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Since the birth of the space age, the "tyranny of the rocket equation" has hindered the dream of embarking on another solar system, which sets great limits to speed and size of the spaceship that we launch into the cosmos. Even with today's most powerful rocket engines, scientists estimate that it would take 50,000 years for our nearest interstellar neighbor, Alpha Centauri. If humans hope to see an extraterrestrial sunrise, the transit times will have to drop considerably.
Of the advanced propulsion concepts that could theoretically solve this problem, few have sparked as much enthusiasm and controversy as the EmDrive. Described for the first time almost two decades ago, EmDrive converts electricity into microwaves and channels this electromagnetic radiation through a conical chamber. In theory, microwaves can exert a force against the walls of the chamber to produce sufficient thrust to propel a spacecraft once into space. At this stage, however, EmDrive exists only as a laboratory prototype and it is still unclear whether it is capable of producing a surge. If this is the case, the forces it generates are not powerful enough to be recorded with the naked eye and even less to propel a spacecraft.
However, in recent years, a handful of teams of researchers, including one from NASA, have managed to create a push with an EmDrive. If this is true, it would be one of the greatest advances 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 is real.
The solution lies in the design of a tool capable of measuring these minimal amounts of thrust. A team of physicists from the Technische Universität Dresden in Germany decided to create a device that would meet this need. Led by physicist Martin Tajmar, the SpaceDrive project aims to create an instrument so sensitive and insensitive to interferences that it would put an end to the debate once and for all. In October, Tajmar and his team presented their second set of experimental EmDrive measurements at the International Astronautical Congress. Their results will be published in Acta Astronautica in August. According to the results of these experiments, Mr. Tajmar said that a resolution of the EmDrive saga might not last a few months.
Many scientists and engineers reject the EmDrive because it seems to violate the laws of physics. The microwaves pushing on the walls of an EmDrive room seem to generate a push ex nihilo, which goes against the conservation of the momentum – it is all action and no reaction. EmDrive supporters, in turn, used marginal interpretations of quantum mechanics to explain how EmDrive could work without violating Newtonian physics. "From the point of view of theory, nobody takes this seriously," says Tajmar. As some groups have claimed, EmDrive is able to produce a boost, he says, they have "no idea of the origin of this push". When there is a theoretical break of this magnitude in science, Tajmar sees only one way to close it: experimentation.
At the end of 2016, Tajmar and 25 other physicists met in Estes Park, Colorado, for the first EmDrive conference and related exotic propulsion systems. One of the most interesting presentations was given by Paul March, a physicist at NASA's Eagleworks Laboratory, where he and his colleague Harold White had tested various EmDrive prototypes. According to March's presentation and an article later published in the Propulsion and power logHe and White have observed several tens of micro-newtons of thrust in their EmDrive prototype. (For comparison, a single SpaceX Merlin engine produces about 845,000 newtons of sea-level thrust.) The problem for Harold and White, however, was that their experimental setup allowed for multiple sources of interference, so that They could not say. for sure if what they observed was pushed.
Tajmar and the Dresden group used a faithful replica of the EmDrive prototype used by Harold and White during their tests at NASA. It consists of a copper trunk – a cone whose top is cut – which is a little less than a foot long. This design can be attributed to the engineer Roger Shawyer, who first described the EmDrive in 2001. During testing, the EmDrive cone is placed in a vacuum chamber. Outside the chamber, a device generates a microwave signal that is relayed, using coaxial cables, to the antennas located inside the cone.
This is not the first time that the Dresden team has been trying to measure almost imperceptible amounts of force. They have built similar gear for their work on ion thrusters, which are used to accurately position satellites in space. These micro-newton thrusters are of the type used by the LISA Pathfinder mission, which requires an extremely precise positioning capability to detect weak phenomena such as gravitational waves. But to study the EmDrive system and its similar propellantless propulsion systems, Tajmar said, it took a nano-newton resolution.
Their approach was to use a torsion balance, a pendulum scale that measures the amount of torque applied to the pendulum axis. A less sensitive version of this balance was also used by the NASA team when it thought their EmDrive had produced a boost. To accurately measure the small amount of force, the Dresden team used a laser interferometer to measure the physical displacement of the scales produced by the EmDrive. According to Tajmar, their torsion scale has a nano-newton resolution and supports thrusters weighing several kilograms, making it the world's most sensitive thrust balance.
But a really sensitive thrust balance is not very useful unless you can also determine if the force detected is a thrust and not an outside interference artefact. And there are many other explanations for Harold and White's observations. To determine if an EmDrive actually produces a surge, researchers must be able to protect the device from interference from the earth's magnetic poles, seismic vibrations from the environment and thermal expansion from the Earth's surface. EmDrive due to the heating of microwaves.
Adjustments in the design of the torsion balance – to better control the power supply of the EmDrive and protect it from magnetic fields – have solved some interference problems, explains Tajmar. A more difficult problem was how to deal with "thermal drift". As the current pbades through the EmDrive, the copper cone heats up and expands, displacing its center of gravity just enough so that the torsion scale can register a force that can be confused with the thrust. . Tajmar and his team were hoping that changing the thruster orientation would solve this problem.
In 55 experiments, Tajmar and his colleagues recorded an average of 3.4 microns of EmDrive strength, which was very similar to what the NASA team had discovered. Unfortunately, these forces do not seem to have pbaded the thermal drift test. The forces observed in the data were more indicative of thermal expansion than a surge.
All hope, however, is not lost for the EmDrive. Tajmar and his colleagues are also developing two other types of thrust balances, including the superconducting balance that will, among other things, eliminate the false positives produced by thermal drift. If they detect the strength of an EmDrive on these scales, there is a high probability that it is a thrust. But if no strength is recorded on these scales, it probably means that all previous EmDrive thrust observations were false positives. Tajmar says he hopes to have a final verdict by the end of the year.
But even a negative result from this job might not kill EmDrive for good. There are many other models of propulsion without propulsion to pursue. And if scientists develop new forms of weak propulsion, the hyper-sensitive thrust balances developed by Tajmar and the Dresden team will almost certainly play a role in sorting the scientific facts of science fiction.
This article was originally published on WIRED US
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