How many people does it take to build a spaceship? The actual fabrication process might be entirely automated, but how large must a community or society be to have the productive muscle, and range of specialized skills, needed to build and operate spacecraft?
This question lurks behind the last couple of discussion threads, and many earlier ones. It is implicated in a number of classic SF tropes. How long can a crew keep their ship going before they need repairs that only a cageworks can perform? Are outpost colonies condemned to slide to pre-industrial conditions? (Or extinction, if they cannot survive without industrial technology.) Can more robust colonies maintain space fleets?
Note that industrial scale is quite different from techlevel, which is more or less whether a society knows how to build and maintain spaceships at all, and what kinds. A familiar example of industrial scale is automobiles. With a good machine shop you could build a car entirely from scratch, fabricating all the parts, but the cost in labor and shop time would be many times the cost of a production car.
A nod to Henry Ford, and once again to Adam Smith, who lived so early in the dawn of the Industrial Revolution that he only mentions the steam engine in a footnote, but who hit on the importance of the division of labor.
So, how many people does it take to build a spaceship? Certainly no more than three billion, the world population at the time of Apollo. And I would say no less than about 100 million, because France had to partner up in the ESA in order to get in the game. Even the grotesque exception that proves the rule, North Korea, has a population of 25 million.
I grant that national space programs are political entities, and an imperfect metric of industrial capacity - which is in any case part of an interdependent world economy, not neatly partitioned by borders. But it is the metric we have, and the ability to build space boosters corresponds roughly to the ability to build large commercial airframes, also confined to a few big economies.
Only a very large economy, a large industrial infrastructure, can support the web of factories and skunkworks, launch and tracking sites, academic institutes and training facilities, with their hundreds of specialized skills, that go into present day space operations.
This blog generally presumes, for the sake of discussion, that in the Plausible Midfuture the cost of space travel will be very much lower than it is today. This is further presumed to be not because spacecraft become cheaper, but because they become more productive. Today, $100 million buys you a booster good for one trip to orbit, carrying a few tons. In the PM it might buy a shuttle capable of hundreds of orbital missions, or a deep space ship making biennial Earth-Mars trips for decades.
The ships may still cost just as much, and building and operating them may likewise require an equally large industrial base. Note that the industrial base means much more than just the shipbuilding industry as such - it means the tools that build the tools that build the tools. There may be a time when spacecraft fabrication, as such, has largely moved into space, but still relies on Earth's vast and mature industry for its own most sophisticated components.
But could future techs drastically reduce the needed industrial scale, to the point where smaller communities - in the extreme case, individual households - could maintain themselves in space?
I am going to sidestep all pseudo-technical discussion of nanotech, 3-D printing, and all of that. Basically we are talking about replicators, where 'replicator' is really just techjargon for a compact super machine shop that can fabricate any desired item, including a copy of itself. Presumably all routine processes can be automated, so that the only human labor is setting up the job (the industrial equivalent of 'rules of engagement' decisions).
I can't think of any reason in principle why a midfuture tech couldn't build that capability on a pretty small scale, whether it fits in a backpack or a Winnebago.
It will not abolish costs, because its existence creates an opportunity cost: It can only make one thing at a time, so you have to choose. And for a portable home replicator to make a duplicate of itself may take quite a long time. My computer has far more speed and power than a 1960s mainframe, but it chugs away for hours on one 3-D render.
And replicators will not abolish economies of scale. Take making cars. The core replicator element might be able to make anything that will fit in its fab chamber - today a car, tomorrow a CAT scan machine. But if you dedicate it to making cars you can set up the shop floor to bring steel in one door and roll cars out the other. You can hire people who know about cars to do the detailed job specifications, so the AIs won't have to waste time on handholding.
Taken one at a time these advantages are incremental, but add them all up across supply chains and industries and they become overwhelming. Organized industries will continue to have an essential advantage over do-it-yourself, an advantage that will drive trade and economic life in general. This does not mean that people cannot live 'off the grid,' but doing so will take more work to maintain any given standard of living.
