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I am trying to think of a reason where on a moon (or small planet), GPS isn't possible/feasible. If you want to go out into the wilderness you need a map and a good sense of direction.

However it's the future. Mankind has already colonized star systems and technology has never been so advanced. So how can there be a planet where GPS isn't possible?

If I remove satellites (like the ones that we have now) I might be limiting my moon colony in many aspects (communication, for example). I tried thinking of ways that the moon itself could interfere but I haven't found much leeway there either.

Is this impossible? Am I trying to have my cake and eat it too?

Thank you!

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  • $\begingroup$ Welcome to worldbuilding.SE. If have a moment, please take our tour. The only way to make GPS useless is to make communication useless (wild magnetosphere for one reason or another). If your people need communication in their story, there's no way to prohibit GPS ... unless some pesky aliens keep shooting down the satellites. $\endgroup$ – JBH Jan 21 '18 at 16:53
  • $\begingroup$ Your biggest problem is technology is super advanced. Any land based obstacles can be bulldozed,blown up, or otherwise destroyed. GPS used to be limited among sky scrapers because of echoing, but the newest generation of GPS eliminates that. We are even advanced enough to colonize 1 star, so this is at least 100yr in the future. $\endgroup$ – cybernard Jan 21 '18 at 21:28
  • $\begingroup$ GPS satellites use radio signals, in practice working as radio beacons. Pretty much the only difference between that and communication satellites is what is carried by signal (and precision needed). You can't kill GPS sats/signal without killing comm sats/signal. You would have to have localised, chaotic and unpredictable changes of gravity within atmosphere (but not on orbit, because that would fling all sats out of stable orbits, neither on surface or you risk killing your cast), but that would still only decrease accuracy, not prevent. Worse, that's "wizard did it" levels of (un)realism. $\endgroup$ – M i ech Jan 22 '18 at 1:48
  • $\begingroup$ Maybe, just no one came up with the idea of GPS? although it's a bit unbelievable. $\endgroup$ – Aequitas Jan 22 '18 at 2:17
  • $\begingroup$ In the book Great North Road by Hamilton, there is such a planet. Satellites are made unviable because of the dust ring of the planet. Satellites would be destroyed quickly by repeated passages through the rings because of increased probability of dust/gravel/rock impacts. No satellite -> no GPS. $\endgroup$ – Legisey Jan 22 '18 at 12:29

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Communications and GPS must either both or neither be present

First off, you imply that you want communication satellites to be possible, but not GPS satellites. This is simply impossible. Communications satellites and their ground stations depend on GPS in order to operate. A ground station must know its exact GPS coordinates in order to meet its timing windows for communicating with a satellite using TDMA, for example. If the ground station is moving, then it has to recompute its distance to the satellite on the fly, every time it moves. The satellite itself is also probably moving, most satellites have some sort of orbital precession. When windows are miliseconds wide, a few hundred kilometers can cause you to miss your window (at the speed of light, 1 ms is worth 300 km, for example)

So, if you have communications satellites, you also have the ability to make some sort of navigation system, and the requirement to have some sort of navigation system in order to allow those satellites to work.

There are several links in the GPS 'chain' that could be broken to prevent GPS (and communications).

How to prevent satellites

This could be accomplished by Kessler Syndrome. Lots of orbital objects can cause cascading failures that all but ensure that anything put into orbit will be hit by particles at tens of kilometers per second. If your planet were colonized at one time, then there was some Kessler Syndrome catastrophe, then it would become cut off from the outside world.

Removing satellites doesn't prevent older electronic navigation systems such as Loran-C. However, it takes time to set up that sort of station. If the colony is young, or doesn't take up that much of the planet, and if the Kessler catastrophe is recent, then perhaps navigation stations haven't been set up over much of the planet. If you find yourself on the far side of the planet, for whatever reason, there is limited radio communication on HF bandwidths (which is not good quality signal) and potentially no navigation beacons.

Preventing all radio signals

In this situation, an atmospheric radiation event has occurred that is causing significant interference. The GPS signal is not powerful, around -160 dbW. This corresponds signal is in the femtowatt range; not much at all! For comparison, this is about three orders of magnitude less than the minimum wireless signal your computer or cell phone can pick up.

All it takes to disrupt this is EM noise at the appropriate frequencies. You can invent some sort of stellar and/or atmospheric phenomenon that is operating at the appropriate frequencies. To prevent existing satellites from being quickly repurposed to alternate frequencies, the noise will have to have a pretty wide band. Fortunately, stellar phenomenal can be pretty wide band...like all bands if your star suddenly starts some kind of radio emission (for details on that...ask a different question!). Given that the wireless in your house isn't killing you with radation (we hope) this stellar interference wouldn't have too much affect on the biology of the planet's surface.

In any case, in this scenario, after colonization of the planet (since who would colonize a planet where radio doesn't work) the star started a period of unusual and unpredictable stellar activity. The planet's magnetic field is protecting the biology of the planet from the unusual radiation activity, but radio spectrum interference makes satellite navigation un-workable. As the planet rebuilds communications capacity with higher power transmitters to cut through the noise, there could be a time gap of decades where communication and navigation is limited. Alternately, the magnitude of the radio interference makes higher power infeasible, rendering communications moot until the star changes its mind.

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    $\begingroup$ "Communications satellites and their ground stations depend on GPS in order to operate." Er ... communications satellites predate GPS by more than a decade. Ground survey is more than good enough to get the position of ground stations and observations from the ground to determine orbital elements. $\endgroup$ – dmckee Jan 21 '18 at 19:56
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    $\begingroup$ @dmckee: Global navigation systems such as LORAN predate satellites. They were developed during WW2 for use by bomber aircraft, and were then used on a wide scale by aircraft and ships. $\endgroup$ – AlexP Jan 21 '18 at 20:35
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    $\begingroup$ @Alexp Learn something every day. Thanks. But it doesn't really change the point that communications satellites were perfectly practical on the basis of ground surveys and orbital elements taken from sightings. $\endgroup$ – dmckee Jan 21 '18 at 23:06
  • $\begingroup$ @dmckee Not if you have a moving receiver. That's the point, a receiver on a ship or airplane won't work once you move a few km. $\endgroup$ – kingledion Jan 21 '18 at 23:16
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    $\begingroup$ @kingledion I still don't think so. (Re)acquisition would be slower if you had to rely on pre-20th-century means of positioning, but it could be done (especially with an adjustable beamwidth antenna), and holding the lock could be done with servo tracking (which is how it's done today anyway, to the best of my knowledge). $\endgroup$ – hobbs Jan 22 '18 at 0:55
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'GPS' in the form of radio beacons was available long before satellite GPS. Even if you cleared the orbits, if someone really wanted an area to be navigable with GPS they'd just need to set up radio beacons at high points around the perimeter.

An area could not yet be covered by such beacons but it wouldn't prevent someone setting them up if needed.

The following could be combined with cleared orbits to prevent such beacons

  • Unstable ground. Either marsh or shifting dunes could do this. It would mean any local beacons could only be temporary
  • Periodic localised radio interference that it wasn't worth developing technology to compensate for, either very rare or highly localised
  • Sabotage
  • Deep winding gorges that blocked any line of sight or signal
  • High winds to prevent static balloons being used

In practice though, you are on a cake and eat it footing here. In theory on a well mapped planet, and given suitable technology, a GPS system could be entirely visual, plotting against a simulation of the skyline, sun, or stars, at almost any point on the planet.

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    $\begingroup$ In fact, the navigation with radio beacons at high points was (and still is) used in aviation, as the VOR/DME system: en.wikipedia.org/wiki/VOR/DME Or for a current example, cell phone towers. Where I live, there are lots of places with no signal, because they're in canyons, or too far from populated places to make placing a tower economic. $\endgroup$ – jamesqf Jan 21 '18 at 21:07
  • $\begingroup$ @jamesqf such navigation is still available to ships as well! $\endgroup$ – NonCreature0714 Jan 22 '18 at 0:32
  • $\begingroup$ How the heck do you imagine plotting against skyline could even work? Unless you have convenient, easy to recognise, mountain nearby, skyline looks pretty much the same. Flatlands, deserts, hills, seas (or even big lakes) or basically 95%+ of planetary surface will look exactly as any other part with similar terrain. You are much better off using odometer, clock and star charts for navigation, like they did for most of history. $\endgroup$ – M i ech Jan 22 '18 at 1:36
  • $\begingroup$ I think this is a very good answer about how to use terrestrial navigation technology. Terrestrial nodes use radio direction finding technology, TDMA, and emit different signals (in unique patterns) from each node, overcoming most of the challenges presented by @Miech $\endgroup$ – NonCreature0714 Jan 22 '18 at 1:58
  • $\begingroup$ @Miech, it wouldn't work at sea using the skyline, but your compass, clock, and sextant, also compose a fundamentally visual check and could be constructed into a single device not requiring expertise to use. $\endgroup$ – Separatrix Jan 22 '18 at 7:55
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Cheap and compact handheld GPS receivers depend on the reception of signals. As Separatrix pointed out, there have been ground transmitters for similar systems.

  • Interfere with radio reception in general. That would also limit smartphones. A lifeform with natural radio transmitters and receivers? Or simply "electric eels" producing static?
  • The moon suffered a Kessler cascade and shuttles/starships in orbit have to maneuver constantly to avoid fragments. That makes sats impractical.
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It is hard to find stable orbits around our own moon. Low altitude orbits are unstable due to uneven distribution of mass within the moon ("lunar mascons"). High altitude orbits are unstable due to interference of earth's gravity. It is possible to find stable orbits, but I'm not sure if it would be possible to create a constellation of satellites such as that needed for a full GPS system.

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hmm, why does it need to be impossible/unfeasible?

So you want a planet without GPS but with maps? Possible solutions:

  • There is GPS but it is military use only. (Because some countries fight at the moment or have a cold war)
  • GPS is too expansive too install when they just make some photos from orbit and have a program make a map.
  • GPS on that world can track the user. And your characters don't want that.
  • there are many mean people/enemy government that spoof GPS. So better to rely on maps..

