The objective is to develop a "generic brick for reuse", explains Jean-Christophe Hénoux, director of future programs at Arianegroup.

And thus to have the technical means to face fierce competition from the American SpaceX, which already successfully uses reusable rockets.

The European program is centered on the Prometheus engine - developed by Arianegroup and reusable five times for a targeted manufacturing cost ten times lower than that of the Vulcain engine of Ariane 5 - and Themis, a rocket stage demonstrator capable of returning ask before being repackaged for reuse.

The latter is developed by ArianeWorks, an innovation platform set up by Arianegroup and Cnes.

The challenge, if the launch rates justify it: reduce the cost of access to space.

In the shadow of the "PF20", a concrete structure abandoned since 1984 after having served as a test bed for the Ariane 1 rocket, workers are busy preparing for the first tests of Themis and Prometheus, planned for April.

"We find with Themis this pioneering logic" from the beginnings of Ariane, enthuses Philippe Girard, Arianegroup's quality director, showing the evacuation flue - a trench used to channel the jets of burnt gas - during finishing.

Workers are at work around the steel supports on which the Prometheus engine and the tanks making up the Themis stage will be placed, a few tens of meters from a grassy mound hiding an underground bunker from which the trials.

Prometheus will be ignited several times for "gunshots lasting a few tens of seconds" fed by two tanks of cryogenic liquid oxygen and methane, explains Olivier Gogdet, head of the Themis project.

A poster of the Themis project, a reusable rocket stage demonstrator, on the Arianegroup site, on December 6, 2021 in Vernon, Eure Eric PIERMONT AFP / Archives

Compared to hydrogen, "methane is interesting because it is much more compact and much less cold than hydrogen" and therefore more conducive to reuse, he explains.

"We cut in the turns"

Symbols of a change of era, the Themis tanks are prepared in the same assembly hall as the Vulcain engines of Ariane 5.

For the time being caged in a metal trellis, they rub shoulders with the last Vulcain engine, protected by a purple skirt while awaiting the final flight of Ariane 5 in 2023.

Without waiting for the first Ariane 6 flight scheduled for the end of the year, the European Space Agency (ESA) is therefore already preparing for the aftermath: it has devoted 210 million euros to the development of Prometheus and 33 million to Themis.

A Vulcain 2 engine from Ariane 5 on the Arianegroup site, December 6, 2021 in Vernon, Eure Eric PIERMONT AFP / Archives

France, for its part, has invested 15 million euros in preparing the Themis test bed in Vernon and accelerating the development of Prometheus by one year.

“Before, we did development in sequences, now we develop the engine, its implementation and the stage at the same time. This reduces development times and costs,” argues Olivier Gogdet.

"We cut in the turns. On Themis, as soon as we can, we manufacture, we test", adds Jean-Christophe Hénoux.

After the first tests, Themis must make its first flights in the summer of 2023 in Kiruna, in northern Sweden, during "Hop tests": the 27-meter high rocket, for nearly 200 tons, must take off and return to land on its launch pad.

The last tests are scheduled for 2025 from Kourou, according to Olivier Gogdet: Themis, powered by three Prometheus engines, will fly at more than Mach 6 (more than 7,400 km / h), "until the moment the boosters are dropped", the Ariane 6 boosters, before going to land on a barge at sea.

This technological brick will be used for future rockets but "allows us to consider the evolution of Ariane 6 with a reusable stage, a reusable engine" or even liquid boosters, "this is what separates first, so the simplest to reuse", imagines Jean-Christophe Hénoux.

Space Europe must look into the roadmap for these future programs on Wednesday during a meeting in Toulouse, then in November during an ESA ministerial conference in Paris.

© 2022 AFP