"plus with a solar sail, how do you get back?" This is actually really simple and not a problem at all -- you just have to understand orbital mechanics a bit.

"plus with a solar sail, how do you get back?" This is actually really simple and not a problem at all -- you just have to understand orbital mechanics a bit. Basically, you angle the solar sail so that its force is directed against your direction of travel along your orbit. This slows you down, causing you to start spiraling in toward the sun. Then you change angle so that you start speeding up again and match orbital velocities just as you arrive at your destination. But it's a separate issue anyway -- solar sail technology (or Vasimir, or Nuclear Thermal) is no more required for exploring Mars than jet airplane technology was required for exploring North America.