The ‘Impossible’ EmDrive Thruster Has Cleared Its First Credibility Hurdle

By Nathaniel Scharping | November 21, 2016 4:52 pm

The experimental setup of the controversial “EmDrive.” (Credit: White

After years of unwarranted hype and dubious experimental claims, the EmDrive, an “impossible” propulsion device that claims to produce thrust while violating Newton’s Laws of Motion, has received its first published, peer-reviewed paper.

A team of researchers from the NASA-affiliated Eagleworks lab published a paper last week describing a series of tests on the EmDrive. They say their methodology accounted for nearly all possible errors and returned results indicating that the device produced thrust, an apparent violation of Newton’s Third Law of Motion. The drive works by bouncing microwaves around the inside of a cone-shaped chamber, apparently producing thrust even though nothing is being emitted from the device. This is in opposition to the laws of physics as we understand them, which state that every action must have an equal and opposite reaction. For example, conventional propellant-based rockets are pushed forward by the ejection of superheated gas from the nozzle.

Litany of Problems

Critics liken the EmDrive to trying to move a car by getting inside and pushing on the windshield. This violation of fundamental principles has drawn criticism from the scientific community ever since the device was first proposed in the early 2000’s by British researcher Roger Shawyer. Tests of the device have been subject to some glaring flaws, and one Chinese team was forced to retract the results of a 2012 experiment after concluding that they were due to thermal expansion in the test device. And EmDrive tests have never before passed peer review, meaning that the results weren’t looked over by other scientists. With this paper, published in the Journal of Propulsion and Power, the researchers have cleared an initial hurdle on the path to legitimacy.

That doesn’t mean that the EmDrive actually works though. Passing peer review simply means that other scientists have examined their data and methodology and declared them sound. There could still be experimental flaws that no one has been able to catch yet. In addition, no one has yet replicated their experiment and produced similar results, another key step in the process.

Better Experiment

To test whether the EmDrive produced thrust, the researchers mounted it on a pendulum that would swing to indicate movement. They tested the device at different levels of current and received positive results every time. Their results indicate that the device puts out 1.2 millinewtons of thrust — or enough to accelerate a satellite weighing one kilogram to one mile per hour over the course of about six minutes — for every kilowatt of power put through it. In an important move, they tested the EmDrive in vacuum conditions as well, and report that it performs nearly the same. A prominent criticism of earlier tests was that the heat generated by the device could have been responsible for the apparent movement. Moving the experiment to a vacuum provides a more perfect environment to run tests in.

Besides opening up new realms of physics, a propellant-less device like the EmDrive would be extremely useful for extended missions in space. The device runs only on electricity, meaning that a spacecraft wouldn’t need to bring any fuel along with it and could power itself using only solar panels. The thruster is far less powerful than conventional rockets, and even the ion engines currently in use on some NASA spacecraft, but both of those thruster designs require fuel to be carried on board. Other fuel-free methods of propulsion do exist, such as light sails and laser propulsion, but they are orders of magnitude weaker than the EmDrive claims to be.

“NASA is looking forward to the scientific discussions with the broader technical community that will occur based on the publication of the Eagleworks team’s experimental findings, said Jay Bolden, an Engineering PUblic Affairs Officer with NASA’s Johnson Space Center. “This is part of what NASA does in exploring the unknown, and the agency is committed to and focused on the priorities and investments identified by the NASA Strategic Space Technology Investment Plan. Through these investments, NASA will develop the capabilities necessary to send humans farther into space than ever before.”

Room for Error

The list of possible confounding variables is long, however. In their paper, the researchers address nine of them, including everything from vibrations to magnetic interactions with external hardware. One of the largest possible sources of error comes from the thermal expansion of the heat sink attached to the device. In their experimental configuration, the heat sink is offset from the device’s center of gravity, meaning that as it expands, it could cause the EmDrive to move.

How could an EmDrive work? Harold “Sonny” White, the principal investigator on the project and a long-time proponent of propulsion devices on the fringes of science, favors a theory that assumes that empty space is not in fact so empty. If so, it should be possible to exchange momentum with this “quantum vacuum.”

“It is proposed that the [EmDrive] pushes off of quantum vacuum fluctuations, and the thruster generates a volumetric body force and moves in one direction while a wake is established in the quantum vacuum that moves in the other direction,” the authors write in the paper.

This theory may be based on a misinterpretation of the quantum vacuum, however. As California Institute of Technology physicist Sean Carroll states in a Discover article from 2014:

“There is a quantum vacuum, but it is nothing like a plasma. In particular, it does not have a rest frame, so there is nothing to push against, so you can’t use it for propulsion.”

