EmDrive

[lstutzman]

It would appear that this has been validated.

http://www.wired.co.uk/news/archive/2014-07/31/nasa-validates-impossible-space-drive

[Streetwind]

...huh. That is quite intriguing.

First, high-ranking NASA scientist Dr. Harold White mentions "quantum thruster" and "TRL3" in the same breath during a public talk at a conference in 2013... and now this. Physics what are you doing? o_O Physics, stahp!

(No honestly, don't stop, if this works it would be awesome.)

[M Drive]

Hm, well to me the only surprising thing to me is the timing. As I'm working on a similar invention myself I guess it was only a matter of time before someone eventually figured out a way to produce 'propellantless thrust', not that it's by any means proved beyond all doubt just yet though.

http://forum.kerbalspaceprogram.com/threads/72265-Could-a-Gyroscopic-inertial-thruster-ever-work/page41

[Sky_walker]

As I'm working on a similar invention myself

It's not similar in any way. Other than both smelling as a total misunderstandings of what exactly is going on there.

[M Drive]

I'll let the evidence do the talking. As for misunderstandings, I've never actually claimed I understood how it works in the first place, just like NASA isn't theorizing what makes the EmDrive apparently work and are just reporting the results of the experiments.

As for the experiment NASA conducted itself, I have a basic understanding of how it works. It's basically a more compact and "measuring instrument friendly" version of the pendulum test, which I'm currently performing.

Edited July 31, 2014 by M Drive

[Red Iron Crown]

Hm, well to me the only surprising thing to me is the timing. As I'm working on a similar invention myself I guess it was only a matter of time before someone eventually figured out a way to produce 'propellantless thrust', not that it's by any means proved beyond all doubt just yet though.

http://forum.kerbalspaceprogram.com/threads/72265-Could-a-Gyroscopic-inertial-thruster-ever-work/page41

Propellantless thrust is no new thing, solar sails have been able to produce it for some time. It's reactionless thrust that is the real trick.

[Red Iron Crown]

Here is the relevant single page NASA document linked in the Wired story, not much meat to it. They suggest the drive might be interacting with "quantum vacuum virtual plasma".

[lstutzman]

Well, I certainly don't claim to understand how this could work, it would seem to violate the principle that thrust requires mass. If this works however, I would love to see how this would affect my probe payloads in-game.

[K^2]

No it doesn't, modern physics cannot validate the conservation of momentum in relativistic scenarios

In relativistic scenarios, conservation of momentum is a consequence of Hamiltonian's invariance under translation, which is one of the assumptions of relativity. In other words, once you said "relativistic scenarios" the conservation of momentum comes as part of the package.

People who invented EmDrive either don't understand anything about relativity, or simply banking on investors who don't. Either way, it's nonsense.

Here is the relevant single page NASA document linked in the Wired story, not much meat to it. They suggest the drive might be interacting with "quantum vacuum virtual plasma".

That still produces a light-like "exhaust". (EM radiation, gravity waves, or the like.) Conservation of momentum is just as much part of the Quantum Field Theory as it is of Relativity.

[christok]

Well, I certainly don't claim to understand how this could work, it would seem to violate the principle that thrust requires mass. If this works however, I would love to see how this would affect my probe payloads in-game.

Consider a pure photon drive. When you stick a light bulb on the back of a spacecraft, you lose mass from your electrical power system in accordance with m = E/c^2 and are in turn propelled forward with a very tiny thrust. This is exactly the same principle as that of a rocket, just with the ultimate exhaust velocity and the need to take some relativity into account. If the electrical power is fed from external energy source such as solar panels you can gain mass at the same rate as you lose it, somewhat similar to a jet engine.

This device--assuming for the sake of argument that it actually works--must obey the same principle.

[Nuke]

makes me wonder if em drive is really just an accidental q thruster. either way you are going to get more thrust by simply throwing the device out the back of your ship.

[Rakaydos]

My understanding was that the EMdrive and Qdrive were two completely different principles.

A Qdrive works by "pushing off the vaccume", that is, magnohydrodynamically accelerating the virtual particle pairs that appear in a vaccume, after which their existance/cancelation becomes someone else's problem. This still requires an exaust, so it is not truely reactionless.

An EMdrive, on the other hand, claimsto bounce microwaves in an asymetric chamber to produce thrust. As there is nothing leaving the chamber, you could literally stack the entire volume of a ship with them to improve your "engine by weigth" rather than be limited to the back of the ship.

The wired article seems to be confusing them- linking a nasa article on the Qdrive as evidence of the EM drive.

