Antigravity

Relax wrote:Oh yea, and if you do a deflection calc on a tower 60,000ft high with a diameter of only 500ft and a wind velocity of 60mph, lets just say, it blew over. Don't know about you, but the wind blows a hell of a lot stronger than 60mph.

The tensile problem only becomes MASSIVELY more pronounced the larger diameter you go. Now if you wish to propose multiple columns of pressurized air 60,000ft high, go for it. Its base is going to be around a mile wide...

Well, of course you use multiple columns.

From the page I quoted before:

Dani Eder wrote: ...
You would build the compressive tower the same way that TV transmission towers are built - as a truss of smaller elements. A reasonable height-to-base ratio is 20:1. So a 100 km tower would have 3 base points 5 km apart, assuming you have a triangular cross section for the tower as a whole. Each principal column would in turn be a truss with 3 sub-columns spaced 250 meters apart, which in turn are made of tertiary columns 12 meters apart and 0.6 meters in diameter each. The tertiary columns have a wall thickness of 0.03 meters.
...
Wind loading is indeed the driving force on the tower in the first 20 km of height. Up to 10 km, higher wind speeds dominate over pressure drops. Above that height, wind speeds no longer increase, and reduced atmospheric pressure dominates. When I did the studies of this type of structure, I used pivoting airfoils around the truss elements to minimize drag. They can lower it quite a bit below that of a circular tube.

Bill Woods wrote:

Relax wrote:Oh yea, and if you do a deflection calc on a tower 60,000ft high with a diameter of only 500ft and a wind velocity of 60mph, lets just say, it blew over. Don't know about you, but the wind blows a hell of a lot stronger than 60mph.

The tensile problem only becomes MASSIVELY more pronounced the larger diameter you go. Now if you wish to propose multiple columns of pressurized air 60,000ft high, go for it. Its base is going to be around a mile wide...

Well, of course you use multiple columns.

From the page I quoted before:

Dani Eder wrote: ...
You would build the compressive tower the same way that TV transmission towers are built - as a truss of smaller elements. A reasonable height-to-base ratio is 20:1. So a 100 km tower would have 3 base points 5 km apart, assuming you have a triangular cross section for the tower as a whole. Each principal column would in turn be a truss with 3 sub-columns spaced 250 meters apart, which in turn are made of tertiary columns 12 meters apart and 0.6 meters in diameter each. The tertiary columns have a wall thickness of 0.03 meters.
...
Wind loading is indeed the driving force on the tower in the first 20 km of height. Up to 10 km, higher wind speeds dominate over pressure drops. Above that height, wind speeds no longer increase, and reduced atmospheric pressure dominates. When I did the studies of this type of structure, I used pivoting airfoils around the truss elements to minimize drag. They can lower it quite a bit below that of a circular tube.

0) Start with it would never be a triangular construction as there is human life involved and that is not a redundant structure.

1) Your quote: Start with he was using 1.4Mpsi carbon that does not exist as there is no matrix that will transfer the load in shear. In short, he would have to somehow "GROW" the graphene as composites do not meet his criteria at all. At which point, his density just jumped to 0.08 minimum from 0.07 which is LOW density epoxy with low shear properties. Composites on airplanes average about 0.1. They can be lower in specific instances at higher carbon density and lower matrix % at around 0.08, but by and large, carbon composites are limited in the extreme by the matrix shear properties. In my calc above, I was assuming 400,000psi. This is ultimately generous as the matrix drops that number down to around 100,000psi. In short, for 1.4Mpsi, one needs a matrix that is over a factor of 10 better than any matrix we have today. Or as I said previously, he has to grow the structures as a single carbon structure. Which also currently cannot be done.

2) He is not using hydraulic pressure transfer tubes as DDHVI is proposing. Not one bit. Just normal truss.

3) Good luck on the pivoting airfoils and all their additional weight/increased area for ice snow load, that over time can easily be a foot thick. Not sure this is on the net, but if you can find it, look up ice loading on windmills when stationary and shut down with their blades optimized for lack of ice(vertical position). When rotating, maximum thickness was found to generally be around 4-6" thick, with a maximum of over a foot thick(near hub 4" at mid point to tips) before dynamic forces shed giant ice blocks turning the nicely balanced windmill into a bearing grinder due to balance issues.

In short, the ice loading on the lower ~10km is going to be WAAAAYYYY in excess of the tower weight itself. Column buckling strength required just increased by a factor of 4-10 or more depending on your assumptions. It could be upwards of 100 depending on how large his "airfoils" are. Go mountain climbing up high. Hoar frost on vertical cliff faces where clouds move through and do not deposit snow is often over a meter(FEEEET) thick, not mere inches.

At minimum defroster system must be integrated into the tower on all its structure.

