5
$\begingroup$

This is my first question in the series "Saturnian Cloud cities". The second question is Ice Harvesting planes

My cloud-city is centred on a low altitude region just below Saturn's cloud tops, and it is lifted by a hot hydrogen balloon, which is heated by graphene cables that are many miles long and dip into the cloud tops to harvest geothermal energy from Saturn's interior. Electricity is harvested by massive wind turbines which spin under the intense hurricane-force winds of Saturn, which is then used for artificial lighting to grow algae and plants for oxygen and food.

The copper weights hanging at the bottom of the cables, weigh the airship down, which can be lifted barely by the hydrogen airship, but cannot be moved due to the sheer weight. And since copper and graphene are good electric conductors, the weights can transfer them to the cables. This would allow the balloon to stay still and not negate the wind energy.

Also, the cloud-city would have a launch pad for rockets to take off and land. And the population of the cloud-city is about 2,000 people, 3,000 pets, and 1,000 livestock creatures. Area of the cloud city is about 100,000 km2, approx. the area of Mudanjiang Megafarm

Can this concept for a cloud city on Saturn work?

A diagram for reference:

enter image description here

Edit 1: So as to clarify some facts about my cloud city:

  • The cloud-city is NOT floating in the water ice layer, instead it is just inside the ammonia ice layer, and let's just assume the rigid-hull balloon has some hydrophobic coating to prevent icing or damping.
  • The geothermal cable doesn't stretch down entirely to the core, it is instead hanging just below the water-ice cloud deck, to get heated by the hot gases.
  • I have edited the diagram to clarify the wind-turbine problem.
  • The livestock consists of cows, goats and sheep
  • The pets are cats and dogs, though you can add some fish or apes or even some exotic livestock like birds, if you want to.
  • The mass of the copper weights are enough for the hydrogen to just barely lift, but not be moved
  • Except for airships and some sophisticated equipment, the development of the people on that airship is just more than that of 2022 Earth i.e. they haven't discovered fusion, or some strange tech. But, they can launch rockets to its moons, like Titan or Enceladus
$\endgroup$
3
  • 3
    $\begingroup$ I don't think that geothermal cables would provide enough anchoring for wind turbines to provide enough power to fuel this stuff. This colony is drifting together with the clouds, so wind strength vs the turbines is close to zero. Also there's a cable+balloon toughness question, as the cables have to be pretty long to reach areas where it's hot, and if there will be wind speed difference down there vs the main hull, these cables can well be pulled out of deep and/or be torn away. $\endgroup$
    – Vesper
    Aug 9 at 10:51
  • 5
    $\begingroup$ Why so many pets? $\endgroup$
    – Gillgamesh
    Aug 9 at 12:13
  • $\begingroup$ I've read through a paper on a Venusian cloud city design a while back and there they just dropped (wind) turbines on a cable into the deeper layers of the atmosphere. The difference in density and windspeed at the habitat vs the deeper turbine height are sufficient to extract a lot of energy. $\endgroup$ Aug 10 at 6:31

3 Answers 3

10
$\begingroup$

There are a few issues with a city based on that design. A floating city will be pushed by the wind until it reaches nearly the same speed as the air around it. This would negate the use of wind turbines, as they would be traveling along with the wind at nearly the same speed. The city would need to be anchored in order to prevent movement, which would be impossible.

The balloon itself does not need to be suspended above the city. Simply encasing an area (similar to a snow globe) with a single atmosphere of pressure (1 bar) would prevent the city from descending beyond a certain depth as the external atmospheric pressure increased. “Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185 to 270 K.” (https://en.wikipedia.org/wiki/Saturn) That temperature ranges from -126 to 26 F so insulation would be needed but water ice could be harvested. There is no need for a hot hydrogen balloon, just a single atmosphere of breathable gases. Depending on the size of your atmosphere, and the weight of the station construction material, you could design it to float at whatever height you desire.

As for energy, Saturn has a hot core, but that core is a heck of a distance from where a city would float. Dangling cables to pull heat up to the city seems silly, and would add tremendous weight to the city, when they could simply pull in hydrogen from the atmosphere and burn that in a generator. There are also trace amounts of fuel grade gases such as propane and methane, which could be captured for energy production. They could always send ships to harvest liquid hydrocarbons from Titan. If your world has discovered fusion power, then you have a nearly unlimited fuel supply floating outside your window. Fusion fixes most problems.

A city floating at a depth where water ice is abundant would potentially face the issue of snow and ice forming on its exterior. Ice would increase the weight of the station, causing it to sink further. There would need to be measures in place to prevent such a build-up. This could be something like a thermal mesh which overlays the surface of the station and keeps the exterior temperature just above freezing. The melted ice could be directed into collection points where it would be pumped into the station or simply be allowed to fall off back into the atmosphere. It could also be something as simple as small robots with RTGs which walk across the surface and melt the ice using their thermal radiation. I am sure you can figure something out.

Edit: The temperature you are trying to capture would range from 80 F (300K) to 260 F (400K). There would be some loss as the heat going up the cable went through the colder regions of atmosphere. The hotter an object, the faster it radiates temperature away. It is unlikely that much heat would be able to reach the station after traveling through the miles of cable suspended in cold air.

As for your weights keeping the station in place, that would not happen unless they were dragging along the surface. Weight does not slow something down, friction does. This is why cars slide on icy roads, a lack of friction. The weight of the car remains the same. But listen, if you want it to work then just say it works. This forum is not designed to figure out new technologies or to brainstorm new ideas, but to answer direct questions. So to answer your question: No, this concept for a hypothetical cloud-city on Saturn would not work in reality… but it can still work for your story. For it to work the way you want, we would need to throw out physics. You can still tell an interesting story even if the world is not based 100% on hard science.

