EM Drive To Receive Peer Review

Discussion in 'Science and Technology' started by Dryson, Sep 3, 2016.

  1. Dryson

    Dryson Captain Captain

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    https://www.google.com/amp/s/www.in...on-and-power?client=ms-android-verizon&espv=1

    The EmDrive is officially headed for its moment of truth, and it’s just a few months away. The physics-violating propulsion device could theoretically open the door to interstellar travel if it somehow works — and while that “if” is pretty damn gigantic, we’re soon going to have a much better sense of how (un)realistic the EmDrive actually is, as the first peer-reviewed paper on the device drops in the December issue of the Journal of Propulsion and Power.

    This will definitely be one of those engine tests that defines the future of rocketry.
     
  2. Asbo Zaprudder

    Asbo Zaprudder Rear Admiral Rear Admiral

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    It doesn't look like it should work but yet apparently the drive does produce thrust when tested. I believe it's been proposed that the propulsive exhaust momentum is in the form of photon pairs, which are very hard to detect as their EM fields cancel out. If this mechanism could be confirmed, I expect that the design of the microwave cavity could be optimised to produce the photon pairs. It still has a whiff of snake oil about it though and reminds me somewhat of the ridiculous notions about gyroscopes made by Eric Laithwaite back in the 70s.
     
  3. YellowSubmarine

    YellowSubmarine Rear Admiral Rear Admiral

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    I'm pretty confident that the EM drive doesn't work (or, less likely, emits radiation / loses mass we have not yet detected). However, I've been cautiously hopeful we might see some challenging discovery in physics within my lifetime that requires additions / modifications to current theories, even major ones. I've been particularly hoping for things that would make it easier to do interplantetary and interstellar travel, as well as things that may allow us to avert the heat death of the universe. By the current laws of physics it is insanely difficult to go between stars, and it seems that we're all going to die.*

    Which is why I spent an hour yesterday in reading about this thing, as it is about as good as any chance to discover something unexpected. I believe these were posted in the previous thread on the subject here, but I didn't read it then.

    First off, a group researchers from Dresden ran tests on the EM drive that challenge the claims (warning: PDF) the drive is producing useful thrust. They were able to observe thrust in different directions, and they attributed it to interaction caused by the power feeding lines, and the net useful thrust was not there.

    Also a group of Chinese researches initially reproduced the experiment and observed thrust (PDF). Now almost the same group of people published a second article that indicates that once the wire interaction is discounted, the thrust can no longer be confirmed (PDF) (or I think it says so, as only the abstract is in English).

    IOW, the EM drive seems to be a pile of poop. However, what I found much more interesting is the potential explanation for why it might work if it does (it does not). A researcher from Plymouth put forward his own controversial theory as an explanation, suggesting it's caused by Unruh waves. Now, forget the explanation itself. I had a lot of fun reading about what the Unruh effect actually is, which I had to do for the abstract of the article to start making any sense. It's pretty interesting. So interesting it nearly made me think the drive worked.

    In reality, my hopes for any breakthroughs are probably false, since there's enough reason to expect that current laws of physics are mostly complete and accurate for just about anything you'd come across, so probably any tweaks will be minor. And the EM drive would require quite a big one, or at least seems to. Now, finding one specific very narrow exotic phenomena that doesn't follow the law of conservation of momentum may not be as big a change as it sounds, as the law would still be true for everything else, but the EM drive sounds too simple to construct, which means it's not really that exotic.



    (* We would have lived and explored more then enough until then, so it's not really a big deal, in fact there wouldn't be much point to live on for so long as a civilization, we would just be repeating our history over and over (bad parts included) at this point. But I have the tendency to get easily depressed by such prospects, so I've been stacking false hope against false problems. Solves them all right. :bolian: )
     
  4. Asbo Zaprudder

    Asbo Zaprudder Rear Admiral Rear Admiral

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    ^ The definitive proof or refutation would be to put the drive on a satellite and see if it has any measurable effect. The lab tests appear to be stymied by interactions with the power lines as you state. If any achievable thrust is quantised, that could suggest that something like the Unruh effect is in play. I understand that the mooted photon pair thrust mechanism would be detectable using interferometric methods but I don't know the details.
     
