Versatile, green rocket engine gets go-ahead from ESA

The “BERTA Green” engine is an extension of the BERTA project, a 5kN-thrust engine using classical storable propellants; that is, propellants which can be stored as liquids at near room temperature and pressure. This engine was developed and tested within ESA’s FLPP (Future Launcher Preparatory Programme). The original BERTA engine is now being applied to the future Ariane 6 kick-stage, ASTRIS. The name BERTA comes from the German acronym for bi-propellant rocket propulsion, as the work has been performed by ArianeGroup’s site in Ottobrunn, Bavaria.  

As a first extension of the original BERTA project, a 3D-manufactured combustion chamber assembly designed for storable propellants was hot-fire tested in 2019. That combustion chamber, tested by ArianeGroup Germany at the Lampoldshausen rocket engine centre of Germany’s DLR aerospace agency, had a reference thrust of 2.5kN. But now, ESA Director of Space Transportation Daniel Neuenschwander and ArianeGroup Germany Chief Executive Pierre Godart have signed at Oberpfaffenhofen, in Bavaria, a Memorandum of Understanding to proceed with development of a green demonstrator engine with a reference thrust of 5kN, the same as the original BERTA engine. 

The goal of the programme – known as BERTA Green – is to proceed with the design, manufacture, assembly, integration and hot-fire testing a full-scale, green propulsion demonstrator engine. Today’s agreement between ESA and ArianeGroup, to manufacture and hot-fire test the demonstrator engine, continues on work performed since 2018 on the identification of potential green propellants and the design of an associated engine.    

Additive layer manufacturing – so-called 3D printing – is an important technology for the BERTA Green project. This technique allows engineers to design structures with fewer parts and more complex internal structures than can be achieved with traditional “subtractive” manufacturing technologies. And, 3D printing can deliver significant cost reduction in serial manufacturing. 

A BERTA engine must satisfy a broad range of mission requirements and be able to re-ignite several times in the vacuum of space, for example to place multiple satellites into different orbits. Future versions of ESA rockets, kick-stages or even exploration missions may incorporate this versatile engine. 

Critically, the concept is devised around “green” and storable propellants. Liquid rocket fuels used today for European launchers are hydrogen and oxygen, which are only liquid when kept ultra-cold – and are hence difficult to store for extended periods. Fuels which are storable at near-room temperature and pressure, such as hydrazine and nitrogen tetroxide, are toxic to human beings and the environment. The green and storable fuels under investigation promise not only to reduce toxicity but also to cut the cost of handling. 

Neuenschwander remarked: “To be both sustainable and cost-effective, our launch vehicles must be both green and versatile. In Europe we have demonstrated that we have the technical capability to be leaders in this regard, so I am delighted to be pressing forward with this initiative.”