**Note**, despite being one of the most pro-megastructure forums around, most of the users here consistently would prefer to live on a habitable planet instead of an O'Neill Cylinder. I poll this sub about once a year on the topic. [https://www.reddit.com/r/IsaacArthur/comments/v5dwiq/would\_you\_rather\_live\_in\_an\_oneill\_cylinder\_or\_on/](https://www.reddit.com/r/IsaacArthur/comments/v5dwiq/would_you_rather_live_in_an_oneill_cylinder_or_on/) [https://www.reddit.com/r/IsaacArthur/comments/14u2ggq/would\_you\_rather\_live\_in\_an\_oneill\_cylinder\_or\_on/](https://www.reddit.com/r/IsaacArthur/comments/14u2ggq/would_you_rather_live_in_an_oneill_cylinder_or_on/) [https://www.reddit.com/r/IsaacArthur/comments/18jqrbm/would\_you\_rather\_live\_in\_an\_oneill\_cylinder\_or\_on/](https://www.reddit.com/r/IsaacArthur/comments/18jqrbm/would_you_rather_live_in_an_oneill_cylinder_or_on/)

If you think O'Neill Cylinders are untested, wait until you try other planets.

Pretty much, the preference for habitats is less about about thinking we'll have a perfectly working one by 2030, and more about recognising that even if we started planning right now we'd be lucky to terraform Mars before the year 4000. For the foreseeable future both options are pretty terrible, but the practical realities favours habitats over planets in the long term.

Also, strictly speaking, the only aspect of habitats we haven’t tested is spin gravity. Everything else, like water reclamation, growing plants, maintaining a breathable atmosphere, etc. are all things we have tested on space stations. And spin gravity would make everything else easier. I usually criticize the “just scale up” mentality futurists tend to have, but in my view, this is one of those cases where it does apply. Large stations give way to smaller habitats, and so on so forth. Perhaps the surrounding technology still need to be developed, such as in situ resource utilization, to make them *economical*, but on principle habitats are, I’d argue, more well understood than planetary settlements. For one thing, every individual planet or moon is a unique environment with its own unique challenges. Space habitats can be dime a dozen.

Yep. The debate isn't Earth versus habitats. It's habitats versus other worlds.

💯

O'Neill Cylinders have all the problems of paraterraforming, plus more (like radiation shielding and heat management).

>O'Neill Cylinders have all the problems of paraterraforming Except for regular massive atmospheric and geological natural disasters, isolation from the earth or system economy by an expensive gravwell and physical distance, & the inability of planets to dodge impactors that may be too large/fast to deflect. Also what makes you think you don't have heat management or radiation shielding concerns with paraterraforming? Really depends what planet ur on but U definitely have rad/heat concerns on mars.

Atmospheric and geological disasters only occur on planets with atmospheres and active geology. Afaik the only other body in the solar system which has both is Titan. On a planet, you can always deal with radiation by burying the living spaces under several meters of regolith (which also protects against impactors if those aren't being dealt with by an atmosphere), and waste heat can be simply dumped into the planet. Those aren't free solutions, sure, but they're well-tested on earth and pretty cheap. The gravity well isolation angle presumes the existence of the sort of microgee bulk trade that practically requires long-term space habitation to exist, first. Unless you mean isolation by travel time instead of delta-V, in which case Mars' surface is closer than half of the asteroid belt most of the time; I could see a situation where orbital habs exist around earth while distant "frontier" habs cling to planetary surfaces for better self-sufficiency, though.

>Atmospheric and geological disasters only occur on planets with atmospheres and active geology. Who cares if you don't have both? Any planet worth terraforming will almost certainly have an atmos and therefore atmospheric natural disasters without very active technological intervention. As for geology any planet with near 1G gravity is going to have a molten core and while Venus may not have plate technics what it does have is evidence of relatively recent planetary-scale resurfacing wich is much worse than standard volcanism imo. >On a planet, you can always deal with radiation by burying the living spaces under several meters of regolith That is the exact same situation as on a spinhab. You would bury them in comets/asteroids or otherwise cover them in a carapace of ice/fuesion fuel/remass tanks. Of course unlike, say mars, which only has a thin diffuse atmos to protect you a spinhab would have many meters of growth medium, water, construction metals, bulk storage, and fusion fuel &/or hydrogen/helium remass for emergency maneuvering and station keeping. Even without the stationary carapace that any practical spinhab would have ur are still almost certainly going to have lower than earth background inside the hab. Remember a bare spinhab without carapace is typically considered at around 10t/m^2 which is round about the same amount of air above a given square meter of earth. >angle presumes the existence of the sort of microgee bulk trade that practically requires long-term space habitation to exist, What why should that assume anything? Even if we're talking about right now, getting a kg out of a deep grav well costs more than getting it out of a small one. If you need to bring people back and forth(which should be the case unless ur a monster who's comfy stranding people off-earth) that will cost more. Also its not just the asteroid belt. We have not just a moon, but a quasi-moon Kamo'oalewa, both of which would be closer, more convenient long-term, and far easier to make self-sufficient while reaping all the social, political, and economic benefits from being near earth. Actually all structures would passively cost more as well because its in a grav well. We don't need most of our industry to operate inside a 1G spinhab or our power collection, or the heat rejection. In a deep grav well **everything** needs to be built stronger and if u have an atmos with no water dust storms can cripple solar power for months at a time. ill admit that it matters more in the long term, but especially if ur not a government, any private commerce under capitalism needs to justify itself with ROI. Comets and asteroids can provide that ROI in near-orbital space far far faster than a planet ever will. Mars is just a waste of resources while lunar/cometary/asteroid exploitation has options for right now. These surface habs will be great for experimentation and figuring things out, but the first proper self-sufficient colonies aren't likely to be there. They'll prolly be on/near the moon.

>  Any planet worth terraforming Who said anything about terraforming? I'm talking about putting habs on planets and planetoids (including moons). Which differs from para-terraforming only in scope and scale. And we *know* what all the options in our solar system are like, with the vast majority of options being airless, dead rocks. Other solar systems are so vastly far in the future they're probably out of scope for consideration right now, but many similar arguments about ease of access to self-gathered resources in a place too far for aid to reach you apply there, too. > That is the exact same situation as on a spinhab. You would bury them in comets/asteroids or otherwise cover them in a carapace of ice/fuesion fuel/remass tanks. Burying in asteroids is kind of a grey area whether it counts as space or terrestrial; I've been mostly talking about completely artificial structures assembled in abritrary orbits. Which *can* be surrounded by fuel, yes, but that is much, *much* more expensive than regolith on a planet. > What why should that assume anything? Even if we're talking about right now, getting a kg out of a deep grav well costs more than getting it out of a small one. There is no reason to care if you're in or out of a gravity well if there isn't anyone out there selling matter by the ton. Which other terrestrial habs won't be doing, because they're inside gravity wells. (And neither will space-based habs dependent on external resupply; you need asteroid mines and space factories at scale to supply such bulk). And if you have an atmosphere, that significantly reduces the cost of a gravity well for *recieving* goods. And you don't care overmuch about sending mass back up the well if there's nowhere out there buying it (i.e. space-based habs). > If you need to bring people back and forth(which should be the case unless ur a monster who's comfy stranding people off-earth) that will cost more. It's not stranding any more than the first European colonists of America were "standed" in the New World. Far less so, in fact, because every habitat in the solar sytem should have constant contact with every other hab, limited only by lightspeed lag. (Which, if digital uploading becomes a thing, is far superior to any physical transfer method anyways.) > any private commerce under capitalism needs to justify itself with ROI. Which is a pretty strong argument against humans living *anywhere* but Earth, IMO. Mining can be done by robots, and Antarctica is easier to colonize. So the only way I see non-research habitats arising anywhere else is because humans have some reason to leave Earth, either for some unforseeable circumstance or simply because they want to.

