Imagine such a closed environment, hurdling through space, several generations on. What interesting possibilities we have here, both narratively speaking as well as culturally and scientifically! It’s a unique concept for certain, one that poses questions you won’t get in regular secondary world-building in science fiction or fantasy. It’s like a terrarium amongst the stars. But how possible is it? And can we create one with simple extrapolations of our known technology of today?

It’s an interesting thought experiment, isn’t it? Strip out the extremely speculative works, dial back the projection for possible and impossible far-future technology, and focus entirely on speculation based on present knowledge. Could we create a sustainable environment that would travel amongst the stars? And would we want to?

It would be a huge financial expenditure, no doubt, and a lot of the technology used would have to be tested, tried out, and invented first. I think that’s an issue with most generation ship stories—they tend to speculate the generation ship and only the generation ship and nothing else. Like, "oh, here’s our one ticket to the stars and that’s it, we’re escaping earth because earth has been used up and ruined by the humans. Bye bye."

An artist's impression of a Generation Ship. Credit: Adrian Mann.

But that’s not how this works, that’s not how science evolves. We’re constantly reusing technology, especially those developed in our current space program. And of course, if we build a generation ship (or ships, depending), we would either reuse already existing technology from terraforming to biomes, or we would create new technology that could be reused on earth (to create a more sustainable existence on our own planet), or in our local solar system (for a human settlement on local planets, like Mars and Venus).

This kind of iterative design can lead to all sorts of interesting futuristic scenarios. With a generation ship acting as the penultimate human achievement, launching us outside of our completely inhabited solar system and into the next stage of species development. So let’s get down to it: what technologies can we make use of to build our generation ship?

Gravity

This will be the biggest hurdle for interstellar travel, and one that would need to be solved before we even consider a ship that would be travelling for generations upon generations to the nearest solar system. We don’t know all of the effects of low gravity or zero gravity on the human body, but we’re starting to get a larger picture of what happens for prolonged stays, and it’s not good. Not good at all.

Bone loss, muscle loss, a change in the shape of the eyes, genetic damage, odd rashes and the like have all been experienced from extended stays on the ISS. Even with daily exercise, it’s a losing war against attrition. This is something that needs to be solved before we even consider hopping around our own solar system, let alone going the long slow travel to another star. We have no idea how an infant would be affected, going from birth to death with low or zero gravity. Could humans survive this? Would we evolve into weird floating blobs over multiple generations and genetic mutations, in order to better fit our new environment? Best not to walk down that road, with all its thorny ethical considerations.

So what to do? There are several different possible solutions, each of these with a large number of drawbacks. The most common one is the idea of linear acceleration—where the propulsion from the ship creates the near-earth gravity necessity for human existence. This kind of propulsion requires a lot of thrust, which can only currently be achieved using rocket fuel. This is a huge issue, one that cannot be easily engineered away. There is the increase of weight, the fact that a lot of rocket fuel would be required for a multi-generational trip, and the very likely possibility of running out of said fuel before the end of the voyage make this a very unlikely idea.

It’s sad, though, since linear acceleration provides a very natural alternative to earth’s gravity, one with the least amount of drawbacks and possible quirks. The other kind of artificial gravity is one that most people know about in some way or another—rotational gravity. Unlike the flaws in gravity caused by linear acceleration, the flaws in rotational gravity can be engineered away. We’ll just have to keep a few things in mind when building our generation ship, so that the gravity feels natural and earth-like, and minimizes the Coriolis effect (which can cause dizziness, disorientation, and the like, things that would make long term, multi-generation travel practically impossible).

The size of the rotating part of the ship is super important. This is where we’re starting to get closer to a super-structure, and perhaps will need to be built off-planet, just because of the sheer size of it. What would be key here is to get it as close to possible as earth gravity (g) with as low a rotation speed as possible. The lower the rotation, the less of a Coriolis effect; and it seems that the sweet spot for human habitation is around 2 rotations per minute (rpms).

