Cast Double Base: Propellant designed to meet internal ballistic requirements

C Rousseau,Robin Pretner,G Steyn,M Leslie

doi:10.2514/6.2011-6138

C Rousseau, Robin Pretner + Show 2 more

https://doi.org/10.2514/6.2011-6138

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Publication Date: Jul 31, 2011

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Cast Double Base (CDB) propellants were first developed in the 1960s and 70s. This propellant, unlike extruded double base propellants, can be cast into any shape. The motor grain can also be cast in several layers with different plateau burn rates to obtain an optimal boost-sustain characteristic. This ability to tailor the burn rate in conjuction with an higher maximum web fraction offsets the lower theoretical impulse when compared to cross liked double base (XLDB) and composite propellants. In addition CDB propellants are true minimum smoke propellant and the secondary combustion in the plume can be suppressed with flame suppressants thus minimizing the chance of early detection. Lockheed Martin’s Hellfire (XLDB), MBDA’s Brimstone (Cast Double Base), and Denel Dynamics’ Mokopa (Composite) missiles are all air/ground launched tactical missiles of the same caliber and mass. Interestingly Brimstone out performs both the Mokopa and the Hellfire in terms of maximum range, reported as 12 km, with Mokopa at 10 km and unexpectedly Hellfire with the highest specific impulse propellant has the shortest range of 8 km. This is because a system that is velocity constrained requires a boost sustain motor that can boost the missile to the maximum velocity as quickly as possible and sustain this velocity as long as possible. In such a system the primary driver is not total impulse but rather the propellant burn rate flexibility. Star port grain designs that use area to obtain the required boost-sustain profile suffer from volumetric losses. High energy propellants such as XLDB have a limited usable burn rate range, limiting their use to all boost motors. This investigation considered the requirements of the internal ballistician rather than the pursuit of maximum impulse. It will be shown that flexibility in propellant burn rate is a far more important factor in the tactical missile environment when single stage motors are the only option.

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