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My graphic novel involves a large flying city on a Venus-like planet. Yes, I have done my research, and for various reasons it will be an aerostat-hibrid megastructure: a metaphor for the elaborate and expensive man-made islands around Dubai – a status symbol of impractical engineering. Please notice the question is not how but WHY.

I am looking for worldbuilding reasons WHY this city was constructed, and the unique set of circumstances that make it viable. In other words, what problem was solved by building a large luxury aerostat in a compromised atmosphere, as opposed to a more common space harbor or moon-based colony?

Some background:

  • The city is a corporate trade hub, and is a Libertarian paradise of luxury rentals and cheap domestic servants. The city has a Metropolis-esque division of wealthy families living on top of an unseen labor class.
  • The star system is a choke point along a strategic trade route (FTL travel takes months, and involves "jumping" from star to adjacent star).
  • The city has control over the star system, and they have politically destabilized surrounding systems (pirates, despots, etc). They support a syndicate-created scarcity of resources that doesn't touch them.
  • There are no other habitable planets in the system. There is a profitable (exploitative) metal asteroid mining operation which was the original "oil money" of the city.
  • I am not interested in debating the feasibility of the structure, thank you.
  • My world is not hard sci-fi. Everyone is human. It's thousands of years in the future.

I offer some loose reasons I think the structure might be better off flying in an atmosphere rather than in space:

  • Politics – the city's location is politically advantageous avoiding taxes/criminal justice of an established government.
  • Astrophysics – solar radiation or frequent meteor storms make an atmospheric canopy necessary.
  • Gravity – Space is fine for the working class, but wealthy people refuse to live in bad gravity.
  • Defense – The city is less vulnerable to attack with a planet at its back. Since they undermine other sovereignties, they have many enemies.
  • Security – Removing the city from the space harbor creates physical distance from terrorists and rebels (and riff raff, NOCD).

I need to show that this structure is elaborate and expensive, but circumstances make it viable or necessary.

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    $\begingroup$ A flying wing is an aerodyne (a heavier-than-air aircraft) not an aerostat. $\endgroup$
    – AlexP
    Commented May 27, 2017 at 17:53
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    $\begingroup$ Do you want us to evaluate your excuses or suggest new ones? $\endgroup$ Commented May 27, 2017 at 18:20
  • $\begingroup$ @AlexP: Thank you, I did not know that word. $\endgroup$
    – wetcircuit
    Commented May 27, 2017 at 18:47
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    $\begingroup$ Just a possibility, but how capable is the science of your world in Terraforming? It could be the purpose of this station to act as a component of that project. Are there valuable resources on the planet surface? Also, is the city enclosed entirely or open to the atmosphere, or containt by transparent force field? Maybe the planet's clouds are absolutely beautiful to look at and make an added luxury tourism market which would be more about the spectacle than the practical. $\endgroup$
    – hszmv
    Commented Oct 24, 2017 at 13:13
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    $\begingroup$ Did you not provide the only sensible reason "why?" when you said, "...status symbol of impractical engineering..."? Why would you want a reason that detracts from your metaphor? $\endgroup$
    – JBH
    Commented Oct 24, 2017 at 23:45

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So you want Libertarian floating city on Venus like planet. Fair enough.

You already pinned down why there should be a city of wealthy despots anywhere in the system: asteroid mining and trading hub. I presume being libertarians, they impose heavy tariffs on use of "their" space for transit, and you either pay up, regularly fight through, get shot down or dragged into indentured servitude for violation of "non-aggression principle" (because you clearly violated it first by trespassing).

Remaining question is, why would it be an anti-intellectual version of Laputa (technically libertarians don't claim to be anti-intellectual, but since they take Austrian "School" of "Economy" and "Praxeology" as core concepts, they actually are)?

This is actually a hard question. A lot depends on history of the system.

