A high-altitude platform station 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 over 32 hours, while civil HAPS are radio stations at an altitude of 20 to 50 km above waypoints, for weeks.
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).
NASA ERAST Program
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The Environmental Research Aircraft and Sensor Technology, or ERAST program was a NASA program to develop cost-effective, slow-flying unmanned aerial vehicles (UAVs) that can perform long-duration science missions at altitudes above 60,000 ft (18,000 m). The project included a number of technology development programs conducted by the joint NASA-industry ERAST Alliance. The project was formally terminated in 2003.
NASA's Altus II UAV developed under ERAST
Perseus A being Towed in Flight
Helios UAV in flight
Image: Altus II high altitude science aircraft descending toward U.S. Navy's Pacific Missile Range Facility on Kauai, Hawaii (EC99 45006 1)