NASA has published a paper demonstrating that an electromagnetic rocket propulsion system called an em-drive actually provides thrust. The problem is that no one seems to understand exactly why the drive works.
The paper in which NASA sets out its findings was previously published, but the publication has since been extensively reviewed and tested by other scientists, a process known as peer reviewing. This greatly increases the chance that no errors were made during the investigation. The big problem with the drive, however, is that physicists can’t quite explain how the em-drive functions. The rocket engine was set out in 1999 by British inventor Roger Shawyer and could propel rockets using electromagnetic radiation, rather than burning rocket fuel. A rocket could therefore be launched without tons of extra fuel and bridge long distances in space.
NASA’s test rig consists of a rotating arm in a strong vacuum on which the em-drive was mounted. The arm can measure thrust forces in the order of 1 micronewton, including via an optical sensor. The em-drive itself consists of a truncated cone-shaped ‘motor’ measuring 22.9 centimeters high and measuring 27.9 cm in diameter on one side and 15.9 cm on the other. A polyethylene disc on one side and an antenna on the other forms the em drive. An em-signal of 1937MHz is placed on that antenna. Those electromagnetic waves would push against the walls of the cavity and thus provide a small thrust. How that would work is still unclear: conventional physics states that every action is followed by an equal opposite reaction: the law of conservation of momentum. The em-drive doesn’t seem to obey that law, because it doesn’t emit particles that push the rocket motor the other way.
Exactly how the em-drive works is not the subject of the published paper. The paper, published in the Journal of Propulsion and Power of the American Institute of Aeronautics and Astronautics, merely demonstrates that the em-drive actually generates thrust and that the measurements would not indicate a measurement error or setup error. The measured thrust is 1.2mN per kilowatt of electrical power. That is relatively small, but this would be ‘free’ thrust: after all, no fuel needs to be carried, but solar panels could supply the required energy. A popular explanation would be that Mars could be reached in just ten weeks with the em-drive.
Another method of providing propulsion in space without carrying fuel is the use of solar sails. However, their thrust is much less, on the order of micronewtons per kilowatt. In addition, the thrust of the em-drive could be even greater if the system were optimized. That was also not the approach of the experiments described in the paper. Various theories have been put forward about how it works, one of which is known as the pilot wave theory, an interpretation of quantum mechanics.