Could we make a sky island?

Factual Questions
21

*The longest and most destructive party ever held is now into its fourth generation, and still no one shows any signs of leaving. Somebody did once look at his watch, but that was eleven years ago, and there has been no follow-up.

The mess is extraordinary, and has to be seen to be believed, but if you don’t have any particular need to believe it, then don’t go and look, because you won’t enjoy it.

There have recently been some bangs and flashes up in the clouds, and there is one theory that this is a battle being fought between the fleets of several rival carpet-cleaning companies who are hovering over the thing like vultures, but you shouldn’t believe anything you hear at parties, and particularly not anything you hear at this one.

One of the problems, and it’s one which is obviously going to get worse, is that all the people at the party are either the children or the grandchildren or the great-grandchildren of the people who wouldn’t leave in the first place, and because of all the business about selective breeding and regressive genes and so on, it means that all the people now at the party are either absolutely fanatical partygoers, or gibbering idiots, or, more and more frequently, both.

Either way, it means that, genetically speaking, each succeeding generation is now less likely to leave than the preceding one.

So other factors come into operation, like when the drink is going to run out.

Now, because of certain things which have happened which seemed like a good idea at the time (and one of the problems with a party which never stops is that all the things which only seem like a good idea at parties continue to seem like good ideas), that point seems still to be a long way off.

One of the things which seemed like a good idea at the time was that the party should fly — not in the normal sense that parties are meant to fly, but literally.

One night, long ago, a band of drunken astro-engineers of the first generation clambered round the building digging this, fixing that, banging very hard on the other and when the sun rose the following morning, it was startled to find itself shining on a building full of happy drunken people which was now floating like a young and uncertain bird over the treetops.

Not only that, but the flying party had also managed to arm itself rather heavily. If they were going to get involved in any petty arguments with wine merchants, they wanted to make sure they had might on their side.

The transition from full-time cocktail party to part-time raiding party came with ease, and did much to add that extra bit of zest and swing to the whole affair which was badly needed at this point because of the enormous number of times that the band had already played all the numbers it knew over the years.

They looted, they raided, they held whole cities for ransom for fresh supplies of cheese crackers, avocado dip, spare ribs and wine and spirits, which would now get piped aboard from floating tankers.

The problem of when the drink is going to run out is, however, going to have to be faced one day.

The planet over which they are floating is no longer the planet it was when they first started floating over it.

It is in bad shape.

The party had attacked and raided an awful lot of it, and no one has ever succeeded in hitting it back because of the erratic and unpredictable way in which it lurches round the sky.

It is one hell of a party.

It is also one hell of a thing to get hit by in the small of the back.*[right]-- Douglas Adams, Life, The Universe, And Everything[/right]

Stranger

22

And if we suspended it from a geostationary asteroid in lower earth orbit?
would that still count as floating?

23

Actually, for a given load, the larger a geodesic sphere is the less strong the materials have to be in order for it to be self-supporting.

There isn’t a huge advantage to launching from, say, 10,000 feet versus sea level. It is true that you can dispense with a relatively small proportion of propellant and attendant dead weight of tankage, and that theoretical rocket performance improves slightly at altitude (albeit requiring a larger exit cone for a traditional de Laval-type nozzle, which also adds to weight) but most of the energy that goes into launching a rocket isn’t achieving altitude but in gaining enough speed to achieve the requisite velocity for the desired orbit. In other words, most of the energy is devoted to going forward, rather than up. There is an advantage for prograde orbits in launching from the equator, thus getting maximum use of the Earth’s rotational momentum; however, it is easier to launch from equatorial ground sites or marine platforms rather than hauling and assembling a rocket structure on some kind of floating city.

Stranger

24

What about the skin that actually holds in the hot air? Would the strength of material needed go up much with size? Is that even an issue?

25

Yes, as responded upthread. I was going to add that in turn Adams was doubtless inspired by the floating island of Laputa in Gulliver’s Travels

26

Almost anything not prohibited by the laws of physics can be accomplished with the application of enough money and resources.

27

I believe Fuller’s original calculations assumed that the entire structure would be made from steel, which gave a half-mile as the minimum size. With better materials, the minimum size would be smaller. In any event, there’s no practical upper bound on the size.

And a tensegrity sphere might not help much for getting to orbit, but I have seen proposals for an orbital balloon, which would float up to where the atmosphere is almost nonexistent, and then get up to orbital speed gradually using a solar-powered ion drive.

28

Im curious too. Bucky proposed a tensgrity sphere, which is held together with tension. This seems like a safety nightmare. How can this be built to withstand the losing of even one node? How can it be serviced? How can it be navigated? Heck, how can it be made to withstand storms or a fire?

A sphere thats 3,000 feet in diameter would have a surface area of 28 million sq feet. Thats quite a bit of material to produce, install, and maintain.

That said, this airship concept is pretty neat:

29

Blather. No matter how many times people claim breakthroughs, a space elevator, while perfectly physically feasible, is still imaginary technology. Fusion power has been 25 years off for the past 40 years. Flying cars and jet packs don’t exist for any practical purposes. Nobody but a government can put a human into orbit. You can claim that not enough money and resources have been put into these, but that just makes your claim unfalsifiable. You might as well claim that an alien attack would make everyone on earth allies.