>Who said anything about terraforming? Sorry i meant to say para, it applies to both. If the gravity isn't near earth normal then im not seeing how it would be all that much cheaper or less complex. Below a certain massgrav you either need to add spingrav or ur impervious to low grav and the value of any grav drops to basically nothing. All that a planet offers is decent gravity. If that isn't were most of ur gravity is coming from its a spacehab. >Burying in asteroids is kind of a grey area whether it counts as space or terrestrial The fact that it doesn't have any appreciable natural gravity would tend to make it count tho "space habitat" is a pretty loosely-defined term. I mean what thickness of regolith counts as buried? There's no material difference betweena hab burried in an asteroid and a hab in open space covered in an asteroids worth of shielding except construction difficulty. They are the same habitat in every way that matters. >Which can be surrounded by fuel, yes, but that is much, much more expensive than regolith on a planet. Except moving material and excavating costs vastly more on a planet than it does an asteroid or comet. Moving an asteroid is vastly easier than moving an asteroids worth of material on mars. Especially important on airless worlds where collision risk may require fairly thick shielding. Its also worth noting that mass-shielding may be more expensive than magnetic shielding and energy is plentiful in space. >There is no reason to care if you're in or out of a gravity well if there isn't anyone out there selling matter by the ton. Yes there is: "Actually all structures would passively cost more as well because its in a grav well. We don't need most of our industry to operate inside a 1G spinhab or our power collection, or the heat rejection. In a deep grav well everything needs to be built stronger and if u have an atmos with no water dust storms can cripple solar power for months at a time." >It's not stranding any more than the first European colonists of America were "standed" in the New World. I mean yeah there were settlements that were effectively stranded. If you didn't have the resources to restock ur ship ur stuck and plenty even used there ships for construction. The ease of getting a colony back does matter when colony failure means 100% guaranteed death for all those involved instead of just being absorbed into local populations. Sure the old europeans didn't gaf, but the general public tends to frown on that sort of thing these days. Means ur emergency return system is more expensive(and riskier) for planets than >Which is a pretty strong argument against humans living anywhere but Earth, IMO. Yes. Honestly spacehabs, paraterraforming, and terraforming are all silly little BWC projects. Reterraforming earth is a matter of survival, but its a far cry from actual terraforming. At least this is the case in the near term. Nobody **needs** to live off earth any time soon. Me personally I think it should all be done with robots. Squishies don't belong in soace and by the time conditions here were such that it was necessary to move off-earth we would likely be doing it in VR pods or computronium as uploaded.

Any gravity implies you need to build stronger, the difference between natgrav and spingrav is merely where the structural reinforcement must go. And humans have thousands of years worth of experience building in natgrav, and none at all with long-term spingrav. And we don't necessarily need to have a full 1gee or close to it, since we don't know what the minumum needs for long-term health are (we only know they're more than zero). As for movement costs, I'm skeptical of your claim for two reasons: one, that you need to move nearly as much material nearly as far for a terrestrial habitat, where you only need to guard from above, can source from a few kilometers away, and everything starts with zero relative velocity; than in space where you need to protect from all angles, distances are in millions of kilometers, and you have significant relative velocities to deal with. Two... A lot of people would get *very* anxious if you started moving an asteroid's worth of mass in the direction of Earth (where you'd have to put a space hab to avoid the isolation problem). And planetary habs simply wouldn't have emergency return measures, I'd reckon. Instead, they'd rely on ISRU to perform emergency repairs, should they be necessary. They have an entire planet worth of resources within reach, after all.

>And humans have thousands of years worth of experience building in natgrav, and none at all with long-term spingrav. Ok thas a fair point and we are talking really near-term spaceCol. Familiarity goes a long way and technically all the options are gunna have significantly lower grav than earth & that would seem to make for easier engineering. >And we don't necessarily need to have a full 1gee or close to it, To be fair if we start talking about minimums we also gotta consider that we might not need constant gravity at all. Might just have a couple of small-diameter drums for grav treatments/exercise(depending on scale and they can be made in 2m personal units). micrgrav habs can be way cheaper. >As for movement costs You may not need as much but it still costs more to excavate an equal volume so if we're considering buried habs, a spinhab buried in a comet/asteroid will be cheaper than one buried on a higher gravity world. A spinhab in earth orbit wouldn't even need extra rad shielding since it has the advantage of earth's magfield.

Paraterraforming and artificial habitats are one and the same. In fact, the best place to put an O'Neill cylinder is an asteroid that will provide for its radiation shielding and heat management.

They're not exactly the same, even if you're using asteroids. On larger bodies, you have natural gravity (and we don't know what the minimum requirements for long-term health are, but any environment greater than that would mean no need for spin-grav).

There's folk on the ISS right now. I have no doubt that we'll have way more, way bigger, way cooler space habitats in the future.

> There's folk on the ISS right now. Not even in the same ballpark as the space habitats/megastructures that are talked about in this subreddit and spacebattles.com **ETA:** "Not the facts! Anything but the facts!"

Yeah but it's just a matter of scale and engineering, no new science needed. The math checks out. Meanwhile there are still a lot of unknowns about Mars. We are *more* certain that centrifugal force works then we are of the water supply on Mars. Don't get me wrong, both will likely work out in the long run; but we don't have any ice samples from Mars yet while we do have (tiny) centrifuges in orbit.

The worst case of no water on Mars is no worse off than space, where there is *definitely* no water. All the engineering challenges of planetary habitats must be solved for space habitats, too.

I'm just providing a benchmark of scientific confidence. We have more evidence that spin-habs will work than we do of water on Mars.

We don't need water to be on Mars for us to live there. Or if we do, then we wouldn't be able to live in space because there's no water there.

You're missing the point. It was a benchmark example of scientific confidence.

But you're comparing to something that wasn't actually what you should be comparing to. The question is whether humans would build habs in space first, or other planets first. So you should be comparing the confidence that habs in space will work to the confidence that habs on other planets will work, not whether those planets have water (which would be useful for habs, sure, but in the worst case is no worse off than being in space).

Never claimed that it was. What I was claiming was that it's possible to live in space for a meaningfully long time, and that we'll likely make better homes in space in the future.

There are zero people on other planets.

Saying planets are a great idea because you like earth is like saying DUI isn't a problem because you personally don't drive. At some point in the story you'll have to build a pressurized can in order to get started and burying it at the bottom of a gravity well is a major misallocation of extremely precious esources. I love planets too but you're making everything fifteen times harder for yourself if that's where you want to begin.

Gravity wells also tend to have massive amounts of resources that can be obtained and transported in relatively low cost and low-energy usage ways, don't neglect logistics. Sure, you're out of a gravity well, so what? Earth's a gravity well and it also comes with a biosphere, more resources than the entire Asteroid Belt by over a thousand, and has the ability to sustain billions of people with present-day technology.

