Countdown Clock &
Time to Liftoff

Countdown Clock

10... 9... 8... 7... 6... 5... 4... 3... 2... 1... Liftoff
The countdown clock would be simple to explain except for the "holds". The countdown clock is a method of representing what pre-launch events or milestones have been accomplished. If an event is late, the clock will hold until that event occurs. Also, the countdown will contain several "built-in" holds. Sometime built-in holds are included to allow synchronization with other countdown clocks (for example, a payload countdown). Other built-in holds allow people to take a break. The built-in holds vary significantly from day-launch missions to night-launch missions.

The shuttle countdown clock typically starts counting at about 43 hours.

Liftoff Clock

The Liftoff server presents a liftoff clock which shows the "wall-clock" time remaining to the beginning of the launch window. If the clock says 1/19:30, then launch is scheduled to occur 1 day, 19 hours, and 30 minutes after the current time.

After a mission is launched, the Liftoff server shows Mission Elapsed Time clock

Other "clocks"

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