Hydrogen-electric eVTOL stratospheric operation

Demonstrate that a hydrogen-electric electric vertical-takeoff-and-landing airframe can sustain rotor-borne lift during ascent to approximately 20 km and operate as a stratospheric HAPS.

Background

The paper identifies hydrogen-electric eVTOL HAPS as a conceptual platform variant that could provide runway-independent launch and recovery while offering a higher payload and power capability than current solar-electric HALE aircraft. Existing hydrogen eVTOL flights demonstrate relevant horizontal range, but not stratospheric operation.

The unresolved technical issue is sustaining rotor-generated lift through the very low-density atmosphere encountered during the climb to roughly 20 km. No eVTOL has yet operated as a stratospheric platform.

References

However, no eVTOL has operated as a stratospheric platform, and sustaining rotor-borne lift through the climb to 20~km is a substantial open problem.

— HAPS through the Lens of Satellites and UAVs: A Function-Level Perspective on the Emerging High Altitude Economy  (2608.16828 - Ahmad et al., 17 Aug 2026) in Section 5.1, “SWaP Envelope,” subsection “Propulsion variants: hydrogen-electric aircraft and eVTOL”