Chinese Say They're Building 'Impossible' Space Drive, the EmDrive ('Relativity Drive')

http://blog.wired.com/defense/2008/09/chinese-buildin.html

by nickb • 18 years ago

11 17 18 years ago

blog.wired.com

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.

mechanical_fish• 18 years ago

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.

DougBTX2• 18 years ago

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

nazgulnarsil3• 18 years ago

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.

DougBTX2• 18 years ago

> 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.

tlrobinson• 18 years ago

"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?

kf• 18 years ago

Sounds like a hoax.

Eliezer• 18 years ago

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

schtog• 18 years ago

which one?

ed• 18 years ago

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

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

tomjen• 18 years ago

They don't care. If just one of these projects pay of, the rest is peanuts.

hugh• 18 years ago

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

DanielBMarkham2• 18 years ago

How about just a plain improbability drive?

MaysonL• 18 years ago

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.

DanielBMarkham2• 18 years ago

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.

ghiotion• 18 years ago

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.

Chinese Say They're Building 'Impossible' Space Drive, the EmDrive ('Relativity Drive')

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