An Experimental Assessment of Soil Contamination by Composite Solid Rocket Propellants

Since the beginning of the space era, solid propulsion has been considered an important technological asset for heavy launchers. Compositions based on ammonium perchlorate represent the current state of the art. The combustion of this class of propellant releases chlorine-based products, though. A consistent fraction of propellant combustion occurs in the troposphere and its exhaust products fall back on ground, due to atmospheric recirculation and rain. On-ground near-field collections from real launch campaigns have been mainly focused on chlorine derivatives and solid particulate. From these early studies, it appeared that concentration and area of influence were sensitive to environmental conditions and wind directions. To the author’s knowledge, only one systematic study on soil analysis after exposure to solid propellant exhaust has been made available to the open literature. The present paper is reporting the results of an experimental campaign which analyzed the pollutant content of a reference soil, after the exposure to the combustion products of a standard aluminized composite propellant and of a neutralized formulation containing metallic magnesium. The analyses covered several aspects of possible contamination, including hydrocarbons, metals, and acid content. Results showed that acidification does not seem to represent a problem, thanks to soil buffering capacity. An incremented presence of some metallic elements was traced back to contamination of ingredients. In general, under the tested conditions, significant markers of pollution were not identified. The most relevant environmental impact of solid propulsion on the terrestrial environment seems to consist in a non-permanent effect of acidification of the soil. This effect can be overcome once a neutralized propellant