"Sleep is important out in deep space. And since there technically is no sun to go by and every planet has a bit of a different day/night cycle, I usually end up listening to my internal clock. I go to sleep when I'm tired, and wake up when I'm not. Of course, I usually set a timer so I don't end up sleeping too much, but my Circadian rhythm generally keeps me on time. Until it doesn't. Then I end up sleeping for 10 hours and miss a meeting with the head of the GA. A purely hypothetical scenario, of course, that has definitely never happened."