EMDrive and other reactionless propulsion claims

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EMDrive and other reactionless propulsion claims

Postby Klotz » Sat Jul 11, 2009 12:10 pm UTC

I'm sure some of you remember the EMDrive, a form of propulsion that produces force from microwaves no propellant, published in only New Scientist and dismissed by legitimate scientists worldwide. The guy claims to have a prototype, but nothing has really come of it.

Anyway, it appears that the Chinese astronautics department has picked it up.

http://www.cqvip.com/qk/95668x/2008005/28361792.html
Google Translate wrote:Microwave promote quality of work is a new concept of propulsion, with a thrust large, simple structure, reliable performance, it can be widely used in spacecraft. In order to later lay the foundation for the design of research, this paper, based on the quantum theory of non-working fluid body cavity microwave thruster microwave treatment of quantum electromagnetic fields is derived formula for calculating the theoretical thrust, the use of finite element analysis software to calculate the different modal intrinsic cavity quality factor Q value, calculated under the different modal value of thrust. The results show that under the TE012 mode Q values of up to 79,523, up to a maximum value of thrust amendment 0.315N, thruster mode is the best choice. (4 total)


You can access the first page here: http://www.cqvip.com/onlineread/onliner ... D=28361792
Can anyone get the whole article? Is anyone here Chinese enough to make something of it?

Anyway, if there's one thing I know it's that the Chinese have some very smart scientists and engineers. Do you think this lends credibility to the idea of a magical reactionless drive?

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Re: China Picks up the EMDrive

Postby gmalivuk » Sat Jul 11, 2009 4:52 pm UTC

It's not reactionless, it's just done without propellant. But photons carry momentum, so there's nothing wrong in theory about an EM drive.
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Re: China Picks up the EMDrive

Postby Mr_Rose » Sat Jul 11, 2009 4:56 pm UTC

gmalivuk wrote:It's not reactionless, it's just done without propellant. But photons carry momentum, so there's nothing wrong in theory about an EM drive.

Except , IIRC, the one that this guy designed had a big old metal plate on the bottom as well as the sides and top, so pretty much any momentum transferred to the angled walls would almost certainly be negated by the momentum transferred to the bottom-plate.
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Re: China Picks up the EMDrive

Postby gmalivuk » Sat Jul 11, 2009 5:03 pm UTC

Yeah, the EMDrive is quackery, but it's not clear to me from the translation that this is actually what the Chinese article is talking about.

If it is, though, I wouldn't bet on it being any more than some kind of government propaganda designed to make other people think China has some magical new propulsion system.
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Re: China Picks up the EMDrive

Postby rho » Sat Jul 11, 2009 6:01 pm UTC

I remember that article in New Scientist. It disgusted me. Worse still they put it on the cover promising flying cars.
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Re: China Picks up the EMDrive

Postby You, sir, name? » Sat Jul 11, 2009 6:35 pm UTC

If the idea is to extract momentum from photons, why not simply stick a light source with a reflector behind it at one end of the craft? It would take forever to get anywhere, and use like 0.001% of the energy to actually move the craft (which is tremendously stupid when solar sails do the same for free), but it's an EM drive none the less.
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Re: China Picks up the EMDrive

Postby gmalivuk » Sat Jul 11, 2009 6:53 pm UTC

You, sir, name? wrote:and use like 0.001% of the energy to actually move the craft

Why is this?
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Re: China Picks up the EMDrive

Postby Technical Ben » Sat Jul 11, 2009 10:12 pm UTC

I have high hopes that someday we find some sort of electrical rocket engine. If only because it means I can have a flying car without stupid propeller props sticking out the sides. :(
The closes thing we have to a usable electric [rocket or thruster] engine is the iron drive and it's relatives. But that's rather useless for atmospheric flight. It's a pity really but a pure electric rocket/thruster seems rather impossible.

[off topic]
Would it be possible to make a kind of electric ram/scram jet? Get it up to speed, then burn atmosphere. Then you have a jet engine that uses zero fossil fuels.
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Re: China Picks up the EMDrive

Postby lulzfish » Sun Jul 12, 2009 12:44 am UTC

I don't think "atmosphere" burns.

You need oxygen and fuel for combustion, unless chemistry has changed a lot recently.

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Re: China Picks up the EMDrive

Postby Klotz » Sun Jul 12, 2009 1:56 am UTC

The creator of the EMDrive has a paper in some obscure journal, and that paper has been cited by the Chinese paper I posted. In addition, wikipedia says that Wired says that the Chinese are making the EMDrive.

