A countdown is a sequence of backward counting to indicate the time remaining before a scheduled event. NASA uses "L-minus" (Launch), "T-minus" (Test/Time), and "E-minus" (Encounter) for rocket launches and spacecraft events. "T-minus" is used in the preparation for a rocket launch, while "E-minus" is used for events involving spacecraft already in space, like encountering a comet or another space object.
1929: Frau im Mond Movie Released
The film "Frau im Mond" (Woman in the Moon), released in 1929, used a countdown sequence to add drama to the rocket launch scene.
1930: Academy Leader Introduced
The Academy Leader, a countdown sequence printed on film leaders starting in 1930, synchronized film reel changeovers. This leader used units of feet instead of seconds.
1959: SMPTE Leader Created
In 1959, the SMPTE leader was created for film synchronization. This version measured in seconds rather than feet, starting at 8 and cutting to black at 2, improving the prior leader's accuracy in the beginning and end of the film.
1980: Formalized Countdown Procedures for Space Shuttle
In 1980, with the launch of the Solar Maximum Mission, NASA began using a five-volume set of procedures known as "Shuttle Countdown (KSC S0007)" or "S0007" to guide Space Shuttle launches. These detailed procedures, constantly updated, ensured the safe and efficient execution of complex launch operations.
March 8, 2009: Kepler Space Telescope Launch
On March 8, 2009, the Delta II rocket carrying the Kepler Space Telescope launched, showcasing the use of acronyms and call signs in launch communication for clear and efficient coordination among the launch team.