The technology developed by Chinese researchers uses a laser beam to power a remote drone. Light energy is converted into electricity to keep the aircraft aloft for as long as necessary.
The autonomy of drones, and in particular quadrotors, remains their weak point. To increase flight time, scientists are imagining hybrid solutions with motors powered by fuel cells, or even mixed motorizations, such as that of the Hybrix 2.1 quadricopter with its thermal engine which serves as a generator to recharge the battery.
Autonomy can exceed ten hours, but it is still not possible to keep a drone in the air for weeks as an unmanned Solar Impulse could do. To make a drone fly permanently, researchers at the Northwestern Polytechnic University (NPU) in China rely on a ground-to-air laser link. They call this process ODD, for Optics driven drones. The drone is equipped with a photovoltaic module which converts the laser beam into electricity.
This principle is not new. Darpa, on behalf of the American army, has been working on this process for several years, and NASA has also been carrying out this type of project since 2011. Darpa has even carried out load tests at a distance of 300 meters. If the developments on these technologies are long, it is because long-distance laser charging is difficult. Ambient air and atmospheric interference affect beam power. The latter must not turn into a laser cannon by delivering too much power. It is precisely on these constraints that Chinese scientists have worked.
Defense secrecy in ambush
The researchers claim to have developed technology to adjust the intensity of the laser automatically to compensate for the effects of atmospheric disturbances. The researchers also developed a protection algorithm. In addition to automatically adjusting the laser power, it knows how to compensate for energy loss when an obstacle is in the path of the laser. It was also necessary to develop an automatic drone tracking system in real time to maintain the link during its evolutions. The algorithm developed must be able to accurately predict the trajectories to adjust the beam continuously.
The research team said they conducted three tests, including one indoor, one daytime outdoor flight and one nighttime flight. These trials took place with the expected success according to the researchers. For the moment, the lab has not provided any details on the range of the system and its charging performance. It must be said that, despite arguments indicating that these ODDs would be real assets for civilian applications – such as rescue and observation – the military potential of the process prevents the laboratory from saying too much.
In addition to staying permanently in the air, this type of drone with unlimited autonomy makes it possible to carry a smaller battery and therefore considerably lighten the aircraft. The mass gained could be used to carry more sensors. In a military context, wireless charging increases the range and autonomy of a swarm of drones. It remains to be seen whether a swarm of laser beams following drones does not make the whole system easy prey.
