Impact of engine cycles, propellants and recovery methods on the launch exhaust profile of reusable booster stages

Kurzfassung

The rapid growth of spaceflight is driven by new engine cycles, propellant combinations, and recovery methods, enabling a new era of reusable launch systems. At the same time, there is an increasing effort to assess the environmental impact of spaceflight. Especially the emissions during the launch itself are a focus of the research, as they are essential to assess the effects of spaceflight on atmospheric chemistry, ozone depletion, and climate change. This study combines these two developments by investigating the impact of engine cycles, propellants, and recovery methods on launch exhaust. The paper analyzes exhaust species, quantity, and distribution generated by different propulsion technologies, including staged combustion and gas-generator cycles, as well as propellants such as LOX-LCH₄, LOX-RP-1, and LOX-LH₂. Additionally, the study examines how first-stage recovery methods influence the overall exhaust profile, comparing vertical takeoff, vertical landing (VTVL) and vertical takeoff, horizontal landing (VTHL) approaches with expendable reference configurations. The European Next Reusable Ariane (ENTRAIN) reusable booster configurations developed by the German Aerospace Center (DLR) are used as case studies, as they are designed for the same use case, of transporting 7.5t of payload to GTO, allowing direct on-par comparison of the exhaust. Furthermore, they directly provide the detailed aerodynamic, mass and propulsion models, that are needed for the simulation of the exhaust profile generated during ascent and booster return. The investigation of spaceflight´s direct atmospheric impact is still at an early stage. Many phenomena like the creation of soot and the post-combustion between the exhaust and surrounding atmosphere are still largely unknown and the exact effects of many emissions into the high atmosphere stay highly debated. The DLR S3D initiative is currently researching these fields and develops and expands climate and post-combustion models that will be shown in later publications. By estimating key pollutants such as CO₂, H₂O and soot, for reusable launcher concepts this study provides valuable first insights into the trade-offs between performance, reusability, and environmental emissions.