Explaining EmDrive, the ‘physics-defying’ thruster even NASA is puzzled over

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Even if you don’t keep up with developments in space propulsion technology, you’ve still probably heard about the EmDrive by now. You’ve probably seen headlines declaring it as the key to interstellar travel, and claims that it will drastically reduce trips across our solar system, making our dreams of people walking on other planets even more of a reality. There have even been claims that this highly controversial technology is the key to creating warp drives.

These are bold claims, and as the great cosmologist and astrophysicist Carl Sagan once said, “extraordinary claims require extraordinary evidence.” With that in mind, we thought it’d be helpful to break down what we know about the enigmatic EmDrive, and whether or not it is, in fact, the key to mankind exploring the stars. So without further ado, here’s absolutely everything you need to know about the world’s most puzzling propulsion device.

What is the EmDrive?

See, the EmDrive is a conundrum. First designed in 2001 by aerospace engineer Roger Shawyer, the technology can summed up as a propellantless propulsion system, meaning that the engine doesn’t use fuel to cause a reaction. By removing the need for fuel, a craft would be substantially lighter, and therefore easier to move (and cheaper to make, theoretically). In addition, the hypothetical drive would also be able to reach extremely high speeds — we’re talking potentially getting humans to the outer reaches of the solar system in a matter of months.

The issue is, the entire concept of a reactionless drive is inconsistent with Newton’s conservation of momentum, which states that within a closed system, linear and angular momentum remain constant regardless of any changes that take place within said system. More plainly: Unless outside force is applied, an object will not move. Reactionless drives are named as such because they lack the “reaction” defined in Newton’s third law: “For every action there is an equal and opposite reaction.” But this goes against our current fundamental understanding of physics, as for an action (propulsion of a craft) to take place without a reaction (ignition of fuel and expulsion of mass) is impossible. In order for such a thing to occur, it would mean an as-yet-undefined phenomena is taking place, or our understanding of physics is completely wrong.

How does the EmDrive “work?”

Setting aside the potentially physics-breaking improbabilities the technology, let’s break down in simple terms how the proposed drive operates. The EmDrive is what is called an RF resonant cavity thruster, and is one of several hypothetical machines that use this model. These designs are said to work by having a magnetron push microwaves into a closed truncated cone, then push against the short end of the cone, and propel the craft forward. This is in contrast to the form of propulsion current spacecraft use, which instead burn large quantities of fuel to expel massive amount of energy and mass to rocket the craft into the air. An often-used metaphor for the inefficacy of this is to compare the particles pushing against the enclosure and producing thrust to the act of sitting in a car and pushing a steering wheel to move the car forward.

While tests have been done on experimental versions of the drive with low energy inputs produced very minimal, resulting in a few micronewtons of thrust (about as much force as the weight of a penny), none of the findings have ever been published in a peer-reviewed journal. That means that any and all purportedly positive test results, and the claims of those who have a vested interest in the technology, should be taken with a very big grain of skepticism-flavored salt. It’s likely that the thrust recorded was due to interference or an unaccounted error with equipment. Until the tests have been verified through the proper scientific and peer-reviewed processes, one can assume the drive does not yet work. Still, it’s interesting to note the number of people who have tested the drive and reported achieving thrust:

  • In 2001, Shawyer was given a £45,000 grant from the British government to test the EmDrive. His test was claimed to have achieved 0.016 Newtons of force and required 850 watts of power, but no peer review of the tests verified this. It’s worth noting, however, that this number was low enough it was potentially an experimental error.
  • In 2008, Yang Juan and a team of Chinese researches at the Northwestern Polytechnical University allegedly verified the theory behind RF resonant cavity thrusters, and subsequently built their own version in 2010, testing the drive multiple times from 2012-2014. Tests results were purportedly positive, achieving up yo 750 mN (micronewtons) of thrust, and requiring 2,500 watts of power.
  • In 2014, NASA researchers, tested their own version of an EmDrive, including in a hard vacuum. Once again, the group reported thrust (about 1/1000 of Shawyer’s claims), and once again, the data was never published through peer-reviewed sources. Other NASA groups are skeptical of researchers’ claims, but in their paper, it is clearly stated that these findings neither confirm or refute the drive, instead calling for further tests.
  • Most recently, in 2015, that same NASA group tested a version of chemical engineer Guido Fetta’s Cannae Drive (née Q Drive), and reported positive net thrust. Similarly, a research group at Dresden University of Technology also tested the drive, again reporting thrust, both predicted and unexpected.

