• The inventor of the physics-defying EmDrive defended his controversial propulsion device.
  • Roger Shawyer, who created the EmDrive in 1998, said competing researchers got the whole design wrong, leading to recent failed tests.
  • Shawyer is currently working on the third-generation EmDrive design.

    After a widely reported set of recent studies all but killed the controversial EmDrive, the propulsion device’s inventor has fired back by pointing out what he calls critical errors in the research. Who’s who in this cutting-edge scientific mudslinging, and what does the future really hold for the “impossible” EmDrive?

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    First, let’s briefly recap how we got here. For such a far-out concept, the idea of the EmDrive is relatively straightforward. The device, which is copyrighted by Satellite Propulsion Research (SPR) Ltd, theoretically works by trapping microwaves in a shaped chamber where their bouncing produces thrust. The chamber is closed, meaning from the outside, it will appear to simply move without any fuel input or any thrust output.

    The EmDrive relies on Newton’s Second Law, where force is defined as the rate of change of momentum, SPR explains. “Thus, an electromagnetic wave traveling at the speed of light has a certain momentum, which it will transfer to a reflector, resulting in a tiny force,” the company says.

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    It’s that accumulated tiny force in great quantity that makes the EmDrive work, SPR Ltd says. The catch? It also defies our existing understanding of physics. If no energy is going in or coming out, then how are the waves initialized? How do they continue to move? And where is their momentum coming from?

    You can’t have spontaneous, created momentum without an explicable push, which is why many scientists don’t take the EmDrive seriously. Still, several research groups—including NASA’s Eagleworks (formally the Advanced Propulsion Laboratory) and DARPA, the Department of Defense’s research projects agency—have continued exploring the device’s viability because of its tantalizing possibilities.

    As Mike McCulloch, the leader behind DARPA’s EmDrive project, told Pop Mech last year, the tech could “transform space travel and see craft lifting silently off from launchpads and reaching beyond the solar system.” With the EmDrive, McCulloch says, we could send an unmanned probe to Proxima Centauri in an actual human lifetime: 90 years. (DARPA’s EmDrive investment, which began in 2018, ends next month.)

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    The crux of the EmDrive is if you bounce microwaves around inside the tube, they exert more force in one direction than the other, creating a net thrust without the need for any propellant. And when NASA and a team at Xi’an in China tried this, they actually got a small-but-distinct net force.

    Last month, however, physicists at the Dresden University of Technology (TU Dresden) threw cold water on the promising breakthrough from NASA, saying the results showing thrust were all false positives that can be explained by outside forces. The scientists presented their findings in three papers at Space Propulsion Conference 2020 +1, with titles like “High-Accuracy Thrust Measurements of the EmDrive and Elimination of False-Positive Effects.” (Read the other two studies here and here.)

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    Using a new measuring scale and different suspension points of the same engine, the TU Dresden scientists “were able to reproduce apparent thrust forces similar to those measured by the NASA team, but also to make them disappear by means of a point suspension,” researcher Martin Tajmar told the German site GreWi.

    The verdict:

    “When power flows into the EmDrive, the engine warms up. This also causes the fastening elements on the scale to warp, causing the scale to move to a new zero point. We were able to prevent that in an improved structure. Our measurements refute all EmDrive claims by at least 3 orders of magnitude.

    Now, shortly after Tajmar and his colleagues seemingly delivered their death blow to the EmDrive, the inventor of the device has offered his rebuttal.

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    In his presentation to the April 3 meeting of the biweekly Alternate Propulsion Engineering Conference (APEC), Roger Shawyer, who developed the EmDrive back in 1998, detailed different tests over time of all three generations of his concept.

    Shawyer broke down the anatomy of the EmDrive itself, from superconducting end to superconducting end. (The in-between parts aren’t made from superconductors because of the high cost and complexity of manufacturing the cavity shape using those materials, Shawyer said.)

    Shawyer said the EmDrive isn’t just viable for interstellar travel—it can be used to lift vehicles into orbit, too. The secret, he said, is to reserve half the EmDrive’s microwave-generating fuel for the intraspace portion, leaving half that can be burned off for liftoff. “If you do the [calculations], you can see there’s sufficient energy to get you into orbit, albeit slowly,” Shawyer said.

    During a Q&A portion of his presentation, several APEC guests asked Shawyer about Tajmar and his team’s papers, which effectively discredited the EmDrive. Shawyer’s answer was simple: Tajmar’s cavity was shaped wrong, and it was never going to work. In fact, Shawyer even warned Tajmar about that as early as 2017.

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    “The NASA cavity, which is the basis for Martin [Tajmar]’s work and at least three other organizations’ work is fatally flawed,” Shawyer said. “It’s a flat endplate cavity for a start. If you do the simple geometry, you’ll see that you’ve got a wavefront phase error approaching half a wavelength. You’re never going to get traveling waves in a flat front cavity. There are many other problems he has.”

    Shawyer continued:

    “What Martin’s done is put a huge amount of effort into basically proving that the principles behind EmDrive are correct. Because if you don’t follow the principles, you don’t produce any thrust whatsoever. So, I’m quite grateful to Martin, actually, and I would have never done all of that work myself, and I don’t know anybody else that would have put all of that effort into it.”

    As for the next practical steps in the continuing development of the device, Shawyer suggested flying first-generation EmDrive thrusters and then flying small unmanned aerial vehicles (UAVs) for the second and third generations.

    “The difference between second and third generation is quite a large increase in complexity,” Shawyer said, “but what it does give you is much higher acceleration while maintaining high levels of [thrust]. You can actually combine all three generations if you want to, but the physics is still the same.”

    It seems, then, that the ending of the EmDrive’s story hasn’t been written just yet. Stay tuned.

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