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EmDrive  (Source:
It's a a propellantless microwave thruster that defies Newton's laws of motion

Chinese scientists have taken on a heavily criticized space drive idea that could one day launch satellites, deep space probes and even flying cars.

The research team hails from Northwestern Polytechnic University in Xi'an, and was led by Yang Juan. What they developed was a propellantless microwave thruster called EmDrive, which is a controversial idea because it goes against Newton's laws of motion -- and many have claimed to create a "propellantless" thruster before and failed.

Newton's laws of motion are all based on the idea that firing propellant out of the back at a high speed will push a craft forward. While solar cells offer infinite power, thrust is limited by propellant. Many have tried to get around this, but several scams have made this particular field a joke in the scientific world.

While space drives tend to rely on Newton's laws of motion, the EmDrive is a closed, conical container that has a net thrust toward the wide end when filled with resonating microwaves. This goes against Newton, who said that no closed system could have a net thrust. However, EmDrive works because the microwaves have a group velocity (the speed of a collection of electromagnetic waves) that is greater in one direction than the other -- which is where Albert Einstein's theory of relativity comes in.

British engineer Robert Shaywer, who began looking at the concept of a propellantless thruster when he opened his own company called Satellite Propulsion Research in 2001, is the original creator of the EmDrive. He made demonstration thrusters to prove it could be done, and even made sure the test results were accurate (meaning, the results weren't affected by friction, ionization, air currents, electromagnetic effects or interference). The first, made in 2003, had a thrust of 16 mN. This was enough to show it could be done.

However, he received a ton of criticism for his idea and was ridiculed in his own country. But the Chinese team at Northwestern Polytechnic University believed in his research and took the project head on to author the latest study, "Net Thrust Measurement of Propellantless Microwave Thruster."

The Northwestern Polytechnic University team was able to create the EmDrive with 720 mN of thrust with a couple of kilowatts of power.

So what purpose does EmDrive have? It could halve launch costs of satellites because as much as half the launch weight of these objects are attributed to propellant.

Shawyer is even working on a superconducting thruster that could be ready as soon as 2016. It would boost the Q value of the cavity, which determines the amount of thrust produced. He said it could be boosted by a factor of several thousand, possibly equating to a tonne of thrust per kilowatt of power.

Source: Wired

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A new use for tin foil.
By drycrust3 on 2/9/2013 3:31:18 PM , Rating: 2
Looking at the picture, I don't think the Emdrive itself needs to be so massively constructed. No microwave oven has such a massive iron structure, so maybe the Emdrive could be made with tin foil as long as the absence of air within that cavity is not essential. If air is permissible within the Emdrive cavity, although it may have to be dry air to prevent arcing, then the only vacuum that is essential is that within the magnetron itself. Maybe a voyage in one of these space craft won't be so bad after all: freshly cooked food will be the norm.
There is a video posted on Youtube supposedly showing this in operation, floating in air with a trolley load of test instruments, but there isn't enough shown within the video to show the claims are credible. The rotation is caused by the Coriolis effect. I think your average magician could produce a similar feat.
If the tray and equipment in that video weighs 30 kilos, and earth's gravitational acceleration is 9.81 m/s downwards, then the force downwards is 294.3 Newtons, so for the trolley load of instruments and cavities to just float means the force upwards is greater than that, i.e. the whole tray should float away unless it was tethered.

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