This engine was making news few years ago, but I have not heard much about it lately. Were there any updates regarding its tests, further development or anything?

  • $\begingroup$ First page of a googling returns this list emdrive.com and a really nice summary (with an annoying advertisement that started playing - lower your volume) cnet.com/news/… Most of the news is in theoretical examinations. This is common in physics; a disruptive yet marginal physical result (e.g. cold fusion, faster than light neutrinos, one of the recent CERN "mystery peaks") generates a flurry of theoretical explanations. The rush is to get those published before the experiment is disproved ;-) $\endgroup$ – uhoh Jan 18 '18 at 4:08
  • 2
    $\begingroup$ The 750 GeV "blip" at CERN generated 500 papers explaining the physics before it was disproved, also Wikipedia. Faster than light (0.002% faster) neutrinos turned out to be a loose connection also Wikipedia. Then there's Cold Fusion. $\endgroup$ – uhoh Jan 18 '18 at 4:17
  • $\begingroup$ Once an anomaly reaches a high enough level of interest, it becomes necessary to "get to the bottom" of the issue, and that takes time, money, and nice institutionally-funded trips to special propulsion conferences in nice resort towns. I would expect that it's going to take a while longer (years) to conclude definitively from an experimental point of view if this effect is real or not. I hope someone posts an answer that highlights any new experimental work in progress. $\endgroup$ – uhoh Jan 18 '18 at 4:26
  • $\begingroup$ In the mean time, read this excellent Physics SE Community Wiki and this Physics SE Meta question for links to more physics discussions. $\endgroup$ – uhoh Jan 18 '18 at 4:31
  • $\begingroup$ Right now there's no real headline news but there's speculation about the Chinese space program, which announced that they were testing this technology in space. Their space program is generally secretive so it's unclear if anything has or will soon come from their research. $\endgroup$ – Dragongeek Jan 18 '18 at 16:06

There's a timely article at Ars Technica today on this.

The conclusion (unsurprisingly to me at least):

And the winner is… Physics, without much doubt. Even with a power of just a couple of Watts, the EM-drive generates thrust in the expected direction (e.g., the torsion bar twists in the right direction). If you reverse the direction of the thruster, the balance swings back the other way: the thrust is reversed. Unfortunately, the EM drive also generates the thrust when the thruster is directed so that it cannot produce a torque on the balance (e.g., the null test also produces thrust). And likewise, that “thrust” reverses when you reverse the direction of the thruster.

The best part is that the results are the same when the attenuator is put into the circuit. In this case, there is basically no radiation in the microwave cavity, yet the WTF-thruster thrusts on.

So, where does the force come from? The Earth’s magnetic field, most likely. The cables that carry the current to the microwave amplifier run along the arm of the torsion bar. Although the cable is shielded, it is not perfect (because the researchers did not have enough mu metal). The current in the cable experiences a force due to the Earth’s magnetic field that is precisely perpendicular to the torsion bar. And, depending on the orientation of the thruster, the direction of the current will reverse and the force will reverse. The researchers made some calculations, based on the location of the experiment and the amplifier current, and got a torque that agreed quite well with the measured torque.

This is, of course, not the final word. But it is an excellent cautionary tale. The thrust that the researchers measured with just a couple of Watts of power was the same as that measured previously with 50W of power. And that was all due to a shielding problem. When the amplifiers are properly mounted and the shielding is in place, it will be even more difficult to detect the thrust, because the effects of noise will grow as well. I expect a flood of null results in the next year.


Space unicorns are not your friend

| improve this answer | |
  • 1
    $\begingroup$ Hey, The Space Unicorn and I are drinking buddies and he's awesome. Especially at beer pong. $\endgroup$ – zeta-band May 21 '18 at 17:59
  • 1
    $\begingroup$ You are a most fortunate being! $\endgroup$ – Organic Marble May 21 '18 at 18:22
  • $\begingroup$ A Helmholtz coil may have been used to compensate the Earth’s magnetic field. Using a 3D arrangement of Helmholtz coils it is possible to study the influence of magnetic fields in all directions and strength. Using mu metal is not the only way to get rid of the Earth’s magnetic field. $\endgroup$ – Uwe May 22 '18 at 13:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.