Dyson Spheres, and Updated Traveller

Our galaxy is an enormous place with billions of stars and doubtless billions of potentially habitable planets. Yet a single Dyson Sphere contains as much living space as all of those planets combined.

I can imagine an Imperium with it’s sole purpose and reason to exist being the construction and protection of human-habitable Dyson Spheres.

(Which are completely different from Matryoshka brains. Honest!)

We’ve talked about special purposes they can be put to, like moving a star via a Shkadov Thruster, or using one to toast planets thousands of light years away in the Nicoll-Dyson Beams episode. But we’ve never sat down and discussed it a dedicated fashion…

  1. So, I now know what the Imperial Navy wants for Christmas…
  2. Don’t forget the Hoopworlds! And the Discworlds! (The Shellworlds are probably too small-fry to really be part of this discussion. And yet, the Dyson Swarm/Dyson Ladder Isaac Artur will discuss are actually composed of good old-fashioned Rotating Habitats… possibly in vast size, and definitely in great numbers.)

One particular aspect of Dyson Spheres is that they don’t make too many appearances in science fiction, especially in Film or TV, even though they are often considered a near-inevitable path that advanced civilizations will pursue, for reasons we’ll get to shortly.

“You can’t handle the truth!”

So, we could reduce all Traveller into so many Dyson Spheres:

  • One for the Zhodani
  • One for the Vilani
  • One for the Solomani
  • One for the Aslan
  • One for the Vargr
  • One for the Hiver
  • One for the K’kree

And the partnership between the Vilani and (some factions on the) Solomani Sphere makes up the Third Imperium.

And everything else, including the billion-pop planets? Million-system empires of habitable worlds?


These things are immense, and would dwarf Earth, the way Earth dwarfs a small village. More in fact, a classic Dyson Sphere outfitted for human habitation is so large that if you randomly scattered every living human around one, they’d each have their own continent to themselves.

You might say that Dyson Spheres work on an Imperial scale.  😉

They are so big that if you only gave a one-page summary atlas entry on every continent sized area of one, it would require several million books and several thousand years to read.

Well, the Imperial Scouts has better get moving, yes?

Even what little [solar energy] actually hits photosynthetic plants goes mostly unused…

An interesting scientific tidbit, there.

What people tend to reference is a big solid spherical shell, where people live in the inside, but that is not what Freeman Dyson, for whom the object is named, actually had in mind. In fact, he wasn’t thinking of an object at all… and it’s never what I’m referring to on the channel either. Such a construct is virtually impossible to build, especially if you don’t have some form of artificial gravity available, but there are other ways and we’ll discuss them later.

Traditionally, the Solomani came late to artificial gravity, so I envision their Dyson Sphere (actually a Dyson Swarm: see below) to be numerous stations, ranging from a few kilometers to thousands of kilometers in size. This helps with the cultural fragmentation as well.

But there is more to the problem than this: you are going to need impossibly strong materials as well, and some way to keep that shell in place (as a shell is naturally unstable in it’s orbit around a star). That’s a good number of technical hurdles to jump, and a need for constant maintenance.

I’d set the Vilani Sphere for maximum stability and redundancy, able to run well with low power/technology; the Aslan Sphere for maximum living space; the K’Kree Sphere as one single flat plane (more likely a discworld than a sphere, or a swarm), less technologically advanced in some ways than even the Vilani Sphere (and a lot less ecologically stable!), ‘but it works’.

In contrast, the Hiver Sphere as a technological wonder, with all the bells and whistles (and more than a few physical impossibilities!)

The Droyne get a busted sphere, with only a few tens of trillions of survivors of the Ancient War holding on to the failing life support & power systems. The Zhodani Sphere, in a nod to their homeworld Zhodane, is remarkably underpopulated, with a mere quadrillion in population. And yet, they remain a real power, with their psionic networks (physical and mental powers) keeping them in the Great Power game… without going full Hive Mind.

At least not yet.

The original Dyson Sphere, typically known as a Dyson Swarm nowdays (just to avoid any confusion)…

The impossible ‘single shell’ format is now known as a Dyson Shell. Good thing Traveller is a work of fiction!

…is really just a giant cloud of object orbiting a star, thickly enough to obstruct most or all of a star’s light.

A myriad of separate space nations fits the Solomani well, so I would not change this for them.

The Aslan Sphere will still have this cloud of space stations outside the new set of high-tech (read: impossible strength) shells they are building. Instead of a hollow shell, the new shells it is filled with (figuratively!) uncountable layers, to use all the three-dimensional living space for MORE LAND AREA.

The Vilani started out like this, being the first spacefaring race (since the end of the Ancients) to 1) get jump drive and 2) build a Dyson Sphere. But soon after discovering artificial gravity, they re-organized all of their stations into a new, more efficient structure – the Rungworld – which we will see later. Still, they never created a single unified Dyson Shell: “the numbers say it’s impossible, so why waste energy trying?”

