Plausible limits of population [now playing: outer space]

[Ars Lande]

Space habitats seem like incredibly inefficient solutions to me; why build a tiny planet when there are huge ones just laying around that can make much of the work for you [incluiding energy capture, atmosphere conservation, and biosphere maintenance].

The problem is, there aren't! Earth excepted, there are two huge desert planets with extremely harsh conditions and some cold, barren moons.

Sure they'll be very useful for stuff like scientific research, asteroid mining supervision,long-term space travel, terraformation, and all kinds of extraplanetary activities but... heck, if you wanted to *live* somewhere a space habitat seems like a horrible idea unless you're either an utopist, a hermit, or have a special predilection for the whole living in space thing: all those are small minorities.

The only constraints about habitats is that you need to fit into one of several designs, (basically, a torus or a cylinder, though something might be said for the sphere for certain specialized cases), lit by a mirror arrangement of some kind. You're then free to decorate the place as you see fit, provided you leave enough vegetation to have a closed O2-CO2 cycle: there's really no reason space habitats should be unpleasant.
Other advantages: perfect climate control, and any industry that involves the handling of toxic chemicals, or nuisance of any kind can be done safely out of the main habitation area.

[Torco]

*one* desert planet, that i know of... Venus isn't a desert, its got plenty of rain... *ahem* sulfuric *ahem* rain that...well...
yeah, Venus is a hellhole, mars is a desert. according to the wiki, earth's atmosphere is 5e18 kilos, so crash pluto against it and you've got yourself 10k times more air on mars than on earth, much more in fact since mars is smaller. This isn't even necessary; if you were to crash a few asteroids into mars, you'd sublimate its ice into a thin atmosphere that would make the planet marginally inhabitable... throw a few comets for some nice water vapor and BAM, instaplanet. Okay, its expensive, but it would give lebensraum to a billion people or so, whereas you need much more effort to build as much room in space stations... and the scenery's pretty dull!

Also, one planet's perfectly enough for, as we've imagined, anywhere from ten to a hundred times our current numbers... and the more advanced we become, the more sophisticated ways we'll find to fit people on this one planet. Sure, they'll be expensive and uncomfortable, but not as much as living in space i think

[Ars Lande]

You're omitting that tiny step where you let the planet cool down for a few centuries and convert part of these 5e18 kg to oxygen

But why not drill through one or two of these asteroids you're moving around while you're at it, and then start to rotate it? Actually, you can do that first, and skip the heavy orbital bombardment
It's about the same order of magnitude in cost, but you get real estate after 20-30 year or so, and you can repeat the operation as desired.

Ultimately, if we're considering a population in the trillions, why restrain ourselves to the limited resources of one planet with the associated headaches, when we could use basically free energy and mineral resources. The asteroid belt alone could support a truly preposterous number, and when we're done with it, we can always blow up an unnecessary planet or two. (What has Mercury done for us lately?)

[KathTheDragon]

We just need negative matter to generate infinite positive energy whilst not violating conservation

I believe infinite energy is very much frowned upon by the laws of physics. So, there's no way to escape the heat death of the universe. We're doomed, dooomed.

You misunderstood!

Negative matter + positive matter together generate energy into infinity. It's just that you get the same amount of negative energy as you get positive energy, thus giving you a net gain of 0 Joules.
It is in violation of no single law of physics.

A real shame we don't have any.

[Salmoneus]

The asteroid belt is full of asteroids. It's like building a greenhouse in the middle of an eternal avalanche. What are the advantages? If you can mine the asteroids, you can get the material back to earth - without FTL it'll take a while, of course, but since the stuff you'll be making in the asteroids is non-perishable that's not really a problem.
Meanwhile, every square foot of 'land' in space has to be manufactured and maintained, expensively. On earth, it's just lying around waiting to be used. The purported advantages of a sealed environment - well if we think that's a good idea, we can do it on earth just as easily. But on earth we don't need to and in space we need to - so earth has everything that space has, and more. Plus energy, of course - available solar power in the asteroid belt is between four (at the inner edge) and sixteen (at the outer edge) times LESS than at earth.