Asteroid mining

If initial wealth comes from asteroid mining, and current crop of governing despots comes from most successful miners, ore traders or industrialists who set up local ore refineries, then you should expect main "city" to be inside hollowed out asteroid, for simple practicality. Rothbard city started out as hollowed city in asteroid, and since everything they needed to control their economic empires already was in place - as they spent less time actually working and more just managing others, their homes kept expanding and it was simply more expedient to add infrastructure and connect other asteroids. Heck, most likely every magnate would have own asteroid-city, where oxygen is expensive and even God is second after him. Or her. No. That won't do.

Interstellar Trade

What about FTL? How does it work? What is used for fuel? You said it works inter-system by jumps which take months. Is it possible that for some reason all viable entry and exit points lie near Ludwig von Mises, the Venus-type planet? Perhaps your FTL jumps need gravitational wells as anchors, which means that ships have to jump from and to planets? Star is right out, because radiated energy would destroy the ships. So now we just need to rule out other planets.

Alternatively you can make it so inexplicably there are no other jump points and skip the rest of this paragraph, your call, heck, it would make for an interesting story if it's not known why jump points are the way there are, and suddenly they reshuffle, or someone discovers way to "bore" new ones, or perhaps Hayek system oligarchy aggressively chases off any explorers to make sure no other entry points are discovered.

Back on track, how about fuel? Are your ships powered by fusion reactors? Preferably ones which can operate on wide range of light elements? That would be perfect, as planet with thick gaseous atmosphere provides ready source of fuel. Normally, smaller ships could utilise scaled down ramscoops to skim very outer layers of atmospheres to refuel, larger ones could carry shuttles to do the same (actually landing on atmosphere-less planet to mine the surface is hard, landing on planet with atmosphere is easier, but take-off is harder, just skimming the outermost layer beats both by huge margin).

Obviously, "government" of von Mises considers that theft, either you buy fuel from them or something unpleasant happens. If other planets lack atmosphere, denying refuelling would require a few automated battle stations to fire on anyone who lands. After they land, why bother shooting them in flight? If they somehow survive destruction of ship you can offer to rescue them. At a price. After they pay fine for trespassing. And compensate you for spent ammo. And pay for depreciation of value of battle-station which shot them. And... well, you get they idea. It's all fine in libertarian world, they got shot for trespassing, and now they can just chose to die, no pressure (pun intended).

As you can see, my answer starts to take shape:

Out of system owners deciding to build their own world

Ships, processing plants and other equipment is expensive. Initial mining was done by ships owned by industrialists form outside the system. Some fat cats residing on Earth or another planet with nice and comfortable 1g surface gravity. Perhaps ships were automated, perhaps they were crewed by contracted crews. Either way, ships were NOT owned by people who operated them. At first, ships stopped at von Mises for fuel, but very quickly gas condensers were built and sale of fuel started, combining both aggressive sales strategies (measured in megatons) and expediency of being able to replace the shuttle with another ore container (I imagine shuttle would usually serve as a lifeboat in case of critical damage, so it's clear that true libertarian would discard it, and loudly complain at any regulations forbidding that).

With time, some owners perhaps decided that they don't like being subject to Earthen (or wherever they used to operate from) laws, and decided to finally claim the system for themselves. After all, it practically already belonged to them already. Since von Mises is such a hub, with fuel stations and cities housing people maintaining gas condensers already built, using it as base of operations was an obvious choice.

Because owners are not spacers, they clearly would prefer aerostat, because it provides some gravitation to stave off all the problems caused by extended living in microgravity, and to separate them from all those lazy bums who can't just stop being poor. That's how Rothbard city was built. What will be the story of its fall?

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  • $\begingroup$ Ha! This is wonderful! This ads color behind the politics and a path of evolution I hadn't considered, Thank you! Rothbard now on my reading list. I have a social reform preacher character, and you've opened my eyes a bit to what his sermons will be about. $\endgroup$
    – wetcircuit
    Commented May 28, 2017 at 2:07
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    $\begingroup$ Plus one for the jibe about the intellectual credentials of the Austrian School alone. Nice to see scenario-building used answer a question. I must wag my finger at you for Bussard ramjets. The concept was discredited in the late 1970s. People read Larry Niven & assume the idea is feasible. Sadly, they're wrong. Only wish I could give your answer more upvotes. $\endgroup$
    – a4android
    Commented Oct 24, 2017 at 12:56
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It seems to me that it is perfectly reasonable to have a city like this. Your preconditions don't leave open a lot of other options.

