The NASA Interface Region Imaging Spectrograph (IRIS) mission is a Small Explorer (SMEX) satellite mission
designed to study plasma dynamics in the “interface region” between the Sun’s chromosphere and corona with high
spatial, spectral, and temporal resolution. The primary instrument is a dual Czerny-Turner spectrograph fed by a 20-cm
Cassegrain telescope measuring near- and far-ultraviolet (NUV, FUV) spectral lines in the ranges 133-141 nm and 278-
283 nm. To determine the position of the slit on the solar disk, a slit-jaw imaging system is used. The NUV slit-jaw
imaging system produces high spatial resolution images at two positions in the Mg II 280 nm spectral line complex using
a birefringent Solc filter with two wide-band interference pre-filters for spectral order selection. The Solc filter produces
a 0.36 nm full-width at half-maximum (FWHM) filter profile with low sidelobes and a peak transmission of 15% at
279.6 nm. The filter consists of two “wire grid’’ polarizers surrounding 8 quartz waveplates configured in a modified
Solc “fan” rotational pattern. The elements are optically coupled using DC200 silicon-based grease. The NUV Solc filter
is sealed in a windowed cell to prevent silicon contamination of the FUV channel. The design of the sealed cell and
assembly of the filter into the cell were among the most challenging optomechanical aspects of the IRIS spectrograph
system.
This paper discusses the design of the IRIS Small Explorer (SMEX) Cassegrain telescope, as well as its intended and measured
performance. Lockheed Martin, along with SAO, Montana State University, and Stanford University are developing
the IRIS instrument for a mission to examine the solar spectra in two bands, one centered on 1369 Å, and the other centered
on 2810 Å. SAO led the design and construction of the telescope feed, with assistance from Lockheed and Montana State
University.
The telescope posed a number of implementation challenges, which are discussed here, including the fact that no effective
filters exist to isolate the science spectra to the exclusion of the rest of the solar flux, making it necessary to allow full
sunlight into the telescope.
The Interface Region Imaging Spectrograph (IRIS) is a NASA SMall EXplorer mission scheduled for launch in January
2013. The primary goal of IRIS is to understand how the solar atmosphere is energized. The IRIS investigation
combines advanced numerical modeling with a high resolution UV imaging spectrograph. IRIS will obtain UV spectra
and images with high resolution in space (0.4 arcsec) and time (1s) focused on the chromosphere and transition region of
the Sun, a complex interface region between the photosphere and corona. The IRIS instrument uses a Cassegrain
telescope to feed a dual spectrograph and slit-jaw imager that operate in the 133-141 nm and 278-283 nm ranges. This
paper describes the instrument with emphasis on the imaging spectrograph, and presents an initial performance
assessment from ground test results.
The Solar Ultraviolet Imager (SUVI) is one of several instruments being fabricated for use on board the upcoming
Geostationary Operational Environmental Satellites, GOES-R and -S platforms, as part of NOAA's space weather
monitoring fleet. SUVI is a Generalized Cassegrain telescope that employs multilayer coatings optimized to operate in
six extreme ultraviolet (EUV) narrow bandpasses centered at 93.9, 131.2, 171.1, 195.1, 284.2 and 303.8 Å. Over the
course of its operational lifetime SUVI will image and record full disk, EUV spectroheliograms approximately every few
minutes, and telemeter the data to the ground for digital processing. This data will be useful to scientists and engineers
wanting to better understand the effects of solar produced EUV radiation with the near-Earth environment. At the focus
of the SUVI telescope is a thin, back-illuminated CCD sensor with 21 μm (2.5 arc sec) pixels. At the shortest EUV
wavelengths, image degradation from mirror surface scatter effects due to residual optical fabrication errors dominate the
effects of both diffraction and geometrical aberrations. Discussed herein, we present a novel forward model that
incorporates: (i) application of a new unified surface scatter theory valid for moderately rough surfaces to predict the bidirectional
reflectance distribution function (BRDF) produced by each mirror (which uses optical surface metrology to
determine the power spectral density, PSD, that characterizes the "smoothness" of an optical surface); (ii) use of the
BRDF for each mirror at each EUV wavelength, in tandem with the optical design, to calculate the in-band point spread
function (PSF); (iii) use of the PSF to calculate the fractional ensquared energy in the focal plane of SUVI; (iv)
comparison of BRDF measurements taken at 93.9 Å with the forward model predictions and (v) final prediction of the
in-band, total system responsivity.
