A city of ten thousand. That flies. And really can't do anything but fly. And I'm serious. Totally.
The idea belongs to Buckminster Fuller, what he called a Cloud Nine. The idea, in a two-sentence nutshell, is that the larger you build a geodesic sphere, the lighter it is relative to the volume of air it contains. Heat that air a few degrees warmer than the surrounding air and you have a rather large hot air balloon. Every time you double the diameter, the volume of the air is cubed. In other words, if you build bigger, the economy of scale rises geometrically. If you build a Cloud that's a mile wide, the payload capacity would be in the thousands of tons. And the amount of usable space is also massive- a whole countryside in fact. You run out of payload much faster than you run out of space.
The principles governing flight are straight forward. There's no debate that such a thing would fly if it could be built. What Fuller never mentioned was how to do that- how to build one. And that's what I'm about to address.
A geodesic- or, rather, preferably, a tensegrity sphere- is not strong enough to support its own weight until a complete ring of its structure is completed.
*** A geodesic uses nearly identical rigid components to form all the parts the structure. A tensegrity is much more complicated, is flexible, and effeciently isolates compression and tension forces into specialized structures. High-compression struts for compression, high tension lines for, well, tension. ***
And even then, a completed ring is only strong perpendicular to the plane of that ring. Nowhere else. Furthermore, if you are building a sphere, you can't build from the bottom up because the bottom is a mere point and then grows outward. You'd have to build some very large scaffolds- scaffolds more extensive than all the architecture found on some entire continents. It would be like building a upside down pyramid. Only magnitudes larger. And you can't start with a hemisphere because you would then need to lift the whole structure up to put the lower half under it. It would be unthinkable to produce the mechanical force needed to do such a thing. You might be able to use the structure's own buoyancy to do this, but you'd be subject to intense stress from wind and weather as you did. Billions of pounds of force even in good weather.
Until a sphere is complete, in all axi, it is extremely fragile. Imagine the difference between an eggshell that has been cracked, and one that is intact. An already-cracked egg shell can't withstand even a few dozen grams of pressure without shattering further. An intact eggshell, on the other hand, can withstand many pounds of equally-applied force (as you may notice, I mix SI and English units at whim. Totally intentional).
A mile-wide sphere cannot be built strong enough to stand up to normal stresses before it is completed. To build it strong enough would make it too heavy to fly. It is an almost intractible problem.
Fuller imagined one solution. You would build the sphere entirely in orbit and then drop it, gently, slowly, into the atmosphere. By the time we have the freight capacity to build such a structure in space, we'll be far more interested in building space stations. Such a system, while technically feasible, is very unlikely to ever be employed. We'd have to run out of places for space stations first.
My solution is accessible today.
What is needed, put simply, is a mile-high system of "cranes." What I mean by cranes- that is something you'll have to bear with me on. But cranes strong enough to support the weight of the incomplete, unskinned sphere. At least the part that doesn't support itself. And a way to protect the incomplete structure from the weather. Basically, virtually, a construction hangar. But I said "accessible today" didn't I?
We know quite well that it is impossible, using current building techniques, to build anything other than a radio tower anywhere near a mile tall. Such towers have never been built. Also, a radio tower is an extremely poor analogy for a crane. A tower needs only to support its own weight, and can be held in place by tension lines. A Cloud-building construction crane would need to support hundreds of tons of weight.
So, next, we examine natural topography to provide the placements for our cranes. A fjord in Norway, some spur of the Grand Canyon, a valley between two peaks. A strip mine in Siberia. Somewhere must work, surely. But it's not as easy as it sounds. While there are many places with a mile of relief, such places rarely appears so abruptly as to afford the ideally-shaped pocket we'd desire. We could compromise. We could build something smaller- give up the economy of scale that allows for a complete flying city- or we could attempt to use a place with mere half-mile relief to build the lower half of a sphere and rotate it 180 degrees so that it becomes a semi-buoyant dome, half-a-mile above ground level. (A mechanical near-impossibility). We could then race to complete the lower half. In any scenario, we would have to imagine running suspension bridges across a huge space. Cables, gondolas, cranes- a massive collection of complex infrastructure. Tens or hundreds of billions of dollars in tools.
In any event, such an approach is not the answer. That is not the way to build a mile-wide sphere.
*** A mile wide anything is absolutely unheard of. We build ships that are over a thousand feet long. We build skyscrapers. We build warehouses. But we don't build anything anywhere near a mile in size- unless it is completely resting on the earth, like a warehouse. Even then, the mile scale is unexplored. A mile-wide structure is not an incremental increase in scale, it is a massive leap forward. It is a magnitude higher. A leap for which few analogies exist. I can't overstate how audacious it would be to work at this scale. ***
The answer is far simpler, more efficient, and- most importantly- cheaper. And it is available today, using existing technology. In fact, the only thing that really stands between a Cloud and reality is the will to build it. Such a structure could even be profitable to build.
There is another place- besides canyons, fjords, and craters- that offers a mile difference between top and bottom. Furthermore, it is a place that allows you to operate from the top down. In fact, it requires that you do. It is also a very calm, predictable place. And it is a naturally protective environment. It is the "virtual hangar" we need. It also can be used as a virtually weightless environment as long as you plan to use it as such.
