Cloud cities

[kahlzun]

Alright, so the mass at 57km would be approx. 500T for the balloon material, and at the alternate of 50km would be 250T? (I've seen 'double the lift force' quoted here a few times), for a total 'city' mass of 100,000T. As you say, a negligible difference of mass compared to whats being lifted.

Using the analogy you provided above, does anyone know how much the airconditioners on a standard aircraft carrier mass? I understand the vehicle is unlikely to experience conditions as extreme as described here in normal service, but it would allow us to see roughly how much mass we would need for the 50km approach.

EDIT: Wikipedia comes through! " There are over 2,500 compartments on board requiring 2,520 tons (2.1 MW) of air conditioning capacity (enough to cool over 2,000 homes)"

Not entirely sure if they use some bizarre tons-to-MW conversion, or if thats the power you get from that mass of AC, but it looks like the difference in balloon material is going to be a fraction of the AC mass, straight out the gate. Also keep in mind that AC is designed for terrestrial operations, which rarely exceed 40 degrees..

Edited March 21, 2014 by kahlzun

[RuBisCO]

Yes for the same setup at 50 km I get 298 tons for the ballons, but that is assuming the temperture of all the air (which is now 20% O2 and 80% N2 at 1.066 bar) is room temp 295 k, and the hydrogen is the same as the venus gas at 350 K, but 1/2 the mass is fine enough approximation for me.

For cooling we need to calculated how much heat is coming in as watts, we then need to caculate the efficiency (COP) of a heat pump having to pump out heat over a differential of 55 K (from room temp at 295 k to 350 K outside) these parameters are very different from an aircraft carrier which does not have such an extreme difference to pump over and often has the ocean as a heat sink. We then need to take a stab at the mass of it based on existing heat pumps.

I've shown the input heat is going to be phenomenal, from conduction alone it could be in the gigawatts since we are dealing with surfaces areas over 1 km^2. of course this assume perfect convection, how much convection there will be is completely unknown, we are going to have hot winds beating against the ballon due to it towing a powersystem at a lower altitudes and thus at different wind velocities causing drag on the habitate balloon. Radiative heating is not even consider but would add to heat input, we also have all the heat from light let in for plant growth.

From wikipedia a real heat pump over the 55 K gradient could move 2.8-2.2 Watts of heat for every watt the heat pump consumes in power. If we scale up a home air conditioner we get between 50-100 W/kg of heat pumping and 20-40 W/kg of power needed at a COP of 2.5. If we assume the powerplant manages 100 w/kg then for a 100 kt city 20-10 MW of heat input would completely negate the reduce mass of smaller balloons in added mass in heat pumps and power plant for those pumps (weight of >250 tons).

We can actually use the light let in for plant growth as the lower limit. Assuming a population of 1000 (1/4 of an aircraft carrier) and minimum of 50 m^2 of plant growth area per person, that means 50,000 m^2 of garden area, receiving 500 W/m^2 on average (1000 W by "day", 0 by "night") the albedo of plants is roughly .25, so of which only 0.5-6% is converted to bio-energy, lets use the absurdly high max of 6%: 71% of the light hitting the plants becomes heat (4% is converted via photosynthesis, 25% is reflected back out) 50,000 m^2 * 500 W/m^2 * .71 = 17.75 MW. So just dealing with the heat to grow food will negate the reduce mass of the balloons, even assuming magical perfect insulation and thus no heat input!

Angel's argument is that flying higher will require twice the volume of gas and twice the weight of balloon mass, but as can plainly be seen flying lower will require so much mass in cooling system and power plant for that cooling system and insulator that having to lift all that will require in the end MORE mass then extra balloon skin and extra gas. The amount of gas required I don't think I have covered but it too is against Angel's argument: the amount of lifting gas needed to be produced per mass actually INCREASES the lower you float, at least within the range of 57 to 50 km. I calculated to lift 100 kt will require 4.1 kt of hydrogen gas and 30 kt of breathable air at 57 km, total volume being 0.2 km^3. At 50 km though you will need 4.3 kt of hydrogen and 36.9 kt of breathable air, despite the volume dropping to 0.09 km^3! This is due to the gas being much more compressed at the lower altitude from 370 mbar to 1066 mbar, so at 57 km the mass is 31 g/m^3 for hydrogen and 459 g/m^3 for breathing air, but at 50 km it is 73 g/m^3 for hydrogen and 1251 g/m^3 for breathing air! So flying lower only saves on balloon skin mass and balloon volume, but adds mass in gas as well as all the aforementioned mass in cooling system, power-plant for that cooling system and insulator.

