Scattering of Polymer Coatings by High Fluence Oxygen Plasma Flow

Polymer coatings are used on the surface of low Earth orbit spacecraft, where they are aggressively exposed to the incoming flow of atomic oxygen. During prolonged stay in orbit (10-20 years), the atomic oxygen fluence reaches 10²² cm^–2 or more, which leads to the destruction of the polymer surface to a depth of hundreds of micrometers. 3 types of promising coatings based on organosilicon polymers have been studied: the ECT-PC composition, ECT varnish, UV-7-21 sealant, intended for use on low earth orbit spacecraft. To assess their resistance to atomic oxygen when simulating an incoming flow with high fluence up to 10²² cm^–2 in laboratory conditions, the technique of accelerated tests in an oxygen plasma stream at oxygen particle energies of 10-40 eV was applied. The dependences of mass loss on equivalent fluence were investigated and the erosion coefficients of coatings were measured: for the ECT-PC composition — 4.2 × 10^–26 g/atom O, for ECT varnish — 3.2 × 10^–26 g/atom O, for UV-7-21 sealant — 1.7 × 10^–26 g/atom O. In comparison with polymers used on the spacecraft (for example, polyimide with 4.3 × 10^–24 g/atom O) the measured erosion coefficients are two orders of magnitude lower, which characterizes the high resistance of the tested materials to atomic oxygen. Based on the obtained dependences of mass loss on fluence, the predicted maximum fluence of atomic oxygen is (7–25) × 10²³ cm^–2, depending on the type and thickness of the coating.