Orbiter: Discovery
Mission: STS-131
Payload: Leonardo
Launch: April 5, 2010
Time: 6:21 a.m. EDT
Site: Pad 39A, Kennedy Space Center
Landing: April 18 @ approx. 8:30 a.m.
Site: KSC's Shuttle Landing Facility

Launch Windows

Countdown Timeline

NASA TV Schedule

Ascent Timeline

Master Flight Plan

Mission Video Vault

High Definition Video

STS-131 Archive

Mission Status Center

By Justin Ray

Welcome to Spaceflight Now's live coverage of space shuttle Discovery's STS-131 mission to the International Space Station. Text updates will appear automatically; there is no need to reload the page.
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2105 GMT (5:05 p.m. EDT)
The shuttle Discovery's Ku-band antenna system, used as a radar dish during rendezvous operations and to transmit video and data to and from the ground through NASA communications satellites, suffered a malfunction of some sort after the shuttle reached orbit Monday. Engineers are troubleshooting, but the system may be out of action for the duration of Discovery's mission.

Read our full story.
1612 GMT (12:12 p.m. EDT)
Flight controllers in Houston are bidding goodnight to commander Alan Poindexter. For now, the crew has been told to assume the Ku-band antenna system is failed entirely.

The astronauts heading to bed for an eight-hour sleep period. They'll be awakened for Flight Day 2 at 8:21 p.m. EDT.
1515 GMT (11:15 a.m. EDT)
Engineers are troubleshooting an apparent malfunction in the shuttle Discovery's Ku-band antenna system.

Read our full story.
1420 GMT (10:20 a.m. EDT)
Troubleshooting continues on the problems experienced during activation of Discovery's Ku-band antenna system, which is used for radar during rendezvous and high-speed data relay. Electronics on both sides of the system have experienced possible failures.

In the near-term, Mission Control says they can deal with the lack of Ku-band. Tomorrow's inspection data can be recorded onboard the shuttle and then downlinked via the space station's assets after docking. And during Wednesday's approach and rendezvous, the astronauts have other tools they can use.
1400 GMT (10:00 a.m. EDT)
Replays from different cameras that tracked this morning's launch have been posted in High Definition for Spaceflight Now+Plus customers. A full listing of video can be seen here.

If you are not yet a subscriber for our premium video service, learn more here.
1350 GMT (9:50 a.m. EDT)
The shuttle Discovery, carrying a crew of seven and 10 tons of supplies and equipment bound for the International Space Station, rocketed into orbit early Monday to kick off a three-spacewalk resupply mission.

Read our full story.
1308 GMT (9:08 a.m. EDT)
Space shuttle Discovery and crew have completed NC1 engine firing to adjust the orbital path to the International Space Station. The 62-second-long course correction maneuver using both Orbital Maneuvering System engines changed the shuttle's velocity by 98 feet per second.
1305 GMT (9:05 a.m. EDT)
A gallery of photos of shuttle Discovery's dazzling predawn launch from Kennedy Space Center can be viewed here.
1243 GMT (8:43 a.m. EDT)
The latest version of the NASA Television schedule (Rev. A) can be downloaded here.
1241 GMT (8:41 a.m. EDT)
The ascent team of flight controllers led by Bryan Lunney is handing over to the Orbit 2 team and flight director Mike Sarafin to oversee the rest of the astronauts' workday.
1228 GMT (8:28 a.m. EDT)
The crew run into some sort of glitch when activating the Ku-band antenna system.
1208 GMT (8:08 a.m. EDT)
CAPCOM astronaut Rick Sturckow in Mission Control just told the crew that launch video and imagery continues to be analyzed but there's no concerns noted so far.
1205 GMT (8:05 a.m. EDT)
Discovery's antenna for Ku-band high-speed communications is being deployed and activated.
1153 GMT (7:53 a.m. EDT)
Go for on-orbit operations! That's the formal call from Mission Control indicating the shuttle is in good shape following launch and the Discovery crew can proceed with mission activities.

Both 60-foot-long payload bay doors of shuttle Discovery have been opened and the radiators deployed.

Over the next few hours, the astronauts will busily begin setting up the onboard computer network and downlinking imagery and data gathered during ascent. The crew will be getting out of their launch and entry spacesuits, stowing away the mission specialists' seats and getting some dinner as well. An eight-hour sleep period begins at 12:21 p.m. EDT.
1145 GMT (7:45 a.m. EDT)
The radiator preparatory steps have been performed and Mission Control has given the astronauts a "go" for payload bay door opening.
1130 GMT (7:30 a.m. EDT)
The crew continues working through its post-launch checklist. The next big milestones will be opening up the payload bay doors and deploying the Ku-band communications antenna.
1121 GMT (7:21 a.m. EDT)
T+plus 60 minutes. High Definition video of the STS-131 launch is available to Spaceflight Now+Plus customers. A full listing of video can be seen here.

