{{Short description|Aircraft that provides common satellite services}}{{redirect-distinguish|Pseudo-satellite|Pseudolite}}{{redirect-distinguish|Atmospheric satellite|Weather satellite}}(File:Compass Cope system concept.png|thumb|A high altitude platform can provide observation or communication services.)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.Very few HALE aircraft are operational like 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 64 days; few are as advanced.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 ObserverStratospheric 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 (HALE): High-altitude, long-endurance (HALE) aircraft are non-weaponized military drones capable of flying at {{cvt|60,000|feet}} over 32 hours, like the USAF RQ-4 Global Hawk or its variants used for ISR. This is above and longer than Medium-Altitude, Long-Endurance (MALE) aircraft flying between {{cvt|25,000 and 50,000|feet}} during 24 hours, more vulnerable to anti-aircraft defense, like the USAF ISR/strike MQ-9 Reaper or its variants.WEB,weblink Future of unmanned capabilities: MALE vs HALE, Mark, Pomerleau, 2015-05-27, Defense One, Government Executive,

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).BOOK,weblink ITU Radio Regulations, Terminology and technical characteristics, Â¶1.66A, HAPS can also be the abbreviation for high-altitude pseudo-satellite.

Studies

File:Helios checkout flight (kauai).ogg|thumb|Video of NASA Helios NASA HeliosIn 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.REPORT, D.W. Hall, etal,weblink A Preliminary Study of Solar Powered Aircraft and Associated Power Trains, NASA Langley Research Centre, December 1983, In 1984 was published the Design of Long Endurance Unmanned Airplanes Incorporating Solar and fuel cell propulsion report.REPORT,weblink C.L. Nickol, etal, High Altitude Long Endurance Air Vehicle Analysis of Alternatives and Technology Requirements Development, NASA, January 1, 2007, 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.JOURNAL, M.D. Maughmer (Pennsylvania State University), D.M. Somers (Langley Research Center, NASA Langley),weblink Design and experimental results for a high-altitude, long-endurance airfoil, Journal of Aircraft, 26, 2, February 1989, 148â€“153, American Institute of Aeronautics and Astronautics, AIAA Association, 10.2514/3.45736, 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.WEB,weblink The NASA ERAST HALE UAV Program, Greg Goebel, 1 March 2010, vectorsite.net,weblink" title="web.archive.org/web/20110629142327weblink">weblink 2011-06-29, In July 1996, the USAF Strikestar 2025 report forecast HALE UAVs maintaining air occupation with 24 hours flights.REPORT,weblink" title="web.archive.org/web/20151210233133if_weblink">weblink B.W. Carmichael, etal, Strikestar 2025, The U.S. Air-force, August 1996, 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.WEB,weblink HALE UAV for intelligence missions, S. Tsach et al. (Israel Aircraft Industries, IAI), International Council of the Aeronautical Sciences, ICAS, September 1996, 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 {{cvt|20|km|ft}} for 40 hours.PERIODICAL,weblink Z. Goraj, etal, High altitude long endurance unmanned aerial vehicle of a new generation â€“ a design challenge for a low cost, reliable and high performance aircraft, Bulletin of the Polish Academy of Sciences, Technical Sciences, 52, 3, 2004, 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 50Â°.NEWS,weblink Luminati: Perpetual Solar-powered Flight Possible, Mark Huber, August 2, 2018, AIN online,

Design

(File:Nasa wind vs alt curves.JPG|thumb|Wind profile variation with altitude from NASA, showing minimum wind speeds between {{cvt|17 and 22|km|ft}}. Although absolute values will vary, the trends shown are similar for most locations.)

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, or in fuel cells.

Altitude selection: Drag is reduced in the tropopause thin air, well above the {{cvt|40 â€“ 160|knots|km/h}} high winds and air traffic of the high troposphere between {{cvt|20,000 to 35,000|ft}}. Maintaining a position facing variable winds is a challenge. Relatively mild wind and turbulence above the jet stream is found in most locations in the stratosphere between {{cvt|17 and 22|km|ft}}, although this is variable with the latitude and season. Altitudes above {{cvt|55000|ft}} are also above commercial air transport.JOURNAL,weblink High-altitude platforms for wireless communications, T. C. Tozer, D. Grace, Electronics & Communication Engineering Journal, June 2001, 13, 3, 127â€“137, 10.1049/ecej:20010303, Flying in the tropopause at {{cvt|65,000|ft}} is above clouds and turbulence with winds below {{cvt|5|kn|km/h|0}}, and above FAA-regulated Class A airspace ending at {{cvt|60,000|feet}}.WEB, Dillow, Clay, The drone that may never have to land,weblink Fortune (CNN), August 23, 2013,

