Close Look at Recent EmDrive Paper

by Paul Gilster on January 3, 2017

The concluding part of the Tau Zero Foundation’s examination of what is being called the ‘EmDrive’ appears today. It’s a close analysis of the recent paper by Harold ‘Sonny’ White and Paul March in the Journal of Propulsion and Power. Electrical engineer George Hathaway runs Hathaway Consulting Services, which has worked with inventors and investors since 1979 via an experimental physics laboratory near Toronto, Canada. Hathaway’s concentration is on novel propulsion and energy technologies. He has authored dozens of technical papers as well as a book, is a patent-holder and has hosted and lectured at various international symposia.

Hathaway Consulting maintains close associations with advanced physics institutions and universities in the US and Europe. Those familiar with our Frontiers of Propulsion Science book will know his paper on gravitational experiments with superconductors, which closely examined past methods and cast a skeptical eye on early claims of anomalous forces (an earlier paper, “Gravity Modification Experiment using a Rotating Superconducting Disk and Radio Frequency Fields,” appeared in Physica C). Like Marc Millis, Hathaway calls for continued testing of EmDrive concepts and increased rigor in experimental procedures.

By George Hathaway

Comments on “Measurement of Impulsive Thrust from a Closed Radio Frequency Cavity in Vacuum” (White, March et al, published online by Jnl. Prop. & Power November 17, 2016).

Introduction

White et al are to be congratulated for attempting to measure the small thrusts allegedly produced by a novel thruster whose operating mechanism is not only not understood but purportedly violates fundamental physical laws. They have made considerable effort to reduce the possibility of measurement artifact. However it appears that there are some fundamental problems with the interpretation of the measurement data produced by their thrust balance. This document will analyse the measurement procedure and comment on the interpretation.

The following comments roughly follow the order in the original text by White et al

Analysis and Comments

1. Null Test Orientation

Tests were performed in both the “Forward” and “Reverse” direction as well as in a “Null” direction where the alleged force vector pointed towards the rotational axis of the balance (pg 23). Apparently no Null tests were performed with the force vector pointing away from the balance axis nor were any tests performed with the “test article” force vector pointing up or down. These additional orientations would have provided much needed control data given the magnitude of the allegedly purely thermal signal seen in their “Null” test.

In addition, the Forward and Reverse tests should also have been performed by just re-orienting the test article whilst keeping all other rotating components untouched. In this type of control experiment, the spurious effect of the rest of the components is largely eliminated.

2. Axis Verticality

An optical bench was used as a platform to mount the vacuum chamber containing the balance. It is not stated whether the optical bench was itself mounted on pneumatic legs, however, this is usually the case with optical benches. The correct operation of any balance of this geometry requires that the pivots around which the balance arm rotates must be perfectly aligned vertically one above the other (for a 2-pivot system). When the pneumatic legs of the table are inflated, the axis of the balance is not typically able to be kept perfectly vertical, as required to obtain the maximum balance sensitivity and repeatability. There is no indication in the text stating how such verticality was assured throughout the test campaign, especially since the balance was housed in a large vacuum chamber.

3. Flexural Bearings

There is no information presented to indicate whether the linear flexure bearings were operating within the manufacturer’s axial loading specification, especially when additional ballast weight was required for the non-“split configuration” tests. It would also have been useful to see data on the natural frequency of the balance when loaded with the equivalent weights used in the thrust tests, given the damping method described. Also missing is an explanation of why none of the traces of the optical displacement sensor return to starting baseline after the calibration and “thrust” pulses. There seems to be an inherent bearing stiction problem preventing the balance from returning to its original baseline after a test. This is not due to general balance drift and is typical for overloaded bearings of this type. Long-term balance stability/drift plots would be useful.

4. Electrostatic Calibrator

Evidently the calibration of the electrostatic “fin” method of applying calibration pulses was performed using an electronic balance (Scientech SA-210). Unfortunately no data was provided to show exactly how this calibration was performed. In particular, no data was provided to show that there was no electrostatic interaction between the high-voltage calibration voltages and the operation of the balance. Since the Scientech balance properly reports vertical forces only, was care taken to translate these vertical forces into the horizontal calibration forces required by the thrust balance? It would have been useful for the authors to have employed a second, independent horizontal force calibration to verify the Scientech method such as a strain gauge-type force gauge with interpolation.

5. Vacuum System

The authors note that although turbomolecular pumps were used to evacuate the vacuum chamber, they caused no artificial vibrational signals. Turbo pumps require mechanical backing pumps to evacuate them to atmosphere. These mechanical pumps are connected to the turbo pumps typically via thick and stiff vacuum hoses. These hoses can transmit backing pump vibrations to the turbo pumps which are usually rigidly connected to the vacuum chamber. Was this source of vibration taken into account as well?

Additionally, no evidence is provided to show how the interior of the test article was evacuated coincidentally with the chamber evacuation. This is a different concern to that stated in the paper (pp 27, 28) regarding outgassing of the dielectric. The concern here is that if the test article cannot be fully evacuated coincidentally with the chamber evacuation, residual gas inside the test article can possibly escape during the time of a test, causing spurious force signals. Moreover, if the test article is rather well-sealed, the shell of the test article, especially the end plates, could expand upon evacuation of the chamber due to air trapped inside prior to chamber pump-down. This would alter the center of gravity (COG) of the balance causing a spurious signal, especially if the trapped air is heated upon application of RF power of tens of watts.

