Active Control of Energetic Material Decomposition

In an effort to create safer and more mission flexible energetic materials, we are exploring the potential of using electrical stimuli to start, stop, restart, and throttle material decomposition/reaction. Specifically, we are examining the ability to actively control the ignition, combustion, and extinguishment of solid propellants. In the roughly 80 years since the first rubbery composite propellants emerged, relatively little has changed in terms of performance, or perhaps more importantly their functionality. Solid propulsion systems are still plagued today with very little operational flexibility. One recent concept for actively manipulating solid propellant combustion involves taking advantage of electrochemical processes with the application of electrical power to the condensed phase of the propellant. Questions linger as to whether electrochemical or thermal processes dominate in these environments. Whether ignition or extinguishment is the goal, the answer likely changes, and satisfying both is challenging. But, by targeting specific ignition and combustion mechanisms, new solid propellants which can be actively controlled are emerging.<br/>Composite propellants at minimum comprise a polymeric binder and crystalline oxidizer but may also include additives such as metal powders to enhance performance. Typical properties that are desirable for binders and oxidizers may be different in electrically controllable propellants where responsiveness may be more important than metrics such as specific impulse. Performance based additives are generally selected to improve the caloric properties of the propellant, however, when responsiveness is desired, different additives may be considered to elicit a specific response designed to improve operability. Additives which allow us to optimize one response for ignition/combustion/or extinguishment are often in opposition to another desired response due to competing mechanisms complicating the situation. That is, materials which tend to promote ignition, tend to impede extinguishment, and vice versa. The role of each of these components, binder, oxidizer, and additives is explored in the development of electrically controlled solid propellants which can be ignited, stopped, and restarted with only the application or removal of electric power. The formulation, fabrication, combustion behavior and properties of propellants controlled by electrical power will be discussed under relevant operating conditions.