Degradation of thin solar-sail membrane films under interplanetary medium

Abstract

Thin metallized films are used in wide field applications of deployable membrane structures. Flexible and thin polyimide foils are covered by highly reflecting metallic surfaces. Unfortunately metals while interact with the solar wind particles indicate formation of tiny molecular hydrogen bubbles on their surface, i.e. ~0.4 μm in diameter. Such bubbles occur as a consequence of recombination processes of the solar protons and the metals’ electrons. Our aim was to experimentally confirm the formation of the bubbles under simulated conditions which mimic those present in the interplanetary space and find physical conditions, i.e. temperature of the membrane material, dose and kinetic energy of the incident protons at which the bubble formation process takes place. We have studied and select possible materials which may protect the metallized surfaces against the phenomenon. Three protection coatings have been chosen, the silicon- and the titanium- dioxide as well as titanate nanotubes. We have experimentally confirmed that metallic specimens exposed to flux of low energy protons (2.5 keV) indicate formation of tiny bubbles on their surface. High surface density of bubbles has its direct influence on the surface thermo-optical properties, which have a major impact on propulsion efficiency of any sail-craft.