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Babylonians had an idea ahead of their time.
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Instead of a Space Elevator, build a large takeoff pad reaching above the atmosphere. Use Helium filled Styrofoam for the base of the structure, and launch into orbit with a rail gun.
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If not Styrofoam, then artificial pumice filled with Helium bubbles.
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Aerogel is much lighter and would float.
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Not very helpful... although it would get you high up there, it isn't that easy to launch off of it because you have no horizontal velocity. You have to reach Mach Twenty-Five to enter LEO, which is why the X-Prizers don't have a prayer of doing that feat for a long time.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Coming to understanding that LEO meant velocity not altitude was quite a shock to my history-major brain but then other stuff started falling into place after that.
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Actually, launching from an altitude in excess of 20km is equivalent to launching from a subsonic jet plane in terms of the potential energy it contributes to the launch. A balloon platform can also carry more than a jet aircraft, allowing larger payloads. It also reduces drag losses, which are a large percentage of fuel consumption for small rockets.
Unfortunately, a helium filled tower from ground to stratosphere is a terrible idea, regardless of what you make it out of. Wind forces would add up very quickly along its length, and it would have a horrendous tendency to twist, kink and pop. It wouldn't stay up, and you couldn't ascend it if it did.
A better idea for a stratospheric tower is to use a set of one or more tethered airships to lift rope guy lines. The working end of the tower is all that requires lift. Modern materials like Spectra rope and cloth are perfectly adequate for such a task, and one could be built today if anyone wanted one. Designs already exist.
I like the idea of making a airship out of aerogel! That would just be too cool. I wonder what the rate of gas loss through the aerogel would be? How often would it be necessary to replace the "envelope"?
Hmm...
"We go big, or we don't go." - GCNRevenger
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I wonder what kind of composites could be constructed with a light gas (say argon, since hydrogen and helium are hard to contain), nanotubs and Kevlar.
Consider a simple cube with Kevlar walls, nano tubes reinforcing the edges and maybe have each corner connected to each other corner with a nano tube cable. The cube would we filled with argon with about one atmosphere of pressure and supported with four inflatable pillars filled with argon at four atmospheres wrapped in Kevlar and reinforced by nano tubes.
More advanced cubes could have cylinder packed walls (kind of like a cardboard box), supported by Kevlar filled with argon at about 3 atmospheres. Although the sturutre should be made strong enough to stand on its own it should have some kind of control system to minize the effect of large winds or earth quakes. Kind of like the building in Japan.
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Why bother with gasses? Fill your 'airship' with vacuum. I know that my low temp freezer at work uses vacuum filled insulation, greatly reducing the wall thickness required. I'm not too faniliar with aerogel strength but could one simply evacuate the aerogel and cover it with a thin metal film? You'd greatly increase the lift capacity of an airship if there was no gas inside of it.
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Why bother with gasses? Fill your 'airship' with vacuum.
What materials would you use? They would have to be strong and rigid.
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Hey, are we talking about airships or towers?
Back to the towers discussion...
It seems from this discussion that a 20 km tall tower will be too weak to stand up to winds and earthquakes. So, since we're talking about ancient architecture, let's use a pyramid!
With a base about as wide as its height - 20 km - the pyramid would hold up well against the wind and earthquakes. It could probably also be made of conventional materials like steel frames and concrete.
An eastward facing rail on one slope could launch payloads into equatorial class orbits, while another on the north slope could launch payloads into polar orbit.
All the manufacturing, refining, construction, and living areas could easily fit inside the city-sized structure.
It would cost many billions of dollars to build, most likely, but you would get a lot of neat benefits, such as:
1. The biggest, coolest monument to human endevour ever built.
2. Since all your factories (pollution producers) would be under one roof it would be easy and economical to recycle by simply piping all waste into another factory where it would be useful.
3. The eastern slope of the pyramid could be covered in solar panels giving you free energy.
4. And you will have created a new way to commit suicide - just ride the elevator to the top and try to breathe.
So, what do ya think?
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Ummm would just putting a vacuum in somthing really produce lift? That doesn't sound quite right... balloons float because the gas inside has the same pressure but less mass.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Hey, are we talking about airships or towers?
If they stay in one place and you can reach the top by cable elevator, what's the difference?
"We go big, or we don't go." - GCNRevenger
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In order to build a 100 mile tall structure, it has to be made of light materials, otherwise it would sink. Mountains "float" on top of heavier materials below. Assuming the 1.5 to 1 slope of rock fall, the base of the structure would be 300 miles wide.
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After reading the posts, it seems that rather than a tower to space, the solution is a ramp to space, supporting a launch tube exiting above the atmosphere. (Subway to Space ?) Inside of the launch tube would be vacuum. The launch tube would be long enough to provide escape velocity. The support ramp for the tube could be called the "Ramp of Babel"
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It would be a Real Estate Developers dream; Condominiums in Space, with a ski resort 100 miles high. If the structure were made a new country; its Tax Haven status would provide the financial incentive. In addition, rivers would form to irrigate the farms below. Should it be built in the Sahara or Southern USA ?
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CME: What you're talking about is a twenty-thousand foot high (readymade) stratovolcano, with a maglev launching track, on the equator e.g., in Ecuador. (This happens to be my favorite scheme.)
