The best advantage of orbital depots is that they allow us to engineer our way towards space exploration. If someone thinks they can use a space plane to get the stuff up cheaper than SpaceX, they are welcome to try. The depot can pay a flat price and let people compete on the cheapest way to deliver the fuel. I think heavy-lift is the clear winner but we could let the market decide.
But orbital depots are not required, at all, for a mission to Mars. You don’t get anything out of a depot that you didn’t put in it, and SpaceX is epxected to demonstrate in 2013 that it can put a pound into orbit for $1000 using heavy lift. We can throw things directly at Mars and let them land on Mars, and then assemble them on the ground. (Columbus didn’t try to build a massive boat in the middle of the Atlantic.)
I understand Dr. Zubrin’s fear that depots, if built, would become politically mandated for a Mars mission, even if they weren’t the best technology for the job. I have personally witnessed many people who think that their personal area of research (such as zero gravity) is required for a Mars mission. In a bureaucracy, there is nothing better than making sure that you are in the path of as many important things as possible. From an engineering process, this is madness.
SpaceX may simply lower launch costs so much that someone like China (or even Elon Musk) could directly fund a Mars mission. Two billion dollars is still a lot of money, but it’s as much cheaper the old reference mission of $30 billion was to the $450 billion plan that Bush 41 got handed.
