The Themis programme is an ongoing European Space Agency programme carried by prime contractor ArianeGroup, aiming to develop a prototype reusable rocket first stage and plans to conduct demonstration flights. The prototype rockets will also be called Themis. As of 2025, two prototypes are being developed: Themis 1-Engine Hop (T1H) and Themis 1-Engine Evolution (T1E). Later, a three-engine variant (T3) will be built.[1][2]
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.[3][non-primary source needed] Themis will be powered by the ESA's Prometheus rocket engine.[3] 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.[4]
Themis is distinct from a similar project CALLISTO under development by CNES, DLR, and JAXA.
Background
Two possible landing sites have been mentioned in discussions surrounding the project:[5]
The former Diamant launch complex, which will be used for the flight testing phase;[6]
The Ariane 5 launch complex, which will become available after the transition from the Ariane 5 to Ariane 6.
The estimated program timeline, as of December 2020[update], was as follows:[7]
On 15 December 2020, ESA signed a contract worth €33 million with 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.[5][non-primary source needed]
In December 2021, ESA completed a series of tanking tests on the steel propellant tanks for Themis.[9]
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.[10]
In November 2024, ESA has awarded a contract to ArianeGroup to build a second Themis demonstrator (T1E)[12] and announced that testing of the Themis main systems has been completed and the assembly of the first demonstrator was underway.[13]
In December 2024, ArianeGroup has brought the main elements of Themis T1H together for the first time during a full-fit check in Les Mureaux, France.[1]
In early June 2025, the website European Spaceflight reported that, according to sources close to the programme, the first test flight of Themis was likely to slip into early 2026.[14]
In June 2025, Themis T1H integration was completed at Les Mureaux. The vehicle was packed and prepared for shipment[15] and on 27 June, it arrived at the Esrange spaceport in Sweden.[16][17]
