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Boeing Selects Solid Oxide Fuel Cell Company For Ultra-Long Endurance Aircraft Project

Boeing’s Integrated Defense Systems has selected Versa Power Systems, Inc., a developer of solid oxide fuel cells (SOFC), to develop a power system for an ultra-long endurance unmanned aircraft as part of Boeing’s contract for Phase 1 of the Defense Advanced Research Projects Agency’s (DARPA) Vulture air vehicle program, an effort to create a new category of ultra-long-endurance aircraft.

Boeing was awarded the DARPA Vulture contract in April. The Vulture program calls for developing technologies and ultimately a vehicle that can deliver and maintain a 1,000-lb (454 kg) airborne payload drawing 5 kW of power on station for an uninterrupted period of more than five years using a fixed-wing aircraft. Boeing is teaming with UK-based QinetiQ Ltd. for the program.

DARPA also selected two other contractor teams for the Phase 1 Vulture program, one led by Aurora Flight Services, the other by Lockheed Martin.

Currently the only systems capable of providing multiple years of coverage over a fixed area are geosynchronous satellites orbiting 22,233 miles above Earth.

Such a pseudo-satellite system, like Vulture, could provide compelling operational advantages in terms of persistent intelligence, surveillance, reconnaissance and communications.

—Pat O’Neil, program manager, Boeing High Altitude Long Endurance Systems

The yearlong Phase 1 covers conceptual system definition, and formal reliability and mission success analysis, concluding with a System Requirements Review. It also requires conceptual designs for sub- and full-scale demonstrators.

In the program’s second phase, DARPA contractors will refine the demonstrator designs, continue technology development and risk reduction efforts, and conduct an uninterrupted three-month flight test of a sub-scale demonstrator. The third and final phase of the program will consist of a flight test of the full-scale demonstrator vehicle, during which the Vulture system will demonstrate the ability to operate continuously for 12 months.

Since the Vulture system must operate over extended periods, there is a premium on the need for long life and extreme reliability in every element of the aircraft starting with its power source, according to Robert Stokes, Versa Power’s CEO.

Solid oxide fuel cells are particularly power dense, generating considerably large amounts of electricity from a relatively low-weight package. They produce energy continuously as long as the basic building blocks of fuel and air are supplied.

Versa Power Systems’ SOFC is a ceramic planar (flat, square or rectangular) cell, with a solid electrolyte that is anode-supported (the thickest component to which all other materials are subsequently mounted) and conducts oxygen ions. Other SOFC technologies exist and can be either cathode- or electrolyte-supported and are sometimes tubular in shape.

Versa Power Systems (VPS) developed a proprietary micro-structure which gives its fuel cells very high power density. Since beginning initial development in the labs of Global Thermoelectric in 1998, VPS power density at 750°C operating temperature has increased more than five-fold to reach the threshold of the US Department of Energy’s 2012 commercial power density goal.

The high power density allows VPS SOFC stacks to be smaller, lighter and less expensive. VPS stacks are intermediate temperature systems—they can operate at temperatures below the 800°C to 1,000°C range of other SOFCs, allowing the interconnect plates used to direct fuel and oxygen flow, collect electrical current and hold the fuel cells in place in the stack to be stamped from commercial stainless steel rather than made of exotic metal alloys or expensive conductive ceramic materials.

Versa Power contributed the SOFC component of Imperial College London’s ABSOLUTE Hybrid (Advanced Battery Solid Oxide Linked Unit to maximize Efficiency)—a series-hybrid powertrain that combined an intermediate-temperature solid oxide fuel cell (IT-SOFC) with a ZEBRA sodium nickel-chloride battery. (Earlier post.)




5 kW for 5 years amounts to 219,000 kWh of energy.

Assuming ~50% efficiency of the fuel cell, that would require a fuel containing about 440,000 kWh of energy.

A very energy-dense fuel such as diesel can contain 14 kWh per kg, so you'd need at least 31 tonnes of fuel to provide 5 kW for 5 years.

Can you really keep 30-40 tonnes aloft or in place with just 5 kW of power?


These SOFC planes are meant to be refueled in air I am rather sure.

