Vacuum Airships - would multi-skinning work?

[DrStupid]

I'm not sure that difference mattered much to the passengers of the Hindenburg

I think it does. 62 of the 97 persons on board survived. I wouldn't expect that in case of an explosion.

 

[Vanadium 50]

This thread is filled with what Perry Mason would call "assuming facts not in evidence."

First is that balloons (primarily weather balloons) are a major consumer of helium. As I said, the National Academies estimates 7% of helium is lifting. Party balloons make up most of this, so that leaves at most a 3% fraction. If one is concerned about reducing helium use, there is at most 3% to be gained here.

"Helium is a finite resource". So is hydrogen. Where does helium come from? It's a natural gas contaminant and is a by-product of natural gas production. Where does hydrogen come from? It'ss a by-product of natural gas production. What is certainly true is that hydrogen is cheaper.

Suppose weather balloons were replaced with hydrogen. So what? You're not transporting people, you're transporting instruments. And balloons fail and instruments are damaged all the time already. You need to demonstrate a) that switching to hydrogen makes things substantially worse, and b) the cost to switch to a technology that is so expensive it doesn't even exist is lower than living with it.

 

[Stormer]

First is that balloons (primarily weather balloons) are a major consumer of helium. As I said, the National Academies estimates 7% of helium is lifting. Party balloons make up most of this, so that leaves at most a 3% fraction. If one is concerned about reducing helium use, there is at most 3% to be gained here.

That is assuming current use. If LEO satellites are to be replaced by balloons as i suggested, and a lot of companies is going to make global wireless internet networks like starlink using balloons that will massively increase the number of balloons in the air by orders of magnitude compared to today's use.

And this is not some far fetched idea. Google, Facebook, Microsoft, and probably many others has had projects making internet networks via high flying "satellites" either in the form of solar powered drones, or in the form of balloons.

 

[russ_watters]

"Helium is a finite resource". So is hydrogen.

Perry, hydrogen is finite only insofar as all resources are finite by definition. The limitation in the hydrogen resource would probably first come from complaints by owners of formerly beach-front property as their property values decreased. Upside: reduced flood insurance costs.

Yes, I know most hydrogen *today* comes from underground sources as biproduct of natural gas production. But alternatives once that resource is expended are thin, and production itself is limited. But the alternative to steam reforming of natural gas is an effectively limitless source.

 

[akhmeteli]

Vacuum airships are a not-even-a-solution looking for a problem.

I am not sure. There is an obvious problem: altitude control. For example, after an airship unloads a heavy load, it needs to take ballast to avoid having too much buoyancy. Releasing helium after each flight is expensive. There are some solutions to the problem (see, e.g., http://aeroscraft.com/technology-copy/4580412172), but they are not simple. With a vacuum aircraft, one can just admit air to decrease buoyancy.

There is another serious problem: (long-term) storage. One may need large hangars as, again, releasing helium is expensive. There is no such problem with hot-air balloons, but they require energy to heat air. On the other hand, one can disassemble vacuum aircraft for storage (at least theoretically).

Another problem: it is not easy to prevent helium leak through the envelope.

There is a market for about two dozen airships in the world.

So maybe the market is small because current lighter-than-air aircraft have a lot of problems.

Making them orders of magnitude more expensive to get at most 30% more lift - and we have not accomplished that - is a non-starter.

It is possible that there will never be a business case for vacuum aircraft, but it is not obvious so far.

 

[Baluncore]

It is possible that there will never be a business case for vacuum aircraft, but it is not obvious so far.

Business can ignore vacuum airships until you can build a toy vacuum airship, or a prototype.
To do that you need a low mass truss, or some other structure to oppose the vacuum implosion.
You will have credibility when you can demonstrate a solution to that structural problem.

 

[akhmeteli]

Business can ignore vacuum airships until you can build a toy vacuum airship, or a prototype.
To do that you need a low mass truss, or some other structure to oppose the vacuum implosion.
You will have credibility when you can demonstrate a solution to that structural problem.

My credibility or lack of it does not seem relevant. I just noted that there are indeed problems that vacuum aircraft could solve. If you disagree, I would like to hear your arguments.

Let me also note that some work on vacuum aircraft is being done at Los Alamos, NASA, Air Force Institute of Technology, and other places.

(https://www.lanl.gov/projects/feynm...techsnapshots.php?id=5d0116573be4dbb4f26c7e87)

(Jenett, B. E., Gregg, C. E., Cheung, K. C., Discrete Lattice Material Vacuum Airship, AIAA SciTech Forum, 7-11 January 2019, San Diego, California, May–June 2015, 52, (3), pp 1-12)

(Adorno-Rodriguez, R., Palazotto, A. N., Nonlinear Structural Analysis of an Icosahedron Under an Internal Vacuum, Journal of Aircraft, May–June 2015, 52, (3), pp 878-883.)

 

[Baluncore]

I just noted that there are indeed problems that vacuum aircraft could solve. If you disagree, I would like to hear your arguments.

There are other ways available now to practically solve all your hypothetical problems.
There is no vacuum aircraft available to magically solve those hypothetical problems.

 

[akhmeteli]

There are other ways available now to practically solve all your hypothetical problems.
There is no vacuum aircraft available to magically solve those hypothetical problems.

What is hypothetical about the problems that I mentioned? So yes, there are other ways to solve them, and no, there is no vacuum aircraft. I just insisted that there are indeed problems that vacuum aircraft could help solve.

 

[russ_watters]

Note: per our PM discussion, we are reviewing whether we can discuss your paper and patent application in this thread.

I am not sure. There is an obvious problem: altitude control.

I don't think you heard what @Vanadium 50 said. You're talking about engineering (and maybe environmental) problems, but he's talking about economics problems. I understand that you are an aspiring inventor, but even if you succeed in inventing a functional vacuum airship, you still have to solve someone's economic/environmental problem in order to sell it. There has to be a market for the product. So when the time comes, you'll need to be able to show that your solution costs less than a traditional helium balloon or that the cost premium is worth the environmental savings. Right now, you seem to be completely ignoring the cost/market issue.

I suggest watching the TV show "Shark Tank" to see how inventors fare on it. One important thing to note: they pretty much always have a working prototype and a pending patent before pitching their ideas to investors. But that's not enough: they need to prove they are solving a market problem.

That said, I think you are downplaying the engineering benefits as well, by basically ignoring completely how the existing solutions work. For the sake of your own business model and the potential time/energy/money wasted in pursuing an idea that really isn't likely to go anywhere, you need to take an honest look at both sides of this. On the engineering side, I can't understand why you wouldn't consider pumping the helium back into a pressurized tank to be a solution to the engineering/environmental problem of wasted helium and airship storage. It seems really obvious. On the other side, since that is obvious but isn't apparently common, maybe that's because ballast is cheap and easy? I suppose you can say that a vacuum balloon with a pump and valves for ballast control is "a solution" to this technical problem, but other solutions clearly exist and I don't see a reason to believe the vacuum balloon would be a cheaper solution (back to the economic problem) -- because ultimately that's what matters most here.

It is possible that there will never be a business case for vacuum aircraft, but it is not obvious so far.

It may not be obvious to you, but it seems obvious to several of us. But here's the thing: the burden of proof is entirely on your side whereas the criteria/demands of proof are entirely on ours (or that of prospective investors). We can tell you what we think it will take and you'll have to provide that. Or not -- it seems you've been working on this for a long time and haven't gotten far.

Step 1: Build a functioning prototype to prove it is actually technically possible. And no, your arxiv paper and patent application are not sufficient as such proof. Even if all the math is right in your paper, it isn't enough.

 

[gmax137]

Vacuum airships are a scifi idea where you evacuate the air out of a chamber to achieve lighter-than-air lift.

...

I'm wondering it would be feasible to use multiple layers of wall, with steadily increasing pressures inside, to prevent it from buckling under the strain.

...

Add another layer at 10psi and you have 3 walls, each only taking 5psi, but with a vacuum on the inside. I don't know whether this would be any lighter than just making the chamber strong enough to withstand 15psi, but that's beside the point.

My question is - would this work? can you stagger the pressures via sequential containers? or am I missing something?

... Of course you can stagger the pressures via sequential containers. That's out of question. However, it doesn't help you. Three containers that withstand 5 psi are as heavy as a single container that withstands 15 psi. ...

(emphasis added)

Has anyone challenged @DrStupid 's contention in post #2? If not, I don't know what all the subsequent posts are for. Question asked and answered.

 

[DrStupid]

Has anyone challenged @DrStupid 's contention in post #2?

It has been challenged insofar that it refers to the theoretically best case. The reality is even worse.

 

[jrmichler]

Just for grins and giggles, I did some quick calculations for a vacuum airship. Some simple assumptions to get started include a tube 100 feet diameter with a perfect vacuum. The lift per foot of length at sea level is then the cross sectional area times the density of air: Liftperfoot=π/4∗1002∗0.075=589lbs/footlength.

The circumferential compressive force per foot length is Forceperfoot=14.7∗144∗100/2=106,000lbs/foot.

The longitudinal force per foot circumferential distance: Forceperfoot=π/4∗1002∗14.7∗144/(100∗π)=53,000lbs/foot.

