I had the opportunity a few years ago to see Buzz Aldrin speak at Facebook for the 45th anniversary of Apollo 11. Someone asked him about the speech that was pr

I had the opportunity a few years ago to see Buzz Aldrin speak at Facebook for the 45th anniversary of Apollo 11. Someone asked him about the speech that was prepared for President Nixon in the event that Neil and Buzz had been stranded on the Moon; Buzz's answer was basically that he wasn't worried since the engineers had told them they had a ~95% chance of making it back to Earth safely, which I thought was interesting, since I have no idea how idea how they could be that confident about doing something so risky for the first time (although I guess the different pieces of hardware involved had been tested on prior missions).