Themis: what is it?

Themis is a demonstrator reusable stage which should enable Europe to equip itself for the launchers of the future with low-cost and reusable technologies. Concretely, with Themis, the goal is to advance existing technologies that are essential for reuse, to acquire new skills in this field of flight if necessary and finally to demonstrate reuse capabilities in Europe. This stage is developed and produced by ArianeWorks, a structure set up by Cnes and ArianeGroup to prepare the generation of launchers that will succeed the Ariane 6 family by accelerating the technological steps to respond to them.

30 meters high for a diameter of 3.5 meters, it will be propelled by the Prometheus reusable motora motor oxygen and methane liquidsdeveloped by ArianeGroup since June 2017. It will use up to three Prometheus engines.

A stage that won’t fly in space

With Themis, the ambition is to produce a reusable low-cost floor by 2025, using the “toss back” mode. This maneuver, used SpaceX to recover the main floor of the Falcon 9, consists of performing a U-turn, a reverse gear and a re-ignition of the engine. In this configuration, the stage uses propulsion rocket to provide the impulses allowing the return to the ground, the braking in the atmospheric phase and the vertical landing. Several other recovery modes exist, and if ArianeWorks is betting on the “toss back”, it is obviously not to copy SpaceX but simply because it is what appeared, after analysis, to be the best suited for our future launchers.

The first attempts at suborbital flights are planned in Kourou (Guyana) between 2023 and 2025. These flights will aim to test the entire flight envelope. That is to say the climb, the turnaround, the descent and the landing with engines forward and vertically (the “toss-back” mode), requiring numerous attitude and speed management maneuvers.

At the same time, the teams of Guiana Space Center began the rehabilitation of the Diamant launch site in order to adapt it to Themis, Callisto as well as future small and micro launchers that do not yet exist on the market.

Themis could also give birth to new boosters to increase the performance ofAriadne 6. Unlike the current boosters, the P120 which work with a fuel solid, the Themis booster would use liquid fuel. Another path under study, adapt Themis to replace the Ariane 6 main stage” with the objective of remaining within a range of similar performance but with enhanced competitiveness. Finally, Themis could give rise to a new architecture of simple and sober launchers, covering a spectrum wide range of missions with only two stages and a single propulsion technology.