Novel Catalysts for Non-Toxic Monopropellants

Abstract : Reduced toxicity ionic salt monopropellants containing hydroxylammonium nitrate (HAN, HO(-)NH3(+)NO3(-)) in highly concentrated aqueous solutions have been proposed as replacements for hydrazine. To be competitive with the rocket performance of hydrazine, HAN-based monopropellants will have to operate at temperatures above the limit of the state-of-the-art catalyst Shell 405 (l37l degrees centigrade). To realize the benefits of reduced toxicity propellants without a concomitant loss of performance, catalysts and chamber materials capable of withstanding operating temperatures above 1371 degrees centigrade have to be developed. Sienna Technologies, Inc., has successfully demonstrated the feasibility of a family of ceramic-based catalysts that can decompose nontoxic HAN-based liquid monopropellants, and withstand the high temperature, acidic and steam-rich environment encountered during thruster operations. Several processing techniques were developed to manufacture these carriers and potential catalysts in granular forms that result in reproducible packing densities in packed bed reactors. Rocket engine tests demonstrated that STI-developed catalysts are more active and more durable than any other catalysts tested to date with the hot AFRL-developed ionic salt monopropellants.