Implications of a working EmDrive

From the sections above, it becomes easy to see how many in the scientific community are wary of EmDrive and RF resonant cavity thrusts altogether. But on the other hand, it raises a few questions: Why is there such a interest in the technology, and why do so many people wish to test it? What exactly are the claims being made about the drive that make it such an attractive idea? While everything from atmospheric temperature-controlling satellites, to safer and more efficient automobiles have been drummed up as potential applications for the drive, the real draw of the technology — and the impetus for its creation in the first place — is the implications for space travel.

Spacecraft equipped with a reactionless drive could potentially make it to the Moon in just a few hours; to Mars in two to three months; and to Pluto within two years. These are extremely bold claims, but if the EmDrive does turn out to be a legitimate technology, they may not be all that outlandish after all. And with no need to pack several tons-worth of fuel, spacecraft become cheaper and easier to produce, and far lighter. For NASA and other such organizations, including the numerous private space corporations like SpaceX, lightweight, affordable spacecraft that can travel to parts of space fast are something of a unicorn. Still, in order for that to become a reality, the science has to add up.

Shawyer is adamant that there is no need for pseudo science or quantum theories in order to explain how EmDrive works. Instead, he believes that current models of Newtonian physics offer an explanation, and has written papers on the subject, one of which is currently being peer reviewed. He expects the paper to be published sometime this year. While in the past Shawyer has been criticized by other scientists for incorrect and inconsistent science, if the paper does indeed get published, it may in fact begin to legitimize the EmDrive, and spur more testing and research.

Despite his insistence that the drive behaves within the laws of physics, it hasn’t prevented him from making bold assertions regarding EmDrive. Shawyer has gone on record saying that this new drive produced warp bubbles which allow the drive to move, claiming that this is how NASA’s test results were likely achieved. Assertions such as these have garnered much interest online, but have no clear supporting data and will (at the very least) require extensive testing and debate in order to be taken seriously by the scientific community — the majority of which remain skeptical of Shawyer’s claims.

Colin Johnston of the Armagh Planetarium wrote an extensive critique of the EmDrive and the inconclusive findings of numerous tests. Similarly, Corey S. Powell of Discovery wrote his own indictment of both Shawyer’s EmDrive and Fetta’s Cannae Drive, as well as the recent fervor over NASA’s findings. Both point out the need for greater discretion when reporting on such instances. Professor and mathematical physicist, John C. Baez expressed his exhaustion at the conceptual technology’s persistence in debates and discussions, calling the entire notion of a reactionless drive “baloney.” His impassioned dismissal echoes the sentiments of many others. Elsewhere, however, Shawyer’s EmDrive has been met with enthusiasm, including the website NASASpaceFlight.com, which is where the information about the most recent Eagleworks’ tests was first posted, and the New Scientist Journal, which published a favorable and optimistic paper on EmDrive. (New Scientist has gone on to make a statement that, despite their enduring excitement over the idea, they should have shown more tact when writing on the controversial subject).

Clearly, the EmDrive and RF resonant cavity thruster technology have a lot to prove. There’s no denying that the technology is an exciting thought, and that the number of “successful” tests are interesting, but one must keep in mind the physics preventing the EmDrive from gaining any traction, and the rather curious lack of peer-reviewed studies done on the subject. If the EmDrive is so groundbreaking (and works), surely people like Shawyer would be clamoring for peer-reviewed verification. A demonstrably working EmDrive could open up exciting possibilities for both space and terrestrial travel — not to mention call into question our entire understanding of physics. However, until that comes to pass, the EmDrive will remain as nothing more than science fiction.