Chinese Say They're Building 'Impossible' Space Drive

[PixyMisa]

Battery, no, yes, maybe, no.

 

[PingOfPong]

INRM, that Eureeka article states that the device is powered by normal electrical means. The question isn't "where does the energy come from?", it should be "where does the energy go?" The inventor claims that the microwaves in the cavity lose some of their energy which somehow tranfers to forward kinetic energy. When he was asked about the physics of the transfer he said, “I am just a microwave engineer and all that matters is that it works.”

BTW, he also claims to have made some succesful tests.

 

[Nogbad]

Battery, no, yes, maybe, no.

Solar panels presumably (if it works)


If it does work someone is going to feel very silly in whichever company had first shout before he went to the Chinese.

 

[sol invictus]

INRM, that Eureeka article states that the device is powered by normal electrical means. The question isn't "where does the energy come from?", it should be "where does the energy go?"

Put the thing in outer space, at rest, ready to be powered by a (disconnected) battery. Flip the switch to connect the battery. It accelerates, and according to the "theory", nothing enters or leaves the cavity (including microwaves). Now flip off the switch.

Initial state: battery and engine at rest. Total momentum zero.

Final state: battery and engine moving rapidly, with all the mass and energy still inside the system. Total momentum non-zero.

That violates conservation of momentum. End of story.

ETA - by the way, it is possible for electromagnetic fields to store and carry momentum. One can create a configuration of fields which has some momentum, and that momentum could be released by interactions with a container or surface. But this is totally useless as an engine - to create those fields in the first place would cost you just exactly as much momentum as you would gain by absorbing them again. It's similar to a can of marbles - if all the marbles are moving one way inside a stationary can, after a short time they run into the wall and the can lurches sideways.

But that's because the system (can plus marbles) had momentum in the first place. If you start with the can and marbles at rest, there's nothing you can do to change the net momentum - except throw some of the marbles out of the can entirely, i.e. build a rocket.

You can't pull yourself up in the air by your own bootstraps, no matter how hard you try or how much money the British government gives you...

 

[PingOfPong]

^^^^^

Just so you know I'm taking the inventor's side. If the thing works in space then he's right. If it doesn't then he was a quack all along. About his tests. He's measuring some very small effects. I wonder if the currents in the waveguide container he's using are strong engouh to create the force from the Earth's magnetic field.

 

[technoextreme]

My professor has mentioned a few times about an equation that prevents EM based perpetual motion machines from being created. I wonder if this has anything to do with that.

 

[PingOfPong]

^^^^^

Just so you know I'm taking the inventor's side. If the thing works in space then he's right. If it doesn't then he was a quack all along. About his tests. He's measuring some very small effects. I wonder if the currents in the waveguide container he's using are strong engouh to create the force from the Earth's magnetic field.

Oops, I meant to say: "Just so you know I'm NOT taking the inventor's side."

 

[ellindsey]

As far as I can tell, none of the tests which seem to demonstrate thrust had the device powered by a battery mounted to the device. They appear to be powering the device via a power lead from some external source. This is significant because a closed circuit with current flowing through it will develop electromagnetic forces which will tend to push the power source and load away from each other. It's an unavoidable result of electromagnetism, and the principle on which a rail gun works. Any load, even a passive resistor, mounted on a sensitive scale and powered through a cable from some external source, will demonstrate a slight thrust when switched on. So claims that this device repeatedly and consistently develops a few grams of thrust when connected to an external source don't impress me. When they power the thruster from a battery, seal the battery and thruster in an airtight metal box, and demonstrate thrust with that setup, I'll take notice.

 

[PingOfPong]

As far as I can tell, none of the tests which seem to demonstrate thrust had the device powered by a battery mounted to the device. They appear to be powering the device via a power lead from some external source. This is significant because a closed circuit with current flowing through it will develop electromagnetic forces which will tend to push the power source and load away from each other. It's an unavoidable result of electromagnetism, and the principle on which a rail gun works. Any load, even a passive resistor, mounted on a sensitive scale and powered through a cable from some external source, will demonstrate a slight thrust when switched on. So claims that this device repeatedly and consistently develops a few grams of thrust when connected to an external source don't impress me. When they power the thruster from a battery, seal the battery and thruster in an airtight metal box, and demonstrate thrust with that setup, I'll take notice.

Ellin, you're question and more are answered in the FAQ at their web page. Of course, the answers are short on details.

 

[nathan]

Ellin, you're question and more are answered in the FAQ at their web page. Of course, the answers are short on details.

Thanks. That FAQ strongly suggests they are willfully ignorant, at least. Examples:

Q4 claims it does not violate Newton's laws. but Q2 says special relativity must be used to understand the device. Special relativity violates Newtons laws (specifically, Newton's laws are the low-velocity approximation of special relativity).

As others have commented Q2's claim that different reference frames are necessary, is bunkum. And Q4's claim that it doesn't violate conservation of momentum is ignorant.