And no you could probably get away with GPS satellites but no communication satellites not the other way around. GPS satellites don't need much data transferred.

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This is not a physical explanation not to have GPS but how about an economical? The company who won the tender for setting up the satellites went bankrupt and the contract is tied up in lengthy legal battles surrounding the bankruptcy and until they are done, no one else can just go and establish a system for legal reasons.

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  • $\begingroup$ Only if there is only a single entity with the means to establish such a system and that entity is locked up in such a bankruptcy mess, which seems implausible unless you have a single world government and no large corporations which might themselves see benefit from such a system (for example: worldwide shipping companies). Earth has three separate government-run satellite positioning systems that I know of: NAVSTAR (US), GLONASS (Russia) and Galileo (EU), all independent of each other. $\endgroup$ – a CVn Jan 22 '18 at 10:42
  • $\begingroup$ @MichaelKjörling I guess I operated on the assumption that this is a newly colonised planet and not Earth. $\endgroup$ – Real Subtle Jan 22 '18 at 11:19
  • $\begingroup$ "I guess I operated on the assumption that this is a newly colonised planet and not Earth." Possibly; OP doesn't say. "Single world government" might have been a somewhat poor choice of words on my part. However, either way, I still think your solution presupposes the non-existence of other entities which see sufficient value in a satellite navigation system to invest in one of their own (given that the technology and the theoretical foundation for such a systme exists). That's possible, depending on the OP's universe, but it's not necessarily a given. $\endgroup$ – a CVn Jan 22 '18 at 11:54
  • $\begingroup$ @MichaelKjörling "I still think your solution presupposes the non-existence of other entities which see sufficient value in a satellite navigation system to invest in one of their own" -- Yes, it does. I assumed a setting where there are so many possible new worlds that people don't migrate en masse to establish a new colony. This makes sense in a world where, say, a company finds a planet to mine and no one else wants to go there to live, or any new arrivals are in short supply. $\endgroup$ – Real Subtle Jan 22 '18 at 15:20
  • $\begingroup$ Just a suggestion, but: you might want to Edit your answer to make that more clear in the answer itself. $\endgroup$ – a CVn Jan 22 '18 at 15:25
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GPS satellites need to have their known positions and clocks calibrated from time to time, otherwise these could drift. Once a satellite has a wrong reading, it will disrupt all readings that involve its usage. On real Earth, this calibration is done by the 2nd Space Operation Squadron.

In your world, central command may have lost access to the satellites, or they may have been hacked or broken. So it is not really that GPS is unavailable - it's that due to equipment malfunction any readings are random and inaccurate.

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Realistically, any civilization capable of colonizing another planet will blanket its orbits with satellites first.

Satellite imaging and communication will simply be too important for maintaining a developing colony, especially if contact with the home world is valued.

GPS would absolutely be one of the vital services provided by the satellite arrays any of our colonies would demand.

Instead of mandating that GPS satellites are not used/ are not reliable, why not posit that the GPS satellites have been taken out or sufficiently damaged?

A large solar flare or Coronal Mass Ejection (CME) could potentially wipe out all the satellites in orbit and even damage ground based positioning systems. https://www.nasa.gov/mission_pages/sunearth/news/flare-impacts.html

If you still need long range comm systems that survive the CME, have the colonies connected by fiber optics rather than relying on satellite communication.

Alternatively, if your GPS satellites were parked in geosynchronous orbits that are far enough outside of the protective magnetic field of the planet they could be critically damaged while those in near-planet orbits were protected.

It could take quite some time before replacements arrive from outside your colony or for your colonists to fabricate and launch their own replacements.

A major part of the need for unguided exploration could be scouting to find deposits of rare earth-metals needed to fabricate replacement GPS satellites.

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Stopping GPS:

You have a fairly large retrograde moon in a fairly low orbit. It plays havoc with satellite orbits.

(Note, however, that in the long run your world is doomed. The moon's orbit will decay.)

This doesn't stop limited-range GPS systems based on transmitters on mountain peaks but GPS is inherently basically a line of sight system (it will measure the distance to the satellite by the path the signal took. If that's not direct your answer will be wrong) and thus limited to areas with four visible peaks with transmitters. Far from civilization that won't exist.

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Due to it being a former military outpost the planet's oceans have an unknown number of ICBM equipped fusion-powered autonomous submarines programmed to attack the source of any unverified artificial radio signals they detect, there may even be autonomous factories in the ocean trenches building more submarines/missiles as needed. Colonists are unaffected by this insofar as they maintain radio silence which for a technologically advanced society is an easier problem to overcome than clearing out a rogue defence system, a system which if attacked may resort to nuking the planet into an asteroid field out of spite.

High frequency short range radio communications may be safe to use inland but anything with enough range to be practical for use as a navigational beacon will probably get attacked and a GPS satellite is going to get destroyed almost immediately.

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