Out of the various propulsion technologies, solid rocket motors (SRMs) find many applications due to their relatively simple operation and quick firing time. In defense applications, many SRMs remain in storage for extended periods of time before being used. Normally, we think of material properties as a constant, but over sufficiently-long periods of time, their properties do indeed change. In particular, solid propellant becomes stiffer and more brittle over time. This can give rise to cracking and debonding of the propellant, which alters its burning rate and can ultimately lead to a catastrophic failure of the rocket. As a first step towards developing accurate models for predicting the failure of SRMs, experimental methods are needed to efficiently characterize the influence of aging on the mechanical properties of propellant. This data can then be input in to material models to use in simulations. In this talk, a new experimental method utilizing Dynamic Mechanical Analysis is presented that allows for the efficient and accurate characterization of the mechanical properties of solid propellant beyond current testing standards. This method is then used to measure the master curves of the relaxation modulus of differently-aged specimens. The resulting data will be used in future finite element calculations as inputs to viscoelastic models such as Prony series to predict the stress and strain distribution in SRMs.