World-first gigabit laser link between aircraft and geostationary satellite
esa.int

・

158 points

・

giuliomagnifico

・

4 days ago

60 comments

icegreentea2 ・ 5 hours ago

Here's a paper (from July 2025) on previous steps in this program, getting up the initial testing in flight. Maximum uplink laser power of 20W, though they got good performance all the way down to 2W. The sat has a laser pointing down that was used to help lock on, but it's not clear if it has any meaningful downlink capability, all discussions are about uplink capability. Lots a nerdy details here.

https://www.spiedigitallibrary.org/conference-proceedings-of...

In addition, here's a random paper on the testing performed on the space borne laser terminals - https://icsos2012.nict.go.jp/pdf/1569586689.pdf

This tells us that the laser terminals have a FOV of +/-2.5mrad in acquisition mode (so before lock on), and +/-0.5mrad in communication/tracking mode. This corresponds ~100km and ~20km radius FOV from GEO to surface.

Meneth ・ 10 hours ago

"low-latency links", says the article. I wonder if they consider 500 ms ping to be low, or if they want to replace Geostationary with Low Earth Orbit.

  • adev_ ・ 5 hours ago

    > "low-latency links", says the article. I wonder if they consider 500 ms ping to be low, or if they want to replace Geostationary with Low Earth Orbit.

    Directional laser beams are orders of magnitude to jam compared to radio wave. That alone makes it of big interest for military applications, even with 500 ms latency.

    There is several known cases where jamming caused the loss of costly military drones.

    https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incid...

    Laser comms could prevent that entirely.

    • shagie ・ 4 hours ago

      > Directional laser beams are orders of magnitude to jam compared to radio wave. That alone makes it of big interest for military applications, even with 500 ms latency.

      I am reminded of RFC 1217 - Memo from the Consortium for Slow Commotion Research (CSCR) https://www.rfc-editor.org/rfc/rfc1217

          2. Jam-Resistant Land Mobile Communications

       This system uses a highly redundant optical communication technique
       to achieve ultra-low, ultra-robust transmission.  The basic unit is
       the M1A1 tank.  Each tank is labelled with the number 0 or 1 painted
       four feet high on the tank turret in yellow, day-glo luminescent
       paint.  Several detection methods are under consideration:
    • SlightlyLeftPad ・ 3 hours ago

      Could these not be jammed by blasting the same wavelength laser at said geostationary satellite?

      • tiagod ・ 3 hours ago
        ・ 3 more

        Please correct me if I'm wrong, but I guess if you aim well enough, there could be a very long, narrow, non-reflective cylinder in front of the receiver that would block all light that is not coming exactly from the direction of the target satellite.

        • scottLobster ・ an hour ago

          "If you aim well enough" is doing a ton of work there. Precise real-time optical tracking of a satellite from a moving platform is an extremely difficult problem. Even if the satellite itself is geostationary, it would also have to rotate to keep the "cylinder" pointed in the right direction to maintain signal.

          I suppose you could make a "cylinder" or "cone" broad enough that, if the threat was static, could blot-out attempted jamming from only certain regions while staying open facing toward friendly zones.

        • Onavo ・ 3 hours ago

          You will probably need to increase the gain (better lens, photomultipliers) on the receiver photodiode too.

  • fidotron ・ 9 hours ago

    Getting it to work with one end stationary first sounds like a reasonable development plan. LEO adds a lot of complexity, but with huge benefits.

    OTOH the number of engineers that focus on throughput over latency is quite staggering.

    • IrishTechie ・ 9 hours ago

      I guess if your goal is just to stream aircraft telemetry and black box like recordings then latency may not be high on the agenda.

      • connicpu ・ 8 hours ago

        Black box data doesn't need that crazy throughput either though. Traditional RF is much easier to get right, and works even when the aircraft starts losing track of where it is and stops being able to track the satellite with its laser

      • SiempreViernes ・ 9 hours ago

        I think it's the opposite? For small telemetry you want it now, but for the big data products there's no hope of "now" and so you settle for soon.

  • rtkwe ・ 4 hours ago

    Geostationary is easier to hit than a LEO constellation like Starlink. With an LEO target you need to switch at least every 2-4 minutes, Starlink ground stations can switch multiple times per minute but that's for obstacle avoidance in the air you'd only have to switch when the current target moves out of LOS entirely.

  • pottertheotter ・ 7 hours ago

    I’ll take 500ms ping for those speeds while temporarily on a plane.

    • oofbey ・ 7 hours ago

      No doubt! I’ve measured literal 5 minute ping times on airplanes. 300,000ms. Where are the buffering the packets!?

      • raddan ・ 6 hours ago
        ・ 5 more

        My guess is that you're getting retransmissions because of dropped frames, not because there's some huge buffer in the sky.