Square feet of structure per foot length: 100∗π=314feet.

Maximum possible weight of structure is the lift per foot divided by the length of structure per foot: Maxweight=589lbs/foot/314feet=1.9lbsperfoot2. The sketch below shows this:

Not shown in the sketch is the vacuum force of 2117 lbs per square foot into the page. The absolute maximum weight of one square foot of the vacuum structure that withstands the above forces is 1.9 lbs. The structure must not buckle. The structure needs attachments for crew, cargo, engines, fuel, control surfaces, mooring, etc.

In practice, the airship structure must weigh about half that much, or about 1 lb per square foot, in order to carry crew, cargo, engines, fuel, control surfaces, mooring, etc. Any person who proposes a vacuum airship needs to do these calculations, and show a solution using commercially available materials

 

[Baluncore]

@jrmichler
Your computations are for sea level. Some things scale sensibly.
I think the idea of using an unmanned vacuum airship at 60,000 feet for mobile phone and internet connectivity is an interesting model. The air pressure at that altitude is only about 1 psi. The airship structure therefore need only counter a 1 psi differential envelope pressure. But the volume must be sufficient to lift the gross weight. At sea level the external pressure is about 14.7 psi, the same volume could have an internal pressure of 13.7 psi and generate the same lift force for the same structure. The differential envelope pressure would still be only 1 psi.

The OP's question, asking about multiple skins, can be dismissed since sea level atmospheric pressure differential will never be present. Any structure that survived with negative 14.7 psi envelope pressure at sea level would be too heavy to rise to an altitude where only one psi difference is available for lift.

 

[russ_watters]

The absolute maximum weight of one square foot of the vacuum structure that withstands the above forces is 1.9 lbs. The structure must not buckle. The structure needs attachments for crew, cargo, engines, fuel, control surfaces, mooring, etc.

In practice, the airship structure must weigh about half that much, or about 1 lb per square foot, in order to carry crew, cargo, engines, fuel, control surfaces, mooring, etc. Any person who proposes a vacuum airship needs to do these calculations, and show a solution using commercially available materials

Great stuff, thanks. By comparison, the Hindenberg class airships were 135ft in diameter, 800 feet long (equivalent 500ft pure cylinder), 7.1 million cubic feet and had a cargo capacity of 22,000 lb. That's a structure weight of 481,000 lb and hydrogen weight of 40,000 lb for a displacement of 543,000 lb of air. Or per square foot, (pure cylinder), that's 0.96 lb of structure. So if they held a vacuum they could carry almost triple the cargo. But...they would have to hold a vacuum. Buoyed by helium they'd need to shed 12,000 lb to get airborne.

Also, they flew at a top speed of 80mph.

By comparison, a 747-8 has a similar empty weight of 485,000 lb and with a full load of fuel can carry 80,000 lb of cargo (or more if you reduce the 422,000 lb of fuel) and cruises around 550 mph.

It also compares quite unfavorably to a modern inflatable/hybrid blimp such as the Zeppelin NT which cruises at about the same speed and has a 4,000 lb cargo capacity at 1/20th the volume.

 

[akhmeteli]

I don't think you heard what @Vanadium 50 said. You're talking about engineering (and maybe environmental) problems, but he's talking about economics problems.

Vanadium 50 wrote: " Vacuum airships are a not-even-a-solution looking for a problem. "
What did I not hear? He did not mention economics until later. I tend to read what people write, not what they think. So I mentioned some problems a vacuum aircraft could solve. What's wrong with that? And let me note that the problems I mentioned have an obvious economics aspect. For example, if we could release helium each time, we would not have a problem with altitude control, but it is economically impractical.

I understand that you are an aspiring inventor, but even if you succeed in inventing a functional vacuum airship, you still have to solve someone's economic/environmental problem in order to sell it. There has to be a market for the product. So when the time comes, you'll need to be able to show that your solution costs less than a traditional helium balloon or that the cost premium is worth the environmental savings. Right now, you seem to be completely ignoring the cost/market issue.

Let us assume for a moment that I indeed ignore the issues of economics. Would that be such a mortal sin? I believe a prototype vacuum balloon will have significant scientific and cultural value and would be of interest for millions. You can find dozens discussions at various forums, where people ask if a vacuum balloon is feasible. People want to know that. There have been at least three popular articles on vacuum balloons over the last year (at New Scientist, Science & Vie, and salon.com). Again, some work on vacuum balloons is being made at Los Alamos, NASA, Air Force Institute of Technologies (I gave references in my post #42 in this thread). Let me add that a vacuum balloon would also be the first lighter-than air solid.

