations. These activities included wavelength calibration, flux calibration, detector flat
field characterization, spectroscopic performance verification, high S/N operation, and thermal and structural stability
measurements. We discuss the design, execution and results of the SMOV program, including the interrelationships
between the various tasks, and how the pre-launch plan was adjusted in real-time due to changing conditions.
The Cosmic Origins Spectrograph (COS) was installed on the Hubble Space Telescope (HST) in May 2009 during
Servicing Mission 4 (SM4). This paper discusses the initial on-orbit performance of the HST-COS far ultraviolet (FUV)
detector designed and built by the Experimental Astrophysics Group at the Univ. of California, Berkeley. The HST-COS
FUV detector is an open face, photon counting, microchannel plate (MCP) based device employing a cross delay
line (XDL) readout. The detector consists of two separate, end-to-end segments (2x 85mm x 10mm - 179mm x 10mm
total with a gap between segments), each digitized within a 16384x1024 space. The input surface is curved to match the
Rowland circle of HST-COS. The CsI photocathode and open face nature result in sensitivity from <900Å to ~1750Å.
Spatial resolution is approximately 25-30μm. Comparisons of on-orbit behavior relative to expectations from ground
testing are performed. Areas of discussion include background (rate and morphology), sensitivity (system throughput
and short wavelength response), and imaging performance (apparent spatial resolution and flat field fixed pattern). A
measured increase in the MCP gain relative to ground testing is also discussed.
The search for extrasolar planets is an exciting new field of astronomy. Since detection of a planet orbiting the
sun-like star 51 Peg,1 the field of planet finding has pushed the limits of sensitivity and accuracy in astronomical
photometry and spectroscopy. To date 455 exoplanets have been detected*, of which the radial velocity technique
is responsible for nearly 80%.2 Radial velocity measurements are also an important complement to photometric
missions such as Kepler and CoRoT, which survey vast numbers of stars simultaneously but which require follow
up measurements for positive identification of planets.
The chief objective in the search for exoplanets is the identification of habitable Earth-like planets in close
proximity to our solar system. Of the currently detected exoplanets, only a few are Earth-like,3 the vast majority
being giants in close orbits. While it is possible that these planets are the most common type, it is likely that
an inherent selection bias in planet finding techniques is the cause. Simply, large radial velocity shifts and
high contrast occultations are the most detectable by radial velocity spectroscopy and photometry, and so we
primarily observe planets capable of inducing them.
The Cosmic Origins Spectrograph,1 COS, will be installed in the Hubble Space Telescope (HST) during the next
servicing mission. This will be the most sensitive ultraviolet spectrograph ever flown aboard the HST.
The calibration pipeline (CALCOS), written in Python, has been developed by the Space Telescope Science
Institute (STScI) to support the calibration of HST/COS data. As with other HST pipelines, CALCOS uses an
association table to specify the data files to be included, and employs header keywords to specify the calibration
steps to be performed and the reference files to be used.
CALCOS is designed with a common underlying structure for processing far ultraviolet (FUV) and near
ultraviolet (NUV) channels which, respectively, use a cross delay line and a Multi Anode Microchannel Array
(MAMA) detector. The pipeline basics and channel dependent specifics are presented. The generation and
application of the current reference files, derived from ground-based calibration data, is described, along with
the pipeline verification process and results.
The CALCOS calibration includes pulse-height filtering and geometric correction for the FUV channel; flat-field,
deadtime, and Doppler correction for both channels. Methods for obtaining an accurate wavelength calibra-tion
using the on-board spectral line lamp are described. The instrument sensitivity is applied to the background
corrected spectrum to produce the final flux calibrated spectrum.
We report accelerated vacuum aging tests on two Pt-Ne lamps identical and/or similar to those installed on
the Cosmic Origins Spectrograph (COS) to be installed in the Hubble Space Telescope (HST) in the fall of
2008. One additional lamp was aged in air at the National Institute of Standards and Technology (NIST). All
lamps were tested at a 50% duty cycle (30 s on/off) at flight nominal (10 mA) constant current until failure.
