The second test campaign for Prometheus finished in June 2025, featuring a series of hot-firing tests with a second model of the Prometheus engine. This test campaign saw the engine fire up repeatedly and increased the total runtime allowing teams to optimise the engine and its various subsystems under various thrust profiles.

Prometheus is a low-cost reusable rocket engine, the first model is being used on Themis, a reusable rocket prototype. Both Prometheus and Themis demonstrators are funded by the Future Launcher Preparatory Programme of the European Space Agency (ESA). The Prometheus reusable rocket engine is also compatible with reusable launcher stages and could be adapted to different rockets.

This second hot-firing campaign was held on the PF20 test bench at ArianeGroup’s site in Vernon, France, and it served to confirm the engine hardware as well as fine-tune design features and technologies and optimization of test bench operations to enhance multiple firing capacities. Prometheus succeeded with 4 consecutive ignitions on 20 June, a first in Europe for this type of engine.