As the Apollo program took form in the early 1960s, NASA engineers always kept the safety of their astronauts at the fore in light of the enormous risks they knew were inherent in the goal of landing on the Moon and returning safely. Wherever possible, they designed backup systems so that if a primary system failed the crew would still have the means to return home safely. Sometimes creating a backup was not always practical. For example, the Service Module’s engine needed to fire while the crew was behind the Moon to place them in a trajectory that would return them to Earth. There was no practical backup if the engine failed. But even in that instance a plan was worked out to use the Lunar Module’s (LM) engine as a backup. D