Optical payloads are hosted on a range of spacecraft and reach orbit on a variety of launch vehicles. Traditionally, each payload imposes specific requirements on the mounts such as surface figure, thermal environment, and first dynamic mode. The product line of mounts described herein as the Common Optical Mount (COM) is designed to work for 80% of Lockheed Martin’s future space applications with no change to the design. Varying in diameter from 25mm to 300mm, each pre-qualified product line provides a different service needed while meeting general requirements and accommodating a wide range of unique optics (i.e. high precision alignment, large FOV systems, thick & heavy optics, lens, mirrors, beam splitters, diffraction gratings, etc.). Payload programs then leverage this qualified design and all the released piece part drawings. Additional requirements can be added to the base requirements for tailoring specific program needs. For example, the same mount product could be used to hold a fused silica beam splitter for a NASA mission in GEO orbit or a BK7 lens for a military customer in LEO orbit. Whether in a satellite constellation of a few large high-value exquisite systems or a prolificated LEO constellation of small satellites, the catalog of space qualified optical mounts serves to reduce cost, schedule, and risk for programs. COM helps deliver a payload that meets the customers future space architecture needs with improved capabilities at a fraction of the past costs.
The design process for an opto-mechanical sub-system is discussed from requirements development through test. The process begins with a proper mission understanding and the development of requirements for the system. Preliminary design activities are then discussed with iterative analysis and design work being shared between the design, thermal, and structural engineering personnel. Readiness for preliminary review and the path to a final design review are considered. The value of prototyping and risk mitigation testing is examined with a focus on when it makes sense to execute a prototype test program. System level margin is discussed in general terms, and the practice of trading margin in one area of performance to meet another area is reviewed. Requirements verification and validation is briefly considered. Testing and its relationship to requirements verification concludes the design process.
The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) has an optical
prescription which employs three triplet lens cells. 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 an
exceptional wavefront during operation. The Lockheed Martin Advanced Technology Center (LMATC) has built and
tested the collimator and camera optics for use on the NIRCam flight instrument. This paper presents an overview of the
driving requirements, a brief overview of the changes in the opto-mechanical design and analysis since our last
presentation, a discussion of the collimator and shortwave camera triplet assembly processes, and finally a summary of
the mechanical and optical test results.
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.
The Near Infrared Camera (NIRCam) for the James Webb Space Telescope (JWST) has undergone Pathfinder
component testing and evaluation. This paper presents the opto-mechanical test results. An overview of the optomechanical
system requirements is provided, followed by a discussion of the opto-mechanical system design and
assembly process. Tolerances in the opto-mechanical system as they relate to system level alignment are also presented.
Mechanical analysis related to vibration and thermal behavior of the design is shown. Finally, the overall performance
of the opto-mechanical system is discussed as it relates to instrument optical performance.
An example is given of how cryogenic optical testing is being performed for the NIRCam instrument.
A 94 mm diameter Lithium Fluoride lens was mounted and thermally cycled between room temperature
and approximately 60 K. Interferometric measurements were taken before, during, and after the cycling
to determine the effects of temperature on the optical performance. We found that the net distortion of
the surface of the lens decreased with temperature. We also found that that the distortion did not
increase as the temperature rose again, and that the transmitted wavefront quality remained unchanged
before and after thermal cycling.
Single crystal Lithium Fluoride has been base-lined as one of the optical materials for the Near Infra-Red Camera
(NIRCam) on the James Webb Space Telescope (JWST). Optically, this material is outstanding for use in the near IR.
Unfortunately, this material has poor mechanical properties, which make it very difficult for use in any appreciable size
on cryogenic space based instruments. In addition to a dL/L from 300K to 30K of ~-0.48%, and a room temperature
CTE of ~37ppm/K, the material deforms plastically under relatively small tensile loading. This paper will update a
paper presented in 2005 on the same optical mount [1]. The mount has been proven via vibration and thermal-vacuum
testing to successfully mount large (70 mm-94 mm) Lithium Fluoride optics for application in space. An overview of
Lithium Fluoride material properties and characteristics is given and updated yield strength test data is provided and
discussed. A design limit load is determined for the material based on strength values from the literature as well as
independent testing. The second generation mount design is then presented along with test data and results. Finally, the
test results are discussed showing survival and performance of the optic and mount during cool-down to the operational
thermal environment.
The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) has an optical
prescription which employs several mirrors, some of which are powered and some of which are flats that aid in
packaging. Two distinct designs for the mirrors and their mounts have been developed such that different requirements
for mass, packaging and induced wavefront error can be met. The instrument will operate at 37K after experiencing
launch loads at ~293K and the mounts must accommodate all associated thermal and mechanical stresses. Two of the
mirrors needed to be redesigned after initial prototype testing of one of the designs. This paper will provide an update
on the design and analysis status for all the mirrors including results of the initial prototype testing.
