Low Gravity & High Atmo Density Question

[Starman4308]

5 hours ago, Snark said:

There are a variety of gases you could choose from, but in terms of convenience, I would think that good old-fashioned water would be a reasonable choice.  At Venusian temperatures, it's a gas, with a molecular mass of 18.  That puts it 26 below the atmosphere's molecular mass, meaning that a water-vapor-filled balloon on Venus would have slightly better relative buoyancy than a helium-filled balloon on Earth, which is plenty enough to lift a good-sized vehicle.

I'm not quite so sure you would actually favor water over hydrogen/helium for such an endeavor, though.

1 kilogram of He⁴ delivered to a CO₂ atmosphere would displace 11 kg of atmosphere, letting you lift 10 kg of useful payload.

1 kilogram of H₂O delivered to a CO₂ atmosphere would displace about 2.44 kg of atmosphere, letting you lift 1.44 kg of useful payload.

While you wouldn't need a much larger balloon volumetrically, you'd need to carry a heck of a lot more mass of lifting gas if you chose water.

Now, specifically when it comes to Venus, I might propose a relatively unorthodox method of filling the balloon: a hydrogen-oxygen fuel cell powering a CO2 condenser. What's left of the Venus atmosphere is mostly nitrogen; mix that with the water from the fuel cell, and you have yourself a lifting gas. Granted, you might want parachutes so you don't fall too far before the mission becomes buoyant.

[PB666]

2 hours ago, Starman4308 said:

I'm not quite so sure you would actually favor water over hydrogen/helium for such an endeavor, though.

1 kilogram of He⁴ delivered to a CO₂ atmosphere would displace 11 kg of atmosphere, letting you lift 10 kg of useful payload.

1 kilogram of H₂O delivered to a CO₂ atmosphere would displace about 2.44 kg of atmosphere, letting you lift 1.44 kg of useful payload.

If you were cheap your could just cleave 2CO to form O2, but again pure O2 is explosive. One could also purify and use nitrogen, the volumn of gas required would trip. Another option is to cleave CO2 and form CO, CO is one of most heat stable compounds that exists and you would need about the same Volume of CO as N2.

3 hours ago, Starman4308 said:

While you wouldn't need a much larger balloon volumetrically, you'd need to carry a heck of a lot more mass of lifting gas if you chose water.

Partly correct. below 100'C external temperature and above 101,300 Pa you would always have some of waters mass as a liquid (at STP of 1/22.4 moles per liter (0.8 kg per meter cubed) but in its condensed state that is 1000 kg per meter cubed). Here is a vapor pressure table for water.

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

if you compare that with the pressure temperature curve for Venus.
Pa  = P * 133.322

And apply this formula to the values in the table  you will find that the permissible atmosphere for a ambient heated dihydrogen oxide gas filled balloon is <= 41,000 meters with a temperature >= 135'C and a pressure of 300,000 Pa. Under all conditions higher in elevation water would have a majority of its mass as a liquid. There is one exception however, if you had a thermonuclear generator in which the heat sink was in a small internal reservoir you could heat the water with the waste heat from the generator and make steam that would condense slowly on the sides and run back to the heating element. You could even use the waste heat to inflate the balloon in order to change altitude. The problem I found with steam is that it is, when heated, rather corrosive, and thus you would have increased maintenance issues with such a system. But that is a decent way to get rid of heat, in particular if the balloon was on a long tether you could use it to get rid of heat and have a bigger reactor, via atmospheric cooling and get the balloon about the H2SO4 cloud layer.

There is not much hydrogen in space, (something like 10-9 moles per cubic meter of space) but if you were going to use it to pressurize balloons you might could scavenge enough to fill a balloon, in particular if you were operating around Venus you probably could use Venus as a lens to focus solar plasma into a space that you could magnetically confine and collect it. Since Venus repels hydrogen, any entering its upper atmosphere would have to travel around Venus which means it is concentrated and could be collected from that space. Again your balloon would have to be very high in the Venusian atmosphere to do this. We also have to stipulate that if you did not do this you would lose hydrogen and eventually sink.
 

[Snark]

5 hours ago, Starman4308 said:

1 kilogram of He⁴ delivered to a CO₂ atmosphere would displace 11 kg of atmosphere, letting you lift 10 kg of useful payload.

1 kilogram of H₂O delivered to a CO₂ atmosphere would displace about 2.44 kg of atmosphere, letting you lift 1.44 kg of useful payload.

Also bear in mind the mass of the container required to contain that helium.  You'll have to transport it as a compressed gas.  And precisely because it's so light, it'll take up quite a bit of space even compressed-- you'll need a large container.  Your kilogram of helium's gonna mass a lot more than a kilogram.

