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My captains and pirates belt out lots of navigational commands and jargon, but none of it can relate to terrestrial maps. So I’m needing a system they use in transit and combat, that they will reference when barking out orders or giving lookout reports.

I need to map across vast swaths of desert on a planet that has no life, magnetic field, no visible sky, no visible sun or moon; merely vast expanses of barren nothingness. The winds are moderate and unvarying, or only slightly variable in direction or force; slowing only at winter which is several months of darkness. I would assume that to use a wind-relative term such as "Lee" as the directional term for East would be best as circulation is unlikely going over the poles. From the ground, this is easy. Use a tattletale. Navigation must be by air or train however; and with no oxygen it must also be by airship as no combustion is possible. I have propulsion already figured out, it is beyond the scope of this question.

I’m building the official map system for this world which harbors a hidden pirate haven : how can I use wind direction to determine the direction of "Lee" and navigate across this planet? The obvious challenge is that my airship moves, meaning all wind direction is relative though it be absolute to the ground. And if I travel too high and out of sight of the ground, I have no reference at all. Dead reckoning seems like my only option. But I need a somewhat useful map that can give me some semblance of control over my travels. How can I go about doing this? The gloomy daylight through the clouds won't help me - a gnomon will be useless without any shadows cast. A compass is useless too since there's no magnetic field. Even if I make a waywiser, it'll have to be done on an extremely large scale to accommodate the rugged terrain. Gravity and wind constancy seem like my only reliable indicators.

Ships’ equipment

For monitoring air, they have tattletales on all 8 quarters of the ship which can infer any change in heading relative to the wind. They also have tattletales to measure engine thrust at each engine. Combine these with clinometers for pitch and roll, and they have a fairly good idea of what the ship is doing relative to the air around it; they can compute set, yaw, turn, and drift fairly well to correct a dead reckoning. They have sparse radio beacon towers laid out, with simple Morse code assignments. As these need maintenance and power, they don’t go far out into the desert and can only give approximations when between the five cities. A wire antenna can give a fair guess about what direction a given beacon is emitting from, but my personal experience with these on metal ships is they are wildly inaccurate, and can give you either the correct direction or the opposite of the correct direction. Quite easy to be completely spun around. Lastly, they do love their gyroscopes and use them religiously. But for inertial nav, they quickly drift out of alignment and as a result, give poor results for long distances. An inertial gyro even today could not make a straight line for more than a few miles. A hybrid system combining tools is needed.

Q: How do they map and reference location in airships?

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  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Commented Sep 16, 2023 at 17:07

3 Answers 3

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Light houses and Nazca Lines

You mention a group pirates in your scenario but no other groups or communities. However since a bunch of pirates with no one to actually commit acts of piracy upon is somewhat redundant I'm going to assume that:

  1. There are an unspecified but large number of societies/communities living on the planet, perhaps even some form of nation states;
  2. That trade between cities and towns is both common and profitable;
  3. That airships are the dominant form of travel unless two communities are close enough together that land caravans or roads/railways are a viable option. And;
  4. That as described conditions on the surface are in general hostile to human life so the bulk of population live in underground communities with minimal structures being visible on the surface

Those points established all but the smallest communities have built commercial landing fields on the surface above them even if after landing the airship is moved underground. These landing strips are designed to be clearly visible from the air and are brightly painted/clearly marked with distinctive patterns that identify each community and give bearings to at least the largest other communities nearby. These markings can clearly be seen from the air for miles in any direction. On top of that they also build light houses that again flash specific patterns of colored lights. (The towns long ago came up with an globally recognized system whereby no one pattern is used by two communities on the same region of the planet to avoid confusion.)

Following on from this a network of NAZCA Lines are cut into hard surfaces where geology permits (tough luck in the sea of sand). These markings can clearly be seen in daylight and provide navigation bearings and distance markers to nearby settlements.

