Centrifugal balance for the detection of mass fluctuations in advanced propulsion concepts

Abstract

Propellantless propulsion with a greater thrust-to-power ratio than photon rockets and functioning independently from the Sun or Earth-based lasers promise to revolutionize interstellar space travel. Claims of micronewtons in force for a Mach-Effect-Thruster on a torsion balance in vacuum, along with theories predicting mass fluctuations in a device with large fluctuations in internal energy, have paved the way for experimental investigations. In this experiment originally conceived by Woodward, devices are subjected to high centrifugal acceleration for direct measurement of mass fluctuations using an embedded force transducer. The test devices included a capacitor stack, a toroid and a pre-stressed, multi-layer piezoelectric stack in which electromechanical energy was varied. This paper first describes the design of a centrifugal balance: a rotating apparatus with low eccentricity and maximal angular frequency of 3600 rpm, capable of applying an acceleration above 1000 g's to the test device. The piezoelectric force transducer was characterized and calibrated under quasi-static conditions using an electrodynamic test instrument. The second harmonic response of the force transducer was then examined at different rotational rates to identify the presence of mass fluctuations. The experiment revealed a maximal resolution of 40 μg over a 100 kHz measurement bandwidth. Results with the electrostatic and inductive devices did not show mass fluctuations, orders of magnitude below the prediction. Even if the measurement resolution with the piezoelectric stack was more strongly affected by the centrifugal force, electromagnetic interaction, and nonlinear behavior, the measured noise reached one order of magnitude below the mass fluctuation prediction as well. Despite some limitations with the calibration and with the piezoelectric test device, the experiments have successfully demonstrated the feasibility of the centrifugal balance for high-frequency and high-precision mass variation measurements and have ruled out the postulated Mach-Effect mass fluctuations.