Mars for Less

http://en.wikipedia.org/wiki/Mars_for_Less

The Mars for Less mission is heavily based on Robert Zubrin's Mars Direct mission design, in which two different spacecraft are used for a single human expedition. One spacecraft (called the Earth Return Vehicle, or ERV) is sent to Mars unmanned on a trajectory similar to a Hohmann Transfer Orbit before the crew. This vehicle lands and fuels itself using a Sabatier process, creating methane/oxygen rocket fuel (bipropellant) out of carbon dioxide obtained from the Martian atmosphere and a relatively small amount of hydrogen imported from Earth. Once the ERV is fuelled, the crew is launched to Mars on a free return trajectory. The crew arrives after about 180 days and lands in the proximity of the ERV. They spend about 500 days on the surface exploring, then return to Earth in the ERV.

The Mars for Less plan is different from Mars Direct in that it uses multiple launches of existing launch vehicles, instead of a few launches of heavy lift boosters. In the MFL plan, separate components are launched individually to low-Earth orbit, where they are mated together over the course of about half a year. Each component is itself autonomous, so that only an orbital assembly, and not construction, would ideally be required. By avoiding the development of a heavy lift launch vehicle like NASA's proposed Ares V, such a mission could theoretically be undertaken today.