[Z-Man]

The device tested is NOT the EMDrive, the Wired article is not very clear on that. Instead, they tested the Cannae Drive. 404s on the theory and numerics pages, very useful.

From what little can be gathered, they tested the actual device and a null device, almost identical but designed to not produce thrust. Both did produce thrust.

With the limited information, my best bet of an explanation would be near field effects. There was plenty of metal around the device (the test chamber, for starters), it operated at around 1 GHz which gives near field effects a range of 30 cm (the wavelength). That should suffice to let the device give itself a good push while pushing the chamber back; the measured force was only 50 micronewtons at best, not enough to lift a common housefly.

[FITorion]

Should have known there would already be a thread... I just found the wired article and rushed here to see what people thought... and hope that KSP... or modders... keep such things in mind for parts...

Also... wouldn't a warp drive (which I'm not saying this is) be reaction massless too? If you managed to change space time so you moved... wouldn't that exhibit the same sort characteristics as this? I imagine there would be a visual warping observed too but...

Edited August 1, 2014 by FITorion

[Z-Man]

Ah, at least they have videos: http://vimeo.com/cannae/videos

The introduction ones I watched. Note that the device is called QDrive there, the name was later changed. It's pretty much identical to the EMDrive in principle. An asymmetric cavity pumped with microwaves. And like the EMDrive, their rationale for it working is purely based on regular electrodynamics. That is wrong with absolute certainty. Provably, the only way to propel yourself in a vacuum with electrodynamics is by emitting radiation, and if you do that, you get a 1/c thrust to power ratio. That does not mean such a device can never work, it just means their theory is rubbish. And if you build a device on a rubbish theory, it's pure mad luck if it works anyway.

Hilarious: In video 1, they boast how this would be so much better than traditional stationkeeping for satellites, which takes up to 20% of the full weight and at some point runs out of fuel, after 15 years... In video 3, they describe how to fully assemble the device, crucial component being liquid helium cooling. Guess how heavy that whole construction is and how long cooling can be maintained in space.

Also... wouldn't a warp drive (which I'm not saying this is) be reaction massless too? If you managed to change space time so you moved... wouldn't that exhibit the same sort characteristics as this? I imagine there would be a visual warping observed too but...

Sort of. The Alcubierre Warp, if it works, would be reactionless in the sense that it moves the ship without losing mass or energy to the surroundings. As soon as you turn it off, though, the ship stops; the drive makes no permanent change to the ship's momentum. It's using a loophole in GR.

[Mazon Del]

Should have known there would already be a thread... I just found the wired article and rushed here to see what people thought... and hope that KSP... or modders... keep such things in mind for parts...

Also... wouldn't a warp drive (which I'm not saying this is) be reaction massless too? If you managed to change space time so you moved... wouldn't that exhibit the same sort characteristics as this? I imagine there would be a visual warping observed too but...

Not quite. While yes a warp drive IS a reaction massless drive, that does not mean these operate on the same principle. Warp drive works by bending space (crushing the space in front of you so you fall forwards, and expanding it behind you to 'push' you forwards) whereas this theoretically works by 'pushing' off of virtual particles (think ether, but its not the ether!). It is sort of the difference between jumping off a building in order to move somewhere and using a fan to push against air to move you.

In both of these you are not actually losing mass (like you would a rocket) but they are not working on the same principles.

Edited August 1, 2014 by Mazon Del

[K^2]

Not quite. While yes a warp drive IS a reaction massless drive, that does not mean these operate on the same principle. Warp drive works by bending space (crushing the space in front of you so you fall forwards, and expanding it behind you to 'push' you forwards) whereas this theoretically works by 'pushing' off of virtual particles (think ether, but its not the ether!). It is sort of the difference between jumping off a building in order to move somewhere and using a fan to push against air to move you.

That's not quite correct either. The difference is in momentum. Momentum of a ship under warp drive does not change. Yes, it's moving, but there is no way to "extract" that motion. You can't, for example, have a warp ship physically push against another object, because there is a warp bubble around the ship. If EmDrive was to work, it would be capable of changing net momentum of the ship. Even if we were to assume that something weird going on with relationship between velocity and momentum, as is the case with a warp ship, the EmDrive ship can physically push a brick, increasing its momentum, withiout having anything to take up recoil. And that's a violation of a conservation law.

In your jumping off a building example, momentum of the person jumping off changes, but total momentum is conserved. That's equivalent to a normal reaction engine. In fact, Earth acts as a reaction mass.

