The European space industry is undergoing a rapid but quiet revolution: instead of toxic propellants that have been the standard for decades, it is increasingly turning to so-called "green" solutions. One of the most interesting new products in this field is ARIEL – a new, 250-Newton chemical hydrogen peroxide thruster developed by the Spanish company Arkadia Space under the umbrella of the European Space Agency (ESA) Future Launchers Preparatory Programme (FLPP). It is an engine intended for Reaction Control Systems (RCS) of rockets and spacecraft, combining environmentally friendlier fuel, a high degree of reliability, and competitive costs, while targeting a market segment where Europe has not previously had a serially available product of these performances.

Thruster for precise spacecraft control

Unlike main propulsion engines that generate large amounts of thrust to get a rocket or spacecraft into orbit or change orbit, ARIEL is designed as a so-called attitude control thruster. Such engines are located on various parts of the space vehicle and work in short bursts or longer, stable "burns" to precisely rotate, stabilize, or orient the spacecraft in the desired direction. With its maximum thrust of about 250 N, ARIEL could hold a 25-kilogram bag of cement in the air on Earth, which translates in the vacuum of space into very fine and controlled handling of large rockets or massive satellites.

Why hydrogen peroxide is replacing hydrazine

The key feature of this thruster is the choice of propellant. Instead of classic hydrazine, which has been the de facto standard in space missions for decades, ARIEL uses High Test Peroxide (HTP) with a purity of about 98%. Hydrogen peroxide as a monopropellant decomposes in the presence of a catalyst into a hot mixture of steam and oxygen, creating a jet that generates thrust without the need for a two-component (bipropellant) system. This simplifies the entire propulsion system, reduces the number of valves, pipes, and tanks, and simultaneously increases safety in operations on the ground and in orbit.

Hydrazine is, on the other hand, an extremely toxic and carcinogenic substance, the storage, handling, and transport of which require expensive protective equipment, specialized facilities, and strictly regulated procedures. Crews on launch pads must not approach it without full protective suits with their own air supply systems, and potential environmental contamination poses a serious risk. Therefore, the space industry has been looking for years for alternatives that would retain the usability of hydrazine but with less impact on human health and the environment. ARIEL occupies precisely this niche, as one of the first hydrogen peroxide monopropellant thrusters of this thrust class developed in Europe.

Rapid development with the support of ESA's FLPP program

The FLPP program, within which ARIEL was created, is conceived as a kind of incubator of technologies for future European launch systems. Through it, ESA financially and technically supports companies developing components and subsystems with potential for application on future rockets, spaceplanes, or advanced space missions. In the case of Arkadia Space, the first contract for the development and testing of ARIEL was signed in June 2023, and just seven months later the engine was ready for its first firing on the test bench. In less than two years from the signing of the contract, ARIEL reached, after a series of tests, the technology readiness level TRL 6, which means that the technology has been demonstrated in a relevant environment and is ready to move towards qualification and commercial applications.

Test center in Castellón and extensive testing campaign

The test campaign was conducted at the Arkadia Space Test Center located at Castellón Airport in Spain, where the company built its own facility specially adapted for testing medium-thrust thrusters and longer run times. The test bench and supporting infrastructure must withstand not only short pulses but also continuous "burns" lasting several minutes, with repeated cycles of ignition and shutdown, pressure and temperature changes, and measurements in conditions approximating the vacuum of space. Such tests allow engineers to precisely characterize the engine's behavior, optimize the design of the combustion chamber, catalyst bed, and injector, and confirm reliability in conditions close to actual flight.

Engine performance confirmed by extensive testing

During that campaign, ARIEL demonstrated a number of key performances. It achieved a specific impulse of the order of 180 seconds in a vacuum, placing it among competitive "green" monopropellant thrusters on the market. The engine is capable of operating continuously for up to five minutes in a single burn, without signs of degradation or performance drop, which is important for maneuvers such as active braking, de-orbiting, or transferring to another orbit. At the same time, it can also work in very short, extremely precise bursts of just 40 milliseconds, which are typical for fine attitude control of the spacecraft during phases such as rocket stage separation, orbital maneuvers, or preparation for atmospheric entry.