(It's also worth reminding everyone - not suggesting that you're unaware yourself, mind you, but just bringing up something that many people know but have forgotten about - that the asteroid belt isn't a place, but a lot of places a long way away from each other. We tend to get into a habit of talking about colonisation of 'the asteroid belt', forgetting that Earth is closer to any place on the Belt than most places on the Belt are to one another...)



Torco: forget about Mars. Useless place. You can spend as much as you want on it and it'll still be cold, and Tibetan in atmosphere, and more importantly the gravity is just appalling. Seriously, it's only about a third of earth's gravity. That's near the bottom limit of what people feel comfortable in, in the short term - some people will have no problem, but some will find it very troubling. This covers up the long-term consequences of living at such a gravity level - there are unknown, but probably very severe. The body just isn't built for low gravity - for instance, with lower gravity, fluid stays higher in the body, raising intercranial pressure, distorting the eyeballs and crushing the optic nerve. On Mars this effect would be less than in space (though the space trip to get to Mars could prove dangerous), but it would also be chronic rather than acute. Brain functions, cardiac functions, and muscle and bone are all affected by lower gravity.
And after all that, you don't even get much land out of it, since much will have to be underwater and much will be sticking up into space.

[Torco]

Naaah, just having an atmosphere makes mars much more easy to make inhabitable that an asteroid, and why would you need to cool it down? Of course it wouldn't be a garden right away, but space is pretty inhospitable. Vacuum is pretty harmful to people, and don't forget radiation, which we don't know how to shield people from and is exceptionally unhealthy.

Why is the asteroid belt free, though? we *know* how to mine stuff from a planet's surface, we've been at it for a while... and free energy doesn't exist: sure, there's no atmosphere so more light, but the asteroid belt is further away from the sun, if you want energy go to mercury [also, blowing up planets is not future tech, its fantasy tech.

I think the issue with space habitats, and with terraforming for that matter, is *why*. its a truly incredible investment of resources and there's no real reason to go to space to live; there's really no economic activity to do there that you can't do here... unless we were to discover life on europa or something, in which case the sheer value of biotech research would make having a small city on the surface of it a necessity for every self-respecting pharmaceutical and biochem firm. or maybe if there was a lot of helium3 or other valuable thing on the moon, then sure, people would move to the moon to extract the thing. Mercury could be a good base for solar energy gathering, but exporting anything from mercury to the moon i'm ambivalent towards [you're climbing the gravity well, but there's solar wind and plenty of energy to do it so i dunno]. The asteroid belt has nothing but rock... and while the idea of colonizing it is awesome, there's plenty of rock already right here on earth. Mars is the easier place to colonize, but its also pretty useless right now, and until its terraformed [which, in turn, could only make sense as a ziggurat i think] ... what is there of value there? I mean... rocks and dust... plenty of both right here!

and no matter what little there is on mars, there is even less in the literal middle of interplanetary nowhere.

Sal: yeah, i know... a damned shame... still, it could be made useful if humanity were to reach the earth's carrying capacity, however many trillions that be. Tibetan atmospheres aren't inherently uninhabitable; plenty of tibetans in tibet, and lower gravity isn't necesarily a curse [hell, can you imagine the bastekball games they'd have?! plus, its conceivable we could genetically modify people to live there]. Also oceans are incredibly useful places, land isn't the only value to be found on a planet. But yeah, Mars is pretty crappy real estate... and the worse thing for the prospect of an interplanetary civilization is... Mars is pretty much the best place on the system outside Earth. Where else, venus? hellhole. Mercury? barren piece of nowhere. The belt? hell, not even anything. The gas giants? worse planets ever. The moons? weeell... depends what's there. We're basically stuck on earth until we find life elsewhere. I've said it before; extraterrestrial life's probably the only good reason to have significant populations outside earth.

way i see it

[makes sense to live there]------earth--------------------------------------------------------------------[probable threshold]-------------------------mars----------everywhere else------------ [makes no sense]

[Ars Lande]

The asteroid belt is full of asteroids. It's like building a greenhouse in the middle of an eternal avalanche. What are the advantages? If you can mine the asteroids, you can get the material back to earth - without FTL it'll take a while, of course, but since the stuff you'll be making in the asteroids is non-perishable that's not really a problem.

