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International Journal of Energetic Materials and Chemical Propulsion
ESCI SJR: 0.149 SNIP: 0.16 CiteScore™: 0.29

ISSN Print: 2150-766X
ISSN Online: 2150-7678

International Journal of Energetic Materials and Chemical Propulsion

DOI: 10.1615/IntJEnergeticMaterialsChemProp.v8.i6.60
pages 541-554


Gideon J. van Zyl
Rheinmetall Denel Munition, Western Cape, P O Box 187, Somerset West, 7129, South Africa
Martin Hubinger
Rheinmetall Denel Munition, Western Cape, P O Box 187, Somerset West, 7129, South Africa


The total impulse delivered by a nozzleless booster rocket motor is mainly determined by the burning rate and ballistic properties of its propellant. Propellants with low burning rate pressure exponents (n-values) and high burning rates permit significant increases in performance. It is common knowledge that ferrocene-based burning rate catalysts reduces the burning rate pressure exponent and increases the burning rate significantly. Therefore, ballistic properties produced by the ferrocene-grafted HTPB polymer, Butacene®, are highly effective in nozzleless booster motors. However, high burning rate Butacene-based propellants may produce a high initial pressure peak during the ignition phase of the nozzleless booster motor, which may necessitate the use of a stronger and thus heavier motor casing. One way to reduce this high ignition pressure is to design a dual-propellant grain that consists of two concentric propellant layers. A thin inner layer contains a propellant with a slightly lower burning rate, while the much larger outer layer consists of a higher burning rate Butacene-based propellant. In this case, the inner propellant layer consisted of a Fe2O3-based reduced smoke propellant, while the outer layer consisted of a Butacene-based reduced smoke propellant. Formulations and properties of the two propellants used in the manufacturing of the dual-propellant nozzleless booster motor are reported. A good bonding interface between the Butacene and Fe2O3 propellant layers was ensured by application of an isocyanate-based activation coat between the layers. A displacement casting process was used for the manufacturing of the dual-propellant grain. The results of the static test-firing of this nozzleless booster motor showed that the high ignition pressure was reduced by using the dual-propellant design concept.


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