This is a writeup by a relativistic electromagnetician explaining why the thing doesn't work.

http://www.assassinationscience.com/joh ... rfraud.pdf

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Re: China Picks up the EMDrive

Postby Carnildo » Sun Jul 12, 2009 2:31 am UTC

Technical Ben wrote:I have high hopes that someday we find some sort of electrical rocket engine. If only because it means I can have a flying car without stupid propeller props sticking out the sides.

We've got lots of them: ion drives, Hall-effect thrusters, ionocraft, etc. The problem is that none of them has a thrust-to-weight ratio better than 1, so none of them is capable of lifting itself off the ground. They're all extremely fuel-efficient, though, which makes them popular for low-thrust applications such as station-keeping or unmanned interplanetary flight.

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Re: China Picks up the EMDrive

Postby gmalivuk » Sun Jul 12, 2009 5:08 am UTC

Meteorswarm wrote:
gmalivuk wrote:
You, sir, name? wrote:and use like 0.001% of the energy to actually move the craft

Why is this?

I think he meant that only .001% of the energy gets used to move the craft - not that it would take .001% of the energy to move it.

I know. Why is that? As in, what is the other 99.999% of the energy doing? That seems awfully high for waste heat.
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Re: China Picks up the EMDrive

Postby You, sir, name? » Sun Jul 12, 2009 7:49 am UTC

gmalivuk wrote:
Meteorswarm wrote:
gmalivuk wrote:
You, sir, name? wrote:and use like 0.001% of the energy to actually move the craft

Why is this?

I think he meant that only .001% of the energy gets used to move the craft - not that it would take .001% of the energy to move it.

I know. Why is that? As in, what is the other 99.999% of the energy doing? That seems awfully high for waste heat.


It is waste light. And 0.001% is actually unrealistically high. It's many orders of magnitude less.

The energy required to produce a photon is [imath]E=\hbar\omega[/imath], and you get [imath]p=\frac{\hbar\omega}{c}[/imath] momentum out of it, and putting it back in E, [imath]E=pc[/imath]. So to accelerate a stationary 1 kg object to 1 m/s, you require 3*108 Joules, and in the end, attain 0.5 Joules of kinetic energy through light propulsion. This is an ideal scenario though, you can probably go a couple of orders of magnitude worse through waste heat and wasted photons (that go in the wrong direction)
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Re: China Picks up the EMDrive

Postby Josephine » Sun Jul 12, 2009 7:10 pm UTC

Technical Ben wrote:[off topic]
Would it be possible to make a kind of electric ram/scram jet? Get it up to speed, then burn atmosphere. Then you have a jet engine that uses zero fossil fuels.


I don't think there's any suitable fuel in enough density in the atmosphere. Oxygen's only half the puzzle. Maybe that would work on Titan...
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Re: China Picks up the EMDrive

Postby Technical Ben » Wed Jul 15, 2009 11:21 pm UTC

lulzfish wrote:I don't think "atmosphere" burns.

You need oxygen and fuel for combustion, unless chemistry has changed a lot recently.


Sorry, A slight misunderstanding plus bad grammar there. I know you need oxygen to burn fuel. And scram jets use fuel + the atmosphere instead of the shuttles oxygen + fuel (hydrogen). However I posted that without thinking about those things. :P

So we are stuck with really weak ion drives. No "antigravity" devices any time soon then.
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Re: China Picks up the EMDrive

Postby Tass » Thu Jul 16, 2009 11:57 am UTC

nbonaparte1 wrote:
Technical Ben wrote:[off topic]
Would it be possible to make a kind of electric ram/scram jet? Get it up to speed, then burn atmosphere. Then you have a jet engine that uses zero fossil fuels.


I don't think there's any suitable fuel in enough density in the atmosphere. Oxygen's only half the puzzle. Maybe that would work on Titan...


Sadly no. On titan you need oxygen. Or rather oxygen would be a fine fuel in the reducing atmosphere there (of course fluorine would be even better, just damned hard to store and control). There are not many places where you find a mixture of gasses that are not very close to their equilibrium, since if it could burn by itself it would tend to have done so already.

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Re: China Picks up the EMDrive

Postby Technical Ben » Thu Jul 16, 2009 6:04 pm UTC

Even if the temperatures are too low? It could make a cool sifi story. Aliens/humans living on a planet that only needs a electric spark to make your own rocket. Cooking could be dangerous though...
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Re: China Picks up the EMDrive

Postby Josephine » Thu Jul 16, 2009 6:08 pm UTC

I have a feeling that any intelligent species evolving on a planet with a combustible atmosphere would die at the Homo Erectus stage...

