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AIRS Instrument Cryo/Thermal Design

JPL’s Atmospheric Infrared Sounder (AIRS) instrument is designed to gather precision global measurements of Earth's air temperature as a function of elevation above the surface; it was designed and built under JPL management by Lockheed Martin Infrared Imaging Systems, Inc. (now BAE Systems) of Lexington, MA and was launched on NASA’s Earth Observing System Aqua platform in May 2002. The above figure illustrates the overall instrument, which is approximately 1.4 m x 1.0 m x 0.8 m in size, with a mass of 150 kg. As of July 2012, the instrument has been successfully operating in orbit for over 10 years.

The technical foundation of the instrument is a cryogenically cooled infrared spectrometer that uses a pair of TRW 55K pulse tube cryocoolers to cool the HgCdTe focal plane to 58 K; the instrument also includes a 150K-190K two-stage cryogenic radiator to cool the optical bench assembly to 150 K. Configurationally, the 58 K IR focal plane assembly is mounted integrally with the 150K optical bench, which is in-turn shielded from the ambient portion of the instrument by a 190K thermal radiation shield and MLI blankets. The spectrometer operates over a wavelength range from visible through 15.4 µm, and places particularly demanding requirements on the instrument temperature control.

In addition to controlling the focal plane and optical bench to cryogenic temperatures, the cryo/thermal design of the AIRS instrument involves the control of 220 watts of power dissipation from the instrument electronics and the cryocoolers. These power-dissipating components pass their heat rejection to a set of 20°C coldplates that conduct the heat to spacecraft-mounted radiators via a system of variable conductance heatpipes (VCHPs).

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