Author Topic: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive  (Read 198629 times)

Offline ppnl

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #280 on: 05/02/2015 01:24 AM »

IT IS NOT THE SAME!!!!!!

Having reaction mass expelled *changes everything*! For one, now you need to include reaction mass' kinetic energy into energy balance.

Constant acceleration reactionless drive of any type violates COE.

Does a magsail?

A magsail is neither constant acceleration nor reaction-less. It is true that it does not carry its reaction mass with it but it is reacting against an external medium. But then so does a car, airplane or boat.

It is argued that the EM-drive is also reacting against an external medium, in its case the quantum vacuum.

Yes but the quantum vacuum must be Lorentz invariant. That is the quantum vacuum must look the same to all observers regardless of their inertial frame of reference. Kinda like the speed of light looks the same to all observers. Otherwise you create a special inertial frame against which you can measure absolute motion. This would be in severe conflict with relativity and just about all of modern science.

Also it creates the problem that the performance of the drive would change drastically depending on the time of year. Your state of absolute motion would differs by many miles per second over the year vastly changing the amount of power needed to operate the drive. Of course that would be one of the least problems caused by a universal frame of reference.

 

Offline Robotbeat

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #281 on: 05/02/2015 03:20 AM »
...

Those people do not know the struggling of a scientist to get just a little more funding in their lab where only 3 or 4 other colleagues work with them. Eagleworks has an old dying RF amp and they do not even have the bucks to replace it… Paul had to build the copper frustum at home, in his wife's dining room! Really people would be shocked if they knew that....
Yes, the more crude the instrumentation, the stronger the effect.
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Offline groundbound

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #282 on: 05/02/2015 04:02 AM »
Commander Chris Hadfield just tweeted it to his 1.3 million followers.  :o

I have a conservation of energy question that I don't think has been asked before in any of these threads.


Where is the energy going to come from to run all the extra servers to handle this new NSF traffic??   ;D

Which leads to a more legitimate question: is there any portion of all of this discussion that makes sense to move inside the L2 bubble? Without putting any damper on the productive open threads, it would be nice to see know there is a little more revenue to offset the traffic.

Offline Prunesquallor

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #283 on: 05/02/2015 04:44 AM »
So let's assume the EM drive works as described and Alpha Centauri can be reached in approximately 130 earth years accounting for acceleration, cruising and  deceleration. Can anyone calculate the approximate time dilation spent? (i.e. the theory of relativity that shows  time slowing down relative to earth time and stops at light speed.) Obviously gravitational effects on time dilation would probably be impossible to factor in.

If time were slowed down enough would it allow reaching Alpha Centauri in a generation or two? Assuming one didn't die of radiation poisoning, a spec of dust piercing a hole through  them at that speed, or outright insanity.  ::)

I get around a month difference.

Yep, me too.  0.067c max velocity, t-tau=36 days for 0.001 g's.  No "cruise", just accelerate then decelerate for minimum flight time.
« Last Edit: 05/02/2015 05:08 AM by Prunesquallor »
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Offline Robotbeat

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #284 on: 05/02/2015 05:01 AM »
So let's assume the EM drive works as described and Alpha Centauri can be reached in approximately 130 earth years accounting for acceleration, cruising and  deceleration. Can anyone calculate the approximate time dilation spent? (i.e. the theory of relativity that shows  time slowing down relative to earth time and stops at light speed.) Obviously gravitational effects on time dilation would probably be impossible to factor in.

If time were slowed down enough would it allow reaching Alpha Centauri in a generation or two? Assuming one didn't die of radiation poisoning, a spec of dust piercing a hole through  them at that speed, or outright insanity.  ::)

I get around a month difference.

Yep, me too.  v=0.067c at turnaround, t-tau = 36 days for 0.001 g's
That violates energy conservation. You're talking about way more kinetic energy than you put into it in the first place.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Prunesquallor

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #285 on: 05/02/2015 11:34 AM »
So let's assume the EM drive works as described and Alpha Centauri can be reached in approximately 130 earth years accounting for acceleration, cruising and  deceleration. Can anyone calculate the approximate time dilation spent? (i.e. the theory of relativity that shows  time slowing down relative to earth time and stops at light speed.) Obviously gravitational effects on time dilation would probably be impossible to factor in.

If time were slowed down enough would it allow reaching Alpha Centauri in a generation or two? Assuming one didn't die of radiation poisoning, a spec of dust piercing a hole through  them at that speed, or outright insanity.  ::)

I get around a month difference.

