Living Inside the Shell…

…complete with artificial suns, spewing clouds as it traverses the space habitat and its unique ecology.

Now THIS is Traveller!

(But first, a brief digression.)

This is an information- and science-dense video — as is common from Issac Arthur — and not keyed to crazy adventures. However, with the long-lived Vilani lurking around (as well as that great Trav life extension drug, anagathaics), this video can make some good background info.

Also, any MegaTraveller / Traveller 2.0 universe that incorporates updated sci-fi concepts (Dyson swarms, a majority-spaceborne population, post-scarcity economics, etc.) will also have to include long, long lifespans. Even more fun character generation!

(And now… the Main Event!)

This episode is more immediately important for adventurers, so MUCH more detail will be given in my post below. Excellent stuff for all space adventurers, and the Referees that have to build these world of adventures!

Now, the massive copy/paste infodump from the video which makes up the bulk of this post:

(Because you can’t do real sci-fi without massive, Wall of Text infodumps!)

In fact, most people are surprised to learn that an enclosed manmade structure would develop weather systems–but they do, particularly when the whole thing is spinning and Coriolis forces become a factor. Even if you designed a habitat to replicate Earth’s environment as closely as possible, there will still be some major differences; and factors such as size, shape, rate of rotation, and lighting can radically alter the dynamics of an ecosystem.


Another term, before we jump into today’s topic, is the ‘axis’, the imaginary line down the middle of the drum, around which it rotates. The axis will come up a lot in this episode because it will be a fairly important and weirdly behaving place in our habitats. We often envision some sort of artificial sun that runs along that central axis like a cable, but the axis might also be an open space where you can enjoy zero-g recreation without a space suit, riding powerful winds or drifting along slowly among the clouds.


In the much bigger drums, the pressure will vary with distance from the axis, and on the really big ones like McKendree Cylinders, Bishop Rings, Banks Orbitals, or Ringworlds, pressure will vary with altitude like on Earth. The air gets thinner as you rise until you get to near-vacuum, but gravity remains essentially the same. Needless to say this results in very different weather than where the gravity rapidly drops off but the air pressure does not, and the mid-sized drums would be a bit of both, a big drop in gravity and pressure as you approach the axis.

That also means on the bigger ones you don’t actually need a closed habitat drum, or ring, because the air sticks there from spin gravity, but it can still spill off the sides and fly into space, so you need walls along the sides that rise quite high to prevent that, called rimwalls, as opposed to caps that the normal cylinders have.

One option is to stylize these as mountain ranges, and very tall ones at that, since while it’s hard to breathe atop Earth’s tallest mountains, there’s still atmosphere there and far above, whereas to contain the atmosphere of our ring habitat, the mountain walls will have to rise all the way up into the vacuum. These are very alien environments as we have nothing like them on Earth. One can imagine over time that critters could evolve to survive or even thrive on the tops of the mountains in a near vacuum. We already know that some organisms can exist in a vacuum too, such as tardigrades.


On Earth, mountains have a timberline, a height at which trees can’t grow anymore because of inhospitable conditions. You would likely still have these on the largest rotating habitats due to changes in evapo-transporative  forces. 

However, on the more modest ones, you might actually get the reverse. Gravity is lower near the axis, which helps trees to grow taller, but the air pressure isn’t dropping off, and for a lot of drum sizes you will have a tendency to get higher humidity as you rise. Depending on drum size, while on Earth it can rain during the day or night, these would be more prone to raining at night when the light goes off and all the water vapor condenses and falls down, as rain or snow.  Interestingly, I’ve never seen a depiction of a space habitat with snow, but I imagine it would be quite spectacular, an entire artificial world clothed in a sparkly white winter wonderland.

