Influence of Water Content in an ADN Based Liquid Monopropellant on Performance Characteristics

Abstract

Hydrazine is advantageous for attitude control systems of satellites because it is space storable for long times and the developed thrusters are reliable for long term operations. Unfortunately hydrazine is very difficult to handle on ground due to its very high toxicity. Especially with regard to the REACH regulation of the European Community, which has passed some years ago, Hydrazine is on the candidate list of substances whose use could be limited in future. Thus strong research efforts have to be conducted today to find and to qualify alternative propellants, which have significantly simpler handling characteristics, are less toxic, environmentally benign and have similar or even better performance characteristics. One of the most promising candidates to replace hydrazine is the ADN based ionic liquid FLP-106, which is a monopropellant and has been developed by FOI. This monopropellant has a higher Isp in comparison to hydrazine and to LMP-103S which is currently used by the ECAPS company from Sweden. Also FLP-106 has a lower vapor pressure than LMP-103S. Thrusters using ionic liquid propellants are working with heated catalysts to decompose the propellant. One of the main drawbacks of this design is the lack of cold-start capability. Additionally, the high combustion temperature is a concern, possibly requiring high-temperature alloys like Iridium/Rhenium. FLP-106 consists of 64.6 % ADN (ammonium dinitramide), 23.9 % water and 11.5 % of a low volatile hydrocarbon fuel. In order to use simpler materials with lower melting points the combustion temperature of FLP-106 can be decreased by increasing the water content in the propellant. However, the increased water content will decrease the specific impulse and may also influence the ignition properties.