Let me give you an example. A few years ago some people made a human-powered helicopter (https://en.wikipedia.org/wiki/Human-powered_helicopter). I suspect it has no business potential, but it was a breakthrough, it was interesting for millions.

I suggest watching the TV show "Shark Tank" to see how inventors fare on it. One important thing to note: they pretty much always have a working prototype and a pending patent before pitching their ideas to investors. But that's not enough: they need to prove they are solving a market problem.

I am not sure it makes much sense to compare a prototype vacuum balloon with a prototype of a run-of-the-mill invention. A prototype vacuum balloon would be a major breakthrough.

That said, I think you are downplaying the engineering benefits as well, by basically ignoring completely how the existing solutions work. For the sake of your own business model and the potential time/energy/money wasted in pursuing an idea that really isn't likely to go anywhere, you need to take an honest look at both sides of this. On the engineering side, I can't understand why you wouldn't consider pumping the helium back into a pressurized tank to be a solution to the engineering/environmental problem of wasted helium and airship storage. It seems really obvious. On the other side, since that is obvious but isn't apparently common, maybe that's because ballast is cheap and easy? I suppose you can say that a vacuum balloon with a pump and valves for ballast control is "a solution" to this technical problem, but other solutions clearly exist and I don't see a reason to believe the vacuum balloon would be a cheaper solution (back to the economic problem) -- because ultimately that's what matters most here.

I don't quite understand that. In my post I referred exactly to this solution of "pumping the helium back into a pressurized tank". I wrote: " There are some solutions to the problem (see, e.g., http://aeroscraft.com/technology-copy/4580412172), but they are not simple." Let me note that pressure vessels bring their own share of problems.

It may not be obvious to you, but it seems obvious to several of us. But here's the thing: the burden of proof is entirely on your side whereas the criteria/demands of proof are entirely on ours (or that of prospective investors). We can tell you what we think it will take and you'll have to provide that. Or not -- it seems you've been working on this for a long time and haven't gotten far.

I respectfully disagree about the burden of proof. We are on Physics Forums, not in an investors' office. Not being sure vacuum balloons are hopeless business-wise is not against the rules of Physics Forums, unless you tell me otherwise:-) What's obvious for you is not necessarily obvious for everybody. And again, it may well be that you are right. I am just not sure at the moment.

Step 1: Build a functioning prototype to prove it is actually technically possible. And no, your arxiv paper and patent application are not sufficient as such proof. Even if all the math is right in your paper, it isn't enough.

I cannot build a prototype. Building a prototype would be a major breakthrough. And I agree, our finite-element analysis (FEA) does not prove that a vacuum balloon is technically possible. "FEA does not eliminate the need for prototypes, but it can shorten the process.” (https://www.asme.org/topics-resources/content/fea-and-the-question-of-credibility)

 

[akhmeteli]

Any person who proposes a vacuum airship needs to do these calculations, and show a solution using commercially available materials

We wrote an article (https://arxiv.org/abs/1903.05171) showing that a vacuum balloon can be made using currently available materials. The design was verified for strength and buckling using finite-element analysis. We also cite designs of vacuum balloons by others.

 

[russ_watters]

Vanadium 50 wrote: " Vacuum airships are a not-even-a-solution looking for a problem. "
What did I not hear? He did not mention economics until later.

Er, well...it was the next sentence:

There is a market for about two dozen airships in the world.

So I mentioned some problems a vacuum aircraft could solve. What's wrong with that?

Broadly, nothing -- what's wrong happens when you get specific. When you try to invent a new thing or method for doing something, the specific details are what matters.

And let me note that the problems I mentioned have an obvious economics aspect. For example, if we could release helium each time, we would not have a problem with altitude control, but it is economically impractical.

This is a good example of a specific issue, but without numbers it is just handwaving. You say it is economically impractical, yet this is how it is currently done, so clearly your claim that it is economically impractical is false. Since ultimately your goal is to bring a vacuum airship to market, you need to know the numbers to prove how your idea would be better than what is currently done: how much helium does a helium airship lose per flight or month or year and how much does that cost? How much would your idea save (taking into account the energy use of the pumps)?

Let us assume for a moment that I indeed ignore the issues of economics. Would that be such a mortal sin?

I'd rather not. If you can show your idea is possible, that would be cool, but to bring it to market is all about the economics. It's boring, but it is what matters. Yes, that makes it a mortal sin.

I believe a prototype vacuum balloon will have significant scientific and cultural value and would be of interest for millions.

Ok. Prove it.

Let me give you an example. A few years ago some people made a human-powered helicopter (https://en.wikipedia.org/wiki/Human-powered_helicopter). I suspect it has no business potential, but it was a breakthrough, it was interesting for millions.

