Childrens book involving two orphans that travel to space and find a space station captain that takes them in

Two orphans are touring a rocket that is about to go into space and they are accidentally launched into space where they get rescued by a captain of a secret space station. They make friends with most of the crew. However, part of the crew tries to take over the station and in the process the station is damaged and crashes on the moon. They survive and manage to find a way back to Earth.