The reversal test

Why the library suggests it

Martin Tajmar's group at TU Dresden built an automated torsion balance carrying a thruster of up to ten kilograms, reading its own deflection with a laser interferometer resolving one picometre, with a noise floor near eleven nanonewtons — far below the micronewton forces claimed — and with the whole experiment box able to turn through 180 degrees inside the vacuum chamber so one device can be measured forward, sideways and reversed without breaking vacuum. Running a Mach-effect thruster, a Dresden-built copy, a magnetostrictive version and four cavity configurations, every signal followed heat or drive current rather than direction (The SpaceDrive project — Thrust balance development and new measurements, 2019; the programme's statement of purpose is The SpaceDrive project – Developing revolutionary propulsion at TU Dresden, 2018). The rebuilt instrument resolves forces below a nanonewton, with the amplifier run off an on-board battery so no cable or liquid-metal contact can push on it, and its sensitivity floor sits at the light-pressure limit itself; its most valuable output is the artefact catalogue showing exactly how a heating cavity fakes a thrust that even reverses sign when the thruster is turned around (High-accuracy thrust measurements of the EMDrive and elimination of false-positive effects, 2021). The claim the protocol was built to test, in its most instrumented form — eight lead-zirconium-titanate discs at 39.3 kilohertz on about 170 watts, giving just over two micronewtons that reverses when the cage is turned — is Theory of a Mach Effect Thruster (2014).

The reversal test

Turn the thruster around inside the vacuum chamber without opening it, and see whether the force turns around with it. Choose a device and an orientation, and the trace redraws with the noise floor and the light-pressure limit on the same axis. The lesson is the one the Dresden group published: a real thrust reverses — and so does a warm cavity acting through its mount. What separates them is the sideways orientation, the shape of the transient, and the size of the reading.

• A Mach-effect thruster, as reported: eight discs at 39.3 kHz on about 170 W
• Noise floor of the 2019 balance, 11 nN

On the balance

A Mach-effect thruster, as reported: eight discs at 39.3 kHz on about 170 WA heated cavity on a cage mount: 1.5 µN for 10 WThe same cavity bolted to the cage: 20 µN for 10 WThe EMDrive on the rebuilt Dresden balance

Mount orientation

ForwardSidewaysReversed

Peak reading:

2,100 nN

Reading per kilowatt:

12,353 nN/kW

Times the light-pressure limit:

3.7×

Light-pressure limit, per kilowatt:

3,336 nN/kW

Turns around with the mount:

Yes

Falls into the noise when turned sideways:

Yes

Peak reading: 2,100 nanonewtons. Falls into the noise when turned sideways: Yes.

A claim that cannot survive the sideways orientation is a thermal claim, and saying so plainly costs the field nothing and saves it years.

The settling measurement is thrust in nanonewtons per kilowatt, measured forward, sideways and reversed in one session, published together with the thermal transient and the drive current on the same time axis.

The open ground the Dresden authors name themselves is the superconducting cavity, where the quality factor rises by orders of magnitude and nobody has yet looked.

Settled physics as a protocol. The sheet for this device

The experiment or build

Build or borrow a balance with a nanonewton floor and a rotating mount. Then do what the Dresden authors themselves name as the open ground: the superconducting cavity, where the quality factor rises by orders of magnitude and nobody has yet looked. The settling measurement is thrust in nanonewtons per kilowatt, measured forward, sideways and reversed in one session, published together with the thermal transient and the drive current on the same time axis. A claim that cannot survive the sideways orientation is a thermal claim, and saying so plainly costs the field nothing and saves it years.