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Floating City Experiment on Earth

Aerostat Habitat Experiment
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In the Venus atmosphere, ~50 km above the surface the air pressure and temperature are the same as here on Earth surface, and you could literally go out and walk with a swimsuit. Furthermore, the atmosphere is made of 95% CO2, meaning that air balloon would have a lifting power due to buoyancy, much like helium in Earth's atmosphere. Thus, establishing aerostat habitats and floating cities has been envisioned.

However, since there are several gasses that are lighter than air, and the same idea (of creating floating cities) could apply to Earth.

The idea is to try to do it on Earth.

To begin, I guess one could start manufacturing relatively small spheric balloons filled with methane (CH4) or (which is cheap, and still has a lifting power comparable to the lifting power of air on Venus). To prevent methane from fires, one would add all of those balloons into another (larger) balloon filled with Nitrogen (N2), which is rather inert, and still slightly lighter than air.

Inyuki, Jun 10 2011

Wikipedia - Aerostat Habitats and Floating Cities http://en.wikipedia...and_floating_cities
[Inyuki, Jun 10 2011]

Wikipedia - Atmosphere of Venus http://en.wikipedia...Atmosphere_of_Venus
[Inyuki, Jun 10 2011]

Wikipedia - Gasses Lighter than Air http://en.wikipedia...ki/Lighter_than_air
[Inyuki, Jun 10 2011]

"Aerostat 'Xities' over Venus" http://www.moonsoci...bpaper.htm#aerostat
[Inyuki, Jun 10 2011]

[link]






       Well a standard hot air balloon lifts a basket, which is rather modest to call “city”. The Hindenberg had rooms with pianos in, which is getting more like a building, but still a far cry from a “city”. How much stuff do we need before we can sensibly call it a city, how heavy will that be, and how much lifting capacity is therefore needed?
pocmloc, Jun 10 2011
  

       Inyuki look up Buck minster Fuller and “cloud nine” floating cities. The idea is to take advantage of ' cube square law'
j paul, Jun 10 2011
  

       [pocmloc], a city usually has buildings and streets, meaning that probably one would have to make them for someone to recognise it as a "city".   

       You need sphere with a radius of only 7.5 meters filled with CH4 gas (under 1 atm pressure) to have a lifting force compensating 1000 kilograms of load.
Inyuki, Jun 10 2011
  

       Yeah, I'm thinking you don't get much street for 1000kg weight.
pocmloc, Jun 10 2011
  

       What [j paul] said. If you build a city on a platform and put a dome over it, the warm air trapped inside will be enough to float it.   

       But you have to build your city either very very big (more than 1000km radius, assuming a mix of buildings and materials similar to London, and assuming the air inside is 5°C warmer than outside, and that the enclosing dome is a hemisphere), or very light (low building density, thin topsoil, not too many roads, no fat people).
MaxwellBuchanan, Jun 10 2011
  

       A "city" with 1000 km radius would cover an area of 3,141,592 square kilometers. European Union is only 4,324,782 square kilometers, according to Wikipedia.
Inyuki, Jun 11 2011
  

       Yeah, well, you gotta thinks big.
MaxwellBuchanan, Jun 11 2011
  

       Maxwell, I hope you are wrong in your estimates I personally hope to own 'cloud 941', a stately home and grounds. No top soil, aero/hydroponics. Built for comfort and privacy, the dome will keep the rain off. And with an MSF hospital in the basement, so I don't loose touch with humanity.
j paul, Jun 11 2011
  

       Well, I calculated for a 10km radius city, covered by a 10km radius hemisphere containing air at 5°C above external temperature.   

       If you assume that the density of a city is about 20 tons per square metre (which would be equivalent to a uniform 10m of concrete everywhere; or a reasonable mix of buildings, roads and open land), it's a long way from floating. Even a density of 1 ton per square metre (which just gives you a 1m layer of soil everywhere - no buildings or hills) won't float at that size.   

       Of course, you could build much, much lighter (a simple floor could be 1/100th as much weight, per square metre), but then you wouldn't really have a "city".
MaxwellBuchanan, Jun 11 2011
  

       (Calculations:   

       Mass of city in kg = pi x r^2 x D
where r=radius in metres, D=density in kg/m^2
  

       Lifting capacity of dome in kg= r^3 x t x 0.008
where t = temperature difference (inside-outside) in degrees celsius
  

       Hence, a 10km-radius city with a density of 20,000kg/m^2 has a mass of 6 x 10^12kg, and a lifting capacity (if temperature difference=5°C) of only 4 x 10^10kg. A 100km city has a mass of 6 x 10^14kg and a lifting capacity of 4 x 10^13kg. A 1000km city has a mass of 6 x 10^16kg and a lifting capacity of 4 x 10^16kg, which is close to break even.   

       Reducing the city density to 1ton per square metre doesn't reduce the necessary size of the city a lot.   

       If you find it easier to think in cubes instead of hemispheres, then each ton of city needs a column of air 1 metre by 1 metre by 50km to support it, given a temperature differential of 5°C.   

       If you replaced the atmospheric nitrogen with helium, your ton of city would only need a 1m x 1m x 1000m column to support it. But then everyone would sound squeaky.
MaxwellBuchanan, Jun 11 2011
  

       )
MaxwellBuchanan, Jun 11 2011
  

       Aeroponics will help create a jungle floating mid-air.
VJW, Jun 11 2011
  

       As I see it even if we switched from half of a balloon to a full sphere those numbers look a bit high,   

       at 15°C according to ISA (International Standard Atmosphere), air has a density of approximately 1.22521 kg/m3. And at 20 the same air has a density of approximately 1.2041 kg/m3. A bit over 20 grams of buoyancy for each cubic metre.   

       Imagine a cube of one metre sides, that weighs one kilogram, 20 grams of buoyancy isn't much use. Now apply square cube law.
Length,---------surface weight,-------volume / lift
1 metre,--------1 kilogram,-----------20 grams
10 metres,------100 kilograms,------20 kilograms
100 metres,----10 000 kilograms,----20 000 kilograms
1 kilometre,---1000 000 kilograms,---20 000 000 kilograms.
For each time the length is increased by 10, the surface area (and therefore it's weight) increases by 100 and the volume (and therefore the buoyancy caused by that volume) increases by 1 000. 166.66 grams per square metre is very heavy for balloon fabric, but then this will need to be more durable than the average balloon. And I like simple numbers.
  

       A 10 km balloon of this type would lift it's self plus nineteen million nine hundred thousand metric tonnes.
j paul, Jun 23 2011
  

       maxwell how did you do your table/list?
j paul, Jun 23 2011
  

       [j paul] Put < br > (without the spaces) at the end of each line.
spidermother, Jun 23 2011
  

       //maxwell how did you do your table/list?//   

       I have a special supply of Manilla envelope-backs reserved for such porpoises. Your figures for air density are about right, and if you make a few guesstimate and assume that pi is about 3, you're in business.
MaxwellBuchanan, Jun 23 2011
  

       Venus' atmosphere has hydrochloric acid, I think. + for testing, though.
Zimmy, Jun 24 2011
  

       thanks [sm]   

       the kg/m3 was ment to be kilograms per cubic metre, it did not come out as intended.
j paul, Jun 27 2011
  

       kg/m³
spidermother, Jun 27 2011
  

       A small apology
in using the cube to show the way that volume increases faster than surface. I may have inadvertently over stated my case. Cube squire law still applies regardless of the shape, but a sphere of a given diameter, will have less volume of the same length.
j paul, Jul 04 2011
  
      
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