This Pelican can hover

THE Pelican, a small, remotely controlled helicopter drone weighing less than a kilogram, is powered by a battery that provides about 20 minutes' flying. And yet, one evening last October, the Pelican took off, rose ten metres and hovered throughout the night. It was brought down in the morning only because the exhibition hall near Seattle, where it was airborne, was about to open for business.

This remarkable feat was achieved with the ingenious use of a laser beam. The laser, aimed from the ground at photovoltaic cells mounted on the Pelican's underside, charged the chopper's battery, keeping her aloft for an unprecedented 12 hours and 27 minutes. An optical-tracking system kept the laser beam on target, creating a “scientifically exciting, yet a little boring” experience, according to Michael Achtelik of the Pelican's German manufacturer, Ascending Technologies, after a long night monitoring flight data.

Keeping drones aloft is not the only putative application of power beaming, as this technology is known. Five years ago NASA, America's space agency, offered prize money to any team that could build a remotely powered robot able to climb quickly up a cable. Only in 2009, however, were the first of these prizes claimed, when three teams from America and Canada demonstrated climbing robots powered by lasers on the ground. LaserMotive, the Seattle company that designed the Pelican's laser system, won $900,000 by powering a 5kg robot up almost a kilometre of cable dangling from a manned helicopter. LaserMotive's beam struck a photovoltaic panel on the robot, generating electricity that turned a set of wheels gripping the cable.

Conventional photovoltaic cells, made of silicon, are designed to collect energy from sunlight. LaserMotive uses special cells made with arsenic and gallium, which are better able to capture the near-infra-red wavelengths of its laser beam. The panel on the climbing robot, about the size of a coffee tray, harvested enough power to run a small lawnmower. One of LaserMotive's founders, Jordin Kare, reckons that a similar laser could deliver about as much energy 20km up if the panel were only a few times larger.

One reason NASA supports power beaming is that it hopes the technology could be used to help run a space elevator. This is a machine, familiar from science fiction, which some engineers think could be made science fact. In essence, it would be a giant cable reaching tens of thousands of kilometres into space to an orbiting satellite. Cable-climbing robots, powered by laser beams shot upward from the ground, or downward from space, would take payloads to orbit. Rockets would thus become redundant. Indeed, Andy Petro of NASA's technology office in Washington, DC, says power beaming might change the economics of space exploration completely. Lasers beamed from landing craft could, he says, power rovers in sunless areas of the moon or Mars, such as craters where water might be found.

Power beaming is also becoming more efficient. A few years ago lasers typically converted less than 40% of the electrical energy used to run them into beam power. The figure is now about 60%, and costs have dropped—the result of efforts to develop better laser printers, CD burners and even hair-removal devices. Moreover, engineers have worked out how to make laser beams more intense by using short lengths of optical fibre to narrow the beam. Such intense lasers are better suited to power-beaming because the cells that collect the laser light can be smaller.

The Pelican's successful flight probably means that the first big application for power beaming will be supplying energy to drones. At the moment, most small drones rely on battery power, so their flights are short. LaserMotive reports that American army officials, including some responsible for special-forces kit, have expressed an interest in power-beaming systems for drones. DARPA, the American Defence Department's technology agency, is also sponsoring research into power beaming. British readers of a certain age may remember that the spaceships flown by Dan Dare, Britain's answer to Buck Rogers, were powered by “impulse waves”, beamed from Earth. That piece of science fiction, too, may prove not to have been quite so wide of the mark.