Can the ‘impossible’ space drive survive falsification in orbit?

 Graham Templeton

The EM Drive is going to get its feather drop, after a fashion. The famous feather drop was about proving something everybody already believed: Drop a feather and a hammer in a vacuum and, without air resistance, they will accelerate downward at the same rate. Now, a similarly space-based concept is getting a similarly space-based test. But this time the topic is much more controversial: Put in space and given only electricity with no fuel at all, the EM Drive will produce thrust. Where the feather drop confirmed several centuries of physics in a moment, a confirmation of the EM Drive could completely overturn just as much just as quickly.

This test is actually being conducted on the Cannae Drive, a sister-tech to the more-famous EM Drive. But since nobody can clearly articulate how the two work differently, they’re largely interchangeable at this point. EM Drive has become the Kleenex of a category of thruster called RF Resonant Cavity Thruster, which super-doesn’t exist, but which might soon come to.

For those who don’t know, the EM Drive is a propulsion device that is proposed to work without any fuel. The claim is that the invention uses only a modest amount of electricity, its intrinsic design, and the physical properties of the universe to produce thrust — a claim that seems to defy the laws of physics as we know them.

This is an older version of the concept than the one NASA tested.

A number of authorities have tested the EM and Cannae drives, up to and including teams from NASA. They, like many before them, measured an extremely small amount of force in the predicted direction, and try as they might they could not figure out what was creating it — unless it was the drive. Skepticism has been widespread and vitriolic, but at the end of the day the results are what they are. Few have been willing to claim the EM Drive actually works, but the teams have nonetheless been unable to conclusively prove that it doesn’t work, and in science that carries a lot of weight.

Harold White’s model for an Alcubierre warp drive. Could this actually be more realistic than Cannae?

NASA’s Eagleworks team conducted a test of an RF Resonant Cavity Thruster, and the paper reporting their inability to prove the null hypothesis only recently passed peer review — the final version will be published in December in the Journal of Propulsion and Power. At this point, the EM Drive will be important — if not for revolutionizing space travel, then at least for dramatically illustrating the difficulty of taking accurate force measurements at extremely low magnitudes.

So, now NASA is taking the testing to space, where fewer variables can muck up their results. Perhaps they’ve realized that, regardless of the outcome, indulging public curiosity in space tech will always pay dividends. Or, maybe they just want the public to stop asking about the damned sci-fi drive. There’s all sorts of unhelpful factoids floating around about the EM Drive, that it could get us to Proxima Centauri in 100 years — no, 20 years, no, two years! Or perhaps just the Moon in four hours. What?

Nonsense aside, you cannot completely ignore any idea with this sort of potential. Remember that this drive is theorized to work with no fuel, meaning that a solar-powered spacecraft could theoretically accelerate infinitely while reasonably close to a star. We could also imagine a nuclear-powered spacecraft with a finite, but still enormous lifetime, or a hybrid that uses nuclear fuel to continue accelerating between stars. We could finally get all that hover-stuff that science fiction once thought so likely — unlimited, clean thrust that even has the likely added benefit of being safe, since there’s no indication that the EM Drive produces a heated or otherwise harmful exhaust.

Ion thrusters are another low-powered solution, applying weak but constant acceleration.

In principle, this means that the drive would be used somewhat like ion thrusters are used today. These drives produce low amounts of thrust for extremely long periods of time, but they do it by slowly consuming a fuel source. A tiny amount of this fuel, perhaps pressurized xenon gas or solid iodine, is released into the reaction chamber, then expelled out the back of the thruster by one of a number of methods. Since the process uses so little fuel per hour, and produces so little heat, it can be left on for long periods of time, more than making up for its lack of accelerating power by slowly accumulating speed or gently applying a constant force.

On the other hand, what does the EM Drive move, in order to move itself? It carries no fuel molecules to expel, which is how ion thrusters work. It doesn’t catch any particles hitting it from the universe, like a solar sail. If it does work, it seems to just… go, and that’s a big problem for physics. Possible explanations have had to invoke things like spontaneously forming particles in the vacuum of space, and a whole new theory of momentum.

Credit: NASA

Yes, it’s possible that the EM Drive accelerates because it is subject to wavelengths of black-body radiation that are larger than the universe itself and thus (obviously) its momentum becomes quantized. That’s the sort of theory needed to explain this “anomalous thrust device.” But in general, supporters have tried to argue that the drive works such that it doesn’t break the laws of physics rather than that the laws of physics have been proven wrong.

The lack of a requirement for fuel lets the imagination run truly wild. Might we one-day have a sort of super-fast powered orbiter, one that stays in orbit despite its huge momentum by constantly applying thrust straight toward the Earth with a big, solar-powered EM Drive? Might we one-day ascend from Earth slowly and smoothly, rather than through an explosive launch?

The ultimate test will come in 2017, when a Cannae Drive will launch as part of a 6U Cubesat. There’s a whole host of tests they could, and will, run. But if the first battery of tests doesn’t falsify the thrust, scientists and even amateurs will be clamoring to apply tests of their own devising. Just how much testing would appease the skeptics is an open question. Perhaps the more relevant question, though, is how its supporters will react if it turns out they’ve launched a paperweight into zero gravity.

Header image credit: NASA.