Abstract: The invention includes a method for forecasting fatigue damage of a solid rocket motor through ignition, where over the lifetime of the motor it can be exposed to a plurality of stressing events, which may have a broad spectrum of mechanical loads with multiple modes. For instance, a mode may be a change in the thermal contraction or a change in a direct mechanical load. The method expresses all stressing events in terms of a common mode. The thermal contraction is the selected common mode measured in units of stress. The stress is proportionally adjusted according to the conditioning temperature, the stress free temperature, the pressures, and the age. Cumulative damage for the time before and after ignition is determined. Finite element analysis reference points are adjusted for the stressing events.