Only NASA knows why it faked the moon landings, but many have surmised that the radiation of the Van Allen Belts would have killed astronauts in a relatively thin-walled spacecraft. It is estimated that a ship would need walls several feet thick to adequately shield the crew from radiation. Unfortunately, however, a ship with several feet thick, radiation-proof walls would have been too heavy to get off the launchpad. D’oh!
http://en.wikipedia.org/wiki/Van_Allen_radiation_belt
The Van Allen Belts are not all bad though. They protect us from the Sun’s lethal radiation and a litany of other cosmic radiation sources while making the Earth uniquely livable for mankind.
A recent article about the Van Allen Belts:
http://news.yahoo.com/liftoff-nasa-launches-twin-probes-study-earths-radiation-083437203.html


