The Korea Aerospace Research Institute says a solar powered drone developed by its researchers has succeeded in entering the stratosphere.
 
The institute said Thursday that its high-altitude EAV-3 drone successfully flew for 90 minutes at an altitude of 18-and-a-half kilometers on August 12. 
 
Only two other aircraft in the world have successfully entered the stratosphere by flying over an altitude of 18 kilometers - Zephyr developed by British firm Qinetiq and the Helios developed by the U.S.’s Aerovironment.
 
It is difficult to fly ordinary aircraft in the stratosphere due to its low density and temperature, but because it does not have strong winds or clouds, it can be reached by solar-powered aircraft.