I'd have to look at the delta-v's involved, but it's probably more interesting to look at near-earth objects first, before getting into the asteroid belt.
You'd have, of course, to move your material, one way or another, into a convenient orbit, close enough to the sun that you get a suitable amount of solar energy, either by sending the mined materials, as you propose, or by altering the asteroid's orbit.
I'm not sure what you meant about avalanches... collisions aren't a particularly significant problem: as you mentioned, the asteroid belt is big. (Though it is an inconvenient location, why go live years away in a place poor in sunlight?)
Asteroid material can be brought back to Earth, though at a high cost. It's probably feasible for small quantities though.

Meanwhile, every square foot of 'land' in space has to be manufactured and maintained, expensively.

No argument here. The trouble is, as we've demonstrated in this thread, past a certain population, so does the same amount of land on Earth. I should mention that I've absolutely no idea what the tipping point is! But if you're talking very long term, it'll eventually be reached. I think it'll be sooner rather than later, myself, but the data is so uncertain that the opposite can be argued. I think that The Club of Rome had pretty much the right idea, but I'm aware that I'm in the minority on this.

I should mention, however, that even at our relatively low density and level of development, land on Earth isn't free, it must be expensively maintained; the amount of fossil fuels and water that must be consumed to maintain agricultural land at its present level of productivity is already at a rather high level.

At this point, I must admit that I also have ethical and esthetic considerations in mind; daydreaming a bit, if it was at all possible, wouldn't it be more desirable to leave Earth largely as it is, rather than turn it into New Jersey (or a Paris suburb, for that matter) on a global scale?

[Ars Lande]

Why is the asteroid belt free, though? we *know* how to mine stuff from a planet's surface, we've been at it for a while... and free energy doesn't exist: sure, there's no atmosphere so more light, but the asteroid belt is further away from the sun, if you want energy go to mercury [also, blowing up planets is not future tech, its fantasy tech.

Sure, it's not free, though a continuous energy source that still has billions of year to go should still count for something What should be kept in mind, though, is that solar power generation is a lot more efficient in (Earth) orbit than on Earth.

I think the issue with space habitats, and with terraforming for that matter, is *why*. its a truly incredible investment of resources and there's no real reason to go to space to live; there's really no economic activity to do there that you can't do here... unless we were to discover life on europa or something, in which case the sheer value of biotech research would make having a small city on the surface of it a necessity for every self-respecting pharmaceutical and biochem firm. or maybe if there was a lot of helium3 or other valuable thing on the moon, then sure, people would move to the moon to extract the thing. Mercury could be a good base for solar energy gathering, but exporting anything from mercury to the moon i'm ambivalent towards [you're climbing the gravity well, but there's solar wind and plenty of energy to do it so i dunno]. The asteroid belt has nothing but rock... and while the idea of colonizing it is awesome, there's plenty of rock already right here on earth. Mars is the easier place to colonize, but its also pretty useless right now, and until its terraformed [which, in turn, could only make sense as a ziggurat i think] ... what is there of value there? I mean... rocks and dust... plenty of both right here!

Oh, there is no economical reason to. This is purely a thought experiment, science fiction even! I don't seriously propose we seriously commit to doing either. In a few centuries, though, who knows? I do think it would make sense, on a scale of millenia (if we don't go back to hunting and gathering or upload ourselves to World of Warcraft or whatever).

[Torco]

At this point, I must admit that I also have ethical and esthetic considerations in mind; daydreaming a bit, if it was at all possible, wouldn't it be more desirable to leave Earth largely as it is, rather than turn it into New Jersey (or a Paris suburb, for that matter) on a global scale?

I don't know... I rather like Paris xD
But seriously, the reason for turning earth into an ecumenopolis won't be planned policy or a globally shared development program: if people keep making new people, that's what will happen; it won't be *done* by any one agency; more people = more houses for people = more land covered in houses. perhaps it would be more desirable, perhaps it would not though: can you imagine the marvels a trillion souls would be capable of ? of out of a trillion minds, how many shakespeares? how many borges? how many einsteins and mozarts ?