The K’kree skipped this phase, as they HATE being isolated, and don’t adapt well to three-dimensional living (or thinking!). Still, they eventually got the technology to make a single shell, so they did so. Being poor/low-tech for a Major Race for various self-inflicted cultural reasons, they didn’t use artificial gravity on their Dyson Shell to save costs.

The Zhodani worked their way up, from a Dyson Swarm to more efficient Rungworld structures. Much of their habitats are given over to wildlife and thinly inhabited wilderness preserves. I can still see them keep a few of the old-school Dyson Swarm habitats around, for old time’s sake.

If the swarm was composed entirely of O’Neill Cylinders, large rotating habitats 4 kilometers in radius and 20 kilometers long, with an internal area of 800 square kilometers, it would contain 350 trillion of them.

Assume three to ten million inhabitants per O’Neil Cylinder.

An O’Neil Cylinder is about as big as we can safely build a rotating habitat with modern materials,


Of course, even O’Neil Cylinders assume a moon colony with mass drivers to get the building material: getting that much material out of Earth’s gravity well is just too expensive without some nice planetary upgrades like orbital rings, launch loops or space towers.

and such a habitat might be sparely populated, a dedicated nature preserve, or home to millions. Also, while their rotation mimics gravity internally, they have virtually no real external gravity. This means that you could easily position them right near each other bound together by cables for vacuum trains, or even long, thin, pressurized corridor-habitats  just thick enough to offer comfortable spin-gravity to the traffic inside.

Even if you do have artificial gravity, there is something to be said for shaving off that expense, if you don’t really need it.

…they could be as close as Mercury or as far as Mars with no serious impediment to maintaining their function or climate.

More good info.

But if you restricted their orbits to 25 million km closer or further than Earth orbit…

These are all constantly moving, but if we took a quick snapshot of the system, on average each habitat would occupy a cube 3000 km or 2000 miles on a side, with them at the center all by themselves. The system is essentially opaque, not because it is densely packed, but because it is so thick, much as fog or clouds are… So collisions are not an issue because they are not close to each other at all.

“Space is big. I mean really, really big.”

Incidentally, these stations have enough access to solar power to “vaporise any debris that wanders their way.” Especially if they work together.

Now, around 12:46 in the video…

We have a type of megastructure known as a Rung World, which is like a Ring World but looks more like a ladder wrapped around in a circle, in this case around the sun. The individual rungs of the ladder are rotating habitats, each connected in that circle by either a cable or even a full-blown one-loop Topopolis, a kind of super-long thin rotating habitat we’ve discussed in passing before.

Such a Rungworld might be a series of a million O’Neil Cylinders connected by a pair of cables, one used for clockwise movement between rungs, and the other counterclockwise perhaps.

Or a good deal bigger, using the more high-tech McKenderee Cylinders. “A McKendree Cylinder is a rotating cylinder using graphene for a hull that can have a radius of roughly 1000 km” as the graphic states.

And whereas an O’Neil Cylinder is basically a decent sized island, populated by hundreds of thousands, a McKendree Cylinder is a continent-class megastructure that could comfortably house a billion people.

Connect these babies up as Rungworlds – the natural subdivision of a Dyson Sphere – and you’re good to go!

In the general swarm your neighbours might be changing a lot, here however, your neighbours remain in the same position on that ring.

The Vilani are not fans of change: the Zhodani also have a preference for stability, although not as strong as the Vilani do.

That would give you a lot more throw-weight in local disagreements too, it takes several million O’Neil Rungworlds to enclose a star, or several thousand McKendree Rungworlds, but even for a smaller one, it is probably better to be one of millions of larger entities than one of a few hundred trillion lone habitats.

It’s a lot harder to unify or control trillions of lone habitats, which is why a good-sized portion of the Solomani Sphere are able to sign up with the Third Imperium… and make their decisions stick over the vigorous (and violent) opposition of their neighbours.

Assuming that a Rungworld = a Ladder State (for political purposes)

Now one hardly has to jam-pack these things with people, but keeping to the modern human densities, we’d expect the average O’Neill Ladder State to have a population of around a trillion, and a McKendree Ladder State to be more like 100 trillion to a quadrillion. Don’t think of these as local super-powers either, compared to a full Dyson Sphere, even a McKendree Ladder State is essentially a micro-nation.

The population of the Canon Third Imperium, at her height, was around 10 trillion (GURPS) or 16 trillion (Digest Group).

Just saying.

To get the material, you can tear apart some of the minor planets – excluding Earth, for sentimental reasons – or use a percentage of the mass of Jupiter, or an even smaller percentage of the Sun’s mass, using starlifting to get your goodies.