Whereas a kilogram of water?  Fits in a 10-cm cube... uncompressed, doesn't need an armored container.

There's also the question of how long you want to stay aloft.  Helium leaks.

[PB666]

6 hours ago, Snark said:

Also bear in mind the mass of the container required to contain that helium.  You'll have to transport it as a compressed gas.  And precisely because it's so light, it'll take up quite a bit of space even compressed-- you'll need a large container.  Your kilogram of helium's gonna mass a lot more than a kilogram.

Whereas a kilogram of water?  Fits in a 10-cm cube... uncompressed, doesn't need an armored container.

There's also the question of how long you want to stay aloft.  Helium leaks.

One stable alternative to hydrogen that can be made CO2 and H20 is and more readily stored is methane. Its half the MW of O2 and little bit more than half of CO and N2 but would be a vapor at all desirous altitude. Also there is ammonia, which is also a gas at all desired altitudes and only slightly heavier.

The discussion of H2, H20 and all hydrogenated compounds that the only source of H on Venus is sulfuric acid.

[Snark]

11 hours ago, PB666 said:

pure O2 is explosive

Well, only if it's in the presence of something it can oxidize.  It's certainly not going to "explode" in an atmosphere of CO₂; the atmosphere is already oxidized.  Granted, the spacecraft itself would likely be at risk, depending on what it's made out of, so yeah, perhaps not a great choice.  And quite aside from corrosion / oxidation concerns, it loses out to (for example) H₂O on several fronts, simply from a physics/engineering perspective:  nearly twice the molecular weight; requires heavy containment to store as pressurized gas; requires large amounts of energy to liberate if it's stored in some chemically bound form.

11 hours ago, PB666 said:

There is not much hydrogen in space, (something like 10-9 moles per cubic meter of space) but if you were going to use it to pressurize balloons you might could scavenge enough to fill a balloon, in particular if you were operating around Venus you probably could use Venus as a lens to focus solar plasma into a space that you could magnetically confine and collect it.

I find it unlikely in the extreme that any reasonable spacecraft would be able to harvest enough bulk hydrogen from space to be able to fill a balloon with it.  Space is empty, and "use Venus as a lens" sounds like hand-waving to me-- where did that come from?

11 hours ago, PB666 said:

Since Venus repels hydrogen

[citation needed]

11 hours ago, PB666 said:

it is concentrated and could be collected from that space.

[citation needed]

...I'd like to see some evidence for both of the above claims.  And even if it both of them were true, you'd still need to demonstrate that whatever apparatus you're proposing (to somehow collect and concentrate such hydrogen to bulk quantities and densities sufficient to use as a lifting agent) wouldn't be so big and heavy that it would defeat the purpose of going for hydrogen in the first place.

3 hours ago, PB666 said:

methane

Slightly lighter than water vapor (molecular weight 16, compared to 18), so it has that going for it.  It's a gas with a low boiling point, though, which means you'll still have the problems with pressurized or refrigerated storage for keeping it around when it's not in gaseous form in the balloon envelope-- which means a lot of extra weight.  Or if you're proposing to manufacture it in situ out of Venusian atmospheric components, there'd be the concern about how heavy would the equipment have to be for doing that (including the needed power source).

3 hours ago, PB666 said:

ammonia

Slightly lighter than water vapor (molecular weight 17, compared to 18), so that's not bad.  Liquefies reasonably readily at manageable pressures, so it's somewhat harder to store than liquid water but a whole lot easier than methane (or other low-boiling-point gases).  Gaseous at a broader pressure/temperature range than water is, so it has that going for it, too.

I could see using ammonia, if you schlep it from Earth as part of the equipment.  If you're planning to somehow extract/synthesize it from the Venusian atmosphere in situ, though, that would add a lot of mass and complexity to the equipment-- again, not sure how practical that would be, and whether it would pass the break-even point (i.e. savings from acquiring gas locally exceeding the weight and reliability risk of the equipment to do it).

11 hours ago, PB666 said:

We also have to stipulate that if you did not do this you would lose hydrogen and eventually sink.

This is true of any gas that you don't have a way of replenishing on-site:  it will eventually leak out and sink.  Some gases leak more rapidly than others, but there's always some leakage.

The only question is how fast it leaks, versus how long one wants the mission to last.  No mission lasts forever.

The idea of replenishing gas on-site from gases available in the atmosphere can seem attractive ("yay, we can float forever!") ... except that equipment to chemically crack gases is likely to be heavy, will need a good power source (which also has weight), and doesn't last forever, either-- things break down.

Another alternative that we haven't really discussed here is using a hot-air balloon, i.e. fill it with atmospheric gas and keep it warmer-than-ambient to generate buoyancy.