All under the compassionate care of the Immortal God-Emperor

[Salmoneus]

The economic reason for asteroid mining is that it's not just rock, it's also metal and minerals. On a scale inconceivably beyond that of earth. In particular, 'siderophile' elements, which are mostly locked up in the earth's core, are open for access in the asteroid belt. Gold, platinum, rhodium and so forth in immeasurable quantities.

As for 'places better than mars': Venus! Venus! Venus! Followed by Saturn, Uranus and Neptune.

Cloud cities have some of the problems of space habitats, but not all of them. All four planets would allow us to have cities with earth gravity - Venus would also give us (warm) earth temperature and an earthlike night/day cycle. Venus would probably allow mining - the surface is likely to be mineral-rich, although of course it wouldn't be easy to access (but limitless acid if we wanted acid!). Saturn would allow tholin mining; Uranus and Neptune would probably be self-powered also, since you'd be floating in fuel gas.

And if you want to go the whole 'terraforming' route, Venus is still better than Mars. Terraformed Venus is lovely.


Ars: I don't think solar power generation is more efficient in orbit, no. Sure, you have twice as much power to play with - but both your construction and your maintenance costs are way, way higher than on solid ground. I think per unit of electricity produced, orbital generation will cost considerably more.

[Torco]

Right, metals... true that, although mercury may be a better place to go metal-hunting; the tidal locking plus the absurd temperatures on the surface mean that even with very basic tech [say, pipes and some water] you could get huge amounts of energy taking advantage of the horizon, not to mention the awesome amounts of solar you could get... that, and you could ship stuff to earth with fuel-less solar sail craft built out of local materials, having only to build a railgun to get stuff out of the surface [and mercury being p. small, wouldn't have to be a huge railgun... and you could build it using, yes, local materials]

Venus??? I don't know, problem with venus is that its surface prevents you from building stuff on it, and is thick enough that getting *out* of the venus surface is pretty damned hard, the rocket would melt and where would you get the fuel?? Plus terraforming mars is relatively simple: throw some icy shit in its vague direction [the kind that's not rare to find floating around the solar system]... how on venus would you go about terraforming venus? adding stuff down a gravity well is much easier than removing stuff up said well. Plus, what's on venus that's not on Mars, Mercury or the Asteroids? Yeah, if we needed acid, that's where one would go... hell, maybe we'll find some FTL method that consumes huge amounts of acid

Saturn, Uranus and Neptune? Again, any and all gasgiant moons that have some sort of life will be a huge boom to the biotech, pharmaceutical, chemical and luxury pet industries, and more than good reason to establish permanent settlements there; however, barring that... why would you need tholins? And the methane giants, pretty as they are, aren't really useful as fuel unless you found sufficient oxygen: they do have the politeness of offering us water, though. What is there on Saturn, Uranus and Neptune, though? <that warrants going halfway to the oort cloud to go get?> okay, maybe cheap hydrogen... lots and lots of hydrogen... and water, but that's not really rare.

[Miekko]

Venus has these things going for it:
- the only other place in the solar system with hospitable temperature and pressure (granted, the cloud tops, but still)
- a lot of chemistry on display that is useful if you're going to try and terraform it, but on the other hand:
- too much of some of the chemistry, and defs too much of some that you don't need to have there
- roughly 1g at the surface

A long term terraforming project for Venus would probably pay off way better than a similar project for Mars. If you only found some kind of microorganism that could survive in the cloud tops while changing the rest of the atmosphere into something less inhospitable.

Altho' I guess this obsession with Venus over Mars for terraforming is rather a trait shared by me and Salmoneus and some other contrarians?

[Salmoneus]

I think we need to distinguish between where's good to go to live, and where's good to go to make money.

In the solar system, the only money is in the asteroids. And maybe in tholins. Tholins are useful because they're fuel. In immense quantities. My SF setting has its society based on tholins - it lets you keep all your lovely fossil-burning technology (with probably a few adjustments), but you can forget about running out of it for centuries and centuries (or longer, with FTL). My setting has FTL, which make tholins a no-brainer, but it's possible they may be worth exploiting even in slow time.

Oh, and maybe helium-3 is worth exploiting, but I've always been a bit skeptical about that one. That's fusion stuff anyway, so who knows what will happen.

