Exposed to space environment, some materials that make up satellites outgas molecules, known as contaminants. These contaminants can recondense on sensitive surfaces of the satellite, significantly altering their properties. The main consequences of this contamination are loss of transmittance in optics [1], reduced solar panel power output [2], and changes in solar absorptance of thermal coatings [3].

In-flight measurements showing differences in aging behaviour of various contaminated materials were previously poorly understood. Recent work suggests differences in morphology (cluster vs. film) of the contaminant deposits may be responsible for these effects. The morphology of contaminant deposits has major consequences on their physical and chemical properties and the performance of contaminated surfaces. For example, re-evaporation rates can be reduced in the case of cluster deposits. In the case of thin-film deposits, the loss of thermal control can be important with UV aging as the coverage is greater than with droplet deposits. Furthermore, the presence of VUV radiations in the satellite environment can not only activate the surfaces on which deposits form, but can also cause photopolymerization of certain contaminants, both these phenomena preventing their re-emission or migration to the surface. Despite the interest in contamination morphology, the processes responsible for it are little studied and difficult to predict.

ONERA has developed a vacuum chamber for studying molecular contamination, called COPHOS (COntamination PHOton Synergy). This facility is equipped with an effusion cell that generates a controlled flow of contaminants towards targets: samples and quartz crystal microbalances whose temperatures are regulated. Experiments carried out in the COPHOS facility are presented in this work. These consist of carefully contaminating various surfaces with different compounds at controlled deposition temperatures. A systematic study of contaminant/substrate/deposition temperature combinations allows a first understanding of the phenomena governing the resulting morphology of a deposit, thus refining predictions.