If you are not yet a subscriber for our premium video service, learn more here.
1101 GMT (7:01 a.m. EDT)
T+plus 39 minutes, 44 seconds. The twin Orbital Maneuvering System engines on the tail of Discovery have been fired successfully to propel the shuttle the rest of the way to orbit.
1058 GMT (6:58 a.m. EDT)
T+plus 37 minutes, 34 seconds. Ignition of the OMS engines has been confirmed.
1057 GMT (6:57 a.m. EDT)
T+plus 36 minutes. Discovery in the proper orientation for the upcoming maneuvering burn to raise the orbit toward the International Space Station. This will be a 2-minute, 9-second firing resulting in an orbit of 161 by 141 statute miles.
1046 GMT (6:46 a.m. EDT)
T+plus 25 minutes. Commander Alan Poindexter and pilot Jim Dutton are getting Discovery maneuvered into the proper position for the OMS 2 engine burn.
1044 GMT (6:44 a.m. EDT)
T+plus 23 minutes. The two flapper doors on the belly of Discovery are being swung closed to shield the umbilicals that had connected to the external fuel tank.
1037 GMT (6:37 a.m. EDT)
T+plus 16 minutes. The three Auxiliary Power Units have been shut down as planned by pilot Jim Dutton.
1030 GMT (6:30 a.m. EDT)
T+plus 9 minutes, 30 seconds. It was a nominal MECO. A quick boost from the Orbital Maneuvering System engines is not required to reach the planned preliminary sub-orbital trajectory.
1030 GMT (6:30 a.m. EDT)
T+plus 9 minutes, 15 seconds. Still cameras embedded in Discovery's umbilical well are taking images of the external tank to document its foam.
1030 GMT (6:30 a.m. EDT)
T+plus 8 minutes, 47 seconds. The emptied external tank has been jettisoned from the belly of space shuttle Discovery. The tank will fall back into the atmosphere where it will burn up harmlessly.
1029 GMT (6:29 a.m. EDT)
T+plus 8 minutes, 31 seconds. MECO. Main Engine Cutoff confirmed! Shuttle Discovery is back in space for its 38th mission, a voyage that is hauling thousands of pounds of vital resupply items, new science gear and living accommodations for the International Space Station.
1029 GMT (6:29 a.m. EDT)
T+plus 7 minutes, 35 seconds. The main engines are beginning to throttle down to ensure the shuttle does not experience forces greater than 3 g's as it continues to accelerate prior to engine shutdown.
1028 GMT (6:28 a.m. EDT)
T+plus 7 minutes, 7 seconds. Single engine press. The shuttle can reach orbit on the power from a single main engine should two fail at this point. But all three continue to fire properly.
1028 GMT (6:28 a.m. EDT)
T+plus 6 minutes, 35 seconds. "Press to MECO." Discovery can now achieve a safe orbit on two engines. All three remain in good shape.
1027 GMT (6:27 a.m. EDT)
T+plus 6 minutes. The shuttle has started rolling to a heads-up position to improve communications with the TDRS satellite network.
1027 GMT (6:27 a.m. EDT)
T+plus 5 minutes, 55 seconds. Discovery is 67 miles in altitude, 351 miles downrange from the launch pad, traveling at 6,000 mph.
1026 GMT (6:26 a.m. EDT)
T+plus 5 minutes, 25 seconds. "Press to ATO". Discovery can reach an orbit, albeit a low orbit, on two engines should one shut down now. But all three powerplants are still running just fine.
1026 GMT (6:26 a.m. EDT)
T+plus 5 minutes. Overseeing today's climb to orbit from the Mission Control Center is ascent flight director Bryan Lunney, son of legendary Apollo flight director Glynn Lunney. Seated alongside in Houston in direct radio contact with the crew is CAPCOM astronaut Rick Sturckow, a four-time shuttle flier.
1026 GMT (6:26 a.m. EDT)
T+plus 4 minutes, 40 seconds. Discovery will be tripling its speed in the next four minutes to reach orbital velocity of nearly 17,500 mph.
1025 GMT (6:25 a.m. EDT)
T+plus 4 minutes, 30 seconds. Discovery is 63 miles in altitude, 181 miles downrange from the launch pad, traveling at 6,000 mph.
1025 GMT (6:25 a.m. EDT)
T+plus 4 minutes. Negative return. The shuttle has passed the point where Discovery could turn around and make an emergency landing at Kennedy Space Center in the event of a main engine problem. Landing sites in France and Spain are now available to Discovery in the unlikely event an abort occurs during the remainder of today's launch.
1024 GMT (6:24 a.m. EDT)
T+plus 2 minutes, 55 seconds. Commander Alan Poindexter just received the "Two-engine TAL" call from CAPCOM Rick Sturckow in Mission Control. The call means Discovery can now reach a Transatlantic Abort Landing site if one main engine fails. However, all three engines continue to burn normally.
1024 GMT (6:24 a.m. EDT)
T+plus 2 minutes, 35 seconds. The Orbital Maneuvering System engines have been ignited for an additional kick of thrust during Discovery's climb uphill.
1023 GMT (6:23 a.m. EDT)
T+plus 2 minutes, 20 seconds. Guidance is converging as programmed. Discovery's engine nozzles are swiveling to steer the ship toward a precise point for main engine cutoff about six minutes from now.
1023 GMT (6:23 a.m. EDT)
T+plus 2 minutes, 10 seconds. Mission Control confirms a good jettison of the solid rocket boosters has occurred. The spent boosters will parachute into the Atlantic Ocean for retrieval. Discovery continues its streak toward space on the power generated by the three liquid-fueled main engines.
1023 GMT (6:23 a.m. EDT)
T+plus 1 minute, 45 seconds. Joining commander Alan Poindexter and pilot Jim Dutton is flight engineer Dottie Metcalf-Lindenburger and mission specialist Rick Mastracchio. Seated down on the flight deck are Stephanie Wilson, Naoko Yamazaki and Clay Anderson.
1022 GMT (6:22 a.m. EDT)
T+plus 90 seconds. The space shuttle now weighs just half of what it did at liftoff. The solid rocket boosters are burning 11,000 pounds of propellant every second. The main engines are guzzling a half-ton of liquid fuel per second from the external tank.
1022 GMT (6:22 a.m. EDT)
T+plus 63 seconds. Discovery's three main engines have revved back up to their 104 percent power setting. And Mission Control has given the "go at throttle up" call.
1022 GMT (6:22 a.m. EDT)
T+plus 60 seconds. Discovery is flying straight and steady on a northeasterly heading that will take the shuttle up the U.S. eastern seaboard over the next several minutes.
1022 GMT (6:22 a.m. EDT)
T+plus 40 seconds. Discovery's three liquid-fueled main engines are throttling down to their 72 percent power setting to ease the strain on the vehicle during passage through the region of maximum aerodynamic stresses.
1021 GMT (6:21 a.m. EDT)
T+plus 20 seconds. Cape Canaveral gets an early sunrise as the shuttle leaves the planet with a blinding light, riding nearly seven million pounds of Earth-shaking thrust toward space.
1021 GMT (6:21 a.m. EDT)
T+plus 15 seconds. Houston is now controlling as Discovery maneuvers to the proper course for intercepting the space station early Wednesday.
1021:25 GMT (6:21:25 a.m. EDT)
T-minus 10 seconds, go for ignition of the space shuttle main engines, 5, 4, 3, 2, 1 and LIFTOFF! Liftoff of shuttle Discovery, launching new science and supplies to support our orbiting space laboratory!
1020:54 GMT (6:20:54 a.m. EDT)
T-minus 31 seconds. AUTO SEQUENCE START! The handoff has occurred from the Ground Launch Sequencer to the space shuttle. Discovery's computers now controlling.