Balloon skin is going to be much cheaper to make and maintain than a cooling system, and the increase in balloon volume is a non-problem: going from 178 m wide balloons to 232 m balloons is not going to present any show stopping problems, the extra habitable area may be for the best.

For 50 km we need a cooling system to remove every watt of heat produced and every watt that enters, just the heat produced for the basics likes food production will be enough to outscales the mass of balloon skin needed to fly higher. At 57 km though or a passive temperature control altitude we need no cooling system, no power for that cooling system, no insulator, we can use simple clear plastics skin. At that altitude kilometers of surface area are a good thing not bad and more surface area is a benefit not a curse, convection is great and so is conduction, all the problems of flying at 50 km cease to exist or even become benefits when floating at 57 km!

A line can be dragged to balloons that are lower and that lift heavy industry (and no habitats) that can operate at higher temperatures not comfortable to humans. All the way down to power conversion systems. A line stretching from 57 to 37 would have a wind speed gradient of 25-100 m/s at 13 bars of pressure (at the bottom) where wind turbines could be (ones able to operate at nearly 300°C though). We don't need to worry about the drag causing increase convection against the habitat because the more convection the smaller the heat difference we need between outside and inside air and the lower we need to fly, as long as we stay above the altitude where the outside is hotter then the inside air.

Edited March 22, 2014 by RuBisCO

[thelegendaryblah]

why even bother with feasability when it isnt even practical to start with?

jupiter has a lot of "fuel", but it also have a **** ton of radiation (not to mention jupiter's bad weather), which would require rediculus amounts of radiation shielding for both the station itself as well as ships going to the station, this made it very impractical to atempt to colonise any gas giants, perhaps an underground base on one of jupiter's moons would be more practical

i think if humanity were to colonise any significantly large part of the solar system, it would be the astroid belts as there are plenty amounts of water (in the form of ice) for breathing, fuel, hydroponic farms and drinking. the astroid belt does have its own problem like solar radiation/solar storms, but we could always hollow out astroids and build bases in them for shielding. the only "unsolvable" problem with living in the astroid belts would be electricity problems and that could still be solved with nuclear reactors. by the way, there are also iron rich astroids, so they could be used to build stuff (not as good as titanium or aluminium, but still)

[RuBisCO]

why even bother with feasibility when it isn't even practical to start with?

Jupiter has a lot of "fuel", but it also have a **** ton of radiation (not to mention Jupiter's bad weather), which would require ridiculous amounts of radiation shielding for both the station itself as well as ships going to the station, this made it very impractical to attempt to colonize any gas giants, perhaps an underground base on one of Jupiter's moons would be more practical

Under the atmosphere of Jupiter there is not a lot of ionizing radiation... but to my knowledge this thread about colonizing Venus's clouds not Jupiter.

i think if humanity were to colonize any significantly large part of the solar system, it would be the asteroid belts as there are plenty amounts of water (in the form of ice) for breathing, fuel, hydroponic farms and drinking. the asteroid belt does have its own problem like solar radiation/solar storms, but we could always hollow out asteroids and build bases in them for shielding. the only "unsolvable" problem with living in the asteroid belts would be electricity problems and that could still be solved with nuclear reactors. by the way, there are also iron rich asteroids, so they could be used to build stuff (not as good as titanium or aluminium, but still)

Well we all argued with Angel that asteroids are the best candidate for colonization to no avail. Angel is dead set on living in the clouds of Venus, worse at a particular altitude for some reason.

[RuBisCO]

I miss talking about this vision of Venus Cloud colonies, its a fun idea, anyone else interesting on expanding the 'vision'?