In-Flight Aging of Thermal Coatings: THERME Experiment

Centre National d’Etudes Spatiales has developed a simple and low-cost experiment called THERME to evaluate the in-flight degradation of common space coatings, in which temperature measurements are taken to monitor the evolution of solar absorptivity. The experiment payload is now carried on low-Earth-orbit satellites such as SPOT 5, HELIOS 2A, and DEMETER. In-orbit results provided for some thermal control coatings (white paint, second surface mirror, and Kapton) show the effects of the low-Earth-orbit space environment. Nevertheless, sometimes coatings are more degraded in flight than in ground simulation tests. A possible explanation is that the coatings are contaminated by organic products outgassed when the satellites are placed in orbit. The degradation of the coating would then be due to this early contamination combined with solar radiation, while the flux of atomic oxygen hitting the coating could reduce the degradation by eroding the contamination layer. This hypothesis is consistent with the space environment, the temperature, and the coating chemistry.