Elon Musk held an AMA (Ask Me Anything) on r/SpaceX two days ago, Musk noted it was meant to supplement his IAC talk, which had focused on the Interplanetary Transit System (ITS) or additionally known as the Heart of Gold and their goal of going to Mars.
Musk gave details about the ITS stating SpaceX must figure out how to seal the carbon tanks in the ITS booster against cryo propellant. “The oxygen tank also has an oxidation risk problem as it is pressurized with pure, hot oxygen. 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 noted that the ITS could handle peak loads of 10 to 15 g’s without breaking up. Musk also noted that “The flight tank will actually be slightly longer than the development tank shown, but the same diameter. That was built with latest and greatest carbon fiber prepreg. In theory, it should hold cryogenic propellant without leaking and without a sealing linker.”
Musk says live mock-ups of the interior of the ITS may be available in one to two years. The plan would be to fly the ITS to Mars, loaded with equipment to build a propellant plant, though SpaceX still has to figure out refueling. Currently the plan includes sending the Dragon on scouting missions, to figure out where to land and what the best way would be to get water for the CH4/O2 sabatier reaction.
The first crew mission would have equipment to build rudimentary bases and complete the propellant plant. Musk also said SpaceX would try to double the number of flights with each Earth-Mars orbital rendezvous, which is every 26 months, until the city can grow by itself.
As for homes, Musk stated that “glass panes with carbon fiber frames to build geodesic domes on the surface, plus a lot of miner/tunneling droids. With the latter, you can build out a huge amount of pressurized space for industrial operations and leave the glass domes for green living space.”