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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, Informative) by takyon on Friday June 17 2016, @01:26AM

    by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Friday June 17 2016, @01:26AM (#361354) Journal

    There's a figure for efficiency: Newtons per Watt. If the thing works, it will become clear if it can compete with state-of-the-art ion drives like VASIMR [wikipedia.org].

    Newtons per Watt isn't necessarily the whole story since emdrive also has the advantage of being "propellantless" (assuming it works). But I have heard talk about emdrive reaching anywhere from 4 times to hundreds of times the Newtons per Watt of ion drives, which would make a clear difference.

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  • (Score: 1, Interesting) by Anonymous Coward on Friday June 17 2016, @01:56AM

    by Anonymous Coward on Friday June 17 2016, @01:56AM (#361362)

    Adding-

    there all different types of efficiency from volumetric efficiency, fuel efficiency, etc. (at least as applied to IC engines).

    Depending on what this drive brings to the table (weight, output, reliability, fuel use), it could be a huge win even if it has low output.

  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @12:06PM

    by Anonymous Coward on Friday June 17 2016, @12:06PM (#361498)

    While ion drives are electric, they still use propellant, usually Xenon. The electricity is used to accelerate the propellant out the exhaust. When the tank is empty, the engine is useless.

    The interesting thing about this, is that it's electric only. No propellant. And electricity can be "refueled" on the fly with solar panels. That means that - if it works - it can run forever.

    While getting into orbit takes huge rockets, due to air resistance, once you are in orbit, the size of the rocket doesn't matter. What matters is thrust multiplied by time. Think about how an engine that can run forever affects the result of that calculation.

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @02:10PM

      by Anonymous Coward on Friday June 17 2016, @02:10PM (#361543)

      >That means that - if it works - it can run forever.

      Like fucking hitler.

      Fucking Nazi.

    • (Score: 2) by takyon on Friday June 17 2016, @04:23PM

      by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Friday June 17 2016, @04:23PM (#361616) Journal

      Yes... I noted that it was propellantless in the comment.

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