(All times are Eastern)

Launch-3 Days (Monday, Feb. 21)

• Prepare for the start of the STS-133 launch countdown
• Perform the call to stations (2:30 p.m.)
• Countdown begins at the T-43 hour mark (3 p.m.)
• Begin final vehicle and facility closeouts for launch
• Check out backup flight systems

Launch-2 Days (Tuesday, Feb. 22)

• Configure avionics systems for launch
  
• Review flight software stored in mass memory units and display systems
  
• Verify backup flight system software in Discovery’s general purpose computer
  
• Activate and test navigational systems (4 a.m.)
  
• Complete preparations to load power reactant storage and distribution system (6 a.m.)
  
• Flight Crew Equipment early stow and flight deck preliminary inspections complete (7 a.m.)
  
  Enter 4-hour built-in hold at T-27 hours (7 a.m.)
  
  
• Clear launch pad of all nonessential personnel
• Perform test of the vehicle's pyrotechnic initiator controllers and range safety system
  
  Resume countdown (11 a.m.)
  
  
• Begin operations to load cryogenic reactants into Discovery’s fuel cell storage tanks (11 a.m.)
  
  
• Enter 8-hour built-in hold at T-19 hours (7 p.m.)
  
  
• Demate orbiter mid-body umbilical unit (11:30 p.m.)

Launch-1 Days (Wednesday, Feb. 23)

• Resume orbiter and ground support equipment closeouts
  
  Resume countdown (3 a.m.)
  
  
• Main engine avionics, pneumatics and controller checkout (3 a.m.)
• External Tank feedline inspection/camera cleaning
• Flight Crew Equipment stowage
• Begin removal of pad ground support equipment
  
  Enter built-in 13 hours, 25 minute hold at T-11 hours (11 a.m.)
  
  
• Activate the orbiter's communications systems
• Lower engine support platforms, retract access platforms
• External Tank Inspections
• Rotating Service Structure begins move away from Discovery to the park position (8 p.m.)
• Perform ascent switch list
• Complete Flight Crew Systems time critical stowage (middeck payloads)
• Fuel cell flow-through purge complete

Launch Day (Thursday, Feb. 24)

Resume countdown at T-11 hours (12:25 a.m.)


• Activate the orbiter's fuel cells (1:35 a.m.)
• Clear the pad of all nonessential personnel (2:25 a.m.)
• Switch Discovery's purge air to gaseous nitrogen (2:25 a.m.)
• Complete final walkdowns
  
  Enter 2-hour built-in hold at the T-6 hour mark (5:25 a.m.)
  
  
• Clear pad of all personnel (5:35 a.m.)
• Complete tanking preparations
• Launch team verifies no violations of launch commit criteria prior to cryogenic loading of the external tank
  
  Resume countdown (7:25 a.m.)
  
  
• Chill down propellant transfer lines (7:25 a.m.)
• Begin loading the external fuel tank with about 500,000 gallons of cryogenic propellants (about 7:35 a.m.)
  
  Enter 2-hour, 30-minute built-in hold at T-3 hours (10:25 a.m.)
  
  
• Perform inertial measurement unit preflight calibration
• Align Merritt Island Launch Area tracking antennas
• Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants (about 10:25 a.m.)
• Final Inspection Team and Closeout Crew proceeds to launch pad
  
  Resume countdown at T-3 hours (12:55 p.m.)
  
  
• Perform open loop test with Eastern Range
• Crew departs Operations and Checkout (O&C) Building for the pad (1 p.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 (1:30 p.m.)
• Astronauts perform air-to-ground voice checks with Launch and Mission Control
• Begin to close Discovery’s crew hatch (2:35 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 10-minute hold at T-20 minutes (3:35 p.m.)
  
  NASA test director conducts final launch team briefings
  
  Resume countdown at T-20 minutes (3:45 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 45-minute hold at T-9 minutes (5:56 p.m.)
  
  
• Final launch window determination
• Launch director, Mission Management Team and NASA test director conduct final polls for "go/no go" to launch
  
  Resume countdown at T-9 minutes (about 4:41 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: 4:50:24 p.m.