High atmospheric pressure precludes surface construction. It is not Venus, but a Venus like planet. Meaning the surface will have crushingly high atmospheric pressure. Higher up means a more earthlike atmospheric pressure. Maybe if there is stratification of the atmosphere, the CO2 will be on the bottom and there will be breathable amounts of oxygen up top. Either way, you can't be on the surface and so the option is floating/flying.

There is a profitable asteroid mining operation in the system, and their system is a choke point. From the OP. 2 good reasons to be there at all.

There are no other habitable planets in the system.. One good reason not to be anywhere else nearby.

So the system is a good place to be, to be in the system you have to be on NeoVenus, and to be on NeoVenus you have to be in the upper atmosphere. All that is left is the structure of your city. I always thought the Cloud City on Bespin was pretty but stupid: that little uvula at the bottom is only some sort of counterweight and it would drift uncontrollably.

If you are going to have a floating city it either needs a tether / anchor, like a buoy, or it needs to be maneuverable, like a ship. You have opted for the latter. Maybe surface conditions are too rough on tethers. High pressure hot acids count as rough.

ADDENDUM: Equinox

I was thinking how nice Minneapolis is in the summer. Not quite as nice in the winter. If only there were some way to move the city so it stayed summer...

That can be the reason your city flies: your planet has seasons and winter is harsh. Twice a year on the equinox the city flies across the planet and takes up residence in the opposite hemisphere, so that the seasons is always spring turning to summer.

Bonus: Equinox is a very cool word and could be the name of this city, or the title of the story.

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Your reason: Defense

Defense is a very valid reason for this city to exist. If, as you say, the owners regularly make enemies, then living on a planet is a good idea.

Assuming you haven't quietly disposed of the laws of thermodynamics in your setting, a space station will be very visible because of its heat signature. Everyone with a good sensor system will know where it is. In addition, assuming you don't have reactionless thrusters, the space station has limited delta-v and cannot engage in preemptive dodging. This is made even worse if the station is being spun for artificial gravity.

In other words, not only does everyone know where a space station is, they will also know where it will be at any time in the future. An enemy could slam a big rock coated in radar-absorbing materials right into the station easily, without being seen doing so.

On the other hand, the dynastat is constantly moving, and (should be) doing so unpredictably. It is also far harder to spot against the backdrop of nice warm planet, requiring a potential target to approach the planet for reconnaissance. This means, absent planetbusters being used against these guys, an enemy cannot simply fling something at the target from halfway across the system and call it a day. Instead, attackers would have to approach the planet and would be in range of whatever defensive systems the city-owners had, making attacking them far harder.

Another reason: Politics and Territory-claiming

Basically, it is politically advantageous to have a settlement on a planet for whatever reason. I will list some possible reasons below:

  1. The city is technically a colony of some larger polity (which of course requires the planetary presence) which entitles them to some military support in case of invasion. Given how this city is supposed to be hyper-libertarian, I doubt this.

  2. According to Space-UN rules, a sovereign nation must have a planetary presence to be recognized. By being a recognized sovereign nation, they gain some benefits in relation to other nations, such as better diplomatic channels or possibly even a free-trade agreement. Or even just being left alone and not being continually invaded by other nations.

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  • $\begingroup$ I hadn't considered the heat of the planet would help mask the city, or dodging boulders after the miners revolt but that's exactly what they would be capable of! Great ideas! Also like the idea they claim territory by maintaining a persistent planetary govt. Thank you! $\endgroup$
    – wetcircuit
    Commented May 28, 2017 at 2:18
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In other words, what problem was solved by building a large luxury aerostat in a compromised atmosphere, as opposed to a more feasible space harbor or moon-based colony, or choosing some other star system altogether?

