High-altitude platform station

; High-altitude long endurance (HALE) : High-altitude, long-endurance (HALE) aircraft are non-weaponized military drones capable of flying at over 32 hours, like the USAF RQ-4 Global Hawk or its variants used for ISR. ; High-altitude platform station (HAPS) : defined by the International Telecommunication Union (ITU) as "a station on an object at an altitude of 20 to 50 km and at a specified, nominal, fixed point relative to the Earth" in its ITU Radio Regulations (RR). HAPS can also be the abbreviation for high-altitude pseudo-satellite. ==Studies==

in flight 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 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 : Power is required for continuous operation, limiting endurance by the need for refueling. Persistent solar-powered aircraft need to store daylight energy for the night, in electric batteries, Flying in the tropopause at is above clouds and turbulence with winds below , and above FAA-regulated Class A airspace ending at . ; Comparison to satellites : A lower altitude covers more effectively a small region, implies a lower telecommunications link budget (a 34 dB advantage over a LEO, 66 dB over GEO), a lower power consumption, and a smaller round-trip delay. A satellite in the vacuum of space orbits due to its high speed generating a centrifugal force matching the gravity. Changing a satellite orbit requires expending its extremely limited fuel supply. ==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. World Mobile is testing a platform flying at around , which can serve an area of 15,000 km² (161,458,656,000 ft²). Within that area, connectivity can be delivered directly to devices across 3G, 4G, 5G, and future 6G standards. ; Surveillance and intelligence : The Northrop Grumman RQ-4 Global Hawk UAV is used by the US Air Force for surveillance and security. It carries a radar, optical, and infrared imagers; and is able to transmit its data in realtime. ; Real-time monitoring : An area could be monitored for flood detection, seismic monitoring, remote sensing and disaster management. ; Weather and environmental monitoring : For environment and weather monitoring, high-altitude balloons can deploy scientific equipment to measure environmental changes or to keep track of weather. In partnership with The National Oceanic and Atmospheric Administration (NOAA), NASA has started using Global Hawk UAVs to study Earth's atmosphere. ; Rocket launch : More than 90% of atmospheric matter is below the high-altitude platform, reducing atmospheric drag for starting rockets: "As a rough estimate, a rocket that reaches an altitude of when launched from the ground will reach if launched at an altitude of from a balloon." Mass drivers have been proposed for launching to orbit. ==Airplanes==

