  The widespread use of metallic structures in space technology brings risk of
degradation which occurs under space conditions. New types of materials
dedicated for space applications, that have been developed in the last decade,
are in majority not well tested for different space mission scenarios. Very
little is known how material degradation may affect the stability and
functionality of space vehicles and devices during long term space missions.
Our aim is to predict how the solar wind and electromagnetic radiation degrade
metallic structures. Therefore both experimental and theoretical studies of
material degradation under space conditions have been performed. The studies
are accomplished at German Aerospace Center (DLR) in Bremen (Germany) and
University of Zielona G\'{o}ra (Poland). The paper presents the results of the
theoretical part of those studies. It is proposed that metal bubbles filled
with Hydrogen molecular gas, resulting from recombination of the metal free
electrons and the solar protons, are formed on the irradiated surfaces. A
thermodynamic model of bubble formation has been developed. We study the
creation process of $\rm{H_2}$-bubbles as function of, inter alia, the metal
temperature, proton dose and energy. Our model has been verified by irradiation
experiments completed at the DLR facility in Bremen. Consequences of the bubble
formation are changes of the physical and thermo-optical properties of such
degraded metals. We show that a high surface density of bubbles (up to $10^8$
$\rm{cm^{-2}}$) with a typical bubble diameter of $\sim 0.4$$\rm{\mu}$m will
cause a significant increase of the metallic surface roughness. This may have
serious consequences to any space mission. Changes in the thermo-optical
properties of metallic foils are especially important for the solar sail
propulsion technology, ...
