High-Altitude Pseudo-Satellites: The Forever-Flying Platforms That Already Exist

A High-Altitude Platform Station (HAPS), also called a high-altitude pseudo-satellite, is a long-endurance, high-altitude aircraft or balloon that delivers observation and communication services like a satellite but from the stratosphere rather than orbit. The ITU defines a HAPS as a station kept at a fixed point relative to Earth at an altitude of 20 to 50 km; the practical sweet spot is around 17-22 km, where winds and turbulence are mild and drag is low. Because the platform sits perhaps 30-50 times closer to its users than a low Earth orbit satellite, its radio link budget is far better, and unlike a satellite it can be landed for maintenance and reconfigured. The solar-aircraft branch of the family is the closest thing to a literal forever-flying machine. The Airbus Zephyr, a 25 m-wingspan solar unmanned aerial vehicle weighing only around 60 kg, stayed aloft for 64 days in a 2022 flight covering about 56,000 km, recharging batteries by day to fly through the night. BAE Systems' BAE Systems PHASA-35, named for its 35 m wingspan, made its first stratospheric flight in 2023, reaching about 66,000 ft and landing in a condition to fly again days later. Their advertised jobs include replacing hundreds of cell towers, emergency 4G/5G after disasters, environmental monitoring, and military reconnaissance. The balloon branch was demonstrated at scale by Project Loon, Alphabet's stratospheric superpressure balloons that rode different wind layers for station-keeping; one balloon stayed up 312 days, and the fleet logged over a million stratospheric flight hours before the project was shut down in 2021. The airship and aerostat branch — tethered military surveillance balloons, and modern rigid airships such as LTA Research's Pathfinder 1 — rounds out the set. All three branches work technically; the open question has always been finding a mission they do better than a satellite or a conventional drone.