High-altitude platform station

A high-altitude platform station (HAPS, which can also mean high-altitude pseudo-satellite or high-altitude platform systems), also known as atmospheric satellite, is a long endurance, high altitude aircraft able to offer observation or communication services similarly to artificial satellites. Mostly unmanned aerial vehicles (UAVs), they remain aloft through atmospheric lift, either aerodynamic like airplanes, or aerostatic like airships or balloons. High-altitude long endurance (HALE) military drones can fly above 60,000 ft (18,000 m) over 32 hours, while civil HAPS are radio stations at an altitude of 20 to 50 km above waypoints, for weeks.
High-altitude, long endurance flight has been studied since at least 1983, and demonstrator programs since 1994. Hydrogen and solar power have been proposed as alternatives to conventional engines. Above commercial air transport and wind turbulence, at high altitudes, drag as well as lift are reduced. HAPS could be used for weather monitoring, as a radio relay, for oceanography or earth imaging, for border security, maritime patrol and anti-piracy operations, disaster response, or agricultural observation.
While reconnaissance aircraft have been capable of reaching high altitudes since the 1950s, their endurance is limited. One of the few operational HALE aircraft is the Northrop Grumman RQ-4 Global Hawk. There are many solar powered, lightweight prototypes like the NASA Pathfinder/Helios, or the Airbus Zephyr that can fly for 64 days; few are as advanced as these. Conventional aviation fuels have been used in prototypes since 1970 and can fly for 60 hours like the Boeing Condor. Hydrogen aircraft can fly even longer, a week or longer, like the AeroVironment Global Observer.
Stratospheric airships are often presented as a competing technology. However few prototypes have been built and none are operational. Among balloons specifically, the most well known high-endurance project was Google Loon, using helium-filled high-altitude balloons to reach the stratosphere. Loon was ended in 2021.
In 1983, Lockheed produced A Preliminary Study of solar powered aircraft and Associated Power Trains for the NASA, as long endurance flight could be compared to suborbital spacecraft. In 1984 was published the Design of Long Endurance Unmanned Airplanes Incorporating Solar and fuel cell propulsion report. In 1989, the Design and experimental results for a high-altitude, long-endurance airfoil report proposed applications as a radio relay, for weather monitoring or cruise missile targeting.
The NASA ERAST Program (Environmental Research Aircraft and Sensor Technology) was started in September 1994 to study high-altitude UAVs, and was terminated in 2003. In July 1996, the USAF Strikestar 2025 report forecast HALE UAVs maintaining air occupation with 24 hours flights. The Defense Airborne Reconnaissance Office made demonstrations of long-endurance UAV craft. In September 1996, Israel Aircraft Industries detailed the design of a HALE UAV.
In 2002, Preliminary reliability design of a solar-powered high-altitude very long endurance unmanned air vehicle was published. The European Union CAPECON project aimed to develop HALE vehicles, while the Polish Academy of Sciences proposed its PW-114 concept that would fly at 20 km (66,000 ft) for 40 hours. Luminati Aerospace proposed its Substrata solar-powered aircraft that would fly in formation like migratory geese to reduce the power required for the trailing aircraft by 79%, allowing smaller airframes to remain aloft indefinitely up to a latitude of 50°.
Atmospheric satellites could be used for weather monitoring, as a radio relay, for oceanography or earth imaging like an orbital satellite for a fraction of the cost. Other uses include border security, maritime patrol and anti-piracy operations, disaster response, or agricultural observation. They could bring internet connectivity to the 5 billion people lacking it, either with 11,000 airplane UAVs or with balloons like Google's Project Loon.
Reconnaissance aircraft like the late 1950s Lockheed U-2 could fly above 70,000 ft (21,000 m) and the 1964 SR-71 above 80,000 ft (24,000 m). The twin-turbofan powered Myasishchev M-55 reached an altitude of 21,360 m (70,080 ft) in 1993, a variant of the M-17 first flown in 1982, which reached 21,830 m (71,620 ft) in 1990.
Kea Atmos Mk1
The Kea Atmos Mk1 solar-powered stratospheric HAPS was designed and manufactured by Kea Aerospace in New Zealand. The maiden test flight was in February 2023 and the first stratospheric flight was on February 8, 2025. It has a wingspan of 12.5 meters and weighs less than 40 kg. The Kea Atmos Mk1 is designed to take 2 kg payloads to the stratosphere on dawn to dusk single day missions and is working with a range of international payload customers. Kea Aerospace is currently designing the Kea Atmos Mk2 to take 6 kg of payload to the stratosphere on multi-month length missions.
By December 2024, it had flown for 24h and reached more than 66,000 ft (20,000 m) from Spaceport America in New Mexico, targeting operational activity by 2026.
Unmanned stratospheric airships are designed to operate at very high 60,000 to 75,000 feet (18.3 to 22.9 km) altitudes during weeks, months or years. Subjected to ultraviolet damage, ozone corrosion and challenging station keeping, they can be solar-powered with energy storage for the night.
The first stratospheric powered airship flight took place in 1969, reaching 70,000 feet (21 km) for 2 hours with a 5 pounds (2.3 kilograms) payload. By August 2002, US company Worldwide Aeros was building a stratospheric demonstrator for the Korea Aerospace Research Institute, as a part the South Korean HAA development program. By April 2004, stratospheric airships were being developed in USA, UK, Canada, Korea and Japan. In May 2004, the Japan Aerospace Exploration Agency shown its test airship in Taiki, Hokkaido, a part of its Stratosphere Platform Project.
A geostationary balloon satellite (GBS) flies in the stratosphere (60,000 to 70,000 ft (18 to 21 km) above sea level) at a fixed point over the Earth's surface. At that altitude the air has 1/10 of its density is at sea level. A GBS could be used to provide broadband Internet access over a large area. One prior project was the Google's Project Loon, which envisioned using helium-filled high-altitude balloons.