What would you see from inside tubular ringworld?

[AotrsCommander]

And some other questions.

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," 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.

 

[andrewkirk]

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)

I don't know what you mean by upper and lower. To talk unambiguously about a structure like this, some terminology needs to be devised. I am reminded of Terry Pratchett's Discworld, in which the word Turnwise (Widdershins) is used to indicate the direction along the land surface that is aligned with (against) the direction of rotation.

First note that the rotating ring structure has an Axis of Rotation, around which it rotates. There is also an Equatorial Plane, which is perpendicular to the axis of rotation and cuts the ring into two presumably symmetric halves, each of which is also a sort of ring.
Now imagine two points on the axis of rotation, each 100 thousand km from the equatorial plane, and 200k km away from each other. Then looking from one of those points the ring appears to be turning clockwise and from the other, anti-clockwise. Call the two points the North and South Poles respectively. At any point on the ring, call the direction that points towards the axis of rotation Proximal and the opposite direction Distal.

Presumably the ring is a closed hollow surface, otherwise it could have no atmosphere. Assume people walk on the Proximal side of the Distal surface, which is flat in the North-South direction, except for maybe local hillocks and troughs. We call that surface the Ground.

What shape should the rest of the surface of the ring be? It could have a rectangular cross section, with flat glass walls on the Northern and Southern boundaries of the Ground, and a roof that is flat in the N-S direction. It could have a semi-circular cross-section, so that it is the part of a torus. Semi-circular would be stronger, but would cause atmospheric pressure to vary along the N-S direction, being greatest at the Equator (the line around the Ground where it meets the equatorial plane) and least at bases of the Northern and Southern walls. But if most pressure comes from forcing gas into the ring and then sealing it, rather than from the weight of the atmosphere (as on Earth), the height of the walls could be low (eg 100m, unless they want to have aeroplanes) and pressure variation between equator and N/S walls would be minor.

Let us call East and West the directions along the Ground that are perpendicular to N and S and point respectively against and with the direction of rotation.

The concern that immediately strikes me is how the ring can be arranged to get regular, appropriate variation between day and night. It is not enough to say that the glass darkens because half the time on average a given point on the Ground will be facing away from the sun and get no light. There is also the question of the orientation of the axis of rotation relative to the sun. It may be hard to avoid extreme seasonal variation in temperature, because the direction of the axis cannot change with the time of year, unless there are incredibly powerful rockets used to do that, and the energy requirement for that would be phenomenal.

But I've got to go to work now. I hope that helps.

EDIT: Actually the sunlight problem can be solved by having the axis of rotation close to perpendicular to the orbital plane of the ring around its sun. If it is perfectly perpendicular, each point on the Ground will get light for half a period of rotation and dark for the other half, all year around. A small portion of the sun's light will be blocked by the far side of the ring, but that should not be significant, provided the N-S width of the Ground is small in comparison to the circumference of the ring. If the axis is tilted slightly, seasons would arise, as they do from Earth's tilted axis.

To obtain Earth-like gravity purely from centrifugal force, the ring would either have to have a much bigger radius than the Earth, or a much faster rotation rate, which would mean shorter days.

 

[AotrsCommander]

Okay, it's a bit late for a more sensible reply, but here is a hopefully more illustrative CAD scribble-sketch of what I was thinking about that I knocked up while fighting with Total Warhammer 2.

The gravity down-direction would be towards the exterior tube; "up" - from the ground - would towards the sky (though at what point that would be "up" compared to the centre of the tube verses towards the sun I'm not so sure about).

The "top" is what might be the north pole on a planet (in this case, taken to be "above" the orbital plane, with south being the "bottom" - "below" the orbital plane.

 

[stefan r]

...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").

..."standard" artifical gravity is generated ...

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?...

Earth's atmosphere is mostly under the Karman line. A glass surface would be excessive. Hydrogen filled plastic bubble wrap would work better. Maybe two or three layers if you are paranoid. The floating plastic would push down the air a little. Holding the bubble wrap down with web of tension lines would be less fragile than a glass span. So you could keep most of the atmosphere much lower than 100 kilometers.

It was not clear to me the size of "similar to earth". You are describing part of a torus. Does the axis of revolution have a 6,374 km radius or is the radius of the circle 6374km? You can make a horn torus where they are equal. But that does not look like your drawing.

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?
...

"Upper" and "lower" is completely meaningless in that picture. If the light source is a rack of LEDs then you can illuminate any part of your tube. If there is a Sun involved you get a wide range of seasons which will depend on where/how the doughnut is orbiting the sun and on which way the doughnut's axis points. You also need to specify if the "ground" is insulated.

