[colorado tanker]

I seem to remember concern about an astronaut surviving transit of the Van Allen belts, perhaps in the 50’s? By the time I heard about it in the 60’s it seemed to be in the same category as the fear an aircraft would break up if it exceed the sound “barrier.”

[Joe 6-pack]

"By the time I heard about it in the 60’s it seemed to be in the same category as the fear an aircraft would break up if it exceed the sound “barrier.”"

At one time it was thought the human body could not survive speeds in excess of 100 mph.

[SunkenCiv]

The Van Allen belts were discovered by instrumentation aboard a satellite, in 1958, so it may have been discussed that early.

http://lasp.colorado.edu/strv/vanallen_strv.html