Now, to add one more chainsaw to juggle, the ability of communities to live independently in space is a matter of techlevel. A space population cannot sustain itself if the cost of keeping one person alive in space is more than one person-year of labor output. (A population can be sustained by Earth, of course, as the ISS is sustained now.)
In fact, for an economically independent society the cost of sustaining one person must be a good deal less than one person-year of output, because a society must support many people - most obviously children - who are not productive in any immediate economic sense.
Today it costs several hundred million a year to keep one person in space, on order of 10,000 person years of output. This cost can surely be reduced dramatically, let us say to 100 (current) person-years of output. Productivity has increased roughly tenfold in the 200 years of the Industrial Revolution; if it continues at the same pace, independently space-living populations become just barely viable in the 25th century, with most adults working to keep the hab going.
This still does not mean that your libertarian commune of 100 households can head off for the stars. There remains that little matter, or all too big a matter, of the industrial scale of space. If the industrial scale of technology - the advantages of scale - remain high, while all-round techlevel increases, it might take a mega-hab cluster of 100 million people to provide the range of skills and internal efficiencies needed to sustain itself in space.
To get small, economically independent and self-sustaining groups living in space you need both an increase in overall techlevel and a similarly dramatic reduction in the industrial scale required to support space operations.
For those of you who want one, which is a lot of you, here are a few escape hatches:
Most obvious and shameless, rich people, whose income is a lot more than average per capita productivity. But unless they are also making their money in space, this is merely a case of Earth subsidizing people in space, not an economically independent space population.
Another escape hatch, invoked in comment threads, is to make do with less. Science as a practice and profession is an outgrowth of Western monasticism. (Take that, mystical Eastern monks!) And there is a distinct ascetic streak in the space movement. Among the stars we can live at one with Nature, drawing on the essentials of energy and matter, unencumbered by smooth talkin' lawyers and fancy talkin' wimmin, or pretty talkin' gents as the case may be.
In practice, what doing with less - living closer to the productivity threshold - means is that people spend much of their time cleaning balky toilets, or fixing plumbing for more exotic but equally noisome fluids. That is what 'keeping spacecraft going' will be largely about, with the occasional call for a replacement part, whether you order it from stock or fab it onboard.
Faking it. Some people may seem to live independently on a small scale without really doing so, or only within narrow limits. Take one of my favorite tropes, the Serenity style space freighter. It is plausible to me that such a ship could keep going for quite a long time, perhaps many years, on just fuel and the most basic supplies. That is what it was designed to do.
Note that a ship like this probably cost more from the builder than a core zone ship that is designed for pull & replace servicing between runs. And eventually it will need to go into a cageworks for replacement or scrapping. But in the meanwhile it goes and goes.
Extend this concept a bit and you have a whole outer-fringe ecosystem that was costly to build in the first place, and would be costly to fully overhaul and restore to factory standard, but is relatively cheap to operate, and can be operated safely for decades or even generations before its service life is finally at the limit.
So this ecosystem, once built, can go for a long time as if it were independent of outside support - and can come, culturally, to take independence for granted. Though the bill will eventually come due.
The practical effect is much like Ken Burnside's 3-Gen rule, but the basis is entirely different. The 3-Gen rule argues that 'normal' human societies lack the social discipline to maintain something as complex as a hab. In my case the hab is not expected to replace or renew itself, only go a long time before either one is needed.
And there you have it. If you want small, independent, more or less self sustaining space habs in the midfuture, I have no Space Patrol, and no reason to send it to stop you if I did. Just be aware of the techlevel you are implying, 4-5 orders of magnitude improvement over what we have achieved in 50 years of space travel.
Space is hard. Even with enormous progress in both our overall capabilities and our specific space techniques it will still be hard.
This image of the ISS from Astronomy Picture of the Day deserved a reprise.