What would you see from inside tubular ringworld?

[Aotrs Commander]

An alien civilisation, for reasons best known only to them, build a form of ringworld, in which the inside of the outer half (i.e. the concave surface) is the habitable surface and the inner half is essentially a giant window. (That nominally darkens to simulate night.) The diameter of said tube is on the order of planet size (for simplicity, assume similar to Earth, a diameter of about 8k miles and thus a 12k "surface").

(The ringworld was never "completed" and as such, only one or more portions, book-ended by giant walls to contain a stretch of (say) 24k miles, have been finished and are inhabited.)

It is assumed that the tubeworld is accelerated to beyond orbital speed to create gravity (either that or "standard" artifical gravity is generated by "conventional," if epic, means on the interior surface).

If one were to be standing inside at the edge of the point where the ground gives way to "glass" (the "top" as it were, as defined by the up-oribital-plane), first of all, would you see the other side of the world, or would is disappear into atmospheric haze? I'm assuming there would be no horizon.

Would it, in fact, have to have a 100 mile atmosphere "skin" over the habitable period to retain conventional atmospheric properties or could it be simply full of gas? (Either one may create... problems I could see.)

Secondly, would I be vastly far out in assuming that the upper (and nearest) parts of the land would be more tropical (like a conventional planet's equator) and the lower portions would be colder (like the poles), on the assumption that the further parts would disperse heat and light in a similar manner to the poles?

Any other commentary or suggestions about issues this setup would create would be welcome.

(I'm not hugely worried about going too hard on the science - this is essentially for a one-shot adventure, and I'm prepared to plaster over the worst of it with some "because advanced technology," - especially since I am rather short of quest-writing time! - but even so, I like to have at least some basis, at the very least so I can describe to the players what they should be seeing.)

[DavidSh]

Any area of atmosphere subject to gravity will be subject to change in pressure with altitude. For this purpose, centrifugal force counts as gravity. You can't have a 100-mile vertical extent with habitable pressure for humans all the way. If you have any vertical mixing of air, the temperature will also change with altitude -- colder higher up, warmer lower down. (This was my objection to Schlock Mercenary's big can of sky.)

So, if the gravity is provided by rotation around the sun at a faster-than-orbital speed, most parts of the tube won't be inhabitable. If the gravity is provided by gravity generators, or, for a sufficiently flexible tube, rotation around the center of the tube, you can probably get by with a layer of atmosphere clinging to the interior surface of the tube, with the center of the tube at a near-vacuum.

Under the thin-layer model, I would expect the sky to be a cross between looking at the Moon in the daytime from the Earth, and looking down on the Earth from orbit. White clouds should be visible against a blue background. Only very prominent variations in ground color would be visible.

And, under this model, the areas higher up on the side of the tube, even though they are slightly closer to the sun, also have the sun closer to the horizon continuously, so will be colder. Compare on the Earth, both the poles at perihelion are closer the sun than the equator is at aphelion, but they are still colder.

[factotum]

I'm with DavidSh on this. If you have habitable conditions down in the middle you're going to have a pretty hard vacuum 4000 miles up, where your observer is standing, just as you would on a real planet. There's thus very little reason to actually build a station like this, because the habitable area is going to be very small compared to the amount of material used to build it. This is why Niven's Ringworld had a completely flat inner surface and thousand-mile-high walls at the edges to keep the air in.

[Lord Torath]

Regarding the temperatures of different elevations, I think that the angle the surface makes with the incoming sunlight will have a much greater effect than the relative distances. A difference in elevation of 10-20,000 meters is nothing compared to the (presumably) 150 million kilometers to the sun. Areas of land roughly perpendicular to the incoming sunlight will be warmer than areas of land (like mountains and canyons) that have a smaller angle to the incoming sunlight.

