MIT Researchers Fire Up the Ionic ThrustersBy
Researchers at MIT have built an ionic thruster—a device that can lift something into the air by charging the air molecules around it. Amazing, right? Though not in the way you might think. As sci-fi as it sounds, the basic technology to build ionic thrusters has been around since the 1960s, and Star Trek-inspired hobbyists have been making small “ionocrafts” for decades. NASA powers some of its unmanned deep-space voyagers using ion thrusters. These are not, however, the sort of thing that will launch Captain Kirk into orbit. NASA’s thrusters were built to work in the gravity- and friction-free environment of space. But even there, they’re more breeze than blast.
Earthbound ion thrusters have thus far been small and weak—able to levitate or propel ionocrafts built from balsa wood, aluminum foil, and wire but nothing heavy. The idea that an ionic propulsion device might power an airplane has long been dismissed as a fantasy—the amount of energy required, it was thought, would make it impractical.
According to Steven Barrett and Kento Masuyama of MIT’s department of aeronautics and astronautics, however, that might be wrong. The two have just published a paper showing that the phenomenon known as ionic wind can be much more efficient than scientists have long assumed—in fact, it’s 50 times more efficient than a conventional jet engine in terms of thrust per kilowatt. Ion thrusters, in other words, might yet move out of the hobbyist realm. Barrett mentions surveillance as a natural fit for the technology—ionic powered drones would be silent, could fly long periods of time without refueling, would have very few moving parts, and, unlike jet or even propellers engines, would be invisible to heat-seeking missiles. According to MIT, Lockheed Martin is looking into it.
Barrett and Masuyama found their results by building and testing their own ionic thruster. The basic mechanism is simple: It’s built out of a thin wire loop, called the emitter, and a loop of thicker wire, called a collector, with a space between the two. When a current is run through the emitter, it strips electrons from the air molecules around it—ionizing them, in other words—and repels them. The collector, on the other hand, attracts the ions, and their movement creates thrust as they collide with other air molecules in their path. If the emitter is placed above the collector, that creates lift; if it’s in front, it generates forward motion. (NASA’s space ion thrusters work differently—in part because, since there’s no air in space to ionize, they have to carry their own propellant with them.)
Barrett cautions that we’re still not sure whether ion thrusters could lift anything of substantial size and weight into the air. The next step, he says, is to determine the “thrust density” of the devices—how big they would need to be to lift an airplane. “Would the aircraft have to be 200 meters wide, or could it be a reasonably normal size?” as he puts it. If it does turn out to be practical, though, Barrett envisions that ion-powered aircraft would look very different from what we’re used to. Rather than the pod-like jet engines of today’s planes, the propulsion system would be “much more integrated into the aircraft design,” he says. “The wings and tail fins could be emitters and collectors.”
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