Radiation-Induced Effects in SiO2 Protective Coatings on Polymeric Spacecraft Materials

Abstract

It is now well-recognized that polymeric materials used for the construction of low Earth orbital (LEO) spacecraft can be protected against atomic oxygen (AO) erosion by thin protective coatings of SiO2, for example. We deposit such coatings by Plasma-Enhanced Chemical Vapor Deposition (PECVD), a technique which results in extremely strong covalent chemical bonding at the substrate/coating interface. However, the thin sub-μam SiO2 coating is transparent to both ultraviolet photons (λ ≥ 180 nm) and to energetic particles such as keV and MeV protons, quite abundant in LEO. We report the results of experiments in which SiO2-coated polymers (Kapton®, Polyimide and Mylar® PET) are exposed to two types of high-energy radiation: on one hand, VUV-VIS photons (λ ≥ 112 nm) from a hydrogen plasma lamp, which have been shown to give rise to photochemically-generated gaseous reaction products from the polymer and, on the other hand, 100 keV protons from the Tandetron accelerator at the Universite de Montreal, corresponding to multi-year exposure in LEO. Possible modification or damage is assessed on the basis of mechanical testing (using a CSEM Microscratch Tester), and by microscopy, compared with untreated witness samples.