Yesterday I lamented the slow pace research sometimes progresses at in fields such as astronomy. In planetary science, one of the largest delays is the vast distance between bodies in the solar system. By the time the New Horizons spacecraft reaches Pluto, it will have been travelling for more than nine and a half years, and it left Earth travelling faster than any other vessel in history. One might wonder why we don't attach bigger rockets to get it there faster, but bigger rockets require more fuel. and more fuel means more weight. and all that weight needs to be launched off the Earth's surface to begin with. Because of this, space probes don't constantly burn their rockets while travelling. Instead, they fire them briefly at certain times to gain speed and direction, but otherwise just coast through space. We've even learned to swing around other planets to pick up a little momentum (and thus speed) from them.
While traditional rockets have some of these severe limitations, other technologies do exist. Ion drives are one such alternative. While probably best known as portrayed in science fiction by Star Wars and Star Trek, ion drives are a real, working technology already employed in the Dawn spacecraft. In simple terms, they work by using an electric field to throw charged particles out of the back of the spacecraft. Newton's Third Law of Motion famously states that for every action there is an equal, but opposite, reaction, so throwing a particle out backwards pushes the spacecraft forwards. Imagine throwing something while standing in an ice rink: you'll probably fall in the opposite direction from where you threw! The catch is, charged particles have almost no mass, while the spacecraft is quite heavy, so each particle moves the ship only a tiny, tiny amount. These little pushes add up, however,and the process is far more efficient than a traditional engine.
NASA"s Evolutionary Xenon Thruster (NEXT) the the newest generation of the ion engine which has been successfully propelling the Dawn spacecraft. It is simpler and lighter, yet more powerful than the previous model. Best of all, it just passed an astonishing 43,000 hours of continuous operations - that's nearly 5 years! In doing so, it processed around 770 kg of propellant, which might seem like a lot, but would be an unfathomably small amount for a traditional rocket.
Engines like NEXT offer the enticing ability to get missions to their destinations more quickly. This means shorter cycles for funding and technology that's less out of date when it arrives (remember New Horizons?). There's no science fiction there.