Bruno Le Maire, the former French finance minister, said in 2021 that the Ariane 6 was a “bad strategic choice.” More recently, in October of last year, the head of ESA said the continent’s space industry must “catch up” with international competitors like SpaceX and develop a reusable launcher “relatively fast.”

In its submission to ESA’s BEST! initiative, ArianeGroup proposes replacing the Ariane 6 rocket’s solid-fueled side boosters with new liquid-fueled boosters. The boosters would be developed by MaiaSpace, a French subsidiary of ArianeGroup working on its own partially reusable small satellite launcher. MaiaSpace and ArianeGroup would convert the Maia rocket’s methane-fueled booster for use on the Ariane 6.

ArianeGroup’s proposal was first reported by European Spaceflight, which said the concept presented to ESA is similar to an ArianeGroup proposal from 2022, when the company described the liquid reusable boosters as a “plug-and-play” alternative to Ariane 6’s solid-fueled boosters, helping reduce operating costs and increase launch rates.

The details of ArianeGroup’s newest proposal have not been published, but the concept was summarized in a paper presented at the European Conference for Aeronautics and Space Sciences in 2025.

Isar Aerospace, a German rocket startup, won a separate BEST! contract from ESA to study a demonstrator for a reusable first stage based on the company’s light-class Spectrum rocket. The Spectrum rocket’s initial design is expendable. Its first test flight last year ended in failure, and Isar is readying the second Spectrum rocket for another launch attempt later this month.

ESA asked ArianeGroup and Isar Aerospace to assess the feasibility of their proposals, develop technology and system development plans, and define plans and costs for a “major flight demonstration.”

MaiaSpace’s rocket won’t launch until 2027, at the earliest, and it’s unlikely any decision to use it as the basis for new Ariane 6 boosters will bear fruit until long after Maia flies on its own. Even if ESA and ArianeGroup take this route, the Ariane 6 rocket would still be predominantly expendable.