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#1 |
Scholar
Join Date: Feb 2008
Posts: 58
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EmDrive? woo or not?
http://www.wired.co.uk/news/archive/...nd-cold-fusion
http://emdrive.com/principle.html I just came across the following article describing a propellantless drive for space applications and wanted some opinions from those with more knowledge in the field than me on whether it is based in reality or not. In the article they claim 'that with a couple of kilowatts of power they can produce 720 mN (about 72 grams) of thrust.' That claim seems believable from a laymans perspective, but they then appear to go off the deep end with the following claim: 'By using superconducting apparatus, Shawyer says that the Q value, and hence thrust, can be boosted by a factor of several thousand -- producing perhaps a tonne of thrust per kilowatt of power. Suddenly it's not about giving a satellite a slight nudge, it's about launching spacecraft.' So what are peoples opinions? Something to watch with interest or a scam for the gullible? |
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#2 |
Daydreamer
Join Date: Jul 2008
Posts: 8,044
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What the hell is a tonne of thrust? What's that in newtons?
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#3 |
Penultimate Amazing
Join Date: Jun 2005
Posts: 14,900
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And how to convert it to 'furlongs per fortnight'?
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#4 |
Banned
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#5 |
Scholar
Join Date: Feb 2008
Posts: 58
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from http://emdrive.com/secondgenengines.html i get:
'At present, superconducting microwave cavities are restricted to high energy physics applications. An example is the European Tesla accelerator where 20,000 S Band niobium cavities cooled with liquid helium will form the basis of the main accelerators. Early production versions of these cavities readily achieve Q values of 5 x 109 (BAUER, S. et al ‘Production of Superconducting 9-cell Cavities for the Tesla test facility, Standford University and Forschungszentrum Rossendorf’ Accel Instruments GmBh). This would lead to a static specific thrust of 3.15 x 104 N/kW (3.2 tonnes / kW). A second generation engine using similar technology would however be subject to equation 2, and the effect at these high values of unloaded Q is dramatic. An average velocity of only 0.1 m/sec will reduce the specific thrust to 0.93 Tonne / kW.' Which means next to nothing to me but hopefully you can translate ![]() |
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#6 |
Banned
Join Date: Oct 2012
Posts: 4,628
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^^^ what he said
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#7 |
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#8 |
Hyperthetical
Join Date: Nov 2006
Location: Pennsylvania
Posts: 13,498
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From the Principle of Operation page:
Quote:
Special Relativity says nothing of the sort. Quite the contrary: it says the laws of physics remain the same in any inertial reference frame. You can choose whatever frame is most convenient to assess the system, as long as you assess the wave and the waveguide with respect to the same reference frame. Laser gyroscopes detect rotation, which is not movement in an inertial reference frame. I suspect that the lengthy equation-filled pdf "theory paper" merely repeats in more detail the same basic misconception about reference frames. That is, it calculates the force at one end of the waveguide in one reference frame, the force at the other end in a different reference frame, and fails to notice (assuming everything else is calculated correctly) that once these forces are translated into the same reference frame there is no net force. However, I haven't gone through it in detail to verify that. Respectfully, Myriad |
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#9 |
Daydreamer
Join Date: Jul 2008
Posts: 8,044
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Ah, that makes sense. I'm not used to seeing force described in units of weight. Looking it up, I did find a calculator for it... http://www.sengpielaudio.com/calculator-forceunits.htm
It looks like a ton of force can be any of three different values, depending on whether you're using short, long or metric units. (I'm more used to seeing figures for power rather than figures for force.) |
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#10 |
Banned
Join Date: Oct 2012
Posts: 4,628
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I had never heard it described as newton/meters until I discovered the UK car show Top Gear. They use both measurements on there relative to the country of origin of the car I guess (as I reckon they use the printed stats and info released by the manufacturer in regards to performance)
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#11 |
Scholar
Join Date: Feb 2008
Posts: 58
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ok so junk science by the sound of it?
Disappointing but not unexpected really. I guess I'll just have to wait to see if they can pull off a working prototype and prove us all wrong then. |
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#12 |
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#13 |
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#14 |
Philosopher
Join Date: Nov 2006
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#15 |
Penultimate Amazing
Join Date: Jul 2006
Posts: 18,534
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The TESLA project has been defunct for nearly a decade, so using it in a paragraph beginning "at present" seems a little odd.
Other than that, yeah, it's nonsense. I think it's been discussed here before. I very nearly wrote a post noting that there was nothing wrong with the principle, since radiation pressure means shooting light out of a waveguide must produce thrust. Then I noticed that they're not actually talking about shooting light out of a waveguide, but having closed off at both ends and just bouncing light backwards and forwards. This absolutely will not produce any thrust. A closed system can't produce a net external force on itself. That's very basic conservation of momentum - if you don't shoot anything out the back, you don't go forwards. |
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#16 |
Penultimate Amazing
Join Date: Mar 2008
Location: New Zealand
Posts: 21,532
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Other than the emdrive looking like woo, the last claim is dubious to say the least. The Saturn V rocket for example had a first stage thrust of 7,648,000 pounds-force (34,020,000 N) to deliver 260,000 pounds (120,000 kg) to LEO.
They are talking about a thrust of about 9810 N. |
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#17 |
Penultimate Amazing
Join Date: Mar 2008
Location: New Zealand
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I can even make a wild guess at what they are actually measuring. They have a closed, tapered microwave guide. Maybe the narrow end is hotter than the broader end. If their apparatus is made of materials that can out-gas than there will be more out-gassing from the narrow end. So what they are measuring could be an actual thrust from their apparatus emitting gas.
