How high can an airship rise?

[akhmeteli]

Where a payload is delivered, a prepared ballast load can be collected.

Still, this is pain in the neck. It is one of the problems with helium ballons, besides helium being pretty expensive, nonrenewable, penetrating through pretty much any envelope. So I believe there can be at least some niche applications for low-altitude vacuum balloons.

 

[Baluncore]

Condensation makes water vapor impractical as lighter-than-air gas for Earth atmosphere.

Except in a partial vacuum balloon.

And again, I don't think water vapor can be practical as a lighter-than-air gas in Earth atmosphere due to condensation at reasonable temperatures.

Your fear of condensation prevents you from researching the diverse possibilities available.

Consider what would happen if you assembled, or fabricated, a rigid envelope underwater. Gradually, as the water is pumped out, the envelope rises through the surface, before it finally lifts off. It will then contain water vapour without air, so has the 61% advantage while it is a partial vacuum balloon.

Any condensate that forms as it rises will be pumped out from the bottom of the envelope. Indeed, a cold condenser would be one way to remove water vapour from inside the envelope.

As it approaches maximum altitude, it begins to approach a full vacuum, the cold steam does not need to be pumped out, as the vapour will condense and be removed as a liquid by the more efficient positive displacement pump.

 

[akhmeteli]

Except in a partial vacuum balloon.

Your fear of condensation prevents you from researching the diverse possibilities available.

Consider what would happen if you assembled, or fabricated, a rigid envelope underwater. Gradually, as the water is pumped out, the envelope rises through the surface, before it finally lifts off. It will then contain water vapour without air, so has the 61% advantage while it is a partial vacuum balloon.

Any condensate that forms as it rises will be pumped out from the bottom of the envelope. Indeed, a cold condenser would be one way to remove water vapour from inside the envelope.

As it approaches maximum altitude, it begins to approach a full vacuum, the cold steam does not need to be pumped out, as the vapour will condense and be removed as a liquid by the more efficient positive displacement pump.

So you seem to consider water vapor just as a means to prevent failure of the vacuum balloon on its way from the Earth's surface to its (high) design altitude. However, condensation strongly limits the water vapor pressure. If I am not mistaken, unless we have some exotic conditions, saturated water vapor is pretty much the same if there is air and if there isn't, so even at 50 deg Celsius it is only about 12% of the atmospheric pressure. Not an attractive design. Your shell would need to be very light to be buoyant at high altitude and very strong to withstand 88% of atmospheric pressure near the Earth's surface.

 

[Baluncore]

Your shell would need to be very light to be buoyant at high altitude and very strong to withstand 88% of atmospheric pressure near the Earth's surface.

Meanwhile, you write about flying vacuum balloons, as having a place transporting loads, then flooding the vacuum with air, to re-ballast the balloon.
Verily. "Your shell would need to be very light to be buoyant at sea level and very strong to withstand 100% of atmospheric pressure near the Earth's surface."

I am prepared to compromise, to reduce the stress where stress is unnecessary. You are insisting on an ideal, a total vacuum balloon at sea level. Perfection is the enemy of progress.

I cannot understand why you believe the laws of physics are so different for you than they are for me.

 

[akhmeteli]

Meanwhile, you write about flying vacuum balloons, as having a place transporting loads, then flooding the vacuum with air, to re-ballast the balloon.
Verily. "Your shell would need to be very light to be buoyant at sea level and very strong to withstand 100% of atmospheric pressure near the Earth's surface."

I don't know, maybe I completely misunderstand what you have in mind, but this is how it looks to me at the moment.

Your design is supposed to withstand 88% of atmospheric pressure at sea level and also to be buoyant at high altitude, where air density is, say, one tenth of that at sea level, so your envelope weighs only one tenth of what would provide minimum buoyancy at sea level.

My design is supposed to withstand 100% of atmospheric pressure at sea level and to be buoyant at sea level, so the envelope can weigh much more than in your design.

It seems obvious to me that it is much easier (although still difficult) to implement my design than yours as a heavier envelope has a much better chance to withstand air pressure comparable to that at sea level.

What do I miss?

I am prepared to compromise, to reduce the stress where stress is unnecessary. You are insisting on an ideal, a total vacuum balloon at sea level. Perfection is the enemy of progress.

I cannot understand why you believe the laws of physics are so different for you than they are for me.

I don't know what laws of physics you use, but I use very standard laws of physics. My design (described in our article cited earlier) uses commercially available materials and is viable according to both (semi)analytical formulas and finite-element analysis.

 

[Baluncore]

My design (described in our article cited earlier) uses commercially available materials and is viable according to both (semi)analytical formulas and finite-element analysis.

Then, as a proof of your analysis, build it.

 

[akhmeteli]

Then, as a proof of your analysis, build it.

And I am trying to do that, but it takes (a lot of) time. Making a vacuum balloon is hard: the idea is 350+ years old, but it has not been realized yet.

As for our design, one of the challenges is making thin boron carbide plates (say, 0.1-0.2 mm thick). I cannot disclose what has been done in that direction, but note that there are commercially available thin plates made of a different ceramic (alumina) . Some of them are 0.127 mm (0.005") thick.

 

[Baluncore]

You appear to be engineering at one extreme, a smooth thin shell, under 2D hoop compression.

I am looking at an hierarchical internal truss structure, that transmits external air pressure forces radially, with a slack external film envelope. Think of a dandelion seed head, without the internal payload of seed.

 

[akhmeteli]

You appear to be engineering at one extreme, a smooth thin shell, under 2D hoop compression.

I am looking at an hierarchical internal truss structure, that transmits external air pressure forces radially, with a slack external film envelope. Think of a dandelion seed head, without the internal payload of seed.

Maybe your approach is better than mine, maybe it's worse, who knows. Are any details publicly available? I guess buckling is critical to your approach too.

 

[Baluncore]

Maybe your approach is better than mine, maybe it's worse, who knows. Are any details publicly available? I guess buckling is critical to your approach too.

Each to their own. You go your way. If I thought your solution was best, I would still take a contrary way, to explore a different valley.

No published analysis. Too many threads yet to pull together, too many still to reject.

Buckling is critical to any chamber subjected to a net positive external pressure. You are concerned with the buckling of a shell. I am concerned with column stability, of structures that spread the load, with sufficient redundancy to allow for some failure.

My envelope is interesting, because it must be lightweight, so it should not be under great tension. By allowing it to flex inwards, the tension can be minimised. The skin then takes on a deeply dimpled surface, so looks a bit like an exaggerated golf ball, or a starved horse.

 

[akhmeteli]

Each to their own. You go your way. If I thought your solution was best, I would still take a contrary way, to explore a different valley.

No published analysis. Too many threads yet to pull together, too many still to reject.

Buckling is critical to any chamber subjected to a net positive external pressure. You are concerned with the buckling of a shell. I am concerned with column stability, of structures that spread the load, with sufficient redundancy to allow for some failure.

My envelope is interesting, because it must be lightweight, so it should not be under great tension. By allowing it to flex inwards, the tension can be minimised. The skin then takes on a deeply dimpled surface, so looks a bit like an exaggerated golf ball, or a starved horse.

Thank you for the information. By the way, what you describe seems similar to US patent 10625842 by Nathan Rapport.