In terms of places to live, however, that's different. The gas giants (minus Jupiter, obviously) are perfectly liveable - the gas itself can power the colonies, even if it's not economically feasible to ship it back to earth. Venus lacks this power, but that shouldn't be too much of a problem - you can build floating solar power-plants (bright white light from all directions!), or just ship fuel from earth if you haven't run out of it (ideally for fission, I guess, since that's the fuel with the best density and lowest transport price).

There's no real reason to go there, of course, but then there's no reason to go to Mars either. Actually, there is one reason: asteroid mining. Or, more generally, access to the rest of the solar system. On average, it's closer to everywhere than Earth is. If, for instance, you're bringing resources in from various places in the asteroid belt, what better place to build factories than on Venus? If you have to send humans out to the asteroid belt, or to research lifeforms on Europa or wherever, where better to give them shore leave than on Venus?


If you terraform Venus, meanwhile, Venus has a big advantage over terraformed Mars: it's Earthlike. People could live on it. They'd have earth gravity, earth pressure, earth temperature. Mars can never be more than a 'radioactive' Gobi desert (not literally radioactive but it would probably be seen similarly, in terms of long term health risks). Venus can be a tropical paradise. Plus it'll probably have resources, thanks to being, it seems, mostly volcanic seabed.

[Torco]

I think we shouldn't distinguish those two too much: people go to live where p*r>x, x being some threshold, p being the possibility to live there and r being the degree to which there's reason to go live there. Life would be much easier for most british pensioners in Peru than in britain <much lower cost of living, for example>, but you don't see them flocking there. Similarly, there are excellent reasons to go live, say, to alaska, or to the middle of the ocean in an oil rig, but since its so inconvenient few people actually do.

Tholins seem extremely unconvincing to me; How has a society figured out FTL while continuing to use internal combustion engines? *we're* pretty much figuring out how to phase out oil, and we're much closer to fusion and practical renewables, fusion, electric cars, and hydrogen power cells. And even if we forget that, oil's valuable, but valuable enough to go get it to the outer solar system? I don't know. Plus Saturn's not so much smaller than Jupiter, so if big jay is unlivable why would saturn be? its got pretty massive electric storms too.. The blue outer planets are much tamer, and there's even probably water deep inside them, but again how do we burn the methane in them without, well, oxygen!

I insist on Mercury looking much better for mining than the asteroids, for the aforementioned reasons that you didn't notice [availability of energy, basically, but also because of the fact that mercury is a thing, as opposed to a billion small asteroids you have to move between; there's not much fuel on the asteroid belt]

If you have to send humans out to the asteroid belt, or to research lifeforms on Europa or wherever, where better to give them shore leave than on Venus?

Quite obviously earth. Its got all the infrastructure, including possibly orbital stations, a space lift, and, don't forget, *air*. Its also closer.

Yeah, the return on the investment for Venus terraformation would be much better, even with hundred-earthday sols... if it was possible. It might, but it would take a shitload of work. Don't get me wrong, you and Miekko are right in that a terraformed venus would be pretty much the Cancun of the solar system, but Mars is still a better plattform from whence to step into the outer solar system; a railgun on mars would need to be much much smaller than one on earth.

Altho' I guess this obsession with Venus over Mars for terraforming is rather a trait shared by me and Salmoneus and some other contrarians?

Quite possibly, not least because to my knowledge no viable method has been proposed to terraform it; you'd have to strip it of its atmosphere, which is a LOT of atmosphere, and microorganisms in the clouds aren't gonna cut it; there's acid in the clouds [although i guess very weird biochems aren't weird on earth either, so who knows]

What do you mean Mars can't be more than gobilike? if you pump enough air and water into it, throwing comets around, it can have as much atmosphere, water and greenhouse gases as you want [for a fraction of what would cost de-veneralizing venus mind you]. And sure, its small and it couldn't hold as much atmosphere, but atmosphere loss isn't quick enough to matter. It may be a low-gee world, but it could be a low-gee garden for much cheaper than venus could go from being a hellhole to a moderately less horrible hellhole.

[2+3 clusivity]

I think given sufficient time, gradual and conservative advancements in technology will allow humans to colonize most of the solar system--if in low population densities outside of Earth. It seems inevitable if perhaps not glamorous. One way slow shots to other solar systems are not even that hard to imagine occuring within the next 100-200 years.

