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posted by cmn32480 on Tuesday November 22 2016, @03:21PM   Printer-friendly
from the that-still-doesn't-mean-it-will-work dept.

After months of speculation and leaked documents, NASA's long-awaited EM Drive paper has finally been peer-reviewed and published [open, DOI: 10.2514/1.B36120] [DX]. And it shows that the 'impossible' propulsion system really does appear to work. The NASA Eagleworks Laboratory team even put forward a hypothesis for how the EM Drive could produce thrust – something that seems impossible according to our current understanding of the laws of physics.

In case you've missed the hype, the EM Drive, or Electromagnetic Drive, is a propulsion system first proposed by British inventor Roger Shawyer back in 1999. Instead of using heavy, inefficient rocket fuel, it bounces microwaves back and forth inside a cone-shaped metal cavity to generate thrust. According to Shawyer's calculations, the EM Drive could be so efficient that it could power us to Mars in just 70 days.

takyon: Some have previously dismissed EmDrive as a photon rocket. This is addressed in the paper along with other possible sources of error:

The eighth [error:] photon rocket force, RF leakage from test article generating a net force due to photon emission. The performance of a photon rocket is several orders of magnitude lower than the observed thrust. Further, as noted in the above discussion on RF interaction, all leaking fields are managed closely to result in a high quality RF resonance system. This is not a viable source of the observed thrust.

[...] The 1.2  mN/kW performance parameter is over two orders of magnitude higher than other forms of "zero-propellant" propulsion, such as light sails, laser propulsion, and photon rockets having thrust-to-power levels in the 3.33–6.67  μN/kW (or 0.0033–0.0067  mN/kW) range.

Previously: NASA Validates "Impossible" Space Drive's Thrust
"Reactionless" Thruster Tested Again, This Time in a Vacuum
Explanation may be on the way for the "Impossible" EmDrive
Finnish Physicist Says EmDrive Device Does Have an Exhaust
EmDrive Peer-Reviewed Paper Coming in December; Theseus Planning a Cannae Thruster Cubesat


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  • (Score: 3, Informative) by butthurt on Tuesday November 22 2016, @10:31PM

    by butthurt (6141) on Tuesday November 22 2016, @10:31PM (#431532) Journal

    VASIMR creates a plasma, which is expelled. This appears, so far, to have no reaction mass.

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  • (Score: 2) by JoeMerchant on Wednesday November 23 2016, @03:52AM

    by JoeMerchant (3937) on Wednesday November 23 2016, @03:52AM (#431649)

    It seems to me that everybody is getting worked up about "no mass" - but didn't Einstein make this famous over 50 years ago? E=mc2... so if we've found a way to convert pure energy to force, or momentum, maybe there's some energy to mass (perhaps and back again) conversion operation at work?

    --
    🌻🌻 [google.com]
    • (Score: 4, Interesting) by butthurt on Wednesday November 23 2016, @05:33AM

      by butthurt (6141) on Wednesday November 23 2016, @05:33AM (#431680) Journal

      Pure energy--light--does indeed have momentum and exerts a force, called radiation pressure. That is how a solar sail works. Microwave radiation is a kind of light; if that were leaking from the device, it could explain the force that's observed. However, the experimenters checked for that and didn't find it happening. That leaves open the possibility that the force is caused by a hitherto unknown mechanism. That is interesting, as is the possibility that forces generated with this device could exceed (for the same power) what we'd expect from radiation pressure.

      https://en.wikipedia.org/wiki/Radiation_pressure [wikipedia.org]
      https://en.wikipedia.org/wiki/Solar_sail [wikipedia.org]

      • (Score: 0) by Anonymous Coward on Wednesday November 23 2016, @09:40AM

        by Anonymous Coward on Wednesday November 23 2016, @09:40AM (#431768)

        I still think there's something wrong.
        They're saying "we have this electro-magnetic device that will accelerate in a certain direction".
        Momentum has to be conserved, so either there are photons taking away the corresponding momentum, or they don't have an electro-magnetic device.
        If this article passed peer review, I would like to see the experiment replicated, but I still say it's a lot less likely they discovered some unknown field than it was for neutrinos to go faster than light a few years ago (and that turned out to be an experimental error).

        The alternative: momentum is not conserved.
        I personally find the concept of the bible being literally true much less disturbing than the idea that momentum is not conserved.

        • (Score: 2) by JoeMerchant on Wednesday November 23 2016, @02:05PM

          by JoeMerchant (3937) on Wednesday November 23 2016, @02:05PM (#431813)

          Some previously unknown interaction between what appears to be a "normal" EM field and momentum would seem to me to be: A) less disruptive to current paradigms than FTL travel, B) much more plausible than a literal transformation of clay into a living, breathing homo sapiens (unless a billion years of evolution was left out to make the story flow better... but then there's still the rib thing.)

          --
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      • (Score: 3, Interesting) by dak664 on Wednesday November 23 2016, @02:11PM

        by dak664 (2433) on Wednesday November 23 2016, @02:11PM (#431815)

        More generally, the electromagnetic interaction transfers action (4-momentum dot 4-distance) between two points in space time. Action transfer is quantized which can be described mathematically by raising and lowering operators on the number of "photons" in a field. However these photons by definition have no space-time existence and can not be detected during transit. To say the photon or field "has" or "carries" momentum is misleading, the action transfer occurs between the endpoints only.

        So not being able to detect EM emission from the device would not preclude momentum transfer to some more distant region. The Aharonov–Bohm effect is an example of such a transfer through a region that contains no EM field (e.g. zero E-squared + B-squared energy).

        However it seems way more probable to me there is some parasitic coupling from the power generator to the thrust-measuring device. Maybe a loose ground connection.

        • (Score: 2) by butthurt on Wednesday November 23 2016, @05:28PM

          by butthurt (6141) on Wednesday November 23 2016, @05:28PM (#431948) Journal

          [...] photons by definition have no space-time existence [...]

          I don't understand. There's evidence that they propagate through space. Are you saying that a resting photon can't exist?

          To say the photon or field "has" or "carries" momentum is misleading, the action transfer occurs between the endpoints only.

          I'm reading it as though you're suggesting that radiation pressure can only occur when there is something to absorb photos. For example, if a space traveller turns on a flashlight and points it at a nearby planet, the traveller's momentum will change, but if the traveller aims the flashlight into deep space, the traveller's momentum will be unaffected because there's no end point to receive the light. Am I misunderstanding?

          • (Score: 2) by dak664 on Wednesday November 23 2016, @06:12PM

            by dak664 (2433) on Wednesday November 23 2016, @06:12PM (#431983)

            Correct, the phase velocity of a massless particle is always C. The group velocity can be different through regions of varying potential.

            Classically the fields do contain energy that propagates in 3 space, and your flashlight launches energy and momentum into the field whether or not it is ever absorbed by distant matter. If it *is* absorbed somewhere the event-separation of that light-like interaction is by definition zero and there can be no intervening events in the space-time manifold. If it is *not* absorbed then it seems there is nothing to enforce the quantized field. But relativistically there has to be some recipient for the action since the emission and absorption of the "photon" is the same event.

            If the EM waves were propagating through some stationary ether, special relativity and quantum mechanics would probably both go away. Along with everything else, I suspect.