International Business Times writes:
A new peer-reviewed paper (open, DOI: 10.1063/1.4953807) on the EmDrive from Finland states that the controversial electromagnetic space propulsion technology does work due to microwaves fed into the device converting into photons that leak out of the closed cavity, producing an exhaust.
So how could something come out that you can't detect? Well, the photons bounce back and forth inside the metal cavity, and some of them end up going together in the same direction with the same speed, but they are 180 degrees out of phase. Invariably, when travelling together in this out-of-phase configuration, they cancel each other's electromagnetic field out completely.
That's the same as water waves travelling together so that the crest of one wave is exactly at the trough of the other and cancelling each other out. The water does not go away, it's still there, in the same way the pairs of photons are still there and carrying momentum even though you can't see them as light.
If you don't have electromagnetic properties on the waves as they have cancelled each other out, then they don't reflect from the cavity walls anymore. Instead they leak out of the cavity. So we have an exhaust – the photons are leaking out pair-wise.
(Score: 1, Interesting) by Anonymous Coward on Friday June 17 2016, @01:00AM
The ISS is still bound to it's orbital gravity, and slightly to the very thin atmosphere still present at that altitude. It would be better tested in deep space.
(Score: 3, Interesting) by jmorris on Friday June 17 2016, @01:15AM
Building a full space probe complete with solar array large enough to drive and launching it beyond LEO is a lot more expensive than just sticking the drive on the ISS. The orbit of the ISS is well understood so any force shifting it, even a fairly small one, would be easy to spot. Remember the whole point of this gadget is that it can deliver a small but continuous thrust without consuming fuel. A small thrust adds up if it can be sustained for days. All they would need is the weight allowance on a supply mission and a single EVA to bolt the thing to the station and connect it to power.
(Score: 2) by Immerman on Friday June 17 2016, @01:54AM
Why do an EVA? If it's real it should generate the same thrust if you just bolt it to an inside wall.
(Score: 3, Insightful) by deimtee on Friday June 17 2016, @02:00AM
Just in case it really is emitting kilowatts of microwaves maybe? If I was on the station, I think I would prefer it to be outside.
No problem is insoluble, but at Ksp = 2.943×10−25 Mercury Sulphide comes close.
(Score: 2) by tangomargarine on Friday June 17 2016, @02:42PM
Are the walls of the ISS thick enough to protect from that anyway?
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by Immerman on Friday June 17 2016, @03:11PM
Should be - microwaves are normally reflected by even a thin sheet of metal (like the mesh on the front of your microwave oven). The only real question is how question would be just how perfectly canceled any emitted photon pairs are. If they're perfectly aligned, then for most practical purposes they cease to exist and it's not a problem. If however they're only *almost* perfect you'll get interference patterns around the device. Not really sure how shielding would effect that... I think all the normal formulas assume that you're dealing with each photon individually, when pairs start effectively popping in and out of existence.... I wouldn't know where to start.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @02:22AM
But that would fail to prove that EmDrive is not somehow dependent on gravity of larger object or some other property, like radio waves etc that are present in and near Earth's Orbit.
(Score: 3, Interesting) by Dunbal on Friday June 17 2016, @02:02AM
Nah, you put it on the end of a boom. Angular momentum doesn't care all that much about the gravitational field and the boom will magnify the torque you get. If you start getting rotation you know it works.
(Score: -1, Troll) by Anonymous Coward on Friday June 17 2016, @02:07PM
They've done that, and it's spun the stuff.