STS-105 Countdown Timeline
SPACEFLIGHT NOW
Updated: August 6, 2001

The STS-105 countdown is timed to hit zero at the opening of the shuttle's theoretical 10-minute launch (planar) window at 5:33 p.m. EDT on August 9. The preferred launch time, the moment when the launch pad is directly in the plane of the international space station's orbit, is 5:38 a.m. The start of a final hold at the T-minus nine-minute mark is timed for the opening of the 10-minute planar window. The hold will be extended as required based on final radar tracking of the space station to hit the preferred launch time. The chart below reflects that extension.

ALL TIMES ARE EASTERN

Launch Minus-3	Monday, August 6
- Prepare for the start of the STS-105 launch countdown - Perform the call-to-stations (4:30 p.m.) - Countdown begins at the T-43 hour mark (5 p.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 Discovery's general purpose computers
Launch Minus-2	Tuesday, August 7
Remove mid-deck and flight-deck platforms (12 a.m.) - Activate and test navigational systems (10 a.m.) - Complete preparation to load power reactant storage and distribution system (1 p.m.) - Flight deck preliminary inspections complete (1 p.m.) - Enter first built-in hold at T-27 hours for duration of 8 hours (9 a.m.) - Clear launch pad of all non-essential personnel - Perform test of the vehicle's pyrotechnic initiator controllers (2 p.m.) - Resume countdown (5 p.m.) - Begin operations to load cryogenic reactants into Discovery's fuel cell storage tanks (5 p.m. - 12 a.m.)
Launch Minus-1	Wednesday, August 8
- Enter 4-hour built-in hold at T-19 hours (1 a.m.) - Demate orbiter mid-body umbilical unit (1:30 a.m.) - Resume countdown (5 a.m.) - Final preparations of the Shuttle's three main engines for main propellant tanking and flight (5 a.m.) - Begin filling pad sound suppression system water tank (7:30 a.m.) - Resume orbiter and ground support equipment close-outs - Pad sound suppression system water tank filling complete (12:30 p.m.) - Close out the tail service masts on the mobile launcher platform - Enter planned hold at T-11 hours for 12 hours, 42 minutes (1 p.m.) - Begin star tracker functional checks (1:30 p.m.) - Activate orbiter's inertial measurement units - Activate the orbiter's communications systems - Install film in numerous cameras on the launch pad (3:30 p.m.) - Flight crew equipment late stow (5:30 p.m.) - Move Rotating Service Structure (RSS) to the park position (9:30 p.m.) - Perform ascent switch list - Fuel cell flow-through purge complete
Launch Day	Thursday, August 9
- Resume countdown at T-11 hours (1:42 a.m.) - Activate the orbiter's fuel cells (2:52 a.m.) - Clear the blast danger area of all non-essential personnel - Switch Discovery's purge air to gaseous nitrogen (3:57 a.m.) - Enter planned 2-hour built-in hold at the T-6 hour mark (6:42 a.m.) - Launch team verifies no violations of launch commit criteria prior to cryogenic loading of the external tank - Clear pad of all personnel - Chilldown of propellant transfer lines (8:12 a.m.) - Begin loading the external tank with about 500,000 gallons of cryogenic propellants (about 8:42 a.m.) - Resume countdown (8:42 a.m.) - Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants (about 11:42 a.m.) - Final Inspection Team proceed to launch pad - Enter planned 2-hour built-in hold at T-3 hours (11:42 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 (1:42 p.m.) - Crew departs Operations and Checkout Building for the pad (1:47 p.m.) - Complete close-out preparations in the white room - Check cockpit switch configurations - Flight crew begins entry into the orbiter (about 2:17 p.m.) - Astronauts perform air-to-ground voice checks with Launch and Mission Control - Close Discovery's crew hatch (about 3:32 p.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 (4:22 p.m.) - NASA Test Director conducts final launch team briefings - Complete inertial measurement unit preflight alignments - Resume countdown at T-20 minutes (4:32 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 (4:43 p.m.) - Launch Director, Mission Management Team and NASA Test Director conduct final polls for go/no go to launch
Final Count	Thursday, August 9
- Resume countdown at T-9 minutes (about 5:23 p.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)