I'll start with the last sentence: Because it would be unnecessarily difficult. There is no reason to leave the star system, if our current one works just fine.

[...] a more feasible space harbor [...]

You already answered this one yourself:

Space is fine for the working class, but wealthy people refuse to live in bad gravity.

Bad (or non-existing) Gravity actually is a thing. Thousands of years of evolution build the human body to be best suited for some gravity. While we are very well able to survive in a space harbor, it takes it toll on the body.

I am looking for worldbuilding reasons why this city was constructed.

The easiest one would be overpopulation on earth. Yes, it's simple as that. It's already a thing to consider at our very time, and your world plays

thousands of years in the future.

A simple reason for it to be build on Venus would be the distance to the sun. I would imagine a city, with the size of an island or metropolis, with thousands if not millions of life ensuring mechanisms, that constantly surfs the atmosphere, requires A LOT of energy. You could say the source for this is sunlight and the city requires such an amount of this, that Venus was the best choice.

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    $\begingroup$ Venus has significant problems for Earth science today. However the future science is able to harvest resources of its violent atmosphere. Thus the city is profitable, although it comes at a cost that only the peasants/workers pay. Add in Earth over-population, politics, perceived criminal persecution provides sufficient reasons to leave Earth and build their safe haven. Surfing on top of the clouds would be a magnificent image, just consider their sunsets. $\endgroup$
    – dcy665
    Commented May 27, 2017 at 22:29
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I actually like this idea. I can see some nice advantages to this.

Gravity

It is not mentioned if artificial gravity is available, but the city would not need it. Venus has surface gravity of 0.904G which is close enough to Earth for humans to adapt to. This would probably be quite comfortable and it would always work without maintenance, energy consumption, spare parts, technology licensing costs and any other issues artificial gravity might come with.

Pressure

At bit over 50km altitude the atmosphere of Venus has roughly Earth normal pressure. While the atmosphere is not breathable having pressure close to Earth normal will make maintaining breathable atmosphere for people much easier and most of all safer. You can maintain same pressure inside and outside and avoid all kinds of issues. Maintain slight overpressure and nothing will leak in.

Temperature

The temperature for that 50km given in Wikipedia is 75°C, for 55km it is 27°C. While this is bit high for humans, it is well within the ability of human machinery. While the city will need to expend energy to dump heat into the atmosphere and will require large heat exchangers to do so, it will still be much easier than trying to dump heat into empty space. So your city will have much easier time doing energy intensive processing than space habitats have.

Volatiles

The atmosphere will be an easy source for oxygen and nitrogen. The atmosphere of Venus is mostly carbon dioxide so you won't run out of carbon either. Hydrogen is relatively scarce, but it will still be easier to harvest it from atmosphere than from space. On the downside the hydrogen is mostly bound to toxic and corrosive compounds so equipment failures would be quite dangerous.

In fact on Venus you would be flying thru clouds of sulphuric acid, so hydrogen would be easily available and corrosion resistance would be kind of important.

Aesthetics

I expect the clouds of sulphuric acid would be kind of pretty, so if this is a vanity project, it kind of makes sense.

Sunlight

Venus is closer to Sun than Earth, so you will have plenty of sunlight to grow plants on and to see the clouds by. Venus has fairly slow rotation so your city would be able to stay in the eternal daylight and probably should do so. While there would probably be windows for admiring the view, most of the city would be lighted by fiber optics or artificial lighting for safety anyway, so darkness is one flip of a switch away. No need to move the entire ship to darkness.

The benefit of staying in constant daylight is that it keeps your machines constant temperature to run in which improves reliability. And it gives you constant and abundant source of energy. You'd probably want some sort of backup energy source and possibly you'd have nuclear reactors for industry, but you'd not be relying on a small number of advanced power plants requiring complex components or special fuel. Instead your main power source would be distributed over the entire upper surface and use fairly simple components manufactured locally. And use no fuel.