Redwoods, the tallest of trees, rely on fog for their water farther up, as it’s hard to transport water that high. If you’re on a cap mountain, with higher humidity and lower gravity, trees could potentially grow far taller than on Earth, with their canopies spread far wider. Imagine that sight, vast, interconnected canopies supporting their own layered ecosystems like we have in rainforests on Earth, but supersized, potentially with two mostly segregated ecosystems, one on the ground, one in the canopy above. They’d be fun mountain forests to visit too, as the lower gravity would make hiking around much more comfortable and safe.


It’s also fairly easy to make floating landmasses or structures inside the habitat drum. You just hang things from the tethers down from the axis. You’d probably have a lot to tethers hanging down as spokes anyway to ease transport around the place and put platforms for observation or maintenance on these.

Birds would adapt easy enough to low gravity flight and other animals might be transported up there or learn to climb or hitch a ride on the elevators. We have plenty of organisms living in the air too and if the gravity is low, flight or buoyancy can become easier, you might get weird seaweed equivalents floating around the sky, patches of skyweed blown by the air currents in the microgravity. End caps are the best place to locate your mountains, since they would place less stress on the hull.

However, your cylinder need not be smooth any more than it need be flat-capped, and you can distort the habitat’s hull to create hills and lakes, you can also use some light but sturdy material like aerogel to fill those fake hills. Though, for your typical drum, you’d have a problem keeping the drum structurally sound if you modified it too much, and even aerogel isn’t so light you could disregard that mass if you were piling it into mountains. So you’d probably limit yourself to hills and valleys and save the mountains and canyons for the sloping caps.

This also means that you are getting that normal feature of rivers running down out of the mountains into lakes below, and same as the caps don’t have to be flat, the drum itself need not be a cylinder, it could bulge near the middle for instance, and there gravity would be a bit higher and you’d get a belt of water.


Weather in a drum is normally going to be fairly mild, enough that you might need to take steps to get some decent wind and storms in them to support an ecosystem’s seasonal cycle. However, this means that you’ll need to take steps to maintain the interior. As even gentle rain or wind wear away at the landscape over time. Now the weather on such habitats will for the most part be similar enough to Earth without much monkeying around, but more mild.

We’ve focussed on rotating habitats, but the reverse is true on bigger artificial worlds we sometimes discuss like Supramundane planets or Mega-earths.

The two biggest factors for weather are sunlight and spin. A Saturn-sized planet turning once every 24 hours to mimic Earth, just a hundreds time larger in surface area, is going to have some vicious winds. As would donut shaped planets like the Hoopworld. Actually, wind speeds on gas giants are almost always in excess of the most violent hurricanes of Earth. On those, you can break it up by including mountain ranges for them to slam against and slow, and you can use this trick inside smaller rotating habitats to help funnel the air around to create more variation and focus areas of high wind for ecosystems that need it.

They can also be used to help vary temperature and precipitation, if you don’t want a single climate across the habitat. For that matter, you will also want to vary your lighting levels, spectrum, and duration to simulate seasons.

Seasons are pretty critical to ecosystems, impacting everything from pest control to reproductive cycles, though one handy thing about such habitats is you can arrange those to be different in severity or duration than on Earth. The weirdest thing about the sky on rotating habitats though is that it doesn’t exist: look up on one and you see your neighbors backyard hanging overhead. 

There’s many ways to deal with that, if you feel a need to,

Good point Arthur made here: you may not feel the need to see the stars and a sun when you look up! For a civilization that has been starfaring for a long, long time (waves to the Vilani and their 10,000 years in space), it may be the standard assumption that you can see your neighbour’s farm by looking up, and a primitive/mystical convention to see the stars when you look up, “the way our Ancestors did.”

(BTW: this is not true in Canon Traveller, not even for the Vilani. In Canon Traveller, most people live on planets, not in space habitats. And just ONE world per system dominates the local demographics, according to Traveller’s out of date System Generation procedures.)

but the most blunt force trick is to stick another small cylinder painted blue inside your drum, maybe with lights in it to fake stars at night. You could stick a lot fins and baffles on such a thing, that could be folded up or extended to push the air around, not really an elegant solution but it does work, and it would be pretty natural looking, even without getting sophisticated and using LED screens, it’s not like painting a sky mural on your ceiling. Though if your sky cylinder is covered in a ton of pixels faking the normal sky, day or night, I could easily imagine companies buying billboard time on those.

