For those of you who forgot basic high school chemistry...cartriges don't need oxygen to fire. There are oxygenators in the propellant so that they could fire in space without the presence of oxygen. Also...the answers of straight up and down are good answers too. As for the fellow who says that Lance Armstrong got around the moon by firing a .45....what planet did you come from. First off...Lance Armstrong won the Tour de France 6 times, Neil Armstrong first stepped on the moon. Second...if you do the math, that's a hell of a lot of .45 caliber shots to fire to get the boost to go around the moon. It's not like they could have just stuck their hand out a window and popped off a few shots! Second, why in the world would have NASA authorized the carry of a pistol when weight constraints on a space launch were so tight.