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      CommentAuthorTrim
    • CommentTimeFeb 6th 2013 edited
     
    W uk

    Did I get this wrong. So it seems did Al.

    EmDrive: China's radical new space drive
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      CommentAuthorDuracell
    • CommentTimeFeb 6th 2013
     
    Very interesting ...
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      CommentAuthorpcstru
    • CommentTimeFeb 6th 2013
     
    You may have found yet another soon.
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      CommentAuthormaryyugo
    • CommentTimeFeb 6th 2013 edited
     
    Suppose this works. You still have to power the microwave source. I suppose you could use an RTG maybe. I wonder what the efficiency is -- what proportion of the microwave energy dissipated ends up as thrust vs how much is radiated or converted to heat.
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      CommentAuthorAngus
    • CommentTimeFeb 6th 2013
     
    I think pcstru's take is likely accurate. But if it does work it would be fantastic - youdon't have to carry the reaction mass with you: you create it as needed, so to speak.

    No more step-rockets.
    • CommentAuthorspinner
    • CommentTimeFeb 6th 2013
     
    >>The latest paper describes their latest thruster and gives the test results in details, showing that with a couple of kilowatts of power they can produce 720 mN (about 72 grams) of thrust.

    A couple of kW, (more or less), for a few grams of "reactionless" trust?
    Not impressed...
    Still, it's more powerful than solar-sailing...
    Or not?

    We need something much more powerful and efficient to fool around the space..
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      CommentAuthorAngus
    • CommentTimeFeb 6th 2013 edited
     
    Hyabusa got back to Earth with the first asteroid sample, after the failure of a whole lot of stuff, using only her four ion engines each having 8 milliNewtons thrust. And two of the ion thrusters quit en route as well.

    20 odd mN is a quite useful thrust, especially if you don't have to drag reaction mass around. 700 mN is downright respectable.

    However, I'm having a lot of trouble believing in it.
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      CommentAuthorTrim
    • CommentTimeFeb 6th 2013
     
    So am I.

    @Spinner

    Sawyer claims that if it is possible to increase the Q by cooling the thruster so that it becomes super conducting the thrust will increase to tons.

    @Angus

    Step rockets will still be needed unless Skylon works.
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    Conservation of momentum? Shawyer's "explanation" has always been bogus, and the linked paper doesn't even mention CofM as far as I can tell.
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      CommentAuthorAngus
    • CommentTimeFeb 6th 2013
     
    @Angus

    Step rockets will still be needed unless Skylon works.


    What for? The purpose of the lower stages is to lift the fuel needed by the upper stage. The reaction mass is burnt fuel. If you don't need reaction mass you can run it on a solar panel all the way to orbit.
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      CommentAuthormaryyugo
    • CommentTimeFeb 6th 2013 edited
     
    Posted By: Angus
    @Angus

    Step rockets will still be needed unless Skylon works.


    What for? The purpose of the lower stages is to lift the fuel needed by the upper stage. The reaction mass is burnt fuel. If you don't need reaction mass you can run it on a solar panel all the way to orbit.
    I'm sort of dumb about this kind of stuff but how do you get the solar panel's mass up off the ground with small amounts of thrust? Wouldn't a very large panel (or a heavy radioisotope generator) be needed to get the high sustained power required for the microwave generator? Are you saying a single rocket can do it? Or what?
    • CommentAuthorspinner
    • CommentTimeFeb 6th 2013
     
    Posted By: TrimSo am I.

    @Spinner

    Sawyer claims that if it is possible to increase theQby cooling the thruster so that it becomes super conducting the thrust will increase to tons.


    Resonance is a wonderful thing, but I don't belive that increased Q would benefit in several orders of magnitude higher thrust...


    Posted By: AngusHyabusa got back to Earth with the first asteroid sample, after the failure of a whole lot of stuff, using only her four ion engines each having 8 milliNewtons thrust. And two of the ion thrusters quit en route as well.

    20 odd mN is a quite useful thrust, especially if you don't have to drag reaction mass around. 700 mN is downright respectable.

    However, I'm having a lot of trouble believing in it.

    Yes, indeed...

    700 mN of thrust is very respectable, considering the technology involved ("reactionless"...), or environment...

    Of course, it's also quite unbelivable.

    Hmm, I'll go and check if an up-link station nearby is still at the same location... ;-)
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      CommentAuthorTrim
    • CommentTimeFeb 6th 2013 edited
     
    @Angus

    When I read about the Emdrive a few years ago it didn't work well going against a gravity well. In theory if the Q was high enough A car with Emdrive could drive off the empire state and keep at the same level with regards the earth, if it tried to rise (using the drive) the 'field' would collapse and it would fall.
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      CommentAuthorAngus
    • CommentTimeFeb 6th 2013
     
    Posted By: Trim@Angus

    When I read about the Emdrive a few ago it didn't work well going against a gravity well. In theory if theQwas high enough A car with Emdrive could drive off the empire state and keep at the same level with regards the earth, if it tried to rise (using the drive) the 'field' would collapse and it would fall.


    It's sounding worser all the time. Is it destroying the Equivalence Principle as well as Conservation of Momentum?
    • CommentAuthortinker
    • CommentTimeFeb 6th 2013
     
    Destroying the Credibility Principle.
    • CommentAuthorcwatters
    • CommentTimeFeb 6th 2013
     
    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


    It might be a viable way to power cars?
    • CommentAuthorjoshs
    • CommentTimeFeb 6th 2013
     
    Posted By: TrimW uk

    Did I get this wrong. So it seems did Al.

    EmDrive: China's radical new space drive
    The Chinese are mistaken. It doesn't work. The maths of why have been around for years. Some idiots even some with Ph.D.s still believe in the Papp myth. It shouldn't be too surprising that some believe Shawyer's tale. Those who have tested carefully have found it doesn't work.
    • CommentAuthorjoshs
    • CommentTimeFeb 6th 2013
     
    Posted By: cwatters
    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


    It might be a viable way to power cars?
    Yes, as long as the only trips taken are downhill it can work for cars.
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      CommentAuthorTrim
    • CommentTimeFeb 6th 2013
     
    He used to say it was no use to accelerate a vehicle in a gravity field but used to confuse me by showing a video of an Emdrive (?) driving a contraption in a circle on an air bearing.
    • CommentAuthorjoshs
    • CommentTimeFeb 6th 2013
     
    The common theme is that you are often confused.