EM Drive Tested By NASA: Lets Not Get Too Excited Just Yet

May 6th, 2015
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A big news story has been making the rounds about a new and potentially game changing space propulsion technology, which was recently tested by NASA scientists in a vacuum chamber at the Manned Space Flight Center in Houston Texas.  The system, called the EM Drive, is based on microwaves bouncing around a specially shaped cavity.  These aledgedly create thrust, thus making it possible for the EM drive to be used as a propulsion system, if attached to a spacecraft.

What  makes the EM drive so much different than any previous propulsion technology is that it does so without expelling any propellant.  All existing rocket engines use some kind of material, known as reaction mass, in order to produce thrust.  Even highly efficient ion engines require a gas of some sort to be used as the reactionary mass.  The need for propellant is a major limiting factor in spaceflight.  It means that propellant must be launched with the spacecraft, often constituting a large percentage of the spacecraft’s mass.  It also limits the duration of the spaceflight.  Eventually the propellant runs out.  However, the EM drive uses only energy, which can be provided almost without limits by solar panels or a nuclear power source, which could provide energy for decades.emdrive

The only problem with this is that the whole concept seems to violate the law of conservation of momentum.  Our current understanding of physics would seem to indicate that this is impossible.  You can’t add momentum to something without pushing off of something else.  Every action has an equal and opposite reaction, and that’s why rockets need to shoot propellant in one direction to go in the other.

Via IO9:

New Test Suggests NASA’s “Impossible” EM Drive Will Work In Space
[T]he EM Drive’s thrust was due to the Quantum Vacuum (the quantum state with the lowest possible energy) behaving like propellant ions behave in a MagnetoHydroDynamics drive (a method electrifying propellant and then directing it with magnetic fields to push a spacecraft in the opposite direction) for spacecraft propulsion.
Last year, NASA’s advanced propulsion research wing made headlines by announcing the successful test of a physics-defying electromagnetic drive, or EM drive. Now, this futuristic engine, which could in theory propel objects to near-relativistic speeds, has been shown to work inside a space-like vacuum.

NASA Eagleworks made the announcement quite unassumingly via NASASpaceFlight.com. There’s also a major discussion going on about the engine and the physics that drives it at the site’s forum.


The EM drive is controversial in that it appears to violate conventional physics and the law of conservation of momentum; the engine, invented by British scientist Roger Sawyer, converts electric power to thrust without the need for any propellant by bouncing microwaves within a closed container. So, with no expulsion of propellant, there’s nothing to balance the change in the spacecraft’s momentum during acceleration. Hence the skepticism. But as stated by NASA Eagleworks scientist Harold White:

The trouble with this theory, however, is that it might not work in a closed vacuum. After last year’s tests of the engine, which weren’t performed in a vacuum, skeptics argued that the measured thrust was attributable to environmental conditions external to the drive, such as natural thermal convection currents arising from microwave heating.

The recent experiment, however, addressed this concern head-on, while also demonstrating the engine’s potential to work in space. (Image: NASA Eagleworks.)

For those who champion the EM drive, the new experiment is certainly a big step toward proving it can actually work. However, it’s only one step, and there are many that will need to be taken.

The fact that it seems to violate a basic law of physics does not mean that it is necessarily impossible. In science, nothing, not even the most well established theories are ever considered absolutely impossible to be wrong.  We do know that Newtonian physics has its limits and that relativity and quantum mechanics allow things to happen that regular Newtonian physics would not predict.  We also don’t necessarily have a full understanding of all that can happen as a result of quantum forces.

None the less, a claim this extraordinary requires extraordinary proof.  No experiment, no matter how apparently well designed and documented, offers enough evidence to come to the conclusion that something as amazing as the EM drive actually works.  What will be needed is for the experimental results to be replicated, by different teams, under different conditions and different scales and for the experimental setups to all be thoroughly examined to rule out any systematic errors or confounding factors.

But there is something more fundamentally wrong with this:

In the world of serious science, it’s never good enough to just provide a claim that an experiment confirms a hypothesis.  It’s never enough to just provide one basic measure of data.  The experiment and the results need to be thoroughly and properly documented and the data provided in full for examination and to allow the basic methodology to be examined.  This should be done in a peer reviewed journal.

Of course, peer review is not infallible.  There can still be errors, and it definitely can’t catch all the problems a study may have.  Regardless of how good the peer review is, something this earth shattering will still need confirmation.  But peer review is, none the less, the minimum standard to take scientific data seriously.  If it’s not peer reviewed, it’s about as reliable as something that your cousin’s friend’s neighbor says they remember overhearing at a cocktail party.  In other words, not very.

Not only was this data not formally reported in a peer reviewed study, it was reported in about the most informal and unverifiable way imaginable.  The data, not only being incomplete, but being posted on an internet form.  If there is a worse source of scientific data than a press release, this is it.

Personally, I would love to find out that the EM drive does work as claimed.  It would mean a new era in space exploration and would be one of the most revolutionary developments in space exploration since the first successful satellite launches.  However, wanting it to be true does not make it true.   If we can get a formal, peer reviewed paper on it, we can at least begin to consider the possibilities.  At minimum, it would give some solid data.  Until then, this really is little more than some unsubstantiated claims and speculation.


This entry was posted on Wednesday, May 6th, 2015 at 12:35 pm and is filed under Bad Science, Good Science, Misc, Space. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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19 Responses to “EM Drive Tested By NASA: Lets Not Get Too Excited Just Yet”

  1. 1
    DV82XL Says:

    I’m not betting the farm on this either, and even if this device is shown to produce net thrust, it will take a far more detailed explanation of how and why before I’ll be willing to accept that it is a violation of the law of conservation of momentum. Having said that it is good to remember that the conservation laws are not necessary scale invariant as they are commonly stated and like other apparent ‘violations’ of the Newtonian laws of motion may only indicate that there is a more complete explanation waiting to be found.


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  2. 2
    James Greenidge Says:

    Okay, I’m a rocket novice, but tell me if this would work — and you all heard it here first for the patent attorneys!! :) . Imagine we have a jar with a electromagnet plate on top and sitting on the bottom is a free steel ball. If I very powerfully magnetize the plate for a moment the steel ball “rams” upward, striking the plate — and in so imparts its momentum before dropping back, correct? Wouldn’t rapidly doing this create thrust “shoving” or ping-ponging the jar up off the ground and onward? If the plate were nuke powered are we looking at a “closed-propulsion” spacecraft? I dunno. Just looking for why it seems too good to be true.

    James Greenidge
    Queens NY


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  3. 3
    Russ Says:

            James Greenidge said:

    Okay, I’m a rocket novice, but tell me if this would work — and you all heard it here first for the patent attorneys!! :) . Imagine we have a jar with a electromagnet plate on top and sitting on the bottom is a free steel ball. If I very powerfully magnetize the plate for a moment the steel ball “rams” upward, striking the plate — and in so imparts its momentum before dropping back, correct? Wouldn’t rapidly doing this create thrust “shoving” or ping-ponging the jar up off the ground and onward? If the plate were nuke powered are we looking at a “closed-propulsion” spacecraft? I dunno. Just looking for why it seems too good to be true.

    James Greenidge
    Queens NY

    No, I don’t believe so. The ball is still within the system, so the net momentum is zero. It imparts some momentum to pat of the system and loses some in another part. When the ball drops off it goes back to equilibrium.

    You can make something shake back and forth by shoving a mass back and forth inside it, but to get it to keep going in one direction, you need to shoot it out and have it leave the system.

    I’m not sure if I made sense with my explanation, but I’m pretty sure it would not work.

    As for the above, we can hope, but I am not betting much on it either.

    My understanding is the thrust it has been producing is tiny and it’s so tiny that anything like convection or ions of air or something could explain it. Having it in a hard vacuum is a good start to showing this is not the case. If they can show it produces thrust in a vacuum, then that’s a major step toward showing it works. It could still be an error in the measurement.

    I understand that is what they did, and it did show thrust in a vacuum. My only problem with that is I just can’t bank much on that when it’s reported on an internet form. Formal report with peer review or it didn’t happen!


