Numerical Investigation of Ground Heat Fluxes from Supersonic Jet Impingement during Vertical Landing of a Reusable First Stage Demonstrator

Abstract

Several actors in the space trasport sector are moving towards reusable launch vehicles (RLV) for the first stages of launchers, among them SpaceX with the Falcon 9 and Rocket Lab with the Neutron. Also the current European long term strategy is aiming towards reusability with plans for THEMIS and Ariane Next. In accordance with this strategy the German Aerospace Center (DLR) has entered into a collaboration with the Japan Aerospace Exploration Agency (JAXA) and the French Space Agency (CNES) for the development of RLV relevant technologies in the frame of a vertical take-off and vertical landing (VTVL) reusable subscale launcher first stage demonstrator - the ``Cooperative Action Leading to Launcher Innovation in Stage Toss back Operations'' (CALLISTO). Generally a VTVL first stage will return to the launch pad utilising retro-propulsion and an Approach and Landing System (ALS) with deployable landing legs. The landing leads to new additional aerothermal design questions compared to traditional launchers. It has been observed, that part of the critical heat loads are happening after touch down and engine shut off. These are caused by heat radiation from the launch pad to the vehicle structure. This can affect an ALS built from carbon fibre, which is prevented from cooling down. The heat fluxes, therefore, influence the structural design and the thermal protection system (TPS) of the ALS. The impact is even more relevant to experimental vehicles if hopper flights are part of the program. To aid the development of reusable launch vehicles in the VTVL configuration we analyse the heat fluxes onto the ground for an impinging supersonic jet from a liquid hydrogen and oxygen engine. The analysis is based on Reynolds averaged Navier-Stokes computational fluid dynamics. We look at some modelling choices and we investigate the influence of the ground distance on the heat flux distribution.