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. Satellites are more expensive, take longer to deploy, and cannot be reasonably accessed for maintenance.WEB, Advantages of HAPS: (ii) Compared with Satellite Services,weblink 2001, SkyLARC Technologies,weblink" title="web.archive.org/web/20061101044134weblink">weblink 2006-11-01, 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. 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: In Europe, scientists are considering HAPS to deliver high-speed connectivity to users, over {{clarify span|areas of up to 400 km|in diameter?|date=August 2016}}. HAPS could deliver bandwidth and capacity similar to a broadband wireless access network, like WiMAX, over a coverage area similar to that of a satellite. Military communications can be improved in remote areas like in Afghanistan, where mountainous terrain interferes with communications signals.WEB, High Altitude Airship, Lockheed Martin,weblink weblink" title="web.archive.org/web/20130126194933weblink">weblink 2013-01-26,

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.WEB,weblink RQ-4A Global Hawk (Tier II+ HAE UAV), Federation of American Scientists, John Pike, Steven Aftergood,

Real-time monitoring: An area could be monitored for flood detection, seismic monitoring, remote sensing and disaster management.CONFERENCE,weblink The airborne Remote Sensing technical system of the Chinese Academy of Sciences, Tong Qingxi, The Joint Center for Remote Sensing of Chinese Academy of Sciences, CAS China, Asian Association on Remote Sensing (AARS) Asian Conference on Remote Sensing (ACRS), 1990,

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.WEB,weblink NASA Recruits Unmanned Aircraft for Earth Science, Space.com, January 17, 2009,

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 {{cvt|20|km|ft}} when launched from the ground will reach {{cvt|100|km|nmi}} if launched at an altitude of {{cvt|20|km|ft}} from a balloon."BOOK, Nobuyuki Yajima, etal, 2004, Scientific ballooning: technology and applications of exploration balloons floating in the stratosphere and the atmospheres of other planets,weblink limited, 978-0-387-09725-1, Springer, 162, 3.7.2.3 Launching Rockets from Ballons (Rockoons), 10.1007/978-0-387-09727-5, Mass drivers have been proposed for launching to orbit.BOOK, Gerard K. O'Neill, 1981, 2081: a hopeful view of the human future, Simon and Schuster, 978-0-671-24257-2,weblink registration, {{page needed|date=February 2023}}

Airplanes

Reconnaissance aircraft like the late 1950s Lockheed U-2 could fly above {{cvt|70,000|feet}} and the 1964 SR-71 above {{cvt|80,000|feet}}.MAGAZINE,weblink HALE UAVs Come of Age, Feb 20, 2007, Defense Update, 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

File:940th Wing - Northrop Grumman RQ-4B Block 20 Global Hawk 04-2015.jpg|thumb|Capable of flying up to 60,000 ft (18,300 m) more than 34 hours, the RQ-4 Global Hawk was put into USAF USAF

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 {{cvt|33|m}} wide, reached 16,329 m (53,574 ft), and can stay airborne during 13 hours.

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.PRESS RELEASE,weblink Northrop Grumman Celebrates 20th Anniversary of Global Hawk's First Flight, February 28, 2018, Northrop Grumman, 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.WEB,weblink RQ-4 Global Hawk, October 2014, USAF, 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. A total 42 of them have been in service with the United States Air Force.NEWS, Northrop Grumman Unmanned Aircraft Systems Achieve 100,000 Flight Hours,weblink Sep 13, 2013, Defense Media Network, Faircount Media Group, It is the basis for the US Navy's MQ-4C Triton.

Prototypes

Solar powered

{{See also|Solar-powered aircraft}}File:Pathfinder Plus solar aircraft over Hawaii.jpg|thumb|NASA Pathfinder Plus ]]

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.WEB,weblink The Prehistory of Endurance UAVs, Greg Goebel, 1 Feb 2022, airvectors.net, It joined the NASA ERAST Program in late 1993 as the Pathfinder, and with solar cells covering the entire wing added later, it reached {{cvt|50,500|feet}} on September 11, 1995 and then {{cvt|71,530|feet}} in 1997. The Pathfinder Plus had four sections of the Pathfinder wing out of five attached to a longer center section, increasing span to {{cvt|121|feet}}, it flew in 1998 and reached {{cvt|80,201|feet}} on August 6 of that year.