Again there is a collective agreement regarding how the info is set out. Initially there were only a few markers giving only 'general' directions. However with time and effort as more lines were put in place the markings were refined to be more accurate. (Old ones were erased and newer, more accurate bearings put in their place). Nowadays maps of these markings are readily available to all.

Finally at least on important trade routes or where the terrain i.e. mountains interferes with carving lines remote lighthouses are also established and resupplied by airship. Again protected and maintained under international agreement. (The gyros are an added bonus and back up!)

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  • $\begingroup$ It was tucked away in there that there were five cities which trade by train and airship - not very boldly however. And radio beacons near the cities. A very detailed description of the work can be found here. You would have had to follow a link within the link here. $\endgroup$
    – Vogon Poet
    Commented Sep 15, 2023 at 3:49
  • $\begingroup$ If you're okay with line carvings (no self-illuminations), then you may not need light houses -- regularly spaced towers, with bearings to the previous/next tower on each, will be enough, and won't need resupply nor too frequent maintenance (abrasion). $\endgroup$ Commented Sep 15, 2023 at 13:39
  • $\begingroup$ Nazca Lines are not a common term, you might want to add a link or clear explanation of what they are. $\endgroup$
    – Nosajimiki
    Commented Sep 15, 2023 at 20:12
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I think 3 gyroscopes and 1 clock can do.

At a reference point, set the gyroscopes to a starting configuration, e.g. with their spinning axis mutually orthogonal and take the time.

Any change to that configuration will depend from their movement on the planet surface, which is a function of the planet rotation and the gyroscopes movement.

By checking the clock it is theoretically possible to know the contribute of the planet rotation and thus determine the movement by difference.

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  • $\begingroup$ This is intensely studied today trying to locate phones in tunnels/structures. Unequivocally a dig into inertial navigation even with modern gyroscopes and accelerometers, the technology has serious problems with incremental drift. It’s guaranteed ships will have this for their medium hauls beyond LOS and less than intermunicipal. But what about orienting yourself periodically for a calibration? Earth has had parallels for centuries to reference with. Can a “line” or “point” of any sort be made with a combination of $\endgroup$
    – Vogon Poet
    Commented Sep 15, 2023 at 0:25
  • $\begingroup$ radio, known wind, gravity, and something? For periodic calibration? $\endgroup$
    – Vogon Poet
    Commented Sep 15, 2023 at 0:25
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    $\begingroup$ Actually, this is a clever solution. We're looking for suspension of disbelief, not perfectly technical applications. This would be very much in keeping with the steampunk tag. For a similar literary method, see Edgar Rice Burrough's Barsoom (John Carter of Mars) books for how he described their airships and their navigation. In fact, that's on-point since they behave very much like your own with similar problems. (And note when he didn't bother to explain all the details....) $\endgroup$
    – JBH
    Commented Sep 15, 2023 at 15:39
  • $\begingroup$ You can substitute a gyrocompass (en.wikipedia.org/wiki/Gyrocompass) for a magnetic compass. This is not the same thing as a gyroscope. $\endgroup$
    – John Doty
    Commented Sep 16, 2023 at 0:42
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Navigation

There are a lot of options for navigation, but I suspect the real answer is to how to navigate is "all of these and then some".

Dead reckoning is maybe actually fine?

You know where you started, the direction you set out in, and the wind is "moderate and unvarying", so you can compensate in your calculations for an expected amount of drift. With all the "tattletales", you should be able to determine very reliably your heading relative to the wind - as well as its strength - since ones pointed upwind will read higher while one in the lee of the ship might even read negative. With enough sensors and knowledge of your ship's cross section from various angles, you could calculate the force applied on the ship, how it's resisted from the other direction, etc.

This could just be fine on its own, since the airship needs to go a couple thousand miles and end up within a couple hundred miles of some other point. We're trying to cross continents, not cities, so we just don't need that much precision.

