Propellantless thruster claimant presents paper at a conference. Hype ensues.

News headlines are buzzing with headlines such as “Scientists Confirm ‘Impossible’ EM Drive Propulsion” (Hacked) and “‘Impossible’ propellantless engine appears to work” (Sydney Morning Herald).

Doubtful News readers may have followed this story from August 2014, as well as renewed claims of results earlier this May.

At a July Propulsion and Energy Forum held by the American Institute for Aeronautics and Astronautics in Orlando, Florida, two researchers (Tajmar and Fiedler) have presented a paper (paywalled, abstract) whose results are suggestive of a replication.

According to the paper’s abstract:

Our test campaign can not confirm or refute the claims of the EMDrive but intends to independently assess possible side-effects in the measurements methods used so far.

It’s worth noting that the paper has not yet undergone peer review, and that those of us on the outside don’t really have anything new to go on since the science-by-Internet-forum release earlier this May.

No Warp Drive Here: NASA Downplays ‘Impossible’ EM Drive Space Engine (

[…]all that outside researchers really have to go on is the forum, which includes a thread of posts stretching back several years, discussing the development of the EmDrive.

[…]It’s unclear from these forum posts if the prototype propulsion system actually generated any thrust during the recent tests, said Ethan Siegel, a physics and astronomy professor at Lewis & Clark College in Portland, Oregon. Siegel also wrote about the EmDrive in Forbes Magazine, to which he regularly contributes.

Siegel said he is seeing claims of thrust happening just a few times over many tests, with a frequency that is “not inconsistent with random chance.” Further, the thrust that was produced in these rare instances was apparently just above the margin of error for measurement, he added.

One of the major hurdles facing propellantless propulsion claimants is Newton’s Third Law of Motion (You may remember the Third Law from an earlier, recent rant by this DN contributor). Over-simply stated, a propulsion method that doesn’t generate force by accelerating mass has some theoretical explaining to do regarding its momentum. Its novelty is without question (and might rewrite/expand physics if it pans out), but it doesn’t have the reliable track record of other rocket-alternatives.

Some other drive types that NASA (and partners) really are working on

Solar sails: These devices unfold to reveal a massive surface area whose purpose is to collect photons. While photons are generally considered mass-less, they still carry momentum. It’s this momentum that the solar sail borrows, as it slowly accelerates through the vacuum of space. Some readers may be familiar with the Planetary Society’s recent crowdfunded lightsail mission.

Ion thrusters: An ion thruster creates thrust by electrostatically accelerating ions. These guys are very slow to accelerate, but have a high efficiency (specific impulse, or ISP). They also look really cool. In fact, they’re so neat-looking, much of the news coverage of the propellantless drive claimants’ paper has snagged the below image of a Hall effect thruster from NASA/JPL!

A Xenon hall thruster, Photo by NASA/JPL.

Not an EMDrive. A Xenon Hall thruster. Photo by NASA/JPL.

See also:

  4 comments for “Propellantless thruster claimant presents paper at a conference. Hype ensues.

  1. Blargh
    July 29, 2015 at 11:40 AM

    For those of you keeping score at home, the EM Drive checks off three whole items on the pathological science checklist:
    * The maximum effect that is observed is produced by a causative agent of barely detectable intensity, and the magnitude of the effect is substantially independent of the intensity of the cause.
    * The effect is of a magnitude that remains close to the limit of detectability; or, many measurements are necessary because of the very low statistical significance of the results.
    * Fantastic theories contrary to experience.

    I’ll let those of you who have been following this closer than I have answer if it also checks “Criticisms are met by ad hoc excuses thought up on the spur of the moment”.

  2. Mike C.
    July 29, 2015 at 11:59 AM

    So it seems to be more like hot air. Maybe not. You can get some thrust from actual hot air.

  3. Kathy Moyd
    July 29, 2015 at 3:00 PM

    The ion engine is already being used. I worked on Deep Space 1, which was a technology mission testing the ion engine for deep space use; it performed flawlessly. The Dawn spacecraft has three ion engines. It’s mission to orbit the asteroids Vesta and Ceres could not have been done with traditional propulsion.

  4. Ivan
    July 29, 2015 at 4:52 PM

    As you correctly point out, photons do carry momentum. In principle, you can have a flashlight in outer space (no friction, away from large gravitational bodies), turn it on, and it will accelerate to a terminal velocity given by the overall momentum of the photons emitted divided by the mass of the flashlight. I don’t expect this speed to be very significant though.

    Similarly, a microwave horn in space will also start moving as microwaves do also carry mechanical momentum.

    The paper in question tries to have a dissimilar group velocity in a microwave waveguide to produce thrust which should happen as long as the output wavelengths top/bottom are dissimilar. I don’t see how this dissimilarity can happen as, once they are out in free space, the wavelengths are the same because the frequency is the same on both sides of the horn.

    At any rate, a simple microwave horn will move to a faster speed than the device presented.

Comments are closed.