Green Propellant vs Hydrazine: How Arkadia Space's In-Orbit Test Changes Satellite Propulsion
Arkadia Space's in-orbit green propellant test validates a non-toxic hydrazine replacement for small satellites. Here's how high-performance green propellants compare to hydrazine — and why the industry is finally switching.
The green propellant vs hydrazine debate has been ongoing for a decade. Now, Arkadia Space — a Madrid-based propulsion startup — has confirmed the successful on-orbit ignition and sustained operation of its high-performance green propellant thruster aboard a demonstration microsatellite, validating a technology that could finally displace toxic hydrazine from a significant portion of the small satellite market within this decade.
The Hydrazine Problem
Hydrazine (N₂H₄) has been the dominant propellant for spacecraft attitude control and orbit maintenance since the 1960s. It is energetically dense, storable at ambient temperature without pressurisation, and produces a clean, predictable combustion in catalytic thrusters. It works extraordinarily well.
It is also extraordinarily toxic. Hydrazine is a probable human carcinogen, acutely toxic by inhalation and skin absorption, and extremely hazardous to handle in bulk quantities. Every satellite that carries hydrazine propellant must be fuelled under strictly controlled conditions by technicians in full protective equipment in certified hazardous materials facilities. The fuelling operation extends the pre-launch processing timeline, increases mission costs, and introduces genuine safety risk.
The restrictions around hydrazine handling are tightening. The European REACH regulation already classifies hydrazine as a Substance of Very High Concern, and the regulatory trajectory points toward progressively more restrictive conditions for its use in new satellite programmes. For small satellite manufacturers — who have built their business models around streamlined, low-cost integration — the handling requirements for hydrazine are increasingly incompatible with their operational tempo.
The alternative is high-performance green propellants (HPGP): ionic liquid propellants such as AF-M315E (developed by AFRL, now produced by Aerojet Rocketdyne) or LMP-103S (developed by ECAPS, a subsidiary of Bradford ORBITGUARD). These substances offer specific impulses comparable to hydrazine — roughly 220-250 seconds in monopropellant configurations, versus hydrazine’s 220-235 seconds — but with dramatically lower toxicity profiles.
Arkadia Space’s Technology
Arkadia Space’s thruster is designed around a European-developed ionic liquid formulation, with a catalyst pack engineered for fast warm-up times and sustained operation over the multi-year mission lifetimes required by commercial constellation operators. The company’s stated specific impulse target for its 1N thruster class is approximately 240 seconds — placing it at the performance frontier for green monopropellant systems.
The on-orbit demonstration focused on validating several aspects of the thruster’s behaviour that ground testing cannot fully characterise: the thermal cycling environment of LEO (where the thruster cycles through eclipse and sunlit periods every 90 minutes), the long-term catalyst bed performance without the mechanical vibration that can refresh catalyst packing in ground testing, and the propellant feed system’s behaviour in weightlessness.
The successful in-orbit firing sequence included both a pulsed mode (simulating attitude control operations, with ignition durations of fractions of a second) and a steady-state mode (simulating orbit maintenance, with continuous burns lasting several minutes). Both modes performed within design specifications.
Why This Matters for the Small Satellite Market
The small satellite market has grown from a niche academic exercise to a commercially significant industry in less than a decade. The number of satellites under 100 kg launched annually has increased by more than an order of magnitude since 2015, driven by imaging constellation operators, IoT service providers, and the rapidly expanding spectrum of Earth observation applications.
The majority of these small satellites carry some form of propulsion for station-keeping, collision avoidance, and — at end of life — de-orbit manoeuvres required under the Inter-Agency Space Debris Coordination Committee (IADC) 25-year re-entry rule. For satellites above 400 km, propulsion is essential to comply with this guideline.
Green propellants offer small satellite operators a practical path to propulsive capability without the facility investment and regulatory burden of hydrazine authorisation. A CubeSat or microsatellite manufacturer working in a standard cleanroom — not a hazardous materials facility — can integrate a green propellant thruster directly, with the satellite arriving at the launch site already fuelled.
This difference in integration workflow is commercially meaningful. Reduced processing time translates to lower integration costs, faster turnaround between builds, and the ability to operate smaller manufacturing facilities without specialised chemical handling infrastructure.
The European Propulsion Ecosystem
Arkadia Space is part of a growing cluster of European startups addressing the propulsion needs of the small satellite market. Enpulsion (Austria) produces indium Field Emission Electric Propulsion (FEEP) thrusters for CubeSats. ThrustMe (France) builds gridded ion thrusters for small satellites. Exotrail (France) focuses on Hall effect thrusters for volume production. Bradford ECAPS (Netherlands/Sweden) has the most heritage with green monopropellants through its HPGP product line.
The diversity of technologies reflects the diversity of mission requirements: electric propulsion offers the highest specific impulse but requires time and power to build up momentum; chemical propulsion delivers higher thrust but uses propellant less efficiently. Different mission types — from low-altitude constellation deployment to high-orbit geostationary transfer — select different thruster technologies based on their specific impulse, thrust, power, and volume requirements.
Arkadia Space’s niche is the overlap between missions requiring significant delta-V in a constrained volume and mass budget, and operators who cannot or do not want to manage hydrazine. It is not a small market.
The Regulatory Tailwind
Beyond market dynamics, the regulatory direction of travel strongly favours green propellant adoption. ESA’s Green Propellant initiative has supported multiple technology development contracts for alternative propellants. The European Commission’s Space Programme regulation explicitly encourages the adoption of cleaner propellants and sustainable orbital operations practices.
The combination of market pull from small satellite operators and regulatory push from European and national authorities has created conditions in which green propellant startups can find both early customers and public funding. Arkadia Space’s orbital demonstration positions the company to convert that early-stage funding and interest into commercial contracts as constellation programmes begin their next build phases.
The shift away from hydrazine in small satellites will not happen overnight. But Arkadia Space’s successful orbital demonstration removes one more argument for staying with the incumbent.