Thickness requirement for solar sail foils

The minimum foil thickness that provides the maximum reflectivity and absorption for a solar sail material is found and its dependence on temperature and on wavelength of the electromagnetic spectrum of solar radiation is investigated. It is shown that the minimal thickness has strong implicit dependence on the temperature through the temperature dependence of the electrical conductivity of the solar sail. The minimal thickness has explicit dependence on the frequency through the factor 1/ω, as well as it has implicit dependence on the frequency, because the conductivity and dielectric function are functions of the frequency. It is shown that when the frequency dependence of the conductivity and dielectric function are taken into account the minimal thickness of the solar sail foil exhibits the slight dependence on the wavelength of the solar radiation. We show that the surface of a solar sail with the required minimal thickness of a foil can withheld the solar pressure within the limit of the elastic deformation of the material. We suggest that these factors should be taken into consideration in the solar sail design.