Radiation still a huge problem in getting to destinations such as Mars

I often write about why Ceres is probably a better destination for a manned mission than Mars, but I am still not of the opinion that we should even be thinking about sending manned missions out that far, and one of the reasons is the radiation problem. The problem is basically this: we can use shielding to protect us from radiation, but doing so would make a craft unbearably massive, and besides the problems that would raise in spacecraft design it would also simply cost too much. This is why I believe that until we have a method of propulsion like VASIMR that it simply isn't practical to consider sending human missions out that far. VASIMR has nothing to do with shielding from protection, but it does lower the one-way trip time to Mars from about six months to just over one month (40 days), so that's 4.5 times less accumulated radiation to worry about there.

It's because of this that I believe the order in which we should proceed should be 1) Near-Earth asteroid mission; 2) The Moon; 3) Other destinations, perhaps Ceres or Mars, or the cloudtops of Venus. But not one before the other. Sending people to a near-Earth asteroid and the Moon again is more than enough for us to handle, and in the meantime we can perfect our unmanned missions, launching ability, and systems of propulsion (VASIMR), after which we can begin to think about other destinations.