One way missions manned missions don't make sense to me, as you'd have to resupply the crews regularly with food ect. from Earth (I don't see an entirely self sufficient Mars colony as a possibility on the first flight). Much better to return, but with ISRU. You can use the CO2 atmosphere of Mars to make liquid oxygen. If you can get an 100kW power supply, liquid methane can also be produced (though you'd need the hydrogen from Earth, 5% of total propellant). This is an actual technology that's been demonstrated (been around since the 1800s), and not new-age far-future nonsense like VASIMIR or space elevators -Joe
