Producing return fuel on Mars rather than carrying it from Earth significantly reduces the mass that must be lifted from Earth for a manned mission to Mars. The most practical propulsion combination that can be produced is methane and oxygen. Using propellant components made on Mars to generate electric power on the return voyage further reduces the mass that must be lifted. We are proposing to develop an energy conversion system to utilize the components of this propulsion combination to generate electricity for that voyage. The core of the system will be a direct methane oxygen solid oxide fuel cell (DMSOFC). To enhance conversion efficiency we will use the waste heat from the fuel cell stack to produce additional electricity before it is radi-ated away. (The combined efficiency of all stages of this system will exceed 70%.) Phase I will select an anode electrocatalyst, demonstrate a single cell fuel cell, select a heat re-covery system, and develop a design for the complete system, which will be built in Phase II.