The cloud cities of Venus

[pendell]

As seen on Space.com (http://www.space.com/29140-venus-airship-cloud-cities-incredible-technology.html?adbid=10152770412826466&adbpl=fb&adbpr=17610706465&cmpid=514630_20150421_44311636&short_code=2u5i7)




NASA researchers have come up with a plan to send piloted, helium-filled airships cruising through the Venusian atmosphere. The idea, called the High Altitude Venus Operational Concept (HAVOC), could eventually lead to the permanent settlement of Earth's hellishly hot sister planet, its developers say. You can see how HAVOC might work in a mesmerizing NASA video on the Venus airships.

...

Venus is another potential target for human exploration, say Jones and his colleague Dale Arney, also of NASA Langley. At first blush, this assertion may seem surprising; the planet's surface temperature is about 860 degrees Fahrenheit (460 degrees Celsius) — hot enough to melt lead — and its atmospheric pressure at ground level is a staggering 90 times that of Earth.

But HAVOC would avoid the surface, instead hovering about 30 miles (50 kilometers) up in Venus' thick, carbon-dioxide-dominated air. Up there, conditions are much more manageable; atmospheric pressure is roughly what we're used to, and the average temperature is 167 F (75 C).

Venus, which is about the same size as Earth, is also the closest planet to our own, making it the easiest (or at least the quickest) to get to.

Venus "is no worse than the second planet we would go to after leaving Earth," Arney told Space.com. "We started with that in mind, and then we started looking at the orbital mechanics, and some of the ways that getting to Venus and living there and operating there are fairly benign and favorable. That's sort of what kick-started this whole study."


... This is just BEGGING for an SF novel of some kind. No indication whether carbonite will be mined there.

Respectfully,

Brian P.

[Ravens_cry]

Hydrogen would make a good lifting gas on Venus as, a, it's more efficient than ever in the carbon dioxide atmosphere, b, can be extracted in-situ from sulphuric acid and water vapour, and c, there is no risk of fire in a atmosphere without free oxygen. For the majority of lift for an actual flying colony, ordinary oxygen would work. It's a lifting gas in carbon dioxide and you don't need a separate envelope and gondola As for power, taking advantage of the heat gradient through thermocouples and flexible solar panels on the top and bottom (why waste all that light reflected off the cloud tops) would provide electrical needs.

[ace rooster]

It is a really cool idea, and surprisingly feasable. The biggest difficulty is a reliable outer skin against the sulphuric acid atmosphere.

After that the problem becomes what you do when you get there. Energy is abudant, with high speed high pressure winds a few kilometers below as well as large temperature gradients. The difficulty is in getting materials other than carbon, as the only place to get them is the surface. :smallfrown:

This is going to be an entertaining technical challenge, but at least carbon is a good material for building robots that have to work at high temperatures and pressures.

[LibraryOgre]

It's shown up before; IIRC, there are such cities in Eclipse Phase, for example.

[Ravens_cry]

It is a really cool idea, and surprisingly feasable. The biggest difficulty is a reliable outer skin against the sulphuric acid atmosphere.

After that the problem becomes what you do when you get there. Energy is abudant, with high speed high pressure winds a few kilometers below as well as large temperature gradients. The difficulty is in getting materials other than carbon, as the only place to get them is the surface. :smallfrown:

This is going to be an entertaining technical challenge, but at least carbon is a good material for building robots that have to work at high temperatures and pressures.
How's carbon fibre's resistance to acid?

[ace rooster]

How's carbon fibre's resistance to acid?

hmm, I had thought it was pretty good, but on investigation strong hot sulphuric acid is one of the few substances that will attack it. It couldn't be that easy could it. :smallamused:

[Yora]

A height of 50 km would still be well within the sulfuric acid clouds.

However, while sulfuric acid is really nasty to most organic materials, the black mush that is left is pure carbon. Since carbon fiber is a polymer, only the other component material would have to be checked for resistance to acid. The carbon itself is safe.

Other nice things about Venus: While temperatures on the surface are hellish, it gets colder the higher up you go, and at 50km, temperature is similar to Earth.

