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Tags emdrive , Propellantless drive , Roger Shawyer

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Old 9th February 2013, 05:25 PM   #1
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EmDrive? woo or not?

http://www.wired.co.uk/news/archive/...nd-cold-fusion
http://emdrive.com/principle.html

I just came across the following article describing a propellantless drive for space applications and wanted some opinions from those with more knowledge in the field than me on whether it is based in reality or not.

In the article they claim 'that with a couple of kilowatts of power they can produce 720 mN (about 72 grams) of thrust.'

That claim seems believable from a laymans perspective, but they then appear to go off the deep end with the following claim:

'By using superconducting apparatus, Shawyer says that the Q value, and hence thrust, can be boosted by a factor of several thousand -- producing perhaps a tonne of thrust per kilowatt of power. Suddenly it's not about giving a satellite a slight nudge, it's about launching spacecraft.'

So what are peoples opinions? Something to watch with interest or a scam for the gullible?
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Old 9th February 2013, 05:50 PM   #2
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What the hell is a tonne of thrust? What's that in newtons?
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Old 9th February 2013, 05:57 PM   #3
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And how to convert it to 'furlongs per fortnight'?
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Old 9th February 2013, 06:04 PM   #4
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Originally Posted by Brian-M View Post
What the hell is a tonne of thrust? What's that in newtons?
We Americans measure torque in foot/pounds.... could he maybe mean 2000 foot/pounds of thrust? maybe?
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Old 9th February 2013, 06:05 PM   #5
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from http://emdrive.com/secondgenengines.html i get:

'At present, superconducting microwave cavities are restricted to high energy physics applications. An example is the European Tesla accelerator where 20,000 S Band niobium cavities cooled with liquid helium will form the basis of the main accelerators. Early production versions of these cavities readily achieve Q values of 5 x 109 (BAUER, S. et al ‘Production of Superconducting 9-cell Cavities for the Tesla test facility, Standford University and Forschungszentrum Rossendorf’ Accel Instruments GmBh). This would lead to a static specific thrust of 3.15 x 104 N/kW (3.2 tonnes / kW).

A second generation engine using similar technology would however be subject to equation 2, and the effect at these high values of unloaded Q is dramatic. An average velocity of only 0.1 m/sec will reduce the specific thrust to 0.93 Tonne / kW.'


Which means next to nothing to me but hopefully you can translate
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Old 9th February 2013, 06:06 PM   #6
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^^^ what he said
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Old 9th February 2013, 06:24 PM   #7
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Originally Posted by Brian-M View Post
What the hell is a tonne of thrust? What's that in newtons?
1 Tonne-force = 9.80665 kN.
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Old 9th February 2013, 07:00 PM   #8
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From the Principle of Operation page:

Quote:
The inevitable objection raised, is that the apparently closed system produced by this arrangement cannot result in an output force, but will merely produce strain within the waveguide walls. However, this ignores Einstein’s Special Law of Relativity in which separate frames of reference have to be applied at velocities approaching the speed of light. Thus the system of EM wave and waveguide can be regarded as an open system, with the EM wave and the waveguide having separate frames of reference.

A similar approach is necessary to explain the principle of the laser gyroscope, where open system attitude information is obtained from an apparently closed system device.

Special Relativity says nothing of the sort. Quite the contrary: it says the laws of physics remain the same in any inertial reference frame. You can choose whatever frame is most convenient to assess the system, as long as you assess the wave and the waveguide with respect to the same reference frame.

Laser gyroscopes detect rotation, which is not movement in an inertial reference frame.

I suspect that the lengthy equation-filled pdf "theory paper" merely repeats in more detail the same basic misconception about reference frames. That is, it calculates the force at one end of the waveguide in one reference frame, the force at the other end in a different reference frame, and fails to notice (assuming everything else is calculated correctly) that once these forces are translated into the same reference frame there is no net force. However, I haven't gone through it in detail to verify that.

