There are a lot of hard calculations, math, and science involved in trying to get men to the moon. Believe or not, one critical concern is - how the hell will astronauts use the bathroom? There's a contraption that allows urine to be ejected out of a small hole on the spacecraft, but even that requires additional calculations. Within the vacuum of space there is very little matter, so even a small amount of force exerted by ... liquid ... exiting a spacecraft can shift its spacecraft
For more info, check the video below by MinutePhysics. If you can't see it, click here.