6. Liquid Metal Connections

“Galinstan screw and socket” rotary connections were employed to prevent any unwanted torques from upsetting the balance due to hard-wire connections between the rotating test article and the power supplies, analytical instruments etc fixed to the lab frame. There must have been quite a few of these connections for DC power, Forward and Reverse RF power, various tuning and drive signals etc. The authors failed to indicate how these connections were arranged geometrically. The ideal mounting arrangement is for such liquid metal connections to be stacked one on top of the other exactly coaxial with the main rotational axis of the balance. It seems unlikely that the design constraints of the balance within the chamber shown would accommodate this tall a stack of connections. Thus it is assumed that these connections were not arranged coaxially with the balance axis. If so, there could be spurious side thrusts generated by Ampère currents set up within the galinstan. This should have been tested and reported.

7. Thermal Expansion and Control Tests

The White et al paper contains considerable information on the effects of thermal expansion of the various test article components. It would be beneficial to see control experiments in which the test article is replaced by a suitable control article such as a purely cylindrical cavity of approximately the same dimensions, materials and construction and which supports similar RF modes as the frustrated conical test article.

According to pg 10, the heat sink unsurprisingly is the greatest source of heat during operation. It would be useful to perform control tests by separating the heat sink mechanically from the rest of the rotating components in such a way as to allow it to be oriented in any direction relative to the rest of the components to see the effect on the optical displacement signal.

Evidently, the test article assembly produces a relatively large thermal “thrust” signal as measured by the optical displacement sensor. The only explanation given is the change in center of gravity (COG) due to thermal expansion of various components causes a spurious torque on the balance. In fact the presence of a thrust signal due to thermal effects is only inferred, not proven. Not only that but it is stated (pg 10) that this thermal effect causes the balance arm to shift “with the same polarity as the impulsive signal” in Forward or Reverse tests. Here also it is implied but not proven that an “impulsive thrust” signal is even present (see below). The authors need to perform such control tests as to ascertain with certainty that there is indeed a “thermal thrust” before assuming without proof that it causes the balance arm to shift “with the same polarity”. One such test would be to construct a “control article” of the same shape, material and weight as the test article but with guaranteed no “impulsive thrust” and substitute it for the test article. Instead of powering it with an RF signal, put a resistor or light bulb inside to simulate the thermal characteristics.

This lack of proof of the presence of either a thermal thrust or an impulsive thrust thus precludes statements such as “the thermal signal in the vacuum runs is slightly larger than the magnitude of the impulsive signal [due to convective issues]”.

8. Confirmation Bias in Thrust Analysis

The entire edifice of the analysis of the signals from the optical displacement sensor rests on the assumption of the correctness and correct application of Fig. 5 to the present test situation. Fig. 5 shows an ad-hoc superposition of two assumed signals, namely a thermal signal and a pulse (impulse) signal. This is presented initially as a “conceptual simulation” and is reasonable in its own right. However, it then takes on the value of an accepted fact throughout the rest of the paper. Fig. 5 represents what the authors expect to see in the signal from the optical displacement sensor. When they see signals from this sensor which vaguely look like the expected superposition signal as represented in Fig 5, they assume that Fig 5 must actually represent what is going on in their system under test. This is a clear inductive reasoning fallacy called Confirmation Bias. This problem leads to baseless assumptions about the timing of the onset of expected effects after application of the stimulus (RF power), their proper shapes, and the joint amplitudes and thus the individual (impulse vs thermal) magnitudes.

In particular, the authors assume that the “true” impulse signal from the test article will look just like the assumed signal shown in Fig. 5, namely that it will look just like their calibration signal. This will include an initial fast-rising but well-behaved exponential slope up to a flat-topped constant thrust followed by a slower exponential falling section back to baseline. Next they assume that the thermal signal will be a well-behaved double exponential starting exactly at the same time as the impulse signal, also as shown in idealized form in Fig. 5. An additional assumption made by the authors is that there are no other spurious effects which might be represented as additional curves in Fig.5. The simple addition of the amplitudes of the thermal and impulse signals produces the resulting superposition signal. This signal is used as a template against which the actual sensor signal is compared. By stretching the imagination, the sensor signal can be force-fit onto the idealized superposition signal and, voila, the simple analysis can proceed to extract the magnitude of the true impulse signal.

This method is applied to all the sensor signals except that in Fig. 10 showing the “split configuration”.

There are additional problems with this force-fitting routine. For example, in Fig. 7, which is analysed in some detail, the initial rising slope of the displacement sensor signal should be an asymptotically flattening exponential according to Fig. 5. But it is clearly an asymptotically rising signal, perhaps exponential in shape. About half-way through the RF power application period, this rising slope suddenly breaks into a markedly linear (rising) slope. According to Fig. 5, this part of the signal should show an asymptotically decreasing (flattening) exponential slope, definitely not a linear slope. The authors even use linear curve fitting in this region, evidence that even they do not consider this part of the slope exponential. All the optical displacement signals shown in the other relevant figures (Figs. 13, 16) show this characteristic as well.

Then a sleight-of-hand is used to tease out the contributions of the assumed thermal vs the impulsive signal. According to pg. 11, “the characteristics of the curve [superposition curve in Fig. 5] after this discontinuity [the break in slope of the rising exponential due to the onset of steady thrust] are used as the baseline to be shifted down so that the line projects back to the “origin” or moment when RF power is activated.” The amount of this baseline shift is taken to represent the “true” impulse signal. Naturally, this assumes that the onset of thrust (and the thermal signal) are all coincident exactly with the application of RF power (and are all of the ideal shape according to Fig. 5). According to Fig. 7, it also assumes that a straight line can be used as this “baseline shift” rather than the more likely broken exponential shaped line depicted in Fig. 5. This has the added bonus of arbitrarily increasing the “calculated” impulsive thrust.

