"Researchers in Germany have performed
an independent, controlled test of the infamous EM Drive with an unprecedented level of precision," writes PvtVoid
. "The result? The thrust is coming from interactions with the Earth's magnetic field
." From the report: Instead of getting ahold of someone else's EM drive, or Mach-effect device, the researchers created their own, along with the driving electronics. The researchers used precision machining and polishing to obtain a microwave cavity that was much better than those previously published. If anything was going to work, this would be the one. The researchers built up a very nice driving circuit that was capable of supplying 50W of power to the cavity. However, the amplifier mountings still needed to be worked on. So, to keep thermal management problems under control, they limited themselves to a couple of Watts in the current tests. The researchers also inserted an enormous attenuator. This meant that they could, without physically changing the setup, switch on all the electronics and have the amplifiers working at full noise, and all the power would either go to the EM drive or be absorbed in the attenuator. That gives them much more freedom to determine if the thrust was coming from the drive or not.
Even with a power of just a couple of Watts, the EM-drive generates thrust in the expected direction (e.g., the torsion bar twists in the right direction). If you reverse the direction of the thruster, the balance swings back the other way: the thrust is reversed. Unfortunately, the EM drive also generates the thrust when the thruster is directed so that it cannot produce a torque on the balance (e.g., the null test also produces thrust). And likewise, that "thrust" reverses when you reverse the direction of the thruster. The best part is that the results are the same when the attenuator is put into the circuit. In this case, there is basically no radiation in the microwave cavity, yet the WTF-thruster thrusts on. So, where does the force come from? The Earth's magnetic field, most likely. The cables that carry the current to the microwave amplifier run along the arm of the torsion bar. Although the cable is shielded, it is not perfect (because the researchers did not have enough mu metal). The current in the cable experiences a force due to the Earth's magnetic field that is precisely perpendicular to the torsion bar. And, depending on the orientation of the thruster, the direction of the current will reverse and the force will reverse.
The researchers' conclude by saying: "At least, SpaceDrive [the name of the test setup] is an excellent educational project by developing highly demanding test setups, evaluating theoretical models and possible experimental errors. It's a great learning experience with the possibility to find something that can drive space exploration into its next generation."