EmDrive

[sgt_flyer]

The chinese results seems too good to be true that gives it a better thrust than an Hipep ion engine, and a lower kw to thrust ratio - without needing propellant !

For comparison with the numbers z-man found above :

Hipep prototype ion thruster :

http://en.m.wikipedia.org/wiki/HiPEP

Peak 670 mN thrust @ 39.3kW - still needs propellant, even with it's 9600s ISP

Edited August 8, 2014 by sgt_flyer

[Jesrad]

And this Wired article gives a little more detail.

The EmDrive is a magnetodynamic plasma thruster, which pushes on 'virtual' plasma that already exists in the quantum vacuum. This 'foam' of particle-antiparticle pairs that spring in and immediately out of existence by sheer (im)probability is already responsible for the Casimir effect. In the Casimir effect, the virtual plasma density variation is symetric so the field obtained is anisotropic and conservative just like a magnetic field and you cannot use it for self-propulsion, whereas in the case of EmDrive, with an asymetric resonant chamber, you get an isotropic density of virtual plasma and can push it in an arbitrary direction with the right magnetic field, and thus gain momentum in the opposite direction.

That means you get a weird micro-Hall thruster which does not need to bring a tank of gas along to make its own plasma from, and uses the pervasive "virtual plasma" that already permeates everything everywhere instead.

Anyway, theory needs adjustments to facts. Experiments suggest 0.4 N / kW thrust or an equivalent ISP in the range of a terasecond Any modder willing to make me one for use in KSP ?

[Z-Man]

Meanwhile, I have to give up looking for useful material on the Q-Thruster thing theoretical background. The picture Rakaydos posted earlier is all there is. It's from this paper:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110023492.pdf

Needless to say, the picture is useless. None of the terms are properly explained. None of the individual bits are evident nonsense, but it's impossible to see how they should fit together.

Link to the relevant talk on the Starship Congress 2013:

Practically the same content. In both sources, they talk about a model of the vacuum developed by White that calculates stuff we already know about with great accuracy (that would be QED) and predicts that Q-Thrusters work (that wouldn't be QED). But that model is nowhere to be found in public view. I'd love to be proven wrong on that.

[Rakaydos]

And this Wired article gives a little more detail.

The EmDrive is a magnetodynamic plasma thruster, which pushes on 'virtual' plasma that already exists in the quantum vacuum. This 'foam' of particle-antiparticle pairs that spring in and immediately out of existence by sheer (im)probability is already responsible for the Casimir effect. In the Casimir effect, the virtual plasma density variation is symetric so the field obtained is anisotropic and conservative just like a magnetic field and you cannot use it for self-propulsion, whereas in the case of EmDrive, with an asymetric resonant chamber, you get an isotropic density of virtual plasma and can push it in an arbitrary direction with the right magnetic field, and thus gain momentum in the opposite direction.

That means you get a weird micro-Hall thruster which does not need to bring a tank of gas along to make its own plasma from, and uses the pervasive "virtual plasma" that already permeates everything everywhere instead.

Anyway, theory needs adjustments to facts. Experiments suggest 0.4 N / kW thrust or an equivalent ISP in the range of a terasecond Any modder willing to make me one for use in KSP ?

The wired article seems to be confusing the EM Drive with the Quantum Thruster.

[Jesrad]

Right.

Q-thruster, EmDrive and Fetta's slotted Cannae "impossible" drive supposedly work differently. What I described is the way the Q thruster (White) is supposed to work, and is explained in the Wired article. The microwave resonant cavity thruster, slotted (Fetta) or not (Shawyer) are supposed to work by bouncing microwaves billions of times inside their chamber while being shaped so as to manipulate the very metrics of space at a low scale so that the waves wouldn't "push" with the same force on one end than on the other. One theory behind that asymetric "bounce" is based on the quantum vacuum too (density of the 'virtual' plasma being decreased at one end). Hence the confusion.

[Z-Man]

...while being shaped so as to manipulate the very metrics of space at a low scale...

You mean, in the general relativistic sense, like gravity does? That would be news to me. (And also way too weak to have any effect with that feeble input power.) Can you provide a source?