It was interesting to millions insofar as it was free entertainment. Cool. But that's not what you are after, is it? You want to eventually sell this as a commercial product, right?

I am not sure it makes much sense to compare a prototype vacuum balloon with a prototype of a run-of-the-mill invention. A prototype vacuum balloon would be a major breakthrough.

Who cares? Answer: Investors -- that's who cares. You have to be trying to sell this idea to someone, right?

I don't quite understand that. In my post I referred exactly to this solution of "pumping the helium back into a pressurized tank". I wrote: " There are some solutions to the problem (see, e.g., http://aeroscraft.com/technology-copy/4580412172), but they are not simple." Let me note that pressure vessels bring their own share of problems.

That first quote is from me, and you didn't state the issue in your post (even if it was mentioned in the link). Regardless, you need a way to prove to investors that your idea is better. To me, there is no obvious reason why an air vacuum pump should be superior to a helium pump.

I respectfully disagree about the burden of proof. We are on Physics Forums, not in an investors' office.

This current discussion is yours to direct as you wish. What is your ultimate goal? If we say, "yep, your idea will work" what have you won? We, the audience have no stake in this game, so winning or losing means nothing to us. If you want us to prove you wrong and we don't, what happens next? Answer: nothing. And that's not what you want, right?

I cannot build a prototype. Building a prototype would be a major breakthrough.

That's unfortunate. Without it, your idea will go nowhere. Do you even know what is required to build a prototype? Specifically? Do you have a written proposal for the next step?

 

[russ_watters]

@jrmichler
Your computations are for sea level. Some things scale sensibly.
I think the idea of using an unmanned vacuum airship at 60,000 feet for mobile phone and internet connectivity is an interesting model. The air pressure at that altitude is only about 1 psi. The airship structure therefore need only counter a 1 psi differential envelope pressure. But the volume must be sufficient to lift the gross weight.

It's a good point: helium balloons are basically altitude agnostic, up to the point where they are fully inflated. A vacuum ballon's lifting capability decreases rapidly as altitude increases.

 

[akhmeteli]

Er, well...it was the next sentence:

I would say, it was in the next paragraph:-) So it was not obvious the first phrase was about economics. And I answered to his "market" paragraph separately.

This is a good example of a specific issue, but without numbers it is just handwaving. You say it is economically impractical, yet this is how it is currently done, so clearly your claim that it is economically impractical is false. Since ultimately your goal is to bring a vacuum airship to market, you need to know the numbers to prove how your idea would be better than what is currently done: how much helium does a helium airship lose per flight or month or year and how much does that cost? How much would your idea save (taking into account the energy use of the pumps)?

I have not heard about airships releasing helium for altitude control. I don't think it is done on a large scale.

I'd rather not. If you can show your idea is possible, that would be cool, but to bring it to market is all about the economics. It's boring, but it is what matters. Yes, that makes it a mortal sin.

Well, different people have different goals.

Ok. Prove it.

I provided some arguments, but if you don't believe that " a prototype vacuum balloon will have significant scientific and cultural value" , it's fine with me.

It was interesting to millions insofar as it was free entertainment. Cool. But that's not what you are after, is it? You want to eventually sell this as a commercial product, right?

No, I want to see a prototype vacuum balloon in my lifetime. I don't see it as a source of income for me. Actually, I spent quite a bit of money on it:-)

Who cares? Answer: Investors -- that's who cares. You have to be trying to sell this idea to someone, right?

I do want to "sell" the idea, but not as a money-making idea at this point. And I believe the idea does "sell" to some extent. As far as I know, our work was the first to show that a light enough structure made of currently available materials can have sufficient strength and stability to buckling. Nowadays, theoretical and experimental work on vacuum balloons is being done in several places, and almost everybody cites our work.

That first quote is from me, not you. Regardless, you need a way to prove to investors that your idea is better.

And the second quote ( " There are some solutions to the problem (see, e.g., http://aeroscraft.com/technology-copy/4580412172), but they are not simple." ) was mine, not yours:-), and the link is about pressurizing helium.

This current discussion is yours to direct as you wish. What is your ultimate goal? If we say, "yep, your idea will work" what have you won? We, the audience have no stake in this game, so winning or losing means nothing to us. If you want us to prove you wrong and we don't, what happens next? Answer: nothing. And that's not what you want, right?

As I wrote to you, I don't expect any significant impact from my posts here. I just thought that the posts may be interesting for some people, as the participants of this thread seem to have some interest in vacuum balloons. So my "goals" here are very limited.

That's unfortunate. Without it, your idea will go nowhere. Do you even know what is required to build a prototype? Specifically?

