The Interface Region Imaging Spectrograph (IRIS) is a NASA SMall Explorer (SMEX) mission launched onboard a Pegasus™ booster on June 27, 2013. The spacecraft and instrument were designed and built at the Lockheed Martin Space Systems Company. The primary mission goal is to learn how the solar atmosphere is energized. IRIS will obtain high-resolution UV spectra and images in space (0.4 arcsec) and time (1s), focusing on the chromosphere and transition region of our sun, which is 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, which operate in the 133-141 nm and 278-283 nm wavelengths, respectively. Within the spectrograph there are sixteen optics, each requiring subtle mounting features to meet exacting surface figure and stability requirements. This paper covers the opto-mechanical design for the most challenging optic mounts, which include the Collimator, UV Fold Mirrors, and UV Gratings. Although all mounts are unique in size and shape, the fundamental design remains the same. The mounts are highly kinematic, thermally matched, and independent of friction. Their development will be described in detail, starting with the driving requirements and an explanation of the underlying design philosophy.
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.
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.
KEYWORDS: Mirrors, IRIS Consortium, Telescopes, Space telescopes, Absorption, Ultraviolet radiation, Optical instrument design, Solar energy, Spectrographs, Control systems design
This paper presents the overall thermal design of the Interface Region Imaging Spectrograph (IRIS) telescope with
focused descriptions of the primary mirror thermal design, telescope active thermal control system, ULE® mirror
substrate thermal properties, and the thermal math model supporting the thermal design. The challenge of the IRIS
primary mirror thermal design was to manage the un-filtered solar flux that directly impinges on the optical substrate,
while maintaining the mirror within a narrow range of temperatures throughout the mission life. This thermal problem is
compounded by a change in the absorption properties of ULE over time, due to UV light.
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 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.
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.
Tunable UV Fabry-Perot etalons have the potential of providing images, dopplergrams, and density maps of the Sun's upper chromosphere and transition region. To study the feasibility of this approach, we developed and built tunable laboratory etalons for the 135 - 141 and 120 - 123 nm wavelength ranges. At 140 nm we achieved a finesse of 10.5 and a peak transmission of 3 percent. This performance is sufficient to observe the density sensitive line pair of O IV at 140.4 and 140.7 nm. At 122 nm (H Lyman alpha) we achieved a finesse of 3.8 and a peak transmission of 0.07 percent.
We report on a continuing program to develop and test reflecting coatings suitable for use in Fabry-Perot etalons operating in the far ultraviolet region of the spectrum. UV etalons are of particular interest for solar studies as they have the potential to enable one to make wide-field high resolution diagnostic images such as spectroheliograms, dopplergrams, and density maps in isolated spectral lines formed in the upper chromosphere, transition region and lower corona. The performance of the high-efficiency coatings required by a UV etalon is limited both by the availability of suitable materials, and by the uniformity and accuracy of the deposition process. The lack of UV transmitting materials with a wide range of refractive index is especially troublesome. The latter problem may be partially overcome by using a vacuum-spaced etalon design. A vacuum-spaced etalon with cultured quartz plates was successfully operated at 160 nm in a previous study. In this study, we investigated a family of coating designs based on the fluoride salts of magnesium and lanthanum, finding that usable etalon performance may be achievable at wavelengths as short as 120 nm. Results of theoretical predictions and the performance of test coatings are presented. This work was supported by NASA under contract NASW-5007.
The Transition Region and Coronal Explorer instrument (TRACE) will use narrow-band interference filters together with other appropriate band limiting elements to make high resolution images of the Sun in the C IV lines at 154.8 and 155.0 nm. Filter observations of solar C IV emission are complicated by the presence of UV Continuum and nearby chromospheric lines because of the relatively wide bandpasses of the narrowest currently available interference filters. TRACE will use a series of filters to estimate the effects of the UV continuum and the long-wavelength `leaks' in the blocking filters which we show are the most important contaminants in the C IV images. Further improvements in filtergraph performance may be realized through the use of tunable Fabry-Perot etalons, which have been under development at Lockheed-Martin. We present test data from a cultured quartz etalon designed for 155 nm, and will discuss the prospects for etalons operation at substantially shorter wavelengths.
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