The Greta engine firing up on a new mobile test stand in Trauen, Germany. Greta was ignited multiple times from July to November 2025 and showed stable operations, including controlled shutdowns. During the test campaign the engine fired continuously for over 40 seconds at a time.

The Greta project, part of the European Space Agency’s Future Launchers Preparatory Programme is developing a 5 kN thrust class rocket engine that can be restarted reliably several times.

Greta uses hydrogen peroxide and ethanol as propellants, a more sustainable alternative with a lower carbon footprint compared to monomethyl hydrazine propellant used by most traditional rocket engines in this thrust range.

Greta was tested on a new, low-cost and versatile mobile test stand with instruments measuring data such as pressure and temperature, which will be used to further optimise the engine.

Greta’s 30-cm high combustion chamber is built up in layers by melting metal powders with a laser. This technique allows for complex shapes to be made that would be difficult to achieve with conventional metallurgy. For example, the Greta engine is cooled by passing fluid through complex channels built into the engine as close as possible to the inner wall of the chamber which is in contact with the hot – over 2000°C – combustion gases.

ArianeGroup in Ottobrunn, Germany is the prime contractor for Greta. This type of engine could be used on lunar landers or on kick stages, such as Astris that is being developed for Europe’s Ariane 6 rocket.