Pg. 13 introduces a “Slope Filtering: Alternate Approach” to the force-fitting approach discussed above whereby the time derivative of the displacement sensor signal is plotted. This procedure produces a curve of magnitudes of slopes (Fig. 9). Sadly, this method starts off with the same assumptions as in the above approach. It compounds these problems by invoking an arcane procedure whereby the parts of the original displacement sensor curve with slopes lower a particular arbitrary (and unstated) value are removed and what’s left of the curve allegedly represents the “true” impulse curve. None of this procedure is shown in detail and only the final result is shown which, conveniently for the authors, is within ~20% of the previous analysis method. Of course, this convenient coincidence is entirely dependent on the arbitrary slope magnitude removal value.

9. Split Configuration

On pg. 15 we learn that by splitting the test article from the rest of the electronics – one on each end of the balance arm, the response time is reduced as expected due to the reduction in ballast weight required, and that the “true” thrust amplitude has been reduced from 106 uN to 63 uN, all other things being equal! Additionally, the displacement sensor curve (Fig. 10) is completely different in shape from the non-split configuration tests. The only explanation proffered for this discrepancy is that “the thermal contribution…is smaller in magnitude compared to the impulsive signal.” No proof of the correctness of this statement is provided. Since the split and non-split configuration curves are so radically different, the authors chose not to apply either of the analysis methods discussed above. They arbitrarily take the amplitude of the displacement signal at the instant it starts an exponentially asymptotic downward slope as the correct point. Why not use a variant of this method and apply it to the non-split configuration? Because it would result in relatively and apparently unacceptably huge (eg ~260 uN at 60 W) thrusts!

10. Difference between Forward and Reverse Thrusts

Tables 2 and 3 allow us to compare “calculated” thrusts (using the ideal curve force-fitting method discussed above) from Forward and Reverse non-split configurations. The Reverse thrusts are consistently lower than their Forward thrust counterparts. For example for 60 W, average Forward thrusts are 108 uN vs 60 uN for Reverse thrusts. For 80 W, these numbers are 104 uN vs 71 uN. No explanation is given for these differences, nor for the fact that in the Forward configuration, the 80 W thrust is lower than the 60 W thrust.

11. Null Thrust Test

It is stated on pg. 23 that “The [COG] shift from thermal expansion causes a downward drift in the optical displacement sensor.” Why not an upward drift? There is no justification given for this statement as no control tests were performed to ascertain what the result of a purely thermal effect might be, expansion or otherwise.

Further, the authors state “The results from the null thrust testing show no impulsive element…only the thermal signal.” This is also an unproven statement since no purely impulsive or purely thermal signal has been positively identified in shape or amplitude. The authors appear to have forgotten the thermal curve they used in Fig. 5, namely a double exponential. There is no evidence for any exponential part of the supposedly “thermal only” curve of the Null Test in Fig. 18. It appears completely linear and if there is a slight hint of an exponential, it is in the wrong sense (asymptotically falling, not flattening)! Another hint as to the problem of assigning a purely thermal explanation of the curve in Fig. 18 is the fact that exactly at the time of shutting off the RF power, there is no thermal lag or overshoot: the linear slope breaks suddenly to become essentially flat.

The implication of the Null Thrust test is that the thermal signal apparently seen in the Null Test would be the same as that seen in the Forward and Reverse tests. If so, then the curve force-fitting routine discussed above is invalid as it assumes a double exponential thermal curve (Fig. 5).

The Null Thrust test depicted in Fig. 18 was run at 80 W RF power. The Reverse Thrust test in Fig. 16 run at 80 W shows an apparent thermal signal of approx. 70 uN using the force-fitting routine. For the same period, the Null Thrust test shows an apparent thermal signal of approx. 275 uN. This is a huge discrepancy begging for detailed explanation.

Conclusion

In addition to mechanical and related considerations, the authors’ methods of analysis of sensor data to derive thrusts rests on untenable grounds. Not only is there an assumption of the presence of only a “true” impulse signal as well as a thermal signal, there is an assumption that the observed signal can be broken down into just these 2 components and amplitudes can be calculated based on an idealized superposition assumption. Therefore, until more control tests are performed allowing a more accurate method for estimation of thrusts, no faith can be placed in the thrust magnitudes reported in the paper.

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{ 37 comments… read them below or add one }

Ron S January 3, 2017 at 11:05

Thank you for this analysis. With my superficial reading of the paper I could not reconcile the plotted results with their explanations, or find consistency throughout the methodology. I read this article in conjunction with the paper, and it was enlightening.

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David Van Buren January 3, 2017 at 12:18

Hi Paul. I read the EM Drive paper when it came out a few months ago.
My take-aways are:

1) The apparatus does not measure what they intend to produce, namely
a torque. Instead it measures the deflection of an optic on the arm
holding the drive. It would be better to measure the torsional strain
in the suspending fiber. Then they could relate the torque to the
thrust. In the current setup where the deflection of the optic is
measured, there are too many potentially confounding effects.

2) The deflections measured do not have the temporal behavior of a
thrust signal.

3) Torsion pendulum experiments are most sensitive when operated at
the natural frequency of the pendulum. But the experiment was not
designed that way.

4) The data are not sufficiently systematic with respect to the
reported error bars, indicating that there are large uncontrolled
effects that dominate the signal but have not been taken into account.

5) My suggestion for a better experiment would be to construct an
error budget and engineer an apparatus that will satisfy it. This is
the way physics experiments are usually conducted.

