Experiments for collection and characterization of particles exiting from solid propellant rocket nozzles

Metals in solid propellants are used to improve specific impulse and increment the energy density. Their combustion generates condensed products that move along the motor chamber and are expelled through the nozzle. The discharge of liquid or solid particles across the gas dynamic nozzle of large boosters is not only a matter of specific impulse loss. Recent climatological studies are addressing possible short and long term environmental effects that may be attributed to space launch activity by large launchers. In this respect, the knowledge of plume content and, specifically, of physical, chemical, and morphological properties of the exhausted particulate is needed. In the frame of the EMAP (Experimental Modelling of Alumina Particulate in Solid Booster) project, an activity financed by the European Space Agency, the Space Propulsion Laboratory (SPLab) of Politecnico di Milano developed a collection method and an analysis protocol for the characterization of the particles contained in the rocket plume. The collection is performed by an intrusive probe capable of capturing the particles directly from the nozzle exit and quenching them. The post-collection protocol enables size measurement, chemical characterization, and morphology observation. In this paper an overview of the collection and analysis activity is presented, along with the final results that were achieved by analyzing the plume of solid propellant rocket motors.