We look back at the Apollo 11 mission and see a triumph of human will, technology and daring. But at the time there was a chance that it would all end in disaster. Setting aside the prior Apollo 1 deaths of three astronauts, Gus Grissom, Roger White and Ed Chaffee, in a "plugs out test" of the Saturn V rocket and the Apollo Command and Service Modules. There was a single, critical piece of equipment that could not be tested until it was time to use it. Specifically, the Lunar Excursion Module's ascent engine. The LEM descended with a more powerful engine on it's descent stage. But rather that tow all the weight of the descent stage, NASA engineers decided to leave it behind and only ascend to rendezvous with the Command and Service modules with a much lighter ascent stage carrying the astronauts and the moon rock samples.
Of course, Murphy also had to intervene. In the tight confines of the LEM, either Aldrin or Armstrong's life support pack broke off the push button that would activate the ascent engine. Aldrin used a pen nib to push the button and the engine activated, but I can't help but imagine that the atmosphere in the LEM was pretty tense as they approached lunar liftoff.
Tension in the White House was also pretty high. As William Safire wrote this speech for President Nixon to read;
IN THE EVENT OF MOON DISASTER:
Fate has ordained that the 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 in their sacrifice.
These two men are laying down their lives in mankind’s most noble goal: the search for truth and understanding.
They will be mourned by their families and friends; they will be mourned by their nation; they will be mourned by the people of the world; they will be mourned by a Mother Earth that dare to send two of her sons into the unknown.
In their exploration, they stirred the people of the world to feel as one; in their sacrifice, they bind more tightly the brotherhood of man.
In ancient days, men looked at the stars and saw their heroes in the constellations. In modern time, we do much the same, but our heroes are epic men of flesh and blood.
Others will follow, and surely find their way home. Man’s search will not be denied. But these men were the first, and they will remain the foremost in our hearts.
For every human being who looks up at the moon in the nights to come will know that there is some corner of another world that is forever mankind.