Also, neither Carbon Dioxide nor Nitrogen is toxic to humans (you just get no oxygen), so sulfuric acid vapor is thankfully the only thing that poses a danger in case you have a leak. And some kind of sprinklers that pump akaline vapor could neutralize it. (Getting the exact balance would be difficult and it would be unpleasant, but damage should be lower than breathing in the pure stuff.) Keep the air pressure inside the platforms and your helmet slightly above outside pressure, and a leak would mean air goes out, instead of Venus atmosphere gets in. Add plenty of pressure detectors inside your structures and any time you notice a drop, you can look for the hole and fix it before a lot of air escapes.
Carbon Monoxide is actively poisoneous, but the dangerous limit for humans is twice as high as in the atmosphere of Venus, so that would not be a threat.

Best thing about being 50 km above the surface of Venus: You still have decent gravity of about 90% of Earth gravity. And being 50 km above the surface is still so close that you wouldn't feel a difference on a hovering platform. (Instead of 90%, you'd have something like 89,9%.) Which is probably really the main selling point of Venus. Mars has only about 40% and from there on it gets only worse.

One claim that I saw, but havn't been able to confirm, is that falling from a platform above Venus would not mean that you fall all the way down to the ground. Human bodies float just at the surface of water, which has a pressure of 1 atmosphere. So you'd only drop to the layer of the Venus atmosphere where the pressure reaches 1 atm and then you just float around, waiting for someone to come and pick you up. Before your air supply runs out, hopefully.

Also, since it has an atmosphere, you also get protection from UV radiation and the like.

Why do people actually care so much about Mars? Screw Mars, Venus is so much better in every way. Well, except the sulfuric acid, that is a bit of a bummer...

[Sith_Happens]

The difficulty is in getting materials other than carbon

Like which ones? The atmosphere also has ample supplies of hydrogen, oxygen, and nitrogen, and there's few things you can't (theoretically) do with just those three and carbon.

[Eldan]

One claim that I saw, but havn't been able to confirm, is that falling from a platform above Venus would not mean that you fall all the way down to the ground. Human bodies float just at the surface of water, which has a pressure of 1 atmosphere. So you'd only drop to the layer of the Venus atmosphere where the pressure reaches 1 atm and then you just float around, waiting for someone to come and pick you up. Before your air supply runs out, hopefully.
.

Uh, no. Pressure has little to do with it. It's about density and I doubt the Venusian athmosphere is ever denser than liquid water or human bodies.

The difficulty, chemistry-wise, would be getting oxygen. Which can be either achieved with electricity, or, more interestingly, with growing plants in an almost-Venusian atmosphere. Plants love high CO2 environments.

[Yora]

Oxygen exist in huge amounts in the form of carbon dioxide. Photosynthesis probably wouldn't be a good option to separate the two, as it requires water, and there barely is any Hydrogen on Venus.

Uh, no. Pressure has little to do with it. It's about density and I doubt the Venusian athmosphere is ever denser than liquid water or human bodies.
The density, even at ground level, is only 6,5% that of water. Though that's still about 50 times as dense as on Earth, that's still practically nothing. How sad.

So the truth remains: Don't fall off.

[ace rooster]

A height of 50 km would still be well within the sulfuric acid clouds.

However, while sulfuric acid is really nasty to most organic materials, the black mush that is left is pure carbon. Since carbon fiber is a polymer, only the other component material would have to be checked for resistance to acid. The carbon itself is safe.

This was my initial thinking too, but turns out that neat sulphuric acid (which it is when there is no water about) will attack even graphite. :smalleek:


Other nice things about Venus: While temperatures on the surface are hellish, it gets colder the higher up you go, and at 50km, temperature is similar to Earth.

Also, neither Carbon Dioxide nor Nitrogen is toxic to humans (you just get no oxygen), so sulfuric acid vapor is thankfully the only thing that poses a danger in case you have a leak. And some kind of sprinklers that pump akaline vapor could neutralize it. (Getting the exact balance would be difficult and it would be unpleasant, but damage should be lower than breathing in the pure stuff.) Keep the air pressure inside the platforms and your helmet slightly above outside pressure, and a leak would mean air goes out, instead of Venus atmosphere gets in. Add plenty of pressure detectors inside your structures and any time you notice a drop, you can look for the hole and fix it before a lot of air escapes.

