Prediction of In-flight Radio Frequency Attenuation by Rocket Plume Applying Diffraction Theories

Abstract

In rocket flights, the ionized exhaust plume of solid rocketmotorsmay interferewith radio frequency transmission under some conditions. It has been reported in many papers that radio frequency propagation is dominated by the diffraction effect around the plume. However, because the plume widely expands at high altitudes, the single knifeedge diffraction theory, the so-called Fresnel diffraction theory, cannot accurately estimate the in-flight radio frequency attenuation. In this paper, a novel diffraction theory that would bemore suitable for the widely expanded plume is proposed to analyze the communication between a vehicle and a ground station. The attenuation levels estimatedusing the single knife-edge diffraction theory andproposed theory are comparedwith thedata recorded inflight. It is found that the new theory proposed in this paper agrees with themeasured attenuation level. Based on the theoretical results and the recorded data, the radio frequency transmission characteristics through the exhaust plume are discussed, and it is clarified that in addition to diffraction, both reflection and refraction influence the radio propagation.