Pulverized-coal combustion research at Brigham Young University

Solid propellants are energetic materials used to launch and propel rockets and missiles. Although their history dates to the use of black powder more than two millennia ago, greater performance demands and the need for "insensitive munitions" that are resistant to accidental ignition have driven much research and development over the past half-century. The focus of this review is the material aspects of propellants, rather than their performance, with an emphasis on the polymers that serve as binders for oxidizer particles and as fuel for composite propellants. The prevalent modern binders are discussed along with a discussion of the limitations of state-of-the-art modeling of composite motors.

Solid Propellants

There has been a considerable interest recently in the attenuation of a microwave signal when it traverses an ionized exhaust plume of a rocket motor. A closely related and sometimes more serious guidance problem is the introduction of amplitude-modulated (AM) or phase-modulated (PM) noise onto the transmitted signal by the rocket exhaust plume. This paper reports the results of a set of measurements wherein X-band attenuation was measured simultaneously with AM/PM noise for seven different double-base propellant systems and a single rubber-base system. The method and limitations of the measurements are discussed. Results are reported for total attenuation and AM/PM noise, together with spectral distributions of the noise, generally between 3.9 and 40 kc. Peak attenuation and noise levels occurred in the aft regions of the plume. Noise and attenuation varied markedly with changes in propellant composition, the more severe levels of each resulting from the more highly aluminized systems. A correlation existed between the level of attenuation and the levels of AM/PM noise. Causes of the induced noise were explained using a model based on turbulent scattering of the radar beam.

Rocket exhaust plume radar attenuation and amplitude/phase noise.

The ionized exhaust plumes of solid rocket motors may interfere with RF transmission under certain flight conditions. To understand the important physical processes involved, we measured microwave attenuation and phase delay due to the exhaust plume during sea-level static firing tests for a full-scale solid propellant rocket motor. The measured data were compared with the results of a detailed simulation performed using the frequency-dependent finite-difference time-domain ((FD)2TD) method. The numerically derived microwave attenuation was in good agreement with experimental data. The results revealed that either the line-of-sight microwave transmission through ionized plumes or the diffracted path around the exhaust plume mainly affects the received RF level, which depends on the magnitude of the plasma-RF interaction.

Frequency-Dependent FDTD Simulation of the Interaction of Microwaves With Rocket-Plume

This valuable resource summarizes the past fifty years' basic research accomplishments in plasma dynamics for aerospace engineering, presenting these results in a comprehensive volume that will be an asset to any professional in the field. It offers a comprehensive review of the foundation of plasma dynamics while integrating the most recently developed modeling and simulation techniques with the theoretic physics, including the state-of-the-art numerical algorithms. Several first-ever demonstrations for innovations and incisive explanations for previously unexplained observations are included. All the necessary formulations for technical evaluation to engineering applications are derived from the first principle by statistic and quantum mechanics, and led to physics-based computational simulations for practical applications. The computer-aided procedures directly engage the reader to duplicate findings that are nearly impossible by using ground-based experimental facilities. Plasma Dynamics for Aerospace Engineering will allow readers to reach an incisive understanding of plasma physics.

Plasma Dynamics for Aerospace Engineering

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.

L. D. Smoot

Papers

Prediction of Microwave Attenuation Characteristics of Rocket Exhausts