After spending all that money, time and training getting to the Moon, does anyone really think he'd just put himself in needless danger like that on a whim? Human vacuum exposure experiments were performed on Earth, in vacuum chambers, prior to Apollo. Under rigidly controlled circumstances, not "Oh, let's pop that helmet off and see what happens".

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort