High-Accuracy Thrust Measurements of the EMDrive and Elimination of False-Positive Effects
The EMDrive is a proposed propellantless propulsion concept claiming to be many orders of magnitude more efficient than classical radiation pressure forces. It is based on microwaves, which are injected into a closed tapered cavity, producing a unidirectional thrust with values of at least one mN/kW. This was met with high scepticism going against basic conservation laws and classical mechanics. However, several tests and theories appeared in the literature supporting this concept. Measuring a thruster with a significant thermal and mechanical load as well as high electric currents, such as those required to operate a microwave amplifier, can create numerous artefacts that produce false-positive thrust values. After many iterations, we developed an inverted counterbalanced double pendulum thrust balance, where the thruster can be mounted on a bearing below its suspension point to eliminate most thermal drift effects. In addition, the EMDrive was self-powered by a battery pack to remove undesired interactions due to feedthroughs. Using a geometry and operating conditions close to the model by White et al that reported positive results published in the peer-reviewed literature, we found no thrust values within a wide frequency band including several resonance frequencies. Our data limits any anomalous thrust to below the force equivalent from classical radiation for a given amount of power. This provides strong limits to all proposed theories and rules out previous test results by more than three orders of magnitude.
Thrust Measurements and Evaluation of Asymmetric Infrared Laser Resonators for Space Propulsion
In addition to the classic EmDrive, Tajmar’s team also analyzed the LemDrive-variation:
“This laser variant of the EmDrive is based on theoretical considerations by McCulloch. In numerous experimental set-ups, we have been able to show that both laser resonators and asymmetrical fiber coils do not show any forces that are above normal photon pressure. His theory (…we limit ourselves here to the laboratory standard and not to his astronomical claims), as well as the experiments cited by him are excluded by 4 orders of magnitude.
Abstract – Thrust Measurements and Evaluation of Asymmetric Infrared Laser Resonators for Space Propulsion
Since modern propulsion systems are insufficient for large-scale space exploration, a breakthrough in propulsion physics is required. Amongst different concepts, the EMDrive is a proposed device claiming to be more efficient in converting energy into propulsive forces than classical photon momentum exchange. It is based on a microwave resonator inside a tapered cavity. Recently, Taylor suggested using a laser instead of microwaves to boost thrust by many orders of magnitude due to the higher quality factor of optical resonators. His analysis was based on the theory of quantised inertia by McCulloch, who predicted that an asymmetry in mass surrounding the device and/or geometry is responsible for EMDrive-like forces. We put this concept to the test in a number of different configurations using various asymmetrical laser resonators, reflective cavities of different materials and size as well as fiber-optic loops, which were symmetrically and asymmetrically shaped. A dedicated high precision thrust balance was developed to test all these concepts with a sensitivity better than pure photon thrust, which is the force equivalent to the radiation pressure of a laser for the same power that is used to operate each individual devices. In summary, all devices showed no net thrust within our resolution at the Nanonewton range, meaning that any anomalous thrust must be below state-of-the-art propellantless propulsion. This puts strong limits on all proposed theories like quantised inertia by at least 4 orders of magnitude for the laboratory-scale geometries and power levels used with worst care assumptions for the theoretical predictions.
With both the EmDrive and the LemDrive, we have achieved a measurement accuracy that is below the photon pressure. That is, even if one of these concepts worked, it would be more effective simply to use a laser beam as a drive.”
In a third paper, the Dresden physicists then describe their research on the “Mach-Effect Thruster”:
“Here we have proven that the Mach-Effect-Thruster (an idea by J. Woodward) is unfortunately a vibration artifact and also not a real thrust.”
Abstract – The SpaceDrive Project – Mach-Effect Thruster Experiments on High-Precision Balances in Vacuum
Concepts for propellantless space propulsion are carefully investigated using high-precision balances in the framework of the SpaceDrive Project. The Mach-Effect-Thruster, an original design from Woodward that relies on the particular vibration of an asymmetric, piezoelectric stack actuator to produce thrust, is one concept that was extensively tested. In an attempt to validate the results published in peer-reviewed literature, several MET devices were tested on two different types of balances in vacuum conditions: a torsion balance and an inverted counterbalanced double pendulum, as well as on a rotating apparatus. The instruments are characterized by background noise lower than 5 nN after averaging and are calibrated using laser interferometry and a voice coil with a high-resolution current source. Encased in grounded mu-metal shielding on the balance, and powered by dedicated amplifiers, the device was swept with a frequency between 20 and 50 kHz in order to identify the operating range with the largest beam deflections. Measurements with the torsion balance from a previous campaign seem to indicate vibration artifacts, thermal noise and changes in the experiment’s center of mass at specific resonance frequencies. These measurements were repeated with different device orientations on the double-pendulum balance, and deflections of similar magnitude that can be explained by thermal expansion and device resonance were also observed. Recording both balance beam displacements with a sampling rate of up to 25 MHz revealed a significant vibration when exciting the actuator around its longitudinal resonance, regardless of the mounting and isolation. Calculations and simple modeling of the resulting pulsed force from the vibrations confirms the hypotheses made from balance measurements. Additional tests were performed on a rotating apparatus to investigate the presence of mass fluctuations in a centrifugal force field without having to synchronize with a push-pull force. Our tests reveal the presence of mechanical artifacts but no thrust.
SOURCES- Dresden University, Conference: Space Propulsion 2020+1
Written By Brian Wang, Nextbigfuture.com
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