During testing, a single engine performed more than 2000 pulses and consumed over 100 kilograms of hydrogen peroxide, providing a solid statistical basis for reliability assessment. In addition to the thruster itself, the project includes prototypes of fuel tanks and a feed system that can operate in the so-called "blowdown" mode: as HTP consumption increases, part of the hydrogen peroxide spontaneously transitions into the gaseous phase and with its pressure pushes the remaining liquid towards the engine chamber. This reduces the need for additional pressurization gas (like helium), which again simplifies the system and reduces mass.

Advantages of hydrogen peroxide in practice

Hydrogen peroxide as a propellant also brings a whole range of additional advantages. Compared to hydrazine, HTP offers a competitive level of specific impulse, although in some configurations it is slightly lower, but this is compensated by simpler system architecture, lower costs, and lower safety requirements. Furthermore, hydrogen peroxide is cheaper, commercially available in numerous industrial sectors and, with adequate precautions, is significantly less dangerous for people and the environment. Unlike hydrazine, which is classified as very hazardous waste and requires complex disposal procedures, the decomposition products of hydrogen peroxide are water and oxygen, which significantly facilitates overall logistics.

From the perspective of ground infrastructure, the transition to hydrogen peroxide means shorter mission preparations, reduced need for special protective suits and equipment, fewer administrative barriers, and lower operating costs. This is precisely why more and more space agencies and satellite operators are considering or already implementing "green" propulsion systems, either in the form of hydrogen peroxide monopropellant engines or in combination with other fuels in hybrid or bipropellant configurations. ARIEL positions itself as one of the tools enabling the European industry to catch up with this trend and simultaneously reduce dependence on external suppliers of key technologies.

Technical challenges: catalyst and additive manufacturing

On the technical side, the development of a reliable hydrogen peroxide monopropellant thruster is not a trivial task. The biggest challenge lies in the development of a catalyst bed that must withstand repeated cycles of HTP decomposition, high temperatures, and potential contaminants, while maintaining stable performance throughout the engine's entire life cycle. Arkadia Space, as part of the ARIEL project, with the support of ESA rocket propulsion experts, optimized the chamber geometry, material selection, and configuration of catalytic elements to reduce pressure drop, prevent local overheating, and ensure that fuel decomposition takes place in a controlled and repeatable manner, from the first to the last ignition.

Another important component in the design of thrusters of this class is the possibility of 3D printing certain parts, thereby reducing the number of joints, shortening production time, and facilitating design modifications. Arkadia developed part of its thrusters precisely with additive manufacturing in mind, which coincides with the general trend in the space industry where more and more critical parts – from injectors to load-bearing structures – are made on 3D printers adapted for the use of high-temperature alloys. Such an approach also enables easier adaptation to different configurations of rockets or satellites, as certain elements can be quickly redesigned and reprinted.

From demonstrator to commercial product

ARIEL does not remain just in the demonstrator phase. Already during 2025, the technology began receiving concrete commercial applications. Arkadia Space signed its first fully commercial contract with the French company MaiaSpace, which is developing a new generation of European small, partially reusable rockets. ARIEL's 250 N thrusters were selected for the Reaction Control System (RCS) on their launch vehicle, where they will ensure precise control of the rocket's orientation after liftoff, during stage separation phases, and the eventual return of rocket parts for reuse. For Arkadia, this contract signifies confirmation of the technology's maturity and the beginning of market entry as a supplier of key propulsion components.

According to publicly available technical data, ARIEL is today categorized at technology readiness level TRL 8, implying that the system is at a high degree of maturity and very close to full operational, serial use. Flight qualification is planned for the end of 2025, which would, upon successful completion of the process, open the door to wider introduction of the engine on future launch and orbital platforms. The thruster design covers a thrust range roughly from 75 to 275 N, with a nominal 250 N, a minimum impulse bit of less than ten Newton-seconds, and a total available impulse of several hundred thousand Newton-seconds over its lifetime, with a projected number of pulses exceeding 10,000.

Wider portfolio of Arkadia Space green thrusters

In the background of this commercial success stands a wider package of ESA projects in which Arkadia participates. Besides ARIEL, the company is also developing smaller engines, such as the 5-Newton DARK thruster for precise satellite orbital maneuvers, thereby covering the entire spectrum of needs – from fine control of small satellites to providing stabilization and control of rockets during launch. The company has already demonstrated its hydrogen peroxide propulsion systems in orbit, on missions of commercial providers of space debris removal and satellite servicing, which further solidifies the status of this technology as a reliable option for operational missions.

European context and strategic autonomy

At the level of the entire sector, the shift towards "green" propulsions also has broader geopolitical implications. In recent years, Europe has actively sought to ensure greater strategic autonomy in space, whether through the development of its own rockets and satellite constellations, or through investment in new generations of propulsion systems. Dependence on hydrazine imports and associated regulations, especially outside the EU, is a long-term weakness that such projects seek to mitigate. Hydrogen peroxide, which can be produced within Europe, with significantly fewer regulatory barriers, fits into the new industrial and security strategy, and ARIEL concretizes this vision in the form of a product entering commercial use.

The environmental aspect is not secondary. Although the total amount of fuel used by the space industry cannot yet match the global consumption of fossil fuels in air or road transport, every technology that reduces emissions and risks is a gain for the environment. Life cycle assessments indicate that hydrogen peroxide as a propellant can reduce emissions by up to approximately 40% compared to hydrazine, if the entire chain from production, storage, and transport to use and disposal is observed. At the same time, the risk of environmental contamination in the vicinity of launch pads or test centers is reduced, because potential leaks decompose into substances that natural systems tolerate more easily.

Applications for satellite and rocket operators

For satellite and launch system operators, ARIEL and similar thrusters represent a way to combine high orbital precision with a more acceptable environmental footprint and lower operating costs. Precise attitude control is key, for example, for satellite constellations in low Earth orbit, where every millisecond of thruster operation can mean the difference between optimal and suboptimal position relative to the rest of the constellation. Given that such missions require thousands and thousands of ignitions over several years of operation, the reliability and repeatability of performance that ARIEL demonstrated in tests directly translate into fuel savings, longer spacecraft life, and more stable service to end users.

What follows for ARIEL and Arkadia Space

In the coming years, further development of the ARIEL product line is expected, including adaptations to different customer requirements – from reusable rockets to large satellites and orbital servicers. Potential also exists for combining HTP with other fuels in hybrid or bipropellant systems, where the same technical foundation – tanks, valves, and part of the propulsion infrastructure – could serve as a basis for more complex engines of higher thrust. But already now, as a 250-Newton hydrogen peroxide monopropellant thruster, ARIEL symbolizes a new generation of European space technology striving to combine innovation, sustainability, and market competitiveness.

Industry and agency collaboration as a development accelerator

The collaboration between ESA and Arkadia Space on this project also shows how European institutional programs can accelerate the path from idea to product. The contract within the FLPP gave Arkadia not only financial support but also access to rocket propulsion experts, test procedures, and standards that have been honed for decades on major European programs like Ariane. Such synergy allows relatively young companies to avoid common "teething troubles" and incorporate requirements related to certification, safety, and integration into complex space systems already in the early stages of development.

For Arkadia Space, founded only a few years ago, ARIEL is also a ticket to the club of companies providing key propulsion technologies in Europe. After a successful test campaign and validation in cooperation with ESA, signing the contract with MaiaSpace represents confirmation that their approach to "green" propulsion makes not only technological but also business sense. As the number of launches increases, and interest in more sustainable and safer propulsion alternatives grows, thrusters like ARIEL could become a standard part of European rockets and satellites, whereby hydrogen peroxide would definitely establish itself as a serious replacement for hydrazine in many applications.