The EM Drive

I am going to introduce you to a fascination of mine. The “EM Drive” was a proposed closed-system reactionless thruster. For those of you without physics degrees, that’s in the category of “big fucking deals,” up there with cold fusion, room-temperature superconductors, and unicorns. In fact, whereas unicorns are theoretically possible, a reactionless thruster very much is not, because it would violate known laws of physics. For some background reading, here’s an instructive Wikipedia page.

The Unicorn Rests in a Garden (from the Unicorn Tapestries), Wool warp with wool, silk, silver, and gilt wefts, French (cartoon)/South Netherlandish (woven)
The EM drive got nothin’ on me.

Now, I don’t shy away from impossible stuff around here, but what makes the EM drive special is the amount of attention it got from Very Serious People. Well, I can’t say I’ve met Dr. White and his team, but NASA’s Eagleworks Labs seemed pretty legit. I can’t tell whether they’re still a going operation, but the idea was to explore advanced propulsion technologies. In this case, they gave the EM drive a try, and found that it… kind of worked??

But wait, remember patents? It’s a blog about patents. The EM drive was first proposed by Roger John Shawyer in 1999, and you can find his UK patent here:

GB 2537119, FIG. 1

The idea is that you fire microwaves a roughly conical enclosed chamber, and the whole thing moves, even though nothing actually leaves the chamber. That violates the law of conservation of momentum, because you can’t get momentum in one direction without throwing some momentum in the opposite direction. Think “equal and opposite forces.” You can’t push forward without something to push against.

But when Dr. White et al. tested the drive, they found that it did produce some thrust. A Chinese team at Northwestern Polytechnical University found similar results. That turned a crackpot idea into a matter of very serious interest, as everyone started trying to explain how it could work.

Unfortunately though, subsequent testing could not replicate the results. The Dresden University of Technology showed that the previously measured thrust was likely due to heating and electromagnetic interference, rather than previously undiscovered physics. And just like that, the dream of the EM drive was busted.

But Shawyer’s patent for it is still valid in the UK! And he has another one pending! I wish him the best of luck in his journey, even though he will need to expend reaction mass to get there.

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