  5. JWPlatt

    JWPlatt Commodore Commodore

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    Not exactly. Just the incident solar radiation on the satellite and its own heat can impart thrust. Difficult to isolate.
     
  6. Asbo Zaprudder

    Asbo Zaprudder Rear Admiral Rear Admiral

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    Current models of the drive are supposedly able to produce ~100 µN of thrust (and 100 mN is claimed to be possible) -- that's significantly more than the typical thrust forces due to thermal and solar radiation, which I believe are much smaller. In any case, I think it should be possible to disambiguate by thrusting in orthogonal directions and measuring the change in acceleration.

    ETA: Personally, I've always had severe doubts about the claims made for the drive for the reasons stated by Greg Egan and John Baez ten years ago.

    https://golem.ph.utexas.edu/category/2006/09/a_plea_to_save_new_scientist.html
    https://golem.ph.utexas.edu/category/2006/10/new_scientist_reacts.html

    The maximum thrust possible with the device firing a beam of photons in one direction is P/c = 3.33 µN/kW. As the quoted thrust per kilowatt is tens to thousands of times greater than this, the device is apparently not conserving energy, never mind momentum.
     
    Last edited: Sep 4, 2016
  7. Dryson

    Dryson Captain Captain

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    Forbes - EM Drive Passes Peer Review - http://www.forbes.com/sites/startsw...-the-emdrive-passes-peer-review/#7e6c09c1692c

    And despite the fact that this seems to violate the known laws of physics, a prototype device was submitted to NASA’s Eagleworks lab for testing. Perhaps surprisingly, the test came back positive: there wasthrust observed despite the lack of a reaction. And if Dr. José Rodal from the NASA Spaceflight forums can be trusted, the paper resulting from the test, “Measurement of Impulsive Thrust from a Closed Radio Frequency Cavity in Vacuum” by Harold White et al., was just accepted for publication in the peer reviewed Journal Of Propulsion And Power, by AIAA
    .
    And despite the fact that this seems to violate the known laws of physics....there are alot of things in space that violate know physics.

    1.Primordial Space
    2.The Big Bang - How can you explain the Big Bang if you cannot explain where the material from the Big Bang came from?
    3.Dark Matter
    4.Black Holes
    5.Em Drive
     
    Last edited: Sep 4, 2016
  8. Asbo Zaprudder

    Asbo Zaprudder Rear Admiral Rear Admiral

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    I have no idea what you mean by this.
    Here's one, non-religious, explanation:
    A Universe From Nothing by Lawrence M. Krauss
    I admit it is known that conservation of energy is a tricky problem in General Relativity, see for example:
    Is Energy Conserved in General Relativity?
    No. We don't even know what it is to be able to state that it violates known physics. All we know is that an invisible something accounts for 27% of the universe's mass-energy. Dark energy (source also unknown) accounts for 68%.
    Er, no they don't. Reference otherwise please.
    Not yet tested in space. So no.

    If more energy comes out than goes in, you have yourself the makings of a perpetual motion machine and possibly a big-ass superweapon. You likely won't get a patent for it.
     
    Last edited: Sep 5, 2016
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  9. Dryson

    Dryson Captain Captain

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    So you are refuting what a trusted Doctor has stated?

    And if Dr. José Rodal from the NASA Spaceflight forums can be trusted, the paper resulting from the test, “Measurement of Impulsive Thrust from a Closed Radio Frequency Cavity in Vacuum” by Harold White et al.,was just accepted for publication in the peer reviewed Journal Of Propulsion And Power, by AIAA.

    I'm going to have to say that NASA is little bit more trustworthy.
     
  10. Asbo Zaprudder

    Asbo Zaprudder Rear Admiral Rear Admiral

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    I would caution against resorting to argument from authority. Even university professors (and Einstein himself) often get (got) things wrong. It seems very unlikely but given that the drive hasn't been exposed as a sham in the last ten years it might work as advertised. I'd like to see it tested in space. Damn the expense.

