Space-Based Quantum Key Distribution: A New Era in Global Network Security – The Fast Mode

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This article is co-authored by Chris Janson from Nokia and Stefan Lespezeanu from Honeywell.
Quantum computing will create limitless potential for society, solving problems in minutes that would take conventional supercomputers thousands of years to crack. But that power could also be used by malicious actors to break the encryption protecting financial transactions, government communications and other sensitive data. If we are to safeguard the world’s digital infrastructure against the looming threat of quantum attacks, multiple advanced cryptographic techniques will need to be deployed in a layered and complementary way.
One of those techniques is quantum key distribution (QKD). By using satellites to expand the reach of QKD beyond what’s achievable through terrestrial infrastructure, it could bring about a new era in global network security.
The limitations of terrestrial QKD
At a high level, QKD uses the principles of quantum mechanics to securely generate and transmit cryptographic keys between Point A (Alice) and Point B (Bob). Any attempt to eavesdrop on the quantum channel will alter its quantum state, so the system can then alert Alice and Bob to the intrusion. In theory, a system using QKD should be secure against any attack, including those from quantum computers. But there are practical challenges to making QKD viable in real-world settings.
The biggest obstacle is the fact that it’s very difficult to establish a dedicated quantum channel on optical fiber over a long distance. After 100 to 150 kilometers, the fiber has absorbed and scattered light to such a degree that it becomes impossible for both Alice and Bob to recover the photons containing the quantum key information. To address that issue, trusted nodes can be installed every 100 kilometers or so. While that’s a practical solution over short distances, if you’re trying to securely distribute keys between, say, New York and Los Angeles — a span of about 4,000 kilometers — a “daisy chain” of nodes quickly becomes prohibitively expensive. And that’s not even considering that terrestrial networks can’t reach every location due to water, mountains and other difficult terrain.
Fortunately, there is a way around these limitations. We just have to look up.
Why space is the future of QKD
Satellites can greatly extend the reach of QKD, making it possible to send cryptographic keys even if Alice is thousands of kilometers from Bob. Here’s how it works.
First, a key management system on the ground makes a request for keys to be generated. That request is sent through a conventional radio frequency (RF) channel to a satellite, which carries a specialized payload that produces quantum keys. Rather than using bits of data to create a random sequence of ones and zeros, the key is encoded within the physical properties of a sequence of photons.
Using the principles of free-space optical communications, a laser terminal on the satellite transmits the photons through the air to receivers on the ground. By measuring the polarization and timing of the photons, the receivers can decode and convert the sequence into the typical ones and zeros of a key. Once both receivers have matching keys, the encryption is activated and data can flow securely between Alice and Bob over traditional channels like subsea cables.
One of the advantages of free-space transmission is that, unlike with fiber, the physical properties of the photons can be preserved over massive distances. When you also consider the position of satellites relative to the receivers on the ground, this overcomes much of the typical QKD distance limitations. A satellite can support global QKD coverage, albeit at different times over a 24-hour window as it passes over various parts of the planet. As more satellites get put in the sky, more keys can be distributed to more locations, making space-based QKD far more scalable than terrestrial QKD.

Of course, space-based QKD isn’t perfect. Preparing the payload and launching a satellite requires significant upfront capital costs, so the technology won’t be an option for every service provider. There’s also the logistics of maintaining a communications link between a receiver on the ground and a satellite hundreds of kilometers above that is moving at speeds of up to 28,000 kilometers per hour. As the satellite passes overhead, it has a window of only about six minutes (if using a low-earth orbit satellite) to transmit cryptographic information to the receiver — and that’s under ideal conditions. The transmission time could be even shorter due to atmospheric turbulence, which can distort the way light travels through the atmosphere.
To compensate, it’s possible to send many keys down to a receiver in one shot, rather than just the single key that’s valid in the moment. A communications channel might rotate keys every hour, so this gives the receiver a buffer of several keys it can store and use as needed, even when conditions aren’t ideal for sending new keys. While this buffering is limited to about a dozen keys right now, over time, advancements in areas like adaptive optics will allow more links to be established between ground and space, so more keys can be sent simultaneously.
How space-based QKD will be used
The biggest benefit of QKD via satellite is that it will add another element to the defense-in-depth approach to building quantum-safe networks — in particular, for transcontinental and intercontinental communications. When married with symmetric key infrastructure (SKI) and post-quantum cryptography (PQC) at the application layer, a crypto-resilient, persistent network connection will be formed.
The first adopters of this technology will likely be organizations responsible for vast amounts of sensitive data, like financial firms with offices around the world that handle transactions worth trillions of dollars each day. At some point in the future, they’ll simply be able to ask their service provider for a quantum-safe connection between London and New York, for instance. Depending on the service provider’s infrastructure, this connection will make use of various technologies to deliver crypto-resilience. This will likely include a mix of PQC, SKI, terrestrial QKD and space-based QKD, all working together to help prevent the kinds of breaches and attacks that lead to financial theft and fraud.
For similar reasons, healthcare and pharmaceutical companies should also be interested in quantum-safe networks. After that, the next wave of adopters will likely be government agencies looking to protect diplomatic communications or national defense infrastructure.
But that’s only the start. QKD is afirst use case of a quantum network — and could even be considered the first real application of quantum communications. In the future, satellites could provide not just the keys but also the connectivity for quantum sensors, data centers, computers and more.
Putting the theories to the test
Although space-based QKD could represent a major breakthrough in how the industry approaches quantum-safe networks, it’s important to temper expectations. The first commercial application of this technology is still a few years away, but it’s actively being advanced now. That includes work done through a partnership between Nokia (a network equipment manufacturer), Honeywell Aerospace (a satellite manufacturer) and Colt Technology Services (a communications service provider). Together, they’re about to conduct the first commercial trial of space-based QKD, with satellite launches scheduled for 2026 and 2027. If those proofs of concept go well, the first operational use cases could be in place in 2028, providing an additional layer of protection against quantum threats.
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Stefan Lespezeanu, Senior Offering and Product Portfolio Manager Quantum Communications at Honeywell, where he oversees the general management and go-to-market strategies for the quantum communications product line. His responsibilities include the execution and commercialization of space-based Quantum Key Distribution (QKD) through advanced quantum-enabled payloads, ground stations, and comprehensive end-to-end missions. Stefan’s work enables Quantum as a Service (QaaS) offerings, driving innovation and expanding Honeywell’s footprint in the quantum communications sector.

Chris Janson follows trends in optical networking technology and its application to enterprise and other network operators. He has long contributed to the communications equipment and semiconductor fields through engineering and marketing roles. Chris enjoys giving back to the community through teaching engineering courses and serving on volunteer boards. In between that, he can be found running, riding bikes or windsurfing on Cape Cod or Maui.
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