The original Apollo 13 prime crew. From left to right are: Commander, James A. Lovell, Command Modul

The original Apollo 13 prime crew. From left to right are: Commander, James A. Lovell, Command Module pilot, Thomas K. Mattingly and Lunar Module pilot, Fred W. Haise. On the table in front of them are from left to right, a model of a sextant, the Apollo 13 insignia, and a model of an astrolabe. The sextant and astrolabe are two ancient forms of navigation. Command Module pilot Thomas “Ken” Mattingly was exposed to German measles prior to his mission and was replaced by his backup, Command Module pilot, John L.“Jack” Swigert Jr.