A launch countdown includes “L Minus” to indicate how far away liftoff is in hours and minutes, and “T Minus” to show a sequence of events built into the launch countdown.

Victor Glover, Jeremy Hansen, Reid Wiseman and Christina Koch's mission is partly intended to pave the way for a future lunar landing in the coming years.

Humans have travelled beyond Earth's orbit for the first time since 1972 as the mission heads for the moon.