Proving yet again that Star Trek was scarily prescient, NASA has announced that its NEXT ion drive â€" NASA’s Evolutionary Xenon Thruster â€" has operated continually for over 43,000 hours (five years). This is an important development, as ion thrusters are pegged as one of the best ways to power long-term deep-space missions to other planets and solar systems. With a proven life time of at least five years, NEXT engines just made a very big step towards powering NASA’s next-gen spacecraft.
Ion thrusters work, as the name suggests, by firing ions (charged atoms or molecules) out of a nozzle at high speed (pictured above). In the case of NEXT, operation is fairly simple. Xenon (a noble gas) is squirted into a chamber. An electron gun (think cathode ray tube TV) fires electrons at the xenon atoms, creating a plasma of negative and positive ions. The positive ions diffuse to the back of the chamber, where high-charged accelerator grids grabs the ions and propel them out of the engine, creating thrust. The energy to power the electron gun can either come from solar panels, or from a radioisotope thermoelectric generator (i.e. a nuclear battery, just like Curiosity).
A diagram of an electrostatic ion thruster (as in NASA’s NEXT, and most other ion thrusters)
The downside of ion thrusters, though, is that the amount of thrust produced is minuscule: State-of-the-art ion thrusters can deliver a grand total of 0.5 newtons of thrust (equivalent to the force of a few coins pushing down on your hand), while chemical thrusters (which power just about every spacecraft ever launched) on a satellite or probe deliver hundreds or thousands of newtons. The flip side of this, though â€" and the reason ion thrusters are so interesting â€" is that they have a fuel efficiency that’s 10 to 12 times greater than chemical thrusters. Obviously, for long trips through space, fuel efficiency is very important.
With such puny thrust, a NEXT-based ion drive would need to run for 10,000 hours â€" just over a year â€" to reach a suitable speed for space travel. Dawn, a NASA probe that’s powered by previous-generation NSTAR ion thrusters, accelerated from 0 to 60 mph in four days. As a corollary, ion thrusters only work at all because of the near-vacuum of space; if there was any friction at all, like here on Earth, an ion drive would be useless. The good news, though, is that the (eventual) max speed of a spacecraft propelled by an ion drive is in the region of 200,000 miles per hour (321,000 kph).
Moving forward, it now remains to be seen if NASA will use the NEXT on an actual spacecraft. In 2011, NASA put out a request-for-proposals for a test mission that will likely use a NEXT engine, and presumably, following this successful engine test, we might soon hear more news about that. Other space agencies, including the ESA, are also working on spacecraft propelled by ion thrusters.
Now read: NASA working on faster-than-light space travel, says warp drives are ‘plausible’
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