Moderator note: Please read post #9 by DH before replying to this thread. This thread will be closely watched by the mentors According to wiki See, I think the first mission of a crew four is too risky. You need a lot of people so that one person can mutually benefit from the labor of a large team. I say send every two years (since the window for flying to Mars is once every two years) about 60 in a huge fleet of about 15 ships. It looks like one ship costs about 10 billion dollars, so 150 billion split among about 20 nations is certainly doable. Sending 4 people is just too risky. The likelihood of death is too high. In order to settle this alien world you're going to have to do it in a major way, make a huge effort because the obstacles are enormous. I'm reading Robert Zubrin's book The Case for Mars right now and it is a real adventurous read.