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#18 |
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#19 |
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#20 |
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#21 |
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Right, that's what I first noticed too. So unless you are accelerating the particles away from you (basically spitting them out the back) you won't get any trust. Certainly not propellant less and I'm not even sure if it reduces the amount of propellant all that much. Ion drives already electromagnetically accelerate charged particles away from you for trust.
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#22 |
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#23 |
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#24 |
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#25 |
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#26 |
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Well, by that definition, IBM is in the same boat.1
![]() The SkyCar has every chance of being possible: the basic principles work, and don't try to rewrite physics. Whether you can get an engine powerful enough and light enough and cost-effective enough all at the same time is just an engineering problem. Trying to get the DOT and FAA to agree on who gets to regulate it might take an act of Hank, though. Achieving thrust by bouncing light around a sealed box, on the other hand... 1Of course, their breakthroughs actually produce results, but there's always another one 'just around the corner', and they actually do provide dividends for investment, but they always like investors. |
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#27 |
Thinker
Join Date: Feb 2013
Posts: 134
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Shawyer claims it's actually an open system because [insert content-free handwaving about laser gyroscopes here]. Of course, for it to be an open system, energy and/or matter must enter or exit the system somehow. It doesn't eject matter, so we can determine that, at best, it must be equivalent to a photon drive...which doesn't give anything like the performance claimed.
And what about laser gyroscopes? Simple: rotating frames are not inertial frames. Same fundamental reason any other gyroscopes work. It's easy to show just how badly this thing breaks conservation laws, despite claims to the contrary. Shawyer put up an updated PDF a while back, 2Gupdate.pdf on the main page of his website. On page 6, amusingly titled "Energy Conservation", Shawyer equates it to a classical electric machine, accelerating when power is input and producing power when accelerated. It's pretty straightforward to see that simply standing an EmDrive on end on Earth's surface would make either an infinite energy sink or an infinite energy source, depending on orientation. |
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#28 |
Banned
Join Date: Oct 2007
Posts: 20,121
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Thermo-dynamics is the morality of science.
Eventually, we can reject free energy because it is immoral. It's against the law. |
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#29 |
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#30 |
Thinker
Join Date: Feb 2013
Posts: 134
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While producing an endless stream of energy from nowhere in one of those cases, and making an unlimited amount vanish from the universe in the other. If you think it might somehow come from or go into the Earth's kinetic energy, just put an identical one on the far side to cancel any planetary accelerations. It's Earth's gravitational acceleration that's relevant to my argument...Shawyer doesn't seem to be aware of the equivalence principle.
It's even worse than that. He's claimed that the EmDrive works best when "stationary relative to its thrust". The "Future" section of his website makes clear what he means...his reactionless thruster works best if you don't let it move (you read that right), and its performance decreases as velocity increases. He suggests vehicles using EmDrive for lift and jet engines for forward propulsion, to "limit kinetic output". Throughout the whole thing, it's clear that he thinks velocity is some absolute universal quantity, completely missing the point of relativity. (In fact, he's assuming Earth is in an absolute rest frame...his claims require a geocentric universe.) |
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#31 |
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#32 |
Technical Admin
Join Date: Jul 2006
Location: Canada's Texas
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A new development in this?
http://www.wired.co.uk/news/archive/...le-space-drive
Quote:
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#33 |
Illuminator
Join Date: Aug 2007
Posts: 3,684
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Or test in a vaccuum chamber.
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#34 |
Penultimate Amazing
Join Date: Jun 2005
Posts: 14,900
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Would it work better in the nano- range? I'll have to take a Pico at the theory.
Hmmm, e=mc2, so the waves have mass? And radio waves sent in one direction should give equal thrust in the opposite direction? And since the velocity of radio waves is the speed of light, thrust would depend on the mass of Rock & Roll? Isn't classical music denser? Or is Country-Western the densest? .... Punk Rock? |
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#35 |
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#36 |
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When the chips are down, the buffalo is empty. If every cloud has a silver lining - doesn't that also mean every silver lining has a cloud? I have learned that if you upset your wife, she nags you. If you upset her even more you get the silent treatment. Don't you think it's worth the extra effort? If the early bird catches the worm - shouldn't the worm have stayed in bed? |
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#37 |
Illuminator
Join Date: Apr 2013
Location: Oklahoma
Posts: 4,088
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I found this: Anomalous Thrust Production from an RF Test Device Measured on a Low-Thrust Torsion Pendulum
and Net thrust measurement of propellantless microwave thrusters* So it seems to me instead of "proving it is impossible" the onus is on physicists to explain the measured results. Maybe he has described how it works incorrectly. But that begs the question, how do you explain it? Because you have the claim made by him, followed by 2 independent teams getting measurable thrust. So at this point it is not about proving it impossible, but instead figuring out the physics of the phenomenon. |
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Scott "Permaculture is a philosophy of working with, rather than against nature; of protracted & thoughtful observation rather than protracted & thoughtless labour; & of looking at plants & animals in all their functions, rather than treating any area as a single-product system." Bill Mollison Biome Carbon Cycle Management |
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#38 |
Penultimate Amazing
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#39 |
Penultimate Amazing
Join Date: Jun 2005
Posts: 14,900
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But I would think a system for use near-eaerth would need to push agaisnt the gtravity waves directly, rather than use the reaction thrust alone.
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#40 |
Illuminator
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Scott "Permaculture is a philosophy of working with, rather than against nature; of protracted & thoughtful observation rather than protracted & thoughtless labour; & of looking at plants & animals in all their functions, rather than treating any area as a single-product system." Bill Mollison Biome Carbon Cycle Management |
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