[N_las]

From the abstract: http://ntrs.nasa.gov/search.jsp?R=20140006052

"Approximately six days of test integration were required, followed by two days of test operations, during which, technical issues were discovered and resolved. Integration of the two test articles and their supporting equipment was performed in an iterative fashion between the test bench and the vacuum chamber. In other words, the test article was tested on the bench, then moved to the chamber, then moved back as needed to resolve issues. Manual frequency control was required throughout the test. Thrust was observed on both test articles, even though one of the test articles was designed with the expectation that it would not produce thrust. Specifically, one test article contained internal physical modifications thatwere designed to produce thrust, while the other did not (with the latter being referred to as the “null†test article)."

In other words: This "perfomance of the experiment in an iterative fashion" means, they just tried again and again and again until finally after six days the measurements showed something. Obviously what they measured can't be the thrust from the machine, since the control machine showed the same behaviour.

Edited August 1, 2014 by N_las

[vger]

Uh, modern physics can do that just fine, so far as I know. Apart from anything else it's what solar sails rely on and spacecraft using solar sails have actually flown so it's not just a nice piece of theory.

'Radiation pressure' was my first thought on what this thing is 'probably' doing in order to get propulsion.

Depending on efficiency, it would still be a nice improvement over solar sails.

Edited August 1, 2014 by vger

[Kerbart]

From the abstract: http://ntrs.nasa.gov/search.jsp?R=20140006052In other words: This "perfomance of the experiment in an iterative fashion" means, they just tried again and again and again until finally after six days the measurements showed something. Obviously what they measured can't be the thrust from the machine, since the control machine showed the same behaviour.

In layman's terms: if this were a medical test, the control group that was given the placebo's showed the same result?

[K^2]

In layman's terms: if this were a medical test, the control group that was given the placebo's showed the same result?

Something like that.

[Streetwind]

In other words: This "perfomance of the experiment in an iterative fashion" means, they just tried again and again and again until finally after six days the measurements showed something.

No, that's not what it means at all. Please read properly and objectively. Not only did they not test for six days, but rather for two days (the setup of the testing environment took six), but there is not a single statement anywhere in the text that correlates results discovered with the sequence of performed tests.

"To resolve issues" can mean anything from "it was working before and now it's not" to "the door of the vacuum chamber won't close properly". It's probably not possible to derive more out of that blurb, considering it's a summary that describes what was done, but not how it was done or how it went down. Unless someone can get their hands on the full research report, we won't learn more than that.

It also says that the vacuum chamber was an ambient pressure, so there was little to no difference in ambient conditions between it and the test stand. They might have used the heavily shielded chamber to try and rule out certain outside effects that they theorized may have caused something unexplained that was observed on the open test stand. And then moved it back out for similar reasons.

Even that much is pure speculation. I think the real purpose of that senstence is simply to provide the information that the device was tested repeatedly in different locations. That summary tells us nothing conclusive, and any attempt to read into it will be meaningless.

Something like that.

Yeah. Basically the people who built it said "we can prove that our device works because we built this one that's functional and that one that's not functional!"

And then NASA tested it carefully and found that both of them work. This largely tells us that the people who built it misunderstood the principle behind their own invention. For example, the EmDrive might not be an EmDrive but rather a different form of quantum vacuum thruster, with the microwaves just happening to invoke the necessary effect by pure chance.

Either that, or the thrust measured did not come from the device after all. But then it seems like they did go to extreme lengths to rule that out, and the Chinese claimed similar results...

Edited August 1, 2014 by Streetwind

[CaptainArchmage]

I checked again, there is a difference between the Q-thruster and the EM drive. To begin with, the Q-thruster doesn’t seem to use microwaves. However, the operating principles behind the Q-thruster seem to be sound - you push against virtual particle pairs (particle-antiparticle), which are already understood to exist.

The EM thruster may work on the same principle, but this was not investigated by NASA. I should probably clarify that on the other two threads here I have posted on.

[sgt_flyer]

Well, according to nasa's abstract, they are going to do independant verifications and tests at other facilities, and they need to devellop automated control systems (they were using manual control sustems)

So, let's wait & see and let experiments do the talking

If they get positive results, they'll try it in orbit sooner or later

[CaptainArchmage]

Well, according to nasa's abstract, they are going to do independant verifications and tests at other facilities, and they need to devellop automated control systems (they were using manual control sustems)

So, let's wait & see and let experiments do the talking

If they get positive results, they'll try it in orbit sooner or later

See the Cubesat project. That’s where it will likely be tested first. If a Cubesat can progressively push its orbital periapsis and apoapsis up, that should be sufficient to prove it. That will be the final proofing stage. Unlike other means of propulsion like the solar sail though, the equipment can be tested on the ground before use, and this doesn’t use toxic materials or have extraordinarily high power requirements (can be tested in the 10-20 W range).