Aerodynamic aspects of rocket-borne in situ studies

In situ measurements from sounding rockets are the only means of small-scale, multi-instrument studies in the mesosphere and lower thermosphere. However, performed in the direct vicinity of the payload, these measurements are potential subject to a variety of aerodynamic perturbations. An analysis of these perturbations is complicated by the different rarefied flow regimes occurring during a rocket flight. In this and two accompanying papers [Ref. 1, 2], we describe modelling and experimental efforts aimed to improve our understanding of payload-atmosphere interactions. Numerically, the rarefied gas requires a microscopic approach. Based on the behaviour of individual molecules, a "Direct Simulation Monte Carlo" code has been developed as a tool both for the design and the analysis of rocket-borne experiments. To validate and to extend these modelling efforts, a series of rarefied wind tunnel experiments has been carried out at the Laboratoire d'Aerothermique du CNRS. This first paper reviews aerodynamic problems and describes basic ideas for their analysis. Colour pictures of wind tunnel and model results are available under http://www.misu.su.se/similar to gumbel/aerodynamics.html.