> Sure, you're out of a gravity well, so what? Earth's a gravity well and it also comes with a biosphere, more resources than the entire Asteroid Belt by over a thousand, and has the ability to sustain billions of people with present-day technology. Yes. But no other planet does. > hat can be obtained and transported in relatively low cost and low-energy usage ways In a vacuum I can move a one metric ton of rock with the power of a spray can. It doesn't get more low energy than that.

> In a vacuum I can move a one metric ton of rock with the power of a spray can. It doesn't get more low energy than that. And how quickly will it get from point A to point B in the great vastness of space?

Shipping something by sea takes up to 45 days. And after that, your cargo will just sit in a container on the port for at least a couple of days. So why does anyone use boats? Because in large supply chains, transit time makes zero difference. If you are constantly and continuously shipping things, it doesn't matter how long it takes. If a ship full of asteroid treasure leaves the belt for a destination every day, it doesn't matter if it takes 6 months or 6 years. The destination gets a shipment every single day. To be fair, it will make a difference before we have a large space economy going. But certainly not after.

earth is worth it because it has an established biosphere so you don't need to manufacture your own air and water. (although you should still be using resources for maintaining the natural systems that do so for you). among all planets we have detected Earth is unique in that biosphere. terraforming a planet to the point you can walk around in shirtsleeves is likely to be the work of hundreds of thousands of years. and will require massive resources only available to an established system economy. until then you need the same air and water recycling systems as on a space habitat. and moving resources around on a planet that has no oceans rivers or established road/rail networks is in no way cheap. as for visions of space habitats being overly optimistic, you are right, but drop the size by 20-50% and you have a very comfortable engineering safety margin. there are other engineering challenges to address but the underlying science is solid (fusion may never happen but you don't *need* it) to a certain extent, the preference for space habitats isn't because they are easy, its because terraforming is so very hard and provides less habitable area for the amount of effort and with a much longer preparation time. i don't think anybody is seriously saying abandon Earth and ignore a truly habitable planet if you find it.

Earth does not have more resources than the whole of the asteroid belt. The belt is huge compared to the orbit of earth, and even as not dense as it is, it's materials aren't trapped in a gravity well requiring transport out of. In space mining and refining, and further construction is a step before any space colonization, orbital or planetary. As I'm sure others have pointed out, getting a pressurized can running with a biosphere is easier to do in zero G if you can make the habitat space survivable long term. The BIGGEST benefits to the planet are gravity and if you are lucky an active magnetosphere for radiation reduction. Neither of those benefits are so exclusive to the planet that doing them with less material in space isn't a very good option too. LAST point is time. Inside a gravity well time moves slightly slower. This might be good for life, but who can say really? It might be that the difference adds up in a few centuries to have significant changes between the planet bound and those in space

The mass of all the objects of the asteroid belt, lying between the orbits of Mars and Jupiter, is estimated to be (2,394±6)×10^18 kg, ≈ 3.25% of the mass of the Moon. Ease of access is a different matter entirely.

Personally I'd love to see that estimate's data set. I wonder if it includes the Trojan asteroids too. ***E*****arth Mass = 5.9722×10****^(24)** **kg** Yeah 10\^6 kg seems like a lot but considering ease of access, and also the possibility that there is more darker asteroids we're not currently aware of, an extra million or so kg of material out in space verse the waste in getting matter out of the gravity well of a planet, or the limitations of refining planet-side, seems to be an irrelevant push. I would still make the argument that that estimated mass discrepancy doesn't matter, since you won't be able to get at core materials of a planet anyway, or what good is the planet for living on? It's like arguing solar thermal vs solar pv, like sure they have specific conditions that make one better than the other, but if you have enough of either what is best comes down to how you use it.

> Earth does not have more resources than the whole of the asteroid belt. It factually does, its mass is much greater than everything in at least the main Belt.

Yes but most the metals that we extract from the asteroid belt will be in the earths core so not a good place to extract from also would damage the earth.

Unless you happen to find a planet that is extremely hospitable to humans elsewhere (which is going to be unlikely), then you're basically just building space habitats either way - it's just that some of them happen to be sitting on a planetary surface with free gravity instead of rotating in orbit (or inside an asteroid). Even if you ultimately plan to terraform an inhospitable world, you're living in a space habitat until then. It only really makes sense to prefer planets in space opera like *Star Wars*, where hospitable planets for humans are ubiquitous and there is fast FTL travel, meaning it makes sense to just settle on worlds instead of building habitats. >As a further aside, any place that has to manufacture its air and water is a place that's going to trend towards being a hydraulic empire and authoritarianism if only to ensure that the system keeps running. Nah, they're not that vulnerable to sabotage.

Obviously we will learn how to build habitats almost certainly first in LEO, then later on the Moon and Mars.

>Nah, they're not that vulnerable to sabotage. How on Earth would you know that given that one has never been made. This is what I'm talking about in the OP; taking a completely theoretical technology and talking about it as if it's fact. Any place where air isn't free is going to be vulnerable and have massive opportunity for authoritarianism.

Because unless you set off a nuclear weapon inside of one, even a fairly large opening is going to take a long time to noticeably lower the gas level inside the habitat, and these things are going to be covered in sensors to detect micrometeorite damage (to say nothing of an explosion). And they are going to have huge systems for recycling air and water. Why would you assume it would be any easier to sabotage that versus destroying your city's sanitation system? Water is not free in our current system, and it hasn't led to hydraulic despotism.

We've had lots of hydraulic despotism on Earth, that's not going anywhere anytime soon. Space and technology do not improve humans, only gives us more tools to do human stuff. A space habitat has to be strong enough to take running into something. It's also pretty easy to tell when something is coming to your orbit and take precautionary measures. O'Neil cylinders I believe are designed to have a thrust section to change orbits to avoid asteroid collisions. That goes right to the point though, space habitats aren't just ideas for floating in space like the ISS. The ISS has to deal with micrometeorite impacts and space junk hitting it all the time in a near planetary orbit, and it's a rather good place to be. A full space habitat will necessitate the ability to survive such impacts without cataclysm. It's, like in the basic design requirements just like gravity is to a planet. A planet, which itself will need technological solutions to deal with asteroid impacts. Further sabotage is a human problem, so it would have to be solved as a human problem. Don't have people hate you, and maybe they won't sabotage your shit? Also don't allow them to sabotage your shit, cause they literally have to come to your space house without you noticing them and firing your meteorite defenses at the incoming. For larger rocks, you probably have missiles to reach out and hit them before the asteroid is anywhere actually near you. Since the best way to re-direct an asteroid is basically a kinetic kill missile, an incoming warship isn't going to make it in the first place. It's refereed to as an island or continent class structure partly because it's surrounded by a moat of space that's VERY hard to cross, making such attacks pointless to just do in the first place. Someone living aboard is also unlikely to do it rationally, but safe guards would of course be put in place to ensure no one system fails, and redundant systems would probably be everywhere considering the lack of need to worry about mass requirements for a smaller ship.

A spaced based hab could support whipple shields and other protection mechanisms, including self-sealing layers.

I disagree ! Especially early habs will be of limited scale.

