High-Altitude Platform Station

A high-altitude platform station (HAPS) is a long-endurance, high-altitude aircraft or balloon that offers observation or communication services similar to an artificial satellite. The International Telecommunication Union defines it as a station on an object at an altitude of 20 to 50 km, kept at a specified nominal fixed point relative to the Earth. In practice the favoured band is about 17-22 km (roughly 56,000-72,000 ft), where winds and turbulence are mild and aerodynamic drag is low. HAPS come in several forms. Solar-powered aircraft such as the Airbus Zephyr and BAE's BAE Systems PHASA-35 use ultra-light, high-aspect ratio wings (see Solar-Powered Aircraft). Hydrogen-fuelled designs like the AeroVironment Global Observer and Boeing Phantom Eye trade indefinite endurance for days-long flights with larger payloads. Stratospheric airships and balloons — including Alphabet's Project Loon — make up the lighter-than-air branch. Closely related military HALE (high-altitude long-endurance) drones such as the Northrop Grumman RQ-4 Global Hawk fly above 60,000 ft for well over a day. The appeal of HAPS over satellites is proximity: sitting tens of times closer to users than a low Earth orbit spacecraft gives a much stronger radio link budget (on the order of a 34 dB advantage over a LEO satellite), lower power needs, cheaper deployment, and the ability to be landed and serviced. Typical applications include broadband and 4G/5G relay to underserved regions, weather and environmental monitoring, border and maritime patrol, and disaster response. Because HAPS occupy fixed points and use radio spectrum, they require dedicated frequency allocations coordinated through the ITU.