NASA Resurrected an 'Impossible' Microwave Thruster Technology

It's always exciting when something seemingly impossible is validated by NASA—the smartest of the smart when it comes to cutting-edge aeronautical technology, right? Well, NASA scientists have just confirmed that an "impossible" technology is in fact possible.

Agency scientists validated that a microwave thruster really works. However, it's an announcement that could turn out to be a bit like the faster-than-light neutrinos that on closer inspection turned out to be regular old slower-than-light particles: These findings are based on just eight days of studies. Still, that NASA is interested means it's something we ought to pay attention to.

The "impossible" technology in this instance is called the EmDrive. It's the brainchild of British engineer Roger Shawyer and it theoretically works by converting electric power into thrust by bouncing microwaves around in a closed container. There's no propellant involved in this system, which makes it a compelling technology for spaceflight. Fuel, or propellant in the case of thrust rockets, is necessarily in limited quantities on any given spacecraft; it's heavy to launch, and when it's used up a spacecraft has little to no way of reorienting itself or altering its trajectory.

But a propellant-free system would be a game changer. If a spacecraft, say a deep space probe like New Horizons, which is less than a year from its encounter with Pluto, didn't need propellant, that extra weight and space could be devoted to scientific instruments, larger solar arrays, or a larger power source.

The problem with the EmDrive is that, according to the laws of the conservation of momentum, it shouldn't work.

To validate Shawyer's system, third parties have tried to build one. Last year, a team of Chinese scientists built an EmDrive that produced 720 microNewtons (which is about 72 grams) of thrust. That's enough power to move a small satellite by a thrust rocket, and it's a level of power that could be gained from solar electricity. And now an American team has followed in the Chinese scientists' footsteps. Guido Fetta built the propellant-less microwave thrust system and a team from NASA's Johnson Spacecraft Centre tested it.

The JSC team ran a series of tests over eight days "to investigate and demonstrate viability of using classical magnetoplasmadynamics to obtain a propulsive momentum transfer via the quantum vacuum virtual plasma." In plain English, the tests were designed to measure any thrust produced by an electric propulsion unit that consisted of a cavity in which radio frequencies were able to resonate or bounce around.

Six of the eight days were devoted to developing the test articles, one of which was designed to produce no thrust (called the null article) as a control to make sure that any observed thrust wasn't coming from the article itself, and setting up the test environments. The articles were calibrated and moved between a test bench and a stainless steel vacuum chamber with an internal ambient atmospheric pressure. In both cases, the scientists used manual frequency control to try to produce the frequency to produce thrust. And no one expected to see any thrust.

Amazingly, they did. The test setup used a torsion pendulum sensitive enough to detect any propulsive force even at a single digit microNewton level. Still imagery of the test in both visible and infrared light showed movement of the pendulum, confirming thrust.

But it wasn't a lot of thrust. The JSC team measured between 30-50 microNewtons in their experiments when they used a radio frequency of about 935 megahertz. That's far less thrust than the 720 microNewtons apparently observed by the Chinese team.

So it's unlikely we'll see propellant-less thrust systems on spacecraft in the near future, and we shouldn't tout the EmDrive as a space exploration game changer quite yet. But that a NASA team was able to record any result at all is pretty interesting. And even small results that fly in the face of a classical electromagnetic theory are also pretty interesting.

In any case, a lot more work will have to be done to prove that the propulsion method is not only viable but something worth pursuing further.