A life cycle perspective of the climate forcing from black carbon emissions of Starship and Falcon 9 launchers

Kurzfassung

The Earth is currently experiencing a significant growth of the space industry resulting from the introduction of cheaper reusable launch vehicles and broad range of new space applications. In parallel, the world is experiencing a severe climate crisis as a result of land use practices and anthropogenic emissions of greenhouse gases (GHG) and aerosols such as black carbon (BC). As a key component of the global economy and the only human activity emitting in all atmospheric layers, the space industry is at an inflexion point where it could become a significant driver of global climate change, or a unique tool to help the world understand, adapt or even de-carbonize the energy system. BC emissions from spaceflight activities have been analyzed in the past with General Circulation Models (GCMs) showing potentially significant radiative forcing in the stratosphere. Given the potential significant growth in intense space activities made possible by heavy launchers (as Starship), it is important to further assess these emissions within a life-cycle perspective, merging with the developments within the space based Life Cycle Assessment(LCA) communities to further understand its role in future climate change, identify the suitability of different launch vehicle technologies and enable a sustainable design of spacecrafts which considers the associated impacts in the high atmosphere. This study firstly derived GWP like metrics from black carbon and other rocket exhaust emissions in the stratosphere from past literature studies, which can be used to compare the climate change impacts of BC emissions with life cycle CO2 emissions within an LCA process. After it, the BC exhaust emission profiles from different launch scenarios with Starship and Falcon 9 vehicles were obtained with an empirical plume post-combustion model, showing a peak in emissions both for ascent and return at around 50 km of altitude, in contrast with past studies. These results were then used within the asteroidImpact GCM model to explore the potential climate forcing signature identified in past studies. Nevertheless, no significant impact was obtained, which might be a consequence of different modelling parameters as the assumed emission altitudes, pulse emission scenario, particle size distribution, and reflectivity properties. These results can be augmented with future studies on the atmospheric perturbations of different propulsive technologies, as those resulting from stratospheric water emissions, NOx and induced cloudiness. The metric derivation process may be extended for stratospheric ozone loss from emitted launch vehicle species for the successful development of an LCA process for space transportation which can ensure eco-design while preventing burden shifting.