Options for future European reusable booster stages: evaluation and comparison of VTHL and VTVL return methods

In the past, the majority of system studies on reusable space transportation performed within Europe focused on concepts relying on lift-generating wings for recovery. Recently, vertically landing concepts similar to those deployed successfully by SpaceX have moved to the center of technical attention. Both recovery and landing strategies have their pros and cons and it is not obvious what would be a sound choice for Europe. Therefore, the German Aerospace Center DLR initiated a parametric system study, named ENTRAIN, that evaluates the impact of different return options on the launcher design on a technical level: the vertical take-off, vertical landing method (VTVL) as used by SpaceX compared to the vertical take-off, horizontal landing (VTHL) method as used for the Space Shuttle. Within this study, launchers were designed using different propellant combinations, staging velocities and engine cycles. The designed launchers are evaluated in this paper regarding performance, technical difficulties, operational aspects, size, mass and complexity.