Navigation without GPS?
April 2, 2022 11:16 AM   Subscribe

After watching a bunch of zombie films, I was wondering what navigation options existed if GPS were unreliable or ceased to function. I'm curious as to what tools would provide as much an automated experience as GPS, such as taking a photo of the stars and your laptop/phone figure out where you are. Googling this it seems that a lot of the doomsday types like the fun of positioning using 19th century techniques. Surely there's something commercially available that does this for you?
posted by geoff. to Science & Nature (16 answers total) 4 users marked this as a favorite
In a military context, I can think of a couple such technologies: automated celestial navigation, as used in aircraft like the SR-71, and terrain contour/satellite imagery matching (TERCOM/DSMAC). Nothing I'm aware of that's a civilian commercial product, though.
posted by kickingtheground at 12:24 PM on April 2, 2022 [3 favorites]

Worth noting that the two kickingtheground mentioned are both Cold War-era systems that predate GPS.

Finding your latitude is pretty trivial with a sextant. Finding your longitude would involve comparing the time noon occurred with that of a known location -- a hard problem if you're a 14th-century mariner, a mostly easy one for anyone with a digital watch.

Some early smartphones (notably, the first model iPhone) didn't have GPS chips and made their best guesses using cell tower data. The cell network relies very heavily on the GPS system for timing data though, and would likely be one of the first things to go in an apocalypse scenario.

(Your zombie scenario reminded me of playing the original version of DayZ... there's absolutely no map or compass available if you don't find one in game, so I had to navigate using the stars.)
posted by neckro23 at 12:57 PM on April 2, 2022 [3 favorites]

Watches were really important back in the day because they helped you figure out your coordinates precisely. You could calibrate from the sun and length of shadows pretty exactly where you were. At night, you used the stars and planets. Hence the macho glamour of watches. No one would go anywhere without a map printed on paper, and the ability to read it. They can be really detailed. If you had printouts of air or satellite photos, like the US forces post WWII, even more so.
As an old person who learnt this from childhood, at a point this becomes so ingrained you don't even think about it. I mean, I don't think "it is 4PM so south must be there and the place I am heading to is 45 degrees to the right", or "the North Star is there, so I need to head 15 degrees left"; I just go there, with just a tiny hint of a thought.
posted by mumimor at 3:09 PM on April 2, 2022 [7 favorites]

There was a recent article about drones being donated to Ukraine which run off of lidar rather than GPS, made by BRINC. At least for localized navigation, that is a viable approach.
posted by Dip Flash at 4:11 PM on April 2, 2022

It's worth noting (though I'm aware it isn't the question) that GPS is pretty robust against terrestrial disaster. If the maps on your phone or GPS unit are offline (as in, downloaded or whatever) then you'd be able to use it indefinitely, since it relies on detecting a signal generated by a satellite in geosynchronous orbit. So even if the internet died and so on you'd still be able to use GPS.

But yeah, precise navigation would probably most commonly be by landmarks and compasses, not many people know how to use a sextant or derive their latitude or whatnot. But most people can say, I'm at this landmark, the next place to go is 25 miles NNE, and I can get there by going 14 miles on this bearing and then turning to this bearing.
posted by BlackLeotardFront at 4:33 PM on April 2, 2022 [3 favorites]

Response by poster: It's worth noting (though I'm aware it isn't the question) that GPS is pretty robust against terrestrial disaster.

I was under the impression, from random articles on this, that the GPS satellites themselves were robust but needed to constantly be adjusted by ground stations. Since anything about their survivability seems to be highly classified, I've seen some wide ranging opinions but the consensus seemed to be there would be a drift noticeable within 48 hours.

This seems to show a rather robust ground operation.
posted by geoff. at 5:33 PM on April 2, 2022

For aircraft, the VOR (civilian) and TACAN (military) systems were the worldwide standard starting in about the 1940s until GPS came into wide use.

These use ground-based radio beams set up a certain way so that you can use a receiver to navigate towards a certain beam, follow the beam, etc.

Since the advent of GPS they have been culling the stations dramatically - from about 3000 stations worldwide in 2000 to 967 recently.

For example, the U.S. is eliminating about half of its VOR stations but is retaining enough for minimum operational capability as a backup to GPS.

