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Humanity discovered a new energy source, virtually infinite, that can produce gigawatts of electric power using devices of few kilograms.

Land and sea transport obviously will switch to electric motors without major changes, but what about air and space transport?

What are plausible propulsion methods for high speed aircraft and space launch vehicles with a very light and powerful electric energy source available?

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    $\begingroup$ The turbines on a modern jet produce somewhere between 25-100 Megawatts each (it's a bit tricky to convert thrust to power), and in modern high-bypass jets (i.e. pretty much all non-military craft) 80-90% percent comes from the main intake fan and not the engine exhaust. So, given we have electric motors that are already nudging jet engine power to weight ratios, you can absolutely have an all-electric A380 jumbo and no-one would be the wiser. $\endgroup$ – Samwise Apr 13 at 1:18
  • $\begingroup$ @Samwise Please make that an answer. $\endgroup$ – StephenS Apr 13 at 3:41
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    $\begingroup$ Does this answer your question? Infinite energy, helicopters and world-wide attention $\endgroup$ – nick012000 Apr 14 at 4:03
  • $\begingroup$ @nick012000 I do not think this is a duplicate - the older question is mostly about helicopters, this one is about vehicles able to reach space. $\endgroup$ – Renan Apr 14 at 13:28
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Railguns. Railguns for Everything.

I feel like I should put a caveat here and say 'not if you want the inhabitants to survive', but it's entirely survivable as long as you have the right set of circumstances. In fact, it's something NASA considered. A railgun is basically just a cannon which fire projectiles, except instead of using explosions, it uses electromagnetic force, which is derived from massive amounts of electricity. Germany developed AA railguns in WWII, but seeing as each railgun needed enough power to light up half of 1947 Chicago, the project was understandably scrapped. So long as you modulate the amount of power on the launching end, railguns can be used for bullet trains, launching airplanes, and launching scramjets into space.

There is a slight flaw here, and that is that railguns only provide a boost upon firing the projectile. That is, it's a single massive thrust at the beginning. Not so bad if you want to have a mag-lev bullet train which doesn't experience much friction, but if you want to fire a rocket into orbit, you can fire the railgun strong enough to do so, you just might run into problems. As in 'turn the atmosphere for hundreds of feet surrounding the projectile to plasma' problems, not to mention that such drastic acceleration might damage things inside the projectile, especially if they are the squishy fragile human type of things. (The NASA launch program is for probes, not manned flights. But the theory is sound to get human up that way too. Just maybe with a bit less initial thrust.)

You'll end up using a combination of railgun / conventional rockets to get to orbit - though of course as shock-absorbing technology gets better you'll be able to lean more heavily on the railgun aspect. Once you get into space, it's going to be ion engines all the way. Ion engines are basically the reverse of a railgun, they fire small ions from the ship and use the gradual acceleration that accumulates to the reaction of said firing. Ion engines are too slow to use in atmosphere, but they work just fine in space.

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  • $\begingroup$ I believe that catapults on the new Ford class aircraft carriers work on similar principles to railguns as well. $\endgroup$ – Jan Dorniak Apr 13 at 8:57
  • $\begingroup$ Some variations on this, such as launch loops and some types of skyhook, seem like they would benefit massively from infinite electricity. Anything requiring active support, for starters, is suddenly significantly more practical. Once high altitude stuff like this is more doable, bigger structures can be built, and those also will use electricity as launch / land assists. The real trouble is that it will still be about as expensive to build the first as it is without, won't it? $\endgroup$ – CAE Jones Apr 14 at 11:04
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    $\begingroup$ I feel like I should put a caveat here and say 'not if you want the inhabitants to survive' well you can't make an omelet without some high G related deaths. $\endgroup$ – Renan Apr 14 at 13:28
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It depends a lot on how you want your power source to work, like if its has draw backs. Air planes could hypothetically use electrically powered turbines to generate thrust, but that would be a lot of power. If you want something a little more creative but realistically less efficient you could have the craft absorb moisture out of the air then super heat it with electricity forcing it out the back it to generate thrust. If you are more inclined to air on the realistic side I'd recommend reading up on modern attempts to make electric air travel, I know they exist, but obviously have not taken off sufficiently.

Space again depends on the power source, I suggest you look at the theory of ion engines or solar sails as both rely on low cost particles (ions and photons) that could be generated from your power source depending on how it functions and are both real world thoughts on how things could be in the future. Again, a more fantastical solution would be having your ships generate magnetic fields using their power to "ride" the fields of the planets and stars. The magnetic fields could also theoretically work for the air craft, but I think if it were employed the travel would be limited to the polar directions, North and South, which could also pose interesting restrictions if you're interested in that.

I hope those ideas help, I'm no expert on them, but I am vaguely familiar with the fact that they have potential

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    $\begingroup$ I'd think that propeller-driven planes would be straight-forward. They may seem old-fashioned, but for shorter hops, they're still used. High-speed trains might also become more interesting. However, note also this and this. $\endgroup$ – Matthew Apr 13 at 15:34
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You can absolutely have an all-electric jumbo jet RIGHT NOW... and here's why:

First off, let's pick an Airbus A380, because if we can do it with one of the largest ever commercial planes then we can do it with any plane.

Now an A380 can carry some 250 tonnes of fuel (which is nearly half the maximum take-off weight), so, provided we can build an electric jet engine that's the same size and weight as a traditional one, then you have a staggering quarter of a million kilograms to play with for the power source, cooling, motor drive electronics, 1/5th of an Olympic swimming pool...

According to this jet engine question on Quora, some 80-odd percent of the thrust of a modern high-bypass engine comes from the intake fan alone (I was a little off in my earlier comment). This means we'll need to run out electric motors 25% harder as we won't have a raging inferno to help with thrust generation as we would in a traditional engine.

Now I couldn't find much info on the weight of modern jet engine cores vs. the whole assembly but this article indicates that the intake fan section can be up to a third of the total weight, which given that the engines on the A380 are nearly 7 tonnes gives over 4 tonnes for the motor and cowling.

Thanks to this KLM blog page they recon the A380's four engines generate 230MW of power, or ~58MW per engine, but considering our need for 25% overdrive gives us ~73MW. The worlds largest electric motors are bigger than that (which in 2018 was 80MW according to GE) so we know that a suitably sized motor can be built (in fact, if you consider generators to be motors - and they kinda are - then you can get them up to at least 700MW... flying aircraft carrier anyone?)

So, we know powerful enough motors exist, we know we have ~4 tonnes to play with, so can we build an electric jumbo? Well, 73MW/4 tonnes is 18kW/kg which is definitely up there in terms of power density for an electric motor (although it's only 11% the power density of the space shuttle's rocket-powered fuel pump!). The EMRAX 268 motor already hits 11.5kW/kg so that's not too bad but not enough. Recently another company claimed to have a motor than suits our needs and if Equipmake's numbers are to be believed then 20kW/kg is doable which is perfect for what we want.

And with that, we've proved you can make an electric jet engine that's just as good as it's gas-guzzling cousins (although, given that we saved 250t on fuel because the power source weighs effectively nothing, the engine could have weight 10 times more and the plane still could have flown), given that half the cost of a flight is fuel, the airlines are going to be your new best friends as you've just come up with a way to reduce maintenance (seeing as an electric jet has only one moving part) while doubling their profits.

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