PS. His tower is supporting 4000tons... Compressive buckling is the critical factor, without any safety factor, ice loading, defects in manufacturing, loss in strength due to water penetration(boats don't care as they are overbuilt), UV wear on outter layer leading to crack initiation points etc.

Uh, its pie in the sky stupid white paper completely ignoring reality as he is ONLY looking at it from an equations perspective and utterly ignores basic engineering realities. Yes, I have done space elevator calcs myself when I was going through school. They all fail miserably.

Relax wrote:

DDHvi wrote:My last on the pneumatic space tower, unless someone comes up with something good.

Lets see total weight "suspended" by a 1000psi bag 500 feet in dia is roughly 200million lbs. Height proposed: ~750,000inches. AT 300,000lbs/in = 2.25 Trillion lbs.

Or bad. What suspension?

1000 PSI at the base is likely too much. I'm no longer doing calculating such as the gas pressure at the base using hydrogen and assuming, say, 10PSI differential (30 inches of steel's weight) at the platform. There would also be the question of just how much the needed weight would be for the platform, and the area of it.

How, suspended? That is just what this is avoiding, not one bit of it would need to be suspended, but rather pushed up from below. This is a shaped bubble. I suspect it would also be a financial bubble due to the point failure mode possibility, even if it can be built.

Truss construction would make the problem worse. You want maximum affordable diameter at the bottom for both higher wind tipping resistance and less overload of the foundation. My point was that 1k PSI can be handled by a foundation, provided that it is a total area slab foundation, not the smaller foundations a truss structure would need.

Think a bubble with the outer wall shaped to contain the radial pressure at each particular level and "floated" on the vertical gas at that particular area. Without calculating the likely gas bottom pressure, I can't calculate needed radial thickness to contain it, and would need to put the whole thing into calculus to get total weight. Note that as the bottom bells out, the ratio of radial thickness needed to contain the gas and vertical thickness to ride on the local pressure changes. And being retired, I'm not calculating it.

Also, hydraulic fluid would be way too dense. The best fluid is the least dense, hydrogen gas. Given gas can compress, the solid outer skin would need strong damping ability, dynamic or otherwise.

Anyone want to look up the formula for density induced pressure change over a height difference, and calculate what surface pressure would be, given such and such gas pressure at the top, assuming 20 km? I'm thinking wind side load would be the major problem, given the leverage from the height of the tower, even if wind loads are limited to the lower half! In any case, it would need a lot of material, no matter what it was built from, but less than a sky hook from a 24 hour orbit.


This isn't my idea, just thought it might provoke some interest. The top diameter might be a few hundred feet, but there is no way the bottom diameter could be anywhere that small, if only because of the need to "float" the local side walls on the local gas pressure. Gas pressure curve calculation I'm not going to do would be needed before determining whether it is practical.

And I still would prefer A/Cgravity, if only we could do it.


Dumb mistakes are very irritating.
Smart mistakes go on forever,
unless you test your assumptions!

DDHV, retired technical nerd.

DDHvi wrote:Or bad.

1000 PSI at the base is likely too much. I'm no longer doing calculating such as the gas pressure at the base using hydrogen and assuming, say, 10PSI (30 inches of steel's weight) at the platform. There would also be the question of just how much the needed weight would be for the platform, and the area of it.

What, suspended? That is just what this is avoiding, not one bit of it would need to be suspended, but rather pushed up from below. This is a shaped bubble. I suspect it would be a financial bubble also due to the point failure mode possibility.

Also, hydraulic fluid would be way too dense. The best fluid is the least dense, hydrogen gas. Given gas can compress, the solid outer skin would need strong damping ability.

Anyone want to look up the formula for density induced pressure drop over a height difference, and calculate what surface pressure would be given such and such gas pressure at the top, assuming 20 km? I'm thinking wind side load would be the major problem, given the leverage from the height of the lever.

Dumb mistakes are very irritating.
Smart mistakes go on forever,
unless you test your assumptions!

DDHV, retired technical nerd.

Sigh. Hydraulics is an entire field of mechanics. The fluid used can be air,hydrogen or any other viscous fluid... You will note I treated the "fluid" with an induced pressure of 0. Reality is much greater than this. I was being kind in your calc. Actually I wasn't. I didn't want to bother with fairly insignificant additional stresses. Whether 1000psi or 1100psi, the difference for this discussion is insignificant.

You want to know the pressure differential? What is the fluid density at pressure and temperature is in a look up table in the back of any Thermodynamics book and can be obtained at engineering.com I believe as well... Density times height = ..... Yea pressure.