File:Centurion-EC98-44822-5.jpg|thumb|NASA Centurion NASA Centurion

AeroVironment/NASA Centurion/Helios Prototype: Flying in late 1998, the Centurion had a redesigned high-altitude airfoil and span increased to {{cvt|206|feet}}, 14 motors, four underwing pods to carry batteries, systems and landing gear. It was modified into the Helios Prototype, with a sixth {{cvt|41|foot}} wing section for a {{cvt|247|feet}} span, and a fifth landing gear and systems pod. It first flew in late 1999, solar panels were added in 2000 and it reached {{cvt|96,863|feet}} on August 13, 2001. A production aircraft would fly for up to six months.WEB, NASA Armstrong Fact Sheet: Helios Prototype,weblink NASA, February 28, 2014, February 23, 2023, January 18, 2017,weblink dead, It broke up in flight in 2003.

Airbus Zephyr: The Zephyr were originally designed by QinetiQ, a commercial offshoot of the UK Ministry of Defence.NEWS, Amos, Jonathan, Strato-plane looks forward, BBC News, 24 June 2003,weblink The UAVs are powered by solar cells, recharging batteries in daylight to stay aloft at night. The earliest model flew in December 2005.NEWS,weblink Energetic Qinetiq, 11 July 2006, Craig Hoyle, flightglobal, In March 2013, the project was sold to Airbus Defence and Space.PRESS RELEASE, First flight of Astrium's Zephyr solar HAPS, Airbus, 25 September 2013,weblink" title="web.archive.org/web/20131005205329if_weblink">weblink The latest Zephyr 8/S model weighs {{cvt|75|kg}}, has a wingspan of {{cvt|25|m}}, and reached {{cvt|76,100|ft|order=flip}}.NEWS, Sampson, Ben, Airbus Zephyr breaks more aviation records during flight testing,weblink Aerospace Testing International, 15 October 2021,

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. Their wing, over {{cvt|160|ft|-1}} wide, would be covered with solar cells to provide energy for day flight, stored in electric batteries for use at night. Costing less than $2 million, they could carry a {{cvt|70|lb|-1}} payload for up to five years, limited by battery deterioration. In 2013, Titan was flying two fifth-scale test models and aimed to flight test a full-sized prototype by 2014. In March 2014, Facebook was interested in the company, led at the time by Eclipse Aviation founder Vern Raburn, for $60 million.NEWS, Perez, Sarah, Constine, Josh, Facebook In Talks To Acquire Drone Maker Titan Aerospace,weblink TechCrunch, March 4, 2014, Google bought Titan Aerospace in April 2014,NEWS,weblink Google buys solar-powered drone maker Titan Aerospace, 14 April 2014, BBC, managed to fly a prototype in May 2015 but it crashed within minutes and Titan Aerospace was shut down by early 2017.NEWS,weblink Google Shuts Down Vern Raburn's Titan Aerospace, Stephen Pope, January 19, 2017, Flying magazine,

File:ì „ê¸°ë™ë ¥ë¬´ì¸ê¸°(EAV-3) ë¹„í–‰ (196).jpeg|thumb|The KARI KARI

KARI EAV: The Korea Aerospace Research Institute (KARI) began developing its Electrical Aerial Vehicle (EAV) in 2010, after subscale demonstrators, its latest {{cvt|20|m}} wide EAV-3 weighs {{cvt|66|kg}} and is designed to fly for months; it flew up to {{cvt|14.2|km|ft}} in August 2015, during 53 hours and up to {{cvt|22|km|ft}} in August 2020.WEB,weblink Electrical Aerial Vehicle (EAV), KARI,

