Particle Collection in High-Enthalpy Supersonic Flows: Objectives and Challenges

The rapid growth of space-related activities over the past decade has prompted increasing attention to their potential environmental impacts, particularly those associated with launch and atmospheric re-entry events. These processes release high-temperature gases laden with solid and liquid particles spanning a wide size range—from nanometric to millimetric—across a broad spectrum of altitudes. Despite their potential relevance to atmospheric chemistry, radiative balance, and long-term sustainability of space operations, the physical and chemical impacts of such particles on the atmosphere remain poorly understood due to the scarcity of dedicated experimental data.

To address this gap, the German Aerospace Center (DLR) is conducting a multidisciplinary research effort aimed at assessing the atmospheric impact of space activities. Within this framework, the Supersonic and Hypersonic Technologies Department in Cologne is developing a particle collection system certified for high-enthalpy environments. The collector is intended to enable in-situ sampling of particles generated by rocket motor exhausts as well as by material ablation during hypersonic flight and atmospheric re-entry. Subsequent post-flight laboratory analyses of the collected samples will support the generation of a comprehensive dataset, contributing to a deeper understanding of particle properties and their implications for environmental sustainability.

Experimental investigations of particle-laden high-enthalpy flows have been carried out at the arc-heated wind tunnel L2K and in the vertical test section VMK in Cologne. A combination of intrusive and non-intrusive diagnostic techniques has been employed to characterize suspended particulate matter. The L2K facility has been used to study particle-laden flows in CO₂ atmosphere, while the VMK facility has focused on assessing the environmental impact of small-scale solid rocket motors.

This contribution presents recent progress and remaining experimental challenges in the design of a high-enthalpy particle collector, alongside the current state of the art in multiphase flow diagnostics within the department. The methodologies and findings discussed are also relevant to planetary science applications and may, in the future, be extended to the characterization of Martian atmospheric entry conditions, including scenarios involving global dust storms.