Single crystal Lithium Fluoride has been base-lined as one of the optical materials for the Near Infra-Red Camera (NIRCam) on the James Webb Space Telescope (JWST). Optically, this material is outstanding for use in the near IR. Unfortunately, this material has poor mechanical properties, which make it very difficult for use in any appreciable size on cryogenic space based instruments. In addition to a dL/L from 300K to 30K of ~-0.48%, and a room temperature CTE of ~37ppm/K, the material deforms plastically under relatively small tensile loading. This paper will present a mount that has been proven via vibration and thermal-vacuum testing to successfully mount a large (70mm-94mm) Lithium Fluoride optic for application in space. An overview of Lithium Fluoride material properties and characteristics is given. A design limit load is determined for the material based on strength values from the literature as well as independent testing. The original design option is shown and the pros and cons discussed. The final mount design is then presented along with analysis results showing compliance to the limit load requirement. Finally, testing results are discussed showing survival of the optic in a space launch vibration environment as well as survival during cool-down to the operational thermal environment of 30K.
Single crystal Lithium Fluoride (LiF) has been base-lined as one of the optical materials for the Near Infra-Red Camera (NIRCam) on the James Webb Space Telescope (JWST). Optically, this material is outstanding for use in the near IR. Unfortunately, it has poor mechanical properties that make it very difficult for use in any appreciable size on cryogenic space based instruments. In addition to a dL/L from 300K to 30K of ~-0.48% and room temperature CTE of ~37ppm/K, LiF deforms plastically under relatively small stresses. This paper will discuss the heritage of LiF in space-based systems and summarize the mechanical and thermal material data for LiF that is available in the literature. New data will be presented relative to a design limit load for the material so that designers can use this material for space flight applications. Additional new data relative to the cryogenic index of refraction of the material over the near infrared is also provided.
The refractive optical design of the James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam) uses three infrared materials in its lenses: LiF, BaF2, and ZnSe. In order to provide the instrument's optical designers with accurate, heretofore unavailable data for absolute refractive index based on actual cryogenic measurements, two prismatic samples of each material were measured using the cryogenic, high accuracy, refraction measuring system (CHARMS) at NASA's Goddard Space Flight Center (GSFC), densely covering the temperature range from 15 to 320 K and wavelength range from 0.4 to 5.6 microns. Data reduction methods are discussed and graphical and tabulated data for absolute refractive index, dispersion, and thermo-optic coefficient for these three materials are presented for selected wavelengths and temperatures along with estimates of index uncertainty. Coefficients for temperature-dependent Sellmeier fits of measured index are also presented with an example of their usage to predict absolute index at any wavelength or temperature within the applicable range of those parameters.
A novel tip-tilt mechanism has been designed which is capable of aligning a small 1-inch optic with one arc second resolution. This mechanism performs this function without the aid of a piezoelectric device or other electronic technology. The optic is bonded to a three bipod mount in series with a spring-loaded flexure. Three manually adjustable differential screws drive the flexure. The bipod/flexure arrangement allows highly accurate and stable adjustment. This paper will give an overview of the design, and present laboratory data and analysis quantifying the adjustment resolution of the mechanism. Material and surface coating selection is also presented.
The compact and stable dual fiber optic refractive collimator is a device that takes laser light from two fiber optic cables, generating two beams of collimated light at increased diameters. This device is designed to be stable over a specific soak temperature range and maintain alignment through adverse vibration. Single or multiple beam configurations are possible with this design and the complexity goes linearly with beam quantity.
What makes this device noteworthy is the simplicity of design plus ease in assembly and alignment. A precision alignment fixture is used instead of cumbersome, built-in, multiple degree of freedom features such as adjustment screws and flexures. This allows the collimator itself to be quite simple, compact and thermally stable.
The dual collimator consists of a common housing, two fiber tip shuttle plugs allowing for adjustment in focus, and two laterally adjustable lens cells for beam alignment. The design has integral adhesive tack bonding features throughout and contains few parts keeping fabrication and alignment costs down.
This paper covers the requirements, design, manufacture, assembly and performance of this optical device. The collimator has utility in precision interferometry. A patent has been filed.
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.
The Space Interferometry Mission (SIM), planned for launch in 2009, will measure the positions of celestial objects to an unprecedented accuracy of 4.0 microarcseconds. In order to achieve this accuracy, which represents an improvement of almost two orders of magnitude over previous astrometric measurements, a ten-meter baseline interferometer will be flown in space. NASA challenges JPL and its industrial partners, Lockheed Martin and TRW, to develop an affordable mission. This challenge will be met using a combination of existing designs and new technology. Performance and affordability must be balanced with a cost-conscious Systems Engineering approach to design and implementation trades. This paper focuses on the Lockheed Martin-led Starlight (STL) and Metrology (MET) subsystems within the main instrument of SIM. Starlight is collected by 35cm diameter telescopes to form fringes on detectors. To achieve the stated accuracy, the position of these white-light fringes must be measured to 10-9 of a wavelength of visible light. The STL Subsystem consists of siderostats, telescopes, fast steering mirrors, roof mirrors, optical delay lines and beam combiners. The MET Subsystem is used to measure very precisely the locations of the siderostats with respect to one another as well as to measure the distance traveled by starlight from the siderostat mirrors and reference corner cubes through the system to a point very close to the detectors inside the beam combiners. The MET subsystem consists of beam launchers, double and triple corner cubes, and a laser distribution system.
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