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The instrument thermal control system of the Geostationary Operational Environmental Satellite may have been affected by speci c contamination problems that arose because of the unique conditions and requirements of the spacecraft mission. This paper addresses some speci c contamination effects from the coatings used in the instrument cavities. Contamination control actions that were implemented during ground processing to ensure limited impact on the on-orbit temperature control are described. The selection of thermal coatings is an integral part of the overall spacecraft design. Molecular contamination accretion on thermal coatings may alter the design properties of the surface coatings. In an effort to quantify the molecular contamination effects from material outgassing, an assessment was conducted to address the concerns inside the instrument cavities. The study results prompted an extensive prelaunch vacuum bakeout effort and an on-orbit solar radiation avoidance exercise. In addition, the thermal performance of the instrument radiant coolers could have been detrimentally affected by scattered solar radiation from particulate contamination. To mitigate the impact of the particulate contamination the radiant cooler surfaces were cleaned to an established criteria prior to launch. Nomenclature A = illuminated area of cooler panel E = energy scattered F 1p, F2p = view factors S = solar constant = solar absorptance Subscripts 1p = rst re ection 2p = second re ection

During Kennedy Space Center processing of the Hubble Space Telescope First Servicing Mission, critical optical components were integrated in a Class 100,000 (M 6.5 at 0.5pm and 5.0jim, per Fed-Std 209E) cicanroom. A Class 10,000 (M 5.5) environment was mandated by the 400B (per Mil-Std 1246B) surface cleanliness requirement of the Scientific Instruments.To maintain a Class M 5.5 environment, a contamination control plan was implemented which addressed personnel constraints, operations, and site management. This plan limited personnel access, imposed strict gowning requirements, and increased cleanroom janitorial operations, prohibited operations known to generate contamination while sensitive hardware was exposed to the environment, and controlled roadwork, insecticide spraying, and similar activities. Facility preparations included a ceiling to floor cleaning, sealing of vents and doors, and revising the garment change room entry patterns. The cleanroom was successfully run below Class 5000 while the instruments were present; certain operations, however, were observed to cause local contamination levels to increase above Class M 5.5.