Going to Mars, you have the following options right now. You can shield the spacecraft from radiation with passive mass. That's relatively expensive option, bu

Going to Mars, you have the following options right now. You can shield the spacecraft from radiation with passive mass. That's relatively expensive option, but hardly technologically infeasible. The question is only the price of each kilogram on LEO, and that goes down steadily. You can use spacecraft magnetic field. An interesting area with a bunch of research to do. You can speed up the way to Mars, say, from 6-8 months today to 3 months, having to spend extra fuel at launch and at arrival. For that, you can e.g. revive Nerva-style engines. A combination of these (and possibly other) methods brings Mars closer even for today's safety standards.