Mars Direct is brilliant! In situ resources for fuel are the way to go.
Read Zubrin's book. The guy is a genius. The original Mars Direct concept assumed using the Martian amosphere as a fuel source to produce methane and oxygen. We now know there is abundant ice on Mars. Making rocket fuel on Mars is now a whole lot easier. Here is how you do it:
Find a site with near surface ice
land the in-situ production rig at the site
drill into the ice
drop an electric heater into the bottom of the bore hole
suck in the water vapor that boils off and condense into liquid water
separate the water into hydrogen and oxygen by electrolysis
liquify the two gases
The enabiling technology is a compact high energy source such as can be provided by Prometheus.
Gary