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 {{cvt|67,000|ft}} for 90 days carrying a {{cvt|25|kg}} payload. OS owns 51% of UK company Astigan, led by Brian Jones, developing the A3 since 2014 with scale model test flights in 2015 and full-scale low-altitude flights in 2016. High-altitude flights should begin in 2019, to complete tests in 2020 with a commercial introduction as for environmental monitoring, mapping, communications and security.NEWS,weblink The Week In Technology, Feb. 18-22, 2019, Feb 18, 2019, Tony Osborne, Aviation Week & Space Technology, In March 2021, the project was ended as no strategic partner was found.NEWS,weblink Cartographic Agency Shuts Down Astigan HAPS Project, March 30, 2021, Tony Osborne, Aviation Week & Space Technology,

Facebook Aquila: The Facebook Aquila UAV was a carbon fiber, solar-powered flying wing UAV spanning {{cvt|132|ft}} and weighing {{cvt|935|lb}}, designed to stay aloft at FL650 for 90 days. It was designed and manufactured by UK company Ascenta for Facebook, to provide internet connectivity.NEWS, Rory Cellan-Jones,weblink Facebook's drones - made in Britain, BBC, 21 July 2016, UAVs would use Laser communication between them and to ground stations.NEWS, Perry, Tekla S., Facebook's Aquila Drone Creates a Laser-net In the Sky,weblink Institute of Electrical and Electronics Engineers, IEEE Spectrum, April 13, 2016, On June 28, 2016, it took its first flight, during ninety minutes and reaching {{cvt|2150|feet}}, but a twenty-foot section of the righthand wing broke off during final approach.WEB,weblink Aviation Investigation - DCA16CA197, NTSB, WEB,weblink Reviewing Aquila's first full-scale test flight, Engineering at Meta, 16 December 2016, It made another low-altitude test flights in 2017. On June 27, 2018, Facebook announced it will halt the project and plan to have other companies build the drones.WEB,weblink High altitude connectivity: The next chapter, 2018-06-27, Yael, Maguire, Engineering at Meta,

China Aerospace Science and Technology Corporation: China Aerospace Science and Technology Corporation flew a {{cvt|147|ft}}-span solar-powered UAV to FL650 in a 15 hours test flight in July 2017.

Lavochkin LA-252: Russia's Lavochkin design bureau is flight-testing the LA-252, an {{cvt|82|ft}}-span, {{cvt|255|lb}} solar-powered UAV designed to stay aloft 100 days in the stratosphere.

Mira Aerospace ApusDuo HAPSWEB, Mira Aerospace,weblink 2024-02-28, miraaerospace.com,: A joint venture between Abu Dhabi-based Bayanat AI and American UAV manufacturer UAVOS, Mira Aerospace's ApusDuo HAPS has completed over 100 test flights across 3 continents, building off technologies first developed in 2014.WEB, Mira Aerospace,weblink 2024-02-28, miraaerospace.com, With a wingspan of {{cvt|14|m}}, 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 {{cvt|19000|m}}, carrying payloads up to {{cvt|6|kg}}. 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.WEB, Writer, Staff, TradeArabia, Mira Aerospace delivers worldâ€™s first 5G connectivity from stratosphere,weblink 2024-02-28, www.zawya.com, en,

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.NEWS,weblink AeroVironment's Stratospheric Satellites Persistence Pays Off, Jan 12, 2018, Graham Warwick, Aviation Week & Space Technology, Resembling the 1999 Helios, the {{cvt|256|ft}} span flying wing with 10 electric-driven propellers would provide 4G LTE and 5G direct to devices over a 200 km (125 mi) diameter areaNEWS,weblink The Week In Technology, April 29-May 3, 2019, Apr 29, 2019, Graham Warwick, Aviation Week & Space Technology, On 21â€“22 September 2020, the HAPSMobile Hawk30 (rebranded as Sunglider) flew 20 hours and reached an altitude of {{cvt|62,500|ft|km}}, testing the long-distance LTE communications developed with Loon for standard LTE smartphones and wireless broadband communications.NEWS,weblink HAPSMobile Sunglider reaches 63,000ft, demos broadband transmission, Garrett Reim, 8 October 2020, Flightglobal,

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 {{cvt|15|kg}} payload at around 70,000 ft for days or weeks.NEWS,weblink BAE joins high-altitude race with maiden PHASA-35 flight, Dan Thisdell, 17 February 2020, Flightglobal,
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. Designed to operate at {{cvt|70,000|feet}}, the persistent {{cvt|72|foot}} UAV weighs less than {{cvt|180|lb}} and can carry up to {{cvt|15|lb}} payloads.PRESS RELEASE,weblink American made Swift High Altitude Long Endurance UAS Completes Landmark Flight, July 20, 2020, Swift Engineering,