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Old 9th February 2013, 07:55 PM   #9
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Originally Posted by StankApe View Post
We Americans measure torque in foot/pounds.... could he maybe mean 2000 foot/pounds of thrust? maybe?
Originally Posted by Pulvinar View Post
1 Tonne-force = 9.80665 kN.
Ah, that makes sense. I'm not used to seeing force described in units of weight. Looking it up, I did find a calculator for it... http://www.sengpielaudio.com/calculator-forceunits.htm

It looks like a ton of force can be any of three different values, depending on whether you're using short, long or metric units.

(I'm more used to seeing figures for power rather than figures for force.)
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Last edited by Brian-M; 9th February 2013 at 07:56 PM.
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Old 9th February 2013, 08:01 PM   #10
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Originally Posted by Brian-M View Post
Ah, that makes sense. I'm not used to seeing force described in units of weight. Looking it up, I did find a calculator for it... http://www.sengpielaudio.com/calculator-forceunits.htm

It looks like a ton of force can be any of three different values, depending on whether you're using short, long or metric units.

(I'm more used to seeing figures for power rather than figures for force.)
I had never heard it described as newton/meters until I discovered the UK car show Top Gear. They use both measurements on there relative to the country of origin of the car I guess (as I reckon they use the printed stats and info released by the manufacturer in regards to performance)
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Old 10th February 2013, 01:33 PM   #11
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ok so junk science by the sound of it?

Disappointing but not unexpected really. I guess I'll just have to wait to see if they can pull off a working prototype and prove us all wrong then.
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Old 10th February 2013, 02:00 PM   #12
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Originally Posted by Brian-M View Post
What the hell is a tonne of thrust? What's that in newtons?
1000 x 9.81 = 9810N. Pure BS.
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Old 10th February 2013, 02:02 PM   #13
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Originally Posted by coops View Post
from http://emdrive.com/secondgenengines.html i get:

'At present, superconducting microwave cavities are restricted to high energy physics applications. An example is the European Tesla accelerator where 20,000 S Band niobium cavities cooled with liquid helium will form the basis of the main accelerators. Early production versions of these cavities readily achieve Q values of 5 x 109 (BAUER, S. et al ‘Production of Superconducting 9-cell Cavities for the Tesla test facility, Standford University and Forschungszentrum Rossendorf’ Accel Instruments GmBh). This would lead to a static specific thrust of 3.15 x 104 N/kW (3.2 tonnes / kW).

A second generation engine using similar technology would however be subject to equation 2, and the effect at these high values of unloaded Q is dramatic. An average velocity of only 0.1 m/sec will reduce the specific thrust to 0.93 Tonne / kW.'


Which means next to nothing to me but hopefully you can translate
Thes cavities are particle accelerators, so require reaction mass...
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Old 10th February 2013, 02:06 PM   #14
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Originally Posted by Myriad View Post
Special Relativity says nothing of the sort. Quite the contrary: it says the laws of physics remain the same in any inertial reference frame. You can choose whatever frame is most convenient to assess the system, as long as you assess the wave and the waveguide with respect to the same reference frame.
Got to wonder if you could ask those guys if they could meet us in our reference frame to discuss investment opportunities. The idea that two things might not share a reference frame is a big clue that you're hearing woo. One of the more amusing ones IMO.
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Old 11th February 2013, 08:27 AM   #15
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Originally Posted by coops View Post
'At present, superconducting microwave cavities are restricted to high energy physics applications. An example is the European Tesla accelerator where 20,000 S Band niobium cavities cooled with liquid helium will form the basis of the main accelerators.
The TESLA project has been defunct for nearly a decade, so using it in a paragraph beginning "at present" seems a little odd.