However, you shouldn’t need to go that route on larger ones at all, air distorts and absorbs light and water vapor does too, and as mentioned in many of these it will tend to accumulate toward the axis in the day time. You should get normal enough cloud formations and haze breaking up your view of the other side of the drum, and it might get a lot more since your artificial sun might need cooling.

There’s many ways to light a drum, you can let light in through side panels in the drum or through the caps using mirrors, you can have a big lightbulb down the middle like a fluorescent tube, but if you’ve got a fusion economy you probably have a big Sun on a trolley that moves along the axis. Such a thing likely needs coolant and may use water as the working fluid for turning its turbines for power generation, and so would be quite the cloud factory. Indeed that’s what we call the nuclear plant in the town over from me, since it’s always visible by the clouds the cooling towers put out. Picturing a big white or yellow sphere on a trolley, trailing clouds, is probably not quite right though.

An artificial sun trailing clouds sounds very exotic, though. Just what I’m looking for in MegaTraveller/UltraTraveller/Traveller 2.0!

In some you might have a noon-spectrum lamp in the middle and red on the edges, pointing their light at an angle, to simulate twilight. This would have the downside of having different times of day throughout the station and that might not be desirable. I don’t really want time zones in my O’Neill Cylinder the size of modest island.

Timezones in an O’Neill cylinder. Hmmmm….

[Discussion on trolley suns, Hoopworlds, and Circle Worlds snipped.]

For now, the neat thing about these, is that if you have a trolley sun moving down the  internal axis of one, it will rise and set just like normal, as it comes around the curve of that torus’ interior. Though you might use multiple such trolley suns spaced around to get the right day night spacings. You’d also get a steady breeze moving along with the trolley suns as they moved. 

So while these would seem at first to be more exotic than a rotating cylinder, they would actually mimic Earth’s environment more easily.  Incidentally you’re not necessarily using reflected sunlight or fusion power for these suns either, kugelblitz black holes of the feedable type are ideal for fakes sun inside rotating habitats or as sun-moons orbiting artificial planets, provided we filter out the dangerous ionizing wavelengths or convert them to other wavelengths.

The amusing thing about using black holes and their Hawking radiation for lighting is that the bigger your space station is, the smaller the black hole you need to light it, since they grow more luminous as they get smaller, but even at the size of an O’Neill cylinder, the mass needed for such a black hole sun is less than that of the station.

[…snipped power management issues…]

Alternatively, since a cylindrical habitat is basically a giant flywheel in a vacuum, you could slow it down a little, lowering gravity, during the day to augment your sunlight power supply, and then dump that power into spinning it up at night.

It might be interesting to live some place where the gravity was normal at dusk and dawn, but maybe 10% lower and higher at noon and midnight. Get a little spring in your step midday and be a bit more lethargic at night. Needless to say that would do peculiar things to not only the weather, but also to the ecosystem, and peculiar isn’t necessarily bad.

A Traveller should discover – and, normally, enjoy – odd and unusual situations.

Now you can have some complete ecologies in fairly small places, even a single petri dish, and even ones including more than microorganisms can be fairly small and complete, or close to it, but by and large we have to accept that any artificial habitat significantly smaller than a continent is going to have some gaps we’ll have to plug with artificial means.

