NASA's 'Impossible' Space Engine Tested—Here Are the Results

The first independent tests of the EmDrive suggest there's a mundane explanation for the wildly controversial device.

An illustration shows what an EmDrive looks like.

Spaceflight is hard. Blasting heavy cargo, spacecraft, and maybe people to respectable speeds over interplanetary distances (not to mention the luxury of stopping at destinations) requires an amount of propellant too massive for current rockets to haul into the void.

That is, unless you have an engine that can generate thrust without fuel.

It sounds impossible, but scientists at NASA’s Eagleworks Laboratories have been building and testing just such a thing. Called an EmDrive, the physics-defying contraption ostensibly produces thrust simply by bouncing microwaves around inside a closed, cone-shaped cavity, no fuel required.

It would be a bit like Han Solo flying the Millennium Falcon just by head-butting the dashboard, and if you think that sounds controversial, you’re right.

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The device last made headlines in late 2016 when a leaked study reported the results of the latest round of NASA testing. Now, independent researchers in Germany have built their own EmDrive, with the goal of testing innovative propulsion concepts and determining whether their seeming success is real or an artifact.

So, what did they find?

The NASA Eagleworks EmDrive sits inside a test chamber.

“The ‘thrust’ is not coming from the EmDrive, but from some electromagnetic interaction,” the team reports in a proceeding for a recent conference on space propulsion.

The group, led by Martin Tajmar of the Technische Universität Dresden, tested the drive in a vacuum chamber with a variety of sensors and automated gizmos attached. Researchers could control for vibrations, thermal fluctuations, resonances, and other potential sources of thrust, but they weren’t quite able to shield the device against the effects of Earth’s own magnetic field.

When they turned on the system but dampened the power going to the actual drive so essentially no microwaves were bouncing around, the EmDrive still managed to produce thrust—something it should not have done if it works the way the NASA team claims.

The researchers have tentatively concluded that the effect they measured is the result of Earth’s magnetic field interacting with power cables in the chamber, a result that other experts agree with.

“In the EmDrive case, interactions with the Earth's magnetic field seems to be the leading candidate explanation of the small thrusts seen,” says Jim Woodwardof California State University, Fullerton.Woodward has theorized a propulsive device of his own called the Mach Effect Thruster, which the Dresden group also tested.

To determine what’s going on with the EmDrive, though, the group needs to enclose the device in a shield made of something called mu metals, which will insulate it against the planet’s magnetism. Importantly, this kind of shield was not part of Eagleworks’ original testing apparatus either, which suggests the original findings could also be a consequence of leaking magnetic fields.

That sounds like a blow to the concept of the EmDrive, but Woodward is not ready to close the case on the contraption just yet. Aside from the lack of mu metal shielding, the Dresden lab’s tests were run at very low power levels, meaning that “any real signal would likely be swamped by noise from spurious sources,” he says.

So, perhaps an even more powerful test is what the space doctors ordered to help settle the debate. 

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This 1946 image of Earth was the first photograph taken in space.

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Astronaut Ed White poses for the first in-flight portrait, taken by astronaut James McDivitt in 1965 on Gemini 4.

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Ed White takes the first space walk made by an American, on the Gemini 4 mission.

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American astronaut Buzz Aldrin in 1966 on the Gemini 12 mission takes the first selfie in space.

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Ed White floats outside the Gemini 4 in a 1965 photo taken by fellow astronaut James McDivitt.

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The 1967 image was the first color photo taken of Earth from space.

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A 70mm Hasselblad camera floats over astronaut Walter Cunningham'sright hand on Apollo 7. This photo was taken by his colleague Wally Schirra in 1968.

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"Grabbing the Hasselblad camera, I perpetrated a photographic no-no: taking this picture looking into the sun," recalled astronaut Walter Cunningham. He took this photo of the Florida Peninsula aboard Apollo 7 in 1968.

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Apollo 8 lifts off from Cape Kennedy, Florida, in 1968. It was the first manned mission to the moon.

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"The color of the moon looks like a very whitish gray, like dirty beach sand with lots of footprints on it," said astronaut William Anders. He took this photo aboard Apollo 8.

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William Anders took this photo of his first earthrise on Apollo 8.

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This photo, taken by a camera mounted on an Air Force jet, shows the Apollo 8 team's 1968 reentry into Earth.

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Astronaut Rusty Schweickart took this photo of fellow astronaut David Scott on an Apollo 9 space walk in 1969.

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These photos of the moon, stitched together into a panorama, were taken on the Apollo 10 mission in 1969.

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Life magazine photographer Ralph Morse mounted a camera on the launch platform to capture this image of the liftoff of the rocket carrying Apollo 11 on its historic mission to the moon in 1969.

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Astronaut Neil Armstrong took this photo of Buzz Aldrin during the Apollo 11 mission. It is the first photograph of a man standing on another world.

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Astronaut Alan Bean holds a container of lunar soil in this 1969 photo from the Apollo 12 mission.

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Astronaut Eugene Cernan tests the lunar rover on the moon. His Apollo 17 partner Harrison Schmitt took this photo in 1972.

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"I captured the Earth, the moon, the man, and the country [the United States] all in one," said Eugene Cernan of this photo, taken in 1972 during the Apollo 17 mission.

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"When the Earth completed eclipsing the sun, you could see a big white light right in the middle of the Earth moving across the ocean," said Alan Bean of Apollo 12's journey home in 1969.

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