Green propellant. The phrase appears in a lot of smallsat programme documents. What it means technically, what the performance numbers actually are, and how different formulations compare against each other and against hydrazine — that is worth understanding before you write it into a procurement specification.
Why Propellant Greenness Became a Programme Requirement
Hydrazine has been the default monopropellant in spacecraft propulsion for 60 years. Isp of 220-230 seconds, excellent thermal stability, well-understood catalyst chemistry with Shell 405 and IRFNA variants. The problem is toxicology: hydrazine is classified as a probable human carcinogen, and its handling requires Class A hazardous materials procedures, dedicated ground support equipment, and specialist personnel certification under ECSS-Q-ST-70.
At small satellite scale, the disproportion between spacecraft mass (2-12 kg) and the ground infrastructure cost of hydrazine handling made alternative propellants economically attractive. By 2015, two formulations had reached operational readiness: AF-M315E (developed by Aerojet Rocketdyne and AFRL in the United States) and LMP-103S (developed by ECAPS, a Viasat subsidiary, in Sweden). Both are referred to as green propellants, though their chemistry, performance, and handling profiles differ meaningfully. Differ significantly, actually.
AF-M315E: Chemistry and Performance
AF-M315E is a hydroxylammonium nitrate (HAN)-based ionic liquid blend. It is aqueous, with approximately 45% water content by mass. This makes it non-volatile (near-zero vapour pressure at ambient temperature), which is the primary green handling advantage: no inhalation exposure pathway during normal operations.
Performance: demonstrated Isp of 231-250 seconds with iridium catalyst, thrust efficiency of 94-97% compared to theoretical vacuum Isp. The NASA Green Propellant Infusion Mission (GPIM, STP-2 launch 2019) demonstrated AF-M315E on orbit with a 100 N thruster, achieving 23% improvement in Isp and 12% reduction in propellant volume versus hydrazine equivalents. NASA mission results are published and peer-reviewed; in our view they remain the best publicly available real-world dataset for this propellant class.
Catalyst bed preheating remains a requirement: 220-280 °C preheat temperature for reliable ignition, consuming 10-20W for 3-8 minutes. That power budget has to exist in your spacecraft power architecture before you commit to AF-M315E.
LMP-103S: Chemistry and Performance
LMP-103S is an ammonium dinitramide (ADN)-based formulation, developed in Sweden under the ECAPS programme. ADN is an oxidiser with lower toxicity than hydrazine and none of the vapour pressure concerns of neat hydrazine. Water content is approximately 14%, and the formulation includes methanol as a stabiliser.
Performance: Isp of 220-235 seconds, with the PRISMA mission (2010) providing the first in-orbit demonstration. Thrust range: 0.1 to 1 N with HPGP (High Performance Green Propulsion) thrusters. Catalyst: proprietary formulation, not Shell 405 compatible. The ADN supply chain in Europe is more established than HAN for European satellite operators, which matters for qualification under ESA procurement rules.
ISPTech's Green Propellant Approach
Our propulsion architecture uses a catalyst system optimised for mixed-monopropellant operation, capable of processing both HAN and ADN formulations with the same thruster hardware within defined propellant-compatibility bounds. This matters for operators procuring spacecraft for constellation batches: propellant supply chain flexibility reduces single-supplier risk.
Verified performance on ISPTech's 1N thruster class: Isp of 228-236 seconds across propellant lot variation, thrust stability ±3% over 5,000-cycle endurance validation. Catalyst bed degradation under accelerated ageing test is less than 8% Isp drop at 15,000 equivalent mission cycles. Those numbers are in our qualification test report, available to qualified primes.
Green vs Hydrazine: The Honest Comparison
| Parameter | Hydrazine | AF-M315E | LMP-103S |
|---|---|---|---|
| Isp (s) | 220-230 | 231-250 | 220-235 |
| Density (kg/L) | 1.01 | 1.46 | 1.24 |
| Vapour pressure (kPa) | 1.4 at 25°C | <0.01 | <0.01 |
| Toxicity class | Carcinogen | Irritant | Irritant |
| Preheat required | No (cold-start capable) | Yes, 220-280°C | Yes, 220-260°C |
| Propellant density advantage | Baseline | +44% denser | +23% denser |
Higher density is a genuine advantage: for the same tank volume, you carry more propellant mass. Combined with equal or better Isp, the green options offer meaningfully more delta-v per litre of tank volume. For a 6U CubeSat where tank volume is constrained, this is not trivial.
Programme Decision Factors
If your programme already has hydrazine handling infrastructure and a launch slot that requires existing propellant certification, switching to green adds qualification cost and schedule risk that may not be justified. If you are starting from a clean-sheet smallsat design with no existing propulsion heritage, there is no reason to start with hydrazine. The handling advantage is real, the performance is equal or better, and the regulatory trajectory is clearly in the direction of green propellants. No question about it.
For ISPTech's propellant compatibility matrix and thruster-level data sheets, see our propulsion systems page or request a technical brief.
What Engineers Actually Ask Us
Three questions come up in nearly every technical exchange we have with spacecraft integrators evaluating green propellants for the first time.
Can I use the same tank hardware? Not directly. AF-M315E and LMP-103S have higher corrosivity to aluminium alloys than hydrazine. Tank materials must be titanium alloy (Ti-6Al-4V ELI) or CRES 347 stainless for wetted surfaces. Existing hydrazine titanium tanks are generally compatible, but Al-alloy tanks common in COTS CubeSat propulsion modules are not. Verify material compatibility through a 500-hour static immersion test per ECSS-Q-ST-70-71C before integration.
How does catalyst preheat affect power budget? AF-M315E requires a 220-280 °C catalyst bed preheat, consuming 10-20 W for 3-8 minutes per cold-start event. In a 6U bus with a 30 W average power budget, this is a real constraint. Plan your firing timeline so that preheat occurs during eclipse-exit when solar panel power is ramping up. We've seen missions fail to achieve planned manoeuvre schedules because preheat power demand was not integrated into the operational timeline.
What happens if propellant water content drifts? Both HAN and ADN formulations are sensitive to water content variation beyond their specification. Elevated water content reduces combustion efficiency and raises ignition temperature requirements. Accept propellant lots with a certified water content measurement from the supplier, and verify storage conditions (sealed, temperature-controlled) are maintained from delivery to fill. Non-negotiable. Full stop.