Yep, me too.  v=0.067c at turnaround, t-tau = 36 days for 0.001 g's
That violates energy conservation. You're talking about way more kinetic energy than you put into it in the first place.

The OP qualified his question "So let's assume the EM Drive works as described..."  My response was based on that qualification.
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Offline Mulletron

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #286 on: 05/02/2015 12:38 PM »
So let's assume the EM drive works as described and Alpha Centauri can be reached in approximately 130 earth years accounting for acceleration, cruising and  deceleration. Can anyone calculate the approximate time dilation spent? (i.e. the theory of relativity that shows  time slowing down relative to earth time and stops at light speed.) Obviously gravitational effects on time dilation would probably be impossible to factor in.

If time were slowed down enough would it allow reaching Alpha Centauri in a generation or two? Assuming one didn't die of radiation poisoning, a spec of dust piercing a hole through  them at that speed, or outright insanity.  ::)

I get around a month difference.

Yep, me too.  v=0.067c at turnaround, t-tau = 36 days for 0.001 g's
That violates energy conservation. You're talking about way more kinetic energy than you put into it in the first place.

The OP qualified his question "So let's assume the EM Drive works as described..."  My response was based on that qualification.

It is known to be impossible to violate energy conservation. Stating that it clearly does is a non-sequitur, as it implies complete knowledge of how Emdrive works (if it really does work). There is no accepted theory of operation for this thing.

For all we know, the universe might be a ginormous energy bank that you can borrow from and loan to; if you know how. You still have to balance the books at the end of the day. (pure conjecture)

I think we need to remember that until proven otherwise, this copper can is a black box. It is what it is, regardless of what some guy's theory says about it, which is likely wrong until proven correct.
« Last Edit: 05/02/2015 12:40 PM by Mulletron »
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Offline tea monster

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #287 on: 05/02/2015 12:51 PM »
The nice thing about this is that it's just a copper kettle with a magnetron attached. Any medium sized lab or even a home enthusiast could make one.

To properly evaluate it, you need a high-energy source and a vacuum chamber and proper equipment. But we aren't talking about a billion dollar research program here.

Online sanman

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #288 on: 05/02/2015 01:18 PM »
So I wanted to ask...

The wave inside the resonant cavity is a standing wave, and it can exert force on the cavity itself. And in regards to its motion, that standing wave can be construed as a soliton. Ordinarily, a soliton on its own (outside of a resonant cavity) is said to be a "delicate balance of linear and nonlinear effects which counter dispersion" - but here we have a resonant cavity to counter the dispersion, with the consequence that cavity has force interaction with the trapped wave.

Is it possible that the power feed to the asymmetric cavity can somehow force the soliton to move, and thus make the cavity move with it? And thus your apparatus is then "surfing the wave"? (ie. surfing the soliton)
« Last Edit: 05/02/2015 01:20 PM by sanman »

Offline Rodal

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #289 on: 05/02/2015 02:00 PM »
So I wanted to ask...

The wave inside the resonant cavity is a standing wave, and it can exert force on the cavity itself. And in regards to its motion, that standing wave can be construed as a soliton. Ordinarily, a soliton on its own (outside of a resonant cavity) is said to be a "delicate balance of linear and nonlinear effects which counter dispersion" - but here we have a resonant cavity to counter the dispersion, with the consequence that cavity has force interaction with the trapped wave.

Is it possible that the power feed to the asymmetric cavity can somehow force the soliton to move, and thus make the cavity move with it? And thus your apparatus is then "surfing the wave"? (ie. surfing the soliton)

I'm not clear as to what effect you are referring to.  Are you referring to a Kerr-type-nonlinearity cavity soliton ?, as for example :

https://www.osapublishing.org/oe/viewmedia.cfm?uri=oe-21-7-9180&seq=0

In any case, whatever effect one can conjecture, the challenge is not only to prove the existence of the effect but just as important, to demonstrate conservation of momentum for a cavity accelerated under such an effect   :)

« Last Edit: 05/02/2015 02:02 PM by Rodal »

Offline JackFlash

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #290 on: 05/02/2015 02:07 PM »
Begging your pardon Dr. Rodal, but when you assert that:

 "In any case, whatever effect one can conjecture, the challenge is not only to prove the existence of the effect but just as important, to demonstrate conservation of momentum for a cavity accelerated under such an effect",

I have to think that this is only necessary in order to preserve the validity of the current understanding of such things.

