SpaceX founder Elon Musk took to internet social media site Reddit to explain his plans to colonize Mars. Musk went on the site Sunday for an “ask me anything” session in which users could ask him questions about his plan to send up to one million people to the Red Planet sometime in the next 40 to 100 years. Musk said the plan would begin with unmanned cargo missions, "Initially just to make sure we know how to land without adding a crater and then to figure out the best way to get water for the CH4/O2 Sabatier Reaction." The first manned crew would be tasked with building a simple base and a propellant plant. Then, would-be colonists would make their way to the base in increasing numbers until it becomes self-sustaining. "[We] will aim to release details of the habitation section when we have actual live mock ups. Maybe in a year or two,"Musk answered. In another answer, Musk said the "biggest question [for the Interplanetary Transport System] right now is sealing the carbon fiber tanks against [cryogenic] propellant with hot autogenous pressurization." "The oxygen tank also has an oxidation risk problem as it is pressurized with pure, hot oxygen," he said. "Will almost certainly need to apply an inert layer of some kind. Hopefully, something that can be sprayed. If need be, will use thin sheets of invar welded together on the inside." Musk admitted much of the technology needed for such an endeavor has yet to be developed.