When it comes to space, there's a problem with our human drive to go all the places and see all the things. A big problem. It's, well, space. It's way too big. Even travelling at the maximum speed the Universe allows, it would take us years to reach our nearest neighbouring star.
Image: David Burns produced an engine concept that, he says, could theoretically accelerate to 99 percent of the speed of light - all without using propellant.. (CREDIT: Creative Commons)