The lander's computer was guiding them toward a crater filled with car-sized boulders that could have tipped the spacecraft upon touchdown.

Before speaking this iconic phrase, Armstrong announced "Houston, Tranquility Base here," formally changing the lunar module's call sign.

Seeking a quieter life away from fame, he spent eight years teaching aerospace engineering at the University of Cincinnati.

NASA required this contingency sample to guarantee they returned with at least some lunar material if an emergency forced an immediate departure.