Direct Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects

The EMDrive has been proposed as a revolutionary propellantless thruster using a resonating microwave cavity. It is claimed to work on the difference in radiation pressure due to the geometry of its tapered resonance cavity. We attempted to replicate an EM Drive and tested it on both a knife-edge balance as well as on a torsion balance inside a vacuum chamber similar to previous setups in order to investigate possible side-effects by proper thermal and electromagnetic shielding. After developing a numerical model to properly design our cavity for high efficiencies in close cooperation with the EM Drive’s inventor, we built a breadboard out of copper with the possibility to tune the resonance frequency in order to match the resonance frequency of the magnetron which was attached on the side of the cavity. After measuring the Q-factor of our assembly, we connected the EMDrive to a commercial 700 W microwave magnetron. Our measurements reveal thrusts as expected from previous claims (due to a low Q factor of <50, we observed thrusts of +/-20 μN) however also in directions that should produce no thrust. We therefore achieved a null measurement within our resolution which is on the order of the claimed thrusts. The purpose of the test program was to investigate the EMDrive claims using improved apparatus and methods. To this end it was successful in that we identified experimental areas needing additional attention before any firm conclusions concerning the EMDrive claims could be made. Our test campaign therefore can not confirm or refute the claims of the EMDrive but intends to independently assess possible side-effects in the measurement methods used so far. We identified the magnetic interaction of the power feeding lines going to and from the liquid metal contacts as the most important possible side-effect that is not fully characterized yet and which needs to be evaluated in the future in order to improve the resolution.