Houston, We've Had a Problem: The History of the Apollo 13 Mission (Unabridged‪)‬

"The only experiment we completed on Apollo 13 was not on the original mission list." - James Lovell, Jr.

In the summer of 1969, Apollo 11 successfully landed men on the Moon for the first time in history, and Apollo 12 successfully landed astronauts on the Moon just a few months after Apollo 11's successful mission. Apollo 12 was actually more successful than Apollo 11 from the standpoint of fulfilling the mission objectives, but it was naturally overshadowed since it did not come first.

Another reason Apollo 12 is mostly forgotten today can be credited to the dramatic and fateful Apollo 13 mission, which took twists and turns nobody could have predicted when it launched on April 11, 1970. Apollo 13's mission was to land on the Moon near the Fra Mauro highlands, which were hills that had somehow formed in the middle of a huge crater tens of miles wide. The mission was supposed to test for seismic activity and take samples to analyze the crater and try to find an explanation for the formation of the hills.

Of course, as is widely known today, Apollo 13 never made the landing. The ever-dependable Saturn V properly thrust Apollo 13 out of the Earth's orbit and toward the Moon, but two days into the voyage, the crew heard a loud bang. At first, the crew was not sure what had happened, leading Commander James Lovell to famously transmit to Mission Control, "Houston, we've had a problem." As it turned out, one of the main oxygen tanks had ruptured in the Service Module, causing a catastrophic failure. The Command/Service Module's fuel cells all shut down, leaving the command/Service Module to run on backup batteries.