...but why aren't they wearing space suit air helmets????
I think back when Tezuka wrote this story he and the general population did not understand that "space" did not have breathable oxygen. A lot of older science fiction has people on places like our own moon or Mars and other places breathing air just fine (when of course we know this is just not something that is possible). Although Tezuka did do a lot of research for some of his stories we must remember he was no scientist and oftentimes his writings just reflected the popular science of the time.