On April 8, the private spaceflight company SpaceX launched a resupply mission to the International Space Station – a task for which NASA has contracted it. However, the more important thing about the flight was the rocket’s first stage, a nine-engine booster, returning safely onto a ocean barge instead of crashing down, a tradition. SpaceX owner and CEO Elon Musk thinks reusing the stage will make future launches cheaper and faster, and doing it repeatedly will help realise his ambition to set foot on Mars in his lifetime.