EmDrive thruster attracts notice from skeptics

The EmDrive apparatus was set up inside a vacuum chamber for testing. (White et al. via AIAA)

For years, space geeks have been intrigued by the idea of propulsion systems that don’t need propellant – and now one of the best-known concepts, known as the EmDrive, is getting a serious once-over.

The EmDrive, short for electromagnetic drive, could be revolutionary for spaceflight if it works. Spaceships could dispense with the mass of rocket fuel, and because the velocity builds up progressively, trips to Mars and beyond would be much faster and simpler.

The concept involves bouncing microwaves around a closed cavity that’s shaped like a cone. The shape supposedly funnels the microwaves to generate forward thrust.

The problem is, Newton’s Third Law of Motion says it shouldn’t work that way. If there’s an equal and opposite reaction for every action, the skeptics say the EmDrive – and the spaceship it’s bolted onto – should stay perfectly still. The effect has been compared to trying to push your car down the road by sitting in the driver’s seat and pushing against the steering wheel.

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By Alan Boyle

Mastermind of Cosmic Log, contributor to GeekWire and Universe Today, author of "The Case for Pluto: How a Little Planet Made a Big Difference," past president of the Council for the Advancement of Science Writing.

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