The general strategy for Apollo shield design was, "Build the ship as if there was no special need for radiation sheilding." Then see how much shielding you got just from the normal structure, skin, etc. If there are any serious problems, solve them at that place in the design, such as adding polymer or fibrous panels or simply using a thicker skin material. In other words, radiation shielding was not a primary design criterion. It did not "drive" the design. The CM was not intended to survive "hard" radiation, nor was any expected during Apollo missions. The more dangerous solar flares are not common enough to worry about. So you get enough shielding incidentally from the ordinary construction.
However for long-duration missions that won't work. Radiation mitigation is a primary design criterion, so we can't just re-use Apollo designs and strategies. That doesn't mean we "still don't know how to do it." I means we have a different problem now than we had. Engineers aren't put off by problems that haven't been solved yet: that's what engineers like.
|