We do have some habitat designs that big or bigger, and for those, we have an easier time creating a stable ecosystem. You might need to maintain a gene bank to artificially insert diversity through cloning or genetic modification, or bring in stock from neighboring habitats. You might need to augment nutrients or fill ecological niches with artificial roles, like tiny robots drones that mimicked bees for pollination. You might use bees or hummingbirds for pollination but have to modify them and other organisms that navigate off the Sun or magnetic fields, so they could navigate off what the habitat has instead. In small habitats you might need to tinker with their genetics so they used something else, and it might be amusing if a habitats bees and birds navigated off the wifi signal inside… which it would presumably have, especially since by default a cylinder habitat is a giant faraday cage so signals from outside need to be received and repeated inside.  Now speaking of bioengineering, all such environments will need constant maintenance by people, not just ecologically, but also mechanically, and for their landscape, and since the critters living inside might need some genetic tweaking, you might as well get them to do some of the work for you.

This has some amusing implications. There’s a theme park in France where they recently trained some crows to pick up trash, and while getting critters to collect trash and take it to deposit site in exchange for food might be hard to do in the first generation, over time or with active intervention, it could be done with many critters. One can probably engineer it to be instinctual if needed, but it’s likely that for many species after you train the first generation or two, parents would teach their kids what to do and which bits of trash are safe and what they got for them. I can imagine after some generations squirrels fighting over cigarette butts or bottle caps as enthusiastically as lions fighting over a kill.


As we mentioned in Space Farming, while you can obviously farm the interior of a habitation drum, you’d likely do most of your food production in simpler, cheaper and more optimized auxiliary space farms near the habitat. So you could produce extra to bribe and pay the critters who can now live in greater numbers. One might also imagine how that might mutate down the centuries as they slip into these ecological roles and add new niches, more scavengers and pirates too, the hawk swoops down on the squirrel not to eat the squirrel, but to steal its bottle caps, and the squirrels bury their bottlecaps for the winter, so they can take them in to the recycling center for food in the lean months.


Our preferred material for making rotating habitats is assumed to be graphene, which is made of carbon, we are carbon-based life, so one might imagine creating organisms which live on the hull and go around eating damaged and micrometeor scarred sections and replacing them with newly spun bits. They might be more machine than organic, or based on an entirely different organic chemistry, but not necessarily

Ah yes, the Cymbeline Chips – the source material of the AI Virus that wrecked Charted Space.

Again we’ve got some very bizarre and robust extremophiles already and often find new ones dwelling and even thriving in environments we’d call barren or even toxic. Finding things that eat plastics or metals or silicon or possibly graphene wouldn’t be that weird, and as time passes they become more likely. Where evolution is involved, if there’s a niche, a food source, something will eventually exploit it.

We’ve now created a new ecosystem outside of the drum, one that might evolve into a very alien one too. This makes mutation a concern as well, because if you make a bunch of organisms that eat graphene hull plating and spin new bits, you will eventually end up with ones that eat undamaged sections and others that adapt to eat each other. This would tend to happen with self-replicating machines too, and I should note that we can do things to curb their mutation rates, but we can also do that to biological organisms. There’s no particular reason you can’t build a checksum function into a robot’s equivalent to DNA, one of many methods we use for data integrity when copying it, to cut down on mutation, and you could probably build that into normal DNA and biological organisms too.


There’s a habit in science fiction of having us come across artificial worlds and habitats abandoned by their makers or who went primitive. I think that’s unlikely but it makes folks focus on how long such places would last without maintenance. To me, that’s a bad way to look at it, the Earth isn’t static; it’s likely most planets that started off like Earth lost their atmosphere or oceans, and if they ever had life, lost it with them.


There’re endless options, and while I think most habitats would try to mimic Earth as close as possible, I’d imagine almost all of them would choose to have at least one peculiar feature that stood out. Be it gardens in the clouds or a sun that gave very long sunsets or environmental controls that made sure it was always Sunny on Sundays. Or freakishly tall trees with enormous canopies spread out across the lower gravity sky, home to whole ecosystem living in those branches. Or ones that incorporate calcium carbonate into their bark and die as small limestone mountains. Or squirrels that rob tourists of their chewing gum so they can turn the wrappers and gum in for treats. A little uniqueness never hurts, and who can say what other interesting things might emerge over time?