• This has the advantage that all your leakage worries go away (you're surrounded by the same stuff you're inflating your balloon with), and also you don't have to transport any of the buoyancy gas from Earth.
• It has the disadvantage that now you have to have a continuous power source, and you can stay up only as long as your power source holds out.  One potential source of power is just passive solar heating-- e.g. a balloon that's transparent on the sunny side and dark-colored on the opposite side, relying on greenhouse effect under direct sunlight to keep it warm.  The energy's free, the technology is simple; the disadvantage being that it doesn't work in the dark, nor will it work if you're deep enough in the atmosphere to be below the Venusian clouds.  Another potential power source would be a radioisotope.  These last for several years.  Not sure what the power-to-weight ratio would be (certainly it would be better than an RTG, since you're not trying to make electricity, you're just harvesting the "waste heat" directly, which would be more efficient).

[Green Baron]

Guys, i admire your enthusiasm and love for the detail. This time i stand aside, next time i'll join in again

Unrelated and ot: "to schlep". I had to grin, i wasn't aware that this is an English word :-)

 

[PB666]

6 hours ago, Snark said:

Well, only if it's in the presence of something it can oxidize.  It's certainly not going to "explode" in an atmosphere of CO₂; the atmosphere is already oxidized.  Granted, the spacecraft itself would likely be at risk, depending on what it's made out of, so yeah, perhaps not a great choice.  And quite aside from corrosion / oxidation concerns, it loses out to (for example) H₂O on several fronts, simply from a physics/engineering perspective:  nearly twice the molecular weight; requires heavy containment to store as pressurized gas; requires large amounts of energy to liberate if it's stored in some chemically bound form.

I find it unlikely in the extreme that any reasonable spacecraft would be able to harvest enough bulk hydrogen from space to be able to fill a balloon with it.  Space is empty, and "use Venus as a lens" sounds like hand-waving to me-- where did that come from?

[citation needed]

[citation needed]

...I'd like to see some evidence for both of the above claims.  And even if it both of them were true, you'd still need to demonstrate that whatever apparatus you're proposing (to somehow collect and concentrate such hydrogen to bulk quantities and densities sufficient to use as a lifting agent) wouldn't be so big and heavy that it would defeat the purpose of going for hydrogen in the first place.

Slightly lighter than water vapor (molecular weight 16, compared to 18), so it has that going for it.  It's a gas with a low boiling point, though, which means you'll still have the problems with pressurized or refrigerated storage for keeping it around when it's not in gaseous form in the balloon envelope-- which means a lot of extra weight.  Or if you're proposing to manufacture it in situ out of Venusian atmospheric components, there'd be the concern about how heavy would the equipment have to be for doing that (including the needed power source).

Slightly lighter than water vapor (molecular weight 17, compared to 18), so that's not bad.  Liquefies reasonably readily at manageable pressures, so it's somewhat harder to store than liquid water but a whole lot easier than methane (or other low-boiling-point gases).  Gaseous at a broader pressure/temperature range than water is, so it has that going for it, too.

I could see using ammonia, if you schlep it from Earth as part of the equipment.  If you're planning to somehow extract/synthesize it from the Venusian atmosphere in situ, though, that would add a lot of mass and complexity to the equipment-- again, not sure how practical that would be, and whether it would pass the break-even point (i.e. savings from acquiring gas locally exceeding the weight and reliability risk of the equipment to do it).

This is true of any gas that you don't have a way of replenishing on-site:  it will eventually leak out and sink.  Some gases leak more rapidly than others, but there's always some leakage.

The only question is how fast it leaks, versus how long one wants the mission to last.  No mission lasts forever.

The idea of replenishing gas on-site from gases available in the atmosphere can seem attractive ("yay, we can float forever!") ... except that equipment to chemically crack gases is likely to be heavy, will need a good power source (which also has weight), and doesn't last forever, either-- things break down.

Another alternative that we haven't really discussed here is using a hot-air balloon, i.e. fill it with atmospheric gas and keep it warmer-than-ambient to generate buoyancy.

• This has the advantage that all your leakage worries go away (you're surrounded by the same stuff you're inflating your balloon with), and also you don't have to transport any of the buoyancy gas from Earth.
• It has the disadvantage that now you have to have a continuous power source, and you can stay up only as long as your power source holds out.  One potential source of power is just passive solar heating-- e.g. a balloon that's transparent on the sunny side and dark-colored on the opposite side, relying on greenhouse effect under direct sunlight to keep it warm.  The energy's free, the technology is simple; the disadvantage being that it doesn't work in the dark, nor will it work if you're deep enough in the atmosphere to be below the Venusian clouds.  Another potential power source would be a radioisotope.  These last for several years.  Not sure what the power-to-weight ratio would be (certainly it would be better than an RTG, since you're not trying to make electricity, you're just harvesting the "waste heat" directly, which would be more efficient).

