Chilling Venus

[kerbiloid]

36 minutes ago, Hannu2 said:

They are ablative materials.

First of all, they are materials with very low thermal conductivity (by 2 orders of magnitude lower than metals').
The ablation happens to them at higher temperatures, they are bad thermal conductors at any temperature.

The silicon carbide fibers do not ablate, that's why they are used in the reentry vehicles. in crew capsules they contain ablative material (the resin), in warheads (where the parasite ablation is undesired) they are used also for their low ablation.
Anyway, you can treat the silicon carbide as both ceramics or fibers, as actually it is both.

Another advantage specially on the Venus is that the evaporative part (the resin) can be manufactured from local materials. Though 450°C is enough low to not replenish it often.

In any case, the ablation isn't necessary, these materials are good with or without it.

36 minutes ago, Hannu2 said:

I would not trust that 150 K temperature difference induce enough mass flow at conditions on Venus.

150 K difference on Venus = 150/750 * 100 %= 20%
On the Earth 20% * 300 = 60 K difference.

So, it should. Also, it is not just vented out, it is an exhaust pipe of a turbine.

So, I guess it will evaporate at least not worse than in a cooling tower on the Earth.

36 minutes ago, Hannu2 said:

How cooling tower work in high density atmosphere and how to build such massive buildings on extreme hostile environment?

No cooling tower on the Venus. Just torches. Unlike on the Earth, you don't need to cool the exhaust, like you don't cool the external heat exchanger of your fridge.

36 minutes ago, Hannu2 said:

. In my opinion it is much more interesting what is practically possible or impossible in foreseeable future and realistic resources.

You mean terraforming?

36 minutes ago, Hannu2 said:

Manned operations on Venus is certainly impossible with these rules.

Hard and impossible with the current existing tech, as nobody even planned them.
But doesn't look requiring any future tech, just engineering.

***

Upd.

The thing is the square/cube law.

The total heat flow from the outside is proportional to the square of the module size.

While the total mass (and thus, the total thermal capacity) of the module is proportional to the volume, i.e. cube.
The cooling system total power as well, as such systems are W/kg ~ const.

So, the larger is the module, the less is heat income / thermal capacity and heat income / cooling power ratio.

And at some critical size (my by-fingers estimation is 100..200 m diameter) the heat income from Venus gets negligible against the inner heat production, so there is no difference if the module is on Mars or Venus.

Edited May 6, 2020 by kerbiloid

[munlander1]

A 50km tall structure. This structure would basically be a giant heat pipe, using the heat from the lower atmosphere to power turbines at the top. There would be a cooling system to allow the turbine's fluids to be recycled.

The electricity generated could be used to cool the lower portions of the structure and the rest can be used to break down CO2.

Edited May 6, 2020 by munlander1

[Nuke]

12 hours ago, kerbiloid said:

No problem, the listed materials are reentry vehicles cover. They survive much greater temperatures than poor 450°C.
Though, the mentioned carbides can be the ceramics you mean.

A hot gas tends to raise up even with no pressure. And the cold room should be shaded from it with a firewall anyway.

I've counted by fingers, it looked workable. Of course, more accurate answers require additional calculations. Probably will do them but currently no time to dive deep.

What is not proved to be impossible can't be considered impossible.

i kind of think your biggest issue will be structural materials. all of which need to be rated to maintain their structural integrity at high temperatures. and granted the plant internals probably aren't as different as a terrestrial plant. then you got corrosion to worry about. how do you maintain the exterior structure, repairs to the hull? going out and  re applying coatings will be a regular occurance. then you got huge heat gradients to worry about which is going to play havoc with metals. and then how do you even build it, or do you just drop the whole thing from orbit?  perhaps an outer structural hull, with the inside pumped down to vacuum. with an internal chamber thermally isolated from the external.you would need some radiant heat shielding on inner dome. i suppose you can put your high temp heat exchangers in this area. of course since the whole thing requires active cooling, you need multiple redundant reactors. and you probably want some kind of crew evac system if there is crew, and it would need to get them to orbit or at least bubble base in the upper atmosphere. 

 i dont think its a matter of impossible or possible, but how much you want to spend. though would probably require significantly more robust space infrastructure to setup. 

Edited May 7, 2020 by Nuke

[K^2]

The main obstacle with colonizing surface of Venus is that without building extensive infrastructure at the cloud layer, trip to Venus is one way. Yeah, we have materials that, in sufficient quantity, will provide adequate protection and can be cooled relatively cheaply. Nothing heavy enough to withstand the pressures of lower layers is leaving that planet, however. In order to connect Venus to the rest of Sol, you have to have a launch complex at the cloud layer, and in that case, there is zero reason for your main population to be locked in tin-cans at the surface. If mining operations on the surface are important, it might be necessary to have some human presence at the surface, but travel between cloud complex and ground stations is actually pretty straight forward. Blimps with bathyscaphe-like crew compartments are entirely viable for surface-to-cloud transport on Venus.