It is not needed that others attempt to replicate. First the
experimenters ought to demonstrate a signal that exceeds the noise in
the apparatus. But they claim that they haven’t ruled out all
confounding effects. Until then…

Again, thanks for your site. It is one of my favorites. Happy New
Year! — Dave Van Buren

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Marshall Eubanks January 3, 2017 at 13:01

This, to me, seems fairly typical for the ongoing review of a fairly tough experiment. It is not proper to claim success, the experiment and analysis need to be improved, but maybe in a few more iterations we can get to a point where we can begin to have confidence in the results.

Now, whether White will get the support to make these improvements is another matter, but I personally think that he (or another group) should.

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Charlie January 3, 2017 at 17:36

Quite an interesting discussion, both on today’s and the preceding days paper on this particular subject. I was especially struck by the comment that an individual, Bart, made because it was a concise statement (at least more concise than I could’ve made it on my own) concerning the particular reaction forces that would arise presumably from this particular type of mechanism (I quote thusly):

“The power being applied is fairly large, and the measured thrust comparatively small. Might it be possible that the application of such high power is causing ions to be ejected from the surface of the device at high velocity, and due to its shape, there is an asymmetry producing a net thrust? Then, it would become an ordinary action-reaction device, with the casing playing the role of a fuel rod in a more conventional such device.”

I have a link which I’ll provide below, which comes from the inventor of this particular drive in which he describes his work in a YouTube video for anybody who wishes to watch it concerning the physics. As for myself, I’m on the fence concerning this particular phenomenon, however, I wasn’t as aware as of the particulars difficulties of which there are many in experimentally determining whether there’s anything to the all of this. It would seem that a far more concerted effort should be made to permit a teasing out of whether or not this is even a phenomenon worth pursuing or not.
One thing that I would note right off the top of my head is the fact that this is a enclosed container essentially like a microwave oven, producing many hundreds if not thousands of watts of power and it would be reasonable to assume that such a container would be consistently warmer than its surroundings – as all objects are when they are above absolute zero. Thus the results obtained by the Chinese which presumably placed a similar device on one of their satellites could be accounted for by nothing but a weak photon emission from the heated chamber. In other words, they would have created nothing less than a limp photon rocket, which could be because of design be somewhat unfocused, but might be interpreted as a positive thrust phenomenon.

There is probably a lot a phenomenon which would need to be teased out and I would say that Mister Mills comments stating that far more money should be thrown at this problem suffers twofold from the fact that usually people with money won’t throw funds at a problem unless they obtain far better results, to justify their expenditures, and usually people who are charged with obtaining results don’t have sufficient monies to obtain better results so they can obtain more funds. The classical Catch-22 that we are all familiar with.
As Bart said so eloquently above, my thinking was that there was an asymmetrical affect of the electromagnetic waves bouncing off a larger and of the cavity, than off the smaller end. Specifically, I wondered whether or not the EM radiation would at the larger and be absorbed differently by the container walls, then they would be at the smaller end and that there would be a more or less difference in coupling between the container walls and the electromagnetic wave. If such a difference in coupling between the container walls was maintained between both ends of the cavity, then perhaps that alone might be sufficient enough to create a Delta thrust. But that is pure speculation here.

In the video that I have providing a link to, Shawyer makes a considerable point of emphasis on what he calls the “group velocity” behind the electromagnetic waves as they oscillate within the cavity. Now I have heard the term before, group velocity, however I don’t know the detailed physical description of what a group velocity is so I’m at a loss here to comment further. But the point in fact is that his explanation in no ways suggest a non-validation of the standard physical laws can be found as an explanation for how his system works, and I firmly come down on the side of retention of current physical laws, no matter what is being discussed; if we throw out the current application of physical laws we will have chaos. That’s not meant to say that there could not be other physical laws that we don’t know about, but let’s not get ahead of ourselves and assume that the laws that have served us so well for 300 plus years are in any way invalid simply because we see something we don’t understand.

I finally like to have a say concerning Woodward’s conception of his particular Mach inertial drive. I’ve read Woodward’s book that describes his work on this particular system and I have to say that I am totally unconvinced that he has a valid theoretical argument for why the operation of this thing will work. I’m especially dubious of the idea that a vibrating masses should send out both Advanced and Retarded waves that movement in the past and the future such that they completely synchronize to create JUST AT THE RIGHT MOMENT effects through the space-time continuum that would justify a push back on his apparatus. Boulder Dash!
That just smacks too much of I needed a explanation for why it works (if indeed the works), and so I’ll grab upon this idea of using Einstein’s theory to explain inertial forces without resorting to instantaneous action at a distance to explain why my apparatus supposedly works. I would suggest that both types of drives be launched into space by the United States and tested independently to see if there’s anything to either of them. Obviously it’s a expensive proposition to resort to, to find out the truth, but at least it should provide answers as to whether or not there’s anything to any of this or not.

Here is the link to the YouTube video below behind Shawyer’s explanation of the EM drive that we have been discussing forth with:

https://www.youtube.com/watch?v=wBtk6xWDrwY

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Robert G January 3, 2017 at 19:56

A correctly done experiment with a torsion balance would give us the proof of it, with the added ability to tinker with the setup in a hands-on way. Why burn rocket fuel to do what some careful labwork can do on Earth?

Once a proper lab setup and procedure are established, the team behind it could crank out lots of results playing with the parameters, sausage-machine fashion. First thing is to get the essential rig and sums right and gain some confidence from other workers in the field.

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Moebius January 5, 2017 at 9:34

Sending ill-designed things into space just to see what happens although we are unsure if they really work is very Kerbal-style. I like the idea but it is probably not the most efficient way to do science in the real world.

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Brett Bellmore January 3, 2017 at 18:33

My thought on this is that torsion pendulums in vacuum are inherently very high “Q” devices, and high “Q” suggests exploiting resonance.

I’d build the test article in a balanced, air tight Faraday cage, lacking any asymmetric external features such as might be expected to produce torque. Include batteries, and a very small optical port to control the system optically, and you eliminate contacts, and likely almost all classical electromagnetic effects.

You’d try to make the thermal response time of the system several times the resonant period of the pendulum, and then turn it off and on at the resonant frequency. Any thermal effects you did get would produce a fixed angular displacement, while the “thrust”, if any, would drive the resonant mode, and so be easily distinguished.

And with the high Q it would be a very sensitive test.

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Paul Titze January 3, 2017 at 18:43

Reminds me of the Pioneer anomaly, people came up with all kinds of new Physics models to explain the unknown acceleration without thoroughly looking at other reasons first…

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Sanford Zane Meschkow January 3, 2017 at 23:51

For those of you old enough to remember the Dean Drive, at least this gadget seems to be getting a much better examination than the Dean Drive did — but then, the Dean Drive was not so subtle and easier to be revealed as a no-show. All those whirling weights might have been fun to experiment with and might make a nice curiosity to stand on one’s mantle.

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Jeremy Alessi January 4, 2017 at 0:13

I’ve been very interested in the EmDrive since it became clickbait in recent months. I’m primarily a game developer and shared a simple visualization/simulation with some other interested folks. It made for a fun debate.

Basically, it does appear that the shape of the tapered cone would result in an asymmetric application of force. That said, I know very little about particle physics. I Googled a few values to plug-in as constants and also accounted for lower than lightspeed collisions as velocity builds for any surface normals that are not facing up. There is no accounting for heat yet.

Please share any thoughts.

http://www.midnightstatus.com/emdrive

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Brett Bellmore January 4, 2017 at 11:21

“Basically, it does appear that the shape of the tapered cone would result in an asymmetric application of force. ”

Actually, if you’ve got any exposure to physics, the idea that the shape of a closed cavity could have any effect on forces produced by a standing EM wave inside of it is amazingly counter-intuitive. It’s like expecting a closed bottle of Coke to go flying off because one end is flat, and the other tapered. The shape of the cavity basically doesn’t matter, because the taper exactly makes up for the difference in area between the ends.

All these forces are “conservative”, they add up to zero no matter the shape of the box, as long as nothing is leaving the box.

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Jeremy Alessi January 4, 2017 at 13:54

Yeah, why don’t the forces cancel out in the sim?

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Stanley Winford January 8, 2017 at 6:04

A few possible reasons:

1. You said “velocity builds for any surface normals that are not facing up”. This is not possible. If a particle collides with an immovable wall without energy loss, the particle’s speed should never change.

2. How do you calculate the thrust, and why does it often go up when the ball is in free flight?

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Marshall Eubanks January 4, 2017 at 12:25

This has risen far enough to begin to bring the theorists out:

Revaluation of Mbelek and Lachièze-Rey scalar tensor theory of gravitation to explain the measured forces in asymmetric resonant cavities.

https://arxiv.org/abs/1701.00454

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Marshall Eubanks January 4, 2017 at 12:28

I have looked, and cannot find any account of how the Mbelek and Lachièze-Rey scalar tensor theory of gravity (and electromagnetism) fares under the classical solar system tests of gravity and Lorentz invariance (which severely constrain both scalar tensor theories and modifications to E&M). Without that, it is frankly hard to take it very seriously.

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Mark T. January 4, 2017 at 13:45

“no faith can be placed in the thrust magnitudes reported in the paper”

Completely agree and you made a solid case for this conclusion, but I will go you one better. If you review the entire history of EM drive and the ridiculous explanations for how it works, the most likely conclusion is that EM drive is a fraud.

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Charlie January 4, 2017 at 13:53

@Brett Bellmore

“Actually, if you’ve got any exposure to physics, the idea that the shape of a closed cavity could have any effect on forces produced by a standing EM wave inside of it is amazingly counter-intuitive. It’s like expecting a closed bottle of Coke to go flying off because one end is flat, and the other tapered. The shape of the cavity basically doesn’t matter, because the taper exactly makes up for the difference in area between the ends. ”

Actually, it’s counter, counter-intuitive; the expectation that a bottle of Coke would fly off into space would be expected not to happen for the simple reason that neutral gas particles is not the same thing as pure EM radiation.
These electromagnetic waves are allowed to impinge against metallic enclosure walls and it’s possible, JUST POSSIBLE that it may be asymmetrical in force simply because of the fact that the absorption of one EM radiation wave on one metallic conducting wall COULD be different at one wall surface than the other (i.e. different wave intensities, at each wall surfaces).

Thus, it’s because of this asymmetrical shaping that it’s conceivable thrust could be produced. Plus energy is always been constantly pumped in-it’s reasonable it would have to be absorbed at both ends of the cavity. This might be the reason why such a configuration may produce a Delta thrust. This is been my thinking from the beginning and as I pointed out above, if you watch the video associated with the link provided previously by myself mentioned above, he speaks about group velocity being different as the electromagnetic wave reflects back and forth. I don’t know anything about group velocity, so I can’t say anything to that. But I suggest you watch the video

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Ron S January 4, 2017 at 14:24

“I don’t know anything about group velocity”

Consider this a learning opportunity.

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Andrew Palfreyman January 4, 2017 at 20:15

George – you’ve outdone yourself this time. Kudos!

