China's EM Drive Explained: Reinvigorate Space Race vs. US, Russia

An EM Drive is already too good to be true, but it appears China's recent developments with its "reactionless" electromagnetic drive (or EM Drive) may blow things out of proportion.

According to Wired, the EM Drive is an engine propelled solely by electromagnetic radiation confined in a microwave cavity. Such an engine would already violate the law of conservation of momentum by generating mechanical action without exchanging matter.

However, it appears China and the U.S. have gone toe-to-toe by pouring resources into the impossible engines. Now China is on the brink of a breakthrough.Chen Yue of the China Academy of Space Technology has just announced that not only has China successfully tested EM Drives in its laboratories, but a proof-of-concept is currently undergoing zero-G testing in orbit.

According to the International Business Times, the test is taking place on the Tiangong 2 Space Station.

However, unlike traditional engines such as ion and combustion engines that expel mass from the system to produce thrust, the reactionless EM Drives use only electricity to make movement.

In the EM Drive, first proposed by Roger Shawyer, the microwave cavity is an asymmetric container like a cone, with one end much larger than the other. 

The narrower end is the source of EM energy and bombards the cavity with microwaves.

According to Popular Science, these waves are contained and bounce off the cavity's walls and create electromagnetic resonance. The imbalanced resonance from the complex geometry of the cone forces the EM field to "push" the drive away from the direction of the larger end.

While the EM Drive may have low impulse, the lack of gravity and friction in deep space allows it to accelerate to a high speed with enough time. This even starting from a low power level. The performance of the engine depends on the material of the cavity to reduce EM loss from absorption, and temperature which can impact the EM field.

This suggests that not only do future EM Drives work from superconducting materials, but that spaceship or satellites must be designed from the ground up to maximize the drive's efficiency.

EM Drives can be ideal for deep space exploration as they remove the need for refueling, and even the weight and space needed to store fuel. This simplifies the logistics and design. All one would need in an EM Drive would be a power source, like an energy or reactor, to fuel anything from a manned mission to robotic probes.