Our Future in Space Habitats: More Thoughts

space habitats

Space habitats and colonization are one of the topics I blog the most about, because I find it quite interesting. Why confine your civilization to a planet when there’s a whole universe out there filled with resources that you can turn into custom-made habitats fit for your people to live in? Mars and the other planets would be wonderful places to visit, and will hold enough attraction for many people to move there, but I have a feeling that the real action in space colonization, especially over the longer term, will be in outer space itself.

Space Habitats in my Science Fiction Setting

I have incorporated this into my very own science fiction setting, where “The Hunt for Count Gleichen’s Treasure” and “Dear Future Me” are supposed to take place, along with some subsequent stories. In “The Hunt for Count Gleichen’s Treasure” the protagonists visit a colony of the Stanford Torus type (a wheel with spokes radiating out from a central module, sort of a star-shaped craft) that orbits Enceladus, hosting a community centered around research of the life down on the moon, which in my setting is complex, not unlike Earth’s deep sea creatures.

They also later visit a transport ship ferrying personnel from a colony in the inner Oort cloud; this transport ship is itself a space habitat, in this case of the Bernal sphere type. In “Dear Future Me” the entire story is set in another space habitat of the Stanford Torus type, this one in low Earth orbit and functioning as a combined tourist destination and transportation hub for transfers from low Earth orbit to destinations further afield.

So space habitats abound in my setting as early as the 2020s (keep in mind this is an alternate timeline, with human spaceflight beginning in the 1940s and the first space habitats being built in the 1970s). Even so, the infrastructure remains relatively undeveloped; Earth still harbors the overwhelming majority of the human population, space habitats and colonies as proven concepts are roughly half a century old and still somewhat experimental, and enormous swaths of space in even the inner solar system, let alone outlying regions, are wildernesses devoid of regular human activity.

Gerard O’Neill didn’t call space “the high frontier” for nothing, and of course who can forget Star Trek’s description of space as “the final frontier”? As I pointed out in a previous post on space demography, even within our own solar system population density will remain extremely sparse for a very long time to come.

The vast Wilderness that is our Solar System

Asteroids and comets today contain most of the solar system’s surface area, at over 10,000 times the amount found on Earth. It would require a population of 80 trillion even to populate this area to as much density as found on Earth today; even with perpetual Baby Boom level birth rates it will take centuries to reach that figure. And that’s not even taking into account the fact that space habitats have a far more efficient surface area-to-volume ratio than asteroids and comets, so the true figure might require millennia to achieve.

For perspective, spreading today’s human population out over a surface area of 10,000 Earths, which is the extreme low end of what’s possible to build with space habitats in our solar system, would mean each Earth-sized tract of land would have a population of 700,000. Such a low population density wouldn’t even need farming or ranching to support itself; you could easily support 200 times that population density through hunting and gathering.

This population density is 85 square miles per person, which is sparse indeed. As humanity spreads throughout the universe, into other solar systems, the area multiplies, and if population doesn’t constantly boom it becomes possible to reach almost arbitrarily low population densities. In another post, I calculated that if you spread the current human population over the whole visible universe the density reaches the almost incomprehensibly sparse figure of 500 trillion solar systems (or 1 octillion square miles) per person. If we assume the universe is infinite it can of course reach arbitrarily low figures.

Even the universe we see provides a level of abundance in resources that is hard for us to imagine. The idea that we are running out of resources, even cheap resources, is absurd; if we swallow our radiophobia and embrace the full potential of nuclear pulse propulsion, which could lower launch costs enough to enable a person (or the equivalent weight) to be transported to orbit for six dollars, the entire solar system becomes as easy to access as a downtown is from a suburb today.

Casual Interplanetary Travel in the near Future

Casually going on and off planet and to and from space colonies separated by millions of miles will be a fact of life, as natural to them as the automobile and the highway are to us. People in this future will find it hard to imagine that there was ever a time when a human mission to Mars was thought of as expensive, long, and arduous.