In the next few seconds, the solid rocket booster hydraulic steering system will be started, the orbiter's body flap and speed brake moved to their launch positions, the firing chain armed. Main engine ignition begins at T-minus 6.6 seconds.
1020:25 GMT (6:20:25 a.m. EDT)
T-minus 1 minute. Computers are verifying that the main engines are ready for ignition. Sound suppression water system is armed. The system will activate at T-minus 16 seconds to suppress the sound produced at launch. And the residual hydrogen burn ignitors are armed. They will be fired at T-minus 10 seconds to burn off hydrogen gas from beneath the main engine nozzles.

Shortly, the external tank strut heaters will be turned off; Discovery will transition to internal power; the liquid oxygen and liquid hydrogen outboard fill and drain valves will be closed; the payload bay vent doors will be positioned for the launch; and the gaseous oxygen vent arm will be verified fully retracted.
1019:55 GMT (6:19:55 a.m. EDT)
Now 90 seconds from the launch of Discovery.
1019:25 GMT (6:19:25 a.m. EDT)
T-minus 2 minutes. The astronauts are being instructed to close and lock the visors on their launch and entry helmets.

At T-minus 1 minute, 57 seconds the replenishment to the flight load of liquid hydrogen in the external tank will be terminated and tank pressurization will begin.
1018:55 GMT (6:18:55 a.m. EDT)
T-minus 2 minutes, 30 seconds. The external tank liquid oxygen vent valve has been closed and pressurization of the LOX tank has started.

Discovery's power-producing fuel cells are transferring to internal reactants. The units will begin providing all electricity for the mission beginning at T-50 seconds.

And pilot Jim Dutton has been asked to clear the caution and warning memory system aboard Discovery. He will verify no unexpected errors in the system.

In the next few seconds, the gaseous oxygen vent hood will be removed from atop the external tank. Verification that the swing arm is fully retracted will be made by the ground launch sequencer at the T-minus 37 second mark.
1018:25 GMT (6:18:25 a.m. EDT)
T-minus 3 minutes. Orbiter steering check is now complete and the main engine nozzles are in their start positions.
1017:55 GMT (6:17:55 a.m. EDT)
T-minus 3 minutes, 30 seconds. The main engine nozzles now being moved through a computer controlled test pattern to demonstrate their readiness to support guidance control during launch.
1017:25 GMT (6:17:25 a.m. EDT)
T-minus 4 minutes. Activation of the APUs is complete. The three units are up and running normally.

And the final helium purge sequence is underway in the main propulsion system. This procedure readies fuel system valves for engine start. In the next few seconds, the aerosurfaces of Discovery will be run through a pre-planned mobility test to ensure readiness for launch. This is also a dress rehearsal for flight of the orbiter's hydraulic systems.
1016:25 GMT (6:16:25 a.m. EDT)
T-minus 5 minutes. The "go" has been given for for Auxiliary Power Unit start. Pilot Jim Dutton is now flipping three switches in Discovery's cockpit to start each of the three APU's. The units, located in the aft compartment of Discovery, provide the pressure needed to power the hydraulic systems of the shuttle. The units will be used during the launch and landing phases of the mission for such events as moving the orbiter's aerosurfaces, gimbaling the main engine nozzles and deploying the landing gear.

