STM-D-0736Paper2019Published and peer-reviewed

The SpaceDrive project - Thrust balance development and new measurements of the Mach-Effect and EMDrive Thrusters

Matthias Kößling · Maxime Monette · Marcel Weikert · Martin Tajmar

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In one page

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.

Why it matters hereChapter 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.

What it claims

01The 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
Published and peer-reviewed
02The 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
Published and peer-reviewed
03Turning 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
Published and peer-reviewed
04The 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
Published and peer-reviewed
05Four 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
Published and peer-reviewed
06The 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
What to watch

The way in

https://doi.org/10.1016/j.actaastro.2019.05.020Published as Acta Astronautica 161, pages 139 to 152, August 2019, by Matthias Kößling, Maxime Monette, Marcel Weikert and Martin Tajmar of the Institute of Aerospace Engineering, Technische Universität Dresden. Licence checked: the journal version carries the Elsevier text-and-data-mining user licence and no Creative Commons grant, so this sheet reproduces none of it — the summary and claims are the site’s own. They were written from the authors’ own conference version of the same campaign, IAC-18,C4,7-C3.5,5,x46021, presented at the 69th International Astronautical Congress in Bremen, 1 to 5 October 2018, which TU Dresden publishes in full on the Chair of Space Systems site; the locators below cite that paper’s numbered sections, which carry the same instrument description and the same measurement runs. The IAC text is copyright the International Astronautical Federation, so it is cited, not reproduced. SpaceDrive is funded by the German space agency DLR from Federal Ministry of Economic Affairs funds approved by the German Parliament, grant 50RS1704. Three companion sheets in this library carry the rest of the EMDrive record: Shawyer’s own 2023 account of the thruster at /library/stm-2acf55ccc6, the NASA Eagleworks torsion-pendulum campaign of Brady, White, March, Lawrence and Davies at /library/stm-a46c32725a, and Tajmar, Neunzig and Weikert’s later high-accuracy Dresden campaign at /library/stm-0d21110734. Tajmar and Fiedler’s earlier 2015 EMDrive campaign is at /library/stm-d79b6648ae.

How 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

Where it sits in the curriculum

Inertial mass reduction and transmedium craft The evidence ladder