Computer experiments on the measurement of reentry plasma with radio waves

Abstract

The present paper deals with computer experiments on the measurement of reentry plasma with radio waves. Around the nose of a reentry vehicle, a dense plasma layer is created due to the ionization of neutral particles by shock wave heating. The density of the plasma layer becomes as dense as 10 18−10 19 m −3 and it causes so-called radio backout. Since probing the hot and dense plasma layer is difficult, we propose a remote measurement of the reentry plasma with the reflectometry method, which uses radio wave emission from the vehicle. To study this method quantitatively, we perform computer experiments with an electromagnetic particle code. In the experiments, we emit a pulse wave form with no DC component from a vehicle antenna toward a Gaussian-shaped reentry plasma put in front of the vehicle surface. The obtained phase difference between the emitted and reflected waves is used in the reflectometry method to estimate the spatial density profile. The spectrum of the reflected waves, which has a cut-off frequency at the maximum plasma frequency, is used to estimate the maximum density in the plasma layer. The results of the computer experiments revealed that the plasma parameters estimated with the reflectometry method agree very well with the ones actually used in the experiments.