Lasers have recently shown they can down a UAV–but they can also keep the drones up in the air. LaserMotive has kept a 22-gram model helicopter hovering for hours at a time on just a few watts of laser power.

LaserMotive won $900,000 from NASA last year by beaming power to a robot that climbed a 900-metre cable dangling from a full-scale helicopter. The technology could help power space elevators to lift objects thousands of kilometres into orbit. But with space elevators still at the concept stage, LaserMotive is keen to find other ways to turn a profit from its technology, says company founder Jordin Kare.

Flying times of conventional UAVs are limited by the fuel or batteries they can carry. Solar power with battery backup for night flight allows flight times lasting several days – defence firm Qinetiq, based in the UK, has flown its ultralight Zephyr for more than 82 hours. But although Swiss company Solar Impulse has demonstrated that solar power can keep even a piloted craft in the air, the uncrewed vehicles typically flown by military agencies are heavier and more rugged, and so need more power to stay in the air than they can get from the sun.

LaserMotive says that ground-based lasers can deliver the required power. At last week's AUVSI Unmanned Systems Conference in Denver, Colorado, the firm focused light from an array of semiconductor-diode near-infrared lasers down to a 7-centimetre beam, which automatically tracked a modified radio-controlled helicopter. The aircraft carried photovoltaic cells optimised for the laser wavelength, which converted about half the laser power reaching them to generate a few watts of electricity – enough to power the rotors of the little copter.

The laser-powered helicopter can hover for 6 hours, company president Tom Nugent told New Scientist from the show. He thinks that limit is set only by the quality of the motor driving the rotors. "It's a little consumer-grade brush motor not meant to run this long," he says. Under laser power, the copter "flies for several hours until the motor burns out".Laser-powered future

"That little helicopter sounds like a nice demonstration," says Robert Van Burdine, a former engineer at NASA's Marshall Space Flight Center in Huntsville, Alabama, who demonstrated laser-powered flight of a fixed-wing craft in 2003. His group manually aimed the laser, but the 300-gram radio-controlled plane with 1.5-metre wingspan had enough momentum to glide if the beam drifted off target; the helicopter would fall if the beam missed it. Although many people expressed interest at the time, he knows of no follow-up work.

LaserMotive has bigger plans for extending flight duration of military craft, says Kare. "We expect we can scale to anything anybody is interested in," including helicopters and UAVs. A craft could hover for long periods over a laser base, or fly missions and return to recharge over the laser, or fly between a series of laser bases. In the longer term, he envisions lasers powering remote ground-based sensors, delivering power to forward military bases, or supplying emergency power during disasters.

Laser-Powered Helicopter Hovers for Hours New Scientist reports, explores and interprets the results of human endeavour set in the context of society and culture, providing comprehensive coverage of science and technology news.