Cool fuel

Although the Prometheus engine that powers Themis has the same thrust as the main engine on Europe’s heavy-lift rocket Ariane 6, it uses different propellants: liquid oxygen and liquid methane. Liquid oxygen is cooled to as low as –183°C, so preparing and handling such cryogenic fluids for fuelling is a feat in itself. Compared to other rocket fuels such as hydrogen and kerosene, methane has advantages: it does not need to be as cooled to such extremes as liquid hydrogen does and is a larger molecule making it easier to handle and less prone to leaks, while delivering a higher performance than kerosene.

Themis, the first European reusable main stage’s full-scale demonstrator, was developed by ESA’s future Space Transportation preparation programme, with ArianeGroup as prime contractor and multiple European industrial partners. Once completed, Themis was taken forward by the Horizon Europe project SALTO – funded by the European Commission – for the launch campaign. The SALTO project is part of the EU Space Research and Innovation Work Programme and managed by the EU executive agency HaDEA, bringing together 25 consortium partners from 12 European Union countries.