Hear that, Star Trek? Technology is catching up! The University of Alabama's Aerophysics Research Center, NASA, Boeing, and Oak Ridge National Laboratory are all getting together to develop an "impulse engine" that's powered in part by "dilithium crystals."
Here's how the scientists describe their own research:
"Star Trek fans love it, especially when we call the concept an impulse drive, which is what it is. The fusion fuel we're focusing on is deuterium [a stable isotope of hydrogen] and Li6 [a stable isotope of the metal lithium] in a crystal structure. That's basically dilithium crystals we're using."
We would be remiss, of course, if we didn't point out that in reality (that is, in Star Trek), dilithium is not quite the same as lithium-6 (which would be, uh, hexalithium?), and also, dilithium regulates the matter/antimatter reaction in the warp drive, not the impulse drive. So good, we've gotten all of our hrrumphing out of the way, let's move on.
The drive should/would/will be based on the principle of Z-pinch fusion. A Z-pinch, for you physics fans, is when you run a huge jolt of electricity through an array of tiny wires, turning them into a plasma and generating a massive magnetic field at the same time. The field "pinches" the plasma, collapsing it down onto a core of deuterium and lithium, causing those atoms to fuse and releasing a big burst of fusion energy- more than it took to set the Z-pinch off in the first place. Here's a picture of what it looks like when they do a Z-pinch on the Z Machine at Sandia National Labs:
At full throttle, the impulse engine will produce Z-pinches nearly continuously, and astronauts onboard a spaceship using this method of propulsion would feel a series of pulses as opposed to some non-stop beastly acceleration. The acceleration will be beastly, though: the researchers say the impulse engine would generate "millions of pounds of thrust out the back of this thing--on the order of Saturn-V-class thrust."
Since a fusion-driven impulse engine is far more efficient than a conventional rocket engine, you can go much farther, much faster, on a lot less fuel, meaning that a trip from Earth to Mars could take just six weeks instead of six months or more. And as for speed, the impulse engine may be able to propel a spacecraft at up to 62,600 miles per hour. This is quite fast, although not up to Star Trek's definition of full impulse, which (depending on who you ask) is probably somewhere between 16 and 17 million miles per hour.
There are a bunch of things that the researchers need to figure out before they're ready to fire this thing up. They need to the the fusion to be self-sustaining, of course, but they also need to figure out how to channel the resulting, er, explosion in the right direction (i.e. away from the spaceship), probably using some sort of magnetic nozzle. It's going to take some work, and some time, but smart people are actually working on a fusion-driven impulse engine as we speak. Wow.