NASA Team Claims ‘Impossible’ Space Engine Works—Get the Facts – National Geographic

 In Science

A prototype of the EmDrive, as seen in a test chamber at a NASA lab

After years of speculation, a maverick research team at NASA’s Johnson Space Center has reached a milestone that many experts thought was impossible. This week, the team formally published their experimental evidence for an electromagnetic propulsion system that could power a spacecraft through the void—without using any kind of propellant.

According to the team, the electromagnetic drive, or EmDrive, converts electricity into thrust simply by bouncing around microwaves in a closed cavity. In theory, such a lightweight engine could one day send a spacecraft to Mars in just 70 days. (Find out why Elon Musk thinks a million people could live on Mars by the 2060s.)

The long-standing catch is that the EmDrive seemingly defies the laws of classical physics, so even if it’s doing what the team claims, scientists still aren’t sure how the thing actually works. Previous reports about the engine have been met with heaping doses of skepticism, with many physicists relegating the EmDrive to the world of pseudoscience.

Now, though, the latest study has passed a level of scrutiny by independent scientists that suggests the EmDrive really does work. Is this the beginning of a revolution in space travel—or just another false start for the “impossible” spaceship engine?

What’s an EmDrive?

First proposed nearly 20 years ago by British scientist Roger Shawyer, this incarnation of the EmDrive has been developed and tested by engineers at NASA’s Advanced Propulsion Physics Research Laboratory, informally known as Eagleworks.

Put simply, the Eagleworks EmDrive generates thrust by bouncing around electromagnetic energy (in this case, microwave photons) in a closed, cone-shaped chamber. As those photons collide with the chamber’s walls, they somehow propel the device forward, despite the fact that nothing is released from the chamber. By contrast, ion drives now in use on some NASA spacecraft create thrust by ionizing a propellant, often xenon gas, and shooting out beams of charged atoms.

What this means, if the EmDrive withstands further scrutiny, is that future vehicles could hurtle through space without needing to carry literal tons of propellant. In space travel, staying light is crucial for fast and cost-effective trips over long distances.

Why does this engine break the laws of physics?

Way back in 1687, Sir Isaac Newton published three laws of motion that formed the foundation for classical mechanics. Over the intervening three centuries, those laws have been tested and verified over and over again. (Also see “Isaac Newton’s Lost Alchemy Recipe Rediscovered.”)

The trouble is, the EmDrive violates Newton’s third law, which states that for every action, there is an equal and opposing reaction. This principle explains, for instance, why a canoe glides forward when someone paddles. The force applied as the paddle moves through the water propels the canoe in the opposite direction. It’s also why jet engines generate thrust: As the engine expels hot gases backward, the plane moves forward.

Weirdly, the EmDrive doesn’t expel anything at all, and that doesn’t make sense in light of Newton’s third law or another tenet of classical mechanics, the conservation of momentum. If the EmDrive moves forward without expelling anything out the back, then there’s no opposing force to explain the thrust. It’s a bit like arguing that a person inside a car could propel it forward by repeatedly hitting the steering wheel, or that the crew of a spaceship could fly the craft to their destination simply by pushing on the walls.

Has anyone tried to test it before?

In 2014, the Eagleworks group made waves when it announced the results of early tests suggesting the EM engine actually worked. Since then, the group has tested the EmDrive in increasingly more stringent conditions, including the latest experiments.

Other groups have also developed and tested various incarnations of the EmDrive. In addition to experiments conducted by U.S., European, and Chinese academics, there’s a community of DIY EmDrivers who are busy making and testing their own impossible physics engines. But no one has been able to say conclusively that such a drive has worked as described. (Let’s be real: Physicists don’t like seemingly miraculous inventions.)

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