The video then spends a lot of time talking about accessing and using the power of the sun, a major goal of any decent Dyson sphere… but not that interesting to me, personally. But just in case you are interested, you can use the power

  • to fire gamma-ray lasers (Grasers) to create small artificial black holes – a “Kugelblitz Black Hole” which can save that energy for a rainy day eon.
  • or use that Kugelblits black hole to power near-lightspeed black hole starships (inc campaigns where Faster-than-Light travel is banned)
  • or move that battery to power other space stations and habitats. They can be far from the sun… or far from the Milky Way, if you feel like.
  • or use Nicoll-Dyson Beams to push large starships to near-c. speeds, or burn worlds on the other side of the galaxy, or push ships around your own starsystem.
  • or to power up more starlifting (getting materials from the sun)
  • or make heavier elements out of lighter elements (for metal-heads, and metal-light areas of space.) “Again, not high-tech, just massive.”

Indeed, any star, even one with no planets locally, just maybe a few rocks to start the process, can be made into an optimum Dyson.


Talking about more starlifting stunts…

You can also use this technique to take very large stars and lower their mass until they won’t go Supernova, thus killing off any nearby life, and walk away from that with several million planet’s worth of heavy matter for construction elsewhere as a reward for your good deed.

“No good deed goes unrewarded.”

  • to set up Matryoshka brains
  • or Shkadov Thrusters (actually using a half-Dyson)
  • or extract all the matter of a star, and turn it to heavier elements (what Isaac Author calls Star Mining, or Dyson Mining)
  • or use it to power a massive radar, a Stellar Beacon, that you can hear galaxies away.

All Dyson Spheres can do any of these things, simultaneously, but there are advantages to specialization.

All of these concepts work around using a star as the central fuel source for some sort of engine or system, which is why these are also often called Stellar Engines. But even if you have better methods of power generation than a star, you still extract that matter to fuel those better methods instead, be it controlled fusion or raw matter to energy conversion.

Stellar Engines – for real interstellar civilizations!

You also still make the swarm because you want to be fairly close to other people or entities to minimize travel time on matter and information, and that’s as close as you can be without getting too hot. That’s a big note: Dyson’s do not absorb energy from a star. They temporarily absorb it, use it, and radiate it away as heat, or light in lower frequencies like infrared. If you did not, you would fry everyone inside, and the only way to avoid that is to break the laws of thermodynamics, which also renders a Dyson unnecessary anyway.

A Dyson is just as bright as the original star, only it will appear physically larger and more diffuse, glowing in the infrared range instead of the visible range of light. They also cannot be mistaken for any natural object.


You generally only go out of your way to hide in fear, and so you only hide a Dyson from something that is bigger or stronger than one, and since any Dyson civilization, a Kardashev 2 civilization, is quite capable of monitoring every single star in a galaxy, those contemplating building one know that anyone who already had one or better already knows where they live.

…and you can do a lot of R&D when a mere millionth of your population is ten trillion people, and a millionth is about what we use for any minor sub-discipline of the sciences, like how many folks specifically study dolphins full-time.

By the way, there are less than 10 million dolphins alive in the world today.

So, 10 trillion divided by 10 million = one million people, studying one dolphin, full-time.

…this is what we expect all technological civilizations to tend to converge towards, barring any radical changes to our understanding of physics. You’d probably have tons of smaller conglomerations of structures far out into deep space too, and interstellar travel is an automatic ability of a Dyson civilization so they’d probably have colonies nearby and be sending out more all of the time.

And when they meet…?

Why, that’s what we have Traveller for, of course!

We’d also expect each colony to eventually do the same; again, no real need for cooperation, even a single O’Neil Cylinder could probably manufacture a colony ark ship with just the kind of technologies available to them that we consider on the radar for the next century or so.


Hopefully by now you have a clearer image on what these things are and why so many of us tend to take their future existence almost for granted.

Traveller Notes:

Note that the only Dyson Sphere in Traveller is in Nooq Sector, Nooq 3201, as described in GURPS Aliens 3, page 124. The sophont race that dominates it are “The Inheritors”, who live in a hydrogen-flouride-sulfur-tetracloride atmosphere at 0.9 atmospheres, 300 F, and cannot tolerate gravity above 0.2 Gs.

Less than 1% of this ringworld have habitable modules, which equal 1,000 earths in living area (Page 128). Enough living space for the Inheritors, if they ever get organized and expansive, to set up a two-sector size empire, more or less.

(Note: this unnamed system does not exist at the Nooq 3201 location in www.travellermap.com )

There is a Ringworld at Leenitakot (Hinterworlds 1432, www.travellermap.com), but the Outcasts of the Whispering Sky, who control the system, have only allowed four expeditions to this site. It does bear a breathable atmosphere, unlike the Dyson Sphere. (The MegaTraveller Hinterworlds Supplement, page 4, Challenge 39).



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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