Evaluation of Future Ariane Reusable VTOL Booster stages

Reusability is anticipated to strongly impact the launch service market if sufficient reliability and low refurbishment costs can be achieved. DLR is performing an extensive study on return methods for a reusable booster stage for a future launch vehicle. The present study focuses on the vertical take-off and vertical landing (VTOL) method. First, a restitution of a flight of Falcon 9 is presented in order to assess the accuracy of the tools used. Then, the preliminary designs of different variants of a future Ariane launch vehicle with a reusable VTOL booster stage are described. The proposed launch vehicle is capable of launching a seven ton satellite into a geostationary transfer orbit (GTO) from the European spaceport in Kourou. Different stagings and propellants (LOx/LH2, LOx/LCH4, LOx/LC3H8, subcooled LOx/LCH4) are considered, evaluated and compared. First sizing of a broad range of launcher versions are based on structural index derived from existing stages. Ascent and descent trajectories of the first stage are optimized together in order to reach the highest payload while keeping mechanical loads at reasonable levels. Another important aspect is the aerothermal environment stressing the structure. During the re-entry boost, the first stage is immersed in the engine exhaust plume. Steady state computational fluid dynamics calculations are performed along the re-entry trajectory to characterise the flow field during retro-propulsion around the first stage. The resulting aerothermal database is coupled with a simple structural model to study the time dependent heating of the hull structure. Based on these first iteration results more detailed preliminary designs are performed in a second iteration for selected configurations: a LOx/LH2 launcher and a LOx/LCH4 launcher both equipped with gas generator engines.