Building an aerodynamic model of a vertical landing reusable launcher based on CFD and wind tunnel experiments in SALTO and CFD4SALTO

Since the Falcon 9 first stage successfully landed the first time in 2015, the perception of reusability of launchers has drastically changed. While it was formerly considered a costly, complex and unprofitable solution, it is now seen as indispensable for the cost effective and environmentally friendly space transport. In this context, the SALTO (reusable Strategic Space Launcher Technologies & Operations) project, funded by the European Union in the frame of the Horizon Europe programme, is supporting the ESA Themis programme in which a demonstrator for a vertically landing launcher first stage is built. A first version for this demonstrator is propelled by one Prometheus engine with about 120 t thrust and performs simple trajectories. This version is called T1H, where the H stands for the “Hop Test” to be performed. A later version, called the Themis 3 or T3, shall have 3 engines and perform more complex flight trajectories. In SALTO the Hop Test of T1H is performed and technologies for the T3 vehicle are matured. In the ESA FLPP project CFD4SALTO, CFD computations for the generation of the aerodynamic databases of the T3 vehicle are performed and the extrapolation of wind tunnel experiments to flight are investigated. The task of the DLR in SALTO is, among others, the aerodynamic design of the T3 vehicle. This paper summarizes how the aerodynamic model of the T3 vehicle is set up. First the strategy for the aerodynamic modelling is described. Then, the various flight configurations are defined. Consequently, the strategies and mathematical formulations are elaborated which are applied to reduce the large amount of necessary data points. Afterwards, low-fidelity computations (generated in SALTO) and high-fidelity computations (generated in CFD4SALTO) are compared to show to which extent simplified modelling approaches can be used for the sizing and aerodynamic design, but to also highlight their limitations. Lastly, the paper discusses first wind tunnel experiments performed in the Trisonic Wind Tunnel Cologne (TMK) for the assessment of the aerodynamic performance of the configuration and for the verification of the modelling approaches. Index Terms— Reusable Launch Vehicle, Retro-Propulsion, Wind Tunnel Tests, CFD, Aerodynamics, SALTO.