Abstract
Several industrial- and research-type solid rocket propellants, of the broad family AP/Metal/HTPB in the ratio 68/18/14, were experimentally analyzed at the Space Propulsion Laboratory of Politecnico di Milano. In general, they feature the same nominal composition, but different metals are investigated as fuel powders and contrasted to a conventional micrometric aluminum (30 mu m average grain size) taken as reference. The effect of the solid ingredient (oxidizer and metal) grain size was taken into account by considering a variety of multimodal distributions. The fundamental ballistic and mechanical properties of the formulations under study were compared to that of a conventional aluminized propellant already certified for flight. Steady burning rates and the associated flame structure were studied by means of a variety of experimental techniques ranging from high-speed and high resolution digital video recording to chemo-physical analyses of the solid combustion residues. Although the metal oxidation process follows a common set of events, aggregation/agglomeration phenomena near the burning surface may be noticeably different depending on the enforced operating conditions and details of the solid propellant formulation. Understanding of these effects opens the path to improved ballistic performance.