This future to be fully realized requires great innovations and economy of scale in the shaped-charge hydrogen bombs that power nuclear pulse propulsion, as well as the scale of traffic demand needed to fill the cargo bays and passenger cabins of spaceships millions of tons in mass, big enough to be small cities in their own right. This might sound crazy but none of it is unrealistic; it would require only incremental improvements on technology that was already demonstrated in the 1960s.

In my science fiction setting they are considerably further toward that goal than we are to say the least; however, as of 2020 much improvement remains to be made in the manufacturing of hydrogen bombs, and most importantly there are not the thousands or even millions of people per day going between Earth and space to support nuclear pulse ships of the “$6 per person” scale.

Now, one of the cases made for space habitats is that the delta-v (change in velocity) needed to go between them and from them to planets is much less than from planet to planet, so why would people live in space habitats if they can live on a planet and just hop on a ride for six dollars to another planet?

Space Habitats: Better than Planets

The answer is the possibility of a custom-made environment. No matter how easily you can travel from Mars, you still have to live on Mars, which for many people won’t be desirable. Ditto for the other planets. Even in the extreme case of terraforming, the gravity will still not be the same as Earth. With space habitats, you can have it all in your living environment, and then visit Mars or Earth when the urge to see something different strikes you.

Which brings us to another crucial advantage: mobility. Nomadism is in our blood; humanity is a race of wanderers, and in the absence of economic pressures to the contrary this trait will inevitably reassert itself in the spacefaring future. With a space habitat, if you want a view of the Earth close-up, you can just move your habitat to Earth orbit, and ditto for the other planets. Try doing that with a colony built into a Martian crater!

Admittedly a colony could be designed to land on a planet and then lift itself back up, but it would likely be more efficient to use separate structures for these two tasks. A centrifuge spinning makes a poor planetary colony, and a dome with a flat floor makes a poor spaceship unless 1g thrust is constantly applied to it to generate gravity. The best that could be done is to attach the dome to a tether and spin it around with a counterweight (another colony) at the other end, sort of like the classic rotating wheel with only two slices of the wheel instead of the whole thing.

Environmental Diversity through Space Habitats

Another destination that space habitats would like to be near to is other space habitats, because the custom-built environments allow for a wide variety of landscapes and climates to be located right next to each other. You could have a beach paradise habitat and a alpine skiing habitat located right next to each other, with only a few miles’ trip by shuttle separating the two. A rain-drenched habitat and a desert habitat could also be located right next to each other. These colonies are all more or less sealed environments, so the owners of each colony could have whatever environment they pleased without it affecting anyone else.

Habitats deliberately placed near each other would of course be only a few miles’ trip, but what about the more ordinary trips between habitats that aren’t located right next to each other?

The Prospects for Inter-Space Habitat Travel

It’s likely that the band of the inner solar system near Earth will see the greatest density of space habitats, at least at first, due to the easier travel time to and from the homeworld. The less alien temperature conditions might also help somewhat. Over the longer term more exotic and further-flung destinations will likely prove more popular, but we’ll confine ourselves to the nearer term for this exercise.

In a future of casual space travel 1g constant acceleration will be the standard for spaceships, because this is the fastest acceleration that is comfortable for humans. If space habitats are spread out all along Earth’s orbit around the sun, the furthest-flung colonies will be 2 AU away from each other, which at 1g is a 4 day trip.

6.3 AU is the circumference of Earth’s orbit, and if we assume 100 space colonies are spread out evenly along its orbit the average travel time to the closest habitat drops to 16 hours. 1000 space colonies would imply average travel time of 5 hours. You would have 44 space habitats within a day’s journey. Of course there are many assumptions that go into this. More likely the colonies would be spread out in a cloud-like formation around Earth, so the true fraction of habitats accessible within a day would be much greater.

As we spread across the solar system, though, travel times will inevitably lengthen. Saturn, for instance, takes 10 days at 1g. Virtually everywhere within the solar system inward of the Oort cloud could be reached within two weeks, though, so it wouldn’t be too bad.