===Aside below===

Traveller has always leaned masculine: conquest, exploration, and trade. But there’s another part of the masculine spirit that should be developed: creation. (A.k.a: “recreation”, “creativity”, “sub-creation”, etc.)

Sadly, the joy of building worlds and societies is usually hogged by the Referee. He should consider being more generous: not only will this increase the fun factor for the players, but it will also increase their emotional investment (and emotional payoffs!) in the game!

It’s all about the storytelling: and the setting is a big part of the story!

===Aside above===

(Bonus material, tied to long-term space habitats and starships.)

When a Traveller is going on one of those long, long multi-generational journeys, it pays to stock up.

You also need to keep stockpiles of reserve raw materials around. You will be losing some with even the best recycling and whatever you are using for power will be slowly depleted — that will likely need to be atomic (be it 25:42 fusion or fission or even passive decay) but such materials are energy dense enough to allow you to power a ship for millions of years.

A thing to remember: some materials have half-lives short enough that a million years might deplete them so you will be losing mass to various factors no matter what you do and that loss can stack up. Just an example: a ship that lost 1% of its mass to outgassing or lost parts every century — a very high rate of efficiency — would arrive just fine at a nearby star a century away. One on a voyage of a thousand years would have lost just under ten percent of its mass. It will be down to 37% of its mass in 10,000 years, and will be down to just 0.0043% of its mass in 100,000 years.

In a million, even a ship that started out the size of mountain would be down to a single atom so you need to do way better than 1% loss a century with an effective ship half-life of 7,000 years. Or you need to be able to pick up material along the way.

For the first, we have some examples: and again, bigger is better. Earth is a spaceship and one working fine after 4 billion years of travel: we do lose material but fall slower than 1% a century. The bigger your ships are, the easier it is to prevent losing mass. You can have thicker ship holds, even multi-layer holds that leak less: and little cracks or losses to an airlock are proportionally much smaller. Build big enough and you’d actually retain some material by gravity but you have to get very big for that and we will discuss planet ships another time.

Planet-sized starships…..


“Will the Scouts reading this please control yourselves? You’re shorting the electronics!”

Now to gather material along the way you either have to stop fairly often or be keeping to speeds that allow you to profitably gather materials. That start-and-stop method is something we’ll discuss more later, to, in “Gardener Ships” since it would tend to make sense to stop for a while and set up a colony then move on, and do it again.

Nowhere in Traveller Canon do we encounter traveling gardener ships: something that should be a Solomani specialty. “Spread life and spread the Race, right across the galaxy… and beyond!”

We also have the “Pac-man” approach, where pods are sent at fairly similar speeds so the ship need not slow to gather those resources. As to grabbing resources as you go: this all has to do with your internal power plants. If you’re flicking along at 2 or 3 percent of light speed on a fusion engine, you can probably absorb interstellar gas as you go: and we’ll find it for fusion fuel and heavier elements. But if you’re going much faster trying to suck that matter in is going to result in slowing you down by more than the energy in that fuel is worth. If you run on uranium or thorium — much rarer than hydrogen and much lower in energy density than fusion — you’ll have to go even slower. Alternatively, if you’ve got matter-to-energy conversion or a black hole drive (something will also discuss more later in the series) you can probably achieve a cruising speed of more like 1/2 of light speed.

So, you get an FTL Imperium using its reactionless engines to catch up to a STL generation ship.

“No FTL? No reactionless drives? No fusion power plants? How primitive!”

“On the official Imperial technological scale, yes. But that primitive, slower-than-light starship we’re approaching has black hole drives and antimatter power plants. Maybe even those zero-point energy devices and pure matter-conversion plants those Solomani sci-fi writers are always ranting about….”

About Alvin Plummer

I'm working to build a better world, a world that blesses Christ and is blessed by Him. I hope that you're doing the same!
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