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.)
Development of Solid Oxide Fuel Cells at Versa Power Systems (October 2007)