The Costs of building Space Habitats

The expense also probably wouldn’t be too bad. Building space colonies now has costs quoted in the trillions, but this presumes lifting material to orbit at costs of thousands of dollars per pound. At a cost of more like ten dollars per ton, which is what nuclear pulse propulsion provides, a ten million ton habitat, the minimum feasible mass for the classic space habitat designs, would be more like a hundred million dollars.

And that assumes it’s all lifted from Earth! If the material is extracted from asteroids the launch cost would be a small fraction of that due to much lower delta-v. At that point the cost to actually mine it and fabricate it would dominate calculations of the total cost, just as it does on Earth. Launch costs would be a small fraction of the total cost. These costs wouldn’t be too different from structures on Earth. It’s surprisingly inexpensive to merely make a given space airtight against a vacuum.

When you consider that in such a future the population will surely be much wealthier than today, and correspondingly more able to bear the costs involved, it suddenly becomes apparent that building a space habitat becomes an almost trivial expense. It would become well within the price range of even affluent individuals; almost all groups and organizations of significant size will easily be able to build their own.

Independence for All who want it

This enables effective independence for anyone who wants it, since by this point the technology needed to live off the land, especially asteroids and comets, and be self-sufficient will be trivially accessible and affordable. Sheer distance will deter any other political power from bothering them; on the off chance that happens or is threatened, they can just retreat further into the infinite black expanse. This process can be repeated forever.

When we colonize space and become this advanced it will mark the end of the oligopoly enjoyed by today’s sovereign states. They will have to accept the reality that some people will escape their control. If you want political independence or sovereignty in the spacefaring future badly enough you can have it.

This applies at even the household or individual level, since artificial gravity can be attained by placing your homestead on a tether and spinning it around with a counterweight. There is no particular minimum size or population for a space colony or habitat.

In my science fiction setting by the 2020s there are homesteaders in space who use this technique, and there are many space habitats, though they don’t yet come remotely close to covering the solar system.

Space Habitats to Alpha Centauri

An interesting aspect of my setting is that a large-scale and long-term project is undertaken to send space habitats to the Alpha Centauri system as part of humanity’s first manned interstellar mission. This mission launches in the 2040s and reaches Proxima Centauri in the 2060s, providing the backstory to my latest story, “Letters from the Airy Deep”. The protagonists, explorers of Thalassa, Proxima Centauri’s verdant ocean planet, come from one of the habitats that are sent to the system; indeed, they were born there during the journey.

My concept for this mission is that a population sufficient to sustain a modern industrial civilization is sent to the new solar system, which in my view would be at least a million people or so. This could be accomplished with only two large cylinders, but a diversity of craft are likely to be sent to maximize the chances of success. If each habitat harbors 100,000 people then only 10 habitats would need to be sent; 100 habitats could send 10 million people. In the actual story I leave the exact numbers vague since I haven’t decided on them yet.

In any event these millions will only be the first of a long stream of colonists heading to the new solar system, particularly given the great discoveries they make on Thalassa, leading it to be called Earth’s sister planet. Given the fact that Thalassa’s atmosphere is breathable, that attracts a lot more attention than a few deep sea monsters on Enceladus does.

The trip times are truly extreme, though, amounting to 20 years even with breakthroughs in solar sail, magnetic sail, and nuclear pulse propulsion all combined together. Laser propulsion is used in the 21st century in my setting for small cargo, and at 1g can bridge the two systems in 6 years, or 3.5 years ship time (time dilation becomes a factor at these speeds).

100g or so might be the practical maximum for acceleration using any propulsion method, and even that would still take a bit over 4 years, close to the time light takes to travel the gap, though from the point of view of the ship it would take more like a month.

Growing Faster than even Nuclear Pulse can Outrun

In the long centuries and even millennia I’m planning for light speed to be the barrier in my setting, that might be the fastest anyone or anything can travel. This limits how low population density can go in that time, and invites the possibility of population growth catching up with mankind, gradually densifying our galactic neighborhood.

Admittedly to catch up with the 20%-of-light-speed spread of colonists population growth would have to be pretty high, but it is not a crazy scenario, especially over thousands of years of time.