Over the course of the next minute, the orbiter's heaters will be configured for launch by commander Alan Poindexter, the fuel valve heaters on the main engines will be turned off in preparation for engine ignition at T-6.6 seconds and the external tank and solid rocket booster safe and arm devices will be armed.
1015:55 GMT (6:15:55 a.m. EDT)
T-minus 5 minutes, 30 seconds. APU pre-start is complete and the units are ready for activation. The orbiters flight data recorders have gone into the record mode to collect measurements of shuttle systems performance during flight.
1015:25 GMT (6:15:25 a.m. EDT)
T-minus 6 minutes. Pilot Jim Dutton has been asked by the orbiter test conductor to pre-start the orbiter Auxiliary Power Units. This procedure readies the three APU's for their activation after the countdown passes T-minus 5 minutes.
1013:55 GMT (6:13:55 a.m. EDT)
T-minus 7 minutes, 30 seconds. The Ground Launch Sequencer has started pulling the orbiter access arm away from the crew hatch on the port side of the vehicle. The arm was the passage way for the astronauts to board Discovery a few hours ago. The arm can be re-extended very quickly should the need arise later in the countdown.
1013:25 GMT (6:13:25 a.m. EDT)
T-minus 8 minutes and counting. Pilot Jim Dutton has flipped the switches in the cockpit of Discovery to directly connect the three onboard fuel cells with the essential power buses. Also, the stored program commands have been issued to the orbiter for antenna alignment and management during launch.
1012:25 GMT (6:12:25 a.m. EDT)
T-minus 9 minutes and counting! The Ground Launch Sequencer has been initiated. The computer program is located in a console in the Firing Room of the Complex 39 Launch Control Center. The GLS is the master of events through liftoff. During the last 9 minutes of the countdown, the computer will monitor as many as a thousand different systems and measurements to ensure that they do not fall out of any pre-determine red-line limits. At T-minus 31 seconds, the GLS will hand off to the onboard computers of Discovery to complete their own automatic sequence of events through the final half minute of the countdown.
1011:25 GMT (6:11:25 a.m. EDT)
Now 10 minutes from blastoff.
1010 GMT (6:10 a.m. EDT)
The countdown will resume from the T-minus 9 minute mark at 6:12:25 a.m. EDT.
1009 GMT (6:09 a.m. EDT)
NASA launch director Pete Nickolenko has conducted his poll and given approval to resume the countdown for liftoff at 6:21 a.m. EDT!
1008 GMT (6:08 a.m. EDT)
The poll by NASA test director Steve Payne confirms there are no technical issues or constraints standing in the way of launch at 6:21 a.m. EDT. The Range also reports "go" on the local weather. And Mission Control says that weather at the abort landing sites is acceptable.
1005 GMT (6:05 a.m. EDT)
The International Space Station has risen above the horizon here at the Kennedy Space Center for a beautiful pass overhead.
1004 GMT (6:04 a.m. EDT)
Eight minutes are remaining in this built-in hold. There are no technical issues being worked by the launch team. Final readiness polls will be conducted over the next few moments.
1001 GMT (6:01 a.m. EDT)
We're now 20 minutes from Discovery's launch on an eight-and-a-half minute trek to space. At main engine cutoff, Discovery will be flying on a suborbital trajectory with a high point of 136 statute miles and low point of 36 statute miles, inclined 51.6 degrees to the equator. A half-hour later, the twin orbital maneuvering engines will be fired to place the shuttle into a 161 by 141 statute mile orbit.
0956 GMT (5:56 a.m. EDT)
The Range is "go" for launch again. Part of the system in question has been restored, which is sufficient to proceed with liftoff.
0955 GMT (5:55 a.m. EDT)
Powering space shuttle Discovery throughout its eight-and-a-half minute climb to orbit will be the three main engines built by Pratt & Whitney Rocketdyne. The cryogenic powerplants are fed with liquid hydrogen and liquid oxygen stored in the external fuel tank.

In the engine No. 1 position today is the Block 2-2045 engine now making its eleventh launch. It has accumulated 5,996 seconds of total firing time on the previous missions, plus ground testing. STS-89 was its debut flight.

Making its second launch is the Block 2-2060 in the engine No. 2 position. This powerplant has 1,931 seconds of firing time including ground tests and the earlier launch on STS-127.

And Block 2-2054 is engine No. 3 on Discovery. It has nine previous flights, starting with STS-101, and some 5,634 seconds of firing time.
0952 GMT (5:52 a.m. EDT)
The Range problem is with the command message encoder verifier, a NASA spokesman says.
0946 GMT (5:46 a.m. EDT)
The Air Force-controlled Eastern Range is reporting a problem of some sort. Teams are working the issue and expect to provide an update to the space shuttle folks by 6:10 a.m. EDT.
0945 GMT (5:45 a.m. EDT)
At launch, the space station will be flying 220 miles over the Atlantic Ocean southwest of Ireland. Liftoff at 6:21 a.m. EDT is timed to place Discovery on course to dock with the station two days from now.
0936 GMT (5:36 a.m. EDT)
The reusable solid rocket boosters, built by ATK, provide the primary thrust to propel the space shuttle away from Earth during the initial two minutes of flight. The 11 sections on each booster flying on Discovery are a mixture of refurbished and brand new hardware. The upper cylinder on the right-hand booster, for example, flew on the very first shuttle mission in 1981. And there are two unused sections on the left-hand booster. In all, the twin boosters flying today have reused segments and pieces that trace back to 60 previous shuttle launches and 10 ground test-firings.

Detailed history information about Discovery's two boosters can be seen in this PDF download here.

The boosters will parachute into the Atlantic Ocean where a pair of retrieval ships are standing by to recover the rockets and tow them back to shore.
0931 GMT (5:31 a.m. EDT)
A reminder that if you will be away from your computer but would like to receive launch updates, sign up for our Twitter feed to get text messages on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)
0927 GMT (5:27 a.m. EDT)
T-minus 9 minutes and holding. Countdown clocks have gone into the planned 45-minute, 25-second built-in hold. Launch is targeted for 6:21:25 a.m. EDT.

Here is a countdown summary of the key events upcoming:

05:27 AM......Begin final built-in hold (T-minus 9m)
05:57:25 AM...NTD launch status verification

06:12:25 AM...Resume countdown (T-minus 9m)
06:16:25 AM...Orbiter access arm retraction
06:16:25 AM...Launch window opens
06:16:25 AM...Hydraulic power system (APU) start
06:16:30 AM...Terminate liquid oxygen replenish
06:17:25 AM...Purge sequence 4 hydraulic test
06:17:25 AM...Inertial measurement units to inertial
06:17:30 AM...Aerosurface profile
06:17:55 AM...Main engine steering test
06:18:30 AM...Liquid oxygen tank pressurization
06:18:50 AM...Fuel cells to internal reactants
06:18:55 AM...Clear caution-and-warning memory
06:19:25 AM...Crew closes visors
06:19:28 AM...Liquid hydrogen tank pressurization
06:20:35 AM...Booster joint heater deactivation
06:20:54 AM...Shuttle computers take control of countdown
06:21:04 AM...Booster steering test
06:21:18 AM...Main engine start (T-6.6 seconds)

