21. April 2021
High up in the air

DLR de­vel­ops an un­manned strato­spher­ic air­craft

HAP alpha design study
HAP al­pha de­sign study
Image 1/3, Credit: DLR (CC BY-NC-ND 3.0)

HAP alpha design study

In con­trast to air­craft and non-geo­sta­tion­ary satel­lites, high-al­ti­tude plat­forms should be per­ma­nent­ly de­ploy­able at any lo­ca­tion and can be used for many tasks in the field of Earth ob­ser­va­tion. These in­clude the mon­i­tor­ing of ship­ping routes, re­con­nais­sance in the event of flood­ing events and for­est fires or the mon­i­tor­ing of ice sur­faces.
Lightweight construction
Lightweight con­struc­tion
Image 2/3, Credit: DLR (CC BY-NC-ND 3.0)

Lightweight construction

The so­lar-pow­ered plat­form has a con­ven­tion­al con­fig­u­ra­tion, but will be ex­treme­ly lightweight, with a to­tal weight of 138 kilo­grams and a wingspan of 27 me­tres. The sen­sor sys­tems, in­clud­ing a high-res­o­lu­tion cam­era and a syn­thet­ic aper­ture radar sys­tem, will not ex­ceed five kilo­grams in weight each.
Demonstration model of a wing segment
Demon­stra­tion mod­el of a wing seg­ment
Image 3/3, Credit: DLR (CC BY-NC-ND 3.0)

Demonstration model of a wing segment

Us­ing a wing demon­stra­tor, the team is test­ing de­sign con­cepts for the main spar, the ribs and the wing sur­face, as well as the in­te­gra­tion of the so­lar cells.
  • 17 DLR institutes are developing an unmanned, solar-powered stratospheric aircraft.
  • The High-Altitude Platform (HAP) alpha weighs 36 kilograms, has a payload capacity of five kilograms, a wingspan of 27 metres and is expected to fly to an altitude of 20 kilometres.
  • The first flight is planned to take place by the end of 2022.
  • Focus: Aeronautics, space, digitalisation, security

Earth observation and global communications – these two terms immediately bring satellites to mind. Constructing these satellites and placing them in orbit is costly and, at the end of their missions, their remains are sometimes left behind to become space debris. Aircraft or helicopters, however, are also not ideal for these tasks. Their deployment is limited by factors of time and location and highly dependent on the weather. A team from the German Aerospace Center (Deutsches Zentrums für Luft- und Raumfahrt; DLR) is researching and developing an unmanned, solar-powered stratospheric aircraft for future scientific experiments that combines the advantages of spaceflight and aeronautics.

DLR researchers have named their technology carrier HAP alpha. "HAP stands for 'High-Altitude Platform'," explains Florian Nikodem from the DLR Institute of Flight Systems. "They are usually solar-powered platforms that are permanently stationed in the lower stratosphere at an altitude of 20 kilometres." At this altitude, they fly far above civilian air traffic and even above the weather. They can be deployed anywhere provided there is sufficient solar power and, depending on their payload, can be used for a wide variety of missions. They are independent of the weather once they have reached the lower stratosphere, and they are also independent of mission durations as there is no crew on board. This is what sets them apart from conventional aircraft.

High-Altitude Platform – unmanned and long-endurance at high altitude
Aircraft capable of flying in the stratosphere are attracting increasing interest in research and industry because of their extensive application potential. Acquiring comprehensive systems expertise for high-altitude aircraft is the goal of the DLR cross-sectoral 'High-Altitude Platform' (HAP)...

HAP alpha is intended to fly to an altitude of 20 kilometres carrying a five-kilogram payload, but it cannot yet be stationed there for an extended period of time. The robust and modular design of the platform makes it easy to modify. With a wingspan of 27 metres, it is comparable to an aircraft capable of continuous flight but its structure weighs only 36 kilograms. "We have been able to achieve the low weight for this size by using an extremely lightweight carbon-fibre-reinforced polymer (CFRP) design," Nikodem explains. "The main spar, fuselage and tail spar of the structure are made of circular wound CFRP tubes. These are very light yet highly stable."

