defensenews.com
Published: 20 April 2009

(Image: Hydrogen and oxygen from a water electorolyzer (tubes on the left) go into hydrogen and oxygen tanks in a model explaining the combination system of sloar cell-fuel cell at the International Hydrogen & Fuel Cell Expo in Tokyo February 25, 2009. Copyright: Reuters)
Over the past decade, small, hand-launched drones have proven so useful that the U.S. military has bought more than 12,000 of them. Some weigh less than a pound and have wings that span just 2.4 feet. Others weigh 14 pounds and stretch 9 feet from wingtip to wingtip.
Small enough to be carried in a backpack, they can be snapped together in minutes and hurled into the air by a soldier.
Typically, these tiny aircraft carry sophisticated cameras that beam an overhead view of the battlefield back to operators on the ground. Driven by electric motors powered by batteries, they can usually stay aloft for an hour or two.
Now the U.S. military wants small drones with longer dwell times. It’s on the verge of getting them, thanks to hydrogen. Not hydrogen as in Hindenburg; hydrogen as in fuel cells.
Fuel-cell maker Protonex has shown it can fly a 14-pound UAV for nine hours on electricity generated by a hydrogen fuel cell and fuel cartridge that together are just a little bigger than a 2-liter soda bottle.
Now, with a $3.3 million contract from the Defense Department, Protonex plans to make a fuel-cell-and-cartridge combination that’s even smaller and has greater energy density, said Scott Pearson, Protonex chief executive.
Hydrogen fuel cells are a power source that automakers intermittently tout as a replacement for gasoline and imported oil. But there are numerous technical problems, ranging from heavy hydrogen tanks to the absence of a hydrogen infrastructure for supplying autos with fuel.
Protonex has overcome those, at least on the scale required by small, hand-launched UAVs.
The company’s new fuel cell is being designed to power to an AeroVironment Puma AE UAV. The 4.6-foot-long Puma has a 9-foot wingspan and carries electro-optical and infrared cameras for day and night surveillance. The fuel cell powers the cameras, communications gear and flight controls, as well as the electric motor that turns the plane’s propeller.
Protonex has built a variety of fuel cells to power UAVs. They produce 100 watts to 500 watts of continuous power, and use a lithium-ion battery to provide extra power for taking off or maneuvering. Electricity from the fuel cell keeps the battery charged.
Fuel-cell-powered UAVs fly two to four times longer than their battery-powered counterparts, Pearson said.
Extra time in the air is important. It means U.S. troops are able to observe targets for longer periods and view larger areas before their UAVs have to return to refuel, said Lt. Mark Roosz, who works on fuel cell-powered UAVs at the U.S. Air Force Research Laboratory.
“Contrary to how Hollywood often depicts it, ‘bad guys’ don’t conduct hostile activities all the time. By increasing the length of time available to observe a potential target, we increase the chances of catching them performing a hostile act,” Roosz said. “On today’s battlefield, information is key, and by enabling longer missions, we increase the amount of information available to friendly forces,” he said.
The power for these fuel-cell systems comes from hydrogen that is stored in the form of sodium borohydride, a white or grayish powder used in manufacturing pharmaceuticals, among other things.
Hydrogen is released when sodium borohydride is mixed with water and exposed to a catalyst and heat. Essentially, “you just add water, shake and you have an instant high-energy-density fuel ready for use,” Protonex literature says.
A control system built into the cartridge regulates the rate of hydrogen production so that it is generated only as needed by the fuel cell to produce electricity.
Hydrogen from the cartridge is fed into the fuel cell to the anode, which uses a small amount of platinum as a catalyst to divide the hydrogen into protons and electrons.
The resulting stream of electrons is an electrical current. The protons are conducted through a hydrogen proton exchange membrane in the fuel cell to a cathode, where they combine with oxygen from the air to produce water.
The water may be discarded – allowed to drip out of the fuel cell and out of the UAV – or it may be recycled back to the fuel cartridge. Protonex is experimenting with recycling, Pearson said, because it may mean that the power system can work with less water, which would reduce weight and may allow for heavier payloads or longer flight times.
When the hydrogen has been extracted, what’s left in the fuel cartridge is a sodium borate solution – essentially borax, a relatively benign chemical that’s used in a variety of products, from detergents to fire retardants.
The cartridges can be saved for recycling or discarded, Pearson said. Both the fuel and the residue are nontoxic, nonflammable and cost-effective, Protonex says.
A small fuel cell-powered UAV is attractive to the military because it makes small, relatively inexpensive UAVs capable of performing persistent surveillance – something now done only by larger, much more costly drones, said Steven Gitlin, a spokesman for Puma producer AeroVironment.
“It would be particularly useful for perimeter monitoring, and for flying ahead of a [ground] convoy for an extended time,” to spot enemy fighters waiting in ambush or to search for roadside bombs, Gitlin said.
The Puma AE may also be attractive to the Navy. “AE” in the name stands for “all-environment,” and the rugged, waterproof Puma can land at sea. AeroVironment is promoting it for maritime intervention operations, search-and-rescue missions, coastal and port patrols and drug interdiction operations.
Pumas are operated with a 6-by-10-inch hand-held controller that features a 4-by-6-inch screen that displays the UAV’s video feed, and five knobs for directing the UAV and its onboard cameras.


