The narrator says, "The silver wings that would carry Gene Kranz aloft were born not of laughter, but fire." This is a reference to the famous poem "High Flight" by RCAF pilot John Gillespie Magee; the poem's first lines are, "Oh! I have slipped the surly bonds of Earth, and danced the skies on laughter-silvered wings." See more
[referring to Freedom 7
Shepard's flight will last only 15 minutes, but it's 15 minutes of pure unknowns, and the future of the entire program is riding on the outcome.
Shepard's flight was literally fraught with danger, and it was the one that we had to make happen if we were to keep moving forward in space.