Sun position based on polarization

Apparently:

According to the Rayleigh scattering theory, the polarization pattern of skylight is mainly determined by the solar position. Therefore the solar position can be retrieved by the polarization pattern of skylight. Based on this mechanism, the partially polarized skylight is utilized by kinds of creatures for navigation, such as ants, crickets, beetles, etc [2–8]. These creatures usually sense the scattering light of the whole sky dome or patches of the sky through their unique compound eyes and optic nerve systems, and then orientate their bodies according to the polarization patterns of skylight. It was reported that the Vikings (between AD 900 and AD 1200) used to orient during their sailings with the help of the “sun-stone”, which was applied to search the solar position by observing the skylight through the “sun-stone” [9,10]. The sun is usually blocked by the clouds and fogs, but the polarization map of the partly polarized skylight remains the same as in the clear sky.

Topography

Even a barren moon covered in sand is going to have some geography. If you know your own barometric altitude and can use radar or a rope with a weight to determine your altitude above ground level (AGL), you can develop a profile of the terrain.

  • Sand constantly shifts, so it's hard to tell what the ground looks like? Carry around a small ground-penetrating radar rig that you can lower to the sand to measure the local bedrock topography.

Beacons of various kinds

They have sparse radio beacon towers laid out, with simple Morse code assignments. As these need maintenance and power, they don’t go far out into the desert and can only give approximations when between the five cities.

If we have constant and largely unvarying wind, it's going to be trivial to build plenty of wind-powered radio beacon nodes. A node could be composed of a 100-Watt (~1m / 3ft) micro wind turbine and a small transmitter hooked up to something that looks like the wheel inside a music box, and that's just if you don't want to have to invest in microchips for reasons.

  • Including the panels, imagine something about the size of a desktop computer. Without them, there's no reason it would need to be larger than a Raspberry Pi.
  • An airship at 5km altitude has a radio line of sight of 291km. That's without any ionospheric bouncing or anything, just line of sight VHF. Two wires can be used to give better accuracy, but a directional antenna (such as a dish, Moxon, yagi) could pin that signal down to easily within a few degrees.
  • Sand gunks up the turbine? Use solar! Diffuse sunlight is still sunlight and the wind should keep the sand buildup to a minimum.
  • Creatures attack them because they don't like the turbines/solar panels/hate EM waves? Use an aerostat! As a bonus, this lets the radio reach even farther. If you keep going higher, you're eventually describing our current GPS.

To top it off, radio waves on a barren planet without a bunch of noisy RF sources are going to go very far on very low power. Currently, there's a network of low-powered (~1W) beacons around the world called WSPRNet that transmit on HF bands and are regularly heard across oceans. Basically, any planet that can support people can have a sufficient radio beacon network good enough for "find the one city within a couple hundred miles". Since your question implies a strong preference for some kind of wind-based navigation system, you might include some explanation for why this isn't done:

  • Something - the pirates? sandworms? - actively hunts these beacons for nutrition/parts/to cause caravans to get lost.
  • There's huge amounts of interference for some reason. Possibly the lack of a magnetosphere means the planet is constantly hit with various grades of solar flares or because the planet's sand and wind create a lot of electrostatic noise. Narratively, this could be fun because it means that it might be easier to navigate at night.

If radio isn't your jam, the beacons could use visible light (a lighthouse), masers, lasers, or even directed pulses of sound.

Seismometer

An airship could carry a couple of seismographs and land every so often to take measurements. I'm not familiar with the sensitivity of these, but I don't think it's crazy to think a a large underground community might well be detectable on seismographs for hundreds of miles without really trying, and could have a "thumper" to create regular impulses that could be detectable much further out. Particularly if there's not a molten core or mantle, I suspect seismographs would have work even better than normal, though deploying them on sand obviously isn't going to be great.

Rope or Chain

Each settlement has a "lifeline" that connects it to the nearest ~3 settlements. Depending on the tech level and context, maybe it's a giant optical fiber for data, maybe it carries power, or maybe it's nothing but a large rope that an airship attaches to for propulsion and navigation. Think an upside-down zipline.