Calibrated spectra of all lamps were taken at NIST using the 10.7-m normal incidence vacuum spectrograph at
various points in the life of the lamps. In this paper we report the results of the photometric, electrical, and
thermal monitoring of the vacuum tested lamps, while the spectroscopic and air aging results are given in a
companion paper (Nave et al., 2008, SPIE 7011-134). We conclude that the lamps will satisfy the requirements
of the HST/COS mission in terms of lifetime, cycles, and thermal and spectral stability.
High resolution spectroscopy is the foundation for many of the most challenging and productive
of all astronomical observations. A highly precise, repeatable and stable wavelength calibration
is especially essential for long term RV observations. The two wavelength references
in wide use for visible wavelengths, iodine absorption cells and thorium/argon lamps, each
have fundamental limitations which restrict their ultimate utility.
We are exploring the possibility of adapting emerging laser frequency comb technology in development
at the National Institute of Standards and Technology in Boulder, Colorado, to the
needs of high resolution, high stability astronomical spectroscopy. This technology has the
potential to extend the two current wavelength standards both in terms of spectral coverage and
in terms of long term precision, ultimately enabling better than 10 cm/s astronomical radial
velocity determination.
We have completed a conceptual design study of the High Resolution Optical Spectrograph for the Thirty Meter Telescope project. We propose the use of a fiber fed integral field unit and a dichroic tree to achieve R=100,000 spectroscopy from 310 to 1100 nm independent of AO performance. The system relies on the dichroic tree to provide coarse wavelength selection, and 32 first order spectro-graph benches. This approach allows for simultaneous optimization of grating and detector performance for all wavelengths, resulting in high efficiency, near uniform dispersion, and reduced program risk and cost due to the high degree of component commonality. We present projected performance and design details.
We present a conceptual design for a High Resolution Optical Spectrograph (HROS) for the Thirty Meter Telescope, a 30-m primary aperture ground-based telescope currently under development (www.tmt.org). To decouple downstream optics sizes from the size of the seeing disk and/or AO performance, we use fiber fed IFUs to generate a 0.1" pseudo-slit. The use of multiple IFUs instead of a slit also allows for spatially resolved spectroscopy, multi-object spectroscopy, positionable sky sampling, and insertion of a simultaneous wavelength calibration signal into the beam. Instead of a cross-dispersed echelle design, our concept uses a dichroic tree to provide spectral separation. The dichroics feed 32 independent first-order spectrographs that cover the 310 to 1100 nm optical waveband at a nominal spectral resolution of R=100,000. This approach allows for the optimization of coatings and on-blaze grating performance in each channel, resulting in high efficiency, near-uniform dispersion, and reduced program risk and cost due to the high degree of component commonality. We also discuss the general applicability of this concept for achieving high resolution spectroscopy in the next generation of ground-based instrumentation.
We discuss and analyze a two reflection grazing incidence spectrograph concept based on the Kirkpatrick-Baez telescope. The classical Kirkpatrick-Baez telescope uses two banks of crossed, cylindrical mirrors to achieve focus. Performance of a two reflection design is discussed for single mirror set and multiple mirror bank configurations.
Radiation induced phosphorescence of uv windows has the potential for generating crippling levels of background signal in space flight sensors. VUV fluorescence spectra have been obtained for three common window materials, and the phosphorescence decay curves have been recorded for a range of temperatures for two of the samples tested. We present this data and employ models used to fit the STIS background data to analyze the observed decay curves.
The Jupiter Magnetospheric Explorer (JMEX) is a UV observatory operating in an earth orbit proposed as part of NASA's Small Explorer (SMEX) class of missions. To meet mission requirements the residual jitter portion of the imaging error budget is set at 0.079 arcsec (3σ) over a 33.3 ms frame integration time and 0.01 arcsec (3σ) for all frequency content higher than 15 Hz. These requirements are challenging for a small, low cost mission and require some innovative system solutions to achieve these goals. The solution, discussed in the paper, was to combine several jitter rejection techniques fine-balanced reaction wheel mounted on an isolation assembly, post processing using science images and reaction wheel momentum control. This paper focuses primarily on meeting the high frequency portion of the requirements. To facilitate system performance verification, we leveraged an integrated model toolset, EOSyM (End-to-end Optical System Model), developed and used on various other advanced space-based missions over the last 9 years. Starting with individual subsystem models for the reaction wheel disturbances, the coupled payload/ spacecraft structural dynamics model, and the optical design, we were able to evaluate the end-to-end LOS performance under varying reaction wheel speeds. At the end we found that the requirements could be met by maintaining the reaction wheels operating range within a well-defined speed band. This paper describes the mission, the technical challenges, the integrated model, and system performance results.