Without building cloud complex first, who's going to sign up to go to the surface, knowing that they have no way of coming back up, and they are forever locked away in tiny hab units surrounded by environment that will kill the occupants instantly if there's ever the tiniest of leaks. Sure, the later is also true of any orbital habitat, or something on an airless rock, but at least you go to these knowing you have at least a chance of leaving it at some point in the future.

[kerbiloid]

I would like to see at least one cloud base in the Earth sky, bigger than a zeppelin.

[Hannu2]

13 hours ago, kerbiloid said:

150 K difference on Venus = 150/750 * 100 %= 20%

On the Earth 20% * 300 = 60 K difference.

So, it should. Also, it is not just vented out, it is an exhaust pipe of a turbine.

It is not so simple. You have to take viscosity and heat capacity of ambient gas into account. You should use Navier and Stokes equations to solve flow field and show that it can transport enough energy at reasonable temperature.

13 hours ago, kerbiloid said:

So, I guess it will evaporate at least not worse than in a cooling tower on the Earth.

What a good starting point to plan a base to extreme hostile planet. Would you like to be first inhabitant in base built using your guesses?  :-)

 

 

13 hours ago, kerbiloid said:

No cooling tower on the Venus. Just torches. Unlike on the Earth, you don't need to cool the exhaust, like you don't cool the external heat exchanger of your fridge.

What? External heat exchanger is fro cooling. It gives heat to ambient air, which warm up and begin to flow. You have to obey fridge manufacturer's instructions when you build your kitchen. If there is not enough room for air flow fridge overheats and its efficiency and lifetime decrease.

It is exactly same problem in Venus. You must make sure that you generate enough gas flow to transport excess heat away without overheating exchanger. You can not guess based on fridges or other familiar applications on Earth. Venus atmosphere is so dense that practical intuition based on air do not work.

 

 

13 hours ago, kerbiloid said:

You mean terraforming?

Hard and impossible with the current existing tech, as nobody even planned them.
But doesn't look requiring any future tech, just engineering.

Terraforming seems clearly impossible for now. Many unexpected developing steps must happen before it is possible and even then it is not clear is it profitable to anyone able to do it. As I said, I think that humans do not need planets at that technical level terraforming will be possible, if it ever be.

 

13 hours ago, kerbiloid said:

So, the larger is the module, the less is heat income / thermal capacity and heat income / cooling power ratio.

And at some critical size (my by-fingers estimation is 100..200 m diameter) the heat income from Venus gets negligible against the inner heat production, so there is no difference if the module is on Mars or Venus.

This is true. But how realistic is building of that scale in Venus? What kind of technology is needed to transport of fabricate materials and build such huge buildings? And if we assume such a technomagic, what is reason to build on such impractical environment? Things may be impossible also if no-one with enough resources to make them has any reason or will to do it.

 

[kerbiloid]

41 minutes ago, Hannu2 said:

It is not so simple. You have to take viscosity and heat capacity of ambient gas into account. You should use Navier and Stokes equations to solve flow field and show that it can transport enough energy at reasonable temperature.

That's what I call "needs additional researches".
You can't just say "it's impossible because too hard".  Similar solutions happily work in powerplants, submarines, and other strange places. This idea is to combine known technologies, mostly an engineering problem rather than a question of scientific discoveries. Maybe it's possible, maybe not, like everything irl.
 

41 minutes ago, Hannu2 said:

What a good starting point to plan a base to extreme hostile planet. Would you like to be first inhabitant in base built using your guesses?  :-)

Would you be among the first Venusian cloud base dwellers?
What did Musk say about his presence on Mars?

41 minutes ago, Hannu2 said:

What? External heat exchanger is fro cooling. It gives heat to ambient air, which warm up and begin to flow. You have to obey fridge manufacturer's instructions when you build your kitchen.

You don't have walls and ceiling around the base on the Venus. The hot exhaust happily expands and flows away.

41 minutes ago, Hannu2 said:

Terraforming seems clearly impossible for now. Many unexpected developing steps must happen before it is possible and even then it is not clear is it profitable to anyone able to do it. As I said, I think that humans do not need planets at that technical level terraforming will be possible, if it ever be.

I see nothing to colonize in the known space. But if, then.

