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.

HH...MM...SS...EDT...........EVENT

Fri  05/13/11

...............06:30 AM......Call to stations
73...56...00...07:00 AM......Countdown begins
63...56...00...05:00 PM......Fuel cell reactant load preps
58...26...00...10:30 PM......MEC/SRB power up
57...56...00...11:00 PM......Clear crew module

57...56...00...11:00 PM......Begin 4-hour built-in hold
57...56...00...11:00 PM......Clear blast danger area
57...11...00...11:45 PM......Orbiter pyro-initiator controller test

Sat  05/14/11

56...56...00...12:00 AM......SRB PIC test
56...11...00...12:45 AM......Master events controller pre-flight BITE test
53...56...00...03:00 AM......Resume countdown

52...26...00...04:30 AM......Fuel cell oxygen loading begins
49...56...00...07:00 AM......Fuel cell oxygen load complete
49...56...00...07:00 AM......Fuel cell hydrogen loading begins
47...26...00...09:30 AM......Fuel cell hydrogen loading complete
46...26...00...10:30 AM......Pad open; ingress white room

45...56...00...11:00 AM......Begin 8-hour built-in hold
45...56...00...11:00 AM......PRSD offload
44...56...00...12:00 PM......Crew module clean and vacuum
41...56...00...03:00 PM......Remove APU vent covers
40...56...00...04:00 PM......SSME throat plug removal
39...26...00...05:30 PM......OMBUU demate
37...26...00...07:30 PM......Countdown resumes

37...56...00...07:00 PM......Main engine preps
37...56...00...07:00 PM......MECs 1 and 2 on; avionics system checkout
34...56...00...10:00 PM......FRCS Tyvek cover remova/inspect

Sun  05/15/11

31...26...00...01:30 AM......Deflate RSS dock seals; tile inspection
30...56...00...02:00 AM......Tile inspection
30...56...00...02:00 AM......TSM prepped for fueling

29...56...00...03:00 AM......Begin 13-hour 36-minute hold
28...26...00...04:30 AM......RSS rotation preps
28...26...00...04:30 AM......OIS communications check with JSC
28...11...00...04:45 AM......Crew weather briefing
27...36...00...05:20 AM......JSC flight control team on station
26...56...00...06:00 AM......L-1 engineering briefing
26...26...00...06:30 AM......Comm activation
25...56...00...07:00 AM......Crew module voice checks
24...56...00...08:00 AM......Flight crew equipment late stow
20...56...00...12:00 PM......RSS to park position
19...56...00...01:00 PM......Final TPS, debris inspection
19...26...00...01:30 PM......Ascent switch list
16...20...00...04:36 PM......Resume countdown

16...00...00...04:56 PM......Pad clear of non-essential personnel
16...00...00...04:56 PM......APU bite test
15...10...00...05:46 PM......Fuel cell activation
14...20...00...06:36 PM......Booster joint heater activation
13...50...00...07:06 PM......MEC pre-flight bite test
13...35...00...07:21 PM......Tanking weather update
12...50...00...08:06 PM......Final fueling preps; launch area clear
12...20...00...08:36 PM......Red crew assembled
11...35...00...09:21 PM......Fuel cell integrity checks complete

11...20...00...09:36 PM......Begin 2-hour built-in hold (T-minus 6 hours)
11...10...00...09:46 PM......Safe-and-arm PIC test
10...32...00...10:24 PM......Crew wakeup
10...20...00...10:36 PM......External tank ready for loading
10...02...00...10:54 PM......Mission management team tanking meeting
09...46...00...11:10 PM......NASA TV fueling coverage begins
09...20...00...11:36 PM......Resume countdown (T-minus 6 hours)

09...20...00...11:36 PM......LO2, LH2 transfer line chilldown
09...10...00...11:46 PM......Main propulsion system chill down
09...10...00...11:46 PM......LH2 slow fill

Mon  05/16/11

08...40...00...12:16 AM......LO2 slow fill
08...35...00...12:21 AM......Hydrogen ECO sensors go wet
08...30...00...12:26 AM......LO2 fast fill
08...20...00...12:36 AM......LH2 fast fill
06...25...00...02:31 AM......LH2 topping
06...20...00...02:36 AM......LH2 replenish
06...20...00...02:36 AM......LO2 replenish

06...20...00...02:36 AM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours)
06...20...00...02:36 AM......Closeout crew to white room
06...20...00...02:36 AM......External tank in stable replenish mode
06...17...00...02:39 AM......Ascent flight control team on console
06...05...00...02:51 AM......Astronaut support personnel comm checks
05...35...00...03:21 AM......Pre-ingress switch reconfig
05...16...00...03:40 AM......NASA TV launch coverage begins
04...25...00...04:31 AM......Final crew weather briefing
04...15...00...04:41 AM......Crew suit up begins
03...50...00...05:06 AM......Resume countdown (T-minus 3 hours)

03...45...00...05:11 AM......Crew departs O&C building
03...15...00...05:41 AM......Crew ingress
02...25...00...06:31 AM......Astronaut comm checks
02...00...00...06:56 AM......Hatch closure
01...30...00...07:26 AM......White room closeout

01...10...00...07:46 AM......Begin 10-minute built-in hold (T-minus 20m)
01...00...00...07:56 AM......NASA test director countdown briefing
01...00...00...07:56 AM......Resume countdown (T-minus 20m)

00...59...00...07:57 AM......Backup flight computer to OPS 1
00...55...00...08:01 AM......KSC area clear to launch

00...49...00...08:07 AM......Begin final built-in hold (T-minus 9m)
00...24...00...08:32 AM......NTD launch status verification
00...09...00...08:47:28 AM...Resume countdown (T-minus 9m)

00...07...30...08:48:58 AM...Orbiter access arm retraction
00...05...00...08:56:28 AM...Launch window opens (placeholder; not needed for STS-134)
00...05...00...08:51:28 AM...Hydraulic power system (APU) start
00...04...55...08:51:33 AM...Terminate LO2 replenish
00...04...00...08:52:28 AM...Purge sequence 4 hydraulic test
00...04...00...08:52:28 AM...IMUs to inertial
00...03...55...08:52:33 AM...Aerosurface profile
00...03...30...08:52:58 AM...Main engine steering test
00...02...55...08:53:33 AM...LO2 tank pressurization
00...02...35...08:53:53 AM...Fuel cells to internal reactants
00...02...30...08:53:58 AM...Clear caution-and-warning memory
00...02...00...08:54:28 AM...Crew closes visors
00...01...57...08:54:31 AM...LH2 tank pressurization
00...00...50...08:55:38 AM...SRB joint heater deactivation
00...00...31...08:55:57 AM...Shuttle GPCs take control of countdown
00...00...21...08:56:07 AM...SRB steering test
00...00...07...08:56:21 AM...Main engine start (T-6.6 seconds)
00...00...00...08:56:28 AM...SRB ignition (LAUNCH)