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Sometimes old, discredited or impractical ideas come back to favor, because a new technology has evolved.

Let us imagine a future Earth-like world (not early 20th century or steampunk) that would consider airships again on large scale, but with a physical principle different than air buoyancy (so no hydrogen, helium or any gas, vacuum balloons, etc.). In the extreme, it could also work on planets with a lighter atmosphere than Earth.

Yet it would achieve a similar "buoyancy" effect (spontaneously staying at a certain equilibrium altitude, floating, bobbing, levitation...), at a low cost. That implies some stable uplifting factor that compensates gravity. It might also not need as big an external envelope as traditional airships, compared to the size of the gondola.

It would presumably be a technology that our current society does not have. What physical principle would it be based on? What kind of technology would it use? What would be the process of building it? How would it use energy for its motion?

As in hard science fiction, some level of scientific extrapolation is allowed (some suspension of disbelief), but it should remain overall credible. It should be articulate enough, that readers could solidly think with the components parts of the technology and how their interact with each other.

In which direction would you go?

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  • $\begingroup$ It sounds like you want to invoke buoyancy without the use of buoyancy? $\endgroup$ – Slarty Oct 8 '17 at 16:28
  • $\begingroup$ It's a good point; let's say something functionally similar. $\endgroup$ – fralau Oct 8 '17 at 18:35
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    $\begingroup$ Condensed your question it becomes: "How do I get a lifting force, without relying on buoyancy"? You are using an awful lot of words and attempts at fancy-talk to say only that. The answer: Newton's Third Law of Motion. That is about it... either a plain old reaction engine that imparts downward momentum on a fuel... or you achieve so much speed that you fall to the ground and miss it (i.e. you get into orbit). $\endgroup$ – MichaelK Oct 8 '17 at 19:28
  • $\begingroup$ From a strictly scientific viewpoint yes; but in that case, that wouldn't be an airship but an airplane. There is something about airships that captures imagination in a way that airplanes don't. And that is likely due to the idea of "floating" or "bobbing" (if you prefer those ordinary terms to "buoyancy"). VTOLs do that, but apart of the fact that they consume too much energy to be viable, they are also noisy. $\endgroup$ – fralau Oct 8 '17 at 20:10
  • $\begingroup$ The creation on an airship would seem to imply some sort of very low-energy (or no-energy) system of levitation, perhaps along the lines of magnetic repulsion (using a permanent magnet). Otherwise, it's more analogous to an aeroplane, helicopter or similar. $\endgroup$ – Matt Bowyer Oct 8 '17 at 21:40
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What you ask for seems to be some sort of antigravity. This technology is common in science fiction, but we don't have any serious clue how to do it in real life. The wikipedia link shows some possible technobabble.

Alternatively, call it magnetic levitation against Earth's magnetic field. Not really feasible, either, but your readers might not notice.

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  • $\begingroup$ These seem indeed two valid directions. I wonder how we could expand this into a "realistic" picture? $\endgroup$ – fralau Oct 8 '17 at 18:31
  • $\begingroup$ @fralau, I pointed out that this is not valid in a hard-science sense. $\endgroup$ – o.m. Oct 9 '17 at 5:08
  • $\begingroup$ Naturally: this would be sci-fi. $\endgroup$ – fralau Oct 9 '17 at 6:10
  • $\begingroup$ @fralau This is not valid in hard sci-fi. $\endgroup$ – M i ech Oct 9 '17 at 8:09
  • $\begingroup$ Well, a genre has to afford some freedom, otherwise everybody would write the same thing. In the end, hard sci-fi is what works for the public, rather than what geology-oriented critics say it should be (but they are welcome to debate!). $\endgroup$ – fralau Oct 9 '17 at 8:55
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You can invoke some kind of magnetic focusing able to do magnetic levitation over large (>100m) superconductive pads arranged on the planet, initially along "aeroroutes" and later more or less evenly distributed to allow freedom to chose whatever course; You would have some problems over the oceans though (perhaps you can put the pads on sea bottom).

Alternative is to stipulate some MagLev not needing superconductivity and thus using as anchor the NiFe core of many planets (including Earth).

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  • $\begingroup$ This is very interesting... Would there be a way to mitigate the radiation risk for humans and animals? Unless you don't see it as a problem? $\endgroup$ – fralau Oct 8 '17 at 18:33
  • $\begingroup$ Currently available Maglev does not have any recognizes health hazards neither for humans nor for animals. We are stipulating a "currently not available" extension so I cannot guarantee anything, not even that it will exist, much less possible impact on health. I would say you can safely forget about the issue, unless your plot would benefit from some "unwanted side effects" (i.e.: semi-savage natives fearing "the thunderous clouds bringing ringing headache"... or worse). $\endgroup$ – ZioByte Oct 8 '17 at 20:18
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Vacuum is the medium currently under consideration for airships that don't use gas buoyancy, a Vacuum Cell has a 14% advantage over Helium in the same role. The current problem is one of material science with vacuum containment requiring components with a Buckling Strength several times greater than that which we can currently obtain. Currently artificial Diamond comes closest at 1.5x10^5 out of the required 4.5x10^5, sorry I can't make sense of the units being used it's kg^-1 m^5 s^-2.