Aurora Odysseus: Aurora Flight Sciences announced its Odysseus in November 2018. The 74.1m (243ft) wide carbon fibre aircraft weigh less than {{cvt|880|kg|lb}} and can carry a 25kg (55lb) payload.NEWS,weblink Aurora Flight Science's long-endurance drone to make first flight in spring 2019, 14 Nov 2018, Garrett Reim, Flightglobal, It was designed to stay above {{cvt|65,000|ft}} up to three months at latitudes up to 20Â°.NEWS,weblink Anatomy Of Aurora Flight Sciences' Odysseus, Nov 22, 2018, Graham Warwick, Aviation Week & Space Technology, Its first flight was indefinitely delayed by July 2019.NEWS,weblink Aurora indefinitely delays first flight of Odysseus ultra-long-endurance UAV, Pat Host, 9 July 2019, Jane's,

HAL CATS InfinityCATS Infinity being developed by HAL, NAL and NewSpace Research. Its scaled down model underwent first flight in 2022. In February 2024, a test flight of the scaled down prototype weighing 23 kg was tested with a wingspan of 12 m at an altitude of 3 km was carried out on Chitradurga Aeronautical Test Range with a duration of eight and a half hours. Officials stated that the development is now expected for completion in 2027. In the next test, expected to happen in March 2024, the duration shall be increased to 24 hours.WEB, 2024-02-10, Meet HAPS: India's very own UAV that can fly 20 km high and float for months,weblink 2024-02-10, The Indian Express, en, {| class="wikitable sortable"|+ Solar-powered HAPS! Model !! First flight !! Span !! Weight !! Payload !! Altitude !! Endurance || Status

NASA Pathfinder>Pathfinder

1993-T4

98.4 ft (29.5 m)

560 lb (252 kg)

100 lb (45 kg)

{{cvt

feet}}

12 hours

80,201

Helios Prototype>Helios

1999-09-08

{{cvt

feet}}

2,048 lb (929 kg)

726 lb (329 kg)

{{cvt

feet}}

goal: >24 hours

2003 crash

Airbus Zephyr >

order=flip}}

{{cvt

order=flip}}

{{cvt

ft}}

64 days

2024 planned intro.

Titan Aerospace Solara >

160

-1}}

{{cvt

520

| 2017 shut down

Korea Aerospace Research Institute>KARI EAV-3

2015-08

{{cvt

order=flip}}

{{cvt

order=flip}}

53 hours

Ordnance Survey>OS Astigan A3

2016

125 ft (38 m)

330 lb (149 kg)

{{cvt

67,000

| 2021 project end

Facebook Aquila >

132

935

2150

| 2018 project halt

China Aerospace Science and Technology Corporation>CASTC

2017-07

{{cvt

ft}}

{{cvt

ft}}

15 hours

Lavochkin LA-252 >

255

order=flip}}

{{cvt

order=flip}}

62,000 ft (19 km)

goal: year-round

HAPSMobile >

256

62,500

km}}

20 hours

BAE Systems PHASA-35 >

150

order=flip}}

goal: 70,000 ft

72 hours

Swift Engineering#Swift Ultra Long Endurance (SULE)>Swift Engineering SULE

2020-07

{{cvt

foot}}

{{cvt

lb}}

{{cvt

lb}}

goal: {{cvt

feet}}

HAL Combat Air Teaming System#CATS Infinity>HAL CATS Infinity|2022-10-19

160

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1100|lb}}|

70,000|feet}}|goal: 3 months|Prototype testing, 2027-28 intro

Hydrocarbon fueled

File:Ryan YQM-98A 72-01872 from below.jpg|thumb|The Ryan YQM-98 R-Tern Ryan YQM-98 R-Tern

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 {{cvt|175|hp}} piston engines, the {{cvt|200|feet}} wide UAV had a {{cvt|20,300|lb}} gross weight and was designed to reach 73,000 ft (22,250 m) and to fly for more than a week.WEB,weblink Condor Unmanned Aerial Vehicle, Boeing,

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 {{cvt|50,000|feet}}. 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 {{cvt|60,280|feet}} on June 27, 1998. Its pusher propeller is powered by a Rotax 914 piston engine boosted by a three-stage turbocharger flat-rated to {{cvt|105|hp}} to {{cvt|60,000|feet}}. It has a {{cvt|2,500|lb}} maximum weight, is able to carry a {{cvt|260|lb}} payload and its {{cvt|71.5|feet}} wing has a high 26:1 aspect ratio.WEB,weblink Feb 28, 2014, NASA Armstrong, Fact Sheet: Perseus B Remotely Piloted Aircraft, 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.