[halfeye]

Regarding the temperatures of different elevations, I think that the angle the surface makes with the incoming sunlight will have a much greater effect than the relative distances. A difference in elevation of 10-20,000 meters is nothing compared to the (presumably) 150 million kilometers to the sun. Areas of land roughly perpendicular to the incoming sunlight will be warmer than areas of land (like mountains and canyons) that have a smaller angle to the incoming sunlight.

So a plateau at 12,000 feet, like around Mt. Blanc, would be as warm as a slightly above sea level river valley at the same latitude? Dream on. The temperature of the air is very important, and mainly depends on height.

[Lord Torath]

So a plateau at 12,000 feet, like around Mt. Blanc, would be as warm as a slightly above sea level river valley at the same latitude? Dream on. The temperature of the air is very important, and mainly depends on height.

On Earth? Certainly. There are many factors involved in ambient temperature, including the angle of the sun (seasons). Proximity to the sun relative to the rest of the planet is completely overwhelmed by other effects, which is part of why high elevations are colder, not warmer than lower elevations. On an artificial space station? It very much depends on how the station functions.

So, what are the reasons air cools as you move up the atmosphere? It's a combination of things.

Sunlight pretty much ignores the air, and warms the dirt and plants and water on the surface, rather than the air. This warmed surface then warms the air, so the air closest to the ground warms before the air higher up. And the angle the sunlight makes with the ground influences how much heat the ground absorbs, and thus how warm the air at the surface is (If this was the only way the air was warmed, you would expect the air around Mt. Blanc's plateau to be just as warm as a low-elevation river valley).

While the air is relatively transparent to sunlight, it is pretty good at trapping the heat radiated from the ground. So as you climb to higher elevations, you have less atmosphere above you, trapping that heat. I suspect this is a pretty minor effect though,

I think the most important factor, though, is that air at higher pressure has a higher temperature at a given volume. As you climb higher, the air pressure drops, which means the air will be colder.

Caveat: I am in no way an expert on atmospheric or climate science. If anyone has better information on temperature variation by elevation, I would sincerely love to hear it.

But as soon as you get to artificial worlds, you start introducing all sorts of other effects.

[DavidSh]

If you want to look up more information about the change in atmospheric temperature with height, look under the term lapse rate. There are some exceptions to the general decrease in temperature with height. Temperature inversions sometimes happen in some places, and occasionally trap smog in places like Los Angeles. Up in the stratosphere there is different behavior also.

[halfeye]

If you want to look up more information about the change in atmospheric temperature with height, look under the term lapse rate. There are some exceptions to the general decrease in temperature with height. Temperature inversions sometimes happen in some places, and occasionally trap smog in places like Los Angeles. Up in the stratosphere there is different behavior also.

Space near Earth is hot. Which seems a bit odd to me, however it seems to be true, and thus the speed of sound up there is relatively high, though there's not enough gas to actually transmit sound.

[Spojaz]

The most distant object photographed ground to ground had443 km of atmosphere between camera and mountain. This shot was only possible because of an exceptionally clear weather, polarizing filter and a really nice camera. Beyond that distance, even silhouettes in front of the sun (impossible on your ring) would become invisible.

Because air is very slightly translucent blue, and any moisture or dust in the air would look like clouds, the land rising just a few degrees above perpendicular would just look like sky. There would not be a clear definable horizon, just a rather sharp gradient. At the same curvature as our planet, even with fuzzy lights from cities across the ring, people could even believe their world to be flat.

[Aotrs Commander]

Noting all the commentary; please continue! Definitely got it backwards with the temperatue, I was thinking of entirely the wrong thing; but that's why I made the thread, right?

(My thinking was "if the land is concave and hot at the top and it gets colder further down you go, that'd be really cool and plot-fodder" and such, but I think that idea is best abandoned. While I could, no doubt, just do something with having, like, a really big chasm or something filling the same purpose with added mystery of "why is it getting colder?" I suspect the scope of that is going to be beyond on little explorartion adventure.)

Will be having a rethink as time allows (hopefully before Monday when I need to do some more quest-writing).

What I was thinking of seems more akin to a giant Stanford Torus than a Ringworld.