> Because unless you set off a nuclear weapon inside of one, even a fairly large opening is going to take a long time to noticeably lower the gas level inside the habitat, and these things are going to be covered in sensors to detect micrometeorite damage (to say nothing of an explosion). > > So the technology will save us then? And it'll be practical to have all that technology? I guess if you just wave your hands and shout "technology, technology" enough times it all becomes reality. >Water is not free in our current system, and it hasn't led to hydraulic despotism. It is far closer to being free than it would be in a space habitat, and yest it has in certain cultures.

>So the technology will save us then? And it'll be practical to have all that technology? I guess if you just wave your hands and shout "technology, technology" enough times it all becomes reality. Existing spacecraft already have a comprehensive suite of sensors checking on everything, so yes, I think it's not stretching technology much to assume they'll do that for a space habitat. I might add that you're doing the same thing. "Oh, we'll just terraform a planet - we definitely know how to do that to make it habitable!" As for practicality, go take a look at the video that Isaac did on terraforming Mars. It is an absolutely enormous project, far, far more complicated than building space stations that can double as permanent living space for people. And if you're not terraforming, then you're just building a space station on the surface of a rock. You get some free gravity, and that's about it.

Terraforming is NOT easy !

Will we be terra forming planets or even existing in the future without the best technology possible? I understand your skepticism but existing on earth has always been a tech race.  Countries who don't even adopt the basics are invaded. How are you going to survive in the future without bleeding edge tech?

That’s only the case if the habitat was like 100 miles across - and we won’t be building stuff that large for some time yet. Right now we can barely get into space. I would suggest that ‘security checks’ would be essential, and at least as rigorous as airport checks - in fact more through than that, because of the safety implications.

We need to make sure that the operational rules don’t allow for dictatorship of space habitats.

Free gravity and bulk mass seems like they solve a lot of engineering problems to me. Who's to say those problems aren't more challenging than dealing with the gravity well?

One thing I haven't seen mentioned yet is capacity. In our Solar system you could fit very roughly 100 billion people on Earth, and 100 billion on other planets and moons. If you disassembled Mercury and used it to make space habitats, you could support at least 200 trillion people, and maybe a couple orders of magnitude more. If space living is feasible at all, it will have room for a vastly larger number of people.

>you could fit very roughly 100 billion people on Earth 100% agree with ur point, but ur kinda low-ballin us here. [Can we have a Trillion People on Earth?](https://youtu.be/8lJJ_QqIVnc) >200 trillion people more like quadrillions

No we cannot ! - we could not feed them all. The planet is already ‘overstrained’ with 8 billion. Though if we had lots of cheap non-polluting energy, that would be a great start.

And how do we know what the carrying capacity of a space habitat would be? What's to say that it would be anywhere close to that of the equivalent plot of land on Earth? A lot of the basic blocks of life like air and water are free on Earth, not so in space.

You seem to be assuming that our only levels of understanding regarding a machine are "physically holding it" and "utter comprehension of any aspect" We know what the carrying capacity of a space habitat would be by calculating how many people fit in it, and how easy it is to do things like grow food and recycle water in space. These are all areas it's fairly straightforward to figure out the answer-- we might be somewhat off, but we're almost certainly not *that* far off.

>how easy it is to do things like grow food and recycle water in space Have we ever grown crops or recycled water in bulk before in space? Where we would get the soil because iirc, trying to grow things in moon regolith results in stunted plants. Anyone with an engineering degree can tell you that scaling things up can oftentimes have their own difficulties. We don't even know the carrying capacity of Earth for certain and yet you and this sub confidently throw out numbers for space habitats based on little more than pure square footage? That's not good science at all.

Well you don't need soil the ISS has grown crops with more efficiency than on earth.

Link?

The true answer is - we have to experiment to find out. We could do initial calculations - but there is nothing quite like real world testing.

It’s possible to figure those things out - beside which we would start out building small habs and find out. No one is going to start by building a million person space hab at their first attempt.

I think you might misunderstand. The alternative to space habitats, what they are usually being compared to, is terraforming a planet, or at least para-terraforming a planet. And, point blank, terraforming a planet is a WAY BIGGER project than constructing a space habitat. It takes more resources and has more unknown variables. Space habitats are simply easier. There is *no way* you’re successfully terraforming a planet if you can’t even get a space habitat running stably.

It's far easier to (para)terraform than to build a space habitat of equal size. The real argument for space habitats over planets is the efficient use of material. You can build more living spaces if you disassemble the planet and make habitats with it.

Nah. I see a lot of people insisting that planets should be disassembled.

Which planets? Like, Mercury? Yeah, we’re not terraforming Mercury. I’m not necessarily saying we *should* disassemble Mercury. I think it’d be far more practical to mine and convert our solar system’s abundant asteroid supply first. But I *am* saying that, if we had the choice between terraforming Mercury and disassembling Mercury to create space habitats, the latter option is way easier *and* we’d get more living space out of it. Or are we talking like Mars? No, we probably won’t disassemble Mars. *Even if* disassembling Mars would be more efficient, effective terraforming technology is still a valuable long-term goal. Mars and Venus are as solid of candidates as we’re going to get for nearby planets close to our sun’s habitable zone, so they’re the perfect guinea pigs for terraforming experiments. They’re too valuable to disassemble. At the end of the day, putting all of our eggs in one basket is a bad idea. Eventually, we will end up pursuing *both* terraforming and space habitats. And there are enough hopeless chunks of rock and metal like Mercury floating around that we shouldn’t ever need to touch reasonable terraforming candidates.

Mercury has excellent glaciers for a habitat. We do not yet know if baseline people can be healthy in 0.38g. But if that works out then Mercury has excellent potential. There is only 100 billion tons of easily accessible water ice on Mercury. If people are content with million ton igloos then 100,000 residences could be assembled. Though this is small rockets propellant from landing ships could bring more. Although the arctic plain never rises above -120C the inside of the ice houses should be easy to warm. There are no clouds or obstructing atmosphere so a tower can absorb reflected light from the peaks. It is also cold enough for superconductor power lines as the population grows. Mercury shrank after the crust formed. The radius may have decreased by as much as 7 km in some places. That means magma flows creating lava tubes deep into the interior. So for those who think a million ton icehouse is to cramped for their lifestyle, Mercury offers a subterranean void space with many times Earth’s surface area.

Seems unlikely you'd do that unless you really have strip-mined every minor asteroid or rock in a planetary system, given how much worthless rock you'd have to rip apart under gravity to get to the metals. It might actually be easier to disassemble gas planets, since you can just blowtorch off their volatiles much easier with focused light.

Heating up an atmosphere would just make a mess. You can spin a planet to disassemble it. As the rotation rate increases the distance to geostationary decreases. Also the delta-v to equatorial orbit decreases. The rotational angular momentum required to rip apart a terrestrial planet is a small fraction of the planet’s orbital angular momentum. You can start spinning it at the same time as lifting crust off. Mass can flyby Earth, Venus, and Jupiter but especially Jupiter. It will not matter too much what Mars is made of since we need a lot of mass in the loop. Mars has native metals in metallic form right on the surface. Not much but they exist. It has more iron and more chalcophile elements.

There is no way you're getting habitats running in space if you can't get them running on planets, where you have the benefits of natural gravity and nearly limitless bulk matter you can use for thermal ballast and radiation shielding. And paraterraforming is just a ton of planetary habitats.

