 is that originally nasa was not going to fly any missions out of earth orbit without a lunar module but they wanted to have the lunar module as a redundancy as a backup as a lifeboat and in fact that's exactly what happened on apollo thirteen when the service module on the apollo capsule blew up and it was out of commission they didn't have any of the oxygen or supplies from the service module they opened up the lunar module and that kept the guys alive until they could get back to earth