Maybe some scaling back might be in order or a change of focus. Still gonna be aiming for "big megastructure built by really long-gone aliens" or something, but... Well, honestly, this quest isn't comig that easy this time, probably because my initial concept was "almost-routine exploration mission" and I haven't fully got the hook - at the moment it's tenatively "PCs find megastructure that pre-dates the oldest known civilisation (which was around 1-2 million years ago), building some evidence as to WHY there didn't appear to be any older civilisations know to current galactic powers, especially as said oldest civ had been confirmed to like messing around with retrocasual probability engineering..." But the nitty-griity of the advanture is still eluding me a bit!)

The most distant object photographed ground to ground had443 km of atmosphere between camera and mountain. This shot was only possible because of an exceptionally clear weather, polarizing filter and a really nice camera. Beyond that distance, even silhouettes in front of the sun (impossible on your ring) would become invisible.

Because air is very slightly translucent blue, and any moisture or dust in the air would look like clouds, the land rising just a few degrees above perpendicular would just look like sky. There would not be a clear definable horizon, just a rather sharp gradient. At the same curvature as our planet, even with fuzzy lights from cities across the ring, people could even believe their world to be flat.

Thanks, that's really useful. Never thought of looking for world record distance viewing.

[factotum]

Yes, if you were to scale things back so the tube of the torus was maybe 5-10km across things get a lot more believable, and it would still be a giant structure. Although there's still the question of why the aliens didn't just build the thing with a flat bottom, thus making something more akin to Niven's ringworld or a Culture Orbital from Iain M. Banks' books.

[Aotrs Commander]

Yes, if you were to scale things back so the tube of the torus was maybe 5-10km across things get a lot more believable, and it would still be a giant structure. Although there's still the question of why the aliens didn't just build the thing with a flat bottom, thus making something more akin to Niven's ringworld or a Culture Orbital from Iain M. Banks' books.

To some extent, there is supposed to be a deliberate element of "why the crap did they build it THAT way?" (I mean, some mystery in your exploration game is sort of part of the draw.)

I'm gonna be bigger than that - a fair bit bigger, but maybe only large-moon/planet size. (I mean, the party in question - actually an Aotrs exploration team if you can believe it - know of super-cruisers¹ bigger than that, so it has o be a bit bigger to be particularly impressive.)



¹Not many, since the Aotrs only ever have built maybe a dozen and a half 6-mile plus super-cruisers, but even so. Hell, one of the PCs actually worked on one of them...

[factotum]

When I said 5-10km I meant the diameter of the actual tube--the torus itself would obviously be a lot larger than that. Heck, it could realistically be any size you like!

However, when you say "Why the crap did they build it this way?" is part of the mystery, you still really need to have an answer to that question yourself, IMHO--even if you never intend to reveal the secret, there are probably going to be other consequences of that reason which would influence other aspects of the way the station is built. I'm a big fan of what happens in a story following from the situation and the characters, not just "the author wanted it this way".

[Aotrs Commander]

When I said 5-10km I meant the diameter of the actual tube--the torus itself would obviously be a lot larger than that. Heck, it could realistically be any size you like!

However, when you say "Why the crap did they build it this way?" is part of the mystery, you still really need to have an answer to that question yourself, IMHO--even if you never intend to reveal the secret, there are probably going to be other consequences of that reason which would influence other aspects of the way the station is built. I'm a big fan of what happens in a story following from the situation and the characters, not just "the author wanted it this way".

Oh, I fully intend to have a reason - when I say "mystery" I mean "for the PCs to solve" - that is, like, part of the point of these adventures is for the PCs to go around prodding stuff and going "so, what happened here then?"

It's just that with time pressing and my VERY long-winded way or writing quests (seriously, I ended up spending most of Monday having to work out how much actual area the sensor drone would actually be able to survey), I was trying to get words on the page a bit describing the scene after they set out of their portal and try and deal with starting the still-having-a-few-problems-with-the-angle-story more next week.