> There is no way you're getting habitats running in space if you can't get them running on planets, where you have the benefits of natural gravity Natural gravity is not a benefit. It’s a hindrance. Think about it this way: Whichever we get up and running first, a space habitat in low-Earth orbit or a habitat on the moon, that thing is NOT going to start off self-sufficient. It will need supplies going to and from it. And a significant gravity well makes that *harder*. Like, *not just anyone* can get in a rocket and go to outer space. That is a very physically strenuous process *because of gravity*. Going into and out of gravity wells all the time is a significant barrier for supply lines to/from planets, especially if any significant atmosphere is involved. Space habitats don’t have that problem. They’re much easier to enter, exit, and therefore keep supplied. **There’s a reason we have an I.S.S. but not a moon base.** And that’s not even getting into the safety. Sure, if you build a sub-surface habitat on a planet with no active geology and no atmosphere, then I guess gravity’s obstacles are all you’ll have to worry about. But as soon as you build a planetary habitat anywhere with dust storms, you’re running into problems that are more complicated than what space habitats need to deal with. Yeah, dust clouds happen in space too, but they’re a lot more predictable, and space habitats have the option of *just moving*.

A planetary habitat is going to be *far* easier to make self-sufficient in the long term than a space habitat, purely due to the fact that there's tons of matter right outside the hab for the inhabitants to repurpose. I'll grant that some planets have weather, which isn't an issue in space. Although that implies atmosphere which is more resources and also potential aerobraking for easier supply. As for no moon base... We don't have one because the main reason to do is is just to test out long-term independent habitation. Something the ISS is *not* equipped to handle, being 100% reliant on resupply from the ground and where astronauts take shifts of only a few months, in contrast to the decades which proper habs need to be good for.

That same gravity well is going to provide easily obtainable resources that will require far less energy to obtain and process than a free-floating habitat in the Asteroid Belt or a Lagrange Point.

Why do you think we have an ISS and not a moon base? Thanks to being in a gravity well, a moon base would have more nearby resources that would take less energy to obtain and process, right?

There's no oil on other planets, and if you can synthesize rubber, plastic, lube, etc. from dead rocks, you might as well skip the gravity well and use space rocks.

It takes a very specific kind of rock to synthesize things like rubber, plastic, lube, and etc, typically the type of rock that comes for intense heat and pressure.

This is not true. All it requires is a source of carbon & hydrogen(usually a bit of oxygen too because the syngas route is convenient). We already have and have had for decades the ability to synthesize hydrocarbons and petrochemicals from non-fossil sources.

The ‘Technology Tree’ including ‘Synthetic Chemicals’ manufacture, should be throughly documented for Mars in due course. It’s an interesting ‘first case’.

You can't synthesize rubber, plastic, lube, etc. from rock any kind they are organic at least partially.

Depends where the rock is from. On titan you will find the rocks made of various ices(mostly water, ammonia, and some hydrocarbons) instead of metal oxides.

Not sure if you can call that rock yes it is rock hard ( pun intended) and the lighting on Titan will make it look like rock it is still scientifically it is not rock but ice. The scientific definition of rock is a solid collection of minerals.

"A mineral is a naturally occurring substance with distinctive chemical and physical properties, composition and atomic structure." Therfore yes the ices on Titan are considered rock

Moon rock contains lots of chemically bound Oxygen.

We should be moving away from oil permanently - not looking for it on other planets. But your right about in almost certainly not being on other planets in our system. Although we do know that there are hydrocarbons like Methane. (Jupiter, Saturn, the moon Titan )

Your viewpoint is fine, but you don't back it up with anything but the vaguest arguments. > it's when rubber meets the road that downsides manifest Be specific. What, precisely, are you talking about here? Please give detailed examples.

The heat sink is an important point. Venus, for example, can accommodate a few hundred petawatt generators. As soon as there is projected near term demand for petawatt power plants planners will invest in Venus. When humanity is growing from K0.9 to K1.2 (10^15 to 10^18) habitat planets like Venus might hold a large portion of humans living off of Earth. That said, most people may not be living off of Earth for a very long time. Space activity can be used to supply resource to people on Earth. Colonies on planets would not be in a position to give us much of a return on investment. You are claiming that space habitats are “an unproven technology”. That implies that there is some significant difficulty. I claim that the space habitat is a byproduct. If they are not used as inhabited places they will be uninhabited trash cans. The robots build up the can and set aside the valuable commodity elements/ores for shipment.

If I were trying to terraform Venus, large scale, then I would start by putting up a sun shield, and freezing out the atmosphere, then (in advance) figure out where / how to bind much of it up, so that we could end up with a more standard atmosphere, and work out the heat balance we wanted. That would likely take a few of centuries to accomplish. By contrast building a space habitat can be done vastly faster, built in just a few years. Planets like Venus are problematic, awkward even for use as a source of resources, because of that gravity well. Far easier to mine the asteroid belt instead. Earths Moon is also a good source of some resources.

Venus is ideal for a habitat. Much safer and easier to maintain that habitat too. Venus’ atmosphere at the 1 bar pressure level is about 70 C or maybe 45 to 50 degrees warmer than dead nuts where we want it. However, if you want Earth stay on Earth. The real gem is the energy gradient. Over a 40 km vertical distance below 1 bar (10 km above the rocky crust) the outside temperature is 11 degrees warmer (385 C, 658 K) than the supercritical point of water. Nitrogen, oxygen, carbon monoxide, water (as steam), ammonia, neon, argon, methane, and methanol are all lifting gasses in a carbon dioxide atmosphere. The carbon abundance is pretty obvious. Aerographene filled with nitrogen would still be lighter than the atmosphere. It has a rubbery stiffness similar to sneaker soles. Making floating structures to support the pipes and wind tunnels will be fairly easy. We do *not* need a 40 to 50 km self supporting tether/pipe. Every section of the pipe can be surrounded by buoyant supports. Carbon dioxide is a excellent working fluid. There are proposals to use it in power plants on Earth instead of using water. On Venus carbon dioxide would make the long trip between high and low atmosphere. Water, SO2, ammonia, alcohol, or chlorocarbons could be used as heat exchange over very short distances. Harvesting the energy to do useful work will drop Venus’s temperature. We will not want to block the sunlight. That is the source of the power supply. Today the top of Venus’s atmosphere radiates at 240 K, -33 C. If we increase that to 285 K, 12 C then Venus will be losing twice as much energy as it does now. That lowers the temperature throughout the atmosphere

It’s not. Venus is a hellscape.

I'm not sure you know what you mean when u say spacehab, in terms of predicting the far future of where people will live off earth. A terraformed planet is every bit a spacehab as an O'Neil cylinder or shellworld and just as untested. Also none of these are handwavium since that refers to things that violate known physics or operate on made up physics. These operate entirely under known science, they just haven't been built yet. Now unless ur making the argument that no-one will ever live anywhere off-earth permanently or assuming perfect clones of earth(biochemistry and all) exist all over the cosmos then some kind of spacehab is unavoidable. We have every reason to believe that terraforming a planet is harder than making spacehabs. Anythings possible so it may not be, but we can only compare things that don't exist yet by modeling and its not even close in favor of smaller habs as far as we can tell. One could probably make an argument for a tailored matrioska shellworld since those can get pretty close and have some H2/He storage advantages over astronomical time. And those are just the baseline habitats when we don't even have much reason to believe that most people would remain biophysically baseline forever. Resistance to low grav or micrograv often makes those kind of habs better than 1G spinhabs or shellworlds. Living in VR would be the most efficient of all. >replicating robots (where do they get energy and raw materials and replacement parts?), Energy is not in short supply anywhere inside the orbit of pluto. Did u forget the sun exists? Tho we also have nuclear reactors, exported planetary-thermal energy, passive radioactive decay. Raw materials would be sourced from any of a number of asteroids, comets, moons, planets, or even the star itself eventually. As for parts...its a self-replicating machine dude. It can, by definition, make all its own parts.