The Jupiter Magnetosphere Explorer (JMEX) is a proposed earth-orbiting satellite which will image the planet Jupiter in the FUV with a 0.5 m telescope at 0.25 arcsec (") resolution. Because the satellite is small and lightweight, vibrations from the reaction wheels (even though isolated by dampers) produce random pointing errors with an amplitude as large as 5" at a frequency around 1 Hz. In order for the telescope to achieve a resolution of 0.25" FWHM during long exposures, we will use a novel post-processing scheme to correct the pointing error. The UV science camera is a photon-counting MCP detector which produces data as a time-stamped photon list with 0.08" spatial resolution and roughly 1 ms temporal resolution. Simultaneously, a 0.5" pixel video camera, fed by a pickoff mirror in the main beam, captures visible images of the planet's disk at 30Hz and, with onboard processing, the centroid of the planet is determined, frame-by-frame, with a resolution <0.02" (1/25 pixel). With inter-frame interpolation, each photon from the UV camera is position-corrected in ground post-processing to an accuracy of 0.02".To rigorously test this scheme, we have constructed a hardware mock-up consisting of a tip-tilt mirror, a beam-splitter, and two video cameras with controlled noise characteristics. The tip-tilt mirror produces controlled image motion over a range of amplitudes and frequencies. With all parameters at worst-case values, we have verified the specified performance of the system and achieved centroid correction close to the limit set by counting noise statistics.
High groove density reflection gratings placed at grazing incidence in the extreme off-plane mount offer improved performance over conventional in-plane mounts in the x-ray. We present test results from the grating evaluation facility at the University of Colorado for gratings optimized for use in the off-plane configuration. The gratings tested are produce via holographic lithography. Gratings tested have radial groove patterns and include both blazed and sinusoidal groove profiles. We present efficiency and sub-aperture resolution results.
High groove density reflection gratings placed at grazing incidence in the extreme off-plane mount offer increased performance over conventional in-plane mounts in the x-ray. We present initial off-plane efficiency test results from the grating evaluation facility at the University of Colorado. The test gratings are holographically ruled, ion-etched gratings with radial groove profiles that were developed and fabricated by Jobin-Yvon Inc.
We present the preliminary calibration results for the Cosmic Origins Spectrograph, a fourth generation replacement instrument for the Hubble Space Telescope due to be installed in mid-2005. The Cosmic Origins Spectrograph consists of two spectroscopic channels: a far ultraviolet channel that observes wavelengths between 1150 and 2000 Åand a near ultraviolet channel that observes between 1700 and 3200 Å. Each channel supports moderate (R≈20,000) and low (R≈2000) spectral resolution. We discuss the calibration methodology, test configurations, and preliminary end-to-end calibration results. This includes spectral resolution, system efficiency, flat fields, and wavelength scales for each channel. We also present the measured transmission of the Bright Object Aperture (BOA) and the measured spatial resolution.
Radiation induced phosphorescence of UV window materials has been identified as a source of background signal in UV detectors for as long as these detectors have flown in space, but there is little detailed knowledge of the spectrum, decay time constants or thermal dependence of the phosphorescence. We present initial results of a study undertaken to characterize this source of background signal, including spectra, decay timescale analysis, and preliminary assessment of depopulation/deexcitation techniques. The ultimate goals of this study are to identify and evaluate phosphorescence mitigation techniques and to identify the source of the phosphorescence in optical materials.
