Multiple reflections of solar radiation and photoelectron emission in satellite interaction with space environment

Abstract

This master’s thesis presents a numerical study of the interaction between plasma and spacecraft. The main contribution of my research consists of im- proving the parameterization of solar illumination and the resulting photoelectron emission from satellite surfaces. The simulations are done with PTetra which is a particle in cell code that uses unstructured tetrahedral meshes to represent space- craft boundaries and geometries. First, the calculation of photoelectron emission is improved in this work by considering multiple rays of light per surface element instead of a single ray as done in the original version of PTetra. This is done by distributing a number of points per triangular element on each satellite surface. The number of these points is determined from the ratio between the triangle area and the smallest triangle area on any of the structure components. Compared with results obtained with the original version of PTetra, the inclusion of multiple rays per triangle accounts for the possibility of partial illumination of elements due to the fact that part of a given triangle can be exposed to solar radiation, while other parts may be in the shade of physical objects. The second part of my work considers multiple reflections assuming an arbi- trary combination of specular and diffuse reflection. The first step here consists of determining whether a triangular element is exposed to solar radiation. If it is, then secondary rays are traced as per specular or diffuse reflection to determine if they intersect other surface elements. If they do, then the process is repeated until the ray is lost to the outer boundary. The simulations considered use an ide- alized geometry for the purpose of illustrating the effects of accounting for several rays per surface triangular element and multiple reflections. Then simulations are made with a more realistic geometry corresponding to a component of the Swarm satellite. In the absence of plasma the effect of multiple reflections is found to be significant. However, with a plasma background representative of the ionosphere, the net effect of multiple reflections on collected current density is negligible.