And what are you using for the alkaline vapor? Sith outlines the elements you have below.




Like which ones? The atmosphere also has ample supplies of hydrogen, oxygen, and nitrogen, and there's few things you can't (theoretically) do with just those three and carbon.


Don't forget sulphur, we have plenty of that too :smalltongue:. While there are many cool things we can do with those elements, the problem is that neat sulphuric acid is an increadably strong oxidiser, and the oxides of all of those elements are gasses (not good for structures). To get something that will resist the atmosphere and stay solid we need elements that will still be a decent structure when oxidised (aluminium, silicon, or most metals). All these elements are already oxidised due to the extreme oxidising atmosphere, and given that our selection criteria is that they must be solid when oxidised, they are naturally all on the surface :smallfrown:.

I can't see any way around it, to build our cloud cities we will need a skin made from the materials harvested from the surface.



In a slightly unrelated note, maybe the greeks were not so wrong with their 4 elements. It seems impossible to build a permanent structure from only air, as given time it will revert to air. To build we will need some earth, and it is not hugely important what the exact composition of it is. While not a complete description, I think in neatly illustrates the difficulty we have.

[Yora]

I don't see any mining taking place on Venus. It seems much more economically feasible to mine asteroids. Getting something down a gravity well is always cheaper than getting it up. Moving stuff in space is also pretty easy, but getting your mined metals from the asteroid belt to Venus would take quite some time. Several years, probably.
Good thing: These transport barges just have to go from A to B, so once you've given them a push to be on their way, they can just drift along with only some automated thrusters to adjust course. Once they get close to Venus, people there would catch the barge and tow it to an orbital factory to be turned into construction parts.

Of course, the first expeditiona would have to bring all their material to build their airships with them.

How exactly would you lower an airship from orbit into the atmosphere. Those things probably would have some difficulty with friction during entry. They would have to be pretty big yet light, which usually translates to "flimsy".


In a slightly unrelated note, maybe the greeks were not so wrong with their 4 elements. It seems impossible to build a permanent structure from only air, as given time it will revert to air. To build we will need some earth, and it is not hugely important what the exact composition of it is. While not a complete description, I think in neatly illustrates the difficulty we have.

Aww... But it would have been a castle made of clouds... :smallfrown:

[factotum]

They would have to be pretty big yet light, which usually translates to "flimsy".


That's not so much of an issue on Venus. The atmosphere is mostly carbon dioxide and the "sea level" pressure is around 90 atmospheres, so it's a *lot* denser than what he have on Earth--thus, you would get the same lift using a much smaller balloon, or could make your airship much heavier and still have it fly.

[Yora]

Yes, but "fly" isn't good enough on Venus. You have to reach an altitude of about 50 km to get above the regions of the atmosphere where everything gets baked by the heat. And at that altitude, atmospheric pressure is so low that it's similar to what you have on Earth near the ground. The density of a C02 atmosphere (1.977 kg/m3) would be noticably higher than an N2 atmosphere (1.250 kg/m3), but your gas tanks probably still would have to have 60 to 70% the volume as you'd need to get off the ground on Earth.

[LibraryOgre]

Oxygen exist in huge amounts in the form of carbon dioxide. Photosynthesis probably wouldn't be a good option to separate the two, as it requires water, and there barely is any Hydrogen on Venus.

The density, even at ground level, is only 6,5% that of water. Though that's still about 50 times as dense as on Earth, that's still practically nothing. How sad.

So the truth remains: Don't fall off.

Usually good advice at 50km above the surface, no matter what's between you and the ground.

[Traab]

Is it wrong of me to wish they would stop theorizing and start trying out something a little simpler, like a colony on the moon? I just want to see them do it in my life time, actually build a self sustaining, (or at least mostly) colony off world. Instead we keep getting all these wild and awesome ideas on ways we COULD colonize other planets and such, but noone ever seems to be interested in going out and TRYING IT.

[Yora]

Because a base on the moon would be boring. And actually building it expensive.

