Key Technologies for Retro Propulsive Vertical Descent and Landing – RETALT – An Overview

Since SpaceX successfully demonstrated the vertical landing of launcher first stages and made this way of returning them to earth a routine operation with over 100 successful landings after 6 years, the interest in Europe to develop the key technologies for this approach has drastically increased. It not only promises large cost savings, but also reduces space debris and is more environmentally friendly as no debris parts fall back to the earth’ surface. The first project funded by the EU commission to investigate key technologies for reusable launch vehicles applying retro propulsion is RETALT (RETro propulsion Assisted Landing Technologies) which received a funding of 3 million Euros in the frame of Horizon 2020. The consortium consists of the German Aerospace Center (DLR), CFS Engineering (CFSE), DEIMOS Space, MT Aerospace, Almatech and Amorim Cork Composites. The key technologies studied in detail are Aerodynamics, Aerothermodynamics, Flight Dynamics and GNC, Structures, Mechanisms, TVC, and TPS. Detailed wind tunnel test series were performed at DLR and were combined with Computational Fluid Dynamics (CFD) studies by DLR and CFSE to generate a sound basis for the understanding of the complex aerodynamic and aerothermodynamic phenomena at play for such configurations. MT Aerospace designed the structure of the aerodynamic control surfaces and landing legs, and closely worked together with Almatech who designed the mechanisms for these applications. Demonstrators were built in a scale of 1/5 of the aerodynamic control surface and the landing leg, and the landing leg was tested in a drop tower. Amorim Cork Composites developed a new cork based TPS material specifically for the application on retro propulsive landing configurations with a focus on an easy applicability of the material. The material was tested in the arc heated facility L2K at DLR. In this paper a detailed overview of the studied technologies will be given and the interplay between the different disciplines will be highlighted. Design challenges for launcher configurations descending and landing through a deceleration using the engines will be discussed. An outlook for the potential for future research and developments will be given