Performance of the PV/PC HgCdTe focal plane/dewar assembly for the Atmospheric Infrared Sounder instrument (AIRS)

AIRS is a key facility instrument in the NASA Earth Observing System (EOS) program, a spaceborne, global observation system being implemented to obtain comprehensive long-term measurements of earth processes affecting global change. Designed to provide new and more accurate data about the atmosphere, land, and oceans for application in climate studies and weather prediction, AIRS performs passive IR remote sensing using a high resolution grating spectrometer with a wide spectral coverage focal plane assembly (FPA) operating at 58 K in a unique vacuum dewar package cooled to 155 K. The hybrid HgCdTe focal plane consists of 12 modules, 10 photovoltaic (PV) utilizing silicon readout integrated circuits (ROICs) in both direct and indirect hybrid configurations, and 2 photoconductive (PC) led out to warm electronics. This complex focal plane has a large optical footprint, 53 mm X 66 mm, and receives energy dispersed from the grating through a precision filter assembly containing 17 narrowband filters. Designed to prevent any interaction between the PV and PC devices, the FPA incorporates extensive shielding and lead routing in the multilayer carriers and flex cables, as well as features in the ROIC design. The 526 lines necessary to operate the FPA are led out of the vacuum dewar, which is cooled via the spectrometer. The focal plane is cooled to 58 K through a sapphire rod interfaced to a pulse tube cooler. The Engineering Model (EM) and Protoflight Model (PFM) detector/dewar assemblies have been fabricated, assembled, tested, and delivered for system integration, and the EM instrument has been assembled and tested. The key design features of the FPA and dewar assembly have been presented in previous SPIE symposiums and will be briefly reviewed. In this paper the emphasis will be on performance results such as sensitivity, linearity, assembly tolerances, environmental test results, and other parameters of interest, as well as a detailed review of the actual flight hardware assembly.