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This paper documents International Space Station (ISS) external contamination observations and surface assessments covering Flights 1A/R through 6A. These observations are based on imaging from ISS missions, as active external contamination monitoring is not present in the configuration at this time. Imaging from ISS missions is a critical resource as it records the condition of ISS surfaces and helps identify visible signs of surface degradation. The observations are divided into three main sections; the first section covers the Functional Cargo Block (FGB - Russian Segment), the second section covers the Service Module (SM - Russian Segment), and the third section covers the U.S. Segment (Node 1 and Primary Mating Adapters 1 and 2). This distinction is important as materials selection, design and contamination control procedures differ between the FGB and Service Module on the Russian Segment and the U.S. Segment. Numerous observations of FGB self-contamination have been made through ISS imaging obtained during Shuttle flights. These observations were not surprising as external contamination studies conducted during the Shuttle-Mir (Phase I) Program showed extensive contamination induced by the Russian hardware. The impact of FGB induced contamination on ISS sensitive surfaces was mitigated due to FGB on-orbit time vacuum baking the Russian hardware prior to the deployment of ISS contamination sensitive hardware. Service Module impacts on ISS hardware were mitigated with a combination of changes in materials selection and on-orbit vacuum baking as there would be less on-orbit time before deployment of sensitive surfaces. While changes were made to materials selection, self-contamination observations have also been made on the Service Module. At this point, the U.S. Segment appears to be largely free of self-induced contamination. This confirms predictions made during the design and integration phase. Observed darkening and degradation of surfaces on the U.S. Segment is limited to a few areas and due to interactions with the on-orbit environment.
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