ATHEAt – advanced technologies for high-energetic atmospheric flights for reusable space transportation systems

ATHEAt (Advanced Technologies for High Energetic Atmospheric Flight of Launcher Stages) is a DLR space research project focusing on the development of re-entry technologies for reusable, reliable and economical space transportation systems.

Re-entering Earth's atmosphere is a highly complex and challenging process. Spacecraft are exposed to extreme conditions, including extremely high speeds of up to 28,000 kilometres per hour (or Mach 25 – 25 times the speed of sound). Above Mach 5, speeds are referred to as hypersonic and are characterised by high-temperature phenomena such as chemical reactions and plasma effects. Re-entry generates very high surface temperatures of over 2000 degrees Celsius as high kinetic energy is converted into thermal energy (heat) through strong compression shocks on the spacecraft. The process also exerts a wide range of aerodynamic forces on its materials and structures.

Closing a global technology gap – a milestone for research and industry

In the ATHEAt project, we at DLR research and test technologies for reusable spacecraft. The focus is on the re-entry phase at high Mach numbers – a particularly critical point. Our goal at DLR is to develop design tools and validate them using real-world data. This knowledge will enable us to build more powerful and reliable spacecraft in the future. With ATHEAt, we are specifically addressing a global technology gap in the research and development of reusable, reliable and economical space transportation systems.

A major component of the ATHEAt project is the implementation of two flight experiments with complimentary goals. The first flies on a special sounding rocket over an extended period, at speeds between Mach 8 and 10. The second flight experiment tests a novel single-stage hybrid rocket with throttleable thrust.

ATHEAt objectives and key activities at a glance:

• Improving the reliability of critical high-temperature structures for reusable launch vehicles
• Tightening safety margins in the design of such structures – thus improving cost-efficiency
• Developing technologies for high-energy atmospheric flight by future space transportation systems and their qualification through ground tests
• Conducting a long-duration flight experiment at high Mach numbers with a new-generation sounding rocket
• Advancing DLR’s hybrid rocket engine VISERION and demonstrating its performance in the single-stage ALDUINA flight experiment
• Developing and validating experimental and numerical methods for application in industrial space projects
• Expanding DLR's expertise in systems analysis and data management for launch vehicles and related technologies

Interaction of modelling, ground tests and flight experiments with scaled components

Ground test facilities can only partially simulate the extreme conditions of flights at high Mach numbers. Numerical design tools are also not yet sophisticated enough to allow such flights to be comprehensively modelled on computers. As such, flight experiments are vital for closing current technology gaps. Yet, flights with full-scale components are rare and expensive to run. At DLR, we develop and build our own flight experiments using application-specific components, launching them on sounding rockets to altitudes of up to several hundred kilometres.

Our researchers collect comprehensive and reliable data during tests of flight components both on the ground and in the air. Existing numerical design tools are used and improved with this flight test data. Numerical design tools are software systems used to model and simulate physical or technical problems. The combination of flight experiments, simulations and modelling is a core element of our space research programme and is firmly embedded in our space transport strategy.

Launch of ATHEAt flight experiment from Andøya Space Center

Our ATHEAt hypersonic flight experiment is scheduled to launch in October 2025 from the Andøya Space Center in northern Norway. Mounted at the top of a sounding rocket, it will fly at speeds between Mach 8 and 10, up to a maximum altitude of 54 kilometres. The scientific payload, together with the supply modules, has a mass of approximately 244 kilograms. ATHEAt will fly at high Mach numbers for approximately 200 seconds – significantly longer than our earlier successful hypersonic flight experiments SHEFEX-I, SHEFEX-II, ROTEX-T, ATEK and STORT.

The front part of the payload is made of a ceramic fibre composite material specially developed and manufactured by DLR. Behind the rocket nosecone are segments with a pointed-arch profile, followed by sections with an octagonal shape, including four control flaps. Two active cooling experiments are also on board.

Several modules are connected to the front body and contain experiments for monitoring the structural integrity of the vehicle. More than 300 sensors are used, including specially developed miniaturised non-invasive sensors, two infrared cameras, radiation thermometers and laser scanners. During the flight, all collected data is sent wirelessly to the ground station near the launch site. Given the extreme conditions during flight, this transmission is also a challenge for our team.

ALDUINA flight experiment – development and testing of DLR VISERION hybrid engine

In hybrid propulsion systems, the oxidising agent is stored in liquid form and the fuel in solid form. This enables their controlled operation and repeated ignition of the engine – combining the advantages of solid and liquid propulsion. In a liquid-engine rocket, liquid chemical components – the oxidiser and the actual fuel – are stored in separate tanks and injected into the engine's combustion chamber for ignition. There, a chemical reaction takes place – the fuel reacts with the oxidiser and increases the pressure and temperature in the combustion chamber. The resulting gas mass is expelled through a nozzle, generating thrust in the opposite direction. Because the oxidiser is carried inside the rocket, combustion can take place without oxygen from the atmosphere – for example in space. Such engines have high thrust efficiency, but the propellants are difficult to store. In solid-fuel engines, the oxidiser and fuel are premixed in a solid form and only need to be ignited. As a result, they have a simpler design and provide high thrust. However, this thrust cannot be controlled during flight.