Human spaceflight has long been a goal for SpaceX, the rocket and satellite manufacturing venture of billionaire Elon Musk. SpaceX this week quietly added a “Human Spaceflight” tab to its website, listing four destinations to which customers can book flights: Earth orbit, the ISS, lunar orbit, and Mars. Pricing information for the missions does not appear to be available. But the webpage directs customers to an email address, humanspaceflight@spacex.com, where they can inquire to book a flight.