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Charley January 5, 2017 at 17:21

Scalar Tensor Theory of gravitation to explain EMDrive

Arxiv – Revaluation of Mbelek and Lachièze-Rey scalar tensor theory of gravitation to explain the measured forces in asymmetric resonant cavities

EMDrives are claimed to be propellentless space propulsion systems. If propellentless propulsion is possible it could enable fast human travel throughout the solar system and possible interstellar missions.

The scalar-tensor theory of gravitation proposed by Mbelek and Lachièze-Rey has been shown to lead to a possible explanation of the forces measured in asymmetric resonant microwave cavities. However, in the derivation of the equations from the action principle some inconsistencies were observed, like the need no to vary the electromagnetic invariant in a scalar source term. Also, the forces obtained were too high, in view of reconsideration of the experiments originally reported and of newly published results. In the present work the equations are re-derived using the full variation of the action, and also the constant of the theory re-evaluated employing the condition that no anomalous gravitational effects are produced by the earth’s magnetic field. It is shown that the equations originally employed were correct, and that the newly evaluated constant gives the correct magnitude for the forces recently reported

The scalar-tensor (ST) gravitational theory of Mbelek and Lachièze-Rey (MLR), allows electromagnetic (EM) fields to modify the space-time metric far more strongly than predicted by General Relativity and standard ST theories.
The theory was applied in cosmological and galactic contexts, and it was used to explain the discordant measurements of Newton gravitational constant as due to the effect of the earth’s magnetic field. It was further shown that a ST theory of the MLR type could explain the unusual forces on asymmetric resonant cavities reported at that time. However, in the derivation of the equations from the action principle some inconsistencies were observed, and also the forces obtained, after reconsideration of the experiments originally reported and new results were too high. In the present work the equations are re-derived using the full variation of the action, and the constant of the theory re-evaluated with the consideration that no anomalous gravitational effects are produced by the earth’s magnetic field. It is shown that the originally employed equations were correct, and that employing the new evaluated constant a correct magnitude for the forces reported recently is obtained.

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Swage January 6, 2017 at 8:02

The physics are beyond me. That being said EMdrives have a long history of being not feasible. Yes, such a device would be great. Unfortunately our current understanding of physics excludes oprational principles for such devices. That being said, it would be foolish to assume we know everything at this (in fact: any) point. All in all a good deal of scepticism and scrunity seems more than justified in my opinion.

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Alex Tolley January 6, 2017 at 12:27

Just bear in mind that Shawyer’s design was based on some interpretation of EM radiation that was “debunked”. At this point people are thrashing around looking for an explanation that is viable, assuming there is an effect.

But why should that particular design work with other physics? Just by chance he stumbled on some effect that worked with a design for some other effect?

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Larry Kennedy January 6, 2017 at 14:32

We don’t have to guess whether we understand everything. We know we don’t have complete explanations for the Universe we observe. Having said that, I share your skepticism on this particular subject.

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torque_xtr January 9, 2017 at 3:58

Been frequently asked by people who “wants to believe”, thought about possible more rigorous experiment setups and came up with different setting. First, the requirements:

1) eliminate ponderomotive forces as much as possible
-from power cables
-from reflections and standing microwaves outside the resonator, but inside the test chamber
-from magnetic fields, if it is possible!

2) damping and measurement phases should be properly separated, to more precisely extract the thrust pattern. Also this could help to evaluate the thrust from outgassing.

3) make the suspension and measurements as simple as possible for the photon and addutional thrusts to be firmly detectable and measureable with the given power levels.

It calls for a radio-controlled test article with on-board accumulators, suspended on a pair of quartz fibers in a vacuum chamber with dielectric walls. If the article assembly weighs 10 kgs and consumes 900 Watts of power, the characteristic photon acceleration is 3e-7 m/s2 (30 nano-g). With 2 m-long suspension it corresponds to 6 nm displacement, easily measurable with low-power multi-pass laser interferometers.

The initial damping is active and achieved by air-core electromagnets onboard of test article and inside the vacuum chamber. First, the chamber is evacuated, position measurement system is activated and damping is conducted. Then the damping system is switched off, the residual motion pattern is recorded, and the test article is powered up. The motion pattern is again recorded, and thrust is evaluated. If it measurably differs from zero, but falls within photon limit, then the outgoing electromagnetic radiation pattern needs to be measured to see if it explains the thrust, even after the thermal thrust from substitute “heat model” article is subtracted, and also “ion wind” thrust needs to be somehow evaluated (one fo the comments here) After the initial measurements, the test article could be reoriented on the suspension, so the thrust vector points in the direction of swinging motion, and the measurements could be conducted with the test article powered up periodically in the resonance with the swinging frequency (another comment here also suggests this)

If the test article is equipped with 2 kg of lithium accumulators, and weighs 10 kg total, around 400 Wh of stored energy is available, corresponding to ~20 minutes of powered-up mode, 0.005 N*s of photon thrust and 0.5 mm/s of pure-photon delta-V available, pretty enough for precise measurements. The additional forces from interferometer position sensors are small compared to photon the thrust, especially if mirrors are symmetrically arranged, and air-core electromagnetic damping excludes residual forces when damping is switched off.

With some modifications, all magnetic forces inside the setup could be eliminated. The power convertors contain ferromagnetic materials, and magnetron itself contains a strong magnetic system which reacts to Earth’s magnetic field, possibly differently when powered on and off (!, has it ever been considered?!), but if it is replaced by Gunn diode and the onboard power convertors are based on switched capacitors, all magnetic forces could be very much reduced. (also enabling much more compact experimental setup)

Extraordinary claims need extraordinary evidence!

