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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. • Development of novel thrust balance to investigate mass fluctuations in high frequency regime up to 100 kHz • Direct measurement of mass fluctuation claim for Mach-Effect thruster concept • Null-measurement sets new limits for theory [ABSTRACT FROM AUTHOR]

Successful interstellar venture depends on the development of propellantless propulsion with a thrust-to-power ratio much greater than a photon rocket and without the limitations of solar sails. Claims of μN thrust for Woodward's MEGA Drive, along with predicted mass fluctuations as a consequence of the Mach-Effect have initiated a few decades of table-top experiments seeking to observe variable mass and using it to generate significant propellantless thrust efficiency. However, using different thrust balances with increasing measurement sensitivity to characterize these effects resulted in a decrease in the claimed effect's magnitude. Large second harmonics begin to appear in the pre-stressed piezoelectric stack's integrated strain gauge signal, showing the vibration present at system resonances, as well as significant nonlinearity. Observation of the balance beam's oscillations reveal sub-harmonic vibration coupling and amplified vibration around electromechanical resonances of the system that can explain the transients observed in the force trace. Different piezo-actuator driving conditions are explored and an account for the different behaviors observed is made. The varying driving conditions do not significantly affect the forces observed, contrary to the theory. It is concluded that the observed effect is a result of coupled vibrations on the torsion balance. • Claim on Mach-Effect propellantless propulsion scheme identified as vibration artefact. • Investigation of material- and electronics-related setup issues. • 1D balance model and simulations of conditions that lead to false thrust signals. [ABSTRACT FROM AUTHOR]

Forces claimed by potential propellantless propulsion systems like the Mach-Effect-Thruster or the EMDrive are in the μN or even sub-μN range. In this paper, an automated thrust balance design capable of measuring forces of 100 nN for devices with a maximum mass of 10 kg is described to test these claims. The torsion balance features an electromagnetic calibration method, adjustable magnetic damping and tilt control as well as electromagnetic shielding. All onboard electronics can be controlled wirelessly via an infrared module for serial communication. Power is supplied to the balance using three separate liquid metal feedthroughs: one for voltages up to 500 V and frequencies up to 200 kHz, one for high voltage up to 30 kV DC or AC, and one for high frequency signals up to 3 GHz. The device can be rotated by 180° to measure three different thrust directions without breaking the vacuum and changing the setup in order to gain confidence and refute e.g. thermal drifts. The whole balance is controlled via a script language implemented in LabVIEW. We tested Mach-Effect-Thrusters provided by Woodward and our self-built model exploring higher frequencies and mixed-signals that are believed to create significantly higher forces. Also a magnetostrictive version was built and tested. For the EMDrive, several different frequencies and setups (with/without dielectric insert, flat/spherical end caps) were tested. Results of the tests performed between August and September 2018 are presented, but no final conclusions can be drawn. • Thorough investigation of breakthrough propulsion concepts. • Thrust balance development to test EMDrive and Mach-Effect Thrusters. • Complementary experiments to test physics behind claims. • Education project towards interstellar spaceflight. [ABSTRACT FROM AUTHOR]

Abstract Propellantless propulsion is believed to be the best option for interstellar travel. However, photon rockets or solar sails have thrusts so low that maybe only nano-scaled spacecraft may reach the next star within our lifetime using very high-power laser beams. Since 2012, a dedicated breakthrough propulsion physics group was founded at the Institute of Aerospace Engineering at TU Dresden to investigate different concepts based on non-classical/revolutionary propulsion ideas that claim to be at least an order of magnitude more efficient in producing thrust compared to photon rockets. Most of these schemes rely on modifying the inertial mass, which in turn could lead to a new propellantless propulsion method. Our intention is to develop an excellent research infrastructure to test new ideas and measure thrusts and/or artefacts with high confidence to determine if a concept works and if it does how to scale it up. At present, we are focusing on two possible revolutionary concepts: The EMDrive and the Mach-Effect Thruster. The first concept uses microwaves in a truncated cone-shaped cavity that is claimed to produce thrust. Although it is not clear on which theoretical basis this can work, several experimental tests have been reported in the literature, which warrants a closer examination. We are building several models of different sizes to understand scaling laws and the interaction with the test environment. The second concept is theoretically much better understood and is believed to generate mass fluctuations in a piezo-crystal stack that creates non-zero time-averaged thrusts. Apart from theoretical models, we are testing and building several such thrusters in novel setups to further investigate their thrust capability. In addition, we are performing side-experiments to investigate other experimental areas that may be promising for revolutionary propulsion. To improve our testing capabilities, several cutting-edge thrust balances are under development to compare thrust measurements in different measurement setups to gain confidence and to identify experimental artefacts. Highlights • Thorough investigation of breakthrough propulsion concepts. • Thrust balance development to test EMDrive and Mach-Effect thrusters. • Complementary experiments to test physics behind claims. • Education project towards interstellar spaceflight. [ABSTRACT FROM AUTHOR]