It is obvious that Venus has lost hydrogen it previously had, so I don't need to cite a source, the atmosphere is simply too hot to retain it. The question whether there is sufficient amount to harvest it is an orbital issue, the question of replenishing is non-orbital issue. Both are valid, again since I am not in favor of the blimp colony scheme I find this all rather silly. The next issue is equipment size, again I am only assuming that 100kg was a scalar, that the OP wanted some numbers that could be used to scale in size, from 100kg to 100,000kg. So that of course a large airship could support the machinery. The harvestability in space around Venus is an unknown, but given collections of Oxygen-hydrogen oxidation products on Mercury this seems doable, the question is how. Again hydrogen is preferred by on Venus would be difficult and expensive to acquire (I think I said this).

The next most obvious issue is Methane, again it can be pressurized, its density is not very good, but it leaks less quickly than hydrogen, and the number of gases that can be used a refridgerants in space to keep it cool and  recycled are higher than with hydrogen. Potentially you could use a new age plastic to store it. Methane can be stored as Lithium Methide, if storage is the largest issue and it can be treated with hydrogen to release it. Li-CH3 in the presence of Acid forms methane (again acids are heavy but can be recycled from lithium chloride). Of course one can also make lithium hydride, which was used in the first hydrogen bombs. Neither compounds are particularly stable around water or oxygen. Making methane on site requires the conversion of CO2 to CO, and the conversion of H2S04 to water and Sulfate. The water is then used to create hydrogen gas and Oxygen which would be released. The hydrogen is then use to make formaldehyde and then methanol, the methanol would then be used to make methane. It is expensive but . . . . . .
 

Ammonia gas can be readily stored in the presence of water, it is released under application of vacuum. It can be obtained by the reduction of Nitrogen with Hydrogen (see above) at high temperature.

Of all the gases CO would be the most economical interms of insitu recycling but the hardest to use in terms of volume containment.

 

 

[Snark]

1 hour ago, PB666 said:

It is obvious that Venus has lost hydrogen it previously had, so I don't need to cite a source, the atmosphere is simply too hot to retain it.

Well, if that's what you meant, fine.  That's not what you actually said, which was:

19 hours ago, PB666 said:

Venus repels hydrogen

...which is very different from saying simply that it can't hang on to hydrogen, thus my confusion.

Especially since you followed that with,

19 hours ago, PB666 said:

any entering its upper atmosphere would have to travel around Venus which means it is concentrated and could be collected from that space

...which really needs a citation.  The fact that Venus can't hang on to hydrogen means the hydrogen escapes Venus, it's not "concentrated"-- it's the exact opposite of concentrated.  You appeared to be claiming, without citing any evidence, that near-Venus space is a good place to harvest enough bulk hydrogen to fill a balloon with, which seems like an extraordinary claim.  I would have thought quite the opposite.  So, was curious what your rationale was for that.

[Starman4308]

I'd been skeptical for a bit of the in-situ gas harvesting schemes, because you'd want to fill up the balloon before you got so low down in Venus's atmosphere that you're roasting the equipment.

One thing to think of, though, goes back to helium. For such a scheme, it wouldn't have to stay in the balloon long, it'd just have to stay long enough to produce lifting gas in situ. You could use a relatively lightweight initial charge of compressed helium to initially inflate the balloon (and probably dump the tanks), and then stay up on those while harvesting solar energy to either convert CO2 to CO, or possibly separate out nitrogen.

[PB666]

1 hour ago, Snark said:

...which really needs a citation.  The fact that Venus can't hang on to hydrogen means the hydrogen escapes Venus, it's not "concentrated"-- it's the exact opposite of concentrated.  You appeared to be claiming, without citing any evidence, that near-Venus space is a good place to harvest enough bulk hydrogen to fill a balloon with, which seems like an extraordinary claim.  I would have thought quite the opposite.  So, was curious what your rationale was for that.

That of course is a question, but the logic is this, and again I would repeat that the studies of Mercuries light-less craters indicate that this process does happen, the sun produces hydrogen which has already saturated the very thin surface layer of mercury as it travels around its still in a more or less plasma state (potentially with no electrons to rejoin it reaches the other termination were if rejoins with oxygen to form water. Here is the assumption. So lets say the solar wind is 300km per second, and lets say its concentration is 1E-9 (the exact number is not neccesary) and the boundary layer as it passe around an object is 1 meter (again its just for demonstration. So if a circle was a meter in radius of the boundary flow around venus would also be a meter.

