Each of the three state-of-the-art instruments flown aboard NASA's Cosmic Background Explorer (COBE)2 were designed, fabricated, and integrated using unique contamination control procedures to ensure accurate characterization of the diffuse radiation in the universe. The most stringent surface level cleanliness specifications ever attempted by NASA were required by the diffuse infrared background experiment (DIRBE) which is located inside a liquid helium cooled dewar along with the far infrared absolute spectrophotometer (FIRAS). The DIRBE instrument required complex stray radiation suppression that defined a cold primary optical baffle system surface cleanliness level of 100A.1.3 The cleanliness levels of the cryogenic instrument and the differential microwave radiometers (DMR) which were positioned symmetrically around the dewar were less stringent, ranging from level 300A to 500A. To achieve these instrument cleanliness levels, the entire flight spacecraft was maintained at level 500A throughout each phase of development. This paper describes the COBE contamination control program and the difficulties experienced in maintaining the cleanliness quality of personnel and flight hardware throughout instrument assembly, spacecraft integration, flight environmental qualification, and launch-site operations.

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