There's precedent for things like this in the form of chain barges and I can imagine doing this so that the sandworms/whatever can't get to you, or because the sand doesn't bear loads well.

Other Stuff

  • Sounding rockets that are fired off late at night at a known time that are visible for hundreds of miles.
  • Plant and wildlife could vary significantly by latitude or longitude or maybe follow some known set of patterns.
  • Wind could vary slightly in different places in a way that's recognizable. If the world is completely barren and has no geography, it should generally flow away from wherever the sun is centered.
  • If the planet has any notable resources, maybe nodes of those resources are detectable by sight/radar/gravity sensors.
  • There could be various anomalies that are used as waypoints. These might emit radio waves, sound, light, or draw animals to or away from them.
  • No matter how much cloud cover there is, you should always be able to determine the position of the sun... it might just take more work and time. You might not be able to see the shadow cast by a gnomon with your eyes, but put the same thing on some barely photosensitive paper for half an hour and look for the arc that is less exposed than the rest.
  • Clouds have a maximum height - they're made of stuff heavier than "empty" atmosphere, so send up an aerostat every so often to get a view of the sky.
  • Some areas of the planet might have distinct smells or dust colors or chemical makeup or radiation.

Questions

And if I travel too high and out of sight of the ground, I have no reference at all.

... how do you get so high that you can't see the ground? Lift from aerofoils and lighter-than-air gases decreases as you go up, so a cargo airship isn't going to travel at high altitude without a very good reason.

A wire antenna can give a fair guess about what direction a given beacon is emitting from, but my personal experience with these on metal ships is they are wildly inaccurate, and can give you either the correct direction or the opposite of the correct direction. Quite easy to be completely spun around.

There's a process for dealing with that. If that were common, I don't think we'd have a network of over a thousand radio beacons in the US alone. I suspect your experience is because a single wire antenna is probably functioning as a dipole with the ship's body as the second pole. These have a two-lobed radiation pattern with two 180-degree opposed lobes which mostly explains your experience with wire antennas. See this image: dipole radiation pattern showing two opposed primary lobes

I have propulsion already figured out, it is beyond the scope of this question. Not a question, just an aside: airships could anchor every so often and run their engines regeneratively to charge up batteries from wind power.

Mapping

The mapping system that you use might vary by community if one group prefers radio beacons while some other group prefers topography because they live near an extinct volcano.

If you're determined to have people yelling lots of wind-related words for guiding craft, I suspect you're going to end up with something akin to the points of sail. Regions would probably be named for whatever makes that area noticeable or distinct, while large tracts of completely identical geography and climate would probably be named as such: "the barrens" is generic while "equatorial dune zone" might be a formal name.

If nothing distinguishes one part of somewhere from other part, it'll just end up with no name, and people will latch onto whatever landmarks they can even if they end up exceedingly distant: "Bunkertown-Muskville Midway" might be an imaginary point halfway between those two towns. If you look at old maps, many had less a focus on the actual shape of the land and more of a focus on the distances between places and any landmarks you might encounter - often measured in transit time instead of physical distance. You can still see this in highway rest stops that have mileage charts: an example mileage chart from Washington State. In your case, each city would be on the chart, along with any known landmarks as mentioned in the first section.

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    $\begingroup$ Quite amazing sir. As a retired Coast Guard who has had to investigate a failed beacon, and learning that all the copper ground radials were pilfered; you have the reason why unmanned beacons don’t work on a planet full of pirates. Polarization in 1890 tech is reasonable, I think. Would a gnomon work with it? Travel in the summer just got easier; months of winter darkness however… brave souls they be. $\endgroup$
    – Vogon Poet
    Commented Sep 15, 2023 at 23:38
  • $\begingroup$ @VogonPoet, I was really impressed by the Viking polarization stone! And if you prefer, they could use a variety of animals for wayfinding via sky polarization. $\endgroup$
    – William
    Commented Sep 18, 2023 at 6:58

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