The objective of this project was to develop a new environmentally benign, insensitive, castable, high-performance, minimum-smoke rocket propellant formulation. The new formulation approached all of the performance requirements associated with the current minimum smoke, double-based propellant - without containing lead, ammonium perchlorate, or cyclotrimethylenetrinitramine (RDX). The study also demonstrated a reduction in toxicity compared to existing propellants and meet insensitive munition (IM) requirements. The Statement of Need (WPSON-11-02) was met in a twofold fashion: First, an innovative tactical grain configuration, Exponent Modified Minimum Smoke (EMMS), was used to eliminate the need for lead catalysts, and second, advanced energetic ingredients were incorporated into this grain design to provide performance levels meeting current minimum smoke double-base propellants, insensitivity to meet IM requirements, and a reduction in toxicity compared to existing propellant ingredients.

The key objectives were to:

• Demonstrate key technologies eliminating lead and RDX in a castable, EMMS-configured rocket-motor test while providing high performance and insensitive munitions capability.

Supporting objectives were to:

• Demonstrate an RDX replacement with a reduction in toxicity, acceptable performance, and insensitivity.
• Demonstrate the use of non-lead catalyzed minimum-smoke propellants incorporating the RDX replacement which will augment insensitive munitions capability.

This effort used an innovative castable, minimum-smoke propellant grain design supported by three key components to eliminate lead catalysts and RDX, provide insensitive munitions capability, provide high-performance, and incorporate materials which give a reduction in toxicity. EMMS uses a ballistic control propellant (BCP) to control the pressure and temperature sensitivity of a rocket motor and a matrix propellant to provide total rocket motor impulse.

A variety of potential RDX replacement materials were considered initially by utilizing thermochemical calculations to rank and help down-select the candidates. These were then placed in a matrix where ease of synthesis, toxicity, density, heat of formation, sensitivity and performance were ranked. Methylene-bis-aminonitrofurazan (MBANF) was thus selected as the RDX replacement material.

The team evaluated MBANF as a potential RDX replacement in minimum-smoke rocket propellants. The sensitivity of MBANF is similar to RDX, and it provides similar performance in propellants. Propellant tailoring efforts were completed, and a propellant meeting all of the technical objectives except a hazard class 1.3 was developed. The evaluation of Naval Surface Warfare Center Indian Head Explosive Ordnance Disposal Technology Division (NSWC IHEODTD) -developed lead-free extruded propellant for the ballistic control portion of the motor was also successfully completed, and recommendations made for the final material to be used in the demonstration. A subscale motor was successfully built, but due to unforeseen issues, the motor could not be tested for safety reasons.

• The rocket motor ballistics responds almost solely on the burning rate behavior of a faster burning BCP. The BCP is only a fraction of the mass of the overall motor propellant, so it has little effect on total delivered performance.
• The rocket motor performance is almost solely a function of the thermochemical performance of the slower burning matrix propellant (MP). Elimination of lead in the matrix propellant is thus also possible. Enhancement of the MP performance is desirable, and thus suitable RDX replacements will be evaluated.
• Use of an end-burning grain enhances insensitive munitions response by preventing the propellant debris field and ignition on bullet and fragment impact typical of center perforated motor configurations. In addition, end-burning grains provide high-performance by allowing high volumetric loading of the propellant in the motor case. Lastly, end-burning grains can be readily manufactured by current industrial infrastructure and are typically made in a cartridge-loaded configuration.