Taking a closer look at SALTO: Performing Europe’s first reusable launcher flight campaign

On 5^th June 2025, representatives from the European Commission executive agency HaDEA, were granted access to the ArianeGroup’s state-of-the-art premises in Les Mureaux, France. ArianeGroup, as coordinator of the SALTO project, leads 25 partners from 12 EU countries working together to develop technologies and building blocks, “stepping stone” towards a first European reusable space launch system.

SALTO is the largest single space R&I project funded by the EC, directly managed by HaDEA.

The visit coincided with the start of the flight test campaign of the Themis T1H launcher reusable first-stage demonstrator, a critical milestone of the project.

The primary objectives of the visit to ArianeGroup premises were to inspect the first vehicle within the European Space Agency THEMIS programme,  and assess the work progress ahead of the transport to Esrange Space Center in Kiruna, Sweden.

During the visit, HaDEA representatives engaged with key engineers involved in the launch vehicle assembly and testing phases. These interactions coupled with a tour of Themis assembly facilities gave us confidence that Themis is ready to be tested in Kiruna.

Current status, observations and the journey to Kiruna

At the time of the visit, Themis T1H was undergoing final functional tests ahead of its transfer to Kiruna, Sweden. The reusable liquid methane and liquid oxygen Prometheus engine powering the rocket had successfully been fired on ground at the ArianeGroup test facility in Vernon. Themis T1H was then cleared for transport.

The Themis T1H vehicle arrived on June 27 2025 at the launch site in the ESRANGE Space Center. The flight campaign will begin with the assembly of key landing components, such as landing legs.

The vehicle will then be prepared for a wet rehearsal, during which cryogenic propellants will be loaded into the vehicle for the first time. This will be followed by a static hot-firing test, where the engines will be ignited to validate stage under realistic conditions.

The first low-altitude "hop"- a vertical takeoff and landing maneuver - is planned before the end of 2025, and two additional hops are scheduled for early 2026.

HaDEA’s presence at Les Mureaux offered a unique opportunity to observe technical progress firsthand and document European efforts in advancing reusable space systems. 

Inside the premises, rocket science takes shape

HaDEA colleagues were granted access to operational zones typically restricted to engineering personnel, including facilities for stage integration, vertical assembly bays, and the staging area where Themis is undergoing final ground checks. 

Grey areas painted on the ground designated the walking path allowed for visitors with virtually no room for errors, moving between the state-of-the-art equipment, machineries and testing facilities. 

Before continuing to the hangar, all bags had to be left behind in the visitors’ welcome room and all smart phones were locked in a phone locker. A heavy steel door separates the welcome area from the landing area where the metal grate floor leads out above the hangar giving the visitors a bird’s eye view of the entire site. 

The hangar floor is superbly clean with designated lines painted in different colors of yellow, white and green. In the distance, a large conveyor robot rolls into view following one of these lines. These are used to carry large pieces of equipment or sections of the rocket from one place of the hangar to another. One notices how silent it is in such a large volume of space (pun intended) with pockets of staff working diligently and silently in different areas of the hangar. 

During the visit, informal discussions provided valuable insights, with many technical details explained in a clear and accessible way. Still, no matter how simply it's explained — it's still rocket science.

Elevating European reusability initiatives

Access to space is a strategic capability for the EU for the deployment of its constellations i.e. Galileo, Copernicus and Iris 2. The EU supports non dependence and strategic autonomy in this field. Launcher reusability is a cornerstone of Europe’s ambition to enhance its autonomous and sustainable access-to-space capability by reducing costs and environmental impact.

Europe is committed to supporting the mastering of launcher reusability, both through ESA and European Commission efforts.

The SALTO project, acronym for “reuSable strAtegic space Launcher Technologies & Operations”, is funded by the European Commission under Horizon Europe Research and Innovation Programme. 

It builds on the first phase of the European Space Agency's (ESA) endeavour for reusable rocket, using the first stage prototype “Themis T1H" manufactured under the ESA's Future Launchers Preparatory Programme (FLPP) with ArianeGroup as Prime contractor.  

The Themis project includes developing the flight test model, as a European demonstrator for low-cost rocket recovery and reuse technologies. It is powered by the reusable, methane-fueled engine Prometheus®, also developed by ArianeGroup.

SALTO focuses on the maturation of key reusability technology, that will be tested on the Themis demonstrator. The project’s main activity includes a test campaign involving three low-altitude flights (vertical take-off and landing), aimed at demonstrating the vehicle’s ability to be refurbished and prepared for subsequent missions. 

The Themis / SALTO project exemplifies effective cooperation between ESA and European Commission. It demonstrates that by aligning goals, coordinating expertise, and resources, Europe can advance key technologies efficiently, further reinforcing Europe’s leadership in the future of space systems development.

The Themis development, and the SALTO flight test campaign represent also a shift in the European mindset, embracing greater risk-taking through a “test and learn” approach. This involves rapidly building prototypes, conducting test flights with known risks, and learning from each step of the process. Real life testing will show critical issues that are difficult to find in simulation. This approach aims at accelerating innovation, substantial cost reductions, and achieving an ever-improving system.

Learn more about Themis and its launch campaign via ESA’s development updates, ArianeGroup’s latest news, or the SALTO project’s coverage.