A small, adaptable, and stable thermal imaging system was developed that can be flown on an aircraft, deployed on the International Space Station as an attached payload, launched on a ride-share as an entirely self-contained 3U CubeSat, flown on a small satellite, or be a co-manifested satellite instrument. When the instrument design is proven, multiple copies of it could be assembled and aligned into an instrument array to enable large-swath thermal imaging from space, all to provide more detailed spatial and temporal data for biomass burning and land surface temperature studies than has heretofore been available from orbit. The instrument has an Earth-observing expected noise equivalent differential temperature (NEDT)

The dual-band infrared imaging system is self-contained to fit within the top two-thirds of a 3U CubeSat envelope. This mid/far infrared (IR) imaging system will utilize a newly conceived strained-layer superlattice (SLS) broadband detector array (640×512 array format) cooled to ≈68 K (–213 °C) by a miniature mechanical cryocooler. It will contain the telescope optics and have two filtered infrared bands centered at 4 μm for fire detection and 10.5 μm for thermal and evapotranspiration Earth science. The heart of the IR camera is the sensor chip assembly (SCA) consisting of a newly developed 25-μm pitch, 640×512 pixel, GaSb/InAs (or gallium free InAs/InAsSb) strained layer SLS detector hybridized to an ISC9803 silicon readout IC (ROIC). This SCA is mounted to a metalized, patterned substrate and wire-bonded to pads leading to the edge of the substrate. The square primary mirror collects light from the end aperture of the CubeSat. The mirror has a cutout in its center, and is placed over the cryocooler cold finger stem. The SCA subassembly is epoxied to the cold tip of a Stirling cryocooler. A frame containing the two (or potentially multiple) filter elements is positioned and secured above the detector surface.

A metal vacuum shroud containing electrical feedthrough pins is welded to the base of the cryocooler. The substrate is wire-bonded to these feedthrough pins that penetrate the shroud. A shroud cover containing an IR window is welded to the shroud body. Once assembled, the entire shroud volume is evacuated, and the body tube is sealed by pinching it closed. A wiring harness connects the camera electronics control box through the primary mirror cutout to soldered feedthrough pins on the cooler shroud.

At the time of this reporting, this effort may lead to the first implementation of an SLS-based detector array in a NASA spaceflight application. Com - pared to other currently available detector technologies (mercury cadmium telluride, GaAs QWIP, indium antimonide, and microbolometers), the SLS appears to consolidate many of the best features in a single technology. These features include a high quantum efficiency, a warmer operating temperature, broad spectral response, ease of fabrication, a scalable format, relative low cost to manufacture, and the availability from multiple sources. QmagiQ, LLC (Nashua, NH) has been an important and integral partner in further developing SLS technology and SLS-based IR camera systems.

This work was done by Murzy Jhabvala, Donald Jennings, and Compton Tucker of Goddard Space Flight Center. GSC-17113-1


NASA Tech Briefs Magazine

This article first appeared in the July, 2015 issue of NASA Tech Briefs Magazine.

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