Experiments and Physical Modeling of Ultraviolet-Enhanced Contamination from Pure Contaminants

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This work aims at understanding the synergistic effects of external contamination and solar ultraviolet (UV). A test facility and a physical model of major phenomena involved in UV-enhanced contamination were developed in collaboration among ONERA, ESA/European Space Research and Technology Center, and Centre National d'Etudes Spatiales. Deposition of contaminant models (pure chemical compounds) was performed on two different microbalances simultaneously with and without UV exposure, followed by a reemission phase and physicochemical analyses. In parallel, a multilayer physical model was developed and used to model experimental data. It takes into account physical phenomena such as adsorption and desorption and chemical mechanisms such as the creation of chromophores and bonds. Different regimes were studied, either at low temperature, resulting in deposit increase even without UV, or at high temperature, where an equilibrium is reached in the absence of UV. The model proved its ability to reproduce both regimes. Its number of free parameters was small enough to prove its predictive character. This work also showed the importance of the generation of oligomers and the existence ofUV-induced bond scissions.