STS-109 Countdown Timeline
SPACEFLIGHT NOW
Updated: February 23, 2002

All times are Eastern Standard Time

Launch Minus-3 Days	Monday, Feb. 25
- Columbia's astronauts arrive at Kennedy Space Center (1 a.m.) - Perform the call-to-stations (9:30 a.m.) - STS-109 launch countdown begins at the T-43 hour mark (10 a.m.) - Begin final vehicle and facility close-outs for launch - Check out back-up flight systems - Review flight software stored in mass memory units and display systems - Load backup flight system software into Columbia's general purpose computers - Remove mid-deck and flight-deck platforms (6 p.m.) - Activate and test navigational systems (11 p.m.)
Launch Minus-2 Days	Tuesday, Feb. 26
-Complete preparation to load power reactant storage and distribution system (1 a.m.) - Flight deck preliminary inspections complete (2 a.m.) - Enter first built-in hold at T-27 hours for duration of 4 hours (2 a.m.) - Clear launch pad of all non-essential personnel - Perform test of the vehicle's pyrotechnic initiator controllers (3 a.m.) - Resume countdown (6 a.m.) - Begin operations to load cryogenic reactants into Columbia's fuel cell storage tanks (6 a.m. - 2 p.m.) - Enter 4-hour built-in hold at T-19 hours (2 p.m.) - Begin filling pad sound suppression system water tank (2 p.m.) - Demate orbiter mid-body umbilical unit (2:30 p.m.) - Resume orbiter and ground support equipment close-outs - Resume countdown (6 p.m.) - Final preparations of the Shuttle's three main engines for main propellant tanking and flight (6 p.m.) - Pad sound suppression system water tank filling complete (7 p.m.) - Close out the tail service masts on the mobile launcher platform
Launch Minus-1 Day	Wednesday, Feb. 27
- Enter planned hold at T-11 hours for 12 hours, 58 minutes (2 a.m.) - Begin star tracker functional checks (3 a.m.) - Activate orbiter's inertial measurement units - Activate the orbiter's communications systems - Install film in numerous cameras on the launch pad (4:50 a.m.) - Flight crew equipment late stow (7:20 a.m.) - Move Rotating Service Structure (RSS) to the park position (11 a.m.) - Perform ascent switch list - Fuel cell flow-through purge complete - Resume countdown at T-11 hours (2:58 p.m.) - Activate the orbiter's fuel cells (4:08 p.m.) - Clear the blast danger area of all non-essential personnel - Switch Columbia's purge air to gaseous nitrogen (4:43 p.m.) - Enter planned 2-hour built-in hold at the T-6 hour mark (7:58 p.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 (9:58 p.m.) - Chilldown of propellant transfer lines (9:28 p.m.) - Begin loading the external tank with about 500,000 gallons of cryogenic propellants (about 9:58 p.m.)
Launch Day	Thursday, Feb. 28
- Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants (about 12:58 a.m.) - Final Inspection Team proceed to launch pad - Enter planned 2-hour built-in hold at T-3 hours (12:58 a.m.) - Perform inertial measurement unit preflight calibration - Align Merritt Island Launch Area (MILA) tracking antennas - Perform open loop test with Eastern Range - Resume countdown at T-3 hours (2:58 a.m.) - Crew departs Operations and Checkout Building for the pad (3:04 a.m.) - Complete close-out preparations in the white room - Check cockpit switch configurations - Flight crew begins entry into the orbiter (about 3:34 a.m.) - Astronauts perform air-to-ground voice checks with Launch and Mission Control - Close Columbia's crew hatch (about 4:48 a.m.) - Begin Eastern Range final network open loop command checks - Perform hatch seal and cabin leak checks - Complete white room close-out - Close-out 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 (5:38 a.m.) - NASA Test Director conducts final launch team briefings - Complete inertial measurement unit preflight alignments - Resume countdown at T-20 minutes (5:48 a.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 (5:59 a.m.) - Launch Director, Mission Management Team and NASA Test Director conduct final polls for go/no go to launch
Final Count	Thursday, Feb. 28
- Resume countdown at T-9 minutes (about 6:39 a.m.) - Start automatic ground launch sequencer (T-9:00 minutes) - Retract orbiter crew access arm (T-7:30) - Start mission recorders (T-6:15) - Start Auxiliary Power Units (T-5:00) - Arm SRB and ET range safety safe and arm devices (T-5:00) - Start liquid oxygen drainback (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 retraction of the gaseous oxygen vent arm (T-2:55) - Fuel cells to internal reactants (T-2:35) - Pressurize liquid hydrogen tank (T-1:57) - Deactivate SRB joint heaters (T-1:00) - Orbiter transfers from ground to internal power (T-0:50 seconds) - Ground Launch Sequencer go for auto sequence start (T-0:31 seconds) - SRB gimbal profile (T-0:21 seconds) - Ignition of three Space Shuttle main engines (T-6.6 seconds) - SRB ignition and liftoff (T-0)