Concept Development of a Cryogenic Tank Insulation for Reusable Launch Vehicle

Kurzfassung

The development of insulation is of crucial importance for spacecraft with cryogenic tank systems. During the fueling procedure with cryogenic liquids the outer tank shell is cooled down and subsequently, as a reaction its surrounding air. The presented work is part of the AKIRA project performed by the German Aerospace Center (DLR). It is based on the Space Liner (SL7-3) concept as reference configuration, which uses a reusable booster stage with a liquid hydrogen/oxygen engine. This study aims to contribute in the development of a reusable insulation system for both, the liquid hydrogen and liquid oxygen tank. For the design of the insulation system, different common insulations types are investigated about their applicability for a RLV. The SL7-3 flight trajectory surface temperatures higher than 1000 K are expected to occur while spacecraft re-entry, which requires a proper Thermal Protection System (TPS). To achieve these temperature requirements, the thickness of the insulation increases and leads into a higher structural mass. To tackle this problem, a Purge Gap between the cryogenic insulation and the TPS is investigated. Purging a gap between the insulation and the TPS with a dry gas provides a small excess pressure that prevents humid air from entering into the system. Thus the total thickness of the insulation system and consequently the structural mass can be reduced. In order to support the design process, 1D-tools were developed for the calculation of transient heat conduction and the temperature profile evolution in the insulation system during the whole flight trajectory. Experimental investigations have been carried out to observe the long-term stability for different types of insulation materials. An experimental setup was developed and serval insulation samples with a 50 mm diameter are tested A cold head system is used which is able to cool down the samples to a temperature of about 20 K. Up to this investigation show that commercial -of the shelf- insulation foams look promising in withstanding typical lifecycles of a RLV, such like the SL7-3.