1m radius  (area = pi)  (perimeter = 2pi) 1E-9 per meter +  0.5E-9 ( There are errors here that disappear as the circle gets larger, this is an over estimate, its just a way of setting up the arguement)
2m radius (area = 4 pi) (perimenter = 2 pi) 1E-9 per meter +  1E-9 (see above)
4m radius (16pi) (8pi) 1E-9 + 2E-9
8m radius (64pi) (16pi) 1E-9 + 4E-9
So eventually we can speculate that if the radius is say 2500000 meters in diameter and the flow along the edge remains tight that the concentration of hydrogen becomes 1250000E-9. If the planet is venus this certainly could be higher. The perimeter of Venus is not a hard surface the boundary flow is not expected to be tight, that hydrogen might mingle for a while in the upper atmosphere. So one might have to scoop atmosphere and extract the hydrogen and release. More than likely this is where the H2SO4 in the Venusian atmosphere comes from, but again if you are trying to rest on a cloud the H2SO4 in the cloud does not help you until after you have rested and established equilibrium, its just that the H20 part of the H20 + SO3 never makes it to the ground. 

The sun carries away 1E36 particles per second (about a 1E9 kg per second, so at mercuries orbit this would be 60,000,000,000 meters so the surface area is 3600000000000000000000 3.703E-13 kg/m²sec at mercury. Along the face of mercury that is 7.27kg per second. So this slips around the perimeter of mercury we don't know how thick so lets just argue a meter thick and if its wider one can just divide by the width . . .at the rate of 0.00000154 kg/sec. So that we can see that in a day you could collect 0.125 kg/day  of H2 with a handwaving meter square capture system. THat does not seem like a lot of hydrogen, but for a blimp, at say half an atmosphere that is 2.781 m³ of gas. So then the question is how much resource does one place into this, so if we imagine we have a heat resilient surface weight something like 1 mm in thickness, it would cost minimally 1.4 kg per square meter, so over a few days we could recover the cost, but again you want to make something big, 100s of kilograms in size so that you are capturing say 1000 meters.

So that is the theory, hydrogen moves over planetary ellipticals at the rate of 1E9*0.75/pi*r2 kg/m²sec were r is the magnitude of the position vector. Anything in the path of that flow (van allen belts, a rocky non-atmospheric planet, a very cloudy planet without a magnetic feild) that does not absorb hydrogen deflects the hydrogens towards its perimeter parallel to the direction of light, so that the hydrogen is concentrated as it passes the perimeter. This is hardly rocket science. So how do we make it work for Venus, thats a question. We don't know it happens on Venus, but at least on mercury the theory is consistent with the presense of ice in areas beyond the termination and ice that is not likely source from Venus.

 

[Green Baron]

7 hours ago, PB666 said:

That of course is a question, but the logic is this, and again I would repeat that the studies of Mercuries light-less craters indicate that this process does happen, the sun produces hydrogen which has already saturated the very thin surface layer of mercury as it travels around its still in a more or less plasma state (potentially with no electrons to rejoin it reaches the other termination were if rejoins with oxygen to form water. Here is the assumption. So lets say the solar wind is 300km per second, and lets say its concentration is 1E-9 (the exact number is not neccesary) and the boundary layer as it passe around an object is 1 meter (again its just for demonstration. So if a circle was a meter in radius of the boundary flow around venus would also be a meter.

Now *this* needs a citation or link. Because it is not even clear which process or observation you are referring to and if it has any real relevance at all. At least there is some confusion with the top of an atmosphere and the surface of a rocky body. But i may be just too dense (or scattered) to understand what you mean ...

Edited January 13, 2018 by Green Baron

[PB666]

7 hours ago, Green Baron said:

Now *this* needs a citation or link. Because it is not even clear which process or observation you are referring to and if it has any real relevance at all. At least there is some confusion with the top of an atmosphere and the surface of a rocky body. But i may be just too dense (or scattered) to understand what you mean ...

Imagine a stream of water, if you place in the stream a stick, the water has to go around the stick or go into the stick. If it goes into the stick then there is flux. dH/dt for venus (or mercury) is positive. In the case of Venus if dH/dt is positive then we expect the conversion of H_²S04 --------> ⁺H₃0+ ^-HSO₄  ----------> Me⁺ SO₄^2- + H₃0+ H₂0. There would be a flux of ions in Venusian atmosphere from their anhydrous form (SO3) into the state observed on Earth (oceanic ^2-SO4). The assumption is that there are enough oxides trapped in the rocks on Venus to convert back to hydroxides then water. Observation reveals that state of Venus is dehydration, surface water has been depleted and H2SO4 is  a minor state of S in the atmosphere most in is sulfer dioxide (which hydrates to H2SO3 and then oxidizes to H2S04)

Quote

A large amount of the planet's hydrogen is theorised to have been lost to space,^[15] with the remainder being mostly bound up in sulfuric acid (H₂SO₄) and hydrogen sulfide (H₂S). The loss of significant amounts of hydrogen is proven by a very high D–H ratio measured in the Venusian atmosphere.^[4]  -wikipedia   

This has too bits of information, first that there is a flux of hydrogen, that which goes into Venus atmosphere and that which leaves. THe proportion that has recently come from the sun is much higher than that of the planets formation.