Yes, I know what is required. The structure is quite simple conceptually: it is a sandwich spherical shell containing two ceramic face skins and an aluminum honeycomb core between them. The ceramic skins are the most problematic part. For a small prototype (say, 5 meter diameter), the face skins are very thin and difficult (but not impossible) to manufacture. Standard technologies can be used to manufacture ceramic skins for a bigger prototype (say, 50 m diameter), but the large size brings its own share of problems.

 

[jrmichler]

I looked at your arxiv paper. I note that you reference your patent application 11/517915, even though it was rejected because of prior art US Patent #1,390,745 by Armstrong. The Armstrong patent issued September 13,1921.

Your paper also references US Patent 7,708,161 by Barton, which uses a series of pressurized chambers so as to use material in tension, and thus avoid the buckling problem. On a quick reading of the Barton patent, I did not see any mention of the mass of the air in the pressurized chambers. A very quick ball park estimate convinced me that the mass of the pressurization air is significant, probably enough to make this concept impractical.

Your references missed the MS Thesis by Metlen, titled Design of a Lighter Than Air Vehicle That Achieves Positive Buoyancy Using a Vacuum, June 2012. Link: https://apps.dtic.mil/dtic/tr/fulltext/u2/a587008.pdf.

I used search terms air buoyant structures and air buoyant structures for vehicles.

It appears that a lighter than air vehicle using vacuum is possible. Practical, however, is a different matter.

 

[Baluncore]

A very quick ball park estimate convinced me that the mass of the pressurization air is significant, probably enough to make this concept impractical.

You are correct.
When considering the section through a vacuum chamber and wall, where the vacuum is opposed only by a pressurised, fixed thickness wall, the effects elegantly cancel to zero lift advantage.

So the structure of a vacuum airship must be kept apart by a solid material, not a gas.
I cannot see any advantage in a liquid filled double wall.

 

[Baluncore]

Following on from my previous post, regarding double walls or envelopes.

Altitude control of a lifting-gas filled balloon is not difficult, and there is no need to compress the selected gas. An external reservoir can contain compressed air. The pressure, and therefor the mass of compressed air can be used as adjustable ballast. That external tank technique could also be used with a vacuum balloon, but a simple vacuum pump would probably be a better investment since no lifting gas is involved, and a vacuum pump is essential to gaining altitude.

Where a balloon has two identical envelopes, one inside the other, the inner containing a fixed mass of lifting gas, can be very thin without any particular strength, since it has zero differential pressure. Buoyancy is changed by adjusting the air pressure in the outer envelope. That outer pressure changes the mass of compressed air, while also compressing the inner envelope lifting gas. That technique is not applicable to a vacuum balloon since it increases stress on the inner vacuum envelope.

 

[akhmeteli]

I looked at your arxiv paper. I note that you reference your patent application 11/517915, even though it was rejected because of prior art US Patent #1,390,745 by Armstrong. The Armstrong patent issued September 13,1921.

Thank you for looking at our paper. I don't see why we should not have referenced our patent application. Yes, USPTO rejected the application as they believed that Armstrong's invention destroys novelty of our application. However, Armstrong did not even say that the walls of what looks like a honeycomb in their pictures can be under compression. It looks like they are under tension in their design. What's worse, Armstrong does not have any calculations of strength, let alone buckling, so one just cannot build a light enough and strong enough structure following their invention (I guess Armstrong's first name Lavanda is a female name, but I am not sure).

Your paper also references US Patent 7,708,161 by Barton, which uses a series of pressurized chambers so as to use material in tension, and thus avoid the buckling problem. On a quick reading of the Barton patent, I did not see any mention of the mass of the air in the pressurized chambers. A very quick ball park estimate convinced me that the mass of the pressurization air is significant, probably enough to make this concept impractical.

I don't think Barton's design is feasible without using at least some lighter-than-air gas. If I remember correctly, he admitted that much somewhere, but I am not sure.

Your references missed the MS Thesis by Metlen, titled Design of a Lighter Than Air Vehicle That Achieves Positive Buoyancy Using a Vacuum, June 2012. Link: https://apps.dtic.mil/dtic/tr/fulltext/u2/a587008.pdf.

We were aware of Metlen's work, but we did not intend to offer a comprehensive bibliography. That work is a thesis by a Palazotto's student. We did reference some representative work by Palazotto and his associates.

It appears that a lighter than air vehicle using vacuum is possible. Practical, however, is a different matter.

I agree. We showed that theoretically it is possible, so I don't doubt that it will be done one day. I would not bet on or against its practicality though.

 

[Stormer]

I wonder if it can be done if it can even compete with LEO satellites. Considering one lighter than air vacuum ship satellite would be a pretty large structure to get enough lift, and with expensive high performance materials. And the cost of that compared to satellites launched to LEO in clusters like Space-X Starlink satellites.

