Joseph Rennigan was a biologist and an astronaut. He was the only survivor of an American mission to Mars in 1994. The First Doctor, Susan Foreman, Ian Chesterton and Barbara Wright encouraged him to not give up hope of rescue. After they departed, he thought they had been hallucinations.
Earlier in 1994, President Carrol gave Rennigan the rank of Commander in the US Army during a White House ceremony. This was because at the time, only US Army personnel were allowed on American spaceflights. (PROSE: Rennigan's Record)