In any case, I'm loving what you folks are doing here. Keep chasing the data :D

Cheers

Offline SH

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #291 on: 05/02/2015 02:17 PM »
I have to think that this is only necessary in order to preserve the validity of the current understanding of such things.

While it is important to recognize that our understanding of physics is never perfectly correct and complete, you really can't mess with the basic conservation laws.  If energy or momentum is not conserved, the universe would become a completely unstable system. 

Online sanman

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #292 on: 05/02/2015 03:22 PM »
In any case, whatever effect one can conjecture, the challenge is not only to prove the existence of the effect but just as important, to demonstrate conservation of momentum for a cavity accelerated under such an effect   :)

Alright, so the standing wave loses energy in an amount that offsets the kinetic energy gain associated with acceleration - and this is supposed to satisfy conservation of energy. And conservation of momentum is satisfied by using energy-mass equivalency?

I was just wondering what the mechanism is by which pumping up the standing wave then creates a net force on the cavity.


Here's a debunking by Greg Egan, showing why you can't have net force just because the cavity happens to be asymmetric:

http://gregegan.customer.netspace.net.au/SCIENCE/Cavity/Simple.html


Offline BroncoBill

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #293 on: 05/02/2015 04:17 PM »
What US/international laws/regulations must be satisfied to legally allow the flight of a nuclear reactor ?  Also, is it possible that the DoD X-37B is carrying such a prototype reactor ?  technology that  would need to be brought back to earth and not wilfully disposed on re-entry.  Or even a prototype thruster ? DoD timing on "Hall" thruster masking more exotic technology ?

Online Stormbringer

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #294 on: 05/02/2015 05:30 PM »
actually no. It was outside critics that insisted they need to see how it performed in a vacuum chamber. :)
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Offline Dmytry

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #295 on: 05/02/2015 05:35 PM »
actually no. It was outside critics that insisted they need to see how it performed in a vacuum chamber. :)
From the day one, they've been performing experiments in a vacuum chamber (at ambient pressure lol).

And I always insisted on shielding it in a box.

edit: I don't think most critics even realized that the test article was un shielded and influencing the measurement apparatus (exhibit A, "baseline drift"). A sealed box in the vacuum would be the best test, a sealed box in the air second best, and without the sealed box you're just rigging an experiment to be as sensitive to as many stray classical forces as possible. Again, widely disrespected scientists (Andrea Rossi for example) are known to deliberately do similar things to get an effect.
« Last Edit: 05/02/2015 06:26 PM by Dmytry »

Offline Rodal

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #296 on: 05/02/2015 06:22 PM »
In any case, whatever effect one can conjecture, the challenge is not only to prove the existence of the effect but just as important, to demonstrate conservation of momentum for a cavity accelerated under such an effect   :)

Alright, so the standing wave loses energy in an amount that offsets the kinetic energy gain associated with acceleration - and this is supposed to satisfy conservation of energy. And conservation of momentum is satisfied by using energy-mass equivalency?

I was just wondering what the mechanism is by which pumping up the standing wave then creates a net force on the cavity.


Here's a debunking by Greg Egan, showing why you can't have net force just because the cavity happens to be asymmetric:

http://gregegan.customer.netspace.net.au/SCIENCE/Cavity/Simple.html

Greg Egan is just showing the standing wave solution to Maxwell's equation for a truncated cone for mode shapes that have constant field in the transverse, azimuthal direction.   The solutions shown by Egan are known since the 1930's. 

That Maxwell's equations and special relativity satisfy conservation of momentum is known in general, for any problem, for any geometrical shape.  Thus, Egan is just "debunking" attempts (as done by Roger Shawyer for example or by Prof. Yang in China) trying to justify EM Drive space propulsion just using Maxwell's equations and special relativity.  Egan's paper does not and cannot debunk Dr. White's conjecture for example, or Prof. Woodward's conjecture.  Dr. White's conjecture can be objected on the grounds that it implies a mutable and degradable quantum vacuum, for example, but not solely on the grounds discussed by Egan.  Prof. Woodward's conjecture can be objected on the grounds that it needs a Wheeler–Feynman absorber theory to justify its instantaneous action from distant objects.
« Last Edit: 05/02/2015 06:44 PM by Rodal »

Offline Dmytry

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #297 on: 05/02/2015 06:35 PM »
If it doesn't work with Maxwell's equations, then it requires a violation of Maxwell's equations, and any violation above some tiny (parts per billion? trillion?) would be very detectable by it's effects on the electromagnetic fields in many practical devices. Keep in mind that 6.66 uN , which are hard to detect, correspond to 1KW worth of EM reflecting off a surface, which is hard *not* to detect.