41 minutes ago, Hannu2 said:

But how realistic is building of that scale in Venus? What kind of technology is needed to transport of fabricate materials and build such huge buildings? And if we assume such a technomagic, what is reason to build on such impractical environment? Things may be impossible also if no-one with enough resources to make them has any reason or will to do it.

What's a reason to colonize Venus at all? No soil, no oil. A cloud city - even more useless even if have it built.
I see no reason for something of that, rather than having a local base at a special place. Maybe a scientific, maybe a mining, maybe a military defense.
And as I say, a permanent local base looks possible. Cities could be, too, but hardly make sense.

Another thing with this cylinder (not that large, it's a normal battleship size) is that once you use fusion reactors, you can produce enough thrust with it (instead of cooling) to make this base actually a landing spaceship.
And this spaceship is equally appropriate for Venus, Earth, Mars, or whatever.

Until that I still don't plan to "build" such base there, but to "land" it with help of its fission plant and thermal nozzles as landing engines.
Just when fusion reactors get plausible such base will can also fly away.

So, the question of this base purpose turns into the question of a landing site.

Edited May 7, 2020 by kerbiloid

[mrfox]

 

22 hours ago, kerbiloid said:

. Your fridge works at 300..350 K, while the Venusian module at 800..1200 K, but the principle is the same.
Of course you need something heat capable as coolant, maybe (but not necessary) hydrogen.

What sort of coolant pressures would this hydrogen based refridgeration system be working at to reject heat at 800-1200K?

Edited May 7, 2020 by mrfox

[kerbiloid]

21 minutes ago, mrfox said:

What sort of coolant pressures would this hydrogen based refridgeration system be working at to reject heat at 800-1200K?

The hydrogen (if really hydrogen, rather than ammonia or nitrogen) is not 800..1200, it's cooled in the turbo adiabatic heat exchanger down to deep minus (say, "-100°C") and gets between the hull layers, never becoming warmer than 450°C in the outer layer and somewhat hotter than room in the internal layer contacting with room. I.e. the "hydrogen" stays in "-100°...+400° C" range.

Then it gets into the turbo heat exchanger, gets adiabatically cooled back to "-100°C" and again passes into the hull cooling system.

Its heat turned into job in the adiabatic exchanger heats the sucked CO2 from +450°C to "+800"C", then the flow of hot CO2 gets exhausted into the +450°C atmosphere as a fiery torch (by 350 K hotter than the external "air") aside the base and dissipates in air.

The pumps and the exchanger are powered by the nuke reactor. All this machinery is cooled same way.

The fiery 800°C torch aside the base is shaded from the base by some firewall, maybe a natural hill or a crater wall.

https://en.wikipedia.org/wiki/Turboexpander

***

In a a short-term mobile device, like a crewed rover, they can use just a high telescopic pipe with golden umbrella.

Edited May 7, 2020 by kerbiloid

[Shpaget]

For floating in cloud bases, the bigger the better, regarding the square/cube law, but what about wind shears? Would large floating structures (and hence, I assume, not very rigid) be capable of withstanding winds? What's the weather like up there anyway?

[Nightside]

1 hour ago, Shpaget said:

For floating in cloud bases, the bigger the better, regarding the square/cube law, but what about wind shears? Would large floating structures (and hence, I assume, not very rigid) be capable of withstanding winds? What's the weather like up there anyway?

Is there a jet stream?

[Rakaydos]

15 minutes ago, Nightside said:

Is there a jet stream?

There's a super rotation, which I've always assumed to be like a jet stream on steroids. Anyone want to correct me on that?

[kerbiloid]

Turbulences turbulate.

P.S.
"disturbed by turbulences" sounds so recursively.

Edited May 7, 2020 by kerbiloid

[K^2]

8 hours ago, Shpaget said:

For floating in cloud bases, the bigger the better, regarding the square/cube law, but what about wind shears? Would large floating structures (and hence, I assume, not very rigid) be capable of withstanding winds? What's the weather like up there anyway?

Pretty consistent. There is no differential heating due to continents, since all the solar energy is absorbed by opaque clouds, and the Coriolis effect is weaker than on Earth. So while there's considerable wind speed in the cloud layers, the shearing isn't as big of a problem. There's some weather, so some amount of steering might be necessary to avoid regions of turbulence, but with good forecast, it might be enough to change elevation. I'm sure there's a limit to how big these can get anyways, but you don't necessarily need these things to be enormous. A square kilometer at city population densities can be in tens of thousands of inhabitants and still have room for infrastructure. Furthermore, you definitely want these to be modular, so there is an option to decouple in case you can't avoid particularly turbulent area.