[Forum Explorer]

Is it wrong of me to wish they would stop theorizing and start trying out something a little simpler, like a colony on the moon? I just want to see them do it in my life time, actually build a self sustaining, (or at least mostly) colony off world. Instead we keep getting all these wild and awesome ideas on ways we COULD colonize other planets and such, but noone ever seems to be interested in going out and TRYING IT.

The problem is transit really. We do not have a good way of getting to Venus, or Mars. IMO, we still don't really have a good way of getting to the Moon. Until we can get to space in a efficient manner, all off world construction is really cost prohibitive.

[LibraryOgre]

The problem is transit really. We do not have a good way of getting to Venus, or Mars. IMO, we still don't really have a good way of getting to the Moon. Until we can get to space in a efficient manner, all off world construction is really cost prohibitive.

Not necessarily. I don't have the details, but several of my friends are in the space industry. Safety is a far bigger concern then how we're going to get there... how are we going to build something there that will be habitable for the long term? In many ways, Mars is actually a bit more feasible; the atmosphere gives us something to work with in terms of creating return fuel, a bit of protection from the weaker solar radiation, and a better place to stand from which to exploit the asteroid belt.

[factotum]

A moon base would help in further Solar System exploration--they could mine materials and build rockets there, and the fuel required for them to get anywhere else would be significantly reduced. If they could find a source of water on the Moon then that covers breathing and fuel requirements in one, which would be the important thing.

[Ravens_cry]

Water on the moon, eh?
Funny you should ask . . . (http://en.wikipedia.org/wiki/Lunar_water)

[Eldan]

Now we just need working fusion technology to use all that helium on the moon.

[Ravens_cry]

Now we just need working fusion technology to use all that helium on the moon.

For early colonies, solar thermal would be better. Just like there is areas of permanent darkness, there is areas of near permanent sunlight, and you can set up power stations at regions that go dark at different times. The beauty of solar thermal is how easy it is to expand.A large mirror of lunar aluminium will hold a shine, well, forever, and extracting the aluminium will be part of getting the oxygen from the rocks. 3D printing will build the parts with much less waste than, say, milling or machining, and it doesn't require the umpteen gallons of lubricant and coolant that requires.

[factotum]

For early colonies, solar thermal would be better. Just like there is areas of permanent darkness, there is areas of near permanent sunlight

Er, citation needed? The Moon always presents the same face to Earth, but that doesn't mean it always presents the same face to the Sun--it has a day/night cycle just like we do. In fact, the day/night cycle in question is 28 days long, which means solar would be a very *bad* method of powering your base--you'd need enormous batteries to keep the power flowing during the 14 days of darkness!

[Ravens_cry]

Er, citation needed? The Moon always presents the same face to Earth, but that doesn't mean it always presents the same face to the Sun--it has a day/night cycle just like we do. In fact, the day/night cycle in question is 28 days long, which means solar would be a very *bad* method of powering your base--you'd need enormous batteries to keep the power flowing during the 14 days of darkness!
Citation given. (http://en.wikipedia.org/wiki/Peak_of_eternal_light#On_the_Moon)
It would be better to store the energy as heat in large tanks of a suitable fluid (salt water is a good one.) wrapped in foil and kept thermally isolated, basically making a giant Thermos, for the rare times they go into shadow.

[ace rooster]

Citation given. (http://en.wikipedia.org/wiki/Peak_of_eternal_light#On_the_Moon)
It would be better to store the energy as heat in large tanks of a suitable fluid (salt water is a good one.) wrapped in foil and kept thermally isolated, basically making a giant Thermos, for the rare times they go into shadow.

While 2 locations that are never dark do exist, they are actually very bad places for solar power. Sunlight is almost perpendicular to the ground at these locations, meaning that the energy delivered per square meter of surface is tiny. You need tall structures to get substantial power, and even in lunar gravity that is a significant difficulty. The shadows cast by these structures mean that you can only really have one working effectively.

Where on the moon are you getting large supplies of salt water? hydrogen is in short supply, which is the biggest difficulty, with the lack of nitrogen being a close second. There may be some ice in craters, but I doupt we will want to use that for heat storage.

