thats like saying how good a bow is without its string the ISS could easy be in transit to mars once it complete why does a space staion have to be stationary. if the space staion cant last a year without assitance what makes ppl think a rocket to mars can cope math is math 1 + 1 Does equal 2 no mater how you look at it ;) maybe a little nudge here and there can help but 3 months away in transit to mars is a bit late to say we send you spares.

the ISS allows us to gain an understanding of the risks as well as try out soultions.

i really think space ships are about to start appearing that go back from a to b to a to z etc... it makes cost sense add ons are most of the time cheaper than complete replacements unless theres a major change.