The laws of physics have won again, it would appear.
For the past few years, researchers at NASA's Eagleworks advanced-propulsion lab have been putting a controversial and potentially revolutionary space engine called the EmDrive to the test.
The EmDrive, which was originally developed by British scientist Roger Shawyer in the early 2000s, purportedly generates thrust by bouncing microwaves around inside a conical chamber. Because the engine doesn't require any fuel, it could theoretically make spaceflight far cheaper and more efficient, opening the heavens to exploration.
In November 2016, engineers from NASA’s Johnson Space Center published EmDrive test results that suggested the theoretical technology should be explored further. And the NASA team's work has given EmDrive enthusiasts some reason for optimism, detecting small amounts of thrust in lab tests of the device.
But now we get to the "controversial" part: The EmDrive really shouldn't work. The engine doesn't blast anything out a nozzle, so Newton's Third Law of Motion — for every action there is an equal and opposite reaction — doesn't come into play.
Nobody really understands how the claimed thrust could actually be generated.
And now it seems that the previously detected thrust was illusory, at least according to a team of researchers in Germany. They built their own EmDrive and tested it in a vacuum chamber, as the NASA researchers did.
A group of German physicists at TU Dresden has tested two proposed means of propellantless propulsion – the EmDrive and Mach Effect Thrusters – But follow-up analysis "clearly indicates that the 'thrust' is not coming from the EmDrive but from some electromagnetic interaction". The researchers – Martin Tajmar, Matthias Kößling, Marcel Weikert and Maxime Monette – presented their findings last week at the Aeronautics and Astronautics Association of France’s Space Propulsion conference. The title of their paper is "The SpaceDrive Project – First Results on EmDrive and Mach-Effect Thrusters." That interaction is likely between EmDrive power cables and Earth's magnetic field, the team concluded.
The new results probably won't be the last word on the EmDrive; other researchers may want to take a crack at it as well. But if you've been counting on this impossible engine to help humanity get out among the stars, you may want to recalibrate your expectations.
The Scientific Method wins again?
Critics of the EmDrive have argued it violates the laws of physics as we currently understand them. The researchers' test results will do nothing to erase that scepticism.
The TU Dresden team constructed an EmDrive similar to the NASA test model. They stuck it in a shielded vacuum chamber and bombarded it with microwaves. They were able to measure thrust but it wasn't correlated with the direction the engine was pointing, leading them to conclude the test apparatus itself was affecting the measurements.
They found that "magnetic interaction from twisted-pair cables and amplifiers with the Earth’s magnetic field can be a significant error source for EMDrives."
"I consider the EMDrive as an experimental claim – and we are assessing if it works or not," said Martin Tajmar, lead author of the research and professor for Space Systems at TU Dresden, in an email to The Register.
"Our test results show that we can come up with thrusts similar to what one expects from other EMDrive tests, however, we could show that the origin of these thrusts is not the microwave cavity but more likely a magnetic interaction from the power feeding cables."
Meanwhile, Mach Effect thrusters are based on a theory proposed by physicist James F. Woodward in 1990. The idea is that mass fluctuation in an object can be used to generate directional propulsion.
NASA contends the theory is "is based on peer-reviewed, technically credible physics."
The German researchers again tested the tech in a vacuum chamber. While they were able to produce thrust that corresponded with engine direction, they found that the force produced was much more than they expected, leading them to believe again that the test regime messed with the measurements. They also were unable to get the thruster to work in reverse.
The test results cast a shadow over these theoretical propulsion schemes, but this isn't the end of it. The researchers intend to continue to their investigation with additional tests in the coming months.
The search for answers continues
Tajmar said his team is now building a better shielded setup to investigate these systems without interference.
"However, our power was an order of magnitude smaller compared to NASA's tests and a dielectric disc inside the cavity was missing," he said. "So we have to ramp up power and adapt the geometry for a perfect comparison. This will take another year. But of course our findings raise doubt regarding previous claims."
Tajmar said the team also need to produce more power in its Mach Effect Thruster test to match previous claims.
He avoided ruling out the possibility that either technology might work.
"It's work in progress, no conclusions yet," he said. "I'm very confident that we will have 'definite' tests within the next year."
Even so, the research paper suggests the real value to come out of the tests will be a lesson in experimental hygiene.
"At least, SpaceDrive is an excellent educational project by developing highly demanding test setups, evaluating theoretical models and possible experimental errors," the paper concludes.