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Countdown to launch: key events before Endeavour's Friday night liftoff
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The famous countdown clock at Kennedy Space Center (KSC) in Florida is ticking, as the launch team prepares for a 7:55 p.m. EST launch Friday of Endeavour and its seven-member crew. They're flying a "home improvement" mission to the International Space Station (ISS), bringing upgrades that include the first-ever refrigerator in space.
The management team is keeping a wary eye on incoming weather systems that might delay the launch.NASA has strict flight safety regulations that deal with not only temperature, but cloud cover, humidity, and lightning.
The STS-126 crew, led by Commander Chris Ferguson, flew into KSC yesterday in their sporty T-38 training jets, taking time to fly over Endeavour on Launch Pad 39A. The team also includes pilot Eric Boe and mission specialists Steve Bowen, Shane Kimbrough, Sandra Magnus, Don Pettit and Heidemarie Stefanyshyn-Piper.
Shown above is the countdown clock with a space shuttle in the background. People often wonder why the clock starts three days ahead of launch at T-43 hours.
That's because the launch sequence has holds built in along the way. Those holds allow extra time to fix any minor glitches, evaluate the weather, hold in-work briefings, and catch up on paperwork along the way.
Here's your handy guide to upcoming key events during the STS-126 launch countdown, starting with the first planned hold at T-27 hours.
T-27 hours and holding
This is the first built-in hold and typically lasts four hours.
* Clear launch pad of all non-essential personnel
T-27 hours and counting
* Begin operations to load cryogenic reactants into the orbiter's fuel cell storage tanks
T-19 hours and holding
This built-in hold typically lasts four hours.
T-19 hours and counting
* Begin final preparations of the orbiter's three main engines for main propellant tanking and flight
* Fill launch pad sound suppression system water tank
* Resume orbiter and ground support equipment close-outs
* Close out the tail service masts on the mobile launcher platform
T-11 hours and holding
This built-in hold varies in length, but typically lasts 12 to 13 hours.
* Flight crew equipment late stow
* Move rotating service structure to "park" position
* Activate the orbiter's inertial measurement units and communications systems
* Perform ascent switch list
T-11 hours and counting
* Activate the orbiter's fuel cells
* Clear the blast danger area of all nonessential personnel
* Switch the orbiter's purge air to gaseous nitrogen
T-6 hours and holding
This built-in hold typically lasts two hours.
* Launch team verifies no violations of launch commit criteria before loading the external tank with propellants
* Clear pad of all personnel
* Chill-down of propellant transfer lines
* Begin loading the external tank with about 500,000 gallons of cryogenic propellants
T-6 hours and counting
* Finish filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants
T-3 hours and holding
This built-in hold typically lasts two hours.
* Perform inertial measurement unit preflight calibration
* Align Merritt Island Launch Area (MILA) tracking antennas
* Final Inspection Team proceeds to the launch pad to conduct a detailed analysis of the vehicle as the team walks up and down the entire launch tower
* Closeout Crew proceeds to the launch pad to configure the crew module for countdown and launch and assist the astronauts with entry into the orbiter
T-3 hours and counting
* Crew departs for the launch pad and, upon arriving at the pad, begins entry into the orbiter via the White Room
* Complete close-out preparations in the launch pad's White Room
* Check cockpit switch configurations
* Astronauts perform air-to-ground voice checks with Launch Control (Kennedy Space Center) and Mission Control (Johnson Space Center)
* Close the orbiter's crew hatch and check for leaks
* Complete White Room close-out
* Close-out crew retreats to fallback area
T-20 minutes and holding
This built-in hold typically lasts 10 minutes.
* Shuttle Test Director conducts final launch team briefings
* Complete inertial measurement unit preflight alignments
* Transition the orbiter's onboard computers to launch configuration
* Start fuel cell thermal conditioning
* Close orbiter cabin vent valves
* Transition backup flight system to launch configuration
T-9 minutes and holding
This is the final built-in hold, and varies in length depending on the mission.
* The Launch Director, Mission Management Team and Shuttle Test Director poll their teams for a go/no go for launchT-9 minutes and counting
* Start automatic ground launch sequencer
* Retract orbiter access arm (T-7 minutes, 30 seconds)
* Start auxiliary power units (T-5 minutes, 0 seconds)
* Arm solid rocket booster range safety safe and arm devices (T-5 minutes, 0 seconds)
* Start orbiter aerosurface profile test, followed by main engine gimbal profile test (T-3 minutes, 55 seconds)
* Retract gaseous oxygen vent arm, or "beanie cap"
(T-2 minutes, 55 seconds)
* Crew members close and lock their visors
(T-2 minutes, 0 seconds)
* Orbiter transfers from ground to internal power
(T-50 seconds)
* Ground launch sequencer is go for auto sequence start (T-31 seconds)
* Activate launch pad sound suppression system
(T-16 seconds)
* Activate main engine hydrogen burnoff system
(T-10 seconds)
* Main engine start (T-6.6 seconds)
T-0
* Solid rocket booster ignition and liftoff!
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