The principle of storing heat and using stirling engines is sound though, but I think we would be better off using gravel in tunnel systems as opposed to fluids. Low heat capacity and low heat transfer can be compensated for by building it bigger without worrying about using scarce resources.



I think we can summerise the possible locations for a colony as follows,

Venus cloud layer: Energy is abundant, but solid minerals are difficult to access. Volitiles are common, though hydrogen is fairly rare (but very easily harvested). Getting off again is tricky. If we can mine the surface then we have everything we need, which is why this looks attractive

Mars: Energy is rarified, but most elements are accessable, though hydrogen might be uncommon. Getting off is considerably easier than earth or venus. The lack of easily accessed hydrogen could be a big problem though, as this is needed in bulk. If we find aquifers then this looks good, but the lower energy might make things hard.

Moon: Decent for energy, and easy access to most minerals. Possibly some hydrogen access, but it will require mining. I don't see much in the way of Nitrogen though, which could make sustainable life difficult. Escape is pretty easy.

Floating asteroid mining: Like the moon, only better in almost evey way. Energy can be more reliable, and even hydrogen can be easily accessed by choosing the correct asteroids. Nitrogen is still the major problem, but because transport is less of a problem ammonia ice can be easily transported from the outer solar system.


It looks to me like we have a case of 'Nitrogen, energy, ease of escape; pick 2'. Close to the sun nitrogen will be rarified due to it's volitility. I can't find much information on nitrogen content of extra terrestrial rocks, so this analysis could be very wrong, (Please correct me if it is) but nitrogen, hydrogen, other elements (which can generally be grouped together), and energy seem to be the 4 criteria that are important to consider.

[TheThan]

As long as there are green skinned Venusian amazons, count me in. :smallbiggrin:

[erikun]

I understand that radiation is the biggest threat to lunar colonization, at least in the immediate sense. There really isn't a good way to avoid radiation outside geomagnetism. It's the reason we don't have space shuttles flying around everywhere just for the heck of things. The ISS is even still within Earth's magnetosphere, somewhat "cheating" at being in space but still useful in giving us information about what it is like to survive in an extended zero-G environment.

The moon doesn't have a magnetosphere, and isn't close enough to be covered by Earth's. It's going to receive the full radiation from the sun, which isn't going to be hospitable to most stuff there. Mars has a similar problem, as I understand it. I understand this to be a problem for Venus as well, since it doesn't have a magnetic field either.

[LibraryOgre]

The moon doesn't have a magnetosphere, and isn't close enough to be covered by Earth's. It's going to receive the full radiation from the sun, which isn't going to be hospitable to most stuff there. Mars has a similar problem, as I understand it. I understand this to be a problem for Venus as well, since it doesn't have a magnetic field either.

Mars has the problem, but to a lesser degree. It's farther away (so gets less radiation), and has an atmosphere which provides some insulation.

If you want to avoid radiation, on both Mars and Luna, you need to dig; rock makes a good insulator. Digging also has the advantage of giving you an easier seal for atmosphere. It is, however, more expensive and slower than popping up some bubblefabs, so it will likely wait a bit.

[Eldan]

I understand that radiation is the biggest threat to lunar colonization, at least in the immediate sense. There really isn't a good way to avoid radiation outside geomagnetism. It's the reason we don't have space shuttles flying around everywhere just for the heck of things. The ISS is even still within Earth's magnetosphere, somewhat "cheating" at being in space but still useful in giving us information about what it is like to survive in an extended zero-G environment.

The moon doesn't have a magnetosphere, and isn't close enough to be covered by Earth's. It's going to receive the full radiation from the sun, which isn't going to be hospitable to most stuff there. Mars has a similar problem, as I understand it. I understand this to be a problem for Venus as well, since it doesn't have a magnetic field either.

Dust might be an even more immediate problem than radiation. Lunar dust is absolutely terrible to everything.

[Flickerdart]

They found a bunch of massive lava tubes under the Moon's surface, so digging's gonna be the way to go on that one for sure.



I think we can summerise the possible locations for a colony as follows...

What about those fancy gas giant moons with subterranean oceans?

[factotum]

What about those fancy gas giant moons with subterranean oceans?