Another explanation relies on the Mach Effect, a theory proposed in 1990 by physicist Jim Woodward, a professor of physics at California State University, suggesting that force applied to an object can be stored within it, to be used later. In this view, the microwaves are simply increasing the EmDrive’s internal energy, which manifests itself as thrust.

Both of those theories remain unproven, however, and are only two of the possible explanations for what’s going on here. What’s more likely is that the scientists simply missing a source of error somewhere in the experimental setup.

“I suspect there may really be something there,” says Woodward, speaking to Motherboard. “But the result they’re seeing can’t actually be explained in terms of the theory they’re proposing. So the question is: what is causing it?”

Physics is no stranger to false positives, of course. Just four years ago, evidence of neutrinos that moved faster than light rattled the physics community. Subsequent tests revealed the phenomenon to be nothing more exciting than the result of a cable that hadn’t been hooked up properly. Similarly, preliminary results from the Large Hadron Collider last December seemed to indicate the presence of a brand new particle. Further testing showed the portentous bump in the data to be just a statistical anomaly.

The EmDrive may very well turn out to be another in a long line of overhyped experiments that fizzle under further inspection. Even so, the experiment does raise interesting questions about our understanding of quantum mechanics and highlights the promise of propellant-free propulsion devices.

At the very least, it should serve as a reminder of the dangers of falling victim to the hype.


CATEGORIZED UNDER: Space & Physics, Technology
  • OWilson

    Like cold fusion, or faster then light neutrinos, it will be news when someone else can replicate the experiment.

    The energy input required, 1,000 watts, to raise one thousandth of a gram 1 meter, is not a very efficient engine.

    But the main reason for this non-scientist’s skepticism, is the throwaway line that this process would be useful for extended space travel.

    Maybe, if you want to orbit the sun where sufficient solar power is available, but further out it becomes not solar, but star power, and the array of solar (star) panels would have to be almost infinite, to pick up enough starlight for interstellar space fight.

    • podumal

      Apparently, it’s not just the principle at stake here. The allegedly observed values seem to be quite interesting when compared to other ways of propulsion. Hall effect thrusters need fuel and generate about 60 mN/kW, best zero fuel “engines” are in the range of 0.0033–0.0067 mN/kW; and the EmDrive produces 1.2 mN/kW and they stated that they were not trying to optimize the efficiency, they just wanted to test it. So, if proven to be real, the efficiency may be improved.

      • OWilson

        Uncle Al, help!

        I’m out of my depth here! :)

    • George Kapotto

      Some confusion about terminology here. milliNewton is a unit of force. F=ma so if m = 1kg, a=.0012 m/s^2. Over 24 hours, delta-V = accel x time = .0012 x 86400 = 103.68 m/s. Ballpark requirement to generate the delta-V for a trip to Mars from LEO is likely on the order of 140-150 days. Since no propellant is required, it isn’t fast but it would be cheap for cargo shipments.

      1. (The big gotcha – The acceleration estimates are for a 1kg mass. I would be surprised if the engine mass to generate that thrust could be kept down below 10 kg. So reduce all acceleration estimates by at least one order of magnitude.

      2. Heat sink issues – 1kW is in the ballpark of your toaster running 24/7 and heat does not dissipate well in a vacuum. It would require lots of radiator surface and reflective shielding to avoid solar heating. Let’s assume that the radiation thrust has a negligible impact on thrust calculations. Optimistically, it may take +50% mass to cool the engine.

      3. On the plus side, maybe appropriate materials can be found to run at ridiculous temperatures like 3000+ degrees C and the engine could run at 10kW througput. This would radically improve the thrust considerations (at least for cargo ships) but it would still need good thermal isolation from the rest of the vessel.

      4. Finally, if (IF, IF, IF!!!) it actually works, it is clearly new physics and just like the first light sources (candles) are about 1/1000 the efficiency of LEDs, there may be significant room for improvement once the principals are understood. *That* would be cool.

  • Uncle Al

    Phong shading:

    Pioneer anomaly
    Rationalized Pioneer anomaly
    Believable rationalized Pioneer anomaly
    Believable Pioneer anomaly updated
    Pioneer anomaly
    Commentary on Pioneer anomaly minutia
    1/3 modeled away
    End of anomaly – Phong shading
    Anomalous slowing is slowing as Pu-238 decay decays.

    • OWilson

      Since there are two Pioneers with the sane deviation in the same direction, one would assume they must be identically configured and oriented?

