Studies said astronauts could face fatal radiation in orbit—how did we get to the Moon?
Nine seconds after 11 o’clock on the night of July 8, 1962, a 2,200-pound W-49 nuclear weapon detonated 248 miles above a tiny island to the west of Hawaii. The blast, which yielded 1.4 megatons, instantly turned the night sky daylight-bright. As the flash dissipated, electrons from the explosion interacted with the Earth’s magnetic field to create an artificial aurora thousands of miles long. The residual light danced across the sky for seven minutes. The blast’s accompanying electromagnetic pulse knocked out street lamps 800 miles away.
The explosion that night wasn’t hostile; it was an American weapons test called Starfish Prime. The Department of Defense and the Atomic Energy Commission were running a program designed to study the effects of nuclear warfare on the atmosphere. The effects the program found were far more profound than a light show. Starfish Prime created an artificial radiation belt that enveloped the Earth and intensified the Van Allen belts, fallout NASA quickly realized could threaten its Apollo program in the race to the Moon. For a brief period, it wasn’t clear whether manned space flight could continue at all.
For the rest of the story: http://arstechnica.com/science/2013/08/how-cold-war-nuclear-testing-once-made-orbit-unsafe-for-apollo/