For his second and final mission in space, Collins served as command module pilot for Apollo 11. While fellow astronauts Neil Armstrong and Buzz Aldrin made the first manned landing on the lunar surface, Collins waited on board of the module for 21 and a half hours. As the command module drifted behind the moon, cutting off his communication with Earth, he wrote:
“This venture has been structured for three men, and I consider my third to be as necessary as either of the other two. I don’t mean to deny a feeling of solitude. It is there, reinforced by the fact that radio contact with the Earth abruptly cuts off at the instant I disappear behind the moon, I am alone now, truly alone, and absolutely isolated from any known life. I am it. If a count were taken, the score would be three billion plus two over on the other side of the moon, and one plus God knows what on this side.”
In a July 2009 interview with The Guardian, Collins revealed that he was very worried about Armstrong and Aldrin’s safety. He was also concerned that, in the event of their deaths on the Moon, he would be forced to return to Earth alone and, as the mission’s sole survivor, be regarded as “a marked man for life”.