"The Johnson Space Center "potty cam," as it is more casually known, is an astronaut training aid. It provides a vivid, arresting perspective on something you've had intimate contact with all your life but never really seen. Perhaps not unlike viewing one's home planet from space for the first time. Positioning is critical because the opening to a Space Shuttle toilet is 4 inches across, as opposed to the 18-inch maw we are accustomed to on Earth."