17 DLR institutes are working towards the first flight

The solar-powered, unmanned demonstrator is not the only thing the team is developing in the project. A ground station, the operational procedures and three payloads to be carried by the platform are also part of the research. The mobile ground station will be used by the researchers coordinate the missions and data reception. It is being set up in transportable containers and should be able to exchange data with the HAP from a distance of over 100 kilometres. The three payloads, including the high-resolution Modular Aerial Camera System High-Altitude Platform (MACS-HAP) and the High-Altitude Platform Synthetic Aperture Radar (HAPSAR), offer a wide range of future applications. A total of 17 DLR institutes from the fields of aeronautics, space and security are working together on HAP alpha, with the project being led by the Institute of Flight Systems in Braunschweig.

In April 2019, the team demonstrated that the established system requirements and the developed aircraft form were suitable to achieve the project goals. At the following Preliminary Design Review, the researchers showed that the preliminary design of the platform fulfilled all system requirements within the cost and deadline specifications and that the risks relating to future changes were as low as possible. The result of the review forms the basis for the continued development of the project in the detailed design stage and confirms that the researchers selected the right design options, identified the necessary interfaces and planned the correct verification methods. The researchers are currently preparing the Critical Design Review, which will check whether the detailed design can achieve the project goals. After that, the production and assembly of the individual components will commence.

HAP takes flight

HAP alpha is scheduled to take off on its first test by the end of 2022. Initially, the aircraft will merely perform low-altitude flights over the site of the National Experimental Test Center for Unmanned Aircraft Systems in Cochstedt. The flight altitude will be a few hundred metres. After successful low-altitude tests, the flight altitude will then be gradually increased up to the target of 20 kilometres during further high-altitude flight campaigns. "Unlike the first test flights in Cochstedt, where the test duration will only be a few hours, a high-altitude flight can take up to 24 hours due to HAP's slow flight speed, even if the platform will only be at an altitude of 20 kilometres for about two hours," says Nikodem, explaining the challenge posed by future tests. In order to carry out these tests, the team has to have several crews available and train for their changeovers.

Payloads will also be used in future high-altitude flights. With every test, the team will gather experience and be able to modify the HAP to enable longer flights. After achieving the sufficient operational safety of the team and the platform at such a high altitude, the stratospheric aircraft could be used as an experimental carrier for payloads and new platform-specific technologies. One example would be using the HAP as a hub for digital communication to support the deployment of a 5G network.

About HAP

17 DLR institutes and facilities are involved in DLR’s internal High-Altitude Platform (HAP) cross-sectoral project: the Institute of Flight Systems, Institute of Composite Structures and Adaptive Systems, Institute of Aeroelasticity, Institute of Aerodynamics and Flow Technology, Institute of Flight Guidance, Institute of Communications and Navigation, Institute for Software Technology, Systemhaus Technik, Institute of System Dynamics and Control, German Remote Sensing Data Center, Microwaves and Radar Institute, Remote Sensing Technology Institute, Institute of Optical Sensor Systems, Institute of Atmospheric Physics, Space Operations and Astronaut Training Facility, Institute of Robotics and Mechatronics, and Institute of Networked Energy Systems.

The HAP project was launched in 2018 and will continue until 2022.

  • Jasmin Begli
    Cor­po­rate Com­mu­ni­ca­tions Braun­schweig, Cochst­edt, Stade and Trauen
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 531 295-2108
    Fax: +49 531 295-12100
    Lilienthalplatz 7
    38108 Braunschweig
  • Florian Nikodem
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Flight Sys­tems
    Safe­ty Crit­i­cal Sys­tems and Sys­tems En­gi­neer­ing
    Lilienthalplatz 7
    38108 Braunschweig


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