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  • $\begingroup$ In my perception, vacuum cell would still be an application of gas buoyancy, since the lift would still be provided by the air in the athmosphere. I assume that it would also fail to work, e.g. on Mars? $\endgroup$ – fralau Oct 8 '17 at 18:26
  • $\begingroup$ It's probably the only technique that would give you any lift on Mars unless you used antigrav or a lifter grid for maglev since there's no native magnetic field. It wouldn't be much lift but you'd get some. $\endgroup$ – Ash Oct 8 '17 at 18:40
  • $\begingroup$ Do you see that it could work on Mars? That might change things. $\endgroup$ – fralau Oct 8 '17 at 18:46
  • $\begingroup$ I said it would provide some, not very much but some, lift I don't think it would be enough, especially in winter when the atmosphere is extra thin. $\endgroup$ – Ash Oct 8 '17 at 18:58
  • $\begingroup$ A vacuum system would work anywhere where there is an atmosphere, albeit there would need to be enough of an atmosphere to offset the mass of the envelope. $\endgroup$ – Matt Bowyer Oct 8 '17 at 21:42
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Flying is all about overcoming gravity. Gravity is a force, so we need to add a second force that is equal or greater, and opposed in direction.

So far, we have brute-force attempts as seen in rockets or, to a degree, helicopters: We apply the engine power fairly directly to push matter down in order to use the resulting force as lift.

Then we have a somewhat more indirect approach in fixed-wing aircraft, and to a degree in helicopters: we use speed and the bernoulli-effect to generate lift.

And finally, in balloons and airships, we use buoyancy, i.e. air pressure applied to a less dense lifting body.

What it all boils down to is countering the effects of the gravitational force.

That leaves us with a number of options for sci-fi flying devices: we can use unobtanium engines to apply force easier, cheaper, more, you name it. But that would simply result in the same type of aircraft with new engines.

Definitely not hipster enough.

Then we could increase buoyancy.
vacuum comes to mind, as that is still lighter than hydrogen. And it doesn't burn, a definite plus. It's also unnatural: the planet will try pretty much everything to fill that vacuum. So we need a way to keep the planet and it's atmosphere out. Today, you would need some kind of rigid structure to counter the pressure of the surrounding air on the vacuum bubble we need for lifting.

Let's say we could flex a material by applying electricity. Let's further say we can do this for an extremely light and gas-tight material. Think in terms of graphene, i.e. one molecule thick and extremely strong, plus our brandnew unobtanium engine to provide electricity to force our cool supermaterial into a large buggble containing nothing (our vacuum). Some more of the electricity from our unobtanium engine goes ito propulsion.

That's already quite hipster.

But let's face it, it's still the same stuff we had for more than a hudred years in a cooler hull.
We can do better than that.

Let's get back do the drawing board.
We want a large, majestic-looking machine, that transports the idea of floating effortlessly overhead, all awe-inspiring, glittering and majestic.

We know that the planet doesn't like large things floating effortlessly. Because gravity.
So be it then, if gravity is the problem, rather than having our own force to work against it, we could simply remove that force.

As of now, we don't really know where mass comes from. (from too many cookies, yes, but where does the mass in the cookies come from?) The higgs-particle might be the primary part of gravity, and as of now, most particles we found either have or are suspected to have an anti-particle.

So here's our solution: We found out about the higgs particle, and the anti-higgs-particle. And we found ways to produce them cheaply (all of that powered by that same unobtanium engine. But we created a much cooler housing for it!).

Now we can create any structure, design it for maximum marketability, add go-faster-stripes and anything (and lots of glitter!), and load a few crates of anti-higgs in the hold, and voilà, floating big awe-inspiring majestic structure in the sky!

Add our fancy-clad unobtanium engine for propulstion as needed.

Or go all the way, have an anti-higgs-shield around our anti-higgs-crates (we don't want people walking on the ceiling of our large stately cabin deck, do we?), and a hole in the shield where the anti-gravity force can work. Now all we need is to direct the anti-gravity (by pointing the hole in the shield in the desired direction), and you can balance your buoyancy, and use the same force for propulsion.

That, i think, would definitely be hipster enough.

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    $\begingroup$ Thanks, this is a delightful. Hard sci-fi is supposed to be accurate to some degree, but it might sell better if it is "hip"! $\endgroup$ – fralau Oct 9 '17 at 8:49
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Your airships could be lifted and propelled by four down-facing rotors that create the buoyancy effect by their lift.

I agree that this technology is quite underwhelming sci-fi-wise as we already have Quadcopters today. But we don't (yet) have them on a really large scale, and the science is sound. Plus they should also work in lighter atmospheres.

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    $\begingroup$ That would, however, just be differently configured helicopter rather than an airship. Additionally, quadcopters have layout advantages that only work in small, simple machines - at a larger scale, traditional single or twin rotor helicopters work better. $\endgroup$ – Matt Bowyer Oct 8 '17 at 21:42
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How about a large scale application of the EM Drive? ADDENDUM: other RF resonant cavity thrusters may be available.

