There is that idea of a floating family, but in some ways they’re not really a family at all - they’re both much more and much less than that. They’re everything to each other for this short stretch of time because they’re all there is. They’re companions, colleagues, mentors, doctors, dentists, hairdressers. On spacewalks, launches, re-entry, in emergencies, they’re each other’s lifelines. They are each to the other a representative of the human race - they each have to suffice for billions of people. They have to make do in lieu of every earthly thing - families, animals, weather, sex, water, trees.