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NASA's Impossible Propulsion EmDrive Is Heading to Space (popularmechanics.com)
An anonymous reader writes:The EmDrive, a hypothetical miracle propulsion system for outer space, has been sparking heated arguments for years. Now, Guido Fetta plans to settle the argument about reactionless space drives for once and for all by sending one into space to prove that it really generates thrust without exhaust. Even if mainstream scientists say this is impossible. Fetta is CEO of Cannae Inc, and inventor of the Cannae Drive. His creation is related to the EmDrive first demonstrated by British engineer Roger Shawyer in 2003. Both are closed systems filled with microwaves with no exhaust, yet which the inventors claim do produce thrust. There is no accepted theory of how this might work. Shawyer claims that relativistic effects produce different radiation pressures at the two ends of the drive, leading to a net force. Fetta pursues a similar idea involving Lorentz (electromagnetic) forces. NASA researchers have suggested that the drive is actually pushing against "quantum vacuum virtual plasma" of particles that shift in and out of existence. Most physicists believe these far-out systems cannot work and that their potential benefits, such as getting to Mars in ten weeks, are illusory. After all, the law of conservation of momentum says that a rocket cannot accelerate forward without some form of exhaust ejected backwards. Yet the drumbeat goes on. Just last month, Jose Rodal claimed on the NASA Spaceflight forum that a NASA paper, "Measurement of Impulsive Thrust from a Closed Radio Frequency Cavity in Vacuum" has finally been peer-reviewed and accepted for publication by the American Institute of Aeronautics and Astronautics, but this cannot be confirmed yet.
That is why i said it needs to go on a little cruise.
Say. A lap up to and back from lunar orbit. A distance that is still both close enough to closely monitor the test article, and far enough that if it were using evaporated cavity materials as reaction mass, the entire test article would need to be consumed.
It is otherwise impossible to rule out what you suggest: it may well be happening, but that kind of issue would be insufficient to satisfy the reaction mass requirements of the proposed test. A successful completion wouldnt rule out vapor release, it wiuld just show it does not dominate the generated thrust. Until a result that can only happen if reactionless drive is produced, and in a big way like that, the argument that there is reaction mass, and that it dominates the recorded thrust will never die.
The press hype goes on despite results of two experimental results that clearly indicated the mythical drive to not thrust: A group of physicists at the university of Dresden measured miniscule thrust, but strangely enough the thrust went into the same direction when the "EMdrive" was rotated by 90. So they figured that what they measured was probably resulting from an interaction of the electric powering from the outside with the magnetic field of earth. They couldn't easily remove this probable source of error in their setup, but a chinese group of physicists managed to do so: They powered the "EM-drive" from a battery that was within the same enclosure - and voila - no more thrust to be measured.
This paper has a possible explanation that was ignored by the article. If the EMDrive works, then the same explanation likely also applies to some of the galactic rotational observations that are used to justify the need for dark matter.
http://arxiv.org/pdf/1604.0344...
I think the arguments can be ended partly by the proposed experiment (actual device in space), and partly by more-complete theory. It just happens that physicists already know about some concepts that can be manipulated rather simply to provide a possible answer, theory-wise.
The most relevant concept is "negative mass-energy". Any physicist talking about wormholes will tell you that you need the stuff to stabilize the mouth of a wormhole. Needing it is of course different from knowing whether or not the stuff actually exists, of course, but the point here is that physicists accept the possibility that negative mass-energy could exist.
So now do a simple thought-experiment involving two masses, one having +1 gram of mass, and the other having -1 gram of mass, on a collision course with each other, at equal and opposite velocities. When you compute the result, you see that all the mass disappears (cancels out), and all the kinetic energy disappears (also cancels out), but all their momentum is left over.
That thought-experiment leads to one of two possible conclusions. Either it is possible for momentum to exist entirely independently of mass-energy, or negative mass-energy cannot exist. IF the first conclusion is true, then how many other ways might there be, to separate momentum from mass-energy? Could the EM drive manifest one of those ways? If so, the net effect would be like "radiating pure momentum", and thereby the device moves.
To be determined!
I've been following emdrive for a while now. Prof McCulloch's book and emdrive paper provide the best description I have yet seen of an emdrive. As mentioned above there are no 'laws' of physics, just a collection of theories which seem to describe observed facts well. The theories change or are expanded to suit fresh observations. The best theories can be used to make predictions and provide explanations in disparate other problematic observations and this is the case with Prof McCulloch's work.
If NASA are prepared to use resources to send one of these things to orbit then the case for emdrive is at least still open. Speaking personally, I would like to use a 3d printer to build a 10x10x10 Cu block of these cavities, that should give a definitive answer. How about it Mr Musk?
Problems always arise on the edge of physics from the difficulties of making measurements. That's the fun of the thing...