Development of a Bi-modal Ammonium Perchlorate Cast Propellant for 54-mm and 76-mm Solid Rockets

This paper presents a study of the development and experimental testing of bimodal ammonium perchlorate propellant with a granular distribution of 400-micron and 200-micron in 54mm and 76mm diameter motors. Solid rocket motors provide reliability using a low-cost and simple design. The development included studying 40%, 50%, and 60% 400-micron ammonium perchlorate with the remainder being 200-micron ammonium perchlorate. The effects of a copper chromite burn-rate catalyst and oxamide burn-rate inhibitor were studied using the 60-40 granular distribution to study the impact on burn rate. Results of the 54-mm 60-40 granular distribution with copper chromite were compared to the same composition with 76mm rocket motors. Developments were also made to apply the copper chromite formula at the 76mm diameter propellant to study the effect of scaling on the propellant formula. Experimental data includes thrust and chamber pressure and the results included time-resolved, thrust, and specific impulse. The results of these studies showed that a bimodal propellant with a granular distribution of 60% 400-micron and 40% 200-micron ammonium perchlorate was the most effective for a slow burn rate with the highest specific impulse. Additionally, it was shown that oxamide worked as an effective burn-rate inhibitor for a longer burn time giving the benefit of lower drag when integrated into a vessel. The 76-mm motor showed no significant differences in the scaling with a comparable specific impulse to that of our tests at the 54-mm scale. Observations from this study provide important information for rocket-assisted take-off (RATO) and high-powered rocketry applications in commercial and military fields.