The prohibitive cost argument you make is not based on projections for the humans-to-Mars mission plan that Zubrin advocates. He spelled out his most current version of his original “Mars Direct” concept at the recent International Space Development Conference (ISDC) in Huntsville, AL. He calls is “Semi-Direct”. You can read a summary of it at the Mars Society’s website (http://marssociety.org). Relying on Space X’s cost estimates for its coming Falcon Heavy booster, Zubrin calculates that a mission to Mars taking place by 2020 that sends two astronauts for a stay on the planet of 1.5 years could be mounted for a “modest” cost falling within NASA’s current budget. You may be thinking of the so-called “Battlestar Gallactica” mission plans that call for on-orbit refueling stations, nuclear-powered spacecraft, and the like, none of which Zubrin supports or thinks feasible.
