As the space industry experiences rapid growth and the development of reusable launch vehicle (RLV) technology, it is crucial to assess the environmental footprint of these systems across their entire life cycle. While RLVs offer the potential for reduced costs and increased launch frequencies, they may also contribute to significant atmospheric pollution and climate impacts. A comprehensive life cycle assessment (LCA) is necessary to quantify the environmental burdens associated with RLV fleets and identify key design drivers for mitigating adverse effects.
Methodology
Researchers from the German Aerospace Center (DLR), University of Strathclyde, and University of Dresden collaborated to conduct an LCA of different RLV fleets designed to serve the forecasted European space market. The study utilized a space-specific LCA approach to evaluate the climate impact, water depletion, and land use of these fleets over their cumulated lifetime of 20 years.
The RLV fleets assessed included ballistic vertical take-off and vertical landing (VTVL) vehicles with hydrogen (LH2) or methane (LCH4) propulsion, as well as winged vertical take-off and horizontal landing (VTHL) vehicles using LH2. Each fleet was composed of multiple launch vehicle types tailored to accommodate the same set of missions, with varying degrees of reusability and staging configurations.
The LCA methodology incorporated the Strathclyde Space Systems Database (SSSD) v1.0.3, with Ecoinvent 3.9.1 as the background inventory. The study considered five midpoint impact categories: water use, land use, and three for climate change (GWP100, GWP20, and GTP100). Characterization factors (CFs) for aviation and high-altitude emissions were applied to account for the unique impacts of rocket exhaust in the upper atmosphere.
Results
Fleet Assessment
The LCA results revealed that the LH2 fleets had the lowest impact across all categories, indicating that propellant choice is a primary factor in the environmental performance of RLVs. The RLVC4 VTHL fleet achieved the best overall performance, followed by the VTVL LH2 fleet with a 46% higher GWP100 and approximately 32% increased water and land use. In contrast, the VTVL LCH4 fleet exhibited a climate impact 2-5 times larger than the LH2 fleets, partially due to black carbon (BC) emissions, as well as 90% higher water and land use compared to the RLVC4 fleet.
When considering high-altitude CFs for BC, water, and aluminium oxide emissions in the stratosphere, the GWP100 climate impacts increased by up to 1000 times, reaching magnitudes comparable to the annual emissions of global commercial aviation. This finding highlights the potential for RLV emissions to exceed Earth’s carrying capacity defined by planetary boundaries, particularly for LCH4 fleets.
Contribution Analysis
A contribution analysis of the life cycle impacts revealed that recurrent activities, such as launch emissions and recovery processes, constitute a significant share of the total impact. Propellant-related impacts were also substantial, with decontamination and handling activities accounting for approximately two-thirds of their impact. However, the underlying inventory data may overestimate these impacts due to its bias towards spacecraft and upper stages, which typically employ hazardous fuels with complex handling requirements.
The launch event itself appeared to have a small impact for LH2 vehicles but dominated the footprint of LCH4 vehicles due to BC emissions. However, the exhaust emissions for methalox engines are subject to considerable uncertainty, and the study’s estimates may underestimate the climate impacts of BC emissions at higher altitudes.
Sensitivity Analysis
A sensitivity analysis of the reuse rates demonstrated that while reusability can reduce environmental impacts by 30-40% for LH2 fleets and 20% for LCH4 fleets, the overall reduction quickly settles as the number of reuses increases. This is due to the significant contribution of recurrent activities to the total impact. In fact, reusability may not always lead to a more sustainable outcome from a carbon footprint perspective, as it introduces additional recovery, refurbishment, and maintenance processes while reducing payload performance.
The study also investigated the sensitivity of the results to different CFs, revealing that the relative advantage of the RLVC4 fleet over the VTVL LH2 fleet is negated when accounting for the demised aluminium oxide emissions from its higher total dry mass. Furthermore, the climate impact of the LCH4 fleet was found to be 100-250% higher when assessed within a 20-year time horizon, emphasizing the importance of the chosen climate metric and time scale.
Discussion
The LCA results underscore the complexity of assessing the environmental sustainability of RLVs and the need for a comprehensive, life cycle perspective. While propellant choice emerges as a critical factor, with LH2 fleets demonstrating lower impacts than LCH4 fleets, the study also highlights the substantial influence of high-altitude emissions on the overall climate footprint.
The contribution analysis reveals that recurrent activities and propellant-related impacts dominate the life cycle impacts, suggesting that efforts to improve environmental performance should focus on these areas. However, the study also acknowledges the uncertainties associated with the underlying inventory data, particularly regarding the handling and decontamination requirements for different propellants.
The sensitivity analyses demonstrate the importance of considering reuse rates, CFs, and climate metrics when assessing the environmental sustainability of RLVs. The findings suggest that reusability alone may not guarantee a more sustainable outcome, as it can introduce additional processes that offset the benefits of reduced material consumption. Moreover, the choice of CFs and climate metrics can significantly influence the relative performance of different RLV fleets, underscoring the need for further research to refine these factors and reduce uncertainties.
Conclusion
This LCA study provides valuable insights into the environmental footprint of RLV fleets and the key drivers of their impact. The results highlight the importance of propellant choice, high-altitude emissions, and recurrent activities in determining the overall sustainability of these systems. However, the study also reveals significant uncertainties and the need for further research to refine the underlying data, characterization factors, and climate metrics.
To support eco-design efforts in the space industry, it is essential to develop a comprehensive sustainability assessment framework that considers the full life cycle of RLVs and the unique impacts of their emissions in the upper atmosphere. This framework should incorporate refined LCA methodologies, climate simulations, and robust sustainability metrics to enable informed decision-making and drive the development of more environmentally sustainable launch systems.
As the space industry continues to grow and evolve, it is important that environmental considerations are integrated into the design and operation of RLVs. By understanding the life cycle impacts of these systems and identifying opportunities for improvement, the industry can work towards mitigating its environmental footprint and ensuring the long-term sustainability of space activities.