The design of the 4 telescopes that make up the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDOAIA)
is described. This includes the optical design, optical mounting system, front aperture filters, and launch protection
system. SDO-AIA is a study of taking a difficult telescope design and making four of them. We describe the technical
challenges associated with the telescope mounting, mirror mounting, and the front aperture filter design and launch
protection.
The Solar X-ray Imager (SXI) was launched 24 May 2006 on Geostationary Operational Environmental Satellite
(GOES-13). SXI is a grazing incidence X-ray telescope that focuses an image of the Sun onto a CCD detector
through a set of selectable filters. The X-ray image data are transmitted at the rate of at least one image per minute,
which permits the reconstruction of near-real-time solar images in the 6-60Å range (photon energy 2000-200 eV).
Thin film filters consisting of aluminum, titanium, and polyimide are used in the entrance of the telescope to
eliminate visible light. During the first six months of on-orbit operations the amount of stray light transmitted
increased approximately linearly with time, consistent with the formation of small (less than 50 micron) pinholes. A
laboratory investigation was initiated and witness sample filters were subjected to energetic particles simulating the
on-orbit radiation environment and their quality was assessed using visible light-leak testing and scanning electron
microscope imaging. It was concluded that galvanic corrosion of aluminum and titanium initiates pinholes that
subsequently grow in dendritic fashion by spalling off of aluminum to relieve the internal film stress. The test
program also revealed that the geostationary radiation dose level can damage polyimide and lead to filter failure.
Radiation damage may have been responsible in part for the increased light levels observed in the GOES-12 SXI and
with increased exposure a similar observation could manifest on GOES-13 SXI. This paper presents the
methodology and results for the entrance filter test program for the GOES SXI telescopes and presents recommended
improvements for future instruments.
On 2006 May 24 NOAA's Geostationary Operational Environmental Satellite (GOES) 13 satellite was launched with the
next generation Solar X-ray Imager (SXI) aboard. This instrument represents a significant step forward in performance
over the previous SXI flown on GOES-12, even before that instrument suffered serious degradation. Like the previous
instrument, the new instrument uses a grazing incidence optical design, but with a new detector and other improvements,
it has about 10 times the sensitivity, twice the spatial resolution, and greatly reduced wide-angle scattering compared to
the GOES-12 SXI. The GOES-13 SXI completed its 6 month checkout period in December 2006. Performance tests
included dark current, flat-field, spatial response, scattered light, pointing stability and jitter. We present initial analyses
and results of these tests as well as comparisons to ground test results. In addition, GOES-13 solar observations are
compared to solar observations by other instruments. When it enters operations, the GOES-13 SXI will provide
continuous, real-time observations of the X-ray Sun at 1-minute cadence.
The SECCHI Extreme Ultraviolet Imager (EUVI) is a pair of EUV telescopes on the NASA STEREO mission that was
successfully launched in October 2006. The two telescopes, one on each STEREO spacecraft observe the solar corona
in three dimensions out to 1.7 solar radii, and with a pixel resolution of 1.59 arcsec. The focus of the EUVI observations
is the initiation and early evolution of coronal mass ejections (CMEs). This paper presents a preliminary assessment of
the on-orbit performance of the EUVI.
The Extreme Ultraviolet Imager (EUVI) is part of the SECCHI instrument suite currently being developed for the NASA STEREO mission. Identical EUVI telescopes on the two STEREO spacecraft will study the structure and evolution of the solar corona in three dimensions, and specifically focus on the initiation and early evolution of coronal mass ejections (CMEs). The EUVI telescope is being developed at the Lockheed Martin Solar and Astrophysics Lab. The SECCHI investigation is led by the Naval Research Lab. The EUVI’s 2048 x 2048 pixel detectors have a field of view out to 1.7 solar radii, and observe in four spectral channels that span the 0.1 to 20 MK temperature range. In addition to its view from two vantage points, the EUVI will provide a substantial improvement in image resolution and image cadence over its predecessor SOHO-EIT, while complying with the more restricted mass, power, and volume allocations on the STEREO mission.