I'm writing, of course, about the ocean. I've even picked a place: just to the west of the Yucatan Penninsula, north of Cárdenas, Mexico.
You start on shore, building flat rings that are carried by track into the water and then towed to your building site. You tow the rings with powerful barges. You build the rings with the capability of varying their own buoyancy, like chains of unmanned submarines. You then lower the scaffold rings into the water. You overlap the scaffolds, like meridians on a globe. You control the process like slow-motion marionettes, cables running from surface to depth.
You then begin to build on the scaffold, at the surface. You use a combination of shallow-depth and just-out-of-the-water construction. As you complete a section, you rotate the incomplete sphere- by pulling the appropriate control cables from the construction ships. The scaffold assists by varying internal buoyancy. At this point, you are building only the framework of the sphere. The skin will be added after the structure is complete, strong, and the scaffold has been disassembled and towed away- ready for reuse.
Using a similar, roll-as-you-go process, you put the skin on next. I'm leaving a lot of detail out. The skin would start as a single surface. A second layer would be added much later.
And here's the hard part (not that everything else is easy).
Using the rotation method you attach uninflated buoyancy bags to the outside of the sphere, especially the upper half. Each unit has a large amount of compressed air inside tanks that self-detach when depleted. You then begin to pump heated air into the top of the dome- the part just beneath the water. At this point, you are putting a massive amount of stress on the skin. You reinforce the topmost portion accordingly.
If you can do this in cold weather, there is a significant lift bonus. You also use all available construction barges, and perhaps a fleet of other ships, and you haul outward and upward. Water drains out of the bottom as the sphere gradually emerges from the water. At first, it is being lifted on external buoyancy, provided by the underwater float bags, by the ships, and by a small amount of mechanical leverage (possibly working against anchors set in the sea floor). As it inches upward, it relies increasingly on its internal buoyancy- the same force that will allow it to fly.
If the sphere can be built large enough, light enough, and with the help of supplemental buoyancy, it rises from the water. The completed structure flies free of the water, is moored to the construction ships, and, by varying its altitude to take advantage of prevailing winds, is "supersailed" toward land. It may be the weather doesn't allow it to go where you want it to. Worst case, you release it and fly it around the world, delivering building material with airships. Up to this point, the structure is far more efficient than necessary. It would actually be prudent to carry millions of pounds of water ballast.
Over time, much of the water ballast is replaced with useful payload. The first task would be to develop an on board airport with a one-mile airstrip (at the equator). Once completed, you can visit it at any time using more conventional aircraft, though jet airliners might be out of the question. Then you build the essential infrastructure. Repair systems, onboard generators, safety systems (lifeboats). Then you build a city. Resorts, estates, offices, schools, and retail space.
Naturally, it would rotate, which might- through a combination of active and passive systems- be used for minor navigation. For the most part, however, it would navigate using the supersailing method. Keep in mind that Cloud would not be a form of point-to-point transportation. It would be a moving destination. A supranational sky island.
*** Though it would be far less interesting, Cloud could also be anchored in place. It would then be the ideal site for a massive wind plant- far more than enough to meet its own needs. ***
Cloud would, before all else, be a real estate investment. Individual apartments would be spacious, with walls built of lightweight materials. Residents would pay based on the weight of the structure and furniture payload, not the number of square feet. Condos would range from around a million dollars to more than fifty million- possibly far more.
Cloud would operate a research university. It would be a magnet community for innovators and luminaries. It would grow some of its own food, using aeroponics. It would have a cold indoor lake which could be dropped, in the form of sudden rain, to add emergency lift- one of several systems in place to provide aggressive course adjustment.
Perhaps the largest part of its economy would be based on tourism. It would carry a small fleet of air taxis- possibly
hybrid airships- that would visit local airports, shuttling visitors back and forth. It would be possible to BASE jump indoors. The views- both internal and external- would be like nothing else on earth. You could play golf at ten thousand feet.
If necessary, it would be capable of "landing"- resting gently on the water, or open land. The base could be built in such a way as to provide a soft buffer zone that would allow it to land in forests with minimum mutual damage. In the event of catastrophic damage, it would also be repairable in flight- as the internal air volume would be sub-divided into a number of sections, like the sections of an orange. The loss of one section should be within the surplus margin of lift available by other means (releasing ballast, super-heating, adding hydrogen, cloud seeding to reduce local external temperatures, and one other) The loss of two sections would cause Cloud to gently land. It should be made capable of surviving a 9/11-type collision with an airliner. For safety sake, it would be illuminated on the outside. From fifty miles away, it would be as large and visible as the full moon. You could display video on its surface to audiences of millions, broadcasting the sound via radio.
There is also the potential for Cloud to become the first example of a previously unexploited method of achieving flight. A mode of lighter-than-air lift that has never been used before. But I'll have to write about that later (
see next post).
I don't seriously expect Cloud to ever be built. It is, first-and-foremost, a thought experiment. I've thought of it as the organizing principle for an introductory physics-and-engineering textbook for high school and college students, as well as a "picture book" for younger children. Possibly the same book. The kind of book you keep for life. The kind of book that inspires you to dream big, the way Buckminster Fuller inspired me.