Derivation of cleanliness requirements for the Atmospheric Infrared Sounder (AIRS)

The Atmospheric Infrared Sounder (AIRS) is a high spectral resolution multispectral sounder providing nearly contiguous coverage between 3.74 and 15.4 micrometers which has been selected as a facility instrument on the Earth Observing System PM series. AIRS is designed to provide data for application in climate studies and weather prediction. The degradation of AIRS by contamination could reduce its performance capabilities, reducing the instrument's expected utility by compromising its accuracy and sensitivity. AIRS contains a number of contamination sensitive subsystems which include an exposed scan mirror, passively cooled optics, mechanically cooled detectors, on board calibrators, and thermal control surfaces. Efforts were undertaken to define the contamination sensitivities of these subsystems based upon system performance goals. A series of analyses have been performed to determine the cleanliness necessary to meet the system performance goals. From this data, a contamination control program and preliminary design guidelines have been implemented. Presented in this paper are an overview of the instrument and its contamination susceptibility, the contamination performance goals for each subsystem area, and the derived cleanliness requirements. The analysis techniques used to derive the subsystem cleanliness requirements from the optical, thermal, and calibration performance goals are included. Also included are the preliminary design concepts for contamination control and contingency decontamination features built into the AIRS design to help assure the contamination requirements are met.