Troops on the ground increasingly are relying on small hand-launched aircraft to track enemy fighters in Afghanistan. The problem with those battery-powered systems is that they can only fly for short periods of time before their energy supply becomes depleted.
To give the remotely operated planes better endurance in the skies, scientists are developing battlefield lasers to recharge the batteries in flight.
Transmitting electricity without wires has become feasible thanks to recent advancements in diode lasers, which are widely used in commercial industries, including communications, electronics, manufacturing and medicine. The lasers have become more powerful, more efficient and less expensive on the per watt basis, said Tom Nugent, president of LaserMotive LLC, a Kent, Wash.-based firm that is developing a power beaming system.
The prototype laser acts like a 24-hour sun.
“Just like solar cells taking sunlight and converting it into energy, we use directed, focused laser light onto specialized photovoltaic cells to generate electricity at a remote location,” he said.
The near-infrared laser converts power drawn from batteries, generators or an electric grid, into a beam of light that is equivalent to a quarter million laser pointers, or roughly 10 times the intensity of sunlight. When focused on a specialized receiver, photovoltaic cells made from gallium arsenide convert the light’s energy back into electricity. The cells have a power density of 1 kilowatt per kilogram, which is higher than or comparable to most batteries, Nugent said.
Small unmanned vehicles, such as the Raven and Puma, can benefit from power beaming, he said. Instead of having to land repeatedly for troops to switch out batteries, the aircraft can fly within one to two kilometers of the laser to recharge and stay aloft for hours.
The receiver could be mounted on the side of the aircraft fuselage. The plane could fly ahead of a Humvee that is transporting the laser. Drawing power from the truck, the laser could recharge the drones.
Nugent and a team of scientists in November demonstrated the concept by powering a small autonomous helicopter for nearly 12.5 hours. The Pelican quadrocopter, made by the German company Ascending Technologies, hovered nonstop overnight in an indoor facility. Its receiver produced about 180 watts of electricity.
“We could have kept on going. It was very stable for the whole time,” Nugent recalled.
At one point, engineers turned off the laser but the aircraft continued its flight by relying on its 5-minute battery as the main power source. Nugent said that feat simulated a safety feature of the laser’s “machine-vision” tracking system, which is designed to shut off the beam if something wanders too close to its path.
Battlefield laser opponents may take issue with the technology’s operational safety. But Nugent said the intensity of the beam is much lower than those levels being pursued for directed energy weapons. “If you stuck your hand in our beam, you’d say, ‘Ow, that’s hot,’ and take your hand out. It’s not going to burn you,” he said. However, the wavelength could cause retinal damage, he conceded. Necessary precautions have been taken to prevent such injuries, and Nugent pointed out that the quadrocopter demonstration showed that the laser could operate in an eye-safe configuration.
Now the company’s focus is on packaging the laser so that a non-scientist can operate it with only a half hour of training. In addition, officials want to conduct demonstrations on more unmanned systems, including fixed-wing aircraft and aerostats. For that effort, Nugent is seeking partnerships with military organizations, labs and industry. His hope is to obtain funding to commercialize the product, which could potentially be ready for deployment in 12 to 18 months.
Company officials believe laser power could help push the autonomous rotary wing market. Troops have said they would like to fly more unmanned helicopters, but because they are less efficient and have less endurance than their fixed-wing counterparts, practical employment on the battlefield has been limited. Having an infinite power source, such as the laser, could reverse the trend, Nugent said.
The system could open up many other opportunities for the Defense Department down the road, LaserMotive officials said. Besides recharging unmanned aircraft from the ground, the laser could go airborne to beam down power to recharge troops’ batteries or sensors while they are out in the field. Or it could even serve as an extension of an existing power grid by beaming light to outposts miles away.
The Defense Department spends upwards of hundreds of dollars per gallon of fuel to run generators in forward operating bases. Some Pentagon officials have expressed a desire for laser-beaming technologies to supplement and even supplant petroleum.
“It would be possible to beam energy to those forward operating bases from someplace where it’s relatively cheap to generate electricity. Now you’re not only saving the cost of gas but also potentially saving the lives of people who are trying to deliver fuel,” said Nugent.