New "impossible" engine works, could change space travel forever.

[Laurie61]

The EmDrive

A New Concept in Spacecraft Propulsion

Satellite Propulsion Research Ltd (SPR Ltd) a small UK based company, has demonstrated a remarkable new space propulsion technology. The company has successfully tested both an experimental thruster and a demonstrator engine which use patented microwave technology to convert electrical energy directly into thrust. No propellant is used in the conversion process. Thrust is produced by the amplification of the radiation pressure of an electromagnetic wave propagated through a resonant waveguide assembly.

Until yesterday, every physicist was laughing at this engine and its inventor, Roger Shawyer. It's called the EmDrive and everyone said it was impossible because it goes against classical mechanics. But the fact is that the quantum vacuum plasma thruster works and scientists can't explain why.

Shawyer's engine is extremely light and simple. It provides a thrust by "bouncing microwaves around in a closed container." The microwaves are generated using electricity that can be provided by solar energy. No propellant is necessary, which means that this thrusters can work forever unless a hardware failure occurs. If real, this would be a major breakthrough in space propulsion technology.

http://sploid.gizmodo.com/nasa-reveals-new-impossible-engine-can-change-space-t-1614549987

http://emdrive.com/background.html

http://ntrs.nasa.gov/search.jsp?R=20140006052

[Grotemobile]

A very interesting read that was.

Steve

[Joe_L]

I'm puzzled by a statement in http://emdrive.com/principle.html.  It says "Thus an electromagnetic (EM) wave, travelling at the speed of light has a certain momentum..." which implies an EM wave has mass. My relativity theory is rusty (as in never had enough mental grease applied)  - how does an EM wave have mass?

The rest of it I follow, sort of (e.g. speed of EM waves in cavities)

[DrRobin]

Hmm,

Sounds very similar to a laser or photon drive. You get a bigger nuclear reactor, connect it to a very powerful laser and shoot it out the back. Eventually you accelerate up to the speed of light.

The key word here is eventually as the mass you are ejecting out the back is very small, so it takes forever to build up speed. I am guessing this will be the same, fine to activate when you are doing a reasonable percentage of the speed of light but useless below this.

We could build a photon drive ship today, it just needs a big power source and an equally big laser, about 10,000 years to accelerate and the same to deaccelerate and we could build a starship. All those who are happy to spend 20,000 years on a ship please step forwards and form an orderly queue now.

The microwaves bouncing around a chamber is called a cavity resonator, most will know these better as a microwave oven, same principle, actually a laser works along the same lines, the central chamber, ruby or whatever is a resonant chamber at the wavelength of the laser. Why scientists should be stumped as to how it works or even laugh is just journalistic license, everyone knows how it works, whether it can provide enough thrust for the weight involved is the key question. Incidentally I undertook a short study of cavity resonators during the late eighties, we weren't looking for a propulation system but looking for a new way to detect leaks from microwave ovens.

Still without this fundamental research nothing would get anywhere so full marks that they have secured further funding.

[Joe_L]

Although one interesting difference is the cavity is closed, it's not radiating energy like a laser drive.

[DrRobin]

Hi Joe,

If the cavity was indeed closed there is no way to get the energy stored in the electromagnetic field out. It would very soon go bang, like a microwave oven with nothing in, the EM eventually builds up to the point where the voltage inside the magnetron exceeds the maximum.

Even if it isn't a hole or a waveguide port then there must be a coupling coil to take the energy out.

I would have to read the detailed document, journalists comments like 'closed container' are too simplified.

One other thing to note, reading one ofthe press releases, they are proposing this as a lift engine to put satellites in to orbit, not an interstellar engine, which seems even more hard to believe.

Robin

[Mukv]

just set the timer put in your bowl of cold beans press the start button and get breakfast while you zoom through space cool!

[Knight of Clear Skies]

It's a little premature to get excited about this I'm afraid. From the abstract of the conference paper:

"Thrust was observed on both test articles, even though one of the test articles was designed with the expectation that it would not produce thrust. Specifically, one test article contained internal physical modifications that were designed to produce thrust, while the other did not (with the latter being referred to as the "null" test article)."

That screams experimental error to me. I found some more details here, the author suspects that the conference paper is intended to garner feedback on their test rig rather than announcing a discovery.

...how does an EM wave have mass?

Photons are thought to have zero rest mass, but have momentum due to mass/energy equivalence.

[Laurie61]

It would be exciting if this, or something similar, could be made to work. How long will we have to wait for the first 1G spacecraft engine   

A few more articles - 

http://www.npl.washington.edu/AV/altvw173.html

http://arxiv.org/abs/1301.6178

http://arxiv.org/ftp/arxiv/papers/1301/1301.6178.pdf

[Zakalwe]

Another view:

https://richarddawkins.net/2014/08/did-nasa-validate-an-impossible-space-drive-in-a-word-no/

[Cath]

Having a closed cavity with no escape for the RF sounds like it would be impossible to work. It would be like having a rocket engine with no exhaust outlet.

The amount of RF energy you'd need to overcome Earths gravity would be I'm pretty sure be pretty enormous!  so much so that anything below the cavity outlet (probably for miles) would be totally destroyed (depending on the beamwidth) - dangerous to say the least.

[Joe_L]

That screams experimental error to me. I found some more details here, the author suspects that the conference paper is intended to garner feedback on their test rig rather than announcing a discovery.

I think I agree with you there.

It is possible to excite RF in a closed cavity though.  However (as I read it) the thrust is from change of momentum due change of propogation velocity within the cavity. I was wondering why the wave reflected off the end wall isn't subject to an equal and opposite change in velocity which would cause a nullifying effect, unless the end of the cavity is open or lossy. Og well, we'll have to wait for the results of further work....

[NickK]

I think I agree with you there.

It is possible to excite RF in a closed cavity though.  However (as I read it) the thrust is from change of momentum due change of propogation velocity within the cavity. I was wondering why the wave reflected off the end wall isn't subject to an equal and opposite change in velocity which would cause a nullifying effect, unless the end of the cavity is open or lossy. Og well, we'll have to wait for the results of further work....

Surely if you're pumping energy in a sealed box - that box would literally disintegrate if there was no outflow of energy? My point being is that there must be an exit point in some way for the energy added to the box. QED if the box is moved by the momentum, then that would be a source of output loss.

Unless one of the fundamental laws of physics about energy is incorrect..