Mars is a destination that seems inevitable for human exploration. We have seen a number of intriguing signs from our series of robotic probes that Mars was once a very different world than it is today. Still, even cold and dry though it now is, it remains a place where humans can go and exist with only some help from life support systems. However, the sheer distances involved, coupled with the combination of moderately strong gravity and a very thin atmosphere make Mars a challenging place to get to. That is why the mission architecture selected does matter.