I think two issues are more pressing, (a) the premature extinction of humanity through some catastrophy of our own making. NOW, that would "limited" the population. (b) Speciation, which becomes more interesting and relevant given advances in genetic engineering possible over the next few hundred years and eventually the increasing dispersal of humans across and outside of the solar system. Populations diverging for varying reasons will drive down the limit (read: count) of the "human" population if only in census terms.

[Ars Lande]

Tholins seem extremely unconvincing to me; How has a society figured out FTL while continuing to use internal combustion engines? *we're* pretty much figuring out how to phase out oil, and we're much closer to fusion and practical renewables, fusion, electric cars, and hydrogen power cells. And even if we forget that, oil's valuable, but valuable enough to go get it to the outer solar system? I don't know. Plus Saturn's not so much smaller than Jupiter, so if big jay is unlivable why would saturn be? its got pretty massive electric storms too.. The blue outer planets are much tamer, and there's even probably water deep inside them, but again how do we burn the methane in them without, well, oxygen!

I don't think we'll keep on with internal combustion much longer, but I wouldn't be surprised if we did. The big thing in the energy industry seems to be shales, not renewables or fusion. (And are we any closer to fusion?)
Jupiter has large nasty radiation belts, due to trapped charges particle in its magnetosphere; this isn't as much of a problem with Saturn.

I insist on Mercury looking much better for mining than the asteroids, for the aforementioned reasons that you didn't notice [availability of energy, basically, but also because of the fact that mercury is a thing, as opposed to a billion small asteroids you have to move between; there's not much fuel on the asteroid belt]

I think the comparative advantage of asteroids is that there's no gravity well to get out of, and they have a wide variety of resources from metal to water to organic compounds. They're also a lot easier to get to; the delta-v requirement from low orbit to a near-earth asteroid is 5.5 km/s, by comparison. Earth orbit to Mercury orbit is 18 km/s.
You also don't have to move between asteroids: one asteroid is already quite a lot of material, (433 Eros weighs 6.3 trillion tons, for instance).
On fuel: a near-earth object has the average insulation of Earth, give or take. What you really need to do is move the material in a convenient place, and for that you can use a very crude mass driver using refuse from your mine as reaction mass.

On the other hand, if you have things to do that needs to be done close to the Sun, for the same reason, Mercury mining is the way to go, since it'd be cheaper to mine material off Mercury than to send it there.

If, for instance, you're bringing resources in from various places in the asteroid belt, what better place to build factories than on Venus?

I'd suggest you build them close to Earth, at L5 for instance. You're looking at a delta-v of 5.5 km/s to get the material to your factory. Then you have to bring back to Earth. Let's assume you have a space elevator. We're looking at a 1.7 km/s delta-v between your factory and your elevator. Total cost: 7.2 km/s.
On Venus, though, you'll have 10 km/s to get the material to Venus, and then 5 km/s to ship it back to Earth. Total cost: 15 km/s.
So you're doubling your delta-v budget at no real advantage.

Mind you, there's nothing wrong with Venus cloud cities (I find the idea awesome myself), you're just not going to finance them through asteroid mining.

[Salmoneus]

I think we shouldn't distinguish those two too much: people go to live where p*r>x, x being some threshold, p being the possibility to live there and r being the degree to which there's reason to go live there. Life would be much easier for most british pensioners in Peru than in britain <much lower cost of living, for example>, but you don't see them flocking there. Similarly, there are excellent reasons to go live, say, to alaska, or to the middle of the ocean in an oil rig, but since its so inconvenient few people actually do.

Counterexample: where you live. The Americas weren't colonised because it made economic sense, but because people wanted to live there. Once they got there, some of them discovered some ways to make money here and there.

Tholins seem extremely unconvincing to me; How has a society figured out FTL while continuing to use internal combustion engines? *we're* pretty much figuring out how to phase out oil, and we're much closer to fusion and practical renewables, fusion, electric cars, and hydrogen power cells. And even if we forget that, oil's valuable, but valuable enough to go get it to the outer solar system? I don't know.

