SpaceX's Interplanetary Transport System
OK, I think I sorta called this one a couple of years ago when SpaceX was experimenting with their Grasshopper demonstrator.
I still don’t know how difficult it will be to refine methane on Mars, but at least Elon has a somewhat reasonable answer. Here’s my post from Hacker News:
That said, the thing I’m struggling with the most right now is some kind of economic reason for why you would build the ITS. From an “awesome” factor, I’m all on board, but Mars doesn’t really have anything that we don’t have on Earth (that we know of). In terms of how to finance this beast though, I feel like maybe setting sight on something closer to home like orbiting space hotels or trips to the moon make a lot more economic sense. With something closer to home you can have a lot of efficiency gains in terms of reusability which you don’t get by only having your ship work every two years.