Reactionless Drive

A reactionless drive is a hypothetical form of propulsion that would produce thrust without expelling any propellant or otherwise exchanging momentum with anything outside itself, which would violate Newtons third law of motion and the conservation of momentum. Proposed devices under this label include Norman Deans mechanical oscillator of 1959, Roger Shawyers microwave cavity thruster known as the EmDrive from around 2001, Thomas Townsend Browns electrogravitics experiments and lifters from the 1920s onward, James Woodwards piezoelectric MEGA drive of 1995, and a relativistic ion beam concept called the helical engine studied by NASA researcher David Burns in 2019. No reactionless drive has been accepted as a viable propulsion technology, and independent testing has repeatedly produced negative results, including friction as the likely cause of the Dean drives apparent motion and anomalous thrust readings for the EmDrive falling below the limit of measurable photon thrust.