 When Apollo 11 launched on July 16, 1969, Commander Neil Armstrong gave them about a 50-50 chance of successfully completing the lunar landing goal. But actually landing on the moon wasn't the only part of the mission that risked turning sour. One part of the mission that was completely vital was firing the Ascent Stage, the stage of the lunar module responsible for getting Armstrong and Buzz Aldrin off the lunar surface at the end of their stay. NASA did have a contingency in place in case the astronauts were stranded on the moon, but it wasn't a rescue. NASA had prepared a statement for President Nixon to read celebrating the brave men who gave their lives to fulfill President Kennedy's lunar landing goal. One core question at the beginning of the Apollo program was how safe is safe enough when you're talking about doing something like sending man a quarter of a million miles away to walk in an airless environment? None of the NASA higher ups was about to delude himself into thinking that 100% reliability was feasible. Engineers are human and they do make mistakes, so management settled on an acceptable failure rate of 0.01%, meaning 99.9% of the time every system would function perfectly. It was a safety rule known as three nines. Of all the systems onboard the spacecraft, the engines were arguably the most important. Almost everything failed on Apollo 13, but having one good engine allowed the crew to get into a free return trajectory and return home safely. But there was always that slim 0.01% chance that one of the engines would fail, and if the Ascent Engine of the lunar module failed, the crew would be stranded on the moon. As permission contingency rules, Mike Collins would return to Earth alone, leaving Neil Armstrong and Buzz Aldrin to die on the lunar surface. If this were to come to pass, President Nixon would first call the widows to be Armstrong and Aldrin's wives, and then address the crew and the nation and the world publicly by a live broadcast. Fate has ordained that these men who went to the moon to explore in peace will stay on the moon to rest in peace. These brave men, Neil Armstrong and Edwin Aldrin, know that there is no hope for their recovery, but they also know that there is hope for mankind and their sacrifice. Those two men are laying down their lives in mankind's most noble goal, the search for truth and understanding. NASA would probably have kept in touch with Armstrong and Aldrin as they ran out of oxygen in the lunar module. After the final transmission with the crew, a clergyman would have taken over the broadcast from NASA and gone through the procedures of a burial, commending the astronaut souls to the deep and concluding with the Lord's prayer. But as we know, the Ascent Engine of Apollo 11's lunar module Eagle did fire, and Armstrong and Aldrin were able to safely rejoin Mike Collins in the command module and all three astronauts splashed down on Earth on July 24th, 1969. You're not too late to jump into the live tweet that I'm doing of Apollo 11's mission. Follow me as AST Vintage Space on Twitter to get blow-by-blow updates of the mission as they happened in real time with a 45-year delay. I'll be going all the way through Splashdown on July 24th. Leave your questions and comments below and don't forget to subscribe.