"Pushed up from below"..... What you wish to believe in make believe pressors and tractors without a physical material to withstand the tensile/compressive stresses to hold said fluid in? Fine, you do not like 1000psi. Use my simple calcs for whatever pressure you like. The problem ultimately is wind shear not compressive buckling forces. Once you get close to a design, then buckling compressive forces dominate. IE compressive + wind shear. Don't forget ice hoar frost buildup on the entire structure. Do remember that at the equator the ice build up due to weather happens at a higher altitude than anywhere else on earth. 60,000ft high thunderclouds are quite common. Why equator? Because away from the equator, the centrifugal forces pulling the building towards the equator add up in a hurry. Of course this also varies at the equator as well, but to a much smaller extent.

Oh yea, and better conquer Ecuador. The highest equatorial point on earth is Mount Chimborazo at slightly over 20,000ft. Just happens that point is the closest to the sun as well. So your tower is "only" ~9 miles high. That should help immensely.

Relax wrote:
You want to know the pressure differential? What is the fluid density at pressure and temperature is in a look up table in the back of any Thermodynamics book and can be obtained at engineering.com I believe as well... Density times height = ..... Yea pressure.

Given this height, I doubt that density would be a constant. The atmosphere with a molecular weight around 30 goes from 15PSI to almost nil over that height. The density change complicates the formula. Not to mention possible other difficulties due to temperature changes, etc.

"Pushed up from below"..... What you wish to believe in make believe pressors and tractors without a physical material to withstand the tensile/compressive stresses to hold said fluid in? Fine, you do not like 1000psi. Use my simple calcs for whatever pressure you like. The problem ultimately is wind shear not compressive buckling forces. Once you get close to a design, then buckling compressive forces dominate. IE compressive + wind shear. Don't forget ice hoar frost buildup on the entire structure. Do remember that at the equator the ice build up due to weather happens at a higher altitude than anywhere else on earth. 60,000ft high thunderclouds are quite common. Why equator? Because away from the equator, the centrifugal forces pulling the building towards the equator add up in a hurry. Of course this also varies at the equator as well, but to a much smaller extent.

Oh yea, and better conquer Ecuador. The highest equatorial point on earth is Mount Chimborazo at slightly over 20,000ft. Just happens that point is the closest to the sun as well. So your tower is "only" ~9 miles high. That should help immensely.

I totally agree on the wind shear bit. By belling out the structure at the bottom, the weight of any side wall needed to hold the radial component of the pressure can be lifted by the vertical component of the same pressure, as long as a total area slab foundation can handle the load. The other problems you mention are also good, and why MAJOR engineering effort would be needed, even if the basic design calculates out.

If you check back in the thread, the most I ever said was that this MIGHT be practical, certainly more so than something suspended with a center of gravity in a 24 hour orbit . The amount of material needed would be orders of magnitude less, which still doesn't mean it is practical.


Dumb mistakes are irritating.
Smart mistakes go on forever,
unless you test your assumptions.

DDHV, retired technical nerd.


I still don't know whether the inventors of this idea have a dumb idea or a smart one. Being retired, I have other things to do instead of testing his/their assumptions. Especially when the primary calculation would require calculus.

Relax wrote:Oh yea, and better conquer Ecuador. The highest equatorial point on earth is Mount Chimborazo at slightly over 20,000ft. Just happens that point is the closest to the sun as well. So your tower is "only" ~9 miles high. That should help immensely.

Something tells me that constructing a "beanstalk" atop Mount Chimborazo isn't a very practical or economical solution. A site in the Galapagos islands is probably a better choice even if the "beanstalk" has to be 20,000 feet taller. At least in the Galapagos you'd have sea transport for building materials and launch vehicles/payloads.

DDHvi wrote:the primary calculation would require calculus.

Guarantee you, calculus would not be required. No engineer would do so today. Iteration at worst today. There are these things called computers...

You link the equations and start plugging numbers in. Initial just WAG it and call it mEaaaah good enough for a starting point.

Does this make us worse engineers than those of yore? In some ways yes as the equations are not memorized. Many have forgotten very basic rules of thumb for say increasing structural weight per linear change in dimension along with forces for MMI(mass moment of inertia) etc.

Relax wrote:

DDHvi wrote:the primary calculation would require calculus.

Guarantee you, calculus would not be required. No engineer would do so today. Iteration at worst today. There are these things called computers...

You link the equations and start plugging numbers in. Initial just WAG it and call it mEaaaah good enough for a starting point.

Does this make us worse engineers than those of yore? In some ways yes as the equations are not memorized. Many have forgotten very basic rules of thumb for say increasing structural weight per linear change in dimension along with forces for MMI(mass moment of inertia) etc.

If I was required to do it, I would iterate, starting at the top and working down. Base diameter would depend on the fill gas density and the tensile hoop strength, this would in turn determine total mass needed. The few reference books I took home on retirement are so out of date that they don't have strength figures for any FRP I guess at a mile minimum base diameter, but calculation would be needed. Local climate would be changed somewhat, given the size of this artificial mountain

Someone might make one for prestige, but it makes too easy of a target to be practical while war continues to exist.