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GCNR: Lift is produced by displacement. If an object is lighter than the air it displaces, it rises. Assuming a constant skin mass, the best lift will come from a vacuum inside the object. Until recently, the problems of air pressure collapsing the object and gas leakage into the object were too great. However, recent advances in polymer tech and so on have started to make this sort of stuff practical. The best way to do it is probably have a small cell foam of a high strength material. Smaller cells have a proportionally higher resistance to being crushed (although at a proportionally higher skin mass). The ultimate building material would be something like a carbon aerogel (which has recently beeen made but I don't know what the material properties are other than it's slightly magnetic for a few hours after creation) with a metallized skin around it.
As long as your skeleton materials and skin are light enough, such a balloon could theoretically go much higher than helium balloons. Although I'm highly dubious about the use of floating structures as launch pads, these superballoons could be used as high altitude astronomical platforms, etc.
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To get an idea of how light the materials have to be I once calculated that a space tower built out of concrete that extended to geosynchronous orbit and had an area of around one m squared at geosynchronous orbit would need a base wider then the earth just to support the compressive loads.
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Geosynchronous, 23,000 mi, is almost 6 times Earth's radius, and the uniform gravity assumption cannot be used.
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100 miles is just a bump compared to 4,000 mi earth radius, and extrapolations have more meaning.
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Mt. Everest has density around 2.5 and is 5 miles high. A Mt. Styrofoam at 0.1 density could be 125 miles high ?
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The Space Mountain could be started, floating in the ocean, sinking till it hit the bottom.
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Lot easier than terraforming Mars, to make it Earth like.
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Mt. Everest has density around 2.5 and is 5 miles high. A Mt. Styrofoam at 0.1 density could be 125 miles high ?
You are assuming that styrofoam is as strong as rock. It is not.
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Geosynchronous, 23,000 mi, is almost 6 times Earth's radius, and the uniform gravity assumption cannot be used.
I am not sure what you mean by uniform gravity assumption. I took into account the rotation of the earth and that gravity varies with altitude. I did not consider the gravitational forces the structure exerts on its self. I looked at the numbers for the assumptions I made and did not think a better model would make a concrete space elevator anywhere near realistic.
100 miles is just a bump compared to 4,000 mi earth radius, and extrapolations have more meaning.
Who said anything about 100 miles. Anyway, MC Edwards did say a tower just 20km high would be useful, but how big would the top platform have to be? Consider the size of the launch faculties for the space shuttle and imagine raising these 20km or 100km. Now consider how many launches per year would be required to make this economical?
Mt. Everest has density around 2.5 and is 5 miles high. A Mt. Styrofoam at 0.1 density could be 125 miles high ?
The Space Mountain could be started, floating in the ocean, sinking till it hit the bottom.
Lot easier than terraforming Mars, to make it Earth like.
Well obviously Styrofoam isn’t strong enough to build a structure by itself. But maybe Styrofoam could be used to help support a structure. In some factories the floors and walls are made of Styrofoam sandwiched between two pieces of sheet metal.
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I was thinking about honey comb composites and was wondering what it would be like to have layers of honey comb composites. Maybe 10 layers and having the pressure in each layer drop by one tenth of an atmosphere. If such a structure surrounded an inner layer of vacuum it would have some interesting structural properties.
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When a beam is bent one side is in compression and the other side is in tension. To deal with the tensile load the outside of the structure could be reinforced with cables (possibly made out of nano tubes.). To deal with the compression it might be worth considering having the air pressure in side some of the honey comb composites greater then one atmosphere. Starting from the outside of the structure the internal pressure would first increase each layer and then decrease each layer until the inner vacuum is reached. If leakage occurs perhaps pumps could be added to ensure the inner layer stays at near vacuum pressures.
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In buildings the more redundancy the better. If sections of the structure are made lighter then air then if a plane runs into part of the structure there will be very little damage to the surrounding areas due to falling pieces of the structure. The structure could be made so that it is supported both from earth and from space. Moreover it could be designed so either method of structural support is sufficient to hold the structure in place. Perhaps the structure could even have thrusters in parts of it for emergency stabilization of position.
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Interesting demo at the Science Fair; 20 people standing on a plywood supported by balloons between the floor and the
plywood.
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I wonder how high you could go with metal foam, formed with high pressure gas inside, layered with high strength materials.
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Large bird bones, hallow inside, provide another clue on building large objects.
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Skyscapers are just now hitting 0.5 - 1km in height.
A tower needs to be conical to deal with wind but its base width can be less than its height, it just needs to be rooted properly.
If you had a 20km steel cone it would likely have to go down 5 km or have a truly massive underground spread. As far as I know nobody has drilled past 2km.
I think 10Km is hitting feasible but that would be horrificaly expensive and occupy everybodies steel production for decades.
Come on to the Future
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Metal foam can have density almost as low as Styrofoam.
Denser commercial foams are rated 8,000 psi compression strength.
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Most of the space inside the Metal Foam structure would be compressed gas, the pressure and bubble size optimized for its location.
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Instead of a conical shape, the structure might look like a modified air pressurized dome structure, as on a sports arena, but elongated for height.
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I don't understand how to optimize such a structure, but starting with a large birdbone and finite element analysis ?
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The tether guy lines of a structure raised by a set of floating bouyancy cells, rather than supported by a column, would only need to resist a few dozen tons of tension, not a few dozen thousand tons of compression. Fully extended through a hurricane, one-inch cables would not catch enough wind to drag the tower down.
Forget pyramids. Tethered airships are an infinitely superior way to raise a 20 mile tower.
"We go big, or we don't go." - GCNRevenger
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