OK so if anything the H flux is negative but D flux may be positive. Given that
In the analogy the stream of water must flow around the obstacle. In a river the water would build amplitude (a standing wave) and travel around the obstacle faster. However in space the dynamics are different, for example on Mercury the hydrogen collides with the then atmosphere, slows down and travels around mercury to the termination were it then in flows back into space, this is going on

https://en.wikipedia.org/wiki/Atmosphere_of_Mercury
Source.

you can see where the space craft detected gas while passing some distance around Mercury. If you would have followed those isoquants back to the surface you would have seen the peak concentration very close to the termination at the poles. In other words Mercury is creating a manifold that redirects and concentrates solar-derived mass. That mass is largely hydrogen. Just like a stick a stream of water, mercury cause the mass flow to increase in some areas an decrease in others. Keep in mind what the image is showing what is sampled as a plane through mercuries axis to the sun, so that the boundary layer that is observed is largely a polar focus. At more than 2 mercurial radii from the surface the concentration remains  up to 5 times more concentrated than the surfaces well behind the planet. If we were to diagram that flow. . . . .

Yes I know expansion is misspelled

Before I leave Mercury I want to point out that unlike water here on Earth, the hydrogen that flows around Mercury is rich in deuterium and the cold flow is particularly rich in deuterium, dueterium accelerates less slowly in response to X-rays and interactions with the solar wind, this is also true for other elements. The grey bar represents termination. So venus is bigger than mercury but further away which means that it receives about 2.5 times the amount of hydrogen. We can see from the diagram above that hydrogen is not likely to flow back in the direction of the sun, in either case mercury or venus. Venus has almost no magnetic field, Although Venus is further from the sun than Mercury we have to remember that mercury is travelings at 10s of kms per second and the solar winds 100s of kms per second. So that the wind barely slows down as it reaches Venus.

These are our givens. Lets see if we can make heads or tails of H flow around Venus.
1. The flow is unlikely to be directed Sun-Rad since the pressure is both + - Conjecture the outflux of hydrogen is much greater at or beyond termination.
2. Venus does not have a magnetic field - conjecture hydrogen cannot be repelled back into space before hitting atmosphere.
3. The -Flux of hydrogen from the Venusian surface is driven by heat + -conjecture - and in the upper atmosphere is driven by sunlight.

We can stop here and theorize about Venusian hydrogen. The only place where the flux statements are simultaneously true is close to termination. But we have to argue that
1. because Venus has an atmosphere and no van Allen belts
2. because sunlight and solar winds drive hydrogen toward Venusian surface
3. that the flux of hydrogen/deuterium/helium  on the sunlit side must be positive.
4. This roughly means, looking at the surface of Venus that the necessary outflow is concentrated somewhere on Venus, so the question then becomes where and how much.

And we can look at the atmsopheric flows and see that there are other reasons not to place a tremendous about of hydrogen out flux on the extreme back side.

Quote

The mesosphere of Venus extends from 65 km to 120 km in height, and the thermosphere begins at approximately 120 km, eventually reaching the upper limit of the atmosphere (exosphere) at about 220 to 350 km.^[17] The exosphere is the altitude at which the atmosphere becomes collisionless.

The mesosphere of Venus can be divided into two layers: the lower one between 62–73 km^[29] and the upper one between 73–95 km.^[17] In the first layer the temperature is nearly constant at 230 K (−43 °C). This layer coincides with the upper cloud deck. In the second layer temperature starts to decrease again reaching about 165 K (−108 °C) at the altitude of 95 km, where mesopause begins.^[17] It is the coldest part of the Venusian dayside atmosphere.^[2] In the dayside mesopause, which serves as a boundary between the mesophere and thermosphere and is located between 95–120 km, temperature increases to a constant—about 300–400 K (27–127 °C)—value prevalent in the thermosphere.^[2] In contrast, the nightside Venusian thermosphere is the coldest place on Venus with temperature as low as 100 K (−173 °C). It is even called a cryosphere.^[2]