30

But a human being CAN be put into orbit, it just takes the resources of a large industiralized nation to accomplish. And you CAN get a jetpack, the only problem is that it’s really dangerous, has limited fuel, and doesn’t work very well. And you CAN get a flying car, except we usually call them airplanes.

I agree about Fusion power.

31

I like the plan at the end, especially the bungee diving platform.

The problem’s going to come when too many millionaires want to moor their pleasure blimps over Central Park (as shown in the conceptual sketch). You just know that those with Big Money are going to jink the laws so that only they can do it. The nouveau riche are going to be forced to moor over the refineries in Elizabeth.

32

Easily, its been done.

Except in this case it was an icbm that was pushed out the back of a c-141 starlifter, drogue shute deployed to slow it down and the engine fired.

I would imagine that something along the same lines would work here.

Declan

33

I think part of the idea is to dispense with local and federal taxes, your example might fit the physical description, but not the fiscal one.

Declan

34

The purpose of air-drop missions with ICBM-based rockets (all of which are targets) is not to achieve greater altitude per se but to offer a wider selection of range profiles than would be possible from existing ground launch facilities. (For a target, it has to simulate a profile relative to the interceptor that is similar to a genuine threat but can’t have enough energy to go off-course during unguided terminal phase, which is sort of like playing horseshoes in a pit surrounded by Fabrege eggs.) Ther is a commercial system, Pegasus, used for air-drop launch of satellite payloads, but the throw-weight is low and the main advantage is achieving optimal inclinational position.

Stranger

35

Out of curiosity, how would that work? I’m a little fuzzy on how tensegrities work, but my understanding is that they basically flex enough to spread out any forces evenly. When you add a skin, especially a (presumably) rigid one like steel, does that compromise the strength of the whole thing? I mean, it’s obviously possible to skin one with a stiff material, since there are geodesic domes all over the place, but do you have to allow for flexing, or is it so minor that it’s a non-issue? Also, when you skin a geodesic sphere, does the skin take any appreciable load, or would it just have to deal with, say, wind forces?

36

The members of a structure in a geodesic takes all the load in pure tension or compression, so that it is possible to build such a structure without using any kind of gusseted joining plates (though in practice some kind of gusset plate or “tinkertoy” spool joint is typically used for simiplicity). In concept this is the same as the more simple pinned-joint truss bridges that engineering students analysis in their basic statics class, and (provided that you can make the bridge as tall and wide as necessary and have adequate footings to accept the reaction loads) can be made to carry any amount of load over any span; the only difference is that a geodesic dome is a three dimensional structure, whereas truss bridges are typically symmetric about a middle plane.

The skin on a “Cloud Nine” would be non-structural, though you may want to attach it to the geodesic frame via some kind of sliding joint in order to keep it tensioned against wind, and would need to have some kind of expansion joints or overlapping elements to allow controlled expansion. It would, of course, have to be made failsafe from damage or unanticipated member/joint failure, such that there are no single failure point (SFP) elements in the design, but the same is true for modern skyscrapers and large suspension bridges, not to mention aircraft. As an engineering project it would enormous (and of dubious utility) but not inconceivable. Indeed, the largest stumbling block I can think of is the actual construction; the “jigs” needed to support the structure before it becomes self-supporting would require more engineering that then actual sphere itself. Imagine trying to erect a dome tent with several thousand poles, all of which have to be held just so, while coping with wind and rain, and you get a general idea of the difficultly.

Stranger

37

When you’re looking at scales of a significant fraction of a mile, steel isn’t stiff.

38

Just off the top of my head, I think I’d build it underwater. Attach floats to each piece to make them neutrally-buoyant, and you could relatively easily move each into position. Then, once it’s all built, slowly pump water out of it to float it to the surface.

39

It’s a clever idea, but assembling a half-mile tall structure under water would be problematic due to depth, and of course in any littoral region you’d have to deal with the effects of differential currents and the daily tides, plus the corrosion that occurs in water and the buildup of sessile lifeforms and organic material.

The idea of neutralizing the buoyancy is worthwhile, though; you could have large fleets of zeppelins and balloons lifting manageable segments of the structure in place for assembly. You’d just have to be really certain about the wind, and be prepared to get everything in position up to the point that you can assembly a bridging structure that allows you to cease lifting.

The alternative, of course, is to assemble it in orbital freefall and then slowly lower it down to a point that it can become self-supporting. This still leaves you with the difficulty of assembling things in orbit (and for a structure this large, measurable tidal forces that will have to be braced against) but it does eliminate compression due to gravity as an issue. I’ll leave the details as an exercise for the practical-minded science fiction enthusiast.

Stranger

40

Doing it in Lake Superior would eliminate all of the tides and much of the currents, and would mean that you’re only dealing with fresh water, not the more corrosive salt. Unfortunately it’s only a quarter-mile deep, though.

An orbit-down approach seems like it’d be even more difficult, though: In orbit above the atmosphere at very high speeds is fine, and down in the atmosphere deep enough to be supported by buoyancy is fine, but getting from one to the other would be problematic: You’d have some period when you’re slowing it down too much to stay in orbit, but at the same time you’re too high up to have enough buoyancy.

Still, it’s obvious I’m a scientist, not an engineer.