06:21:25 AM...Booster ignition (LAUNCH)

06:21:35 AM...Shuttle roll begins
06:21:43 AM...Roll program complete
06:22:03 AM...Main engine throttle down to 72 percent
06:22:17 AM...Main engine throttle up to 104.5 percent
06:22:24 AM...Maximum aerodynamic pressure
06:23:30 AM...Booster separation
06:24:00 AM...Trans-Atlantic abort options available
06:25:12 AM...KSC abort options end (negative return)
06:26:36 AM...Abort to orbit options available
06:27:12 AM...The shuttle rolls to a heads up orientation
06:27:40 AM...Can reach planned orbit with one engine out
06:29:49 AM...Main engine cutoff command
06:34:00 AM...Launch replays on NASA TV
07:30:00 AM...Post-launch news conference on NASA TV
07:46:00 AM...Payload bay doors open
10:56:00 AM...External tank video downlink
12:21:00 PM...Crew sleep begins
08:21:00 PM...Crew wakeup (begins flight day 2)
0924 GMT (5:24 a.m. EDT)
The Main Propulsion System helium system is being reconfigured by pilot Jim Dutton. Soon the gaseous nitrogen purge to the aft skirts of the solid rocket boosters will be started.
0923 GMT (5:23 a.m. EDT)
Commander Alan Poindexter is enabling the abort steering instrumentation.
0922 GMT (5:22 a.m. EDT)
Mission Control in Houston is loading Discovery's onboard computers with the proper guidance parameters based on the projected launch time.
0921 GMT (5:21 a.m. EDT)
Now one hour away from liftoff.

Pilot Jim Dutton has configured the displays inside Discovery's cockpit for launch.
0918 GMT (5:18 a.m. EDT)
The Orbiter Closeout Crew is driving away from the pad.
0916 GMT (5:16 a.m. EDT)
T-minus 20 minutes and counting. The countdown has resumed after a 10-minute hold. Clocks will tick down for the next 11 minutes to T-minus 9 minutes where the final planned hold is scheduled to occur. The hold length will be adjusted to synch up with today's preferred launch time of 6:21:25 a.m. EDT.

Discovery's onboard computers are now transitioning to the Major Mode-101 program, the primary ascent software. Also, engineers are dumping the Primary Avionics Software System (PASS) onboard computers. The data that is dumped from each of PASS computers is compared to verify that the proper software is loaded aboard for launch.
0914 GMT (5:14 a.m. EDT)
The official launch window has been revised based on the latest radar tracking of the space station's orbit. The usable liftoff period extends from 6:18:43 to 6:27:15 a.m. EDT.
0906 GMT (5:06 a.m. EDT)
T-minus 20 minutes and holding. The countdown has paused for a 10-minute built-in hold. Launch is scheduled for 6:21 a.m. EDT.

During this built-in hold, all computer programs in Firing Room 4 of the Complex 39 Launch Control Center will be verified to ensure that the proper programs are available for the countdown; the landing convoy status will be verified and the landing sites will be checked to support an abort landing during launch today; the Inertial Measurement Unit preflight alignment will be verified completed; and preparations are made to transition the orbiter onboard computers to Major Mode 101 upon coming out of the hold. This configures the computer memory to a terminal countdown configuration.
0900 GMT (5:00 a.m. EDT)
The latest High Definition video of the STS-131 launch preparations is available to Spaceflight Now+Plus customers. A full listing of video can be seen here.

If you are not yet a subscriber for our premium video service, learn more here.
0857 GMT (4:57 a.m. EDT)
The work to seal the shuttle's crew compartment hatch for flight is complete. And the closeout team that assisted the astronauts into Discovery today is stowing equipment in the White Room before leaving the launch pad now.
0856 GMT (4:56 a.m. EDT)
Commander Alan Poindexter is pressurizing the gaseous nitrogen system for Discovery's Orbital Maneuvering System engines and pilot Jim Dutton activated the gaseous nitrogen supply for the orbiter's Auxiliary Power Units' water spray boilers.
0852 GMT (4:52 a.m. EDT)
Mainline of the Ground Launch Sequencer has been completed. This is the master computer program that will run the final nine minutes of the countdown.
0848 GMT (4:48 a.m. EDT)
The ground pyrotechnic initiator controllers (PICs) are scheduled to be powered up around this time in the countdown. They are used to fire the solid rocket hold-down posts, liquid oxygen and liquid hydrogen tail service mast and external tank vent arm system pyros at liftoff and the space shuttle main engine hydrogen gas burn system prior to engine ignition.

The shuttle's two Master Events Controllers are being tested. They relay the commands from the shuttle's computers to ignite, and then separate the boosters and external tank during launch.
0826 GMT (4:26 a.m. EDT)
Current weather conditions at the Kennedy Space Center remain favorable and there's just a 20 percent chance of fog developing by launch time. And the overseas weather at the emergency landing sites won't be a worry today.
0823 GMT (4:23 a.m. EDT)
Discovery's hatch has been closed and locked.
0818 GMT (4:18 a.m. EDT)
The orbiter closeout team at the launch pad is shutting Discovery's crew module hatch for flight.
0815 GMT (4:15 a.m. EDT)
The pad crew is ready to close up Discovery's hatch.
0810 GMT (4:10 a.m. EDT)
A reminder that if you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text messages on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)
0805 GMT (4:05 a.m. EDT)
The astronauts are completing a series of radio communication checks with ground controllers.
0747 GMT (3:47 a.m. EDT)
The final Discovery astronaut has boarded the shuttle today. Former high school science teacher Dottie Metcalf-Lindenburger, mission specialist No. 2 and flight engineer, has now entered the hatch.

