From discussion here several of unmanned Apollo CSM spacecraft travelled through the strongest parts of the van Allen belts, whereas the crewed flights skirted them.
Do we know enough about the trajectories of Zond 4-8 to say whether they flew the core or the fringes of the vAB?
I would guess than testing the radiation protection would make the first desirable, but the integrity of the biological payload might make the second preferable. Thoughts?
