Radiation and Scattering of EM Waves in Large Plasmas Around Objects in Hypersonic Flight

Abstract

The hypersonic flight regime is conventionally defined for Mach > 5; in these conditions, the flying object becomes enveloped in a plasma. This plasma is densest in thin surface layers, but, in typical situations of interest, it impacts electromagnetic wave propagation in an electrically large volume. We address this problem with a hybrid approach. We employ the equivalence theorem to separate the inhomogeneous plasma region from the surrounding free space via an equivalent (Huygens) surface and the Eikonal approximation to Maxwell equations in the large inhomogeneous region for obtaining equivalent currents on the separating surface. Then, we obtain the scattered field via (exact) free-space radiation of these surface equivalent currents. The method is extensively tested against reference results and then applied to a real-life reentry vehicle with full 3-D plasma computed via computational fluid dynamic (CFD) simulations. We address both scattering [radar cross section (RCS)] from the entire vehicle and radiation from the onboard antennas. From our results, significant radio link path losses can be associated with plasma spatial variations (gradients) and collisional losses to an extent that matches well the usually perceived blackout in crossing layers in the cutoff. Furthermore, we find good agreement with existing literature concerning significant alterations of the radar response (RCS) due to the plasma envelope.