We present the instrument design, the image motion correction algorithm, and the predicted performance of the Ultraviolet Imager (UVI) proposed for the Jupiter Magnetospheric Explorer (JMEX) mission. The JMEX mission is a small explorer mission (SMEX) designed to observe the Jovian system and to study the dynamical relationship between Jupiter's magnetosphere and Io, the primary source for the Io plasma torus. JMEX was selected as one of six SMEX missions for review by NASA following additional design and analysis. While not selected for flight, the design includes several innovative design features which permit 0.25" imaging on a SMEX class spacecraft which are of general interest.
The UVI consists of the Ultraviolet Telescope (UVT) and the Ultraviolet Imager Instrument Package (UVIIP). The UVT is a 50 cm Cassegrain telescope, and the UVIIP consists of an elliptical tertiary mirror, an eight position filter/prism wheel, a cross-delay line microchannel plate detector and a visible light image motion sensor. The integrated system will provide 0.25" imaging over a 100" field of view between 115 and 200nm.
The Cosmic Origins Spectrograph (COS) will be the most sensitive UV spectrograph to be flown aboard the Hubble Space Telescope. The COS FUV and NUV channels will provide high sensitivity at resolution greater than 20000 over wavelengths ranging from 115nm to 320nm. We present a brief review of the instrument design, results from the optical testing of FUV gratings and predicted on orbit performance.
The Cosmic Origins Spacecraft (COS) will be the most sensitive UV spectrograph to be flown aboard the Hubble Space Telescope. The COS FUV and NUV channels will provide high sensitivity at resolution greater than 20000 over wavelengths ranging from 115 nm to 320 nm. We present a brief review of the instrument design and grating test plan as well optical test results for the first FUV grating delivered.
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.
A grazing incidence x-ray interferometer design capable of micro-arcsecond level resolution is discussed. This practical design employs a Michelson Stellar interferometer approach to create x-ray interference fringes without the use of Wolter style optics or diffraction crystals. Design solutions accommodating alignment, vibration, and thermal constraints are reviewed. We present the development and demonstration of a working experiment along with tolerance studies, data analysis, and results.
The Center for Astrophysics and Space Astronomy (CASA) recently delivered to the Johns Hopkins University the Far Ultraviolet Spectrograph Instrument for integration into the far ultraviolet spectroscopic explorer (FUSE) satellite. In addition to the optical design of the FUSE instrument, the CASA/FUSE team was responsible for development of major optical components of the spectrograph and the final assembly and alignment of the instrument.In this paper we present the optical design, alignment methodologies employed, and performance characteristics of the instrument as delivered to the Johns Hopkins University. In addition, we discuss how we determined the resolution of the instrument capable of resolving powers in excess of 30,000. We also discuss the contamination control and monitoring and stability testing of the instrument, i.e. vibration, thermal distortion, and longterm stability testing.
The Special Sensor Ultraviolet Limb Imager (SSULI) program involves the development of a series of five ultraviolet limb imaging spectrographs by the Naval Research Laboratory for the Defense Meteorological Satellite Program. In addition, a duplicate sixth instrument, the Low Resolution Airglow/Aurora Spectrograph (LORAAS) will be flown aboard the Space Test Program ARGOS satellite in late 1997. These instruments will measure vertical intensity profiles of the Earth's airglow in the extreme and far ultraviolet (800 to 1700 angstroms) with 19 angstroms resolution. The instruments view the limb using a rotating mirror to scan the 0.1 degree(s) X 2.4 degree(s) field of view from 750 km to 50 km tangent altitude. SSULI measurements will be used to infer altitude profiles of ion, electron and neutral density. The first SSULI is scheduled to launch in 2000, and coverage from all the instruments will provide a continuous atmospheric data set spanning an entire solar cycle. The first four SSULI instruments are complete, and detailed optical calibrations have been performed. Assembly and calibration of the remaining SSULI instrument and LORAAS are underway, and preliminary results are available. Preliminary results of the first SSULI instrument were reported in 1994. This paper updates the calibration results of the first instrument and presents a summary of the results of the next three SSULI instruments. Comparison between instrument characteristics are also discussed, including variations in calibration techniques. A brief discussion on the periodic calibration verification of the SSULI instruments during storage and prior to launch is included.
