Boundary Layer Electron Profiles for High-Altitude Entry of a Blunt Slender Body

Theme A KEY factor in prediction of radio blackout during entry into a planetary atmosphere is determination of the magnitude and distribution of electron concentration (Ne) in the plasma layer. Several of the contributions made in the past ten years to improve this prediction capability can be credited to the RAM (Re-entry Attenuation Measurement) project—a carefully coordinated program of laboratory tests, flight experiments, and theoretical analysis carried out at the Langley Research Center. Because a complex chemistry system is necessary to calculate accurately trace species concentrations, computation of chemical changes along streamlines in a previously-calculated flowfield proved to be satisfactory and more economical than a complete flowfield calculation with nonequilibrium chemistry. Except for minor displacement effects boundary layer has little influence on Ne profiles for blunt nosed bodies at the lower altitudes of interest, since the entropy layer is relatively thick and the Ne maxima fall in the inviscid portion. At higher altitudes, where boundary layers are no longer thin relative to the entropy layer and often include the peak of the Ne profile, a method was devised for following streamlines into the boundary layer. The approach was useful, but, because ambipolar diffusion of charged particles could not be included, the results are invalid above a threshold altitude. In this paper the boundary-layer portions of previously published Ne profiles are calculated by means of a nonequilibrium, multicomponent diffusion, boundary-layer program, and the results are compared with previously published profiles obtained by following streamlines into the boundary layer. Comparisons are made with experimentally measured profiles and also with profiles calculated for nonequilibrium fully viscous flow.