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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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RE: Interesting...keep moving forward
By nafhan on 2/11/2013 10:54:58 AM , Rating: 0
Propellentless thrust is impossible? Not true. A laser or other light source aimed out the back would cause some small (but measurable) amount of thrust - with no propellent.

The key thing here would be if this is both propellentless and more efficient than a laser AND more efficient than just carrying propellent.

RE: Interesting...keep moving forward
By delphinus100 on 2/11/2013 10:14:24 PM , Rating: 2
Propellentless thrust is impossible? Not true. A laser or other light source aimed out the back would cause some small (but measurable) amount of thrust - with no propellent.

It depends on what you mean by 'propellant.' Photons do carry away momentum (solar sails could not work, otherwise), and that satisfies Newton's Third Law. They are the 'reaction mass.' That's what 'photon rockets' are about, and you described a crude but accurate form of one.

RE: Interesting...keep moving forward
By maugrimtr on 2/12/2013 8:36:53 AM , Rating: 2
Rocket which streams photons out the back is still streaming something, i.e. a propellant, out the back. Saying something is true does not make it true.

RE: Interesting...keep moving forward
By JKflipflop98 on 2/12/2013 10:03:46 AM , Rating: 2
Likewise, people have labelled things "impossible" for as long as they've been around. Things are impossible until they're not - just like propellantless thrusters. If you really understand science, you understand how dumb it is to call anything impossible.

Sailing around the world? Impossible once. Going faster than the speed of sound used to be impossible. Going to the moon? Same. And it won't be too long before I can add EM engines and FTL travel to that list.

RE: Interesting...keep moving forward
By 91TTZ on 2/12/2013 3:35:26 PM , Rating: 2
You seem to misunderstand basic science and the meaning of the word "impossible". You're confusing it with "not feasible".

At no time did anyone claim that sailing around the world is impossible.

By maugrimtr on 2/14/2013 9:33:04 AM , Rating: 2
In an infinite Universe with uncertain laws of Physics (the multiverse), nothing can ever be impossible.

That said, Science is a study of facts and evidence. You start with an assumption. Saying something is impossible is just such an assumption. It remains a truthful assertion UNTIL PROVEN OTHERWISE because it fits with what we already understand as being true.

If we took your approach, it misses the point of the Scientific Method. If you haven't proven it, it hasn't happened. It's one reason why a lot of social research appears to be self-obvious - we know that people deny Evolution because their reason has been overcome by blind faith. However, in Science that is NOT true unless it's proven, i.e. someone actually goes out, performs a poll, and collects hard data.

By nafhan on 2/12/2013 3:31:24 PM , Rating: 2
I've generally only seen the term propellant used for massive particles, but I wouldn't necessarily say your definition is wrong. It is however kind of irrelevant. You are probably looking for the term reactionless.

Anyway, the point I was making is that in both situations (photon drive and "EmDrive") you're deriving your forward movement from the expenditure of electrical energy. Thus both have the same advantage for space travel: no need to carry propellant mass . This sets both apart from standard chemical rockets, ion drives, and anything else that throws mass (i.e. propellant) out the back to move forward.

Photon drives and the "EmDrive" also have something else in common: neither are practical with current tech. :)

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