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.

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

Fri  04/02/10

02:30 AM......Call to stations
03:00 AM......Countdown begins
12:00 PM......Crew sleep begins
01:00 PM......Fuel cell reactant load preps
06:30 PM......MEC/SRB power up
07:00 PM......Clear crew module

07:00 PM......Begin 4-hour built-in hold
07:00 PM......Clear blast danger area
07:45 PM......Orbiter pyro-initiator controller test
07:55 PM......SRB PIC test
08:00 PM......Crew wakeup
08:55 PM......Master events controller pre-flight BITE test
11:00 PM......Resume countdown

Sat  04/03/10

12:30 AM......Fuel cell oxygen loading begins
03:00 AM......Fuel cell oxygen load complete
03:00 AM......Fuel cell hydrogen loading begins
05:30 AM......Fuel cell hydrogen loading complete
06:30 AM......Pad open; ingress white room

07:00 AM......Begin 9-hour built-in hold
07:00 AM......PRSD offload
09:00 AM......Crew module clean and vacuum
12:00 PM......Crew sleep begins
12:30 PM......OMBUU demate
01:00 PM......Remove APU vent covers
01:30 PM......MPS 2000 psi GSE
04:00 PM......Countdown resumes

04:00 PM......Main engine preps
04:00 PM......MECs 1 and 2 on; avionics system checkout
06:00 PM......FRCS Tyvek cover remova/inspect
08:00 PM......Crew wakeup
10:30 PM......Deflate RSS dock seals; tile inspection
11:00 PM......Tile inspection
11:00 PM......TSM prepped for fueling

Sun  04/04/10

12:00 AM......Begin 13-hour 56-minute hold
12:00 AM......L-1 engineering briefing
12:15 AM......Crew weather briefing
12:30 AM......Crew orbiter/payload briefings
01:00 AM......NASA TV coverage of Soyuz TMA-18 docking
01:28 AM......Soyuz TMA-18 docking with ISS
01:30 AM......ASP crew module inspection
01:30 AM......OIS communications check
03:20 AM......JSC flight control team on station
03:30 AM......Comm activation
04:00 AM......Crew module voice checks
04:30 AM......Soyuz TMA-18/ISS hatch opening
05:00 AM......Flight crew equipment late stow
09:30 AM......RSS to park position
10:30 AM......Final TPS, debris inspection
11:00 AM......Ascent switch list
12:00 PM......Crew sleep begins
01:56 PM......Resume countdown

02:16 PM......Pad clear of non-essential personnel
02:16 PM......APU bite test
03:06 PM......Fuel cell activation
03:56 PM......Booster joint heater activation
04:26 PM......MEC pre-flight bite test
04:41 PM......Tanking weather update
05:26 PM......Final fueling preps; launch area clear
05:56 PM......Red crew assembled
06:41 PM......Fuel cell integrity checks complete

06:56 PM......Begin 2-hour built-in hold (T-minus 6 hours)
07:06 PM......Safe-and-arm PIC test
07:56 PM......External tank ready for loading
08:00 PM......Crew wakeup
08:19 PM......Mission management team tanking meeting
08:45 PM......NASA TV fueling coverage begins
08:56 PM......Resume countdown (T-minus 6 hours)

08:56 PM......LO2, LH2 transfer line chilldown
09:00 PM......Final crew medical checks
09:06 PM......Main propulsion system chill down
09:06 PM......LH2 slow fill
09:36 PM......LO2 slow fill
09:41 PM......Hydrogen ECO sensors go wet
09:46 PM......LO2 fast fill
09:49 PM......Crew medical checks
09:56 PM......LH2 fast fill
11:51 PM......LH2 topping
11:56 PM......LH2 replenish
11:56 PM......LO2 replenish

11:56 PM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours)
11:56 PM......Closeout crew to white room
11:56 PM......External tank in stable replenish mode

Mon  04/05/10

12:11 AM......Astronaut support personnel comm checks
12:41 AM......Pre-ingress switch reconfig
01:15 AM......NASA TV launch coverage begins
01:56 AM......Final crew weather briefing
02:01 AM......Crew suit up begins
02:26 AM......Resume countdown (T-minus 3 hours)

02:31 AM......Crew departs O&C building
03:01 AM......Crew ingress
03:51 AM......Astronaut comm checks
04:16 AM......Hatch closure
04:46 AM......White room closeout

05:06 AM......Begin 10-minute built-in hold (T-minus 20m)
05:16 AM......NASA test director countdown briefing
05:16 AM......Resume countdown (T-minus 20m)

05:17 AM......Backup flight computer to OPS 1
05:21 AM......KSC area clear to launch

05:27 AM......Begin final built-in hold (T-minus 9m)
05:57:23 AM...NTD launch status verification
06:12:23 AM...Resume countdown (T-minus 9m)

06:16:23 AM...Orbiter access arm retraction
06:16:23 AM...Launch window opens
06:16:23 AM...Hydraulic power system (APU) start
06:16:28 AM...Terminate LO2 replenish
06:17:23 AM...Purge sequence 4 hydraulic test
06:17:23 AM...IMUs to inertial
06:17:28 AM...Aerosurface profile
06:17:53 AM...Main engine steering test
06:18:28 AM...LO2 tank pressurization
06:18:48 AM...Fuel cells to internal reactants
06:18:53 AM...Clear caution-and-warning memory
06:19:23 AM...Crew closes visors
06:19:26 AM...LH2 tank pressurization
06:20:33 AM...SRB joint heater deactivation
06:20:52 AM...Shuttle GPCs take control of countdown
06:21:02 AM...SRB steering test
06:21:16 AM...Main engine start (T-6.6 seconds)
06:21:23 AM...SRB ignition (LAUNCH)