Politics

If all the people on a planet live in your city, you are the planetary government. In most settings and political systems, being a planetary government is a good thing. There might be strings attached, but you will almost certainly be given more freedom to implement your own local policies than a crummy space habitat with the same population. Of course, you'd have more responsibilities and oversight too, but if you just want to avoid interference, and not hide dirty secrets from powers to be, being a planetary government is nice.

If nothing else, a planetary government would almost certainly have a legit claim on all the resources of its star system by convention. A planetary government could also do diplomacy with neighbouring systems on an equal basis.

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Helium 3 with lots of side benefits
If the Venus like planet is the only planet in the system or if all of the other planets are gas giants or too far out from the sun or too close in, then it would be a better location for a base than in orbit because an atmosphere would provide shelter from solar radiation as well as a ready source of materials such as water and oxygen. It would make maintenance of internal pressure much easier if external pressure was roughly the same.

If the surface was like Venus then the surface would not be a good location due to temperature and pressure considerations. If the surface was highly volcanic that would make it an even less favourable place for a base and it could provide a city sized variable temperature back drop making the hiding a lot easier especially as the aerostat is moveable around the planet and possibly has the capacity to dive deeper within the atmosphere if need be (within bounds) to help avoid detection.

Being located high up in the atmospher also makes launching into space much easier as there is no need to fight through the dense lower atmosphere.

An added reason why the aerostat should be used could be the presence of Helium 3 in the atmosphere at very low but extractable levels. If this was necessary in fusion drives for the FTL travel then it would be a valuable commodity.

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Politics

Current space treaty says that asteroids and planetary surfaces are free game, and can't be sovereign. Add to it. make it cover all kinds of uses of space and surface. Add years of treaties, documents, agreements to make it bizarre construction most of our real world international politics is. And then...

make them "overlook" atmospheric objects.

To an extent it may be the case already. Nations keep jurisdiction on objects in space and on objects on celestial bodies. I agree that this probably also means objects in atmosphere. But we have no precedent. Make it in your world. Make it out of any national jurisdiction as long as it does not touch the ground. No jurisdiction means no taxes, no worker unions, banks that does not report to good old Earth, and many other benefits. Like tax haven on steroids.

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Fuel Mining

Let's say there's an aspect to FTL travel in your 'verse that requires the manufacture of a very expensive compound, a key ingredient of which can be harvested from the atmosphere of your planet, call it Element-X

Element-X is rarer than rocking horse droppings, but it's emitted from a couple of huge volcanoes that have been spewing massive amounts of it and other toxic crap into the atmosphere for a couple of hundred thousand years. Element-X breaks down quickly outside of it's natural environment, so your city has to hover directly above the volcanoes as close as possible to maximise the Element-X they harvest. But if it gets any lower then planetary conditions and/or volcanic exhaust compromise the citys infrastructure, it's something they can tolerate for short amounts of time maybe as a defensive mechanism.

Make your city like a vertical tube with the upper end protruding above the atmosphere, this will allow visiting ships to dock without getting too deep into the gravity well or having to bother with rigging their ships for atmospheric conditions or landings. Also makes it a lot easier for those ships to leave.

So your tube city has a figurative and literal upper and lower class. The lower parts of the city won't get much light, that'll be where the heavy industry and harvesting takes place. It'll be a whole bunch of no-fun to live there. The upper sections of the city are where the exotic ships come and go, where the elite work in a bright, bustling cosmopolitan environment. They have the opportunity to travel unlike the "underlings". They'd also be physically closer to any attacks from pirates, so maybe there's an implied historical-societal debt. The "angels" might've successfully defended the city in the past (think Battle of Britain) and aren't shy about using that fact as justification for keeping the underlings in their place. After all, only the elite are smart enough to be pilots, right ?

