After almost twenty years of trying to make the counter-intuitive Electromotive Force Drive work, the Association Aéronautique et Astronautique de France has reached the reluctant conclusion that it doesn’t. And while fuel-less propulsion would make deep space exploration a lot simpler (for some pretty wild values of ‘simple’) it looks like the ‘radio frequency resonant cavity thruster’ is not going to do the job.
Experimental results were presented last month at the Space Propulsion Conference, at Seville, Spain, and you can read the details here.
In simple terms, researchers were seeing a tiny amount of thrust generated apparently from nothing, which sounds pretty exciting if you’re trying to figure out how to get to the nearest star. Using current technology you’d need the energy output of a small star to get there. Unfortunately, after a great deal of testing and cross checking, they’ve discovered that the amount of observed thrust could be explained by experimental error, and could not even be reliably reproduced.
They used a laser to measure movement of an EM drive hung in a vacuum chamber. They found that no matter what they did to the power being put through the device, it always behaved as though it was producing about the same amount of thrust.
The idea of an engine that could produce thrust without fuel has been around since about 2001. Devices based on the idea of shoving electrical power out one end of a thruster directly have been sort of a unicorn in physics. Testing has suggested that electromagnetic radiation was providing direct thrust, in violation of what we thought we knew about the mass of subatomic particles and how this is all supposed to work.
The EM Drive consists of a metal cone containing an electromagnetic field that produces thrust without ejecting any material. Of course, this violates Newtonian physics, where a force is defined as a combination of mass and acceleration. Unfortunately, the EM drive doesn’t actually expel any mass.
The thrust produced by the EM drive was purportedly roughly the equivalent of the weight of a bit of dryer lint on the palm of your hand. Still if its effects could be scaled up, such a system could allow us to reach nearby planets in weeks, and even distant stars within single generations. Unfortunately, it turns out that the tiny amount of thrust may be being produced by the device’s resonance with Earth’s magnetic field. Any further tests are going to have to be magnetically shielded to eliminate this possibility, but it’s not looking good for the EM Drive. It’s still doing things nobody can explain, but producing thrust is apparently not one of those things.