The Themis programme is an ongoing European Space Agency programme that is developing a prototype reusable rocket first stage and plans to conduct demonstration flights. The prototype rocket will also be called Themis.

This article relies excessively on references to primary sources. (December 2020)

Themis is expected to provide valuable information on the economic value of reusability for the European government space program and develop technologies for potential use on future European launch vehicles.^{[1][non-primary source needed]}

Themis will be powered by the ESA's Prometheus rocket engine.^[1]

Two possible landing sites have been mentioned in discussions surrounding the project:^[2]

• The former Diamant launch complex, which will be used for the flight testing phase;^[3]
• The Ariane 5 launch complex, which will become available after the transition from the Ariane 5 to the next-generation Ariane 6.

The estimated program timeline, as of December 2020^[update], is as follows:^[4]

• 2020: Basic stage testing, composed of tank filling and ground support equipment tests.^[5]
• 2021: Prometheus engine testing
• 2022: Low-altitude hop tests (short flights up from and down to the launch site)
• 2023: Initial flight test
• 2023–2024: Loop tests (repeated flights of the reusable demonstration vehicle)
• 2025: Full flight envelope test

Suborbital flight tests were slated to begin as early as 2023 at Europe's Spaceport in Kourou, French Guiana, but have been delayed.^[2]

Eventually, lessons learned with Themis' development will pave the way for developing the European reusable launcher Ariane Next, which should first fly in the 2030s.^[6]

On 15 December 2020, ESA signed a contract worth €33 million with prime contractor ArianeGroup in France for the ‘Themis Initial Phase’. This first phase of the Themis programme involves development of the flight vehicle technologies and test bench and static fire demonstrations in Vernon, France. It also includes the preparation of the ground segment^{[clarification needed]} at the Esrange Space Center in Kiruna, Sweden, for the first hop tests and any associated flight vehicle modifications.^{[2][non-primary source needed]}

On 22 June 2023, the first hot-fire test of the Prometheus engine, as a part of the Themis first stage demonstrator, was successfully conducted in Vernon, France.^[7]

• Future Launchers Preparatory Programme
• CALLISTO
• Prometheus (rocket engine)
• Ariane Next
• SpaceX reusable launch system development program
• Miura 5