Comparison of contamination model predictions to LDEF surface measurements

Contaminant deposition measurements have been made on species content and depth profiles on three experiment trays from the Long Duration Exposure Facility (LDEF). Auger, Argon sputtering, ESCA and SEM analysis was used to define the contaminant deposits. The Integrated Spacecraft Environments Model (ISEM) was used to predict the deposition levels of the contaminants measured on the three trays. The details of the modeling and the assumptions used are presented along with the predictions for the deposition on select surfaces on the trays. These are compared to the measured results. The trays represent surfaces that have a high atomic oxygen flux, an intermediate oxygen flux, and no oxygen flux. All surfaces received significant solar UV flux. It appears that the atomic oxygen is necessary for significant deposition to occur. Surfaces that saw significant contaminant flux, solar UV and no atomic oxygen did not show any appreciable levels of observable deposition. The implications of the atomic oxygen interaction with contaminant deposits from silicon contaminant sources is discussed. The primary contaminant sources in the LDEF analysis are DC6-1104 adhesive and Z-306 paint. The results and interpretation of the findings have a potential significant impact on spacecraft surfaces that are exposed to solar UV and atomic oxygen in low Earth orbit.