Forty-three years ago today, the crew of Apollo 11 set down on the surface of the Moon, with Neil Armstrong taking mankind’s first bold steps onto the lunar surface. The event was a marvelous display of human perseverance and engineering design, but mental_floss reminds us of the day it could have been. The publication quotes the personal essay of speechwriter William Safire, published in the New York Times,

The most dangerous part of the trip was not landing the little module on the moon, but in launching it back up to the mother ship. If that failed, Neil Armstrong and Buzz Aldrin could not be rescued. Mission Control would have to “close down communications” and, as the world agonized, let the doomed astronauts starve to death or commit suicide.

In the event that things had gone horribly wrong, Safire had a speech ready for then-President Nixon.

It read:

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 dared 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 stars and saw their heroes in the constellations. In modern times, 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.