A facility for calibrating far ultraviolet and extreme ultraviolet instruments has recently been completed at the Naval Research Laboratory. Our vacuum calibration vessel is 2-m in length, 1.67-m in diameter, and can accommodate optical test benches up to 1.2-m wide by 1.5-m in length. A kinematically positioned frame with four axis precision pointing capability of 10 microns for linear translation and .01 degrees for rotation is presently used during vacuum optical calibration of SSULI. The chamber was fabricated from 304 stainless steel and polished internally to reduce surface outgassing. A dust-free environment is maintained at the rear of the vacuum chamber by enclosing the 2-m hinged vacuum access door in an 8 ft. by 8 ft. class 100 clean room. Every effort was made to obtain an oil-free environment within the vacuum vessel. Outgassing products are continually monitored with a 1 - 200 amu residual gas analyzer. An oil-free claw and vane pump evacuates the chamber to 10-2 torr through 4 in. diameter stainless steel roughing lines. High vacuum is achieved and maintained with a magnetically levitated 480 l/s turbo pump and a 3000 l/s He4 cryopump. Either of two vacuum monochrometers, a 1-m f/10.4 or a 0.2-m f/4.5 are coaxially aligned with the optical axis of the chamber and are used to select single UV atomic resonance lines from a windowless capillary or penning discharge UV light source. A calibrated channeltron detector is coaxially mounted with the SSULI detector during calibration. All vacuum valves, the cooling system for the cryopump compressor, and the roughing pump are controlled through optical fibers which are interfaced to a computer through a VME board. Optical fibers were chosen to ensure that complete electrical isolation is maintained between the computer and the vacuum system valves-solenoids and relays.
The special sensor ultraviolet limb imager (SSULI) is an ultraviolet limb imaging spectrograph under development by the Naval Research Laboratory for the Defense Meteorological Satellite Program (DMSP). The instrument will measure limb intensity profiles of the earth's airglow in the extreme and far ultraviolet (800 to 1700 angstrom) with 12 - 15 angstrom resolution. The SSULI uses a rotating mirror to scan the instrument field-of-view through 17 degrees to view from 750 km to 50 km tangent altitude. SSULI measurements will be used to infer altitude profiles of ion and electron density and neutral density. A total of five SSULI instruments will be flown on the DMSP Block 5D3 satellites the first of which is scheduled for launch in the latter half of the decade. An additional copy will be flown aboard the Space Test Program (STP) ARGOS satellite in late 1995. Every optical component in SSULI was independently measured followed by system level instrument calibrations. The first SSULI instrument is complete and the preliminary calibration results validate the design expectations. Assembly and calibration of the remaining instruments is underway. This paper presents the preliminary calibration results from SSULI #1 and component test results of the wedge and strip anode microchannel plate detector, grating, collimator and scan mirror. In addition, calibration techniques used to determine detector quantum efficiency, counting linearity, resolution, wavelength and absolute calibration are discussed. A brief discussion of the log term calibration plans for the SSULI instruments including periodic calibration checks during storage, in-flight calibrations using stars and ground truth measurements is presented.
We have calibrated a high resolution EUV spectrometer in three spectroscopic orders using the National Institute for Science and Technology's Synchrotron Ultraviolet Radiation Facility (SURF-II) at Gaithersburg, MD. The spectrometer was the principal instrument on a University of Colorado sounding rocket experiment, with a first order bandpass of roughly 5.8 nm centered at 155.5 nm, and resolving power of 4 X 104. Synchrotron radiation provides a well calibrated, columnated and polarized light source well suited to photometric calibration. The spectral distribution of synchrotron radiation is extremely well known from the theory of synchrotron radiation, and the spectral shape and intensity are directly related to the electron beam energy and current. If the instrument is calibrated at as many different beam energies as there are spectroscopic orders, then the spectrometer efficiency in each order can be determined from a single set of simultaneous equations. A difficulty arises in that the system of equations can be sensitive to perturbations of the level of experimental uncertainty. We have been able to reduce the number of unknowns by independently determining the first order efficiency and thus overdetermine the set of equations. The resulting efficiency measurements are accurate and reliable.
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