The beginnings of a theoretical basis for the EmDrive

[simonh]

Article link: MIT Technology Review article on the EmDrive

So fair enough, I'll go from thinking this almost certainly all bunk to admitting they've got the beginnings of a credible theory. There's still a long way to go though. We still don't have any really robust experimental evidence. For example this theory might explain why microwave resonance in the cavity might product thrust, but the disabled 'control' version of the experiment that vented the microwaves so they couldn't resonate still supposedly measured the same thrust as the resonating version. So the theory and the experiment produce some results that correlate, but also still produce at least some directly contradictory results.

Also there's this little gem: "McCulloch’s theory could help to change that, although it is hardly a mainstream idea. It makes two challenging assumptions. The first is that photons have inertial mass. The second is that the speed of light must change within the cavity."

Right. So now we're in Acubierre territory. We have a theory of how it might work, _if_ this and that impossible thing are actually possible. That's better than having no theory at all though, I suppose.

Simon Hibbs

 

[Tenacious-Techhunter]

Some clarification:

“EmDrive”s and “M-Drive”s are not the same thing; in this case, “Em” is short for “Electromagnetic”, which refers to the microwaves providing the thrust. Additionally, “M-Drive” behavior varies between different versions of Traveller; the “EmDrive” discussed in the article is incompatible with Mongoose’s M-Drive requirements, since M-Drives can be placed anywhere inside the ship and still work, and “EmDrives” need an output nozzle.

Also, don’t consider being published in “MIT Technology Review” as “endorsed by MIT”; they’re just a magazine with the same usual fallible reporters.

I would also describe the current state of affairs differently:

They have a somewhat reliable observable phenomenon, but no reliable theory to explain that phenomenon, much less test and prove that theory, and provide a direction for improving power, efficiency, and other such things. More like what used to be “flying bumblebee” territory, except we get how those fly now.

 

[simonh]

Yes to all of that, except I'm not sure the microwave thruster (to give it's other commonly used name) needs a nozzle does it? It's an echo chamber for microwaves bouncing back and forth in the cavity. I suppose the energy needs to be vented somehow, but I'd have though that would be in the form of heat and some microwave radiation leaking out.

Also if the proposed effect is what's going on, the drive can only ever work for very low thrust. No EmDrive-6, or even EmDrive-1.

Simon Hibbs

 

[Reynard]

It's similar to an ion drive.

 

[Tenacious-Techhunter]

Ion thrusters use Ions as propellant. The point of an "Em-Drive" is it doesn't need propellant. They are not similar. Sorry.

 

[madmike]

The EM drive is reactionless as it does not need any form of reaction mass to eject rearwards to provide thrust. An ion drive uses a gas such as argon to create ions which are ejected rearwards at high velocity to provide low thrust.