A SpaceX Falcon 9 rocket launched the Spaceflight SSO-A: SmallSat Express mission to low Earth orbit on Dec. 3, 2018. It is carrying 64 satellites. SpaceX has re-flown used first stages many times, but today's launch marked the first time a booster had ever propelled payloads to orbit on three separate occasions. The success is therefore an important milestone for SpaceX, which aims to fly all its vehicles repeatedly and frequently. Such rapid reuse could slash the cost of spaceflight, opening the heavens to exploration, company founder and CEO Elon Musk has said.