This is kinda the issue actually, I set this quest up without - for once - a pretty clear idea of The Plot, beyond "PCs for the first time are allowed to do a normal mission with all the available options to pick from and An Adventure Happens" and I've been struggling a bit with the last part.

(I mean, it's normally fairly simple, like "PCs go to Anicent Space IKEA" or "PCs search ruins to find out what's causing the anomoly with an eye to finding out why all the intelligent life on the planet died" or "PCs have to assassinate two people simultaneously" or "PCs inflirate a convoy and end up secretly saving it from a magic sentient disease monster" (not all of these were from the same party), but this time, I'm strugglin which is a problem, because the adventure is on the 11th of August. I'd been hoping my recent holiday would have provided an appropriate image with which to craft the quest on (that happens a lot too), but for once, nothing struck me.)

[snowblizz]

Someon mentioned Schlock Mercenary upthread and I'm thinking maybe have a look at the attendant story, where the protagonists, a band of mercenaries get a mission to explore a Can Full of Sky (tm). There must be some plothooks you can pull out of it.
Relevant bit (Part II: Can Full of Sky) starts here: https://www.schlockmercenary.com/2013-02-24

[factotum]

Although, as also pointed out upthread, the Can Full of Sky wouldn't actually *be* full of sky--the actual atmosphere would be around the edges and the middle would be a vacuum. This is not how it's portrayed in the story.

[snowblizz]

Although, as also pointed out upthread, the Can Full of Sky wouldn't actually *be* full of sky--the actual atmosphere would be around the edges and the middle would be a vacuum. This is not how it's portrayed in the story.

To quote the OP:

(I'm not hugely worried about going too hard on the science - this is essentially for a one-shot adventure, and I'm prepared to plaster over the worst of it with some "because advanced technology,"

However the reason I brought it up is because there are ideas for almost all of the "whats" and "whys" AORTS Commander mentions in the Schlock story.

I don't know the rules/system/etc of what AORTS is using, so I'm not gonna say crib it wholesale, but that's certainly where I'd start.

Basically instead of technical details of line of sight and such. Look for the actual problem here (as best I can tell), what are player gonan be doing a in can of sky?

The exchange about what direction is up and down (north? south? east? west?) alone would make for a great first scene. "Currently travelling Eastdown-southeast, sir!"

[S@tanicoaldo]

I'm not very good at Science stuff but I'm kind of good at finding pictures. Maybe these pictures will help you illustrate and visualize the inside structure of a tubular ringworld? I dunno, trying to help.

Spoiler

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[halfeye]

Although, as also pointed out upthread, the Can Full of Sky wouldn't actually *be* full of sky--the actual atmosphere would be around the edges and the middle would be a vacuum. This is not how it's portrayed in the story.

That's true if there's any sort of gravity in there, but is there gravity away from the surfaces? I'm not at all sure that it's rotating (that could well be me forgetting stuff, I do a lot of that). It was, after all, built for blimp entities that would intend to use all the sky they could get.

[factotum]

That's true if there's any sort of gravity in there, but is there gravity away from the surfaces?

There's a permanent storm in the place because one of the Godwalls was broken. That could only happen if the station was rotating, since otherwise there would be no energy source for the storm. There also wouldn't be any point building the Godwalls in the first place if you didn't have a problem with the atmosphere sloshing around due to rotation.

[Excession]

That's true if there's any sort of gravity in there, but is there gravity away from the surfaces? I'm not at all sure that it's rotating (that could well be me forgetting stuff, I do a lot of that). It was, after all, built for blimp entities that would intend to use all the sky they could get.

There isn't any gravity. The spinning only simulates it, and it's not quite the same. In the case of a spinning cylinder, an air molecule sitting on the axis experiences no force toward the "ground" at all. Even as you move away from the axis, it will take only a gust of wind against rotation to render a whole bunch of air weightless, and with only pressure acting on it that air will move to fill any vacuum above it.

It depends on size and other variables, but I don't find a huge spinning cylinder full of air implausible.