If I’ll see a peer-reviewed paper describing the results of an experiment similar to that, with the thrust after all subtractions compareable to or exceeding the photon limit, I’ll start to consider something weird is going on :-)

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Robert January 9, 2017 at 12:26

This analysis and the comments are about what I expected from this group. I think the EmDrive paradigm offends the vision of many CD readers. Keep in mind that there is a lot of data beyond the NASA paper which is one of the weakest sets of data. I think much has not been publicly released yet. I hear the Chinease are actually conducting orbital tests. Finally, when the author of this review accused the NASA authors of confirmation bias, a personal attack against their competence and credibility, I can only conclude that this review is entirly discredited.

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Ron S January 9, 2017 at 14:11

All you have is “secret” evidence, rumor, innuendo and ad hominem attacks? Impressive.

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Robert January 10, 2017 at 13:27

Published evidence. It’s not my problem if most people ignore it. Mr. Hathaway that attacked the NASA authors competence and it discredits the review in my mind. I have to ask myself do I trust the original authors more that Mr. Hathaway or less. Since they did the real work while Mr. Hathaway just critiqued it, that lends weight to the original paper. It’s entirely too easy for critics to invent long lists of issues or problems without real evidence these are real issues in the experiment under review.

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Ron S January 10, 2017 at 15:44

Yet you find no flaw in that critique. Perhaps that is why you resort to ad hominem and flail at trying to shift the burden of proof. As you may have noticed you are not alone in taking this approach. That tells me quite a lot.

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Robert January 11, 2017 at 14:31

Do you not see that when the author claims the NASA authors are the victims of ‘confirmation bias’ he is very strongly attacking their competence? He would he know such a thing? It’s an opinion.

And what I fail to see is how you can possible consider anything I said as an ad hominem attack just because I don’t buy his arguments or equate them to the original work. I don’t have to challenge each statement. The burden of proof of his argument is his alone. The redeeming value of this review is that the author at least called for continued testing of the EmDrive concept.

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Ron S January 11, 2017 at 22:34

Confirmation bias? Indeed. He explained with reference to the paper’s content. Label it what you will the critique is accurate in this regard.

“It’s entirely too easy for critics to invent long lists of issues or problems without real evidence these are real issues in the experiment under review.”

You either didn’t read the critique or you are trying to dismiss it without addressing its specific points. You try to “discredit” the review without addressing a single technical point in the critique and instead attack the reviewer. That’s ad hominem.

We’re going in circles. Feel free to have the last word.

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jlandau January 12, 2017 at 10:39

“You either didn’t read the critique or you are trying to dismiss it without addressing its specific points. You try to “discredit” the review without addressing a single technical point in the critique and instead attack the reviewer. That’s ad hominem.”

Exactly so. I count 11 specific and highly detailed points in Hathaway’s review, none of which have been addressed in Robert’s criticism.

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Robert January 12, 2017 at 14:57

I’ll address a few points but I not claiming to be an expert. My main argument is the way Hathaway reviews the NASA paper not that he is skeptical. I’m fine with being skeptical at this point.

“1. Null Test Orientation

Tests were performed in both the “Forward” and “Reverse” direction as well as in a “Null” direction where the alleged force vector pointed towards the rotational axis of the balance (pg 23). Apparently no Null tests were performed with the force vector pointing away from the balance axis nor were any tests performed with the “test article” force vector pointing up or down. These additional orientations would have provided much needed control data given the magnitude of the allegedly purely thermal signal seen in their “Null” test.

In addition, the Forward and Reverse tests should also have been performed by just re-orienting the test article whilst keeping all other rotating components untouched. In this type of control experiment, the spurious effect of the rest of the components is largely eliminated.”

>> Apparently? Hathaway doesn’t know? Is Hathaway the expert on EmDrive experiments? Did Hathaway talk to the NASA team to clarify anything? Apparently not but why not? It would have been very useful to call up Paul March or Sonny White and have a discussion regarding these issue.

“3. Flexural Bearings

There is no information presented to indicate whether the linear flexure bearings were operating within the manufacturer’s axial loading specification, especially when additional ballast weight was required for the non-“split configuration” tests. It would also have been useful to see data on the natural frequency of the balance when loaded with the equivalent weights used in the thrust tests, given the damping method described. Also missing is an explanation of why none of the traces of the optical displacement sensor return to starting baseline after the calibration and “thrust” pulses. There seems to be an inherent bearing stiction problem preventing the balance from returning to its original baseline after a test. This is not due to general balance drift and is typical for overloaded bearings of this type. Long-term balance stability/drift plots would be useful.”

>>After complaining about the lack of information, the author seems confident jumping to a conclusion! It’s stiction! No numbers to even suggest stiction might account for the recorded data and trends. It’s all a vague assertion. Not even a back of the envelope calculation.

“4. Electrostatic Calibrator

Evidently the calibration of the electrostatic “fin” method of applying calibration pulses was performed using an electronic balance (Scientech SA-210). Unfortunately no data was provided to show exactly how this calibration was performed. In particular, no data was provided to show that there was no electrostatic interaction between the high-voltage calibration voltages and the operation of the balance. Since the Scientech balance properly reports vertical forces only, was care taken to translate these vertical forces into the horizontal calibration forces required by the thrust balance? It would have been useful for the authors to have employed a second, independent horizontal force calibration to verify the Scientech method such as a strain gauge-type force gauge with interpolation.”

>>>Evidently? “Fin”? “No data….” So, Hathaway is not sure! Not showing calibration data does not equate to inferior calibration. Hathaway should have discussed this with the authors first. Now Hathaway suggests a vague electrostatic interaction. What happened to stiction? One wonders how any science can ever be done. This seems like the kinds of arguments which are mainly used to justify apriori doubt about an experiment. Mud throwing. Hathaway should at least show a back of the envelope calculation to show feasibility that such an interaction might occur and that is is of the proper magnitude and direction to possibly be confused as the primary signal.