You'd have to get through a few dozen miles of ice to reach them, though. Building on the surface of such a moon and using the surface ice as a source of fuel and oxygen would probably work, though, so long as you didn't put your ice mine too close to your base!

[Sith_Happens]

They found a bunch of massive magma tubes under the Moon's surface, so digging's gonna be the way to go on that one for sure.

Fixed that for you. This is the science subforum, we have standards here.:smalltongue:

[ace rooster]

They found a bunch of massive lava tubes under the Moon's surface, so digging's gonna be the way to go on that one for sure.


What about those fancy gas giant moons with subterranean oceans?

Generally they are good for all elements, but lacking in energy. Io is the exception, with prevelant volcanism meaning that energy is easy, but because it is hot all the hydrogen and nitrogen has boiled off. The low gravity of the jovian moons means trade between them is possible, but the only advantage over asteroid mining is the timescales for moving stuff.

[Gnoman]

It is, however, more expensive and slower than popping up some bubblefabs, so it will likely wait a bit.

Luna seems like a pretty good place to use nuclear explosives for excavating - just dumping the leftover radioactives on the surface would be a pretty good way to get rid of them, and you'd have to truck just as much out no matter what you used. That would provide fairly large artificial caves to use as staging areas and hubs for the main tunnels.

[Knaight]

Yes, but "fly" isn't good enough on Venus. You have to reach an altitude of about 50 km to get above the regions of the atmosphere where everything gets baked by the heat. And at that altitude, atmospheric pressure is so low that it's similar to what you have on Earth near the ground. The density of a C02 atmosphere (1.977 kg/m3) would be noticably higher than an N2 atmosphere (1.250 kg/m3), but your gas tanks probably still would have to have 60 to 70% the volume as you'd need to get off the ground on Earth.

This is a huge oversimplification. Gas phase densities are highly variable, changing with local conditions. For earth atmosphere you can pretty much use the ideal gas law and look at the decrease in pressure with height when plugging data in (at sea level it's about 1 atm, and the IGL is generally a pretty decent approximation until about 10 atm or so, though it depends on the gas in question, the temperature, and just how precise you need to be). At 50 km on Venus it's also a pretty solid approximation (the ground level atmosphere is a super-critical fluid, it's not being modeled with the IGL well anytime soon).

As for the actual density, the inverse of density is a metric called specific volume. Generally this means mass specific volume, although molar specific volume is also used. Using V as specific volume, you can use the ideal gas law as V=RT/P, or for density ρ=MP/RT. The actual type of molecule isn't hugely important at conditions that can be reasonably modeled with the ideal gas law. Pressure change as the distance from the surface increases is an exponential decay based on the atmosphere and the gravitational conditions, and it decays pretty quickly. So, the density of the atmosphere overall isn't all that important, what matters is the density at a particular point. With Venus having similar pressure and temperature at an elevation of 50 km that Earth has at surface level, the density of the atmosphere can also be reasonably assumed to be fairly similar, barring a huge change in molecular weight.

As for the gravity, it is true that the lower gravity will make one accelerate slower when falling. With that said, that doesn't make a huge difference - for a floating city to be all that viable, it pretty much has to be at stable state, where lower down it's buoyant enough to rise, and higher up it's buoyant enough to fall. If the buoyancy is supplemented with continual generation of thrust, then the gravity becomes more relevant. As is though, the density is going to be extremely similar. It's no more viable than a city that floats ever so slightly off the ground on Earth, and that's before getting into building the things and the transportation difficulties involved.

[Sith_Happens]

ρ=P/RT

That's not the density, it's the concentration. You need to multiply by molar mass to get the density.

[Knaight]

That's not the density, it's the concentration. You need to multiply by molar mass to get the density.

Fixed. Figures that a term got dropped.

[Yora]

One thing just occured to me: With barely any free oxygen in the atmosphere, could hydrogen still ignite and explode? Using hydrogen airships on Earth is quite risky, but if it can't burn on Venus, it would be an excelent lifting gas, having only a quarter the weight of helium.