And yeah, at relevant altitudes, there's effectively just the equatorial jetstream. Things get more exciting at the boundary with thermosphere, but that's too high for cloud cities, anyways. At the relevant altitudes, the atmosphere is super-rotating, which means the cloud city will be "orbiting" the planet. Location is dynamically unstable, and left to its own devices, the cloud city would drift towards polar vortices, which would be bad. However, you can utilize the thermals at the equator to actively stabilize the cities there, giving you most stable weather conditions and a good location for launching to orbit.

[kerbiloid]

The place where all the solar energy is absorbed by opaque clouds is the best for photosynthesis and agriculture.

And an aerial Balloon City is the best place to place ~10 tonnes of soil or algae tanks per 70 kg human in a city of thousands of inhabitants to let them eat something.
If they are vegans. Flesh eaters need several times more plowland.

A non-rigid envelope in a turbulent air.

Spoiler

Hope, the cloud dwellers have strong stomachs.

[KerikBalm]

On 5/6/2020 at 4:27 AM, sevenperforce said:

Genetically engineer a photosynthetic, acid-resistant bacteria that can reproduce in aerosol form and loves to split CO2 into diatomic oxygen and carbon-carbon chains it uses to make its own encapsulation (which allows it to float).

Accidentally release it on Earth and wipe out all life.

Physics says no.

You can't just say "genetic engineering", and get little machines to do whatever you want. There are massive problems to solve.

One is a lack of water, Venus has very little hydrogen. Life uses hydrocarbon chains, and the hydrogen bonding between is extremely important for all of life's processes. Life will not just subsist on Carbon and Oxygen.

On top of that, you've got very little nitrogen... 3.5%... is that enough? 3.5% of 90 atm is, but if the life is going to be floating in the upper clouds around 1 atm... its not. Life needs CHONP in relatively high amounts and to a lesser amount S , plus trace amounts of metals for catalytic processes. In the atmosphere of Venus, you've got basically just C,O, and a little N. Life is not going to survive there, it needs to be able to get material from the surface, and the 20 ppm water vapor is not going to supply enough hydrogen... nor has any life ever been found to survive in a water activity so low. That is much lower than the putative brines that max transiently exist on Mars, and even those have water activities too low for any life we know... and there's plenty of selection for life that can reproduce in low water activity environments on Earth.

It hasn't evolved on Earth despite 4 billion years or so of selection, so it seems very likely to be impossible.

On 5/6/2020 at 12:51 AM, Nightside said:

If we added something reflective to the atmosphere to reduce solar radiation, what would happen as it cooled off? 

Would the sulphur dioxide cool enough to precipitate out of the atmosphere?

Could atmospheric gasses liquefy at lower temps?

As already stated, Venus' atmosphere is already pretty reflective. The best bet (as suggested) would be a sunshade at the L1 point.

Any gas will liquefy at lower temperatures, if you get the temp low enough (and have enough pressure for a liquid phase, otherwise it will do like dry ice and directly freeze and become solid).

But what liquids will you get?

https://en.wikipedia.org/wiki/Atmosphere_of_Venus

Not very useful ones... liquid CO2... liquid nitrogen? 20 parts per million of the atmosphere is water. That is 0.002%. Compare that to Earth's 0.25%. Sure, Venus' atmosphere is about 93x more massive, so you might say that its equivalent to 0.186% water on Earth if you were to get rid of most of the other atmosphere constituents and bring the pressure down to 1 atm...

So, now imagine we removed all the icecaps, oceans, and lakes from Earth, and the only water left was what was in the atmosphere... sure some of it would rain down.. but that would be insignficant.

The mass of Earth's hydrosphere is about 1.4x10¹⁸ tonnes, of which only 2.0x10¹³ tonnes are in the atmosphere

https://en.wikipedia.org/wiki/Hydrosphere

Thats 1/70,000th the amount of water on Earth, and Venus has less than that. 70,000 *.25/.19 = 92,100.

Earth has roughly 92,000x more water than Venus. That's nearly 6 orders of magnitude more. This poses a serious problem for any teraforming project for Venus, and a serious problem for putting any life as we know it on Venus.

Edited May 8, 2020 by KerikBalm

[kerbiloid]

So, if they liquefy and collect the whole Venusian atmosphere, they can build an underglass oasis full of water, soil, and plants.

Sounds inspiring.

***

Btw, if build such underglass oasis, where should it be placed, when the Venusian days lasts for several months, and the disappeared atmosphere won't be protecting from the day heat and night frost?

Edited May 8, 2020 by kerbiloid