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
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 Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) has an optical
prescription which includes numerous fold mirror assemblies. The instrument will operate at 35K after experiencing
launch loads at ~293K. The optic mounts must accommodate all associated thermal and mechanical stresses, plus
maintain exceptional optical quality during operation. Lockheed Martin Space Systems Company (LMSSC) conceived,
designed, analyzed, assembled, tested, and integrated the mirror assemblies for the NIRCam instrument. This paper
covers the design, analysis, assembly, and test of two of the instruments key fold mirrors.
The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) includes numerous
optical assemblies. The instrument will operate at 35K after experiencing launch loads at ~293K and the optic mounts
must accommodate all associated thermal and mechanical stresses, plus maintain exceptional optical quality during
operation. Lockheed Martin Space Systems Company (LMSSC) conceived, designed, analyzed, assembled, tested, and
integrated the optical assemblies for the NIRCam instrument. With using examples from NIRCam, this paper covers
techniques for mounting small mirrors and lenses for cryogenic space missions.
The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) has an optical
prescription which employs four triplet lens cells. The instrument will operate at 35K after experiencing launch loads at
approximately 295K and the optic mounts must accommodate all associated thermal and mechanical stresses, plus
maintain an exceptional wavefront during operation.
Lockheed Martin Space Systems Company (LMSSC) was tasked to design and qualify the bonded cryogenic lens
assemblies for room temperature launch, cryogenic operation, and thermal survival (25K) environments. The triplet lens
cell designs incorporated coefficient of thermal expansion (CTE) matched bond pad-to-optic interfaces, in concert with
flexures to minimize bond line stress and induced optical distortion. A companion finite element study determined the
bonded system's sensitivity to bond line thickness, adhesive modulus, and adhesive CTE. The design team used those
results to tailor the bond line parameters, minimizing stress transmitted into the optic.
The challenge for the Margin of Safety (MOS) team was to design and execute a test that verified all bond pad/adhesive/
optic substrate combinations had the required safety factor to generate confidence in a very low probability optic bond
failure during the warm launch and cryogenic survival conditions. Because the survival temperature was specified to be
25K, merely dropping the test temperature to verify margin was not possible. A shear/moment loading device was
conceived that simultaneously loaded the test coupons at 25K to verify margin.
This paper covers the design/fab/SEM measurement/thermal conditioning of the MOS test articles, the thermal/structural
analysis, the test apparatus, and the test execution/results.
Lockheed Martin Space Systems Company (LMSSC) has performed a feasibility study for bonded cryogenic optical mounts. That investigation represents a combined effort of design, experiments and analysis with the goal to develop and validate a working cryogenic mount system for refractive lens elements. The mount design incorporates thermal expansion matched bond pads and radial flexures to reduce bondline stress and induced optical distortion. Test coupons were constructed from lens and selected mount materials and bonded with candidate adhesives to simulate the design's
bond pads. Thermal cycling of those coupons to 35K demonstrated both the system's survivability and the bond's structural integrity. Finally, a companion finite element study determined the bonded system's sensitivity to bondline thickness, adhesive modulus and adhesive CTE. The design team used those results to tailor the bondline parameters to minimize stress transmitted into the optic.
A high bandwidth, gimbaled, fast steering mirror (FSM) assembly has been designed and tested at the Lockheed Martin Space Systems Company (LMSSC) Advanced Technology Center (ATC). The design requirements were to gimbal a 5 cm diameter mirror about its reflective surface, and provide 1 KHz tip/tilt/piston control while maintaining λ/900 flatness of the mirror. The simple, yet very compact and rugged device also has manual tip/tilt/piston alignment capability. The off-the-shelf Piezo translators (PZT) actuators enable reliable and repeatable closed loop control. The adopted solution achieves a good mass balance and gimbaled motion about the center of the mirror front surface. Special care was taken to insure the best positioning means with the mounted mirror assembly held kinematically in place. The manual adjusters have very good resolution, with the capability to be locked in place. All solutions were thoroughly modeled and analyzed. This paper covers the design, analysis, fabrication, assembly, and testing of this device. The FSM was designed for ground test only.
The Terrestrial Planet Finder (TPF) employs an aggressive coronagraph designed to obtain better than 1e-10 contrast inside the third Airy ring. Minute changes in low-order aberration content scatter significant light at this position. One implication is the requirement to control low-order aberrations induced by motion of the secondary mirror relative to the primary mirror; sub-nanometer relative positional stability is required. We propose a 6-beam laser truss to monitor the relative positions of the two mirrors. The truss is based on laser metrology developed for the Space Interferometry Mission.
Researches have suggested several techniques (ie.: pupil masking, coronography, nulling interferometry) for high contrast imaging that permit the direct detection and characterization of extrasolar planets. Our team at JPL, in previous papers, has described an instrument that will combine the best of several of these techniques: a single aperture visible nulling corograph. The elegant simplicity of this design enables a powerful planet-imaging instrument at modest cost. The heart of this instrument is the visible light nulling interferometer for producing deep, achromatic nulls over a wide optical band pass, and a coherent array of single mode optical fibers 2 that is key to suppressing the level of scattered light. Both of these key components are currently being developed and have
produced intial results. This paper will review, in detail, the design of the nulling interferometer experiment and review the latest experimental results. These results illustrate that we are well on our way to developing the fundamental components necessary for planned mission. Likewise, our results demonstrate that the current nulling levels are already consistent with final requirements.
A sensitivity evaluation of mounting 100mm optics using elastomer or bipod flexures was completed to determine the relative effects of geometry, structure, material, thermal and vibration environment as they relate to optical distortion. Detailed analysis was conducted using various finite element-modeling methods. Parts were built and the results were verified by conducting brassboard tests.
What makes this evaluation noteworthy is the two vastly different approaches, and how they both exhibited athermal properties and minimized optical distortion. Materials were carefully selected while the geometry and structure were optimized through analytical iteration.
The elastomeric optical mount consists of 12 equally spaced pads of RTV placed around the circumference of the optic. These pads were sized to maximize stiffness and minimize surface deformations. The surrounding material was appropriately selected in order to contribute to an athermal design.
The bipod flexure optical mount uses three flexures cut from a single piece of material. Each flexure is a bipod oriented to comply radially with changes in temperature. This design is monolithic and uses conventional epoxy at the optical interface. The result is a very stiff athermal design.
This paper covers both opto-mechanical designs, as well as analytical results from computer modeling and brassboard tests.
Visible interferometry at µarc-second accuracy requires measurement of the interferometric baseline length and orientation at picometer accuracy. The optical metrology instruments required for these interferometers must achieve accuracy on order of 1 to 10 picometers. This paper discusses the progress in the development of optical interferometers for use in distance measurement gauges with systematic errors below 100 picometers. The design is discussed as well as test methods and test results.