Retric outlined the best economic solution. Mainly it's not anything to worry about. You need some small area with heavy shielding to huddle in during solar fla

Retric outlined the best economic solution. Mainly it's not anything to worry about. You need some small area with heavy shielding to huddle in during solar flares, but the rest of the trip shielding isn't important. Explorers will happily a small increase in their lifetime cancer risk in exchange for visiting new worlds. Eventually we'll have faster transits, and Aldrin Cyclers, and the problem will become even more minute.