If you provide a drone with a constant supply of energy, it can fly almost forever, until parts wear out or gets into an accident. But just a multiple increase in flight time is interesting for the military - DARPA is testing the concept of recharging the drone's batteries by firing a laser at it. The Silent Falcon was selected as the test platform.
The idea is simple, you need to place solar panels not only on the upper side of the wing of an aircraft type machine, but also on the lower one. In a broad sense, laser light, as a source of energy, is not much different from sunlight. And if we can catch the light of the Sun with one set of panels, then the second will become a target for a ground-based laser, which in this way will transfer a certain amount of energy there. The main thing is to choose such radiation parameters that will not destroy the target.
Preliminary calculations by DARPA engineers showed the theoretical possibility of recharging the drone with a laser at a distance of up to 10 km. However, this is in ideal conditions, and shooting at a target in fog, snow or strong winds significantly reduces the effectiveness of the procedure. To make matters worse, the power of the laser poses some danger to third-party targets if the shot passes by. There is no exact information, but in the first experiments the Americans were afraid to shoot straight into the sky; instead, they would force the drone to circle around the hill, on which the laser would be placed.
We will soon find out what will come of this venture. Or we won't, because if successful, the technology will probably be hidden in the interests of the military. Although it would be useful to civilians much more - how many low-power multicopters could simply hover over gas stations at high altitudes, and not descend, creating a risk for others. In general, laser power transmission systems for urban infrastructure and the Internet of Things appear to be an alluring technology of the future.