Apollo and the van Allen belts

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.

In a 3rd book, "Spaceflight Dynamics", Wiesel, 1989, page 255, they
say that Apollo did in fact go near the edge (high latitudes) of
the Van Allen belts. I quote:

In a 300-km-altitude circular orbit, the daily radiation dose to an
unshielded human being would be only about 0.1 rad. However, at the
maximum intensity point within the Van Allen belts (at about 3000 km
over the equator), an astronaut would receive a dose of about 300 rads
per day. Apollo spacecraft are the only manned vehicles ever to
penetrate this region, and they crossed the belts at moderately high
latitudes and during the highest speed portion of their flight, so the
accumulated dose to their crews was within acceptable limits.

-- Vince