[Yora]

Spoiler

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I think this picture shows accurately the direction of the force that pushes everything (people and air) down to the ground. Even though you have a curved bottom, the down force is not in a direction away from the center of the tube, but from the axis around which the ring rotates. As you get from the bottom of the tube towards the walls, you would find the floor to become increasinly steep and eventually vertical. If you fill the tube with air, it will all be pulled towards the bottom like water would. On the tube side closest to the axis of rotation (where the star would be) you would have the lowest air pressure and on the side furthest away from it the highest pressure. If at the bottom you want to have normal Earth atmospheric pressure at sea level, then air pressure would decrease with height the same way it does on Earth. On the highest point of the roof (closest surface to the star) you would have the same air pressure as you would have 12,000 km above the surface of the Earth. Which is pretty much nothing.

To everyone inside the tube, their world would be like an incredibly long canyon flanked by 6,000 km high cliff sides and 12,000 km across. Since the maximum habitable altitude on Earth is maybe something like 6 km, the habitable strip at the bottom of the canyon would be very narrow. With such a huge ring diameter it would probably still be a couple of hundred kilometers wide, but still only a tiny fraction of the whole 40,000 km circumference.

As for what you would see. I think it would look identical to being on a normal planet because of atmospheric haze.

Added: I made some quick scribblings to make an estimate for the width of the area "below 6000 m" and it came out as a strip 500 km wide. And towards the edges we're talking about altitudes like the peaks of the Andes. That strip would also be about 500 million kilometers long. For a total area of land 35 million times as large as the surface of the Earth.

I wanted to make an image of the interior of the ring, but at these scales the maximum image size my computer can handle would make the space with breathable air less then a pixel thick.

[factotum]

There isn't any gravity. The spinning only simulates it, and it's not quite the same. In the case of a spinning cylinder, an air molecule sitting on the axis experiences no force toward the "ground" at all.

But that air molecule is in an unstable equilibrium. If it moves a tiny amount in any direction (which it will do, because molecules are moving around all the time) then it will move into a part of the station where the air is rotating along with the station's spin. (It has to do that, because friction between the "ground" and the air mass will cause it to spin up to the same speed as the station). Once it does that, its mean free path will tend to move toward the ground, because the molecule can't maintain an "orbit" without some sort of force pulling it toward the axis. So, overall the air molecules will tend to move toward the outside of the station.

[Excession]

But that air molecule is in an unstable equilibrium. If it moves a tiny amount in any direction (which it will do, because molecules are moving around all the time) then it will move into a part of the station where the air is rotating along with the station's spin. (It has to do that, because friction between the "ground" and the air mass will cause it to spin up to the same speed as the station). Once it does that, its mean free path will tend to move toward the ground, because the molecule can't maintain an "orbit" without some sort of force pulling it toward the axis. So, overall the air molecules will tend to move toward the outside of the station.

Sorry, I think I explained myself poorly. The difference I'm getting at is one of degree, not kind. On Earth gravity doesn't vary much through the height of the atmosphere. In a rotating cylinder though the pseudo-gravity drops to zero as you go toward to centre. That means the atmosphere column in a cylinder will a lot taller than on a planet with the same surface pressure.

I'm unsure of the effects of convection (from sunlight heating the surface) and coriolis forces on the air. I think you could get some really interesting turbulence going on, and I wonder if some of that could serve to fluff the atmosphere up somewhat, making the column taller still.

[factotum]

Sorry, I think I explained myself poorly. The difference I'm getting at is one of degree, not kind. On Earth gravity doesn't vary much through the height of the atmosphere. In a rotating cylinder though the pseudo-gravity drops to zero as you go toward to centre. That means the atmosphere column in a cylinder will a lot taller than on a planet with the same surface pressure.

Yeah, but the can full of sky from Schlock requires your air column to still have pretty much normal pressure a thousand miles above the ground, and that's in a station 8000 miles across--so the "gravity" is still going to be three-quarters of what it is at ground level. I just don't think that's possible.

