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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: Violating laws of physics?
By PaFromFL on 2/11/2013 8:15:09 AM , Rating: 2
With an ion drive, the conserved momentum is the directed (vector) sum of mass times velocity. The ions have a very low mass and a very high velocity. The spacecraft has a high mass and therefore receives a very small velocity increase per ion. The thrust force is the rate of change of momentum (Newton).

This new drive concept does not appear to have anything that balances the forward momentum gained by the spacecraft. Photons could provide a very small thrust force if they exited the engine. When they are trapped inside a cavity, they can't provide any net change in momentum.

If a bomb goes off in a very strong conical chamber, no net thrust occurs unless the chamber ruptures and lets high speed gas escape.

RE: Violating laws of physics?
By JediJeb on 2/11/2013 10:24:47 PM , Rating: 2
This new drive concept does not appear to have anything that balances the forward momentum gained by the spacecraft. Photons could provide a very small thrust force if they exited the engine. When they are trapped inside a cavity, they can't provide any net change in momentum.

This applies if the only source of thrust comes from movement of mass. But take something like a rail gun, the projectile is not moved by any expulsion of mass but by interaction of the projectile with alternating magnetic fields. What if the resonate microwaves are causing thrust not through their mass equivalency but through their magnetic equivalency? Could the moving electromagnetic fields of the microwave photons be interacting with the Earth's magnetic fields in a way that appears to give thrust? Does anyone know for certain that a resonate microwave does not somehow interact with a gravitational field? Until we know more about gravity it can not be positively ruled out.

RE: Violating laws of physics?
By PaFromFL on 2/12/2013 8:07:27 AM , Rating: 2
The recoil force pushes the rail gun backwards. If it were not attached to the earth, the rail gun would move backwards with a noticeable velocity. Otherwise, the rail gun and earth receive a tiny velocity contribution in the opposite direction of the projectile.

BTW, the recoil force is transmitted by the virtual photons of the magnetic field. Momentum is still conserved.

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