Prometheus engine test

Prometheus engine test at ArianeGroup's Vernon site in France in 2023. Unlike all European cryogenic rocket engines to date, Prometheus will use liquid methane at –162 °C as a fuel instead of hydrogen. This has advantages as methane is denser and easier to handle than hydrogen, so it will reduce costs in engine and launcher design and will ease in-flight vehicle reignition. This ability to reignite mid-flight is key as Themis will need to restart its Prometheus engine several times as it descends back to Earth to land.

Europe’s largest rocket engine in use today – the Vulcain – runs on hydrogen and has comparable power to Prometheus. However, the Vulcain engine does not restart during the flights of Ariane 5 and Ariane 6 – Prometheus will be just as powerful, restartable and about ten times cheaper. The Themis stage is about the same length as an Ariane 5 core stage (the lower portion of the rocket without the upper stage and fairing) but is smaller in diameter.