Modified view factor method for estimating molecular backscattering probability in space conditions

Satellite contamination by backscattered molecules has been considered difficult to handle due to the strong directional anisotropy of the backscattering flux. Common analysis methods such as the Bhatnagar-Gross-Krook theory and the direct simulation Monte Carlo, (DSMC) technique are rather inefficient in that they are complicated or take a long time for analysis. A new simple and easy-to-use technique of estimating the backscattering contamination is presented. This method is equivalent to the DSMC in so far as the molecular thermal velocity is much smaller than the satellite velocity and the mean free path for molecular collision is much longer than the satellite size. Based on the characteristics of backscattering seen from the satellite coordinate frame, backscattering is modeled as a diffuse reflection from a single hemispherical reflector, with the view factors modified by the direction cosine, and the effects of imperfect and distributed scattering are accounted for with proper correction factors.