High-altitude platform station

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.

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.

[4] 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.

[5] 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.

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.

[68] 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.

[71] 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.

A high altitude platform can provide observation or communication services.
Video of NASA Helios in flight
Wind profile variation with altitude from NASA, showing minimum wind speeds between 17 and 22 km (56,000 and 72,000 ft). Although absolute values will vary, the trends shown are similar for most locations.
Capable of flying up to 60,000 ft (18,300 m) more than 34 hours, the RQ-4 Global Hawk was put into USAF service in 2001.
NASA Pathfinder Plus
NASA Centurion
The KARI EAV-3 flew during 53 hours and up to 22 km (72,000 ft).
The Ryan YQM-98 R-Tern of the Compass Cope program first flew on 17 August 1974 and was designed to fly up to 70,000 ft (21,340 m) and during 30 hours
The piston-powered General Atomics Altus II first flew on May 1, 1996, and reached 57,300 ft (17,500 m)
The hydrogen -powered Boeing Phantom Eye should have reached 65,000 ft (19,800 m) during four days.
USAF Integrated Sensor Is Structure project
Stratobus airship
A Google Project Loon balloon