Late edit: Something else is bothersome about that vacuum technobabble. They always cite the enormous energy density you get when you sum up all of the modes of the EM field up to the Planck Lenght when they argue how much untapped potential there is... Well, to a practical device, only a tiny fraction of that is accessible. How much? Well, give or take a factor of 1000 and some pis and twos we're going to drop right away, a microwave cavity has access to one mode of vacuum fluctuations, the one of the frequency it is excited with. Its energy is

E = hbar * omega

and that energy has to be though of as distributed over the whole cavity. If it were to flow freely, that energy stays in the cavity for the time 1/omega and is replaced with new energy to potentially exploit. So the total power usable is about

P = hbar * omega²

And photons of that power deliver a force of

F = P/c = hbar * omega²/c

Plug in 1 GHz for omega and we get an estimate for the total thrust available:

F = 3.5 * 10^-25 N

Ouch. That will not take anyone to Mars. Due to dimensional analysis coincidence, this is also the ballpark formula for the Casimir Force on the cavity from the outside, another possible logical entry point for determining the maximum thrust for a given geometry.

A more thorough analysis will show you that you can improve the value by making the cavity flat in the direction you want the thrust in. Like what the Cannae drive is actually doing. Only it's not doing it enough, you'd need to shrink it down to the micrometer range. And you need to find a way to make the Casimir force only act on the backward side. A real one-way mirror would be neat. Hmm. Hang on a sec, I need to file a patent, think of a name and register a trademark. Then figure out whether it can work. Yes, definitely, that is the correct order.

Edited August 8, 2014 by Z-Man

[Jesrad]

So I've been watching the presentation from Shawyer to try and understand what is the theory behind EmDrive. Here it is. It's not a reactionless thruster, and it does not violate momentum conservation.

Basically, it's a microwave pumped solar-sail in a shoebox.

At a glance, you'd assume that radiative pressure would be the same at both ends of the resonating chamber. But according to Shawyer there's a doppler shift occurring between the two ends and the photons at the tight end are lower frequency than at the wide end, yet they have the same speed (c ) so they do not have the same momentum when they bounce on different ends, and that is where the thrust comes from. The pumping required to force the waves inside the chamber and shift them in frequency is where the energy for the momentum gained comes from.

Supposedly.

[Red Iron Crown]

So I've been watching the presentation from Shawyer to try and understand what is the theory behind EmDrive. Here it is. It's not a reactionless thruster, and it does not violate momentum conservation.

Basically, it's a microwave pumped solar-sail in a shoebox.

At a glance, you'd assume that radiative pressure would be the same at both ends of the resonating chamber. But according to Shawyer there's a doppler shift occurring between the two ends and the photons at the tight end are lower frequency than at the wide end, yet they have the same speed (c ) so they do not have the same momentum when they bounce on different ends, and that is where the thrust comes from. The pumping required to force the waves inside the chamber and shift them in frequency is where the energy for the momentum gained comes from.

Supposedly.

I'm having a hard time with the bolded parts. A solar sail that carries the emitter is the same concept as using a boat mounted fan to fill the sails.

[ZetaX]

In addition to the previous post:

it does not violate momentum conservation.

How can it ever generate thrust without anything leaving it, yet accelerating¿ You only talked about energy in the post.

[Mazon Del]

I'm having a hard time with the bolded parts. A solar sail that carries the emitter is the same concept as using a boat mounted fan to fill the sails.

Only more obtuse! The mythbusters tried this and to their surprise it worked....because the air was being forced into the center of the sail, which had ballooned into a bowl-like shape, forcing previous air out the sides to provide forward thrust. It was funny and unexpected but makes sense.

[Jesrad]

Well, I didn't make it up That's what the inventor claims. I'm just putting it in in simple words for everyone to pick apart. I have no idea how the Doppler shift is supposed to happen and why that shift induces no counter momentum transfer.

[Red Iron Crown]

Only more obtuse! The mythbusters tried this and to their surprise it worked....because the air was being forced into the center of the sail, which had ballooned into a bowl-like shape, forcing previous air out the sides to provide forward thrust. It was funny and unexpected but makes sense.

Maybe not the best analogy, as it's not a truly closed system. The redirection of the air turns it into a propulsive fan, which would work better if you turned the fan around and got rid of the sail altogether.

[Mazon Del]

Yup, not a good analogy, just a funny anecdote.

[Yourself]

Only more obtuse! The mythbusters tried this and to their surprise it worked....because the air was being forced into the center of the sail, which had ballooned into a bowl-like shape, forcing previous air out the sides to provide forward thrust. It was funny and unexpected but makes sense.

Essentially it worked like a thrust reverser on a jet. Had the sail not been there and they'd just run the fan, the boat would have traveled in the opposite direction. I also imagine it's quite a bit more efficient that way as well.