Grob Strato 2C: Designed to fly at 24,000 m (78,700 ft) and for up to 48 hours, the manned Grob Strato 2C first flew on 31 March 1995 and reached 18,552 m (60,897 ft). The 56.5 m (185 ft) wide aircraft was powered by two 300 kW (400 hp) piston engines turbocharged by a PW127 turboprop as the gas generator.

File:ALTUS UAV takes off from Rogers Dry Lake (EC97-44175-14).jpg|thumb|The piston-powered 57,300|feet}}

General Atomics ALTUS: Part of the NASA ERAST Program, the high-altitude UAV General Atomics ALTUS I & II were civil variants of the Gnat 750 (which also spawned the USAF Predator A) which had a 48 hours endurance, with a longer wingspan at {{cvt|55.3|ft}}. Powered by a {{cvt|100|hp}} turbocharged Rotax 912 piston engine, The {{cvt|2,130|lb}} MTOW testbed could carry up to {{cvt|330|lb}} of scientific instruments. The Altus II first flew on May 1, 1996, had an endurance over 26 hours, and reached a maximum density altitude of {{cvt|57,300|feet}} on March 5, 1999. They led to the larger, turboprop-powered General Atomics Altair.NEWS,weblink Fact Sheet: Altus II, NASA Armstrong, February 28, 2014, Aug 7, 2017, Yvonne Gibbs,

Scaled Composites Proteus: The manned Scaled Composites Proteus operates at altitudes of 19.8 km (65,000 ft), while carrying a {{cvt|1,100|kg}} payload.NEWS,weblink Fact Sheet: Proteus High-Altitude Aircraft, NASA Armstrong, February 28, 2014, Aug 7, 2017, Yvonne Gibbs, 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 {{cvt|450|km/h|kn}} and stay 22 hours at {{cvt|{{#expr:3700/4round0}}|km|nmi|-1}} of its base.

Virgin Atlantic GlobalFlyer: The manned GlobalFlyer, built by Scaled Composites, was designed to fly around the world. Powered by a single Williams FJ44, the 114 ft (35 m) wide aircraft can weigh up to 22,100 lb (10 t). Having a 50,700 ft (15,450 m) ceiling, it flew for 76 hours and 45 minutes in February 2006.

Aurora Flight Sciences Orion: The initial Boeing/Aurora Flight Sciences Orion platform would cruise at {{cvt|65,000|ft}} for 100 hours, powered by liquid hydrogen feeding piston engines; its takeoff weight of 7,000 lbs (3.2 tons) allowing 400 lbs (180 kg) payloads. It evolved into a twin turbo-diesel-powered MALE UAV burning jet fuel with an increased gross weight to {{cvt|11,000|lb}}, designed to fly at {{cvt|20,000|ft}} during 120 hours (five days) with a 1,000lb payload, or a week with a smaller one; it made its first flight in August 2013 and flew during 80 hours in December 2015, landing with enough fuel for 37 hours more.NEWS,weblink" title="web.archive.org/web/20150122223803if_weblink">weblink Aurora Claims Endurance Record For Orion UAS, Jan 22, 2015, Graham Warwick, Aviation Week & Space Technology,

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.WEB,weblink Divine Eagle UAV spotted at China's Malan airbase, Sean O'Connor, IHS Jane's Defence Weekly, 14 November 2018,weblink 2018-11-18, The twin boom, twin tail aircraft has a canard wing and wind tunnel test were up to a ceiling of {{cvt|25|km|ft}} and Mach 0.8.NEWS,weblink China Flies Its Largest Ever Drone: The Divine Eagle, Jeffrey Lin, P.W. Singer, Popular Science, Feb 6, 2015,

Hydrogen fueled

File:Boeing's Phantom Eye lift off.jpg|thumb|The hydrogen-powered Boeing Phantom Eye Boeing Phantom Eye

