Van Allen Belts

The Van Allen belts are a band of concentrated radiation around the Earth.  It's been estimated that you'd need a foot of lead casing to protect yourself from this, which the Apollo crafts didn't have.  Why didn't this kill the astronauts on the way to the moon?

Radiation is a big problem when it comes to space travel and the Earth's magnetic field concentrates this radiation into the Van Allen belts that surround the Earth.   No matter what, the Apollo crafts had to go through these belts and there was no way the Apollo crafts could afford to take all the weight of lead shielding with them.   So they were bound to be exposed.   The question is, just how serious would this exposure be?

What you have to realize that the radiation involved isn't the same kind or intensity as you might get from a nuclear bomb.  You don't fall sick and your hair doesn't all fall out.    It's been calculated that travelling at speed through the Van Allen belt would result in exposure of 1 rem.  Radiation sickness symptoms don't start to show until you get around 25.  Once you reach 100 you're going to be ill.   500 and you're probably dead.   So the exposure the astronauts received is pretty mild.

But that isn't to say either that it can't do you any harm.  Added to the exposure they got actually out on the moon, it is a risk that can't be fully quantified.   Who knows what cancers could result from it?   Given the choice most people would want to avoid this kind of exposure to radiation.  But the astronauts risked it because they thought it was worth it.   This, and all the other risks they faced, is what makes them remarkable people.

This page has a whole heap of scientific info about the Van Allen Belt and travelling through it.  It's all a bit complicated.