Combined cryogenic insulation and thermal protection systems for reusable stages
Creators: name:  J. WILKEN 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: REUSABLE SYSTEMS
SYSTEM DESIGN
REUSABLE LAUNCH VEHICLES

description: Combined cryogenic insulation and thermal protection systems for reusable stages Jascha Wilken1, Alexander Fischer1, Henning Scheufler1, Dennis Daub2, Martin Sippel1 1 German Aerospace Center (DLR), Institute of Space Systems, Robert-Hooke-Strasze 7. 28359 Bremen, Germany 2 German Aerospace Center (DLR), Institute of Aerodynamics and Flow Technology, Linder Hoehe, 51147 Cologne, Germany Reusable launch vehicles experience a large range of thermal boundary conditions during their mission, ranging from the temperatures of the propellants over the heat loads encountered during reentry to the vacuum of space. The range of temperatures is extended substantially when using deep cryogenic propellants. This necessitates the use of external thermal protection and cryogenic insulation subsystems in order to keep all elements of the vehicle in their functional temperature range. However, the operational experience with reusable versions of these subsystems is limited, especially for the cryogenic insulation. The total number of operational reusable launch vehicles (RLV) in the history of spaceflight is small. None of them (Space Shuttle, Energia Buran, Falcon 9 booster stage) have made use of a cryogenic tank insulation on their reusable stages. The US Space Shuttle and the Soviet Buran were orbital stages without any large cryogenic tanks. The Falcon 9 is a typical booster stage with integral tanks, however, using the propellant combination LOX-RP-1, which has a heritage of being flown on rockets without cryo-insulation (e.g. Atlas, Saturn V, Soyuz). Therefore, no practical experience with an operational RLV implementing reusable cryogenic tank insulation exists. For future RLVs however, the use of cryogenic fuels has large benefits with regard to vehicle size, mass and environmental impact. For a winged system the cryogenic insulation has to be integrated with the thermal protection system onto the propellant tank surface, imposing new requirements on both. Within the DLR this topic was first explored within the AKIRA project, which investigated selected technologies that were deemed critical for operational reusable booster stages but are not covered by the ongoing flight demonstrator projects of the DLR. Different design options for integrating the cryogenic insulation and external thermal protection onto the propellant tanks were investigated and a design including a purge gap in order to avoid ice formation within the thermal protection system was chosen for further testing. Segments meant to represent a slice of an RLV tank were manufactured and equipped with the selected cryogenic insulation and thermal protection system. These test objects were then subjected to launch pad scenarios that correspond to potential launch sites for European launchers on one side and cryogenic temperatures on the other. Other versions of the representative test objects were also tested under the thermal loads expected during reentry. The ongoing status of the AKIRA project was presented previously [1][2][3][4], this paper contains the final results, with a focus on the experimental campaign investigating the behavior of the system at various launch pad conditions including the successful operation of the purge gap. Finally, this paper will contain an outlook and summary of the current status of the TRANSIENT project, started in 2020 to further investigate and test the derived designs for reusable thermal protection and cryogenic insulation under thermal as well as mechanical loads. References [1] Rauh, C., Reimer, T., Sippel, M., Investigation of an RLV Cryogenic Tank Insulation Including a Purge Gap System, International Conference on Flight Vehicles Aerothermodynamics and Re-entry Missions Engineering (FAR 2019), Monopoli 2019 [2] Darkow N. et al: Concept Development of a Cryogenic Tank Insulation for Reusable Launch Vehicle, 8th European Conference for Aeronautics and Space Sciences, Madrid 2019 [3] Sippel, M. et al: Enhancing Critical RLV-technologies: Testing Reusable Cryo-Tank Insulations, 70th International Astronautical Congress, Washington 2019 [4] Sippel M. et al.: Focused research on RLV-technologies: the DLR project AKIRA, 8th European Conference for Aeronautics and Space Sciences, Madrid 2019