AeroVironment Global Observer: Fueled by liquid hydrogen and designed to fly at up to {{cvt|65,000|feet}} for up to 7 days, the AeroVironment Global Observer first flew on 5 August 2010.PRESS RELEASE,weblink AeroVironment's stratospheric global observer unmanned aircraft system makes first flight, August 16, 2010, AeroVironment, After a crash in April 2011, the Pentagon shelved the project.NEWS,weblink AeroVironment teams with Lockheed Martin on Global Observer, Stephen Trimble, 7 February 2014, Flightglobal,

Boeing Phantom Eye: An evolution of the Boeing Condor developed by Boeing Phantom Works, the Boeing Phantom Eye first flew in June 2012. Powered by two {{cvt|150|hp}} turbocharged Ford 2.3 liter piston engines running on liquid hydrogen, the 150 ft (46 m) wide UAV has a gross takeoff weight of 9,800 lbs (4.4 t) and can carry a {{cvt|450|lb}} payload. It cruises at {{cvt|150|kn|km/h}}, can reach 65,000 ft (19,800 m) and have a four days endurance. A full size variant is designed to carry a {{cvt|2000|lb}} payload during ten days.WEB, Boeing,weblink Phantom Eye, In August 2016, the Phantom Eye demonstrator was transferred to the Air Force Flight Test Museum.PRESS RELEASE,weblink Air Force Flight Test Museum taking in more NASA history with Phantom Eye, LLRV, Aug 25, 2016, Edwards Air Force Base,

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 {{cvt|45,000|ft}}, the start-up is developing a hydrogen-fuel cell-powered HAPS UAV built by Scaled Composites, with a wingspan of {{cvt|60|m}}, that would fly at {{cvt|60,000|ft}} for nine-days with a payload of {{cvt|140|kg}}.NEWS,weblink Hydrogen-powered UAV to fly 'beast' of the world's biggest airborne 5G antenna, Tim Robinson, 23 October 2020, Royal Aeronautical Society,

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.Subjected to ultraviolet damage, ozone corrosion and challenging station keeping, they can be solar-powered with energy storage for the night.{{citation |chapter-url=weblink |title= Modern Airships â€“ Part 1 |orig-date= August 18, 2019 |author= Peter Lobner |date= 9 January 2023 |chapter= 5.6 Stratospheric airships }}The first stratospheric powered airship flight took place in 1969, reaching {{convert|70000|ft|km}} for 2 hours with a {{convert|5|lb|kg|abbr=off}} payload.WEB, Aerostar, Stratospheric Airships, 15 February 2023,weblink 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.PRESS RELEASE, Aeros Completes 50 M Envelope For South Korea High-Altitude Airship Program, Worldwide Aeros Corp, 30 August 2002,weblink weblink" title="web.archive.org/web/20081121114603weblink">weblink 2008-11-21, By April 2004, stratospheric airships were being developed in USA, UK, Canada, Korea and Japan.WEB, Airships: Making a Comeback,weblink Aviation Today, 1 April 2004, In May 2004, the Japan Aerospace Exploration Agency shown its test airship in Taiki, Hokkaido, a part of its Stratosphere Platform Project.WEB, Expectations soar for our huge new airship,weblink Japan Aerospace Exploration Agency, December 3, 2004,

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 {{convert|74000|ft|km}}.PRESS RELEASE, Stratospheric airship reaches near-space altitude during demonstration flight, Southwest Research Institute News,weblink 17 November 2005,weblink" title="web.archive.org/web/20060819234528weblink">weblink 2006-08-19,

File:Integrated Sensor is Structure 1.jpg|thumb|USAF Integrated Sensor Is Structure Integrated Sensor Is Structure

Integrated Sensor Is Structure: The USAF Integrated Sensor Is Structure (ISIS) airship would have stayed for up to ten years at {{cvt|70,000|ft}}, providing a persistent early warning against cruise missiles at up to {{cvt|600|km|nmi}} or enemy combatants at up to {{cvt|300|km|nmi}}.