Reconnaissance aircraft 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 (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. Operational ; Grob G 520 Egrett : The manned Grob G 520 first flew on 24 June 1987 and was certified in 1991. Powered by a Honeywell TPE331 turboprop, it is wide, reached 16,329 m (53,574 ft), and can stay airborne for 13 hours. was put into USAF service in 2001. ; Northrop Grumman RQ-4 Global Hawk : The Northrop Grumman RQ-4 Global Hawk first flew on 28 February 1998 and was put into USAF service in 2001. The 131 ft (40 m) wide, 48 ft (14.5 m) long RQ-4 is powered by a single Rolls-Royce F137 turbofan, weighs up to 32,250 lb (14.6 t) at takeoff, and carries a 3,000 lb (1,360 kg) payload up to 60,000 ft (18,300 m) over more than 34 hours. It can be used as a radio relay and can carry electro-optical, infrared, synthetic aperture radar (SAR), and high and low band SIGINT sensors. It is the basis for the US Navy's MQ-4C Triton. Prototypes Solar powered ; AeroVironment/NASA Pathfinder : The HALSOL prototype, a 185 kg (410 lb), 30 m (98.4 ft) wide flying wing propelled by eight electric motors, first flew in June 1983. It joined the NASA ERAST Program in late 1993 as the Pathfinder, and with solar cells covering the entire wing added later, it reached on September 11, 1995 and then in 1997. It broke up in flight in 2003. The UAVs are powered by solar cells, recharging batteries in daylight to stay aloft at night. The earliest model flew in December 2005. In March 2013, the project was sold to Airbus Defence and Space. The latest Zephyr 8/S model weighs , has a wingspan of , and reached . ; Solar Impulse : The first Solar Impulse manned demonstrator made its first flight on 3 December 2009, and flew an entire diurnal solar cycle in a July 2010 26-hour flight. The 71.9 m (236 ft) wide, 2.3 tonnes (5,100 lb) Solar Impulse 2 first flew on 2 June 2014, it could reach 12,000 m (39,000 ft) and its longest flight was from Nagoya, Japan to Kalaeloa, Hawaii over 117 h 52 min on 28 June 2015. ; Titan Aerospace Solara : Founded in 2012 in New Mexico, Titan Aerospace was developing large solar-powered, high-altitude atmospheric satellites similar to the AeroVironment Global Observer or QinetiQ Zephyr. Google bought Titan Aerospace in April 2014, managed to fly a prototype in May 2015 but it crashed within minutes and Titan Aerospace was shut down by early 2017. EAV-3 flew during 53 hours and up to . ; KARI EAV : The Korea Aerospace Research Institute (KARI) began developing its Electrical Aerial Vehicle (EAV) in 2010, after subscale demonstrators, its latest wide EAV-3 weighs and is designed to fly for months; it flew up to in August 2015, during 53 hours and up to in August 2020. ; Astigan A3 : UK mapping agency Ordnance Survey (OS), a subsidiary of the Department for Business, Energy & Industrial Strategy, is developing the A3, a 38 m (125 ft) wingspan, 149 kg (330 lb) twin-boom solar-powered HAPS designed to stay aloft at for 90 days carrying a payload. In March 2021, the project was ended as no strategic partner was found. ; Facebook Aquila : The Facebook Aquila UAV was a carbon fiber, solar-powered flying wing UAV spanning and weighing , designed to stay aloft at FL650 for 90 days. UAVs would use Laser communication between them and to ground stations. On June 28, 2016, it took its first flight, during ninety minutes and reaching , but a twenty-foot section of the righthand wing broke off during final approach. It made another low-altitude test flights in 2017. ; China Aerospace Science and Technology Corporation : CASTC flew a -span solar-powered UAV to FL650 in a 15 hours test flight in July 2017. With a wingspan of , the unmanned ApusDuo 14 aircraft utilizes a flexible tandem wing design with high-efficiency solar cells to fly continuously for months at altitudes up to , carrying payloads up to . During a test flight in Rwanda in October 2023, Mira Aerospace became the first company to successfully deliver 5G connectivity from a fixed-wing HAPS autonomous aircraft in the stratosphere. ; Aurora Odysseus : Aurora Flight Sciences announced its Odysseus in November 2018. It was designed to stay above up to three months at latitudes up to 20°. Its first flight was indefinitely delayed by July 2019. ; AeroVironment HAPSMobile : AeroVironment will design and development solar-powered UAV prototypes for $65 million for HAPSMobile, a joint venture 95% funded and owned by Japanese telco SoftBank. Resembling the 1999 Helios, the span flying wing with 10 electric-driven propellers would provide 4G LTE and 5G direct to devices over a 200 km (125 mi) diameter area On 21–22 September 2020, the HAPSMobile Hawk30 (rebranded as Sunglider) flew 20 hours and reached an altitude of , testing the long-distance LTE communications developed with Loon for standard LTE smartphones and wireless broadband communications. ; BAE Systems PHASA-35 : Designed by Prismatic Ltd., now BAE Systems, the 35 m (115 ft)-wingspan BAE Systems PHASA-35 made its maiden flight in February 2020 from the Woomera Test Range in South Australia; it should fly its payload at around 70,000 ft for days or weeks. By December 2024, it had flown for 24h and reached more than from Spaceport America in New Mexico, targeting operational activity by 2026. ; Swift Engineering SULE : The Swift Engineering's Swift Ultra Long Endurance SULE completed its maiden flight partnership with NASA's Ames Research Center in July 2020. On Sep. 29-30, 2024, it reached in a 24-hour flight. It took off from and landed at Spaceport America in New Mexico. ; HAL CATS Infinity : CATS Infinity is being developed by HAL, NAL and NewSpace Research. Its scaled down model first flew in 2022. In February 2024, the scaled down prototype with a wingspan reached from Chitradurga Aeronautical Test Range during eight and a half hours, development completion was then expected for 2027. In May 2024, the scaled down prototype flight tests reached during 27 hours from Chitradurga. The subscale prototype has a goal of a 7-day flight at an altitude of cruising at . The full-scale, CATS Infinity target is a ninety-day endurance at high altitudes, with a payload. The Indian Navy is also interested in this project. ; 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. Hydrocarbon fueled 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 ; USAF Compass Dwell and Compass Cope : The USAF Compass Dwell UAV program saw the flight of the LTV XQM-93 in February 1970, based on a turboprop-powered Schweizer SGS 2-32 sailplane and designed to fly 24 hours and to reach 50,000 ft (15,240 m); and the Martin Marietta Model 845 in April 1972, based on a piston engine-powered Schweizer SGS 1-34 sailplane, designed to reach 40,000 feet (12,000 m) and capable to fly 28 hours. The following Compass Cope program saw the Boeing YQM-94 B-Gull first flight on 28 July 1973: powered by a General Electric J97 turbojet, it was designed to fly 30 hours up to 70,000 ft (21,340 m), and managed to fly during 17.4 hours and up to 55,000 feet (16,800 m); the competing Ryan YQM-98 R-Tern was powered by a Garrett ATF3 turbofan, first flew on 17 August 1974 and was designed to fly during 30 hours. ; Boeing Condor : The Boeing Condor first flew on October 9, 1988, it reached 67,028 ft (20,430 m) and stayed aloft for nearly 60 hours; powered by two piston engines, the wide UAV had a gross weight and was designed to reach 73,000 ft (22,250 m) and to fly for more than a week. ; Aurora Perseus and Theseus : Built by Aurora Flight Sciences for what would become the NASA ERAST Program, the Perseus Proof-Of-Concept UAV first flew in November 1991 followed by Perseus A on 21 December 1993, which reached over . Designed to fly at 62,000 ft (18.9 km) and up to 24 hours, Perseus B first flew on 7 October 1994 and reached on June 27, 1998. Its pusher propeller is powered by a Rotax 914 piston engine boosted by a three-stage turbocharger flat-rated to to . It has a maximum weight, is able to carry a payload and its wing has a high 26:1 aspect ratio. A larger follow-on powered by two Rotax 912 piston engines, the Theseus first flew on May 24, 1996. Designed to fly during 50 hours up to 65,000 ft (20,000 m), the 5,500 (2.5 t) maximum weight UAV was 140 ft (42.7 m) wide and could carry a 340 kg (750 lb) payload. ; Scaled Composites Proteus : The manned Scaled Composites Proteus operates at altitudes of 19.8 km (65,000 ft), while carrying a payload. Powered by two Williams FJ44 turbofans, it had tandem wings with a 17 m (55 ft) front wing and a wider 24 m (78 ft) wide back wing for a maximum takeoff weight of 6.6 t (14,500 lb), could cruise at and stay 22 hours at of its base. ; Shenyang Aircraft Corporation Divine Eagle : The Divine Eagle, produced by Shenyang Aircraft Corporation, is a large turbofan-powered UAV developed since 2012 and possibly in service by 2018. The twin boom, twin tail aircraft has a canard wing and wind tunnel test were up to a ceiling of and Mach 0.8. Hydrogen fueled -powered Boeing Phantom Eye should have reached 65,000 ft (19,800 m) during four days. ; AeroVironment Global Observer : Fueled by liquid hydrogen and designed to fly at up to for up to 7 days, the AeroVironment Global Observer first flew on 5 August 2010. After a crash in April 2011, the Pentagon shelved the project. ; Boeing Phantom Eye : An evolution of the Boeing Condor developed by Boeing Phantom Works, the Boeing Phantom Eye first flew in June 2012. In August 2016, the Phantom Eye demonstrator was transferred to the Air Force Flight Test Museum. ; Stratospheric Platforms : UK Stratospheric Platforms, created in 2014, went public on 19 October 2020; after flight trials of a 4G/5G relay on a Grob G 520 at , the start-up is developing a hydrogen-fuel cell-powered HAPS UAV built by Scaled Composites, with a wingspan of , that would fly at for nine-days with a payload of . == Airships ==