Other than that, yeah, it's nonsense. I think it's been discussed here before. I very nearly wrote a post noting that there was nothing wrong with the principle, since radiation pressure means shooting light out of a waveguide must produce thrust. Then I noticed that they're not actually talking about shooting light out of a waveguide, but having closed off at both ends and just bouncing light backwards and forwards. This absolutely will not produce any thrust. A closed system can't produce a net external force on itself. That's very basic conservation of momentum - if you don't shoot anything out the back, you don't go forwards.
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Old 11th February 2013, 12:56 PM   #16
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Originally Posted by coops View Post
http://www.wired.co.uk/news/archive/...nd-cold-fusion
http://emdrive.com/principle.html

...producing perhaps a tonne of thrust per kilowatt of power. Suddenly it's not about giving a satellite a slight nudge, it's about launching spacecraft.'
Other than the emdrive looking like woo, the last claim is dubious to say the least. The Saturn V rocket for example had a first stage thrust of 7,648,000 pounds-force (34,020,000 N) to deliver 260,000 pounds (120,000 kg) to LEO.
They are talking about a thrust of about 9810 N.
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Old 11th February 2013, 01:07 PM   #17
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I can even make a wild guess at what they are actually measuring. They have a closed, tapered microwave guide. Maybe the narrow end is hotter than the broader end. If their apparatus is made of materials that can out-gas than there will be more out-gassing from the narrow end. So what they are measuring could be an actual thrust from their apparatus emitting gas.
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Old 11th February 2013, 02:03 PM   #18
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Originally Posted by Brian-M View Post
Ah, that makes sense. I'm not used to seeing force described in units of weight. Looking it up, I did find a calculator for it... http://www.sengpielaudio.com/calculator-forceunits.htm

It looks like a ton of force can be any of three different values, depending on whether you're using short, long or metric units.

(I'm more used to seeing figures for power rather than figures for force.)
"Tonne" (with that spelling) means a metric ton (10e6 grams) . Using it as a unit of force, rather than mass is non-standard.
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Old 11th February 2013, 02:11 PM   #19
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Originally Posted by casebro View Post
And how to convert it to 'furlongs per fortnight'?
Since thrust is force,rather than velocity, that's not possible,but perhaps we could convert it to whatever the unit of force is called in the fsf (furlong-stone-fortnight) system.
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Old 11th February 2013, 02:29 PM   #20
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Originally Posted by RecoveringYuppy View Post
Got to wonder if you could ask those guys if they could meet us in our reference frame to discuss investment opportunities. The idea that two things might not share a reference frame is a big clue that you're hearing woo. One of the more amusing ones IMO.
It works in the humberverse.
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Old 11th February 2013, 03:15 PM   #21
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Originally Posted by Mikemcc View Post
Thes cavities are particle accelerators, so require reaction mass...
Right, that's what I first noticed too. So unless you are accelerating the particles away from you (basically spitting them out the back) you won't get any trust. Certainly not propellant less and I'm not even sure if it reduces the amount of propellant all that much. Ion drives already electromagnetically accelerate charged particles away from you for trust.
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Old 11th February 2013, 06:28 PM   #22
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Imma votin' woo. Again.
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Old 11th February 2013, 07:28 PM   #23
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Originally Posted by GodMark2 View Post
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Imma votin' woo. Again.
Looks like it's gettin' about the same mileage as the Moller SkyCar.
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Old 12th February 2013, 04:45 PM   #24
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Originally Posted by Brian Jackson View Post
Looks like it's gettin' about the same mileage as the Moller SkyCar.
No, the SkyCar has managed to actually hover (for a short time, while tethered) and has multiple working prototypes.
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Old 12th February 2013, 05:42 PM   #25
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Originally Posted by GodMark2 View Post
No, the SkyCar has managed to actually hover (for a short time, while tethered) and has multiple working prototypes.
You are right. I was referring to the "seeking investors" part where a breakthrough is always just around the corner.
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Old 13th February 2013, 05:54 PM   #26
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Originally Posted by Brian Jackson View Post
You are right. I was referring to the "seeking investors" part where a breakthrough is always just around the corner.
Well, by that definition, IBM is in the same boat.1

The SkyCar has every chance of being possible: the basic principles work, and don't try to rewrite physics. Whether you can get an engine powerful enough and light enough and cost-effective enough all at the same time is just an engineering problem. Trying to get the DOT and FAA to agree on who gets to regulate it might take an act of Hank, though.

Achieving thrust by bouncing light around a sealed box, on the other hand...


