ADN-based Formulations Analysis for Green Solid Propellants
Creators: name:  L. POZZONI 
name:   C. PARAVAN 
name:   L. GALFETTI 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: PROPULSION PHYSICS
NEW PROPELLANTS

description: Space industry and space propulsion, in particular, are deeply affected by the growing awareness about the values of ecology and the needs of environmental friendly technological developments.. Current state-of-the-art technologies for both liquid and solid propellants employ formulations that produce environmental hazardous and toxic products. In particular, liquid storable combinations for mono- and bi-propellants mainly rely on hydrazine or hydrazine-derived substances, which are proved to have carcinogenic implications. Regarding solid propulsion, the oxidizer in the most common formulations is ammonium perchlorate (AP), which is toxic and whose production leads to contamination of groundwater. Moreover, combustion of AP-based propellants produces great amounts of hydrogen chloride, a substance responsible for acid rains and ozone depletion. It is therefore necessary to investigate materials for the so called green propellants. Over the last decade, much research has been conducted in order to develop such materials, in particular in the context of several European Committee funded projects, like HISP and GRAIL. This paper provides a preliminary implementation of green propellants in a solid rocket booster. One of the most promising substances for a possible application in both liquid and solid green propellant is ammonium dinitramide (ADN). Regarding liquid systems, ADN-based formulations proved to have the following advantages with respect to hydrazine: an easier handling, which leads to a lower overall cost of the entire life cycle, better performance in terms of specific impulse and a higher density [1]. On the other hand, for solid propulsion, the challenge of finding a satisfactory composition that could match the requirements to start an effective usage is still open. Several issues, such as incompatibility with isocyanates-based curing agents normally employed in the most common binders, high pressure exponent and high impact and friction sensitivities, affect ADN-based propellants [2]. However, the potential performance advantage and absence of polluting combustion products that ADN would bring are worthy of the effort of studying it. Within the present paper, after an introduction about green-propellants and ADN characteristics, three different ADN-based formulations are discussed. The first two use Glycidylazide polimer (GAP) as binder and a double-oxidizer configuration with ADN/HMX in the former [3] and ADN/ammonium nitrate in the latter [4]; the third formulation [5] contains a double-binder matrix of GAP and Desmophen D2200. Moreover, a further state-of-the-art composition based on the one of Ariane 5 boosters (EAP) is considered as a reference for comparisons. Analysis of the thermophysical properties, performance and chemical composition of the combustion products of each mixture is performed with the NASA Cea code. The obtained results are then used to compute the most important features (mass, volume, combustion chamber pressure etc.) that a solid rocket motor employing each of the investigated formulations would require to match the thrust mission profile of the EAP boosters.