A research paper outlining NASA’s investigation into the propellantless EM Drive has been leaked, and their conclusion is that the controversial engine does indeed work. The paper hasn’t been submitted for peer review yet, meaning it still requires external verification, but it is now part of a number of independent studies that suggest that the EM Drive could legitimately revolutionize space travel.

The radio frequency resonant cavity thruster, better-known as the EM Drive, is a cone-shaped device that makes use of microwaves rebounding within the device’s interior to produce its thrust. Traditional propulsion requires a physical reactant of some sort, a material to be accelerated out the back end of the engine to produce thrust. While the EM Drive uses fuel — in this case, electricity — it dispenses with the heavy reactant that would otherwise be required, not only reducing the weight of the vehicle it’s attached to, but also allowing it to accelerate as long as it’s being fed power — traditional rockets typically fire only for a matter of minutes, as they expend their fuel extremely quickly.

While the concept of such a device has been around for decades, in 2001 engineer Roger Shawyer was the first to publicize his success in building a working prototype, demonstrating a measurable, albeit meager, generation of thrust. His claim was widely criticized, with the majority of the scientific community dismissing, it believing that such a device would violate the laws of physics.

NASA’s investigation into the EM Drive was aimed at eliminating factors that critics say may have influenced earlier experiments, and still concluded that the device was producing thrust. "The test campaign included a null thrust test effort to identify any mundane sources of impulsive thrust, however none were identified," according to the paper.

"Thrust data from forward, reverse, and null suggests that the system is consistently performing with a thrust to power ratio of 1.2 ± 0.1 millinewtons per kilowatt."

This 1.2 millinewtons might only appear to be a gentle push on the surface, but when compared to the plasma-based Hall thruster prototype’s 60 millinewtons per kW, it might be 50 times less powerful, but the Hall thruster still needs conventional reactant to produce its plasma, making it much less efficient. Also, the EM drive is still at the proof-of-concept stage, meaning there hasn’t been any work put into figuring out how to make the device more efficient.

Conversely, solar sails, the only other major contender that doesn’t need to carry its own reactant, only produces thrust of 0.00667 millinewtons per kilowatt — 180 times less than the EM Drive. Proposals for sending photon sail-propelled craft to Mars using 100-gigawatt lasers with a travel time of three days have already been made. This means that if researchers find that the EM Drive does wind up working as advertised, it would prove to be hundreds of times more efficient, and ultimately faster, than the miles-wide sails would be. 

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