These landings are part of SpaceX's effort to develop fully reusable rockets and spacecraft — technology that company founder and CEO Elon Musk has said will slash the cost of spaceflight. To date, SpaceX has re-flown five of these landed boosters, as well as two of its uncrewed Dragon cargo capsules, which make resupply runs to the International Space Station. (The Falcon 9 that lifted off tonight was brand-new.)