A jitter compensation system is incorporated in the Solar X-ray Imager
(SXI) that will be mounted to the solar array wing of the GOES N
spacecraft, the next in the series of NOAA weather satellites. The SXI obtains images in a back-thinned CCD with 5 arcsec pixels. The SXI incorporates a pointing aspect sensor manufactured by the Adcole
Corporation that is used in a semi-closed loop system with the SXI
flight computer to shift the detected image during an exposure along the readout columns of the CCD in order to compensate for jitter in one dimension. Simulations of the predicted motions caused by the GOES spacecraft and self-induced by the SXI filter wheels indicate that the jitter as experienced by the SXI instrument will be primarily along one axis, parallel to the east-west direction, with amplitudes in the tens of arcseconds and with dominant frequencies less than approximately 10 Hz. The SXI CCD columns are aligned along this direction in order to make possible on-chip compensation. The SXI motion compensation system has been evaluated with realistic models for the expected spacecraft jitter and assuming a performance algorithm for the SXI instrument. Our analysis indicates that the X-ray spatial imaging performance will be improved when the jitter compensation system is used. We discuss the design and analysis predictions.
A new Solar X-ray Imager (SXI) using back-illuminated, anti-blooming
CCD technology will become part of the instrument complement on
NOAA's GOES (Geosynchronous Orbiting Environmental Satellite) N and
O spacecraft, with probable launch dates beginning in the 2004-2005
time frame. SXI N and O were developed under a NASA contract by the
Solar and Astrophysics Laboratory at the Lockheed Martin Advanced
Technology Center, and are currently being integrated into their
respective spacecrafts by Boeing Space Systems. SXI N and O will
each provide full disk images of the Sun from 0.2 to 1.2 keV (10-60
Å) through the combination of a grazing incidence telescope,
bandpass filters, and an X-ray imaging CCD. The custom designed,
back-illuminated CCDs were fabricated and initially tested by
Marconi Technologies (formerly EEV Ltd, now e2v technologies),
screened in visible light by the Mullard Space Science Laboratory,
and fully characterized in both visible light and X-rays at LMSAL.
By minimizing the field-free region within the CCD, the spatial
resolution at low X-ray energies was significantly improved. The SXI
CCDs also exhibit only very modest response changes as a result of
solar X-ray exposure, based upon extended life tests. The flight
CCDs meet or surpass all specifications for quantum efficiency (QE),
spatial uniformity, defects, charge transfer efficiency, QE
stability in vacuum, read noise, linearity, full well and dark
current. A QE model based on earlier work with ion-implanted,
laser-annealed CCDs provides a consistent picture of the CCD
response from soft X-rays through far UV wavelengths.
The X-ray calibration of the GOES Solar X-ray Imagers (SXI) was accomplished at the component level and at the instrument level. The CCD and thin film filters were characterized in the facilities at the Lockheed Martin Solar and Astrophysics Laboratory. The grazing incidence telescope mirrors and the completed instruments were calibrated at the X-ray Calibration Facility (XRCF) at NASA’s Marshall Space Flight Center. The XRCF consists of an X-ray source at one end of a 518 m long evacuated tube and a large vacuum chamber at the opposite end. The X-ray source has a variety of interchangeable anodes and filters to provide filtered characteristic K- and L-shell line emission in the range from 0.109 to 8.6 keV. The absolute Photometric calibration of the SXI telescopes is very important for analysis and interpretation of their data, and to monitor the long-term solar variations at X-ray wavelengths. This paper describes the results of these calibrations.
