Modern solid propellants are highly filled composite materials. The essential ingredients of a composite propellant are a crosslinked binder, a polymer like polyurethane and an oxidizer. Furthermore, most propellant formulations contain a stabilizer, ballistic modifiers, high energy fuel additives, a wetting agent, plasticizers and other additives to adjust physical properties. The aging behavior of composite propellants is correlated with a change in mechanical properties. Background of the aging behavior of a composite propellant are micromechanical phenomena. Therefore, the understanding of micromechanical phenomena like matrix filler detachment, crosslinking and chain cleavage is the key to the understanding of aging behavior of composite propellants. In this paper it is shown how micromechanical phenomena can be observed by MRI (Magnetic Resonance Imaging).