Error Inherent in Simulating Planetary Thermal Effect on the Spacecraft Surface by using Isotropic Planetary Radiation Intensity Field Model Instead of Anisotropic

In order to mathematically simulate the thermal effect that radiation emitted by planets has on spacecraft, two intensity field models describing planetary radiation may be used depending on the emitter specifics: isotropic and anisotropic. The isotropic model is based on the assumption that the local surface density of outgoing radiation flux is the same for all surface regions visible from orbit. In the case of the anisotropic model this value is assumed to be proportional to the zenith angle cosine for each surface element on the side of the planet that is illuminated by the Sun. Published results of studies concerning developing planetary radiation field simulators indicate that thermal vacuum installations where the working volume is comparable to the total installation volume can only reproduce the sotropic planetary radiation intensity field model. It is a pressing issue to determine whether and when it is possible to replace the anisotropic model with an isotropic one when physically simulating the effect that the solar radiation reflected from a planet and intrinsic radiation flows generated by planets with no atmosphere have on spacecraft. The investigation that we conducted regarding this issue was based on comparing the results of computing the irradiance of spacecraft elements using the models under consideration. These computation results allowed us to conclude that it is possible to physically simulate the effect of solar radiation flows reflected from planets combined with intrinsic (infrared) radiation flows generated by planets with no atmosphere by means of using simulators reproducing isotropic radiation fields in their working volumes