The first human beings to land on Mars should not come back to Earth. They should be the beginning of a build-up of a colony/settlement, I call it a 'permanence'.
You need propellants to accelerate toward Mars, then to decelerate at Mars, again to re-accelerate from Mars to Earth, and finally to decelerate back at Earth. Accordingly, the mass of these required propellants, in short, drives our need for innovative launch vehicles.
I know: If you're looking down at Earth, you're looking through an atmosphere that has a bit of haze in many places and not just occasional clouds.
