Low-Density Aerothermodynamics

Abstract

A review is made of the low-density gas flows that are associated with the operation of current and projected spacecraft. Typical applications are related to orbital contamination studies, the early stages of re-entry, high-altitude aerobraking, the interaction of rocket plumes with vehicles and with the atmosphere, and the orbital drag problem. Criteria are established for determining whether a continuum or a particle model is appropriate in particular cases. It is shown that satisfactory procedures now exist for the application of the direct simulation Monte Carlo method to real-gas flows involving nonequilibrium of the translational and internal modes, chemical reactions, and thermal radiation. On the other hand, the necessary physical data base is seriously deficient, particularly in regard to gas-surface interactions under orbital conditions and chemical reaction cross sections in the 8 to 10 eV energy range. It is concluded that both laboratory and in-orbit measurements will be needed if these deficiencies are to be remedied.