Since the dawn of the Space Age, science fiction enthusiasts have fantasized about reusable rockets. Over the past year, Elon Musk and his company, SpaceX, made those visions a reality. Now, the tech mogul has his sights set on a bigger, redder prize. SpaceX has tried four times in the past two years to land one of its Falcon 9 rockets at sea; each exploded. But in April, a Falcon 9 successfully touched down on a drone ship in the Atlantic — a first — after ferrying cargo to the I…