[Aotrs Commander]

So, the sharper of those among you will have noticed that I have had other problems this week, which have used up most of my thinking time. However, it is quest-writing day, so I need to get something down.

In desparation, one draws ideas from current events, so what has gelled together from last week's half-ideas comes from this past week's events and Total Warhammer 2...



The PC's Myst Gate takes them to a partially completed megastructure. The structure dates back to approximately 560 million years ago – which is before the Sienetic Harbingers, the earliest-know civiliation. (Long suspected not to have been the actual first, though the discovery of their retro-casual probabiity engineering has called this into somewhat disturbing question.)

The ancient unknown builders began to create a ringworld around a dwarf star with a radius of 0.2 AU. The ringworld is abou five hundred miles wide, but only a stretch of 26520 miles was finished. The potential total size of the ringworld would have been exactly 189 million miles circumferance with a total surface area of 94.5 billion miles, just under 480 times the surface area of a typical HPE planet. The “completed” area is (1/7200th or 5% of a degree) or a mere 0.014% of the total area. The ringworld is rectangular in cross-section, long-edge perpendicular to the orbital plane, with the “top” and “bottom” rounded into not-quite semicircles.

This habitable stretch – capsule, for want of a better term – was never fully finished by the creators. Inside it, there was nothing but flat carbon rock and an dense atmosphere of helium, awaiting the activation of the terraforming systems to create landscapes, atmospere – and seed it with life from a genetic repository.

The Harbingers arrived about two million years ago. The capsule provided them with a place to do some early relatively testing on probability engineering. Modifying the capsule’s systems with their own probability engineering nexus, the Harbingers retrocasually ran repeated experiments in the interior of the capsule. Thanks to the Harbinger’s extra-temporal data-storage systems, the computer system was able to keep logs for every time it was retrocasually reset to allow a roughly 500 million year stretch of evolution.

The Harbingers eventually just abandoned the capsule (as their civilisation was believed to have lasted millions of years) and it lay forgotten – until it was affected by the massive scale probability engineering project which created the known universe.

This makes this world a truly ground-breaking find. Not only is there evidence of civilisations before the Harbingers, but the technology inside it – the mega-structure engineering, the terraforming systems, let alone the probability engineering hardware – is incalculably valuable (and indescribably dangerous). It is a find that will absolutely warrant the Aotrs’ full attention. However – there is a problem.

The system is finally struggling under the weight of millions of years and has become corrupted, the most critical issue of which is the gravity generators glitching erractically. Aside from the general havoc that causes to the life inside (not because of standard gravity but the system can simulate tides), it also runs the risk of destabilising the incomplete ring and causing it to lose it orbit, which runs a hole slwe of potential catastrophies.

The habitable area is surrounded by a layer of atmosphere inside a transparent metal surface, which can simply be darkened to create a night. The transparency works more like a computer screen and thus does not necessarily have all change at once or the same way. This lensing system has started to glitch, randomly darkening or lightening in patches every so often. Finally, there is the danger of the terraforming systems glitching and causing havoc.

The solution is relatively simple – to repair the corrupted software, all it needs to do is retrive the basic operting system data from the Harbinger’s extra-temporal data-storage. Essentially, it just needs a reboot and repair from its boot disk. (The more things change…!)

Of course, to do this, the PCs need to reach one of the computer cores – once they even figure out that something is up. The problem is, as usual, not that straight forward, however, as the land inside the dome has intelligent life in it – not quite HPE-L (crude translation "typical fantasy planet"), but certainly high-background HPE (harbinger probability-engineered - basically "Earth-habitability compatible - thsi is why the galaxy has so many places which are 1g with oxygen nitorgen atmosphere etc).

The nearest entrance to the main super structure lies within the depths of a pyramid, believed cursed by the natives. Not without merit, for within, in his sarcophagus, lies an ancient Undead lord (let's call him... Uh, Shemttra the Shimperishable¹, stirring at last after centuries of torpor and eager for revenge…

(And/or negotiation with a reasonable group of Evil Undead that happen to show up on his doorstep…!)

