In this story from the 1950s, which is ahead of its time in other respects, the astronauts are lying on their stomachs for launch in the moon rocket. That wouldn't work because their diaphragms would be compressed by the acceleration and their heads pushed into the bunks, so they would not be able to breathe. Real astronauts - who only came years later than the comic book this is based on - lie on their backs during acceleration for that reason.