High-altitude platform station
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, they remain aloft through atmospheric lift, either aerodynamic like airplanes, or aerostatic like airships or balloons.
High-altitude long endurance 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.
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.
Definitions
; High-altitude long endurance; High-altitude platform station
Studies
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 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 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°.
Design
; Power; Altitude selection
; Comparison to satellites
Applications
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.
; Radiocommunication services
; Surveillance and intelligence
; Real-time monitoring
; Weather and environmental monitoring
; Rocket launch
Airplanes
like the late 1950s Lockheed U-2 could fly above and the 1964 SR-71 above.The twin-turbofan powered Myasishchev M-55 reached an altitude of 21,360 m in 1993, a variant of the M-17 first flown in 1982, which reached 21,830 m in 1990.
Operational
; Grob G 520 EgrettFile:940th Wing - Northrop Grumman RQ-4B Block 20 Global Hawk 04-2015.jpg|thumb|Capable of flying up to 60,000 ft more than 34 hours, the RQ-4 Global Hawk was put into USAF service in 2001.
; Northrop Grumman RQ-4 Global Hawk
Prototypes
Solar powered
; AeroVironment/NASA Pathfinder; AeroVironment/NASA Centurion/Helios Prototype
; Airbus Zephyr
; Solar Impulse
; Titan Aerospace Solara
; KARI EAV
; Astigan A3
; Facebook Aquila
; China Aerospace Science and Technology Corporation
; Lavochkin LA-252
; Mira Aerospace ApusDuo
; Aurora Odysseus
; AeroVironment HAPSMobile
; BAE Systems PHASA-35
; Swift Engineering SULE
; HAL CATS Infinity
; Kea Atmos Mk1
| Model | First flight | Span | Weight | Payload | Altitude | Endurance | Status |
| AeroVironment Pathfinder | 1993-T4 | 98.4 ft | 560 lb | 100 lb | 00-12:00 | ||
| AeroVironment Pathfinder plus | 1998 | 121 ft | 700 lb | 150 lb | |||
| AeroVironment Helios | 1999-09-08 | 2,048 lb | 726 lb | goal: > 1-00:00 | 2003 crash | ||
| Airbus Zephyr | 2005-12 | 64-00:00 | 2026 planned intro. | ||||
| Titan Aerospace Solara | 2015-05-01 | 00-00:04 | 2017 shut down | ||||
| KARI EAV-3 | 2015-08 | 02-05:00 | |||||
| UK OS Astigan A3 | 2016 | 125 ft | 330 lb | goal: | goal: 90-00:00 | 2021 project end | |
| Facebook Aquila | 2016-06-28 | 00-01:30 | 2018 project halt | ||||
| CASTC | 2017-07 | 00-15:00 | |||||
| Lavochkin LA-252 | 2017-T4 | goal: stratosphere | goal: 100-00:00 | ||||
| Mira Aerospace's ApusDuo | 2018-10 | 00-10:30 | |||||
| AeroVironment HAPSMobile | 2019-09-11 | 00-20:00 | |||||
| BAE Systems PHASA-35 | 2020-02 | 115 ft | + | 03-00:00 | 2026 operations target | ||
| Swift Engineering SULE | 2020-07 | 01-00:00 | |||||
| HAL CATS Infinity | 2022-10-19 | 01-03:00 | subscale testing |
Hydrocarbon fueled
; USAF Compass Dwell and Compass Cope; Boeing Condor
; Aurora Perseus and Theseus
; Grob Strato 2C
; General Atomics ALTUS
; Scaled Composites Proteus
; Virgin Atlantic GlobalFlyer
; Aurora Flight Sciences Orion
; Shenyang Aircraft Corporation Divine Eagle
Hydrogen fueled
; AeroVironment Global Observer; Boeing Phantom Eye
; Stratospheric Platforms
Airships
Unmanned stratospheric airships are designed to operate at very high 60,000 to 75,000 feet 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 for 2 hours with a 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.
; SwRI HiSentinel
; Integrated Sensor Is Structure
; Lockheed-Martin HAA
; Lockheed-Martin HALE-D
; Lindstrand HALE airship
; Thales Alenia Stratobus
; H-Aero
; Stratoship SZ-155
Balloons
A geostationary balloon satellite flies in the stratosphere 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.