Effects of inclusions on the performance of a solid rocket motor

Some of the most common defects that can be generated during the production of solid propellant are voids and porosity, usually associated with the casting process, and cracks and debonding, typically initiated by the high stresses caused by the curing process. This paper presents the development of an algorithm capable of evaluating the burning surface regression of a solid rocket booster when inclusions are present within the grain. The effects produced by the cavities are evaluated both in terms of performance (i.e., comparison with the behavior of the nominal combustion surface), and in terms of safety (i.e., evaluation of the thermal protection increased exposure). The paper also documents the influence of uncertainties in the knowledge of the real dimension and position of the inclusions detected within the motor. The radiography inspection of the motor is able to detect the presence of cavities within a certain level of accuracy, and the worst combination of these uncertainties has to be determined in order to guarantee, even under such circumstances, the safe and successful firing of the motor. The methodology developed in the paper is adapted in order to identify the worst uncertainty combination, and to subsequently determine the corresponding performance deviation.