A number of high-profile missions lifted off, others reached their destinations after long journeys through deep space, and a few, sadly, crashed and burned. Some of the most exciting spaceflight action of 2016 involved rockets coming down rather than going up. California-based company SpaceX managed to land the first stage of five different Falcon 9 rockets during operational orbital launches this year; one of the boosters touched down back at the launch pad, whereas the other four landed on robotic "drone ships" stationed in the Atlantic Ocean. And the Washington-based company Blue Origin launched and landed the same suborbital New Shepard rocket four times this year, finally retiring the booster after a successful October test flight . Both SpaceX and Blue Origin -- which are headed by billionaire entrepreneurs Elon Musk and Jeff Bezos, respectively -- aim to develop fully reusable rockets as a way to slash the cost of spaceflight and open up the heavens to exploration.