Themis during wet dress rehearsal

Themis during a wet dress-rehearsal on 23 July 2026 that allowed ArianeGroup and SSC Space to practice countdown procedures and post-flight procedures. The rocket prototype was filled with liquid nitrogen at –196°C to test the whole system and see how it holds up under the extreme cold and highly-pressurised systems as well as checking if all electronic systems work correctly in these conditions.

Themis is an ESA rocket prototype – a flagship European demonstrator for low-cost rocket recovery and reuse technologies. Powered by the reusable, liquid oxygen and methane-fuelled engine Prometheus, Themis is on the launch pad at the Esrange Space Center in Sweden.

The data gathered during this test will play a key role in preparing Themis for its first flight, particularly during complex operations such as getting the cryogenic engine ready for ignition.

Themis will run on liquid methane and oxygen, but for this rehearsal liquid nitrogen was used for safety – it has similar properties in terms of cryogenic temperature and density, but is not flammable nor explosive.

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.