RAM-and SCRAM-Jet engines can not generate static thrust and only work at high speeds. This starting velocity of the motor v 0 is usually generated by carrier rockets or boosters, which mostly use solid propellants based on ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB). Modern solid propellants based on ammonium dinitramide (ADN) and Glycidyl Azide Polymer (GAP) have significant advantages in terms of environmental compatibility and thermodynamic performance. In the present work, it is shown that the already high burning rate of ADN solid propellants can be more than doubled by means of metallic fibers, which significantly increases the thrust of such engines. In order to achieve such results, 3 wt% of AlÀ Mg alloy fibers are added to the propellant. A formulation with 3 mm long fibres shows the highest burning rate with 84.0 mm/s at 26.5 MPa. Small scale motor tests confirm these investigations. The burning mechanism is studied by SEM/EDX investigations and by measuring the thermal conductivity. These show that the fibres remain on the burning surface and thus transfer the heat from the flame to the depth of the propellant. The thermal conductivity of samples with AlMg5 fibers is about 22 % higher than the reference.

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Solid rocket propulsion enjoys unique properties favoring its use in space exploration and military missions still for decades to come. Yet, it also suffers a limited performance especially in terms of gravimetric specific impulse. Although new high-energy materials have been identified, most of them are far from being practically usable in the short range. Presently, no integrated vehicle designs make use of these new ingredients. A broad overview is discussed in this paper and attention is paid to Ammonium Dinitramide, ADN to overcome the current limitations of Ammonium Perchlorate, AP. The latter imply not only a limited gravimetric specific impulse but also a negative impact on the environment and personal health. ADN-based dual-oxidizer formulations, with Al-based dual-metal fuels and inert or energetic binders, are promising solutions for a variety of solid rocket propulsion missions aiming respectively at minimizing environmental impact (ADN + AN) or maximizing performance (ADN + AP).

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