Check out her profile graphic.

Read Metcalf-Lindenburger's biography here.
0743 GMT (3:43 a.m. EDT)
Japanese astronaut Naoko Yamazaki, mission specialist No. 4 and "load master" for the supplies being delivered the space station on the flight, is taking the center seat on the middeck.

Check out her profile graphic.

Read Yamazaki's biography here.
0731 GMT (3:31 a.m. EDT)
Rick Mastracchio, mission specialist No. 1 and the lead spacewalker is ingressing the flight deck's aft-right seat.

Check out his profile graphic.

Read Mastracchio's biography here.
0730 GMT (3:30 a.m. EDT)
The weather status panel is all green and "go" once again.
0724 GMT (3:24 a.m. EDT)
Robotic arm operator and mission specialist No. 3 Stephanie Wilson has boarded to take the left-hand seat on the middeck.

Check out her profile graphic.

Read Wilson's biography here.
0723 GMT (3:23 a.m. EDT)
A check of the current weather conditions shows a "no go" situation because the visibility/cloud ceiling rule is being violated.
0721 GMT (3:21 a.m. EDT)
Three hours and counting until liftoff time. The countdown remains on schedule for launch at 6:21 a.m. EDT.
0715 GMT (3:15 a.m. EDT)
Discovery pilot Jim Dutton is making his way to the flight deck's front-right seat right now.

Check out his profile graphic.

Read Dutton' biography here.
0704 GMT (3:04 a.m. EDT)
Mission specialist No. 5 Clay Anderson just crawled through the hatch to take the right-hand seat on the middeck. He is one of the spacewalkers for the flight.

Check out his profile graphic.

Read Anderson's biography here.
0702 GMT (3:02 a.m. EDT)
Commander Alan Poindexter is the first astronaut to board the shuttle today, taking the forward-left seat on the flight deck.

Check out his profile graphic.

You can read Poindexter's biography here.
0650 GMT (2:50 a.m. EDT)
The astronauts are taking a few moments to gaze up at their spacecraft from the pad surface and getting their picture taken before ascending the tower.
0649 GMT (2:49 a.m. EDT)
Discovery's crew has arrived at launch pad 39A. The AstroVan came to a stop on the pad surface near the Fixed Service Structure tower elevator that will take the seven-person crew to the 195-foot level to begin boarding the shuttle.
0641 GMT (2:41 a.m. EDT)
The AstroVan is passing the 52-story Vehicle Assembly Building where Discovery was attached to its external tank and solid rocket boosters and the adjacent Launch Control Center.

The Press Site is located across the street, and reporters went outside to watch the passing convoy. This is a launch day tradition to say farewell and good luck to the astronaut crews.
0631 GMT (2:31 a.m. EDT)
The crew of commander Alan Poindexter, pilot Jim Dutton, spacewalkers Rick Mastracchio and Clay Anderson, robotics operator Stephanie Wilson, flight engineer and former teacher Dottie Metcalf-Lindenburger, and Japanese astronaut Naoko Yamazaki just emerged from their quarters to board the AstroVan for the ride from the Kennedy Space Center Industrial Area to launch pad 39A on the edge of the Atlantic Ocean.
0629 GMT (2:29 a.m. EDT)
The astronauts are heading down the hallway from the suitup room to board the elevator that will take them down to the AstroVan.
0626 GMT (2:26 a.m. EDT)
T-minus 3 hours and counting. The countdown clocks are ticking again after the planned two-and-a-half hour built-in hold. Clocks will proceed to T-minus 20 minutes when the next hold is scheduled. A final hold occurs at the T-minus 9 minute mark to synch up with the 6:21:25 a.m. EDT launch time.
0603 GMT (2:03 a.m. EDT)
Our launch webcast anchored by Miles O'Brien, with journalist David Waters and for space station commander Leroy Chiao is streaming live on the right-hand side of our page.
0600 GMT (2:00 a.m. EDT)
Space shuttle Discovery's astronauts -- four men and three women -- are donning their day-glow orange launch and entry partial pressure spacesuits. After final adjustments and pressure checks, the astronauts will depart the suitup room and take the elevator down to the ground level of the Operations and Checkout Building to board the AstroVan for the trip to launch pad 39A around 2:31 a.m.
0558 GMT (1:58 a.m. EDT)
The weather conditions at the Kennedy Space Center are favorable at this hour. The only worry for launch time is the development of fog that could violate visibility requirements. But so far, things are looking good.
0550 GMT (1:50 a.m. EDT)
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0525 GMT (1:25 a.m. EDT)
No technical issues are being reported by the launch team and weather conditions are acceptable right now.

Recent activities in the countdown have included calibrations of the orbiter's inertial measurement units, powering up Discovery's navigation systems, the pre-flight alignment of ground station antennas with the launch pad and communications checks with the Eastern Range.
0500 GMT (1:00 a.m. EDT)
The Final Inspection Team is out at the launch pad to scan the vehicle for any ice or debris concerns following fueling operations. The team is responsible for checking the shuttle and launch pad one last time prior to liftoff.

The team is comprised of engineers and safety officials from NASA, United Space Alliance and tank-builder Lockheed Martin. At the conclusion of their two-hour tour-of-duty, the team will have walked up and down the entire fixed service structure and mobile launcher platform.

The team is on the lookout for any abnormal ice or frost build-up on the vehicle and integrity of the external tank foam insulation.

The team uses a portable infrared scanner that gathers temperature measurements on the surface area of the shuttle and can spot leaks. The scanner will be used to obtain temperature data on the external tank, solid rocket boosters, space shuttle orbiter, main engines and launch pad structures. The scanner can also spot leaks of the cryogenic propellants, and due to its ability to detect distinct temperature differences, can spot any dangerous hydrogen fuel that is burning. The team member also is responsible for photo documentation.

