DLR completes ground roll tests of HAP alpha uncrewed high altitude solar aircraft

by Robert Schreiber
Berlin, Germany (SPX) Jan 01, 2026
The German Aerospace Center has successfully completed ground roll tests of HAP alpha, an uncrewed high altitude solar powered aircraft designed to operate in the lower stratosphere for extended periods, marking a key milestone toward future flight testing.

Ground roll tests verified the aircraft's steering, braking, propulsion response, and ground handling behavior under realistic operating conditions. These tests are a critical step in validating the interaction between the lightweight airframe, landing gear, and control systems prior to takeoff and climb into high altitude flight regimes.

High altitude pseudo satellites, commonly referred to as HAPS, are aircraft systems designed to operate for weeks or months at altitudes of around 18 to 25 kilometers. At these heights, platforms fly above weather systems and commercial air traffic while remaining far below orbital spacecraft, allowing persistent regional coverage with lower latency than satellites.

Unlike conventional unmanned aerial vehicles, HAPS platforms rely on ultra lightweight structures, very large wingspans, and electric propulsion powered primarily by solar energy. During daylight, solar cells integrated into the wings generate electricity for propulsion and onboard systems, while surplus energy is stored in batteries to sustain flight overnight.

HAP alpha is part of a broader European research effort to develop stratospheric platforms that can complement satellite constellations. While satellites provide global coverage, they are constrained by orbital mechanics and fixed revisit times. High altitude aircraft can be repositioned as needed, maintained on the ground, and upgraded more rapidly, offering flexibility for regional missions.

Potential applications include Earth observation, environmental monitoring, atmospheric research, and communications relay. In communications roles, HAPS platforms can act as aerial base stations, providing broadband connectivity or emergency communications in areas affected by natural disasters or lacking terrestrial infrastructure.

DLR's program follows similar developments worldwide, including solar powered stratospheric aircraft designed for multi week endurance. These platforms face significant technical challenges, including extreme temperature variations, low air density, energy management, and structural loads on long, flexible wings operating in turbulent conditions during ascent and descent.

The ground roll campaign focused on validating propulsion performance, autonomous control integration, and safety procedures during runway operations. Engineers also assessed the aircraft's response to crosswinds and surface irregularities, which are particularly critical for ultra lightweight designs operating at low takeoff speeds.

DLR stated that data collected during the tests will inform refinements to control algorithms, energy management strategies, and operational procedures ahead of first flight. Subsequent phases are expected to include low altitude flight trials followed by incremental expansion to higher altitudes and longer endurance missions as confidence in the system grows.

As interest in persistent aerial platforms increases across civil, scientific, and security domains, successful demonstration of systems such as HAP alpha could strengthen Europe's capabilities in high altitude long endurance aviation and provide new options for bridging the gap between airborne and space based infrastructure.