"Hogy ez eddig nem volt probléma... ? :-D"

szerintem az a probléma, hogy ennek a kérdésnek a felvetése egyáltalán megfogalmazódott benned.
szerencsére a NASA felkészült erre (is), itt találod helyes megoldásokat:

"4. Some people believe that the Apollo moon landings were a hoax because astronauts would have been instantly killed in the radiation belts. According to the US Occupation Safety and Health Agency (OSHA) a lethal radiation dosage is 300 Rads in one hour. What is your answer to the 'moon landing hoax' believers?

Note: According to radiation dosimeters carried by Apollo astronauts, their total dosage for the entire trip to the moon and return was not more than 2 Rads over 6 days. 

https://spacemath.gsfc.nasa.gov/

természetesen a jövőbeli küldetések is biztonságosak lesznek:

Moon safe for long-term human exploration, first surface radiation measurements show

"The results are nothing that scientists didn’t already suspect, says Francis Cucinotta, who studies the health effects of space radiation at the University of Nevada, Las Vegas, and who wasn’t involved in the work. But it’s good to have the specific measurements, which verify that if astronauts live in shielded bases, they can spend up to 6 months on the Moon without exceeding NASA’s legally mandated limits, he adds."