Secure quantum communication from the stratosphere: QKD network with HAPS
Quantum communication is the key technology for secure, encrypted data transmission in the future, for example to protect digital infrastructure. The MobixHAP project is developing an innovative component for modern QKD networks: mobile communication nodes on high-altitude platforms (HAPS) that can operate in the stratosphere. This creates a QKD backbone network, that can bridge large distances while meeting the highest safety requirements.
Photo: QKD payload on a TAO high-altitude platform, in cooperation with project partner Mo-Space (QKD payload)
QKD from the stratosphere: A new dimension in communication
Future quantum key distribution (QKD) networks will be based largely on free-space links – for example, between satellites, ground stations and mobile nodes. The stratosphere offers ideal conditions for this: High Altitude Platform Stations (HAPS), such as drones, balloons or special airships (such as the TAO SkyDragon), can be used to establish long-range QKD connections.
Unlike satellites, HAPS are:
- controllable and reusable
- cost-efficient and maintainable
- stationary and deployable over specific areas
- free of space debris
German airspace is permanently used and monitored for air traffic; this opens up excellent opportunities for a secure QKD network with trusted nodes in the stratosphere at an altitude of approx. 18–20 km as a bridge between terrestrial networks and satellite-based quantum communication.
Photo: Ascent of the TAO-HAP into the stratosphere in approx. 2 hours
TAO SkyDragon airship as a mobile QKD platform
TAO Trans Atmospheric Operations GmbH is developing a particularly powerful flying communication platform with the SkyDragon airship. This specially designed HAP system is:
- capable of taking off and landing,
- has its own propulsion system,
- can be used long-term as a flying QKD node over an area
- and is ideal for heavy QKD payloads.
The modular airship structure of the SkyDragon allows for a distributed payload arrangement on the device. This is an optimal prerequisite for the use of different payload applications with varying masses and dimensions in complex communication networks that are yet to be designed.
Project objectives: Modular QKD payload for mobile platforms
The Mobile Nodes project (QuNet+ project MobixHAP) has two main objectives:
- Research and development of a mobile QKD backbone in the stratosphere
- Design and testing of a standardised, modular QKD payload for HAPS platforms
This payload will play a crucial role in the distribution of quantum keys over long distances – both as part of the regular infrastructure and as a backup solution in the event of disasters.
Technological challenges for QKD in the stratosphere
The extreme conditions at an altitude of 18–20 km place high demands on the system design and technology of the HAP:
- Cold resistance (down to approx. -70 °C) and long-term operation even in the Earth's shadow (night phases)
- Development of efficient solar-electric energy storage systems
- Stable alignment of the laser communication terminals (LCT) despite movement and turbulence
- Multidimensional control systems for active stabilisation of the connection
- AI-based control for a potential swarm concept involving multiple platforms
The payload will be protocol-agnostic and will support various wavelength ranges (e.g. 810, 850, 1550 nm) as well as DV and CV protocols. Multiple flying HAPs will enable a QKD network across Germany or, of course, worldwide.
Photo: From HAP to HAP – An independent, encrypted network in the stratosphere
First demonstrator in a real-world test environment
An initial test system will be set up during the course of the project: a QKD demonstrator that will be validated in a terrestrial end-to-end test and then tested on a specially developed stratospheric airship. This will significantly accelerate the readiness of the entire system for deployment.
Contribution to the QuNET initiative and Germany's QKD network
The ‘Mobile Nodes’ project is part of the national research initiative QuNET, which is funded by the Federal Ministry of Research, Transfer and Space (BMFTR). QuNET aims to develop a secure, quantum-based IT infrastructure. Strategic workshops clearly identified the need for stratospheric QKD. This project directly addresses that need.
By establishing a HAPS-based backbone with mobile nodes in the stratosphere, the project is making a significant contribution to the networking of ground stations and flying platforms over medium distances, thereby increasing the flexibility and scalability of QKD networks.
Mobile QKD nodes in the stratosphere open up new avenues for secure quantum communication: sustainable, highly secure and forward-looking.
Photo: Encrypted communication from HAP to the satellite and ground infrastructure
QKD with HAPS from the stratosphere: a resilient alternative in the event of network failures
The global failure of the Starlink satellite internet system in July 2025, which lasted several hours, impressively demonstrated how vulnerable central communication systems can be. This has global implications for navigation, infrastructure and cloud services.
Mobile nodes in the stratosphere, such as those being developed as part of the QuNET project, offer a sustainable solution here: as a supplementary communications infrastructure based on quantum communication, they can provide an independent, highly secure connection layer in the event of satellite-based system failures.
Thanks to their position in controlled airspace, their flexibility in use and their technological independence from traditional networks, HAPS-based QKD systems make an important contribution to digital resilience, both for critical infrastructures and for international data connections.
KD HAPs are not competitors to satellites (such as Starlink), but rather a useful addition: they increase resilience in the event of disasters, for example, through redundancy, thereby creating reliability and offering quantum-based security, which is particularly relevant for critical infrastructures and sovereign networks.
The MobixHAP research project is funded by the German Federal Ministry of Research, Transfer and Space (BMFTR). Project partners in the joint research project are Mo-Space, Mynaric, IPMS Fraunhofer, IOF Fraunhofer, Qssys and TAO Trans. GmbH.