Electromagnetic Propagation through Shock Ionized Air Surrounding Glide Re-Entry Spacecraft

Radio frequency communication with spacecraft is necessary during all phases of flight including the period of atmospheric re-entry. During re-entry, the velocity of these vehicles is sufficiently high to induce thermal ionization of the air surrounding the vehicle. Resultant electron concentrations are in some cases high enough to interfere with normal communications with the vehicle. This interference takes the form of attenuation or reflection of signals transmitted from the vehicle. Exact analysis of the problem requires precise information regarding the flow field surrounding the vehicle of interest. Since these data are generally unavailable until late in the vehicle design phase, it is the purpose of this paper to examine means by which an approximation of the interference effects may be obtained when only the trajectory and body configuration are known. Many glide vehicle designs are complex in their shape; however, for the purposes of analysis of phenomena associated with the vehicle configuration, the vehicle may be considered to be composed of combinations of shapes having more elemental forms. A procedure is described by which analysis of propagation effects for these elemental bodies may be used to approximate the conditions to be expected in the corresponding region of the more complex vehicle. A sample problem is presented as a demonstration of the procedure.