Prometheus (rocket engine)

The Prometheus rocket engine is an ongoing European Space Agency (ESA) development effort begun in 2017 to create a reusable methane-fueled rocket engine for use on the Themis reusable rocket demonstrator and Ariane Next, the successor to Ariane 6, and possibly a version of Ariane 6 itself.^[1][2]

Prometheus

Model of the Prometheus rocket engine, featured at IAC 2022.
Country of origin	France European Union
Designer	ArianeGroup
Manufacturer	Ariane Group
Associated LV	Themis · Ariane Next
Liquid-fuel engine
Propellant	LOX / CH4
Cycle	Gas-generator
Performance
Thrust, sea-level	980 kN (220,000 lbf)
Throttle range	30% to 110%
Chamber pressure	100 bar (10,000 kPa)

Prometheus is a backronym from the original French project designation PROMETHEE, standing for "Precursor Reusable Oxygen Methane cost Effective propulsion System", and for the Titan Prometheus, from Greek mythology, creator of humanity, and god of fire, known for giving fire to humanity in defiance of the gods.

The engine is aimed to be reusable with substantially lower costs than traditional engines manufactured in Europe. The cost goal is to manufacture the Prometheus engine at one-tenth the cost of the Ariane 5's first-stage engine.^[3][4]

By 2020, the program was funded and is under development by ArianeGroup.^[4] By 2025, the engine had completed two successfull test firing campaigns including four successive ignitions in a single day.^[5]

General characteristics

The engine is planned to have the following features:

• Methane–oxygen propellant.
• Extensive use of metal 3D printing (up to 50% of the engine).^[4]
• Open gas-generator cycle.^[6]
• 980 kN of thrust (~100 tonnes), variable from 30% to 110% thrust.^[6]
• 100 bar (10,000 kPa) chamber pressure.^[6]
• 360 s specific impulse (I_sp).^{[citation needed]}
• Reusable 5 times.^[7]
• Around 1 million euros production cost.^[6]

History

The European Space Agency (ESA) began funding Prometheus engine development in June 2017 with €85 million provided through the Future Launchers Preparatory Programme, 63% of which came from France.^[1]

By June 2017, Patrick Bonguet, lead of the Ariane 6 launch vehicle program at Arianespace, indicated that it was possible the Prometheus engine could find a use on a future version of the expendable Ariane 6 launcher. In this scenario, a "streamlined version of Vulcain rocket engine called Vulcain 2.1 would have the same performance as Vulcain 2". The expendable Ariane 6 was then expected to make an initial launch in 2020.^[3]

By June 2020, the ESA was on board with this plan and had agreed to completely fund the development of the Prometheus precursor engine to bring the "engine design to a technical maturity suitable for industry". The objective of the overall program as stated in June 2020 was to utilize Prometheus technology to eventually "lower the cost of production by a factor of ten of the current main stage Ariane 5 Vulcain 2 engine".^[4] In 2021, ESA invested an additional €135 million in the project,^[8] including €30 million from DLR.^[9]

The engine was started up in Nov 2022. It had a successful 12 second test firing in June 2023, at the THEMIS test stand in Vernon, France.^[10] An additional successful hot fire test was reported at the end of 2024.^[11] The second test campaign for Prometheus in Vernon finished in June 2025 after a second model of the engine performed a series of repeated hot-firing tests under various thrust profiles. On 20 June 2025, the engine successfully demonstrated 4 consecutive ignitions, a first in Europe for this type of engine. A third model of Prometheus will be tested at DLR's Lampoldshausen test site.^[5][12]

See also

• Future Launchers Preparatory Programme – European Space Agency rocket development projects
• CALLISTO – Type of reusable rocket
• Themis programme – European Space Agency programme to develop a prototype reusable rocket first stage
• Ariane Next – Orbital recoverable launch vehicle of the European company ArianeGroup