Eventually, if we want to establish outposts in our solar system, starting with the Moon, we will need a continuous source of propellants. A space station in LEO and in lunar orbit would be needed. Let's say the propellant of choice is hydrogen and oxygen. What would be the best way of getting these propellants to the space stations? I figure the hydrogen would have to come from Earth, since no other body in the inner solar system has a sufficient amount. What would be the best way to bring this up into space? Would storing it as liquid hydrogen or storing it as water be the best method? If I did my figures right a tank of H2O would have 1.5X more H2 in it then a tank of LH2 of similar size, but it would weigh 14.4 times more (not taking into account active cooling to prevent boil-off). I also figure that LOX would come from the Moon, since it is pretty heavy to bring up from Earth and the Moon is 45% oxygen by mass. What do you think?