Scientists pinpoint source of "impossible" EmDrive's thrust

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 "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.

Source: Grenzwissenschaft-Aktuell via Popular Mechanics