

Chinese Say They're Building 'Impossible' Space Drive, the EmDrive ('Relativity Drive') - nickb
http://blog.wired.com/defense/2008/09/chinese-buildin.html

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tlrobinson
_"According to Roger Shawyer, the British scientist who developed the concept,
the drive converts electrical energy into thrust via microwaves, without
violating any laws of physics."_

Wouldn't it be much more interesting if they actually _did_ violate the laws
of physics?

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MaysonL
Obviously, this is a crazy idea. But, with Feynman, I have to ask: "Is it
crazy enough to be worth taking seriously?". I wish I had enough physics to
answer that question.

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nazgulnarsil
interesting. in essence what we have here is a variation on the photon drive
where instead of being bounced off an open reflector to generate momentum you
have a closed cone. at first glance this would seem absurd since the forces
acting on the two ends of the cone should cancel each other out. where it gets
interesting is that this guy claims that the math shows that the photons are
operating in a special frame of reference: essentially even though the photons
are enclosed they behave as if they were not. thus momentum is imparted in one
direction and all you have to do is keep pumping microwaves into the cone.
being able to use electricity instead of some sort of stored propellant would
be a huge step towards sustainable space flight. here's hoping it works.

and even if it doesn't, science needs weirdos who are willing to work on edge
cases. tesla's professor told him that the AC motor was a perpetual motion
device and thus impossible.

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mechanical_fish
_science needs weirdos who are willing to work on edge cases_

Yes, but there's more than one kind of edge.

The edge of scientific knowledge is worth paying people to explore.

The edge of your own knowledge is worth exploring on your own.

The edge of your funding agent's credulity is very profitable to explore, but
such work doesn't help science at all.

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DougBTX
He ignores the forces on the sides of the tapered wave-guide, calculating
forces only for the end caps[1]. If he was to include the forces on the sides,
I'm quite sure he would find that F_g1 = F_g2 + F_sides exactly.

[1] page 2, <http://emdrive.com/theorypaper9-4.pdf>

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nazgulnarsil
He mentions that axial forces (the momentum imparted by deflection off the
tapered sides of the cone) are taken into account, it might still be wrong but
he didn't just ignore it. keep in mind that the force being produced here is
tiny: 85 milli newtons, and it obviously needs a power source to run. assuming
that the math doesn't add up to a 100% or greater efficiency in the conversion
from electrical energy to momentum i see no reason why this is impossible.

If the drive works as claimed i wonder what the efficiency is in the
transformation from electrical energy to momentum.

~~~
DougBTX
> He mentions that axial forces are taken into account

If he does, he's not included it in his theory paper. Take a look, there is no
mention of "axial forces" or "deflection" in the paper.

In equation 7, he calculates the thrust T using only the difference in
propagation velocity at each plate, but makes no mention of _how_ the
propagation velocity changes. If he did, it would be obvious that you have to
account for radiation pressure on all sides on the tube, not just sides which
happen to be perpendicular to the tube's axis.

> efficiency in the conversion from electrical energy to momentum

The efficiency will be about 0%, so no need to worry.

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nazgulnarsil
you're right. in the paper he is simply doing F2-F1 to give the thrust without
any mention of the surface area of the cone walls. he mentions constructing
the cone to give a "reflection free transmission" which is impossible.

i guess junk science is right. oh well.

from page 6: Note that the reflection-free interface, with matched wave
impedances , will ensure no forces are produced at the interface. <\-- that
doesn't sound possible.

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Eliezer
China doesn't seem to have very good science filters. They're also funding one
of the most hopeless AI projects I know of.

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schtog
which one?

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ed
Maybe he's thinking of Japan's Fifth Generation Computer project?

<http://en.wikipedia.org/wiki/Fifth_generation_computer>

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ghiotion
The Chinese also said their female Olympic gymnasts were 16 years old. I think
it's a good policy to take what the Chinese say with a grain of salt.

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rms
Sounds like a hoax.

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hugh
I'll be more interested once they start building a possible one.

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DanielBMarkham
How about just a plain improbability drive?

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DanielBMarkham
I have no doubt that one day one of these crazy web stories will be true --
somebody will invent a field propulsion system.

Odds are this ain't it, though.