The team wears the highly visible day-glow orange coveralls that are anti-static and flame resistant. Each member also has a self-contained emergency breathing unit that holds about 10 minutes of air.
0437 GMT (12:37 a.m. EDT)
For those of you keeping score at home, fueling began at 9:28 p.m. and concluded at 12:21 a.m. EDT.
0434 GMT (12:34 a.m. EDT)
With the hazardous tanking operation now completed, the Orbiter Closeout Crew and Final Inspection Team have arrived at the pad to perform their jobs. The closeout crew will ready Discovery's crew module for the astronauts' ingress in a couple of hours; and the inspection team will give the entire vehicle a check for any ice formation following fueling.
0429 GMT (12:29 a.m. EDT)
TANK FULL. Liquid oxygen has entered stable replenishment mode, officially completing today's three-hour external tank filling process.
0415 GMT (12:15 a.m. EDT)
The topping phase is underway on liquid oxygen. That tank is 98 percent full.
0401 GMT (12:01 a.m. EDT)
Liquid hydrogen loading has been completed. After reaching the 98 percent level, the topping sequence was performed. And now the stable replenishment mode has been activated to keep the tank full through the rest of the countdown, replacing the supercold propellant that naturally boils away.
0356 GMT (11:56 p.m. EDT Sun.)
T-minus 3 hours and holding. Clocks have entered a planned two-hour, 30-minute built-in hold. Additional pauses are scheduled at the T-minus 20 and T-minus 9 minute marks, setting up the countdown for launch at 6:21 a.m. EDT.
0330 GMT (11:30 p.m. EDT Sun.)
There are two tanks inside the shuttle's external fuel tank. The liquid oxygen tank occupies the top third of the bullet-shaped tank. It will be filled with 143,000 gallons of liquid oxygen chilled to minus 298 degrees Fahrenheit. The liquid hydrogen tank is contained in the bottom two-thirds of the external tank. It holds 385,000 gallons of liquid hydrogen chilled to minus 423 degrees Fahrenheit.
0258 GMT (10:58 p.m. EDT Sun.)
All is going well 90 minutes into the fueling operations for space shuttle Discovery.

The cryogenics flow from storage spheres at the pad, through feed lines to the mobile launcher platform, into Discovery's aft compartment and finally into the external fuel tank.
0227 GMT (10:27 p.m. EDT Sun.)
A short time ago, mission specialist Clay Anderson posted this message on his Twitter account: "This might be last ground Tweet before launch...have to pack and ready for suit up! God Bless you all for following along! Peace to you!"
0224 GMT (10:24 p.m. EDT Sun.)
Liquid hydrogen and liquid oxygen loading have switched to the "fast-fill" mode as fueling of space shuttle Discovery proceeds via remote control at launch pad 39A.

The low-level sensors in the liquid hydrogen tank are reading "wet" as they get submerged by the cryogenics. The tank is about five percent fill now.
0218 GMT (10:18 p.m. EDT Sun.)
You can watch our space shuttle Discovery launch coverage on your iPhone or iPod Touch. Check it out! http://iphone.livestream.com/spaceflightnowmobile
0208 GMT (10:08 p.m. EDT Sun.)
Liquid oxygen loading has completed the chilldown thermal conditioning of the transfer lines and main propulsion system. And now the LOX loading has begun the slow-fill process.
0150 GMT (9:50 p.m. EDT Sun.)
No further issues have been noted with space shuttle Discovery's electricity-generating fuel cells, a NASA spokeswoman says. Earlier this evening, a voltage spike was detected on fuel cell No. 2. However, engineers believe the lights in the orbiter's cockpit was to blame.

"They haven't seen any other surges in fuel cell No. 2, and if none are seen during the crew insert into space shuttle Discovery, then they will have more confidence that the surge was a configuration issue," spokeswoman Candrea Thomas says from the Launch Control Center.
0146 GMT (9:46 p.m. EDT Sun.)
The liquid hydrogen loading has transitioned from the chilldown thermal conditioning process to the "slow-fill" mode. This fills a small fraction of the tank, then the loading switches to "fast-fill" mode.
0135 GMT (9:35 p.m. EDT Sun.)
The fueling sequence started with the chilldown thermal conditioning of the liquid oxygen system.
0129 GMT (9:29 p.m. EDT Sun.)
FUELING UNDERWAY. Today's filling of space shuttle Discovery's external fuel tank started at 9:28 p.m. EDT. The brief delay of 32 minutes in beginning the fueling process will not impact the planned launch time since the countdown has plenty of margin to recover from issues of this nature.
0120 GMT (9:20 p.m. EDT Sun.)
A NASA spokeswoman projects that fueling should get underway in about 20 minutes.
0115 GMT (9:15 p.m. EDT Sun.)
In the latest forecast issued this evening, meteorologists continue to predict an 80 percent chance of acceptable weather conditions for launch. Patchy ground fog is the only concern for the 6:21 a.m. EDT liftoff time.

"High pressure is in control of the weather in Central Florida creating pleasant conditions at Kennedy Space Center with partly cloudy skies, light winds, and moderate temperatures. hese stable conditions caused by the high pressure also create a slight concern for fog restricting visibility. Our primary concern for launch is limited visibility due to fog," the Air Force weather team says.

The outlook includes just a few low clouds at 3,000 feet, easterly winds from 090 degrees at 5 knots, a temperature of 64 degrees F and the dew point at 62 degrees F.
0110 GMT (9:10 p.m. EDT Sun.)
All ground workers have cleared the launch pad, NASA says, in preparation for the start of fueling the space shuttle.

