Researchers at the Technical University of Dresden measured the thrust of the "impossible engine" EmDrive, which does not require fuel to operate and violates the law of conservation of momentum, and concluded that there is no magic here. The experiment showed that the registered thrust is explained by insufficient shielding of the installation and, as a consequence, the previously unaccounted for influence of the Earth's magnetic field. Scientists shared their findings at the Space Propulsion Conference.
Researchers led by Martin Taimar measured the thrust of the EmDrive using a torsion rig, which she perfected consistently over four years. The principle of operation of this installation is reminiscent of the torsion balance, invented at the end of the 18th century and used to experimentally test the laws of Coulomb and Newton. A torsion balance is a balanced arm suspended on a vertical thread. When external forces act on the lever, it turns, and the angle of deflection can be used to judge the magnitude of the applied forces. In the installation of the German scientists, instead of a thread, sensitive torsion springs were used, which held the camera with a motor, and the camera displacement was measured using a laser interferometer. This made it possible to fix the thrust force of the order of several micronewtons.
The chamber for the experiment and its layout.
Of course, the researchers tried to reduce as much as possible the possible impact of external forces, which could be confused with the thrust from the "impossible engine". For this, the camera was installed on a separate concrete block, which suppresses the vibrations of the foundation. The chamber was evacuated to a pressure of the order of one pascal (100 thousand times less than atmospheric), all important parts of the installation were protected from external electromagnetic radiation using metal sheets, and they also tried to prevent the electronics from overheating by controlling its temperature using infrared cameras.
Before doing basic experiments, physicists calibrated the setup to make sure they had really ruled out all external factors. Finally, when measuring thrust, the researchers turned the engine inside the chamber to see if any unaccounted for factors were affecting the results. In an ideal situation, when there are no such factors, the direction of the camera displacement should be opposite to the direction of the engine thrust - for example, at an angle of rotation of the engine of 0 degrees, the displacement of the camera is positive, at 180 degrees, negative, and at an angle of 90 degrees, it is completely absent.
Measurements with the EmDrive showed a slightly different behavior. Of course, at zero angle, the thrust reached four micronewtons with an amplifier power of the order of two watts, and when the engine was turned 180 degrees, the displacement changed sign. Thus, it turned out that the ratio of thrust to power is approximately equal to two millinewtons per kilowatt, which is almost twice as much as the results of previous experiments. Nevertheless, at an angle of 90 degrees, the physicists still recorded camera displacement, although it should have been absent. In addition, when the force of electromagnetic oscillations inside the engine was suppressed by almost a hundred thousand times, the magnitude of the thrust practically did not change. This means that, in reality, the thrust observed in the experiment was associated not with the engine, but with unaccounted for external factors.
The Earth's magnetic field can act as such factors, the researchers note. Physicists add that all devices participating in the experiment were shielded, and coaxial cables were used wherever possible, but the field could still penetrate into the installation through their joints. Of course, it should have been greatly weakened, but the magnitude of the measured thrust is so small that it can be easily attributed to this effect. In fact, the strength of the earth's magnetic field is approximately 50 microtesla, and the current that powers the amplifier was up to two amperes. Using Ampere's law, it is easy to calculate that under such conditions, a thrust of about two micronewtons can create a section of wire only two centimeters long. To eliminate this force, shield the amplifier and the camera at the same time,increasing the size of the metal Faraday cage. The authors of the article emphasize that in all previous measurements of the EmDrive thrust, such shielding was not performed, and therefore their results should be carefully checked.
People have long dreamed of interstellar travel, but many technical difficulties prevent this dream from coming true. One of the biggest is the need to carry a huge mass of fuel on board the spacecraft, since we do not yet have other technologies that would allow us to develop high speeds in outer space. We rely on jet thrust, and this is one of the problems.
Promotional video:
For the spacecraft to be able to fly to the closest star to the solar system - Proxima Centauri, (distance about 4.2 light years), it will take a mass of fuel, comparable to the mass of the Sun.
At the moment, the development of alternative ways to accelerate spacecraft, for example, with the help of the same solar sails, which use the energy of the solar wind or laser radiation for movement. For example, the Breakthrough Starshot project proposes to launch tiny ships (about one gram in mass) to Proxima Centauri, which will be accelerated by the solar wind and reach the star within twenty years. However, such technologies cannot be scaled to human sizes.
The EmDrive engine, another alternative to jet propulsion, showed promise as a technology that will open the way for us to interstellar travel. The engine was proposed by Roger Scheuer back in 1999. It consists of an asymmetric resonator and a magnetron, which directs electromagnetic radiation into it and excites standing electromagnetic waves. In turn, due to the asymmetry of the structure, the waves create different pressures on the walls of the engine and are a source of thrust.
The operation of such an engine violates the law of conservation of momentum, one of the fundamental laws of physics. However, numerous experiments claimed that EmDrive still creates traction. For example, in a paper published in November 2016, engineers from NASA reported a thrust of about 80 micronewtons with an applied electrical power of about 60 watts. And in September last year, Chinese researchers also announced a working prototype of the engine, "impossible" from the point of view of science.
Nikolay Khizhnyak