Greta, A New ESA Rocket Engine, Successfully Completes Testing
Additive manufacturing has established itself as a fundamental technology in rocket development, especially in the production of combustion chambers, as it allows for great freedom in terms of geometry. The most recent example of this application is the Greta engine, a joint development by the European Space Agency (ESA) and ArianeGroup.
After completing its first test campaign, Greta has demonstrated stable operation during shutdowns and multiple starts. Although manufacturing details are often kept confidential, the ESA has mentioned that “Greta’s 30 cm high combustion chamber was built up in layers by melting metal powders with a laser.” This points to laser powder bed fusion, a technique that ArianeGroup has used in the past.
Greta is a 5 kN engine designed for upper stages such as Astris (Ariane 6) or future lunar landers.
What stands out most about Greta is the architecture of its combustion chamber. It incorporates complex channels built directly into the walls of the structure. These channels allow the coolant to circulate just a few millimeters from the combustion zone, where temperatures exceed 2000°C. Achieving this proximity is an engineering challenge that conventional metallurgy would struggle to solve.
Greta breaks with the dependence on hydrazine (monomethylhydrazine), the propellant traditionally used in this thrust range. Instead, it uses a combination of hydrogen peroxide and ethanol. According to the ESA, this mixture is a more sustainable alternative with a lower carbon footprint. During tests conducted between July and November 2025 in Trauen, Germany, the engine demonstrated complete operational stability, even during continuous firings of more than 40 seconds.
Following its success, the project is entering a new €3 million phase. The aim is to develop the current prototype into a flight engine design. At this stage, European collaboration is intensifying with partners such as Safran Aero Boosters (Belgium), the Aviation Institute (Poland), and InPraise Systems (Czech Republic), who will work on refining the engine’s peripheral components. You can read the official ESA press release here.
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*All Photo Credits: ESA
