What is Flight Day?

A frequently used method of marking time during a shuttle mission is "flight days". Liftoff occurs on the first flight day; the second flight day starts after the first on-orbit sleep period; etc.

Flight days can be a little confusing when the crew are on different sleep cycles. When the crew works on different shifts, the shifts are given names (usually red and blue); then the terms "blue flight day" and "red flight day" are used.

Other "clocks"

| MET | UTC | Countdown & Liftoff | Flight day | Apollo era |