Sorontar

If you are reading this, I want your insight on specs for drone fuel cells. Let's start with why:

American drones need more power.

While expensive turbines work for big drones, small drones have no great energy sources. This drastically curtails range, payload, and performance.

The RU/UA war highlights this problem:

• Impact recordings frequently show LOW BATTERY alarms: these drones are being pushed to their limits.
• Fiberoptic cables are a short term hack for control in comms-denied environments. But we can't replace fiberoptics with onboard AI unless we have have a way to power that AI!
• Medium sized drones (V-BAT, Bayraktar, Shahed) resort to piston engines, which are loud, shaky, heavy, and less reliable than turbines. Additionally, they deliver power in the wrong form: we want electrical power for compute and nimble electric motors rather than torque, gearboxes, and driveshafts.

Off the battlefield, small commercial drones, like Zipline's Platform 2 VTOL drone, have tiny service ranges of ~10 miles!

If autonomous systems are reshaping warfare and commerce, and if power sources are a key limiting factor on autonomous system performance, America must lead the world in solving drone power.

Existing solutions can't solve the problem.

• Internal combustion engines: we've had a century or so to perfect these. They are still loud, hot, relatively unreliable, and shaky. Advanced drone systems in the year 2035 will not be flying lawnmowers, but this is sometimes the best we can do for medium sized drones today.
• Lithium batteries: we might reach 1 kWh/kg with solid state batteries, but further breakthroughs are speculative. Despite poor energy density, rechargeable lithium batteries are convenient and cost-effective, making them the best solution for small drones today. Their high gravimetric power density (~5 kW/kg burst) means they will remain useful for hybrid power sources.
• Turbines: energy dense JP-8 fuel (12 kWh/kg) and high power density (~5 kW/kg) are hard to beat. They will likely remain the best solution for very large drones, but they are too inefficient for small vehicles under ~10 kW (tip clearance, combustor residence time, surface-to-volume ratio, and reynolds number effects all improve as turbines get bigger).

After evaluating alternative solutions including magnetohydrodynamic generators, free piston linear generators, and lightcells, one practical technology remains.

Fuel cells can.

If you're rolling your eyes, I get it! For decades proton exchange membrane (PEM) fuel cells have been touted, but they never really materialized. The promise is clear:

• hydrogen has a spectacular energy density of 33 kWh/kg,
• proton exchange membrane (PEM) fuel cells are quiet, cool, clean, reliable, and deliver > 2 kW/kg as electricity.

So why haven't they caught on? US programs like Puma, 2007 and Ion Tiger, 2009 were tried (heck, I lived practically next door to the first hydrogen refueling station in Palo Alto) but they were never adopted because hydrogen gas is a terrible fuel despite its gravimetric energy density. We haven't found a great way to store it!

• compressed hydrogen tanks are heavy (5% gravimetric efficiency) and bulky (1.4 kWh/L system). Their volume per unit of energy is comparable to lithium ion batteries and far lower than JP-8's volumetric density, 10 kWh/L,
• liquid hydrogen and cryo-compressed hydrogen logistics are expensive and complex. Cryogenic tanks are heavy (7% gravimetric efficiency) and bulky (1.5 kWh/L system), so cryogenics aren't much better than compression.

OK, if we can't store hydrogen directly, can we power fuel cells with more complex molecules? Yes: solid oxide fuel cells based on yttria-stabilized zirconia can run directly on hydrocarbons, but they are heavy (1 kW/kg) and require slow preheating to reach operating temperature, making them less suitable for drones (really cool oxide transport mechanisms though).

Can we break larger molecules into hydrogen through reforming? Yes: reforming light hydrocarbons into H2 and CO2 is feasible in situ, but reforming JP-8 is probably not (the military has tried for decades but desulfurization, coking, and steam process complexity are big problems). Additionally, the carbon monoxide reforming byproduct poisons many fuel cells.

So what should the Aerospace Republic do?

Proposal

We think we see a way to thread this needle and create the world's best power source for < 25kg drones in the form of fuel cell energy pods, achieving:

• high gravimetric & volumetric energy & power density
• clean, quiet, reliable electric power
• simple supply chain for chemically bound hydrogen
• simple onboard chemical conversion
• established fuel cell technology

So we're doing some very early, small-scale tests (exotic industrial equipment is arriving to our mountaintop shipping-container-as-lab daily) to see if this can really work in practice, targeting usable prototypes in 2026. No promises yet, but no scientific breakthroughs required either.

Help us define the spec!

To standardize, we want to build a single energy pod form factor. Rather than expensive integrations for every platform, we can drive costs down with a standard solution:

• one form factor
• one mounting method enabling automated swaps and recharging
• one drone-to-pod communication protocol
• one base station for recharging the pods

Could this form factor work for your drone missions? If so, what parameters would actually meaningfully improve the performance envelope for you?

• Voltage: 24, 48, 72, 96 V?
• Max pod mass (kg) and dimensions
• Min energy (kWh/kg) and power (kW/kg) density
• Max pod cost ($/ea.)
• Preferred electrical connection standard
• Preferred communication protocol (UAVCAN/TSN/?)

If you have thoughts, I'd love to hear them: chris@ckwalker.com / 509.999.0449 / google meet. Thank you!