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Comment by aphextron | Hacker News Reader

This is why all modern navy ships still carry sextants and train extensively in celestial navigation. It's pretty much a forgone conclusion that GPS will become immediately useless in any large scale nation state war of the future.

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Yeah, maybe we can have a "digital" sextant that instead of relying on specialized training to humans, just pushes all the sextant data plus altitude, barometer, universal time (UTC), timezone and sunset/sunrise from a perpetual calendar and such inputs to an android gizmo that gives us an approximate location, something that can be sold commercially for hikers, boaters and everyone for fun.

A sextant requires a flat level horizon, and sky clear enough to see the sun, or stars at night, and a compass that indicates true north (with correction for magnetic declination). In an urban environment, there is usually not a clear shot at a flat horizon, nor an area free from metal structures for far enough to get an accurate magnetic north.

All the more reasons to use something digital, isn't it? Would make it much easier to figure out the horizon without actually seeing it.

Or you can simply buy an artificial horizon for less than US$ 40:

* https://www.davisinstruments.com/product/artificial-horizon/

* https://www.starpath.com/catalog/accessories/1840h.htm

* https://www.celestaire.com/product/davis-artificial-horizon/

They've been around since (at least) 1907:

* https://www.scientificamerican.com/article/an-artificial-hor...

Shouldn't a gyroscope compensate or at least allow getting flat level? I think maybe they didn't use it because they didn't have accurate gyroscopes we have now.

For clear shot, would tiny drones that go up work? How high do we need to get a clear shot?

Go outside, do you see a flat level horizon?

You could use the accelerometer to get a good idea of "down" but not enough resolution for navigation.

You cannot escape the burden of training people to do it, because someone has to check the machines figures for drift due to defect, improper implementation, or damage.

See the Patriot missile systen fiasco.

Navy also uses inertial navigation. It needs to be calibrated with GPS every now and then but you can get away without a GPS downlink for a while before drift becomes a problem.

Automated stellar navigation systems have been around for decades.

https://www.thedrive.com/the-war-zone/17207/sr-71s-r2-d2-cou...

I bet it's also why cruise missiles use terrain navigation.

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