[scrumper]

Why would you want to store your propellant water separately as O2 and H rather than as water? You'd have to react it to turn it into water, water is pretty inert, there's no mass advantage (more of a problem than volume). What am I missing?

[nkrisc]

I was thinking of volume, but if the craft doesn't need to ever be in an atmosphere then that wouldn't be an issue as I had first thought.

[pavel_lishin]

A bigger volume might even be an advantage - easier to turn your ship if you can mount engines far from the center of mass. Plus, built in shielding.