The army announcement gave no further details of the incident, save to say that there were no injuries to personnel or damage to other aircraft, and that an investigation had been launched. One thing was already crystal clear, however – the previous 63 days had been a monumental success.
While it missed the all-time world record for longest powered flight by just under four hours, the stratospheric flight demonstration of the Airbus drone more than doubled the unmanned air system (UAS) endurance record, which it had set in 2018 with a flight of just under 26 days.
“The 1,500 flight hours beat all known unmanned aircraft endurance records, marking significant capability and informing future mission requirements,” said the US Army.
Equivalent to more than one lap around the Earth, the flight of 30,000+ nautical miles included a number of firsts for the UAS, including its departure from US airspace, flight over water, flight in international airspace, data collection and direct downlink while outside US airspace, the longest continuous duration (seven days) using satellite communications, and the demonstration of command and control from three locations – Huntsville in Alabama, Yuma, and Farnborough in Hampshire.
‘Fly them ’til they break’
The extraordinary flight was enabled by some equally ground-breaking engineering. Despite a 25m wingspan that would cover an entire tennis court, the Zephyr 8 only weighs 75kg, reducing the energy required from the gallium arsenide solar panels that powered the flight to more than 60,000ft. The panels also charge lithium-ion batteries during the day to enable overnight flight.
Experiments during the mission successfully demonstrated Zephyr’s energy-storage capacity, flight endurance, station-keeping and ‘agile positioning’ abilities, said the US Army.
The record-breaking success of the mission means its unfortunate end should be little cause for concern, said Steve Wright, senior research fellow in aerospace engineering at the University of the West of England. As the aircraft is uncrewed it can be pushed to its absolute limit, helping develop the technology further.
“You can just keep flying them ’til they break and fall out of the sky,” he said. “It means that you can take a much more pragmatic and high-performance approach to your development.”
Optimisation could include a stronger focus on protecting the aircraft’s systems from the elements, Wright suggested, to enable even longer flights. High radiation levels and extreme temperatures of -50ºC and below pose a major threat to continuous operation.
“That plays havoc with all the materials, all the systems onboard the aircraft,” said Wright. Factors requiring investigation could include embrittlement of components and moisture ingress, he suggested.
Disaster response
The US Army’s use of the high-altitude aircraft shows the likely direction of the first applications. “The military are fascinated by these things… having them hovering and circling around in any random place in the world,” said Wright.
Civilian applications will soon follow, however. The aircraft could provide improved mobile connectivity in remote areas, high-speed data transfers, and Earth observation at 18cm resolution, according to Airbus, with uses including disaster response and wildfire management.
The payload will likely be limited to a few kilograms of communications equipment for now, Wright said. In future, he suggests that the aircraft could even carry smaller drones up to high altitudes, drop them, then recapture them later.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.