Thread

1. gorgoiler · 1790191708 · focus · HN ↗

   Presumably when World War 3 kicks off the very first thing each adversary will do is knock out their opponents satellites? These are like flying lightbulbs that shine down usefulness from above, so step one is to cut the lights.

   Presumably-squared there is some kind of military backup to survive once the lights (GPS) go dark? Whatever that technology is, why hasn’t it proliferated into civilian life so that we all benefit from a resilient, non-GPS backup?

   Perhaps the answer is that every tank has a 10lb inertial navigation gyro or some other thingy in it as a backup, and the platoon around it uses the tank as a moving trig point? In that case I can see it being infeasible to deploy that for civilians.

   Perhaps-squared it’s just economics — GPS is cool and cheap now, so why burn profit margin on developing an alternative?

   1. PJDK · 1790193768 · focus · HN ↗

      I think the general assumption is GPS is denied in most combat zones, it's constantly being jammed in and around Ukraine.

      For most things the fallback is going to be everything we used to use. Maps, stellar navigation, inertial navigation that sort of thing.

      Guided weapons wise, terrain mapping is pretty common for cruise missiles. Storm Shadow, for example uses GPS, terrain and inertial guidance systems. Trident uses inertia and stellar navigation.

      As for why it hasn't proliferated into civilian use? Mostly it has its just the old things. You can perfectly well drive your car with a road map and sign posts. Pilots still train to use dead reckoning and beacons. Etc.

      1. stult · 1790200333 · focus · HN ↗

         We also have visual navigation systems that can use satellite imagery to produce guidance packages. They will become increasingly less useful the longer the imagery goes without updates after a Kessler syndrome type event, though. Another strategy, which I believe the Ukrainians have been experimenting with, is scattering small radio beacons throughout the battlespace to provide a network of navigation aids.

         In a true Kessler scenario where LEO is denied for an extended period of time, I expect a variation of that strategy is how we would replace GPS for most civilian use cases. Likely by using cell towers to triangulate, possibly enhanced with additional transmitters to improve accuracy and coverage. Pure cell tower triangulation would have much worse coverage than GPS, obviously especially in rural areas where cell service is often already poor, but also anywhere that getting a signal from multiple towers isn't easy or possible. Cell towers are never distant enough to use the relativity-based timing tricks GPS relies on, so multiple signals would be required to triangulate. We'd likely end up with substantially less precise positioning, maybe something more on the order of the 10-20m of error we used to see with GPS before the US stopped limiting civilian access to the deaccuratized version. Cell tower triangulation also obviously doesn't work for aviation or oceanic shipping, where trident-like inertial+stellar nav would probably be the only workable option.

         1. wildzzz · 1790223178 · focus · HN ↗

            Luckily, GNSS satellites sit in MEO with sufficient altitude between the various systems. GPS would survive a Kessler Syndrome.

            1. stult · 1790355116 · focus · HN ↗

               I assume in that situation they would be targeted specifically with ASATs at the beginning of the conflict, with the denial of LEO then preventing us from launching replacement sats.

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