Aging of Thermal Coatings on Low Earth Orbit: In-Flight Measurements and Modeling

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Aging of Thermal Coatings on Low Earth Orbit: In-Flight Measurements and Modeling

Vanhove, E. / Roussel, J. F. / Remaury, Stéphanie / Faye, Delphine / Guigue, Pascale

The aging of thermal coatings critically impacts spacecraft thermal balance. Because few in-flight data were available about the aging of materials after a long exposure on sun-synchronous orbit, Centre National d’Études Spatiales developed a low-cost experiment called THERME aiming to characterize the evolution of solar absorptivity through a temperature measurement. A data set covering 27 years has thus been generated. The objective of this work is to analyze this very large set of telemetry measurements, taking into account the available satellite parameters (orbit and orientation) and environmental parameters (ultraviolet and atomic oxygen) to identify the most likely causes for the solar absorptivity evolution. To this end, a quantitative model of the evolutions of solar absorptivity has been developed. This model includes the intrinsic degradation of the substrate under ultraviolet radiation, the degradation attributed to contamination, and the erosion of this contamination by atomic oxygen. Although deliberately simple to limit the number of model parameters, it enables one to satisfyingly reproduce the time evolution of solar absorptivity and to explain the differences observed depending on the solar cycle, on the orbit of the satellite and on the position of the THERME devices on the satellite.