EmDrive - Fact or fiction

Posted by Šadi El Assadi Thursday, Dec 22, 2016

Just recently, NASA Eagleworks laboratory have published a peer reviewed paper on EmDrive – a new type of drive which doesn’t require propellant to generate thrust. Is this a game breaking technology that will change how we perceive space traveling or is it just another headline that will be forgotten before years end?

Even if you don’t keep up with developments in space industry, you have most likely ran across EmDrive, since it has been used as a headline many times over the last couple of months and even years. Before diving into the details, I’m going to give you a short overview of EmDrive, and why is it so controversial.

What is EmDrive?

EmDrive or radio frequency (RF) resonant cavity thruster is a reactionless spacecraft drive which provides thrust by electromagnetic waves bouncing in the closed cavity. Key part of this definition is word reactionless. Reactionless means that the drive is providing thrust without consuming a propellant. This goes against our current understanding of physics defined in Newton’s third law: “For every action there is an equal and opposite reaction”. Hot gasses resulting from fuel combustion are directed through exhaust nozzles at the rear end of the spacecraft, which is in turn accelerating the spacecraft in the opposite direction. But how can we have an action (propulsion of the spacecraft) without the reaction (ignition of fuel and expulsion of mass)?

Because of this, the reactionless drive concept has been received with skepticism and some scientists have even labeled it as pseudoscience. However, just recently, a breakthrough has been made: NASA Eagleworks’ laboratory paper on the EmDrive test passed the peer review process and will soon be published by the American Institute of Aeronautics and Astronautics’ AIAA Journal of Propulsion and Power. This is not the first time physicists reported measuring thrust from the EmDrive, but it’s the first paper on the subject, that has passed the peer review.

A little bit of history of EmDrive

EmDrive was first designed by British aerospace engineer Roger Shawyer back in 2001. As a propulsion system capable of generating thrust without consuming the fuel, it enables the craft to be substantially lighter, and therefore easier to move. In addition, the hypothetical drive is able to reach extremely high speeds which would allow traveling the distances which so far seemed unreachable.

In 2002, Shawyer described a working prototype with a total thrust of about 0.02 newtons requiring 850 watts of power. In 2006, Shawyer conducted a new set of tests and reported that it had increased thrust. Results of those tests were published in New Scientist magazine in September 2006 issue, but the reactions were mostly negative. Experiments Shawyer conducted were characterized as flawed and the whole theory was labeled as impossible.

However, multiple other people also tested the drive and reported it generated thrust:

  • Multiple experiments were performed by Chinese team of researchers at Northwestern Polytechnical University, led by professor Yang Juan between 2008 and 2014. They also have built their own prototype and reported positive, achieving up to 0,75 newtons  of thrust, requiring 2500 watts of power.

  • NASA team of researchers tested multiple versions of drives in 2014 and 2015, and reported that they generated thrust. However, the data was never published through peer-reviewed sources and research clearly stated that the findings neither confirm nor refute the drive, but are instead calling for further tests. Among others, experiments included the tests on the version of drive proposed by engineer Guido Fetta, called Cannae Drive.

  • A research group at Dresden University of Technology lead by physicist Martin Tajmar, investigated the drive in 2015. At first Tajmar claimed that thrust measured on EmDrive was a result of a mistake in experimental setup and an error in the gyroscope. However, when the group built their own EmDrive, it appeared to really produce thrust, and they weren’t able to find and experimental error that would explain it.

So, does the EmDrive actually work or not?

Even though multiple teams of researchers managed to measure thrust produced on the EmDrive, there is still not a clear understanding of if and how it works, or even if the results were due to an experimental error.

One of the theories that tries to explain the EmDrive, was put forth by physicist Michael McCulloch mid this year. McCulloch’s theory deals with inertia and something called the Unruh effect. If the McCulloh theory was confirmed, it would offer an entirely plausible explanation for the EmDrive’s seemingly impossible thrust observations. Problem with the theory is that it deals with the unconfirmed concept of Unruh radiation.

Another theory that could explain the EmDrive was presented by a Finnish team who recently published a peer-reviewed paper proposing that such a drive could work because of an unseen exhaust of paired photons that cancel out each other's visible effects but still carry momentum.

On the other hand, a way to cut through all technical arguments about EmDrive is to test the drive in space. A successful test in space would mean a huge deal for the whole satellite industry. With that in mind, a company called Cannae Corporation was formed to commercialize the propulsion technologies based on Cannae drive. In August this year Cannae announced their plans to launch a cubesat mission into low Earth orbit, using their own proprietary thruster which requires no on-board propellant. Plan is that satellite stays in the orbit for at least six months.

Besides Cannae Corporation, multiple other organizations and/or individuals are looking to test the drive in space. Among others, an open source community of EmDrive enthusiasts has stepped up, and are building their own satellites to test EmDrive propulsion in space.

With all those competitors in place, there is no doubt that interesting times are ahead. NASA Eagleworks paper only opened the door, but it’s yet to be seen the impact it will have on satellite and space industry, not to mention questioning the fundamentals of physics as we know it.

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