Preliminary Analysis of Winged Reusable First Stages in Two- and Three-Stage to Orbit Configurations (RLVC4 Gas Generator)

Abstract

The realization of reusability for launch vehicles is expected to lower launch costs – subsequently enabling a thriving space industry. Therefore, several high-performance semi-reusable launch vehicle concepts are designed and investigated based on the premise of potential implementation into the Ariane program by using stage and engine parts from future Ariane 6 hardware. These vehicles are imagined as a combination of a winged reusable booster and one to two expendable upper stages for injection into a geostationary transfer orbit (GTO). First stage reusability is achieved by the ”In-Air Capturing” method proposed by DLR which is currently studied in the H2020 project FALCon. A payload mass of approximately 14 tons into GTO is pursued, consequently surpassing the anticipated payload mass of the Ariane 64. This paper presents the current technical status of the different investigated RLV configurations including geometrical shape, layout, propellant system, propulsion, aerodynamics and structural layout. Additionally, the designs shall be critically analyzed regarding their suitability and applicability for a potential implementation into the European launcher roadmap. The rocket propulsion for the first two stages is either based on a 2000-2500 kN full-flow staged combustion LOX/LH2 engine, based on the SpaceLiner Main Engine, or a proposed variant of the European Prometheus 1000 kN gas-generator engine which can be operated both with LOX/LH2 and LOX/LCH4. The third stage is in all cases powered by the Vinci closed expander cycle LOX/LH2 engine which will be used on the upper stage of the Ariane 6. Two variants with FFSC engines are designed which differ mainly in the design of the wings and the aerodynamic performance. Because of the versatility of the gas-generator engine, multiple designs are analyzed: A pure LOX-hydrogen version, a pure LOX-methane version as well as a hybrid version combining a LOX-methane RLV-stage and a LOX-hydrogen expendable second stage. Within the design space of these combinations, the density of the propellants and consequently size of the vehicle as well as the mass distribution along the winged stage play a crucial role in the determination of a stable re-entry performance from hypersonic down to subsonic velocities. First stage separation velocities of not more than 2.5 km/s are targeted in order to limit the re-entry loads. Wings with a double-delta geometry and winglets are the baseline for the RLV-stage. In order to safely perform the ”In-Air-Capturing” maneuver, the wings are designed for a high trimmed lift-to-drag ratio of larger than 6. Two wing configurations for the FFSC engine variants are analyzed – a fixed and a foldable wing. The gas generator versions are all equipped with a fixed double-delta wing. However, further design options such as the addition of canards or an enlarged bodyflap have been exploited to achieve maximum aerodynamic performance throughout the whole mission.