Prometheus is a reusable methalox rocket engine that is being developed under a European Space Agency contract. The project was initiated by CNES in 2015 and adopted by ESA in 2017 with the goal of developing a universal propulsive solution for future European launchers.
The project aims to develop an engine capable of producing 980 kN of thrust at a cost of around €1 million per unit, a 10th of the current Ariane 5 main engine. A total of 70% of the mass of the engine, including the combustion chamber, will be 3D printed to hit this ambitious cost goal.
Potential applications for the engine include an upgraded Ariane 6, Ariane Next (a proposed successor to Ariane 6), and the Maiaspace microlauncher
. However, before it is utilised aboard operational vehicles, it will power the reusable Themis demonstrator.
Callisto is a reusable demonstrator project being undertaken by CNES, DLR, and JAXA. The project expands on the lessons learned from Frog, a three-metre tall demonstrator that was utilised to test navigation and thrust control algorithms. Frog completed its first flight powered by a turbojet in May 2019.
Standing at 15 metres tall with a diameter of one metre, Callisto is powered by a 40 kN class LOX/LH2 engine. The primary aim of the vehicle is to test the full “toss-back manoeuvre” in Kourou on a vehicle that is about half the size of Themis. A secondary objective of the program is to study the refurbishment process required between flights. The lessons learned here will feed directly into the development of Themis.
The first flight of Callisto is scheduled for late 2022 from the Guiana Space Centre. The flight will see the vehicle climb to an altitude of 30 to 40 km before returning to Earth. Following the initial flight, an additional 10 flights are expected to be conducted in 2023.
Themis is, according to the skunk works division of ArianeGroup, ArianeWorks, both a demonstrator and a prototype of a low coast reusable first stage for future Ariane vehicles. The vehicle’s design utilises technologies and lessons learned from the Callisto programme and will be powered by Prometheus methalox engines.
A basic prototype of the Themis vehicle is currently being tested at an ArianeGroup facility in Vernon, France. This phase of the vehicle’s development will conclude with the first successful hot fire tests of the Prometheus engine. The first hop tests of a flight-ready prototype are expected to begin in 2023 from the Esrange Space Center in Sweden.
Themis is intended to be a building block for a number of future European launchers, including Ariane Next and possibly even an Avio Vega variant. However, Avio has indicated that they intend to develop their own methalox first stage engine based on the architecture of the company’s M10 engine that will power the upper stage of the Vega E launch vehicle. It could also be utilised to replace the Ariane 6 solid fuel boosters with a liquid fuel alternative, a move that may be necessitated if ESA adopts a European crew launch initiative at the ministerial-level council meeting later this year.
Ariane Next, as the name suggests, is aimed at evaluating launch systems that could replace the current Ariane 6 architecture. The primary goal of the initiative is to reduce launch costs by 50% from Ariane 6. The vehicle’s design will implement lessons learned from Callisto, Themis, and Icarus, a lightweight upper stage upgrade planned for Ariane 6.
Ariane Next will make use of an upgraded variant of the Prometheus engine for both the first and second stages to optimise development and production costs. Although there has not yet been a decision made on the exact format of the vehicle, it will likely utilise a multiple engine cluster for the first stage and offer mission flexibility with optional boosters.
The aim is to launch the maiden flight of the new vehicle by 2030.
Proposed reusable upper stage
Like SpaceX and Rocket Lab, the European Space Agency sees fully reusable launch vehicles as a key element of future vehicles. As a result, the agency plan to propose an initiative to develop a reusable upper stage at its ministerial-level council meeting later this year. The initiative will examine the reusability of an upper stage in two distinct roles: as a launch vehicle asset that would be recovered and then reused, and as an in-orbit transfer/maintenance vehicle that could be utilised for a variety of missions.
Beyond Ariane Next and into the 2040s, Ariane Ultimate is a radical single-stage-to-orbit design that utilises next-gen material science like carbon nanotubes and graphene, and propulsion systems that utilise new high-energy-dense propellants capable of drastically reducing the mass and cost of the launcher. Rather than an actual launch vehicle, Ariane Ultimate is more of a technology roadmap that is exploring the very edges of what could be possible in the future.