$\endgroup$
7
  • 3
    $\begingroup$ Your opinion is valuable but there is a problem. In order to burn the hydrogen gas in order to heat the airship poses a dangerous shortage of oxygen to the colony, as the algae simply cannot keep up with the amount of oxygen being consumed. Also, there are only "traces" of methane and propane in the atmosphere. The airship would need one hell of a filter in order to filter out the methane and propane, also using up tremendous amounts of energy. $\endgroup$ Aug 9 at 17:25
  • $\begingroup$ @FuriousNukefrostArcturus - Can't you just solve the oxygen problem with more algae? $\endgroup$
    – Bobson
    Aug 9 at 19:39
  • 2
    $\begingroup$ The burning of hydrogen emits water, not CO2. The oxygen can be recovered through the use of electrolysis, but it is not an energy positive process if done in this way. If you want to avoid future tech like fusion, then you could always use nuclear power on board your station. Any waste could simply be dropped over the edge of the station. They could also pump liquid methane from the surface of Titan, burn that to produce energy/CO2, and pump the CO2 into algae vats to recover the oxygen. $\endgroup$ Aug 9 at 19:43
  • $\begingroup$ Btw, if the copperweights don't solve the problem and the wind turbine can't work, then would it be possible to simply use the waste heat from the geothermal cables and use it for electricity generation? Or if the geothermal cables also lose their heat, then is there any alternative solution for fuel and electricity. Specifically, how would I heat the balloon to stay aloft, and generate electricity? BTW, my colony uses modern laws of physics, no magic. $\endgroup$ Aug 11 at 10:07
  • $\begingroup$ @FuriousNukefrostArcturus You do not need to heat the air in the balloon, simply have less air inside than outside. This will make it more buoyant than the air around it. Since Saturn has such a thick atmosphere, you can have an Earth level of pressure and still float. As for electricity, use nuclear. It is the most efficient for its size, and the waste can be tossed overboard. $\endgroup$ Aug 11 at 14:50
2
$\begingroup$

I like the geothermal cables.

Mostly because they would glow at night. ALso because deep Saturn beasts might sometimes bite one and tow the whole city around, like in Old Man and the Sea except on Saturn.

But @Gilgamesh is right in the comments - the Saturnalians would not perceive the fast wind because they would be moving nearly as fast. Turbines might not generate that much. That is OK. You can use your geothermal cables to generate electricity. People do that on Earth but unfortunately not with cables. Use the cables to heat a working fluid and then have the fluid turn a turbine.

I would like an electrical turbine that both generates electricity and captures heated waste gas for the balloon.

If you really want another system for electricity generation you could have the 1000 pygmy goats take turns on a treadmill. This will generate electricity and help them stay fit.

$\endgroup$
10
  • $\begingroup$ That was @Vesper Not I :) True that the city would drift along nearly the speed of the wind. There would still be a significant difference and depending on design of the city itself it could maximise the air flow around it to capture as much of the difference as possible. Which will be significant. Along the same lines the geothermal lines might be better used to capture the electrical differential between the atmospheric layers. $\endgroup$
    – Gillgamesh
    Aug 9 at 13:56
  • $\begingroup$ @Gillgamesh - that electrical differential is a sweet idea. Lightning harvester! $\endgroup$
    – Willk
    Aug 9 at 14:10
  • $\begingroup$ The risk isn't the fast, it is turbulence, upwellings, and shear. $\endgroup$ Aug 9 at 14:59
  • $\begingroup$ @Gillgamesh Anytime the city is not moving at the local windspeed, it is accelerating to match the local windspeed. In a steady wind, the city will eventually have zero apparent windspeed, so the turbines will only work when the wind changes speed/direction. And if that's the case, you now have the whole city lurching around as it accelerates in whatever direction the wind is blowing, making it a rather uncomfortable place to live. $\endgroup$ Aug 9 at 15:08
  • 1
    $\begingroup$ @Gillgamesh Drag causes relative deceleration between the air and an object meaning that whatever the windspeed is, the city's speed will change to match it (if the city is moving too slow it will speed up, if it is moving too fast it will slow down). Similarly, a hot air balloon drifts at exactly whatever the local windspeed is - you don't feel any wind as a passenger. $\endgroup$ Aug 9 at 15:33
2
$\begingroup$

It is a napkin sketch, so not enough information.

Do you have star-trek level of technology and materials?

Where, in terms of latitude, were you thinking. Near the equator those winds are going at ~1000 miles per hour while comparatively small north-south changes can make that vary substantially. Up around 40 degrees it looks like they are relatively negative, suggesting that there may be quiescent regions that have adjacent less quiescent regions.

https://solarsystem.nasa.gov/resources/11480/saturns-winds/

Perhaps something that looks like a Phantom-Menace style pod racer, but done with wind turbines? On Saturn they would be extracting energy from the air, and sending it to the colony pod.

kerbal prototype saturnian wind generator

Here is what the ESA says about the atmosphere of Saturn, in terms of its depth: https://www.esa.int/Science_Exploration/Space_Science/Cassini-Huygens/Saturn_s_atmosphere

The ammonia outer layer (ammonia is a great refrigerant aka material for phase-change driven powered heat transfer) is about -250 C, or about 25K, its very very very cold.

Just above the tropopause (130km in) it is about 0C, or merely ice cold. That is a big temperature swing, but it takes about 130km to happen. Near the core it is upwards of 11000C. A decent heat pipe, if it were strong enough, would be a plentiful energy source.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .