The AWE AMTM is a widefield of view (WFOV) infrared imaging radiometer designed for use in measuring the P1(2) and P1(4) emission lines of the earth’s OH layer to determine temperature and produce images of gravity waves. The sensor was designed, built, and characterized by Utah State University (USU) Space Dynamics Laboratory (SDL) and has been externally mounted to the International Space Station (ISS) looking nadir to collect images for analysis for a minimum of two years. The Opto-Mechanical Assembly (OMA) consists of four identical imaging telescopes, each comprised of a fisheye lens, a field lens, and a re-imager lens and share a common filter wheel with four narrow band filters. The sixteen lenses in each telescope are coaligned and bonded into five stress stabilized aluminum lens barrels. Precision machining allowed the barrels to be mated together via mechanical tolerances (i.e., snap-to-fit) to form the fore and aft assemblies of each telescope that mount to the front and rear of a common, central tombstone assembly which houses the filter wheel mechanism. The detectors were aligned, supported, and thermally compensated via a titanium thermal compensator and custom focus shim attached to the aft end of each telescope. Following assembly, the OMA was environmentally tested including EMI/EMC, vibration, and thermal cycling. Prior to and following each environmental test, the point response function of each telescope was measured and compared to verify performance.
This paper will present an overview of the design, fabrication, assembly, integration, and environmental testing of the OMA.
The AWE AMTM is a wide field-of-view (WFOV) infrared imaging radiometer designed for use in measuring the P1(2) and P1(4) emission lines of the earths OH layer. From these measurements, the atmospheric temperature is determined and finally images of gravity waves will be produced as the AWE field of view transverses the OH layer. Designed, built, and characterized by Utah State University (USU) and its Space Dynamics Laboratory (SDL), the sensor has been externally mounted to the International Space Station (ISS) looking nadir. Images will be collected and analyzed for a minimum of two years. The optical sensor assembly, also known as the Optomechanical Assembly (OMA), consists of four identical imaging telescopes, each comprised of a fisheye optical assembly, a field lens, and a re-imager optical assembly. The four telescopes share a common filter wheel with four narrow band filters. The 16 lenses in each telescope are coaligned and bonded into five aluminum lens barrels. The detectors were aligned, supported, and thermally compensated via a titanium thermal compensator and custom focus shim attached to the aft end of each telescope. Following assembly, the OMA was environmentally tested including EMI/EMC, vibration, and thermal cycling. Prior to and following each environmental test the point response function of each telescope was measured and compared to verify no degradation of performance had occurred. This paper will present an overview of the optical design, tolerance analysis, lens alignment, detector focusing, and image quality verification testing in vacuum of the OMA.
The Ocean Color Instrument (OCI), which will be integrated with the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite, will collect science data that will be used to monitor the health of Earth’s oceans and atmosphere. The Short-Wave Infrared (SWIR) Detection Assembly (SDA), built and characterized by Utah State University Space Dynamics Laboratory (SDL), is a subsystem of OCI consisting of 32 channels covering seven discrete optical bands of interest. A total of 16 SWIR Detection Subassemblies (SDSs) compose the SDA and house the cold optical system. The science data optical input for each SDS is supplied by a 0.22 NA multimode fiber interfacing with a fiber adapter. The diverging light from the fiber is collimated, split by a dichroic beamsplitter to two separate channels, filtered by the science filter, and then reimaged onto the single-element detectors with a final 0.76 NA. Aspheric, diamond-turned powered elements are used throughout the optical design. Fabrication and alignment tolerance analysis/budgets are balanced to ensure the optical system meets throughput requirements. All systems are aligned at ambient temperature using an InSb camera and an in-line illumination microscope system to directly image the active detector area through the science filters. Compensators used during alignment are detector focus and decenter, which are adjusted via photoetched shims in increments of 25 μm. Average focus and centering errors were less than 8 μm among all 32 flight and 10 flight spare detectors. Each SDS spectral response and conversion gain was verified at operational temperature of -65°C in vacuum.
Multispectral space telescopes with visible to long wave infrared spectral bands provide difficult alignment challenges. The visible channels require precision in alignment and stability to provide good image quality in short wavelengths. This is most often accomplished by choosing materials with near zero thermal expansion glass or ceramic mirrors metered with carbon fiber reinforced polymer (CFRP) that are designed to have a matching thermal expansion. The IR channels are less sensitive to alignment but they often require cryogenic cooling for improved sensitivity with the reduced radiometric background. Finding efficient solutions to this difficult problem of maintaining good visible image quality at cryogenic temperatures has been explored with the building and testing of a telescope simulator. The telescope simulator is an onaxis ZERODUR® mirror, CFRP metered set of optics. Testing has been completed to accurately measure telescope optical element alignment and mirror figure changes in a cryogenic space simulated environment. Measured alignment error and mirror figure error test results are reported with a discussion of their impact on system optical performance.
KEYWORDS: Diffraction, Commercial off the shelf technology, Cameras, Aluminum, Temperature metrology, Zemax, Modulation transfer functions, Imaging systems, Spatial frequencies, Optical transfer functions
A potential cubesat payload for low resolution study of planet Earth from space is an optical imaging system. Due to
budget, space, and time constraints, commercial photographic lenses of the double Gauss type are prime candidates for
limited duration cubesat optics. However, photographic objectives are not designed to operate in a space environment
and modifications are usually necessary. One method of improving optical performance of the objective over large
temperature variations is by replacing the stock lens mount with a different material. This paper describes the thermo-opto-
mechanical analysis of several lens mount materials for a double Gauss imaging system suitable for a cubesat.
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