EFFECT OF PROPELLANT COMPOSITION ON THE SPECIFIC IMPULSE OF SOLID ROCKET MOTORS

Specific impulse (Isp) is the principal figure of merit used to evaluate the performance of a solid rocket motor, and it is governed almost entirely by the chemical composition of the propellant grain. This paper presents a complete formulation-based design study of a composite solid propellant system: the governing Isp and characteristic-velocity equations, Vieille's burning-rate law, the mass and thrust balance equations, and compositional parameters estimated from representative literature formulations (AP = 68-72 wt.%, HTPB binder system = 12-16 wt.%, Al = 14-18 wt.%). A compositional sensitivity framework is developed and cross-checked against reported literature trends. Comparative analysis of representative formulations confirms that the aluminum-content sensitivity curve peaks near 18-20 wt.% Al, beyond which two-phase flow losses erode delivered Isp, while reported Isp gains of up to 37 s are achievable through nanocarbon additives and secondary high-energy oxidizers relative to an ungmodified AP/HTPB/Al baseline. A test-basis normalization framework, cross-checked during literature screening, is documented as the practical protocol for comparing Isp values reported under different chamber-pressure and expansion-ratio conditions.