WASHINGTON — European rocket builder ArianeGroup, the company leading development and production of the Ariane 5 and upcoming Ariane 6 rockets, on Sept. 4 awarded a contract to a Swedish supplier for a reusable engine program.

GKN Aerospace’s space business unit in Trollhättan, Sweden, will build two turbines for Prometheus, a reusable liquid-oxygen-and-methane engine projected to cost $1 million per unit — one-tenth the cost of Ariane 5’s Vulcain 2 first-stage engine.

GKN, which has participated in Ariane launch programs since 1974, will supply components for the first and second stage engines of the expendable Ariane 6 rocket slated to debut in 2020. For Prometheus, the company said it will use 3D printing to reduce the number of turbine parts from over 100 to two, helping lower costs while enabling the engine to meet high temperature, pressure and velocity criteria.

Prometheus is one of a growing number of engines being designed to use methane. SpaceX’s Big Falcon Rocket calls for 31 methane-fueled Raptor engines for the reusable booster and seven more for the reusable spacecraft.

The BE-4 engines Blue Origin is making to power its New Glenn orbital rocket also burn methane, as does Zhuque-2, a Chinese rocket that startup Landspace envisions launching in 2020.

Prometheus isn’t expected to see use until 2030, though ArianeGroup has said in the past the engine could be used on the expendable Ariane 6.

The European Space Agency signed a 75 million euro ($86.7 million) contract with ArianeGroup in December for the first two Prometheus prototypes. The agency said then that knowledge of liquid-oxygen-and-methane propulsion systems from Prometheus “will allow fast and informed decisions to be made on useful applications” by 2020.

Prometheus can power the first and second stages of a rocket, and “will propel a range of next-generation launchers, including future evolutions of Ariane 6,” ESA said.