Investigation of insulation and thermal protection systems for reusable cryogenic stages

Abstract

Reusable launch vehicle stages encounter large heat fluxes during their mission, especially during reentry. For winged stages decelerating through aerodynamic forces this means, large areas of the of the vehicle have to be covered with a thermal protection system (TPS). For reusable systems with integral cryogenic tanks the TPS is exposed to the cryogenic temperatures of the propellants within. If the propellant tanks are covered in cryogenic insulation, required for hydrogen-fueled stages, the TPS and cryogenic insulation cannot be treated as separate technical domains but have to be designed and integrated jointly, considering the boundary conditions of each other. Additional complexity is introduced by the fact that no operational experience for orbital stages exist for the reuse of cryogenic insulation. Within the DLR this topic was first explored in the AKIRA project, and the work is being continued within the currently ongoing project TRANSIENT. The design of the combined subsystem from AKIRA is further refined and applied to both metallic and composite tank materials. In addition to the thermal loads previously considered, the mechanical loads acting on the vehicle throughout the mission are assessed and incorporated into the design of the experimental devices. For both cases segments meant to represent a slice of an RLV propellant tank are being manufactured and equipped with the combined cryogenic insulation and thermal protection systems and will be tested under representative loads for up to 50 cycles. In addition to the thermal loads, mechanical loads will also be applied to the test objects. The current status of the integration and preparation of the test objects is shown and the planned experiments discussed.