Thermal Control Subsystem Design for the EOS Thermal Infrared Radiometer

The Thermal Infrared Radiometer (TIR) is part of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) complement of instruments to be flown on NASA's Earth Observing System (EOS) spacecraft. ASTER'S function is to measure atmospheric and terrestrial optical and thermal emissions. TIR provides coverage of the long wave emissions and utilizes several independent thermal control elements to support the exacting thermal requirements of the optical train and electronic assemblies. The widely differing temperature ranges and narrow control bands of the instrument components dictate the need for a combination of active and passive thermal control techniques. The very low temperature required of the thermal emission detector using a Stirling cycle cooler, contrasts with the moderate temperatures needed by the optical train and blackbody. These components are cooled by uniquely configured remote radiators and thermostatically controlled heaters. The electronics assemblies and compressor are cooled by rejecting heat into a cold plate via the instrument baseplate. The cold plate is part of a Capillary Pumped Heat Transport System (CPHTS) baselined for instrument thermal control aboard the EOS spacecraft. Heat transport for waste heat removal is achieved by the extensive use of heat pipes which have been selected to meet the individual needs of the components. This paper discusses the thermal control techniques implemented to meet the stringent thermal design constraints of the TIR instrument.