From: vince@offshore.ai (Vincent Cate)
Newsgroups: sci.space.policy,sci.space.tech,sci.space.science
Subject: Re: Apollo and the van Allen belts
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In another book [1] they also indicate that Apollo should go through 
the edge of the Van Allen belts.  They studied a number of different 
vehicle configurations and found that inherent shielding which exists 
due to vehicle structure and equipment is sufficient to permit safe 
passage through the edge of the belts.

They have a graph showing radiation intensity contour lines and the 
normal path Apollo would take. The radiation level is much lower 
(maybe 1/10th), and the distance through is much shorter (maybe 
1/5th) at the edge where Apollo would go through than at the center.  
So, in the nominal case, the radiation dose was small.

An abort path could end up going more through the center of the Van 
Allen belts.  They show abort cases with as much as 22 rem.  They 
note that adjusting the abort trajectory can reduce this.

From this it seems that avoiding the middle of the Van Allen belts 
was an important part of the Apollo plan.

This work was done in 1961.  So the ideas for avoiding most of the 
radiation were known very early on.  I suspect that NASA knew even 
before Kennedy's speech earlier that year.  

  -- Vince

[1] "Advances in the Astronautical Sciences Vol 10, Manned Lunar Flight", 
    1963.  This is the proceedings of the Symposium on Manned Lunar 
    Flight in Dec 1961.   Pages 75 and 76.