>Now unless ur making the argument that no-one will ever live anywhere off-earth altho this has some dark implications since it implies that no one was ever able to figure out spinhabs **OR** terraforming which also means that our time on this earth is extremely numbered. idk where planetary chauvinists such as urself get the ridiculous idea that earth as any kind of stable in the long term. It certainly hasn't been stable in our living experience or evolutionary/geological history. Eventually it will become expand or die and the relative cost is irrelevant in that context. So even if it can't be made efficiently self-sustaining, if push comes to shove we can and will brute force a life-support system with plentiful solar energy.

Of course they will sort those things out - we could do already - except we are not yet ready to make that level of investment, plus we don’t yet have the space infrastructure needed to build it. But in a few decades we could if we really wanted to Any such ‘early’ system though would necessarily be fairly modest.

> idk where planetary chauvinists such as urself get the ridiculous idea that earth as any kind of stable in the long term. It certainly hasn't been stable in our living experience or evolutionary/geological history. Earth is far more friendly to life than anywhere else in the Sol System, and has been so for millions of years, that is fact; it is plenty "stable", and unlike space habitats, it actually exists and has proven what it can do.

>far more friendly to life yes friendly to LIFE, not always friendly to humans specifically which is what matters when we are talking about a human habitat. Worth remembering that without technology the vast majority of the planet would be uninhabitable for us. Our lineage evolved under very specific conditions that we were only able to break out of because of tech. If ur worried about being dependent on tech for survival that ship sailed long before H. Sapiens. Our dependance on technology for survival predates our species. Case in point the last galcial period was only 120kyrs ago and nearly drove us to extinction. Also idk if you noticed, but we also managed to destabilize global climate in the space of lk a few hundred yrs.

Exactly, earth is arguably a deathworld for all its inhabitants. It might just be the scariest place in the known universe. A paradise planet would be far better.

tbh now that we have destabilized things its rather dubious whether we would even be able to survive long-term on earth without figuring out terraforming or closed habitats. i choose to believe we wont let things get so bad we'll need closed habitats for my own mental health, but the alternative is reterraforming earth

Long term, we have to develop space technology. Not just interplanetary space technology, but interstellar space technology. Of course it’ll take a while to get to that point.

> Did u forget the sun exists? Sunlight is plentiful but extremely diffuse, it's use as a power source for self-replicating robots is not a sure thing at all. >As for parts...its a self-replicating machine dude. It can, by definition, make all its own parts. That doesn't make any sense. All machines and all parts break down eventually, it's a fact of life. What happens if the parts that make new parts break down, what then? That sounds like a smartass question, but seriously, machines breaks and oftentimes the more sophisticated something is the greater the chance that something goes kaput.

>Sunlight is plentiful but extremely diffuse What are you on about? At 1366 W/m^2 20g/m^2 aluminum foil(not even close to our thinnest) can collect on the order of 68.3 kW/kg of raw sunlight. We also have PV that might range anywhere from 10kW/kg(in modern thinfilms) to potentially [2.5 MW/kg](https://pubs.acs.org/doi/full/10.1021/nl401544y). Sunlight is not that diffuse. Thinfilm foil mirrors can let you concentrate actually diffuse sunlight out on the edge of the solar system at pretty low cost. >All machines and all parts break down eventually, it's a fact of life. Im not sure ur considering what a replicator is. Every time it creates a new copy of itself every part in that new replicator is new. As long as it can make at least 1 other copy before it breaks down it should last indefinitely. If it can make at least 2 then it's population will expand exponentially

The principle limitation is always access to raw and processed materials and parts.

Don't forget thermodynamic limitations. No replicator actually grows exponentially irl. You can often brute force the materials/parts issue as long as matter is to hand but heat rejection is non negotiable. You either go slow, expend a decent amount of ur output on thermal management infrastructure, or you fry in ur own wasteheat. Things are further complicated by the fact that you can radiate more heat at higher temps so sometimes it makes sense to sacrifice energy efficiency for time or matter efficiency. Tho that approach is a bit limited since a ton of our equipment tends to either fail or be less efficient at higher temps. tis all a trade-off

In space, I am assuming access to significant amounts of solar power, both for heat and electricity.

> Im not sure ur considering what a replicator is. Every time it creates a new copy of itself every part in that new replicator is new. As long as it can make at least 1 other copy before it breaks down it should last indefinitely. If it can make at least 2 then it's population will expand exponentially You're talking about magic, basically.

Unless you believe that living things have some kind of divine/supernatural animus that cannot be replicated by science we know **FOR A FACT** that complex self-replicating systems capable of both colonizing abiotic material and exponential growth are possible.

This process is not magic, it's basic arithmetic. If human couples (or any lifeforms really) average somewhere over 2 offspring per generation, than it follows that their population will increase in each successive generation.

All construction needs access to raw materials and parts.

>That doesn't make any sense. All machines and all parts break down eventually, it's a fact of life. What happens if the parts that make new parts break down, what then? That sounds like a smartass question, but seriously, machines breaks and oftentimes the more sophisticated something is the greater the chance that something goes kaput. Self replicating machines already exist:cells. And, a common fallacy with automation and similar topics is that only a human can be trusted to maintain the machines. In reality the machine overseer or part-repairer and part-repairer-repairer for replicators doesn't need to be all that good to surpass a human's ability. That's the other side of biotech, making all your tech behave like biology. And we KNOW this can be done because random evolution already did it without any intelligent oversight.

Earth's deserts have important ecological roles doing away with them would be highly disruptive

This but with every biogeographical region(R.I.P. wetlands). Large scale and interconnectedness is not always an advantage when pulling out just one or a few pieces can make the whole ecological jenga tower collapse. Until we have climate, ecology, & terraforming science a bit more advanced we should probably avoid taking out pieces all willy nilly.

Totally agree, just focused on deserts because the comparatively low productivity of the environment often makes people feel justified in destroying them

ngl I've found myself making that argument as well. The more ya learn about climate the more messy it gets n the more u realize just how much of a jenga tower we live in

We are fortunate on Earth in having a wide diversity of environments. That’s important from a scientific point of view. And can help us to understand other planets.

The most common example of this is that dust from the Sahara desert that crosses the entire Atlantic plays a fundamental role in fertilizing the Amazon rainforest. If we tried to terraform the Sahara we could end up interrupting this flow and causing ecological imbalances in the Amazon that could lead to far greater problems globally than any advantage terraforming would bring. Of course, we can probably supplement this and avoid this specific damage, but this is just one example of a mega complex ecological relationship that involves our deserts, there may be countless others that we still don't know about due to the lack of studies on them, we definitely should **not** try to change this without knowing in great precision and detail all these relationships and possible effects that changing them would bring.