The rotating spaceship in Interstellar

Another issue with rotational gravity is the energy required to keep it spinning, as we’re looking a large super structure here, that needs to hold multiple generations, a breathable atmosphere, and the 2rpm speed. The most common design for a ship like this would be a ring shape, or a wagon wheel with zero gravity tubes acting like spokes towards the center, a propulsion system. The most common example of this basic design is the Stanford Torus, and if you’ve ever seen the ending of the movie Interstellar, you’ve seen these in action.

Propulsion and Energy

Next up we’ve got the thorny issue of what to use for propulsion. The size of this ship, and fuel conservation, are going to cause a lot of issues when it comes to ways of piloting it through the cosmos. A Bussard Ramjet is a concept that’s usually tossed around, where the ramjet scoops up hydrogen, compresses it, and uses it as thermonuclear rocket. This always felt a bit perpetual-motion-ish for me to feel feasible, and it has been proven that the region surrounding our solar system has nowhere near enough hydrogen to make this work in a practical, and efficient way.

A solar sail. Art by Andrzej Mirecki, from Wikimedia Commons.

What then? A solar sail? There might be long points in this voyage without access to solar energy. The same could be said for using solar power at all for technology on board our generation ship. In a way, these two ideas are tied up together when talking about our generation ship—we’re going to need both fuel as propulsion and some form of energy for powering the interior of the ship itself.

Even if we have humans doing the brunt of the work, and AI/machination doing the bare minimum (to save on energy expenditure, among other things), we’re still going to need a form of artificial light, one that can provide humans, plants, and animals on board with the required nutrients they need to survive out in space. The usual Stanford Torus design uses mirrors to reflect sunlight into the interior, but again this won’t be feasible for long journeys between galaxies, since there will be long stretches of time when we wont have access to any sun, at all. We could use battery walls to store energy between the solar systems, but this probably wouldn’t last the several decades (or more) we would need for a generation ship style voyage.

Recently there was a proposal for a kind of nuclear fusion propellent called the Ghost Ship. It’s an interesting concept, not using the normal ignition of nuclear bombs for propulsion, but instead using nuclear lasers to create a Deuterium reaction. This kind of propulsion uses a fast ignition scheme, where fusion conditions are created through ignition instead of compression. Think of it like adding a fuse to the rockets, using a high powered laser for ignition. Instead of carrying around weighty fuel, we can use compressed fuel pellets that simply need to be ignited. the reaction itself will propel the ship forward, and the cast off energy of the fusion reaction could be stored in a battery wall, for powering the ship as well as igniting the next fuel pellet. This would allow a good deal of thrust without carrying a lot of heavy fuel around with us in space. It also has the built in bonus of allowing the ship to use the castoff neutrons from thrust to power the ship itself. It’s a win-win that tidily solves two issues. But the downside to this is that it’s untested and mostly theoretical. I have a suspicion that this might be another ramjet situation, where an ideal solution turns out to be less practical the more we learn about our universe.

Either way, energy conservation aboard the ship itself will also be key, no matter what system we use.

Also related to energy and propulsion is the necessity of shielding. Luckily for us, our current space technology of today has sufficient shielding for most interstellar crafts, by using a Whipple Shield (thin metallic bumpers, set off at some distance from the ship, which diffuse or break down the energy, so that the fragments scatter along the bumper wall.)

Resource Management

And with that said, I’m going to go on a bit of a rant for a moment, here. One of the key issues that bugs me when we discuss generation ships, or when generation ships are used in fiction, is that the idea of resource management seems to go out the window. We act like 3D printers will solve all ills, and that energy and objects are pretty much as plentiful as they would be on earth. Water, in our minds, would need to be reusable. But plastic waste from 3d printing? And how could complex technology be commonplace and bountiful?

That doesn’t make sense. We would not only need to have technology that’s built to last, but also technology that’s easy to fix. We would need technology that helps us conserve energy instead of wastes it. This, of course, brings its own issues to bear.

An interesting, and fun experiment to think about here would be the use of clockpunk-style technology for day-to-day tasks, while the main ship itself (the propulsion, navigation, atmospheric regulation, heat, light, etc) relies on our current technology. This way, the most important functionality of the ship can be as up to date as possible before launching out of our solar system, while energy conservation for individuals on board the ship will allow them to have some modern conveniences powered by wind-up springs.

