AIRS Pulse Tube Cooler System-Level and In-Space Performance Comparison

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AIRS Pulse Tube Cooler System-Level and In-Space Performance Comparison

Ross, R. G. Jr.

Abstract During this past year, JPL’s Atmospheric Infrared Sounder (AIRS) instrument completed thermal vacuum testing at the spacecraft level, was launched into Earth orbit on NASA’s Earth Observing System Aqua platform on May 4, 2002, and cooled down to operating temperature on June 12, 2002. The instrument, which is designed to make precision measurements of atmospheric air temperature over the surface of the Earth, uses a redundant pair of TRW pulse tube cryocoolers operating at 55 K to cool its sensitive IR focal plane. This use of redundant coolers with no thermal switches creates certain challenges when it comes to performance measurement and verification at the systems level. In support of the mission, new test and analysis techniques have been developed to allow accurate intercomparison of cooler-level, instrument-level, spacecraft-level, and in-space performance of the coolers. The driver for the development of these techniques is the strong dependency of the performance of the cooler system on gravity. Specifically, the off-state conductance of the non-operating redundant cooler is highly dependent on convection, and thus gravity level and orientation. Because the instrument-level, spacecraft-level, and in-space environments have substantially different orientations and gravity levels, special test and analysis techniques had to be developed to allow accurate intercomparison of the results. This paper presents the derivation of the test and analysis techniques as well as the measured system-level performance of the flight AIRS coolers during instrument-level, spacecraft-level, and in-space operation.