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There are a few reasons you might have an aerostat city

Defense

Your city (assuming the planet has venus like conditions) would be floating around where the atmospheric conditions are similar to earth which is to say a comfortable temperature and pressure which on venus is at about 50 km of altitude which leave a large amount of atmosphere in between you and anyone that may be trying to find you from space. You could also easily design the city to "fall" lower in the atmosphere in an emergency putting more kilometers of hot clouds between you and any observers. You could also use the thick atmosphere to hide uninhabited anti orbital defense weapon platforms deep in the atmosphere floating randomly around the planet. So if the creators of your city were scared of attack an aerostat would be a much better choice than an easy to spot space station

Safety

In space if you get shot or someone breaches the outer hull you start to rapidly lose air with no real way of getting it back other than somehow refining it from the minerals around on the surface, or getting it shipped in if your city is not on a planet or moon. In an aerostat since the pressure outside is almost at the internal pressure(and you would want to keep the internal pressure higher than the outside so you would leak out and not let atmosphere in) leaks are much slower on an aerostat and you can relatively easily separate what you need out of the local atmosphere so having leaks in your system may not even be that big a deal. Also if anything fails outside or your aerostat since the outside will be a similar pressure and a comfortable temperature you could walk outside without a bulky space suit, just a tank of air, a mask, and likely some form of full body suit to protect you from anything not good in the air. (on venus this would be sulfuric acid clouds) So if your founders like a guaranteed source of air they may want an aerostat

Gravity

Even if your setting has artificial gravity for space borne structures and ships you will need to power it somehow, perhaps your founders saw how much energy it took to run the artificial gravity on space stations with citizens numbering in the millions and decided it would be much better and cheaper to have natural gravity.

Alternatively if you don't have artificial gravity all you have is spin gravity which some people may not like as it's not "real" gravity. Not to mention spin gravity adds a lot of complexity and stress that is a single bulkhead from the airless void

Refineries

Most methods of refining metals generate a lot of heat and heat is very hard to get rid of in space so your cities original purpose could have been to refine the metals that the asteroid miners brought in quicker than any space based facilities. Since you also said that ftl takes month I imagine that shipping ore to another system would be prohibitively expensive so why would anyone want to ship unrefined ore anywhere?

Fuel

Depending on what you use for fuel in your setting the aerostat may be the only source for it. If ships run on hydrogen they can skim out of the atmosphere of your planet the aerostat and its many defenses may shoot at anyone trying to "steal their air" forcing people to buy fuel from your aerostat which sits on a chokepoint of interstellar trade

Surface mining

Just because the surface is inhospitable to people does not mean you cant mine from the surface of your planet, your aerostats could have legions of robots mining valuable ores and metals from the surface of the planet that they can then send up in planes to the aerostat. It would be much more costly to launch all the goods to orbit from the ground through all that atmosphere and against gravity. Also you could have large pipelines running from your station to the ground pump stations to siphon oceans of (depending on how horrible it is at ground level) oceans of acid, metals, or something more exotic.

Tourism

They actively encourage people to come see their glorious city floating in the clouds, see sights that you can't see anywhere else in the galaxy. You can do things that are impossible anywhere else, go base diving in the clouds, rent a glider and fly around the aerostat, take advantage of the lax drug and weapon laws, experience their luxury spas, etc. Or alternatively advertise that anyone can start a business on the aerostat, that your ability to move up in society is solely based on the amount of profit you make, you have the best universities and labs in the sector and there are always rich people willing to finance novel science tests. (also again the very lax laws on human testing may attract some less than reputable scientists)

Terra Forming Legalities

The elites living on the aerostat want to terraform the world into a veritable eden, but according to interstellar law no one may claim land on a planet/moon/asteroid they do not have a physical presence on and unclaimed land may be claimed by anyone who is passing by that wants to set up. So to ensure they have claim to the world under interstellar law they established a physical presence (the city) and of course these elites who want to claim the entire world don't want to live like the common people in the gravity less and dangerous hell of a space station they made the aerostat a luxury resort for themselves and added any of the above industries because why not make more money while we wait for our investment in real estate to pay off

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