        • reactordev ・ 5 hours ago

          Indicated airspeed 280kts, ground speed 470kts, FL410, the packets are trying to catch up…

        • JackFr ・ 5 hours ago
          ・ 2 more

          I like "huge buffer in the sky".

          That's where I imagine all my deleted data goes.

          • 0_____0 ・ 2 hours ago

            we're all just riding the ring buffer of samsara, maaan

        • BobbyTables2 ・ 5 hours ago

          There’s one huge buffer in the sky!

          The huge buffers are at the two endpoints (:->

tart-lemonade ・ 7 hours ago

> These developments entail a future where travellers could enjoy reliable, high‑speed internet while flying, and where people on ships or in vehicles crossing remote regions can stay connected without interruption.

How reliable/feasible would this be on the ground? From what I understand, shining non-trivial lasers in the sky is a massive liability because of the potential to interfere with aircraft. I don't see anything about the wavelength used, but even if it's outside the visible spectrum, it would still be subject to interference from aircraft when used on the ground or at sea.

db48x ・ 8 hours ago

Some miniaturization required.

cm2187 ・ 10 hours ago

But that means you need to have a different laser pointed at every single individual aircraft right? Doesn’t really scale.

  • eqvinox ・ 8 hours ago

    You can probably do phased arrays. (It might already be a phased array.)

    • mohaine ・ 8 hours ago

      Pretty sure phased array LASERs are not yet a thing.

      • aidenn0 ・ 7 hours ago

        Lasers are coherent emitters; you can definitely make interference patterns with them, so I don't see why LASER MIMO wouldn't be possible, in theory.

      • eqvinox ・ 7 hours ago

        Yeah but this is research, if they're to come up somewhere, where else would it be?

  • voidUpdate ・ 9 hours ago

    If starlink satellites get laser downlink, it might work :P

    • cm2187 ・ 2 hours ago

      laser downlink to one point, isn't it? Not to 300 moving aircrafts at once.

myrmidon ・ 11 hours ago

I'm really curious how the tracking works in such a system, and how "bad" the beam spread is (my impression is that from the diffraction limit alone the beam has to be spread over at least a ~10m radius after travelling 36000km).

Some info on the laser itself would also be very interesting (power? wavelength?).

Really cool project though!

  • amelius ・ 10 hours ago

    > and how "bad" the beam spread is

    The spread makes the tracking easier, I suppose.

    • TimorousBestie ・ 9 hours ago

      Perhaps a little, however. Different paths through the atmosphere will perturb the phase of the signal; depending on conditions not all of that ~10m beam width is going to decode with an acceptable bit error rate.

  • mytailorisrich ・ 8 hours ago

    Tracking and actuation is nothing new or particularly challenging, IMHO. It's the laser/optical part combined with throughput at that distance that is the main area of R&D, I think.

burnt-resistor ・ an hour ago

I marvel at the ability to track a target in both directions ~40k+ km away while moving quickly (kinematic) considering atmospheric and relativistic effects.

xnx ・ 12 hours ago

Impressive! I believe round trip latency would be 0.5 seconds.

  • 1e1a ・ 11 hours ago

    That's ~162.5 MB in transit at any time

    • kipchak ・ 6 hours ago

      There's a patent (2017/0280211 A1) for using this as a data storage method, and there was a company called Lyteloop trying to leverage the idea for data storage with estimations for petabytes across constellation.

    • arethuza ・ 6 hours ago

      That could you used like RAM like the delay-line memory used by early computers!

    • htgb ・ 11 hours ago

      Shouldn't it be 1000/16 = 62.5? Impressive nonetheless, of course!

      • 1e1a ・ 9 hours ago
        ・ 2 more

        The article says 2.6 gigabits/second which is 2,600,000,000 bits/second, 2,600,000,000b/s * 0.5s / 8 is 162,500,000 bytes, 162,500,000 / 1,000,000 is 162.5 megabytes

        • htgb ・ 7 hours ago

          Right, thanks

    • zppln ・ 11 hours ago

      Weird.

philipwhiuk ・ 7 hours ago

> Because laser beams spread far less than radio waves, they provide more secure links

Basing your security on laser diffusion seems sus.

  • Tepix ・ 7 hours ago

    These beams are much harder to detect and eavesdrop upon. You increase the difficulty for a remote attacker. I wouldn't stop encrypting the data, however: The Alphasat TDP‑1 has a telescope with an 135mm aperture. The beam diameter is likely to be at least 700m wide according to the diffraction limit.

  • Schlagbohrer ・ 7 hours ago

    It's worth it as another layer of security. The beam width being so narrow means even intercepting it becomes harder. This is more relevant for down-to-earth links where the spot hitting the earth is so narrow it could be confined withing a geographically controlled area, rather than hitting an entire continent like longer wavelengths do.

  • kube-system ・ 4 hours ago

    All security is based on a combination of individually flimsy ideas