Historical research guide · 0736 · 2019
The SpaceDrive project - Thrust balance development and new measurements of the Mach-Effect and EMDrive Thrusters
Matthias Kößling · Maxime Monette · Marcel Weikert · Martin Tajmar
In one minute
Martin Tajmar’s SpaceDrive group at TU Dresden set out to do the thing propellantless propulsion most needed done: build an instrument good enough to settle arguments. Kößling, Monette, Weikert and Tajmar describe an automated torsion balance that carries a thruster of up to ten kilograms, reads its own deflection with a laser interferometer resolving one picometre, and holds a noise floor near eleven nanonewtons — far below the micronewton forces claimed for the Mach-Effect thruster and the EMDrive. Three liquid-metal feedthroughs carry power onto the swinging beam, up to 30 kilovolts and up to 3 gigahertz; mu-metal shields the thruster; and the whole experiment box turns through 180 degrees inside the vacuum chamber, so one device can be measured forward, sideways and reversed without opening the tank. Running Woodward’s own thruster, a Dresden-built copy, a magnetostrictive version and four EMDrive configurations, every signal they saw followed heat or drive current rather than direction. The measurement recipe is the result.
Connection
Chapter 8 asks what it would take to move a craft without throwing mass overboard, and this is the paper that turns that question into an instrument: reverse the thruster, and a real thrust reverses with it while a hot cavity does not. Chapter 1’s evidence ladder gains its most useful rung here — a published, funded group with a nanonewton balance, an artefact catalogue and a named next measurement.
From the source
The instrument is the contribution: an automated torsion balance for thrusters of up to 10 kg, read by an attocube laser interferometer with 1 picometre resolution, carrying its own wirelessly controlled electronics, magnetic eddy-current damping and mu-metal shielding, and fed through three separate liquid-metal contacts — one to 500 volts and 200 kilohertz, one to 30 kilovolts, one to 3 gigahertz — with a measured noise floor of 11 nanonewtons over 140 averaged profiles.Sections 2.2 Features and 2.3.2 Noise
The balance is calibrated against a separately calibrated voice coil at seven commanded forces from minus 12 to plus 12 micronewtons, giving a conversion factor of 6.7 micronewtons per micrometre; 200 overnight one-micronewton pulses show the balance reads steady forces to about 10 percent at 60 seconds, and for pulses shorter than 30 seconds it is too slow to read the force exactly but still resolves impulse-like behaviour to about 80 percent.Section 2.3.4 Calibration
Turning the thruster around is what separates thrust from heat. Woodward’s Mach-Effect thruster at its 31 kilohertz mechanical resonance gave a 2 micronewton peak at 140 volts in the forward orientation, but the reversed orientation did not return the same magnitude and the trace lacked the impulse-like step a real force produces, which the authors read as non-linear thermal drift; the Dresden-built thruster stayed below 100 nanonewtons at both 36 and 72 kilohertz, where the theory predicts thrust rising as the fourth power of frequency.Sections 3.3 Results and Discussion and 3.4 Conclusion
The cleanest artefact test in the paper is the substitution: a magnetostrictive Terfenol-D transducer showed roughly 0.3 micronewton on-off transients that did not reverse with the device, and replacing the transducer with a plain 26 ohm resistor drawing the same current at 75 volts reproduced the same signal — identifying the current, not the actuator, as its source.Sections 4.3 Results and Discussion and 4.4 Conclusion
Four EMDrive configurations were run with the amplifier outside the vacuum chamber and the power carried in over the radio-frequency liquid-metal feedthrough: the NASA geometry with a 4 centimetre HDPE dielectric disc at 1933 megahertz averaged 3.4 micronewtons over 55 profiles of 60 seconds — the same size as the 4.7 micronewtons for 3.2 watts reported by March — the disc-free cavity at 1920 megahertz gave a larger displacement at larger delivered power, and spherical end caps at 2576 megahertz gave 3.0 micronewtons; in every case the trace has the shape of a thermal drift rather than the step the voice-coil calibration produces.Section 5.3 Results and Discussion
The authors name the measurements that would settle it: rebuild the Mach-Effect thruster and its drive chain to match Woodward’s original device exactly, including the audio amplifier and matching transformer, and test other vibration modes; and on the EMDrive side add a second circulator between the coupler and the feedthrough to stop reflected waves corrupting the power reading, quantify the power actually delivered into the cavity, raise the power level, and repeat the runs in all three thrust directions.Sections 3.4, 5.4 and 6 Conclusion
The way in
https://doi.org/10.1016/j.actaastro.2019.05.020How to cite it
Matthias Kößling, Maxime Monette, Marcel Weikert, Martin Tajmar (2019) The SpaceDrive project - Thrust balance development and new measurements of the Mach-Effect and EMDrive Thrusters doi:10.1016/j.actaastro.2019.05.020