The circulation patterns in the upper mesosphere and thermosphere of Venus are completely different from those in the lower atmosphere.^[2] At altitudes 90–150 km the Venusian air moves from the dayside to nightside of the planet, with upwelling over sunlit hemisphere and downwelling over dark hemisphere. The downwelling over the nightside causes adiabatic heating of the air, which forms a warm layer in the nightside mesosphere at the altitudes 90–120 km.^[4][2] The temperature of this layer—230 K (−43 °C) is far higher than the typical temperature found in the nightside thermosphere—100 K (−173 °C).^[2] The air circulated from the dayside also carries oxygen atoms, which after recombination form excited molecules of oxygen in the long-lived singlet state (¹Δ_g), which then relax and emit infrared radiation at the wavelength 1.27 μm. This radiation from the altitude range 90–100 km is often observed from the ground and spacecraft.^[30] The nightside upper mesosphere and thermosphere of Venus is also the source of non-local thermodynamic equilibrium emissions of CO₂ and nitric oxide molecules, which are responsible for the low temperature of the nightside thermosphere

Source- https://en.wikipedia.org/wiki/Atmosphere_of_Venus#Upper_atmosphere_and_ionosphere

If this is true and if hydrogen is a significant component of the upper atmosphere at oxygen airglow then water would be readily forming at the cold maximum, but this is not likely the case, because H2S04 rains out of the cloud layer before reaching the cold maximum which means little H2S03 is forming. So that hydrogen is most likely leaving the Venusian atmosphere along the same angles relative to termination as Mercury, probably slightly behind because of the cooling and heat redistributing effects of that atmosphere and the distance for Venus from the sun relative to Mercury. If I were to redraw the image

We can see that hydrogen is mixing into the thermosphere layer and working into the upper atmosphere. Two forces are fighting each other, thermal heating of the Venusian atmosphere is pushing out and the photon force and solar winds are pushing in, the atmosphere swells but cannot release the excess gas. As it rolls around to termination the photon force and the solarwind are no longer pushing -rad, they are pushing tangential with the flow of atmosphere which allows the gas to regain some of its incident (solar wind) velocity so that the atmosphere is free to degas, as the circulation moves to the back the gas is now free to escape, albeit at a much lower velocity. The gas continues to evolve beyond termination because sunlight (UV scatters better than light) is being scattered into the gas keeping the tangential pressure high. thereis also, at distance outflow scattered solarwind the provides tangential pressure. As the air flows behind Venus the thermospheres temperature drops and hydrogen no longer has the kinetic energy to escape Venus field and must be carried back to the sunlit side and driven out in a different pass. Again there are capture mechanisms for hydrogen in the Venusian atmosphere so that if this was significant hydrogen should persist. So in theory at least there should be concentrated hydrogen outflow tangential to the termination plane originating at the termination position vectors.

This is all I can give you on the theory, its more developed for Mercury than Venus.

Edit: Disclaimer, before everyone starts salivating here, remember we are talking about a total flux per day for the entire planet of 10s of kilotons, the images are above are magnifying the presence of hydrogen so that we can examine potential behaviors to determine if concentration of free hydrogen is possible. It is plausible based on theory at least, that does not mean its possible to support an Airship.

 

 

Edited January 13, 2018 by PB666

[Green Baron]

Well, sir, your efforts in honour, but i can read Wikipedia myself. I meant more a published and reviewed work to cement your thoughts. And less is more !

That sounds all great and mighty. Are you saying that Hydrogen flows from the sun to the inner planets Mercury and Venus ? As part of the solar wind ? Where is that from ? An alpha particle isn't exactly a hydrogen atom ... and afaik the solar wind rather drove hydrogen away from the inner solar system long ago than, it is not a cause of it.

In how far does photon flux point to hydrogen gas flowing from the sun around Mercury (your link "Atmosphere of Mercury") ? Wouldn't it rather point to airglow in a thin atmosphere, caused by charged particles from cosmic (or solar) radiation instead ? I mean, is that a possibility ?

Ice in Mercury's craters as depicted in your drawing is unconfirmed, laser measurements from the Messenger probe found no reflectivity that supported water ice, while radar and altimeter did hint in that direction. Or is there something newer ?

 

Or, in short, in my eyes the whole thing of hydrogen flowing from the sun outwards needs to be principally reworked, or not ? If that's the foundation of your thoughts there is a high probability that there is basic fault in it ... but still, i may have a principal problem in understanding and said fault might be on my side.

[PB666]

Just now, Green Baron said:

Well, sir, your efforts in honour, but i can read Wikipedia myself. I meant more a published and reviewed work to cement your thoughts. And less is more !

That sounds all great and mighty. Are you saying that Hydrogen flows from the sun to the inner planets Mercury and Venus ? As part of the solar wind ? Where is that from ? An alpha particle isn't exactly a hydrogen atom ... and afaik the solar wind rather drove hydrogen away from the inner solar system long ago than, it is not a cause of it.