Now - whether such ground-based stations will be available in your zombie apocalypse, you will have to be the one to decide. Also these stations are most useful for aircraft as the VHF signal is very much line-of-sight.

But they are a system that allows somewhat automated navigation using available equipment. Aircraft autopilot systems can set to follow a given VOR beam, for example.

Also note that same page outlines the modern autopilot type navigation that allows you to preset a route that the aircraft will auto-fly. In addition, you can engage the GPS system for added accuracy. I'm am not exactly sure of the systems the FMS uses to maintain position and course in the absence of GPS, though.
posted by flug at 5:40 PM on April 2, 2022 [1 favorite]

It's worth noting (though I'm aware it isn't the question) that GPS is pretty robust against terrestrial disaster.

For what its worth, Russia shot down one of their satellites a few months ago, and China did the same in 2007. They might be safe from nuclear detonations on earth, but not from any geopolitical situations that would motivate such a thing.

Surely there's something commercially available that does this for you?

Assuming your phone still has a charge, and offline maps, most phones have a built-in magnometer (compass). You'd have to be really lost to even have to fall back to star positioning. Once you know where you are on a map, Inertial navigation might work, but would probably accumulate a lot of error real fast at highway speeds.

But at least once you get to a highway, there is a code to navigate them, loosely speaking
posted by pwnguin at 5:41 PM on April 2, 2022

There were a couple of radio-based systems used by mariners that used ground stations instead of satellites. Consolan and later loran. I'm not sure to what degree they were used by aircraft.

Aviation used a number of additional systems. Lowest tech was big arrows on the ground. There were strings of ground-based lights, sort of like light houses. There was one on the mountain in Palmerton, PA that shone into my bedroom window when I visited my grandparents. Aircraft used celestial navigation, too.

There was a radio system used for airport approaches the would make sounds in the left or right ear if you got off course.

For drivers, there were signs with distances to destinations. I remember using such driving across New Jersey with my mother around 1960. Gas stations had maps, mostly for free.
posted by SemiSalt at 6:02 PM on April 2, 2022

The Mozilla Location Service uses nearby Bluetooth, Wi-Fi, and cell signals to determine a phone’s location.

Nevertheless I can’t imagine zombies that killed GPS maintainers but left Wi-Fi (ISP) and cell tower maintainers alone.
posted by Monochrome at 6:42 PM on April 2, 2022

Most modern smartphones have inertial sensors and are perfectly capable of navigation... IF you can give it a proper reference point.

Just for experiment, you can download "Privus" on the Apple store, and "InertialNav" from the Google Play Store.

The problem is it can only tell you how you've moved. Without a map it doesn't exactly tell you where you are.

Navigating by stars is "possible", but unless the phone can stay on accurate time, and have a properly aligned inclinometer (how far did it pitch up to see the sky) AND a working compass its utility in navigation is dubious and little better than a genuine sextant.
posted by kschang at 7:02 PM on April 2, 2022

Very good book on this topic is "Emergency Navigation: Improvised and No-Instrument Methods for the Prudent Mariner"
posted by sammyo at 5:28 AM on April 3, 2022 [1 favorite]

Related previously from me and the Blue.
posted by MonkeyToes at 7:34 AM on April 3, 2022

Vehicle odometers are really pretty accurate. I navigate a motorbike all the time by odometer and a map. Once you're used to the mental arithmetic, you can pretty accurately work out estimated arrival times, as well.
posted by Fiasco da Gama at 5:30 PM on April 3, 2022

I don't see anything in your question that excludes the use of a good old paper atlas. Or maps you pick up from the gas station. Or paper Triptiks from AAA. You can pretty easily find where you are from all of those and plan a route.
posted by booth at 6:08 AM on April 4, 2022

What's usable depends very much on context, too.

If you're on land, with recognisable landmarks, then all you need is paper maps. You can follow along on the map as you travel, and use local landmarks to orient yourself. If you've lost of where you are, you can find the nearest town and then look up its name in the index of your road atlas.

You can do that in the air, too - I used to fly gliders cross-country with nothing more than a paper map. But it's a lot more critical not to lose track of where you are in that case, because small towns in flat country all look very similar from the air.

Out on the open sea, all this goes out of the window: you need a sextant, a clock, and a compass.
posted by automatronic at 8:02 AM on April 4, 2022

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