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) is one of the four science instruments installed into the Integrated Science Instrument Module (ISIM) on JWST intended to conduct scientific observations over a five year mission lifetime. NIRCam's requirements include operation at 37 kelvins to produce high resolution images in two wave bands encompassing the range from 0.6 microns to 5 microns. In addition NIRCam is used as a metrology instrument during the JWST observatory commissioning on orbit, during the initial and subsequent precision alignments of the observatory's multiple-segment 6.3 meter primary mirror. JWST is scheduled for launch and deployment in 2012. This paper is an overview of the NIRCam instrument with pointers to several NIRCam subsystem papers to be presented in the same conference. This paper will introduce and explain at top level the structural, optical, mechanical and thermal subsystems of NIRCam.
Space flight optical instruments and their support hardware must reliably operate in stressing environments for the duration of their mission. They must also survive the mechanical and thermal stresses of transportation, storage and launch. It is necessary to qualify the hardware design through environmental testing and to verify the hardware's ability to perform properly during and/or after some selected environmental tests on the ground. As a rule, flight electronics are subjected to thermal, mechanical and electromagnetic environmental testing. Thermal testing takes the form of temperature cycling over a temperature difference range (Delta) T of up to 100 degrees C for a minimum of six cycles, with additional performance verification testing at the hot and cold extremes. Mechanical testing takes the form of exposure to random vibration, sine sweep vibration, shock spectra and static loading on a centrifuge or by sine burst on a vibration table. A standard series of electromagnetic interference and electromagnetic compatibility testing is also performed.
This paper presents the on-orbit performance of the Cryogenic Limb Array Etalon Spectrometer (CLAES) cryostat through the mission, and compares its performance to pre-launch predictions for lifetime and for temperature vs. time for the CLAES cryogenic subsystems. Absolute temperatures of various subsystems in the instrument are presented along with temperature gradient discussions and their correlation to predictions of mission lifetime. The cryostat's thermal performance during ground operations, at spacecraft integration and during launch preparations at the Kennedy Space Center are also presented.
A topical workshop on Cryogenic Optical Systems and Instruments was held on Monday 4 April, from 8:00 to 10:00 pm, moderated by James B. Heaney, NASA Goddard Space Flight Center.
The paper describes the Cryogenic Limb Array Etalon Spectrometer (CLAES) launched on September 12, 1991 aboard the NASA Goddard's Upper Atmosphere Research Satellite the purpose of which is to measure the global concentrations of stratospheric species and their temperature, as a function of altitude. Particular attention is given to the design-level thermal predictions and their correlation to the results of ground tests, and to the on-orbit performance of CLAES. Also presented are data on the cryostat's thermal performance during ground operations, at spacecraft integration and during launch preparations. The CLAES functional block diagram and the cryostat schematic diagram are included.
The mechanical testing performed on the Cryogenic Limb Array Etalon Spectrometer (CLAES) instrument installed on the Upper Atmosphere Research Satellite is discussed. The CLAES determines temperatures and concentrations of stratospheric minor species as a function of altitude by measuring the atmospheric infrared emission spectra. CLAES is based on a telescope optical system and infrared spectrometer which are cooled with cryogens.
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