The objective of this project was to develop a perchlorate-free replacement propellant for Hercules Inc., Hercules Experimental Smokeless (HES) 5808 in Cartridge Actuated Devices (CAD) systems with a burn rate and granulation as close as possible to those of HES 5808 so that its ballistic performance could be easily adjusted to match that of HES 5808 in existing cartridge applications. The new propellant is a composite-modified nitramine type that consists primarily of cyclotetramethylene tetranitramine (HMX), nano-sized aluminum fuel, strontium nitrate oxidizer, and small quantities of mixing and processing aids.
Ammonium perchlorate is used as the oxidizer in most solid composite rocket/missile propellants. HES 5808, one of the most commonly used CAD propellants, contains as much as 86% percent by weight of ammonium perchlorate. Energetic ingredients that are well characterized have been incorporated in previously qualified propellants and are presently found in conventional propellant formulations, were selected to comprise a new propellant formulation to replace HES 5808 propellant. An additional consideration, that they must also have a lower environmental impact, was also applied to the ingredient selection process, making this a novel propellant formulation.
Multiple formulations were developed and evaluated during this study. The ingredients considered to enhance the baseline formulation were selected based on the following factors:
- Energy contribution
- Thermal stability
- Safety and handling
- Performance in other qualified forumulations
- Intended formulation role(s)
- Impact on baseline formulation
- Required additives
- Technical maturity
- Long term availability
The known ingredient toxicity risks and chemical energy properties were thoroughly considered before proceeding with producing the formulation.
The addition of the nano-aluminum and oxidizer to the HMX was found to significantly increase the burn rate, while replacement of the nano-aluminum with micron-sized aluminum showed little effect on burn rate. The replacement propellant has met the performance criteria that were established to determine its readiness for demonstration testing in selected CAD applications. Most importantly, the burning rate and simulated ballistic performance of the replacement propellant have been found to be within ranges that would allow it to be produced in granulations similar to HES 5808, thus assuring that it will function as a drop-in replacement in the applications envisioned for its use.
Replacement of perchlorate-based propellant will eliminate the release of perchlorate into the environment during propellant manufacturing, CAD production, field use, testing, open burning/open detonation (OB/OD) and demilitarization of the affected CADs. The benefit would be three-fold in that it would reduce a source of perchlorates into the environment from the site where the perchlorates are produced, the two propellant manufacturing sites, and ultimately the site (Tooele Army Depot), where the end items are demilitarized. Beyond these sites, there are approximately 20 cartridge vendors in the US that routinely manufacture and test CAD/Propellant Actuated Device (PAD) devices that containing perchlorates. Eliminating perchlorates from CAD items would eliminate the risk and cost associated with handling and disposal.
An added benefit is that HES 5808 and other perchlorate propellants have a history of being difficult to manufacture to the specified requirements due to their inherent chemical and physical nature. Changing ingredient providers, frequent repeat batches, and low yields are some of the manufacturability issues associated with HES 5808. This impacts propellant procurement cost and schedule due to the testing, rejection and disposal of the propellant with increasing potential for unnecessary release of perchlorates into the environment. The perchlorate free CAD propellant formulation will be designed with a more efficient manufacturing process than was established for HES 5808.