Thrusters On! Reactionless Spacecraft Engines?

Discussion in 'General Science & Technology' started by Yazata, Nov 20, 2016.

  1. Yazata Valued Senior Member

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    Here's something peculiar that a friend tipped me off about:

    NASA researchers say that they injected microwaves into a closed assymmetrical cavity and obtained directional thrust. Not very much thrust, since all they got was about 1.2 millinewton per kilowatt (a newton is the force necessary to accelerate 1 kg at 1 meter/sec/sec), but they note that they might be able to increase this by optimizing the cavity or whatever. The interest in this is twofold:

    1. Practically, used as an engine it wouldn't require that a spacecraft carry the mass associated with fuel. All it requires is electricity which can conceivably be produced by solar panels or radioactive isotopes. One can imagine it being used to produce low-thrust but long-duration continuous impulse to power small interstellar space probes.

    2. Theoretically, this thrust shouldn't be observed. If it doesn't have a mundane explanation, it might just be one of those little observational anomalies that leads to big theoretical developments in physics. The scientific community is apparently very skeptical, but it's a testable result that should be easy to reproduce and can be further investigated.

    Here's the published paper. Read the 'discussion' section where the authors speculate about how this could work without violating the conservation of momentum. It's interesting, if exceedingly speculative to my eye. But no doubt others will investigate it.

    http://arc.aiaa.org/doi/10.2514/1.B36120
     
    Last edited: Nov 20, 2016
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  3. paddoboy Valued Senior Member

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    Yep, this has been discussed at length before......
     
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  5. paddoboy Valued Senior Member

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  7. Q-reeus Valued Senior Member

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    Russ_Watters and ajanta like this.
  8. ElectricFetus Sanity going, going, gone Valued Senior Member

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    EMdrive is interesting, but I am going to need to see one in space actually moving about before I believe it
     
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  9. paddoboy Valued Senior Member

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    Bingo! According to a previous article, they were going to make plans to put it in space.
    Still waiting though.
     
  10. Yazata Valued Senior Member

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    Obviously we will need to see that before we can say that this will be a practical spacecraft drive.

    So far, it appears that it's only about two percent of an ion drive's thrust, but the ion drive requires fuel (and its mass). On the other hand, this new thing appears to have as much as one hundred times the thrust of light sails or laser propulsion. So conceivably it might be able to power small interstellar space probes to high velocities by continuously adding small velocity increments over many years during the the first half of the flight, and deceleration after that. (That would require some long-lived and relatively low-mass source of electricity, such as a radioisotope decay powered generator, perhaps.)

    Of course, that's assuming that the effect is real and not the result of some subtle experimental error.

    But the thing that really interests me is the possibility that there might be some important new physics implicit in how this thing seems to violate the conservation of momentum. (Again, assuming that the effect is real, which is as-yet uncertain.) There is a chance, however small, that this could be another photoelectric effect or Michaelson-Morley experiment.

    I suppose that isolating one of these test-rigs in space might reduce the chances of some kinds of error, such as electromagnetic interactions with the surroundings.
     
    Last edited: Nov 21, 2016
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  11. Russ_Watters Not a Trump supporter... Valued Senior Member

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    It isn't new. It's been around for 15 years. Don't hold your breath that it will pan-out.
     
  12. exchemist Valued Senior Member

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    I've read it. I love the idea of a "wake" in the vacuum, created by a device that pushes on vacuum fluctuations. Very Arthur C. Clarke!
    But I can't say I believe it. Yet. As others have commented, they need to get a thing like this up into space and and try it, to remove sources of error related to the size of the vacuum chamber etc.

    I am also intrigued to see the old "pilot wave" hypothesis in QM given a new lease of life. The 7th duc de Broglie must be smiling.
     
  13. Yazata Valued Senior Member

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    Me either.

    A distinction needs to be drawn between the experimentally observed thrust effect and the proposed 'explanation' in the paper. The former seems to be on a more solid basis than the latter, which seems exceedingly speculative to me. I'd still like to see more experimental confirmation of the thrust effect from other research groups though.

    Yeah, get the experimental rig isolated from anything solid that it might be interacting with, electromagnetically or otherwise. Then see if the thrust is still observed. NASA is well positioned to do that experiment.

    If it still works in space, they still won't know how its working. I kind of like the idea of something ostensibly 'impossible' happening, since it holds out the possibility (however remote) that there's some interesting new physics showing its head. I'm thinking of how the seemingly innocuous photoelectric effect let to the idea of energy quantization, and how the seeming failure of the Michelson-Morley either-wind experiment led to Einstein's theory of special relativity.