The closer the surface gets to the axis of rotation the more it will be like a steep mountain. Temperature's drop as altitude increases.

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

Some serious proposals:
Bernal Sphere
Stanford Torus
O'neil cylinder also McKendree cylinder

Awesome science fiction rings made from unobtainium that are worth knowing about:
Banks orbital
Niven Ring

 

[AotrsCommander]

After consultation with another thread in the meantime and somethinking (not as much as I would have liked, because I had serious computer issues last week) I scrapped that idea and went with this:

(Having snipped out the least relevant bits pertaining to the adventure slash background.)The ancient unknown builders began to create a ringworld around a dwarf star with a radius of 0.2 AU. The ringworld is about 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 Earth-equivilent 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 centred on and perpendicular to the orbital plane, with the “top¹” 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 habitable area is surrounded by a layer of atmosphere inside a transparent metal surface, which can simply be darkened to create a night.

The aforementioned "view from the tuberingworld segment" is thus (read-aloud-text text copied wholesale - the PCs are sending a drone recon through and watching the telemetry):

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.

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.

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 (the gate direction being technically “south”) is ten miles distant and 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 traveling 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?

¹As standard for for non-typical systems the organisation in question, "top" or "north" is designated specifically as "perpendicular and away from the orbital plane's spinward (anti-clockwise) direction."

 

[Tiran]

If the tube is 8000km in diameter, there is only going to be habitable in the lowest 6km (6km above the outermost diameter). That means that the vast majority of the tube will be close to vacuum and the beginning of the glass will be at an altitude of 4000km. Despite 12,000km of "land", the actual habitable width will be a strip a few hundred kms wide in the bottom of the tube, like a trickle of water running through big pipe.

That's why the usual cross section is a flat bottom with 100km tall walls and roof. Anything else is a waste of materials.

 

[DaveC426913]

The sun appear to be directly overhead – it must be almost exactly midday – and there are few shadows.

Sorry, maybe I missed a bit of exposition. Doesn't this tubeworld have its sun at its centre? If so, it would be eternally midday.

 

[DaveC426913]

The closer the surface gets to the axis of rotation the more it will be like a steep mountain.

Surely the axis of rotation runs through the centre of the torus. i.e. nowhere near the torus itself. (OP did say it was spun up for gravity.)

Certainly, the denizens will feel like they're in a long valley with increasingly steep slopes to either side.

But I'm not sure what you mean by "The closer the surface gets to the axis of rotation".

 

[DaveC426913]

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.

This is a common depiction of atmosphere in ringworlds. In general, atmosphere becomes opaque over a few hundred miles. So when you're looking through it the "long way", the landscape fades out. But at some point, far enough along the ring, you not looking through a thousand miles of atmo - you're looking down into the atmo from above - which, in ringworlds, is often only 100 miles thick.

So, you can see land in the close distance, and in the very far distance, but not in the middle distance.

 

[stefan r]

Surely the axis of rotation runs through the centre of the torus. i.e. nowhere near the torus itself. (OP did say it was spun up for gravity.)

Certainly, the denizens will feel like they're in a long valley with increasingly steep slopes to either side.

But I'm not sure what you mean by "The closer the surface gets to the axis of rotation".

I think I used correct wording. When I climb onto a table I stand 1 meter closer to the clouds. That does not mean that the table top is anywhere near the clouds. It is just 1 meter closer than the floor. I was trying to avoid the words "up" and "higher" because that can be confusing. "Hubward" should be the same as "up".

A point 6,999 km from the hub is 1 km away from a point 7,000 km from the hub. It is "1 km closer to the hub". Climbing 1 km should change the atmosphere in a way similar to climbing to 1 km elevation on Earth.

Sorry, maybe I missed a bit of exposition. Doesn't this tubeworld have its sun at its centre? If so, it would be eternally midday.

The original post has the radius equal to Earth's radius. The Sun at the center would be problematic. Wikipedia says the smallest know star is EBLM J0555-57Ab. which has 10 times Earth's radius. Most white dwarfs would not fit. Sirius B could squeeze in but the tube would still be highly irradiated. Glass and iron would boil. I doubt that would work for his short story.

Larry Niven's ringworld had a star at the center of rotation.

 

[DaveC426913]

I think I used correct wording. When I climb onto a table I stand 1 meter closer to the clouds. That does not mean that the table top is anywhere near the clouds. It is just 1 meter closer than the floor. I was trying to avoid the words "up" and "higher" because that can be confusing. "Hubward" should be the same as "up".

So you mean "When you move toward one of the two edges, the surface will rise before you like a mountain."