@anon47883- That is an interesting question. I thought about it a little, and I think that maybe a mars mission would be planned when mars was closest to earth. If this were the case, then earth would be between mars and the sun. The earth would then in effect protect anything traveling toward mars from sun flares and coronal mass ejections.
The only thing that might negate the effect of the earth blocking a coronal mass ejection would be if the flare circled around the earth and caught up with the mission. If a mars mission had to be planned around sun flares and the proximity of the planets to each other, It would likely leave a very small window of opportunity for such a mission. I wonder if operational considerations like these had any plan with scrapping a manned mission to mars. It is a lot cheaper and safer to fly robots to mars than people are.