Changes and additions:
- Sept. 21: Posting initial release

Editor's Note: The launch window is roughly 10 minutes long. To maximize ascent performance, NASA targets the middle of the window. A final hold in the countdown at the T-minus nine-minute mark will be extended as required to hit the desired launch time.

The following countdown only covers the day of launch. A detailed countdown will be posted here as soon as it is available.

EST...........EVENT

Thu  11/12/09

12:05 AM......Pad clear of non-essential personnel
12:05 AM......APU bite test
12:55 AM......Fuel cell activation
01:45 AM......Booster joint heater activation
02:15 AM......MEC pre-flight bite test
02:30 AM......Tanking weather update
03:15 AM......Final fueling preps; launch area clear
03:45 AM......Red crew assembled
04:30 AM......Fuel cell integrity checks complete

04:45 AM......Begin 2-hour built-in hold (T-minus 6 hours)
04:55 AM......Safe-and-arm PIC test
05:45 AM......External tank ready for loading
06:08 AM......Mission management team tanking meeting
06:45 AM......Resume countdown (T-minus 6 hours)

06:45 AM......LO2, LH2 transfer line chilldown
06:55 AM......Main propulsion system chill down
06:55 AM......LH2 slow fill
07:25 AM......LO2 slow fill
07:30 AM......Hydrogen ECO sensors go wet
07:35 AM......LO2 fast fill
07:38 AM......Crew medical checks
07:45 AM......LH2 fast fill
09:40 AM......LH2 topping
09:45 AM......LH2 replenish
09:45 AM......LO2 replenish

09:45 AM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours)
09:45 AM......Closeout crew to white room
09:45 AM......External tank in stable replenish mode
10:00 AM......Astronaut support personnel comm checks
10:30 AM......Pre-ingress switch reconfig
11:00 AM......NASA TV coverage begins
11:45 AM......Final crew weather briefing
11:50 AM......Crew suit up begins
12:15 PM......Resume countdown (T-minus 3 hours)

12:20 PM......Crew departs O&C building
12:50 PM......Crew ingress
01:40 PM......Astronaut comm checks
02:05 PM......Hatch closure
02:35 PM......White room closeout

02:55 PM......Begin 10-minute built-in hold (T-minus 20m)
03:05 PM......NASA test director countdown briefing
03:05 PM......Resume countdown (T-minus 20m)

03:06 PM......Backup flight computer to OPS 1
03:10 PM......KSC area clear to launch

03:16 PM......Begin final built-in hold (T-minus 9m)
03:46:25 PM...NTD launch status verification
04:01:25 PM...Resume countdown (T-minus 9m)

04:05:25 PM...Orbiter access arm retraction
04:05:25 PM...Launch window opens
04:05:25 PM...Hydraulic power system (APU) start
04:05:30 PM...Terminate LO2 replenish
04:06:25 PM...Purge sequence 4 hydraulic test
04:06:25 PM...IMUs to inertial
04:06:30 PM...Aerosurface profile
04:06:55 PM...Main engine steering test
04:07:30 PM...LO2 tank pressurization
04:07:50 PM...Fuel cells to internal reactants
04:07:55 PM...Clear caution-and-warning memory
04:08:25 PM...Crew closes visors
04:08:28 PM...LH2 tank pressurization
04:09:35 PM...SRB joint heater deactivation
04:09:54 PM...Shuttle GPCs take control of countdown
04:10:04 PM...SRB steering test
04:10:18 PM...Main engine start (T-6.6 seconds)
04:10:25 PM...SRB ignition (LAUNCH)