NASA's Impossible Space Engine, The EMdrive, Passes Peer Review (But That Doesn't Mean It Works)

Forbes ^ | September 2, 2016 | Ethan Siegel

[2ndDivisionVet]

“For every action, there’s an equal and opposite reaction.” So goes Newton’s third law, and despite the developments of relativity and quantum mechanics, that fundamental law of the Universe — otherwise known as the conservation of momentum — has never been challenged. Yet a few years ago, a new space drive that claims to break that exact law was proposed and put forth by inventor Roger Shawyer, the EMdrive. Unlike conventional rocket engines, which cause thrust in one direction by propelling exhaust outwards in the opposite direction, the EMdrive claims to take an external source of power and convert it into a positive thrust with no corresponding reaction.

And despite the fact that this seems to violate the known laws of physics, a prototype device was submitted to NASA’s Eagleworks lab for testing. Perhaps surprisingly, the test came back positive: there was thrust observed despite the lack of a reaction. And if Dr. José Rodal from the NASA Spaceflight forums can be trusted, the paper resulting from the test, “Measurement of Impulsive Thrust from a Closed Radio Frequency Cavity in Vacuum” by Harold White et al., was just accepted for publication in the peer reviewed Journal Of Propulsion And Power, by AIAA....

[Rockingham]

The conventional answer would be that the microwaves are converted to heat. A new theory has it that the thrust is generated by Unruh radiation being converted to inertial force, but that is much contested.

[mikrofon]

[minnesota_bound]

It needs to pass Sheldon’s review.

[CMB_polarization]

There is no need to use the “Unruh force” or new physics to explain these results. We would have seen evidence of this long ago in far better run physics experiments.

[CMB_polarization]

There is also EM leakage, resonant effects, and other ways energy can flow through the system. The major problem with any drive, photon drive or any space system is the power generation source. You could light up a large bank of 100-watt light bulbs at the the focus of a parabolic mirror and you would still have to power them from some source. Solar power, nuclear, fuel cells, etc., but that system would have to be up and running, with all its attendant requirements and maintenance issues.

[Rockingham]

If the thrust demonstrated by the EM drive devices could be explained easily, surely someone would have done so by now. Yet the thrust observed has persisted in test after test. Perhaps the EM drive will eventually fail validation and be explained as due to some conceptual or experimental error, but, for now, the device is still in the running as something new.

NASA has a number of thermal nuclear reactor designs that could efficiently power an EM drive in space. That would offer an immense improvement over thrust from chemicals generating thermal expansion and spewing out reaction mass from rocket nozzles -- the same principle used by fireworks rockets.

[CMB_polarization]

It can be explained easily and Shawyer does it (he declares in his writing that there is no new physics here). The particular configuration exploits wave properties and the fact that electromagnetic waves possess momentum. The real challenge, and will forever be, the power source that can function in space for long periods at a reasonable power output to weight, or a system that can transfer power via beam, and collect it at the spacecraft.

[CMB_polarization]

A solar sail is a correct way to illustrate the effect that light pressure can have on an object in zero-g and vacuum. https://en.wikipedia.org/wiki/Solar_sail

[Rockingham]

The marvel of the EM drive is that, from microwaves generated and contained within, the device produces directional thrust without emitting any other form of energy. It is as if a radiometer were painted black, but powered by an internal light drawing power from a battery, it was configured so as to produce measurable thrust.