(All times are Eastern)
May 1, 2009

Launch-3 Days (Friday, May 8)

Prepare for the start of the STS-125 launch countdown
Perform the call to stations (3:30 p.m.)
Countdown begins at the T-43 hour mark (4 p.m.)
Begin final vehicle and facility closeouts for launch
Check out backup flight systems
Configure avionics systems for launch
Review flight software stored in mass memory units and display systems
Verify backup flight system software in Atlantis’ general purpose computer

Launch-2 Days (Saturday, May 9)

Complete preparations to load power reactant storage and distribution system (3 a.m.) Activate and test navigational systems (5 a.m.)
Flight deck preliminary inspections complete (5:30 a.m.)

Enter first built-in hold at T-27 hours for duration of 4 hours (8 a.m.)

Clear launch pad of all nonessential personnel
Perform test of the vehicle's pyrotechnic initiator controllers

Resume countdown (12 p.m.)

Begin operations to load cryogenic reactants into Atlantis’ fuel cell storage tanks (12 p.m.)

Enter 4-hour built-in hold at T-19 hours (8 p.m.)

Demate orbiter mid-body umbilical unit (8:30 p.m.)
Resume orbiter and ground support equipment closeouts

Launch-1 Day (Sunday, May 10)

Resume countdown (12 a.m.)

Begin filling pad sound suppression system water tank (1 a.m.)
Main engine avionics, pneumatics and controller checkout completed (2 a.m.)
Pad sound suppression system water tank filling complete (4 a.m.)
Begin star tracker functional checks (7:50 a.m.)

Enter planned hold at T-11 hours for 13 hours, 41 minutes (8 a.m.)

Activate the orbiter's communications systems
Move Rotating Service Structure to the park position (6 p.m.)
Perform ascent switch list
Fuel cell flow-through purge complete

Resume countdown at T-11 hours (9:41 p.m.)

Clear the blast danger area of all nonessential personnel
Switch Atlantis’ purge air to gaseous nitrogen (9:41 p.m.)
Activate the orbiter's fuel cells (9:51 p.m.)

Launch Day (Monday, May 11)

Enter planned 2-hour built-in hold at the T-6 hour mark (2:41 a.m.)

Launch team verifies no violations of launch commit criteria prior to cryogenic loading of the external tank
Clear pad of all personnel

Resume countdown (4:41 a.m.)

Chill down propellant transfer lines (4:41 a.m.)
Begin loading the external fuel tank with about 500,000 gallons of cryogenic propellants (about 4:51 a.m.)

Enter planned 2-hour, 30-minute built-in hold at T-3 hours (7:41 a.m.)

Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants (about 7:41 a.m.)
Final Inspection Team proceeds to launch pad
Perform inertial measurement unit preflight calibration
Align Merritt Island Launch Area tracking antennas

Resume countdown at T-3 hours (10:11 a.m.)

Perform open loop test with Eastern Range
Crew departs Operations and Checkout Building for the pad (10:16 a.m.)
Complete closeout preparations in the White Room
Check cockpit switch configurations
Begin Eastern Range final network open loop command checks
Flight crew begins entry into the orbiter (10:46 a.m.)
Astronauts perform air-to-ground voice checks with Launch and Mission Control
Begin to close Atlantis’ crew hatch (12:01 p.m.)
Perform hatch seal and cabin leak checks
Complete White Room closeout
Closeout crew moves to fallback area
Primary ascent guidance data is transferred to the backup flight system

Enter planned 10-minute hold at T-20 minutes (12:51 p.m.)

NASA test director conducts final launch team briefings

Resume countdown at T-20 minutes (1:01 p.m.)

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

Enter estimated 40-minute hold at T-9 minutes (1:12 p.m.)

Launch director, Mission Management Team and NASA test director conduct final polls for "go/no go" to launch

Resume countdown at T-9 minutes (1:52 p.m.)

Start automatic ground launch sequencer (T-9 minutes)
Retract orbiter crew access arm (T-7:30)
Start APU recorders (T-6:15)
Start auxiliary power units (T-5)
Terminate liquid oxygen replenish (T-4:55)
Start orbiter aerosurface profile test (T-3:55)
Start main engine gimbal profile test (T-3:30)
Pressurize liquid oxygen tank (T-2:55)
Begin retracting the gaseous oxygen vent arm (T-2:50)
Fuel cells to internal reactants (T-2:35)
Pressurize liquid hydrogen tank (T-1:57)
Deactivate bi-pod heaters (T-1:52)
Deactivate solid rocket booster joint heaters (T-0:50 seconds)
Orbiter transfers from ground to internal power (T-0:50 seconds)
Ground launch sequencer go for auto sequence start (T-0:31 seconds)
Booster gimbal profile (T-0:21 seconds)
Ignition of three space shuttle main engines (T-6.6 seconds)
Booster ignition and liftoff (T-0)

Preferred launch time 2:01:49 p.m.

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