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(All times Eastern)
(All times Eastern)

Launch-3 Days (Saturday, Oct. 20)

Prepare for the start of the STS-120 launch countdown
Perform the call to stations (1:30 p.m.)
Countdown begins at the T-43 hour mark (2 p.m.)
Begin final vehicle and facility closeouts for launch
Check out backup flight systems
Review flight software stored in mass memory units and display systems
Load backup flight system software into Discovery's general purpose computers
Mid-deck and flight-deck platform removal complete (10 p.m.)

Launch-2 Days (Sunday, Oct. 21)

Activate and test navigational systems (3 a.m.)
Complete preparations to load power reactant storage and distribution system (5 a.m.)
Flight deck preliminary inspections complete (6 a.m.)

Enter first built-in hold at T-27 hours for duration of 4 hours (6 a.m.)

Clear launch pad of all non-essential personnel
Perform test of the vehicle's pyrotechnic initiator controllers

Resume countdown (10 a.m.)

Enter 4-hour built-in hold at T-19 hours (6 p.m.)

Begin operations to load cryogenic reactants into Discovery's fuel cell storage tanks (6 p.m.)
Demate orbiter mid-body umbilical unit (6:30 p.m.)
Resume orbiter and ground support equipment closeouts

Resume countdown (10 p.m.)

Final preparations of the shuttle's three main engines for main propellant tanking (10 p.m.)

Launch-1 Day (Monday, Oct. 22)

Begin filling pad sound suppression system water tank (3 a.m.)
Close out the tail service masts on the mobile launcher platform
Begin star tracker functional checks (5:50 a.m.)
Pad sound suppression system water tank filling complete (6 a.m.)

Enter planned hold at T-11 hours for 13 hours, 13 minutes (6 a.m.)

Activate orbiter's inertial measurement units
Activate the orbiter's communications systems
Install film in numerous cameras on the launch pad (6:55 a.m.)
Flight crew equipment late stow (11:10 a.m.)
Move Rotating Service Structure to the park position (3 p.m.)
Perform ascent switch list
Fuel cell flow-through purge complete

Resume countdown at T-11 hours (7:13 p.m.)

Activate the orbiter's fuel cells (8:23 p.m.)
Clear the blast danger area of all non-essential personnel
Switch Discovery's purge air to gaseous nitrogen (8:58 p.m.)

Launch Day (Tuesday, Oct. 23)

Enter planned 2-hour built-in hold at the T-6 hour mark (12:13 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 (2:13 a.m.)

Chill down propellant transfer lines (2:13 a.m.)
Begin loading the external fuel tank with about 500,000 gallons of cryogenic propellants (about 2:23 a.m.)
Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants (about 5:13 a.m.)
Final Inspection Team proceeds to launch pad

Enter planned 2-hour, 30 minute built-in hold at T-3 hours (5:13 a.m.)

Perform inertial measurement unit preflight calibration
Align Merritt Island Launch Area tracking antennas
Perform open loop test with Eastern Range

Resume countdown at T-3 hours (7:43 a.m.)

Crew departs Operations and Checkout Building for the pad (7:48 a.m.)
Complete closeout preparations in the White Room
Check cockpit switch configurations
Flight crew begins entry into the orbiter (about 8:18 a.m.)
Astronauts perform air-to-ground voice checks with Launch and Mission Control
Begin to close Discovery's crew hatch (9:23 a.m.)
Begin Eastern Range final network open loop command checks
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 (10:23 a.m.)

NASA test director conducts final launch team briefings
Complete inertial measurement unit preflight alignments

Resume countdown at T-20 minutes (10:33 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 45-minute hold at T-9 minutes (10:44 a.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 (about 11:29 a.m.)

Start automatic ground launch sequencer (T-9 minutes)
Retract orbiter crew access arm (T-7:30)
Start mission recorders (T-6:15)
Start Auxiliary Power Units (T-5)
Arm solid rocket booster and external tank range safety safe and arm devices (T-5)
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 bi-pod heaters (T-1:52)
Deactivate solid rocket booster joint heaters (T-0:50)
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)

Commander: Pam Melroy
Pilot: George Zamka
Mission Specialist: Scott Parazynski
Mission Specialist: Doug Wheelock
Mission Specialist: Stephanie Wilson
Mission Specialist: Paolo Nespoli
Mission Specialist: Daniel Tani

Televised events (times may vary slightly)
All times Eastern

Tuesday, Oct. 23
1:30 a.m. --- Crew wakes up
7:08 a.m. --- Weather briefing
7:18 a.m. --- Don flight suits
7:48 a.m. --- Depart for launch pad
8:18 a.m. --- Arrive at White Room and begin ingress
9:33 a.m. --- Close crew hatch
11:38 a.m. --- Launch