      A simple 180 degree rotation of one vehicle should cause it to diverge from it’s present course if there are unbalanced or uneven radiators.

      Maybe next time!

      I was hoping that the “Pioneer Anomaly” had other, more exotic causes, like strange attractors, dark energy, or a flaw in Newtons math. :)

  • darryl

    1000 watts to raise 1 miliigram 1 meter. I would think you’d get more net velocity by throwing the solar panel you were using to generate the electricity.
    But hey, if they can get it to work, great!


    • podumal

      The problem would be how to use that electricity to propel the spaceship without a reaction mass, which is exactly what the EmDrive is supposedly doing.

  • matheworman

    I heard that real solid state drive which produces external force was invented 10 years ago and is now in development showing results which make flying car possible…

  • Melvin T Pelvis

    Wait until they find out that every time they turn it on universal expansion accelerates.

  • Vidar Gander Skrindo

    This is as if the Pope finally said the dinosaurs actually existed.

    • Kevin Mc

      He has, please catch up,

      • Vidar Gander Skrindo

        That is really good news. Hopefully, the rest will catch up and comply. Furthermore, hopefully, the scientific fundamentalists will comply as well to this NASA revelation.
        Do you have a link to the Pope’s statement about the dinosaurs?

        • Kevin Mc

          He didn’t specifically say dinosaurs, but both of the past two Popes have acknowledged that evolution is true, and that Catholics should accept it. I don’t have a link (using my phone), but should be easy to Google.

  • Uncle Al

    accounted for nearly all possible errors” Podkletnov anti-gravitation beam: Cold nitrogen is denser than warm air when a test mass is immersed within it, then Archimedes’ buoyancy.

    Ground lasers fired into a rocket chamber as thruster! Thrust varies as square of dimension (chamber normal area), mass varies as the cube. Great demo, crappy reduction to practice.

    Coriolis thruster in a sealed box in a small boat or on a track including vertical. Zoom!, violating Newton. Now try it without a keel or rudder, or dangling from a string. “nearly all possible errors” Crap only needs one.

  • Gary S

    OK, everyone, just FORGET “1.2 millinewtons of thrust.” That is just part of a derived ratio, per kilowatt. The alleged “real” maximum thrust was less than 90 MICRO-newtons. And the two larger power inputs did not yield any significant INCREASE in thrust! The experiment could have a much clearer result if they had simply applied many more than ONLY THREE input power levels. I’m puzzled why smart people didn’t.

    • J. Kevin Dix

      If the thrust doesn’t vary reasonably with the power input, this will not scale well to practical uses.

      • Matthew Slyfield

        Assuming for the moment that it is genuinely producing even a tiny amount of thrust, We don’t understand the physics of how that’s happening, so the lack of scaleability could be a product of the specific design of the thruster mechanism rather than with the base physics.

        Verify if the thrust is real or a product of the test apparatus,

        If it is real, figure out how it is generated.

        Then worry about scaleability.

        Even if it isn’t scaleable, the underlying physics if real could have other interesting applications.

  • Lorie Franceschi

    If this actually works, how much faster will it be than what we use today to lift space vehicles?

    • jonathanpulliam

      It does not work and it is a fraud.

  • Ajay Sharma

    Sharma published paper in the journal “Acta Ciencia Indica ” in 1998, pointed out its limitations of the Third Law of Motion and modified as

    “to every action there may be a reaction but not always equal and opposite.”
    Thus, reaction may be equal less or more than action.

    In NASA’s experiment, the reaction is reported to be nil, but definite action (thrust).
    Further in his book ‘Beyond Newton and Archimedes’ published from Cambridge England; Sharma has discussed in Chapters 8-10, limitations and modified form of the Third Law.
    At page 315 it is clearly mentioned, that rocket and jet motion, Newton’s Third Law is regarded as true without mathematical equations and experiments.

    Recently in 2016, Ajay Sharma published Physics Essays published from USA-CANADA. This paper discussed in-depth the modified form of Newton’s Third Law.

  • Cliff Clavin

    Reminds me of global cooling theory in the 60s and 70s, and global warming in the 90s, and global climate change currently. None of it has come to pass.

  • J. Kevin Dix

    If the heat sink is the largest possible source of error, is it not possible to warm the mechanism in some other way which produces the same heat signature on the sink as the thrust tests and thereby measure and allow for that effect? Or redesign the heat sink to be symmetrical about the CG?

  • jonathanpulliam

    H * O * A * X
    Same idiots who came up w/ AGW hoax I bet.
    Prosecute these phony scientists for fraud.


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