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Innovations in uncrewed systems are disrupting the way wars are fought and the way in which they will be won. According to the U.S. Defense Intelligence Agency’s threat review for 2025: “More advanced UxS swarms complicate the threat posed to traditional U.S. defense systems, given continued improvements in range, payload, and power.” It continues: “UxS technology’s continued maturation and convergence with other technologies, including AI, big data, Internet of Things, and 5G telecommunications will exacerbate this threat.”
With critical aspects of performance involving range, stealth, payload and power, fuel cells emerge as a key technology for achieving superiority.
Drone technologies can have an asymmetric effect on the battlefield given the deployment of cheap, attritable vehicles capable of inflicting damage on significantly more costly hardware.
The year before last (2024) was seen as the year that military UAV usage saw a significant uptick. Ukraine ramped up drone production from 300,000 in 2023 to a projected 1.5 million in 2024, while Russia produced 1.4 million drones in 2024, a nearly 10x increase from previous years. Ukraine has used drones to offset Russia’s numerical superiority, with drones accounting for 70–80% of battlefield casualties in the war.
The deployment of UAV enables a low-cost, high-volume strategy, and rapid deployment and replenishment, and achieving operational superiority is fast becoming a key strategic consideration.
Hydrogen fuel cells offer significantly longer operational times/ranges and faster turnarounds compared to traditional battery technologies, as well as delivering reduced detectability and lower maintenance and operational costs compared to combustion-powered alternatives.
“Leveraging hydrogen fuel cells gives operating forces new capabilities. These include longer flight and drive ranges, less electronic signature, lower maintenance requirements, higher energy resilience, and, most importantly, reduced dependence on fuel supply chains, which are vulnerable to disruption in contested logistics environments.”
Experiments conducted at Arkansas Tech suggest that hydrogen-powered drones can fly three to five times longer, enabling extended surveillance, reconnaissance, and strike missions without the need for frequent refueling.
For our recently published Hydrogen in Defense white paper, ZeroAvia has analyzed a potential retrofit of a representative Class I(d) (small) tactical 100 kg multirotor drone with a hydrogen-electric powertrain.
The results show poor battery trade in terms of swapping payload for increased stored energy to deliver more range, for a maximum endurance of only 30 minutes. Even for a gaseous hydrogen storage fuel cell system, the heaviest hydrogen-electric solution available, the story is dramatically different, with the ability to increase the range and endurance of the system five-fold at half load. A custom designed drone for hydrogen-electric application could significantly outperform this.
In addition to weight, battery suffers from issues of cycle life, with degradation impacting operations and ultimately leading to costly replacements. In addition, the requirements for rare earth materials (cobalt, nickel and lithium), cause significant supply chain constraints and risks. Fuel cells, by contrast, rely primarily on platinum, and in small quantities.
Hydrogen fuel cells can also offer significant capability improvements compared to existing combustion-powered platforms due to improved energy efficiency (2-3 times better than combustion equivalents according to U.S. Department of Energy) and weight of fuel (three times lower on a per unit of energy basis), either replacing the incumbent system (as a re-engining effort) or as a range extender or providing a more efficient method of meeting high onboard electrical power demands.
According to ZeroAvia analysis, re-engining a Class III (large) strategic high-altitude intelligence, surveillance, target acquisition and reconnaissance (ISR)/strike drone with a hydrogen-electric propulsion system can extend the envelope of the existing aircraft (see chart).
With an already impressive 40-hour endurance using gas turbine propulsion, switching to advanced fuel cell and electric propulsion, supported by liquid hydrogen fuel storage, could increase to beyond 60 hours based on the latest commercial sector literature on liquid hydrogen management system performance.
As well as retrofitting opportunities, there are several projects underway to design and build new hydrogen-electric UAVs. In France’s project RAPACE, civilian and military researchers at the Centre de Recherche de l’École de l’Air (CREA) aimed to develop a 100% French hydrogen UAV, integrating a complete hydrogen energy system. The researchers performed successful test flights in May 2023.
Drones with internal combustion engines can today fly longer than electrified equivalents (although the fuel cell and liquid hydrogen technology development roadmap predictions challenges that paradigm in the coming years). However, combustion engine aircraft also have a high thermal/acoustic signature that makes them easy to target and intercept. That signature is orders of magnitude lower in drones using hydrogen power generation and electrical propulsion systems.
Reduced Temperature
Fuel cells operate at much lower temperatures than typical UAV jet engines, with exhausts three times cooler. This has a significant impact on operational safety, as well as design and maintenance, with increased component lives, and wider, more economical material options. The lower temperature would also mean substantially reduced optical distortion (heat haze) around the vehicle that can betray the presence of hardware in the air or on the ground.
Reduced Thermal Radiation
The quantity of IR radiation from fuel cell systems is reduced by up to 80 times as this scales strongly with temperature, therefore reducing detectability. This also minimizes weight of thermal shielding and exhaust hardware.
Reduced Noise
Electrical propulsion systems are also much quieter than their combustion equivalents. There is a total elimination of jet engine noise, which for some vehicles means reducing noise levels by up to 85%. With around 10 times lower air flow rates than an equivalent jet engine, hydrogen-electric powertrains would have a reduced plume size (affecting IR cross-section) and associated flow noise.
These theoretical advantages of fuel cell powered drones are being recognised and explored by armed forces, governments and industry, and progressing towards deployment.
The US Defense Innovation Unit added Heven Aerotech’s Z1 Blue UAS Select list, making it the first hydrogen-powered drone to be recognized within the program’s highest tier of trusted systems approved for rapid acquisition and deployment. ZeroAvia is already shipping its SuperStack Flex 150-200kW fuel cell power generation system to the defense sector. And just last week media reports suggested that hydrogen-electric UAV were in operation in Ukraine.
Beyond fixed-wing applications and smaller rotor drones, the defense sector is also turning its attention to how commercial eVTOL designs can be adapted to provide new capabilities, from enabling rapid deployment from and to austere environments without runway, to reducing detectability. Practically, these benefits are likely difficult to realize with battery energy density, durability and recharging limitations.
Hydrogen is therefore a key tool for delivering eVTOL’s promised benefits in defense arenas, and we will explore this in the next installment of this Hydrogen in Defense blog series.
To download the Hydrogen in Defense white paper, please click here.