# GPS and post-apocalyptic world



## stephenspower (Nov 1, 2014)

In a post-apocalyptic world without the internet and phone services, would a GPS program on a smart phone still work?  

The satellites would still beam their signals, and you could charge a phone with a hand-crank radio. What I don't know is how a mapping app actually translates GPS location data. Does it receive data directly from the GPS satellites or does it receive data from cell towers, which wouldn't be working?


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## CupofJoe (Nov 1, 2014)

As far as I know GPS satellites rely on a ground based "clock" to keep them in sync and accurate.
They would be increasingly inaccurate over the days and months but still pretty dammed good for weeks if not months...
Some GPS systems use ground based systems as a backup WW2 systems...
I'm not sure I'd want to launch a nuclear attack on their accuracy but if it was hitting or missing a city I'd feel okay...
Cell towers would fail as soon as the generated power supply failed. In some circumstances that can be hours and not days.... It can be very fragile....
I keep a magnetic compass in my backpack just in case...


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## Steerpike (Nov 1, 2014)

They do use the ground-based systems, I believe, but I think the clocks on GPS satellites are atomic clocks, so they might be accurate enough for longer periods than you might expect. I don't know how quickly atomic clocks lose time, but I don't think it is very fast.

The data goes between the GPS satellite and the receiver directly, from what I understand, so the lack of cell towers shouldn't be a problem.


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## stephenspower (Nov 1, 2014)

Thanks. My protagonist will now collect cell phones from zombies and also use their ereaders.


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## psychotick (Nov 1, 2014)

Hi,

My understanding is that the satelites themselves would fall out of the sky pretty quickly. They require multiple course corrections to keep them in orbit and in position for even as long as they remain there, and those are calculated and computered from the ground. Also GPS requires multiple satellite connections to work. My guess would be that even if GPS continued to operate it would likely only be for a matter of months at best.

Cheers, Greg.


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## Steerpike (Nov 1, 2014)

I think you need at least four to make it work.

GPS satellites are around 12K to 13K feet, so it certainly seems like you'd get a fair amount of orbital decay at that height. I don't know whether you're talking months or years, though, and I also don't know whether the atmospheric drag that causes a lot of orbital decay could also cause the satellite to malfunction even if it doesn't come crashing down. Seems like it would heat up.

However, I think you could write the story in such a way as to make it work.


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## ThinkerX (Nov 2, 2014)

There are satellites...and then there are satellites...civilian and military.  The civilian system would probably get pretty patchy after a few years at most.  But some of the military birds...different story.


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## stephenspower (Nov 2, 2014)

Mmm. Maybe my guy will just use the phones to play Angry Birds.


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## Steerpike (Nov 2, 2014)

The post-apocalyptic world could be set in the near future and you could presuppose advances in GPS satellite tech. Maybe they're put into higher orbits, or have software and systems onboard to correct for orbital decay. Relying on solar power they could stay up a long time indeed.


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## Devor (Nov 2, 2014)

To jump in on this, it might make for an interesting background story if somebody, seeing that it was the apocalypse, uploaded software into a number of satellites to keep them in orbit.  I think that those kinds of details can make a story like this more real.


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## stephenspower (Nov 2, 2014)

I agree Devor. My guy's holed up in a farmhouse, but it would be interesting to look at a zombie apocalypse from a guy in a nuclear silo. What do you do? Do you keep society going? Nagasaki and Hiroshima were free of radiation after a couple of weeks, but you could annihilate a whole lot of zombies. What if you called in strike on your own position that you could survive?


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## Malik (Nov 2, 2014)

Two things:

1.) We used a system in Africa back in 2012 that charged a cell phone from a small fire. It had a mesh canister that you built a fire in using twigs, and the heat spun a little flapdoodle inside a coil and created a charge. It was COTS (commercial off the shelf) at the time but super pricey. Which reminds me, I need to get one and put it in the bunker -- ahem, I mean my, uh, camping supplies. Yeah. But these things exist and there's no reason you couldn't have a functioning cell phone during an apocalypse. Assuming that the net stays up.

2.) Believe it or not, nukes are not that big of a deal. They were blown out of proportion in the fiction of the day. You can walk away from a nuclear strike if you know it's coming. As long as you're not within the immediate flash-burn area where you'll be fried into ashes (and even then it's not that big of a deal if you're far enough underground when it goes off) and if you're outside of the initial burst, as long as the structure that you're in is sturdy enough to not kill you when the overpressure wave hits it, you can live to a ripe old age. 

People like to write about it, but in reality the chances of a nuclear apocalypse are vanishingly small. We'd have to unload pretty much everything we have left at Russia and vice versa. Call for a tactical nuke Danger Close, and shut the top door to the silo. You'll be fine. You might want to put your fingers in your ears and have a biteguard in (personally, I'd go with a cigar) -- it's gonna be loud and it will bounce you around a bit. You'll want to sit tight for a couple of weeks and then put on heavy clothing and head upwind as far and as fast as you can.


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## Penpilot (Nov 2, 2014)

Whether something works or not is based on if you want it powered by Plot-onium or not. If you want something to work, then you can just say it works because "hand-wave". Absolute realism isn't necessary. In fact absolute realism tends to make for a boring story.

If you look at many post-apocalyptic stories, you have people finding stashes of food, gas, vehicles, batteries, etc. Canned food can expire. Gas can go bad, too. Rubber tires on cars can dry-rot. And batteries don't hold their charge forever.

If it makes for a more interesting story, just say the GPS works.


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## psychotick (Nov 2, 2014)

Hi Malik,

Off topic I know, but you might want to rethink your thoughts about nukes. 

This is the information about the expected death toll from Chernoble (a meltdown not even a nuke) WHO | Health effects of the Chernobyl accident: an overview

This is the information about Hiroshima - which I might point out was a tiny one megaton bomb. Hiroshima and Nagasaki: The Long Term Health Effects | K1 Project

And this is the IPPNW listing in the wiki. International Physicians for the Prevention of Nuclear War - Wikipedia, the free encyclopedia You might want to check out some of the links.

But the heads up of it is simple. Yes if you can stay out of the blast zone of a nuke and then run away to a fresh spot upwind, you can survive. But the more nukes fall the less safe areas are left, and the higher the total background radiation levels get. It's unlikely that mankind would survive even a limited nuclear war. And its unlikely that a nuclear war once it began would be limited.

Cheers, Greg.


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## stephenspower (Nov 3, 2014)

Yes the WW2 nukes were very small, but the land wasn't destroyed, only the people who got sick from the initial blast. That said, both those bombs only cleared out relatively small areas. They could be easily repopulated. It's not like zombies would care.

I decided that my protagonist used to play games and read books on cellphones, but gave it up, having no real leisure and finding it indulgent to play games and perverse to try to identify with other people's struggles when that world was gone. (Imagine Carl reading The Walking Dead. It wouldn't be as entertaining.) He's not right in many ways, and may come to see that. The question I'm realizing my story is about is, What's the point of existing for existing's sake? It's also about the crows, who eat the zombies and take the protagonist, well, under their wings.


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