Physics

Scientists pinpoint source of "impossible" EmDrive's thrust

Scientists pinpoint source of ...
According to one peer-reviewed paper, the EmDrive thruster was able to produce 720 mN of thrust from an electricity input of 2.5 kW
According to one peer-reviewed paper, the EmDrive thruster was able to produce 720 mN of thrust from an electricity input of 2.5 kW
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According to one peer-reviewed paper, the EmDrive thruster was able to produce 720 mN of thrust from an electricity input of 2.5 kW
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According to one peer-reviewed paper, the EmDrive thruster was able to produce 720 mN of thrust from an electricity input of 2.5 kW

In 2014, no less an authority than NASA proclaimed in peer-reviewed papers that it was getting mysterious thrust from the EmDrive, a strange, brassy trumpet of a thing that its creators claimed could produce thrust with no propellant. NASA's findings replicated 2009 experiments in China. A zero-propellant thruster? The world sat up and listened.

The ability to generate thrust without having to carry the parasitic mass of fuel would be a game-changer in space, and even if the EmDrive's experimental thrust figures were small (720 millinewtons per 2.5 kW of input power in the 2009 Chinese experiment), they'd be several times more effective per weight and per watt of input than current ion propulsion systems, which need to carry fuel.

The trouble is, where ion drives are easily explained (a propellant is ionized, then electromagnetically thrown out the back of the thruster to push the vehicle forward), nobody could figure out how the EmDrive was producing Newtons while apparently disagreeing with Newton on the whole conservation of energy thing.

The inventor had a theory, but so did German scientists Martin Tajmar, Oliver Neunzig and Marcel Weikert, and the three have spent the last four years fine-tuning their experiments to prove it. In 2018, the team showed some weird results suggesting that the EmDrive's thrust didn't seem to be coming from the EmDrive itself, and they hypothesized that the results were possibly something to do with electromagnetic interference from the prototype's power cables interacting with the Earth's magnetic field.

So they set out to eliminate those effects, using an on-board battery and relocating other components to stop any electromagnetic effects, and redesigning the experiment to address some hypotheses raised by other teams trying to get a handle on the EmDrive as well.

Now, the team says it's found exactly where the thrust is coming from – and it's bad news for EmDrive enthusiasts.

“We found out that the cause of the ‘thrust’ was a thermal effect," Tajmar told Grenzwissenschaft-Aktuell.de. "For our tests, we used NASA's EmDrive configuration from White et al. (which was used at the Eagleworks laboratories, because it is best documented and the results were published in the ‘Journal of Propulsion and Power’. With the aid of a new measuring scale structure and different suspension points of the same engine, we 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."

"When power flows into the EmDrive," he continued, "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 three orders of magnitude.” The team presented its results at this year's Space Propulsion 2020+1 conference, which was held online due to the pandemic.

The entire EmDrive kerfuffle, then, comes down to this: it's really, really hard to precisely measure tiny amounts of thrust, and the standard design everyone's been using to figure out how hard the EmDrive's pushing has been susceptible to an almost imperceptible thermal expansion that made it look like there was thrust, where there was actually none. Newton stands undefeated.

In a double victory lap, Tajmar and the team also killed two other EmDrive variants, the LemDrive, and the Mach-Effect Thruster, saying that while it was disappointing that the team couldn't verify the claimed capabilities of these "impossible" engines, at least it had done some great work pushing measuring technology forward. So hopefully the next impossible drive can be proven impossible a lot sooner and with less effort.

The German team's paper is freely accessible at ResearchGate, and enjoy EmDrive's explanation of how the thing was supposed to work in the video below.

EmDrive Fundamentals

Source: Grenzwissenschaft-Aktuell via Popular Mechanics

18 comments
toni24
I always thought that the best way to test an impossible space drive, would be to place the test engine in the vacuum of space and turn it on. If it works then it works. We can figure out why it works later.
Juanjo
The problem is to test anything complex in space. It is at least 1000 times the cost compared to the surface of Earth. And, if you need an specialized item to test a different variable, you need to carry it from Earth to the Space Station, for example.
David
If thrust is produced from heat generated by the impossible device itself, imagine what a nice hot cup of tea at Milliways would do. ;-)
FB36
IMHO, EmDrive could easily really work & w/o requiring any new/exotic physics!
All photons (including MW) carryaway momentum (just like atom/molecules of any rocket fuel)!
What EmDrive really needs, to actually produce thrust, is just someone open a hole in the back, to let MW photons escape & so carryaway momentum!!!
akarp
@toni24: Yes! There is a lot in life that 'works'...where understanding why may not be found out in my life time.
Aaron MacTurpen
I suspect Big Space had something to do with quashing this revolutionary propulsion system. Who funds these "scientists?" :P
David Knowles
Isn't anyone else sadden by the tone of this article. We need to keep testing because one day a so called impossible drive may work.
fasteddie2020
Duh.....Is anyone else on this string old enough to remember the Dean Space Drive System and gravitational-intertial radiation? EmDrive falls into the same category. Past concepts of this type have caused politicians to insist that government organizations study the effect, resulting in the dump of taxpayer dollars. Make it stop!
EJ222
@FB36

Photon rockets are a solid idea, one that pops up frequently in sci fi. While technically not a reactionless drive, their ISP is literally the theoretical maximum for a rocket.

Problem is, you need A LOT of photons to produce any thrust. That kind of power output would make nuclear fusion look like a toy, and then one has to send all those photons out the back without annihilating the spaceship. The kind of exotic matter needed for such a design is barely even theorized yet.


Solar sails operate on a similar theory, but sunlight is so weak that an impossibly large and lightweight sail is needed to really get anywhere.
Chuck
I spent 25 years working with electron beams. The Von Ardenne type gun produced a considerable amount of pressure exerted on the target material and relies on a high level of vacuum to operate. I would think a space based use would be ideal. It also needs DC current that might be supplied by a solar array. It produces a high energy stream of electrons that may provide thrust