Atmospheric Infrared Sounder (AIRS) thermal test program

The Atmospheric Infrared Sounder (AIRS) has been developed for the NASA Earth Observing System (EOS) program with a scheduled launch on the first post meridian (PM-1) platform in December 2000. AIRS is designed to provide both new and more accurate data about the atmosphere, land and oceans for application to climate studies and weather predictions. Among the important parameters to be derived from AIRS observations are atmospheric temperature profiles with an average accuracy of 1K in 1 kilometer (km) layers in the troposphere and surface temperatures with an average accuracy of 0.5K. The AIRS measurement technique is based on passive infrared remote sensing using a precisely calibrated, high spectral resolution grating spectrometer providing high sensitivity operation over the 3.7 mu m - 15.4 mu m region. To meet the challenge of high performance over this broad wavelength range, the spectrometer is cooled to 155K using a passive two-stage radiative cooler and the HgCdTe focal plane is cooled to 58K using a state-of-the-art long life, low vibration Stirling/purse tube cryocooler. Electronics waste heat is removed through a spacecraft provided heat rejection system based on heat pipe technology. All of these functions combine to make AIRS thermal management a key aspect of the overall instrument design. Additionally, the thermal operating constraints place challenging requirements on the test program in terms of proper simulation of the space environment and the logistics issues attendant with testing cryogenic instruments. The AIRS instrument has been fully integrated and thermal vacuum performance testing is underway. This paper provides an overview of the AIRS thermal system design, the test methodologies and the key results from the thermal vacuum tests, which have been completed at the time of this publication.