 

[Baluncore]

I wonder if it can be done if it can even compete with LEO satellites.

We all wonder things like that.

I expect someone will build a vacuum novelty that can hover near sea level inside a big sheltered building, just to prove it can be done. I wonder if one could survive the impact of a 10 knot gust of wind without imploding.

I don't expect vacuum airships will ever be safe working outside at sea level. They would be so much safer and insurable, if they were filled with hydrogen.

I am pretty certain that no vacuum airship will ever reach 60,000 feet, where many HBALs are today.

 

[Vanadium 50]

If a prototype vacuum balloon will interest millions, why not do a kickstarter and make one? I suspect the interest is broad, or deep, but not both.

Also consider this: will the vacuum inside be absolute? Better than in space? Of course not - it would cost billions to get that last nanogram of lift. What we really mean is that there is less air on the inside than on the outside. But we already have balloons that do this: hot air balloons. So this is really a question of whether the operating point is right: is high lift, high cost better than low lift, low cost?

The market for non-party balloons is pretty much concentrated at the low-lift low-cost end. There are about 10,000 hot air balloons and 1000 weather balloons (with an increasing fraction using hydrogen). The argument is that there are huge new markets on the other end of this continuum.

 

[akhmeteli]

If a prototype vacuum balloon will interest millions, why not do a kickstarter and make one? I suspect the interest is broad, or deep, but not both.

I don't feel kickstarter is the way to go right now, although I may be mistaken. Other people tried and failed to raise funds for a vacuum balloon at kickstarter.

Also consider this: will the vacuum inside be absolute? Better than in space? Of course not - it would cost billions to get that last nanogram of lift. What we really mean is that there is less air on the inside than on the outside. But we already have balloons that do this: hot air balloons. So this is really a question of whether the operating point is right: is high lift, high cost better than low lift, low cost?

Of course, absolute vacuum is not needed. I think very rough vacuum (say, 1% of atmospheric density) would be enough. It will not affect lift much.

Hot-air balloons are indeed great: no problem with altitude control, easy storage. However, they have a serious weakness: one needs fuel to maintain buoyancy.

The market for non-party balloons is pretty much concentrated at the low-lift low-cost end. There are about 10,000 hot air balloons and 1000 weather balloons (with an increasing fraction using hydrogen). The argument is that there are huge new markets on the other end of this continuum.

Vacuum balloons will have their strong and weak points, different from those of helium and hot-air balloons, so maybe they will have their niches. It's difficult to predict their future now. It will probably depend on the specific technology.

 

[Baluncore]

It's difficult to predict their future now. It will probably depend on the specific technology.

If you cannot demonstrate a vacuum balloon with positive lift at sea level, with a 14.6 psi external pressure, how are you going to increase that performance over fourteen times, to lift in the 1 psi pressure expected at 60,000 feet? Without that advance it cannot become a substitute for LEO satellites.
Your concept of commuting between the surface and operating altitude with the same structure is fascinating, but fabulous.

Of course, absolute vacuum is not needed. I think very rough vacuum (say, 1% of atmospheric density) would be enough. It will not affect lift much.

1% at sea level is not much, but at 60k feet the pressure is 1 psi = 6.8% of SL.
That same 1% at 60k feet reduces the differential pressure from 6.8% to 5.8%.

 

[akhmeteli]

I expect someone will build a vacuum novelty that can hover near sea level inside a big sheltered building, just to prove it can be done. I wonder if one could survive the impact of a 10 knot gust of wind without imploding.

So 10 knot wind provides a pressure of 0.5 rho v^2=17 Pa, according to my calculation (I used air density rho=1.29 kg m^-3). This figure seems to agree with information at https://www.engineeringtoolbox.com/wind-load-d_1775.html . However a vacuum balloon withstands atmospheric pressure of about 10^5 Pa. So it does not look like this kind of wind would be dangerous for a vacuum balloon.

 

[Baluncore]

So it does not look like this kind of wind would be dangerous for a vacuum balloon.

Gusts of wind and wind shear do not act symmetrically, so they induce a bending moment in the structure. That is quite different to atmospheric pressure which is applied equally over the entire surface area.

 

[akhmeteli]

If you cannot demonstrate a vacuum balloon with positive lift at sea level, with a 14.6 psi external pressure, how are you going to increase that performance over fourteen times, to lift in the 1 psi pressure expected at 60,000 feet? Without that advance it cannot become a substitute for LEO satellites.
Your concept of commuting between the surface and operating altitude with the same structure is fascinating, but fabulous.