Q8 about buoyancy, claims this is eliminated by hermetically sealing the device. Hm, unless I'm misunderstanding you can only eliminate buoyancy by sealing it in a vacuum. However Q9 says convection currents did not affect the results. But the explanation of that non-effect is not that the device was in a vacuum.

I stopped reading then

 

[INRM]

Regarding that statement about frames of reference... are they saying they've figured out some way to alter the speed of light?


INRM

 

[RecoveringYuppy]

They actually said reference plane, so it's pretty hard to tell if the statement means anything at all.

 

[BenBurch]

It should be easy enough to prove. Space-X probably needs some more volunteer payloads for their new booster...

 

[Dr. Trintignant]

The faster you fling the reaction mass, the more efficient it is.

It depends on your definition of efficiency. Faster reaction mass is more mass-efficient but less energy-efficient. Shining a laser out the rear of your rocket is as mass-efficient as you can get but has horrific energy efficiency. On the other hand, leaping off the earth has horrific mass efficiency (using the entire Earth as reaction mass!), but very good energy efficiency (to the point where we can ignore the Earth when computing how high I jump given a certain energy input).

So any given rocket design has to account for these considerations and others. And this isn't even getting into cost efficiency...

- Dr. Trintignant

 

[Spud1k]

Something stinks here. The FAQ was woefully unconvincing; I don't care how much he says it doesn't contravene Newton's laws or whatever, if you were to take a bunch of these and arrange them all tangentially on a wheel, you'd have something that would generate torque from nothing and you'd have a classic perpetual motion machine. The talk of making these things being an 'art' is strangely reminiscent of the explanations given for the lack of experimental reproduction in cold fusion.

My gut feeling is that the fudge is in the argument about reference planes; it doesn't matter how much you dress up relativity and nonlinearities and stuff, all the forces balance out when you have photons interacting with static objects such as waveguides. If he'd only publish a paper on it...

 

[Dave Rogers]

My gut feeling is that the fudge is in the argument about reference planes; it doesn't matter how much you dress up relativity and nonlinearities and stuff, all the forces balance out when you have photons interacting with static objects such as waveguides. If he'd only publish a paper on it...

Having looked at the paper he did publish on it, it turns out that the argument about reference frames is simply post hoc rationalisation of an incorrect result. Shawyer has carried out his calculations based on the assumption that the radiation pressure on the sidewalls of a tapered waveguide has no axial component, which is geometrically absurd. His calculations are therefore purely and simply wrong. If he did them properly, and included the axial component of the momentum transferred to the sidewalls by each oblique reflection of a photon in the cavity, it's trivial to show that the net momentum transferred to the cavity by the radiation field is zero; it follows from the fact that at resonance the momentum of each photon must time-average to zero. The stuff about frames of reference is pure woo.

Take a look at his paper archived by New Scientist.

http://www.newscientist.com/data/images/ns/av/shawyertheory.pdf

The error is in fig. 2.4, which assumes that the reflection at the sidewalls is not specular. Specular reflection must give an axial force.

Dave

 

[sphenisc]

The error is in fig. 2.4, which assumes that the reflection at the sidewalls is not specular. Specular reflection must give an axial force.

Dave

I vaguely remember reading something about non-specular reflection in "The Strange Theory of Light and Matter". Can anyone recall the details and if it has any bearing on DR's point?

 

[Soapy Sam]

"microwave photons, travelling at nearly the speed of light"?

I'm sure I could think of uses for slow photons in communications.

Get back to me about this- say three days ago.

 

[Dave Rogers]

I vaguely remember reading something about non-specular reflection in "The Strange Theory of Light and Matter". Can anyone recall the details and if it has any bearing on DR's point?

I'm pretty certain it'll be irrelevant. Shawyer's paper also, in effect, assumes specular reflection, because that's the mechanism by which the group velocity differs between the waveguide ends. Therefore he's assuming specular reflection to calculate the end forces, and violation of specular reflection to justify neglecting the axial component of the sidewall forces. Bit of a dog's dinner really.

Dae

 

[neutrino_cannon]

It depends on your definition of efficiency. Faster reaction mass is more mass-efficient but less energy-efficient. Shining a laser out the rear of your rocket is as mass-efficient as you can get but has horrific energy efficiency. On the other hand, leaping off the earth has horrific mass efficiency (using the entire Earth as reaction mass!), but very good energy efficiency (to the point where we can ignore the Earth when computing how high I jump given a certain energy input).

So any given rocket design has to account for these considerations and others. And this isn't even getting into cost efficiency...

- Dr. Trintignant

What is this "energy efficiency" you speak of? For a chemical rocket it's almost a null value, unless you're talking nozzle design or something esoteric like that. Once the thing is in space there's no reason to trade off specific impulse for thrust unless you need to fight gravity, which is only because you'll actually save on the delta-v budget.

If it's an electrically powered rocket like, say, some sort of plasma drive, your energy comes from a nuclear pile or solar panels, and there's more electricity where that came from. In all designs so far considered reaction mass will still be the limiting consideration.

Tsiolkovsky makes things almost depressingly simple.