Green Propellants Based on Ammonium Dinitramide (ADN)

Abstract

Ammonium perchlorate (AP) and hydrazine are today widely used as propellants. AP as oxidizer in solid propellants and hydrazine as liquid monopropellant (Brown, 1995; Sutton and Biblarz, 2001). These propellants are well known for their good performance characteristics, but their limitations and liabilities regarding toxicity, operational handling and environmental impact are also well documented. Perchlorate contamination is becoming a more widespread concern in the United States (EPA, 2005). In 2009, a workshop organised by the US Department of Defence identified AP as one of the key environmental, safety and occupational health issues (DoD, 2009). Perchlorate anions (ClO4–) has been found in drinking water supplies throughout the southwestern United States, and perchlorate may be a problem for water supplies in some regions of the USA (Urbansky, 2002). At high concentrations, perchlorate can affect thyroid gland functions, where it is mistakenly taken up in place of iodide. Apart from impacting the thyroid activity in humans, AP forms vast amount of hydrochloric acid on combustion. For instance the space shuttle and the Ariane 5, generates 580 and 270 tons of concentrated hydrochloric acid, respectively, per launch (Wingborg et al., 2008). Hydrazine is highly toxic and carcinogenic (ATSDR, 1997; Ritz et al., 2006), and handling it requires costly safety measures. A less toxic monopropellant is expected to offer substantial cost savings (Bombelli et al., 2003; Palaszewski et al., 1998; Hurlbert et al., 1998). These economic benefits were analysed and quantified in a study funded by the European Space Agency (ESA) and were considered sufficiently large to support interest in the development of hydrazine substitutes and related propulsion hardware (Bombelli et al., 2004). Propellants of the future must not present major hazards to the crew or ground handling personnel. The use of green propellants would greatly reduce the risks associated with toxicity, operational handling complexity, spacecraft contamination, and hazardous contamination of the environment. Green propellants have also shown promise from a system performance and total life cycle cost perspective. One material that has the potential to replace AP as well as hydrazine is ammonium dinitramide (ADN), NH4N(NO2)2.