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TES Instrument Cryo/Thermal Design

JPL's Tropospheric Emission Spectrometer (TES) is an infrared space instrument designed to measure and profile the infrared-active gas molecules in the Earth's troposphere; it was launched into polar orbit aboard NASA's third earth observing systems spacecraft (EOS-Aura) on July 15, 2004. The overall instrument is approximately 1.5 m x 1.3 m x 1.0 m in size, with a mass of around 350 kg.

The technical foundation of the instrument is a cryogenically-cooled Fourier Transform spectrometer that uses a pair of TRW 57 K pulse tube cryocoolers to cool the HgCdTe focal planes to 65 K; the instrument also includes a 180K-230K two-stage cryogenic radiator to cool the optical bench assembly to 177 K; the radiator uses advanced high thermal conductivity composites and a highly specular earth shield. Configurationally, the 65 K IR focal plane assemblies are mounted integrally with the 177 K optical bench, which is in-turn shielded from the ambient portion of the instrument by a 230 K thermal radiation shield and MLI blankets. The interferometer operates over a wavelength range from 3.2 to 15.4 Ám.

In addition to controlling the focal plane and optical bench to cryogenic temperatures, the cryo/thermal design of the TES instrument involves the control of approx. 300 watts of power dissipation from the instrument electronics and the cryocoolers. These power-dissipating components reject their heat to a set of instrument-mounted room-temperature radiators on the instrument's nadir face. Heat is conducted from the power-dissipating assemblies to the radiators via a system of loop heat pipes (LHPs) designed and fabricated by Dynatherm, Corp. After delivery of the flight loop heat pipes and radiators in July 2000, characterization testing was carried out at JPL in preparation for integration into the TES instrument.

Also in support of the TES cryo/thermal activities, a materials characterization testing program was conducted. This included thermal conductivity measurements of candidate composite materials, including various adhesives, invar, and honeycomb panels. Interface contact conductance measurements were made at cryogenic temperatures for a number of different interface materials including bare-metal-to-bare-metal contact interfaces. Other testing involved characterization and qualification of the Earth shade's specular reflective surface with respect to thermal-cycle endurance.

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