Experimental Modeling of Alumina Particulate in Solid Booster: Final Report

Abstract

The ESA-EMAP project (Saile et al., 2019) is dedicated to the experimental modeling of alumina particulates in solid boosters. The motivation roots in the uncertainty regarding the impact of the alumina particles emitted by the solid rocket motors (SRMs) of European launch systems on the ozone depletion in the stratosphere. This uncertainty needs to be addressed in the face of the expected growth and significantly increased number of rocket launchers as predicted in studies associated with the new space era. For this reason, the ESA-EMAP project focused on the experimental investigation of the particle formation processes and the quantification of the corresponding flow conditions by means of sub-scale tests. The particle formation was assessed from the combustion chamber throughout the nozzle to its final state as it would be expected in the atmosphere. These tests were executed with a solid rocket motor (SRM) mimicking a launch system and operating under flight-realistic conditions with an ambient flow. As it can be seen in fig. 1, this task was accomplished by integrating the rocket motor into a subsonic wind tunnel nozzle of the ’Vertical Test Section Cologne’ (VMK). Numerous measurement techniques were applied to capture the flow conditions and formation of the particles. In detail, the high-speed schlieren measurements were applied to capture the density gradients and the topology of the jet. Spectroscopic measurement methods such as UV-Vis spectroscopy, Fourier transform infrared spectroscopy, alumina emission measurement shed light on the exhaust gas composition and temperature distribution of the jet. The velocity was captured by means of particle image velocimetry, direct image particle size determination, and laser-2-focus (fig. 2). The heat release from the jet was assessed with a Gardon gauge and infrared thermography. Finally, the particle size (fig. 5) was quantified by means of measurements with an aerodynamic particle sizer and rocket plume collector (Maggi et al., 2020). In summary, a vast data base on solid rocket exhaust plume was generated. At three different planes along the path line of the particles, there is now information available on the particle size, the particle velocity, the temperature distribution, the density gradient distribution, and the gas composition of the plume. That data base provides a foundation for further analytical explorations and provides the opportunity to validate models associated with the physics of solid rocket exhaust plumes.