Changes and additions:
- January 2: Posting initial release
- January 22: Updating throughout
- February 4: Launch delayed to Feb. 19
- February 6: Launch delayed to Feb. 22
- February 11: Updating throughout
- February 13: Launch delayed to Feb. 27
- February 17: Updating throughout
- March 2: Updating for March 12 launch
- March 6: Updating for March 11 launch
- March 12: Updating for March 15 launch

As always, all countdown events prior to the end of the T-minus nine-minute hold are targeted to the opening of the shuttle's launch window. For station flights, the shuttle must take off within five minutes or so of the moment Earth's rotation carries the launch pad into the plane of the station's orbit. NASA targets the middle of that window for launch. Please note that NASA rounds down, not up, for countdown calculations. The release of the final hold at T-minus nine-minutes is targeted to the actual launch time (times in EST).

EDT...........EVENT

Sunday, March 15

03:18 AM......ASP cockpit config
03:38 AM......Pad clear of non-essential personnel
03:38 AM......APU bite test
04:28 AM......Fuel cell activation
05:18 AM......Booster joint heater activation
05:48 AM......MEC pre-flight bite test
06:03 AM......Tanking weather update
06:48 AM......Final fueling preps; launch area clear
07:18 AM......Red crew assembled
08:03 AM......Fuel cell integrity checks complete

08:18 AM......Begin 2-hour built-in hold (T-minus 6 hours)
08:28 AM......Safe-and-arm PIC test
09:18 AM......External tank ready for loading
09:41 AM......Mission management team tanking meeting
10:18 AM......Resume countdown (T-minus 6 hours)

10:18 AM......LO2, LH2 transfer line chilldown
10:28 AM......Main propulsion system chill down
10:28 AM......LH2 slow fill
10:58 AM......LO2 slow fill
11:03 AM......Hydrogen ECO sensors go wet
11:08 AM......LO2 fast fill
11:11 AM......Crew medical checks
11:18 AM......LH2 fast fill
01:13 PM......LH2 topping
01:18 PM......LH2 replenish
01:18 PM......LO2 replenish

01:18 PM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours)
01:18 PM......Closeout crew to white room
01:18 PM......External tank in stable replenish mode
01:33 PM......Astronaut support personnel comm checks
02:03 PM......Pre-ingress switch reconfig
02:30 PM......NASA TV coverage begins
03:18 PM......Final crew weather briefing
03:23 PM......Crew suit up begins
03:48 PM......Resume countdown (T-minus 3 hours)

03:53 PM......Crew departs O&C building
04:23 PM......Crew ingress
05:13 PM......Astronaut comm checks
05:38 PM......Hatch closure
06:08 PM......White room closeout

06:28 PM......Begin 10-minute built-in hold (T-minus 20m)
06:38 PM......NASA test director countdown briefing
06:38 PM......Resume countdown (T-minus 20m)

06:39 PM......Backup flight computer to OPS 1
06:43 PM......KSC area clear to launch

06:49 PM......Begin final built-in hold (T-minus 9m)
07:19 PM......NTD launch status verification
07:34:44 PM...Resume countdown (T-minus 9m)

07:36:14 PM...Orbiter access arm retraction
07:38:44 PM...Launch window opens
07:38:44 PM...Hydraulic power system (APU) start
07:38:49 PM...Terminate LO2 replenish
07:39:44 PM...Purge sequence 4 hydraulic test
07:39:44 PM...IMUs to inertial
07:39:49 PM...Aerosurface profile
07:40:14 PM...Main engine steering test
07:40:49 PM...LO2 tank pressurization
07:41:09 PM...Fuel cells to internal reactants
07:41:14 PM...Clear caution-and-warning memory
07:41:44 PM...Crew closes visors
07:41:47 PM...LH2 tank pressurization
07:42:54 PM...SRB joint heater deactivation
07:43:13 PM...Shuttle GPCs take control of countdown
07:43:23 PM...SRB steering test
07:43:37 PM...Main engine start (T-6.6 seconds)
07:43:44 PM...SRB ignition (LAUNCH)