  Theoretical aspects of a solar sail material degradation are presented when
the solar electromagnetic and corpuscular forms of radiation were considered as
sources of degradation. The analysis of the interaction of two components of
solar radiation, the electromagnetic radiation and radiation of low- and
high-energy electrons, protons, and helium ions emitted by the Sun with the
solar-sail materials is discussed. The physical processes of the interactions
of photons, electrons, protons and alpha-particles with sail material atoms and
nuclei, leading to the degradation and ionization of solar sail materials are
analyzed. The dependence of reflectivity and absorption for solar sail
materials on temperature and on wavelength of the electromagnetic spectrum of
solar radiation is investigated. It is shown that the temperature of a solar
sail increases approximately as T r^(-2/5), with the decrease of the
heliocentric distance r, when are taking into account the temperature
dependence of optical parameters of the solar sail material.
