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posted by martyb on Friday June 17 2016, @12:39AM   Printer-friendly
from the invisible-light dept.

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.


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  • (Score: 3, Interesting) by jmorris on Friday June 17 2016, @12:53AM

    by jmorris (4844) on Friday June 17 2016, @12:53AM (#361343)

    How hard would it be to just install one on the ISS, turn it on and see if it produces thrust in space? ISS has the electrical capacity, we know the device doesn't explode or do anything dangerous. Run it a week and it should produce a tiny but measurable change in the station's orbit.

    If it works we can worry about discovering the theory behind it and refining it to be more efficient and if it doesn't we can stop dreaming about an electric rocket engine.

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  • (Score: 1, Interesting) by Anonymous Coward on Friday June 17 2016, @01:00AM

    by Anonymous Coward on Friday June 17 2016, @01:00AM (#361344)

    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

      by jmorris (4844) on Friday June 17 2016, @01:15AM (#361350)

      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

        by Immerman (3985) on Friday June 17 2016, @01:54AM (#361361)

        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

          by deimtee (3272) on Friday June 17 2016, @02:00AM (#361365) Journal

          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.

          --
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          • (Score: 2) by tangomargarine on Friday June 17 2016, @02:42PM

            by tangomargarine (667) on Friday June 17 2016, @02:42PM (#361571)

            Are the walls of the ISS thick enough to protect from that anyway?

            --
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            • (Score: 2) by Immerman on Friday June 17 2016, @03:11PM

              by Immerman (3985) on Friday June 17 2016, @03:11PM (#361589)

              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

        by Anonymous Coward on Friday June 17 2016, @02:22AM (#361369)

        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

      by Dunbal (3515) on Friday June 17 2016, @02:02AM (#361366)

      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

        by Anonymous Coward on Friday June 17 2016, @02:07PM (#361540)

        They've done that, and it's spun the stuff.

        ...

        ...

        NIGGER!

  • (Score: 2) by takyon on Friday June 17 2016, @01:22AM

    by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Friday June 17 2016, @01:22AM (#361351) Journal

    If it has a strong enough thrust to be measured reliably, it doesn't need to be tested in space.

    The creator of the Emdrive has hinted at domestic applications of emdrive and thrust good enough to counteract Earth gravity (yup, Back to the Future 2 style flying cars, and probably bullshit). But there is no need to send an emdrive in space in order to determine if it can compete with ion drives. If it works, it will be very obvious. The Chinese teams testing emdrive have reported higher thrusts than NASA, the creator of emdrive is hiding behind trade secrets, so perhaps the problem is not the concept but the specific design and small budget that NASA scientists have to work with.

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    • (Score: 2) by jmorris on Friday June 17 2016, @02:25AM

      by jmorris (4844) on Friday June 17 2016, @02:25AM (#361371)

      Those high thrust figures are for a proposed version built with superconductors. To date the trusts have been small enough for reasonable people to suspect it is measurement error or side effects like the heat generating drafts of air, magnetic fields attractingt the test stand, etc. If the thing were levitating in mid air I doubt there would be any debate about whether it worked.

  • (Score: 3, Funny) by RamiK on Friday June 17 2016, @02:31AM

    by RamiK (1813) on Friday June 17 2016, @02:31AM (#361372)

    Here's the thing: Since the Higgs, all the theoretical physicists broke down and started mumbling about simulations and the matrix and AIs taking over the world...

    Now, you drop this EmDrive gizmo that shows tests with results they just can't explain... Are you trying to get them all committed? Have some heart man.

    --
    compiling...
  • (Score: 2) by fritsd on Friday June 17 2016, @02:31PM

    by fritsd (4586) on Friday June 17 2016, @02:31PM (#361565) Journal

    How hard would it be to just install one on the ISS, turn it on and see if it produces thrust in space?

    They were going to do that with the experimental VASIMR [wikipedia.org] drive, but I think they forgot..

  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @05:03PM

    by Anonymous Coward on Friday June 17 2016, @05:03PM (#361654)

    YES, install on ISS and push it to Mars!! Big mobile warehouse.