Korea Challenges the 'Stratospheric Solar-Powered Drone' That Even Facebook Failed At [Reading Science]

The high-altitude solar-powered unmanned aerial vehicle EAV3 being developed by the Korea Aerospace Research Institute.

[Asia Economy Reporter Kim Bong-su] The government has announced plans to develop solar-powered unmanned aerial vehicles (stratospheric drones) capable of staying in the stratosphere at altitudes of 10 to 50 km for a month, aiming to lead the global market. But what exactly are these devices used for, and what challenges must be overcome?

◇ What is a Stratospheric Drone?

It can be compared to a satellite floating in the sky. Its missions include ground surveillance and communication relay, just like satellites. It has various applications such as monitoring abnormal weather and wildfires, marine pollution surveillance, seawater changes, real-time precise weather observation, and maritime border monitoring. It is much more economical than satellites because it costs far less to manufacture and does not require expensive launch fees. It can obtain Earth observation video information comparable to high-performance satellites that cost 200 to 300 billion KRW to produce and launch, and can also be used for communication relay, but costs less than one-tenth of that amount. Additionally, it is a zero-emission flying vehicle suitable for the carbon-neutral era, as it flies by generating power using solar energy on its lightweight, long wings and fuselage. Its main operating altitude is the stratosphere at 11 to 50 km, where it can fly freely without interference from passenger planes or fighter jets (below 10 km).

However, its cruising speed is only about 20 to 100 km/h, and because it has a long fuselage and wings for lift, if the wing tips break or twist during rotational movements, recovery is impossible. As a result, it sometimes crashes when encountering turbulence in the troposphere. Except for the battery, it is made lightweight using carbon fiber, weighing tens to hundreds of kilograms. It uses lithium-ion batteries, but current technology limits capacity, making long-duration flights difficult.

The Ministry of Science and ICT explained, "Drones that can loiter for long periods in the stable stratosphere can continuously monitor the ground from high altitudes like satellites, but with lower introduction, operation, and maintenance costs," adding, "They do not generate the recently problematic 'space debris,' making them a promising new drone industry."

Aquila drone, a high-altitude solar-powered unmanned aerial vehicle developed and discontinued by Facebook.

◇ Continuous Failures Including Facebook

According to the Korea Aerospace Research Institute (KARI), the era of high-altitude solar-powered unmanned aerial vehicles began in 1981 when the U.S. Solar Challenger succeeded in flying solely on solar power. However, over the past 40 years, only a handful of models have succeeded in flight. Representative examples include Facebook's Aquila drone, NASA's Helios, and KARI's EAV3. The Aquila drone and Helios are famous for being composed only of wings without a fuselage, resembling a boomerang. However, vulnerable to turbulence, the Aquila drone crashed due to a tropospheric gust during its first flight in 2016, and development was halted after the second test flight in 2017. Helios also crashed into the Pacific Ocean in 2003 after failing to withstand mild turbulence.

The difficulty in developing stratospheric drones is primarily due to jet streams. Strong jet streams reaching speeds of up to 500 km/h blow near 10 km altitude, making it very difficult for unmanned aerial vehicles to fly normally. Additionally, the stratosphere's temperature can drop to as low as minus 70 degrees Celsius, requiring unmanned flight systems that can withstand extreme temperatures.

◇ Challenges: Developing High-Performance Batteries and Ultra-Lightweight Materials

The Ministry of Science and ICT plans to invest 37.47 billion KRW from next year through 2025 to develop the world's highest-performance stratospheric drone for continuous disaster monitoring. Currently, the world's best stratospheric drones can fly continuously for 26 days and carry 5 kg of mission equipment such as surveillance devices. The ministry aims to develop a stratospheric drone capable of continuous flight for over 30 days and carrying more than 20 kg of mission equipment, targeting export markets as well.

South Korea's technological level has already reached a considerable stage. Since 2010, KARI has invested 15 billion KRW over five years in a high-altitude solar-powered UAV development project. Through a total of 54 flight tests lasting 188 hours, it succeeded in two stratospheric flights: 10 minutes in the first phase and 90 minutes in the second. Subsequent research for performance improvement has continued, with initial flights succeeding in 2019 and 2020. Notably, in 2020, it set a domestic record for the longest flight at 53 hours.

A stratospheric drone expert explained, "For drones to loiter for long periods in the stratosphere, the most critical technologies are those that secure, store, and operate power for extended durations and ultra-lightweight airframe technologies to maximize energy efficiency," adding, "Development of high-performance batteries such as lithium-sulfur, securing materials and parts technologies like carbon fiber composites, and developing mission equipment considering various applications are urgently needed."