[factotum]

It may have only a quarter of the atomic weight of helium, but hydrogen gas is a little over half as dense as helium gas is--so it doesn't offer as big an improvement as you might think. Can't see any reason for not using it on Venus, though, and in fact, it would probably be easier to get than helium too--dry as Venus is, there's still more water vapour in its atmosphere than there is helium!

[Yora]

Extracting the hydrogen from the water vapor also has the nice byproduct of oxygen, which comes quite convenient.

[ace rooster]

One thing just occured to me: With barely any free oxygen in the atmosphere, could hydrogen still ignite and explode? Using hydrogen airships on Earth is quite risky, but if it can't burn on Venus, it would be an excelent lifting gas, having only a quarter the weight of helium.

Hydogen airshops are considerably less risky than people imagine here on earth,

The Hindenburg outer shell was coated in nitrocellulose (http://en.wikipedia.org/wiki/Nitrocellulose), mixed with aluminium powder. Nitrocelluose was rejected as an explosive because it was too unstable, and aluminium powder is sometimes used to increase the energy density in rocket fuel. Those visible flames that are so impressive in the film are mostly the result of black body radiation from microscopic soot particles, which you do not get in hydrogen fires (which is why the shuttle main engine had a clear flame). These particles are radiating even more strongly in the IR spectrum, which is how heat is able to travel against the flow in gas fires. Without a coating burning and producing vast amounts of soot hydrogen fires will rapidly blow themselves out if venting into open air. Even when hydrogen does burn it will generally move upward if there is any leak, while people move down, unlike something nasty like kerosine, which will stick around and burn at ground level. To top it off, a modern transatlantic jet will have half the calorific value per person in kerosine that the airship would need for lift anyway! Rant over, and irrelevant, but hydrogen is only a problem for PR reasons.


but the assumption that a lack of oxygen implies a lack of an oxidiser is wrong. Hydrogen might 'burn' with the sulphuric acid clouds, and I think would do so on contact (not sure). A quick google search does not come up with anything, but I would have thought
H2+H2SO4 ->2H2O+SO2.
Anyone got more experties on the matter?

[Sith_Happens]

The Hindenburg outer shell was coated in nitrocellulose (http://en.wikipedia.org/wiki/Nitrocellulose), mixed with aluminium powder.

http://d2ws0xxnnorfdo.cloudfront.net/character/tile/koala-cant-believe-it.jpg

http://i62.tinypic.com/21ostpi.jpg

[factotum]

Mythbusters disproved that one. They made a scale model of the Hindenberg out of similar materials and painted it with *actual thermite*, clearly far more dangerous and flammable than the real airship's paint. Yes, it burned, but actually quite slowly. They then filled a duplicate model with hydrogen and did the same test, and it burned *much* faster. So, if the Hindenberg had been filled with helium it might well still have burned, but probably so slowly that everyone aboard would have survived.

[ace rooster]

Mythbusters disproved that one. They made a scale model of the Hindenberg out of similar materials and painted it with *actual thermite*, clearly far more dangerous and flammable than the real airship's paint. Yes, it burned, but actually quite slowly. They then filled a duplicate model with hydrogen and did the same test, and it burned *much* faster. So, if the Hindenberg had been filled with helium it might well still have burned, but probably so slowly that everyone aboard would have survived.

Obviously if you have a fire and you add more fuel rather than a noble gas then the fire will burn better, but that is not the point. The soot released by the burning skin acts a bit like a wick in a candle, and without it the hydrogen does not burn. If somehow you get a leak and a source of ignition then some hydrogen will burn, but without the soot most of the cooling comes from mixing with the air rather than radiation, which means that the energy will tend to go upwards rather than being a further source of ignition.
With soot in the fire you get a very different beast, because the red hot soot acts like a grill to heat the skin, which burns giving off more hot soot, which mixes with the hydrogen and some air. The grill effect is able to heat the soot air hydrogen mix, which can ignite the hydrogen releasing lots of heat. That heat conducts into the soot, which then reradiates it down at the skin, continuing the effect. Additionally the hydrogen will burn preferentially to the carbon soot, meaning that the soot will last longer in the flames and you will get even better heat transfer, so hydrogen will make the process massively faster than you might expect. For any of this to occur though, the soot is vital.