[Heimdall5008]

And with this replies were back with the photon drive

[John FX]

You are using advanced Fermi rounding here, rounding intermediate values to the nearest power of 1000.

Text quotes in part from Wikipedia:

That's a thrust to power ratio of 288 mN/kW.

(Note the different units) That's 7 mN/kW at peak. A factor of 40 lower.

That's 1.7 mN/kW. Even lower.

The EMDrive like device tested at NASA really is quite similar to the original, the only difference is the added dielectric. And I agree with them that IF the device works, that's something that would help. So essentially, the NASA test says that at least 97.5% of the Chinese results are wrong. Chances are very high that the remaining 2.5% are also a fluke, despite all the effort put into the measurements.

Not to disagree with your post, but I feel I must mention the vast differences in power from combustion engines in their early development. Had someone looked at them trying to validate the theory of combustion they could have made the same argument. Losses from internal friction and so forth because of tolerances would have made the larger engines much more efficient than smaller ones. A quick Wiki check shows a difference in engine powers of a factor of ten for 4 cylinder early designs. These were commercial designs, not prototypes.

Also the exhaust from an internal combustion engine is not powerful enough to provide the forward acceleration seen (j/k)

I don`t have the background to be able to say for sure if that is the case here. My prejudice wants to say all Chinese science results are fake, hehe.

Can I now talk to an actual physicist please¿

To do that you may actually have to go talk to an actual physicist. At the end of the day this is a forum for a space game featuring little green aliens.

[Mazon Del]

At the end of the day this is a forum for a space game featuring little green aliens.

Shut your dirty mouth! This isn't a game! It's real! WE are the game!

Right now NASA is likely looking into how expensive and feasible it is to make a version of this system that pumps up the power quite a bit. That should hopefully make the results less ambiguous.

[crazyewok]

Im really looking forward to there next test on this.....

I still harbour doubts but if not the the results will be interesting.

[magnemoe]

So I've been watching the presentation from Shawyer to try and understand what is the theory behind EmDrive. Here it is. It's not a reactionless thruster, and it does not violate momentum conservation.

Basically, it's a microwave pumped solar-sail in a shoebox.

At a glance, you'd assume that radiative pressure would be the same at both ends of the resonating chamber. But according to Shawyer there's a doppler shift occurring between the two ends and the photons at the tight end are lower frequency than at the wide end, yet they have the same speed (c ) so they do not have the same momentum when they bounce on different ends, and that is where the thrust comes from. The pumping required to force the waves inside the chamber and shift them in frequency is where the energy for the momentum gained comes from.

Supposedly.

So you say you would get the same result using an microwave transmitter and a directional antenna who is that the solar sail would work like if shaped like an parabola.

In short the minimum effect we will get would be an photon drive. The interesting thing if we have other effects giving more trust.

[RuBisCO]

What photon drive can give 0.1N per kW?

[Mazon Del]

Well, strictly speaking the minimum effect is nothing but heat-death contribution. > but yeah, it would be interesting to see what happens if it works, and works well. The guy who is working on the EMDrive made a claim that I would LOVE to be true, but likely isn't. I may or may not have said it here earlier, apologies if so. He basically stated that he believes his 2nd generation version using superconductors will be capable of 3.3 TONS of thrust...off of 1 kilowatt of power... Feels like a math error...but if its true...*drools*

Edited August 14, 2014 by Mazon Del

[Z-Man]

Well, at least that claim will be easily falsifiable.

John FX: Difference being, the early combustion engines still worked without a shadow of a doubt. You put gasoline in and got a reliable and easily measurable amount of work out of them, far more work than could be explained by the fuel just flowing down (but also not so much that they'd violate known laws of thermodynamics).

[RuBisCO]

Well, strictly speaking the minimum effect is nothing be heat-death contribution. > but yeah, it would be interesting to see what happens if it works, and works well. The guy who is working on the EMDrive made a claim that I would LOVE to be true, but likely isn't. I may or may not have said it here earlier, apologies if so. He basically stated that he believes his 2nd generation version using superconductors will be capable of 3.3 TONS of thrust...off of 1 kilowatt of power... Feels like a math error...but if its true...*drools*

IF that turns out to be true, we WILL have flying cars, silent, reliable, liquid hydrogen powered, back-to-the-future, flying cars.

[Red Iron Crown]

3.3kN of thrust from 1kW would seem to imply greater than 100% efficiency.

[RuBisCO]

3.3kN of thrust from 1kW would seem to imply greater than 100% efficiency.

What is the theoretical minimum amount of power needed to hold up 3.3 tons?