“5. Vacuum System

“The authors note that although turbomolecular pumps were used to evacuate the vacuum chamber, they caused no artificial vibrational signals. Turbo pumps require mechanical backing pumps to evacuate them to atmosphere. These mechanical pumps are connected to the turbo pumps typically via thick and stiff vacuum hoses. These hoses can transmit backing pump vibrations to the turbo pumps which are usually rigidly connected to the vacuum chamber. Was this source of vibration taken into account as well?

>> Here the author again fundamentally questions the competence of the NASA researchers without any evidence. Did he bother to call them up and discuss it before he wrote this? If not, why not? If the author wants to assert such potential vibrations as an alternate source of signal, did he calculate the effect? Since he is familiar with turbo pumps that should be straightforward. Would the turbo pump vibration be consistent with a signal primarily in one direction? Hathaway should put some numbers to this if instead of just throwing it at the NASA team.

“Additionally, no evidence is provided to show how the interior of the test article was evacuated coincidentally with the chamber evacuation. This is a different concern to that stated in the paper (pp 27, 28) regarding outgassing of the dielectric. The concern here is that if the test article cannot be fully evacuated coincidentally with the chamber evacuation, residual gas inside the test article can possibly escape during the time of a test, causing spurious force signals. Moreover, if the test article is rather well-sealed, the shell of the test article, especially the end plates, could expand upon evacuation of the chamber due to air trapped inside prior to chamber pump-down. This would alter the center of gravity (COG) of the balance causing a spurious signal, especially if the trapped air is heated upon application of RF power of tens of watts.”

>> Again, vague spurious forces are invoked. No effort to correlate the potential magnitude of such forces and compare them to the signal, or the directionality or probability they would mimic what the EmDrive is thought to do. Hathaway throws out vague spurious forces from test article out gassing with no actual data that it would be in the same order. Hathaway also makes assumptions about the timing of the running of the experiment as compared to out gassing. Did he bother to ask the NASA team? Numbers and direction from potential out gassing must be included for it to be an effective criticism beyond mud throwing.

“8. Confirmation Bias in Thrust Analysis

“The entire edifice of the analysis of the signals from the optical displacement sensor rests on the assumption of the correctness and correct application of Fig. 5 to the present test situation. Fig. 5 shows an ad-hoc superposition of two assumed signals, namely a thermal signal and a pulse (impulse) signal. This is presented initially as a “conceptual simulation” and is reasonable in its own right. However, it then takes on the value of an accepted fact throughout the rest of the paper. Fig. 5 represents what the authors expect to see in the signal from the optical displacement sensor. When they see signals from this sensor which vaguely look like the expected superposition signal as represented in Fig 5, they assume that Fig 5 must actually represent what is going on in their system under test. This is a clear inductive reasoning fallacy called Confirmation Bias. This problem leads to baseless assumptions about the timing of the onset of expected effects after application of the stimulus (RF power), their proper shapes, and the joint amplitudes and thus the individual (impulse vs thermal) magnitudes.”

>> What they did is reasonable and the fact that it seems to correlate well gives a measure of confidence. They applied theoretical numbers to the data which Hathaway avoids. The Confirmation Bias argument is a very big stretch. Many papers discussed in this group follow similar techniques analyzing various types of astronomical data against assumed models. Now, Hathaway demands every conceivable pulse shape and magnitude, probably impossible to get.

“In particular, the authors assume that the “true” impulse signal from the test article will look just like the assumed signal shown in Fig. 5, namely that it will look just like their calibration signal. This will include an initial fast-rising but well-behaved exponential slope up to a flat-topped constant thrust followed by a slower exponential falling section back to baseline. Next they assume that the thermal signal will be a well-behaved double exponential starting exactly at the same time as the impulse signal, also as shown in idealized form in Fig. 5. An additional assumption made by the authors is that there are no other spurious effects which might be represented as additional curves in Fig.5. The simple addition of the amplitudes of the thermal and impulse signals produces the resulting superposition signal. This signal is used as a template against which the actual sensor signal is compared. By stretching the imagination, the sensor signal can be force-fit onto the idealized superposition signal and, voila, the simple analysis can proceed to extract the magnitude of the true impulse signal.”

>> Well, at least they are doing some science! This review is anything but science. Now Hathaway accuses the authors of using their imaginations which is highly insulting. What the authors did is again a reasonable thing. It’s done all the time is science.

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jlandau January 12, 2017 at 16:46

Thank you. This helps to clarify where you’re coming from.

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Robert January 13, 2017 at 15:12

You are welcome!

Ron S January 13, 2017 at 12:33

Robert, so much to respond to and so little time. Plus I promised to say no more. Only after which you finally provided the detail of your objections!

Rather than a point by point response, which might only obfuscate the essence of the matter, I’ll save myself some time and merely link to someone who says it better than I ever could. It especially echoes Hathaway’s critique. The paper by White et al fits like a glove.

While the description by Hall specifically targets medical science it is applicable to any scientific endeavor.

http://skepdic.com/toothfairyscience.html

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Robert January 13, 2017 at 15:11

Thanks. I also follow a forum some here may be interested in where EmDrive is discussed by experts, builders, enthusiasts as well as skeptics. So it’s a balanced discussion. One of the NASA paper authors, Paul March, occasionally answers questions.

http://forum.nasaspaceflight.com/index.php?topic=41732.0

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Mark Zambelli January 19, 2017 at 12:20

Thankyou Ron :)

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