History isn't a progression from the primitive to the sophisticated. We could have stopped burning oil (ok, for electricity, not so much for transport) decades and decades ago if we'd wanted - but we haven't, because oil is cheaper than solar or fission or any of the alternatives (and because of inertia from our existing industries). In my setting, rising oil prices do mostly convert the world to solar power... until they get FTL, at which point they revert to burning tholins. Why? Because they don't sit around saying "oh, but burning hydrocarbons is so much more PRIMITIVE than this funky solar stuff we have, can we really look at ourselves with pride as a space-faring race if we still use internal combustion engines?", instead they sit around saying "hey, if we do this we can save a shitload of money! Aesthetics be damned!"

Plus Saturn's not so much smaller than Jupiter, so if big jay is unlivable why would saturn be? its got pretty massive electric storms too.. The blue outer planets are much tamer, and there's even probably water deep inside them, but again how do we burn the methane in them without, well, oxygen!

I'm not sure you're really up to speed on the gas giants. Saturn and "the big jay" are nothing like each other. Saturn is 95 times the mass of earth - Jupiter is 320 times the size of earth. It's more than three times the size! This has consequences. Eg Saturn's magnetic field is 0.2 gauss (a little less than earth's), whereas Jupiter's is 4.2 gauss. This means tha Jupiter is all hideously and fatally radioactive, whereas Saturn isn't. As a lesser problem, leaving Saturn is tricky, whereas leaving Jupiter is utterly impossible with any currently-known technology.

I insist on Mercury looking much better for mining than the asteroids, for the aforementioned reasons that you didn't notice [availability of energy, basically, but also because of the fact that mercury is a thing, as opposed to a billion small asteroids you have to move between; there's not much fuel on the asteroid belt]

Mercury and the asteroids aren't equatable. Mercury is just a giant hunk of rock. Sure, it will have exploitable resources, but only in the same sense that Earth has - possibly less, even, given the lack of volcanism. In planets, much of the good stuff is stuck down in the core. In asteroids, that good stuff is on the surface.

If you have to send humans out to the asteroid belt, or to research lifeforms on Europa or wherever, where better to give them shore leave than on Venus?

Quite obviously earth. Its got all the infrastructure, including possibly orbital stations, a space lift, and, don't forget, *air*. Its also closer.

No, it's further away. At least geographically, I don't know about the ITN, and I'm not taking orbital velocity into account here. This is a common misconception, based on the fact that, if all planets are aligned, earth is closer to the outer planets than venus is. But most of the time they're not perfectly aligned, so on average venus is closer than earth is.

Yeah, the return on the investment for Venus terraformation would be much better, even with hundred-earthday sols... if it was possible. It might, but it would take a shitload of work. Don't get me wrong, you and Miekko are right in that a terraformed venus would be pretty much the Cancun of the solar system, but Mars is still a better plattform from whence to step into the outer solar system; a railgun on mars would need to be much much smaller than one on earth.

Except that we probably can't live on Mars, even if it's terraformed.

[Ars Lande]

No, it's further away. At least geographically, I don't know about the ITN, and I'm not taking orbital velocity into account here. This is a common misconception, based on the fact that, if all planets are aligned, earth is closer to the outer planets than venus is. But most of the time they're not perfectly aligned, so on average venus is closer than earth is.

True, but I have to disagree with you on this. Geography (Astrography?) doesn't matter, orbits and delta-v do: Earth is 'closer' than Venus to the asteroid belt because you don't need as much fuel to get there (Earth also wins in terms of transit time). Unless you're willing to do continuous acceleration instead of orbital transfers, that is, but the cost would be horrific. You might justify for your crew (well except for the fact that it's beyond modern science), but for asteroid material, you don't want to.

In your setting, though, if you have cheap FTL, then none of this business matters. Though I wouldn't want to be in your shoes: cheap FTL has so many consequences I don't even want to think of working out

While doing quick research on the orbital transfers involved, I did come across a very strong argument in favour of Venus though: the delta-v budget is slightly lower than Mars, and the orbital transfers are a lot more convenient, with transit times reduced to four months; launch windows are much more frequent too (several a year if I'm not mistaken, as opposed to once every two years or so for Mars). So a Venus colony would be a great deal easier to get to from Earth.

