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by adev_7 hours ago |
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upvoteby shagie6 hours ago|
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> 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:
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upvoteby Spoom4 hours ago|
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I love that this was ostensibly written by Vint Cerf.
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upvoteby shagie3 hours ago|
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It's listed in his computer science bibliography https://dblp.org/pid/c/VintonGCerf.html and https://en.wikipedia.org/wiki/Vint_Cerf#Author

Though the edit for that authorship to the RFC came much later. https://datatracker.ietf.org/doc/rfc1217/history/

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upvoteby 5 hours ago|
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upvoteby SlightlyLeftPad5 hours ago|
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Could these not be jammed by blasting the same wavelength laser at said geostationary satellite?
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upvoteby tiagod5 hours ago|
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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.
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upvoteby scottLobster3 hours ago|
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"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.

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upvoteby cyberax51 minutes ago|
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It's a geostationary sat. It doesn't move.
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upvoteby scottLobster36 minutes ago|
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No, but the airplane it would be talking to does. Hard enough when your transceiver is wide open, if you narrow your FOV to a thin cone in order to block jamming signals, the GEO now has to physically track the airplane somehow.

Either the whole satellite rotates or the transciever is on a mount that can rotate

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upvoteby vlovich12315 minutes ago|
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Unless you plan on having 1 satellite per airplane, something tells me it's harder to constrain the FOV than you might suggest. There's also the small problem of the energy, complexity, & weight of having motorized parts on the satellite (or fine-grained attitude control for the satellite itself to track the craft).
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upvoteby scottLobster4 minutes ago|
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Agreed, my point is it's a lot harder than tiagod made it sound.

It also doesn't account for some kind of mobile jammer making it inside the cone, particularly if it's staring at an adversarial nation where secure comms would be needed the most, but the adversary would have freedom of movement.

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upvoteby Onavo5 hours ago|
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You will probably need to increase the gain (better lens, photomultipliers) on the receiver photodiode too.
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