CORDIS - EU research results

Retro Propulsion Assisted Landing Technologies

Periodic Reporting for period 2 - RETALT (Retro Propulsion Assisted Landing Technologies)

Reporting period: 2020-03-01 to 2022-08-31

RETALT (RETro propulsion Assisted Landing Technologies) is a European project which got funded with 3 Mio. € by the European Commission in the frame of Horizon 2020. The partnering organizations are the DLR (Germany), CFS Engineering (Switzerland), DEIMOS Space (Spain), MT Aerospace (Germany), Almatech (Switzerland) and Amorim Cork Composites (Portugal).

During the 3.5 years of the project lifetime the consortium investigated the areas of aerodynamics, aerothermodynamics (i.e. the temperatures that evolve at the surface of the vehicle during flight), flight dynamics, guidance, navigation and control, and advanced structural parts, materials and mechanisms. For this purpose, two types of rocket launchers were investigated which both start and land in an upright position. Up to now, orbital heavy lift rockets are only used once. This is one of the reasons for high launch costs. Landing a rocket and reusing it afterwards has the potential of big cost savings. One of the rockets investigated has two stages and is similar to conventional rockets like the Falcon 9 or the Ariane 5 launcher. For this launcher only the first stage will be landed again. The second launcher has only a single stage. It was designed for smaller payloads and when returning it brakes not only with retro propulsion but also with the aid of a large aerodynamic base surface at the bottom.

These rockets will not really be launched; however, they were used as the reference configurations for the investigation of the different technologies in the project. Aerodynamic wind tunnel experiments, numerical simulations and ground tests of several components served to verify the outcomes of the project.

The project started in March 2019 and ended in August 2022. More information on the project can be found on The publications can be found on
The first step of the project was the design of convergent configurations (or rockets) that combines the technologies that shall be investigated in the project. Therefore, their general design was developed (which Engines to be used, which masses have to be lifted etc.) and basic aerodynamic properties were determined. After that, some trajectories were simulated to see how far the rocket can get and how much mass it can deliver.

With the defined reference rockets, work started on the structural design of the landing legs and the wings (or aerodynamic control surfaces) which are needed to steer the rockets to the ground and land them safely. At the same time, investigations were performed on the thermal protection system (TPS) for the forward-facing base plate of the rockets, on a mechanism to steer the landing rockets with the engines (TVC) and on a control system for the landing approach. Furthermore, the aerodynamic characterization of the rockets was refined.

Then aerodynamic tests were performed in the wind tunnels at DLR in Cologne, were the reentry burn was simulated with cold and hot air and the landing burn was simulated with air and by a combustion of hydrogen and oxygen in the wind tunnel model. The material for the thermal protection system was tested in an arc heated facility (L2K) at DLR in Cologne. Also a fin was built and a landing leg was built and tested in a drop tower to see how the actuators and structures behave under load conditions. Furthermore, the guidance, navigation and control algorithms were improved over the project in several loops.
Once reusability has become the state-of-the-art in Europe it will not only impact the scientific community and space technology industry but also the European society as a whole, as for modern societies access to space is indispensable. Many applications in the everyday lives of the citizens of the European Union rely on space technologies. Modern communication systems, navigation, weather forecasts, monitoring and forecast of global climate change, are only some of many applications of these technologies. Decreasing costs for space transportation directly impacts the society as it directly influences the costs for these services.
Research activities in space (e.g. on the ISS) are also directly influenced by the space transportation costs. This research is crucial for the society, as it is often directly related to human lives (e.g. in space medicine). By reducing costs for space research, RETALT directly contributes to better lives for the European citizens.
By lowering costs of space transportation and therefore for space technologies and research, RETALT contributes to ensures a globally competitive and innovative European space sector, by making it easier for companies and start-ups to access space data as it becomes more affordable. Thus, it directly contributes to the European competitiveness and growth in the space industry and related sectors.
Sketch of the RETALT2 spacecraft. Left to right: launch, descent and landing
Sketch of the RETALT1 spacecraft. Left to right: launch, stage separation, descent, landing