Molecular Back Flow from the Exhaust Plume of a Space-Based Laser

摘要

Back flow from the exhaust of a chemical laser in low earth orbit may be detrimental to the integrity and operation of the selfsame system. Difficulties arise in the calculation of exhaust plume properties and molecular flux as the gas expands from continuum to free-molecular flow. The solution of the governing Boltzmann equation is exceedingly complex; similarly, numerical solutions such as the Direct Simulation Monte Carlo technique required prohibitive amounts of computer processing time. This thesis presents and alternate method of the assessment of molecular flux in which the continous transition from viscous to collisionless flow is approximated by a suitably defined breakdown surface. The molecular flux incident on a given area of the spacecraft surface is determined by integration of flux from all significant portions of the breakdown surface. Results are presented for exhaust plumes of various stagnation and exit plane conditions emanating from an axisymmetric ring nozzle. Keywords: Spacecraft contamination; Rarefied gas dynamics; Exhaust gases; FORTRAN; FLUX computer program; Rarefaction.