Space rockets were the ultimate disposable, millions of dollars worth of expensive hardware just tossed away like a piece of Kleenex after doing their job. And as every TreeHugger knows, we pay the price for that convenience, both in the cost of the disposable and the embodied energy of the materials in it. That's why building a reusable rocket is such a big step forward; It could cut a couple of zeroes off the cost of each launch.
Because SpaceX has to fire its rockets downrange to get into orbit instead of straight up for a suborbital flight, they have to land somewhere out in the ocean. That's why they needed what Musk calls the "Autonomous Spaceport Drone Ship" named “Of Course I Still Love You” in homage to science fiction author Iain M. Banks. It really is more than a barge; it has four big diesel engines that can move it around and keep it in place. According to Gizmodo,
The drone ships are capable of maneuvering autonomously, using GPS information for precision positioning, but they can also be remotely controlled by an accompanying support ship with a crew of technicians standing by. A wide array of sensors are used in tandem with the GPS information to manage the “attitude and placement” of the drone ship and communicate with the incoming rocket and the onlooking teams to control and coordinate the complicated precise landings.
Click through to watch the video of the landing in high definition; you will be at it all day.