The aforementioned "view from the tuberingworld segment" is thus:

Your first look into MGL-046 is a view down a steep mountain pass. This is not atypical – the Myst Gate has a prevalence of opening on high-up places with a view. Major Scimitar suspects this is probably design. The mountains are covered in what appears to be a luxuriant covering of a green moss-like plant. You can spot the thin glisening streams of a few streams, trickling down to forma narrow river headwater towards the farthest end of the pass. Here and there, trees and shrubs dot the flatter areas. They do not look completely alien, but nor do they look immediately familiar species – though with the distance, even Snowward would be hard-pressed to identify more obscure HPE-standard flora.

However, this does tell you that the flora and fauna is likely to be closer to terrestrial, if not actually terrestrial, which indicates it is more likely to be a HPE or HPE-L than a HPE-B and almost certainly rules out an alternate Earth.

The sun appear to be directly overhead – it must be almost exactly midday – and there are few shadows. External temperaure and humidity readings indicate this is a tropical region – which might explain the lack of snow.

The Sentry Drone’s sensors report it cannot detect a cardinal direction and the magnetic field readings are… Odd, though without a more through scan (which is what you and the Astrometrics Analyser are for), you can’t determine why.

The Drone completes its initial entry pause to ascertain the immediate area. The standard search pattern is to make a single 360º panoramic sweep for a purely visual inspection of the exit point before starting the sensor sweep.

It is not until the Drone turns clockwise as it styarts the visual sweep that you spot something that indicates this is far from standard. A few miles away is a massive wall. It stretches away into the atmospheric haze further than the Drone’s vision can see horizontally and vertically out of its line of sight. As the Drone’s view continues to shift, bringing it around to more or less opposite the Gate exit, you can see the huge wall terminates vertically with another solid wall, which must be also enormous to be visible even above the mountains, which runs straight horizontally across the line of vision and out of sight as the drone completes its 360, like an artifical horizon.

Neither wall appears to cast a shadow, which suggests that they are more or less perpendicular to the angle of the sun.

The PCs have entered the ringworld at the “north” of the spinward (anti-clockwise) end of the capsule.

If they have the drone look up, they will see the wall does have an appreciable arc, and arc is more visible further away higher up than lower down (less atmospheric haze). The wall behind the gate exit direction (ten miles distant – and technically “south”) is the point at which the land ends and the transparent canopy rises and starts to curve. While this canopy is easily visible to sensors, it is (by design) invisible to the naked eye (or eyeglow).

The end wall (“east”) is approximately five miles away.

The local area consists of a low mountain range which extends back to to the “north” and “east” walls, getting much sharper and more rugged quite quickly and making travelling to the face of the wall by foot difficult. The mountains are not high enough here to create snow in the permenant summer. The range continues for another fifty or so miles of hills and low mountains “west.” To the “south”, the passes descend over about a dozen miles across a broad, flat and sandy plain to a shallow sea.



Thoughts, commentary, obvious things I have missed?



¹Not actual name.

[Bucky]

First, the narrow band of habitable atmospheric pressure could be widened to practically the whole structure. Humans can comfortably adapt to a ~2km elevation range in earth gravity - this includes overpressuring the bottom end beyond 1 atm - and reducing the gravity expands peoples' vertical range proportionally. At 2/3 gravity it would have habitable pressure until the floor becomes too steep to navigate.

Things that may affect your description:
Is the skybox reflective at all? If so, there will be a faint mirage at the horizon of the skybox, most easily noticed at twilight with daylight reflecting from a darkened sky.


Does the survey drone have survey equipment more precise than "A few miles away"? Why wouldn't it use rangefinders in the initial scan?

Your description, from "the huge wall terminates vertically with another solid wall" to "like an artificial horizon" isn't really clear - it sounds like the 'another solid wall' is a ceiling. Split up the sentence to make it clearer which description refers to which wall.