In that post I was not replying to you or to Stormer, but to Vanadium 50, so I did not have in mind high altitude balloons or substitutes for LEO satellites.

However, let us compare zero buoyancy vacuum balloons for the altitudes of 0 feet (sea level) and 60000 feet (let us call them 0-balloon and 6-balloon). So the atmospheric pressure at 60000 feet is 1 psi, and the air density is 0.0949 of sea level density (http://www.pdas.com/e2.html). Note that the temperature at 60000 feet is -70 deg C. So the average density of 6-balloon needs to be 11 times less than that of 0-balloon. That's tough. It means the structure will be much weaker. However, the pressure it needs to withstand is 15 times less. That's good. So it is indeed more difficult to manufacture 6-balloon, but maybe not incredibly more difficult than 0-balloon.

Let us imagine now that one has a 6-balloon and needs to deploy it at 60000 feet. One can, say, fill it with air to prevent crushing by sea-level atmospheric pressure and gradually move it upwards (say, by heating the air inside) and gradually bleeding out air. This approach is not easy, but not quite "fabulous".

1% at sea level is not much, but at 60k feet the pressure is 1 psi = 6.8% of SL.
That same 1% at 60k feet reduces the differential pressure from 6.8% to 5.8%.

Again, I considered "sea-level" balloons. If one needs a vacuum balloon for 60000 feet, the vacuum should be, say, 15 times better than 1%. It is still rough vacuum.

 

[akhmeteli]

Gusts of wind and wind shear do not act symmetrically, so they induce a bending moment in the structure. That is quite different to atmospheric pressure which is applied equally over the entire surface area.

Still, what I calculated is four orders of magnitude less than the atmospheric pressure. If you believe the factors you mention change the situation dramatically, I would like to see your calculation.

 

[Baluncore]

Consider two hovering balloons, one a vacuum balloon, the other filled with lifting gas. For the same volume, they will have identical mass. The vacuum balloon will have almost all the mass in the rigid structural envelope. The gas balloon will have almost all the mass in the lifting gas. Neither has more inertia than the other, so both will be affected by the wind in a similar way. When one is hit by a gust of wind, or is involved in a collision, the gas balloon will be more flexible, while the vacuum balloon will be structurally vulnerable.

Let us imagine now that one has a 6-balloon and needs to deploy it at 60000 feet. One can, say, fill it with air to prevent crushing by sea-level atmospheric pressure and gradually move it upwards (say, by heating the air inside) and gradually bleeding out air. This approach is not easy, but not quite "fabulous".

When you build a 6-balloon it will contain air, not vacuum. It must be supported during construction. The hangar will need to support the rigid airframe during construction. When it is evacuated, it will "lift off" inside the shed, be disconnected from the suspension, and then move out onto the field.

Heating the air inside a partial vacuum balloon is an expensive and pointless exercise. What advantage could it be? Once the envelope is closed, the mass of air inside will not change with temperature. It is the vacuum pump that removes air mass from the volume. Bidirectionally asymmetric safety valves should prevent over pressure in either direction.

Your 6-balloon with a rigid envelope will need to operate at a reasonably constant differential pressure of about 1 psi, all the way from SL to 60k ft. That must offer sufficient lift to rise, but the light weight structure will only be able to handle the 1 psi external envelope pressure. The structure will have 15 times the volume of a true vacuum balloon at SL, but the structure will have the same approximate weight. Once a vacuum balloon is first flown, the fastest way to reach the 60k ft ceiling will be to design it for a maximum differential pressure of 1 psi.

I assume that the vacuum balloon will be powered by PV to move through the air. To reduce drag, the structure could be airship shaped, a horizontal cylinder with a hemispherical nose and a tail tapered to a point. The problem comes when the two ends are in different winds and the envelope may then implode as it folds in half. Fat and short cylinders will be more resistant to bending collapse, but will have greater drag when travelling.

What cylinder aspect ratio should be used to enable the structure to survive the differential winds encountered at all altitudes? Long and thin is vulnerable and heavy. Short and fat is more secure, with higher volume to structure weight, but it is slower to travel.

To maintain station the balloon will need to fly at twice the wind speed during the day, so it can drift back at night.
At what airspeed will the nose implode? Reinforcing the nose will add weight. Maybe it will need a different nose profile.
What would happen if the balloon flew into a rising thermal. The front half will tend to rise, standing the structure on it's tail. Will it survive that upset, and how will it recover?

 

[Stormer]

Fat and short cylinders will be more resistant to bending collapse, but will have greater drag when travelling.

If it is to be used as a satellite in a global network then does drag really matter much? Can it not then just drift with the wind only doing small maneuvers and let other satellites take over when it drifts away from a ground station and towards another?