In how far does photon flux point to hydrogen gas flowing from the sun around Mercury (your link "Atmosphere of Mercury") ? Wouldn't it rather point to airglow in a thin atmosphere, caused by charged particles from cosmic (or solar) radiation instead ? I mean, is that a possibility ?

The wikipedia quotes were drawn out for the OP who appears to have less experience than you or I do.

The overwhelming majority of mass detected on Mercury is molecular hydrogen and oxygen

Here molecules per meter cubed (remember these are static + flux divided by area at a meter (they used centimeter) thickness, my discussion is only about flux, not stasis. On one side of mercury you have alot of static molecules and on the other side you have alot of fluxing atoms, while the pressure may be greater (PV = nRT) on one side the mass on the other side my be greater. The solar photons and incident particles are compressing the volume on the hot side and increasing pressure.

Molecular Oxygen        2.5 x 10¹³
Molecular hydrogen  < 1.4 × 10¹³ 
Water   . . . . . . .  . . .  . < 1.5 x 10¹³
Helium . . . . . . . . . . . .  . .  6 x 10⁹

The amount of hydrogen (atomic) is trivial. Again if we are to compare this with space. 1E36 particles per second divided by the radius of Mercury places the density at mercury as 2.2 x 10¹³ assuming all is molecular the static atmosphere of mercury is only about 4 times thicker than the solar wind. Again if there was significant discharge effects the amount of atomic hydrogen would be higher than 1/100,000th the amount of molecular hydrogen (atomic hydroge is 2.5 x 10⁸ ) so . . . . .My opinion is that the real interesting stuff is occurring right at termination that's where you need to be. Heat drives the evolution of hydrogen more so than any other element, so you need to be at the place where heat is driving the element in your direction = less work for the extractor. 

 

Just now, Green Baron said:

Ice in Mercury's craters as depicted in your drawing is unconfirmed, laser measurements from the Messenger probe found no reflectivity that supported water ice, while radar and altimeter did hint in that direction. Or is there something newer ?

 

Or, in short, in my eyes the whole thing of hydrogen flowing from the sun outwards needs to be principally reworked, or not ? If that's the foundation of your thoughts there is a high probability that there is basic fault in it ... but still, i may have a principal problem in understanding and said fault might be on my side.

The trend is generally true that indications of water are more often than not proven true. But Mercury's atmosphere is in flux that is the overriding truth, but for the solar wind there is virtually no persistent atmosphere, it has a very peculiar year due to the eccentricity of its orbit, and we could have ice sublimating and then evaporating in a 2 mercurial year cycle. That does not per say rule out colonizing of Mercury, it just mean we have to be very very selective about the colonization site. There is one good protection that Mercury affords, the intense solar wind at termination affords some protection from exosolar cosmic radiation (the most damaging type), the problem however is that the suns own cosmic radiation produces X-rays upon recombination these will be difficult to avoid in the collisions at termination, it would be akin to having an atomic bomb going off in the atmosphere 50 miles over your head.

I do believe with proper engineering that we can capture hydrogen and water on Mercury. The biggest problem with that plan is the dV required in the transfer and matching burns. Mercury is an easier target to land and launch from than either Mars or Venus (obviously).

Extending the logic to Venus, if you asked me . . . .Is there a place on Venus were it is easier to capture water . . . meaning 4H2 + H2SO4  -------> H2S +  4H₂0 I would have to argue yes that place will be near termination. If you asked me the question choose a planet to capture hydrogen, obviously I would choose Mercury because we know how to do the ground kinetics. That is we know how to plant a facility in the place whereby the possibility of extracting hydrogen and water is good. I am also stating beyond static harvesting of water that the poles of Mercury should still have surface oxides not too far down, so that there should be an ample means of forming metal hydroxides with water which we can be used as both a source of metals and component water.

The mass fluxes in the Venusian atmosphere, particularly at termination cannot be trivialized. Solar radiation is not only driving hydrogen flux, but also the fluxes of all the other gases in the atmosphere. Yes one could possibly set up between the back (night side) flow and front flow layer, but then access to the hydrogen would be lower, you might have to have something ( a balloon reaching that highest layer) that you also use to scavenge gas, and in the lower section as a counter flow agent something that captures SO3 or H2SO4. However, my opinion is that this is always too turbulent to exploit.

Proof of the pudding is always in the eating. I believe that anyone who proposed settling the Venusian atmosphere is setting up a Hindenburg, probably shorter lived. The presence of hot sulfuric acid in the atmosphere is probably too much of a driver of unstable behavior than any Earth made vessel can withstand, at least in the foreseeable future.