    My bet would be similar to Russ' though, that nothing much will come of this. But you never know. This is the kind of thing that makes science fun.

    I'm inclined to think that our understanding of quantum mechanics is still a work-in-progress, especially its physical interpretations. I'd love to see some unexpected new light shined on it from a new direction.
     
    Last edited: Nov 22, 2016
  14. exchemist Valued Senior Member

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    The pilot wave idea seems to be becoming more popular all round, due possibly to this oil drop demonstration that is all the rage. My 13yr old son has even seen it at school. To me, that gives it a fashionability that makes it instantly suspect, but who knows.
     
  15. ElectricFetus Sanity going, going, gone Valued Senior Member

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    According to the paper if this thruster works it could prove pilot wave theory radically changing how quantum mechanics is interpreted.
     
  16. danshawen Valued Senior Member

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    In microwave telecommunication theory, there used to be an idea that certain modes of propagation in a waveguide could have a PHASE velocity that exceeded the velocity of light in a vacuum, but the corresponding GROUP velocity (the maximum velocity at which information modulated on this carrier or pilot wave) was still limited by c.

    If you could arrange an experiment in which the two modes (modulated, unmodulated) combined and interfered with each other going in opposite directions, then the answer is yes, theoretically, you could achieve a net thrust in this manner against the vacuum with no moving parts other than the original microwave source. It may also prove to be a very lossy thrust, requiring many times the amount of energy pumped into it compared to the net thrust out.

    Also, a directed microwave beam also sources thrust all by itself, like any other source of photons or ions would. Not much, but some.

    I know this response will be controversial, and I make no claims to understand the principles involved other than the brief description of the effect I mentioned in these short paragraphs.
     
  17. exchemist Valued Senior Member

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    Er, well, hold on a sec. No theory is ever proved, though an observation can provide evidence for one. Also, they have only a highly speculative hypothesis involving pilot waves. And I don't think that pilot wave theories in themselves predict reactionless thrust, i.e. violation of the conservation of momentum, do they? And if they, or a particular version of a pilot wave theory did, someone would still have to show how to reconcile that with Noether's theorem, wouldn't they?
     
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  18. Yazata Valued Senior Member

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  19. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    This reminds me of the LHC when that Italian group reported finding evidence of super-luminal neutrinos, and published in peer-reviewed, then found a technical glitch as the explanation.
     
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  20. Yazata Valued Senior Member

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    Yeah, I agree. There are lots of examples of what appeared at first to be earth-shaking experimental results, that eventually resolved into experimental errors.

    But the possibility that a relatively simple and easy to replicate experiment has violated Newton's third law has such huge implications that I can't help but be fascinated, even if the chance of it surviving further investigation is relatively low.
     
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  21. OceanBreeze Registered Member

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    The size of the thrust they are getting can be satisfactorily explained by the Lorentz force on the apparatus reacting with the earth’s magnetic field.
     
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  22. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    Details, details. When you're making new discoveries that violate known physics, you tend to overlook the obvious?

    Do you have a reference for this?

    And along these lines, any further word on Rossi and his eCat? Anyone making money by selling the energy (as opposed to selling the hype)?
     
    Last edited: Nov 25, 2016
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  23. OceanBreeze Registered Member

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    I can’t offer any specific details; all I am saying is the magnitude of the measured force is within a range that is not disproportionate with the strength of the earth’s magnetic field and the power being used. To drive the DUT

    The Tesla has the dimensions N*s / C*m where N is Newton, s second, C coulomb, m meter.

    Lorentz Force = I L T, where I is current in coulombs/second and L is length in meters. T is Tesla as defined above

    The observed power/force ratio was on the order of ~ 0.001 N / 1KW of RF power. The DC power into the magnetron would be about 1500 Watts, drawing 10 Amps. Taking the magnetic field strength of the earth to be a nominal 50 uT and 1 meter conductor length. F = 0.0005 N fully 50% of what was measured.

    If you remember the neutrino fiasco, it isn’t out of the question the researchers are overlooking this possible source. Since the earth’s magnetic field cannot be shielded from the experiment, it would be interesting to know what steps were taken to prevent this Lorentz force from interfering with the experimental results.

    I suppose Rossi is still thriving on the theory of P.T. Barnum "There's a sucker born every minute"
     
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