The first US satellite into space was called Explorer 1. It had a simple geiger counter on board to detect radiation in space. As it was the very first of its kind, nobody knew how many counts of radiation hits would be recorded and so didn't know how to calibrate the equipment. The leading scientist of the time expected around 10-100 counts a minute. The geiger counter was set for that. After achieving orbit, the hits were higher and went off scale. It could mean 101 hits per minute or 1,000,001. The next satellite to study it (Explorer 4) would be calibrated better. But in the meantime the press were asking tough questions and wanted answers. The higher figure was constantly quoted for the headlines and let to an impression that space was full of deadly radiation that would kill a human in a few hours. This radiation zone became known as the Van Allen Radiation Belt after the scientist who interpreted the results. Later satellites proved this not to be the case. Part of the belts did have higher counts but as any spacecraft would only be in it for short periods, it didn't matter too much.
Bart Sebrel on the documentary said 'Hardly anybody knew about the Van Allen Radiation Belts...' Oohh really? Pick up any book on astronomy printed since around 1958 and there it all is. It was no secret.