For almost a decade now, there's been a lot of controversy about the EmDrive, a reactionless engine that should not be possible according to the accepted laws of physics. Invented by Roger Shawyer, this electric-based drive is believed to create a tiny thrust without consuming a propellant.
If this fuel-free thruster really works, it could have profound implications, especially for space travel as it would make it possible to accelerate a spacecraft using solar or nuclear energy. This could significantly cut the travel time to Mars and could make it possible to send probes to other star systems like Alpha Centauri.
Today there's exciting news as leaked results from a NASA Eagleworks paper that will be published in the December edition of American Institute of Aeronautics and Astronautics suggest the EmDrive is indeed capable of generating thrust. Slashdot reports that, after accounting for error measurements, the EmDrive is capable of consistently generating a force of around 1.2 millinewtons per kilowatt in a vacuum. The test was designed to rule out that the thrust could be generated by another anomaly in the system, but the team acknowledges further testing is needed to eliminate the possibility of thermal expansion somehow interfering with the results.
It's also stressed that this experiment was set up simply to test whether the EmDrive works, it's possible that further tweaking could make the EmDrive more efficient and powerful. So far, it seems to stack up very favorably versus solar sails:
The paper concludes that, after error measurements have been accounted for, the EM Drive generates force of 1.2 millinewtons per kilowatt in a vacuum. That's not an insignificant amount -- to put it into perspective, the super-powerful Hall thruster generates force of 60 millinewtons per kilowatt, an order of magnitude more than the EM Drive. But the Hall thruster uses fuel and requires a spacecraft to carry heavy propellants, and that extra weight could offset the higher thrust, the NASA Eagleworks team conclude in the paper. Light sails on the other hand, which are currently the most popular form of zero-propellant propulsion, use beams of sunlight to propel them forward rather than fuel. And they only generate force up to 6.67 micronewtons per kilowatt - two orders of magnitude less than NASA's EM Drive, says the paper.