We have used solid-state NMR to monitor the aging dynamics of a polyurethane based on glycidyl azide polymer (GAP) used as a binder in solid rocket propellants. me have shown by deuterium NMR longitudinal relaxation time (T-1) measurements that it is possible to monitor the degradation of the binder as a function of time for samples with different NCO/OH ratios. The longitudinal relaxation was found to be nonexponential. Thus, we have used a stretched exponential equation of the type Kohlrausch-Williams-Watts to determine the value of T-1ww. With the help of the gamma function, the average value of T-1 ([T-1]) was determined without knowing the shape of its distribution function. Since the solid-state NMR method has the advantage of being nondestructive, we were able to monitor the aging of the polyurethane samples that; were kept in ambient conditions rather than in the extreme thermal conditions usually applied in aging studies of polymers.