James Lemen, Dexter Duncan, Christopher Edwards, Frank Friedlaender, Bruce Jurcevich, Mons Morrison, Larry Springer, Robert Stern, Jean-Pierre Wuelser, Marilyn Bruner, Richard Catura
The next generation of the National Oceanic and Atmospheric Administration's (NOAA) Geo-Stationary Operational Environmental Satellite (GOES) spacecraft will include an X-ray telescope that will monitor the Sun for predicting solar energetic events and for providing information about the large-scale solar magnetic field. The Solar X-ray Imager that will be flown on the GOES N spacecraft in late 2004 makes use of a super-polished grazing incidence mirror, a highly efficient back-thinned CCD, and thin metalized filters to observe the million-degree corona with 10-arcsec resolution (5 arcsec pixel size). Full-sun images will be acquired with SXI on a one-minute cadence at wavelengths between approximately 10 and 60 Å. SXI data will be used to forecast 'space weather', i.e., the effects of charged particles that are produced at the Sun as they interact at the earth. Major contributors to space weather include: variations in the Sun's solar wind, solar flares, and solar mass ejections. Effects of space weather include: radiation damage and particle events in high-inclination orbit spacecraft, disruption of various kinds of communications equipment, degradation of navigational tools such as GPS, potential health hazards during space walks, and power blackouts. Data acquired by the SXI will additionally provide invaluable context information for upcoming solar missions such as STEREO and SDO. The Lockheed Martin Solar and Astrophysics Laboratory has prepared two flight model SXIs that are being readied for flight on the GOES N and GOES O or P spacecraft.
We have measured the x-ray imaging performance of a grazing incidence telescope mirror, the HT #17, employing a hyperboloid-hyperboloid design. This design provides improved wide-field imaging compared to an optimally defocused Wolter Type I mirror. This improvement will be advantageous for future Geostationary Operational Environmental Satellite (GOES) missions that will provide full disk images of the sun with the Solar X-ray Imager (SXI). The x-ray measurements were made in the X-Ray Calibration Facility (XRCF) at Marshall Space Flight Center and the results are presented here.
This paper describes the conceptual design of a soft x-ray telescope, super-x, which we will propose for the Japan/US/UK Solar-B mission. Super-X will break new ground in both angular resolution and solar coronal temperature discrimination. The telescope design is based upon the successful transition region and coronal explorer instrument. It features four XUV spectral channels spanning the 0.3 to 20 MK temperature range with an angular resolution of approximately 0.27 seconds of arc. We will describe considerations affecting spectral line selection and some details of the characteristics of the instrument.
J. Daniel Moses, Guenter Brueckner, Kenneth Dere, Clarence Korendyke, Norman Moulton, Dianne Prinz, John Seely, Dennis Socker, Marilyn Bruner, James Lemen
The Naval Research Laboratory Skylab SO82A slitless spectrograph provided solar flare observations that have never been equaled in diagnostic capabilities for interpreting thermal flare physics. Improvements in detector technology, optics and optical coating technology, and almost two decades of analysis of SO82A data can be combined with the basic concept of an EUV objective grating spectrograph to build an instrument to address many of the remaining mysteries of solar flares. This next generation instrument incorporates two sets of two identical, orthogonally mounted slitless spectrographic Cassegrain telescopes. Each telescope consists of a multilayer coated, Wadsworth mount objective grating and multilayer coated spherical secondary mirror; a backside illuminated CCD detector is installed at the focal plane. The orthogonal mounting changes the dispersion direction by 90 degrees on the disk image; processing on the two resulting images allows recovery of the undispersed disk image and spectral line profiles. The resulting instrument will obtain high time cadence, spectrally-dispersed images with improved spatial resolution, dynamic range, signal-to-noise ratio, and velocity discrimination.
The quantum efficiency (QE) and flat field characteristics of back-illuminated 1024 X 1024 Tektronix CCDs have been measured in the extreme ultraviolet (EUV) between 44 and 1216 angstroms. These CCDs have been fabricated for the focal plane detector of the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observing spacecraft. The back-side surface of the EIT CCDs have been specially processed to enhance and stabilize the EUV QE. All requirements for QE are met by these devices, although a poorly understood variation of QE with temperature will complicate data analysis.
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