  Metals are the most common materials used in space technology. Metal
structures, while used in space, are subjected to the full spectrum of the
electromagnetic radiation together with particle irradiation. Hence, they
undergo degradation. Future space missions are planned to proceed in the
interplanetary space, where the protons of the solar wind play a very
destructive role on metallic surfaces. Unfortunately, their real degradation
behavior is to a great extent unknown.
  Our aim is to predict materials' behavior in such a destructive environment.
Therefore both, theoretical and experimental studies are performed at the
German Aerospace Center (DLR) in Bremen, Germany.
  Here, we report the theoretical results of those studies. We examine the
process of H2-bubble formation on metallic surfaces. H2-bubbles are metal caps
filled with Hydrogen molecular gas resulting from recombination processes of
the metal free electrons and the solar protons. A thermodynamic model of the
bubble growth is presented. Our model predicts e.g. the velocity of that growth
and the reflectivity of foils populated by bubbles.
  Formation of bubbles irreversibly changes the surface quality of irradiated
metals. Thin metallic films are especially sensitive for such degradation
processes. They are used e.g. in the solar sail propulsion technology. The
efficiency of that technology depends on the thermo-optical properties of the
sail materials. Therefore, bubble formation processes have to be taken into
account for the planning of long-term solar sail missions.
