Musk makes no secret of the end goal: Create a new civilization on Mars. Speaking at the National Press Club in Washington, D.C., in September, he outlined the business plan—if that’s the right term for something that looks decades into the future. “If you can reduce the cost of moving to Mars to around the cost of a middle class home in California—maybe to around half a million dollars—then I think enough people would buy a ticket and move to Mars,” he said. “You obviously have to have quite an appetite for risk and adventure. But there are seven billion people on Earth now, and there’ll be probably eight billion by the midpoint of the century. So even if one in a million people decided to do that, that’s still eight thousand people. And I think probably more than one in a million people will decide to do that.” Talking about a city on Mars by the middle of this century—even as SpaceX has yet to fly its first cargo mission to Earth orbit—is one of the reasons space professionals are skeptical about Musk’s claims.