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  4. 4
    Gordon Says:

    As I understand it, NASA has not officially come out and confirmed this in any official capacity nor has the science been published in a proper journal. It is just what the individual researchers have stated personally. There are a lot of red flags there.


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  5. 5
    DV82XL Says:

    The smell of the Fleischmann–Pons cold fusion claims of twenty-five years ago is getting rather strong around this topic.


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  6. 6
    Paul Studier Says:

    The EM drive has big EM fields in this device which is in, presumably, a metal and glass vacuum chamber. It is very difficult to calculate all the forces between the device and chamber. I won’t believe it until someone does an experiment in space, far away from any metal objects.

    What forces have they measured? It must exceed the force of just beaming microwave photons out of the device in order to be interesting for space travel.


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  7. 7
    drbuzz0 Says:

            Paul Studier said:

    The EM drive has big EM fields in this device which is in, presumably, a metal and glass vacuum chamber. It is very difficult to calculate all the forces between the device and chamber. I won’t believe it until someone does an experiment in space, far away from any metal objects.

    What forces have they measured? It must exceed the force of just beaming microwave photons out of the device in order to be interesting for space travel.

    It’s small. Very small. More than would come from just photons, but it’s measured in micronewtons.

    You can probably find it online. I don’t remember exactly what it was, but I recall it was only a little bit higher than the minimum that could be reliably measured with the instruments they had.


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  8. 8
    Anon Says:

    From what I can tell this looks like an example of an engineer thinking a few physics classes (less than a quarter what a physics major takes and including almost no modern physics) somehow makes him a qualified physicist, it is a common malady among a minority of engineers. The results also seem to be rather close to the limit of sensitivity of their instruments and also appears to decrease every time a better experiment is conducted.

            DV82XL said:

    The smell of the Fleischmann–Pons cold fusion claims of twenty-five years ago is getting rather strong around this topic.

    Agree completely.


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  9. 9
    BMS Says:

            Anon said:

    From what I can tell this looks like an example of an engineer thinking a few physics classes (less than a quarter what a physics major takes and including almost no modern physics) somehow makes him a qualified physicist, it is a common malady among a minority of engineers.

    For the majority of engineers (that is, the ones who went through engineering school) that I know, physics ranks at the bottom of their favorite required classes.

    This is almost as bad as when professional physicists try to pretend to be engineers. Notice how many celebrity physicists are so enthusiastic about solar power.

    One of the worst cases of this are the high-energy physicists who are pushing the “accelerator driven reactor” designs for nuclear power. If there were ever a clearer case of Maslow’s hammer, I have yet to see it.


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  10. 10
    drbuzz0 Says:

            BMS said:

    For the majority of engineers (that is, the ones who went through engineering school) that I know, physics ranks at the bottom of their favorite required classes.

    I would say, with something as amazing and groundbreaking as a reactionless thruster, you should really consult some actual experts in physics before concluding you have discovered something. In fact, you should consult several. I’d even say, if you are a physicist, you should consult other physicists and get some second and third opinions on it.

    It helps avoid you looking like a fool in the end.


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  11. 11
    Ben Says:

    1. Reaction mass, not reactionary.

    2. All perpetual motion devices are based on the same underlying design flaw. You have a complicated calculation for where the energy or momentum goes, and on one side you make a simplifying assumption (“we can neglect this term”). Hey presto you put the two sides together and they are unequal – a tiny excess! That’s exactly what this device is doing (failed to make an exact calculation of the momentum transferred via the sloping sides versus the ends). An exact calculation would reveal that this was a waste of time and money.

    Of course electromagnetic radiation has momentum, so you can use e.g. light as a form of propulsion, in principle. In fact it is the most efficient way to convert energy to momentum, but the radiation has to leave the device in the other direction.


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  12. 12
    L.Long Says:

    1st…How is this drive powered? Lets say you are far from a sun, so an Atom reactor is needed. Battery is no good.
    Then just apply Newtons laws of motion and you get the velocity desired and the energy to get it.
    So at micronewtons its going to take a LLLLoooooonnnnnnggggg time to get the payload moving and later stopped, unless you use the crash-into-it method.
    So even if it works no one may be around to care.