Although that would be awesome to watch.
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Re: China Picks up the EMDrive

Postby Charlie! » Thu Jul 16, 2009 11:28 pm UTC

That planet would have to never have a single rockslide. It couldn't even handle a single dark object near the equator. And volcanic activity? Right out. In short, under any realistic conditions, fuhgedaboutid.
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Re: China Picks up the EMDrive

Postby You, sir, name? » Fri Jul 17, 2009 12:17 pm UTC

Charlie! wrote:That planet would have to never have a single rockslide. It couldn't even handle a single dark object near the equator. And volcanic activity? Right out. In short, under any realistic conditions, fuhgedaboutid.


Well, it could be rather far away from it's star, and have an opaque atmosphere. But the problem with asteroids entering the atmosphere and heating up from the friction is sort of hard to tackle.

Though a planet covered in thermite might be possible (?). If it has a seismically stable core, a crust consisting of aluminum and iron, and a turbulent but very dense oxygen rich atmosphere (so as to burn any asteroids before hitting the surface). The wind would wear down the surface forming aluminum and iron oxide dust, eventually covering the planet in a desert-like fashion.
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Re: China Picks up the EMDrive

Postby gmalivuk » Sat Jul 18, 2009 1:32 am UTC

And this planet is never going to have anything at all that develops enough static charge to create lightning?
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Re: China Picks up the EMDrive

Postby Josephine » Sat Jul 18, 2009 7:58 am UTC

I think we've pretty convincingly determined that a combustible planet is a Bad IdeaTM
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Re: China Picks up the EMDrive

Postby roundedge » Sat Jul 18, 2009 8:25 am UTC

I remember writing to Shawyer after reading the article at newscientist about his EMdrive when I had just got out of highschool... actually, screw writing anything, I just found the e-mail:
Image

A lot of my humility was feigned, so that he'd be more likely to respond to me. It's obviously clear to anyone who has taken highschool physics that his theory was wrong to the point that if he had had any physics training, it was likely he was a fraudster, and not just a misguided crackpot.

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Re: China Picks up the EMDrive

Postby You, sir, name? » Sat Jul 18, 2009 11:30 am UTC

Well, I think the construction might in theory extract minute amounts of work from the photons, just maybe enough to overcome the momentum from launching the photon in the first place, but you still only extract order of magnitude [imath]10^{-8}[/imath] J of energy for every Joule put in. That is if it works like I think it does, which after a second glance does not seem to be the way it works.

gmalivuk wrote:And this planet is never going to have anything at all that develops enough static charge to create lightning?


Hmm, if the atmosphere is full of metallic dust, the resistive heating should be relatively low, since the discharge can simply use them as charge carriers.
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Re: China Picks up the EMDrive

Postby BSamuels » Sat Jul 18, 2009 2:56 pm UTC

roundedge wrote:A lot of my humility was feigned, so that he'd be more likely to respond to me. It's obviously clear to anyone who has taken highschool physics that his theory was wrong to the point that if he had had any physics training, it was likely he was a fraudster, and not just a misguided crackpot.


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Re: China Picks up the EMDrive

Postby Tass » Sun Jul 19, 2009 4:13 pm UTC

You, sir, name? wrote:Well, I think the construction might in theory extract minute amounts of work from the photons, just maybe enough to overcome the momentum from launching the photon in the first place, but you still only extract order of magnitude [imath]10^{-8}[/imath] J of energy for every Joule put in.


How so?

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Re: China Picks up the EMDrive

Postby AvatarIII » Sat Feb 09, 2013 7:38 pm UTC


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Re: China Picks up the EMDrive

Postby scarecrovv » Sat Feb 09, 2013 8:37 pm UTC

This is my favorite quote from the article:

Even the most advanced theoretical critique, produced by John Costella, a PhD in relativistic electrodynamics, amounted to arguing about the direction of an arrow on one of Shawyer's diagrams.


The reason that the most advanced theoretical critique was on the direction of an arrow on a diagram, is that that's where the mistake was!

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Re: China Picks up the EMDrive

Postby Sockmonkey » Thu Feb 14, 2013 3:54 pm UTC

Technical Ben wrote:
lulzfish wrote:I don't think "atmosphere" burns.

You need oxygen and fuel for combustion, unless chemistry has changed a lot recently.


Sorry, A slight misunderstanding plus bad grammar there. I know you need oxygen to burn fuel. And scram jets use fuel + the atmosphere instead of the shuttles oxygen + fuel (hydrogen). However I posted that without thinking about those things. :P

So we are stuck with really weak ion drives. No "antigravity" devices any time soon then.

