How Did NASA Know It Was Safe to Land on the Moon?
There was a lot of build-up to the first manned moon landing, including several unmanned missions to the moon flown by the space programs from both the U.S. and the U.S.S.R. Based on the data gathered during these missions, NASA scientists were able to develop procedures and equipment that would be most likely to lead to a safe manned mission to the moon.
The development of a high tech space suit was another factor in NASA's confidence in the first manned space mission. This suit was designed with cooling and breathing systems that could allow a human to survive in the moon's atmosphere. NASA did a lot of "what if" brainstorming and error-proofing in the several missions leading up to Apollo 11, and the space suit was meticulously tested down to the stitching and craftsmanship.