European Next Reusable Ariane (ENTRAIN): A Multidisciplinary Study on a VTVL and a VTHL Booster Stage

The recent success of the emerging private space companies SpaceX and Blue Origin in landing, recovering and relaunching reusable first stages have demonstrated the possibility of building reliable and low-cost reusable first stages. Thus, the importance for assessing whether such a reusable launch vehicle (RLV) could be designed and built in Europe has increased. Due to this renewed interest in RLVs, the German Aerospace Center (DLR) has initiated a study on reusable first stages named ENTRAIN (European Next Reusable Ariane). Within this study two return methods, respectively vertical take-off, vertical landing (VTVL) and vertical take-off, horizontal landing (VTHL) with winged stages, are investigated. The goal is to assess the impact of the return method on the launcher and to conduct a preliminary design of a possible future European RLV. In the first part of the study, which ended in 2018, a broad range of possible launcher designs considering different propellant combinations, engine cycles and staging velocities were investigated and compared. By the end of this part, the most promising VTVL stage such as the most promising VTHL stage were selected to be investigated in more detail. Those two concepts were subjected to a preliminary system design and performance estimation, coupled with an aerodynamic and aerothermodynamic investigation of the re-entry loads and their impact on the structure. Furthermore, analyses of the dynamic behavior of descending RLV stages are considered. With the know-how gained within this study, the design of both launchers shall be enhanced to a level that brings it closer to a viable future reusable European launcher