Aerodynamic effects on atmospheric composition measurements from rocket vehicles in the thermosphere

Several distinct classes of rocket-borne instrumentation have been used for composition measurements in the upper atmosphere and there is a possibility that some of these have been affected by the aerodynamic flowfield that surrounds the rocket vehicle. The flowfield is near-continuum at the mesopause, with distinct shock waves and boundary layers. These features thicken and merge with increasing altitude and lose their identity as free-molecule flow is approached at the thermospause. The aerodynamic effects are illustrated through reference to existing studies in rarefied gas dynamics. In addition, the direct simulation Monte Carlo method is used to make some new calculations of the flow past a representative rocket vehicle. The implications of the results for the various classes of instrumentation are discussed.