Typically, the launch team will conduct a safety check on the pyrotechnic circuits to ensure they are in a good configuration before fueling starts. That's the final step before the tanking preps can commence.
0056 GMT (8:56 p.m. EDT Sun.)
T-minus 6 hours and counting. The countdown has resumed ticking after a two-hour hold. The next scheduled built-in hold will occur at T-minus 3 hours.
0050 GMT (8:50 p.m. EDT Sun.)
The start of fueling will be delayed at least a few minutes due to a technical issue that arose tonight. NASA spokeswoman Candrea Thomas explains:

"About an hour ago, Discovery's fuel cell No. 2 exhibited a jump in voltage. The jump was not in violation of the Launch Commit Criteria, but engineers gathered more data on the temporary jump to determine if the shift was caused by the configuration of cockpit lighting. Tanking will begin as soon as the pad has been cleared of all personnel."
0043 GMT (8:43 p.m. EDT Sun.)
The Mission Management Team met for the pre-fueling meeting and gave the "go" to load a half-million gallons of supercold rocket fuel into Discovery's external tank for launch.
2325 GMT (7:25 p.m. EDT)
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2256 GMT (6:56 p.m. EDT)
T-minus 6 hours and holding. The countdown has gone into the scheduled two-hour built-in hold prior to the start of fueling. The Mission Management Team is scheduled to convene its critical pre-fueling meeting at 8:15 p.m. EDT.
2115 GMT (5:15 p.m. EDT)
Discovery's seven astronauts spent the past day visiting with their families and touring the shuttle at the pad. They also received briefings on orbiter preparations, the payload status and the weather forecast from the ascent team of flight controllers in Houston.

"Touring pad w/spouses. Discovery looks beautiful! What an awesome example of American engineering. God bless the USA!!!" mission specialist Clay Anderson posted on his Twitter account Saturday night.

They went to sleep at 12 noon EDT and will be awakened for launch day at 8 p.m. tonight. They'll have breakfast at 8:30 p.m. and then undergo final medical exams at 9 p.m. Suit up begins shortly before 2 a.m. and departure from crew quarters is scheduled for 2:31 a.m. in preparation for blastoff at 6:21 a.m. EDT.
1800 GMT (2:00 p.m. EDT)
The official launch window for Monday's shot at getting space shuttle Discovery into orbit has two panes, leading to docking with the International Space Station either on Flight Day 3 or Flight Day 4.

Based on the latest radar tracking of the space station's orbit and subsequent revision from Mission Control, the first pane for a preferred Flight Day 3 rendezvous with the space station would extend from 6:16:25 a.m. to 6:26:25 a.m. EDT. The targeted liftoff time occurs in the middle of the period at 6:21:25 a.m. EDT. That's the moment when Earth's rotation carries the launch pad into the plane of the station's orbit.

An additional three minutes and 10 seconds in the form a second pane of the launch window exists until 6:29:35 a.m. EDT. However, launching within that pane would lead to a Flight Day 4 rendezvous and docking, something that is acceptable but not desired.

If the launch is delayed to Tuesday morning for some reason, a single-pane window and Flight Day 3 docking scenario will be available for the backup liftoff opportunity. The window would stretch from 5:53:53 to 6:03:54 a.m. and include an optimum launch time of 5:58:53 a.m. EDT.
1645 GMT (12:45 p.m. EDT)
Spaceflight Now captured these photos of Discovery on a picturesque Easter morning in Florida.
1400 GMT (10:00 a.m. EDT)
On this Easter Sunday at Kennedy Space Center's launch pad 39A, space shuttle Discovery has been uncovered from the cocoon-like service gantry in advance of Monday morning's liftoff.

Technicians will spend the next few hours getting ground equipment configured and secured in preparation for tonight's fueling with supercold rocket propellant.

Clocks will resume counting at 1:56 p.m. EDT after the half-day hold at T-minus 11 hours. The orbiter's fuel cells are activated about an hour later, and the hazard area around the pad gets cleared of personnel during the afternoon.

The next planned hold is T-minus 6 hours beginning at 6:56 p.m. EDT. During this two-hour pause of the clocks, the Mission Management Team convenes its pre-fueling meeting to review the status of work, the readiness of shuttle systems and the latest weather forecast.

If all goes according to plan, loading of the external tank with propellant will start at 8:56 p.m. EDT. The process should take three hours to complete.

Joinh us tonight here in the Mission Status Center for live play-by-play updates throughout the countdown. And don't miss our launch webcast anchored by Miles O'Brien that begins at 2 a.m. EDT (0600 GMT). Miles will be joined by former space station commander Leroy Chiao, journalist David Waters and several special guests!
1345 GMT (9:45 a.m. EDT)
A reminder that if you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text messages on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)
1340 GMT (9:40 a.m. EDT)
After initially moving at a glacial pace, the speed has picked up and the massive gantry is clear of the shuttle now as it continues to back away.
1324 GMT (9:24 a.m. EDT)
Rollback of the rotating service structure to reveal shuttle Discovery has started at launch pad 39A. You can watch the tower retraction in our live streaming video.
0900 GMT (5:00 a.m. EDT)
The shuttle Discovery, carrying a crew of seven and 10 tons of supplies and equipment bound for the International Space Station, is poised for blastoff Monday on a three-spacewalk mission to deliver ammonia coolant, experiment hardware, a darkroom, a crew hygiene station and an experiment sample freezer.

Read our full story.

Read our earlier status center coverage.

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The astronauts launching on Discovery: Rick Mastracchio, Stephanie Wilson, pilot James Dutton, Dorothy Metcalf-Lindenburger, commander Alan Poindexter, Naoko Yamazaki of Japan, and Clayton Anderson.

Join Miles O'Brien, David Waters and Leroy Chiao for our live launch webcast from Kennedy Space Center starting at 2 a.m. EDT on launch morning.