Functionally Graded Solid Rocket Propellants are being developed at NSWC-Indian Head in conjunction with the University of Maryland. The approach being used treats these propellants as typical Functionally Graded Materials (FGMs), which by definition are structures that possess gradual variations in material behavior that enhance material and/or structural performance. For functionally graded propellants, Twin Screw Extrusion (TSE) processing is used to continuously vary the composition throughout a grain in a controlled manner. As a result, TSE processing allows the burning rates of propellants to be tailored as a function of burning web thickness. This in turn will allow for direct Thrust Magnitude Control (TMC) for a solid rocket motor, which has proven difficult to achieve in the past. To realize the benefits of functionally graded propellants in rocket motors, an Inverse Design Procedure (IDP) is being developed that couples processing, property, and performance models with mathematical optimization techniques to enable designers to determine realistic gradient architectures that will meet the performance objectives. An essential part of this program is the development of a model that is capable of predicting the ballistic performance of functionally graded propellants. The development of such a model requires that new parameters be taken into account that would not be considered for a conventional solid propellant. For instance, not only will the burning rate change as a function of pressure and initial temperature, but the burning rate characteristics will also change as a function of position in the grain. Furthermore, the density and the thermochemistry associated with the graded architecture of the propellant will be changing in a continuous manner, whereas the grain will conventionally be represented by a web with discrete thickness. The details of the ballistics model and the effect on performance predictions related to discrete representations of continuously graded architectures will be discussed in the paper.