Research

The mythical space engine finally passes the real test

Since the birth of the cosmic age, the dream ofthe trip to another solar system was kept in a "rocket restraint", which severely limits the speed and size of the spacecraft that we launch into space. Scientists estimate that even using the most powerful rocket engines today will take about 50,000 years to reach our nearest interstellar neighbor, Alpha Centauri. If people ever hope to see the sunrise of the alien sun, the transit time should be significantly reduced.

Does an impossible EmDrive engine work?

Among the advanced concepts of the engine that couldto get it all off the ground, very few caused as much excitement - and contradiction - as EmDrive. First described almost twenty years ago, EmDrive works by converting electricity into microwaves and directing this electromagnetic radiation through a conical chamber. In theory, microwaves can exert pressure on the chamber walls and create sufficient thrust to move a spacecraft in space. At the moment, however, EmDrive exists only as a laboratory prototype, and it is still unclear whether it can generate traction at all. If it creates, then the forces that are not strong enough to be seen with the naked eye, not to mention moving the device.

However, over the past few years severalscientists, including NASA, have claimed that they have successfully produced cravings with EmDrive. If this is true, we are waiting for one of the biggest breakthroughs in the history of space exploration. The problem is that the thrust observed in these experiments is so small that it is difficult to say whether it exists at all.

The solution is to develop a toolwho can measure these minor manifestations of thrust. Therefore, a team of physicists from the German Technische Universität Dresden decided to create a device that would solve this problem. The SpaceDrive project, led by physicist Martin Tymar, is to create a tool so sensitive and immune to interference that it will put an end to the discussion once and for all. In October, Tymar and his team presented their second set of experimental measurements of EmDrive at the International Astronautical Congress, and their results will be published in Acta Astronautica this August. Based on the results of experiments, Tymar says that the resolution of the saga with EmDrive is waiting for us in a couple of months.

Many scientists and engineers do not believe in EmDrive,because it violates the laws of physics. The microwaves pushing the walls of the EmDrive chamber appear to generate ex nihilo thrust, that is, from nothing, which goes against the preservation of the impulse - action and no counteraction. The supporters of EmDrive, in turn, are looking for answers in clever interpretations of quantum mechanics, trying to understand how EmDrive could work without violating Newtonian physics. “From a theoretical point of view, no one takes it seriously,” says Tymar. If EmDrive is capable of generating cravings, as some groups claim, “no one has any idea where it comes from.” When science has a theoretical gap of this magnitude, Tymar sees only one way to close it: experimental.

At the end of 2016, Tymar and 25 other physicistsgathered in Estes Park, Colorado, for the first EmDrive conference and related exotic motor systems. One of the most interesting speeches was made by Paul Marsh, a physicist at NASA Eagleworks laboratory, in which he and his colleague Harold White tested various EmDrive prototypes. According to Marsh’s presentation and the subsequent report published in the Journal of Propulsion and Power, he and White observed several dozen micronewons of thrust in their EmDrive prototype. For comparison, a single SpaceX Merlin engine produces about 845,000 newtons of thrust at sea level. However, the problem for Marsh and White was that their experimental setup included several sources of interference, so they could not say for sure what caused the thrust or specific interference.

Tymamar and the Dresden group used accuratea copy of the prototype EmDrive used in the NASA lab. It is a truncated copper cone — with a cut off top — a little less than a foot in length. This design came up with another engineer, Roger Scheuer, who first described EmDrive in 2001. During testing, the EmDrive cone is placed in a vacuum chamber. Outside the camera, the device generates a microwave signal that is transmitted over coaxial cables to antennas inside the cone.

This is not the first time that a team in Dresdentrying to measure an almost imperceptible force. They created similar devices to work on ion engines, which are used to accurately position satellites in space. These micronewton engines help satellites detect weak phenomena, such as gravitational waves. But to study EmDrive and similar engines without fuel, nanonewton resolution is required.

A new approach was to apply torsionscales, pendulum balance type, which measures the amount of torque applied to the axis of the pendulum. A less sensitive version of this balance was also used by the NASA team when they decided that EmDrive was producing cravings. To accurately measure this small force, the Dresden team used a laser interferometer to measure the physical displacement of the balance weights produced by the EmDrive. According to Taymara, their torsion scales have nanonewton resolution and support thrusters weighing several kilograms, which makes these scales the most sensitive of the existing ones.

But really sensitive thrust scales are unlikelywill be useful if you can not determine whether the detected force, and not a manifestation of external intervention. And there are many alternative explanations for the observations of Marsh and White. In order to determine whether EmDrive actually produces thrust, scientists must be able to shield the device from interference of the Earth’s magnetic fields, environmental seismic vibrations and EmDrive thermal expansion associated with microwave heating.

According to Taymar, making changes tothe torsion balance design - to better control the EmDrive power supply and protect it from magnetic fields - will solve a number of interference problems. It was much harder to solve the problem of “thermal drift”. When power is supplied to the EmDrive, the copper cone heats and expands, which shifts its center of gravity so much that the torsion balance registers a force that can be mistaken for a thrust force. Taiman and his team hoped that changing the orientation of the engine would help solve this problem.

In the course of 55 experiments Tymar and his colleaguesregistered an average of 3.4 micronewton strengths from EmDrive, which was very similar to what they found in NASA. Alas, these forces, apparently, did not come the test of thermal displacement. They were more characteristic of thermal expansion than thrust.

But for EmDrive, hope is not lost. Tymar and his colleagues are also developing two additional types of thrust weights, including superconducting balance, which will help eliminate false alarms caused by heat drift. If they find strength from EmDrive on these scales, there is a high probability that this is really a push. But if no scales are detected, it will mean that all previous observations of EmDrive were false positive. Tymar hopes to get a final verdict before the end of the year.

But even negative results will notmean sentence for EmDrive. There are many other types of engines without fuel. And if scientists ever develop a new form of motion on a weak burden, supersensitive traction scales will help to separate fiction from fact.

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