Well, one may not be able to use an atmosphere as fuel without introducing something that combusts with it but there's nothing stopping you from using it as reaction mass for in-atmosphere operations. That's kind of what a prop plane does.

Now, IIRC you can create something similar to an MHD drive that works on air. Basdically you use a high-voltage charge to ionize it and another charge to move the air along. Takes crazy amounts of juice to do it though, so you couldn't build a practical helicopter with it without superconductors or something.

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Re: China Picks up the EMDrive

Postby quadmaster » Wed Feb 27, 2013 6:20 pm UTC

Of course you could always just take a jet engine and replace the combustion chamber with a heating element or even just an arc gap with a few tens of thousands of amps
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Re: China Picks up the EMDrive

Postby idobox » Wed Feb 27, 2013 6:29 pm UTC

You can also use microwaves to heat air.
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NASA scientists report positively on propellant-less drive

Postby elasto » Fri Aug 01, 2014 7:14 am UTC

Nasa is a major player in space science, so when a team from the agency this week presents evidence that "impossible" microwave thrusters seem to work, something strange is definitely going on. Either the results are completely wrong, or Nasa has confirmed a major breakthrough in space propulsion.

British scientist Roger Shawyer has been trying to interest people in his EmDrive for some years through his company SPR Ltd. Shawyer claims the EmDrive converts electric power into thrust, without the need for any propellant by bouncing microwaves around in a closed container. He has built a number of demonstration systems, but critics reject his relativity-based theory and insist that, according to the law of conservation of momentum, it cannot work.

According to good scientific practice, an independent third party needed to replicate Shawyer's results. As Wired.co.uk reported, this happened last year when a Chinese team built its own EmDrive and confirmed that it produced 720 mN (about 72 grams) of thrust, enough for a practical satellite thruster. Such a thruster could be powered by solar electricity, eliminating the need for the supply of propellant that occupies up to half the launch mass of many satellites. The Chinese work attracted little attention; it seems that nobody in the West believed in it.

However, a US scientist, Guido Fetta, has built his own propellant-less microwave thruster, and managed to persuade Nasa to test it out. The test results were presented on July 30 at the 50th Joint Propulsion Conference in Cleveland, Ohio. Astonishingly enough, they are positive.

The Nasa team based at the Johnson Space Centre gave its paper the title "Anomalous Thrust Production from an RF [radio frequency] Test Device Measured on a Low-Thrust Torsion Pendulum". The five researchers spent six days setting up test equipment followed by two days of experiments with various configurations. These tests included using a "null drive" similar to the live version but modified so it would not work, and using a device which would produce the same load on the apparatus to establish whether the effect might be produced by some effect unrelated to the actual drive. They also turned the drive around the other way to check whether that had any effect.

Back in the 90s, Nasa tested what was claimed to be an antigravity device based on spinning superconducting discs. That was reported to give good test results, until researchers realised that interference from the device was affecting their measuring instruments. They have probably learned a lot since then.

The torsion balance they used to test the thrust was sensitive enough to detect a thrust of less than ten micronewtons, but the drive actually produced 30 to 50 micronewtons -- less than a thousandth of the Chinese results, but emphatically a positive result, in spite of the law of conservation of momentum:

"Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma."

This last line implies that the drive may work by pushing against the ghostly cloud of particles and anti-particles that are constantly popping into being and disappearing again in empty space. But the Nasa team has avoided trying to explain its results in favour of simply reporting what it found: "This paper will not address the physics of the quantum vacuum plasma thruster, but instead will describe the test integration, test operations, and the results obtained from the test campaign."

The drive's inventor, Guido Fetta calls it the "Cannae Drive", which he explains as a reference to the Battle of Cannae in which Hannibal decisively defeated a much stronger Roman army: you're at your best when you are in a tight corner. However, it's hard not to suspect that Star Trek's Engineer Scott -- "I cannae change the laws of physics" -- might also be an influence. (It was formerly known as the Q-Drive.)

Fetta also presented a paper at AIAA on his drive, "Numerical and Experimental Results for a Novel Propulsion Technology Requiring no On-Board Propellant". His underlying theory is very different to that of the EmDrive, but like Shawyer he has spent years trying to persuade sceptics simply to look at it. He seems to have succeeded at last.

Shawyer himself, who sent test examples of the EmDrive to the US in 2009, sees the similarity between the two.

"From what I understand of the Nasa and Cannae work -- their RF thruster actually operates along similar lines to EmDrive, except that the asymmetric force derives from a reduced reflection coefficient at one end plate," he says. He believes the design accounts for the Cannae Drive's comparatively low thrust: "Of course this degrades the Q and hence the specific thrust that can be obtained."

