from the imagine-the-possibilities dept.
The proposed radio frequency (RF) resonant cavity thruster is unlike conventional thrusters and uses no reaction mass and emits no directional radiation. Designed using principles that are not supported by prevailing scientific theories, it apparently violates the law of conservation of momentum. The EmDrive, has roiled the aerospace world for the several years now, ever since it was proposed by British aerospace engineer Robert Shawyer. The essence of the claim is that by bouncing microwaves in a truncated cone, thrust will be produced out the open end. Most scientists have snorted at the idea, noting correctly that such a thing would violate physical laws. However, prestigious organizations like NASA have replicated the results showing thrusts.
MIT Technology Review has some reasoning on the subject, (possibly pay-walled) with a picture of the device. It's supposedly the so called unruh effect at play. When NASA tested the device, they measured with input of 17 W an average thrust of 91 µN (5.4 µN/W). A Chinese team used 2500 W and measured a thrust of 720 mN (288 µN/W). The expected radiation pressure is closer to 0.003 µN/W.
After months of speculation and leaked documents, NASA's long-awaited EM Drive paper has finally been peer-reviewed and published [open, DOI: 10.2514/1.B36120] [DX]. And it shows that the 'impossible' propulsion system really does appear to work. The NASA Eagleworks Laboratory team even put forward a hypothesis for how the EM Drive could produce thrust – something that seems impossible according to our current understanding of the laws of physics.
In case you've missed the hype, the EM Drive, or Electromagnetic Drive, is a propulsion system first proposed by British inventor Roger Shawyer back in 1999. Instead of using heavy, inefficient rocket fuel, it bounces microwaves back and forth inside a cone-shaped metal cavity to generate thrust. According to Shawyer's calculations, the EM Drive could be so efficient that it could power us to Mars in just 70 days.
takyon: Some have previously dismissed EmDrive as a photon rocket. This is addressed in the paper along with other possible sources of error:
The eighth [error:] photon rocket force, RF leakage from test article generating a net force due to photon emission. The performance of a photon rocket is several orders of magnitude lower than the observed thrust. Further, as noted in the above discussion on RF interaction, all leaking fields are managed closely to result in a high quality RF resonance system. This is not a viable source of the observed thrust.
[...] The 1.2 mN/kW performance parameter is over two orders of magnitude higher than other forms of "zero-propellant" propulsion, such as light sails, laser propulsion, and photon rockets having thrust-to-power levels in the 3.33–6.67 μN/kW (or 0.0033–0.0067 mN/kW) range.
Previously: NASA Validates "Impossible" Space Drive's Thrust
"Reactionless" Thruster Tested Again, This Time in a Vacuum
Explanation may be on the way for the "Impossible" EmDrive
Finnish Physicist Says EmDrive Device Does Have an Exhaust
EmDrive Peer-Reviewed Paper Coming in December; Theseus Planning a Cannae Thruster Cubesat