Launch Emission Assessment Tool (LEAT v1.0): Part I – Development of a tool to calculate altitude-dependent rocket launch emissions for use in chemistry-climate models

Abstract. Rocket launches generate gaseous and particle emissions throughout all layers of the atmosphere, affecting both Earth's atmospheric composition and radiative balance. Emissions caused by rocket launches depend on the propellant, launch vehicle, and atmospheric conditions. To assess the atmospheric effects of rocket launch emissions, comprehensive chemistry-climate models are needed, which rely on emission inventories. These inventories need to provide detailed information on the mass profile of burned propellant in space and time, as well as the amount and chemical species emitted. However, existing emission inventories typically assume simplified burn profiles and all but one neglect the altitude dependence of post-combustion. Furthermore, the dependence of chemical reactions on engine specifics — such as engine cycle, mixture ratio, and nozzle shape — are not considered. This leads to uncertainties in the associated effects on atmospheric composition and climate. We therefore developed the launch emission assessment tool (LEAT v1.0), which allows the calculation of both the trajectory and the emission mass based on specific vehicle parameters such as the mass, staging, and geometry of the launch vehicle, as well as the propellants and engine specifics. In this paper, the underlying models and methods used for the launch trajectory and emission calculation are presented. Using LEAT, we show that launch emissions depend strongly on the launch vehicle type, engine parameters and the assumed in-mixing of ambient air during post-combustion, which determines the altitude-dependent afterburning efficiency. We also discuss different methods to calculate rocket launch emissions and compare results for selected rocket launch case studies, focusing on the calculation of the mass profile, the exhaust at nozzle exit level and final emissions after post-combustion within the atmosphere. Results from LEAT are compared with flight data for trajectories and common literature approaches for emissions. The approach also considers emissions of minor species such as OH, H2, and NO2 which are not yet covered by existing inventories but might affect atmospheric composition. Our results show that emissions of minor species are highly dependent on the chosen post-combustion efficiency. LEAT can be used to create a global, vehicle- and launch-specific rocket launch emission inventories. Additionally, uncertainties in rocket launch emissions can also be estimated. Overall, this will enable comprehensive assessments of the atmospheric effects from rocket launches using chemistry-climate models including a detailed uncertainty characterization.