“Impossible engine” was really impossible

Researchers from Dresden University of technology measured the pull of the “impossible engine” EmDrive, which does not require fuel and violates the law of conservation of momentum, and came to the conclusion that there is no magic here. The experiment showed that the thrust was due to insufficient shielding of the installation and, as a consequence, the previously unaccounted influence of the magnetic field of the Earth. Their findings shared at the conference, Space Propulsion Conference.

Researchers under the leadership of Martin Tamara measured the thrust of EmDrive using a torsion setup, which it has consistently improved over four years. The principle of operation of this installation is reminiscent of the torsion balance, invented in the late XVIII century and used for experimental verification of Coulomb’s law and Newton. Torsional Libra is a balanced lever, suspended by vertical thread. When the lever of external forces, it rotates, and the angle of deviation it is possible to judge the magnitude of the applied forces. To install German scientists instead of thread were used a sensitive torsion spring that held the camera motor and the camera displacement was measured using a laser interferometer. This helped fix the traction force of the order of several micronewtons.

Camera for the experiment and its circuit

Of course, the researchers tried as much as possible to reduce the potential impact of external forces, which could be confused with rod from “impossible engine”. To do this, the camera was mounted on a separate concrete block, the overwhelming vibration of the Foundation. The chamber was evacuated to a pressure of about one Pascal (100 thousand times less than atmospheric), and defended all the important parts of the machine from external electromagnetic radiation with the metal sheets, and tried to prevent overheating of the electronics by controlling the temperature using the infrared cameras.

Before conducting the main experiments we calibrated the installation to ensure that they actually ruled out all the external factors. Finally, measurements of thrust, the researchers turned the engine inside the camera to check not have any impact on the results of any unaccounted factors. In an ideal situation, when these factors are not present, the offset direction of the camera is opposite to the direction of thrust of the engine — so, when the angle of rotation of the motor is 0 degrees, the camera displacement is positive, at 180 degrees is negative, and at an angle of 90 degrees is non-existent.

Measure with the engine EmDrive showed somewhat different behavior. Of course, at the zero angle, the thrust reached four micronewtons at a power amplifier about two watts, and turning the engine 180 degrees offset changed sign. Thus, it turned out that the ratio of thrust power to power approximately equal to two millinewtons per kilowatt, which is almost two times more than the results of previous experiments. However, when a 90-degree angle physics still recorded the displacement of the camera, although it was absent. In addition, the suppression of power of electromagnetic oscillations inside the motor for almost a hundred thousand times the magnitude of thrust is almost not changed. This means that actually observed in the experiment, the thrust was not connected with the engine, and unaccounted externalities.

As such factors may be the Earth’s magnetic field, the researchers note. Physics adds that all involved in the experiment, the devices were shielded and used coaxial cables wherever possible, but the field could still get inside through the places of their connections. Of course, it was much weakened, however, the measured thrust is so small that it can be attributed to this effect. In fact, the magnetic field of the Earth is approximately equal to 50 microtesla, and the current feeding the amplifier, up to two amps. Using the law of ampere, it is easy to calculate that under such conditions the thrust of about two Newton can create a plot of wire length of only two inches. To eliminate this force should be shielded amplifier and camera at the same time, increasing the size of the metal Faraday cage. The authors stress that in all previous measurements of thrust of EmDrive such shielding is not performed, and therefore their results should be carefully rechecked.

People have been dreaming of interstellar travel, however, to realize this dream prevents a lot of technical difficulties. One of the biggest is the need to carry on Board the spacecraft huge mass of fuel, as other technologies allowing to develop high speed in outer space we have yet. We rely on rocket thrust, and in this lies one of the problems.

That spaceship was able to fly to the nearest Solar system star — Proxima Centauri (a distance of about 4.2 light years) will be required propellant mass comparable to the mass of the Sun.

At the moment, we are developing alternative ways of acceleration of the spacecraft, for example, using the same solar sails, which are used for movement energy wind solar or laser radiation. For example, the project Breakthrough Starshot offers to run to Proxima Centauri, the tiny spacecraft (weighing about one gram), which will be dispersed by the solar wind and reach the stars for twenty years. However, such technology cannot be scaled to human dimensions.

Engine EmDrive, another alternative to jet propulsion, had shown promise as a technology that will pave the way for interstellar travel. The engine was proposed by Roger Scheuer in 1999. It consists of a single-ended resonator and the magnetron, which directs electromagnetic radiation and excites a standing electromagnetic wave. In turn, because of the asymmetry of the structure of the wave create various pressure on the walls of the engine and are a source of traction.

The work of such an engine violates the law of conservation of momentum, one of the fundamental laws of physics. However, numerous experiments have argued that the thrust of EmDrive still creates. For example, published in November 2016, the work of engineers from NASA reported on deadlift with about 80 micronewtons when the applied electric power of about 60 watts. And in September of the last year working on the prototype engine, “the impossible” from the point of view of science, also said Chinese researchers.

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