[Aotrs Commander]

First, the narrow band of habitable atmospheric pressure could be widened to practically the whole structure. Humans can comfortably adapt to a ~2km elevation range in earth gravity - this includes overpressuring the bottom end beyond 1 atm - and reducing the gravity expands peoples' vertical range proportionally. At 2/3 gravity it would have habitable pressure until the floor becomes too steep to navigate.

Things that may affect your description:
Is the skybox reflective at all? If so, there will be a faint mirage at the horizon of the skybox, most easily noticed at twilight with daylight reflecting from a darkened sky.

No.

The assumption is that it is basically made using a version of the transparent blahblahblahblah stuff they make the viewports in starships out of, only write large and with very complicated refracvtion systems such that when it is transparant, it is completely transparent (effectively invisible), and when it darkens, it is completely black.

So the only way you would get stars at night as if you told the system to artificially make some - the second assumption being that the canopy would also be capable of producing (or modifying via some sort of lensing) light to create an illusory starfield or moon. I mean, this thing was set-up to be fully terraformable BEFORE the Harbingers started messing around with retrocasuality engineering there; sufficiently-advanced-technology space window/starfields are nothing.

(And yes, you could have used literal magic to do it, but the Harbingers were more about technology and doing all sorts of nonsensical and alien things for little apparent rhyme or reason.)

Does the survey drone have survey equipment more precise than "A few miles away"? Why wouldn't it use rangefinders in the initial scan?

It does and the distance is noted (just not in the read-aloud text - ten miles). The read-aloud - especially for an adventure like this - is sometimes "what you can see/first impressions" (and even Liches can't estimate distances like that easily) with the "what specific data your instruments gather" being supplied later when they start actually interacting with what they see. (Like asking "how far away is the wall?")

Your description, from "the huge wall terminates vertically with another solid wall" to "like an artificial horizon" isn't really clear - it sounds like the 'another solid wall' is a ceiling. Split up the sentence to make it clearer which description refers to which wall.

It is not until the Drone turns clockwise as it styarts the visual sweep that you spot something that indicates this is far from standard. A few miles away is a massive wall. It stretches away into the atmospheric haze further than the Drone’s vision can see horizontally and vertically out of its line of sight. As the Drone’s view continues to shift, bringing it around to more or less opposite the Gate exit, you can see the huge wall does have an end, meeting a horizontal wall at ninety degrees. This second wall runs straight horizontally across the line of vision and out of sight as the drone completes its 360, like an artifical horizon. It too
must be also enormous to be visible even above the mountains.

Better?

[Bucky]

The assumption is that it is basically made using a version of the transparent blahblahblahblah stuff they make the viewports in starships out of, only write large and with very complicated refracvtion systems such that when it is transparant, it is completely transparent (effectively invisible), and when it darkens, it is completely black.

I think it's physically impossible not to have a tiny bit of refraction somewhere in the air/ceiling/vacuum boundaries in fully transparent mode, but they could probably make it small enough that it wouldn't be noticed on a naked-eye scan. It would definitely show up if they tried to take precise laser measurements that passed through the ceiling at a very shallow angle, though, and a skilled meteorological analysis of the scan might spot an 'atmospheric anomaly' around the tangent-point where there's a small mirage against the ceiling.

It is not until the Drone turns clockwise as it styarts the visual sweep that you spot something that indicates this is far from standard. A few miles away is a massive wall. It stretches away into the atmospheric haze further than the Drone’s vision can see horizontally and vertically out of its line of sight. As the Drone’s view continues to shift, bringing it around to more or less opposite the Gate exit, you can see the huge wall does have an end, meeting a horizontal wall at ninety degrees. This second wall runs straight horizontally across the line of vision and out of sight as the drone completes its 360, like an artifical horizon. It too
must be also enormous to be visible even above the mountains.

Better?

Better. I'd still use "a more distant wall" instead of a "horizontal wall" in case the players think "horizontal wall" means "ceiling".