O-191 Reaction Mechanisms for Rocket Motors

Rocket motors are designed to propel payloads towards their final destination by ejecting hot gases through a nozzle. The gases are produced by the combustion of fuel and oxidizers which can be either separated (hybrid combustion) or embedded into each other (gun propellant, propellant grain). However, when a rocket motor, and therefore its propelling charge, is subjected to an accidental threat, it may cause an abnormal decomposition behavior. Depending on the stimulus, its intensity and its duration, the reaction type may range from combustion to detonation with corresponding gradual damages in the surrounding environment.
New generations of propellants may contain high energy constituents such as nitramines, or energetic polymeric binders in order to attain a higher burning performance or to better control them. These new ingredients usually lead to a greater sensitivity to mechanical stimuli and also to smaller critical diameters. Hence, their ability to detonate may be increased and this is a major challenge for new munitions. More specifically for propellant grains, geometrical aspects also have to be considered as they may lead to unexpected shockwave concentrations and therefore, to more violent reactions.

This paper consists of an overview of reaction mechanisms possible for a rocket motor propellant under dynamic mechanical loading such as fragment or bullet impacts, and how those reactions have evolved with the most recent advances in propelling charges.

Finally, a focus will be made to present mitigation measures recently developed by the community and especially designed to mitigate the reaction level of rocket motors subjected to high energy mechanical stimuli.