DARPAs Vulture: What Goes Up, Neednt Come Down
In April 2008, 3 teams received Phase 1 contracts to begin developing develop a radical new aircraft, under a US Defense Advanced Research Projects Agency (DARPA) program known as “Vulture.”
DARPA’s goals for Vulture are not trivial: 5 years on station with a 450kg/ 1,000lb payload, 5kW of onboard power, and sufficient loiter speed to stay on station for 99% of the time against winds encountered at 60,000-90,000 feet.
The Designers & The Designs
DARPA contract winner Aurora Flight Science is involved in building Northrop Grumman’s high-altitude Global Hawk UAV, has worked on a “Mars Flyer”/ARES vehicle for NASA, and is also collaborating with Boeing and with General Dynamics on the hydrogen fuel cell powered, high altitude Orion HALL.
Aurora’s design is called “Odysseus,” using solar energy to power the aircraft during daylight, and stored solar energy to power the aircraft at night. Aurora’s Odysseus uses a “modular shuttling” approach, using 3 UAVs with 160 foot wingspans that can dock and separate in the air. This simplifies take-off and flight to altitude, while providing options if any of the 3 vehicles need to be recalled for maintenance or replaced. Solar power with fuel cells will keep Odysseus in the air, and the 3-vehicle design can go from a Z-shaped configuration to capture more of the day’s sunlight, to a straight wing configuration for low drag at night.
DARPA contract winner Boeing also has a varied team drawn from inside and outside the company. Boeing Integrated Defense Systems (IDS) Advanced Systems, IDS Space and Intelligence Systems, Boeing Spectrolab and Boeing Phantom Works are all involved. Their major partner is the British firm QinetiQ, whose solar-powered, carbon-fiber Zephyr high-altitude, long-endurance unmanned aerial system is currently flying under a joint British-American program. Other partners include Versa Power Systems and C.S. Draper Laboratories.
Zephyr is a an ultra-lightweight carbon-fibre aircraft with a wingspan of up to 18 meters/ 59 feet, but weighing just 30 kg/ 66 pounds. By day it flies on solar power generated by amorphous silicon arrays on the wings that are no thicker than sheets of paper. By night it is powered by rechargeable lithium-sulphur batteries that are recharged during the day using solar power. Many of its design approaches and technologies will be leveraged for Vulture, but the winning single-aircraft SolarEagle design is very different from Zephyr.
The third competitor was Lockheed Martin. Their solar-powered design is reportedly a single UAV over 300 feet long, with tails that rotate to collect the most sunlight and systems that capture photovoltaic energy from the Earth’s albedo. The power feeds electric ring motors, which can drive propellers directly at a distance without using heavy gearboxes. There are reports that their system will be launched from a lighter-than-air craft. Lockheed’s Vulture program manage Derek Bye is quoted as saying that says their Skunk Works is drawing on the satellite experience of Lockheed Space Systems business, which has to deal with even more extreme environmental and reliability challenges.