    The problem of where the excess energy or momentum is coming from remains -- it might well be being extracted from the vacuum field, Unruh effect, whatever as suggested although the inventor claims otherwise with some mathematics that is generally thought to be nonsense, even by supporters of the device. However, I think there would be serious ramifications for nation states gaining access to an unlimited supply of "zero-point energy" by relatively simple means. No-one knows what destructive spin-off technologies might be exploitable militarily.
     
    Last edited: Sep 5, 2016
  11. psCargile

    psCargile Commander Red Shirt

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    Read "The Hidden Reality" by Dr. Brian Greene.

    On the EM drive, when it first was announced, I wondered why they didn't do the obvious layman test and put it in a wagon and have it roll across the floor. Obviously no one saw a need to bolt it down like a jet engine in a test stand after pulling it's remains from the wall on the first fire-it-up. I mean, there is thrust, and there is thrust that can be used in a Jetson's car.

    Am I missing something?
     
  12. sojourner

    sojourner Admiral Admiral

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    The EM drive (if it works) thrusts at such a low level it would only be useful in space.
     
  13. JWPlatt

    JWPlatt Commodore Commodore

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    Are Greene's books as bound up in cheesy real-world analogues as his TV specials? I used to like physics specials, but they became far too dumb.
     
  14. Asbo Zaprudder

    Asbo Zaprudder Rear Admiral Rear Admiral

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    Unlike the TV shows, his books are not aimed at a lowest common denominator audience. The shows probably make him more money.
     
  15. psCargile

    psCargile Commander Red Shirt

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    ^^Kind of, yes. One involved slicing a loaf of bread to explain. . .something. But the part in this book that described the inflaton field as repulsive gravity that upon dropping to its lowest energy state littered the universe with matter was quite clear.

    ^^^Better than an ion drive?
     
  16. Asbo Zaprudder

    Asbo Zaprudder Rear Admiral Rear Admiral

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    Unlike ion drives, no propellant mass required as an Em drive is (supposedly) reaction-less -- as long as you can generate electricity, you have thrust. The claimed thrust is about the same as for current ion drives (25 - 250 mN).

    ETA: 25 - 250 mN is equivalent to 0.005625 - 0.05625 lbf (1 pound-force (lbf) is equal to the force of Earth's surface gravity acting on a mass of 1 lb; 1 N (newton) is the force required to accelerate a 1 kg mass at 1 m/s^2 in the direction of the applied force; Earth's surface gravitational acceleration is 9.81 m/s^2 so a 1 kg mass experiences a force of 9.81 N; 1N = 0.225 lbf).
     
    Last edited: Sep 6, 2016
  17. psCargile

    psCargile Commander Red Shirt

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    So great for small probes. Solar panels or RTGs. . . huge delta v budget.
     
  18. Asbo Zaprudder

    Asbo Zaprudder Rear Admiral Rear Admiral

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    Fine outside of gravity wells -- just keep thrusting.
     
  19. psCargile

    psCargile Commander Red Shirt

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    It's essentially a magnatron, so cavity size determines frequency. Is the thrust a result of input power, frequency, both, or something else? In other words, how is acceleration controlled?

    I'm more sceptical about application than producing thrust.
     
  20. Asbo Zaprudder

    Asbo Zaprudder Rear Admiral Rear Admiral

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    I don't know those details with any reliability and I'm sceptical about the whole thing. It smells so badly of pseudoscientific nonsense or a snake-oil scam that I never delved that deeply and I'm not going to unless either the Em drive or the Cannae drive is tested in space and is found to work. I'm highly suspicious because, although some groups have claimed to have tested the Em drive on Earth, there seems to be wide variation in the thrust achieved and the drive's operational characteristics. One theoretical analysis by Mike McCulloch claims that the obtainable thrust will be quantised and suggests experiments to test his hypothesis.
    http://iopscience.iop.org/article/10.1209/0295-5075/111/60005/meta