This article was written by Richard Cochrane, Director of Education and Senior Lecturer in Renewable Energy at University of Exeter, and first was published on The Conversation. Read the original article here. The opinion of the authors does not necessarily correspond with that of the editorial team. Want your opinion to be featured on AeroTime? Send us a line at

The British military is reportedly set to purchase two planes that can fly for months on end without needing to land. These large solar-powered “Zephyr” drones would likely be sent to carry out long-term surveillance missions and could constantly monitor an area with high-quality imagery. They could also be used to provide mobile and internet communication signals in remote areas, to support ground missions, and even conduct long-term research projects.

Alongside efforts by Facebook and Google to develop similar technology, the launch of the Zephyr aircraft by European aerospace firm Airbus could mark the start of a new era of continuous flight. What made this possible was a series of breakthroughs in lightweight materials, solar power and batteries, and autonomous navigation. These advances have come together to create planes that can fly day and night without intervention, potentially for months at a time.

Self-guided and self-powered planes started with NASA, which began working with the team behind the manned Solar Challenger plane that flew across the English Channel in 1981. By 1994, NASA’s Pathfinder aircraft had demonstrated solar panels were able to power aircraft to high altitude. But the planes still needed a power source at night. Batteries at the time were too heavy so the NASA engineers turned to hydrogen fuel cells, which they integrated into their Helios prototype, aiming to demonstrate round-the-clock operation.

Unfortunately, the Helios proved structurally fragile and broke up dramatically on a test flight in 2003 after encountering turbulence, marking the end of NASA’s pursuit of solar powered drones. Just two years later, however, AC Propulsion’s SoLong plane proved it was possible to integrate lightweight batteries into a solar aircraft and flew for 48 hours, controlled remotely by a team of six pilots.

Today the Zephyr, originally developed by UK firm QinetiQ, has a 23m wingspan and yet only weighs 55kg (compared to the Helios’s 726kg). It cruises at 20km, high above commercial aircraft and the fast-flowing atmospheric winds of the jet stream.

More importantly, it can fly for potentially months on end without the need for refueling. So far it has only flown for 14 days straight but, theoretically, the only limit is how many times the battery can charge and discharge before it degrades. To enable this, the craft has overcome the crucial challenge of generating and storing enough power to both keep it continuously aloft and run its cameras and communication equipment.