Ion propulsion systems have long been a technological daydream. But now, they may the future of space exploration.
Ultimately (and not too far in the future) the same concept could reduce the cost of trips beyond the moon. Slow electric tankers could go ahead of human missions to Mars or asteroids, dramatically reducing the amount of propellant needed to launch crews to those destinations. Eventually, propellants could be manufactured on-site (for example, manufacturing methane and liquid oxygen from the Martian atmosphere). But early propellant caches could create an "interplanetary highway system," similar to the gas stations that allow the terrestrial interstate system to function—and hasten the day that travel throughout the inner and outer solar system becomes routine.