As the founder, CEO and lead designer at SpaceX, a private company that makes rockets and spacecraft, Elon Musk envisions a time when his reusable rockets will bring people to the moon and Mars. He’s focused on humans becoming a “multi-planet species,” and on the 50th anniversary of the Apollo 11 mission, he speaks with Jeffrey Kluger (editor-at-large at Time magazine, and the co-author of “Apollo 13”) about his vision for the future.