Offline Robotbeat

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #298 on: 05/02/2015 06:57 PM »
In any case, whatever effect one can conjecture, the challenge is not only to prove the existence of the effect but just as important, to demonstrate conservation of momentum for a cavity accelerated under such an effect   :)

Alright, so the standing wave loses energy in an amount that offsets the kinetic energy gain associated with acceleration - and this is supposed to satisfy conservation of energy. And conservation of momentum is satisfied by using energy-mass equivalency?

I was just wondering what the mechanism is by which pumping up the standing wave then creates a net force on the cavity.


Here's a debunking by Greg Egan, showing why you can't have net force just because the cavity happens to be asymmetric:

http://gregegan.customer.netspace.net.au/SCIENCE/Cavity/Simple.html

Greg Egan is just showing the standing wave solution to Maxwell's equation for a truncated cone for mode shapes that have constant field in the transverse, azimuthal direction.   The solutions shown by Egan are known since the 1930's. 

That Maxwell's equations and special relativity satisfy conservation of momentum is known in general, for any problem, for any geometrical shape.  Thus, Egan is just "debunking" attempts (as done by Roger Shawyer for example or by Prof. Yang in China) trying to justify EM Drive space propulsion just using Maxwell's equations and special relativity.  Egan's paper does not and cannot debunk Dr. White's conjecture for example, or Prof. Woodward's conjecture.  Dr. White's conjecture can be objected on the grounds that it implies a mutable and degradable quantum vacuum, for example, but not solely on the grounds discussed by Egan.
Right. A lot of the handy-wavy "theoretical" justification isn't even falsifiable. Someone just makes up some other theoretical nonsense.

And the computer simulations are worse. They are based on Maxwell's Equations which literally don't allow something like the EM-drive as they conserve both momentum and energy perfectly. If you get a different result, it's either because you modified the equations that you're solving or you're just seeing an artifact of the computation.

So the theoretical work can be safely ignored.
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Offline Rodal

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #299 on: 05/02/2015 07:27 PM »
...

And the computer simulations ...are based on Maxwell's Equations which literally don't allow something like the EM-drive as they conserve both momentum and energy perfectly. ..
...
Yes, the COMSOL Finite Element solutions are just based on Maxwell's equations (which satisfy conservation of momentum and conservation of energy).  NASA Eagleworks performed those finite element calculations for the following reasons:

1) To calculate the natural frequencies of the truncated cone cavity, so that they know at what frequency they can excite resonance at a high Q

2) To calculate the Q for the different mode shapes

3) To calculate the different mode shapes (whether they are transverse magnetic or transverse electric modes) and the field distributions for different modes

4) To calculate the resulting temperature from induction heating by the magnetic field (those calculations compare very well with the temperatures measured by a thermal camera)

NASA Eagleworks does not use the COMSOL Finite Element analysis to calculate any thrust forces.


Of course, there is an implicit admission here by NASA Eagleworks team that any claimed interaction with the Quantum Vacuum does not have any appreciable effect on the above calculated quantities (which are solely based on Maxwell's equations).

NASA Eagleworks has not reported any force calculations (based on Maxwell's stress tensor) or Poynting vector calculations based on Maxwell's equations.  They say that they are aware that such force calculations would give zero net thrust.  This is much better than Prof. Yang's Chinese publications that report calculations for net thrust based on Maxwell's stress tensor (which does not make sense.  Therefore any such calculation reported in Prof. Yang's calculation may be due to incorrect restraining in the finite element analysis, preventing  rigid body modes, as the finite element matrix becomes singular for an unrestrained structure.)

Dr. White's calculations for the thrust are based on a separate code, which apparently he wrote based on his Quantum Vacuum theory.  I have not seen the actual formulation for this code.

Since nobody (Shawyer, Yang or NASA) had published images of the Poynting vector field for the EM Drive truncated cone I calculated the Poynting vector field, based on the exact solution of Maxwell's equations for a truncated cone (with two eigenvalue problems: one for associated Legendre functions and the other for spherical Bessel functions solved numerically) "for fun" and curiosity, to see what it looks like.  Other authors have referred to the Poynting vector.  Of course one cannot obtain a thrust of the EM Drive from the Poynting vector (for solutions of Maxwell's equations) because it flips orientation every half period, and hence it is self-cancelling. 
« Last Edit: 05/02/2015 09:03 PM by Rodal »

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