The question is not whether the Hindenburg could have been made safer, but whether hydrogen is a safe lifting gas in a modern airship with non flammable skin. Mythbusters did not check that.

incidently, the airships used in the first world war were surprisingly difficult to shoot down, with some people believing they were filled with inert gas for precisely this reason. The first one to be shot down was targeted with specially designed incendiary explosive ammunition (incendiaries did not work) and required a full three drums worth. By the time this had happened, several had already crash landed, which was the bigger problem with airships. Not having to land would make airships on Venus considerably safer.

[Max™]

The question is not whether the Hindenburg could have been made safer, but whether hydrogen is a safe lifting gas in a modern airship with non flammable skin. Mythbusters did not check that.

I'm surprised because that is the first thing that popped into my head when hearing Mythbusters did anything related to it, seems kinda obvious to set up a helium+flammable skin, hydrogen+flammable skin, helium+non-flammable skin, hydrogen+non-flammable skin and see how they all behave.

[factotum]

I'm surprised because that is the first thing that popped into my head when hearing Mythbusters did anything related to it, seems kinda obvious to set up a helium+flammable skin, hydrogen+flammable skin, helium+non-flammable skin, hydrogen+non-flammable skin and see how they all behave.

The test run with the thermite airship filled with ordinary air ought to have been enough of a check of what happens with a helium airship--after all, the helium airship isn't going to burn *faster* than an air-filled one, is it? I'm pretty sure they also did a test with a hydrogen-filled airship without the thermite paint, but it's a long time since I've seen the episode and I may be misremembering.

[Yora]

The Hydrogen made the fire a lot worse than the same material just burning with air (or whatever they had filled it with).

The fire will allow the hydrogen to eacape and the heat will cause it to mix with air until at some point it will reach the right mixture to ignite into a huge fireball. While it looks very dramatic, I am not sure how much fire damage the hydrogen combustion actually deals. Since the non-hydrogen dummy also burned down completely very quickly it might not have made a big difference.

[Sith_Happens]

You all are missing the point here. It's not about burning speed, it's about the presence of nitrocellulose making it far easier to start a fire. That stuff is extremely sensitive.

[Solaris]

The test run with the thermite airship filled with ordinary air ought to have been enough of a check of what happens with a helium airship--after all, the helium airship isn't going to burn *faster* than an air-filled one, is it? I'm pretty sure they also did a test with a hydrogen-filled airship without the thermite paint, but it's a long time since I've seen the episode and I may be misremembering.

No it's not, because of the potential for interactions between the body being made of IED and the lifting gas. To properly examine it scientifically, you need all four combinations of body material and lifting gas. If you don't, you leave unexamined the potential possibility that it was, say, the soot from the incredibly touchy envelope material that exacerbated the hydrogen fire rather than an intrinsic property of hydrogen itself that makes it dangerous.

[factotum]

They weren't trying to prove how dangerous the hydrogen was, though. They were trying to *disprove* the theory that the hydrogen had *no* effect on the Hindenberg fire--it's actually been stated by some people that it was purely the nitrocellulose paint that was burning and that the hydrogen inside made no difference at all, which was not the case in the Mythbusters test.

[Tyndmyr]

They weren't trying to prove how dangerous the hydrogen was, though. They were trying to *disprove* the theory that the hydrogen had *no* effect on the Hindenberg fire--it's actually been stated by some people that it was purely the nitrocellulose paint that was burning and that the hydrogen inside made no difference at all, which was not the case in the Mythbusters test.

As the resident mad scientist who actually does use these things, I have to point out that thermite isn't at all fast burning, and nitrocellulose is essentially flash paper, which IS very fast burning.

One is a poor substitute for the other. You use thermite when you want things to burn very HOT, not when you want them to burn fast. Thus, much as I enjoy mythbusters, this really isn't anything like a valid test.

[factotum]

OK, now that's definitely a valid criticism of their technique--I got the impression from the episode they chose thermite because it was much faster burning than the Hindenberg paint and would thus be a "taken to extreme test", but if it's actually known to be slower burning then you're right, it completely invalidates the point they were making. Objection withdrawn, m'lud.