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.
The Near InfraRed Camera (NIRCam) for the James Webb Space Telescope (JWST) is a refracting instrument. Its
unique optical performance derives from the Lithium Fluoride, Barium Fluoride and Zinc Selenide lenses that provide
aberration and color correction over the large operating wavelengths, 0.6-5 microns. This paper describes cryogenic test
results of the mounted camera lenses in a flight-like configuration. These data, which evaluate the foundation for
NIRCam optical performance, reveals design strengths and challenges. This is a follow-up paper from SPIE paper
590409 (1) which presented the initial camera lens design.
The Lockheed Martin - University of Arizona Infrared Spectrometer (LAIRS) is designed to image the emission
lines of celestial objects in the 1.3-2.5 μm regime. The Instrument has been built and tested at the Lockheed
Martin Space Systems Advanced Technology Center, and demonstrated to work at cryogenic
temperatures. The Instrument employs a tunable Fabry-Perot Interferometer (FPI) to select the wavelength at
which the Instrument images targets. The FPI employs voice coil actuators and capacitive sensors to maintain
parallelism of its reflective lenses and control their gap spacing. During functional tests of the FPI and the
LAIRS instrument, finesse numbers of 60 and 24 were measured for the interferometer at room temperature
and 80K, respectively. This measurement was performed using a laser operating at 1529.33 nm. This paper
presents an overview of the optical, mechanical, and control design of the FPI, as well as a summary of cryogenic
test results.
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.
The Near InfraRed Camera (NIRCam) for the James Webb Space Telescope (JWST) is a refracting camera system. Its unique performance derives from the Lithium Fluoride, Barium Fluoride and Zinc Selenide lenses that provide aberration and color correction over the large operating wavelength. This paper describes the optical prescription, lens materials and prototype characterization for the camera lenses.
Good wavefront quality, easy to align, and stable mounts are desired requirements for any optical system. Small variations in design parameters of mounts can radically diminish these qualities and performance of an optical system if tolerances of mounts don’t match optical requirements. We present design considerations required to create a stable ball knuckle mount with 5 degrees of freedom for a secondary mirror. Our system also required a rigid hub-mounted primary mirror with minimal optical deformation. Wavefront figure will be traced during design development of each mount. Overall final optical alignment was stable in 2 gravity vectors.
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