Electrically controllable propellants (ECPs) provide a new method to increase the control and functionality of rocket motors in particular solid rockets. Traditional solid rockets do not have the capability to modify the burning rate on demand during operation, which greatly limits operational capabilities. The research outlined in this dissertation explores the fundamentals in the creation of ECPs to enable increased control in the burning rate of solid rockets. The research is organized into four studies which step through the fundamentals of ECPs, starting with a focus on the solid oxidizers, then moving into the creation of electrically controllable gel propellants (ECGPs). Next, electrically controllable solid propellants (ECSPs) were explored under atmospheric conditions, and then finally under elevated pressures. The first study explores the ability to electrically control the decomposition characteristics of various solid oxidizers. Typical composite solid propellants are composed of solid fuels and oxidizers and isolating the oxidizer in this study enables the ability to characterize critical components of ECSPs individually. This study discovered that certain solid oxidizers respond differently to applied voltages, but generally the decomposition rate of the solid oxidizers is greatly increased when voltage is applied using metal electrodes. The melt layer formed in the decomposition of the solid oxidizers was observed to be critical in the ability to manipulate the decomposition rate of the oxidizers. The second study built upon the knowledge that the melt layer was critical in the functionality of ECPs and explored the utilization of ECGPs which combined a viscous liquid polymer fuel in which solid oxidizers were dissolved. The ECGPs used in this study readily decomposed and ignited when a voltage potential was applied. The composition of the ECGPs along with the magnitude of the voltage being applied greatly impacted the ignition delay and overall burning characteristics of the propellants. This study illustrated the potential to create ECPs that enable increased control over the burning characteristics compared to conventional propellants. The third study utilized a solid polymer binder along with the solid oxidizers to create ECSPs that would readily decompose and ignite when a voltage potential was applied. Compositional changes in the propellant along with the magnitude of the applied voltage potential were observed to impact the regression rate of the ECSPs utilized in this study. The electrochemical decomposition characteristics of the ECSPs were explored to better characterize the contribution of the electrochemical reactions and how they differ from the more conventional thermochemical decomposition. The fourth and final study builds upon the prior ECSP study, but now experiments utilize compositions with electrically conductive additives to increase the responsiveness of the ECSPs to the applied voltage. This enabled the creation of ECSPs which ignite much more readily and with a higher degree of consistency. Experiments were also conducted at elevated pressures to analyze the combined impact that voltage and pressure play on the regression rate of the ECSPs.

Solid rockets have many applications in both the civilian and defense industries due to their relatively low costs and long-term storage capabilities. However, traditional solid rockets have a limited degree of control as a result of the fuel and oxidizer being combined in the propellant and the combustion of the propellant being self-sustaining. The ability to change the thrust of the solid rocket motor on demand is something not currently possible without greatly increasing the complexity of the rocket motor, and even then the thrust control is limited. The addition of a simple method to vary the thrust of the rocket motor would drastically improve the functional capabilities and safety of the rocket. The method explored in this study to enable the creation of controllable solid rockets is through the use of electrically controllable propellants. These are propellants whose burning characteristics can be modified when subjected to an electric field. The work outlined in this dissertation develops a fundamental understanding of the methods to create electrically controllable solid and gel propellants. The electrically controllable propellants in this study demonstrated the capability to have their burning rate greatly increase or decrease by increasing or decreasing the voltage being applied to them. In addition to changing the burning rate, several compositions developed in this study were able to have their burning extinguished by removing the voltage and reignited by reapplying the voltage. These capabilities and the fundamentals behind their development enable the creation of much more functional rocket motors that overcome the limitations of current systems.

Doctor of Philosophy