Europe is making bold strides toward the future of space launch systems. A key challenge in increasing launch flexibility and reducing costs, lies in the development of reusable launch systems. This is implemented through two programmes working very closely together – Themis (ESA) and SALTO (European Union – Horizon Europe programme)

The global picture of the main goal

In the search of breakthrough in terms of launch rate flexibility, the development of European reusable launcher first stages is key. The ESA programme THEMIS, addresses this challenge through an agile, step-by-step development process, starting with ground demonstrations and gradually advancing to increasingly complex in-flight tests. This approach allows for iterative learning, incorporating failures and corrections along the way.

The first milestone was a successful T0 demonstration at ArianeGroup’s facility in Vernon, France. In this full-scale test, fluidic and electrical ground operations were conducted, including the filling and draining of tanks with liquid oxygen and liquid methane, along with active pressure management. This ground qualification paved the way for the T1G series of hot-fire tests using the high-thrust, throttleable methalox reusable Prometheus® engine developed by ArianeGroup.

TEMIS is now completing the preparation of the T1H vehicle, the first European prototype of liquid oxygen-liquid methane, reusable first stage, equipped with one Prometheus® engine.

The T1H demonstrator

The T1H vehicle is a reusable first-stage demonstrator developed within ESA’s Themis programme. It consists of three primary structural segments:

  • Flight control bay
  • Tank bay (housing separate tanks for liquid oxygen and liquid methane)
  • Engine bay (housing the Prometheus® engine)

To enable recovery, the vehicle is equipped with four landing legs. It stands 29 meters tall with a diameter of 3.5 meters.

The main structural integration, including the engine, took place at ArianeGroup’s facility in Les Mureaux, France, with final assembly (including SALTO experiment integration and landing legs) to be completed at SSC’s facilities in Sweden.

The vertical fit check was performed at the end of the 2024, in ArianGroup’s premises. Learn more.

The T1H demonstrator_SALTO

SALTO: The flight campaign & Technology maturation

Here the SALTO project comes in – Funded by the European Union, under Horizon Europe programme. The next critical step will be the first Europe’s full-scale prototype of a reusable first stage powered by liquid oxygen and liquid methane, equipped with a single Prometheus® engine. This prototype will be the centerpiece of SALTO, which will conduct Europe’s first ever full-scale reusable flight test campaign.

The campaign will begin with a low-altitude hop test at the Swedish Space Corporation’s facility in Kiruna. SALTO’s goal is to demonstrate controlled vertical takeoff and landing, providing invaluable data to mature reusability technologies.

Supporting technologies for reusability

The overall objective of the SALTO project is to raise the technological maturity of reusable launcher components. SALTO is structured around two main pillars:

  1. Prototyping of reusability subsystems
    Development and validation of key technologies aligned with future European reusable launch needs—many of which are currently lacking in Europe.
  2. Integrated “Hop test” flight demonstration
    Selected SALTO experiments will fly aboard the T1H demonstrator to gain real flight data.

The SALTO consortium contributes to the final integration of the T1H system, ensuring both the vehicle (T1H) and its ground systems are fully operational and safe for testing.

Preparation of THEMIS (T1H) include

  • Make sure T1H vehicle is ready for tests
  • Work closely with consortium partners to embark their experiments on T1H
  • Make sure ground means are ready for tests
  • Prepare all the procedures to operate T1H
  • Ensure the safety of the team at all times…

Technologies under development

SALTO supports a broad spectrum of reusable launcher technologies, including:

  • Aerodynamics and Aerothermodynamics
  • Structural Design and Landing Systems
  • Mechanisms and Thermal Protection
  • System Monitoring for Flight and Ground Operations
  • Safety Systems (e.g., automated flight termination)
  • Avionics and Guidance, Navigation & Control (GNC)
  • Reusable Propulsion

Ground infrastructure and operations

The T1H test campaign requires a dedicated ground infrastructure, including:

  • Launch Vehicle Integration Building in Sweden for horizontal integration of technologies within the vehicle.
  • Landing leg mounting tools – for mounting the landing legs of T1H close to the launch pad and vertically.
  • Control center for remote vehicle operations
  • Fuel storage, Cryogenic storage and pressurization systems
  • Robotic ground systems for safe remote operations, including tank filling and power the launcher before flight and draining and power after flight. Safety is a top priority. The robotic systems ensure tanks are safely emptied, minimizing risk and enabling rapid access for inspection and refurbishment after flight.

What’s Next in 2025?

Key milestones for 2025 include:

  • Completion and validation of the launch and landing pads
  • Final integration and control tests within the Launch Vehicle Integration Building of T1H
  • Transfer of T1H to the launch pad and mounting of landing legs
  • Commencement of the test flight campaign under the SALTO initiative