Space Shuttle Launch Countdown Clock Explanation
Tags: launch, countdown, T-minus, time, space, shuttle
T-minus.... The Countdown Clock is one of the most watched timepieces in the world. On this page we explain how to understand the countdown:
| ||T-43 hours and counting - Start Countdown Clock|
The countdown gets underway with the traditional call to stations by the NASA Test Director.
Mid-deck and flight-deck platforms are removed.
Navigational Systems activated and tested.
| ||T-27 hours & holding |
Preliminary Flight Deck inspections completed.
Complete preparation to load power reactant storage and distribution system and complete flight deck preliminary inspections
| ||T-27 hours & counting |
Clear launch pad of all nonessential personnel.
Begin operations to load cryogenic reactants into Atlantis's fuel cell storage tanks
| ||T-19 hours & holding|
Demating of the Orbiter's mid-body umbilical unit takes place.
Final preparations for Shuttle's three main engines begins.
| ||T-19 hours & counting |
Begin filling sound suppression systems water tank.
Close out the tail service masts on the mobile launcher platform
| ||T-11 hours & holding|
Move Rotating Service Structure (RSS) to park position.
Activate Orbiter's inertial measurement units.
Activate Orbiter's communications systems.
Perform ascent switch list
| ||T-11 hours & counting |
Activate the Orbiter's fuel cells.
Clear the blast danger area of all nonessential personnel.
Switch Atlantis's purge air to gaseous nitrogen.
| ||T-6 hours & holding|
The Final Inspection Team conducts a detailed analysis of the vehicle as they walk up and down the entire launch tower.
Begin loading the external tank with about 500,000 gallons of cryogenic propellants as we begin T-6 and counting.
| ||T-6 hours & counting|
| ||T-3 hours & holding|
| ||T-3 hours & counting|
| ||T-20 minutes & holding|
| ||T-20 minutes & counting|
| ||T-9 minutes & holding|
| ||T-9 minutes & counting|
| ||T-0 - Liftoff!|
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