Lockheed-Martin HAA: The United States Department of Defense Missile Defense Agency contracted Lockheed Martin to build an unmanned High-Altitude Airship (HAA) for its Ballistic Missile Defense System.WEB, High Altitude Airship (HAA), Lockheed Martin,weblink weblink" title="web.archive.org/web/20101114211650weblink">weblink 2010-11-14, In January 2006, Lockheed won a $149M Contract to build it and demonstrate its technical feasibility and military utility.NEWS, Lockheed Wins $149.2M Contract for High Altitude Airship, Jan 16, 2006, Defense Industry Daily,weblink It would operate above {{cvt|60000|ft|m}} 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 {{cvt|500|ft|m}} long and {{cvt|150|ft|m}} in diameter. Powered by solar cells, it would stay in the air for up to one month and was intended to survey a {{cvt|600|mi|km|adj=on}} 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.PRESS RELEASE,weblink Lockheed Martin, U.S. Army Demonstrate HALE-D During Abbreviated Flight, Lockheed Martin, July 27, 2011, HALE-D had a {{cvt|500,000|ft3}} volume, was {{cvt|240|ft}} long and {{cvt|70|ft}} wide, had {{cvt|15|kW}} solar cells charging 40 kWh Li-ion batteries and {{cvt|2|kW}} electric motors to cruise at {{cvt|20|kn|km/h}} TAS at {{cvt|60,000|ft}} with a {{cvt|50|lb}} payload during 15 days.WEB,weblink High Altitude Airship (HAA), GlobalSecurity.org, At {{cvt|32000|ft|m}} a problem with the helium levels prevented it and the flight was terminated.NEWS, Jim Mackinnon,weblink Lockheed Martin's prototype blimp crashes during maiden voyage, Akron Beacon Journal, July 27, 2011,weblink" title="web.archive.org/web/20130411063122weblink">weblink 2013-04-11, It descended and crashed in a Pittsburgh area forest.WEB,weblink Lockheed Martin High Altitude Airship's Maiden Voyage Aborted, Lighter-Than-Air Society, July 27, 2011, Two days after, it was destroyed by a fire before its recovery.NEWS, Jim Mackinnon,weblink Lockheed Martin's prototype airship burns, Akron Beacon Journal, August 2, 2011,weblink" title="web.archive.org/web/20160408033319weblink">weblink 2016-04-08, 2016-03-25, live,

Lindstrand HALE airship: Lindstrand Technologies designed a Helium-filled non-rigid airship covered with solar cells. The {{cvt|14|t|lb}} aircraft could carry a {{cvt|500|kg}} 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. A {{cvt|80|kW}} motor would allow a {{cvt|24|m/s|kn}} maximum speed.WEB,weblink HALE Airship - Manufacture, Flight and Operation, John Pattinson, Lindstrand Technologies,

(File:Stratobus artiste.jpg|thumb|Stratobus airship)

Thales Alenia Stratobus: Thales Alenia Space develops the Stratobus unmanned, solar-powered stratospheric airship, {{cvt|377|ft}} long and weighting {{cvt|15,000|lb}} including a {{cvt|550|lb}} payload, it is designed for a five-year mission with annual servicing and a prototype was planned for late 2020.

H-Aero: H-Aero LTA-based launch systems for Mars exploration,JOURNAL, Ultralight Solar Powered Hybrid Research Drone, Singer, Cs, Concepts and Approaches for Mars Exploration, June 2012, 1679, 4059, 1304.5098, 2012LPICo1679.4059S, with development taking place via terrestrial high-altitude platforms. The first systems were tested by 2021.WEB,weblink Flugzeug, Hubschrauber und Luftschiff in einem: Baden-Badener Konstrukteur entwickelt neues FluggerÃ¤t, 11 February 2021, Badische Neueste Nachrichten, de, {{better source needed|reason=an english ref would be more appropriate in the english wikipedia|date=February 2023}}

Balloons

File:Google Loon - Launch Event.jpg|thumb|A Google Project Loon Project LoonA geostationary balloon satellite (GBS) flies in the stratosphere ({{cvt|60,000|to|70,000|ft|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.CONFERENCE, A low cost alternative for satellites- tethered ultra-high altitude balloons, IEEE,weblink Proceedings of 5th International Conference on Recent Advances in Space Technologies - RAST2011, June 2011, Izet-Unsalan, Kunsel, Unsalan, Deniz, 13â€“16, 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.PRESS RELEASE,weblink FDC/aerofilter selected by Boeing Phantom Works for the A160 Hummingbird, FDC/aerofilter, Vertical magazine, MHM publishing, October 28, 2005, 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.

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High-altitude platform station

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