Transmission Loss of Spacecraft Optical Materials Due to Ultraviolet-Induced Contamination

The aim of this study was to investigate the transmission properties of optical windows intentionally contaminated and exposed to simulated solar radiation simulating the Meteosat Third Generation mission's conditions. The testing campaign consisted of three test phases: first, an outgassing test on space-qualified paints, used as contamination sources in this study, to derive input parameters for long-term outgassing predictions; the second phase, in which optical windows are contaminated to match the predictions; and the third phase, during which the contaminated optical windows were subjected to the vacuum UV/UV illumination exposure, as per mission profile, after the contamination and irradiation exposure. Transmission losses of the optical material were measured in the UV/near infrared and Fourier-transform infrared range. The findings demonstrated that UV exposure of contaminated surfaces, depending on the contamination source type, can result in chemical reactions and bonding of contaminants to the substrate or nearby molecules, or in contrary can act as a cleaning agent, causing reemission of contaminants. This study shows that performance loss based only on total surface contamination may lead to erroneous estimation and that outgassing and radiation should be treated as synergistic effects in the mission preparation phase.