Solar sail propulsion limitations due to hydrogen blistering: Progression of reflectance decrease

• Progression of thermo-optical properties in dependence of fluence • Possibility to predict via semi-empirical equations the evolution of the specular reflectance and hence the performance of solar sails • Investigation on the temperature dependence of thermo-optical properties during proton irradiation • Novel flux models predict reflectance degradation in space to be slower than expected Solar sails are an advancing technology for transportation in interplanetary space. Metallized thin films are commonly used to build their membranes. During their lifetime the functional surfaces are exposed to various types of radiation, among them the low energy solar wind (SW) protons and other element ions. In Sznajder et al. (2020) , it was investigated what influence the recombination processes of SW protons with metal electrons has on the thermo-optical properties of the sail membrane. The results indicated a harsh degradation of membrane material samples when subjected to the laboratory simulated interplanetary space solar wind conditions, especially for exposure at low temperatures. However, more recent studies Sznajder (2023) indicate that the blistering process in this severity would take several years to appear in space. In view of the drastic degradation observed due to proton irradiation, it is the aim of this work to understand the development of the specular reflectance over the accumulated fluence. Furthermore, this data is mapped to certain mission scenarios, so that an understanding of the process with its change of specular reflectance over mission time is gained. Specimens reflectance and temperature over fluence data was further evaluated to gain knowledge on the processes during irradiation. Therefore, time-lapse pictures of the radiation tests were analysed. In particular, the brightness of pixels and its change from picture to picture were evaluated. This data was combined with spectrometric measurements taken before and after the test such that a progression over time or fluence, respectively, could be derived. Improved evaluation of previously presented experiments are given. The progression of the specular reflectance over fluence and hence a mission time is derived. The analyses allows a more accurate assessment of the performance of solar sails in dependence of the mission scenario (e.g. fluence and temperature) for future missions.