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  13. 13
    BMS Says:

            Ben said:

    1. Reaction mass, not reactionary.

    That mass is reactionary — as in, “extremely conservative.” It absolutely insists on conserving momentum (and energy too). ;-)


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  14. 14
    DV82XL Says:

    These guys at Eagleworks have so little standing in the scientific community that, according to Eric Davis, a physicist at the Institute for Advanced Studies at Austin, no peer-reviewed journals will publish their papers and even arXiv, the open-access pre-print server, (the default goto in these cases) has reportedly turned away Eagleworks results. Hardly a ringing endorsement.


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  15. 15
    drbuzz0 Says:

            Ben said:

    1. Reaction mass, not reactionary.

    Sorry I don’t even know what I was thinking on that one. Corrected.

            Ben said:

    2. All perpetual motion devices are based on the same underlying design flaw. You have a complicated calculation for where the energy or momentum goes, and on one side you make a simplifying assumption (“we can neglect this term”). Hey presto you put the two sides together and they are unequal – a tiny excess! That’s exactly what this device is doing (failed to make an exact calculation of the momentum transferred via the sloping sides versus the ends). An exact calculation would reveal that this was a waste of time and money.

    Of course electromagnetic radiation has momentum, so you can use e.g. light as a form of propulsion, in principle. In fact it is the most efficient way to convert energy to momentum, but the radiation has to leave the device in the other direction.

    In this case, apparently, from some of the things I have read, they are not even claiming to have a full theoretical understanding of what is happening or have the calculations. They are claiming this based on actual experimental observations.

    Of course, experimental observations are enough to confirm something, even in the absence of an understanding of why it is so, but in this case, I believe the experimental data is, at best, questionable.

            L.Long said:

    Then just apply Newtons laws of motion and you get the velocity desired and the energy to get it.
    So at micronewtons its going to take a LLLLoooooonnnnnnggggg time to get the payload moving and later stopped, unless you use the crash-into-it method.
    So even if it works no one may be around to care.

    I *think* the presumption here is that this somehow could be scaled up


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  16. 16
    DV82XL Says:

            drbuzz0 said:

    I *think* the presumption here is that this somehow could be scaled up

    One would think, however some device that could provide even a small amount of thrust more or less indefinitely would still be useful as (over years) it could accelerate a ship to very near c. A number of postulated generation ships have been proposed that would do just that. Of course the ideal engine of this sort would produce a constant acceleration of 1G to create artificial gravity for the occupants.


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  17. 17
    Ben Says:

    Actually this has been reported before:

    https://en.wikipedia.org/wiki/EmDrive#Theory

    The most likely explanation for any observed force is an electromagnetic interaction with the surrounding equipment. For example at those frequencies, induced currents in nearby metallic objects could result in either an attractive or repulsive force depending on the distance (because of the phase). Alternatively there is the earth’s own magnetic field.


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  18. 18
    J Santos Says:

            DV82XL said:

    The smell of the Fleischmann–Pons cold fusion claims of twenty-five years ago is getting rather strong around this topic.

    I agree 100% That was one of the first things that came to mind for me. That and the incident last year about neutrinos traveling faster than the speed of light. Looks like a big oops on that!

    Even smart people make mistakes! If you have something that seems to be this groundbreaking, exercise some healthy skepticism, and it will likely save you some embarrassment in the end.


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  19. 19
    J Santos Says:

            drbuzz0 said:

    Sorry I don’t even know what I was thinking on that one. Corrected.

    In this case, apparently, from some of the things I have read, they are not even claiming to have a full theoretical understanding of what is happening or have the calculations. They are claiming this based on actual experimental observations.

    Of course, experimental observations are enough to confirm something, even in the absence of an understanding of why it is so, but in this case, I believe the experimental data is, at best, questionable.

    Yeah, but the actual thrust detected is tiny. It is so tiny it barely overcomes the limits of the instruments. There are so many alternate possibilities: Bad calibration, electrical forces on the vacuum chamber, magnetic forces, electromagnetic forces, the earth’s magnetic field…. etc etc etc


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