EDIT: I should probably mention why I get so bothered about delta-v: fuel requirement is an exponential function of required delta-v, and by fuel I mean the mass ratio, that is the amount of propellant you have to carry around. So a huge delta-v means you have to carry around an absurd quantity of reaction mass (not very practical when you have to carry around thousands of tons of material). You can get around this by positing a sufficiently powerful engine: the trouble is, 'sufficiently powerful' is code for 'detonating an atomic bomb at regular intervals' and a major engineering issue is preventing the engine from melting.

[Torco]

On the other hand, if you have things to do that needs to be done close to the Sun, for the same reason, Mercury mining is the way to go, since it'd be cheaper to mine material off Mercury than to send it there.

Not only that, its easier to send stuff *from* mercury to anywhere.and sure, 5 to 18 km/s... *but* i think the ratio of solar-on-mercury to solar-on-the-asteroids is quite bigger.

There was plenty of economic sense to be made: tobacco,silver, gold, slaves, furs, and above all lands, swathes and swathes of land. Why do you think people went to america, if not for lands and riches? "hacer la américa", to make the america, is still a common expression to say "to get rich". People wanted to live there *because* there was land and other resources to be had, that is, and that *because it made economic sense*. <also ideological sense, in the case of north america's religiously-motivated early migrations, I guess>. Actually, land and cheap unfree labor <non-easy to sell slaves> was the reason the southern cone got populated, that and Almagro was openly searching for silver here.

Sure, people don't adopt new tech because its newer, but because its better <cheaper, stronger, better, faster, etc>: surely there are more practical technologies than going halfway to neptune to get oil. But I guess if FTL is cheap enough, it makes some sense.

Regarding gas giants... right, i thought the difference was less.

In your setting, though, if you have cheap FTL, then none of this business matters. Though I wouldn't want to be in your shoes: cheap FTL has so many consequences I don't even want to think of working out

its not cheap FTL, its cheaper-than-oil FTL. p. awesome.

As for mercury, sure, its buried; but since gravity is much less and evergy so plentiful, making holes in mercury probably isn't hard [also, you can hit it with asteroids, while we're stripping venus of its atmosphere]. Still, asteroids do have the small and available thing going for them

[Ars Lande]

On the other hand, if you have things to do that needs to be done close to the Sun, for the same reason, Mercury mining is the way to go, since it'd be cheaper to mine material off Mercury than to send it there.

Not only that, its easier to send stuff *from* mercury to anywhere.and sure, 5 to 18 km/s... *but* i think the ratio of solar-on-mercury to solar-on-the-asteroids is quite bigger.

Unfortunately, delta-v requirements work both ways. So it's 18 km/s anywhere to Mercury and Mercury to anywhere. Plus there's gravity, adding 4.25 km/s, and no atmosphere. (On planets with atmosphere, you can aerobrake so you get a free orbit-to-surface ride). Since you insist on mining Mercury, though, you always have the option of building a big-ass laser powered by large solar arrays, and power a solar sail with it. Actually, building said big ass laser is a pretty good reason to mine Mercury, it's always nice to have access to a few petawatts of power.

[Drydic]

On the other hand, if you have things to do that needs to be done close to the Sun, for the same reason, Mercury mining is the way to go, since it'd be cheaper to mine material off Mercury than to send it there.

Not only that, its easier to send stuff *from* mercury to anywhere.and sure, 5 to 18 km/s... *but* i think the ratio of solar-on-mercury to solar-on-the-asteroids is quite bigger.

Unfortunately, delta-v requirements work both ways. So it's 18 km/s anywhere to Mercury and Mercury to anywhere. Plus there's gravity, adding 4.25 km/s, and no atmosphere. (On planets with atmosphere, you can aerobrake so you get a free orbit-to-surface ride). Since you insist on mining Mercury, though, you always have the option of building a big-ass laser powered by large solar arrays, and power a solar sail with it. Actually, building said big ass laser is a pretty good reason to mine Mercury, it's always nice to have access to a few petawatts of power.

That's no moon...It's a space station.

[Torco]

I was thinking of a huge railgun, but perhaps a solar sail and some sort of microwave laser or something would be similarly awesome. They're not exclusive, of course. But yeah, mercury could be sort of the power station of a solar system economy.