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. 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 : On December 4, 2005, a team led by Southwest Research Institute (SwRI), sponsored by the Army Space and Missile Defense Command (ASMDC), successfully demonstrated powered flight of the HiSentinel stratospheric airship at an altitude of . project ; Integrated Sensor Is Structure : The USAF Integrated Sensor Is Structure (ISIS) airship would have stayed for up to ten years at , providing a persistent early warning against cruise missiles at up to or enemy combatants at up to . In January 2006, Lockheed won a $149M Contract to build it and demonstrate its technical feasibility and military utility. It would operate above in a quasi-geostationary position to deliver persistent orbital station keeping as a surveillance aircraft platform, telecommunications relay, or a weather observer. Launch was originally proposed in 2008, the production aircraft would be long and in diameter. Powered by solar cells, it would stay in the air for up to one month and was intended to survey a diameter of land. ; Lockheed-Martin HALE-D : On July 27, 2011, the "High Altitude Long Endurance-Demonstrator" (HALE-D) subscale demonstrator was launched on a test flight. HALE-D had a volume, was long and wide, had solar cells charging 40 kWh Li-ion batteries and electric motors to cruise at TAS at with a payload during 15 days. At a problem with the helium levels prevented it and the flight was terminated. It descended and crashed in a Pittsburgh area forest. Two days after, it was destroyed by a fire before its recovery. ; Lindstrand HALE airship : Lindstrand Technologies designed a Helium-filled non-rigid airship covered with solar cells. The aircraft could carry a payload during 3 to 5 years as helium loss would be minimal at high altitudes. For energy storage, a 180kW electrolyser would fill H2 and O2 tanks, to be converted back to water by a 150kW fuel cell. An motor would allow a maximum speed. ; Thales Alenia Stratobus : Thales Alenia Space develops the Stratobus unmanned, solar-powered stratospheric airship, long and weighting including a payload, it is designed for a five-year mission with annual servicing and a prototype was planned for late 2020. with development taking place via terrestrial high-altitude platforms. The first systems were tested by 2021. ; Stratoship SZ-155 : The SZ-155 was designed and manufactured by Stratoship in Australia. The SZ-155 flew two low altitude test flights in 2022 and 2024 before reaching the stratosphere on its first high altitude flight on May 5th, 2025. It flew for 11 hours and 12 minutes in total, and spent over 8 hours in the stratosphere. The SZ-155 is 25 meters long and was designed for flights of up to 7 days endurance. It can carry up to 10kg of payload to the stratosphere. Stratoship is currently designing a future model for multi-month flights. ==Balloons==

balloon A geostationary balloon satellite (GBS) flies in the stratosphere ( 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. ==Rotorcraft==

; Boeing A160 Hummingbird : The Boeing A160 Hummingbird is a rotorcraft produced by Boeing. First flown in 2002, the program had goals of a 24-hour endurance, and 30,000 ft (9,100 m) altitude, but was abandoned in December 2012. ==See also==