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High Performance Solid Rocket Propellant Replacement

Description:

TECHNOLOGY AREA(S): Space Platforms 

OBJECTIVE: Design and develop a form-fit-and-function replacement for Aluminum in Ammonium Perchlorate Compound Propellant (APCP) solid rocket propellant that produces minimum HCl and aluminum slag bi-products while maintaining equivalent or better combustion efficiencies (c*), and maintaining or improving munition safety rating. Minimize performance degradation due to water condensation on proposed fuel grain during storage, transportation, and flight operations. 

DESCRIPTION: High performance solid rocket propellants currently have two primary problems: the metal fuel (aluminum powder) sinters and agglomerates at the propellant surface, forming large molten droplets (LMD) which burn slowly and cause significant two-phase flow losses as the LMD pass through the nozzle; and they use ammonium perchlorate as an oxidizer, which also forms copious amounts of corrosive hydrochloric acid (HCl) during combustion. These bi-products are harmful to the atmosphere, and degrade the space environment by producing debris in the form of Al slag which can co-orbit and collide with resident space objects. Some replacement fuels have yielded propellants that have reduced performance (lower specific impulse), only work at low altitudes, and/or become unsafe to handle (detonable). For air-launched missile applications, a munition may be loitered at a colder, higher altitude for an extended period of time; and then be returned to a warmer, low altitude environment. Condensation is likely to occur, resulting in the fuel being compromised. 

PHASE I: Design a solid rocket fuel propellant to replace the current fuel used in munitions and rocket boosters which reduces degradation due to water condensation, maintains or improves munition insensibility, and produces thrust equivalent to or greater than that of current solid rocket fuel propellants. Major Milestone for Phase I is to assess the safety and material compatibility of proposed fuel material by itself and in relevant propellant formulations. This includes fully characterizing the material handling concerns and protocols. The overall objective of the Phase I work is to develop one to two candidate self-fragmenting structural reactive materials (SF-SRM) that can be used as a novel explosive ordnance casing material. This effort could include developing and manufacturing self-fragmenting, self-reacting materials (SF-SRM) for preliminary testing; testing the sensitivity of SF-SRM materials for electrostatic shock, friction, and drop-weight impact; investigating the microexplosive tendency of the candidate SF-SRM materials under high heating rates; and investigating the casing combustion efficiency of pellet size candidate SF-SRM powders under strong explosive shock. 

PHASE II: Build and test, in a relevant environment, the above described solid rocket fuel propellant. Phase II milestones include determining burn rate and pressure exponent for a relevant formulation as well as determining small-scale ballistic performance and mechanical properties. Further, accelerated aging studies and cold-soak tests will be conducted to give an indication of shelf life. 

PHASE III: Milestones will include formulation optimization, performance assessment under high-fidelity laboratory conditions, and engineering trade studies to assess the utility/benefit of the material based upon delivered density*Isp. Military Application: Use as a fuel replacement in a prototype solid rocket fuel rocket motor in a sounding rocket or small-scale missile. For air-launch, use in precision guided munitions propellant to ensure quick and reliable response to adversarial activities. Civilian Application: Use as a rocket fuel propellant replacement for civilian solid fuel rocket launches. Here, the reduction in HCl acid and Al slag is useful in minimizing the negative environmental impact, allowing more frequent launches. 

REFERENCES: 

1. B.C. Terry, I.E. Gunduz, M.A. Pfeil, T.R. Sippel, and S.F. Son. "A mechanism for shattering microexplosions and dispersive boiling phenomena in aluminum–lithium alloy based solid propellant". https://www.sciencedirect.com/science/article/pii/S1540748916301572; 2. Terry, B., Sippel, T., Pfeil, M., Gunduz, I., and Son, S., "Removing Hydrochloric Acid Exhaust Products from High Performance Solid Rocket Propellant Using Aluminum-Lithium Alloy", Journal of Hazardous Materials (2016).

KEYWORDS: APCP, Solid Rocket Fuel Propellant, Rocket Booster, Munitions, 

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