Development of cryogenic upper-stage concepts for future European launchers after Ariane 6

Abstract

This thesis work on the development of concepts for future European launchers’ cryogenic upper stages proposes three conceptual architectures which are modelled in an iterative fashion. The upper stage concepts are designed for use in combination with the reusable main stage concept RLVC4-III-B by the German Aerospace Center, which is a winged first stage for horizontal in-air recovery with 340 tons of ascent propellant and 59.5 m in length. The upper stage concepts are (1) single-staged with carbon-fibre structures, (2) two-staged with metallic structures and (3) twostaged with carbon-fibre structures. The design payload target is at least 7.5 tons to GTO. A variety of potential innovation approaches aimed at different sub- or primary components of cryogenic upper stages is presented towards their technological readiness. Promising and realistic innovations, which are expected to have a measurable and positive impact on an architectures’ mass, are included in specific upper stage architectures and accounted for throughout the modelling process. The architectures’ performance, structural and aerodynamic analysis is described and discussed. The models are initially foreseen to have ratios of ascent propellant to wet stage mass of (1) 89 %, (2) 85 % and (3) 87 %. The final, validated models show propellant ratios of (1) 88 % , (2) 87.3 % and (3) 87.2 % after consideration of the designated innovation approaches. The second concept, which shows a large deviation from the expected propellant ratio for which it was pre-dimensioned, reaches a low dry mass due to the implementation of hydrogen tank self-pressurization, an advanced propellant management device, wireless avionics and Aerogel as insulation material. Ascent simulation and optimization has been performed for the upper stage concepts in combination with the reusable RLVC4-III-B as main stage. All launch arrangements have gross lift-off masses below 600 tons. The integrated systems show payload performances of (1) 10.4 tons, (2) 19.3 tons and (3) 18.5 tons to GTO with a perigee of 250 km. The second stages of the two-staged architectures, which carry propellant masses similar to the Ariane 6 upper stage, are additionally simulated in combination with the Ariane 6 main stage and 4 boosters, reaching (2) 24.4 % and (3) 28.9 % higher GTO payload than with the nominal upper stage. The concepts developed in this thesis are optimized towards minimum total lift-off mass with the RLVC4-III-B as reference main stage, while cost and manufacturability are disregarded. Basic stage dimensions and architectural decisions are frozen early on in the iterative design process. Taking these aspects into account in an extensive trade-off analysis would increase the relevance of the development of modern launcher stage concepts and is proposed as potential future work.