Next development step should be to outfit them with 8, 100 lb precision guided weapons so that they can provide around the clock and instant heavy bombing as well. It should not be impossible to invent a system for munitions reload in air as well. Non-stop instant bombing and surveillance capabilities have recently been introduced in a number of Iraq locations by unmanned surveillance bombers that work in 8-12 hours shifts. This has had a dramatic impact on the battleground essentially preventing enemy combatants to move in force or ‘train in peace for combat’. These planes are a game changer in modern warfare and we will see a lot more of it in the coming years. It will enable the US army to provide massive heavy bombing and surveillance to local allies without the need to put our own soldiers in harm’s way since these airplanes can be controlled from safe bases in the US and fueled and reloaded from fortresses set up locally or from aircraft carriers. The potential of these planes is enormous and it could be the thing that enables the US to pull most of its troops out of Iraq and Afghanistan long before the local governments are capable of controlling the situation without any external support.


If these planes have large wings, covered with solar cells, at high altitude they could produce a lot of power during daytime, using part of the energy for splitting water, which can be used in the fuel cell if needed. So you don't need to 'burn' fuel at a rate of 5kW during a period of 5 years. You 'burn' it when you need it, and you can recycle the water when the sun shines. Consider it a rechargeable battery with a very high energy-density.


Its not what you think. The plane doesnt need 5kw the pacjage does. As they are using a sofc obviously they are running it on jet fuel from a refuleab le in flight tank.

So all this realy is is an unmanned plane with a very dependable fuelcell system powering something interesting...



If the engine is going to be running all the time, surely the attached generator must be equally reliable?

Electric machines wear out a lot less quickly than ICEs, turbines etc.



I agree, high performance solar cells (money is no object here) are a great range extender and will pay for their weight many times over. But drop the water. The Solid Oxide Fuel Cell has a higher energy density per unit weight then does water for sunless flight.



Boeing could very easily source multi-junction cells from their subsidiary, Spectralab. These cells are ~44% efficient, if I recall.

Assume 1kw/m insolation
Assume 40% insolation->motor efficiency
Assume 183m^2 wing surface area (about that of Helios)

That gives us .4(1,000W/m^2)x183/m^2=73,200W

Or 73kW continuous. Seems high.... where did I screw up?


Just checked. Helios' motors used 21kW. The solar cells used were 19% efficient silicon based. The 44% efficient multi-junction cells would enable up to 48kW of motor draw.

Perhaps the wing could go (Top to bottom):

-Polycarbonate Fresnel lens
-Multi-junction solar cell
-Helium filled wing support structure
-The whole thing could be wrapped in a sheet of graphene



you might not always get vertical sunlight. But your ballpark calculation is correct.
The difficult part is storing the power (night). Generating sufficient power during daytime is not difficult.

Why don't they just use a blimp? Lots of area, lots of payload and low speeds.



I'd agree with you, but DARPA is specific that they don't want a "dirigible" for this program.



Maybe speed to station or covert operation, is in the spec.


Greenplease, instead of using helium filled wing support structure, why not use a hydrogen filled support structure ?
If you use big wings (for the solar cells) and let the hydrogen pressure inside the wings vary between 5 and 25 bar, it can be made cheap and light. That way, your fuel tank and your support system are the same. Since you don't care about a large volume tank anymore, you can use low pressure tanks that can still cary a lot of fuel.

Roger Pham

Clett asked: "Can you really keep 30-40 tonnes aloft or in place with just 5 kW of power?"

Clett, first of all, 1kg of diesel fuel contains 140 kwh of thermal energy, not 14 kwh. So, that reduces the required tonnage of fuel by a factor of 10, down to 3.1 tonnes. But, that is assuming that no solar cells will be used to provide power during the daytime.

With enough solar cells, may be only 1.5 tonnes of fuel will be necessary. You can easily keep aloft a 2,500-kg aircraft on 5 kw of power if you fly real slow and have a lot of wing area. Human-powered aircraft weighs on the order of 150kg fully loaded and able to cross the English channel using under 0.15kw of human power, for a power-to-weight ratio of about 1/1000 (1kw/1000kg) Of course, at higher altitude above clouds and weather system, you will need a higher power-to-weight ratio to keep aloft, due to the thinner air, so I figure 2kw/1000kg would be about right.

Of course, if your aircraft can produce H2 from solar panels for use during sunless hours, then you don't have to carry any additional fuel aboard. Cruising in the upper atmosphere above the weather system, there will never be any clouds. The sun will shine constantly everyday, so your solar power production will be very reliable. Lithium battery is an alternative to SOFC and H2, but would be heavier and would not have the durability that Boeing is looking for.

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