Fetta is working on a number of projects which he is not able to discuss at present, and Nasa's PR team was not able to get any comments from the research team. However, it's fair to assume that the results will be picked over very closely indeed, like CERN's anomalous faster-than-light neutrinos. The neutrino issue was cleared up fairly quickly, but given that this appears to be at least the third independent propellant-less thruster to work in tests, the anomalous thrust may prove much harder to explain away.

A working microwave thruster would radically cut the cost of satellites and space stations and extend their working life, drive deep-space missions, and take astronauts to Mars in weeks rather than months. In hindsight, it may turn out to be another great British invention that someone else turned into a success.


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Re: NASA scientists report positively on propellant-less dri

Postby tomandlu » Fri Aug 01, 2014 9:46 am UTC

Is it just me, or, if this is true, is the most bizarre and exciting discovery for the last fifty years or so?
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Re: NASA scientists report positively on propellant-less dri

Postby Qaanol » Fri Aug 01, 2014 10:14 am UTC

Is this any more or less energy-efficient than just shining the light out the back of the spaceship, and if so why?
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Re: NASA scientists report positively on propellant-less dri

Postby elasto » Fri Aug 01, 2014 10:20 am UTC

Qaanol wrote:Is this any more or less energy-efficient than just shining the light out the back of the spaceship, and why?


Well, going by the Chinese figures (which were based on a different design to the one NASA tested) it produced 72 grams of thrust and could be powered by solar power. Since I don't feel a recoil when I turn on a torch or step outside the house I have to presume that's a lot higher order of magnitude :D

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Re: NASA scientists report positively on propellant-less dri

Postby Qaanol » Fri Aug 01, 2014 10:33 am UTC

Also, what is up with Fig 2 on page 6 of the EmDrive theory paper, which seems to indicate that the thrust produced depends on the absolute velocity of the engine? If this were being derived from quantum theory and made reference to the CMBR it could be plausible, but the derivation is entirely from special relativity and the only relative velocities are the speeds of light at each end of the waveguide, which should not change as the whole apparatus moves faster.

Edit: Figs 3.1 and 3.2 also indicate thrust to be velocity-dependent. Still makes no sense from relativity.
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Re: NASA scientists report positively on propellant-less dri

Postby eSOANEM » Fri Aug 01, 2014 11:34 am UTC

I'm not sure equation 5 on page 4's right. I think the λ0g term should be the other way up (in which case it's just the statement that the wave's frequency doesn't change).

The fact that they predict velocity-dependent thrust (and therefore acceleration which is invariant) is very worrying and strongly suggests to me that something has gone very wrong somewhere. Also, the fact this "theory paper" appears to just be a word document with diagrams drawn in word doesn't inspire confidence.

For the record, figure 2 is definitely talking about the velocity of the waveguide although the text never says wrt what.

So yeah, if this thing is working then it certainly isn't for the reasons they think it is.

Edit: this paper (apparently from a conference in Beijing gives a different derivation.)

Additionally, all this talk about how SR means that we have to consider the two ends in separate frames suggests that they'll end up with some relative velocity. This interpretation is patently absurd as it means this thing necessarily must tear itself apart. How do we stop that? By adding the stresses to the material this guy rejects. It's quite likely we do still need to consider them in separate frames, but ignoring stresses in the waveguide is stupid.
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Re: NASA scientists report positively on propellant-less dri

Postby Izawwlgood » Fri Aug 01, 2014 11:46 am UTC

Can someone explain how this works, even in... uh... theory?

The first paragraph of the wiki is using a bunch of terms I'm unfamiliar with -
The device uses a magnetron producing microwaves directed inside a specially shaped, fully enclosed tapering high Q resonant cavity whose area is greater at one end, upon which radiation pressure would act differently due to a relativistic effect caused by the action of group velocity in different frames of reference.
... with gigantic melancholies and gigantic mirth, to tread the jeweled thrones of the Earth under his sandalled feet.

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Re: NASA scientists report positively on propellant-less dri

Postby elasto » Fri Aug 01, 2014 1:16 pm UTC

eSOANEM wrote:The fact that they predict velocity-dependent thrust (and therefore acceleration which is invariant) is very worrying and strongly suggests to me that something has gone very wrong somewhere


That would mean it could accelerate through the light barrier, right? (Well, become a black hole first I guess)

That seems rather implausible to say the least :p

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elliptic
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Re: NASA scientists report positively on propellant-less dri

Postby elliptic » Fri Aug 01, 2014 1:23 pm UTC

Nowhere in that "paper" does he consider an equal and opposing force on the tapered walls of the waveguide.

*sigh*


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