This technology is currently controversial because it seemingly violates the law of conservation of momentum (though various theoretical frameworks have been proposed that get around that) and is described as working by maximising the ratio of allowed electromagnetic wavelengths at one end of a resonating cavity to the allowed wavelengths at the other end of the cavity (it’s ‘q value’). It’s been tested by the British, the Chinese and NASA’s Eagleworks labs, and could break mankind free of the tyranny of the rocket equation (if, that is, it actually functions properly and isn’t just some weird artefact of the experimental procedure)

While current research is looking at supercooling the thrusters to create higher q values and this better thrust, you could imagine a world where large arrays or manifolds of sub-optimal thrusters work in conjunction to provide >1g of thrust. If their mass to thrust ratio is barely enough to allow for this you would need large volumes of thrusters (perhaps contained in some form of cooled envelope that the actual ship hangs below) to produce sufficient lift and maintain control.

It’s an out there notion, but it doesn’t require a vast amount of handwavium on top of the already quite weird science behind it.

At least until someone proves they don’t work.

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  • $\begingroup$ There is little controversy about the EM Drive. It simply doesn't work. Every positive measurement was more or less at the error level, the hypothesis to explain how it works is a farce and it violates the most fundamental laws of physics (as in, the entire world so far works based on it). Though if it worked, that would be a good explanation for the Fermi paradox: any civilisation advanced enough to build a microwave oven can build an unstoppable weapon that you can simply send to outerspace, drive it back and hit the homeworld at an arbitrarily high fraction of c, destroying it. $\endgroup$ – Eth Oct 9 '17 at 12:34
  • $\begingroup$ @Eth: pretty much every test I’ve seen has come back positive, though, and I trust the guys over at Eagleworks not to publish (and more importantly get successfully peer reviewed) unless there’s something odd going on. Perhaps I’ve missed the latest few months on this topic though. Anything recent I should be aware of? $\endgroup$ – Joe Bloggs Oct 9 '17 at 12:43
  • $\begingroup$ @Eth: your last point reminds me of a short story I once read where everyone had the schematics for a really easy to build infinite power generator... $\endgroup$ – Joe Bloggs Oct 9 '17 at 12:48
  • $\begingroup$ A slightly old but still accurate summary can be found here: projectrho.com/public_html/rocket/… and I haven't seen anything recently that broke the trend. Then again, I may have missed something, but something as huge as an actual reactionless drive, let alone one as simple to build as this one, would be bigger news than Heliocentrism, Darwinism, the Big Bang or both Relativities. Probably even all those combined. $\endgroup$ – Eth Oct 9 '17 at 12:54
  • $\begingroup$ @Eth: this is exactly what I meant by controversial. The fact that people have plans to (or if you believe the Chinese already have) test the concept in space means I remain vaguely optimistic about it for the time being. I’ll happily grant that some theoretical frameworks need a kick up the backside if it really does work. $\endgroup$ – Joe Bloggs Oct 9 '17 at 13:06
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They could be dangled on long tethers attached to asteroids orbiting the planet? To be honest, I can't explain how this would work but wikipedia has a couple of articles about it: https://en.wikipedia.org/wiki/Space_tether

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The closest thing to a buoyancy-like aircraft be a ionocraft.

It would probably have an even lower top speed than a helicopter, but would be completely silent. NASA actually worked on a hand-sized flying saucer drone based on it.

The main problem is that you need an absurdly high voltage, so current technologies aren't quite up to it. Assume future tech can take care of this, and you have extremely dense energy storage, probably based on superconductors, or safe portable fusion reactors, and you should be able to build those.

Another problem is environmental pollution: on Earth, those tend to produce short-lived but dangerous ozone and slightly less dangerous but longer-lived nitrogen oxides. So massive use of those will cause lung damage and acid rain. But then, future people may not care about the environment, future environment may be resistant to those, there may not be a future environment left in the first place, or future people already have efficient countermeasures to neuter those polluting gas.

Also, actual hard-SF flying saucers, including eerily glowing propulsion rings if those aren't covered.

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In the Back to the Future series hoverboards exist. These seem to be devices that create a repulsive force against the earth. Same with automobiles in the future, but at longer range. Perhaps something like that. Of course the technology is never explained. One thing about science fiction vs fantasy is to be careful about unintended consequences of your technology. A good understanding of the real laws of physics is strongly recommended. One way to prevent too much questioning about the fantastic aspects of your story is to set up constraining rules about your futuristic science and stick to them. Perhaps the anti-gravity/gravity lifting technology requires an electric current to work. Perhaps the efficiency vs power consumption of the technology follows an asymptotic curve with minimal electricity for a hoverboard, moderate power for a hovercar and nearly infinite energy for a space shuttle. Another possibility is that the technology requires a small bag of a specialized gas mixture to work. This would give you the option of having armored airships with ridiculously small gas bags as seen in fantasy pictures.

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