The Van Allen Belts were discovered by Explorer I, which was NOT shielded because no one knew of the belts beforehand. But the belts did not destroy Explorer I. Even the fuselage of the Apollo capsule counts as shielding---provided you zip through the belts at a speed of ~10 km/second. Multiple visits to the Moon. No particular problem with the belts. The Big Insight is that you don't just stop and loiter in them, like it's some kind of sauna. That would be idiotic. (Do we all take dental X-rays? Yes? Nobody is dead? Same thing.)
The Van Allen Belts were discovered by Explorer I, which was NOT shielded because no one knew of the belts beforehand. But the belts did not destroy Explorer I. Even the fuselage of the Apollo capsule counts as shielding---provided you zip through the belts at a speed of ~10 km/second. Multiple visits to the Moon. No particular problem with the belts. The Big Insight is that you don't just stop and loiter in them, like it's some kind of sauna. That would be idiotic. (Do we all take dental X-rays? Yes? Nobody is dead? Same thing.)