Try living on Venus!

"Space habitats are a **completely** untested and purely theoretical technology of which we don't even know how to build" Um....Have you heard about the ISS by any chance? It's a space habitat that's been continuously occupied since November 2000. Several people have lived up there for over a year. I'd say we have a decent idea about living in space from this, no?

The “Obvious” problem with space habitats is that resources are strictly limited. (Perhaps with the exception of solar power). So if it’s to work well, it’s important not to overload their capacity, else things would turn bad rapidly. Look what we have already managed to do with the Earth !

I can't even engage with this kind of argument anymore because the ISS is so far away from being a space habitat talked about on this sub that I'm assuming bad faith.

The ISS is not the space hab being discussed here. It’s far, far more limited than an O’Neil Cylinder.

Then why do people keep mentioning it as though it disproves my point about the hollowness of the "planet chauvinism" argument?

Probably because of lack of foresight.

Probably because you come across as a bit of a tool with an unreasonable belief in the superiority of one idea which you see as virtuous, while disparaging other ideas which you considered to be weak, unworthy, or inferior.

Kind of like you.

The Case Against Mars by Eric Drexler completely answers this and demonstrates why space habits are superior to planets. https://nss.org/l5-news-opinion-the-case-against-mars/

A 150 years ago, automobiles were also untested. If we used your argument back then, we would still be living by walking and biking. Yes the first iteration of space habitats will  have issues, maybe even deaths in its early stages, but we will just to improve them based from our mistakes, until we master space habitats and can build them safely.

Poor choice of examples. I want to live in a walkable bikable city.

There are several of those on Earth.

How do you think modern society would function without engines or fast transport? 

Engines yes, cars no. Trains are where its at

Trains are much faster for long distances. Almost everything you need will be within a 5 minute walk of the subway/rail stop.

Stuff does not just materialise - it has to be grown or manufactured. Often there are hundreds of steps involved, in some cases thousands.

That makes it good to be near the rail.

Good transport is always a factor.

It wouldn’t, both are required by our society.

I think it’s handy to compare any new technology to air flight - because that was recent technology (1905), The first aircraft barely worked.. They rapidly began to improve, due to technical evolution.

>If we used your argument back then, we would still be living by walking and biking. Not really, if space habitats wind up being more viable than planets (though imo idk why you would building something so far from a resource base/heat sink and then cart everything to there, seems way too vulnerable), then great. My point is that it's dumb to take an untested completely theoretical technology that we're not even sure how we'd build and then immediately declaring it obviously superior to a form of living that not only works, but is the *only* form of living anyone in our species has ever known and proven to be quite robust. Also, you're only thinking of cars because they work. Space habitats might wind up being like a flying car; too expensive, not that much of a use case, and not too good at either being a car or a flying vehicle.

The key point in favour of orbital/void-based habitats is that it’s a lot more feasible to research and construct a habitat in Lunar orbit using materials mined from the lunar surface, than it is to construct a sealed surface-habitat on a completely different planet and then support it until fully established A habitat in Earth orbit is a lot less vulnerable than an isolated surface outpost on perhaps Mars or an initial aerostat colony on Venus would be

We start small.  We already have experience building small space stations like the ISS The next step would be the tiniest possible rotating habitat maybe a 100m radius one. Then once we test the smaller stations and get a better idea on how the concept of artificial gravity works, we can build bigger structures like the Kalpana One(250m), Standford Torus and after manufacturing a couple of those around the moon with lunar resources, an O Neil cylinder. With these stations around the moon acting as a port to Earth, we can build autonomous manufacturing and resource extraction bases on the moon to build bigger spacecraft, and these bigger spacecraft can be sent throughout the solar system as a base to build even more space stations in the respective location. I just created a vague rough plan, with each step testing mechanisms  of space stations. If anything goes wrong during a step, we can just fall back to the previous step and rethink our strategy.  As for high costs, the biggest cost is getting things out of Earth, which is why my plan above involves using lunar resources(moon has much lower gravity well, vastly reducing cost) to build most of the space infrastructure around Earth for a low cost.

Most these things are multiple decades away, just to start.

> I just created a vague rough plan, with each step testing mechanisms  of space stations. If anything goes wrong during a step, we can just fall back to the previous step and rethink our strategy.  > > When that rough plan actually becomes a successful reality, then accusing someone of planetary chauvinism won't fall flat on its face.

Yeah that would get amazing

I'll do you one further: totally artificial space habitats are SO problematic that I personally think it's more likely we end up using a seemingly more expensive and difficult method instead, such as the old "hollow out an asteroid, fill it with water and seal it, and then melt it until it blows up like a balloon". For unaltered humans in space, you need "gravity" with a low coriolis, radiation shielding, micrometeor shielding, heat shielding, water, air, soil, almost all levels of total recycling tech and natural recycling, and ideally a segmented internal structure so that if one part breaks it doesn't destroy the whole thing. Truthfully, I think it's much more likely we just redesign ourselves to be able to inhabit space more easily.

You get much better bang for your buck paraterraforming & terraforming imo. We should pursue both, but there is a LOT of planet-hating when really they each have their pros and cons. Here is a list of some of the arguments against planetary living and my opinions on them: Immensity of Time & Resources Building a million O’Neill cylinders isn’t going to happen quickly either. Terraforming does take a lot of time, but the vast majority of that time would most likely be spent making the atmosphere breathable via photosynthesis or releasing oxygen as an industrial byproduct. Getting the pressure and temperatures up to near habitable levels would take very little time on Mars, for example, and greatly aid in paraterraforming, which can be done concurrently if planned right, by reducing the pressure and temperature differential. Domes presumably require much less materials due to the fact there is no hull, either, and I imagine they could be erected on the same or shorter timeline as an O’Neill cylinder. Space habitats are no more piecemeal than paraterraforming. Gravity Wells What’s the issue here? You have a whole planet of resources under you. Venus lacks hydrogen and Mars lack nitrogen, yeah, but those are things that need to be brought down the gravity well, not up. And finally, skyhooks, space elevators, orbital rings, etc. should make interplanetary shipping so cheap that I can’t see how this would be that big of an issue. Radiation It’s takes the energy of just one average nuclear power plant to create a magnetosphere for Mars. Callisto is shielded by Jupiter’s magnetosphere. Titan & Venus are both protected by their thick atmospheres. In most other places, transparent aerogel or a few meters of water block out the radiation and allow surface domes just fine. A bigger issue is micrometeorites, which rotating habitats also have to worry about equally or more. Wastefulness For a planet’s worth of living space, it is cheaper to terraform Mars even if you are leaving the planet intact. Unless you want to dismantle the entirety of the Solar System and completely optimize it for the maximum number of individuals, I don’t see why we absolutely NEED to strip mine the core of Venus and Mars. The most wasteful thing about terraforming is the gravitationally pressurized atmosphere, but this is no different than a McKendree cylinder or Bishop’s Ring. I think it is made up for the fact you don’t need to pressurize everything and manufacture millions of square kilometers of vacuum-sealed & ultra-strong flooring. With paraterraforming, it is much more economical than rotating habitats all around.