It would require advances in a different kind of technology altogether. Everything would be built to last, and easy to fix once one learned the necessary tricks and tools. This is quite different from the micro-engineering that’s necessary on most breadboards these days (and that technology is always going obsolete, so it’s built to last maybe a decade, tops. If you’re lucky, you could stretch that out longer, but not by much).

This does pose some interesting thought experiments about what a culture that lived like this for several generations would be like. And it raises some interesting questions on the nature of society, and how prepared they will be for landing, and then populating an off world planet.

Biomes, Food, and Artificially Closed Loops

Here is where a generation ship has a lot in common with other aspects of space travel and colonization. We need a complex ecosystem that will keep humans alive within a closed loop. That is, it will provide enough calories, oxygen, and water that humanity can survive several generations, without any input from the outside world itself. It needs several reacting biomes that would create an atmosphere that can create its own water and oxygen levels, as well as other biological necessities for earthling life. It needs to be self-sustaining in all ways, and this requirement here seems to be the most tricky when it comes to getting humans off this rock and elsewhere.

Biosphere 2: An experimental closed system

We’ve already begun work on several different closed ecological systems. The most popular was the one failure from the 80’s called Biosphere 2. It got a lot of press coverage, which made its very public failure ingrained into the public mind. When most people think of a closed biological system, they think of what happened here, the risks and the issues, the petty fighting, and the fact that it had to close early.

But what most people don’t know, is that there have been many other attempts at creating a self-sustaining closed ecological system. Some of them very successful in their meager attempts. Of course, these were far less flashy, and have been building up incrementally over the years. MELiSSA, BIOS-2 and BIOS-3, have all been far more successful, albeit less flashy and farther from the public eye.

We still have a way to go before we find the right combination of plant life, bacterial life, and insect life that would work well on an interstellar mission and keep humans alive for a long period of time. But from what we’ve seen so far, it is very possible. It’s just not going to be a quick solution to a problem. I think that’s the case with most of the technology we’re going to use to build our (speculative, for the time being) generation ship. We’re looking at iterative technologies, built over long periods of time for various uses throughout our exploration of our own solar system.

One of the key benefits our generation ship will have over other space missions will be the sheer size of it. As we said above, the size will be important in so many different ways. But when it comes to controlled environment agriculture (for growing food, using hydroponics and other methods), this will be to our benefit: large fields of environmentally controlled closed loop systems. Vats of algae, hydroponic forests producing oxygen rich atmosphere, and tubes of hanging gardens, with fruit and vegetables growing in waste-reused gardens. Plains of grass and wheat fields, with herds of cattle, pigs, and the like grazing slowly and waiting to give humans the required nutrients for long travel through space.

We already have the technology for most of this, the tricky part will be making certain that it’s self-sustaining. It needs to act like a terrarium in the stars, self-sufficient, with each organism containing a purpose to help all the other organisms live in this artificial environment. The size of the ship will be very helpful here, since we’re looking at a mega-structure for the various reasons we listed before: the plant life, farm life, and the rest have room to grow, flourish, and thrive (unlike smaller closed systems, where the encapsulation itself is part of the issue). Artificial wind, light, gravity, and weather can also help the various flora and fauna in our proposed spaceship survive.

Culture, Society, and Economy

Let’s get one thing out of the way right now. We have yet to come up with cryogenic sleep that doesn’t kill us. One that would also stop ageing, stop the body changing, growing old, etc. Using what we know of our current possible technology, we would need to have everyone alive, thriving, and moving about on this generation ship if it is to be a true colony ship.

Hence the need for a sustaining ecosystem on the ship itself. This sustaining ecosystem, a terrarium in space, would also work as a stop-gap once we reach our foreign star, allowing us to slowly terraform outwards from where we land, giving us a living environment that’s proven to work for at least two or three generations of space travel, if not more.

But this raises the questions of culture, society, and economy. One of the benefits of our generation ship will be its massive size, since we won’t have to worry so much about issues of confinement on the human psyche. It will be no less of a stress on an individual’s frame of mind than living in an isolated, small town or community.