In my setting natalist sects who believe in natural fertility, i.e. not limiting population growth and marrying and bearing children as early in life as is feasible, take to space and build habitats of their own. Their fertility rate of around 15 children per woman make even the Amish seem like population control fanatics by comparison. Although small in number they actually attract converts on net, and number in the millions by the end of the 21st century. A few centuries more and they will become most of the human population, driving species-wide population growth rates sky-high.

Of course other factors, like various sects drifting away from the original vigor as has happened to religious sects such as the Hutterites and defection rates increasing over time (the Amish have an 80% retention rate; if 80% left instead their population wouldn’t be growing at all), can and almost certainly would intervene before they completely took over.

Human Overpopulation in Space

Nevertheless it does raise an interesting question: what is the maximum population the solar system could support? This fascinating page suggests that using the most advanced technology currently conceived to convert energy into calories the entire solar system could support at least 440 quintillion people, possibly considerably more. That is 50 billion times today’s population. Of course at the “natural fertility” rate of 6% growth per year it will take only six centuries or so for a population of even a million to grow to a number much larger than that.

If our natalists have enough foresight to send out interstellar expeditions six centuries can cover more than enough ground to compensate for that, and that’s assuming that they take over in the first place. More likely they grow rapidly, become a significant minority, then through defection stabilize at that number or perhaps even decline. That’s my plan for them at any rate.

And in any case, in my setting the breakthroughs in harnessing wormholes for travel will obviate all those concerns. With any point in the infinite expanse of the universe accessible instantly, population growth will become irrelevant. In an infinite universe, and multiple universes potentially being accessible, any finite amount of population is infinitesimal compared to the amount of space, mass, and energy out there.

A billion, a quadrillion, a googol, a googolplex; it wouldn’t make any difference. Each band of people could put as much distance between themselves and each other as they wanted, and the arbitrarily low population densities discussed earlier will become realizable in practical reality. In my setting this is merely centuries to millennia away.

Human Cosmography of the Far Future

Once this technology comes to the fore, the cosmography (geography on a cosmic scale) of mankind will be drastically altered. Instead of huddling near a star in our own galactic neighborhood, why not go somewhere much more interesting, like the center of our galaxy? Camping out next to a supermassive black hole might be fascinating, not to mention all the beautiful star clusters in the region.

Another kind of place that might be interesting is a quasar. 3C 273, for example, is luminous enough to be as bright as the Sun as seen from Earth at a range of over 30 light-years! I’m sure at least a few will visit such regions. A nebula doesn’t look very beautiful from inside it due to the low density of gas, but at close range, where the object takes up a significant fraction of the sky, it would be beautiful.

Such places near but not in nebulae, and in places like globular clusters and galactic cores would probably be the most popular places to live and visit if we had a propulsion system capable of going anywhere, as the people in the far future in my setting will have.

Wormholes also have more pedestrian applications. By shortening the path from one space habitat to another to only a few miles a ship or shuttle can venture from one colony to another in a matter of minutes. Entire habitats can also open up wormholes for themselves to traverse to where they are now to any point in the universe (or beyond!) they choose.


In the far future the norm might be for people to live in huge habitats, likely with a low internal population density; after all, given infinite resources and economic powers much higher up the Kardashev scale from where we are today, there would be no reason not to include natural wilderness in generous proportions in any given habitat.

Upon the approach of such a colony to a new location, there would be a sphere of distorted spacetime, almost like a bubble, appearing seemingly spontaneously in a given location in space, expanding to much larger than the habitat’s dimensions (for a habitat a few tens of miles long the bubble would be perhaps a thousand miles wide), stabilizing in size before the habitat emerges out of the bubble. Once the ship is clear of the bubble it would contract into nothingness.

Very cool, and it will be a regular occurrence in my setting, at least in those regions of space that are almost inconceivably lucky enough to even see such an event (the odds that any particular location would ever see a human colony pass by, considering their density will be as most one colony per thousands of galaxies).

Such will be the human future in my science fiction setting over the next few millennia and well beyond. If we ever master such a drive in real life, it will be our future too, but of course that future is not (as far as I know!) fated to follow what I write, so who can say?

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