EmDrive: or, Warp Isn't the Important Part

So, the other day, I stumbled across this article on the EmDrive.1 Which is pretty cool, if you think about it.

I mean, my biggest problem with the laws of physics as they’re currently understood is that they are depressing as hell. No, seriously – other than some kajiggering with wormholes, there’s basically no way to get to another star system other than freezing yourself and then waiting fifty years.2

Throw in quantum physics and you get the almost-impossible quantum teleportation,3 but that’s still gonna wind up being obnoxiously expensive in terms of energy if we figure out how to do it.4

But then this happens, and suddenly the idea of creating an Alcubierre drive doesn’t seem so unlikely. And, at the very least, if this doesn’t turn out to be a viable way to build one but it does turn out to be messing with physics in the way it looks like it’s doing… that is still incredibly exciting. The coolest stuff happens in science when nobody has any idea what the rules are.5

But all I could think the whole time I was reading about this was that that isn’t the cool part. Okay, yes, it totally is the cool part, I would absolutely love to have the depressing parts of the laws of physics6 break down.

The part that I’m excited about showed up in this article that I found when digging into the history of the EmDrive.

Which, yeah, the folks at Wired made some good points – flying cars are always a cool idea, although the concept of a ‘stealth missile’ is deeply terrifying and combines in a truly horrifying way with the current proliferation of drone technology. But they missed out on a couple big things.

First, all the controversy about whether this thing works or not isn’t actually about whether it works or not. It’s about whether it works the way it’s claimed to work. Nobody is arguing that it just doesn’t work, they’re trying to argue that it’s using… atmospheric something or other, or some kind of confusing stuff about the Earth’s magnetic field. So? Even if it doesn’t work in space, it still works on-planet.

So, big whoop, it’s a new engine technology. Except: it’s all-electric, and it’s a purely directional force generator. Point it down, and you’ve got a way to levitate.

And look at the numbers that Wired included:

Previous thrusters generated relatively modest forces; the latest version now being built is based on a cooled superconductor and should generate more than 300 pounds of thrust for a 6-kilowatt input, Shawyer promises. (But does not yet appear to have done so.)

300 pounds of thrust for a 6-kilowatt input. That’s 50 lbs per kilowatt. Which is… eh, could be better. Still, four of those thrusters, swapped out for wheels, can lift 1200 pounds at a total cost of 24 kW. For reference, the latest Nissan Leaf weights about 3200 lbs and has an 80 kW motor – which means it would take 11 of those thrusters to lift it, at a total cost of 66 kW. Hey, that leaves some leftover for forward propulsion, or you can strap some more thrusters on it and carry more weight. Not too shabby.

Now I bring in some more numbers:

very high Q superconducting resonant cavities could produce static specific thrusts of about 30 kN/kW, which is 3 tonnes of thrust per kilowatt of input power

That’s a much nicer number. That’s 1 kW to lift the Leaf; call it 3 kW to be safe,7 and we’ve still got weight to spare, plus an extra 77 kW of power output – that’s a lot of extra right there.8

And, I’ll admit, I have barely scratched the surface of what you can do with this. My current favorite examples? This would make it pretty easy to loft something into orbit to make a space elevator – or, heck, just skip the elevator entirely, you’ve got enough force output to not even bother.

Or, even better: a Nimitz-class aircraft carrier puts 194 MW into propulsion. That’s 194,000 kW, or, in terms of our potential thrusters, nearly 600,000 tons of thrust. According to Wikipedia, a Nimitz-class carrier weighs on the order of 100,000 tons. Somebody call Nick Fury, because I’m gonna start building a helicarrier.

(Disclaimer: I didn’t put much effort into converting between units, because, again, ‘a ton’ can mean several different things depending on how you pronounce it. So… I might be spectacularly wrong about some of these things. On the other hand, I’m fairly certain that the aircraft carrier measurements are of a large enough magnitude that it’s possible regardless of how wrong I was about which kind of ‘ton’ is which, so… Still a success.)

  1. Every once in a while I don’t regret clicking on a link on Facebook, and this was one of those infrequent times. 
  2. And that’s just to get to, like, Barnard or something. Want to get to the galactic core? Hope you’ve got a few thousand years to spare. Which, I suppose, would be one way to pass the time until the next season of Sherlock… 
  3. Whatever you’re thinking, that’s not how it works. Unless you’ve got a doctorate in quantum physics, in which case you probably know better than I do why you’re still wrong. 
  4. This is based on the idea that, if it were easy, we’d have accidentally done it by now. Or found an animal that does, because there’s no way that something wouldn’t fall into the evolutionary niche of ‘teleports away from predators.’ 
  5. Example: back when we thought aetheric flow was a thing? The experiments that disproved that were both awesome and elegant. Victorian-era science was objectively awesome. Not very accurate, but awesome. 
  6. Depressing parts of the laws of physics: anything to do with entropy, the eventual heat-death of the universe, and anything that says that FTL travel and/or communications are impossible. So… a lot of physics, unfortunately. 
  7. And account for the fact that ‘a ton’ can mean like six different numbers
  8. It’s at this point that I start thinking of someone dumping the entire power output of the Leaf (and it’s vitally important that it’s a Leaf still) into these thrusters, all pointed down. Guy gets in the car, turns the key, presses the gas… and is catapulted into orbit at a couple hundred Gs. Someone call Randall Munroe and ask him to illustrate this. 

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