When it comes to the economy, capitalism and laissez-faire free market just wouldn’t work in an environment like this one. Money itself as a form motivation and work brings out the worst in humanity, a competitive gaming of abilities and competition wouldn’t be the way to run a ship like this.

Instead, we should limit work. Do only what’s necessary, split between the people, with lots of free time for study, preparing for landing, and the rest. With enough people on the ship, minding the farmlands and the various technological needs, the amount of time regulated to work would be minimal, while free time would be plentiful. Since we’re using a mega structure to house our portable world, we could have a decent number of people on board the ship, even at the start of the journey from earth. We’re looking at maybe a modestly-sized agrarian city of people at the start, with the population growing slowly over the years.

I say "slowly" because the low amount of work and high amount of free time for study, pleasure, and the like, as well as a longer life-span (since there will be advances in technology by the time, and we could keep these advances separate and powered by the power we get from the thruster runoff), our society would be akin to any industrialized society on earth with a strong middle class. And one thing we know from monitoring earth’s fertility rates is that this kind of social and economic environment naturally reduces birthrates. So the need for population control is practically non-existent.

The actual governing of a generation ship like this would require a democracy with a well-founded charter and set of rules, to keep it from devolving into a dictatorship or a feudal system. Pure democracy with vigilant debate might be the best way to go, but since a large number of any population experiences vote fatigue (and lack of knowledge of issues), it might be prudent either to set aside certain times on the on-ship calendar (would they even use years?) to address certain issues. The leadership would exist only to enforce the basic structures of democracy itself, making sure the quorum is counted properly, and the various legislature follows the existing rules.

The need for an AI to control everything, including birthrates, marriages, and the like makes no sense and seems like an arbitrary SFnal idea, in order to add conflict into this society for the needs of fiction and plot. That’s not so say there won’t be conflict, but that conflict doesn’t need to an AI as a dictator to resolve.

From an anthropological standpoint, what would arise on the ship after several generations of life like this would be extremely interesting. Most sfnal versions of this concept seems to leave religion out, or have them be a-religious. But since so much of terrestrial life seems to focus on religion of some sort, it makes it hard for me to believe that there would be none in such a unique environment. How would it evolve through the generations on the spaceship? Would we see a kind of neo-paganism erupt out of the needs of this primarily agrarian community? If so, would religion create a different societal hierarchy outside of whatever democratic government set up on the ship itself?

Of course, these issues are no different than issues we face daily on earth, only magnified. Visit any small town and you can see exactly what I’m talking about here. One of the benefits of a small town is that when democracy works, it really works and has a direct effect on the population. It’s not some distant abstract thing, but rather some close and personal.

In Conclusion

Paul Jessup

A generation ship is not the solution to our problems on earth, but instead should be seen as an end-goal for our current space technology. It won’t be a technology built all at once and spat out to the stars, but instead would be the culmination over the years, perhaps several generations and iterations of various technology used for space travel and habitation.

This is necessary for cutting down costs, and working out any issues that would happen on a long, one way journey across the stars. Don’t get me wrong, one of the biggest roadblocks to creating a generation ship will still be cost, and even though reusing technology we discover and test out elsewhere will cut down the cost significantly, a project of this size would still be extremely expensive and without any way of making a profit from such a journey.

Our free market and capitalism being what it is, we can’t expect super rich CEOs to fund a generation ship. It would need to be backed by one or several governments, and without any expectation of a return on investment. In other words, the time and price to build something like a generation ship or a colony ship would mean that it could not be a solution to our current environmental crisis. That should be priority number one. The nice thing about that, though, is that the technology we use to rebuild and save our own planet could be reused very easily into space travel as well as slow interstellar voyages.

Of course, that has the same issue that a generation ship has when it comes to cost. It will be expensive, with little to no projected return on investment. Well, except for the obvious—by saving the planet we can live and make more money in the future for these same CEOs, instead of dying in a long drawn out dumpster fire of a burning world.

Though that doesn’t seem to be motivating them right now, does it?