1Of course, their breakthroughs actually produce results, but there's always another one 'just around the corner', and they actually do provide dividends for investment, but they always like investors.
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Old 26th February 2013, 04:48 AM   #27
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Originally Posted by Cuddles View Post
Other than that, yeah, it's nonsense. I think it's been discussed here before. I very nearly wrote a post noting that there was nothing wrong with the principle, since radiation pressure means shooting light out of a waveguide must produce thrust. Then I noticed that they're not actually talking about shooting light out of a waveguide, but having closed off at both ends and just bouncing light backwards and forwards. This absolutely will not produce any thrust. A closed system can't produce a net external force on itself. That's very basic conservation of momentum - if you don't shoot anything out the back, you don't go forwards.
Shawyer claims it's actually an open system because [insert content-free handwaving about laser gyroscopes here]. Of course, for it to be an open system, energy and/or matter must enter or exit the system somehow. It doesn't eject matter, so we can determine that, at best, it must be equivalent to a photon drive...which doesn't give anything like the performance claimed.

And what about laser gyroscopes? Simple: rotating frames are not inertial frames. Same fundamental reason any other gyroscopes work.

It's easy to show just how badly this thing breaks conservation laws, despite claims to the contrary. Shawyer put up an updated PDF a while back, 2Gupdate.pdf on the main page of his website. On page 6, amusingly titled "Energy Conservation", Shawyer equates it to a classical electric machine, accelerating when power is input and producing power when accelerated. It's pretty straightforward to see that simply standing an EmDrive on end on Earth's surface would make either an infinite energy sink or an infinite energy source, depending on orientation.
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Old 26th February 2013, 11:50 AM   #28
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Thermo-dynamics is the morality of science.

Eventually, we can reject free energy because it is immoral.
It's against the law.
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Old 27th February 2013, 12:08 AM   #29
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Originally Posted by cjameshuff View Post
It's pretty straightforward to see that simply standing an EmDrive on end on Earth's surface would make either an infinite energy sink or an infinite energy source, depending on orientation.
No, you'd just be using it to change the velocity of the earth.
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Old 27th February 2013, 05:14 AM   #30
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Originally Posted by Brian-M View Post
No, you'd just be using it to change the velocity of the earth.
While producing an endless stream of energy from nowhere in one of those cases, and making an unlimited amount vanish from the universe in the other. If you think it might somehow come from or go into the Earth's kinetic energy, just put an identical one on the far side to cancel any planetary accelerations. It's Earth's gravitational acceleration that's relevant to my argument...Shawyer doesn't seem to be aware of the equivalence principle.

It's even worse than that. He's claimed that the EmDrive works best when "stationary relative to its thrust". The "Future" section of his website makes clear what he means...his reactionless thruster works best if you don't let it move (you read that right), and its performance decreases as velocity increases. He suggests vehicles using EmDrive for lift and jet engines for forward propulsion, to "limit kinetic output". Throughout the whole thing, it's clear that he thinks velocity is some absolute universal quantity, completely missing the point of relativity. (In fact, he's assuming Earth is in an absolute rest frame...his claims require a geocentric universe.)
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Old 27th February 2013, 11:22 AM   #31
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Originally Posted by cjameshuff View Post
While producing an endless stream of energy from nowhere in one of those cases, and making an unlimited amount vanish from the universe in the other. If you think it might somehow come from or go into the Earth's kinetic energy, just put an identical one on the far side to cancel any planetary accelerations. It's Earth's gravitational acceleration that's relevant to my argument...Shawyer doesn't seem to be aware of the equivalence principle.

It's even worse than that. He's claimed that the EmDrive works best when "stationary relative to its thrust". The "Future" section of his website makes clear what he means...his reactionless thruster works best if you don't let it move (you read that right), and its performance decreases as velocity increases. He suggests vehicles using EmDrive for lift and jet engines for forward propulsion, to "limit kinetic output". Throughout the whole thing, it's clear that he thinks velocity is some absolute universal quantity, completely missing the point of relativity. (In fact, he's assuming Earth is in an absolute rest frame...his claims require a geocentric universe.)
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