Themis, Prometheus complete first hot-fire tests in France

by Bella Richards

Europe has just completed the first successful hot-fire test of its reusable Prometheus engine integrated with the Themis first-stage demonstrator at the ArianeGroup site in Vernon, France. The hot-fire test consisted of Prometheus performing a 12-second burn on the Themis demonstrator on June 22, 2023.

The two components are part of a broader European launch program, called Ariane Next, which is focused on developing a fleet of reusable rockets that will enter into service in the 2030s. The program is a joint effort between the European Space Agency (ESA) and the French Space Agency (CNES) with ArianeGroup as the prime contractor.

Initial Testing Begins

The Prometheus engine is powered by oxygen and methane, but to align with ArianeGroup’s environmental innovation endeavors, the first hot-fire test included a bio-methane fuel. ArianeGroup said in a statement that carrying out these tests with Prometheus and Themis indicated the behavior of the components operating together within an extended mission profile.

“Yesterday’s test reached all the test objectives (operating points, duration) and is a crucial milestone on the long way to an operational product, confirming a viable product,” Jérôme Breteau, Head of the Future Space Transportation systems at ESA, told NSF.

“Further activities are planned to improve and complete the engine. For example, the engine configuration does not incorporate nozzle extension, and some combustion element manufacturing technologies are developed in parallel and not yet embarked.”

Prometheus engine testing is scheduled to continue at the end of 2023 at the German Aerospace Center (DLR) test bench in Lampoldshausen, Germany.

Prometheus and Themis hot-fire test lasted 12 seconds. (Credit: ArianeGroup)

Ariane Next – Europe’s Future Fleet

Ariane Next forms the building blocks of Europe’s ambitions to develop reusable launch vehicles, and Themis and Prometheus are some of the first concepts to be tested and developed.

Between 2015 and 2017, CNES and ArianeGroup conceived the idea of Prometheus, a reusable rocket engine powered by oxygen and methane. Then, following ESA’s Space19+ Ministerial Conference in 2019, which focused on proposing ‘next generation’ launch technologies, Themis was born.

One of the main differences between Prometheus compared to the oxygen and hydrogen-powered Vulcain engine that powered the Ariane 5 — and Vulcain 2.1 that will power the Ariane 6 — is that Prometheus will burn oxygen and methane. The transition to methane is largely because it is considered cheaper, easier to handle, and keeps liquid at a similar temperature as oxygen.

According to CNES, the engine will be reusable up to five times and can deliver variable thrusts of up to 100 tonnes. Although the engine will provide lower thrust than the Vulcain 2.1, which delivers 130 tonnes in a vacuum, methane is six times denser than hydrogen and will enable “more compact” rocket stages that are easier to recover.  The Prometheus is re-ignitable, which makes it suitable for core, booster, and upper-stage application. The engine could also serve as a precursor for Vulcain 2.1 improvements, Breteau said.

“From an economic perspective, Prometheus is aiming to reduce production costs tenfold with respect to the Vulcain engine—which has a unit cost of €1 million—thanks to a different architecture, extensive use of 3D printing, and a production rate of 50 engines per year,” CNES says.

“From a schedule perspective, the goal is to equip the lower (with the Themis demonstrator) and upper stages of Europe’s future range of launchers—from micro-launchers to Ariane Next—by 2030.”

Marking the first real progress for Prometheus, the engine completed its first successful thrust chamber ignition in November 2022 in preparation for future hot-fire tests.

For Themis, ESA began its first step in developing the reusable rocket stage in December 2020, after inking a contract with ArianeGroup for €33 million to begin the ‘Themis Initial Phase.’ ESA has said its aim with the program is to complete tests early on in the development cycle through an “agile and cost-driven” approach.

According to ESA, the ‘Themis Initial Phase’ follows a project timeline from 2020 to 2025. The initial timeline estimated that in 2020, basic stage testing composed of tank filling and ground support equipment tests would be completed, followed by Prometheus engine testing in 2021. In 2022, low-altitude hop tests for the Themis demonstrator were expected to occur, followed by initial flight and loop tests in 2023 and 2024 from the Esrange Space Center in Kiruna, Sweden. In 2025, ESA expects to accomplish a full flight envelope test.

Themis reusable rocket timeline. (Credit: CNES)

This series of hop tests will be like SpaceX’s Grasshopper and Falcon 9R-Dev demonstrator vehicles, which performed smaller scale vertical-takeoff-and-landings and provided insight into the performance of the boosters during a controlled landing.

While Themis completed tanking tests in December 2021, the latest hot-fire test is slightly behind schedule according to the project timeline, but Breteau asserts Prometheus will be application-ready by the end of 2025.

“Prometheus is an agile and success-oriented demonstrator programme, and solving technical issues, while inherent to these cutting-edge activities, take some time and cannot be planned upfront, and is responsible for some delays,” Jérôme Breteau said.

“The programme has been also impacted by the commonality of means and teams with Ariane 6, such as P5 test bench.”

The next test campaign for Themis in Sweden is part of a European Union (EU) Horizon Europe program, called SALTO (reusable strategic space launcher technologies and operations). In July 2022, ArianeGroup was selected by the EU to oversee both the SALTO project and the ENLIGHTEN (European iNitiative for Low cost, Innovative & Green High Thrust Engine) project, which is designed to develop and produce reusable engines following on from Prometheus.

Europe’s Steps Towards Sustainable Space

With Europe’s plans to become carbon neutral by 2050, ESA has also taken steps to reduce its carbon footprint, and the reusability of rocket stages has been hailed as a strong method of reducing the environmental impacts of the launch industry. While there is still possibly a decade until Ariane Next vehicles enter into service, the technology will provide Europe with the necessary competition between other reusable options.

Europe’s space industry is also looking at other ways to support a sustainable sector. In 2020, ESA and CNES announced the agencies would work together to switch to renewable energy sources at the Centre Spatial Guyanais (CSG) in Kourou, French Guiana. The energy transition would cut costs and reduce reliance on the French Guiana grid. ESA announced it would build solar fields and two biomass units, which could save up to 50 GWh per year, reducing the carbon footprint by about 45,000 tonnes of carbon dioxide (CO2).

The engine burned oxygen and bio-methane. (Credit: ArianeGroup)

In February 2023, France began lobbying the EU for subsidies that would enable the nation to build biomass power plants in French Guiana, despite strong opposition from environmental organizations.

Most recently, ESA announced a Zero Debris Charter initiative during the Paris Air Show, supported by Airbus Defence and Space, OHB, and Thales Alenia Space. The initiative is focused on encouraging member states to implement a “Zero Debris approach for its missions.”

ESA and CNES have also worked on other reusability projects, including FROG and CALLISTO.  FROG was a small demonstrator mission to test the vertical landing of a rocket stage. The 2.5-meter rocket performed a series of test flights in 2019, mostly focused on testing GNC (Guidance, Navigation, and Control) software.

CALLISTO (Cooperative Action Leading to Launcher Innovation in Stage Toss-Back Operations) is a fully-reusable, 15-meter-high rocket that is set to fly as a demonstrator rocket, mostly focused on testing the technologies of returning a launcher to Earth. The mission is in conjunction with the Japan Aerospace Exploration Agency (JAXA) and the German space agency (DLR) and was supposed to fly in 2022, but there have been no further updates.

(Lead image: Prometheus and Themis hot fire test in Vernon, France. Credit: ArianeGroup)

Related Articles