Prediction of Microwave Attenuation Characteristics of Rocket Exhausts

TLDR: In this paper, an approximate technique for predicting microwave attenuation from propelant composition for a given motor configuration and missile trajectory is presented. But the prediction of the electron density requires treatment of the effects of thermal ionization of alkali metals, detachment and recombination processes during nozzle expansion, inviscid plume expansion, plume-air mixing, afterburning, and missile velocity and altitude.

Abstract: This paper summarizes an approximate technique for predicting microwave attenuation from propel]ant composition for a given motor configuration and missile trajectory. The solution involves calculations of electron density and collision frequency and knowledge of microwave frequency. The prediction of the electron density requires treatment of the effects of thermal ionization of alkali metals, detachment and recombination processes during nozzle expansion, inviscid plume expansion, plume-air mixing, afterburning, and missile velocity and altitude. The collision frequency is calculated using existing techniques and data. Effects of propellant composition, motor configuration, and missile trajectory are examined. Predicted X and K band attenuation is generally lower than measured values for sea level, static motor firings. This may be caused by other mechanisms not considered, such as chemi-ionizat ion. Predicted effects of mixing and afterburning were not great, but this area needs further study. Although the predictions are only approximate, they are useful for assessing microwave attenuation characteristics of rocket systems during early design and development stages.