Countdown

NASA commonly employs the terms "L-minus" and "T-minus" during the preparation for and anticipation of a rocket launch,[1] and even "E-minus" for events that involve spacecraft that are already in space, where the "T" could stand for "Test" or "Time", and the "E" stands for "Encounter", as with a comet or some other space object, like a spacecraft.

[3] One of the first known associations with rockets was in the 1929 German science fiction movie Frau im Mond (English: Woman in the Moon) written by Thea von Harbou and directed by Fritz Lang in an attempt to increase the drama of the launch sequence of the story's lunar-bound rocket.

By that time everything that needs doing has been done, and therefore everybody has twenty minutes in which to think of what may not have been done, or else what could possibly go wrong.A countdown is a carefully devised set of procedures ending with launch of a rocket.

A hold is the suspension of the normal countdown process, during which the T-minus clock is stopped and no planned activities take place.

These provide an opportunity to perform non-launch activities, handle unexpected issues, or to catch up on the schedule if it is running long.

The launch weather guidelines involving the Space Shuttle and expendable rockets are similar in many areas, but a distinction is made for the individual characteristics of each.

[11] For example, dialogue heard during the launch of a Delta II rocket carrying the Kepler Space Telescope on March 8, 2009, included: Time: T minus 3 minutesLaunch Control (LC): OSM, third stage S&A arm permit to close.Operations Safety Manager (OSM): Closed.LC: SSC, third stage S&A armed.System Sequence Controller (SSC): Armed.LC: Prop 1, vehicle fuel tank press openProp 1: Open.LC: Fuel umbilical purge to open.Prop 1: Open.LC: SSC, vent 1 heater control exit.SSC: Exit.LC: SSC, vent 2 heater control exit.SSC: Exit.LC: NSC reports spacecraft is go.Mission Director: Kepler spacecraft is go.LC: SSC - FTS bat one and two heater controls heaters off.SSC: Off.LC: Prop 1, pressurized first stage LOX tanks to relief.Prop 1: Pressurized.LC: Prop 2, top first stage LOX to 100 percent levels.Prop 2: Up and down, 100 percent.Time: Ninety seconds.LC: SSC, hydraulic external power to on.SSC: External.Time: Eighty seconds.LC: RCO, report range go for launch.Range Control Officer (RCO): Range go for launch.Mission Director: LC (Viera), you're go for launch.LC: Roger.

After a launch, most countdown clocks begin to show Mission Elapsed Time, which is typically shown as "T plus."

Liquid-fueled rocket engines (which can be turned off after ignition) are normally lit a few seconds before T−0 and brought to full throttle around T−0.

The countdown was carried out at 11:59:50 pm and ended with chanting Merdeka 8 times and singing the national anthem.