The effect of the flux densit3', the flux, and the energy of electrons on the change in reflection spectra and the total solar radiation absorption by the reflecting coating of a space vehicle fabricated from a Kapton,film with deposited aluminum in the People's Republic of China is investigated.
Various types of radiation act on materials of external surfaces of objects in outer space (OS): solar electromagnetic radiation (EMR), including vacuum ultraviolet ~VUV), near-ultraviolet (NUV), visible, and near-IR ranges of the spectrum, electron and proton radiation, ionospheric plasma with atomic oxygen, and the plasma of the solar wind (SW). In addition to irradiation, materials are subjected to the action of the intrinsic external atmosphere tlEA), micrometeorites, meteoritic dust, cosmic debris, vacuum, and temperature.
Heat-regulation coatings (HRC) occupy an important place among materials of satellite technology [1]. They cover external surfaces of space vehicles (SV) and are subjected to the action of the above-indicated factors. In an orbital flight, the optical HRC properties are deteriorated, which may lead to a disruption of the SV operation, and its operating characteristics may fall beyond allowable limits. Therefore, to guarantee extended SV operation, HRC are tested under conditions close to field ones. The study of changes in the main SV operating characteristic -the total coefficient of solar radiation absorption a~ determined from diffuse (specular) reflection spectra Pz under the action of OS factors -is of scientific and practical interest.
Electrons and protons with energies E lying in the range from 102 to l0 s eV are the main OS charged particles concentrated mostly in the region affected by the Earth's magnetic field (the Van Allen radiation belt, the plasma layer, etc.). The maximum electron flux density qo, corresponding to an energy of several tens of keV, is 108-109 cm-2.s -l [2-4].
It is difficult or almost impossible to reproduce electron or proton spectra in the laboratory due to the narrow emission spectra of available sources. Therefore, the integral spectrum is replaced by monochromatic radiation beams, and effective fuxes, modeling the effect of the integral spectrum, are calculated by special methods [5]. The radiation flux density is increased many times in ground-based tests, and the legitimacy of these accelerated tests is an urgent problem.
The necessity of experimental investigations of the joint effect of various radiation types imitating the cosmic radiation has been established in the last few years [5, 6]. This is due to the nonadditivity of joint and separate effects of various radiation types caused by the synergy effects. However, investigations of the effect of a specific radiation type, for example, of electron radiation, on changes in the properties of HRC and other materials are also important. First, they give information on the type and the "kinetics of reactions producing an increased concentration of color centers. Second, they are of practical importance, because they allow one to answer the question whether the accelerated tests are feasible and legitimate. Third. they allow one to choose an accelerated regime of joint action of various radiation types imitating OS conditions.
A fairly large number of works studied the optical HRC properties, but only few works considered the effect of the flux density of charged particles, including electrons. In [7] it was concluded that the change in as of coatings is independent of the electron parameter ~0, because the experimental values of Aa~ obtained for different q) fit in the curve of the dependence of Aas on the electron flux. Investigations of HRC fabricated from TiO_,/A1203 + acrylic resin, ZnO + polymethylsiloxane, ZnO + polymethylphenylsiloxane, and F4MB-grade fluoroplastic with deposited aluminum performed in [2] demonstrated that the dependence Aa~ =flq0) is manifested in the range from 10 ~~ to 1013 cm-"-s -I and must be considered in ground-based tests.
In the present work, dependences of p, Ap, and Aa~ on the flux density, the flux, and the energy of electrons are investigated for HRC fabricated from the most radiation-resistive polymer called Kapton (polyimide) with deposited aluminum.