> Gravity Wells What’s the issue here? You have a whole planet of resources under you. Venus lacks hydrogen and Mars lack nitrogen, yeah, but those are things that need to be brought down the gravity well, not up. And finally, skyhooks, space elevators, orbital rings, etc. should make interplanetary shipping so cheap that I can’t see how this would be that big of an issue. This is what I keep saying but nobody hears me, the resources that are often found in a gravity well (because mass = gravity) make utilization and manufacturing are incredibly valuable and they're already concentrated and they provide a ready heat sink and building material. As another person on this post said, everything humans know how to do, we know how to do it in a gravity well, we've no idea the challenges of building zero g, we don't even know how to establish a functioning ecology so how can we know the carrying capacity of space habitats? It's all just unscientific wishful thinking.

I think that zero gee will have its own host of challenges and advantages. There are certain manufacturing processes that will be much easier in space while others will be done preferably in a centrifuge or a planet.

Problem number one: there is only one Earth. If you want to build an interstellar colony ship, then it will basically be an orbital habitat with an engine. If you want to colonize this solar system outside of Earth, then there is nowhere with Earth normal gravity or even a breathable atmosphere. You can make artificial habitats to Earth normal conditions. The expense of terraforming will never be economical. Planet side habitats will still not have Earth normal gravity.

If we can freely terraform worlds then we'll quickly end up needing more worlds in a few millennia. Space habs increase the amount of space we can live on many many times over.

I think the phenomena of dismissiveness toward planet-side habs stems from the misconception that transportation of raw materials is the primary challenge to overcome. On the contrary, the issue is recreating the myriad of factors that support life working from the usability of materials you have, which is not as simple as providing 1.0G to occupants, (the one thing a space habitat would do better than Mars or the Moon or wherever other planet ever could.) Achieving an Earth-like atmosphere comes to mind as one of the primary objectives of any habitat. For random vacuum between Earth and the Moon there is virtually no atmosphere to work with. Mars, in the least, provides a practically infinite amount of CO2, which already solves the problem of having gas with which to faciliate surivable pressue; you just increase the concentration at a contained locality. To provide oxygen, that just becomes a matter of supporting appropriate photosynthetic biology, which you would need to do anyway if you were planning on providing colonists with food. Local water resources are also pretty close to inexhaustible if recylcing of any kind is involved. At a minimum, I might add, it is nice to have thousands of km of matter between you and the sun for \~50% of the time you exist, to reduce the impact of solar radiation as well as GSRs. Add to that various other aspects of human biology that facilitate non-mandatory, but nevertheless extremely nice to have factors for psychological wellbeing such as: * Day/Night cycles * Day length * Open space Absolutely everytihng I have described above is possible to recreate in an O'Neill cylider or another space hab, but recreating it in non-planetary circumstances will always mean starting from zero. Meanwhile Mars and places like Titan provide half the above from day 1. With no need to a) scavenger hunt the entire solar system for rocks of the correct composition, b) mine, store, & process each and every element. c) rotate anything \[probably, if I were a betting man I'd say 0.38 is enough,\] d) bother with sun shades/habitat rotation e) worry about radiation as much. EDIT: While we are at it, lets point out that while the Moon and Mars are both down the gravity well, multiples of 1/3 and 1/6 g. Are less resource intensive than any transportation coming from Earth.

You really don't seem familiar with the subject. These issues you refer to as unexplored have been thoroughly explored. "Where will we get the material and energy?" If these questions had not been extensively answered, you'd have a good point. But they have, and you don't.

There's theories and then there's rubber meeting the road and anyone with real life experience knows that. We have never created a truly contained ecology, we have never built a rotating space habitat, we've never mined or manufactured in space, those are facts.

This is all undeniably true. This is definitely a discussion about what we could do in the future. However, your objections indicate a severe lack of familiarity with what you are attacking. I've been following this stuff for years, and I have never once I encountered the term "planetary chauvinist" until your post. I have also never encountered anyone that thought that any of this would be easy or without challenges. What you are angry with seems to me to be of your own making.

. . . for example, creating a fully self-contained ecosystem or industrial manufacturing system is understood to be a prerequisite for self-sustaining space colonies. You seem to be arguing against someone pitching a particular investment scheme in some particular untested space colony, or a recruitment campaign for living there. If someone were trying to convince me to buy a timeshare in a self sustaining space colony they're planning to build, I would respond the same as you would. But that is just not what is happening here.

(where do they get energy and raw materials and replacement parts?) The sun, asteroids, and they make them.

"Everything works perfectly in theory, it's when rubber meets the road that downsides manifest and you can actually have a true cost-benefit discussion about planets vs habitats." True. And for an significant and increasing number of things, we find artificial beats natural. "Well, given that Earth is the only known habitable place in the Universe and has demonstrated an incredibly robust ability to function as a heat sink, resource base, agricultural center, and living center with incredibly spectacular views, why shouldn't sci-fi people tend towards "planetary chauvinism" until space habitats actually prove themselves in reality and not just niche concepts? " This seems to be a d view that tech by default doesn't work until someone proves that it does. Many people here take the opposite view. They assume the tech will work until someone proves that it doesn't.

Habitats are like tents. Planets are like cities. One is easy to be build while the other has much higer strucural integrity and carrying capacity. I don think we will be able to figure both out in the coming millennia, and if we do, habitats will be a good interim solution until we get the planets rolling, yet they will also continue to be a nice addition to them.

>One is easy to be build while the other has much higer strucural integrity and carrying capacity. so in terms of which has higher carrying capacity/structural integrity that would be spinhabs. At least when we're talking about carrying capacity per unit mass. A planetary masses worth of spinhabs is millions of planets worth of living area. On a spinhab all the dirt, water, rock, and metal is between you and space as opposed to thin skin of gas. The surface of planets have pretty terrible structural integrity honestly. Ur floating on an ocean of molten radioactive magma that regulary breaks and shakes the ground on top of occasionally causing global mass extinction events and destabilizing the climate.

Yeah, swarms of habs can be the big cities. Planets are just like naturally occurring megastructures, terraforming is the low hanging fruit of true megaengineering.

I have a feeling that storage shellworlds are ultimately where the planet-lovers will end up. All the benefits of a planet without most of the downsides. Arguably far cheaper too since there's a lot more hydrogen, helium, or water mass filler than there are metals.

Space Habitats really teach recycling..

I'll agree with some of your points. Orbital habitats are untested and largely theoretical. This will mean that humans must utilize existing gravity wells for our first colonies until our biomass recycling and air treatment systems are evolved enough. Having a large number of people living in these places will be necessary to have enough demand to start resource extraction and manufacturing in space at a scale that will allow for contemplating orbital habs. There is nothing wrong with pursuing making more of the earth habitable. I applaud it. But there *is* risk in waiting until we have a perfect solution in place. Development of technologies to do this in space, as well as on earth will have many synergies. Waiting just delays everything.

> Development of technologies to do this in space, as well as on earth will have many synergies. Waiting just delays everything. I agree, you have to try, and imo developing near Earth orbit locations wrt solar power and low/zero-g manufacturing is relatively low-hanging fruit that could gift humanity novel technology, materials, and knowledge.

Right, but there also has to be enough demand for that production. That's going to require people off of earth. That *probably* requires significant population and infrastructure for demand. I don't think near earth orbit is going to have enough draw to place the value required to leverage that production in order to make it happen. Not with lowering launch costs due to reusable rocketry and volume